FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
POWER CONVERSION SYSTEM;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED
AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-
3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310, JAPAN
5
10
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
15
20
2
DESCRIPTION
Field
[0001] The present invention relates to a power
5 conversion system installed on an electric vehicle for
converting an alternating-current power output from an
alternating-current power supply into a direct-current
power.
10 Background
[0002] Typically, an electric vehicle is configured to
draw power from overhead power lines by a power collector,
use the drawn power, and drive a motor by a power
converting apparatus to move the electric vehicle. In
15 particular, an electric vehicle that receives supply of
power from an alternating-current power supply typically
employs a scheme to supply power to a motor for driving the
electric vehicle, via a voltage transformer that lowers an
overhead line voltage, a converter that converts the
20 alternating-current power into a direct-current power, and
an inverter that converts the direct-current power into an
alternating-current power. Hereinafter, the term “electric
vehicle” will refer to an electric vehicle that receives
power from an alternating-current power supply. In
25 addition, a device including a voltage transformer, a
converter, an inverter, and a motor will be referred to as
a “propulsion controller”.
[0003] A voltage transformer of an electric vehicle
includes a primary winding connected to an overhead power
30 line, a secondary winding connected to a converter, and a
tertiary winding connected to other electric devices. Of
these windings, the secondary winding is associated one-toone
with the converter, and two or more secondary windings
3
are provided in many cases. In addition, the number of
turns typically becomes smaller in the order of the primary
winding, the secondary winding, and the tertiary winding.
That is, the voltage becomes lower in the order of the
5 primary winding, the secondary winding, and the tertiary
winding. Note that the primary winding is called a highvoltage
winding, and the secondary winding and the tertiary
winding are called low-voltage windings.
[0004] For control of the converter, information on the
10 overhead line voltage is needed. Note that, in some cases,
a voltage sensor for obtaining an overhead line voltage is
installed on a tertiary winding of a voltage transformer.
In the case of such configuration, a value obtained from
the voltage sensor is converted in a turn ratio of the
15 voltage transformer and used for controlling the converter.
Connection of the voltage sensor to the tertiary winding
enables use of a voltage sensor of a lower withstand
voltage performance. A configuration of such a power
conversion system is described in Patent Literature 1
20 mentioned below, for example.
Citation List
Patent Literature
[0005] Patent Literature 1: Japanese Patent Application
25 Laid-open No. 2005-304156
Summary
Technical Problem
[0006] Forthe voltage transformer of the electric
30 vehicle described above, three or more windings, which
share magnetic paths, have magnetic couplings present
between all the windings. Thus, a current flowing in a
winding affects the voltage induced by another winding.
4
Specifically, the output of the voltage sensor connected to
the tertiary winding changes depending on the magnitude of
power required by the converter connected to the secondary
winding. As a result, a difference occurs between a true
5 overhead line voltage and an overhead line voltage obtained
from an obtained value of the voltage sensor, which causes
a problem of failure to control a power factor of the
propulsion controller from the overhead power line, that is,
a power factor on the primary side of the voltage
10 transformer,as instructed by a command value from a
controller of the converter.
[0007] Patent Literature 1 teaches a technique of
intentionally making a converter operate in such a manner
that the power factor becomes smaller than 1. Specifically,
15 Patent Literature 1 teaches a technique of making a
converter operate by carrying a reactive current in such a
manner as to prevent fluctuation of a received voltage
received by the voltage transformer. Unfortunately, such a
technique does not take into consideration the difference
20 between the true overhead line voltage and the overhead
line voltage obtained from the obtained value of the
voltage sensor. Nor that techniquedoes guarantee that the
actual power factor is controlled as instructed by a
command value from the controller of the converter.
25 [0008] The present invention has been made in view of
the above, and an object thereof is to provide a power
conversion system capable of controlling a power factor on
a primary side of a voltage transformer such that the power
factor is a command value even in a case where a voltage
30 sensor is installed on a low-voltage winding of the voltage
transformer to obtain an overhead line voltage.
Solution to Problem
5
[0009] To solve the aforementioned problems and achieve
the object, a power conversion system according to the
present invention comprises a power converting apparatus
and a voltage transformer. The power converting apparatus
5 includes a converter to convert an alternating-current
power into a direct-current power, a first voltage sensor
to obtain a direct-current voltage generated on a directcurrent
side of the converter, and a control unit to
control an operation state of the converter. The voltage
10 transformer includes a primary winding connected to an
alternating-current power supply, a secondary winding, and
a tertiary winding connected with a second voltage sensor.
The control unit includes a phase computing unit to compute
a reference phase from a value obtained by the second
15 voltage sensor. The control unit also includes an active
current command value computing unit to compute an active
current command value on the basis of a deviation of a
direct-current voltage command valuefrom the direct-current
voltage obtained by the first voltage sensor. The control
20 unit further includes a first reactive current command
value computing unit to compute a first reactive current
command value proportional to a square of the active
current command value, by using, as a proportionality
coefficient, a first coefficient determined by coupled
25 inductances of the voltage transformer and a received
voltage of the voltage transformer. The control unit
further includes a voltage command value computing unit to
compute an alternating-current voltage command value on the
basis of the reference phase, the active current command
30 value, and the first reactive current command value.
Advantageous Effects of Invention
[0010] A power conversion system according to the
6
present invention produces an effect that a power factor on
a primary side of a voltage transformer can be controlled
such that the power factor is a command value even in a
case where a voltage sensor is installed on a low-voltage
5 winding of the voltage transformer to obtain an overhead
line voltage.
Brief Description of Drawings
[0011] FIG. 1 is a configuration diagram of an electric
10 vehicle driving system including a power conversion system
according to a first embodiment.
FIG. 2 is a schematic diagram illustrating an example
of a configuration of main part of the power conversion
system illustrated in FIG. 1.
15 FIG. 3 is a first vector diagram for explaining an
operation principle of a converter illustrated in FIGS. 1
and 2.
FIG. 4 is a second vector diagram for explaining the
operation principle of the converter illustrated in FIGS. 1
20 and 2.
FIG. 5 is a block diagram illustrating an example of a
basic configuration of a control unit illustrated in FIGS.
1 and 2.
FIG. 6 is a vector diagram relating to a current
25 command value when the control unit illustrated in FIG. 5
operates.
FIG. 7 is a block diagram illustrating an example of a
basic configuration of the control unit illustrated in FIGS.
1 and 2, which is different from that in FIG. 5.
30 FIG. 8 is a diagram illustrating an equivalent circuit
expressing a voltage transformer illustrated in FIGS. 1 and
2 by using an ideal voltage transformer and coupled
inductances.
7
FIG. 9 is a vector diagram for explaining a phase
difference between an instantaneous current command that
can occur in the control unit in FIG. 5 or FIG. 7 and a
converted secondary operating voltage.
5 FIG. 10 is a graph illustrating time waveforms of a
sensor obtained voltage, a converted secondary operating
voltage, and an alternating current when the phase
difference illustrated in FIG. 9 occurs.
FIG. 11 is a first vector diagram for explaining a
10 control technique according to the first embodiment.
FIG. 12 is a graph illustrating time waveforms of a
sensor obtained voltage, a converted secondary operating
voltage, and an alternating current when the control
technique according to the first embodiment is used.
15 FIG. 13 is a second vector diagram for explaining the
control technique according to the first embodiment.
FIG. 14 is a block diagram illustrating an example of
a configuration of a current command value computing unit
according to the first embodiment.
20 FIG. 15 is a block diagram illustrating an example of
a hardware configuration implementing the computation
functions of the control unit in the first embodiment.
FIG. 16 is a block diagram illustrating another
example of a hardware configuration implementing the
25 computation functions of the control unit in the first
embodiment.
FIG. 17 is a block diagram illustrating an example of
a configuration of the current command value computing unit
according to the first embodiment, which is different from
30 that in FIG. 14.
FIG. 18 is a first vector diagram for explaining a
control technique according to a second embodiment.
FIG. 19 is a block diagram illustrating an example of
8
a configuration of a current command value computing unit
according to the second embodiment.
FIG. 20 is a block diagram illustrating an example of
a configuration of the current command value computing unit
5 according to the second embodiment, which is different from
that in FIG. 19.
FIG. 21 is a block diagram illustrating an example of
a configuration of main part of a propulsion controller
according to a third embodiment.
10 FIG. 22 is a diagram illustrating an equivalent
circuit expressing a voltage transformer illustrated in FIG.
21 by using an ideal voltage transformer and coupled
inductances.
FIG. 23 is a block diagram illustrating an example of
15 a configuration of a current command value computing unit
according to the third embodiment.
FIG. 24 is a block diagram illustrating an example of
a configuration of a current command value computing unit
according to a fourth embodiment.
20
Description of Embodiments
[0012] A power conversion system according to certain
embodiments of the present invention will be described in
detail below with reference to the drawings. Note that the
25 present invention is not limited to the embodiments below.
[0013] First Embodiment.
FIG. 1 is a configuration diagram of an electric
vehicle driving system 100 including a power conversion
system 50 according to a first embodiment. In FIG. 1, the
30 electric vehicle driving system 100 includes a feeding
system 110, and a propulsion apparatus 60 that performs
propulsion control on an electric vehicle, which is not
illustrated. The feeding system 110 provides an
9
alternating-current power supply. The feeding system 110
includes a power supply installation 106 that generates an
alternating-current power, and a power line 108 for
supplying the alternating-current power to the propulsion
5 apparatus 60.
[0014] Thepropulsion apparatus 60 includes the power
conversion system 50, and a load 120. The power conversion
system 50 converts the alternating-current power received
from the feeding system 110 into a direct-current power,
10 and supplies the direct-current power to the load 120. The
power conversion system 50 includes a voltage transformer 1,
and a power converting apparatus 10. The voltage
transformer 1 lowers a received voltage and supplies the
resulting voltage to the power converting apparatus 10.
15 [0015] The power converting apparatus 10 includes a
converter 2a, a capacitor 2b, and a control unit 3. The
converter 2a is a pulse width modulation (PWM) converter
that converts from an alternating-current power to a
direct-current power as well as from a direct-current power
20 into an alternating-current power. The converter 2a
converts an alternating-current power supplied from the
feeding system 110 via the voltage transformer 1 into a
direct-current power, and supplies the direct-current power
to the load 120. The capacitor 2b is a smoothing capacitor
25 that smooths an output of the converter 2a.
[0016] One side of the converter 2a on which the voltage
transformer 1 is located will be referred to as an
“alternating-current side”, and the other side of the
converter 2a on which the load 120 is located will be
30 referred to as a “direct-current side”. The control unit 3
generates PWM signals for performing PWM control on the
converter 2a. The control unit 3 controls the operation
state of the converter 2a by the PWM signals. Specifically,
10
the control unit 3 controls the voltage of on the directcurrent
side of the converter 2a. The control unit 3 also
controls the current flowing into and out of the
alternating-current side of the converter 2a. Hereinafter,
5 the voltage on the direct-current side of the converter 2a
will be referred to as a “direct-current voltage of the
converter 2a” or simply as a “direct-current voltage”. In
addition, the current flowing into and out of the
alternating-current side of the converter 2a will be
10 referred to as an “alternating current of the converter 2a”
or simply as an “alternating current”. In addition, the
voltage on the alternating-current side of the converter 2a
will be referred to as an “alternating-current voltage of
the converter 2a” or simply as an “alternating-current
15 voltage”. Note that there are many known documents on
techniques for generating PWM signals, and detailed
description thereof will thus be omitted herein.
[0017] The load 120 includes an inverter 120a, and a
motor 120b. The inverter 120a converts a direct-current
20 power output from the converter 2a, into an alternatingcurrent
power. The motor 120b is driven by the
alternating-current power obtained by the conversion at the
inverter 120a. The motor 120b provides a propulsive force
to the electric vehicle, which is not illustrated. Note
25 that the number of motors 120b driven by one inverter 120a
may be more than one.
[0018] In addition, while a single inverter 120a
connected with one power converting apparatus 10 is
illustrated in FIG. 1, the single power converting
30 apparatus 10 may be configured to supply power to a
plurality of inverters 120a. Alternatively, a plurality of
power converting apparatuses 10 may be configured to supply
power to one inverter 120a. Note that, a case where the
11
number of power converting apparatuses 10 is more than one
will be described later.
[0019] FIG. 2 is a schematic diagram illustrating an
example of a configuration of main part of the power
5 conversion system 50. In addition to the voltage
transformer 1 and the power converting apparatus 10
illustrated in FIG. 1, FIG. 2 illustrates a current sensor
4, a voltage sensor 5, which is a first voltage sensor, and
a voltage sensor 6, which is a second voltage sensor.
10 [0020] As illustrated in FIG. 2, the voltage transformer
1 includes a primary winding 1a, a secondary winding 1b,
and a tertiary winding 1c. The primary winding 1a is
connected with the power line 108, the secondary winding 1b
is connected with the converter 2a, and the tertiary
15 winding 1c is connected with the voltage sensor 6. While
the number of power converting apparatuses 10 and the
number of secondary windings 1b are both one, for
simplicity, in FIG. 2, the number of power converting
apparatuses 10 and the number of secondary windings 1b may
20 be two or more. The power converting apparatuses 10 and
the secondary windings 1b are, however, connected one-toone
with each other.
[0021] The current sensor 4 obtains a current value of
an alternating current is of the converter 2a. The voltage
25 sensor 5 obtains a voltage value of a direct-current
voltage Ed of the converter 2a. The voltage sensor 6
obtains a voltage value of a voltage v^s induced in the
tertiary winding 1c. The respective values obtained by the
current sensor 4 and the voltage sensors 5 and 6 are input
30 to the control unit 3. Note that “v^” in the expression
“v^s” is a substitute for a character “v” with the hat
symbol “^” thereon. In the present specification, this
substitute is used unless the expression is inserted as an
12
image. Note that the value obtained by the voltage sensor
6 is an equivalent value to a secondary voltage converted
using a turn ratio of the secondary winding 1b and the
tertiary winding 1c in the voltage transformer 1. The
5 secondary voltage used herein is a voltage induced in the
secondary winding 1b. The turn ratio is also a voltage
ratio. Hereinafter, “v^s” will be referred to as a “sensor
obtained voltage”.
[0022] Next, an operation principle of the converter 2a
10 will be explained with reference to FIGS. 3 and 4. FIG. 3
is a first vector diagram for explaining the operation
principle of the converter illustrated in FIGS. 1 and 2.
FIG. 4 is a second vector diagram for explaining the
operation principle of the converter illustrated in FIGS. 1
15 and 2. Note that a state in which a positive power is
transmitted from the alternating-current side to the
direct-current side of the converter 2a is defined as
“power-running”, and a state in which a positive power is
transmitted from the direct-current side to the
20 alternating-current side” is defined as “regeneration”. On
the basis of these definitions, the direction in which the
alternating current is of the converter 2a obtained by the
current sensor 4 flows into the converter 2a is defined as
positive.
25 [0023] FIG. 3 illustrates the relation between a voltage
vector and a current vector in a steady state when the
converter 2a consumes power with a power factor of 1. In
FIG. 3, “is” represents the alternating current of the
converter 2a, “xl” represents a leakage reactance of the
30 voltage transformer 1, and “vc” represents the alternatingcurrent
voltage of the converter 2a. The voltage
transformer 1 receives from the power line 108 and converts
that received voltage into an equivalent value to a
13
secondary voltage, using a turn ratio of the primary
winding 1a and the secondary winding 1b in the voltage
transformer 1, thereby providing“vs”. “vs” will be
referred to as a “converted secondary operating voltage”.
5 [0024] Note that, in reality, a resistance component is
present in the voltage transformer 1in addition to the
leakage reactance xl. A sum of the resistance component
and the leakage reactance xl is called “leakage impedance”.
In the leakage impedance, the resistance component is
10 sufficiently small as compared with a reactance component.
Thus, for simplicity, the resistance component will be
ignored in the following description.
[0025] As illustrated in FIG. 3, in the power-running
and steady state with a power factor of 1, the alternating
15 current is and the converted secondary operating voltage vs
are in phase with each other. A voltage drop across the
leakage reactance xl of the voltage transformer 1 can be
expressed as “jxlis”. “j” is an imaginary unit, and the
voltage drop jxlis has a phase advanced by 90 degrees from
20 the alternating current is and the converted secondary
operating voltage vs. Note that, because a voltage
difference between the converted secondary operating
voltage vs and the alternating-current voltage vc of the
converter 2a is applied to the leakage reactance xl,
25 thereby generating the alternating current is. Thus, a
result of vectorial addition of the alternating-current
voltage vc of the converter 2a and the voltage drop jxlis
across the leakage reactance xl is equal to the converted
secondary operating voltage vs. Namely, the converted
30 secondary operating voltage vs, the alternating-current
voltage vc, and the voltage drop jxlis satisfy the relation
of vs=vc+jxlis.
[0026] In addition, FIG. 4 illustrates the relation
14
between a voltage vector and a current vector in a steady
state when the converter 2a regenerates power with a power
factor of 1. In FIG. 4, the alternating current is and the
converted secondary operating voltage vs are in opposite
5 phase to each other. Note that the voltage drop jxlis
across the leakage reactance xl in the voltage transformer
1 has a phase advanced by 90 degrees from the alternating
current is but delayed by 90 degrees from the converted
secondary operating voltage vs. The relation of
10 vs=vc+jxlis is satisfied as in the vector diagram of FIG. 3,
and a result of vectorial addition of the alternatingcurrent
voltage vc and the voltage drop jxlis across the
leakage reactance is equal to the converted secondary
operating voltage vs.
15 [0027] Thus, the vector diagrams of FIGS. 3 and 4 show
that either one or both of the amplitude and the phase of
the alternating-current voltage vcare adjusted to thereby
control the alternating current issuch that the alternating
current iscan have any given amplitude and any given phase.
20 [0028] Next, a basic configuration and operation of the
control unit 3 illustrated in FIGS. 1 and 2 will be
described with reference to FIGS. 5 and 6. FIG. 5 is a
block diagram illustrating an example of a basic
configuration of the control unit 3 illustrated in FIGS. 1
25 and 2. FIG. 6 is a vector diagram relating to a current
command value when the control unit illustrated in FIG. 5
operates.
[0029] The control unit 3 illustrated in FIG. 5 includes
a phase computing unit 30, a current command value
30 computing unit 32, a voltage command value computing unit
34, and a switching command generating unit 36.
Hereinafter, an operation of each of the units will be
explained.
15
[0030] The phase computing unit 30 generates a voltage
phase θ on the basis of the sensor obtained voltage v^s.
The voltage phase θ is a reference phase for generation of
an instantaneous current command value is*, which will be
5 described later. Hereinafter, the voltage phase will be
referred to as a “reference phase”. The reference phase θ
is input to the voltage command value computing unit 34.
Note thatvarious known schemes have been proposed to
configure the phase computing unit 30, and detailed
10 description thereof will thus be omitted herein.
[0031] The current command value computing unit 32 is a
component that computes an active current command value Ip
and a reactive current command value Iq on the basis of a
direct-current voltage command value Ed*, the direct15
current voltage Ed obtained from the voltage sensor 5, and
a power factor angle command value φ. Specifically, as
illustrated in FIG. 5, the current command value computing
unit 32 includes a subtractor 321, a voltage controlling
unit 322, a tangent value computing unit 336, and a
20 multiplier 323. The direct-current voltage command value
Ed* is a command value for controlling the direct-current
voltage Ed such that the direct-current voltage Ed has a
desired value.
[0032] Thesubtractor 321 computes a direct-current
25 voltage deviation, which is a deviation of the directcurrent
voltage command value Ed* from the direct-current
voltage Ed. The voltage controlling unit 322 computes the
active current command value Ip on the basis of an output
from the subtractor 321. The active current command value
30 Ip is input to the voltage command value computing unit 34
and the multiplier 323. The subtractor 321 and the voltage
controlling unit 322 define an active current command value
computing unit.
16
[0033] In addition, the tangent value computing unit 336
generates a tangent value, which is a tangent, of the power
factor angle command value φ. The multiplier 323
multiplies the active current command value Ip by the
5 output of the tangent value computing unit 336. The output
of the multiplier 323 is the reactive current command value
Iqinput to the voltage command value computing unit 34.
The tangent value computing unit 336 and the multiplier
323define a reactive current command value computing unit.
10 [0034] Note thata proportional integral (PI) compensator
is often used as the voltage controlling unit 322. In
addition, when the power factor angle command value φ is
given, the relation between the active current command
value Ip and the reactive current command value Iq for
15 achieving a desired power factor is as expressed by the
following formula.
[0035]
[Formula 1]
...(1)
[0036] Thus, the current command value computing unit 32
in FIG. 5 computes the reactive current command value Iq by
20 multiplying the active current command value Ip by tanφ,
which is a tangent value of the power factor angle command
value φ. In the case of FIG. 5, when the power factor
angle command value φ is positive, the reactive current
command value Iq is also positive and Iq represents a
25 leading reactive current. When the power factor angle
command value φ is negative, the reactive current command
value Iq is also negative and Iq represents a lagging
reactive current. When the reactive current command value
Iq is determined in this manner, and the instantaneous
30 current command value is* is computed so that the power
Iq = Iptan
17
factor of the alternating-current power follows a desired
value. The instantaneous current command value is* will be
described later.For a reactive power amount to follow a
desired value, the reactive current command value Iq can be
5 directly computed by another means without use of the power
factor angle command value φ.
[0037] Next, the voltage command value computing unit 34
will be described. The voltage command value computing
unit 34 is a component that computes the instantaneous
10 current command value is* on the basis of the active
current command value Ip, the reactive current command
value Iq, and the reference phase θ. The voltage command
value computing unit 34 is also a component that computes
an alternating-current voltage command value vc* on the
15 basis of the instantaneous current command value is* and
the alternating current is obtained from the current sensor
4. The alternating-current voltage command value vc* is a
command value of a voltage which the converter 2a should
output to the alternating-current side.Specifically, as
20 illustrated in FIG. 5, the voltage command value computing
unit 34 includes a sine value computing unit 341, a cosine
value computing unit 342, multipliers 343 and 344, an adder
345, a subtractor 346, and a current controlling unit 347.
[0038] The sine value computing unit 341 computes a sine
25 value of the reference phase θ, and the cosine value
computing unit 342 computes a cosine value of the reference
phase θ. The multiplier 343 multiplies the active current
command value Ip by the sine value of the reference phase θ.
The active current command value Ip is an output of the
30 current command value computing unit 32. The sine value of
the reference phase θ is an output of the sine value
computing unit 341. The multiplier 344 multiplies the
reactive current command value Iq by the cosine value of
18
the reference phase θ. The reactive current command value
Iq is the output of the current command value computing
unit 32. The cosine value of the reference phase θ is the
output of the cosine value computing unit 342. The adder
5 345 adds Ipsinθ and Iqcosθ. Ipsinθ is the output of the
multiplier 343, and Iqcosθ is the output of the multiplier
344. The output of the adder 345 is the instantaneous
current command value is*. The instantaneous current
command value is* a command value of a current that should
10 flow to the alternating-current side of the converter 2a.
[0039] Note that the active current command value Ip and
the reactive current command value Iq are both direct
current quantities, while the instantaneous current command
value is* is an alternating current quantity. For the
15 configuration of FIG. 5, a product of the active current
command value Ip and sinθ, which is the sine value of the
reference phase θ, is an alternating current quantity that
is in phase with the sensor obtained voltage v^s. A
product of the reactive current command value Iq and cosθ,
20 which is the cosine value of the reference phase θ, is an
alternating current quantity that is 90-degree out of phase
with the sensor obtained voltage v^s. For the
configuration of FIG. 5, thus, the reference phase θ is
based on the sine value of the sensor obtained voltage v^s.
25 The sensor obtained voltage v^s and the instantaneous
current command value is* therefore satisfy the relation
illustrated in the vector diagram of FIG. 6.
[0040] The instantaneous current command value is* is
input to the subtractor 346. The subtractor 346 computes a
30 deviation of the instantaneous current command value is*
from the alternating current is. The alternating current is
an alternating current of the converter 2a obtained by the
current sensor 4. The current controlling unit 347
19
amplifies the deviation of the instantaneous current
command value is* from the alternating current is, and
outputs the amplified signal as the alternating-current
voltage command value vc* to the switching command
5 generating unit 36. Note that a proportional (P)
compensator or a PI compensator is often used as the
current controlling unit 347.
[0041] The switching command generating unit 36
generates a switching command sw* on the basis of the
10 alternating-current voltage command value vc*. The
switching command sw* is a PWM signal for performing PWM
control on the converter 2a. Note that a known technique
is used for generating the switching command sw*, and
detailed description thereof will thus be omitted herein.
15 [0042] Note that the voltage command value computing
unit 34 illustrated in FIG. 5 may be replaced, such as with
a voltage command value computing unit 35 illustrated in
FIG. 7. FIG. 7 is a block diagram illustrating an example
of a basic configuration of the control unit 3 illustrated
20 in FIGS. 1 and 2, which is different from that in FIG. 5.
In FIG. 7, components that are the same as or corresponding
to those in FIG. 5 are represented by the same reference
numerals.
[0043] The configuration of FIG. 7 differs from the
25 configuration of FIG. 5 in converting an actual current
into a direct current quantityunlike the configuration of
FIG. 5 that converts the current command value into the
alternating current quantity. Specifically, as illustrated
in FIG. 7, the voltage command value computing unit 35
30 includes a rotational coordinate transforming unit 351,
subtractors 352 and 353, current controlling units 354 and
355, and a stationary coordinate transforming unit 356.
Note that like the voltage command value computing unit 34
20
illustrated in FIG. 5, the voltage command value computing
unit 35 illustrated in FIG. 7 is configured to compute the
alternating-current voltage command value vc* on the basis
of the active current command value Ip, the reactive
5 current command value Iq, the reference phase θ, and the
alternating current is obtained from the current sensor 4.
The alternating-current voltage command value vc* is a
voltage which the converter 2a should output to the
alternating-current side.
10 [0044] The rotational coordinate transforming unit 351
uses the reference phase θ to transform the alternating
current is into a value on the rotational coordinates to
thereby compute an actual active current Ip'and an actual
reactive current Iq'. The actual active current Ip' is a
15 component that is in phase with the sensor obtained voltage
v^s. The actual reactive current Iq' is a component that
is 90-degree out ofphasewith the sensor obtained voltage
v^s.
[0045] Thesubtractor 352 computes a deviationof the
20 active current command value Ipfrom the actual active
current Ip'. The active current command value Ip is an
output of the current command value computing unit 32. The
actual active current Ip' is an output of the rotational
coordinate transforming unit 351. In addition, the
25 subtractor 353 computes a deviation of the reactive current
command value Iq from the actual reactive current Iq'. The
reactive current command value Iq is an output of the
current command value computing unit 32. The actual
reactive current Iq' is an output of the rotational
30 coordinate transforming unit 351.
[0046] The current controlling unit 354 amplifies the
deviation of the active current command value Ipfrom the
actual active current Ip', and outputs the amplified signal
21
as a p-axis voltage command value vp* to the stationary
coordinate transforming unit 356. In addition, the current
controlling unit 355 amplifies the deviation of the
reactive current command value Iqfrom the actual reactive
5 current Iq', and outputs the amplified signal as a q-axis
voltage command value vq* to the stationary coordinate
transforming unit 356.
[0047] The stationary coordinate transforming unit 356
uses the reference phase θ to transform the p-axis voltage
10 command value vp* and the q-axis voltage command value vq*
into a value on the stationary coordinates and outputs the
value obtained by the transformation, as the alternatingcurrent
voltage command value vc* to the switching command
generating unit 36.
15 [0048] Ina case where the alternating-current power is
single phase, instantaneous spatial vectors of a voltage
and a current cannot be defined. For this reason,
additional computation processes are necessary for mutual
transformation of rotational coordinates and stationary
20 coordinates. Specifically, for rotational coordinate
transformation of the alternating current is, jis, which is
a component with a phase advanced by 90 degrees from the
alternating current is, is computed in advance, and the
rotational coordinate transformation is then performed on
25 the alternating currents is and jis. When a transformation
matrix in this process is represented by C, the
transformation matrix C is expressed by the following
formula.
[0049]
[Formula 2]
...(2)








cos sin
sin cos
C =
22
[0050] It should be noted that the transformation matrix
of the formula (2) varies depending on the manner of
definition of the reference phase θ.
[0051] In addition, using the transformation matrix C of
5 the aforementioned formula (2), the actual active current
Ip' and the actual reactive current Iq' described above are
expressed by the following formula.
[0052]
[Formula 3]
...(3)
10 [0053] In addition, the alternating-current voltage
command value vc* is expressed by the following formula by
using the transformation matrix C of the formula (2).
[0054]
[Formula 4]
...(4)
15 [0055] Next, the influence of the voltage transformer 1
on the control will be explained with reference to FIGS. 8
to 10. FIG. 8 is a diagram illustrating an equivalent
circuit expressing the voltage transformer illustrated in
FIGS. 1 and 2 by using an ideal voltage transformer and
20 coupled inductances. FIG. 9 is a vector diagram for
explaining a phase difference between the instantaneous
current command value is* that can occur in the control
unit in FIG. 5 or FIG. 7 and the converted secondary
operating voltage vs. FIG. 10 is a graph illustrating time
25 waveforms of the sensor obtained voltage v^s, the converted
secondary operating voltage vs, and the alternating current














jis
is
C
Iq
Ip
















Vq
Vp
C
jvc
vc 1
23
is when the phase difference illustrated in FIG. 9 occurs.
[0056] In FIG. 8, the voltage transformer 1 is expressed
by an ideal voltage transformer 70 and coupled inductances
74. The coupled inductances 74 express a leakage
5 inductance between a high-voltage winding and a low-voltage
winding, and magnetic coupling between low-voltage windings
in the voltage transformer 1. The leakage inductance is
also referred to as a leakage reactance.
[0057] In FIG. 8, “v1” represents a primary voltage, “v2”
10 represents a secondary voltage, “v3” represents a tertiary
voltage, “i1” represents a primary current, “i2” represents
a secondary current, and “i3” represents a tertiary current.
Specifically, the primary voltage v1 is a voltage applied
to the primary winding, and the primary current i1 is a
15 current flowing through the primary winding. In addition,
the secondary voltage v2 is a voltage induced by the
secondary winding, the secondary current i2 is a current
flowing through the secondary winding, the tertiary voltage
v3 is a voltage induced by the tertiary winding, and the
20 tertiary current i3 is a current flowing through the
tertiary winding. Note that, for convenience of
explanation, the primary winding may be referred to as a
“high-voltage winding”, and the secondary winding and the
tertiary winding may be collectively referred to as “low25
voltage windings”. In addition, “n2” represents a turn
ratio of the secondary winding to the primary winding, and
“n3” represents a turn ratio of the tertiary winding to the
primary winding. Note that, when the number of turns of
the primary winding is expressed by “1” as illustrated, the
30 turn ratio n2 and the turn ratio n3 are real numbers equal
to or lager than 0 and smaller than 1.
[0058] Note that, in the equivalent circuit of FIG. 8,
circuit equations of the following formulas are satisfied.
24
[0059]
[Formula 5]
...(5)
[Formula 6]
...(6)
[0060] A coefficient matrix on the right side of the
5 formula (6) will be referred to as a “reactance matrix”.
The reactance matrix is a parameter expressing the coupled
inductances 74 in terms of impedance. Diagonal terms of
the reactance matrix are terms coming from self-inductances
of the low-voltage windings, and off-diagonal terms are
10 terms coming from a mutual inductance of the low-voltage
winding. In addition, the reactance matrix is a symmetric
matrix. The second line of the formula (6) is developed,
thereby providing the following formula.
[0061]
[Formula 7]
...(7)
15
[0062] The formula (7) shows that the tertiary voltage
v3 changes depending on the current of the low-voltage
winding.
[0063] In addition, the formula (7) is deformed, thereby
20 providing the following formula.
[0064]
[Formula 8]
...(8)
i1 = n2 i2 + n3 i3
























i3
i2
x32 x33
x22 x23
j
v3
v2
v1
n3
n2
v3 = n3 v1j(x32 i2 + x33 i3)
n2 v1= (n2/n3 )v3+ j(n2/n3)(x32 i2 +x33 i3)
25
[0065] Note that, in the configuration of FIG. 2, the
load of the tertiary winding 1c is the voltage sensor 6
only and the current flowing in the voltage sensor 6 is
5 small. For this reason, assume the tertiary current i3 is
zero, i3=0. Although an electric vehicle may have another
load such as an auxiliary power supply connected to the
tertiary winding 1c, the power capacity thereof is smaller
than that of the converter of the secondary winding in most
10 cases. Thus, the assumption that the tertiary current i3
is ignored, i.e.,the tertiary current is zero (i3=0) is
reasonable and appropriate.
[0066] In addition, the left side of the formula (8) is
a value obtained by converting the primary voltage v1 into
15 a secondary voltage, and this value is referred to as the
converted secondary operating voltage vs defined as
described above. Furthermore, the first term on the right
side is a value obtained by converting the value obtained
by the voltage sensor 6 into a secondary voltage equal to
20 the sensor obtained voltage v^s. Because the secondary
current i2 of the voltage transformer 1 is equal to the
alternating current is of the converter 2a, and the
alternating current isis controlled such that the
alternating current isis the instantaneous current command
25 value is*. For this reason, assume that the current i2 is
equal to is* (i2=is*). Furthermore, when a proportionality
coefficient “(n2/n3)x32” in the second term on the right
side is defined as “xm”, i.e., xm=(n2/n3)x32, the following
formula is obtained.
30 [0067]
[Formula 9]
vs = vˆs + jxmis ...(9)
26
[0068] Assumingthat a control target is a power factor
of 1 and that the reactive current command value Iq is zero,
the relation in the formula (9) can be expressed by the
5 vector diagram of FIG. 9. In FIG. 9, the instantaneous
current command value is* is in phase with the sensor
obtained voltage v^s. In addition, a phase difference
angle δ is present between the sensor obtained voltage v^s
and the converted secondary operating voltage vs. Thus, a
10 phase difference corresponding to the phase difference
angle δ is also produced between the instantaneous current
command value is* and the converted secondary operating
voltage vs.
[0069] In this case, time waveforms of the sensor
15 obtained voltage v^s, the converted secondary operating
voltage vs, and the alternating current is are as in FIG.
10. In FIG. 10, the sensor obtained voltage v^s and the
alternating current is are illustrated in solid curves, and
the converted secondary operating voltage vs is illustrated
20 in a broken curve. As illustrated in FIG. 10, a phase
difference corresponding to the phase difference angle δ is
produced between the sensor obtained voltage v^s and the
converted secondary operating voltage vs. In addition, as
a result of the alternating current isbeing controlled such
25 that the alternating current isfollows the instantaneous
current command value is*, the alternating current is is in
phase with the sensor obtained voltage v^s. Thus, a phase
difference corresponding to the phase difference angle δ is
also produced between the converted secondary operating
30 voltage vs and the alternating current is. This means that,
a control target is a power factor of 1, but the power
factor on the primary side of the voltage transformer 1 is
not 1.
27
[0070] As described above, in the basic configuration
illustrated in FIG. 5 or FIG. 7, the sensor obtained
voltage v^s can have a phase different from that of the
converted secondary operating voltage vs. This results in
5 a problem: the power factor or the reactive power amount of
the alternating-current power on the primary side of the
voltage transformer 1 is notprovided as instructed by the
control unit 3. A control technique of the first
embodiment solves this problem by correcting the
10 instantaneous current command value is*, as will be
explainedhereinbelow.
[0071] FIG. 11 is a first vector diagram for explaining
a control technique in the first embodiment. First, as
illustrated in FIG. 11, an axis in phase with the sensor
15 obtained voltage v^s is defined as a p-axis, and an
axishaving a phase advanced by 90 degrees from the p-axis
is defined as a q-axis. Next, the instantaneous current
command value is* is resolved into a p-axis component ip
and a q-axis component iq1', assuming that the
20 instantaneous current command value is* is in phase with
the converted secondary operating voltage vs. Note that
the amplitude of the p-axis component ip corresponds to the
active current command value Ip output from the current
command value computing unit 32in the configuration ofthe
25 control unit 3 illustrated in FIG. 5 or FIG. 7. In
addition, the amplitude of the q-axis component iq1' is
newly defined as a first reactive current command
correction value Iq1'. When the vector diagram of FIG. 11
is solved geometrically, the relation between the active
30 current command value Ip and the first reactive current
command correction value Iq1' is expressed by the following
formula.
[0072]
28
[Formula 10]
...(10)
[0073] Note that, with k=xm/|vs|, the formula (10) is
expressed by the following formula.
[0074]
[Formula 11]
...(11)
5
[0075] In this case, time waveforms of the sensor
obtained voltage v^s, the converted secondary operating
voltage vs, and the alternating current is are as in FIG.
12. FIG. 12 is a graph illustrating time waveforms of the
10 sensor obtained voltage v^s, the converted secondary
operating voltage vs, and the alternating current is when
the control technique of the first embodiment is used.
[0076] According to FIG. 12, a phase difference
corresponding to the phase difference angle δ is produced
15 between the sensor obtained voltage v^s and the converted
secondary operating voltage vs. However, the instantaneous
current command value is* is in phase with the converted
secondary operating voltage vs, as illustrated in FIG. 11.
Thus, the alternating current is is controlled such that
20 the alternating current isis in phase with the converted
secondary operating voltage vs in FIG. 12. As compared
with the waveforms of FIG. 10, the phase different between
the converted secondary operating voltage vs and the
alternating current is is eliminated. Thus, this means
25 that the power factor on the primary side of the voltage
transformer 1 is 1.
[0077] FIG. 13 is a second vector diagram for explaining
2 2 2 Iq1xmI p / vs xmIp
2 2 Iq1kI p / 1k Ip
29
the control technique according to the first embodiment.
FIG. 13 illustrates a vector diagram as in FIG. 11 in a
case of regenerative operation with a power factor of 1.
In the case of the regenerative operation with a power
5 factor of 1, the instantaneous current command value is* is
in opposite phase to the converted secondary operating
voltage vs, and the first reactive current command
correction value Iq1' has a phase delayed by 90 degrees
from the active current command value Ip. In contrast, the
10 relation between the active current command value Ip and
the first reactive current command correction value Iq1' is
the same as that in the case of FIG. 11, which satisfies
the relation of the formula (11).
[0078] Note that the sign of Iq1' that satisfies the
15 formula (11) is positive regardless of the sign of Ip when
k>0. In other words, when xm>0, the value of the first
reactive current command correction value Iq1' is positive
regardless of power-running or regeneration. Conversely,
with xm<0, the value of the first reactive current command
20 correction value Iq1' is negative regardless ofpowerrunning
or regeneration.
[0079] Note that, the formula (11), which includes
calculation of a square root and division, provides the
computation load that is not necessarily light. In view of
25 this, simplification of the formula (11) is attempted.
Where a base capacity is represented by Sb, a base voltage
is represented by |vs|, base impedance is represented by Zb,
and xm and Ip expressed in a per-unit system are
represented by %x and %i, respectively, the relations of
Ip=(Sb/|vs|)×%i and xm=Zb×%x=(|vs|230 /Sb)×%x are satisfied.
These relations are substituted into the denominator of the
formula (11), thereby providing the following formula.
[0080]
30
[Formula 12]
...(12)
[0081] On the right side of the formula (6), diagonal
terms in the reactance matrix are several %to several
tens % of the base capacity. Furthermore, off-diagonal
5 terms in the reactance matrix are typically still smaller
than the diagonal terms. Thus, (%x)2<<1 canhold true in the
formula (12), lq1’ can be approximated as Iq1'≈kIp2. Thus,
as expressed by the following formula, the approximated
first reactive current command correction value Iq1' is
10 newly defined as a first reactive current command value Iq1.
[0082]
[Formula 13]
...(13)
[0083] As described above, the voltage command value
computing unit 34 may compute the alternating-current
15 voltage command value vc* on the basis of the first
reactive current command value Iq1. Such very simple
computationachieves an object of controlling the power
factor of the alternating-current power on the primary side
of the voltage transformer 1 such that the power factor is
20 1. The current command value computing unit that achieves
this function is configured as illustrated in FIG. 14, for
example. FIG. 14 is a block diagram illustrating an
example of a configuration of the current command value
computing unit according to the first embodiment. In FIG.
25 14, components that are the same or corresponding to those
in FIGS. 5 or FIG. 7 are represented by the same reference
numerals.
2 2 2 Iq1kI p / 1%x %i
Iq1: kI p 2 
31
[0084] The current command value computing unit 32A
illustrated in FIG. 14 includes a first reactive current
command value computing unit 324 instead of the tangent
value computing unit 336 and the multiplier 323 in the
5 current command value computing unit 32 illustrated in FIG.
5 or FIG. 7. In FIG. 14, the subtractor 321 and the
voltage controlling unit 322 define an active current
command value computing unit 320. An active current
command value Ip computed by the active current command
10 value computing unit 320 and a coefficient k, which is a
first coefficient, are input to the first reactive current
command value computing unit 324. Note that, the
coefficient k is expressed as k=xm/|vs| as described above.
In addition, the proportionality coefficient xm is a
15 coefficient coming from the coupled inductances 74 of the
voltage transformer 1. Furthermore, the converted
secondary operating voltage |vs| is a value determined by
the received voltage of the voltage transformer 1. Thus,
the coefficient k can be defined by the coupled inductances
20 74 of the voltage transformer 1 and the received voltage of
the voltage transformer 1.
[0085] The first reactive current command value
computing unit 324 uses the coefficient k as a
proportionality coefficient, and computes a first reactive
25 current command value Iq1 that is proportional to the
square of the active current command value Ip. The active
current command value Ip and the first reactive current
command value Iq1 computed by the current command value
computing unit 32A are input to the voltage command value
30 computing unit 34 or 35 illustrated in FIG. 5 or FIG. 7.
Subsequently, the alternating-current voltage command value
vc* is computed on the basis of the active current command
value Ip and the first reactive current command value Iq1.
32
The switching command sw* is generated on the basis of the
alternating-current voltage command value vc* for
controlling the operation state of the converter 2a.
[0086] As described above, according to the first
5 embodiment, the current command value computing unit of the
control unit computes the first reactive current command
value proportional to the square of the active current
command value, using,as the proportionality coefficient,
the coefficient k determined by the coupled inductances of
10 the voltage transformer and the received voltage of the
voltage transformer. The current command value computing
unitthen outputs the first reactive current command value
together with the active current command value to the
voltage command value computing unit. In addition, the
15 voltage command value computing unit computes the
alternating-current voltage command value on the basis of
the reference phase computed from the obtained value from
the second voltage sensor, the active current command value,
and the first reactive current command value. This makes
20 it possible to control the power factor on the primary side
of the voltage transformer such that the power factor is a
command value even in the case where the second voltage
sensor is installed on the tertiary winding of the voltage
transformer to obtain an overhead line voltage.
25 [0087] Next, hardware configurations for implementing
the computation functions of the control unit 3 in the
first embodiment will be described with reference to FIGS.
15 and 16. FIG. 15 is a block diagram illustrating an
example of a hardware configuration implementing the
30 computation functions of the control unit in the first
embodiment. FIG. 16 is a block diagram illustrating
another example of a hardware configuration implementing
the computation functions of the control unit in the first
33
embodiment.
[0088] As illustrated in FIG. 15, for implementing all
or some of the computation functions of the control unit 3
in the first embodiment by software, a configuration
5 including a processor 300 that performs computation, a
memory 302 in which programs to be read by the processor
300 are saved, and an interface 304 for signal input and
output can be used.
[0089] The processor 300 may be computing means such as
10 a computing device, a microprocessor, a microcomputer, a
central processing unit (CPU), or a digital signal
processor (DSP). In addition, examples of the memory 302
include a volatile or nonvolatile semiconductor memory such
as a random access memory (RAM), a read only memory (ROM),
15 a flash memory, an erasable programmable ROM (EPROM), or an
electrically EPROM (EEPROM: registered trademark), a
magnetic disk, a flexible disk, an optical disk, a compact
disc, a mini disc, and a digital versatile disc (DVD).
[0090] The memory 302 stores programs for implementing
20 all or some of the computation functions of the control
unit 3. The processor 300 can perform PWM control on the
converter 2a by providing and receiving necessary
information via the interface 304 and executing programs
stored in the memory 302.
25 [0091] Alternatively, the processor 300 and the memory
302 illustrated in FIG. 15 may be replaced with processing
circuitry 303 as in FIG. 16. The processing circuitry 303
may be a single circuit, a composite circuit, an
application specific integrated circuit (ASIC), a field30
programmable gate array (FPGA), or a combination thereof.
[0092] The hardware configurations for implementing the
computation functions of the control unit 3 in the first
embodiment have been described above. Note that, in a case
34
where there is a leftover computation capacity of the
processor 300 and the memory 302 or the processing
circuitry 303, the configuration of the current command
value computing unit 32A illustrated in FIG. 14 may be
5 changed to that in the FIG. 17. FIG. 17 is a block diagram
illustrating an example of a configuration of the current
command value computing unit according to the first
embodiment, which is different from that in FIG. 14. In
FIG. 17, components that are the same or corresponding to
10 those in FIG. 14 are represented by the same reference
numerals.
[0093] A current command value computing unit 32B
illustrated in FIG. 17 further includes a first correction
computing unit 325 in the configuration of FIG. 14. The
15 active current command value Ip computed by the active
current command value computing unit 320, the coefficient k,
and the first reactive current command value Iq1 computed
by the first reactive current command value computing unit
324 are input to the first correction computing unit 325.
20 [0094] Note that, when the newly defined first reactive
current command value Iq1 expressed by the formula (13) is
used, the formula (11) can be expressed by the following
formula.
[0095]
[Formula 14]
...(14)
25
[0096] The first correction computing unit 325 in FIG.
17 is a computation unit that performs the computation
expressed by the formula (14). Specifically, the first
correction computing unit 325 computes a first reactive
30 current command correction value Iq1' on the basis of the
2 Iq1Iq1/ 1kIp
35
first reactive current command value Iq1 output from the
first reactive current command value computing unit 324,
and the coefficient k that is a proportionality coefficient.
The first reactive current command correction value Iq1' is
5 a corrected value of the first reactive current command
value Iq1. The current command value computing unit 32B
then outputs,to the voltage command value computing unit 34,
the first reactive current command correction value Iq1' as
the first reactive current command value.
10 [0097] The active current command value Ip and the first
reactive current command correction value Iq1' computed by
the current command value computing unit 32B are input to
the voltage command value computing unit 34 or 35
illustrated in FIG. 5 or FIG. 7. Subsequently, the
15 alternating-current voltage command value vc* is computed
on the basis of the active current command value Ip and the
first reactive current command correction value Iq1’. The
switching command sw* is generated on the basis of the
alternating-current voltage command value vc* for
20 controlling the operation state of the converter 2a.
[0098] The current command value computing unit 32B
provides an improved accuracy in controlling the power
factor such that the power factor is a command value, as
compared with the current command value computing unit 32A.
25 [0099] Second Embodiment
The first embodiment discloses the magnitude of a
reactive current which the current command value computing
unit should output when the control target is a power
factor of 1 is disclosed. In contrast, the power factor
30 may be controlled such that the power factor is a value
other than 1 or a reactive power may be purposely
generated,for a purpose of, for example, stabilizing the
operation of a converter under a light load,or stabilizing
36
the operating voltage in cooperation with an alternatingcurrent
power supply. An explanation will be made as to
how the current command value computing unit computes a
reactive current so that the control unit controls the
5 power factor or the reactive power amount as intended.
[0100] FIG. 18 is a first vector diagram for explaining
a control technique according to a second embodiment.
First, as illustrated in FIG. 18, an axis in phase with the
sensor obtained voltage v^s is defined as a p-axis, and an
10 axis having a phase advanced by 90 degrees from the p-axis
is defined as a q-axis. Next, the instantaneous current
command value is* is resolved into a p-axis component ip
and a q-axis component iq3, assuming thatthe instantaneous
current command value is* has a phase advanced by a power
15 factor angle command value φ from that of the converted
secondary operating voltage vs. The p-axis component ip
has an amplitude corresponding to the active current
command value Ipprovided by the control unit 3. In
addition, the amplitude of the q-axis component iq3 is
20 represented by Iq3. In addition, a phase difference angle
that is an angle between the converted secondary operating
voltage vs and the sensor obtained voltage v^s is
represented by δ. In this case, the amplitude of the qaxis
component iq3 is expressed by the following formula.
25 [0101]
[Formula 15]
...(15)
[0102] Note that, k in the formula (15) is defined as
k=xm/|vs| as in the first embodiment. In the first
embodiment, in deriving the formula (13) from the formula
30 (11), “xm” expressed in a per-unit system is defined as “%x”
Iq3 IptanIptan k is / cos
37
and the approximation of (%x)2<<1 is used. This
approximation has essentially the same meaning as
approximation of δ≈0. Thus, the relation between the
instantaneous current command value is* and the active
5 current command value Ip is expressed by the following
formula.
[0103]
[Formula 16]
...(16)
[0104] The formula (16) is then substituted into the
10 formula (15), and the following formula is obtained.
[0105]
[Formula 17]
...(17)
[0106] Adesired reactive current is defined as a second
reactive current command value Iq2. In addition, the
15 alternating current is is controlled such that the
alternating current is is consistent with the instantaneous
current command value is*. For this reason, it is only
required that the instantaneous current command value is*
include a component orthogonal to the converted secondary
20 operating voltage vs, which component is consistent with
the second reactive current command value Iq2.
[0107] In addition, the instantaneous current command
value is* includes a componentthat is in phase with the
converted secondary operating voltage vs, which component
25 corresponds to the magnitude of the actual active current.
With the approximation of δ≈0, that in-phase component,
which is in phase with the converted secondary operating
is Ip/ cos~Ip/ cos
2 2 Iq3 Iptan kI p/ cos
38
voltage vs, can be deemed to be equal to the active current
command value Ip. In this case, tanφ=Iq2/Ip and
1/cos2φ=1+(Iq2/Ip)2hold true. Thus, the formula (17) can be
deformed as the following formula.
5 [0108]
[Formula 18]
...(18)
[0109] The second term on the right side of the formula
(18) is equal to the first reactive current command value
Iq1 explained in the first embodiment. Furthermore, when
10 the third term on the right side of the formula (18) is
defined as a second reactive current command correction
value Iq2', the formula (18) can be expressed by the
following formula.
[0110]
[Formula 19]
...(19)
15
[0111] Thus, a voltage command computing unit computes
an alternating-current voltage on the basis of the reactive
current command value Iq3 computed by the formula (19),
thereby achieving a desired reactive current even in the
20 presence of a phase difference angle δ. A configuration of
the current command value computing unit that achieves this
function is as in FIG. 19, for example. FIG. 19 is a block
diagram illustrating an example of a configuration of the
current command value computing unit according to the
25 second embodiment. In FIG. 19, components that are the
same or corresponding to those in FIG. 14 are represented
by the same reference numerals.
Iq3 Iq2 kI p kI q2 2 2 
Iq3 Iq1Iq2Iq2
39
[0112] A current command value computing unit 32C
illustrated in FIG. 19 further includes a second reactive
current command value computing unit 326 and a second
correction computing unit 327 in the configuration of FIG.
5 14. In FIG. 19, the second reactive current command value
computing unit 326 computes the second reactive current
command value Iq2 for a purpose of, for example,
stabilizing the operation of the converter under a light
load, or stabilizing the operating voltage in cooperation
10 with an alternating-current power supply. The second
correction computing unit 327 computes a second reactive
current command correction value Iq2' proportional to the
square of the second reactive current command value Iq2, on
the basis of the second reactive current command value Iq2
15 and the coefficient k that is a proportionality coefficient.
The second reactive current command value Iq2 and the
second reactive current command correction value Iq2' are
then added by an adder 328. The addition result provided
by the adder 328 is added to the first reactive current
20 command value Iq1 by an adder 329. Aresult of the addition
by the adder 329 is output as a reactive current command
value Iq3 to the voltage command value computing unit 34.
[0113] Note that, in FIG. 19, a value obtained by adding
the second reactive current command value Iq2 and the
25 second reactive current command correction value Iq2' is
added to the first reactive current command value Iq1 and
output to the voltage command value computing unit 34 by
the adder 329. As an alternative to this configuration,
the outputs may be individually output to the voltage
30 command value computing unit 34. In this case, needless to
say, a value obtained by adding the second reactive current
command value Iq2 and the second reactive current command
correction value Iq2' and the first reactive current
40
command value Iq1 are added within the voltage command
value computing unit 34, thereby providing the reactive
current command value.
[0114] FIG. 20 is a block diagram illustrating an
5 example of a configuration of the current command value
computing unit according to the second embodiment, which is
different from that in FIG. 19. In FIG. 20, components
that are the same or corresponding to those in FIG. 17 are
represented by the same reference numerals. A current
10 command value computing unit 32D illustrated in FIG. 20 is
an example configuration in a case where the control unit 3
has an enough computation capacity as in the first
embodiment. The configuration of FIG. 20uses the first
reactive current command correction value Iq1' expressed by
15 the formula(14) instead of the first reactive current
command value Iq1 in the formula (19). The configuration
of FIG. 20 can further improve the accuracy in controlling
the reactive current such that the reactive currentis a
desired value.
20 [0115] Note that the degree of freedom of the three
variables, the power factor, the active current, and the
reactive current is two, and when any two of these
variables are determined, the remaining one variable is
determined automatically. Because the active current is an
25 operation amount for controlling the direct-current voltage
such that the direct-current voltage is constant, the
remaining degree of freedom is either the reactive current
or the power factor. Thus, the second reactive current
command value computing unit may compute the second
30 reactive current command value Iq2 on the basis of a
command value for a power factor or a power factor angle,
which is not illustrated, and the active current command
value Ip.
41
[0116] As described above, according to the second
embodiment, the current command value computing unit of the
control unit computes the second reactive current command
value, and uses the coefficient k described above as the
5 proportionality coefficient to compute the second reactive
current command correction value proportional to the square
of the second reactive current command value. In addition,
the current command value computing unit outputs, to the
voltage command value computing unit, the second reactive
10 current command value and the second reactive current
command correction value, together with the first reactive
current command value described in the first embodiment.
In addition, the voltage command value computing unit
computes the alternating-current voltage command value on
15 the basis of the reference phase computed from the obtained
value from the second voltage sensor, the active current
command value, the first reactive current command value,
the second reactive current command value, and the second
reactive current command correction value. As a result, in
20 addition to the effects of the first embodiment, a desired
reactive current can be achieved even in the presence of
the phase difference angle, thereby making it possible for
the control unit to control the power factor or the
reactive power amount.
25 [0117] Third Embodiment
In a third embodiment, a case where the number of
power converting apparatuses is more than one will be
described. Note that, because the power converting
apparatuses and secondary windings of the voltage
30 transformer are connected in a one-to-one relationship with
each other as described above, the number of secondary
windings of the voltage transformer is,for example, twowhen
the number of power converting apparatuses is two.
42
[0118] FIG. 21 is a block diagram illustrating an
example of a configuration of main part of a power
conversion system according to the third embodiment. As
one example of a case where the number of power converting
5 apparatuses is more than one, FIG. 21 illustrates a
configuration in which two power converting apparatuses 10a
and 10b are each connected with a secondary winding 1b of a
voltage transformer 1A via a switch 12. Note that the role
of the switches 12 will be described later.
10 [0119] For an electric vehicle, as illustrated in FIG. 1,
the load 120 including the inverter 120a is connected to
the direct-current side of the converter 2a. The inverter
120a drives the motor 120b in order to apply driving force
to the electric vehicle. In addition, when the driving
15 force necessary for the entirety of the electric vehicle is
shared among a plurality of inverters 120a or when the
power capacity per one inverter 120a is large, a plurality
of power converting apparatuses 10a and 10b are each
connected with a secondary winding 1b of the voltage
20 transformer 1A as in FIG. 21. A device used for an
apparatus can be also used for another apparatus if these
apparatuses are the same in power capacity. For this
reason, the power converting apparatuses are equal in rated
power. In addition, the configurationas illustrated in FIG.
25 21, which supplies power to a plurality of power converting
apparatuses 10a and 10b via a single voltage transformer 1A,
can provide a smaller volume of the entire voltage
transformer than a configuration which includes power
converting apparatuses provided in a one-to-one
30 correspondence for voltage transformers.
[0120] FIG. 22 is a diagram illustrating an equivalent
circuit expressing the voltage transformer illustrated in
FIG. 21 by using an ideal voltage transformer and coupled
43
inductances. In FIG. 22, the voltage transformer 1A
illustrated in FIG. 21 is expressed by an ideal voltage
transformer 72 and coupled inductances 76.
[0121] In FIG. 22, “v1” represents a primary voltage,
5 “v2a” represents a first-group secondary voltage, “v2b”
represents a second-group secondary voltage, “v3”
represents a tertiary voltage, “i1” represents a primary
current, “i2a” represents a first-group secondary current,
“i2b” represents a second-group secondary current, and “i3”
10 represents a tertiary current. The other symbols represent
the same as those in FIG. 8.
[0122] Note that, in the equivalent circuit of FIG. 22,
circuit equations of the following formulas are satisfied.
[0123]
[Formula 20]
...(20)
15
[Formula 21]
...(21)
[0124] For the circuit equations of the equivalent
circuit in FIG. 22, the order of the reactance matrix,
whichincreases by one, is three because the number of
20 secondary windings increases as compared with the circuit
equations of the equivalent circuit in FIG. 8. The third
line of the formula (21) is developed, and the following
formula is thus obtained.
[0125]
i1 = n2i2a + n2i2b + n3i3





































i3
i2b
i2a
x3a x3b x33
xba xbb xb3
xaa xab xa3
j
v3
v2b
v2a
v1
n3
n2
n2
44
[Formula 22]
...(22)
[0126] As described above, in the basic configuration
illustrated in FIG. 5 or FIG. 7, the active current and the
reactive current are each controlled on the basis of the
5 reference phase θ. As expressed in the second term on the
right side of the formula (22), however, the tertiary
voltage v3 obtained by the voltage sensor 6 can have a
phase different from that of the primary voltage v1. This
results in a problem: the power factor or the reactive
10 power amount of the alternating-current power on the
primary side of the voltage transformer 1A is not as
instructed by the control unit 3. Thus, hereinafter, a
technique of the third embodiment that solves this problem
by correcting the instantaneous current command value is*
15 will be explained.
[0127] First, the formula (22) is deformed as the
following formula.
[0128]
[Formula 23]
...(23)
20 [0129] Note that, in the configuration of FIG. 21, the
load of the tertiary winding 1c is the voltage sensor 6
only. For this reason, assume that the tertiary current i3
is zero, i3=0. Althoughan electric vehicle may have
another load such as an auxiliary power supply connected to
25 the tertiary winding 1c, the power capacity thereof is
smaller than that of the converter of the secondary winding
in most cases. Thus, the assumption that the tertiary
v3 n3v1jx3ai2a x3bi2b x33i3
n2v1n2/ n3v3jn2/ n3x3ai2a x3bi2b x33i3
45
current i3 is ignored, i.e.,the tertiary current is zero
(i3=0) is reasonable and appropriate.
[0130] In addition, the left side of the formula (23) is
a value obtained by converting the primary voltage v1 into
5 a secondary voltage, and equal to the converted secondary
operating voltage vs. Furthermore, the first term on the
right side is a value obtained by converting the value
obtained by the voltage sensor 6 into a secondary voltage
equal to the sensor obtained voltage v^s. Because the
10 converters typically have the same rated power as described
above, it is assumed that the first-group secondary current
i2a and the second-group secondary current i2b in the
voltage transformer 1A are equal to each other. In
addition, because each of the secondary currents of the
15 voltage transformer 1A is equal to the alternating current
is of the corresponding converters, and the alternating
current is is controlled such that the alternating current
isisthe instantaneous current command value is*, the
currents i2a, i2b, is* are equal to one
20 another(i2a=i2b=is*). Furthermore, when a proportionality
coefficient “(n2/n3)(x3a+x3b)” in the second term on the
right side is defined as xm', i.e., xm'=(n2/n3)(x3a+x3b),
the following formula is thus obtained.
[0131]
[Formula 24]
...(24)
25
[0132] Comparison of the formula (24) with the formula
(9) reveals that these formulas(9) and (24) differ from
each other only in that the proportionality coefficient “xm”
in the second term on the right side in the formula (9) is
30 replaced with “xm'” in the formula (24). Thus, assuming
vs vˆs jxmis 
46
that xm'/|vs| is defined as k, i.e., k=xm'/|vs|, the
reactive current command value Iq which the current command
value computing unit should output is either one of the
following.
5 [0133]
[Formula 25]
...(25)
[Formula 26]
...(26)
[0134] Next, the role of the switches 12 illustrated in
FIG. 21 will be described. The power conversion systemof
10 an electric vehicle configured as illustrated in FIG. 21
may have the switches 12 opened so as to stop one or more
power converting apparatuses 10 under a specific condition.
Note that the specific condition is, for example,occurrence
of a failure in the operation of a power converting
15 apparatus. When a required propulsive force is small, only
a small number of power converting apparatuses may be
operated, which is advantageous in terms of power
efficiency.
[0135] For example, assume that the power converting
20 apparatus 10b of the second group is stopped and
disconnected by the switch 12 in the configurations of FIGS.
21 and 22. In this case, because of i2b=0, the formula
(23) is expressed by the following formula.
[0136]
[Formula 27]
Iq1 k I p 2 
2 Iq1Iq1/ 1kIp
47
...(27)
[0137] In addition, with i3=0, i2a=is*, xm"=(n2/n3)x3a,
and k"=xm"/|vs|as in the first embodiment, the reactive
current command value Iq which the current command value
5 computing unit shouldoutput is either one of the following.
[0138]
[Formula 28]
...(28)
[Formula 29]
...(29)
[0139] Comparison of the formulas (28) and (29) with the
10 formula (13) and the formula (14) reveals that the formula
(13) and the formula (14) differ from the formulas (28) and
(29) only in that the coefficient k in the formulas (13)
and (14) is replaced with k" in the formulas (28) and (29),
respectively. Thus, when the operating state or the
15 stopped state of a power converting apparatus is changed,
it is only required that the current command value
computing unit compute the reactive current in accordance
with the formula (13) or the formula (14) as in the first
embodiment, and change only the coefficient k.
20 [0140] When the reactance matrix is defined as expressed
by the formula (21)by way of example, the coefficient k
depending on the operating or stopped states of the power
converting apparatus 10a in the first group and the power
converting apparatus 10b in the second group can be
25 expressed as in the following table.
n2v1n2/ n3v3jn2/ n3x3ai2a x33i3
Iq1 k I p 2 
2 Iq1Iq1/ 1kIp
48
[0141] [Table 1]
First Group
Operating Stopped
Second
Group
Operating
Stopped
-
[0142] In addition, a configuration of the current
command value computing unit that achieves the function as
5 described above is as in FIG. 23, for example. FIG. 23 is
a block diagram illustrating an example of a configuration
of the current command value computing unit according to
the third embodiment. In FIG. 23, components that are the
same or corresponding to those in FIG. 14 are represented
10 by the same reference numerals.
[0143] A current command value computing unit 32E
illustrated in FIG. 23 further includes a coefficient
computing unit 330 in the configuration illustrated in FIG.
14. In addition, the coefficient computing unit 330
15 includes a first constant selector 3301, and a divider 3302.
[0144] In FIG. 23, information on an operating state of
the power converting apparatuses is input to the first
constant selector 3301. In accordance with the operating
states of the power converting apparatuses, thefirst
20 constant selector 3301 then selects a first constant xm
from a list held in advance. The divider 3302 then divides
the first constant xm by a rated value of the amplitude of
the converted secondary operating voltage vs. The output
of the divider 3302 is output as the coefficient k to the
25 first reactive current command value computing unit 324.
The divider 3302 may be omitted, and instead, results of
vs
x3a x3b
n3
n2 

vs
x3b
n3
n2

vs
x3a
n3
n2

49
division of the first constant xm by the rated value of the
amplitude of the converted secondary operating voltage vs
may be held on the list in advance. Subsequent operations
are as described above.
5 [0145] Alternatively, the coefficient computing unit 330
may be a component of the first reactive current command
value computing unit 324. Still alternatively, the
coefficient computing unit 330 may be included in a host
control system that is not illustrated, and the coefficient
10 k determined depending on the operating states of the power
converting apparatuses may be input to the current command
value computing unit.
[0146] While the technique of switching the coefficient
k to be used in the first reactive current command value
15 computing unit 324 in accordance with the operating or
stopped states of the power converting apparatuses has been
described above as being applied to the first embodiment by
way of example, a similar technique is also applicable to
the second embodiment,needless to say.
20 [0147] As described above, according to the third
embodiment, the control unit changes the first coefficient
in accordance with the operating or stopped states of a
plurality of power converting apparatuses. As a result,
even when the tertiary voltage obtained by the second
25 voltage sensor has a phase different from that of the
primary voltage, the power factor or the reactive power
amount of the alternating-current power on the primary side
of the voltage transformer can be controlled as instructed
by the control unit.
30 [0148] Fourth Embodiment
In the current command value computing unit of the
first to third embodiments, the coefficient k is determined
on the basis of the off-diagonal terms of the reactance
50
matrix and the amplitude of the converted secondary
operating voltage vs. Of these elements, those which come
from the off-diagonal terms of the reactance matrix are
desirably variable depending on the operating states of the
5 power converting apparatuses, as described in the third
embodiment. The amplitude of the converted secondary
operating voltage vs may vary depending on the states of
loads or time. In the vector diagrams of FIGS. 11, 13, and
18, the voltage drop across the reactance xm is smaller
10 than the converted secondary operating voltage vs and the
sensor obtained voltage v^s. Thus, the amplitude of the
sensor obtained voltage v^s can be treated as the amplitude
of the converted secondary operating voltage vs. Computing
the amplitude of the sensor obtained voltage v^s and,in
15 accordance with the value of the computed amplitude,
adjusting the coefficient k to be used in the current
command value computing unit enables the power factor on
the primary side of the voltage transformer 1Ato be
controlled more accurately as instructed by the control
20 unit 3.
[0149] A configuration of the current command value
computing unit that achieves the function as described
above is as in FIG. 24, for example. FIG. 24 is a block
diagram illustrating an example of a configuration of the
25 current command value computing unit according to a fourth
embodiment. In FIG. 24, components that are the same or
corresponding to those in FIG. 23 are represented by the
same reference numerals.
[0150] A current command value computing unit 32F
30 illustrated in FIG. 24 further includes an amplitude
computing unit 3303 in the coefficient computing unit 330A
in the configuration of FIG. 23. The amplitude computing
unit 3303 computes the amplitude of the sensor obtained
51
voltage v^s. A known technique is used for the technique
of computing the amplitude from an alternating-current
signal, and description thereof will thus be omitted herein.
A value obtained by dividing the first constant xm by an
5 output of the amplitude computing unit 3303 is then
obtained as the coefficient k, and output to the first
reactive current command value computing unit 324.
Specifically, in the fourth embodiment, the value of the
coefficient k is changed such that the value of the
10 coefficient kis inversely proportional to the output of the
amplitude computing unit 3303.
[0151] Note that, as in FIG. 23, the coefficient
computing unit 330A may be a component of the first
reactive current command value computing unit 324, or may
15 be included in a host control system, which is not
illustrated. While the technique of changing the value of
the coefficient k to be used in the current command value
computing unit in accordance with the amplitude of the
sensor obtained voltage v^shas been described above as
20 being applied to the third embodiment by way of example, a
similar technique is also applicable to the first and
second embodiments,needless to say.
[0152] As described above, according to the fourth
embodiment, a signal proportional to the amplitude of the
25 output of the first voltage sensor is computed, and the
value of the first coefficient is changed such that the
value of the first coefficientis inversely proportional to
the computation output. As a result, in addition to the
effects of the third embodiment, the power factor on the
30 primary side of the voltage transformer can be controlled
more accurately as instructed by the control unit even in a
case where the amplitude of the converted secondary
operating voltage changes depending on the states of loads
52
or time.
[0153] Note that the configurations presented in the
embodiments above are examples of the present invention,
and can be combined with other known technologies or can be
5 partly omitted or modified without departing from the scope
of the present invention.
Reference Signs List
[0154] 1, 1Avoltage transformer; 1aprimary winding;
10 1bsecondary winding; 1ctertiary winding; 2aconverter;
2bcapacitor; 3control unit; 4current sensor; 5, 6voltage
sensor; 10, 10a, 10bpower converting apparatus; 12switch;
30phase computing unit; 32, 32A, 32B, 32C, 32D, 32E,
32Fcurrent command value computing unit; 34, 35voltage
15 command value computing unit; 36switching command
generating unit; 50power conversion system; 60propulsion
controller; 70, 72ideal voltage transformer; 74, 76coupled
inductances; 100electric vehicle driving system; 106power
supply equipment; 108power line; 110feeding system;
20 120load; 120ainverter; 120bmotor; 300processor; 302memory;
303processing circuitry; 304interface; 320active current
command value computing unit; 321, 346, 352, 353subtractor;
322voltage controlling unit; 323, 343, 344multiplier;
324first reactive current command value computing unit;
25 325first correction computing unit; 326second reactive
current command value computing unit; 327second correction
computing unit; 328, 329, 345adder; 330, 330Acoefficient
computing unit; 336tangent value computing unit; 341sine
value computing unit; 342cosine value computing unit; 347,
30 354, 355current controlling unit; 351rotational coordinate
transforming unit; 356stationary coordinate transforming
unit; 3301first constant selector; 3302divider;
3303amplitude computing unit.
53
We Claim:
1. A power conversion system comprising: at least one
power converting apparatus including a converter to convert
an alternating-current power into a direct-current power, a
5 first voltage sensor to obtain a direct-current voltage
generated on a direct-current side of the converter, and a
control unit to control an operation state of the
converter; and a voltage transformer including a primary
winding connected to an alternating-current power supply,
10 at least one secondary winding, and a tertiary winding
connected with a second voltage sensor, the at least one
secondary winding being connected in a one-to-one
relationship with the at least one power converting
apparatus, wherein
15 the control unit includes:
a phase computing unit to compute a reference phase
from a value obtained by the second voltage sensor;
an active current command value computing unit to
compute an active current command value on the basis of a
20 deviation of a direct-current voltage command valuefrom the
direct-current voltage obtained by the first voltage
sensor;
a first reactive current command value computing unit
to compute a first reactive current command value
25 proportional to a square of the active current command
value, by using, as a proportionality coefficient, a first
coefficient determined by coupled inductances of the
voltage transformer and a received voltage of the voltage
transformer; and
30 a voltage command value computing unit to compute an
alternating-current voltage command value on the basis of
the reference phase, the active current command value, and
the first reactive current command value.
54
2. The power conversion system according to claim 1,
wherein
the control unit includes:
5 a first correction computing unit to compute a first
reactive current command correction value Iq1' by using a
formula (1) below on the basis of the active current
command value Ip, the first reactive current command value
Iq1, and the first coefficient k, and
10 the control unit outputs the first reactive current
command correction value as the first reactive current
command value to the voltage command value computing unit.
[Formula 1]
...(1)
15 3. The power conversion system according to claim 1 or 2,
wherein
the control unit includes:
a second reactive current command computing unit to
compute a second reactive current command value; and
20 a second correction value computing unit to compute a
second reactive current command correction value
proportional to a square of the second reactive current
command value, by using the first coefficient as a
proportionality coefficient, and
25 the control unit adds the second reactive current
command value and the second reactive current command
correction value to the first reactive current command
value, and outputs a resulting value to the voltage command
value computing unit.
30
4. The power conversion system according to claim 3,
2 Iq1Iq1/ 1kIp
55
wherein the second reactive current command computing unit
computes the second reactive current command value on the
basis of a power factor angle command value and the active
current command value.
5
5. The power conversion system according to any one of
claims 1 to 4, wherein
The at least one power converting apparatus is a
plurality of power converting apparatuses, and the at least
10 one secondary winding is a plurality of secondary windings,
and
the control unit changes a value of the first
coefficient in accordance with operating or stopped states
of the plurality of power converting apparatuses.
15
6. The power conversion system according to any one of
claims 1 to 5, wherein
the control unit includes an amplitude computing unit
to compute a signal proportional to an amplitude of an
20 output of the second voltage sensor, and
the control unit changes a value of the first
coefficient such that the value of the first coefficient is
inversely proportional to an output of the amplitude
computing unit.