Description
Title of Invention: POWER CONVERSION UNIT AND CONTROL ARRANGEMENT
THEREFOR
Technical Field
[0001]
The present invention relates to a power conversion unit and a
control arrangement therefor. More particularly, the present
invention is concerned with an AC~AC direct conversion type power
conversion unit that converts one three-phase alternating-current {AC}
power into another three-phase AC power of a variable amplitude or
frequency, and a control arrangement therefor.
Background Art
[0002]
A m.odular m.ultilevel converter (MMC) is a circuit having series
bodies {hereinafter, referred to as arms) , each of which includes plural
bidirectional chopper circuits and a reactor, coupled in a bridged
manner, and represents a circuit method for rectifiers or inverters
making it possible to output a voltage that is higher than a blocking
voltage of a power semiconductor device employed in each unit cell.
[0003]
For example, non-patent document 1 has disclosed that a direct
current {DC) transmission system (HVDC) can be formed by coupling DC
links of two MMCs.
[0004]
By coupling the DC links of two three-phase MMCs, a first
three-phase alternating-current (AC) power can be converted into a
" 2 -
second three-phase AC power of a variable amplitude or frequency.
Further, by applying the second three-phase AC power to an AC motor,
the AC motor can be operated at a variable velocity. Therefore, the
two MMCs can be adapted to a motor drive unit.
Citation List
Non-patent Literature
[0005]
Non-patent literature 1: T. Westerweller, K. Friedrich, U.
Armonies, A. Orini, D. Parquet, S. Wehn, "Trans Bay Cable - World's
First HVDC System using Multilevel Voltage-sourced Converter," CIGRE
2010, B4_101__2010
Summary of Invention
Technical Problem
[0006]
In an MMC, one reactor is needed for each arm. Therefore, in case
tvjo three-phase MMCs are used to form a motor drive unit, a total of
twelve reactors are needed.
[0007]
In case MMCs are used to form a high-voltage motor drive unit that
is linked directly to, for example, a 6. 6-kV system in a transformer-less
manner, assuming that an insulated gate bipolar transistor (IGBT) whose
blocking voltage is 4.5 kV is adopted, at least 144 on-off control
switching elements such as IGBTs (hereinafter, simply referred to as
IGBTs) are needed. The reason will be described below.
[0008]
For linkage'to the 6.6-kV system in a transformer-^less manner,
" 3 -
a series foody of plural bidirectional chopper circuits included in each
arm has to be able to output a phase voltage, that is, a voltage of
6.6/V3 approximately equal to 3.8 kV.
[0009]
Assuming that a DC capacitor voltage of one bidirectional chopper
circuit is 2.25 kV that is 50% of the blocking voltage of 4.5 kV of
IGBTs, and a maximum modulation factor is 0.9, an effective value of
a maximum AC voltage which the one bidirectional chopper circuit can
output is 2.25/2/^2x0.9 approximately equal to 0.716 kV.
[0010]
By dividing 3.8 kV by 0. 716 kV, a necessary number of bidirectional
chopper circuits needed for each arm is determined. 3.8/0.716
approximately equal to 5. 31 ensues. At least six bidirectional chopper
circuits are needed, where 6 is an integer exceeding 5.31.
[0011]
A three-phase MMC to be coupled to a 6.6-kV system is formed by
coupling six arms, each of which includes six bidirectional chopper
circuits and one reactor, in a bridged manner, and a three-phase MMC
to be coupled to an AC motor is formed by coupling six other arms in
the bridged manner. Therefore, twelve arms are needed in total. As
for the number of bidirectional chopper circuits, at least 6x6x2=72
circuits are needed.
[0012]
Since at least two IGBTs are needed for one bidirectional chopper
circuit, 2x72=144 IGBTs are needed for the total of 72 chopper cells.
[0013] : . • - ...
4
Accordingly, an object of the present invention is to provide a
power conversion unit making it possible to realize a variable amplitude
or frequency despite a simple configuration while reducing the number
of reactors and the number of IGBTs, and a control arrangement therefor.
Solution to Problem
[0014]
In order to accomplish the above object, in the present invention,
a leg is formed by coupling in series with one another a reactor, a
first cluster that is a series body of plural unit cells, and a second
cluster that is a series body of plural unit cells. Three legs are
delta-connected. Three junction points of the delta-connected legs
are coupled to the respective phases of a first three-phase AC facility,
and junction points between the first and second clusters of the legs
are coupled to the respective phases of a second three-phase AC facility.
[0015]
One of the first three-phase AC facility and second three-phase
AC facility is a power system.
[0016]
Both the first three-phase AC facility and second three-phase AC
facility are power systems.
[0017]
The first three-phase AC facility is a power system, and the second
three-phase AC facility is a motor.
[0018]
The unit cells are two-terminal elements capable of outputting
an arbitrary voltage. •,-
- 5 -
[0019]
The unit cells can output a positive, negative, or zero voltage,
and each include an energy storage element.
[0020]
Each of the unit cells is formed with a full bridge circuit.
[0021]
In order to accomplish the foregoing object, in the present
invention, in a control arrangement for a power conversion unit in which:
a leg is formed by coupling in series with one another a reactor, a
first cluster that is a series body of plural unit cells, and a second
cluster that is a series body of plural unit cells; three legs are
delta-connected; three junction points of the delta-connected legs are
coupled to the respective phases of a first three-phase Ac facility;
and junction points between the first and second clusters of the legs
are coupled to the respective phases of a second three-phase AC facility,
control is extended so that the sum of an active power produced with
a frequency component of the first three-phase AC facility of an output
voltage of each of the clusters and a frequency component of the first
three-phase AC facility of a current flowing through each of the clusters,
and an active power produced with a frequency component of the second
three-phase AC facility of the output voltage of each of the clusters
and a frequency component of the second three-phase AC facility of the
current flowing through each of the clusters becomes substantially
zero.
[0022]
In order to accomplish the foregoing object, in the present
- 6 -
invention, in a control arrangement for a power conversion unit in which:
a leg is formed by coupling in series with one another a reactor, a
first cluster that is a series body of plural unit cells, and a second
cluster that is a series body of plural unit cells; three legs are
delta-connected; three junction points of the delta-connected legs are
coupled to the respective phases of a first three-phase AC facility;
and junction points between the first and second clusters of the legs
are coupled to the respective phases of a second three-phase AC facility,
control is extended so that the sum of a reactive power produced with
a frequency component of the first three-phase AC facility of an output
voltage of each of the clusters and a frequency component of the first
three-phase AC facility of a current flowing through each of the clusters,
and a reactive power produced with a frequency component of the second
three-phase AC facility of the output voltage of each of the clusters
and a frequency component of the second three-phase AC facility of the
current flowing through each of the clusters becomes substantially
zero.
[0023]
In order to accomplish the foregoing object, in the present
invention, in a control arrangement for a power conversion unit in which:
a leg is formed by coupling in series with one another a reactor, a
first cluster that is a series foody of plural unit cells, and a second
cluster that is a series body of plural unit cells; three legs are
delta-connected; three junction points of the delta-connected legs are
coupled to the respective phases of a first three-phase AC facility;
and junction points between the first and second clusters-of the legs
„ 7 -
are coupled to the respective phases of a second three-phase AC facility,
three first control signals are obtained with line currents of the first
three-phase AC facility regarded as target signals, three second
control signals are obtained with line currents of the second
three-phase AC facility regarded as target signals, and the first and
second clusters of each of the legs are controlled based on a sum signal
of the first control signal and second control signal on the lines
involved with the clusters.
Advantageous Effects of Invention
[0024]
Compared with a high-voltage motor drive unit of a type employing
two MMCs, a power conversion unit in accordance with the present
invention enables reduction in the number of necessary reactors and
the num.bor of necessary IGBTs.
[0025]
According to, for example, an embodiment of a high-voltage motor
drive unit linked to a 6.6-kV system in a transformer-less manner, the
number of reactors can be reduced from twelve to three, and the number
of IGBTs can be reduced from 144 to 120. The reason will be described
later in relation to a first embodiment.
Brief Description of Drawings
[0026]
Fig. 1 is a diagram showing an example of a high-voltage motor
drive unit employing a power conversion unit of the present invention.
Fig. 2 is a diagram showing the internal configuration of a unit
c e l l . -.••••
Fig. 3 is a vector diagram showing the relationship of currents
and voltages of circuit components shown in Fig. 1.
Fig. 4 is a diagram showing waveforms of voltages and currents
of components observed when output voltages of clusters are controlled.
Fig. 5 is a diagram showing the configuration of a leg having
reactors symmetrically disposed.
Fig. 6 is a configuration diagram in which a power interchange
unit is realized using a power conversion unit of the present invention.
Fig. 7 is a diagram presenting an output voltage control method
for a unit cell.
Fig. 8 is a diagram showing an example of a control arrangement
for a power conversion unit of the present invention.
Description of Embodiments
[0027]
Embodiments of the present invention will be described below in
conjunction with the drawings.
First Embodiment
[0028]
Fig. 1 shows the configuration of a power conversion unit in
accordance with a first embodiment of the present invention.
[0029]
In the embodiment shown in Fig. 1, a high-voltage motor drive unit
102 is formed that: has three legs 104, each of which is a series body
of one reactor 103, a first cluster 105 formed with a series body of
five unit cells 106, and a second cluster 105 formed with a series body
of five'unit cells, 10,6, delta-connected; has junction points, at which
- 9 ~
the three legs 104 are delta-connected, coupled to, for example, a6.6~kV
power system 101; has three junction points between the first and second
clusters 105 of the legs 104 coupled to an AC motor 107; converts a
power obtained from the 6.6~k:V power system 101 into a
variable-amplitude or variable-frequency power; and feeds the power
to the AC motor 107.
[0030]
Compared with a related art employing two MMCs, the first
embodiment has the advantage of enabling reduction in the number of
reactors and the number of IGBTs. The reason and a reason why the number
of unit cells 106 included in each of the clusters 105 is five will
be described later successively to a description of the configuration
and principle of operation of the high-voltage motor drive unit of the
present embodiment.
[0031]
The overall configuration of the first embodiment will be described
below in conjunction with Fig. 1.
[0032]
A high-voltage motor drive unit 102 is coupled to a three-phase
power system 101 and a three-phase AC motor 107, and controls a power
to be transferred between the power system 101 and AC motor 107 . Herein,
the phases of the three-phase power system 101 are denoted with R, S,
and T respectively, and the phases of the three-phase AC motor are
denoted with U, V, and W respectively. The phase voltages of the
three-phase power system 101 are denoted with VGR, VGS, and VGT
respectively, and the line voltages of the three-phase power system
10
101 are denoted with VGRS, VGST, and VGTR respectively.
[0033]
The high-voltage motor drive unit 102 includes legs 104 for the
lines of the three-phase power system 101. The leg provided for the
R and S phases of the three-phase power system 101 is a leg 104RS.
Likewise, the leg provided for the S and T phases is a leg 104ST, and
the leg provided for the T and R phases is a leg 104TR.
[0034]
Each of the legs 104 is formed with a series body of one reactor
103, a first cluster 105, and a second cluster 105. Junction points
between the first clusters and second clusters are coupled to the
respective phases U, V, and W of the three-phase AC motor 107.
[0035]
For exam.ple, the RS-phase leg 104RS coupled to the R phase and
S phase of the power system 101 is a series body of the reactor 103,
RU-phase cluster 105RU, and US-phase cluster 105US. The junction point
between the RU-phase cluster 105US and US-phase cluster 105US is called
a U point, and the U point is coupled to the U phase of the AC motor
107.
[0036]
The ST-phase leg 104ST coupled to the S phase and T phase of the
power system 101 is a series body of the reactor 103, SV-phase cluster
105SV, and VT-phase cluster 105VT. The junction point between the
SV-phase cluster 105SV and VT~phase cluster 105VT is called a V point,
and the V point is coupled to the V phase of the AC motor 107.
[0037] • '-. ., ' . •.•••.' -
- 11 ~
The TR-phase leg 104TR coupled to the T phase and R phase of the
power system 101 is a series body 6T the reactor 103, TW-phase cluster
105TW, and WR-phase cluster 105WR. The junction point between the
TW-phase cluster 105TW and WR~phase cluster 105WR is called a W point,
and the W point is coupled to the W phase of the AC motor 107.
[0038]
Each of the clusters 105RU, 105US, 105SV, 105VT, 105TW, and 105WR
is a series body of five unit cells 106.
[0039]
In the foregoing description, two alphabets (any of R, S, T, U,
V, and W) appended to a numeral (104 or 105) signifying a device denotes
lines onto which the device is coupled. In addition, one alphabet (R,
S, T, U, V, or W) appended to a voltage or current (VG or I) signifies
that the voltage or current has a relevant phase. Hereinafter, the
alphabets (R, S, T, U, V, and W) appended to numerals or alphabets will
signify the phases or lines according to the above denotation approach,
though a description will not especially be made.
[0040]
The internal configuration of the unit cell 10 6 and an output
voltage control method therefor will be described below. Thereafter,
the principle of operation of the high-voltage motor drive unit 102
will be described. To begin with, the internal configuration of the
unit cell 106 will be described in conjunction with Fig, 2.
[0041]
Fig. 2 shows as an example the internal configuration of a first
unit cell of the cluster 105RU. The unit.cell 106 is a full bridge
- 12 -
circuit and includes two legs (X~phase leg and Y-phase leg) and a DC
capacitor 203 coupled to each of the legs. The X-phase leg is a series
body of a parallel body including an IGBT 201XH and antiparallel diode
202XH and a parallel body including an IGBT 201XL and antiparallel diode
202XL. The Y~phase leg is a series body of a parallel body including
an IGBT 201YH and antiparallel diode 202YH and a parallel body including
an IGBT 201YL and antiparallel diode 202YL,
[0042]
In the thus-configured unit cell 106, an output of the unit cell
is fetched as a potential difference VRUl between a parallel-body
junction point X of the X-phase leg and a parallel-body junction point
Y of the Y-phase leg. The DC capacitor 203 is coupled to the upper
and lower terminals of the legs 201 that are coupled to each other in
parallel with each other. The terminal voltage of the DC capacitor
203 is denoted with VCRUl. In the embodiment shown in Fig. 2, the unit
cell is formed using IGBTs. As long as semiconductor switching elements
are employed, the unit cell is not limited to the IGBTs.
[0043]
Next, the output voltage control method for the unit cell will
be described in conjunction with Fig. 7. The output voltage VRUl of
the unit cell 106 can be controlled through switching of four
semiconductor switching elements IGBTs (201XH, 201XL, 201YH, and 201YL)
included in the full bridge circuit. Now, the relationship of the
on/off states of the IGBTs to the output voltage of the unit cell will
be described below by taking for instance the first cell of the RU-phase
cluster a04RU.
- 13 ~
[0044]
In this case, the effective combinations of on and off states of
the four semiconductor switching elements are, as shown in Fig. 7, four
combinations described below.
[0045]
The first combination is such that the element 201XH is on, the
element 201XL is off, the element 201YH is on, and the element 201YL
is off. In this case, the output voltage VRUl is substantially zero.
[0046]
The second combination is such that the element 201XH is on, the
element 201XL is off, the element 201YH is off, and the element 201YL
is on. In this case, the output voltage VRUl is substantially equal
to the DC capacitor voltage VCRUl.
[0047]
The third combination is such that the element 201XH is off, the
element 201XL is on, the element 201YH is off, and the element 201YL
is on. In this case, the output voltage VRUl is substantially zero.
[0048]
The fourth combination is such that the element 201XH is off, the
element 201XL is on, the element 2 01YH is on, and the element 201YL
is off. In this case, the output voltage VRUl is substantially equal
to a voltage -VCRUl whose polarity is opposite to that of the DC capacitor
voltage.
[0049]
Other combinations may be made. For example, as a combination
causing the legs to be strapped, the elements 201XH and 201XL are
- 14 -
simultaneously turned on. In this case, the DC capacitor 203 is
short-circuited. Therefore, the actions are inhibited. Likewise,
when the elements 201YH and 201YL are simultaneously turned on, the
DC capacitor 203 is short-circuited. Therefore, the actions are
inhibited.
[0050]
The principle of operation of the high-voltage motor drive unit
102 will be described below.
[0051]
Each of the clusters 105 is a series body having the output
terminals (X node and Y node in Fig. 2) of five unit cells 106 coupled
in series with one another. Therefore, the terminal voltage of, for
example, the cluster 105RU is the sum of terminal voltages of the five
unit cells 106 forming the cluster 105RU. In the exam.ple shown in Fig.
2, the terminal voltage of the first unit cell is denoted with VRUl.
Assuming that the other unit cell voltages are denoted with VRU2, VRU3,
VRU4, and VRU5 respectively, the sum of the voltages becomes the terminal
voltage VRU of the cluster 105RU.
[0052]
The relationship is also established for the output voltages (VRU,
VUS, VSV, VVT, VTW, and VWR) of all the clusters 105. Each of the output
voltages is the sum of output voltages of five unit cells 106 included
in each of the clusters. Therefore, by controlling the on/off states
of IGBTs included in each of the unit cells 106, the output voltage
(VRU, VUS, VSV, VVT, VTW, or VWR) of each of the clusters can be
controlled. : . . , •• . • •;
- 15
[0053]
By adopting phase-shift pulse-width modulation (PWM), the output
voltages VRU, VUS, VSV, VVT, VTW, and VWR of the respective clusters
can be controlled to be arbitrary waves having a frequency component
equal to or lower than a triangle-wave carrier frequency.
[0054]
A description will be made below by noting only a frequency
component of the power system 101 (hereinafter, referred to as a system
frequency component), which is a must for the function of the
high-voltage motor drive unit 102, and a frequency component of the
AC motor 107 (hereinafter, referred to as a motor frequency component)
out of frequency components contained in the output voltages (VRU, VUS,
VSV, VVT, VTW, and VWR) of the clusters. To begin with, the principle
of operation of the high-voltage motor drive unit 102 will be outlined
below. Thereafter, the principle of operation will be detailed in
conjunction with Fig. 3.
[0055]
As shown in Fig. 1, the high-voltage motor drive unit 102 is coupled
to each of the power supply (power system 101) and load (AC motor 107) ,
and transfers an active or reactive power to or from the power supply
and load. Therefore, in the high-voltage motor drive unit 102, circuit
connections to the power system 101 and actions, and circuit connections
to the AC motor 107 and actions are present.
[0056]
In the high-voltage motor drive unit 102, for the power system
101,.the RU-phase cluster 105RU and US-phase cluster 105US act-as a
- 16 ~
first pair coupled to the R and S phases of the power system 101. The
SV-phase cluster 105SV and VT-phase cluster 105VT act as a second pair
coupled to the S and T phases of the power system 101. The TW~phase
cluster 105TW and WR-phase cluster 105WR act as a third pair coupled
to the T and R phases of the power system 101. The pairs transfer an
active or reactive power to or from the power system 101.
[0057]
In contrast, for the AC motor 107, the US-phase cluster 105US and
SV-phase cluster 105SV act as a first pair coupled to the U and V phases
of the AC motor 107. The VT-phase cluster 105VT and TW-phase cluster
105TW act as a second pair coupled to the V and W phases of the AC motor
107. The WR-phase cluster 105WR and RU-phase cluster 105RU act as a
third pair coupled to the W and R phases of the AC motor 107. The pairs
transfer an active or reactive power to or from the AC motor 107.
[0058]
If an active power each of the clusters 105 receives from the power
system 101 is equal to an active power to be fed to the AC motor 107,
inflow energy and outflow energy of the DC capacitors 202 of the unit
cells 106 forming each of the clusters 105 are balanced. By
substantially sustaining the balanced state, overcharge or
over-discharge of the DC capacitors 202 can be avoided. Accordingly,
the high-voltage motor drive unit 102 can be operated uninterruptedly.
A control method for a DC capacitor voltage will be detailed later.
[0059]
Referring to Fig. 3, the principle of operation of the high-voltage
motor drive unit 102 will be detailed below. ; Fig. 3 is a vector diagram
- 17 -
showing the relationship of currents and voltages of circuit components
shown in Fig. 1.
[0060]
In the vector diagram of Fig. 3, R, S, and T denote power supply-side
junction points shown in Fig. 1, and VGRS, VGST, and VGTR denote
inter-junction point voltages, that is, line voltages of the power
system 101. Hereinafter, the voltages shall be referred to as system
line voltages.
[0061]
The system line voltages (VGRS, VGST, and VGTR) are applied to
the respective terminals (R, S, and T) of the legs 104. Each of the
legs 104 is a series body of the reactor 103, first cluster, and second
cluster. Therefore, Fig. 3 shows the inter-junction point voltages
of the elements.
[0062]
To begin with, the junction point voltage between the reactor 103
and first cluster will be described by taking for instance the leg 104RS.
Assuming that the junction point between the reactor 103 and first
cluster 105RU is denoted with R', the terminal voltage VLRS of the
reactor 103 is a voltage that lags 90° behind the system line voltage
VGRS. The relationship is also established with respect to the other
system line voltages VGST and VGTR. However, the junction points are
denoted with S' and T' respectively, and the terminal voltages of the
reactors 103 are denoted with VLST and VLTR respectively.
[0063]
•As a result," a voltage, to be applied to the terminals of• the first
~ 18 ~
and second clusters (hereinafter, referred to as a leg voltage) is a
voltage VRS between the junction point R' and junction point S in the
case of the leg 104RS. Likewise, in the case of the leg 104ST, the
leg voltage is a voltage VST between the junction point S' and junction
point T. In the case of the leg 104TR, the leg voltage is a voltage
VTR between the junction point T' and junction point R.
[0064]
Next, the junction point voltage between the first cluster and
second cluster will be described below by taking for instance the leg
104RS. The junction point between the first cluster 105RU and second
cluster 105US is the U point. The terminal voltage of the cluster 105RU
is denoted with VRU, and the terminal voltage of the second cluster
105US is denoted with VUS. The sum of the voltages VRU and VUS is the
leg voltage VRS. Likewise, in the case of the leg 104ST, the junction
point is the V point, the voltages of the clusters are denoted with
VSV and VVT, and the sum of the voltages VSV and VVT is the leg voltage
VST. In the case of the leg 104TR, the junction point is the W point,
the voltages of the clusters is denoted with VTW and VWR, and the sum
of the voltages VTW and VWR is the leg voltage VTR.
[0065]
In Fig. 1, a current flowing from the junction point R into the
leg 104RS is denoted with IRU, and a current flowing out from the leg
104RS to the junction point S is denoted with lUS, though the currents
are not shown in Fig. 3. Likewise, in Fig. 1, a current flowing from
the junction point S into the leg 104ST is denoted with ISV, and a current
flowing out from-the leg 104TR to the junction point T is denoted with
19
IVT. A current flowing from the junction point T into the leg 104TR
is denoted with ITW, and a current flowing out from the leg 104TR to
the junction point R is denoted with IWR.
[0066]
A current flowing in or out from the junction point R, S, or T
is not shown in Fig. 3. However, a system frequency component contained
in common in the inflow current IRU and outflow current lUS of the leg
104RS, a system frequency component contained in common in the inflow
current ISV and outflow current IVT of the leg 104ST, and a system
frequency component contained in common in the inflow current ITW and
outflow current IWR of the leg 104TR are shown in Fig. 3 while being
denoted with IGRS, IGST, and IGTR respectively. The system frequency
components IGRS, IGST, and IGTR are in phase with the aforesaid leg
voltages (VRS, VST, and VTS) respectively.
[0067]
In Fig. 3, the foregoing currents and voltages represent the vector
relationship of the high-voltage motor drive unit 102 to the side of
the power system 101. In contrast, the vector relationship of the
high-voltage motor drive unit 102 to the side of the AC motor 107 will
be described below.
[0068]
In this case, a voltage to be applied to each of the phases of
the AC motor 107 (applied phase voltage of the AC motor 107 : hereinafter,
referred to as a motor phase voltage) is a voltage between a neutral
point N and the junction point U, V, or W, and shall be denoted with
VU,- VV,. or VW. The applied line -voltage of the.AC-motor 107 at- this
- 20 -
time (hereinafter, referred to as a motor line voltage) shall be denoted
with VUV, W W , or VWU.
[0069]
As currents on the side of the AC motor 107, phase currents lU,
IV, and IW and motor frequency components IM are shown in Fig. 3. As
for the motor frequency components IM, a motor frequency component
contained in common in the currents lUS and ISV which flow through the
clusters 105 is denoted with IMUV, a motor frequency component contained
in common in the currents IVT and ITW which flow through the clusters
105 is denoted with IMVW, and a motor frequency component contained
in common in the currents IWR and IRD which flow through the clusters
105 is denoted with IMWU.
[0070]
Further, in Fig. 3, a voltage between the neutral point N of the
AC motor 107 and the junction point R' , S' , or T' is shown and denoted
with VR, VS, or VT.
[0071]
In Fig. 3, the power factor of the high-voltage motor drive unit
102 with respect to the power system 101 and the power factor of the
AC motor 107 with respect to the high-voltage drive unit 102 are
substantially Is . Even if the power factors are not Is, a similar vector
diagram can be drawn.
[0072]
Fig. 3 is a vector diagram drawn with the system frequency
components (IGRS, IGST, and IGTR) regarded as references. Therefore,
if the.system frequency,and motor frequency are different from:each
- 21
other, although a triangle RST formed with the vectors of the system
line voltages VGRS, VGST, and VGRS is fixed, a triangle UVW formed with
the vectors of the motor phase voltages VU, VV, and VW is turned based
on a difference frequency between the system frequency and motor
frequency.
[0073]
Fig. 3 may be interpreted as a vector diagram drawn with the motor
frequency components {IMUV, IMVW, and IMWU) regarded as references.
In this case, if the system frequency and motor frequency are different
from each other, although the triangle UVW formed with the vectors of
the motor phase voltages VU, VV, and VW is fixed, the triangle RST formed
with the vectors of the system line voltages VGRS, VGST, and VGRS is
turned based on the difference frequency between the system frequency
and m.otor frequency.
[0074]
To begin with, the principle on which the high-voltage motor drive
unit 102 receives an active power from the power system 101 will be
described by noting the RU-phase cluster 105RU and US-phase cluster
105US that are coupled to the R and S phases of the power system 101.
[0075]
In Fig. 3, the phase of the leg voltage VRS {=VRU+VUS) of the
RS-phase leg 104RS is caused to lag behind that of the system line voltage
VGRS, and the tip of the vector VRS is controlled to meet, for example,
the R' point, whereby the voltage VLRS across the reactor 103 becomes
a voltage substantially orthogonal to the leg voltage VRS.
[007.6] : . •, . • :••..••• - . . • - '•
- 22 -
Since a current flowing through the reactor 103 is a current that
lags 90° behind the voltage VLRS across the reactor 103, the current
IGRS shown in Fig. 3 flows. The power factor to the current IGRS and
leg voltage VRS is substantially 1. An active power flows from the
power system 101 to the RU~phase cluster 105RU and US-phase cluster
105US that form the RS-phase leg 104RS.
[0077]
As mentioned previously, the current IGRS is a system frequency
component contained in common in the current IRU, which flows through
the RU-phase cluster 105RU, and the current lUS that flows through the
US-phase cluster 105US.
[0078]
In the foregoing description, the RS-phase leg 104RS is taken for
instance. The ST-phase leg 104ST and TR~phase leg 104TR act in a sim.ilar
manner, though the phases are turned 120°.
[0079]
Therefore, the current IGST that is a system frequency component
is contained in common in the currents ISV and IVT that flow through
the SV-phase cluster 105SV and VT-phase cluster 105VT respectively
which are included in the ST-phase leg 104ST. The current IGTR that
is a system frequency component is contained in common in the currents
ITW and IWR that flow through the TW-phase cluster 105TW and WR-phase
cluster 105WR respectively which are included in the TR~phase leg 104TR.
[0080]
Next, the principle on which the high-voltage motor drive unit
102 feeds an activepower to the AC motor 107 will be described by noting
- 23 -
as an example the US-phase cluster 105US and SV-phase cluster 105SV
that are coupled to the U and V phases respectively of the AC motor
107.
[0081]
In Fig. 3, the line voltage VUV between the U and V phases of the
AC motor 107 is seen to be expressed as VUV=VSV+VLST+VUS. Therefore,
by controlling the output voltage VUS of the US-phase cluster 105RU
and the output voltage VSV of the SV-phase cluster 105SV, the line
voltage VUV to be applied to the AC motor 107 can be controlled. Not
only the line voltage between the U and V phases but also the line voltage
between the V and W phases or the line voltage between the W and U phases
can be controlled by controlling the output voltages of the clusters.
[0082]
The phase voltage VU, VV, or VTA^ to be applied to the AC motor 107
is expressed as formula (1) , formula (2) , or formula (3) using the line
voltage VUV, W W , or VWU.
[Math. 1]
VU = (VUV-VWU)/3 (1)
[Math. 2]
VV = (VVW-VUV)/3 (2)
[Math. 3]
VW = (VWU-VVW)/3 (3)
If the voltage VU, VV, or VW is applied, to the AC motor 107, the
current lU, IV, or IW dependent on an equivalent impedance of the AC
motor 107 flow. Therefore, as long as the power factor of the AC motor
107 is not zero, an active power-can be fed fromthe high-voltage motor
24
drive unit 102 to the AC motor 107.
[0083]
The current IMUV that is a motor frequency component travels in
common in the currents IDS and ISV that flow through the US-phase cluster
105US and SV-phase cluster 105SV respectively coupled to the U and V
phases of the AC motor 107. The current IMUV of the motor frequency
component is expressed as a formula (4).
[Math. 4]
IMUV - -(lU-IV)/3 (4)
Likewise, the current IMVW that is a motor frequency component
travels in common in the currents IVT and ITW that flow through the
VT-phase cluster 105VT and TW-phase cluster 105TW respectively. The
current IMVW of the motor frequency component is expressed as a formula
[Math. 5]
IMVW = -(IV~IW)/3 (5)
Likewise, the current IMWU that is a motor frequency component
travels in common in the currents IWR and IRU that flow through the
WR-phase cluster 105WR and RU~phase cluster 105RU respectively. The
current IMWU of the motor frequency component is expressed as a formula
(6) .
[Math. 6]
IMWU - -(XW-IU)/3 (6)
Now, a control method for the voltage vectors of the clusters and
the currents flowing through the clusters will be described below.
.[0084]. . . ••-. . •. . ,••::::.,
- 25 -
As apparent from the foregoing description, in order to receive
an active power from the power system 101 and feed the active power
to the AC motor 107, what will be described below should be carried
out in relation to each of the phases. First, the vector of the voltage
VRU of the RU-phase cluster 105RU should be controlled to be a vector
extending from the U point in Fig, 3 to, for example, the R' point.
The current IRU flowing through the RU-phase cluster 105RU becomes the
sum of the system frequency component IGRS and motor frequency component
IMWU.
[0085]
Likewise, the vector of the voltage VUS of the US-phase cluster
105US should be controlled to be a vector extending from the S point
in Fig. 3 to the U point. At this time, the current lUS flowing through
the US-phase cluster 105US becomes the sum. of the system frequency
component IGRS and motor frequency component IMUV.
[0086]
Likewise, the vector of the voltage VSV of the SV-phase cluster
105SV should be controlled to be a vector extending from the V point
in Fig. 3 to, for example, the S' point. At this time, the current
ISV flowing through the SV-phase cluster 105SV becomes the sum of the
system frequency component IGST and motor frequency component IMUV.
[0087]
Likewise, the vector of the voltage VVT of the VT-phase cluster
105VT should be controlled to be a vector extending from the T point
in Fig. 3 to the V point. At this time, the current IVT flowing through
the VT cluster lOSVT becomes the sum of the system frequency, component
26
IGST and motor frequency component IMVW.
[00883
Likewise, the vector of the voltage VTW of the TW-phase cluster
105TW should be controlled to be a vector extending from the W point
in Fig. 3 to, for example, the T' point. At this time, the current
ITW flowing through the VT-phase cluster 105VT becomes the sum of the
system frequency component IGTR and motor frequency component IMVW.
[0089]
Likewise, the vector of the voltage VWR of the WR-phase cluster
105WR should be controlled to be a vector extending from the R point
in Fig. 3 to the W point. At this time, the current IWR flowing through
the WR-phase cluster 105R becomes the sum of the system frequency
component IGTR and motor frequency component IMWU.
[0090]
As mentioned above, when the power conversion unit shown in Fig.
1 is interposed between two three-phase AC facilities, transfer of a
power can be achieved by performing as mentioned below. That is to
say, control should be extended so that the sum of an active power
produced with a frequency component of the first three-phase AC facility
of an output voltage of each of the clusters and a frequency component
of the first three-phase AC facility of a current flowing through each
of the clusters, and an active power produced with a frequency component
of the second three-phase AC facility of the output voltage of each
of the clusters and a frequency component of the second three-phase
AC facility of the current flowing through each of the clusters becomes
substantially zero. .: Herein^ the active powers may be'read for reactive
- 27 -
powers being controlled to be substantially constant.
[0091]
Fig. 4 shows examples of waveforms of voltages and currents
observed at components in case the output voltages of the clusters 105
are controlled as mentioned above. In Fig. 4, the right side shows
the waveforms of the currents^ and the left side shows the waveforms
of the voltages. The upper part shows an example of the waveforms of
the voltages and currents of the clusters 105, the intermediate part
shows an example of the waveforms of phase voltages, line voltages,
and phase currents of the AC system 101, and the lower part shows an
example of the waveforms of phase voltages, line voltages, and phase
currents of the AC motor 107.
[0092]
The drawing shows the examples of the waveforms of the voltages
and currents on the assumption that the line voltage effective value
of the power system 101 is 6.6 kV, the freguency thereof is 50 Hz, the
line voltage effective value of the AC motor 107 is 3. 96 kV, the frequency
thereof is 30 Hz, and an active power is 1 MW. A carrier frequency
employed in phase-shift PWM is 450 Hz.
[0093]
In the drawing, the waveforms of the cluster voltages VRU, VUS,
VSV, VVT, VTW, and VWR are shown to have command values VRU*, VUS*,
VSV*, VVT*, VTW*, and VWR* thereof superimposed thereon with white lines .
[0094]
As shown in Fig. 4, both a system frequency {50 Hz) component and
motor frequency {30 Hz) component are seen to be present, in.the output
- 28 -
voltages and currents of the respective clusters 105.
[0095]
Next, a description will be made of the fact that the high-voltage
motor drive unit 102 receives an active power from the power system
101.
[0096]
In Fig. 3, the phases of fundamental-wave components of the output
voltages VRS, VST, and VTR of the respective legs lag behind those of
the line voltages VGRS, VGST, and VGTR respectively of the power system
101. Accordingly, the currents IGRS, IGST, and IGTR that are system
frequency components substantially in phase with the voltages VRS, VST,
and VTR respectively flow through the reactors 103.
[0097]
A current obtained by perform.ing delta-star transformation, which
is expressed with formulas (7) , (8) , or (9) , on the current IGRS, IGST,
or IGTR is a current IR, IS, or IT that flows from the power system
101 to the high-voltage motor drive unit 102.
[Math. 7]
IR = IGRS-IGTR (7)
[Math. 8]
IS - IGST-IGRS (8)
[Math. 9]
IT - IGTR-IGSV (9)
The phases of the currents IR, IS, and IT are identical to the
phases of the phase voltages VGR, VGS, and VGT respectively of the power
system'101. This demonstrates that the high-voltage'motor .drive unit
- 29 ~
102 receives an active power from the power system 101.
[0098]
Next, a description will be made of the fact that the high-voltage
motor drive unit 102 feeds an active power to the AC motor 107.
[0099]
The applied phase voltages VU, VV, and VW of the AC motor 107 are
substantially in phase with the currents IV, IV, and IW respectively
that flow into the AC motor 107. This demonstrates that the
high-voltage motor drive unit 102 feeds an active power to the AC motor
107.
[0100]
Now, a method for controlling a DC capacitor voltage of each of
the unit cells 106 will be described by taking for instance the RU-phase
cluster 105RU.
[01013
For calculating an active power which the RU-phase cluster 105RU
receives from the power system 10.1, it is necessary to note a system
frequency component alone of each of voltages and currents. Therefore,
it is necessary to perform calculation using a mean vector of each of
the voltages and currents over one turn of the triangle UVW.
[0102]
As seen from Fig. 3, a mean of the vector VRU over one turn of
the triangle UVW is equal to a vector VR extending from the center N
point of the triangle UVW to the R' point.
[0103]
Therefore, as for.a mean over one turn of the- triangle UVW, an.
- 30 -
active power PGRU which the RU-phase cluster 105RU receives from the
power system 101 is an inner product of the vector VR and vector IGRS,
and expressed as a formula (10).
[Math. 10]
PGRU - VR-IGRS (10)
For calculating an active power which the RU-phase cluster 105RU
feeds the AC motor 107, it is necessary to note a motor frequency
component alone of each of voltages and currents. Therefore, it is
necessary to perform calculation using a mean vector of each of the
voltages and currents over one turn of the triangle RST on the assumption
that the triangle RST is turned with the triangle UVW fixed as a
reference.
[0104]
As seen from Fig. 3, a mean of the vector VRU over one turn of
the triangle RST is equal to a vector extending from the U point to
the center N point of the triangle UVW, that is, an inverse vector -VU
of the vector VU,
[0105]
Therefore, as for a mean over one turn of the triangle RST, an
active power PMRU which the RU-phase cluster 105RU feeds to the AC motor
107 is an inner product of the vector -VU and vector IMWU, and expressed
as a formula (11) .
[Math. 11]
PMRU = -VU-IMWU (11)
In the case of PGRUH-PMRU<0, the DC capacitor voltage of each of
the- unit cells 106 included.in the RU-phase cluster-105RU;. drops.
31
[0106]
In the case of PGRUH-PMRU>0, the DC capacitor voltage of each of
the unit cells 106 included in the RU~phase cluster 105RU rises.
[0107]
The power PGRU is controlled by controlling the vector VR that
represents a mean value of the vector VRU over one turn of the triangle
UVW. By sustaining a state in which the sum of the powers PGRU and
PMRU is substantially zero^ the DC capacitor voltage of each of the
unit cells included in the RU-phase cluster 105RU can be controlled
to be constant.
[0108]
The foregoing description is made by taking for instance the
RU-phase cluster 105RU. The other clusters can be controlled in the
same manner.
[0109]
The principle of operation of the high-voltage motor drive unit
102, the examples of waveforms of voltages and currents, and the DC
capacitor voltage control method have been described so far.
[0110]
In comparison with a case where a high-voltage motor drive unit
to be linked to a 6.6-kV system in a transformer-less manner is formed
using two MMCs, a reason why the number of IGBTs (whose blocking voltage
is 4.5 kV) necessary for the high-voltage motor drive unit 102 in
accordance with the present invention can be reduced from 144 to 120
will be described below.
[0111] • • : -.::,••.,.••.•••
~ 32 "
In the example shown in Fig. 4, the line voltage of the AC motor
107 is 3.96 kV. As a high-voltage motor drive unit, it is desirable
that a voltage up to 6.6 kV which is equal to that of the power system
101 can be applied to the AC motor 107. In this case, in the vector
diagram of Fig. 3, the size of the triangle UVW is consistent with the
size of the triangle RST.
[0112]
Since the triangle UVW turns, there arises, for example, a case
where the U point coincides with the T point, or an instant when each
of the clusters outputs up to 6.6 kV that is the line voltage of the
power system 101. Therefore, each of the clusters has to be able to
output up to substantially 6. 6 kV that is the line voltage of the power
system 101.
r Ai T o T
[ U J. J. O J
When four IGBTs whose blocking voltage is 4.5 kV and four
antiparallel diodes are used to form the unit cell (full bridge circuit)
shown in Fig. 2, assuming that the DC capacitor voltage is 2.25 kV which
is 50% of the blocking voltage of the IGBTs and the maximum modulation
factor is 0.9, a voltage one unit cell can output is 2.25 kV/V2x0.9
approximately equal to 1.43 kV.
[0114]
The number of unit cells included in one cluster has to be equal
to or larger than five that is a minimum integer exceeding 6.6/1.43
approximately equal to 4.6. Therefore, the present embodiment has been
described on the assumption that the number of unit cells included in
each cluster is five.
- 33 ~
[0115]
When the number of unit cells included in one cluster is five,
the number of IGBTs included in the entire high-voltage motor drive
unit 102 comes to 4x5x6-120.
[0116]
For the foregoing reason, the number of IGBTs can be reduced to
120, though 144 IGBTs are needed in the related art employing two MMCs.
[0117]
Since one reactor 103 is included in one leg 104, three reactors
are included in the entire high-voltage motor drive unit 102.
[0118]
For the foregoing reason, the number of reactors can be reduced
to three, though twelve reactors are needed in the related art employing
two MMCs.
[0119]
The number of reactors included in each of the legs 104RS, 104ST,
and 104TR shown in Fig. 1 is one. A leg having two reactors (103RU
and 103US) coupled to each other as shown in Fig. 5 may be substituted
for each of the legs 104RS, 104ST, and 104TR. Nevertheless, the legs
can be operated as a high-voltage motor drive unit. In this case, the
number of reactors in the entire high-voltage motor drive unit 102 is
six. Nevertheless, the number of reactors can be reduced compared with
twelve that is the number of reactors needed in the related art employing
two MMCs.
[0120]
',--In the present embodiment, the power system 101-is coupled to the
~ 34 -
R point, S point, and T point, and the AC motor 107 is coupled to the
U point, V point, and W point. Even when the power system 101 is coupled
to the U point, V point, and W point and the AC motor 107 is coupled
to the R point, S point, and T point, the same advantage can be provided.
[0121]
The present embodiment has been described by taking for instance
a case where a high-voltage motor drive unit is linked to the 6.6-kV
system in a transformer-less manner and IGBTs whose blocking voltage
is 4.5 kV are employed. Even if the line voltage of the power system
101 is different from 6.6 kV, the transformer is disposed between the
power system 101 and high-voltage motor drive unit 102, or IGBTs (or
any other on-off control switching elements) whose blocking voltage
is different from 4.5 kV are employed, the present invention can be
applied.
[0122]
The present embodiment has been described on the assumption that
the unit cell 106 is a full bridge circuit. If the unit cell 106 is
a half bridge circuit, three-level full bridge circuit, or the like,
or if the unit cell 106 can output a positive, negative, or zero voltage,
and includes an energy storage element such as a capacitor, the unit
cell 106 can be used as it is in place of the full bridge circuit.
Second Embodiment
[0123]
A second embodiment of the present invention will be described
in conjunction with Fig. 6.
[0124] • . • • -.
- 35 -
The present embodiment is such that a unit which interchanges a
power between two power systems is formed using a power conversion unit
in accordance with the present invention.
[0125]
In the present embodiment, a second power system 602 is coupled
to the U, V, and W points in substitution for the AC motor 107 of the
first embodiment in order to form a power interchange unit 601 that
interchanges a power between the power system 101 and second power system
601. In the first embodiment shown in Fig. 1, the power conversion
unit of the present invention is adapted to a high-voltage motor drive
unit as an embodiment unit that has the advantage of being able to provide
a variable amplitude or frequency. In the second embodiment shown in
Fig. 6, the power interchange unit 601 can be realized using both the
power systems as power supplies. The power interchange unit 601 is
a frequency conversion facility for, for example, conversion between
50 Hz and 60 Hz.
[0126]
Specifically, in the power conversion unit of the present invention,
one of three-phase AC facilities coupled to the power conversion unit
is a power supply, and the other three-phase AC facility coupled to
the power conversion unit is a power supply or load. Thus, the power
interchange unit 601 or high-voltage motor drive unit can be realized.
[0127]
In the present embodiment, the power system 101 shall be called
a "first power system 101. " For the first power system 101, the RU-phase
cluster 105RU and US-phase cluster 105US operate as a first pair coupled
~ 36 ~
to the R and S phases of the power system 101, the SV-phase cluster
105SV and VT~phase cluster 105VT operate as a second pair coupled to
the S and T phases of the power system 101, and the TW-phase cluster
105TW and WR~phase cluster 105WR operate as a third pair coupled to
the T and R phases of the power system 101. The pairs transfer an active
power to or from the first power system 101,
[0128]
The principle on which the power interchange unit 601 transfers
an active power to or from the first power system 101 is identical to
that described in relation to the first embodiment.
[0129]
For the ''second power system 602," the US-phase cluster 105US and
SV-phase cluster 105SV act as a first pair coupled to the U and V phases
of the AC motor 107, the VT-phasc cluster 105VT and TW-phase cluster
105TW act as a second pair coupled to the V and W phases of the AC motor
107, and the WR-phase cluster 105WR and RU-phase cluster 105RU act as
a third pair coupled to the W and R phases of the AC motor 107. The
pairs transfer an active power to or from the second power system 602,
[0130]
The principle on which the power interchange unit 601 transfers
an active power to or from the second power system 602 will be described
below.
[0131]
Control is extended so that the phase of the sum VUS+VSV of the
outputs of the US-phase cluster 105US and SV-phase cluster 105SV lags
behind that of the difference V.U-VV of the line voltages^ to the U and
- 37 -
V phases of the second power system 602, whereby a voltage that leads
the difference VU-VV by a phase of substantially 90° is impressed on
the applied voltage VLST of the reactor 103 of the ST-phase leg 104ST.
[0132]
As a result, a current substantially in phase with the difference
VU-VV flows through the reactor 103, and the current is contained as
a frequency component of the second power system in the current lUS
that flows through the US-phase cluster 105US and the current ISV that
flows through the SV-phase cluster 105SV. Therefore, the US-phase
cluster 105US and SV-phase cluster 105SV receive an active power from
the second power system 602.
[0133]
Control is extended so that the phase of the sum VUS+VSV of the
output voltages of the US phase cluster 105US and SV-phase cluster 105SV
leads the difference VU-VV of the line voltages to the U and V phases
of the second system 602, whereby a voltage that lags the difference
VU-VV by a phase of substantially 90° is impressed on the applied voltage
VLST of the reactor 103 of the ST-phase leg 104ST.
[0134]
As a result, a current whose phase is substantially opposite to
that of the difference VU-VV flows through the reactor 103, and the
current is contained as a frequency component of the second power system
in the current lUS that flows through the US-phase cluster 105US and
the current ISV that flows through the SV-phase cluster 105SV.
Therefore, the US-phase cluster 105US and SV-phase cluster 105SV feed
an active power to the secondpower system 602 . As for the-other phases,
38 -
the clusters act in the same manner, though the phases are turned 120°.
[0135]
Even if the voltages and frequencies of the first power system
101 and second power system 602 are different from each other, the power
interchange unit 601 can interchange an active power between the first
and second power systems.
Third Embodiment
[0136]
A third embodiment of the present invention will be described in
conjunction with Fig. 8. Herein, a control arrangement for controlling
the power conversion unit shown in Fig. 1 or Fig. 6 will be described
below.
[0137]
The control arrangem.cnt for the power conversion unit includes
a control system for one of three-phase AC facilities (power system
101), and a control system for the other three-phase AC facility (AC
motor 107 or power system 602). In the example shown in Fig. 3, the
control system for one of the three-phase AC facility (power system
101) is, for example, a power system current control system 300, and
the control system for the other three-phase AC facility (AC motor 107)
is, for example, a motor current control system 400.
[0138]
The control system 300 or 400 obtains a feedback signal 302 or
402 relevant to a target signal 301 or 401, executes a predetermined
arithmetic 303 or 403, and obtains a control signal 305 or 405. The
control is implemented in a quantity of electricity on-an appropriate
39
one of the lines.
[0139]
To be more specific, for realizing a high-voltage motor drive unit,
the target signal 301 for the power system current control system 300
serves as a current command for fetching a power, which is needed to
control the voltage of the DC capacitor 203 of each of the unit cells
106 so that the voltage remains constant, from the power system. The
current command 301 is a current on each of the lines of the power system
101. In the arithmetic 303, a voltage signal 304 is added to a signal,
which is obtained by multiplying a current deviation signal by a
predetermined gain, in order to obtain the control signal 305.
[0140]
The target signal 401 for the power system current control system
400 is obtained by applying the formula (4), (5), or (6) to the values
of phase currents lU, IV, or IW determined with a requirement for a
mechanical load of a motor (the number of revolutions or torque) . The
current command 401 is a current on each of the lines of the AC motor
107. In the arithmetic 403, a current deviation signal is multiplied
by a predetermined gain in order to obtain the control signal 405.
[0141]
As mentioned above, the control signal 305 or 405 to be calculated
according to the situation of each of the power system 101 and AC motor
107 that are three-phase AC facilities is prepared for each of the lines.
By the way, a practical operating end of the power conversion unit
includes six clusters, and a PWM control circuit 5 is provided for each
of,the clusters. - ••• •,•• r- ~ • • •;• •• '.-•• -.-"
40
[0142]
Now, the control signal 305 or 405 is a control signal on each
of the lines of the power system 101 or AC motor 107, while the PWM
control circuit 5 included in the operating end is disposed in units
of a cluster. Therefore, talking of, for example, the PWM control
circuit 5RU of the cluster 105RU, the cluster voltage VRU is determined
with a WU-phase control signal 305 out of the control signals 305
obtained from the power system 101 and an RS~phase control signal 405
out of the control signals 405 obtained from the AC motor 107. The
same relationship is established for the other cluster voltages.
[0143]
This signifies that by controlling each cluster voltage using the
control signals 305 and 405 on the respective sides of the power system
101 and AC motor 107, a cluster voltage capable of satisfying the control
requirements for the power system and AC motor can be obtained.
[0144]
In the control circuit shown in Fig. 8, three control signals of
the power system current control system 300 are each bisected in units
of a phase, and three control signals of the motor current control system
400 are each bisected in units of a phase. In an adder circuit group
306, control signals associated with each of the clusters are added
up in order to produce a cluster control signal.
[0145]
As mentioned above, in control of the power conversion unit, for
the power system 101, a control action is performed by regarding two
clusters (for example, cluster lOSRU.and cluster 105US) of a leg (for
41
example, 104RS} coupled to the lines of the power system 101 as a first
pair. For the AC motor 107, a control action is performed by regarding
two clusters (for example, cluster 105RU and cluster 105WR) coupled
to the lines of the AC motor 107 as a second pair.
Industrial Applicability
[0146]
The present invention can widely be adapted to motor control, a
variable-frequency power supply, or the like despite the simple
configuration.
List of Reference Signs
[0147]
101: power system, 102: high-voltage motor drive unit, 103:
reactor, 104: leg, 105: cluster, 106: unit cell, 107: AC
m.otor, 201XH: X-phase upper IGBT, 201XL: X-phase lower IGET,
201YH: Y-phase upper IGBT, 201YL: Y-phase lower IGBT, 202XH:
X-phase upper antiparallel diode, 202XL: X-phase lower antiparallel
diode, 202YH: Y-phase upper antiparallel diode, 202YL: Y-phase
lower antiparallel diode, 203: DC capacitor, 103RU: RU-phase
reactor, 104US: US-phase reactor, 601: power interchange unit,
602: second power system.
- 42
We Claim:
Claim 1
A power conversion unit, wherein:
a leg is formed by coupling in series with one another a reactor,
a first cluster that is a series body of a plurality of unit cells,
and a second cluster that is a series body of a plurality of unit cells;
three legs are delta-connected;
three junction points of the delta-connected legs are coupled to
the respective phases of a first three-phase AC facility; and
junction points between the first and second clusters of the legs
are coupled to the respective phases of a second three-phase AC facility.
Claim 2
The power conversion unit according to claim 1, wherein one of
the first three-phase AC facility and second three-phase AC facility
is a power system.
Claim 3
The power conversion unit according to claim 1, wherein both of
the first three-phase AC facility and second three-phase facility are
power systems.
Claim 4
The power conversion unit according to claim 1, wherein the first
three-phase AC facility is a power system, and the second three-phase
facility is a motor.
Claim 5
The power conversion unit according to any of claims 1 to 4, wherein
the unit cells are two-terminal elements capable of outpatting. an

_ 43 -
arbitrary voltage.
Claim 6
The power conversion unit according to any of claims 1 to 4, wherein
the unit cells can output a positive, negative, or zero voltage, and
are each provided with an energy storage element.
Claim 7
The power conversion unit according to any of claims 1 to 4, wherein
each of the unit cells is formed with a full bridge circuit.
Claim 8
A control arrangement for a power conversion unit in which a leg
is formed by coupling in series with one another a reactor, a first
cluster that is a series body of a plurality of unit cells, and a second
cluster that is a series body of a plurality of unit cells, three legs
are delta-connected, three junction points of the delta-connected legs
are coupled to the respective phases of a first three-phase AC facility,
and junction points between the first and second clusters of the legs
are coupled to the respective phases of a second three-phase AC facility,
wherein:
the control arrangement has a control function for extending
control so that the sum of an active power produced with a frequency
component of the first three-phase AC facility of an output voltage
of each of the clusters and a frequency component of the first
three-phase AC facility of a current flowing through each of the clusters,
and an active power produced with a frequency component of the second
three-phase AC facility of the output voltage of each of the clusters
and a frequency component of the second three-phase AC facility of the.
AA
current flowing through each of the clusters becomes substantially
zero.
Claim 9
A control arrangement for a power conversion unit in which a leg
is formed by coupling in series with one another a reactor, a first
cluster that is a series body of a plurality of unit cells, and a second
cluster that is a series body of a plurality of unit cells, three legs
are delta-connected^ three junction points of the delta-connected legs
are coupled to the respective phases of a first three-phase AC facility,
and junction points between the first and second clusters of the legs
are coupled to the respective phases of a second three-phase AC facility,
wherein;
the control arrangement has a control function for extending
control so that the sum. of a reactive power produced with a frequency
component of the first three-phase AC facility of an output voltage
of each of the clusters and a frequency component of the first
three-phase AC facility of a current flowing through each of the clusters,
and a reactive power produced with a frequency component of the second
three-phase AC facility of the output voltage of each of the clusters
and a frequency component of the second three-phase AC facility of the
current flowing through each of the clusters becomes substantially
zero.
Claim 10
A control arrangement for a power conversion unit in which a leg
is formed by coupling in series with one another a reactor, a first
cluster that is^a series body of a plurality of unit cells-, and a second
45
cluster that is a series body of a plurality of unit cells, three legs
are delta-connected, three junction points of the delta-connected legs
are coupled to the respective phases of a first three-phase AC facility,
and junction points between the first and second clusters of the legs
are coupled to the respective phases of a second three-phase AC facility,
wherein:
three first control signals are obtained with the line currents
of the first three-phase AC facility regarded as target signals;
three second control signals are obtained with the line currents
of the second three-phase AC facility regarded as target signals; and
the first and second clusters of each of the legs are controlled
based on a sum signal of the first control signal and second control
signal on the lines involved with the clusters.