FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
POWER CONVERSION APPARATUS, MOTOR DRIVE UNIT, AND
REFRIGERATION CYCLE APPLICATION APPARATUS;
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
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED
2
DESCRIPTION
Field
[0001] The present disclosure relates to a power
conversion apparatus that converts AC power into desired5
power, a motor drive unit, and a refrigeration cycle
application apparatus.
Background
[0002] There have been power conversion apparatuses that10
convert AC power supplied from an AC source into desired AC
power and supply the AC power to a load such as an air
conditioner. For example, Patent Literature 1 discloses a
technique in which a power conversion apparatus that is a
controller of an air conditioner rectifies AC power15
supplied from an AC source by a diode stack that is a
rectifier unit, converts the power further smoothed by a
smoothing capacitor into desired AC power by an inverter
consisting of a plurality of switching elements, and
outputs the AC power to a compressor motor that is a load.20
Citation List
Patent Literature
[0003] Patent Literature 1: Japanese Patent Application
Laid-open No. H07-07180525
Summary
Technical Problem
[0004] However, the above conventional technique has a
problem that aging deterioration of the smoothing capacitor30
is accelerated because a large current flows through the
smoothing capacitor. To this problem, a method of reducing
ripple changes in capacitor voltage by increasing the
3
capacitance of the smoothing capacitor, or using a
smoothing capacitor having a high tolerance to
deterioration caused by ripple can be considered, which,
however, increases the cost of the capacitor component and
increases the size of the device.5
[0005] The present disclosure has been made in view of
the above, and an object thereof is to provide a power
conversion apparatus that can reduce the deterioration of a
smoothing capacitor while preventing the device from
becoming larger.10
Solution to Problem
[0006] In order to solve the above-described problem and
achieve the object, a power conversion apparatus according
to the present disclosure comprises: a converter rectifying15
a first AC voltage supplied from an AC source; a capacitor
connected to an output end of the converter, the capacitor
smoothing a first DC voltage rectified by the converter
into a second DC voltage including a first ripple; an
inverter connected across the capacitor, the inverter20
converting the second DC voltage into a second AC voltage
corresponding to a desired frequency; and a detection unit
acquiring a physical quantity correlated with the second DC
voltage. The power conversion apparatus controls the
second AC voltage to superimpose a second ripple correlated25
with the first ripple on an output voltage of the inverter.
Advantageous Effects of Invention
[0007] The power conversion apparatus according to the
present disclosure has the effect of being able to reduce30
the deterioration of the smoothing capacitor while
preventing the device from becoming larger.
Brief Description of Drawings
4
[0008] FIG. 1 is a diagram illustrating an exemplary
configuration of a power conversion apparatus according to
a first embodiment.
FIG. 2 is a diagram illustrating the operating state
of the power conversion apparatus that depends on the5
presence or absence of control to reduce a charging and
discharging current of a capacitor in a control unit of the
power conversion apparatus according to the first
embodiment.
FIG. 3 is a diagram illustrating the charge and10
discharge states of the capacitor in the power conversion
apparatus according to the first embodiment.
FIG. 4 is a first block diagram illustrating a
configuration to generate a q-axis current command to
reduce the pulsation of a DC bus voltage included in the15
control unit of the power conversion apparatus according to
the first embodiment.
FIG. 5 is a diagram illustrating an example of a
filter included in the power conversion apparatus according
to the first embodiment.20
FIG. 6 is a diagram illustrating a connection example
when a plant model is included in the control unit of the
power conversion apparatus according to the first
embodiment.
FIG. 7 is a second block diagram illustrating a25
configuration to generate a q-axis current command to
reduce the pulsation of a DC bus voltage included in the
control unit of the power conversion apparatus according to
the first embodiment.
FIG. 8 is a first diagram illustrating the proportions30
of the amounts of current for controls to a q-axis current
command by the control unit of the power conversion
apparatus according to the first embodiment.
5
FIG. 9 is a second diagram illustrating the
proportions of the amounts of current for controls to a q-
axis current command by the control unit of the power
conversion apparatus according to the first embodiment.
FIG. 10 is a diagram illustrating an example of the5
relationship between frequency and the effective value of
current of the capacitor when the control to reduce the
charging and discharging current of the capacitor is
performed in the power conversion apparatus according to
the first embodiment.10
FIG. 11 is a diagram illustrating a concrete example
of pulsating component extraction in the power conversion
apparatus according to the first embodiment.
FIG. 12 is a flowchart illustrating the operation of
the control unit of the power conversion apparatus15
according to the first embodiment.
FIG. 13 is a diagram illustrating an example of a
hardware configuration that implements the control unit
included in the power conversion apparatus according to the
first embodiment.20
FIG. 14 is a first diagram illustrating an exemplary
configuration of a power conversion apparatus according to
a second embodiment.
FIG. 15 is a second diagram illustrating an exemplary
configuration of a power conversion apparatus according to25
the second embodiment.
FIG. 16 is a diagram illustrating an exemplary
configuration of a refrigeration cycle application
apparatus according to a third embodiment.
30
Description of Embodiments
[0009] Hereinafter, a power conversion apparatus, a
motor drive unit, and a refrigeration cycle application
6
apparatus according to embodiments of the present
disclosure will be described in detail with reference to
the drawings.
[0010] First Embodiment.
FIG. 1 is a diagram illustrating an exemplary5
configuration of a power conversion apparatus 1 according
to a first embodiment. The power conversion apparatus 1 is
connected to an AC source 110 and a compressor 315. The
power conversion apparatus 1 converts a first AC voltage of
a source voltage Vs supplied from the AC source 110 into a10
second AC voltage having desired amplitude and phases, and
supplies the second AC voltage to the compressor 315. The
AC source 110 may be a single-phase AC source or a three-
phase AC source. The following describes a case where the
AC source 110 is a single-phase AC source as an example.15
The power conversion apparatus 1 includes a voltage
detection unit 501, a converter 150, a smoothing unit 200,
a voltage detection unit 502, an inverter 310, current
detection units 313a and 313b, and a control unit 400. The
converter 150 includes a reactor 120 and a rectifier unit20
130. The power conversion apparatus 1 and a motor 314
included in the compressor 315 constitute a motor drive
unit 2.
[0011] The voltage detection unit 501 detects a voltage
value of the first AC voltage of the source voltage Vs25
supplied from the AC source 110, and outputs the detected
voltage value to the control unit 400. The voltage
detection unit 501 is a detection unit that detects the
power state of the first AC voltage. The voltage detection
unit 501 may detect zero-crossings of the first AC voltage30
as the power state of the first AC voltage.
[0012] The converter 150 rectifies the first AC voltage
of the source voltage Vs supplied from the AC source 110,
7
which is a single-phase AC source. In the converter 150,
the reactor 120 is connected between the AC source 110 and
the rectifier unit 130. The rectifier unit 130 includes a
bridge circuit composed of rectifier elements 131 to 134,
and rectifies the first AC voltage of the source voltage Vs5
supplied from the AC source 110 for output. The rectifier
unit 130 performs full-wave rectification.
[0013] The smoothing unit 200 is connected to an output
end of the rectifier unit 130. The smoothing unit 200
includes a capacitor 210 as a smoothing element, and10
smooths the voltage rectified by the rectifier unit 130.
The capacitor 210 is, for example, an electrolytic
capacitor, a film capacitor, or the like. The capacitor
210 is connected to an output end of the converter 150,
specifically, to the output end of the rectifier unit 130,15
and has a capacitance to smooth the voltage rectified by
the rectifier unit 130. The voltage generated in the
capacitor 210 by the smoothing does not have a full-wave
rectified waveform shape of the AC source 110, but has a
waveform shape in which a voltage ripple corresponding to20
the frequency of the AC source 110 is superimposed on the
DC component, and does not pulsate greatly. When the AC
source 110 is a single-phase AC source, the frequency of
the voltage ripple has the main component that is a
component twice the frequency of the source voltage Vs.25
When power input from the AC source 110 and power output
from the inverter 310 do not change, the amplitude of the
voltage ripple is determined by the capacitance of the
capacitor 210. For example, the voltage pulsates in such a
range that the maximum value of the voltage ripple30
generated in the capacitor 210 is less than twice the
minimum value. Thus, the capacitor 210 is connected to the
output end of the converter 150, and smooths a first DC
8
voltage rectified by the converter 150 into a second DC
voltage including a first ripple.
[0014] The voltage detection unit 502 detects a DC bus
voltage Vdc that is a voltage across the smoothing unit 200,
that is, the capacitor 210 charged with current rectified5
by the rectifier unit 130 and passed from the rectifier
unit 130 into the smoothing unit 200, and outputs the
detected voltage value to the control unit 400. The
voltage detection unit 502 is a detection unit that detects,
as the power state of the capacitor 210, a physical10
quantity correlated with the second DC voltage including
the first ripple. In the following description, the
voltage detection unit 502 is sometimes referred to as a
first detection unit, and the physical quantity detected by
the voltage detection unit 502 as a first physical quantity.15
[0015] The inverter 310 is connected across the
smoothing unit 200, that is, the capacitor 210. The
inverter 310 includes switching elements 311a to 311f and
freewheeling diodes 312a to 312f. The inverter 310 turns
the switching elements 311a to 311f on and off under the20
control of the control unit 400, converts the voltage
output from the rectifier unit 130 and the smoothing unit
200 into the second AC voltage having the desired amplitude
and phases, that is, generates the second AC voltage, and
outputs the second AC voltage to the motor 314 of the25
compressor 315 to which the inverter 310 is connected. The
inverter 310 converts the second DC voltage including the
first ripple into the second AC voltage corresponding to a
desired frequency.
[0016] Each of the current detection units 313a and 313b30
detects the current value of one phase of three-phase
current output from the inverter 310, and outputs the
detected current value to the control unit 400. The
9
control unit 400 can calculate the current value of the
remaining one phase output from the inverter 310 by
acquiring the current values of the two phases of the
current values of the three phases output from the inverter
310. The current detection units 313a and 313b are5
detection units that acquire a second physical quantity
including a third ripple correlated with a rotational speed
generated by the motor 314. In the following description,
the current detection units 313a and 313b are sometimes
referred to as a second detection unit.10
[0017] The compressor 315 is a load including the motor
314 for compressor drive. The motor 314 rotates according
to the amplitude and phases of the second AC voltage
supplied from the inverter 310, performing a compression
operation. When the compressor 315 is, for example, a15
hermetic compressor used in an air conditioner or the like,
the load torque of the compressor 315 can often be regarded
as a constant torque load. For the motor 314, FIG. 1
illustrates a case where motor windings are Y-connected,
which is an example. The present invention is not limited20
to this. The motor windings in the motor 314 may be Δ-
connected, or may be designed to be switchable between Y
connection and Δ connection.
[0018] In the power conversion apparatus 1, the
arrangement of the components illustrated in FIG. 1 is an25
example. The arrangement of the components is not limited
to the example illustrated in FIG. 1. For example, the
reactor 120 may be disposed downstream of the rectifier
unit 130. The power conversion apparatus 1 may include a
booster unit, or the rectifier unit 130 may have the30
function of a booster unit. In the following description,
the voltage detection units 501 and 502 and the current
detection units 313a and 313b are sometimes collectively
10
referred to as detection units. The voltage values
detected by the voltage detection units 501 and 502 and the
current values detected by the current detection units 313a
and 313b are sometimes referred to as detected values.
[0019] The control unit 400 acquires the voltage value5
of the source voltage Vs of the first AC voltage from the
voltage detection unit 501, acquires the voltage value of
the DC bus voltage Vdc of the smoothing unit 200 from the
voltage detection unit 502, and acquires the current values
of the second AC voltage having the desired amplitude and10
phases converted by the inverter 310 from the current
detection units 313a and 313b. The control unit 400
controls the operation of the inverter 310, specifically,
performs on-off control on the switching elements 311a to
311f included in the inverter 310, using the detected15
values detected by the detection units. The control unit
400 controls the operation of the motor 314 using the
detected values detected by the detection units. In the
present embodiment, the control unit 400 controls the
operation of the inverter 310 such that the second AC power20
including pulsation corresponding to the pulsation of the
current flowing from the rectifier unit 130 into the
capacitor 210 of the smoothing unit 200 is output from the
inverter 310 to the compressor 315, which is a load. The
pulsation corresponding to the pulsation of the current25
flowing into the capacitor 210 of the smoothing unit 200 is,
for example, pulsation that varies depending on the
frequency of the pulsation of the current flowing into the
capacitor 210 of the smoothing unit 200, etc. Thus, the
control unit 400 reduces the current flowing through the30
capacitor 210 of the smoothing unit 200. Note that the
control unit 400 does not need to use all the detected
values acquired from the detection units, and may perform
11
control using some of the detected values. The control
unit 400 controls the second AC voltage to superimpose a
second ripple correlated with the first ripple detected by
the voltage detection unit 502 on the output voltage from
the inverter 310.5
[0020] The control unit 400 performs control such that
any of the speed, voltage, and current of the motor 314
reaches a desired state. Here, when the motor 314 is used
to drive the compressor 315, and the compressor 315 is a
hermetic compressor, it is difficult to attach a position10
sensor for detecting the rotor position to the motor 314
because of the structure and the cost. Therefore, the
control unit 400 performs position sensorless control on
the motor 314. There are two types of methods for the
position sensorless control on the motor 314, constant15
primary flux control and sensorless vector control. In the
present embodiment, as an example, a description is given
based on sensorless vector control. A control method
described below can be applied to constant primary flux
control with minor changes. In the present embodiment, as20
will be described later, the control unit 400 controls the
operations of the inverter 310 and the motor 314, using dq
rotating coordinates that rotate in synchronization with
the rotor position of the motor 314.
[0021] Next, control in the control unit 400 to reduce25
the current flowing through the capacitor 210 of the
smoothing unit 200 will be described. As illustrated in
FIG. 1, in the power conversion apparatus 1, an input
current from the rectifier unit 130 to the capacitor 210 of
the smoothing unit 200 is an input current I1, an output30
current from the capacitor 210 of the smoothing unit 200 to
the inverter 310 is an output current I2, and a charging
and discharging current of the capacitor 210 of the
12
smoothing unit 200 is a charging and discharging current I3.
In this case, the relationship, input current I1=output
current I2+charging and discharging current I3, is
established. The flow of the charging and discharging
current I3 through the capacitor 210 means the charging and5
discharging of the capacitor 210. The charging and
discharging of the capacitor 210 causes the voltage across
the capacitor 210, that is, the DC bus voltage Vdc to
pulsate. Therefore, the control unit 400 performs control
to reduce the pulsation of the DC bus voltage Vdc, thereby10
reducing the charging and discharging current I3 of the
capacitor 210. By adding a current corresponding to the
pulsation of the DC bus voltage Vdc to the output current
I2, the control unit 400 can reduce the charging and
discharging current I3 of the capacitor 210.15
[0022] FIG. 2 is a diagram illustrating the operating
state of the power conversion apparatus 1 that depends on
the presence or absence of the control to reduce the
charging and discharging current I3 of the capacitor 210 in
the control unit 400 of the power conversion apparatus 120
according to the first embodiment. In FIG. 2, (a) and (b)
illustrate the first AC voltage of the source voltage Vs
supplied from the AC source 110, and the rectified voltage
output from the rectifier unit 130. In FIG. 2, (c) and (d)
illustrate currents flowing from the inverter 310 to the25
motor 314. In FIG. 2, (e) and (f) illustrate the current
flowing through the capacitor 210, that is, the charging
and discharging current I3 of the capacitor 210. In FIG. 2,
(a), (c), and (e) on the left side illustrate the state
without the control to reduce the charging and discharging30
current I3 of the capacitor 210 in the control unit 400.
In FIG. 2, (b), (d), and (f) on the right side illustrate
the state with the control to reduce the charging and
13
discharging current I3 of the capacitor 210 in the control
unit 400.
[0023] As illustrated in (a) in FIG. 2, the rectified
voltage output from the rectifier unit 130 pulsates at a
frequency twice the power frequency of the AC source 110,5
which is a single-phase AC source. In FIG. 2, (b)
illustrates those in the same state as (a). Without the
control to reduce the charging and discharging current I3
of the capacitor 210 in the control unit 400, the pulsation
of the DC bus voltage Vdc, that is, the pulsation of the10
charging and discharging current I3 of the capacitor 210
also pulsates at a frequency twice the power frequency of
the AC source 110, which is a single-phase AC source, as
illustrated in (e) in FIG. 2. Here, the control unit 400
performs control to add a current corresponding to the15
pulsation of the charging and discharging current I3 of the
capacitor 210 to the output current I2, which is currents
flowing from the inverter 310 to the motor 314, that is, to
change from the state of (c) to the state of (d) in FIG. 2.
Consequently, the charging and discharging current I3 of20
the capacitor 210 can be reduced as illustrated in (f) in
FIG. 2. In FIG. 2, a frequency twice the power frequency
of the AC source 110 is denoted as power 2f, where f is the
power frequency of the AC source 110, which is a single-
phase AC source, that is, the fundamental frequency of the25
first AC voltage. In the actual power conversion apparatus
1, pulsations in various frequency bands occur depending on
the effects of wiring of the AC source 110 and the
operating state of the compressor 315, which is a load, but
are omitted here.30
[0024] FIG. 3 is a diagram illustrating the charge and
discharge states of the capacitor 210 in the power
conversion apparatus 1 according to the first embodiment.
14
As illustrated in (a) and (b) in FIG. 3, when the voltage
from the AC source 110 is smaller than the voltage of the
capacitor 210, the capacitor 210 discharges, so that
current flows from the capacitor 210 through the inverter
310 to the motor 314. As illustrated in (c) and (d) in FIG.5
3, when the voltage from the AC source 110 is larger than
the voltage of the capacitor 210, the capacitor 210 charges
by the amount of discharge, so that current flows from the
AC source 110 through the rectifier unit 130 and the
inverter 310 to the motor 314.10
[0025] The purpose of the control by the control unit
400 to reduce the charging and discharging current I3 of
the capacitor 210 is to reduce the current flowing through
the capacitor 210 to reduce the capacitance of the
capacitor 210. Here, a conceivable way to reduce the15
current flowing through the capacitor 210 is to directly
detect the current flowing through the capacitor 210 to
implement feedback control in the power conversion
apparatus 1. However, when a current sensor is used, the
cost is high. A current detection circuit using a shunt20
resistor is complicated in the design of measures against
noise, heat, etc. In the present embodiment, as
illustrated in FIG. 1, the power conversion apparatus 1
detects the DC bus voltage Vdc correlated with the current
of the capacitor 210, and the control unit 400 extracts a25
pulsating component and controls the output of the inverter
310 to reduce the pulsation, thereby indirectly reducing
the current of the capacitor 210. In particular, by
reducing the capacitance of the capacitor 210, the
pulsation of the DC bus voltage Vdc increases, so that the30
power conversion apparatus 1 has an advantage that the
signal-to-noise (S/N) ratio is good in the detection of the
DC bus voltage Vdc. Pieces of information required for
15
this control in the present embodiment is the detected
value of the DC bus voltage Vdc and the power frequency of
the AC source 110. The control unit 400 extracts the
frequency component of the pulsation of the DC bus voltage
Vdc from the DC bus voltage Vdc, and generates a q-axis5
current command.
[0026] FIG. 4 is a first block diagram illustrating a
configuration to generate the q-axis current command to
reduce the pulsation of the DC bus voltage Vdc included in
the control unit 400 of the power conversion apparatus 110
according to the first embodiment. The configuration
illustrated in FIG. 4 is formed by a feedback loop in which
the value of the q-axis current command is zero to make the
pulsation of the DC bus voltage Vdc zero. The DC bus
voltage Vdc can be obtained from the detected value of the15
voltage detection unit 502. In the following description,
the value of the q-axis current command being zero is
sometimes abbreviated as the command value 0.
[0027] Here, a way to detect the DC bus voltage Vdc in
the power conversion apparatus 1 will be described. In the20
power conversion apparatus 1, for example, the value of the
DC bus voltage Vdc divided by the resistor series ratio by
the voltage detection unit 502 is typically detected by the
control unit 400. However, it is only required that a
physical quantity including the ripple component of the DC25
bus voltage Vdc can be detected. Thus, the present
invention is not limited to this way. The control to
reduce the charging and discharging current I3 of the
capacitor 210 does not require, in particular, the DC
component of the DC bus voltage Vdc. Thus, it is not30
necessarily required to directly detect the voltage value
of the DC bus voltage Vdc in the way as described above.
To directly detect the charging and discharging current I3
16
of the capacitor 210, an expensive sensor such as a direct-
current current transformer (DCCT) or an alternating-
current current transformer (ACCT) is required. In
detection using a shunt resistor or the like, loss, heat,
etc. become problems. By contrast, a circuit that detects5
the DC bus voltage Vdc is generally inexpensive as compared
with current detection, and is easy to introduce because
there is no need to worry about loss, heat, etc.
Furthermore, a circuit that detects the DC bus voltage Vdc
can be used in combination with a converter including a10
booster unit as in a second embodiment described later.
[0028] For timing to detect the DC bus voltage Vdc, the
voltage detection unit 502 may detect the DC bus voltage
Vdc in synchronization with the carrier of the inverter 310,
or may detect the DC bus voltage Vdc in synchronization15
with the carrier of a converter when the converter uses a
booster unit as described later. Considering the sampling
theorem, the voltage detection unit 502 is only required to
be able to perform sampling at a frequency at least twice
the power frequency of the AC source 110, that is, to20
detect the DC bus voltage Vdc at periods faster than a
frequency twice the power frequency of the AC source 110.
Thus, the voltage detection unit 502 detects the physical
quantity at periods shorter than the frequency of the first
ripple. Alternatively, the voltage detection unit 502 may25
detect the physical quantity in synchronization with the
timing of change in conduction or nonconduction of the
switching elements 311a to 311f included in the inverter
310.
[0029] For a measure against noise in a circuit that30
detects the DC bus voltage Vdc, the voltage value of the DC
bus voltage Vdc itself does not greatly pulsate due to the
capacitor 210, but noise may be superimposed on a detected
17
value signal line itself. Therefore, the power conversion
apparatus 1 may include a filter at an input end of the
control unit 400 that acquires the detected value of the DC
bus voltage Vdc from the voltage detection unit 502. FIG.
5 is a diagram illustrating an example of a filter 5135
included in the power conversion apparatus 1 according to
the first embodiment. The power conversion apparatus 1
includes, for example, the filter 513 consisting of a
resistor 511 and a capacitor 512. Since the pulsating
component of the DC bus voltage Vdc required by the control10
unit 400 is a frequency twice the power frequency of the AC
source 110, the cutoff frequency of the filter 513 can be
designed to be equal to or higher than the frequency twice
the power frequency of the AC source 110. For example,
when the resistance value of the resistor 511 is 10 kΩ and15
the capacitance of the capacitor 512 is 1000 pF, the cutoff
frequency of the filter 513 is 16 kHz. The power
conversion apparatus 1 may alternatively be configured to
include a digital filter inside the control unit 400
instead of the filter 513 illustrated in FIG. 5 as long as20
a measure against noise can be taken. Thus, the power
conversion apparatus 1 uses either an analog filter
composed of electronic components to attenuate a specific
frequency component, or a digital filter to attenuate a
specific frequency component by the calculation of the25
control unit 400, to attenuate a specific frequency
component of the physical quantity to attenuate noise. The
cutoff frequency of the analog filter or the digital filter
described above is a frequency two or more times the
frequency of the first ripple.30
[0030] Return to the description of FIG. 4. A second-
order low-pass filter 401 allows the DC component of the DC
bus voltage Vdc to pass therethrough. A subtractor 402
18
subtracts the DC component of the DC bus voltage Vdc that
has passed through the second-order low-pass filter 401
from the DC bus voltage Vdc to remove the DC component from
the DC bus voltage Vdc. That is, a filter 403 is a kind of
high-pass filter to remove the DC component from the DC bus5
voltage Vdc. The filter 403 is intended to allow highly
accurate extraction of a pulsating component to be
described later, and thus the filter 403 may be omitted. A
subtractor 404 calculates a difference between the command
value 0 and the DC bus voltage Vdc from which the DC10
component has been removed.
[0031] A pulsating component extraction unit 405 DC-
converts and extracts a specific frequency component,
specifically, a cos2f component from the difference between
the command value 0 and the DC bus voltage Vdc from which15
the DC component has been removed. The term “2f” indicates
a frequency twice the power frequency of the AC source 110,
that is, the fundamental frequency of the first AC voltage.
A pulsating component extraction unit 407 DC-converts and
extracts a specific frequency component, specifically a20
sin2f component from the difference between the command
value 0 and the DC bus voltage Vdc from which the DC
component has been removed. The pulsating component
extraction units 405 and 407 extract and reduce only the
pulsation of the specific frequency component, thereby25
preventing the occurrence of beats, sideband waves, etc.
and making the waveform less distorted. The control unit
400 performs simple Fourier transform by integrating a
trigonometric function cos2f of the same frequency as the
specific frequency component to be extracted by the30
pulsating component extraction unit 405 and integrating a
trigonometric function sin2f of the same frequency as the
specific frequency component to be extracted by the
19
pulsating component extraction unit 407.
[0032] For example, the DC bus voltage Vdc from which
the DC component has been removed is Vdc=Asin(ωt). Note
that ω=2πf1, and f1 is 100 Hz or 120 Hz. The pulsating
component extraction unit 405 calculates formula (1), and5
the pulsating component extraction unit 407 calculates
formula (2).
[0033]
Asin(ωt)×2cos(ωt)=2Asin(ωt)cos(ωt)=Asin(2ωt)...(1)
[0034] Asin(ωt)×2sin(ωt)=2Asin2(ωt)=A-Acos(2ωt)...(2)10
[0035] The pulsating component extraction unit 405
filters a value obtained by formula (1) with a low-pass
filter to remove the sin component. Likewise, the
pulsating component extraction unit 407 filters a value
obtained by formula (2) with a low-pass filter to remove15
the cos component. Consequently, the pulsating component
extraction units 405 and 407 can extract the amplitude
value A of sin(ωt). The low-pass filters used in the
pulsating component extraction units 405 and 407 are
designed, for example, with a cutoff frequency of ω/1020
since it is only required to sufficiently remove a
frequency twice the frequency component to be extracted.
Note that the low-pass filters used in the pulsating
component extraction units 405 and 407 are not limited
these. Other filters such as band-pass filters may be used25
as long as the amplitude value A that is the DC component
can be extracted.
[0036] An integral control unit 406 performs integral
control such that the frequency component extracted by the
pulsating component extraction unit 405 becomes zero, to30
calculate a required amount of current. An integral
control unit 408 performs integral control such that the
frequency component extracted by the pulsating component
20
extraction unit 407 becomes zero, to calculate a required
amount of current. Note that the integral control units
406 and 408 may perform calculation with proportional
control, differential control, etc. in combination with the
integral control. A gain factor K used in the integral5
control units 406 and 408 is designed to be an inverse
function of a function representing a plant model
illustrated in FIG. 6. FIG. 6 is a diagram illustrating a
connection example when a plant model 420 is included in
the control unit 400 of the power conversion apparatus 110
according to the first embodiment. The actual gain factor
K varies depending on a specific circuit configuration of
the plant model 420, etc. The control unit 400 can perform
the control to reduce the charging and discharging current
I3 of the capacitor 210 with high robustness by a feedback15
configuration by the integral control units 406 and 408.
[0037] An AC restoration processing unit 409 receives
input of the results of calculation of the integral control
units 406 and 408, and restores the calculation results to
one AC signal. The AC restoration processing unit 40920
outputs the restored AC signal as a q-axis current command.
For example, the AC restoration processing unit 409
calculates a q-axis current command Iqd2v as in formula (3)
where Iq2f-cos is an output from the integral control unit
406 and Iq2f-sin is an output from the integral control unit25
408.
[0038] Iqd2v=Iq2f-cossin(2ωint)-Iq2f-sincos(2ωint)...(3)
[0039] The AC restoration processing unit 409 shifts the
phase by 90 degrees at the time of AC restoration because
the phase difference between the DC bus voltage Vdc and the30
charging and discharging current I3 of the capacitor 210 is
90 degrees. Consequently, the control unit 400 can pulsate
the q-axis current at the same frequency as that of the DC
21
bus voltage Vdc and pulsate the output voltage of the
inverter 310.
[0040] The inventor has confirmed by analysis that the
effective value of the current flowing through the
capacitor 210 is reduced by actually outputting, from the5
inverter 310, a pulsating component of the same frequency
as twice the power frequency of the AC source 110 in the
power conversion apparatus 1. The analysis results are as
illustrated in FIG. 2 described above. It can be confirmed
that the effective value of the capacitor current is10
reduced with the control to reduce the charging and
discharging current I3 of the capacitor 210 as compared
with that without the control to reduce the charging and
discharging current I3 of the capacitor 210. This is
because in the example of FIG. 3 and others, the control15
unit 400 reduces the charging and discharging of the
capacitor 210 by increasing the inverter output when the
voltage from the AC source 110 is high and decreasing the
inverter output when the voltage from the AC source 110 is
low.20
[0041] In the example of FIG. 4, in order to reduce the
pulsation of a frequency component that is twice the
fundamental frequency of the first AC voltage, the control
unit 400 extracts a frequency component that is twice the
fundamental frequency of the first AC voltage by the25
pulsating component extraction units 405 and 407. When it
is desired to reduce the pulsation of a harmonic component
of a frequency component that is twice the fundamental
frequency of the first AC voltage, for example, when it is
desired to reduce the pulsation of frequency components30
that are two and four times the fundamental frequency of
the first AC voltage, as many pulsating component
extraction units and integral control units as the
22
frequencies can be placed in parallel to extract the
frequency components two and four times the fundamental
frequency of the first AC voltage.
[0042] FIG. 7 is a second block diagram illustrating a
configuration to generate a q-axis current command to5
reduce the pulsation of the DC bus voltage Vdc included in
the control unit 400 of the power conversion apparatus 1
according to the first embodiment. The configuration
illustrated in FIG. 7 is obtained by adding pulsating
component extraction units 410 and 412 and integral control10
units 411 and 413 to the configuration illustrated in FIG.
4.
[0043] The pulsating component extraction unit 410 DC-
converts and extracts a specific frequency component,
specifically, a cos4f component from the difference between15
the command value 0 and the DC bus voltage Vdc from which
the DC component has been removed. The term “4f” indicates
a frequency four times the power frequency of the AC source
110, that is, the fundamental frequency of the first AC
voltage. The pulsating component extraction unit 412 DC-20
converts and extracts a specific frequency component,
specifically, a sin4f component from the difference between
the command value 0 and the DC bus voltage Vdc from which
the DC component has been removed. Effects obtained by the
pulsating component extraction units 410 and 412 are as25
those in the explanation of the pulsating component
extraction units 405 and 407 described above.
[0044] The integral control unit 411 performs integral
control such that the frequency component extracted by the
pulsating component extraction unit 410 becomes zero, to30
calculate a required amount of current. The integral
control unit 413 performs integral control such that the
frequency component extracted by the pulsating component
23
extraction unit 412 becomes zero, to calculate a required
amount of current. Note that the integral control units
411 and 413 may perform calculation with proportional
control, differential control, etc. in combination with the
integral control.5
[0045] The AC restoration processing unit 409 receives
input of the results of calculation of the integral control
units 406, 408, 411, and 413 and restores the calculation
results to one AC signal. The AC restoration processing
unit 409 outputs the restored AC signal as a q-axis current10
command. Consequently, the control unit 400 can pulsate
the q-axis current at the same frequency as that of the DC
bus voltage Vdc and pulsate the output voltage of the
inverter 310.
[0046] As described above, the control unit 400 includes15
a pulsating component extraction unit that extracts at
least one specific frequency component from the physical
quantity detected by the voltage detection unit 502, and
controls the output voltage of the inverter 310 such that
the extracted frequency component approaches zero.20
Alternatively, the control unit 400 may include one or more
pulsating component extraction units that extract at least
one specific frequency component from the physical quantity
detected by the voltage detection unit 502, and change the
pulsating component extraction units that extract the25
frequency component depending on the period of a pulsating
component of the extracted frequency component. That is,
when the control unit 400 includes two or more pulsating
portion extraction units capable of extracting frequency
components as illustrated in FIG. 7, the control unit 40030
may select pulsating portion extraction units to use and
perform control.
[0047] The control unit 400 adds the q-axis current
24
command required to reduce the pulsation of the DC bus
voltage Vdc to an existing q-axis current command. Here,
the existing q-axis current command will be described. The
magnetic flux direction of motor magnets is defined as a d-
axis, and a direction leading the d-axis by 90 degrees in5
electrical angle phase, that is, a direction orthogonal to
the d-axis is defined as a q-axis. By passing a current Iq
through motor coils in the q-axis direction, torque is
produced in the motor 314, generating a turning force,
which is a known technique. The control unit 400 of the10
power conversion apparatus 1 connected to the motor 314
typically includes a speed control unit (not illustrated)
for controlling the motor 314 to a desired rotational speed.
The configuration of the speed control unit may be a
general configuration, and thus a detailed description15
thereof will be omitted. The existing q-axis current
command iq* is expressed as in formula (4) where iqpi is an
output of the speed control unit.
[0048] iq*=iqpi...(4)
[0049] Next, the q-axis current command required to20
reduce the pulsation of the DC bus voltage Vdc is expressed
as in formula (5) where Iqvdc is the amplitude component of
the pulsation of the DC bus voltage Vdc, 2ωin is the angular
velocity of a frequency that is twice the fundamental
frequency of the first AC voltage supplied from the AC25
source 110, and δ is the phase of the pulsation of the DC
bus voltage Vdc.
[0050] Iqd2v=Iq2f-cossin(2ωint)-Iq2f-
sincos(2ωint)=Iqvdcsin(2ωin+δ)...(5)
[0051] Therefore, the addition of the q-axis current30
command required to reduce the pulsation of the DC bus
voltage Vdc to the existing q-axis current command iq* is
expressed as in formula (6).
25
[0052] iq*=iqpi+Iqvdcsin(2ωin+δ)...(6)
[0053] To reduce the pulsation of the DC bus voltage Vdc,
the control unit 400 generates the q-axis current command
iq* shown in formula (6) to control the operations of the
inverter 310, the motor 314, and others. When reducing the5
pulsation of the DC bus voltage Vdc for a plurality of
frequencies, specifically, for frequencies two and four
times the fundamental frequency of the first AC voltage,
the control unit 400 may generate the q-axis current
command iq* shown in formula (7) to control the operations10
of the inverter 310, the motor 314, and others.
[0054] iq*=iqpi+Iqvdcsin(2ωin+δ)+Iqvdcsin(4ωin+δ)...(7)
[0055] For a frequency to be controlled together with a
frequency twice the fundamental frequency of the first AC
voltage, the control unit 400 is not limited to a frequency15
four times the fundamental frequency of the first AC
voltage, and can control one or more frequencies that are
multiples of the fundamental frequency of the first AC
voltage, such as six times the fundamental frequency of the
first AC voltage and eight times the fundamental frequency20
of the first AC voltage. That is, the control unit 400
superimposes, on the inverter output, pulsation of a
harmonic component that is twice the fundamental frequency
of the first AC voltage and one or more harmonic components
that are multiples of the fundamental frequency of the25
first AC voltage. In the example of FIG. 4, the frequency
of the first ripple is a frequency twice the fundamental
frequency of the first AC voltage, which is the power
frequency of the AC source 110. In the example of FIG. 7,
the frequency of the first ripple is the sum of a frequency30
component twice the fundamental frequency of the first AC
voltage, which is the power frequency of the AC source 110,
and a frequency component that is a multiple of the
26
fundamental frequency of the first AC voltage.
[0056] The control unit 400 may further add a q-axis
current command for vibration reduction control of the
motor 314 to the q-axis current command iq* shown in
formula (6) or (7). Load pulsation caused by the rotation5
of the motor 314 of the compressor 315 can be reduced by a
q-axis current command output by a pulsation compensation
unit as described, for example, in Japanese Patent No.
6537725. Thus, the control unit 400 may include such a
pulsation compensation unit. The q-axis current command10
output from the pulsation compensation unit is expressed as
in formula (8) where Iqavs is the amplitude component of the
load pulsation of the compressor 315, ωm is the angular
velocity of the mechanical angular rotation frequency of
the compressor 315, and ε is the phase of the load15
pulsation of the compressor 315.
[0057] Iqavssin(ωm+ε)...(8)
[0058] The control unit 400 controls the second AC
voltage to superimpose a fourth ripple correlated with the
above-described third ripple on the output voltage from the20
inverter 310. Therefore, the addition of the q-axis
current command for the vibration reduction control to the
q-axis current command in formulas (6) and (7) is expressed
as in formulas (9) and (10), respectively.
[0059] iq*=iqpi+Iqvdcsin(2ωin+δ)+Iqavssin(ωm+ε)...(9)25
[0060]
iq*=iqpi+Iqvdcsin(2ωin+δ)+Iqvdcsin(4ωin+δ)+Iqavssin(ωm+ε)...(
10)
[0061] To reduce the pulsation of the DC bus voltage Vdc
and further perform the vibration reduction control, the30
control unit 400 generates the q-axis current command iq*
shown in formula (9) or (10) to control the operations of
the inverter 310, the motor 314, and others. Here, there
27
is a limit to the amount of current that can be actually
passed as the q-axis current, that is, there is a maximum
amount of current. Consequently, there may be cases where
the amount of current according to the q-axis current
command iq* in formulas (6), (7), (9), and (10) cannot be5
passed. Therefore, the control unit 400 sets a limit value
to the q-axis current command for each control. Ways to
set the limit values include, for example, a way of
determining the priority order and allocating q-axis
currents each time, and a way of allocating q-axis currents10
at a predetermined ratio from the beginning. For the
former, for example, the priority order is determined like
iqpi>Iqvdc>Iqavs. For the latter, for example, the limit
value of usable q-axis current is divided like
iqpi:Iqvdc:Iqavs=4:3:3.15
[0062] Alternatively, the control unit 400 may not limit
the q-axis current command iqpi from the speed control unit,
and may allocate the remaining amount of current when the
q-axis current command iqpi is subtracted from the maximum
amount of current to the q-axis current command Iqvdc for20
reducing the pulsation of the DC bus voltage Vdc and the q-
axis current command Iqavs from the pulsating load
compensation unit. FIG. 8 is a first diagram illustrating
the proportions of the amounts of current for the controls
to the q-axis current command iq* by the control unit 40025
of the power conversion apparatus 1 according to the first
embodiment. FIG. 9 is a second diagram illustrating the
proportions of the amounts of current for the controls to
the q-axis current command iq* by the control unit 400 of
the power conversion apparatus 1 according to the first30
embodiment. Note that FIGS. 8 and 9 are for formula (9),
and Iqvdc2 represents Iqvdcsin(2ωin+δ). As illustrated in FIG.
8, the control unit 400 may allocate the q-axis current
28
command iqpi and the q-axis current command Iqvdc2 directly
to the maximum amount of current, and allocate the
remaining amount of current to the q-axis current command
Iqavs. Alternatively, as illustrated in FIG. 9, the control
unit 400 may allocate the q-axis current command iqpi5
directly to the maximum amount of current, and divide the
remaining amount of current into two equal parts and
allocate them to the q-axis current command Iqvdc2 and the
q-axis current command Iqavs. When the example of FIG. 9 is
applied to formula (10), the control unit 400 may allocate10
the q-axis current command iqpi directly to the maximum
amount of current, and divide the remaining amount of
current into three equal parts and allocate them to the q-
axis current command Iqvdc2, the q-axis current command Iqvdc4,
and the q-axis current command Iqavs. Note that Iqvdc415
represents Iqvdcsin(4ωin+δ).
[0063] The control unit 400 basically prioritizes the q-
axis current command iqpi because if the current of the q-
axis current command iqpi, which is an output from the speed
control unit, is limited, the rotation of the motor 31420
cannot be desirably maintained. However, depending on the
purpose such as to continue the operation even by reducing
the rotational speed of the motor 314, the control unit 400
may limit the q-axis current command iqpi. Furthermore, in
FIGS. 8 and 9, the control unit 400 may set the ratio for25
the controls freely depending on the purpose. For example,
when vibration is a concern at low speed, the control unit
400 may allocate a large amount of current to the q-axis
current command Iqavs. In this manner, the control unit 400
changes the proportions of the second ripple and the fourth30
ripple to be superimposed on the output voltage from the
inverter 310 at a specified ratio.
[0064] As described above, the control unit 400 can
29
reduce the pulsation of the DC bus voltage Vdc by
superimposing, on the inverter output, pulsation including
the same frequency component as the pulsation of the DC bus
voltage Vdc generated by the AC source 110, which is a
single-phase AC source. The control unit 400 uses, as the5
above-described frequency component, a frequency that is
twice the power frequency of the AC source 110, which is a
single-phase AC source, that is, the fundamental frequency
of the first AC voltage.
[0065] The control unit 400 periodically calculates the10
fundamental frequency of the first AC voltage, which is the
power frequency of the AC source 110, which is a single-
phase AC source, using the detected value of the voltage
detection unit 501. The power frequency of the AC source
110 may slightly fluctuate in frequency even in a day.15
Therefore, by periodically calculating the fundamental
frequency of the first AC voltage, which is the power
frequency of the AC source 110, the control unit 400 can
improve the accuracy of the controls described so far.
[0066] A method by which the control unit 40020
periodically calculates the fundamental frequency of the
first AC voltage, which is the power frequency of the AC
source 110, will be specifically described. The power
frequency of the AC source 110 fluctuates by about 0.5 Hz
even in a day. FIG. 10 illustrates how much the current of25
the capacitor 210 decreases relative to the actual power
frequency of the AC source 110 when the control unit 400
performs the control to reduce the charging and discharging
current I3 of the capacitor 210 on the assumption that the
power frequency of the AC source 110 is 50 Hz. FIG. 10 is30
a diagram illustrating an example of the relationship
between the frequency and the effective value of the
current of the capacitor 210 when the control to reduce the
30
charging and discharging current I3 of the capacitor 210 is
performed in the power conversion apparatus 1 according to
the first embodiment. As illustrated in FIG. 10, the
effect of the control to reduce the charging and
discharging current I3 of the capacitor 210 decreases, that5
is, the current of the capacitor 210 increases with an
error of about 0.1 Hz. Therefore, in order to obtain a
desired effect in the control to reduce the charging and
discharging current I3 of the capacitor 210, the power
conversion apparatus 1 needs to always correctly detect the10
power frequency of the AC source 110.
[0067] As described above, with the DC bus voltage Vdc
from which the DC component has been removed as
Vdc=Asin(ωt), the pulsating component extraction units 405
and 407 remove the sin component and the cos component by15
filtering the values obtained by formulas (1) and (2) with
the low-pass filters, to extract the amplitude value A of
sin(ωt). Here, with an error Δω in ω taken into account,
the DC bus voltage Vdc from which the DC component has been
removed is expressed as in formula (11).20
[0068]
Asin(ωt+Δωt)=Asin(ωt)cos(Δωt)+Acos(ωt)sin(Δωt)...(11)
[0069] As above, the pulsating component extraction unit
405 multiplies the DC bus voltage Vdc from which the DC
component has been removed shown in formula (11) by25
2cos(ωt) to obtain formula (12), and the pulsating
component extraction unit 407 multiplies the DC bus voltage
Vdc from which the DC component has been removed shown in
formula (11) by 2sin(ωt) to obtain formula (13).
[0070] Asin(ωt+Δωt)×2cos(ωt)30
=2Acos(ωt)sin(ωt)cos(Δωt)+2Acos2(ωt)sin(Δωt)
=Asin(Δωt)+Acos(2ωt)sin(Δωt)+Asin(2ωt)cos(Δωt)...(12)
[0071] Asin(ωt+Δωt)×2sin(ωt)
31
=2Asin2(ωt)cos(Δωt)+2Asin(ωt)cos(ωt)sin(Δωt)
=Acos(Δωt)-Acos(2ωt)cos(Δωt)+Asin(2ωt)sin(Δωt)...(13)
[0072] As described above, the pulsating component
extraction units 405 and 407 filter the values obtained by
formulas (12) and (13) with the low-pass filters to remove5
the sin component and the cos component. Consequently, the
pulsating component extraction units 405 and 407 can
extract the amplitude value A including the Δω component of
sin(ωt+Δωt). Specifically, assuming a case where a
frequency twice the power frequency of the AC source 11010
recognized by the control unit 400 is 100 Hz while a
frequency twice the actual power frequency of the AC source
110 is 101 Hz, the DC bus voltage Vdc from which the DC
component has been removed when a frequency twice the power
frequency of the AC source 110 is 101 Hz is expressed as in15
formula (14).
[0073] Asin(ωt+Δωt)=Asin(2π100t+2π1t)...(14)
[0074] Therefore, when extracting a pulsating component
of 100 Hz in the pulsating component extraction units 405
and 407, the control unit 400 can use formula (14) to20
obtain formulas (15) and (16) from formulas (12) and (13).
[0075] Asin(2π100t+2π1t)×2cos(2π100t)
=Asin(2π1t)+Acos(2π100t)sin(2π1t)+Asin(2π100t)cos(2π1t
)...(15)
[0076] Asin(2π100t+2π1t)×2sin(2π100t)25
=Acos(2π1t)-
Acos(2π100t)cos(2π1t)+Asin(2π100t)sin(2π1t)...(16)
[0077] As described above, the pulsating component
extraction units 405 and 407 filter the values obtained by
formulas (15) and (16) with the low-pass filters to remove30
the sin component and the cos component. Consequently, the
pulsating component extraction units 405 and 407 can
extract the amplitude value A including the 2π1t component
32
of sin(2π100t+2π1t). FIG. 11 is a diagram illustrating a
concrete example of pulsating component extraction in the
power conversion apparatus 1 according to the first
embodiment. In (a) in FIG. 11, Vin represents the power
frequency of the AC source 110, and Vdc represents the DC5
bus voltage. In (b) in FIG. 11, α represents Asin(2π1t) in
the first term on the right side of formula (15), and β
represents Acos(2π1t) in the first term on the right side
of formula (16).
[0078] The control unit 400 detects the primary voltage10
or zero-crossings of the AC source 110 to periodically
calculate the power frequency of the AC source 110, and
constantly updates the power frequency of the AC source 110
recognized by the control unit 400. The control unit 400
may not be able to calculate a correct power frequency by15
zero-crossing detection due to the effects of noise, a
delay in a detection circuit, etc., and thus typically uses
several moving averages. If the control unit 400 can
detect a frequency of 1 Hz of 2π1t by zero-crossing
detection for an extracted pulsating component, for example,20
Vdccos2f in FIG. 11, and correct the power frequency of the
AC source 110 recognized by the control unit 400 from 100
Hz to 101 Hz, the frequency calculation by the zero-
crossing detection of the AC source 110 becomes unnecessary.
[0079] For example, the voltage detection unit 501 is25
used as a third detection unit to detect a third physical
quantity correlated with the voltage value of the first AC
voltage. In this case, the control unit 400 periodically
calculates the fundamental frequency of the first AC
voltage, which is the power frequency of the AC source 110,30
from the third physical quantity detected by the voltage
detection unit 501.
[0080] Alternatively, the voltage detection unit 501 is
33
used as a fourth detection unit to detect that the voltage
value of the first AC voltage that changes with the lapse
of time exceeds or falls below a specified value. In this
case, the control unit 400 periodically calculates the
fundamental frequency of the first AC voltage, which is the5
power frequency of the AC source 110, from an output signal
of the voltage detection unit 501. The control unit 400
calculates a value from an output signal of the voltage
detection unit 501 two or more times and sets the average
value as the fundamental frequency of the first AC voltage,10
which is the power frequency of the AC source 110.
[0081] The operation of the control unit 400 will be
described with reference to a flowchart. FIG. 12 is a
flowchart illustrating the operation of the control unit
400 of the power conversion apparatus 1 according to the15
first embodiment. In the power conversion apparatus 1, the
control unit 400 acquires a physical quantity correlated
with the DC bus voltage Vdc (step S1). The control unit
400 identifies first ripple included in the DC bus voltage
Vdc (step S2). The control unit 400 generates a q-axis20
current command to superimpose second ripple correlated
with the first ripple on the output voltage from the
inverter 310 (step S3).
[0082] Next, a hardware configuration of the control
unit 400 included in the power conversion apparatus 1 will25
be described. FIG. 13 is a diagram illustrating an example
of a hardware configuration that implements the control
unit 400 included in the power conversion apparatus 1
according to the first embodiment. The control unit 400 is
implemented by a processor 91 and memory 92.30
[0083] The processor 91 is a central processing unit
(CPU, also called a central processor, a processing device,
an arithmetic device, a microprocessor, a microcomputer, a
34
processor, and a digital signal processor (DSP)), or a
system large-scale integration (LSI). The memory 92 can be
exemplified by nonvolatile or volatile semiconductor memory
such as random-access memory (RAM), read-only memory (ROM),
flash memory, an erasable programmable read-only memory5
(EPROM), or an electrically erasable programmable read-only
memory (EEPROM) (registered trademark). The memory 92 is
not limited to these, and may be a magnetic disk, an
optical disk, a compact disk, a mini disk, or a digital
versatile disc (DVD).10
[0084] As described above, according to the present
embodiment, in the power conversion apparatus 1, the
voltage detection unit 502 detects the DC bus voltage Vdc,
and the control unit 400 superimposes, on the inverter
output, pulsation including the same frequency component as15
the pulsation of the DC bus voltage Vdc generated by the AC
source 110, which is a single-phase AC source, that is,
pulsation of a frequency that is twice the fundamental
frequency of the first AC voltage, which is the power
frequency of the AC source 110, so that the pulsation of20
the DC bus voltage Vdc can be reduced. Furthermore, the
power conversion apparatus 1 can reduce the deterioration
of the smoothing capacitor 210 while preventing the device
from becoming larger.
[0085] By detecting the DC bus voltage Vdc by the25
voltage detection unit 502, the power conversion apparatus
1 can reduce the cost of the detection circuit as compared
with a case where current flowing through the capacitor 210
is directly detected, and can facilitate the introduction
since there is no concern about heat effects. Furthermore,30
since the DC bus voltage Vdc detected by the voltage
detection unit 502 is a voltage smoothed by the capacitor
210, the power conversion apparatus 1 eliminates the need
35
for a measure against high-frequency ripple caused by
pulse-width modulation (PWM), as compared with a case where
current flowing through the capacitor 210 is directly
detected. In the power conversion apparatus 1, the
capacitance of the capacitor 210 is reduced, so that a5
pulsating component to be controlled has a high signal-to-
noise ratio, facilitating detection. The power conversion
apparatus 1, in which the control unit 400 performs
feedback control, thus allows control with high robustness.
The power conversion apparatus 1, in which the control unit10
400 extracts and controls a specific frequency component,
thus allows control with waveform distortion reduced.
[0086] Second Embodiment.
The second embodiment describes a case where a
converter includes a booster circuit.15
[0087] FIG. 14 is a first diagram illustrating an
exemplary configuration of a power conversion apparatus 1a
according to the second embodiment. The power conversion
apparatus 1a is obtained by replacing the converter 150 and
the control unit 400 with a converter 150a and a control20
unit 400a in the power conversion apparatus 1 of the first
embodiment illustrated in FIG. 1. The converter 150a
includes the reactor 120, the rectifier unit 130, and a
booster unit 140. The booster unit 140 includes a reactor
141, a switching element 142, and a rectifier element 143,25
constituting a booster circuit. The booster unit 140
boosts the voltage rectified by the rectifier unit 130 by
the control unit 400a performing on-off control on the
switching element 142. The boost operation of the booster
unit 140 may be a general one, and thus will not be30
described in detail. The control unit 400a has a function
of performing the on-off control on the switching element
142 of the booster unit 140 in addition to the functions of
36
the control unit 400. That is, the control unit 400a
controls the operation of the converter 150a including the
booster unit 140. The power conversion apparatus 1a and
the motor 314 included in the compressor 315 constitute a
motor drive unit 2a.5
[0088] The power conversion apparatus 1a is equipped
with the booster circuit to increase the DC bus voltage Vdc,
thereby eliminating the need for current for, for example,
flux-weakening control over the rotation of the motor 314,
and thus can increase the amount of current that can be10
used for a q-axis current more than when the converter 150
is a passive circuit as in the first embodiment. As
compared with the power conversion apparatus 1 of the first
embodiment, the power conversion apparatus 1a can increase
current that can be allocated to Iqvdc even at the same load15
condition, rotational speed, etc., and can enhance the
effect of reducing the pulsation of the DC bus voltage Vdc.
The power conversion apparatus 1a needs to detect the
voltage that has been boosted by the booster unit 140.
However, since the power conversion apparatus 1a includes20
the voltage detection unit 502 for detecting the DC bus
voltage Vdc, it is not necessary to add a new detection
unit in the second embodiment.
[0089] Note that the configuration of the converter of
the power conversion apparatus including the boost function25
is not limited to the example of FIG. 14. The converter
150 of the power conversion apparatus 1 in the first
embodiment is a passive circuit composed of passive
components, and the value of the DC bus voltage Vdc is
determined by the amplitude value of the first AC voltage30
supplied from the AC source 110. However, in the first
embodiment, it is sufficient that the pulsation of the DC
bus voltage Vdc can be correctly detected, and pulsation of
37
the same frequency component as that of the pulsation of
the DC bus voltage Vdc can be output from the inverter 310.
Therefore, for example, in the rectifier unit 130, a
booster circuit may be configured by replacing the
rectifier elements 131 to 134 such as diodes with5
semiconductor devices, that is, active elements such as
switching elements, and the control unit 400 or the like
may control the operation of the active elements.
[0090] FIG. 15 is a second diagram illustrating an
exemplary configuration of a power conversion apparatus 1b10
according to the second embodiment. The power conversion
apparatus 1b is obtained by replacing the converter 150 and
the control unit 400 with a converter 150b and a control
unit 400b in the power conversion apparatus 1 of the first
embodiment illustrated in FIG. 1. The converter 150b15
includes the reactor 120 and a rectifier unit 130b. The
rectifier unit 130b includes switching elements 161 to 164.
The switching elements 161 to 164 are, for example,
semiconductor devices, and are turned on and off under the
control of the control unit 400b. The rectifier unit 130b20
can boost and output the voltage by the switching elements
161 to 164 being turned on and off. The control unit 400b
has a function of performing on-off control on the
switching elements 161 to 164 of the rectifier unit 130b in
addition to the functions of the control unit 400. That is,25
the control unit 400b controls the operation of the
converter 150b. Note that the rectifier unit 130b may have
a configuration in which some of the four elements are
switching elements and the other elements are rectifier
elements such as diodes. Also in this case, the same30
effects as those of the power conversion apparatus 1a
illustrated in FIG. 14 can be obtained. The power
conversion apparatus 1b and the motor 314 included in the
38
compressor 315 constitute a motor drive unit 2b.
[0091] As described above, the converter 150a in the
power conversion apparatus 1a or the converter 150b in the
power conversion apparatus 1b includes at least one
switching element. In this case, the voltage detection5
unit 502 may detect a physical quantity in synchronization
with the timing of change in conduction or nonconduction of
the switching element(s) included in the converter 150a or
the converter 150b.
[0092] Third Embodiment.10
FIG. 16 is a diagram illustrating an exemplary
configuration of a refrigeration cycle application
apparatus 900 according to a third embodiment. The
refrigeration cycle application apparatus 900 according to
the third embodiment includes the power conversion15
apparatus 1 described in the first embodiment. The
refrigeration cycle application apparatus 900 can include
the power conversion apparatus 1a or the power conversion
apparatus 1b described in the second embodiment, but here,
as an example, a case where the refrigeration cycle20
application apparatus 900 includes the power conversion
apparatus 1 will be described. The refrigeration cycle
application apparatus 900 according to the third embodiment
can be applied to a product with a refrigeration cycle,
such as an air conditioner, a refrigerator, a freezer, or a25
heat pump water heater. In FIG. 16, components having the
same functions as those of the first embodiment are denoted
by the same reference numerals as those of the first
embodiment.
[0093] In the refrigeration cycle application apparatus30
900, the compressor 315 incorporating the motor 314 in the
first embodiment, a four-way valve 902, an indoor heat
exchanger 906, an expansion valve 908, and an outdoor heat
39
exchanger 910 are installed via refrigerant piping 912.
[0094] A compression mechanism 904 that compresses a
refrigerant and the motor 314 that operates the compression
mechanism 904 are provided inside the compressor 315.
[0095] The refrigeration cycle application apparatus 9005
can perform heating operation or cooling operation by the
switching operation of the four-way valve 902. The
compression mechanism 904 is driven by the motor 314 that
is variable-speed controlled.
[0096] During the heating operation, as indicated by10
solid arrows, the refrigerant is pressurized and delivered
by the compression mechanism 904, passes through the four-
way valve 902, the indoor heat exchanger 906, the expansion
valve 908, the outdoor heat exchanger 910, and the four-way
valve 902, and returns to the compression mechanism 904.15
[0097] During the cooling operation, as indicated by
dashed arrows, the refrigerant is pressurized and delivered
by the compression mechanism 904, passes through the four-
way valve 902, the outdoor heat exchanger 910, the
expansion valve 908, the indoor heat exchanger 906, and the20
four-way valve 902, and returns to the compression
mechanism 904.
[0098] During the heating operation, the indoor heat
exchanger 906 acts as a condenser to release heat, and the
outdoor heat exchanger 910 acts as an evaporator to absorb25
heat. During the cooling operation, the outdoor heat
exchanger 910 acts as a condenser to release heat, and the
indoor heat exchanger 906 acts as an evaporator to absorb
heat. The expansion valve 908 decompresses and expands the
refrigerant.30
[0099] The configurations described in the above
embodiments illustrate an example, and can be combined with
another known art. The embodiments can be combined with
40
each other. The configurations can be partly omitted or
changed without departing from the gist.
Reference Signs List
[0100] 1, 1a, 1b power conversion apparatus; 2, 2a, 2b5
motor drive unit; 110 AC source; 120, 141 reactor; 130,
130b rectifier unit; 131 to 134, 143 rectifier element;
140 booster unit; 142, 161 to 164, 311a to 311f switching
element; 150, 150a, 150b converter; 200 smoothing unit;
210, 512 capacitor; 310 inverter; 312a to 312f10
freewheeling diode; 313a, 313b current detection unit; 314
motor; 315 compressor; 400, 400a, 400b control unit; 401
second-order low-pass filter; 402, 404 subtractor; 403,
513 filter; 405, 407, 410, 412 pulsating component
extraction unit; 406, 408, 411, 413 integral control unit;15
409 AC restoration processing unit; 420 plant model; 501,
502 voltage detection unit; 511 resistor; 900
refrigeration cycle application apparatus; 902 four-way
valve; 904 compression mechanism; 906 indoor heat
exchanger; 908 expansion valve; 910 outdoor heat20
exchanger; 912 refrigerant piping.
41
We Claim:
[Claim 1] A power conversion apparatus, comprising:
a converter rectifying a first AC voltage supplied5
from an AC source;
a capacitor connected to an output end of the
converter, the capacitor smoothing a first DC voltage
rectified by the converter into a second DC voltage
including a first ripple;10
an inverter connected across the capacitor, the
inverter converting the second DC voltage into a second AC
voltage corresponding to a desired frequency; and
a detection unit acquiring a physical quantity
correlated with the second DC voltage, wherein15
the second AC voltage is controlled to superimpose a
second ripple correlated with the first ripple on an output
voltage of the inverter.
[Claim 2] The power conversion apparatus according to claim20
1, comprising
a pulsating component extraction unit extracting at
least one specific frequency component from the physical
quantity detected by the detection unit, wherein the output
voltage of the inverter is controlled such that the25
extracted frequency component approaches zero.
[Claim 3] The power conversion apparatus according to claim
1, comprising
one or more pulsating component extraction units30
extracting at least one specific frequency component from
the physical quantity detected by the detection unit,
wherein the pulsating component extraction units extracting
42
the frequency component are changed depending on a period
of a pulsating component of the extracted frequency
component.
[Claim 4] The power conversion apparatus according to any5
one of claims 1 to 3, wherein
the inverter is connected to a motor, the detection
unit is a first detection unit, and the physical quantity
is a first physical quantity,
the power conversion apparatus further comprises a10
second detection unit acquiring a second physical quantity
including a third ripple correlated with a rotational speed
generated by the motor, and
the second AC voltage is controlled to superimpose a
fourth ripple correlated with the third ripple on the15
output voltage from the inverter.
[Claim 5] The power conversion apparatus according to claim
4, wherein
proportions of the second ripple and the fourth ripple20
to be superimposed on the output voltage from the inverter
are changed at a specified ratio.
[Claim 6] The power conversion apparatus according to any
one of claims 1 to 5, wherein25
a frequency of the first ripple is a sum of a
frequency component that is twice a fundamental frequency
of the first AC voltage, and a frequency component that is
a multiple of the fundamental frequency of the first AC
voltage.30
[Claim 7] The power conversion apparatus according to any
one of claims 1 to 5, wherein
43
a frequency of the first ripple is a frequency that is
twice a fundamental frequency of the first AC voltage.
[Claim 8] The power conversion apparatus according to any
one of claims 1 to 7, wherein5
the detection unit detects the physical quantity at
periods shorter than a frequency of the first ripple.
[Claim 9] The power conversion apparatus according to any
one of claims 1 to 7, wherein10
the detection unit detects the physical quantity in
synchronization with a timing of change in conduction or
nonconduction of switching elements included in the
inverter.
15
[Claim 10]The power conversion apparatus according to any
one of claims 1 to 7, wherein
the converter includes at least one switching element.
[Claim 11]The power conversion apparatus according to claim20
10, wherein
the detection unit detects the physical quantity in
synchronization with a timing of change in conduction or
nonconduction of the switching element included in the
converter.25
[Claim 12]The power conversion apparatus according to any
one of claims 1 to 11, wherein
either an analog filter including electronic
components and attenuating a specific frequency component,30
or a digital filter attenuating a specific frequency
component by calculation is used to attenuate a specific
frequency component of the physical quantity.
44
[Claim 13]The power conversion apparatus according to claim
12, wherein
a cutoff frequency of the analog filter or the digital
filter is a frequency two or more times a frequency of the5
first ripple.
[Claim 14]The power conversion apparatus according to any
one of claims 1 to 13, wherein
the detection unit is a first detection unit, and the10
physical quantity is a first physical quantity,
the power conversion apparatus further comprises a
third detection unit detecting a third physical quantity
correlated with a voltage value of the first AC voltage,
and15
a fundamental frequency of the first AC voltage is
periodically calculated from the third physical quantity.
[Claim 15]The power conversion apparatus according to any
one of claims 1 to 13, wherein20
the detection unit is a first detection unit,
the power conversion apparatus further comprises a
fourth detection unit detecting that a voltage value of the
first AC voltage that changes with a lapse of time exceeds
or falls below a specified value, and25
a fundamental frequency of the first AC voltage is
periodically calculated from an output signal of the fourth
detection unit.
[Claim 16]The power conversion apparatus according to claim30
15, wherein
a value is calculated from the output signal of the
fourth detection unit two or more times, and an average
45
value of the values is set as the fundamental frequency of
the first AC voltage.
[Claim 17]A motor drive unit, comprising the power
conversion apparatus according to any one of claims 1 to 16.5
[Claim 18]A refrigeration cycle application apparatus,
comprising the power conversion apparatus according to any
one of claims 1 to 16.
10