FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
POWER CONVERSION DEVICE, MOTOR DRIVE DEVICE, 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
TITLE OF THE INVENTION:
POWER CONVERSION DEVICE, MOTOR DRIVE DEVICE, AND
5 REFRIGERATION-CYCLE APPLICATION APPARATUS
Field
[0001] The present disclosure relates to a power
conversion device that converts Alternating-Current (AC)
10 power into desired power, to a motor drive device, and to a
refrigeration-cycle application apparatus.
Background
[0002] A power conversion device that converts AC power
15 into desired power is applied to, for example, an air
conditioner. In a compressor such as a rotary compressor
included in such an air conditioner, a load torque of a
motor periodically varies in the course of fluid
compression including a set of suction, compression, and
20 discharge processes. Thus, if an output torque of the
motor is kept constant, a rotational speed of the
compressor varies and the compressor produces vibrations.
In response to this problem, Patent Literature 1 discloses
a power conversion device (converter) that performs torque
25 control to vary an output torque in accordance with
variations in a load torque that occurs in a single
rotation of a motor of a compressor, thereby reducing
vibrations of the compressor.
30 Citation List
Patent Literature
[0003] Patent Literature 1: Japanese Patent Application
Laid-open No. H02-017884
3
Summary of Invention
Problem to be solved by the Invention
[0004] However, in performing the control to vary an
5 output torque in accordance with variations in a load
torque, it is necessary to vary an input power to and an
input current to an inverter that generates an output
torque to the motor. Additionally, in varying the input
power to and the input current to the inverter, a current
10 flowing to a smoothing capacitor (hereinafter, such a
current may be referred to as a capacitor current)
increases in response to the variations in the input
current. Here, the smoothing capacitor is provided at the
preceding stage of the inverter in order to smooth a
15 current output from a converter that rectifies AC power.
In view of the increase in the capacitor current, it is
necessary to select a capacitor having a current tolerance
higher than that in a case where control to make the output
torque of the motor constant is performed. That is, the
20 capacitor needs to be increased in size, resulting in a
problem of an increase in size of the power conversion
device.
[0005] The present disclosure has been made in view of
the circumstances, and an object of the present disclosure
25 is to provide a power conversion device that can reduce an
increase in size of an apparatus.
Means to Solve the Problem
[0006] To solve the problem and achieve the object
30 described above, a power conversion device according to the
present disclosure comprises: a converter rectifying a
first alternating-current power supplied from an
alternating-current power supply and boosting a voltage of
4
the first alternating-current power rectified; a smoothing
unit connected to an output end of the converter; and a
control unit controlling the converter to cause an input
current to the converter to change in accordance with at
5 least one of a first frequency or a second frequency, and
reducing a current flowing to the smoothing unit, the first
frequency being a frequency of pulsation of input power to
a load unit connected across the smoothing unit, the second
frequency being a frequency of pulsation of input power to
10 the converter due to a frequency of the alternating-current
power supply.
Effects of the Invention
[0007] The power conversion device according to the
15 present disclosure has an effect of capable of reducing the
increase in size of the apparatus.
Brief Description of Drawings
[0008] FIG. 1 is a diagram illustrating a schematic
20 configuration of a power conversion system implemented by
applying a power conversion device according to a first
embodiment.
FIG. 2 is a diagram illustrating an exemplary
configuration of the power conversion device according to
25 the first embodiment.
FIG. 3 is a diagram illustrating an exemplary
configuration of an inverter and a compressor.
FIG. 4 is a diagram illustrating, as a first
comparative example of the first embodiment, an example of
30 operation waveforms of the power conversion device in a
case where constant torque control is performed.
FIG. 5 is a diagram illustrating, as a second
comparative example of the first embodiment, an example of
5
operation waveforms of the power conversion device in a
case where vibration reduction control is performed.
FIG. 6 is a diagram illustrating an example of a
control block constituting a control unit of the power
5 conversion device according to the first embodiment.
FIG. 7 is a diagram for describing a current command
in a case where control using the control block illustrated
in FIG. 6 is applied.
FIG. 8 is a diagram illustrating, as a comparative
10 example, an example of operation waveforms of the
respective constituent components in a case where the power
conversion device drives a motor of the compressor using
the vibration reduction control and general high power
factor control.
15 FIG. 9 is a diagram illustrating an example of
operation waveforms of the respective constituent
components in a case where the power conversion device
drives the motor of the compressor using the vibration
reduction control and capacitor current reduction control.
20 FIG. 10 is a diagram illustrating an example of a
control block constituting a control unit of a power
conversion device according to a second embodiment.
FIG. 11 is a diagram illustrating an example of
operation waveforms of the power conversion device
25 according to the second embodiment.
FIG. 12 is a diagram illustrating a frequency analysis
result of a converter input power illustrated in FIG. 11.
FIG. 13 is a diagram illustrating, as a comparative
example, an example of operation waveforms of the
30 respective constituent components in a case where the power
conversion device according to the second embodiment drives
a motor of a compressor using the general high power factor
control.
6
FIG. 14 is a diagram illustrating an example of
operation waveforms of the respective constituent
components in a case where the power conversion device
according to the second embodiment drives the motor of the
5 compressor using the capacitor current reduction control.
FIG. 15 is a diagram illustrating, as a first
comparative example of a third embodiment, an example of
operation waveforms in a case where the high power factor
control and the vibration reduction control are performed
10 in combination.
FIG. 16 is a diagram illustrating, as a second
comparative example of the third embodiment, an example of
operation waveforms in a case where the high power factor
control, the vibration reduction control, and inverter
15 current pulsation control are performed in combination.
FIG. 17 is a diagram illustrating an example of
operation waveforms in a case where the control according
to the third embodiment is performed.
FIG. 18 is a diagram for describing an operation of a
20 power conversion device according to a fourth embodiment.
FIG. 19 is a diagram illustrating a first exemplary
configuration of a power conversion device according to a
fifth embodiment.
FIG. 20 is a diagram illustrating a second exemplary
25 configuration of the power conversion device according to
the fifth embodiment.
FIG. 21 is a diagram illustrating a third exemplary
configuration of the power conversion device according to
the fifth embodiment.
30 FIG. 22 is a diagram illustrating an example of a
hardware configuration that implements the control unit
included in the power conversion device.
FIG. 23 is a diagram illustrating an exemplary
7
configuration of a refrigeration-cycle application
apparatus according to a sixth embodiment.
Description of Embodiments
5 [0009] Hereinafter, with reference to the drawings, a
description will be given in detail of a power conversion
device, a motor drive device, and a refrigeration-cycle
application apparatus according to embodiments of the
present disclosure.
10 [0010] First Embodiment.
FIG. 1 is a diagram illustrating a schematic
configuration of a power conversion system implemented by
applying a power conversion device according to a first
embodiment. As illustrated in FIG. 1, the power conversion
15 system according to the first embodiment includes a power
supply unit 100, a smoothing unit 200, and a load unit 300.
The power supply unit 100 includes a commercial power
supply, a rectifier circuit, and the like. The smoothing
unit 200 includes a smoothing element such as an
20 electrolytic capacitor. The load unit 300 includes a
motor, an inverter that drives the motor, and the like.
[0011] In the power supply unit 100, AC power supplied
from an AC power supply such as a commercial power supply
is rectified by the rectifier circuit. The rectified power
25 is output to the smoothing unit 200. The smoothing unit
200 smooths Direct-Current (DC) power that is the rectified
power output from power supply unit 100. The smoothed DC
power is output to the load unit 300 and consumed by the
motor constituting the load unit 300.
30 [0012] FIG. 2 is a diagram illustrating an exemplary
configuration of a power conversion device 1 according to
the first embodiment. The power conversion device 1 is
connected to an AC power supply 110 such as a commercial
8
power supply and to a compressor 315. The power conversion
device 1 converts first AC power supplied from the AC power
supply 110 into second AC power having a desired amplitude
and a desired phase, and supplies the second AC power to
5 the compressor 315. The compressor 315 is, for example, a
hermetic compressor to be applied to an air conditioner,
and has the motor installed therein. That is, the power
conversion device 1 constitutes a motor drive device that
supplies the second AC power to the motor included in the
10 compressor 315 to drive the motor.
[0013] The power conversion device 1 includes a voltagecurrent detector 501, a converter 120, a voltage detector
502, the smoothing unit 200, an inverter 310, and a control
unit 400. Note that, the converter 120 and the AC power
15 supply 110 constitute the power supply unit 100 of the
power conversion system illustrated in FIG. 1, and the
inverter 310 and the compressor 315 constitute the load
unit 300 of the power conversion system illustrated in FIG.
1. Additionally, one or both of the voltage-current
20 detector 501 and the voltage detector 502 may be included
in the converter 120.
[0014] The converter 120 is connected to the AC power
supply 110. The converter 120 includes rectifiers 121 to
124, a switching element 125, a rectifier 126, and a
25 reactor 127. The rectifiers 121 to 124 perform full-wave
rectification of a power supply voltage supplied from the
AC power supply 110. The switching element 125 is provided
for boosting the full-wave rectified voltage. That is, the
converter 120 rectifies the first AC power supplied from
30 the AC power supply 110 and boosts the voltage of the
rectified power. The rectifiers 121 to 124 constitute a
rectifier circuit 130. The switching element 125, the
rectifier 126, and the reactor 127 constitute a booster
9
circuit 140. In the booster circuit 140, the switching
element 125 is controlled by the control unit 400 to be
turned on or off, thereby boosting the voltage that has
been rectified by the rectifier circuit 130.
5 [0015] The smoothing unit 200 includes a smoothing
capacitor 210. The smoothing capacitor 210 is connected to
an output end of the converter 120. The smoothing unit 200
smooths DC power and supplies, as the smoothed power, the
DC power to the inverter 310. The DC power is generated by
10 the converter 120 executing a process of converting the
power supply voltage from AC to DC.
[0016] The voltage-current detector 501 is provided
between the AC power supply 110 and the converter 120,
detects a voltage value and a current value of the first AC
15 power supplied from the AC power supply 110 to the
converter 120, and outputs the detected voltage value and
current value to the control unit 400. In the present
embodiment, the voltage value and the current value, which
are detected by the voltage-current detector 501, are Vin
20 and Iin, respectively.
[0017] Note that, although the present embodiment has
described the configuration in which the voltage-current
detector 501 is provided between the AC power supply 110
and the converter 120, the position where the current is
25 detected is not limited to this configuration. A
configuration may be adopted in which a current detector
that detects the current flowing to the reactor 127 is
provided, and a detection value of the current flowing to
the reactor 127 is output to the control unit 400.
30 [0018] The voltage detector 502 is provided between the
converter 120 and the smoothing unit 200, detects a voltage
value of DC power supplied from the converter 120 to the
inverter 310, and outputs the detected voltage value to the
10
control unit 400. In the present embodiment, the voltage
value detected by the voltage detector 502 is Vdc.
[0019] Note that in the following description, as
illustrated in FIG. 2, a current flowing from the converter
5 120 to the smoothing unit 200 and the inverter 310 is
referred to as a current I1, a current flowing to the
inverter 310 is referred to as I2, and a capacitor current
that is a current flowing to the smoothing capacitor 210 is
referred to as a current I3. The currents I1 to I3 are
10 regarded as positive when the currents I1 to I3 flow in
respective corresponding directions indicated by arrows
illustrated in FIG. 2.
[0020] The inverter 310 is connected across the
smoothing unit 200, that is, the smoothing capacitor 210.
15 The inverter 310 converts the smoothed DC power supplied
from the smoothing unit 200 into second AC power and
supplies the second AC power to the compressor 315.
[0021] An exemplary configuration of the inverter 310
and the compressor 315 will be described. FIG. 3 is a
20 diagram illustrating the exemplary configuration of the
inverter 310 and the compressor 315.
[0022] As illustrated in FIG. 3, the inverter 310
includes switching elements 311a to 311f and freewheeling
diodes 312a to 312f each connected in parallel with any
25 corresponding one of the switching elements 311a to 311f.
The compressor 315 is a load having a motor 314 for driving
the compressor. Current detectors 313a and 313b are
provided between the inverter 310 and the motor 314.
[0023] The inverter 310 turns on and off the switching
30 elements 311a to 311f under the control of the control unit
400, and converts power Pinv received from the converter
120 and the smoothing unit 200 into the second AC power
having a desired amplitude and a desired phase. The
11
current detectors 313a and 313b each detect a current value
of a corresponding one phase among the currents of the
three phases output from the inverter 310, and output the
detected current value to the control unit 400. Note that,
5 the control unit 400 can calculate the current value of the
remaining one phase output from the inverter 310 by
acquiring the current values of two phases among the
current values of three phases output from the inverter
310. The motor 314 of the compressor 315 rotates in
10 accordance with the amplitude and the phase of the second
AC power supplied from the inverter 310, thus performing a
compression operation. For example, in a case where the
compressor 315 is a hermetic compressor for use in an air
conditioner or the like, the load torque of the compressor
15 315 can be considered as a constant torque load in many
cases.
[0024] Returning to the description of FIG. 2, the
control unit 400 acquires, from the voltage-current
detector 501, the voltage value Vin and the current value
20 Iin of the first AC power that are input to the converter
120, acquires, from the voltage detector 502, the voltage
value Vdc of the DC power that is output from the converter
120, and acquires, from the current detectors 313a and
313b, the current values of the second AC power that are
25 output from the inverter 310 to the compressor 315. The
control unit 400 controls the operation of the converter
120, specifically, the on and off states of the switching
element 125 included in the booster circuit 140 of the
converter 120, using the detection value detected by each
30 of the voltage-current detector 501, the voltage detector
502, and the current detectors 313a and 313b.
Additionally, the control unit 400 controls the operation
of the inverter 310, specifically, the on and off states of
12
the switching elements 311a to 311f included in the
inverter 310, using the detection value detected by each of
the voltage-current detector 501, the voltage detector 502,
and the current detectors 313a and 313b. At this time, the
5 control unit 400 controls the on and off states of the
switching elements 311a to 311f so as to reduce the
vibrations of the compressor 315. For example, similarly
to the conventional power conversion device disclosed in
Patent Literature 1, the control unit 400 controls the on
10 and off states of the switching elements 311a to 311f such
that the output torque changes in accordance with the
variations in the load torque. Hereinafter, this control
is referred to as vibration reduction control.
[0025] As described above, in performing the vibration
15 reduction control, the current I2 flowing to the inverter
310 needs to be varied, resulting in a problem of an
increase in the capacitor current (current I3) flowing to
the smoothing capacitor 210 in response to the variations
in the current I2. In view of this, the control unit 400
20 applies control different from the conventional control to
the control for the converter 120, thereby reducing the
capacitor current. Specifically, the control unit 400
controls the switching element 125 included in the
converter 120, thus allowing input power Pin to the
25 converter 120 (hereinafter, such input power Pin may be
referred to as converter input power Pin) to be changed in
accordance with the rotational speed of the motor 314
included in the compressor 315. Thus, the control unit 400
reduces the capacitor current flowing to the smoothing
30 capacitor 210. Hereinafter, the control to change the
input power Pin to the converter 120 in accordance with the
rotational speed of the motor 314 performed by the control
unit 400 in order to reduce the capacitor current may be
13
referred to as capacitor current reduction control.
[0026] Here, a description will be given of, as a
comparative example, an operation in a case where the
control unit 400 does not perform the control to change the
5 input power Pin to the converter 120 in accordance with the
rotational speed of the motor 314. Specifically, a
description will be given of a first comparative example
and a second comparative example. The first comparative
example represents an operation in a case where constant
10 torque control, which is the control to make the output
torque of the motor 314 included in the compressor 315
constant, is performed. The second comparative example
represents an operation in a case where the above-described
vibration reduction control is performed.
15 [0027] FIG. 4 is a diagram illustrating, as the first
comparative example of the first embodiment, an example of
operation waveforms of the power conversion device in the
case where the constant torque control is performed. FIG.
5 is a diagram illustrating, as the second comparative
20 example of the first embodiment, an example of operation
waveforms of the power conversion device in the case where
the vibration reduction control is performed. FIGS. 4 and
5 each illustrate the respective waveforms, in the order
from top to bottom, of the input power Pinv to the inverter
25 310 (hereinafter, such input power Pinv may be referred to
as inverter input power Pinv), the input current I2 to the
inverter 310 (hereinafter, such an input current I2 may be
referred to as an inverter input current I2), the current
I3 flowing to the smoothing capacitor 210 (hereinafter,
30 such a current I3 may be referred to as a capacitor current
I3), the rotational speed of the motor 314, the load
torque, and the output torque of the motor 314
(hereinafter, such an output torque may be referred to as a
14
motor output torque). Since the inverter 310 constitutes
the load unit 300, the inverter input power Pinv is also
input power to the load unit 300. Note that in FIGS. 4 and
5, the illustration of current pulsation components due to
5 the converter 120 is omitted from the capacitor current I3
in order to improve viewability of the increase in the
capacitor current I3 caused by the performing of the
vibration reduction control. Additionally, the
illustration of pulsation components due to a switching
10 frequency of the inverter 310 is also omitted.
[0028] According to the comparison of the respective
waveforms illustrated in FIGS. 4 and 5, the performing of
the vibration reduction control, that is, as illustrated in
FIG. 5, the performing of control to vary the motor output
15 torque in synchronization with the variations in the load
torque achieves a reduction in the variations in the
rotational speed of the motor 314. Thus, it can be said
that the vibrations of the compressor 315 are reduced.
However, in performing the vibration reduction control, in
20 order to vary the load torque, it is necessary to cause the
inverter input power Pinv and the inverter input current I2
to pulsate similarly to the motor output torque. This
causes an increase in the capacitor current I3.
[0029] On the other hand, in the present embodiment, as
25 described above, the control unit 400 performs the
capacitor current reduction control to change the input
power Pin to the converter 120 in accordance with the
rotational speed of the motor 314. More specifically, the
control unit 400 detects pulsation of the inverter input
30 power Pinv due to the vibration reduction control or the
like, and causes the input power Pin to the converter to
pulsate at a frequency same as a first frequency that is
the frequency of the detected pulsation. This achieves the
15
reduction in the capacitor current I3 flowing to the
smoothing capacitor 210 of the smoothing unit 200. Note
that, since the pulsation of the inverter input power Pinv
is due to the rotation of the motor 314, the first
5 frequency that is the frequency of the pulsation of the
inverter input power Pinv corresponds to the rotational
speed of the motor 314.
[0030] FIG. 6 is a diagram illustrating an example of a
control block constituting the control unit 400 of the
10 power conversion device 1 according to the first
embodiment. A control block 410 illustrated in FIG. 6 is
provided to generate a control signal for the converter
120, and implements the capacitor current reduction
control.
15 [0031] The control block 410 includes a voltage
controller 411, a high-power-factor current command
converter 412, a current controller 413, and a capacitor
current reduction correction generator 414. Note that, the
control block in a case of implementing a converter that
20 performs the general high power factor control does not
include the capacitor current reduction correction
generator 414. That is, the capacitor current reduction
control implemented by the control block 410 is control to
reduce the capacitor current while performing the high
25 power factor control, and is a type of high power factor
control.
[0032] The voltage controller 411 illustrated in FIG. 6
performs a control operation such that a DC voltage Vdc
follows a DC voltage command Vdcref that is a command for
30 the voltage controller 411. The current controller 413
illustrated in FIG. 6 performs a control operation such
that a converter input current Iin follows a converter
input current command Iinref that is a command for the
16
current controller 413. The DC voltage Vdc is a DC voltage
supplied from the converter 120 to the inverter 310 via the
smoothing unit 200, and this voltage may be referred to as
a capacitor voltage in the following description. The
5 converter input current Iin is an AC current supplied from
the AC power supply 110 to the converter 120. The voltage
controller 411 and the current controller 413 each perform
the above-described control operation using, for example,
Proportional Integral Differential (PID) control,
10 Proportional Integral (PI) control, Proportional (P)
control, and the like. Note that, the control block 410
illustrated in FIG. 6 is configured to perform feedback
control using the command value and the detection value.
However, a part or all of the control block 410 may be
15 configured to perform feedforward control by obtaining in
advance a control amount that achieves a desired current
and a desired voltage.
[0033] The capacitor current reduction correction
generator 414 generates a current command Iinrefc that is a
20 correction command for the current command value Iinrefpfc
generated by the high-power-factor current command
converter 412.
[0034] A description will be given of a method of
deriving the current command Iinrefc output from the
25 capacitor current reduction correction generator 414. The
input power in a case where the converter circuit performs
only the high power factor control is expressed by Formula
(1).
[0035] Formula 1:
30
[0036] In Formula (1), Is is the maximum value of the
input current Iin to the converter 120, and Vs is the
maximum value of the voltage Vin supplied from the AC power
17
supply 110. Additionally, ωin is a frequency of the AC
power supply 110 (hereinafter, such a frequency is referred
to as an AC power supply frequency). Note that, when the
converter 120 can be controlled such that the output power
5 of the converter 120 is provided at a desired current and a
desired voltage in a steady state, the output Iinrefpfc of
the high-power-factor current command converter 412 in FIG.
6 is the same as Issinωint in Formula (1).
[0037] In the case of the control block 410 in FIG. 6,
10 the input power Pin to the converter 120 is expressed by
Formula (2).
[0038] Formula 2:
[0039] The respective terms on the right side of Formula
15 (2) represent, in the order from left to right, a DC
component, pulsation of a frequency component twice the AC
power supply frequency ωin, and the product of the current
command Iinrefc that is the correction command and Vssinωint
that is the voltage Vin supplied from the AC power supply.
20 [0040] Next, when the inverter input power Pinv is
separated into a DC component PDC and a pulsation component
Pm due to the vibration reduction control, the inverter
input power Pinv can be expressed by Formula (3).
[0041] Formula 3:
25
[0042] The pulsation of the actual load torque includes,
as illustrated in FIG. 5, not only a single sine wave but
also a high-order component, and the torque control is not
performed using a single sine wave even in the vibration
30 reduction control. However, in order to simplify the
18
derivation, and since most of the components are composed
of the fundamental wave components, only the fundamental
wave frequency ωm component is used for expression in
Formula (3). Note that, the fundamental wave frequency ωm
5 can be considered as being the same as the rotational speed
fm of the motor 314.
[0043] In order to reduce the current flowing to the
smoothing unit 200 in performing the vibration reduction
control, the converter input power Pin is only required to
10 be caused to pulsate similarly to the inverter input power
Pinv. That is, from Formula (2) and Formula (3), the
current command Iinrefc generated by the capacitor current
reduction correction generator 414 may be expressed by
Formula (4).
15 [0044] Formula 4:
[0045] In Formula (4), the pulsation of the input power
(the second term from the left on the right side of Formula
(2)) due to the control for the converter 120 (hereinafter,
20 such control may be referred to as converter control) is
not canceled, and only the pulsation of the inverter input
current is canceled.
[0046] Here, as can be seen from Formula (4), Iinrefc
includes the AC power supply voltage in the denominator.
25 Thus, when the input voltage to the converter 120 is close
to zero crossing, the denominator becomes infinitely small,
and the value to be corrected becomes large. Thus, there
are concerns about deterioration of the power factor, an
increase in harmonics of the AC power supply current, and
30 an increase in loss of the converter 120. In view of this,
the capacitor current reduction correction generator 44
obtains Iinrefc by changing a calculation method, instead of
19
calculating Iinrefc using Formula (4) without change. For
example, in a state where the absolute value of the
denominator in Formula (4) is equal to or less than a
predetermined threshold value, Iinrefc is calculated using
5 the threshold value instead of the AC power supply voltage.
[0047] As illustrated in FIG. 6, information on the
numerator in Formula (4) is obtained from inverter drive
information that is drive information related to the
inverter 310. For example, a method to be used may be a
10 method of obtaining information on the numerator in Formula
(4) using the input current I2 to and the DC voltage Vdc to
the inverter 310 as the inverter drive information.
[0048] The current controller 413 adjusts a duty ratio
Duty in turning on and off the switching element 125 such
15 that the converter input current Iin approximates the
converter input current command Iinref.
[0049] FIG. 7 is a diagram for describing a current
command in the case where the control using the control
block 410 illustrated in FIG. 6 is applied. FIG. 7
20 illustrates the respective waveforms, in the order from top
to bottom, of the AC power supply voltage Vin input to the
converter 120, Iinrefdc generated by the voltage controller
411, Iinrefpfc generated by the high-power-factor current
command converter 412, the Iinrefc generated by the capacitor
25 current reduction correction generator 414, the converter
input current command Iinref that is a command for the
converter input current Iin, and the converter input
current Iin. The power pulsation of the load is 30 Hz.
[0050] The Iinrefc illustrated in FIG. 7 is derived using
30 Formula (4). In order to prevent an excessive current
flow, the capacitor current reduction correction generator
414 derives Iinrefc such that 150 V is fixed when the
absolute value of the denominator in Formula (4) is equal
20
to or less than 150 V.
[0051] As illustrated in FIG. 6, the command Iinrefpfc
output from the high-power-factor current command converter
412 and the command Iinrefc output from the capacitor current
5 reduction correction generator 414 are added together to
generate the converter input current command Iinref. Here,
as can be seen from a portion surrounded by a dotted line
circle in FIG. 7, the polarities (plus and minus) of the AC
power supply voltage Vin and the converter input current
10 command Iinref are different. Since the current in this
portion cannot be made to follow the converter input
current command Iinref in terms of the circuit
configuration, the converter input current command Iinref is
zero in this portion. Note that, the operation of causing
15 the switching element 125 to be switched may be stopped
instead of setting the converter input current command
Iinref to zero. It can be confirmed from the converter
input current Iin illustrated in FIG. 7 that the input
current pulsates at 30 Hz.
20 [0052] FIG. 8 is a diagram illustrating, as a
comparative example, an example of operation waveforms
(power waveform, current waveform, voltage waveform) of the
respective constituent components in a case where the power
conversion device 1 drives the motor 314 of the compressor
25 315 using the vibration reduction control and the general
high power factor control. Additionally, FIG. 9 is a
diagram illustrating an example of operation waveforms
(power waveform, current waveform, voltage waveform) of the
respective constituent components in a case where the power
30 conversion device 1 drives the motor 314 of the compressor
315 using the vibration reduction control and the capacitor
current reduction control. The operation waveforms
illustrated in FIG. 9 are operation waveforms in a case
21
where the current command illustrated in FIG. 7 is
generated to control the converter 120.
[0053] FIGS. 8 and 9 each illustrate the respective
waveforms, in the order from top to bottom, of the
5 converter input current Iin, the AC power supply voltage
Vin, the converter input power Pin and the inverter input
power Pinv, the converter output current I1 and the
inverter input current I2, the capacitor current I3, and
the DC voltage Vdc. The illustration of pulsations of the
10 converter output current I1 and the capacitor current I3
due to the switching frequency is omitted. The inverter
310 and the motor 314 are simulated by a variable power
load, only the fundamental wave component is used for the
pulsation component similarly to Formula (3) above, PDC is
15 1 kW, Pm is 500 W, and frequency ωm is 30 Hz.
Additionally, the maximum value Vs of the AC power supply
voltage Vin is 200√2 V, and the AC power supply frequency
ωin is 50 Hz. The DC voltage command Vdcref input to the
control block 410 illustrated in FIG. 6 is 360 V.
20 [0054] By applying the capacitor current reduction
control implemented by the control block 410 illustrated in
FIG. 6, the converter input power Pin varies in accordance
with the pulsation of the inverter input power Pinv as
illustrated in FIG. 9. As a result, the capacitor current
25 I3 is reduced from 2.27 A to 2.05 A as compared with the
case in FIG. 8 to which the capacitor current reduction
control is not applied. Additionally, a ripple voltage of
the DC voltage Vdc is also reduced.
[0055] As described above, the power conversion device 1
30 according to the first embodiment changes the converter
input current Iin in accordance with the rotational speed
of the motor 314 constituting the compressor 315 that is a
connected load, more specifically, in accordance with the
22
first frequency that is the frequency of the pulsation of
the inverter input power Pinv that can be considered as the
rotational speed of the motor 314, and causes the converter
input power Pin to pulsate. The power conversion device 1
5 according to the first embodiment can reduce the capacitor
current I3 flowing to the smoothing unit 200, thus making
it possible to use, as the smoothing capacitor 210, a
capacitor having a lower ripple current tolerance, and to
achieve cost reduction. Furthermore, the pulsation voltage
10 of the DC voltage Vdc decreases, thus making it possible to
achieve a reduction in the capacitance of the smoothing
capacitor 210 constituting the smoothing unit 200, that is,
size reduction of the smoothing capacitor 210, and reduce
the increase in size of the apparatus. For example, in a
15 case where the capacitor current reduction control is
applied to a power conversion device in which a smoothing
unit that smooths a rectified DC voltage includes a
plurality of capacitors, the current flowing to the
smoothing unit is reduced, thus making it possible to
20 reduce the number of capacitors constituting the smoothing
unit and achieve size reduction of the apparatus.
[0056] A description will now be given of a current
sensor that detects a current value used in the control for
the converter 120.
25 [0057] In a case of a power conversion device having a
converter to which the general high power factor control is
applied instead of the capacitor current reduction control
described above, the current sensor used for current
detection needs to satisfy the relationship expressed by
30 Formula (5):
fin > fisen ... (5)
where fin represents the AC power supply frequency and
fisen represents a lower limit frequency of the current
23
observable by the current sensor.
[0058] However, in the power conversion device 1
according to the first embodiment to which the capacitor
current reduction control is applied, there is a concern
5 that when a lower limit frequency (lower limit rotational
speed) fmin of the motor 314 is lower than an AC power
supply frequency fin, the current is unobservable in a case
of using the current sensor satisfying Formula (5) and the
capacitor current reduction control cannot be performed.
10 In view of this, in the case where the capacitor current
reduction control is applied, the converter input current
Iin is detected using a current sensor in which the
observable lower limit frequency fisen satisfies the
relationship expressed by Formula (6). That is, the
15 voltage-current detector 501 is configured using the
current sensor in which the observable lower limit
frequency fisen satisfies the relationship expressed by
Formula (6):
fmin > fisen ... (6).
20 [0059] With the configuration in which the current value
for use in the control for the converter 120 is detected by
the current sensor satisfying the relationship expressed by
Formula (6), the capacitor current reduction control can be
performed using a correct current value, and the
25 reliability of the operation for reducing the capacitor
current is enhanced.
[0060] Note that in the present embodiment, the
converter 120 is controlled such that the converter input
current Iin includes the pulsation component of the
30 fundamental wave frequency ωm of the pulsation of the load
torque corresponding to the rotational speed fm of the
motor 314. However, the converter 120 may be controlled
such that the converter input current Iin also includes a
24
pulsation component corresponding to an integral multiple
of the fundamental wave frequency ωm. This can further
reduce the capacitor current I3.
[0061] Second Embodiment.
5 A description will next be given of a power conversion
device according to a second embodiment. The configuration
of the power conversion device according to the second
embodiment is similar to that of the power conversion
device 1 according to the first embodiment except for an
10 operation of the control unit 400 controlling the converter
120. In the present embodiment, a description will be
given of a control operation for the converter 120, which
is an operation different from that of the first
embodiment.
15 [0062] In the power conversion device 1 according to the
second embodiment, the control unit 400 controls the
converter input current Iin so as to reduce the pulsation
due to the AC power supply frequency fin, the pulsation
being included in the converter input power Pin, thus
20 reducing the capacitor current I3.
[0063] FIG. 10 is a diagram illustrating an example of a
control block 420 constituting the control unit 400 of the
power conversion device 1 according to the second
embodiment. The control block 420 illustrated in FIG. 10
25 is provided to generate a control signal for the converter
120, and implements the capacitor current reduction control
according to the second embodiment.
[0064] The control block 420 includes the voltage
controller 411, a capacitor current reduction command
30 converter 415, and the current controller 413. The voltage
controller 411 and the current controller 413 of the
control block 420 are the same as the voltage controller
411 and the current controller 413 of the control block 410
25
described in the first embodiment.
[0065] A description will be given of a method of
deriving the converter input current command Iinref by the
capacitor current reduction command converter 415. AC
5 power supply information input to the capacitor current
reduction command converter 415 can be, for example, the AC
power supply frequency fin.
[0066] FIG. 11 is a diagram illustrating an example of
operation waveforms of the power conversion device 1
10 according to the second embodiment. FIG. 11 illustrates an
example of operation waveforms in the case where the power
conversion device 1 drives the motor 314 of the compressor
315 using the general high power factor control, and in the
case where the power conversion device 1 drives the motor
15 314 of the compressor 315 while controlling the converter
120 using the control to which the control block 420
illustrated in FIG. 10 is applied. In FIG. 11, the
waveform at the upper section indicates the AC power supply
voltage Vin. The two waveforms at the middle section
20 indicate the converter input current command Iinref. A
broken line indicates the converter input current command
Iinref in performing the high power factor control. A solid
line indicates the converter input current command Iinref in
performing the control to which the control block 420 is
25 applied. The three waveforms at the lower section indicate
the converter input power Pin and the inverter input power
Pinv. A broken line indicates the converter input power
Pin in performing the high power factor control. A solid
line indicates the converter input power Pin in performing
30 the control to which the control block 420 is applied. In
the operations corresponding to the operation waveforms
illustrated in FIG. 11, the maximum value Vs of the AC
power supply voltage Vin is 200√2 V, and the AC power
26
supply frequency fin is 50 Hz. Additionally, only a DC
component is used for the input power to the inverter 310
and is 1 kW.
[0067] FIG. 12 is a diagram illustrating a frequency
5 analysis result of the converter input power Pin
illustrated in FIG. 11. A broken line indicates a
frequency analysis result of the converter input power Pin
in performing the high power factor control. A solid line
indicates a frequency analysis result of the converter
10 input power Pin in performing the control to which the
control block 420 is applied.
[0068] It can be seen, from FIG. 12 and the second term
on the right side of Formula (2) above, that the converter
input power Pin pulsates at a frequency twice the AC power
15 supply frequency fin (ωin = 50 Hz) in performing the high
power factor control. In the following description, the
frequency of such pulsation may be referred to as a second
frequency. In the capacitor current reduction control
according to the second embodiment, that is, the control to
20 which the control block 420 is applied, the converter input
current Iin is controlled so as to reduce the component
included in the converter input power Pin and pulsating at
the second frequency that is the frequency twice the AC
power supply frequency fin.
25 [0069] Here, as an example of a control method of
reducing, from the converter input power Pin, the component
pulsating at the second frequency that is the frequency
twice the AC power supply frequency fin, as illustrated at
the middle section of FIG. 11, the capacitor current
30 reduction command converter 415 outputs a rectangular-wave
converter input current command Iinref. Note that, the
converter input current command Iinref only needs to have a
waveform that reduces the component pulsating at the second
27
frequency, and, for example, may have a waveform of
trapezoidal wave or such a waveform that the upper portion
and the lower portion of the sine wave are clamped.
[0070] It can be seen from FIG. 11 that the pulsation of
5 the converter input power Pin is reduced because of the
rectangular-wave converter input current command Iinref. It
can be seen, also from the frequency analysis result
illustrated in FIG. 12, that the frequency component twice
the AC power supply frequency fin is reduced.
10 [0071] FIG. 13 is a diagram illustrating, as a
comparative example, an example of operation waveforms
(power waveform, current waveform, voltage waveform) of the
respective constituent components in a case where the power
conversion device 1 according to the second embodiment
15 drives the motor 314 of the compressor 315 using the
general high power factor control. Additionally, FIG. 14
is a diagram illustrating an example of operation waveforms
(power waveform, current waveform, voltage waveform) of the
respective constituent components in a case where the power
20 conversion device 1 according to the second embodiment
drives the motor 314 of the compressor 315 using the
capacitor current reduction control (converter control
implemented by applying the control block 420 in FIG. 10).
[0072] FIGS. 13 and 14 each illustrate the respective
25 waveforms, in the order from top to bottom, of the AC power
supply voltage Vin, the converter input current Iin, the
converter input power Pin and the inverter input power
Pinv, the converter output current I1 and the inverter
input current I2, the capacitor current I3, and the DC
30 voltage Vdc. The illustration of pulsations of the
converter output current I1 and the capacitor current I3
due to the switching frequency is omitted. The inverter
310 and the motor 314 are simulated with a constant power
28
load, and the load power is 1 kW. Additionally, the
maximum value Vs of the AC power supply voltage Vin is
200√2 V, and the AC power supply frequency fin is 50 Hz.
The DC voltage command Vdcref input to the control block 420
5 illustrated in FIG. 10 is 360 V.
[0073] By applying the capacitor current reduction
control, according to the second embodiment, implemented by
the control block 420 illustrated in FIG. 10, as
illustrated in FIGS. 13 and 14, the capacitor current I3 is
10 reduced from 1.94 A to 1.51 A as compared with the case
where the capacitor current reduction control according to
the second embodiment is not applied. Additionally, a
ripple voltage of the DC voltage Vdc is also reduced.
[0074] As described above, the power conversion device 1
15 according to the second embodiment controls the converter
input current Iin so as to reduce the component included in
the converter input power Pin and pulsating at the second
frequency due to the AC power supply frequency fin, thereby
reducing the capacitor current I3 that is the current
20 flowing to the smoothing capacitor 210 constituting the
smoothing unit 200. The power conversion device 1
according to the second embodiment can reduce the current
I3 flowing to the smoothing unit 200, and thus can have the
same effects as those of the power conversion device 1
25 according to the first embodiment. That is, it is possible
to use, as the smoothing capacitor 210, the capacitor
having the lower ripple current tolerance, and to achieve
cost reduction. Additionally, the pulsation voltage of the
DC voltage Vdc decreases, thus making it possible to
30 achieve a reduction in the capacitance of the smoothing
capacitor 210 constituting the smoothing unit 200, that is,
size reduction of the smoothing capacitor 210, and reduce
the increase in size of the apparatus.
29
[0075] Note that in the second embodiment, the converter
input current Iin is controlled so as to reduce the
pulsation due to the AC power supply frequency fin.
However, the converter 120 may be controlled so as to also
5 reduce the pulsation due to a frequency that is an integral
multiple of the AC power supply frequency fin. This can
further reduce the capacitor current I3.
[0076] Additionally, in the second embodiment, the
converter 120 is controlled using the control to reduce the
10 increase in the capacitor current I3 due to the AC power
supply frequency fin in the state where the vibration
reduction control is not applied to the inverter 310.
However, the control for the converter 120 described in the
second embodiment may also be performed when the vibration
15 reduction control is performed. That is, the control for
the converter 120 described in the first embodiment and the
control for the converter 120 described in the second
embodiment may be performed. In the following description,
for convenience, the control for the converter 120
20 described in the first embodiment may be referred to as
first capacitor current reduction control, and the control
for the converter 120 described in the second embodiment
may be referred to as second capacitor current reduction
control.
25 [0077] Third Embodiment.
A description will next be given of a power conversion
device according to a third embodiment. The configuration
of the power conversion device according to the third
embodiment is similar to those of the power conversion
30 devices 1 according to the first and second embodiments
except for an operation of the control unit 400 controlling
the converter 120 and the inverter 310. In the present
embodiment, a description will be given of the operation of
30
the control unit 400 controlling the converter 120 and the
inverter 310. Note that, in the operation of the control
unit 400, the description of the operation common to those
in the first and second embodiments will be omitted.
5 [0078] In the first and second embodiments, the
converter 120 is controlled, that is, the input current Iin
to the converter 120 is controlled, thereby reducing the
current flowing to the smoothing capacitor 210.
[0079] On the other hand, there is also a method of
10 controlling the inverter 310 to reduce the current flowing
to the smoothing capacitor 210. For example, in a case
where the input current I2 to the inverter 310 is constant,
the capacitor current I3 flowing to the smoothing capacitor
210 pulsates in accordance with a change in the converter
15 input current Iin. In this case, the inverter 310 is
controlled such that the inverter input current I2 pulsates
in accordance with the change in the converter input
current Iin, thereby reducing the pulsation of the
capacitor current I3. As a result, the capacitor current
20 I3 is reduced. However, there is a concern about an
increase in heat generation of the semiconductor elements
(switching elements 311a to 311f and freewheeling diodes
312a to 312f) constituting the inverter 310 since the
pulsation of the inverter input current I2 causes an
25 increase in the effective current value. In view of this,
the pulsation of the inverter input current I2 is permitted
only within a range in which the semiconductor elements are
thermally established, and thus the effect of reducing the
capacitor current I3 is limited.
30 [0080] Thus, in the power conversion device 1 according
to the third embodiment, the operation of controlling the
inverter 310 to reduce the capacitor current I3 and the
operation of controlling the converter 120 to reduce the
31
capacitor current I3 are performed in combination, thereby
improving the effect of reducing the capacitor current I3.
Note that in the following description, the control to
operate the inverter 310 so as to reduce the capacitor
5 current I3 is referred to as inverter current pulsation
control.
[0081] FIG. 15 is a diagram illustrating, as a first
comparative example of the third embodiment, an example of
operation waveforms in a case where the high power factor
10 control and the vibration reduction control are performed
in combination. FIG. 16 is a diagram illustrating, as a
second comparative example of the third embodiment, an
example of operation waveforms in a case where the high
power factor control, the vibration reduction control, and
15 the inverter current pulsation control are performed in
combination. FIG. 17 is a diagram illustrating an example
of operation waveforms in a case where the control
according to the third embodiment is performed,
specifically illustrating an example of operation waveforms
20 in a case where the vibration reduction control, the
inverter current pulsation control, and the capacitor
current reduction control are performed in combination.
[0082] In each of FIGS. 15 to 17, waveforms at the upper
section indicate the input power Pin to the converter 120
25 and the input power Pinv to the inverter 310, and a
waveform at the lower section indicates power Pc of the
smoothing unit 200.
[0083] In the operation corresponding to each of FIGS.
15 to 17, in consideration of the vibration reduction
30 control, the inverter input power Pinv is given, in Formula
(3) above, wherein PDC is 400 W, Pm is 200 W, and the
fundamental wave frequency ωm is 10 Hz. Additionally, the
maximum value Vs of the voltage Vin of the AC power supply
32
110 is 200√2 V, and the frequency fin of the AC power
supply 110 is 50 Hz.
[0084] The capacitor current reduction control applied
to the operation corresponding to FIG. 17 is, as an
5 example, the first capacitor current reduction control that
is the control for the converter 120 described in the first
embodiment. Note that, in a case where the capacitor
current I3 flowing to the smoothing unit 200 has a
pulsation that does not correspond to either the pulsation
10 at the frequency due to the AC power supply frequency fin
or the pulsation at the frequency due to the motor
rotational speed, the pulsation component may be reduced by
the control for the converter 120.
[0085] In the operation corresponding to FIG. 16, the
15 performing of the inverter current pulsation control causes
the pulsation of the inverter input power Pinv, thereby
reducing the pulsating power included in the power Pc of
the smoothing unit 200. The inverter current pulsation
control causes the inverter input power Pinv to pulsate
20 with the magnitude of a pulsation 0.5 times the pulsation
component included in the converter input power Pin, that
is, a power pulsation component due to the AC power supply
frequency fin. Since the DC voltage Vdc is substantially
constant, the pulsation waveform of the power Pc of the
25 smoothing unit 200 and the waveform of the capacitor
current I3 are similar to each other. Thus, it can be seen
from FIG. 16 that the capacitor current I3 can be reduced
by performing the high power factor control, the vibration
reduction control, and the inverter current pulsation
30 control in combination.
[0086] In the operation, according to the third
embodiment, corresponding to FIG. 17, the performing of the
first capacitor current reduction control achieves a
33
reduction in the pulsation of the power of the smoothing
unit 200 due to the vibration reduction control, and the
performing of the inverter current pulsation control and
the second capacitor current reduction control achieves a
5 reduction in the pulsation of the power of the smoothing
unit 200 due to the AC power supply frequency fin.
Specifically, the first capacitor current reduction control
causes the converter output current I1 to pulsate with the
magnitude of a pulsation 0.5 times the pulsation due to the
10 vibration reduction control, the inverter current pulsation
control causes the inverter input current I2 to pulsate
with the magnitude of a pulsation 0.5 times the pulsation
due to the AC power supply frequency fin, and the second
capacitor current reduction control causes the converter
15 output current I1 to pulsate with the magnitude of a
pulsation 0.25 times the pulsation due to the AC power
supply frequency fin.
[0087] It can be seen from FIGS. 16 and 17 that the
performing of the control according to the third embodiment
20 can further reduce the pulsation of the power Pc of the
smoothing unit 200 as compared with the performing of the
control to obtain the operation waveforms of FIG. 16.
Thus, it can be said that the effect of reducing the
capacitor current I3 can be improved.
25 [0088] Note that, although both the first capacitor
current reduction control and the second capacitor current
reduction control are performed as the control according to
the third embodiment, any one of the two capacitor current
reduction controls may be performed as the control
30 according to the third embodiment.
[0089] As described above, the power conversion device 1
according to the third embodiment performs the inverter
current pulsation control to control the inverter 310 such
34
that the inverter input current I2 pulsates in accordance
with the change in the converter input current Iin and at
least one of the first capacitor current reduction control
described in the first embodiment or the second capacitor
5 current reduction control described in the second
embodiment, thereby causing the inverter input current I2
and the converter output current I1 to pulsate. Thus, the
effect of reducing the capacitor current I3 can be improved
more than that in the case where only the inverter current
10 pulsation control is performed to reduce the capacitor
current I3. Additionally, the effect of reducing the
capacitor current I3 can be improved more than those in the
first and second embodiments.
[0090] Fourth Embodiment.
15 A description will next be given of a power conversion
device according to a fourth embodiment. The configuration
of the power conversion device according to the fourth
embodiment is similar to those of the power conversion
devices 1 according to the first to third embodiments
20 except for the operation of the control unit 400
controlling the converter 120. In the present embodiment,
a description will be given of the operation of the control
unit 400 controlling the converter 120. Note that, in the
operation of the control unit 400, the description of the
25 operation common to those in the first to third embodiments
will be omitted.
[0091] FIG. 18 is a diagram for describing an operation
of the power conversion device 1 according to the fourth
embodiment. In the first capacitor current reduction
30 control described in the first embodiment and the second
capacitor current reduction control described in the second
embodiment, the converter 120 is operated in a Continuous
Current Mode (CCM) in which a reactor current IL, which is
35
a current flowing to the reactor 127 of the converter 120,
has a waveform as indicated by a broken line in FIG. 18.
On the other hand, in the power conversion device 1
according to the fourth embodiment, the converter 120 is
5 operated in a Discontinuous Current Mode (DCM) in which the
reactor current IL has a waveform as indicated by a solid
line in FIG. 18. In the CCM operation, there is no period
of time during which the reactor current IL is zero, and in
the DCM operation, there is a period of time during which
10 the reactor current IL is zero. That is, in the power
conversion device 1 according to the fourth embodiment, the
control unit 400 controls the converter 120 such that an
interval of time occurs during which the reactor current IL
is zero.
15 [0092] That is, the power conversion device 1 according
to the fourth embodiment is configured such that the
converter 120 is to be operated in the DCM operation in
each of the power conversion devices 1 described in the
first to third embodiments.
20 [0093] The control such that the converter 120 is to be
in DCM achieves a reduction in inductance of the reactor
127 constituting the converter 120, and the size and cost
reduction of the power conversion device 1.
[0094] Fifth Embodiment.
25 The power conversion device to which the capacitor
current reduction control described in the first to fourth
embodiments can be applied is not limited to the power
conversion device 1 having the configuration illustrated in
FIG. 2. For example, the capacitor current reduction
30 control may be applied to a power conversion device having
a configuration illustrated in each of FIGS. 19 to 21.
[0095] FIG. 19 is a diagram illustrating a first
exemplary configuration of a power conversion device
36
according to a fifth embodiment. A power conversion device
1a illustrated in FIG. 19 includes a converter 120a and a
control unit 400a in place of the converter 120 and the
control unit 400 of the power conversion device 1
5 illustrated in FIG. 2. Note that, the converter 120a
constitutes a power supply unit 100a.
[0096] The converter 120a is a rectifier circuit having
a Diode Bridge Less (DBL) configuration, and includes the
reactor 127, switching elements 125a to 125d, and
10 rectifiers 121 to 124 respectively connected in parallel
with the switching elements 125a to 125d. The converter
120a turns on and off the switching elements 125a to 125d
under the control of the control unit 400a, rectifies and
boosts the first AC power supplied from the AC power supply
15 110, and outputs the boosted DC power to the smoothing unit
200. The converter 120a is controlled by the control unit
400a using full Pulse Amplitude Modulation (PAM) which
allows the switching elements 125a to 125d to be switched
continuously. The converter 120a performs power factor
20 improvement control, thereby increasing the capacitor
voltage Vdc of the smoothing capacitor 210 of the smoothing
unit 200 to a voltage higher than the power supply voltage.
[0097] Since the other points of configuration are
similar to that of the power conversion device 1 described
25 above, the description thereof will be omitted.
[0098] The power conversion device 1a can achieve higher
efficiency than the power conversion device 1 illustrated
in FIG. 2.
[0099] FIG. 20 is a diagram illustrating a second
30 exemplary configuration of the power conversion device
according to the fifth embodiment. A power conversion
device 1b illustrated in FIG. 20 includes a converter 120b
and a control unit 400b in place of the converter 120 and
37
the control unit 400 of the power conversion device 1
illustrated in FIG. 2. Note that, the converter 120b
constitutes a power supply unit 100b.
[0100] The converter 120b includes the reactor 127, a
5 rectifier circuit 131, and a booster circuit 141. In the
converter 120 constituting the power conversion device 1
illustrated in FIG. 2, the booster circuit 140 is connected
in series at the subsequent stage of the rectifier circuit
130. On the other hand, in the converter 120b constituting
10 the power conversion device 1b, the booster circuit 141 is
connected in parallel with the rectifier circuit 131.
[0101] The rectifier circuit 131 of the converter 120b
constituting the power conversion device 1b includes
rectifiers 121a to 124a, and performs full-wave
15 rectification of the first AC power supplied from the AC
power supply 110. The rectifier circuit 131 is a circuit
similar to the rectifier circuit 130 of the converter 120
constituting the power conversion device 1.
[0102] The booster circuit 141 includes rectifiers 121b
20 to 124b and the switching element 125. The booster circuit
141 turns on and off the switching element 125 under the
control of the control unit 400b, boosts the first AC power
supplied from the AC power supply 110, and outputs the
boosted power to the smoothing unit 200. The booster
25 circuit 141 of the converter 120b is controlled by the
control unit 400b using simplified switching in which the
switching element 125 is switched one or more times in
every half period of the frequency of the first AC power
supplied from the AC power supply 110. The converter 120b
30 performs the power factor improvement control, thereby
increasing the capacitor voltage Vdc of the smoothing
capacitor 210 of the smoothing unit 200 to a voltage higher
than the power supply voltage.
38
[0103] Since the other points of configuration are
similar to that of the power conversion device 1 described
above, the description thereof will be omitted.
[0104] The power conversion device 1b can achieve higher
5 efficiency than the power conversion device 1 illustrated
in FIG. 2. The power conversion device 1b can also achieve
noise reduction.
[0105] FIG. 21 is a diagram illustrating a third
exemplary configuration of the power conversion device
10 according to the fifth embodiment. A power conversion
device 1c illustrated in FIG. 21 includes a converter 120c
and a control unit 400c in place of the converter 120 and
the control unit 400 of the power conversion device 1
illustrated in FIG. 2. Note that, the converter 120c
15 constitutes a power supply unit 100c.
[0106] The converter 120c is a totem pole converter, and
includes the reactor 127, the rectifiers 121 and 122,
rectifiers 123A, 123B, 124A, and 124B, the switching
elements 125a, 125b, 125c, and 125d, and a capacitor 128.
20 [0107] The reactor 127 limits an input current from the
AC power supply 110. The rectifier 121 and the rectifier
122 are connected in series with each other to constitute a
first series circuit 601 that is a rectifier bridge circuit
that rectifies the AC power supplied from the AC power
25 supply 110. A connection point between the rectifier 121
and the rectifier 122 is connected to one of output
terminals of the AC power supply 110 via the reactor 127.
[0108] The four switching elements, that is, the
switching elements 125a, 125b, 125c, and 125d are connected
30 in series with each other, and constitute a second series
circuit 602 together with the rectifiers 123A, 123B, 124A,
and 124B each connected in parallel with a corresponding
one of the four switching elements. The first series
39
circuit 601 and the second series circuit 602 are connected
in parallel with each other.
[0109] A connection point between the second switching
element 125b and the third switching element 125c among the
5 four switching elements constituting the second series
circuit is connected to the other of the output terminals
of the AC power supply 110. One end of the capacitor 128
is connected to a connection point between the first
switching element 125a and the second switching element
10 125b among the four switching elements, and the other end
of the capacitor 128 is connected to a connection point
between the third switching element 125c and the fourth
switching element 125d.
[0110] The converter 120c turns on and off the switching
15 elements 125a to 125d under the control of the control unit
400c, rectifies and boosts the first AC power supplied from
the AC power supply 110, and outputs the boosted DC power
to the smoothing unit 200. The converter 120c performs the
power factor improvement control, thereby increasing the
20 capacitor voltage Vdc of the smoothing capacitor 210 of the
smoothing unit 200 to a voltage higher than the power
supply voltage.
[0111] Since the other points of configuration are
similar to that of the power conversion device 1 described
25 above, the description thereof will be omitted.
[0112] The power conversion device 1c can achieve higher
efficiency than the power conversion device 1 illustrated
in FIG. 2. The power conversion device 1c can also achieve
a reduction in inductance.
30 [0113] A description will next be given of a hardware
configuration of the control unit (control units 400, 400a,
400b, and 400c) included in the power conversion device
(power conversion devices 1, 1a, 1b, and 1c) described in
40
each of the embodiments. Note that, the hardware
configurations of the control units are similar to one
another.
[0114] FIG. 22 is a diagram illustrating an example of
5 the hardware configuration that implements the control unit
included in the power conversion device. The control unit
of the power conversion device is implemented by, for
example, a processor 91 and a memory 92 illustrated in FIG.
22.
10 [0115] The processor 91 is a Central Processing Unit
(CPU) (also known as processing unit, computing unit,
microprocessor, microcomputer, processor, and Digital
Signal Processor (DSP)). The memory 92 is, for example, a
Random Access Memory (RAM), a Read Only Memory (ROM), a
15 flash memory, an Erasable Programmable Read Only Memory
(EPROM), or an Electrically Erasable Programmable Read Only
Memory (EEPROM; registered trademark).
[0116] The memory 92 stores a program for operation as
the control unit of the power conversion device. The
20 control unit of the power conversion device is implemented
by the processor 91 reading and executing the program
stored in the memory 92. For example, the program stored
in the memory 92 may be provided to a user or the like by
being stored in a storage medium such as a Compact Disc
25 (CD)-ROM or a Digital Versatile Disc (DVD)-ROM, or may be
provided via a network.
[0117] Note that, the control unit may also be
implemented by a dedicated processing circuit such as a
single circuit, a composite circuit, an Application
30 Specific Integrated Circuit (ASIC), a Field Programmable
Gate Array (FPGA), or a circuit obtained by combining these
circuits.
[0118] Sixth Embodiment.
41
In the present embodiment, a description will be given
of an apparatus that can be implemented by applying each of
the power conversion devices described in the first to
fifth embodiments. As an example, a description will be
5 given of a refrigeration-cycle application apparatus
including the power conversion device 1 described in the
first embodiment.
[0119] FIG. 23 is a diagram illustrating an exemplary
configuration of a refrigeration-cycle application
10 apparatus 900 according to a sixth embodiment. The
refrigeration-cycle application apparatus 900 according to
the sixth embodiment includes the motor drive device 10 to
which the power conversion device 1 described in the first
embodiment is applied.
15 [0120] Additionally, the refrigeration-cycle application
apparatus 900 includes a refrigeration cycle having a
configuration in which a four-way valve 902, a compressor
903, a heat exchanger 906, an expansion valve 908, and a
heat exchanger 910 are attached to each other via a
20 refrigerant pipe 912. The compressor 903 corresponds to
the compressor 315 illustrated in, for example, FIG. 2.
[0121] The compressor 903 includes a compression
mechanism 904 that compresses a refrigerant circulating in
the refrigerant pipe 912, and a motor 905 that operates the
25 compression mechanism 904. The motor 905 corresponds to
the motor 314 illustrated in FIG. 3.
[0122] For example, the refrigeration-cycle application
apparatus 900 having such a configuration can be used for
an air conditioner, a heat pump water heater, a
30 refrigerator, a freezer, and the like.
[0123] The configurations described in the above
embodiments are illustrative only and may be combined with
the other known techniques, the embodiments may be combined
42
with each other, and part of each of the configurations may
be omitted or modified without departing from the gist.
Reference Signs List
5 [0124] 1, 1a, 1b, 1c power conversion device; 10 motor
drive device; 100, 100a, 100b, 100c power supply unit; 110
AC power supply; 120, 120a, 120b, 120c converter; 121 to
124, 121a to 124a, 121b to 124b, 123A, 123B, 124A, 124B,
126 rectifier; 125, 125a to 125d, 311a to 311f switching
10 element; 127 reactor; 128 capacitor; 130, 131 rectifier
circuit; 140, 141 booster circuit; 200 smoothing unit;
210 smoothing capacitor; 300 load unit; 310 inverter;
312a to 312f freewheeling diode; 313a, 313b current
detector; 314, 905 motor; 315, 903 compressor; 400, 400a,
15 400b, 400c control unit; 410, 420 control block; 411
voltage controller; 412 high-power-factor current command
converter; 413 current controller; 414 capacitor current
reduction correction generator; 415 capacitor current
reduction command converter; 501 voltage-current detector;
20 502 voltage detector; 601 first series circuit; 602
second series circuit; 900 refrigeration-cycle application
apparatus; 902 four-way valve; 904 compression mechanism;
906, 910 heat exchanger; 908 expansion valve; 912
refrigerant pipe

We Claim :
[Claim 1] A power conversion device comprising:
a converter rectifying a first alternating-current
power supplied from an alternating-current power supply and
5 boosting a voltage of the first alternating-current power
rectified;
a smoothing unit connected to an output end of the
converter; and
a control unit controlling the converter to cause an
10 input current to the converter to change in accordance with
at least one of a first frequency or a second frequency,
and reducing a current flowing to the smoothing unit, the
first frequency being a frequency of pulsation of input
power to a load unit connected across the smoothing unit,
15 the second frequency being a frequency of pulsation of
input power to the converter due to a frequency of the
alternating-current power supply.
[Claim 2] The power conversion device according to claim 1,
20 wherein
the load unit includes an inverter converting power
output from the converter and the smoothing unit into
second AC power and outputting the second AC power to a
motor, and
25 the control unit controls the converter to cause the
input current to the converter to pulsate in accordance
with a rotational speed of the motor.
[Claim 3] The power conversion device according to claim 2,
30 wherein
the control unit controls the converter to cause the
input current to the converter to include a component that
pulsates at a frequency same as the rotational speed of the
44
motor.
[Claim 4] The power conversion device according to claim 3,
wherein
5 the control unit controls the converter to cause the
input current to the converter to also include a component
that pulsates at a frequency that is an integral multiple
of the rotational speed of the motor.
10 [Claim 5] The power conversion device according to any one
of claims 2 to 4, comprising a current sensor detecting the
input current to the converter, wherein
the current sensor is capable of observing a current
having a lower limit frequency less than a lower limit
15 rotational speed of the motor.
[Claim 6] The power conversion device according to any one
of claims 1 to 5, wherein
the control unit controls the converter to cause the
20 input current to the converter to be changed so as to
reduce a pulsation component due to the frequency of the
alternating-current power supply, the pulsation component
being included in the input power to the converter.
25 [Claim 7] The power conversion device according to claim 6,
wherein
the control unit controls the converter to cause a
component of the input current to the converter having a
frequency same as the frequency of the alternating-current
30 power supply to be changed.
[Claim 8] The power conversion device according to claim 7,
wherein
45
the control unit controls the converter to cause a
component of the input current to the converter having a
frequency being an integral multiple of the frequency of
the alternating-current power supply to be also changed.
5
[Claim 9] The power conversion device according to any one
of claims 1 to 8, wherein
the control unit controls an inverter included in the
load unit to cause an input current to the load unit to
10 pulsate in accordance with a change in the input current to
the converter.
[Claim 10] The power conversion device according to any
one of claims 1 to 9, wherein
15 the control unit controls the converter to cause an
interval of time to occur during which a current flowing to
a reactor included in the converter is zero.
[Claim 11] The power conversion device according to any
20 one of claims 1 to 10, wherein
the converter includes:
a rectifier circuit including a plurality of
rectifiers; and
a booster circuit including a rectifier and a
25 switching element whose on and off states are controlled by
the control unit, and
the rectifier circuit and the booster circuit are
connected in series or in parallel with each other.
30 [Claim 12] The power conversion device according to any
one of claims 1 to 10, wherein
the converter includes:
a plurality of switching elements whose on and off
46
states are controlled by the control unit; and
a plurality of rectifiers each connected in parallel
with a corresponding one of the plurality of switching
elements.
5
[Claim 13] The power conversion device according to any
one of claims 1 to 10, wherein
the converter includes:
a first series circuit in which two rectifiers are
10 connected in series with each other; and
a second series circuit including four switching
elements connected in series with each other and four
rectifiers each connected in parallel with a corresponding
one of the four switching elements, the second series
15 circuit being connected in parallel with the first series
circuit.
[Claim 14] A motor drive device comprising the power
conversion device according to any one of claims 1 to 13.
20
[Claim 15] A refrigeration-cycle application apparatus
comprising the power conversion device according to any one
of claims 1 to 13.