FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
POWER CONVERSION APPARATUS AND OUTDOOR UNIT OF AIR
CONDITIONER
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 rectifies and then converts5
alternating-current power supplied from a commercial power
supply into alternating-current power, and outputs the
alternating-current power, and an outdoor unit of an air
conditioner including the power conversion apparatus.
10
Background
[0002] In a power conversion apparatus that rectifies
and then converts alternating-current power supplied from a
commercial power supply into alternating-current power, and
outputs the alternating-current power, a smoothing15
capacitor is conventionally used in order to smooth power
rectified by a rectifier unit that rectifies an alternating
current supplied from the commercial power supply.
[0003] Patent Literature 1 discloses a power conversion
apparatus that reduces degradation of a smoothing capacitor20
by suppressing a large current flowing through the
smoothing capacitor.
Citation List
Patent Literature25
[0004] Patent Literature 1: WO 2022/091184 A
Summary of Invention
Problem to be solved by the Invention
[0005] However, in the power conversion apparatus30
disclosed in Patent Literature 1, a pulsation corresponding
to a pulsation of power flowing into the smoothing
capacitor is included in an output from an inverter to a
3
device including a motor, thereby reducing a current of the
capacitor. Therefore, in the power conversion apparatus
disclosed in Patent Literature 1, there is a problem in
that the output of the inverter tends to increase and loss
increases regardless of the magnitude of a capacitor load5
of the smoothing capacitor, which results in deterioration
of energy-saving performance.
[0006] The present disclosure has been made in view of
the above, and an object thereof is to provide a power
conversion apparatus that reduces degradation of a10
smoothing capacitor and reduces deterioration of energy-
saving performance.
Means to Solve the Problem
[0007] In order to solve the above-described problem and15
achieve the object, a power conversion apparatus according
to the present disclosure comprises: a rectifier unit to
rectify first alternating-current power supplied from a
commercial power supply; a capacitor connected to an output
end of the rectifier unit; an inverter to convert power20
output from the rectifier unit and the capacitor into
second alternating-current power, and to output the second
alternating-current power to a load including a motor, the
inverter being connected to both ends of the capacitor; and
a control unit to execute capacitor load reduction control25
of reducing a current flowing through the capacitor by
controlling an operation of the inverter so as to output,
from the inverter to the load, the second alternating-
current power including a pulsation corresponding to a
pulsation of power flowing into the capacitor from the30
rectifier unit. The control unit estimates a capacitor
load in the capacitor, and determines whether to execute
the capacitor load reduction control on a basis of an
4
estimate value of the capacitor load.
Effects of the Invention
[0008] The power conversion apparatus according to the
present disclosure achieves an effect that degradation of a5
smoothing capacitor is reduced and deterioration of energy-
saving performance can be reduced.
Brief Description of Drawings
[0009] FIG. 1 is a diagram illustrating a configuration10
of a power conversion apparatus according to a first
embodiment.
FIG. 2 is a diagram illustrating examples of
respective currents and a capacitor voltage of a capacitor
of a smoothing unit in a case where a control unit of the15
power conversion apparatus according to the first
embodiment smooths a current output from a rectifier unit
by the smoothing unit to make a current flowing through an
inverter constant.
FIG. 3 is a diagram illustrating examples of the20
respective currents and the capacitor voltage of the
capacitor of the smoothing unit when the control unit of
the power conversion apparatus according to the first
embodiment controls an operation of the inverter to reduce
the current flowing through the smoothing unit.25
FIG. 4 is a flowchart illustrating an operation of the
control unit included in the power conversion apparatus
according to the first embodiment.
FIG. 5 is a diagram illustrating an example of a
hardware configuration that realizes the control unit30
included in the power conversion apparatus according to the
first embodiment.
FIG. 6 is a diagram illustrating a configuration of
5
the power conversion apparatus according to a second
embodiment.
FIG. 7 is a diagram illustrating a configuration of
the power conversion apparatus according to a third
embodiment.5
FIG. 8 is a diagram illustrating an operation of the
power conversion apparatus according to a fourth embodiment.
FIG. 9 is a diagram illustrating an operation of the
power conversion apparatus according to a fifth embodiment.
FIG. 10 is a diagram illustrating an operation of the10
power conversion apparatus according to a sixth embodiment.
FIG. 11 is a diagram illustrating an example of a
relationship between a capacitor current and a capacitor
load reduction control amount of the power conversion
apparatus according to an eighth embodiment.15
FIG. 12 is a diagram illustrating a configuration of
an outdoor unit of an air conditioner according to a ninth
embodiment.
Description of Embodiments20
[0010] Hereinafter, a power conversion apparatus and an
outdoor unit of an air conditioner according to each
embodiment will be described in detail with reference to
the drawings.
[0011] First Embodiment.25
FIG. 1 is a diagram illustrating a configuration of a
power conversion apparatus according to a first embodiment.
A power conversion apparatus 1 is connected between a
commercial power supply 110 and a compressor 315. The
power conversion apparatus 1 converts first alternating-30
current power of a power supply voltage Vs supplied from
the commercial power supply 110 into second alternating-
current power, and supplies the second alternating-current
6
power to the compressor 315. At least one of an amplitude
and a phase of the second alternating-current power may be
different from that of the first alternating-current power,
or both the amplitude and the phase may be the same as
those of the first alternating-current power.5
[0012] The power conversion apparatus 1 includes a
voltage current detection unit 501, a reactor 120, a
rectifier unit 130, a voltage detection unit 502, a
smoothing unit 200, an inverter 310, current detection
units 313a and 313b, and a control unit 400. The10
compressor 315 is a device serving as a load including a
motor 314 for driving a compressor to which power is
supplied from the power conversion apparatus 1. The motor
314 included in the compressor 315 and the power conversion
apparatus 1 constitute a motor driving apparatus 2.15
[0013] The voltage current detection unit 501 detects a
voltage value and a current value of the first alternating-
current power supplied from the commercial power supply 110,
and outputs the detected voltage value and current value to
the control unit 400. The voltage of the first20
alternating-current power is the power supply voltage Vs.
The reactor 120 is connected between the voltage current
detection unit 501 and the rectifier unit 130. The
rectifier unit 130 includes a bridge circuit configured by
rectifier elements 131, 132, 133, and 134. The rectifier25
unit 130 rectifies and outputs the first alternating-
current power supplied from the commercial power supply 110.
In the power conversion apparatus 1 according to the first
embodiment, the rectifier unit 130 performs full-wave
rectification. The voltage detection unit 502 detects a30
voltage value of the power rectified by the rectifier unit
130, and outputs the detected voltage value to the control
unit 400. The smoothing unit 200 is connected to an output
7
end of the rectifier unit 130 via the voltage detection
unit 502. The smoothing unit 200 includes a capacitor 210
which is a smoothing element, and smooths the power
rectified by the rectifier unit 130. The capacitor 210 is,
for example, an electrolytic capacitor, a film capacitor,5
or the like. The capacitor 210 has a capacitance for
smoothing the power rectified by the rectifier unit 130,
and a voltage generated in the capacitor 210 by the
smoothing does not have a full-wave rectified waveform
shape of the commercial power supply 110, but has a10
waveform shape in which a voltage ripple corresponding to a
frequency of the commercial power supply 110 is
superimposed on a direct-current component, and does not
greatly pulsate. In a case where the commercial power
supply 110 has a single phase, a frequency of the voltage15
ripple is a component which is twice a frequency of the
power supply voltage Vs, and in a case where the commercial
power supply 110 has three phases, the frequency of the
voltage ripple has a component which is six times the
frequency of the power supply voltage Vs as a main20
component. In a case where power input from the commercial
power supply 110 and power output from the inverter 310 do
not change, an amplitude of the voltage ripple is
determined depending on the capacitance of the capacitor
210. For example, the voltage generated in the capacitor25
210 by the smoothing pulsates in such a range that a
maximum value of the voltage ripple generated in the
capacitor 210 is less than twice a minimum value.
[0014] The inverter 310 is connected to both ends of the
capacitor 210 included in the smoothing unit 200. The30
inverter 310 includes switching elements 311a, 311b, 311c,
311d, 311e, and 311f, and freewheeling diodes 312a, 312b,
312c, 312d, 312e, and 312f. The inverter 310 turns on and
8
off the switching elements 311a, 311b, 311c, 311d, 311e,
and 311f under the control of the control unit 400,
converts the power output from the rectifier unit 130 and
the smoothing unit 200 into second alternating-current
power, and outputs the second alternating-current power to5
the compressor 315. Each of the current detection units
313a and 313b detects a value of a current of one phase
among currents of three phases output from the inverter 310,
and outputs the detected current value to the control unit
400. Note that, by acquiring current values of two phases10
among current values of the three phases output from the
inverter 310, the control unit 400 can calculate a current
value of the remaining one phase output from the inverter
310. The motor 314 rotates depending on the amplitude and
the phase of the second alternating-current power supplied15
from the inverter 310, and performs a compression operation.
For example, in a case where the compressor 315 is a
hermetic compressor used in an air conditioner or the like,
a load torque of the compressor 315 can be regarded as a
constant torque load in many cases.20
[0015] Note that, in the power conversion apparatus 1,
the disposition of each component illustrated in FIG. 1 is
merely an example, and the disposition of each
configuration request is not limited to the example
illustrated in FIG. 1. For example, the reactor 120 may be25
disposed subsequent to the rectifier unit 130. In the
following description, the voltage current detection unit
501, the voltage detection unit 502, and the current
detection units 313a and 313b may be collectively referred
to as detection units. In addition, the voltage value and30
the current value detected by the voltage current detection
unit 501, the voltage value detected by the voltage
detection unit 502, and the current values detected by the
9
current detection units 313a and 313b may be referred to as
detection values.
[0016] The control unit 400 acquires the voltage value
and the current value of the first alternating-current
power from the voltage current detection unit 501, acquires5
the voltage value of the power rectified by the rectifier
unit 130 from the voltage detection unit 502, and acquires
the current value of the second alternating-current power
having the amplitude and the phase converted by the
inverter 310 from the current detection units 313a and 313b.10
The control unit 400 uses the detection values detected by
respective detection units to control an operation of the
inverter 310, specifically, turning on and off of the
switching elements 311a, 311b, 311c, 311d, 311e, and 311f
included in the inverter 310. In the present embodiment,15
the control unit 400 controls the operation of the inverter
310 so that the second alternating-current power including
a pulsation corresponding to a pulsation of the power
flowing into the capacitor 210 of the smoothing unit 200
from the rectifier unit 130 is output from the inverter 31020
to the compressor 315 which is a load. The pulsation
corresponding to the pulsation of the power flowing into
the capacitor 210 of the smoothing unit 200 is, for example,
a pulsation that varies depending on a frequency of the
pulsation of the power flowing into the capacitor 210 of25
the smoothing unit 200. Consequently, the control unit 400
reduces the current flowing through the capacitor 210 of
the smoothing unit 200. Note that the control unit 400 may
not use all the detection values acquired from the
respective detection units, and may perform control by30
using some of the detection values.
[0017] It is known that there is a correlation between a
capacitor load which is the amount of charge transfer in
10
the capacitor 210 and the amount of variation of a voltage
applied to the capacitor 210. Therefore, the control unit
400 removes a direct-current component of a voltage across
the capacitor 210 and extracts an alternating-current
component, thereby detecting the amount of variation of the5
voltage applied to the capacitor 210 and estimating the
capacitor load. The control unit 400 determines whether to
execute the capacitor load reduction control on the basis
of an estimate value of the capacitor load. The capacitor
load reduction control will be described later.10
[0018] Next, an operation of the control unit 400
included in the power conversion apparatus 1 will be
described. The following description will be given
assuming that in the power conversion apparatus 1 according
to the first embodiment, a load generated by the inverter15
310 and the compressor 315 can be regarded as a constant
load, and a constant current load is connected to the
smoothing unit 200 when viewed in terms of a current output
from the smoothing unit 200. Here, as illustrated in FIG.
1, the current flowing from the rectifier unit 130 is a20
current I1, the current flowing to the inverter 310 is a
current I2, and the current flowing from the smoothing unit
200 is a current I3. The current I2 is a current obtained
by combining the current I1 and the current I3. The
current I3 can be expressed as a difference between the25
current I2 and the current I1, that is, the current I2-the
current I1. In the current I3, a discharging direction of
the smoothing unit 200 is a positive direction, and a
charging direction of the smoothing unit 200 is a negative
direction. That is, a current may flow into the smoothing30
unit 200, and a current may flow out therefrom.
[0019] FIG. 2 is a diagram illustrating examples of
respective currents and a capacitor voltage of the
11
capacitor of the smoothing unit in a case where the control
unit of the power conversion apparatus according to the
first embodiment smooths a current output from the
rectifier unit by the smoothing unit to make a current
flowing through the inverter constant. In the paper plane5
of FIG. 2, the current I1, the current I2, the current I3,
and a capacitor voltage Vdc are illustrated in this order
from the top. The capacitor voltage Vdc is a voltage of
the capacitor 210 generated in response to the current I3.
The vertical axes of the currents I1, I2, and I3 each10
indicate a current value, and the vertical axis of the
capacitor voltage Vdc indicates a voltage value. All
horizontal axes represent time t. Note that carrier
components of the inverter 310 are actually superimposed on
the currents I2 and I3, but are omitted here. The same15
applies to the following description. As illustrated in
FIG. 2, in the power conversion apparatus 1, if the current
I1 flowing from the rectifier unit 130 is sufficiently
smoothed by the smoothing unit 200, the current I2 flowing
through the inverter 310 has a constant current value.20
However, a large current I3 flows through the capacitor 210
of the smoothing unit 200, which may cause degradation.
Therefore, in the present embodiment, in the power
conversion apparatus 1, the control unit 400 controls the
current I2 flowing through the inverter 310, that is,25
controls the operation of the inverter 310 so as to reduce
the current I3 flowing through the smoothing unit 200.
[0020] FIG. 3 is a diagram illustrating examples of the
respective currents and the capacitor voltage of the
capacitor of the smoothing unit when the control unit of30
the power conversion apparatus according to the first
embodiment controls an operation of the inverter to reduce
the current flowing through the smoothing unit. In the
12
paper plane of FIG. 3, the current I1, the current I2, the
current I3, and the capacitor voltage Vdc are illustrated
in this order from the top. The capacitor voltage Vdc is a
voltage of the capacitor 210 generated in response to the
current I3. The vertical axes of the currents I1, I2, and5
I3 each indicate a current value, and the vertical axis of
the capacitor voltage Vdc indicates a voltage value. All
horizontal axes represent time t. The control unit 400 of
the power conversion apparatus 1 controls the operation of
the inverter 310 so that the current I2 as illustrated in10
FIG. 3 flows through the inverter 310, and thereby it is
possible to reduce a frequency component of the current
flowing from the rectifier unit 130 to the smoothing unit
200 and to reduce the current I3 flowing to the smoothing
unit 200 as compared with the example in FIG. 2.15
Specifically, the control unit 400 controls the operation
of the inverter 310 so that the current I2 including a
pulsating current having a frequency component of the
current I1 as a main component flows through the inverter
310.20
[0021] The frequency component of the current I1 is
determined depending on a frequency of an alternating
current supplied from the commercial power supply 110 and a
configuration of the rectifier unit 130. Therefore, the
control unit 400 can set a frequency component of the25
pulsating current to be superimposed on the current I2 as a
component having an amplitude and a phase determined in
advance. The frequency component of the pulsating current
to be superimposed on the current I2 has a waveform similar
to the frequency component of the current I1. As the30
control unit 400 approximates the frequency component of
the pulsating current to be superimposed on the current I2
to the frequency component of the current I1, it is
13
possible to reduce the current I3 flowing through the
smoothing unit 200 and to reduce a pulsating voltage
generated in the capacitor voltage Vdc.
[0022] The control unit 400 controls the pulsation of
the current flowing through the inverter 310 by controlling5
the operation of the inverter 310, which is the same as
controlling the pulsation of the first alternating-current
power output from the inverter 310 to the compressor 315.
The control unit 400 controls the operation of the inverter
310 so that a pulsation included in the second alternating-10
current power output from the inverter 310 is smaller than
a pulsation of the power output from the rectifier unit 130.
The control unit 400 controls an amplitude and a phase of
the pulsation included in the second alternating-current
power output from the inverter 310 so that a voltage ripple15
of the capacitor voltage Vdc, that is, a voltage ripple
generated in the capacitor 210 is smaller than a voltage
ripple generated in the capacitor 210 when the second
alternating-current power output from the inverter 310 does
not include the pulsation corresponding to the pulsation of20
the power flowing into the capacitor 210. Alternatively,
the control unit 400 controls the amplitude and the phase
of the pulsation included in the second alternating-current
power output from the inverter 310 so that a current ripple
flowing into and out from the capacitor 210 is smaller than25
a current ripple generated in the capacitor 210 when the
second alternating-current power output from the inverter
310 does not include the pulsation corresponding to the
pulsation of the power flowing into the capacitor 210.
What is meant by the expression of “when the second30
alternating-current power output from the inverter 310 does
not include the pulsation corresponding to the pulsation of
the power flowing into the capacitor 210” is control as
14
illustrated in FIG. 2.
[0023] The alternating current supplied from the
commercial power supply 110 is not particularly limited,
and may be a single-phase current or a three-phase current.
It is sufficient that the control unit 400 determines the5
frequency component of the pulsating current to be
superimposed on the current I2 depending on the first
alternating-current power supplied from the commercial
power supply 110. Specifically, the control unit 400
performs control so that a pulsatile waveform of the10
current I2 flowing through the inverter 310 is formed into
a shape obtained by adding a direct-current component to a
pulsatile waveform whose main component is a frequency
component which is twice the frequency of the first
alternating-current power in a case where the first15
alternating-current power supplied from the commercial
power supply 110 is single-phase power, or to a pulsatile
waveform whose main component is a frequency component
which is six times the frequency of the first alternating-
current power in a case where the first alternating-current20
power supplied from the commercial power supply 110 is
three-phase power. The pulsatile waveform has, for example,
a shape of an absolute value of a sine wave or a shape of a
sine wave. In that case, the control unit 400 may add at
least one frequency component among components of integral25
multiples of the frequency of the sine wave to the
pulsatile waveform as a predefined amplitude. The
pulsatile waveform may have a shape of a rectangular wave
or a triangular wave. In that case, the control unit 400
may set the amplitude and the phase of the pulsatile30
waveform to predefined values.
[0024] The control unit 400 may calculate a pulsation
amount of the pulsation included in the second alternating-
15
current power output from the inverter 310 by using the
voltage applied to the capacitor 210 or the current flowing
through the capacitor 210, or may calculate the pulsation
amount of the pulsation included in the second alternating-
current power output from the inverter 310 by using the5
voltage or the current of the first alternating-current
power supplied from the commercial power supply 110.
[0025] The operation of the control unit 400 will be
described with reference to a flowchart. FIG. 4 is a
flowchart illustrating the operation of the control unit10
included in the power conversion apparatus according to the
first embodiment. In step S1, the control unit 400
acquires detection values from the respective detection
units of the power conversion apparatus 1. In step S2, the
control unit 400 estimates the capacitor load. In step S3,15
the control unit 400 determines whether it is necessary to
reduce the capacitor load. If the control unit 400
determines that it is necessary to reduce the capacitor
load, Yes is selected in step S3, and the control unit 400
executes the capacitor load reduction control in step S4.20
That is, when outputting the second alternating-current
power from the inverter 310 to the load, the control unit
400 includes the pulsation corresponding to the pulsation
of the power flowing into the capacitor 210. In a case
where the capacitor load reduction control is already being25
executed, the control unit 400 continues the capacitor load
reduction control. On the other hand, if the control unit
400 determines that it is not necessary to reduce the
capacitor load, No is selected in step S3, and the control
unit 400 adopts no execution of the capacitor load30
reduction control in step S5. That is, when outputting the
second alternating-current power from the inverter 310 to
the load, the control unit 400 does not include the
16
pulsation corresponding to the pulsation of the power
flowing into the capacitor 210. In a case where no
execution of the capacitor load reduction control is
already adopted, the control unit 400 continues no
execution of the capacitor load reduction control.5
[0026] Next, a hardware configuration of the control
unit 400 included in the power conversion apparatus 1 will
be described. FIG. 5 is a diagram illustrating an example
of a hardware configuration that realizes the control unit
included in the power conversion apparatus according to the10
first embodiment. The control unit 400 is realized by a
processor 91 that executes various processes, a memory 92
which is a main memory, and a storage device 93 that stores
information.
[0027] The processor 91 may be an arithmetic means such15
as an arithmetic device, a microprocessor, a microcomputer,
a central processing unit (CPU), or a digital signal
processor (DSP). As the memory 92, a nonvolatile or
volatile semiconductor memory such as a random access
memory (RAM), a read only memory (ROM), a flash memory, an20
erasable programmable read only memory (EPROM), or an
electrically erasable programmable read only memory (EEPROM
(registered trademark)) can be used. The storage device 93
stores a program for executing a capacitor load reduction
control process. The processor 91 reads a program stored25
in the storage device 93 into the memory 92 and executes
the program. The processor 91 reads the program stored in
the storage device 93 into the memory 92 and executes the
program, thereby realizing a function of the control unit
400.30
[0028] As described above, in the power conversion
apparatus 1 according to the first embodiment, the control
unit 400 controls the operation of the inverter 310 on the
17
basis of the detection values acquired from the respective
detection units, and superimposes the pulsation of the
frequency component corresponding to the frequency
component of the current I1 flowing from the rectifier unit
130 on the current I2 flowing through the inverter 310,5
thereby reducing the current I3 flowing through the
smoothing unit 200. Consequently, the current I3 flowing
through the smoothing unit 200 is reduced, so that the
power conversion apparatus 1 can use a capacitor having a
small ripple current capability as compared with a case10
where the control of the first embodiment is not performed.
In addition, due to the decrease in the pulsation voltage
in the capacitor voltage Vdc, the power conversion
apparatus 1 can reduce the capacitance of the capacitor 210
to be mounted as compared with the case where the control15
of the first embodiment is not performed. For example, in
a case where the smoothing unit 200 includes a plurality of
capacitors 210, the power conversion apparatus 1 can reduce
the number of capacitors 210 included in the smoothing unit
200.20
[0029] Since the control unit 400 estimates the
capacitor load and determines whether to execute the
capacitor load reduction control on the basis of an
estimate value of the capacitor load, it is possible to
prevent generation of loss due to reduction in the25
capacitor current for reducing the capacitor load in a case
where the degradation of the capacitor 210 when not
executing the capacitor load reduction control falls within
an allowable range.
[0030] Second Embodiment.30
FIG. 6 is a diagram illustrating a configuration of
the power conversion apparatus according to a second
embodiment. The power conversion apparatus 1 according to
18
the second embodiment includes a first current detection
unit 601 and a second current detection unit 602, which is
a difference from the power conversion apparatus 1
according to the first embodiment. The first current
detection unit 601 is installed in the rectifier unit 130.5
That is, the first current detection unit 601 is installed
closer to the commercial power supply 110 than the
capacitor 210 is. The second current detection unit 602 is
installed between the inverter 310. That is, the second
current detection unit 602 is installed closer to the10
compressor 315 which is a load than the capacitor 210 is.
The control unit 400 calculates the current flowing through
the capacitor 210 from a difference between a current value
detected by the first current detection unit 601 and a
current value detected by the second current detection unit15
602, and estimates the capacitor load.
[0031] The power conversion apparatus 1 according to the
second embodiment estimates the capacitor load on the basis
of the current flowing through the capacitor 210 calculated
on the basis of the difference between the current value20
detected by the first current detection unit 601 and the
current value detected by the second current detection unit
602, and thus can estimate the capacitor load more
accurately than the power conversion apparatus 1 according
to the first embodiment. Accordingly, the power conversion25
apparatus 1 according to the second embodiment can more
accurately determine whether it is necessary to execute the
capacitor load reduction control, and thus can reduce the
degradation of the capacitor 210.
[0032] Note that since the first current detection unit30
601 and the second current detection unit 602 are generally
installed in the power conversion apparatus 1 for the
purpose of motor control and control and protection of the
19
booster circuit, when the capacitor load is estimated by
using the first current detection unit 601 and the second
current detection unit 602 installed for motor control and
control and protection of the booster circuit, it is
possible to eliminate the necessity to newly add the first5
current detection unit 601 and the second current detection
unit 602 for estimation of the capacitor load.
[0033] Third Embodiment.
FIG. 7 is a diagram illustrating a configuration of
the power conversion apparatus according to a third10
embodiment. The power conversion apparatus 1 according to
the third embodiment includes a first voltage detection
circuit 701 and a second voltage detection circuit 702,
which is a difference from the power conversion apparatus 1
according to the second embodiment. The first voltage15
detection circuit 701 is installed between the reactor 120
and the rectifier unit 130. That is, the first voltage
detection circuit 701 is installed closer to the commercial
power supply 110 than the capacitor 210 is. The second
voltage detection circuit 702 is installed between the20
smoothing unit 200 and the inverter 310. That is, the
second voltage detection circuit 702 is installed closer to
the compressor 315 which is a load than the capacitor 210
is.
[0034] The control unit 400 calculates a first power25
value from a current value detected by the first current
detection unit 601 and a voltage value detected by the
first voltage detection circuit 701. Accordingly, the
first current detection unit 601 and the first voltage
detection circuit 701 form a first power detection unit 801.30
In addition, the control unit 400 calculates a second power
value from a current value detected by the second current
detection unit 602 and a voltage value detected by the
20
second voltage detection circuit 702. Accordingly, the
second current detection unit 602 and the second voltage
detection circuit 702 detect a second power detection unit
802. The first power detection unit 801 is installed
closer to the commercial power supply 110 than the5
capacitor 210 is, and the second power detection unit 802
is installed closer to the compressor 315 which is a load
than the capacitor 210 is.
[0035] The control unit 400 calculates power consumption
in the capacitor 210 on the basis of the first power value10
and the second power value to estimate the capacitor load.
[0036] The power conversion apparatus 1 according to the
third embodiment calculates the power consumption in the
capacitor 210 on the basis of the first power value
calculated from the current value detected by the first15
current detection unit 601 and the voltage value detected
by the first voltage detection circuit 701 and the second
power value calculated from the current value detected by
the second current detection unit 602 and the voltage value
detected by the second voltage detection circuit 702 to20
estimate the capacitor load, and thus can estimate the
capacitor load more accurately than the power conversion
apparatus 1 according to the second embodiment.
[0037] Fourth Embodiment.
A circuit configuration of the power conversion25
apparatus 1 according to a fourth embodiment is similar to
that of the power conversion apparatus 1 according to the
first embodiment. In the fourth embodiment, the compressor
315 which is a load including the motor 314 that receives
power supply from the power conversion apparatus 1 is30
applied to an outdoor unit of an air conditioner, and
compresses a refrigerant flowing through a refrigerant
circuit. In the fourth embodiment, the air conditioner
21
including the compressor 315 is operated in any of a
plurality of operation modes with different power
consumption. The power conversion apparatus 1 according to
the fourth embodiment performs switching between execution
of the capacitor load reduction control and no execution5
thereof in line with the operation mode of the air
conditioner. Here, it is assumed that the air conditioner
is operated in any one operation mode of a normal operation
mode and an energy-saving operation mode, and the control
unit 400 executes the capacitor load reduction control in a10
case where the operation mode of the air conditioner is the
normal operation mode, and adopts no execution of the
capacitor load reduction control in a case where the
operation mode of the air conditioner is the energy-saving
operation mode.15
[0038] FIG. 8 is a diagram illustrating an operation of
the power conversion apparatus according to the fourth
embodiment. In FIG. 8, a mode switching signal is a signal
for switching the operation mode of the air conditioner,
and a high level corresponds to the normal operation mode20
and a low level corresponds to the energy-saving operation
mode. At time t10, the mode switching signal is at the
high level, and the air conditioner is operating in the
normal operation mode. Therefore, at time t10, the control
unit 400 executes the capacitor load reduction control. At25
time t11, the control unit 400 changes the mode switching
signal from the high level to the low level, and thereby
the air conditioner switches from the normal operation mode
to the energy-saving operation mode. Therefore, at time
t11, the control unit 400 adopts no execution of the30
capacitor load reduction control. By the control unit 400
adopting no execution of the capacitor load reduction
control, a capacitor load reduction control amount starts
22
to decrease at time t11. The decrease in the capacitor
load reduction control amount results in an increase in the
capacitor load, but since the loss of the motor 314 is
ameliorated, input power of the capacitor 210 decreases.
At time t12, the control unit 400 changes the mode5
switching signal from the low level to the high level, and
thereby the air conditioner switches from the energy-saving
operation mode to the normal operation mode. Therefore, at
time t12, the control unit 400 starts the capacitor load
reduction control, and the capacitor load reduction control10
amount starts to increase. The increase in the capacitor
load reduction control amount results in a decrease in the
capacitor load, and the input power of the capacitor 210
increases. Since the work of the motor 314 on the
refrigerant circuit of the air conditioner does not change15
depending on the capacitor load reduction control amount,
air conditioning capacity of the air conditioner is
constant regardless of the capacitor load reduction control
amount.
[0039] Since the power conversion apparatus 1 according20
to the fourth embodiment performs switching between
execution of the capacitor load reduction control and no
execution thereof in line with the operation mode of the
air conditioner, in a case where the input power of the
capacitor 210 is small and the capacitor load can be kept25
small without executing the capacitor load reduction
control, the loss of the motor 314 can be reduced and
energy-saving performance can be improved by adopting no
execution of the capacitor load reduction control.
[0040] Fifth Embodiment.30
A circuit configuration of the power conversion
apparatus 1 according to a fifth embodiment is similar to
that of the power conversion apparatus 1 according to the
23
first embodiment. The power conversion apparatus 1
according to the fifth embodiment starts the capacitor load
reduction control when the capacitor load exceeds a preset
capacitor load upper limit threshold, and stops the
capacitor load reduction control when the capacitor load5
becomes less than or equal to a preset capacitor load lower
limit threshold.
[0041] FIG. 9 is a diagram illustrating an operation of
the power conversion apparatus according to the fifth
embodiment. In the fifth embodiment, after the capacitor10
load exceeds the capacitor load upper limit threshold and
the capacitor load reduction control is started, the power
conversion apparatus 1 increases or decreases the capacitor
load reduction control amount in line with the increase or
decrease in the input power or the capacitor load until the15
capacitor load becomes less than or equal to the capacitor
load lower limit threshold. At time t20, the control unit
400 executes the capacitor load reduction control. At time
t21, the control unit 400 decreases the air conditioning
capacity of the air conditioner. Consequently, the input20
power of the capacitor 210 decreases, and the capacitor
load also decreases. At time t22, the capacitor load
becomes less than or equal to the capacitor load lower
limit threshold. Consequently, the control unit 400 adopts
no execution of the capacitor load reduction control. When25
no execution of the capacitor load reduction control is
adopted, the capacitor load increases. At time t23 and
time t24, the capacitor load does not exceed the capacitor
load upper limit threshold, so that the control unit 400
continues no execution of the capacitor load reduction30
control. At time t25, the capacitor load exceeds the
capacitor load upper limit threshold. Therefore, the
control unit 400 executes the capacitor load reduction
24
control, and the capacitor load reduction control amount
starts to increase. The increase in the capacitor load
reduction control amount results in a decrease in the
capacitor load, and the input power of the capacitor 210
increases. At time t26 and time t27, the capacitor load is5
not less than or equal to the capacitor load lower limit
threshold, so that the control unit 400 continues the
execution of the capacitor load reduction control.
[0042] In a case where the capacitor load is low, the
power conversion apparatus 1 according to the fifth10
embodiment can switch to operation in which performance is
prioritized over capacitor load reduction, and can improve
energy-saving properties.
[0043] In the first to fifth embodiments, switching
between execution of the capacitor load reduction control15
and no execution thereof is performed. However, a
threshold as a target value of the capacitor load may be
set in advance, and the capacitor load reduction control
amount may be continuously changed depending on a
difference between the threshold as the target value and20
the capacitor load. Not by including or not including a
pulsation amount output from the inverter 310 to the load,
but by continuously adjusting the pulsation amount to be
included in the output from the inverter 310, it is
possible to operate the air conditioner while balancing the25
life of the air conditioner and the air conditioning
performance.
[0044] Sixth Embodiment.
A circuit configuration of the power conversion
apparatus 1 according to a sixth embodiment is similar to30
that of the power conversion apparatus 1 according to the
first embodiment. FIG. 10 is a diagram illustrating an
operation of the power conversion apparatus according to
25
the sixth embodiment. In order to make the capacitor load
less than or equal to a target load amount, the power
conversion apparatus 1 according to the sixth embodiment
stops control for reducing the capacitor load in a case
where a control amount of the control for reducing the5
capacitor load to be needed becomes less than or equal to a
predetermined capacitor load reduction control amount
threshold, and resumes output of the control for reducing
the capacitor load in a case where an estimate value of the
capacitor load exceeds a predetermined capacitor load10
threshold.
[0045] At time t30, the control unit 400 is executing
the capacitor load reduction control, and the capacitor
load is maintained at the target load amount. At time t31,
the control unit 400 starts to decrease the air15
conditioning capacity of the air conditioner. Therefore,
from time t31, the capacitor load reduction control amount
also decreases in line with the decrease in the air
conditioning capacity. At time t32, the capacitor load
reduction control amount becomes less than or equal to the20
predetermined capacitor load reduction control amount
threshold. Therefore, the control unit 400 stops the
capacitor load reduction control. Accordingly, at time t32,
the capacitor load reduction control amount decreases to 0.
The decrease in the capacitor load reduction control amount25
results in an increase in the capacitor load, but since the
loss of the motor 314 is ameliorated, the input power of
the capacitor 210 decreases. At time t33 and time t34, the
capacitor load does not exceed the predetermined capacitor
load threshold, so that the control unit 400 continues a30
state in which the capacitor load reduction control is
stopped. At time t35, the capacitor load exceeds the
predetermined capacitor load threshold, so that the control
26
unit 400 resumes the capacitor load reduction control, and
the capacitor load reduction control amount increases. The
increase in the capacitor load reduction control amount
results in a decrease in the capacitor load to the target
load amount, and the input power of the capacitor 2105
increases. At time t36, the capacitor load reduction
control amount is not less than or equal to the
predetermined capacitor load reduction control amount
threshold, so that the control unit 400 continues the
capacitor load reduction control.10
[0046] The power conversion apparatus 1 according to the
sixth embodiment performs control so that the capacitor
load does not increase to exceed the predetermined
capacitor load threshold, meanwhile, in a case where the
capacitor load becomes less than or equal to a certain15
value, the power conversion apparatus 1 allows the
capacitor load to deteriorate to a certain value to make
the control amount a minimum necessary amount, and thereby
it is possible to improve the energy-saving properties in
an operating state in which the capacitor load is low.20
[0047] Seventh Embodiment.
A circuit configuration of the power conversion
apparatus 1 according to a seventh embodiment is similar to
that of the power conversion apparatus 1 according to the
first embodiment. The power conversion apparatus 125
according to the seventh embodiment continuously changes
the capacitor load reduction control amount so that the
life of the capacitor 210 estimated from the capacitor load
does not fall below a preset period.
[0048] It is known that the life of a capacitor follows30
Arrhenius law. Therefore, the life of a capacitor can be
generally obtained from an ambient temperature of the
capacitor, a voltage applied to the capacitor, and the
27
amount of capacitor current caused by heat generation of
the capacitor, in addition to a constant determined by the
specification of the capacitor. The ambient temperature of
the capacitor 210 can be obtained by, for example, adding a
temperature difference between an outside air temperature5
and the ambient temperature of the capacitor 210 checked in
a preliminary evaluation or the like on the basis of an
outside air temperature detected by the air conditioner. A
voltage applied to the capacitor 210 can be obtained from
the detection value of the voltage detection unit 502. The10
current amount of the capacitor current can be obtained
from the amount of variation in the voltage applied to the
capacitor, or can be obtained from a difference between a
current amount of a grid power supply and a motor current
amount.15
[0049] The power conversion apparatus 1 according to the
seventh embodiment does not execute the capacitor load
reduction control in a case where it is estimated that the
life of the capacitor 210 does not fall below the preset
period, and executes the capacitor load reduction control20
only in a case where it is estimated that the life of the
capacitor 210 falls below the preset period. Accordingly,
in a case where it is predicted that the life of the
capacitor 210 does not fall below the preset period, the
life of the capacitor 210 is allowed to be shortened to the25
preset period and no execution of the capacitor load
reduction control is adopted, and thereby it is possible to
reduce deterioration of the energy-saving properties due to
the execution of the capacitor load reduction control.
Consequently, the power conversion apparatus 1 according to30
the seventh embodiment can ensure that the life of the
capacitor 210 is longer than or equal to the preset period
while reducing the deterioration of the energy-saving
28
properties.
[0050] Eighth Embodiment.
A circuit configuration of the power conversion
apparatus 1 according to an eighth embodiment is similar to
that of the power conversion apparatus 1 according to the5
second embodiment. In the power conversion apparatus 1
according to the eighth embodiment, the control unit 400
decomposes the capacitor current for each frequency
component, and changes the control amount of the capacitor
load reduction control so that the root of the sum of10
squares of each of frequency components which are twice the
power supply voltage Vs or components which are integer
multiples of the power supply voltage Vs does not become
larger than or equal to a predetermined certain value.
Furthermore, in a case where the root of the sum of squares15
of each of the frequency components which are twice the
power supply voltage Vs or the components which are
integral multiples of the power supply voltage Vs is less
than or equal to the predetermined certain value, the
control unit 400 allows the root of the sum of squares of20
each of the frequency components which are twice the power
supply voltage Vs or the components which are integral
multiples of the power supply voltage Vs to increase to the
predetermined certain value to make the capacitor load
reduction control amount a minimum necessary amount.25
[0051] In a case where the current flowing through the
capacitor 210 is a ripple current including a plurality of
frequency components, a ripple current IR is calculated by
the following formula (1). In the following formula (1),
IR represents an effective value [Ams] of the ripple30
current at a prescribed frequency, IX1 to IXN represent
effective values [Ams] of the ripple current at respective
frequencies, and K1 to KN represent frequency correction
29
coefficients at respective frequencies. Since the
frequency correction coefficients in the above respective
frequency components are different for each capacitor
component applied as the capacitor 210, the control unit
400 stores in advance information on the component5
specifications of the capacitor components applied as the
capacitor 210.
[0052] Formula 1:
[0053] FIG. 11 is a diagram illustrating an example of a10
relationship between the capacitor current and the
capacitor load reduction control amount of the power
conversion apparatus according to the eighth embodiment.
The control unit 400 decomposes the capacitor current into
the frequency components which are twice the power supply15
voltage Vs and components which are integral multiples of
the frequency components which are twice the power supply
voltage Vs by band-pass filters 401 and 402. The
components which are integral multiples of the frequency
components which are twice the power supply voltage Vs are,20
for example, frequency components which are four times the
power supply voltage Vs. Then, the control unit 400
divides, by a divider 403, the frequency components which
are twice the power supply voltage Vs by the frequency
correction coefficient, and divides, by a divider 404, the25
components which are integral multiples of the frequency
components which are twice the power supply voltage Vs by
the frequency correction coefficient. Then, the control
unit 400 calculates, by an adder 405, the root of the sum
of squares of each of the frequency components which are30
twice the power supply voltage Vs divided by the frequency
30
correction coefficient and the components which are
integral multiples of the frequency components which are
twice the power supply voltage Vs divided by a frequency
correction background number. Then, the control unit 400
calculates, by a subtractor 406, a difference between a sum5
which is a calculation result of the adder 405 and a preset
threshold, and changes the capacitor load reduction control
amount on the basis of a calculation result of the
subtractor 406. Note that the capacitor load reduction
control amount can be prevented from being frequently10
changed by using not an instantaneous value but an average
value in preset time, as the sum calculated by the adder
405 used in the process performed by the subtractor 406.
[0054] The power conversion apparatus 1 according to the
eighth embodiment makes the control amount variable on the15
basis of the magnitude of the root of the sum of squares of
each of, among a plurality of frequency components included
in the capacitor current, the frequency components which
are twice the power supply voltage Vs at which the
capacitor load is efficiently reduced by control or the20
frequency components which are twice the power supply
voltage Vs and the components which are integral multiples
thereof, and thereby it is possible to prevent a situation
in which when a total capacitor load increases due to other
frequency components at which reduction by control is not25
efficient, the control amount for preventing the capacitor
current from becoming larger than or equal to a certain
value rapidly increases, and thus the energy-saving
properties are impaired.
[0055] In the above description, the capacitor current30
is decomposed into the frequency components which are twice
the power supply voltage Vs and the components which are
integral multiples of the frequency components which are
31
twice the power supply voltage Vs, but the capacitor
current may be decomposed into frequency components which
are integral multiples of the power supply voltage Vs. The
capacitor current may be decomposed into the frequency
components which are integral multiples of the power supply5
voltage Vs and frequency components of the rotational speed
of the compressor 315, or the capacitor current may be
decomposed into the frequency components which are integral
multiples of the power supply voltage Vs and frequency
components which are twice a control period of the inverter10
310 or a converter. The capacitor current may be
decomposed into the frequency components which are integral
multiples of the power supply voltage Vs, or at least one
of the frequency components of the rotational speed of the
compressor 315 and the frequency components which are twice15
the control period of the inverter 310 or the converter.
[0056] Ninth Embodiment.
FIG. 12 is a diagram illustrating a configuration of
an outdoor unit of an air conditioner according to a ninth
embodiment. An outdoor unit 900 of an air conditioner20
according to the ninth embodiment includes the power
conversion apparatus 1 according to any one of the first to
eighth embodiments.
[0057] In the outdoor unit 900 of an air conditioner,
the compressor 315 incorporating the motor 314 described in25
the first to eighth embodiments, a four-way valve 902, an
indoor heat exchanger 906, an expansion valve 908, and an
outdoor heat exchanger 910 are attached via a refrigerant
pipe 912.
[0058] A compression mechanism 904 that compresses a30
refrigerant and the motor 314 that operates the compression
mechanism 904 are provided inside the compressor 315.
[0059] The outdoor unit 900 can perform heating
32
operation or cooling operation by a switching operation of
the four-way valve 902. The compression mechanism 904 is
driven by the motor 314 which is variable speed controlled.
[0060] During the heating operation, as indicated by
solid arrows, the refrigerant is pressurized and sent by5
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.
[0061] During the cooling operation, as indicated by10
dotted arrows, the refrigerant is pressurized and sent 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 the four-way
valve 902, and returns to the compression mechanism 904.15
[0062] 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 absorb
heat. During the cooling operation, the outdoor heat
exchanger 910 acts as a condenser to release heat, and the20
indoor heat exchanger 906 acts as an evaporator to absorb
heat. The expansion valve 908 decompresses and expands the
refrigerant.
[0063] The configurations described in the embodiments
above are merely examples of the content and can be25
combined with other known technology and part of the
configurations can be omitted or modified without departing
from the gist thereof.
Reference Signs List30
[0064] 1 power conversion apparatus; 2 motor driving
apparatus; 91 processor; 92 memory; 93 storage device;
110 commercial power supply; 120 reactor; 130 rectifier
33
unit; 131, 132, 133, 134 rectifier element; 200 smoothing
unit; 210 capacitor; 310 inverter; 311a, 311b, 311c, 311d,
311e, 311f switching element; 312a, 312b, 312c, 312d, 312e,
312f freewheeling diode; 313a, 313b current detection
unit; 314 motor; 315 compressor; 400 control unit; 401,5
402 band-pass filter; 403, 404 divider; 405 adder; 406
subtractor; 501 voltage current detection unit; 502
voltage detection unit; 601 first current detection unit;
602 second current detection unit; 701 first voltage
detection circuit; 702 second voltage detection circuit;10
801 first power detection unit; 802 second power
detection unit; 900 outdoor unit; 902 four-way valve; 904
compression mechanism; 906 indoor heat exchanger; 908
expansion valve; 910 outdoor heat exchanger; 912
refrigerant pipe.15
34
We Claim:
[Claim 1] A power conversion apparatus comprising:
a rectifier unit to rectify first alternating-current5
power supplied from a commercial power supply;
a capacitor connected to an output end of the
rectifier unit;
an inverter to convert power output from the rectifier
unit and the capacitor into second alternating-current10
power, and to output the second alternating-current power
to a load including a motor, the inverter being connected
to both ends of the capacitor; and
a control unit to execute capacitor load reduction
control of reducing a current flowing through the capacitor15
by controlling an operation of the inverter so as to output,
from the inverter to the load, the second alternating-
current power including a pulsation corresponding to a
pulsation of power flowing into the capacitor from the
rectifier unit, wherein20
the control unit estimates a capacitor load in the
capacitor, and determines whether to execute the capacitor
load reduction control on a basis of an estimate value of
the capacitor load.
25
[Claim 2] The power conversion apparatus according to claim
1, comprising a unit to detect a voltage across the
capacitor.
[Claim 3] The power conversion apparatus according to claim30
1 or 2, comprising:
a first current detection unit installed closer to the
commercial power supply than the capacitor is, and a second
35
current detection unit installed closer to the load than
the capacitor is, wherein
the control unit estimates the capacitor load on a
basis of a detection value of the first current detection
unit and a detection value of the second current detection5
unit.
[Claim 4] The power conversion apparatus according to any
one of claims 1 to 3, wherein the control unit decomposes a
capacitor current for each frequency component, executes10
the capacitor load reduction control in a case where a
magnitude of a root of a sum of squares of each of at least
frequency components that are twice a power supply voltage
frequency or components that are integer multiples of the
power supply voltage frequency is larger than or equal to a15
predetermined certain value, and stops the capacitor load
reduction control in a case where the magnitude of the root
of the sum of squares of each of the at least frequency
components that are twice the power supply voltage
frequency or the components that are integer multiples of20
the power supply voltage frequency is less than the
predetermined certain value.
[Claim 5] The power conversion apparatus according to claim
1 or 2, comprising:25
a first power estimation unit installed closer to the
commercial power supply than the capacitor is, and a second
power estimation unit installed closer to the load than the
capacitor is, wherein
the control unit estimates the capacitor load on a30
basis of an estimate value of the first power estimation
unit and an estimate value of the second power estimation
unit.
36
[Claim 6] The power conversion apparatus according to any
one of claims 1 to 5, wherein
the control unit
performs switching between execution of the capacitor5
load reduction control and no execution thereof depending
on an operation mode of the load.
[Claim 7] The power conversion apparatus according to any
one of claims 1 to 5, wherein the control unit starts the10
capacitor load reduction control when the capacitor load
exceeds a preset capacitor load upper limit threshold, and
stops the capacitor load reduction control when the
capacitor load becomes less than or equal to a preset
capacitor load lower limit threshold.15
[Claim 8] The power conversion apparatus according to any
one of claims 1 to 5, wherein the control unit continuously
adjusts a pulsation amount corresponding to a pulsation of
power flowing into the capacitor in the capacitor load20
reduction control.
[Claim 9] The power conversion apparatus according to any
one of claims 1 to 5, wherein
the control unit starts the capacitor load reduction25
control when the capacitor load exceeds a preset capacitor
load threshold, and stops the capacitor load reduction
control when a capacitor load reduction control amount by
the capacitor load reduction control becomes less than or
equal to a preset capacitor load reduction control amount30
threshold, and
continuously adjusts a minimum necessary pulsation
amount corresponding to a pulsation of power flowing into
37
the capacitor in the capacitor load reduction control so
that an estimate value of the capacitor load becomes less
than or equal to a predetermined target load amount.
[Claim 10] The power conversion apparatus according to5
any one of claims 1 to 5, wherein the control unit
continuously adjusts a minimum necessary pulsation amount
corresponding to a pulsation of power flowing into the
capacitor in the capacitor load reduction control so that a
life of the capacitor estimated from the capacitor load10
becomes longer than or equal to a predetermined period.
[Claim 11] An outdoor unit of an air conditioner
comprising the power conversion apparatus according to any
one of claims 1 to 10.15