DESCRIPTION
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
POWER CONVERSION APPARATUS AND AIR CONDITIONER;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION
ORGANISED AND EXISTING UNDER THE LAWS OF JAPAN,
WHOSE ADDRESS IS 7-3, MARUNOUCHI 2-CHOME, CHIYODAKU, 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
5 conversion apparatus that converts an alternating-current
(AC) voltage into a direct-current voltage and further
converts the direct-current voltage into an AC voltage.
The present disclosure also relates to an air conditioner.
10 Background
[0002] With a conventional drive control apparatus that
includes an inverter, refrigerant stagnation can occur as a
phenomenon in which a liquid refrigerant collects in a
compressor for a refrigeration cycle apparatus such as an
15 air conditioner during low-temperature suspension. When
the refrigerant stagnation phenomenon has occurred, it
causes problems such that a start-up load on the compressor
increases and results in impairing the compressor, and a
large current flows in the inverter during start-up of the
20 compressor so that the system is determined to be
anomalous and the compressor cannot be started.
[0003] To address such problems, Patent Literature 1
discloses a technique that a drive control apparatus
performs constraining energization control that heats a
25 motor of a compressor through constraining energization to
eliminate the refrigerant stagnation phenomenon. The drive
control apparatus described in Patent Literature 1 is
capable of stably outputting constraining energization with
high efficiency to restrain the refrigerant stagnation
30 phenomenon, and also preventing additional cost since a
heating component such as a heater is not required. In the
drive control apparatus described in Patent Literature 1,
switching elements of an inverter undergoes high-frequency
3
switching for the constraining energization, thus
generating a motor current in which a reactive power
component is dominant due to impedance characteristics of
the motor. The motor current regeneratively flows into a
5 capacitor, and the capacitor is charged with this
regenerative current as energy.
Citation List
Patent Literature
10 [0004] Patent Literature 1: Japanese Patent Application
Laid-open No. 2012-67706
Summary
Technical Problem
15 [0005] Capacitances of capacitors disposed in a latter
stage of rectifier circuits in power conversion apparatuses
are now reduced for purposes of harmonic improvement, power
factor improvement, apparatus downsizing, and others. When
a power conversion apparatus with a capacitor having
20 smaller capacitance performs high-frequency switching as in
Patent Literature 1, a capacitor is charged with the
regenerative current as the energy; however, a smaller
amount of energy is stored in the capacitor. Therefore,
compared with a power conversion apparatus with larger
25 capacitance of capacitor, in the power conversion apparatus
with the smaller capacitance of capacitor, energy is
charged faster and a voltage across the capacitor
significantly varies. There is a problem in the power
conversion apparatus with the smaller capacitance of
30 capacitor in that, when the capacitor is overcharged, a bus
voltage that is the voltage across the capacitor increases
and may exceed withstand voltages of the capacitor,
switching elements of an inverter, and others.
4
[0006] The present disclosure has been made in view of
the above, and an object of the present disclosure is to
provide a power conversion apparatus that is capable of
avoiding an effect on elements that is caused from
5 constraining energization control for getting rid of
refrigerant stagnation while avoiding increase in
capacitance of a capacitor.
Solution to Problem
10 [0007] In order to solve the above-stated problem and
achieve the object, a power conversion apparatus according
to the present disclosure includes a rectifier circuit that
rectifies a first alternating-current voltage; a reactor
connected to the rectifier circuit; a capacitor connected
15 to an output end of the rectifier circuit; an inverter that
is connected to the capacitor, generates a second
alternating-current voltage through operations of a
plurality of switching elements, and applies the second
alternating-current voltage to a compressor motor including
20 a stator and a rotor; and a control unit that performs
operation controls on the plurality of switching elements.
The control unit causes the inverter to apply, to the
compressor motor, the second alternating-current voltage
having a higher frequency than when the compressor motor is
25 in compression operation so as not to rotate the rotor.
The application of the second alternating-current voltage
having high-frequency from the inverter to the compressor
motor generates a regenerative current and a current flows
to the capacitor due to the regenerative current without
30 impairing the capacitor.
Advantageous Effects of Invention
[0008] The power conversion apparatus according to the
5
present disclosure has an effect of avoiding an effect on
the elements that is caused from constraining energization
control for getting rid of refrigerant stagnation, while
avoiding increase in capacitance of the capacitor.
5
Brief Description of Drawings
[0009] FIG. 1 is a diagram illustrating a configuration
example of an air conditioner that includes a power
conversion apparatus according to a first embodiment.
10 FIG. 2 is a diagram illustrating a first configuration
example of the power conversion apparatus according to the
first embodiment.
FIG. 3 is a diagram illustrating a second
configuration example of the power conversion apparatus
15 according to the first embodiment.
FIG. 4 is a diagram illustrating an example of pulsewidth modulation (PWM) signals that a control unit of the
power conversion apparatus according to the first
embodiment generates.
20 FIG. 5 is a diagram illustrating an example of
voltages and currents at parts in relation to switched
states of switching elements of an inverter included in the
power conversion apparatus according to the first
embodiment.
25 FIG. 6 is a diagram exemplary illustrating those PWM
signals for the inverter’s switching elements included in
the power conversion apparatus according to the first
embodiment and a U-phase motor current that flows in a
motor.
30 FIG. 7 is a diagram illustrating an example of a
current path when the power conversion apparatus according
to the first embodiment is in a V0 vector state.
FIG. 8 is a first diagram illustrating an example of a
6
current path when the power conversion apparatus according
to the first embodiment is in a V4 vector state.
FIG. 9 is a second diagram illustrating an example of
a current path when the power conversion apparatus
5 according to the first embodiment is in the V4 vector state.
FIG. 10 is a diagram illustrating an example of a
current path when the power conversion apparatus according
to the first embodiment is in a V7 vector state.
FIG. 11 is a first diagram illustrating an example of
10 a current path when the power conversion apparatus
according to the first embodiment is in a V3 vector state.
FIG. 12 is a second diagram illustrating an example of
a current path when the power conversion apparatus
according to the first embodiment is in the V3 vector state.
15 FIG. 13 is a diagram illustrating an example of a
hardware configuration that implements the control unit of
the power conversion apparatus according to the first
embodiment.
FIG. 14 is a diagram illustrating a configuration
20 example of a power conversion apparatus according to a
second embodiment.
FIG. 15 is a diagram illustrating a configuration
example of a power conversion apparatus according to a
third embodiment.
25
Description of Embodiments
[0010] With reference to the drawings, a detailed
description is hereinafter provided of power conversion
apparatuses and an air conditioner according to embodiments
30 of the present disclosure.
[0011] First Embodiment.
FIG. 1 is a diagram illustrating a configuration
example of an air conditioner 300 that includes a power
7
conversion apparatus 200 according to a first embodiment.
The air conditioner 300 includes a power supply 100, the
power conversion apparatus 200, a compressor 320 including
a motor 310, a four-way valve 330, an outdoor heat
5 exchanger 340, an expansion valve 350, an indoor heat
exchanger 360, and refrigerant piping 370. In FIG. 1, the
compressor 320, the four-way valve 330, the outdoor heat
exchanger 340, the expansion valve 350, and the indoor heat
exchanger 360 are connected via the refrigerant piping 370.
10 The compressor 320 internally includes the motor 310 that
runs a compressor mechanism not illustrated. The motor 310
includes a stator and a rotor. The motor 310 is a
compressor motor that is driven by input of an alternatingcurrent (AC) voltage that, generated by the power
15 conversion apparatus 200, includes a desired voltage and a
desired frequency. As the internal motor 310 of the
compressor 320 rotates, a refrigerant is compressed inside
the compressor 320 and circulates between the outdoor heat
exchanger 340 and the indoor heat exchanger 360 through the
20 refrigerant piping 370. In this way, the air conditioner
300 can control air conditioning. The power conversion
apparatus 200 and the motor 310 are electrically connected.
The power conversion apparatus 200 is connected to the
power supply 100. The power conversion apparatus 200 uses
25 an AC voltage supplied from the power supply 100 to
generate the AC voltage to be supplied to the motor 310.
[0012] A description is provided of configurations for
the power conversion apparatus 200. FIG. 2 is a diagram
illustrating a first configuration example of the power
30 conversion apparatus 200 according to the first embodiment.
As mentioned earlier, the power conversion apparatus 200 is
connected to the power supply 100 and the motor 310, which
is included in the compressor 320. FIG. 2 illustrates an
8
example in which the power supply 100 is a three-phase AC
power supply. The power conversion apparatus 200 includes
a rectifier circuit 210, a reactor 220, a capacitor 230, an
inverter 240, a voltage detection unit 250, a current
5 detection unit 260, and a control unit 270. In the power
conversion apparatus 200, the rectifier circuit 210, the
reactor 220, and the capacitor 230 constitute a converter.
[0013] The rectifier circuit 210 includes six diode
elements 211 to 216 and rectifies or converts the three10 phase AC voltage supplied from the power supply 100 into a
direct-current voltage. One end of the reactor 220 is
connected to one of output ends of the rectifier circuit
210. One end of the capacitor 230 is connected to the
other end of the reactor 220, and the other end of the
15 capacitor 230 is connected to the other one of the output
ends of the rectifier circuit 210. In other words, the
capacitor 230 is connected to the output end of the
rectifier circuit 210 via the reactor 220. The inverter
240 includes a plural of switching elements 241 to 246.
20 The inverter 240 is connected to both of the ends of the
capacitor 230 and generates the AC voltage through
operations, i.e., on and off operations of the plural
switching elements 241 to 246. The inverter 240 applies
the generated AC voltage to the motor 310. The voltage
25 detection unit 250 detects a voltage across the capacitor
230, namely a bus voltage Vdc that is input as a directcurrent voltage to the inverter 240 and outputs a detection
value to the control unit 270. The current detection unit
260 detects currents that flow from the inverter 240 to the
30 motor 310, and outputs detection values to the control unit
270. In the example of FIG. 2, the motor 310 is a threephase motor having a U phase, a V phase, and a W phase.
[0014] The control unit 270 performs operation control
9
on the power conversion apparatus 200 on the basis of the
detection values obtained from the voltage detection unit
250 and the current detection unit 260. Specifically, the
control unit 270 generates and outputs, to the inverter 240,
5 drive signals that control the operations, i.e., the on and
off operations of the switching elements 241 to 246 in the
inverter 240, such as PWM signals. Using the PWM signals,
the control unit 270 performs the operation control on the
inverter 240, that is to say, operation controls on the
10 switching elements 241 to 246. The control unit 270 also
obtains an internal temperature of the compressor 320, a
refrigerant state, and other information with sensors and
other devices that are not illustrated to determine whether
or not refrigerant stagnation has occurred. Upon judging
15 that the refrigerant stagnation has occurred while the
compressor 320 is stopped, the control unit 270 outputs the
PWM signals to the switching elements 241 to 246 of the
inverter 240 at a higher frequency than that when the motor
310 causes the compressor 320 to perform normal compression
20 operation. In other words, the control unit 270 causes the
inverter 240 to apply, to the motor 310, the AC voltage at
a higher frequency than that when the motor 310 is in the
compression operation so as not to rotate the rotor in the
motor 310. Thus, the inverter 240 can apply the AC voltage
25 having high-frequency to the motor 310 so that the motor
310 is heated to vaporize the refrigerant that blends into
oil inside the compressor 320, thereby improving the
refrigerant stagnation.
[0015] The power supply 100 connected to the power
30 conversion apparatus 200 is the three-phase AC power supply
in the example of FIG. 2 but may be a single-phase AC power
supply. FIG. 3 is a diagram illustrating a second
configuration example of the power conversion apparatus 200
10
according to the first embodiment. FIG. 3 illustrates an
example in which the power supply 100 is the single-phase
AC power supply. The rectifier circuit 210 of the power
conversion apparatus 200 illustrated in FIG. 3 includes the
5 four diode elements 211 to 214, and rectifies or converts a
single-phase AC voltage supplied from the power supply 100
into a direct-current voltage. Moreover, the power
conversion apparatus 200 illustrated in FIG. 3 differs from
the power conversion apparatus 200 illustrated in FIG. 2 in
10 the installation position of the reactor 220 and the
current detection unit 260. No matter what the power
supply 100 is, the current detection unit 260 may be
disposed either in the position in FIG. 2 or the position
in FIG. 3. The power conversion apparatus 200 illustrated
15 in FIG. 3 in which the power supply 100 is the single-phase
AC power supply is described below as an example. In the
following description, the AC voltage that is supplied from
the power supply 100 to the rectifier circuit 210 may be
referred to as the first AC voltage, and the AC voltage
20 that is applied from the inverter 240 to the motor 310 may
be referred to as the second AC voltage.
[0016] A description is made for the PWM signals that
the control unit 270 of the power conversion apparatus 200
generates. FIG. 4 is a diagram illustrating an example of
25 the PWM signals that the control unit 270 of the power
conversion apparatus 200 according to the first embodiment
generates. The control unit 270 generates voltage command
signals Vu*, Vv*, and Vw* for the phases of the motor 310
on the basis of detection values obtained from the voltage
30 detection unit 250 and the current detection unit 260, and
generates the PWM signals UP, VP, WP, UN, VN, and WN for
the switching elements 241 to 246 of the inverter 240 on
the basis of comparison between the voltage command signals
11
Vu*, Vv*, and Vw* and a carrier signal. FIG. 4
specifically illustrates an example when the control unit
270 generates, for the U phase of the motor 310, the PWM
signal “UP” for the switching element 241 and the PWM
5 signal “UN” for the switching element 242 by comparing the
voltage command signal Vu* and the carrier signal. “Vdc”
in FIG. 4 is the bus voltage Vdc that is detected by the
voltage detection unit 250 and is the voltage across the
capacitor 230. Using the same method, the control unit 270
10 is capable of generating the PWM signals “VP” and “VN” for
the switching elements 243 and 244 that correspond to the V
phase of the motor 310 and the PWM signals “WP” and “WN”
for the switching elements 245 and 246 that correspond to
the W phase of the motor 310. By causing each of the
15 switching elements 241 to 246 of the inverter 240 to turn
on when the corresponding PWM signal is high and to turn
off when the corresponding PWM signal is low, the control
unit 270 can cause the inverter 240 to generate and apply,
to the motor 310, the AC voltage having the desired
20 frequency and the desired voltage value.
[0017] A description about capacitance of the capacitor
230 included in the power conversion apparatus 200 is made.
In a power conversion apparatus 200 that has a
configuration like FIG. 3, a capacitor 230 having a
25 relatively large capacitance is used when the capacitor 230
is used to smooth a direct-current voltage rectified by a
rectifier circuit 210 from an AC voltage. Since the power
conversion apparatus 200 stores the voltage that has
undergone the alternating-to-direct current conversion in
30 the rectifier circuit 210 in the larger-capacitance
capacitor 230, the power conversion apparatus 200 provides
an inverter 240 with a stable direct-current voltage, thus
can supply a constant voltage to be applied to the motor
12
310. However, when the capacitance of the capacitor 230 is
increased for the purpose of smoothing the direct-current
voltage, it may result in cost increase and size increase
of the power conversion apparatus 200. Moreover, due to a
5 circuit configuration of a capacitor 230 input type, a
current that flows through the power supply 100 causes
harmonics and a power supply is deteriorated. While the
power supply harmonics can be improved when the reactor 220
is made larger in size, it affects cost increase and size
10 increase of the power conversion apparatus 200 even in this
case.
[0018] If the capacitor 230 is made to have a smaller
capacitance to address the above problems, it is possible
to reduce cost, downsize the apparatus, improve the power
15 supply harmonics, etc. On the other hand, as the smaller
capacitance of the capacitor 230, a smaller amount of
energy stored in the capacitor 230. Accordingly, the
energy that the capacitor 230 can supply reduces faster if
the same amount of energy is required by the inverter 240,
20 the motor 310, or the like. Therefore, there are two
supply voltage paths for the inverter 240 in the power
conversion apparatus 200 in this case: “the direct-current
voltage supplied from the capacitor 230” and “the directcurrent voltage rectified from the power supply voltage”.
25 [0019] FIG. 5 is a diagram illustrating an example of
voltages and currents at parts in relation to switched
states of the switching elements 241, 243, and 245 of the
inverter 240 included in the power conversion apparatus 200
according to the first embodiment. FIG. 5(a) illustrates
30 the bus voltage Vdc, which is the voltage across the
capacitor 230, and the power supply voltage Vs of the power
supply 100. FIG. 5(b) illustrates the on-off operation of
the switching element 241 that is based on the PWM signal
13
“UP”. FIG. 5(c) illustrates the on-off operations of the
switching elements 243 and 245 that are based on the PWM
signals “VP” and “WP”. FIG. 5(d) illustrates the U-phase
motor current “Iu” that flows from the inverter 240 to the
5 motor 310. FIG. 5(e) illustrates the inverter input
current Idc that is input to the inverter 240, the
rectifier circuit output current Iin that is output from
the rectifier circuit 210, and the capacitor input current
Icc that is input to the capacitor 230. In FIG. 5(e), the
10 inverter input current Idc and the capacitor input current
Icc added becomes the rectifier circuit output current Iin.
In FIG. 5(e), a section labeled “REGENERATION” is a section
where a regenerative current flows from the motor 310 into
the capacitor 230. As illustrated in FIG. 5(a), the bus
15 voltage Vdc, which is the voltage across the capacitor 230,
increases in the section labeled “REGENERATION”.
[0020] During constraining energization, in which the
switching elements 241 to 246 of the inverter 240 undergoes
high-frequency switching under the control of the control
20 unit 270 in the power conversion apparatus 200, that is to
say, during motor induction heating, a large amount of
reactive current flows due to an inductance component of
the motor 310. For the current flowing in the motor 310,
there are conditions to flow as the regenerative current
25 into the capacitor 230 depending on the PWM signals for the
switching elements 241 to 246 of the inverter 240. For
example, if the capacitance of the capacitor 230 is large
enough and only the direct-current voltage supplied from
the capacitor 230 is the direct-current voltage to be
30 supplied to the inverter 240, the capacitor 230 is charged
with the regenerative current through the high-frequency
switching, and the voltage across the capacitor 230 that is
the bus voltage Vdc does not change significantly. On the
14
other hand, when the capacitance of the capacitor 230 is
small and the direct-current voltage for the inverter 240
is supplied through two paths, that is to say, “the directcurrent voltage supplied from the capacitor 230” and “the
5 direct-current voltage rectified from the power supply
voltage Vs”, the energy regeneratively flows into the
capacitor 230 after the state of the high-frequency
switching shifts from a zero-vector state to a real-vector
state until a current polarity is reversed.
10 [0021] The regenerative energy that flows into the
capacitor 230 includes energy from power supplied directly
from the power supply 100 to the motor 310. In the power
conversion apparatus 200, the regenerative current is
stored in the capacitor 230 instead of regeneratively
15 flowing to the power supply 100 due to the diode elements
211 to 214 of the rectifier circuit 210 , thus the bus
voltage Vdc increases in value. For the capacitor 230,
particularly if the capacitor 230 has a small capacitance,
the bus voltage Vdc may become an excessive value through
20 the regeneration.
[0022] The power conversion apparatus 200 according to
the present embodiment includes the capacitor 230 having a
relatively small capacitance for the purpose of reducing
cost, reducing size, ensuring reliability, improving the
25 power supply harmonics, etc. and thus on the assumption
that the two supply direct-current voltage paths for the
inverter 240 are present, namely “the direct-current
voltage supplied from the capacitor 230” and “the directcurrent voltage rectified from the power supply voltage Vs”.
30 The power conversion apparatus 200 improves the refrigerant
stagnation of the compressor 320 by heating the motor 310
through the high-frequency switching of the switching
elements 241 to 246 of the inverter 240, and also prevents
15
the voltage across the capacitor 230 from becoming
excessive during the high-frequency switching.
Specifically, a lower limit is set for the capacitance of
the capacitor 230 in the power conversion apparatus 200,
5 and regenerative power is to be consumed by such as a
control power supply. On the basis of this configuration,
the capacitance of the capacitor 230 is appropriately
selected for avoiding breakdowns of the capacitor 230, the
switching elements 241 to 246 of the inverter 240, etc.
10 that might be caused from an increase in bus voltage Vdc.
The control unit 270 of the power conversion apparatus 200
causes the inverter 240 to generate, with power supplied
directly from the rectifier circuit 210 to the inverter 240,
the AC voltage having high-frequency. In the power
15 conversion apparatus 200, the high-frequency AC voltage is
applied from the inverter 240 to the motor 310 and causes
the regenerative current, which results in the current flow
to the capacitor 230 without impairing the capacitor 230.
[0023] A description is provided about high-frequency
20 switching control that the power conversion apparatus 200
performs to remedy the refrigerant stagnation. On the
basis of temperatures of the compressor 320, the outdoor
heat exchanger 340, the indoor heat exchanger 360, the
refrigerant state, etc., the control unit 270 determines
25 whether or not the refrigerant stagnation has occurred
while operation of the compressor 320 is stopped. Upon
judging that the refrigerant stagnation has occurred, the
control unit 270 causes the inverter 240 to generate the
high-frequency AC voltage by using the PWM signals and
30 apply the high-frequency AC voltage to the motor 310. Thus,
the control unit 270 heats up the motor 310 inside the
compressor 320 by the induction heating due to the
inductance component of the motor 310 and heating from
16
copper loss due to a resistance component of the motor 310.
As a result, it becomes possible to eliminate the
refrigerant stagnation by heating the oil, the refrigerant,
etc., inside the compressor 320.
5 [0024] On the basis of the detection values obtained
from the voltage detection unit 250 and the current
detection unit 260, the control unit 270 generates the
voltage command signals Vu*, Vv*, and Vw* for the phases of
the motor 310 expressed in equations (1), (2), and (3):
10 [0025] Vu*=Acosθ ... (1)
Vv*=Acos[θ-2π/3] ... (2)
Vw*=Acos[θ+2π/3] ... (3)
[0026] The control unit 270 compares the voltage command
signals Vu*, Vv*, and Vw*, which have been obtained from
15 equations (1) to (3), to the carrier signal that has a
specified frequency and an amplitude Vdc/2 and generates
the PWM signals UP, VP, WP, UN, VN, and WN on the basis of
a magnitude relation, as illustrated in FIG. 4. The method
is not limited to the above method, and the control unit
20 270 may use two-phase modulation, third-harmonic
superposition modulation, spatial vector modulation, or
another method to generate the PWM signals UP, VP, WP, UN,
VN, and WN.
[0027] In the high-frequency switching that remedies the
25 refrigerant stagnation, the control unit 270 operates the
switching elements 241 to 246 of the inverter 240 at a
higher frequency than an operation frequency for the
compression operation to apply the high-frequency AC
voltage to the motor 310. The operation frequency for the
30 compression operation is a frequency lower than or equal to
1 kHz. Therefore, it becomes possible for the control unit
270 to efficiently heat up the motor 310 by utilizing iron
loss of the motor 310 through application of the high-
17
frequency AC voltage, copper loss caused by the current
flowing in windings of the motor 310, etc., without causing
rotational torque, vibration, etc., to the motor 310. When
the motor 310 is heated, the liquid refrigerant stagnating
5 in the compressor 320 is heated and vaporizes, and is
discharged out of the compressor 320. When such
refrigerant discharging has made by a specified amount or
has taken place for a specified time, the control unit 270
determines whether or not the state has restored to a
10 normal state from a stagnation state and upon judging that
the state has restored to the normal state, completes the
heating of the motor 310.
[0028] Furthermore, when the control unit 270 sets the
frequency of the high-frequency AC voltage to be applied
15 from the inverter 240 to the motor 310 at 14 kHz or greater,
it is possible to reduce noise because vibration sound of
an iron core of the motor 310 becomes almost out of an
audible range in this case. In addition, when the motor
310 is an interior permanent magnet motor, a rotor surface
20 crossed by a high-frequency magnetic flux also becomes a
part that generates heat, which results in increasing
contact area with refrigerant and speedily heating the
compressor mechanism. Thus, it is possible to efficiently
heat the refrigerant.
25 [0029] Since the power conversion apparatus 200
according to the present embodiment heats the motor 310 by
applying the high-frequency AC voltage from the inverter
240, the inductance component increases due to the high
frequency and winding impedance increases. Accordingly,
30 the current flowing in the windings of the motor 310 is
reduced, and thus the copper loss decreases. On the other
hand, the high-frequency AC voltage causes the iron loss ,
which enables effective heating by the power conversion
18
apparatus 200. Furthermore, since the current flowing in
the windings of the motor 310 is small, loss in the
inverter 240 is also small and the power conversion
apparatus 200 can perform heating with lesser loss.
5 [0030] Next description is about the current and the bus
voltage Vdc during the high-frequency switching, in
association with the capacitance of the capacitor 230 of
the power conversion apparatus 200. Current paths in the
power conversion apparatus 200 during the high-frequency
10 switching are explained first. FIG. 6 is a diagram
exemplary illustrating the PWM signals UP, VP, WP, UN, VN,
and WN for the switching elements 241 to 246 of the
inverter 240 included in the power conversion apparatus 200
according to the first embodiment, and the U-phase motor
15 current Iu that flows in the motor 310. A voltage vector
changes, depending on the PWM signals that the control unit
270 of the power conversion apparatus 200 generates for the
switching elements 241 to 246, in the order illustrated in
FIG. 6 as follows: V0(UP=VP=WP=0), V4(UP=1, VP=WP=0),
20 V7(UP=VP=WP=1), V3(UP=0, VP=WP=1), V0(UP=VP=WP=0). As
illustrated in FIG. 6, when the V4 vector is applied, the
motor current represented as +Iu flows. When the V3 vector
is applied, the motor current represented as -Iu flows in
the U-phase winding of the motor 310.
25 [0031] As illustrated in FIG. 4, patterns of the V4 and
V3 vectors appear during one carrier period (1/fc).
Therefore, the power conversion apparatus 200 is capable of
generating an AC synchronized with a carrier frequency fc.
FIGS. 7 to 12 illustrate the current paths when the voltage
30 vector changes from V0 vector, V4 vector, V7 vector, V3
vector, to V0 vector as illustrated in FIG. 6 in the power
conversion apparatus 200.
[0032] FIG. 7 is a diagram illustrating an example of
19
the current path when the power conversion apparatus 200
according to the first embodiment is in a V0 vector state.
For the V0 vector, the PWM signals for the switching
elements 241 to 246 of the inverter 240 satisfy UP=VP=WP=0
5 and UN=VN=WN=1. When the voltage vector is the V0 vector,
the current flows between the inverter 240 and the motor
310.
[0033] FIG. 8 is a first diagram illustrating an example
of the current path when the power conversion apparatus 200
10 according to the first embodiment is in a V4 vector state.
For the V4 vector, the PWM signals for the switching
elements 241 to 246 of the inverter 240 satisfy UP=VN=WN=1
and UN=VP=WP=0. FIG. 8 illustrates the V4 vector state and
a regenerative state. In the state of FIG. 8, the
15 regenerative current flows from the U phase of the motor
310 through the switching element 241 to the capacitor 230.
[0034] FIG. 9 is a second diagram illustrating an
example of the current path when the power conversion
apparatus 200 according to the first embodiment is in the
20 V4 vector state. FIG. 9 illustrates the V4 vector state
and a state in which the current flows to the inverter 240
from the power supply 100 through the rectifier circuit 210
as well as from the capacitor 230. In the state of FIG. 9,
due to the smaller capacitance of the capacitor 230, a
25 larger amount of current flows from the power supply 100
through the rectifier circuit 210 to the inverter 240, and
a smaller amount of current flows from the capacitor 230 to
the inverter 240.
[0035] FIG. 10 is a diagram illustrating an example of
30 the current path when the power conversion apparatus 200
according to the first embodiment is in a V7 vector state.
For the V7 vector, the PWM signals for the switching
elements 241 to 246 of the inverter 240 satisfy UP=VP=WP=1
20
and UN=VN=WN=0. When the voltage vector is the V7 vector,
the current flows between the inverter 240 and the motor
310.
[0036] FIG. 11 is a first diagram illustrating an
5 example of the current path when the power conversion
apparatus 200 according to the first embodiment is in a V3
vector state. For the V3 vector, the PWM signals for the
switching elements 241 to 246 of the inverter 240 satisfy
UP=VN=WN=0 and UN=VP=WP=1. FIG. 11 illustrates the V3
10 vector state and a regenerative state. In the state of FIG.
11, the regenerative current flows from the V phase and the
W phase of the motor 310 through the switching elements 243
and 245 to the capacitor 230.
[0037] FIG. 12 is a second diagram illustrating an
15 example of the current path when the power conversion
apparatus 200 according to the first embodiment is in the
V3 vector state. FIG. 12 illustrates the V3 vector state
and a state in which the current flows to the inverter 240
from the power supply 100 through the rectifier circuit 210
20 as well as from the capacitor 230. In the state of FIG. 12,
due to the smaller capacitance of the capacitor 230, a
larger amount of current flows from the power supply 100
through the rectifier circuit 210 to the inverter 240, and
a smaller amount of current flows from the capacitor 230 to
25 the inverter 240.
[0038] As the high-frequency AC voltage, a positive
voltage and a negative voltage are alternately applied from
the inverter 240 to the motor 310. Between application of
the positive voltage and the negative voltage, lines of the
30 motor 310 are short-circuited. The regenerative current
generates in the power conversion apparatus 200 according
to the present embodiment when the high-frequency AC
voltage is generated from an input voltage to the inverter
21
240 and is applied to the motor 310, as represented for the
V4 vector illustrated in FIG. 8 and the V3 vector
illustrated in FIG. 11. Specifically, with the highfrequency AC voltage output in the state of V4 and V3
5 vectors that are real vectors, the regenerative current
flows from the motor 310 to the capacitor 230 until the
current polarity reverses. As mentioned earlier, if the
power conversion apparatus 200 has the capacitor 230 having
larger-capacitance, the regenerative current as the charge
10 current for the capacitor 230 causes the voltage across the
capacitor 230 to rise gradually. However, as the
capacitance of the capacitor 230 of the power conversion
apparatus 200 becomes smaller, a rate of change of the
voltage across the capacitor 230 or the bus voltage Vdc
15 increases, even for the same regenerative current. The
rate of change ΔVcc of the voltage across the capacitor 230
is expressed by equation (4).
[0039] ΔVcc=1/C×(i*dt) ... (4)
[0040] In equation (4), C is the capacitance of the
20 capacitor 230, and i is the current that flows to the
capacitor 230. As equation (4) shows, even for the same
regenerative current that flows to the capacitor 230, the
voltage across the capacitor 230 becomes about 1000 times
greater when the capacitance C of the capacitor 230 is
25 reduced, for example, by a factor of 1000. If the voltage
across the capacitor 230 increases and exceeds a design
withstand voltage of the capacitor 230, it poses a risk of
breaking the capacitor 230. When a capacitor 230 having a
greater withstand voltage is used, cost of the power
30 conversion apparatus 200 may increase. As mentioned
earlier, the voltage across the capacitor 230 refers to the
bus voltage Vdc that is the input voltage for the inverter
240. If increased, the bus voltage Vdc may exceed a
22
withstand voltage of the inverter 240. Similarly to the
capacitor 230, introducing switching elements with greater
withstand voltages causes increase in the cost of the power
conversion apparatus 200.
5 [0041] Therefore, the capacitance of the capacitor 230
used in the power conversion apparatus 200 according to the
present embodiment is configured to have a capacitance that
is capable of fully absorbing the energy during the
regenerative-current generation, namely energy per phase
(1/2*L*i2 10 ) that is held by the inductance component of the
motor 310. It is to be noted that L is inductance in the
inductance component of the motor 310. With the
capacitance of the capacitor 230 used in the power
conversion apparatus 200 being specifically greater than or
15 equal to 10 uF, it is possible to reduce cost and size of
the power conversion apparatus 200, etc., while the
breakdowns of the elements used in the power conversion
apparatus 200 are avoided. Taking FIG. 5(a) as an example,
the power conversion apparatus 200 is configured such that
20 the bus voltage Vdc does not exceed a voltage at which the
element breakdown occurs even if the bus voltage Vdc
increases. With the capacitance of the capacitor 230 used
being smaller than or equal to 150 uF, the power conversion
apparatus 200 can also obtain an effect of improving power
25 factor in relation to harmonic. Consequently, for the
power conversion apparatus 200, it is possible to reduce
cost and size of the power conversion apparatus 200, etc.
while the breakdowns of the elements used in the power
conversion apparatus 200 are avoided, and further obtain
30 the effect of improving power factor in relation to
harmonics. The capacitor 230 is thus configured to have
the capacitance that prevents a rated voltage from being
exceeded due to power supplied from the motor 310 when the
23
switching elements 241 to 246 are in operation to apply the
high-frequency AC voltage from the inverter 240 to the
motor 310. Moreover, the capacitance of the capacitor 230
is set so that a power can be directly supplied from the
5 rectifier circuit 210 to the inverter 240.
[0042] Next, a hardware configuration of the control
unit 270 included in the power conversion apparatus 200 is
described. FIG. 13 is a diagram illustrating an example of
the hardware configuration that implements the control unit
10 270 of the power conversion apparatus 200 according to the
first embodiment. The control unit 270 is implemented with
a processor 91 and a memory 92.
[0043] The processor 91 is a central processing unit
(CPU) (also referred to as a processing unit, an arithmetic
15 unit, a microprocessor, a microcomputer, a processor, or a
digital signal processor (DSP)) or a system large-scale
integration (LSI). The memory 92 is, for example, a
nonvolatile or volatile semiconductor memory such as a
random-access memory (RAM), a read-only memory (ROM), a
20 flash memory, an erasable programmable read-only memory
(EPROM), or an electrically erasable programmable read-only
memory (EEPROM) (registered trademark). The memory 92 is
not limited to these and may be a magnetic disk, an optical
disk, a compact disk, a mini disk, or a digital versatile
25 disc (DVD).
[0044] As described above, when the refrigerant
stagnation has occurred in the compressor 320 used in the
air conditioner 300, etc. the power conversion apparatus
200 according to the present embodiment is capable of
30 remedying the refrigerant stagnation by having the inverter
240 apply, to the motor 310, the AC voltage having the high
frequency than in the compression operation. Moreover, the
capacitance of the capacitor 230 in the power conversion
24
apparatus 200 is configured to be small but capable of
storing the energy generated by the regenerative current
that generates and flows to the capacitor 230 when the
regenerative current is generated in the motor 310 by the
5 application of the high-frequency AC voltage from the
inverter 240 to the motor 310. In this way, the power
conversion apparatus 200 can obtain effects such as the
cost reduction, the size reduction, the reliability
assurance, and the improvement of the power supply
10 harmonics. The power conversion apparatus 200 can also
avoid the breakdowns of such as the capacitor 230 and the
switching elements 241 to 246 of the inverter 240 caused by
the increase of bus voltage Vdc. Thus the power conversion
apparatus 200 can avoid the effect on the elements of the
15 power conversion apparatus 200 that is caused from the
constraining energization control for getting rid of the
refrigerant stagnation, while reducing or preventing
increase in capacitance of the capacitor 230.
[0045] Second Embodiment.
20 In the first embodiment, the regenerative current
caused in the motor 310 has been assumed to flow to the
capacitor 230 through the inverter 240. In a second
embodiment, it is described that the regenerative current
caused in the motor 310 is used for other purposes.
25 [0046] FIG. 14 is a diagram illustrating a configuration
example of a power conversion apparatus 200a according to
the second embodiment. Compared with the power conversion
apparatus 200 according to the first embodiment that is
illustrated in FIG. 2 or 3, the power conversion apparatus
30 200a includes a diode element 281, a capacitor 282, and an
inverter 283 as additions. While the voltage detection
unit 250, the current detection unit 260, and the control
unit 270 are omitted in FIG. 14 for simplicity, the power
25
conversion apparatus 200a actually includes the voltage
detection unit 250, the current detection unit 260, and the
control unit 270.
[0047] The power conversion apparatus 200a includes,
5 between the capacitor 230 and the inverter 240 and in
parallel with the capacitor 230 and the inverter 240, a
circuit in which the diode element 281 and the capacitor
282 are connected in series. In other words, the capacitor
282 for the regenerative current is provided in parallel
10 with input ends of the inverter 240. The power conversion
apparatus 200a stores energy in the capacitor 282 with the
regenerative current caused in the motor 310, that is to
say, charges the capacitor 282. Using power charged in the
capacitor 282, the power conversion apparatus 200a can
15 control the inverter 283 to drive, for example, a motor 400
that drives a fan (not illustrated) in the air conditioner
300. Furthermore, the power conversion apparatus 200a uses
the power charged in the capacitor 282 to generate a
control power supply 500 for the air conditioner 300. By
20 using the regenerative current caused in the motor 310 in
this way, the power conversion apparatus 200a is capable of
reducing increase of the voltage across the capacitor 230,
namely the bus voltage Vdc. Capacitance of the capacitor
282 is configured to be greater than or equal to a
25 specified capacitance in relation to the capacitance of the
capacitor 230.
[0048] While the power conversion apparatus 200a
includes the capacitor 282 in addition to the capacitor 230
in this case, it is not limited thereto. The power
30 conversion apparatus 200a may use power charged in the
capacitor 230 to drive the motor 400 through control of the
inverter 283 or generate the control power supply 500.
[0049] Third Embodiment.
26
In the first embodiment, the regenerative current
caused in the motor 310 has been assumed to flow to the
capacitor 230 through the inverter 240. In a third
embodiment, it is described that the regenerative current
5 caused in the motor 310 flows to another circuit.
[0050] FIG. 15 is a diagram illustrating a configuration
example of a power conversion apparatus 200b according to
the third embodiment. Compared with the power conversion
apparatus 200 according to the first embodiment that is
10 illustrated in FIG. 2 or 3, the power conversion apparatus
200b includes a rectifier circuit 291, a switch 292, and a
capacitor 293 as additions. While the voltage detection
unit 250, the current detection unit 260, and the control
unit 270 are omitted in FIG. 15 for simplifying the
15 description, the power conversion apparatus 200b actually
includes the voltage detection unit 250, the current
detection unit 260, and the control unit 270.
[0051] In the power conversion apparatus 200b, the
rectifier circuit 291 rectifies the regenerative current
20 caused in the motor 310 to output to the capacitor 293.
The control unit 270 controls the switch 292 and has the
switch 292 turned on during a period when the capacitor 293
is charged with or absorb the regenerative current and a
period when power is supplied from the capacitor 293
25 through the rectifier circuit 291 to the motor 310. The
control unit 270 has the switch 292 turned off during
another period. By storing the regenerative current caused
in the motor 310 in this way, the power conversion
apparatus 200b is capable of reducing increase of the
30 voltage across the capacitor 230, namely the bus voltage
Vdc.
[0052] Moreover, setting the capacitor 293 at the same
capacitance as the capacitor 230 enables cost reduction of
27
the power conversion apparatus 200b, size reduction of the
power conversion apparatus 200b, etc.
[0053] The above configurations illustrated in the
embodiments are illustrative, can be combined with other
5 techniques that are publicly known, and can be partly
omitted or changed without departing from the gist. The
embodiments can be combined with each other.
Reference Signs List
10 [0054] 100 power supply; 200, 200a, 200b power
conversion apparatus; 210, 291 rectifier circuit; 211 to
216, 281 diode element; 220 reactor; 230, 282, 293
capacitor; 240, 283 inverter; 241 to 246 switching
element; 250 voltage detection unit; 260 current
15 detection unit; 270 control unit; 292 switch; 300 air
conditioner; 310, 400 motor; 320 compressor; 330 four-way
valve; 340 outdoor heat exchanger; 350 expansion valve;
360 indoor heat exchanger; 370 refrigerant piping; 500
control power supply.
20
28
We Claim:
[Claim 1] A power conversion apparatus comprising:
5 a rectifier circuit that rectifies a first
alternating-current voltage;
a reactor connected to the rectifier circuit;
a capacitor connected to an output end of the
rectifier circuit;
10 an inverter that generates a second alternatingcurrent voltage through operations of a plurality of
switching elements and applies the second alternatingcurrent voltage to a compressor motor including a stator
and a rotor, the inverter being connected to the capacitor;
15 and
a control unit that performs operation controls on the
plurality of switching elements, wherein
the control unit causes the inverter to apply, to the
compressor motor, the second alternating-current voltage
20 having a higher frequency than when the compressor motor is
in compression operation so as not to rotate the rotor, and
a regenerative current generates when the highfrequency second alternating-current voltage is applied
from the inverter to the compressor motor and a current
25 flows to the capacitor due to the regenerative current
without impairing the capacitor.
[Claim 2] The power conversion apparatus according to claim
1, wherein
30 the control unit causes the inverter to generate the
high-frequency second alternating-current voltage with
power supplied directly from the rectifier circuit to the
inverter.
29
[Claim 3] The power conversion apparatus according to claim
2, wherein
the capacitor is set at a capacitance to prevent
5 exceeding a rated voltage due to power supplied from the
compressor motor when the switching elements are in
operation for applying the high-frequency second
alternating-current voltage from the inverter to the
compressor motor.
10
[Claim 4] The power conversion apparatus according to claim
2 or 3, wherein
the capacitor is set at a capacitance that enables a
power supplying directly from the rectifier circuit to the
15 inverter.
[Claim 5] The power conversion apparatus according to any
one of claims 1 to 4, wherein
the high-frequency second alternating-current voltage
20 is applied alternately as a positive voltage and a negative
voltage from the inverter to the compressor motor, and
lines of the compressor motor are short-circuited between
application of the positive voltage and the negative
voltage.
25
[Claim 6] The power conversion apparatus according to any
one of claims 1 to 5, comprising
a capacitor for the regenerative current is provided
in parallel with an input end of the inverter, the
30 capacitor for the regenerative current having a capacitance
set greater than or equal to a specified capacitance.
[Claim 7] The power conversion apparatus according to any
30
one of claims 1 to 6, wherein
a regenerative current flows from the compressor motor
to the capacitor until a current polarity reverses while
the high-frequency second alternating-current voltage is
5 output in a state of real vector.
[Claim 8] An air conditioner comprising the power
conversion apparatus according to any one of claims 1 to 7.