FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
POWER CONVERSION DEVICE, MOTOR DRIVE UNIT, AND
REFRIGERATION CYCLE APPARATUS;
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION ORGANISED
AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE ADDRESS IS 7-3,
MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 100-8310, JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
2
DESCRIPTION
TITLE OF THE INVENTION:
POWER CONVERSION DEVICE, MOTOR DRIVE UNIT, AND
5 REFRIGERATION CYCLE APPARATUS
Field
[0001] The present disclosure relates to a power
conversion device that converts alternating current (AC)
10 power into desired power, to a motor drive unit, and to an
apparatus that utilizes a refrigeration cycle (hereinafter
referred to as refrigeration cycle apparatus).
Background
15 [0002] Power conversion devices have conventionally been
used that convert AC power supplied from an AC power supply
into desired AC power, and supply the resulting AC power to
a load such as an air conditioner. For example, Patent
Literature 1 discloses a technology in which a power
20 conversion device, which is an air conditioner control
device, rectifies AC power supplied from an AC power supply
in a diode stack, serving as a rectification unit, smooths
the power in a smoothing capacitor, converts the resulting
power into desired AC power in an inverter consisting of
25 multiple switching elements, and outputs the resulting AC
power to a compressor motor, which is a load.
Citation List
Patent Literature
30 [0003] Patent Literature 1: Japanese Patent Application
Laid-open No. H7-71805
Summary
3
Technical Problem
[0004] However, the above conventional technology causes
a high current to flow to the smoothing capacitor. This
presents a problem of faster aging degradation of the
5 smoothing capacitor. Possible countermeasures include
increasing of the capacitance of the smoothing capacitor to
reduce or prevent a ripple variation in the capacitor
voltage, and use of a smoothing capacitor having high
resistance to degradation caused by ripples. These
10 countermeasures, however, lead to an increase in cost of
components of the capacitor, and an increase in size of
apparatus.
[0005] The present disclosure has been made in view of
the foregoing, and it is an object of the present
15 disclosure to provide a power conversion device that
reduces degradation of the capacitor for smoothing, and can
also prevent an increase in size of apparatus.
Solution to Problem
20 [0006] In order to solve the above problem and achieve
the object, a power conversion device according to the
present disclosure includes: a rectification unit that
rectifies first alternating current power supplied from a
commercial power supply; a capacitor connected to an output
25 end of the rectification unit; an inverter that converts
power output from the rectification unit and from the
capacitor into second alternating current power, and
outputs the second alternating current power to a load
including a motor, the inverter being connected to both
30 ends of the capacitor; and a control unit that controls
operation of the inverter to output the second alternating
current power from the inverter to the load to reduce
current flowing to the capacitor, the second alternating
4
current power including a pulsation that depends on a
pulsation of power flowing from the rectification unit to
the capacitor, wherein no discharge circuit and no
overvoltage protection circuit are provided for the
5 capacitor
Advantageous Effects of Invention
[0007] A power conversion device according to the
present disclosure provides an advantage in reduction of
10 degradation of the capacitor for smoothing, and capability
to prevent an increase in size of apparatus.
Brief Description of Drawings
[0008] FIG. 1 is a diagram illustrating an example
15 configuration of a power conversion device according to a
first embodiment.
FIG. 2 is a diagram illustrating, as a comparative
example, an example of currents and of a capacitor voltage
of a capacitor in a smoothing unit when the current output
20 from the rectification unit is smoothed by the smoothing
unit to maintain the current flowing into the inverter to
be constant.
FIG. 3 is a diagram illustrating an example of
currents and of the capacitor voltage of the capacitor in
25 the smoothing unit when the control unit of the power
conversion device according to the first embodiment
controls the operation of the inverter to reduce the
current flowing into the smoothing unit.
FIG. 4 is a flowchart illustrating an operation of the
30 control unit included in the power conversion device
according to the first embodiment.
FIG. 5 is a diagram illustrating an example of
equivalent circuit when the inverter is stopped operating
5
in the power conversion device according to the first
embodiment.
FIG. 6 is a diagram illustrating examples of the
capacitor voltage when the inverter is stopped operating in
5 the power conversion device according to the first
embodiment.
FIG. 7 is a diagram illustrating differences between
the current flowing to the capacitor when control has not
been performed to reduce the current flowing to the
10 capacitor and the current flowing to the capacitor when
such control has been performed, in the power conversion
device according to the first embodiment.
FIG. 8 is a diagram illustrating an example of
hardware configuration that implements the control unit
15 included in the power conversion device according to the
first embodiment.
FIG. 9 is a diagram illustrating an example
configuration of a power conversion device according to a
second embodiment.
20 FIG. 10 is a flowchart illustrating an operation of
the control unit included in the power conversion device
according to the second embodiment.
FIG. 11 is a diagram illustrating differences between
the current flowing to the capacitor when control has not
25 been performed to reduce the current flowing to the
capacitor and the current flowing to the capacitor when
such control has been performed, in the power conversion
device according to the second embodiment.
FIG. 12 is a diagram illustrating an example
30 configuration of a power conversion device according to a
third embodiment.
FIG. 13 is a diagram illustrating an example
configuration of a power conversion device according to a
6
fourth embodiment.
FIG. 14 is a diagram illustrating an example
configuration of a refrigeration cycle apparatus according
to a fifth embodiment.
5
Description of Embodiments
[0009] A power conversion device, a motor drive unit,
and a refrigeration cycle apparatus according to
embodiments of the present disclosure will be described in
10 detail below with reference to the drawings.
[0010] First Embodiment.
FIG. 1 is a diagram illustrating an example
configuration of a power conversion device 1 according to a
first embodiment. The power conversion device 1 is
15 connected to a commercial power supply 110 and to a
compressor 315. The power conversion device 1 converts
first alternating current (AC) power having a supply
voltage Vs supplied from the commercial power supply 110
into second AC power having desired amplitude and phase,
20 and supplies the second AC power to the compressor 315.
The power conversion device 1 includes a voltage-current
detection unit 501, a reactor 120, a rectification unit
130, a voltage detection unit 502, a smoothing unit 200, an
inverter 310, current detection units 313a and 313b, and a
25 control unit 400. Note that the power conversion device 1
and a motor 314 included in the compressor 315 together
form a motor drive unit 2.
[0011] The voltage-current detection unit 501 detects a
voltage value and a current value of the first AC power
30 having the supply voltage Vs supplied from the commercial
power supply 110, and outputs the voltage value and the
current value detected to the control unit 400. The
reactor 120 is connected between the voltage-current
7
detection unit 501 and the rectification unit 130. The
rectification unit 130 includes a bridge circuit including
rectifying elements 131 to 134. The rectification unit 130
rectifies the first AC power having the supply voltage Vs
5 supplied from the commercial power supply 110, and outputs
the power resulting from rectification. The rectification
unit 130 performs full-wave rectification. The voltage
detection unit 502 detects a voltage value of the power
resulting from rectification performed by the rectification
10 unit 130, and outputs the voltage value detected to the
control unit 400. The smoothing unit 200 is connected to
an output end of the rectification unit 130 via the voltage
detection unit 502. The smoothing unit 200 includes a
capacitor 210, which functions as a smoothing element, to
15 smooth the power resulting from rectification performed by
the rectification unit 130. The capacitor 210 is, for
example, an electrolytic capacitor, a film capacitor, or
the like. The capacitor 210 has a capacitance sufficient
for smoothing the power resulting from rectification
20 performed by the rectification unit 130. The voltage
appearing on the capacitor 210 resulting from the smoothing
has a waveform shape including a voltage ripple dependent
on the frequency of the commercial power supply 110 being
superimposed on a direct current (DC) component, rather
25 than a waveform shape of a full-wave rectified voltage of
the commercial power supply 110, meaning that the voltage
appearing on the capacitor 210 resulting from the smoothing
does not have a high pulsation. This voltage ripple has a
frequency that is twice the frequency of the supply voltage
30 Vs when the commercial power supply 110 is of a singlephase type, and has a primary component that is six times
the frequency of the supply voltage Vs when the commercial
power supply 110 is of a three-phase type. In a condition
8
where the power input from the commercial power supply 110
and the power output from the inverter 310 do not change,
this voltage ripple has an amplitude that is determined
based on the capacitance of the capacitor 210. For
5 example, the voltage ripple appearing on the capacitor 210
pulsates in a range having the maximum value thereof that
is less than twice the minimum value thereof.
[0012] The inverter 310 is connected to both ends of the
smoothing unit 200, i.e., both ends of the capacitor 210.
10 The inverter 310 includes switching elements 311a to 311f
and freewheeling diodes (i.e. reflux diode) 312a to 312f.
The inverter 310 turns on or off the switching elements
311a to 311f under control of the control unit 400 to
convert the power output from the rectification unit 130
15 and from the smoothing unit 200 into second AC power having
desired amplitude and phase, and outputs the second AC
power to the compressor 315. The current detection units
313a and 313b each detect a current value of one of three
phase currents output from the inverter 310, and output the
20 current value detected to the control unit 400. Note that
obtaining current values of two phases of the three-phase
current output from the inverter 310 allows the control
unit 400 to calculate the current value of the other one
phase output from the inverter 310. The compressor 315 is
25 a load including the motor 314 for driving the compressor.
The motor 314 rotates according to the amplitude and phase
of the second AC power supplied from the inverter 310 thus
to perform compression operation. For example, when the
compressor 315 is a hermetic compressor for use in an
30 apparatus such as an air conditioner, the load torque of
the compressor 315 can often be considered as a constant
torque load.
[0013] Note that, in the power conversion device 1, the
9
arrangement of the components illustrated in FIG. 1 is
merely by way of example, and the arrangement of the
components is not limited to the example illustrated in
FIG. 1. For example, the reactor 120 may be disposed
5 downstream of the rectification 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 referred to as detection unit without
distinction. In addition, the voltage value and the
10 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
current detection units 313a and 313b may each be referred
to as detection value.
15 [0014] The control unit 400 obtains a voltage value and
a current value of the first AC power having the supply
voltage Vs from the voltage-current detection unit 501,
obtains a voltage value of the power resulting from
rectification performed by the rectification unit 130 from
20 the voltage detection unit 502, and obtains, from the
current detection units 313a and 313b, a current value of
the second AC power having desired amplitude and phase,
obtained by conversion performed by the inverter 310. The
control unit 400 controls the operation of the inverter
25 310, specifically, turning on or off of the switching
elements 311a to 311f included in the inverter 310, using a
detection value detected by each of the detection units.
In the present embodiment, the control unit 400 controls
the operation of the inverter 310 to output, from the
30 inverter 310 to the compressor 315, which is a load, the
second AC power including a pulsation that depends on the
pulsation of the power flowing from the rectification unit
130 to the capacitor 210 of the smoothing unit 200. An
10
example of pulsation that depends on the pulsation of the
power flowing to the capacitor 210 of the smoothing unit
200 is a pulsation that varies depending on a factor such
as the frequency of the pulsation of the power flowing to
5 the capacitor 210 of the smoothing unit 200. The control
unit 400 reduces the current flowing to the capacitor 210
of the smoothing unit 200 through such operation. Note
that the control unit 400 does not need to use all of the
detection values obtained from the respective detection
10 units, but may provide control using part of the detection
values. In the present embodiment, the power conversion
device 1 is configured such that the capacitor 210 and the
inverter 310 are connected in parallel with each other, and
does not include a discharge circuit or an overvoltage
15 protection circuit for the capacitor 210.
[0015] In this respect, a discharge circuit is a circuit
including an active element such as a switching element and
a resistor to control the connect-disconnect status of the
resistor for the capacitor 210 by turning on and off of the
20 active element. Thus, no resistor is included that is
connected in parallel with the capacitor 210 for a purpose
of smoothing the voltages of respective capacitors
connected in series, for a purpose of detecting the
capacitor voltage, or for another purpose. The resistor to
25 be included in the discharge circuit is used for a purpose
of discharging an electric charge in the capacitor 210 in a
certain time period, and thus, in one example, has a
resistance value in a range from several ohms (Ω) to
several hundred ohms (Ω) rather than a high resistance
30 value of, e.g., 1 kΩ or higher. One example of the
discharge circuit is a circuit including a switching
element and a resistor connected in series with each other,
and connected in parallel with the capacitor 210.
11
[0016] In addition, an overvoltage protection circuit is
a circuit that protects a device to prevent the voltage of
the capacitor 210 from increasing by a certain voltage or
more by regenerative power of the motor 314, by a
5 disturbance of a portion including the commercial power
supply 110, or by another cause. An overvoltage protection
circuit is not a snubber circuit for protecting a switching
element from a surge voltage generated upon switching of a
switching element. Examples of the type of snubber circuit
10 include an RC snubber including a resistor and a capacitor,
and a C snubber including only a capacitor. One example of
overvoltage protection circuit is a circuit including a
diode, a resistor, and a protection capacitor connected in
series with one another, and connected to the capacitor
15 210. Note that, in an overvoltage protection circuit, in
order to prevent the capacitor voltage from increasing, a
capacitance greater than a capacitor capacitance for a
snubber circuit is required, and a capacitor of 10 uF or
higher is required. In addition, a resistor is not
20 necessarily essential, and only a diode and a protection
capacitor may be used in series connection.
[0017] An operation of the control unit 400 included in
the power conversion device 1 will next be described. In
the power conversion device 1 of the present embodiment,
25 the load generated by the inverter 310 and the compressor
315 can be considered as a constant load, and the following
description therefore assumes that a constant current load
is connected to the smoothing unit 200 in view of the
current output from the smoothing unit 200. In this
30 respect, as illustrated in FIG. 1, the current flowing from
the rectification unit 130 is referred to as current I1,
the current flowing into the inverter 310 is referred to as
current I2, and the current flowing from the smoothing unit
12
200 is referred to as current I3. The current I2 is the
total current of the current I1 and the current I3. The
current I3 can be expressed as the difference between the
current I2 and the current I1, i.e., (current I2)–(current
5 I1). The direction of the current I3 is defined such that
the direction causing discharge of the smoothing unit 200
is the positive direction, and the direction causing charge
of the smoothing unit 200 is the negative direction. That
is, a current may flow into the smoothing unit 200 and may
10 flow out of the smoothing unit 200.
[0018] FIG. 2 is a diagram illustrating, as a
comparative example, an example of the currents I1 to I3
and a capacitor voltage Vdc of the capacitor 210 of the
smoothing unit 200 when the current output from the
15 rectification unit 130 is smoothed by the smoothing unit
200 to maintain the current I2 flowing into the inverter
310 to be constant. FIG. 2 illustrates, in order from top
to bottom, the current I1, the current I2, the current I3,
and the capacitor voltage Vdc of the capacitor 210
20 appearing depending on the current I3. The vertical axes
for the currents I1, I2, and I3 each represent a current
value, and the vertical axis for the capacitor voltage Vdc
represents a voltage value. The horizontal axes all
represent time t. Note that a carrier component of the
25 inverter 310, which is in fact superimposed on the currents
I2 and I3, is omitted here. This also applies to the
description and illustration given below. As illustrated
in FIG. 2, if the current I1 flowing from the rectification
unit 130 is smoothed by the smoothing unit 200 to a
30 sufficient degree in the power conversion device 1, the
current I2 flowing into the inverter 310 would have a
constant current value. However, a high current I3 flows
to the capacitor 210 of the smoothing unit 200, which
13
causes degradation. Accordingly, in the power conversion
device 1 of the present embodiment, the control unit 400
controls the current I2 flowing into the inverter 310, that
is, controls the operation of the inverter 310, to reduce
5 the current I3 flowing into the smoothing unit 200.
[0019] FIG. 3 is a diagram illustrating an example of
the currents I1 to I3 and the capacitor voltage Vdc of the
capacitor 210 of the smoothing unit 200 when the control
unit 400 of the power conversion device 1 according to the
10 first embodiment controls the operation of the inverter 310
to reduce the current I3 flowing into the smoothing unit
200. FIG. 3 illustrates, in order from top to bottom, the
current I1, the current I2, the current I3, and the
capacitor voltage Vdc of the capacitor 210 appearing
15 depending on the current I3. The vertical axes for the
currents I1, I2, and I3 each represent a current value, and
the vertical axis for the capacitor voltage Vdc represents
a voltage value. The horizontal axes all represent time t.
The control unit 400 of the power conversion device 1
20 controls the operation of the inverter 310 to cause the
current I2 such as one illustrated in FIG. 3 to flow into
the inverter 310, thereby reducing the frequency component
of the current flowing from the rectification unit 130 into
the smoothing unit 200 to a lower level than that of the
25 example of FIG. 2. This enables a reduction in the current
I3 flowing into the smoothing unit 200. Specifically, the
control unit 400 controls the operation of the inverter 310
to cause a current I2 including a pulsating current having
a primary component that is the frequency component of the
30 current I1 to flow into the inverter 310.
[0020] The frequency component of the current I1 is
determined based on the frequency of the AC current
supplied from the commercial power supply 110 and on the
14
configuration of the rectification unit 130. This enables
the control unit 400 to bring the frequency component of
the pulsating current superimposed on the current I2 to a
frequency component having predetermined amplitude and
5 phase. The frequency component of the pulsating current
superimposed on the current I2 has a waveform similar to
the waveform of the frequency component of the current I1.
As the control unit 400 causes the frequency component of
the pulsating current superimposed on the current I2 to
10 approach the frequency component of the current I1, the
current I3 flowing into the smoothing unit 200 is more
reduced, thereby enabling the pulsation voltage appearing
on the capacitor voltage Vdc to be more reduced.
[0021] The control operation performed by the control
15 unit 400 on a pulsation of the current flowing into the
inverter 310 through control of the operation of the
inverter 310 is equivalent to controlling a pulsation of
the first AC power output from the inverter 310 to the
compressor 315. The control unit 400 controls the
20 operation of the inverter 310 to reduce the pulsation
included in the second AC power output from the inverter
310 to less than the pulsation of the power output from the
rectification unit 130. The control unit 400 controls the
amplitude and phase of the pulsation included in the second
25 AC power output from the inverter 310 to reduce the voltage
ripple of the capacitor voltage Vdc, i.e., the voltage
ripple appearing on the capacitor 210, to less than the
voltage ripple appearing on the capacitor 210 of when the
second AC power output from the inverter 310 includes no
30 pulsation that depends on the pulsation of the power
flowing to the capacitor 210. The situation in which the
second AC power output from the inverter 310 includes no
pulsation that depends on the pulsation of the power
15
flowing to the capacitor 210 is a situation that is under a
control such as one illustrated in FIG. 2.
[0022] Note that the AC current supplied from the
commercial power supply 110 is not particularly limited,
5 and may be a single-phase current or a three-phase current.
The control unit 400 can determine the frequency component
of the pulsating current to be superimposed on the current
I2 according to the first AC power supplied from the
commercial power supply 110. Specifically, the control
10 unit 400 provides control to cause the pulsation waveform
of the current I2 flowing into the inverter 310 to have a
shape generated by addition of a DC component to a
pulsation waveform whose primary component is a frequency
component that is twice the frequency of the first AC power
15 when the first AC power supplied from the commercial power
supply 110 is of a single-phase type, or to a pulsation
waveform whose primary component is a frequency component
that is six times the frequency of the first AC power when
the first AC power supplied from the commercial power
20 supply 110 is of a three-phase type. The pulsation
waveform is assumed to be, for example, a shape
representing the absolute value of a sine wave or a shape
of a sine wave. In this case, the control unit 400 may
add, to the pulsation waveform, at least one frequency
25 component among the components that are each an integer
multiple of the frequency of the sine wave, as a predefined
amplitude. The pulsation waveform may otherwise have a
shape of a rectangular wave or a shape of a triangular
wave. In this case, the control unit 400 may use
30 predefined values for the amplitude and phase of the
pulsation waveform.
[0023] The control unit 400 may compute the magnitude of
the pulsation included in the second AC power output from
16
the inverter 310 using the voltage applied across the
capacitor 210 or the current flowing to the capacitor 210,
or using the voltage or current of the first AC power
supplied from the commercial power supply 110.
5 [0024] An operation of the control unit 400 will next be
described using a flowchart. FIG. 4 is a flowchart
illustrating an operation of the control unit 400 included
in the power conversion device 1 according to the first
embodiment. The control unit 400 obtains detection values
10 from the respective detection units of the power conversion
device 1 (step S1). The control unit 400 controls the
operation of the inverter 310 to reduce the current I3
flowing into the smoothing unit 200 based on the detection
values obtained (step S2).
15 [0025] In this operation, in the power conversion device
1 illustrated in FIG. 1, the capacitance C of the capacitor
210 is determined within a range of Formula (1), where L
[H] represents the inductance component in the power
conversion device 1, C [F] represents the capacitance of
20 the capacitor 210, Lm [H] represents the inductance
component for one phase of the motor 314, Vcmax [V]
represents the maximum voltage of the capacitor 210 in a
stationary state, Im [A] represents the maximum current
value of the motor 314, Is [A] represents the maximum
25 current value of the commercial power supply 110, and
Vdclim [V] represents the withstand voltage of the element
to which the capacitor voltage Vdc is applied.
[0026] Formula 1:
30 [0027] Note that the inductance component L in the power
conversion device 1 is a sum of an inductance component La
of the reactor 120 and a system impedance Lk. The system
17
impedance Lk includes a leakage from a transformer, a
parasitic inductance component of wiring, or the like. A
higher L value causes a greater increase in the capacitor
voltage Vdc. The value of the system impedance Lk is thus
5 assigned a maximum value conceivable in a practical use
environment. This also applies to the description given
below. In addition, the reactor 120 may be disposed, as
described above, downstream of the rectification unit 130,
that is, between the rectification unit 130 and the voltage
10 detection unit 502.
[0028] FIG. 5 is a diagram illustrating an example of
equivalent circuit when the inverter 310 is stopped
operating in the power conversion device 1 according to the
first embodiment. FIG. 5 illustrates a simplified
15 equivalent circuit. Thus, characteristics such as the
voltage of the commercial power supply 110 and the induced
voltage of the motor 314 are not simulated. FIG. 5 assumes
that the inverter 310 is stopped at a time of 50 ms, and
presents the current and voltage values at a time of 50 ms.
20 Some waveforms in conditions where the inverter 310 is
stopped operating when operating within and outside the
range given by Formula (1) are illustrated in FIG. 6. FIG.
6 is a diagram illustrating examples of the capacitor
voltage Vdc when the inverter 310 is stopped operating in
25 the power conversion device 1 according to the first
embodiment. FIG. 6(a) in the upper portion illustrates an
inverter stop signal from the control unit 400. FIG. 6(b)
in the lower portion illustrates the capacitor voltage Vdc.
Parameter values are as follows, by way of example: L=2
30 [mH], Is=15 [A], Lm=9 [mH], Im=15 [A], Vdclim=400 [V], and
Vcmax=310 [V]. The capacitance C of the capacitor 210 is
given as 20 [uF], which is a value outside the range of
Formula (1), 55 [uF], which is the value when the left-hand
18
side and the right-hand side of Formula (1) have an equal
value, and 100 [uF], which is a value within the range of
Formula (1) when the right-hand side of Formula (1) has a
large value.
5 [0029] As can also be seen in FIG. 6, use of the
capacitance C of the capacitor 210 within the range of
Formula (1) enables the power conversion device 1 to limit
the increased voltage to the withstand voltage Vdclim of
the element, thereby enabling a failure of the element to
10 be prevented. Note that L of Formula (1) may additionally
include an inductance component of an element such as a
filter not illustrated in FIG. 1, a system impedance, and
the like. In addition, Formula (1) is a simplified
formula, and may further include the induced voltage of the
15 motor 314, a voltage increase component due to the voltage
of the commercial power supply 110, and the like.
[0030] In the power conversion device 1 of the present
embodiment, the control unit 400 causes the output power of
the inverter 310 to pulsate based on the frequency of the
20 commercial power supply 110 as described above to reduce
the current of the capacitor 210. This enables the ripple
voltage of the capacitor 210 to be lower than the ripple
voltage provided by use of a control method that causes an
output power pulsation to flow at a constant value as in a
25 typical inverter. “Causing power to pulsate” means causing
the current of the inverter 310 to pulsate, and thus the
above description also means that the capacitance C of the
capacitor 210 can be reduced according to the pulsation of
the output current of the inverter 310. In addition,
30 causing the output of the inverter 310 to pulsate is
equivalent to causing the input current to the inverter 310
to pulsate.
[0031] In this operation, when the power conversion
19
device 1 is configured as illustrated in FIG. 1, the
current of the capacitor 210 pulsates at a frequency of
2fs, which is twice the frequency of the commercial power
supply 110, and the ripple voltage of the capacitor 210
5 also pulsates according to the frequency of 2fs as can also
be seen in FIG. 3 or the like. Thus, the allowable ripple
voltage can be determined based on the frequency of 2fs
with respect to the ripple voltage of the capacitor 210,
and the capacitance C of the capacitor 210 depends on the
10 value of the allowable ripple voltage. The capacitance C
of the capacitor 210 under the control of the present
embodiment will fall within the range of Formula (2), where
ΔV_2fs represents the allowable ripple voltage of the
capacitor 210 at the component of frequency 2fs, Ic_2fs
15 represents the current of the capacitor 210 at the
component of frequency 2fs when the output current of the
inverter 310 under normal control includes no pulsation at
the component of frequency 2fs, and Im_2fs represents the
pulsation of the input current of the inverter 310 at the
20 component of frequency 2fs when the control of the present
embodiment is performed.
[0032] Formula 2:
[0033] Note that Formula (2) uses the frequency 2fs as
25 the frequency that is twice the frequency of the commercial
power supply 110, but this frequency is not limited to the
frequency 2fs. The frequency 2fs may be replaced with a
frequency that is an integer multiple of the frequency 2fs.
Thus, satisfaction of the foregoing conditional
30 expressions, i.e., Formulae (1) and (2), allows the power
conversion device 1 to use the capacitor 210 having less
capacity without addition of a discharge circuit or an
20
overvoltage protection circuit to the capacitor 210.
[0034] As described above, in the power conversion
device 1, the capacitance C of the capacitor 210 is greater
than or equal to the capacitance of the capacitor 210 that
5 would be set in a case where an overvoltage protection
circuit will be connected to the capacitor 210. The
capacitance C of the capacitor 210 is determined by a value
calculated using the impedance of the reactor 120 disposed
in the power conversion device 1, the system impedance Lk,
10 the maximum current value Is of the commercial power supply
110, the inductance component Lm for one phase of the motor
314, the maximum current value Im of the motor 314, the
withstand voltage Vdclim of the element to which the
voltage from the capacitor 210 is applied, and the maximum
15 voltage Vcmax of the capacitor 210 in a stationary state.
The capacitance C of the capacitor 210 may be further
limited by the system voltage of the commercial power
supply 110 when the inverter 310 is out of operation, the
induced voltage of the motor 314, and/or the like. In
20 addition, the capacitance C of the capacitor 210 is less
than the capacitance C of the capacitor 210 that would be
set when first control is not performed, where the first
control is control of the operation of the inverter 310
performed by the control unit 400 to output, from the
25 inverter 310 to the load, the second AC power including a
pulsation that depends on the pulsation of the power
flowing from the rectification unit 130 to the capacitor
210. The capacitance C of the capacitor 210 is determined
by a value calculated using the frequency 2fs, which is the
30 frequency of the pulsation of the current of the capacitor
210, and is twice the frequency of the commercial power
supply 110; the allowable ripple voltage ΔV_2fs of the
capacitor 210 at the frequency 2fs that is twice the
21
frequency of the commercial power supply 110; the capacitor
current Ic_2fs of the capacitor 210 at the frequency that
is twice the frequency of the commercial power supply 110
when the control unit 400 does not perform the first
5 control; and the input current pulsation Im_2fs of the
inverter 310 at the frequency 2fs that is twice the
frequency of the commercial power supply 110 when the
control unit 400 performs the first control.
[0035] In addition, the power conversion device 1
10 illustrated in FIG. 1 has been described as simulating no
ripple current pulsation caused by switching of the
switching elements 311a to 311f included in the inverter
310. However, driving the inverter 310 in practice causes
a current having frequency components illustrated in FIG. 7
15 to flow to the capacitor 210. FIG. 7 is a diagram
illustrating differences between the current flowing to the
capacitor 210 when control has not been performed to reduce
the current flowing to the capacitor 210 and the current
flowing to the capacitor 210 when such control has been
20 performed, in the power conversion device 1 according to
the first embodiment. FIG. 7(a) in the upper portion
illustrates the case in which control has not been
performed to reduce the current flowing to the capacitor
210 in the power conversion device 1. FIG. 7(b) in the
25 lower portion illustrates the case in which control has
been performed to reduce the current flowing to the
capacitor 210 in the power conversion device 1. As can be
seen in FIG. 7, use of the control of the present
embodiment causes the capacitor current Ic_2fs to be
30 comparable to or less than a first capacitor current
Ic_2fcinv, where Ic_2fs is the capacitor current at the
frequency component that is twice the frequency of the
commercial power supply 110, and the first capacitor
22
current Ic_2fcinv is the capacitor current at the frequency
component that is twice a switching frequency fcinv of the
switching elements 311a to 311f included in the inverter
310. In this case, the current flowing to the capacitor
5 210 is limited as expressed by Formula (3).
[0036] Formula 3:
[0037] Note that Formula (3) uses the frequency 2fs as
the frequency that is twice the frequency of the commercial
10 power supply 110, but this frequency is not limited to the
frequency 2fs. The frequency 2fs may be replaced with a
frequency that is an integer multiple of the frequency 2fs.
Thus, satisfaction of the foregoing conditional expression,
i.e., Formula (3), allows the power conversion device 1 to
15 use a capacitor 210 having a low ripple current resistance
capacity. As described above, the capacitor current Ic_2fs
at the frequency component that is twice the frequency of
the commercial power supply 110, of the current flowing to
the capacitor 210, is less than or equal to the first
20 capacitor current Ic_2fcinv at the frequency component that
is twice the switching frequency of the switching elements
311a to 311f included in the inverter 310. The first
capacitor current Ic_2fcinv may include a current component
caused by rotation of the motor 314.
25 [0038] A hardware configuration of the control unit 400
included in the power conversion device 1 will next be
described. FIG. 8 is a diagram illustrating an example of
hardware configuration that implements the control unit 400
included in the power conversion device 1 according to the
30 first embodiment. The control unit 400 is implemented by a
set of a processor 91 and a memory 92.
[0039] The processor 91 is a central processing unit
(CPU) (also known as processing unit, computing unit,
23
microprocessor, microcomputer, processor, and digital
signal processor (DSP)) or a system large scale integration
(LSI). The memory 92 is, by way of example, a non-volatile
or volatile semiconductor memory such as a random access
5 memory (RAM), a read-only memory (ROM), a flash memory, an
erasable programmable read-only memory (EPROM), or an
electrically erasable programmable read-only memory
(EEPROM) (registered trademark). Note that the memory 92
is not limited thereto, and may be a magnetic disk, an
10 optical disk, a compact disc, a MiniDisc, or a digital
versatile disc (DVD).
[0040] As described above, in the power conversion
device 1 according to the present embodiment, the control
unit 400 controls the operation of the inverter 310 based
15 on detection values obtained from the respective detection
units, and superimposes, on the current I2 flowing into the
inverter 310, a pulsation having a frequency component that
depends on the frequency component of the current I1
flowing from the rectification unit 130, thereby reducing
20 the current I3 flowing into the smoothing unit 200. Thus,
the reduction in the current I3 flowing into the smoothing
unit 200 enables the power conversion device 1 to use a
capacitor having a ripple current resistance capacity less
than the ripple current resistance capacity of when the
25 control of the present embodiment is not performed. In
addition, a reduction in the pulsation voltage of the
capacitor voltage Vdc enables the power conversion device 1
to use therein a capacitor 210 having a capacitance less
than the capacitance of when the control of the present
30 embodiment is not performed. For example, in a case in
which the smoothing unit 200 includes multiple capacitors
210, the power conversion device 1 can reduce the number of
the capacitors 210 included in the smoothing unit 200.
24
[0041] Moreover, by performing the control of the
present embodiment, the power conversion device 1 can
reduce vibration of the compressor 315 that may occur due
to pulsation of the current I2.
5 [0042] Second Embodiment.
A second embodiment will be described with respect to
a case in which the power conversion device boosts the
voltage of the first AC power supplied from the commercial
power supply 110.
10 [0043] FIG. 9 is a diagram illustrating an example
configuration of a power conversion device 1a according to
the second embodiment. The power conversion device 1a is
connected to the commercial power supply 110 and to the
compressor 315. The power conversion device 1a converts
15 the first AC power having the supply voltage Vs supplied
from the commercial power supply 110 into the second AC
power having desired amplitude and phase, and supplies the
second AC power to the compressor 315. The power
conversion device 1a includes the voltage-current detection
20 unit 501, the rectification unit 130, the reactor 120, a
booster unit 600, the voltage detection unit 502, the
smoothing unit 200, the inverter 310, the current detection
units 313a and 313b, and the control unit 400. Note that,
in the power conversion device 1a, the rectification unit
25 130, the reactor 120, and the booster unit 600 together
form a rectification-boost unit 700. In addition, the
power conversion device 1a and the motor 314 included in
the compressor 315 together form a motor drive unit 2a.
[0044] The voltage-current detection unit 501 detects a
30 voltage value and a current value of the first AC power
having the supply voltage Vs supplied from the commercial
power supply 110, and outputs the voltage value and the
current value detected to the control unit 400. The
25
rectification unit 130 includes a bridge circuit including
the rectifying elements 131 to 134. The rectification unit
130 rectifies the first AC power having the supply voltage
Vs supplied from the commercial power supply 110, and
5 outputs the power resulting from rectification. The
reactor 120 is connected between the rectification unit 130
and the booster unit 600. The booster unit 600 includes a
switching element 611 and a rectifying element 621. The
booster unit 600 turns on or off the switching element 611
10 under control of the control unit 400 to boost the voltage
of the power output from the rectification unit 130, and
outputs the power having a boosted voltage to the smoothing
unit 200. In the present embodiment, the booster unit 600
is fully controlled by the control unit 400 using full
15 pulse amplitude modulation (PAM), which allows the
switching element 611 to be switched steplessly. The power
conversion device 1a uses the booster unit 600 to perform
control for improving the power factor of the commercial
power supply 110 thus to increase the capacitor voltage Vdc
20 of the capacitor 210 of the smoothing unit 200 to a voltage
higher than the supply voltage Vs. By using the
rectification unit 130 and the booster unit 600, the
rectification-boost unit 700 rectifies the first AC power
supplied from the commercial power supply 110 and boosts
25 the voltage of the first AC power supplied from the
commercial power supply 110. The rectification-boost unit
700 of the present embodiment is configured such that the
rectification unit 130 and the booster unit 600 are
connected in series with each other.
30 [0045] The voltage detection unit 502 detects a voltage
value of the power having a voltage boosted by the booster
unit 600, and outputs the voltage value detected to the
control unit 400. The smoothing unit 200 is connected to
26
an output end of the booster unit 600 via the voltage
detection unit 502. The smoothing unit 200 includes the
capacitor 210, which functions as a smoothing element, to
smooth the power having a voltage boosted by the booster
5 unit 600. The capacitor 210 is, for example, an
electrolytic capacitor, a film capacitor, or the like. The
capacitor 210 has a capacitance sufficient for smoothing
the power, resulting from rectification performed by the
rectification unit 130 and having a voltage boosted by the
10 booster unit 600. The voltage appearing on the capacitor
210 resulting from the smoothing has a waveform shape
including a voltage ripple dependent on the frequency of
the commercial power supply 110 being superimposed on a DC
component, rather than a waveform shape of a full-wave
15 rectified voltage of the commercial power supply 110,
meaning that the voltage appearing on the capacitor 210
resulting from the smoothing does not have a high
pulsation. This voltage ripple has a frequency that is
twice the frequency of the supply voltage Vs when the
20 commercial power supply 110 is of a single-phase type, and
has a primary component that is six times the frequency of
the supply voltage Vs when the commercial power supply 110
is of a three-phase type. In a condition where the power
input from the commercial power supply 110 and the power
25 output from the inverter 310 do not change, this voltage
ripple has an amplitude that is determined based on the
capacitance of the capacitor 210. For example, the voltage
ripple appearing on the capacitor 210 pulsates in a range
having a maximum value thereof that is less than twice a
30 minimum value thereof.
[0046] The inverter 310 is connected to both ends of the
smoothing unit 200, i.e., both ends of the capacitor 210.
The inverter 310 includes the switching elements 311a to
27
311f and the freewheeling diodes 312a to 312f. The
inverter 310 turns on or off the switching elements 311a to
311f under control of the control unit 400 to convert the
power output from the rectification-boost unit 700 and from
5 the smoothing unit 200 into the second AC power having
desired amplitude and phase, and outputs the second AC
power to the compressor 315. The current detection units
313a and 313b each detect a current value of one of three
phase currents output from the inverter 310, and output the
10 current value detected to the control unit 400. Note that
obtaining current values of two phases of the three-phase
current output from the inverter 310 allows the control
unit 400 to calculate the current value of the other one
phase output from the inverter 310. The compressor 315 is
15 a load including the motor 314 for driving the compressor.
The motor 314 rotates according to the amplitude and phase
of the second AC power supplied from the inverter 310 thus
to perform compression operation. For example, when the
compressor 315 is a hermetic compressor for use in an
20 apparatus such as an air conditioner, the load torque of
the compressor 315 can often be considered as a constant
torque load.
[0047] Note that, in the power conversion device 1a, the
arrangement of the components illustrated in FIG. 9 is
25 merely by way of example, and the arrangement of the
components is not limited to the example illustrated in
FIG. 9. The rectification-boost unit 700 does not
necessarily need to include the reactor 120 depending on
the disposition position of the reactor 120. In the
30 following description, the voltage-current detection unit
501, the voltage detection unit 502, and the current
detection units 313a and 313b may be referred to as
detection unit without distinction. In addition, the
28
voltage value and 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 current detection units 313a and
5 313b may each be referred to as detection value.
[0048] The control unit 400 obtains a voltage value and
a current value of the first AC power having the supply
voltage Vs from the voltage-current detection unit 501,
obtains a voltage value of the power having a voltage
10 boosted by the booster unit 600 from the voltage detection
unit 502, and obtains, from the current detection units
313a and 313b, a current value of the second AC power
having desired amplitude and phase, obtained by conversion
performed by the inverter 310. The control unit 400
15 controls the operation of the booster unit 600 of the
rectification-boost unit 700, specifically, turning on or
off of the switching element 611 included in the booster
unit 600, using a detection value detected by each of the
detection units. The control unit 400 also controls the
20 operation of the inverter 310, specifically, turning on or
off of the switching elements 311a to 311f included in the
inverter 310, using a detection value detected by each of
the detection units. In the present embodiment, the
control unit 400 controls the operation of the
25 rectification-boost unit 700. The control unit 400
controls the operation of the rectification-boost unit 700
to perform control for improving the power factor of the
first AC power supplied from the commercial power supply
110 and control of the average voltage of the capacitor 210
30 of the smoothing unit 200. The control unit 400 also
controls the operation of the inverter 310 to output, from
the inverter 310 to the compressor 315, which is a load,
the second AC power including a pulsation that depends on
29
the pulsation of the power flowing from the rectification
unit 130 to the capacitor 210 of the smoothing unit 200.
An example of pulsation that depends on the pulsation of
the power flowing to the capacitor 210 of the smoothing
5 unit 200 is a pulsation that varies depending on a factor
such as the frequency of the pulsation of the power flowing
to the capacitor 210 of the smoothing unit 200. The
control unit 400 reduces the current flowing to the
capacitor 210 of the smoothing unit 200 through such
10 operation. Note that the control unit 400 does not need to
use all of the detection values obtained from the
respective detection units, but may provide control using
part of the detection values.
[0049] An operation of the control unit 400 included in
15 the power conversion device 1a will next be described. The
control unit 400 operates similarly to the control unit 400
in the first embodiment. In the description of the second
embodiment, the current flowing from the rectification unit
130 of the first embodiment is to be read as the current
20 flowing from the booster unit 600.
[0050] The frequency component of the current I1 is
determined based on the frequency of the AC current
supplied from the commercial power supply 110, on the
configuration of the rectification unit 130, and on the
25 switching speed of the switching element 611 of the booster
unit 600. This enables the control unit 400 to bring the
frequency component of the pulsating current superimposed
on the current I2 to a frequency component having
predetermined amplitude and phase. The frequency component
30 of the pulsating current superimposed on the current I2 has
a waveform similar to the waveform of the frequency
component of the current I1. As the control unit 400
causes the frequency component of the pulsating current
30
superimposed on the current I2 to approach the frequency
component of the current I1, the current I3 flowing into
the smoothing unit 200 is more reduced, thereby enabling
the pulsation voltage appearing on the capacitor voltage
5 Vdc to be more reduced.
[0051] The control operation performed by the control
unit 400 on the pulsation of the current flowing into the
inverter 310 through control of the operation of the
inverter 310 is equivalent to controlling the pulsation of
10 the second AC power output from the inverter 310 to the
compressor 315. The control unit 400 controls the
operation of the inverter 310 to reduce the pulsation
included in the second AC power output from the inverter
310 to less than the pulsation of the power output from the
15 rectification-boost unit 700. The control unit 400
controls the amplitude and phase of the pulsation included
in the second AC power output from the inverter 310 to
reduce the voltage ripple of the capacitor voltage Vdc,
i.e., the voltage ripple appearing on the capacitor 210, to
20 less than the voltage ripple appearing on the capacitor 210
of when the second AC power output from the inverter 310
includes no pulsation that depends on the pulsation of the
power flowing to the capacitor 210. The situation in which
the second AC power output from the inverter 310 includes
25 no pulsation that depends on the pulsation of the power
flowing to the capacitor 210 is a situation that is under a
control such as one illustrated in FIG. 2.
[0052] In addition, when the control unit 400 controls
the inverter 310 to output, from the inverter 310 to the
30 compressor 315, the second AC power including a frequency
component different from the frequency component of the
first AC power supplied from the commercial power supply
110, the control unit 400 may superimpose the frequency
31
component included in the second AC power that is output
from the inverter 310 to the compressor 315, on a drive
signal for turning on or off to the switching element 611
of the booster unit 600. That is, the control unit 400
5 controls the operation of the rectification-boost unit 700,
specifically, the operation of the switching element 611 of
the booster unit 600, to output power including a variable
frequency component from the rectification-boost unit 700,
where the variable frequency component is different from a
10 frequency component that is twice the frequency of the
first AC power when the first AC power supplied from the
commercial power supply 110 is of a single-phase type, and
different from a frequency component that is six times the
frequency of the first AC power when the first AC power
15 supplied from the commercial power supply 110 is of a
three-phase type, of the power pulsation of the second AC
power output from the inverter 310 to the compressor 315.
The control unit 400 may control the variable frequency
component using a command value for the commercial power
20 supply 110, or may control the variable frequency component
to be not an integer multiple of up to 40th order of the
frequency of the first AC power supplied from the
commercial power supply 110, or to be less than or equal to
a predetermined value, e.g., a desired specification value.
25 [0053] An operation of the control unit 400 will next be
described using a flowchart. FIG. 10 is a flowchart
illustrating an operation of the control unit 400 included
in the power conversion device 1a according to the second
embodiment. The control unit 400 obtains detection values
30 from the respective detection units of the power conversion
device 1a (step S1). The control unit 400 controls the
operation of the inverter 310 to reduce the current I3
flowing into the smoothing unit 200 based on the detection
32
values obtained (step S2). The control unit 400 controls
the operation of the booster unit 600 to perform control
for improving the power factor of the commercial power
supply 110 and control of the average voltage of the
5 capacitor voltage Vdc of the capacitor 210 of the smoothing
unit 200, based on the detection values obtained (step S3).
[0054] Note that, similarly to the power conversion
device 1 of the first embodiment, the power conversion
device 1a of the second embodiment also determines the
10 capacitance C of the capacitor 210 within the ranges of
Formulae (1) and (2) above. When the power conversion
device 1a is configured as illustrated in FIG. 9, the
inductance component L in the power conversion device 1a is
a sum of an inductance component Lc of the reactor 120 for
15 boosting and the system impedance Lk.
[0055] In addition, similarly to the power conversion
device 1 of the first embodiment, the power conversion
device 1a of the second embodiment also limits the current
flowing to the capacitor 210. When the power conversion
20 device 1a illustrated in FIG. 9 drives the inverter 310 in
practice, a current having frequency components illustrated
in FIG. 7 flows to the capacitor 210 as described above.
In addition, when the power conversion device 1a
illustrated in FIG. 9 drives the booster unit 600 in
25 practice, a current having frequency components illustrated
in FIG. 11 flows to the capacitor 210. FIG. 11 is a
diagram illustrating differences between the current
flowing to the capacitor 210 when control has not been
performed to reduce the current flowing to the capacitor
30 210 and the current flowing to the capacitor 210 when such
control has been performed, in the power conversion device
1a according to the second embodiment. FIG. 11(a) in the
upper portion illustrates the case in which control has not
33
been performed to reduce the current flowing to the
capacitor 210 in the power conversion device 1a. FIG.
11(b) in the lower portion illustrates the case in which
control has been performed to reduce the current flowing to
5 the capacitor 210 in the power conversion device 1a. Note
that FIG. 11 omits the current pulsation components caused
by the inverter 310 illustrated in FIG. 7. As can be seen
in FIG. 11, use of the control of the present embodiment
causes the capacitor current Ic_2fs to be comparable to or
10 less than a second capacitor current Ic_fccnv, where Ic_2fs
is the capacitor current at the frequency component that is
twice the frequency of the commercial power supply 110, and
the second capacitor current Ic_fccnv is the capacitor
current at the frequency component of a switching frequency
15 fccnv of the switching element 611 included in the booster
unit 600. In this case, the current flowing to the
capacitor 210 is limited as expressed by Formula (4).
[0056] Formula 4:
20 [0057] Note that Formula (4) uses the frequency 2fs as
the frequency that is twice the frequency of the commercial
power supply 110, but this frequency is not limited to the
frequency 2fs. The frequency 2fs may be replaced with a
frequency that is an integer multiple of the frequency 2fs.
25 Thus, satisfaction of Formula (3) above, and the foregoing
conditional expression, i.e., Formula (4), allows the power
conversion device 1a to use a capacitor 210 having a low
ripple current resistance capacity. As described above,
when the power conversion device 1a includes the booster
30 unit 600, which boosts the voltage of the first AC power,
the capacitor current Ic_2fs at the frequency component
that is twice the frequency of the commercial power supply
110, of the current flowing to the capacitor 210, is less
34
than or equal to the second capacitor current Ic_fccnv at
the frequency component that is twice the switching
frequency of the switching element 611 included in the
booster unit 600. The second capacitor current Ic_fccnv
5 may include a current component caused by rotation of the
motor 314.
[0058] As described above, in the power conversion
device 1a according to the present embodiment, the control
unit 400 controls the operation of the inverter 310 based
10 on the detection values obtained from the respective
detection units, and superimposes, on the current I2
flowing into the inverter 310, a pulsation having a
frequency component that depends on the frequency component
of the current I1 flowing from the rectification unit 130,
15 thereby reducing the current I3 flowing into the smoothing
unit 200. Thus, the reduction in the current I3 flowing
into the smoothing unit 200 enables the power conversion
device 1a to use a capacitor having a ripple current
resistance capacity less than the ripple current resistance
20 capacity of when the control of the present embodiment is
not performed. In addition, a reduction in the pulsation
voltage of the capacitor voltage Vdc enables the power
conversion device 1a to use therein a capacitor 210 having
a capacitance less than the capacitance of when the control
25 of the present embodiment is not performed. For example,
in a case in which the smoothing unit 200 includes multiple
capacitors 210, the power conversion device 1a can reduce
the number of the capacitors 210 included in the smoothing
unit 200.
30 [0059] Moreover, by performing the control of the
present embodiment, the power conversion device 1a can
reduce vibration of the compressor 315 that may occur due
to pulsation of the current I2.
35
[0060] Furthermore, the boosting operation of the
booster unit 600 enables the power conversion device 1a to
increase the capacitor voltage Vdc of the capacitor 210,
and thus to increase the range of voltage that can be
5 output from the inverter 310. In the power conversion
device 1a, the control unit 400 superimposes, on the drive
signal for the switching element 611 of the booster unit
600, a frequency component of the pulsation included in the
second AC power output from the inverter 310, and can thus
10 reduce pulsations of the current I3 and of the capacitor
voltage Vdc caused by that frequency component.
[0061] Third Embodiment.
A third embodiment will be described with respect to a
power conversion device including a rectification-boost
15 unit having a circuit configuration different from the
circuit configuration of the rectification-boost unit 700
of the power conversion device 1a of the second embodiment.
[0062] FIG. 12 is a diagram illustrating an example
configuration of a power conversion device 1b according to
20 the third embodiment. The power conversion device 1b
includes a rectification-boost unit 701 in place of the
rectification-boost unit 700 of the power conversion device
1a of the second embodiment illustrated in FIG. 9. Note
that the power conversion device 1b and the motor 314
25 included in the compressor 315 together form a motor drive
unit 2b. The rectification-boost unit 701 includes
switching elements 611 to 614 and rectifying elements 621
to 624 connected in parallel with respective corresponding
ones of the switching elements 611 to 614. The
30 rectification-boost unit 701 turns on or off the switching
elements 611 to 614 under control of the control unit 400
to rectify and boost the first AC power output from the
commercial power supply 110, and outputs the power having a
36
boosted voltage to the smoothing unit 200. In the present
embodiment, the rectification-boost unit 701 is fully
controlled by the control unit 400 using full PAM, which
allows the switching elements 611 to 614 to be switched
5 continuously. The power conversion device 1b uses the
rectification-boost unit 701 to perform control for
improving the power factor of the commercial power supply
110 thus to increase the capacitor voltage Vdc of the
capacitor 210 of the smoothing unit 200 to a voltage higher
10 than the supply voltage Vs.
[0063] The control unit 400 obtains a voltage value and
a current value of the first AC power having the supply
voltage Vs from the voltage-current detection unit 501,
obtains a voltage value of the power having a voltage
15 boosted by the rectification-boost unit 701 from the
voltage detection unit 502, and obtains, from the current
detection units 313a and 313b, a current value of the
second AC power having desired amplitude and phase,
obtained by conversion performed by the inverter 310. The
20 control unit 400 controls the operation of the inverter
310, specifically, turning on or off of the switching
elements 311a to 311f included in the inverter 310, using a
detection value detected by each of the detection units.
In addition, the control unit 400 controls the operation of
25 the rectification-boost unit 701, specifically, turning on
or off the switching elements 611 to 614 included in the
rectification-boost unit 701, using a detection value
detected by each of the detection units. The control unit
400 controls the operation of the rectification-boost unit
30 701 and the operation of the inverter 310 to provide an
advantage similar to the advantage described in connection
with the first embodiment.
[0064] The other part of the operation of the power
37
conversion device 1b is similar to the corresponding part
of the operation of the power conversion device 1a of the
second embodiment. Also in this respect, the power
conversion device 1b can provide an advantage similar to
5 the advantage of the power conversion device 1a of the
second embodiment.
[0065] Note that the power conversion device 1b of the
third embodiment limits the range of the capacitance C of
the capacitor 210 and the current flowing to the capacitor
10 210 in a similar manner to the power conversion device 1a
of the second embodiment. When the power conversion device
1b is configured as illustrated in FIG. 12, the inductance
component L in the power conversion device 1b is a sum of
the inductance component La of the reactor 120 and the
15 system impedance Lk. Thus, when the power conversion
device 1b includes the rectification-boost unit 701, which
rectifies the first AC power supplied from the commercial
power supply 110, and boosts the voltage of the resulting
first AC power, the capacitor current Ic_2fs at the
20 frequency component that is twice the frequency of the
commercial power supply 110, of the current flowing to the
capacitor 210, is less than or equal to the second
capacitor current Ic_fccnv at the frequency component of
the switching frequency of the switching elements 611 to
25 614 included in the rectification-boost unit 701. The
second capacitor current Ic_fccnv may include a current
component caused by rotation of the motor 314.
[0066] Fourth Embodiment.
A fourth embodiment will be described with respect to
30 a power conversion device including a rectification-boost
unit having a circuit configuration different from the
circuit configuration of the rectification-boost unit 700
of the power conversion device 1a of the second embodiment
38
and from the circuit configuration of the rectificationboost unit 701 of the power conversion device 1b of the
third embodiment.
[0067] FIG. 13 is a diagram illustrating an example
5 configuration of a power conversion device 1c according to
the fourth embodiment. The power conversion device 1c
includes a rectification-boost unit 702 in place of the
rectification-boost unit 700 of the power conversion device
1a of the second embodiment illustrated in FIG. 9. Note
10 that the power conversion device 1c and the motor 314
included in the compressor 315 together form a motor drive
unit 2c. The rectification-boost unit 702 includes the
reactor 120, the rectification unit 130, and a booster unit
601. In contrast to the second embodiment, in which the
15 booster unit 600 is connected downstream of the
rectification unit 130, that is, connected in series with
the rectification unit 130 inside the power conversion
device 1a, the booster unit 601 in the fourth embodiment is
connected in parallel with the rectification unit 130
20 inside the power conversion device 1c. The booster unit
601 includes the rectifying elements 621 to 624 and the
switching element 611. The booster unit 601 turns on or
off the switching element 611 under control of the control
unit 400 to boost the voltage of the first AC power output
25 from the commercial power supply 110, and outputs the power
having a boosted voltage to the rectification unit 130. In
the present embodiment, the booster unit 601 of the
rectification-boost unit 702 is controlled by the control
unit 400 using simplified switching, in which the switching
30 element 611 is switched one or more times in every half
period of the frequency of the first AC power supplied from
the commercial power supply 110. The power conversion
device 1c uses the booster unit 601 to perform control for
39
improving the power factor of the commercial power supply
110 thus to increase the capacitor voltage Vdc of the
capacitor 210 of the smoothing unit 200 to a voltage higher
than the supply voltage Vs.
5 [0068] The control unit 400 obtains a voltage value and
a current value of the first AC power having the supply
voltage Vs from the voltage-current detection unit 501,
obtains a voltage value of the power resulting from
rectification performed by the rectification unit 130 from
10 the voltage detection unit 502, and obtains, from the
current detection units 313a and 313b, a current value of
the second AC power having desired amplitude and phase,
obtained by conversion performed by the inverter 310. The
control unit 400 controls the operation of the inverter
15 310, specifically, turning on or off of the switching
elements 311a to 311f included in the inverter 310, using a
detection value detected by each of the detection units.
The control unit 400 also controls the operation of the
booster unit 601, specifically, turning on or off of the
20 switching element 611 included in the booster unit 601,
using a detection value detected by each of the detection
units. The control unit 400 controls the operation of the
booster unit 601 and the operation of the inverter 310 to
provide an advantage similar to the advantage described in
25 connection with the second embodiment.
[0069] The other part of the operation of the power
conversion device 1c is similar to the corresponding part
of the operation of the power conversion device 1a of the
second embodiment. Also in this respect, the power
30 conversion device 1c can provide an advantage similar to
the advantage of the power conversion device 1a of the
second embodiment. In addition, the power conversion
device 1c reduces the number of switchings as compared to
40
the power conversion device 1a of the second embodiment and
to the power conversion device 1b of the third embodiment,
and can thus reduce a loss and noise. Moreover, the power
conversion device 1c is configured such that the
5 rectification unit 130 and the booster unit 601 are
connected in parallel with each other, and can thus reduce
the number of elements in conduction by not switching when
the switching element 611 needs no switching in the booster
unit 601, thereby allowing a reduction in loss.
10 [0070] Note that the power conversion device 1c of the
fourth embodiment limits the range of the capacitance C of
the capacitor 210 and the current flowing to the capacitor
210 in a similar manner to the power conversion device 1a
of the second embodiment. When the power conversion device
15 1c is configured as illustrated in FIG. 13, the inductance
component L in the power conversion device 1c is a sum of
the inductance component La of the reactor 120 and the
system impedance Lk.
[0071] Fifth Embodiment.
20 FIG. 14 is a diagram illustrating an example
configuration of a refrigeration cycle apparatus 900
according to a fifth embodiment. The refrigeration cycle
apparatus 900 according to the fifth embodiment includes
the power conversion device 1 described in the first
25 embodiment. The refrigeration cycle apparatus 900 may
include, in place of the power conversion device 1, the
power conversion device 1a described in the second
embodiment, the power conversion device 1b described in the
third embodiment, or the power conversion device 1c
30 described in the fourth embodiment. The refrigeration
cycle apparatus 900 according to the fifth embodiment is
usable in products including a refrigeration cycle, such as
an air conditioner, a refrigerator, a freezer, and a heat
41
pump water heater. Note that in FIG. 14, components having
functionality similar to the functionality in the first
embodiment are designated by the same reference characters
as those used in the first embodiment.
5 [0072] The refrigeration cycle apparatus 900 is
configured to include the compressor 315 incorporating the
motor 314 of the first embodiment, a four-way valve 902, an
indoor heat exchanger 906, an expansion valve 908, and an
outdoor heat exchanger 910, all of which are connected to
10 each other with a refrigerant pipe 912 interposed
therebetween.
[0073] The compressor 315 includes therein a compression
mechanism 904 for compressing a refrigerant, and the motor
314 for driving the compression mechanism 904.
15 [0074] The refrigeration cycle apparatus 900 is capable
of heating operation or cooling operation based on a
switching status of the four-way valve 902. The
compression mechanism 904 is driven by the motor 314 under
variable-speed control.
20 [0075] During heating operation, as indicated by the
solid line arrow, the refrigerant is compressed and
discharged by the compression mechanism 904, flows through
the four-way valve 902, the indoor heat exchanger 906, the
expansion valve 908, the outdoor heat exchanger 910, and
25 the four-way valve 902, and then returns to the compression
mechanism 904.
[0076] During cooling operation, as indicated by the
broken line arrow, the refrigerant is compressed and
discharged by the compression mechanism 904, flows through
30 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 then returns to the compression
mechanism 904.
42
[0077] During heating operation, the indoor heat
exchanger 906 functions as a condenser to release heat, and
the outdoor heat exchanger 910 functions as an evaporator
to absorb heat. During cooling operation, the outdoor heat
5 exchanger 910 functions as a condenser to release heat, and
the indoor heat exchanger 906 functions as an evaporator to
absorb heat. The expansion valve 908 decompresses and
expands the refrigerant.
[0078] The configurations described in the foregoing
10 embodiments are merely examples. These configurations may
be combined with a known other technology, and
configurations of different embodiments may be combined
together. Moreover, part of the configurations may be
omitted and/or modified without departing from the spirit
15 thereof.
Reference Signs List
[0079] 1, 1a, 1b, 1c power conversion device; 2, 2a,
2b, 2c motor drive unit; 110 commercial power supply; 120
20 reactor; 130 rectification unit; 131-134, 621-624
rectifying element; 200 smoothing unit; 210 capacitor;
310 inverter; 311a-311f, 611-614 switching element; 312a312f freewheeling diode; 313a, 313b current detection
unit; 314 motor; 315 compressor; 400 control unit; 501
25 voltage-current detection unit; 502 voltage detection
unit; 600, 601 booster unit; 700, 701, 702 rectificationboost unit; 900 refrigeration cycle apparatus; 902 fourway valve; 904 compression mechanism; 906 indoor heat
exchanger; 908 expansion valve; 910 outdoor heat
30 exchanger; 912 refrigerant pipe.
43
We Claim :
[Claim 1] A power conversion device comprising:
a rectification unit that rectifies first alternating
current power supplied from a commercial power supply;
5 a capacitor connected to an output end of the
rectification unit;
an inverter that converts power output from the
rectification unit and from the capacitor into second
alternating current power, and outputs the second
10 alternating current power to a load including a motor, the
inverter being connected to both ends of the capacitor; and
a control unit that controls operation of the inverter
to output the second alternating current power from the
inverter to the load to reduce current flowing to the
15 capacitor, the second alternating current power including a
pulsation that depends on a pulsation of power flowing from
the rectification unit to the capacitor, wherein
no discharge circuit and no overvoltage protection
circuit are provided for the capacitor.
20
[Claim 2] The power conversion device according to claim 1,
wherein
the capacitor has a capacitance greater than or equal
to a capacitance of the capacitor that would be set when an
25 overvoltage protection circuit is connected to the
capacitor.
[Claim 3] The power conversion device according to claim 2,
wherein
30 the capacitance of the capacitor is determined by a
value calculated using impedance of a reactor disposed in
the power conversion device, system impedance, a maximum
current value of the commercial power supply, an inductance
44
component for one phase of the motor, a maximum current
value of the motor, a withstand voltage of an element to
which a voltage from the capacitor is applied, and a
maximum voltage of the capacitor in a stationary state.
5
[Claim 4] The power conversion device according to claim 3,
wherein
the capacitance of the capacitor is further limited by
a system voltage of the commercial power supply when the
10 inverter is out of operation, and by an induced voltage of
the motor.
[Claim 5] The power conversion device according to any one
of claims 1 to 4, wherein
15 the capacitor has a capacitance less than a
capacitance of the capacitor that would be set when first
control is not performed, the first control being control
of operation of the inverter performed by the control unit
to output, from the inverter to the load, the second
20 alternating current power including a pulsation that
depends on a pulsation of power flowing from the
rectification unit to the capacitor.
[Claim 6] The power conversion device according to claim 5,
25 wherein
the capacitance of the capacitor is determined by a
value calculated using a frequency of pulsation of current
of the capacitor, the frequency being twice a frequency of
the commercial power supply, an allowable ripple voltage of
30 the capacitor at the frequency that is twice the frequency
of the commercial power supply, a capacitor current of the
capacitor at the frequency that is twice the frequency of
the commercial power supply when the control unit does not
45
perform the first control, and an input current pulsation
of the inverter at the frequency that is twice the
frequency of the commercial power supply when the control
unit performs the first control.
5
[Claim 7] The power conversion device according to any one
of claims 1 to 6, wherein
a capacitor current at a frequency component that is
twice the frequency of the commercial power supply, of the
10 current flowing to the capacitor, is less than or equal to
a first capacitor current at a frequency component that is
twice a switching frequency of a switching element included
in the inverter.
15 [Claim 8] The power conversion device according to claim 7,
wherein
the first capacitor current includes a current
component caused by rotation of the motor.
20 [Claim 9] The power conversion device according to claim 7
or 8, comprising:
a booster unit that boosts a voltage of the first
alternating current power, or in place of the rectification
unit, a rectification-boost unit that rectifies the first
25 alternating current power supplied from the commercial
power supply, and boosts the voltage of the first
alternating current power, wherein
the capacitor current at the frequency component that
is twice the frequency of the commercial power supply, of
30 the current flowing to the capacitor, is less than or equal
to a second capacitor current at a frequency component that
is twice a switching frequency of a switching element
included in the booster unit or in the rectification-boost
46
unit.
[Claim 10] The power conversion device according to
claim 9, wherein
5 the second capacitor current includes a current
component caused by rotation of the motor.
[Claim 11] The power conversion device according to any
one of claims 1 to 10, wherein
10 the capacitor is an electrolytic capacitor or a film
capacitor.
[Claim 12] The power conversion device according to any
one of claims 1 to 11, wherein
15 a voltage ripple appearing on the capacitor has a
maximum value thereof less than twice a minimum value
thereof.
[Claim 13] The power conversion device according to any
20 one of claims 1 to 8, wherein
the rectification unit performs full-wave
rectification, and a voltage appearing on the capacitor
does not have a waveform shape of a full-wave rectified
voltage of the commercial power supply.
25
[Claim 14] The power conversion device according to any
one of claims 1 to 13, wherein
the discharge circuit includes an active element and a
resistor, and switches a connect-disconnect status of the
30 resistor for the capacitor by turning on or off of the
active element.
[Claim 15] The power conversion device according to any
47
one of claims 1 to 14, wherein
the overvoltage protection circuit protects a device
to prevent a voltage of the capacitor from increasing by a
certain voltage or more, the overvoltage protection circuit
5 not being a snubber circuit that protects a switching
element from a surge voltage generated upon switching of a
switching element.
[Claim 16] A motor drive unit comprising the power
10 conversion device according to any one of claims 1 to 15.
[Claim 17] A refrigeration cycle apparatus comprising
the power conversion device according to any one of claims
1 to 15.