DESCRIPTION
FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
POWER CONVERTING APPARATUS, HEAT PUMP 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, 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
Field
[0001] The present disclosure relates to a power
5 converting apparatus that converts alternating-current
power into direct-current power, a heat pump apparatus, and
an air conditioner.
Background
10 [0002] Conventionally, damage due to overvoltage of a
circuit element connected to an output bus of a rectifier
is prevented while harmonic components in an input power
source current are reduced without using a capacitor with a
high capacitance. Patent Literature 1 discloses a
15 technique in which a value of a capacitance C [F] of a
smoothing capacitor satisfies “443×10-6·Pm/Vac2≤C≤1829×10-
6·Pm/Vac2”, where Vac [V] is a power supply voltage of a
three-phase alternating-current power supply, and Pm [W] is
power to be consumed by a three-phase alternating-current
20 motor.
Citation List
Patent Literature
[0003] Patent Literature 1: Japanese Patent Application
25 Laid-open No. 2012-157242
Summary of Invention
Problem to be solved by the Invention
[0004] According to the conventional technique above,
30 the inverter device of Patent Literature 1 uses a capacitor
with a capacitance of 110.8 uF to 457.3 uF when power to be
consumed by the three-phase alternating-current motor is 10
kW. Since the inverter device of Patent Literature 1 uses
3
a capacitor with a capacitance lower than that of a
generally used capacitor, charging and discharging current
of the capacitor, that is, ripple current increases.
Therefore, there has been a problem that when an
5 electrolytic capacitor, which is a life-limited component,
is used, heat generation increases and this adversely
affects the life of the electrolytic capacitor. In the
inverter device of Patent Literature 1, it is also possible
to use a film capacitor with a high current ripple
10 tolerance so as to increase the life. However, a film
capacitor is more expensive than an electrolytic capacitor,
so that an increase in cost cannot be avoided.
[0005] The present disclosure has been made in view of
the above, and an object of the present disclosure is to
15 obtain a power converting apparatus capable of reducing
ripple current of a capacitor and prolonging the life of
the capacitor.
Means to Solve the Problem
20 [0006] In order to solve the above-described problems
and achieve the object, a power converting apparatus
according to the present disclosure includes: a rectifier
that rectifies alternating-current power output from an
alternating-current power supply; a capacitor provided at
25 an output end of the rectifier; a reactor provided on a
path from the alternating-current power supply to the
capacitor; a load connected across the capacitor; and a
control unit that reduces a charging and discharging
current of the capacitor by controlling an operation state
30 of the load such that power pulsation occurs in power to be
consumed by the load. A range of an inductance value of
the reactor is defined by use of a maximum value of an
output voltage of the rectifier, a minimum value of the
4
output voltage of the rectifier, a direct-current component
of output power of the load, a number of phases of the
alternating-current power supply, and an angular frequency
of the alternating-current power supply.
5
Effects of the Invention
[0007] The power converting apparatus according to the
present disclosure has the effect of enabling reduction of
ripple current of a capacitor and prolongation of the life
10 of the capacitor.
Brief Description of Drawings
[0008] FIG. 1 is a diagram showing a configuration
example of a power converting apparatus according to a
15 first embodiment.
FIG. 2 is a diagram showing an example of an output
voltage of a rectifier of the power converting apparatus
according to the first embodiment.
FIG. 3 is a diagram showing an example of output power
20 of a load of the power converting apparatus according to
the first embodiment.
FIG. 4 is a diagram illustrating a relationship
between an alternating-current component of the output
power of the load and ripple current of a capacitor in the
25 power converting apparatus according to the first
embodiment.
FIG. 5 is a diagram illustrating a relationship
between an inductance value of a reactor and the ripple
current of the capacitor in the power converting apparatus
30 according to the first embodiment.
FIG. 6 is a diagram showing, as a comparative example,
an example of results of analysis performed when the power
converting apparatus does not change the output power of
5
the load.
FIG. 7 is a diagram showing an example of results of
analysis performed when the power converting apparatus
according to the first embodiment changes the output power
5 of the load to reduce a charging and discharging current of
the capacitor.
FIG. 8 is a diagram illustrating a relationship
between the inductance value of the reactor and the
alternating-current component of the output power of the
10 load in the power converting apparatus according to the
first embodiment.
FIG. 9 is a flowchart illustrating operation of the
power converting apparatus according to the first
embodiment.
15 FIG. 10 is a diagram showing an example of a hardware
configuration for implementing a control unit included in
the power converting apparatus according to the first
embodiment.
FIG. 11 is a diagram showing a configuration example
20 of an air conditioner according to a second embodiment.
FIG. 12 is a diagram illustrating a circuit
configuration of a heat pump apparatus according to the
second embodiment.
FIG. 13 is a Mollier chart illustrating the state of a
25 refrigerant in the heat pump apparatus according to the
second embodiment.
Description of Embodiments
[0009] Hereinafter, a power converting apparatus, a heat
30 pump apparatus, and an air conditioner according to
embodiments of the present disclosure will be described in
detail with reference to the drawings.
6
[0010] First Embodiment.
FIG. 1 is a diagram showing a configuration example of
a power converting apparatus 100 according to a first
embodiment. The power converting apparatus 100 is
5 connected to an alternating-current power supply 10, and
converts alternating-current power output from the
alternating-current power supply 10 into direct-current
power. The power converting apparatus 100 includes a
rectifier 20, a reactor 30, a capacitor 33, a load 40, and
10 a control unit 45. The reactor 30 includes an inductance
component 31 and a resistance component 32.
[0011] The alternating-current power supply 10 outputs
alternating-current power to the power converting apparatus
100. The alternating-current power supply 10 is described
15 as a three-phase power supply in the example of FIG. 1, but
may be a single-phase power supply. In a case where the
alternating-current power supply 10 is a single-phase power
supply, two wires are provided between the alternatingcurrent power supply 10 and the rectifier 20, and a single20 phase rectifier is used as the rectifier 20. A powersupply frequency f of the alternating-current power supply
10 may be 50 Hz or 60 Hz as with a general commercial power
supply, or may be another frequency.
[0012] The rectifier 20 rectifies the alternating25 current power output from the alternating-current power
supply 10. The rectifier 20 outputs the rectified power to
the capacitor 33 connected to an output end of the
rectifier 20. The rectifier 20 is a circuit including a
plurality of diodes, but the circuit configuration of the
30 rectifier 20 is not limited thereto.
[0013] The reactor 30 is located between and connected
to the rectifier 20 and the capacitor 33 in the example of
FIG. 1, but may be located between and connected to the
7
alternating-current power supply 10 and the rectifier 20.
In a case where the reactor 30 is located between and
connected to the rectifier 20 and the alternating-current
power supply 10 that is a three-phase power supply, three
5 reactors 30 are required. This is because the reactor 30
is inserted on each line. That is, the reactor 30 is
provided on a path from the alternating-current power
supply 10 to the capacitor 33.
[0014] The capacitor 33 is provided at the output end of
10 the rectifier 20. Note that, in the example of FIG. 1, the
capacitor 33 is connected to the output end of the
rectifier 20 via the reactor 30.
[0015] The load 40 is connected across the capacitor 33.
The load 40 is not particularly limited as long as the load
15 40 is a load using direct-current power. Although not
illustrated, it is assumed here, as an example, that the
load 40 includes an inverter that converts direct-current
power into alternating-current power, and an inductive load
such as a motor.
20 [0016] The control unit 45 controls operation of the
power converting apparatus 100. Specifically, the control
unit 45 reduces charging and discharging current of the
capacitor 33 by controlling the operation state of the load
40 such that power pulsation occurs in power to be consumed
25 by the load 40. Note that although not illustrated in FIG.
1, the power converting apparatus 100 includes detection
units capable of detecting an output voltage Vdb of the
rectifier 20, a voltage Vdc across the capacitor 33, a
current Ic flowing through the capacitor 33, a current Iz
30 flowing through the load 40, and the like, and the control
unit 45 controls the operation state of the load 40 on the
basis of respective results of detection performed by the
detection units.
8
[0017] Note that the power converting apparatus 100 can
also be applied to a power converting apparatus equipped
with a power factor correction circuit, a booster circuit,
or the like.
5 [0018] FIG. 2 is a diagram showing an example of the
output voltage Vdb of the rectifier 20 of the power
converting apparatus 100 according to the first embodiment.
In FIG. 2, the horizontal axis represents time and the
vertical axis represents voltage. As illustrated in FIG. 2,
10 when the output voltage Vdb of the rectifier 20 is
approximated by a cosine wave that is twice the product of
the number P of phases of the alternating-current power
supply 10 and an angular frequency ω of the alternatingcurrent power supply 10, the output voltage Vdb is
15 expressed by formula (1).
[0019] Formula 1:
[0020] In formula (1), Vmax denotes the maximum value of
the output voltage of the rectifier 20, and Vmin denotes the
20 minimum value of the output voltage of the rectifier 20.
Note that the angular frequency ω of the alternatingcurrent power supply 10 is expressed by ω=2πf, where f is
the power-supply frequency of the alternating-current power
supply 10. In addition, in the power converting apparatus
25 100 illustrated in FIG. 1, circuit equations are expressed
by formulas (2) to (4) below. Note that in a case where
the alternating-current power supply 10 is a three-phase
power supply, Vmax may be defined as the maximum value of
line voltage of the power supply voltage, and Vmax×cos30°
30 may be substituted for Vmin. In addition, in a case where
the alternating-current power supply 10 is a single-phase
power supply, Vmax may be defined as the maximum value of
9
the power supply voltage, and Vmin may be set such that
Vmin=0.
[0021] Formula 2:
5 [0022] Formula 3:
[0023] Formula 4:
[0024] In formulas (2) to (4), Vdc denotes the voltage
10 across the capacitor 33, R denotes the resistance component
32 of the reactor 30, that is, a resistance value, Idc
denotes a current flowing through the reactor 30, L denotes
the inductance component 31 of the reactor 30, that is, an
inductance value, Iz denotes the current flowing through
15 the load 40, Pout denotes output power of the load 40, and C
denotes the electrostatic capacitance of the capacitor 33.
Note that formula (4) represents the current Ic flowing
through the capacitor 33. Here, when it is assumed that
there is no charging or discharging of the capacitor 33 and
20 the capacitor 33 operates with the voltage Vdc across the
capacitor 33 kept at a constant level at the center of the
amplitude of the output voltage Vdb of the rectifier 20,
formulas (5) and (6) are established. Formulas (5) and (6)
represent a state in which the output voltage Vdb of the
25 rectifier 20 is directly supplied to the load 40 without
being stored in the capacitor 33.
[0025] Formula 5:
[0026] Formula 6:
10
[0027] Formula (7) is obtained by transformation of
formula (1).
[0028] Formula 7:
5
[0029] Here, assuming that Vdb-Vdc>>RIdc, formulas (1) and
(6) are substituted into formula (7). Then, formula (8) is
obtained. In formula (8), Const is an integration constant.
[0030] Formula 8:
10
[0031] Based on formulas (3), (5), and (8), the output
power Pout of the load 40 for reducing the charging and
discharging current of the capacitor 33 is obtained as
expressed by formula (9). Here, a first term on the right
15 side of formula (9) is an alternating-current component
that changes, and a second term on the right side is a
direct-current component. Therefore, if the output power
Pout of the load 40 is changed by means of a pulsation
command of 2Pωt, the current Ic flowing through the
20 capacitor 33 can be reduced. Note that the first term on
the right side of formula (9) applies to a case where the
charging and discharging current of the capacitor 33 is
controlled and kept at substantially zero, and in a case
where the charging and discharging current is not
25 controlled and kept at substantially zero, the alternatingcurrent component may be set to an amplitude equal to or
less than the value obtained in the first term on the right
side of formula (9).
11
[0032] Formula 9:
[0033] FIG. 3 is a diagram showing an example of the
output power Pout of the load 40 of the power converting
5 apparatus 100 according to the first embodiment. In FIG. 3,
the horizontal axis represents time, and the vertical axis
represents voltage. An alternating-current component Pout_ac
of the output power Pout of the load 40 is expressed by
formula (10). The alternating-current component Pout_ac of
10 the output power Pout of the load 40 is power pulsation
caused in power to be consumed by the load 40.
[0034] Formula 10:
[0035] As illustrated in FIG. 3, an amplitude
15 corresponding to a direct-current component of zero is a
limit value of the alternating-current component Pout_ac of
the output power Pout of the load 40. That is, formula (11)
represents the integration constant Const that causes the
output power Pout of the load 40 to become zero (Pout=0) when
20 sin{(2P)ωt}=-1.
[0036] Formula 11:
[0037] A direct-current component Pout_dc of the output
power Pout of the load 40 is expressed by formula (12) based
25 on formulas (9) and (11).
[0038] Formula 12:
[0039] Therefore, it is possible to reduce the charging
12
and discharging current of the capacitor 33 by ensuring the
inductance value L of the reactor 30 equal to or greater
than a value shown in formula (13) in the direct-current
component Pout_dc of the output power Pout of the load 40,
5 which is the average power of the output power Pout of the
load 40.
[0040] Formula 13:
[0041] Here, in a case where the integration constant
10 Const is obtained which causes the output power Pout of the
load 40 to become zero (Pout=0) when sin{(2P)ωt}=-1, the
output power Pout of the load 40 changes in a range shown in
formula (14), based on formulas (9) and (11). Therefore,
when the load 40 is a motor or the like, rotation speed or
15 the like may greatly fluctuate to adversely affect the
operation of the power converting apparatus 100.
[0042] Formula 14:
[0043] Thus, there is a case where it is desired to set
20 the alternating-current component to, for example, 1/α of
rated power in the power converting apparatus 100. However,
when controlling and keeping the charging and discharging
current of the capacitor 33 at substantially zero, the
power converting apparatus 100 needs to ensure an
25 alternating-current component based on formula (14), that
is, a first term on the right side. Therefore, assuming
that the output power Pout of the load 40 is 1-(1/α) when
sin{(2P)ωt}=-1 in a case where the amplitude of the
alternating-current component is 1/α of the direct-current
30 component, the integration constant Const is expressed by
13
formula (15).
[0044] Formula 15:
[0045] Thus, the direct-current component Pout_dc of the
5 output power Pout of the load 40 is expressed by formula
(16) based on formula (15). Accordingly, the output power
Pout of the load 40 is expressed by formula (17).
[0046] Formula 16:
10 [0047] Formula 17:
[0048] Here, in order to reduce the charging and
discharging current of the capacitor 33, it is important to
cause the output power Pout of the load 40 to pulsate with
15 the alternating-current component of a first term on the
right side of formula (17). In addition, it can be seen
that a necessary pulsating quantity is determined by the
maximum value Vmax of the output voltage of the rectifier 20,
the minimum value Vmin of the output voltage of the
20 rectifier 20, the inductance value L of the reactor 30, the
number P of phases of the alternating-current power supply
10, and the angular frequency ω of the alternating-current
power supply 10 in the first term on the right side. The
above-described elements are determined by specifications
25 of the alternating-current power supply 10, except for the
inductance value L of the reactor 30. Therefore, it can be
14
seen that the setting of the inductance value L of the
reactor 30 is important.
[0049] Assume that Pout(α=1) denotes the output power Pout
of the load 40 to be obtained when α=1, and Pout(α=10)
5 denotes the output power Pout of the load 40 to be obtained
when α=10. Since the first term on the right side of
formula (17) is an alternating-current component, an
average value thereof is treated as 0. Then, in order to
match the direct-current component in the second term on
10 the right side, the inductance value L of the reactor 30 to
be obtained when α=10 just needs to be set to a value that
is 10 times the inductance value L of the reactor 30 to be
obtained when α=1. With this setting, the output power
Pout(α=1) of the load 40 and the output power Pout(α=10) of
15 the load 40 have equal average values, and have a
relationship of 10:1 in terms of the amplitude of the
alternating-current component in the first term on the
right side. As a result, the pulsating quantity of the
output power Pout of the load 40 can be reduced. That is,
20 as a result of setting the inductance value L of the
reactor 30 as shown in formula (18), it is possible to
reduce the amplitude of the alternating-current component
in the first term on the right side of formula (17) without
changing the direct-current component in the second term on
25 the right side of formula (17).
[0050] Formula 18:
[0051] When the coefficient α is less than 1, the
amplitude of the alternating-current component of the
30 output power Pout of the load 40 becomes larger than the
direct-current component of the output power Pout of the
load 40, so that power becomes negative. Therefore, the
15
coefficient α is desirably equal to or greater than 1.
Furthermore, there are no particular restrictions on the
upper limit of the coefficient α. Meanwhile, since an
increase in the coefficient α will reduce the ratio of the
5 pulsation amplitude of the alternating-current component of
the output power Pout of the load 40 to the direct-current
component thereof, so that the amount of change in the
output power Pout of the load 40 can be reduced. However,
since an increase in the inductance value L of the reactor
10 30 causes an increase in size, the coefficient α is
desirably equal to or less than about 10. That is, the
power converting apparatus 100 can reduce the charging and
discharging current of the capacitor 33 without increasing
the size of the reactor 30, by setting the coefficient α in
15 this way. In addition, the required number of the
capacitors 33 is also reduced due to a reduction in
electrostatic capacitance. As a result, the area of a
portion where a substrate is mounted is reduced, so that
miniaturization and weight reduction can be achieved.
20 [0052] The method for controlling the output power Pout
of the load 40 and the method for setting the inductance
value L of the reactor 30, so as to control and keep the
charging and discharging current of the capacitor 33 at
substantially zero, have been described thus far. However,
25 there is a tolerance for a prescribed charging and
discharging current, that is, a ripple tolerance, in the
capacitor 33. In the power converting apparatus 100, when
the ratio of an alternating-current pulsation amplitude to
the direct-current component is reduced or the inductance
30 value L of the reactor 30 is reduced regardless of, for
example, formulas (17) and (18), the charging and
discharging current increases proportionally. However, it
is possible to reduce the inductance value L of the reactor
16
30 and the ratio of the alternating-current pulsation
amplitude to the direct-current component of the output
power Pout of the load 40 without affecting the ripple
tolerance of the capacitor 33, the life of the capacitor 33
5 due to a temperature rise, and the like.
[0053] Here, a ripple current Ir of the capacitor 33
with respect to the alternating-current component Pout_ac of
the output power Pout of the load 40 is expressed by formula
(19). Note that when Ir0 denotes a ripple current value to
10 be obtained in a case where the output power Pout of the
load 40 is not pulsated, and Pout_ac0 denotes an alternatingcurrent component of the output power Pout of the load 40
that allows the ripple current Ir to be controlled and kept
at substantially zero, characteristics are obtained as
15 illustrated in FIG. 4.
[0054] Formula 19:
[0055] FIG. 4 is a diagram illustrating a relationship
between the alternating-current component Pout_ac of the
20 output power Pout of the load 40 and the ripple current Ir
of the capacitor 33 in the power converting apparatus 100
according to the first embodiment. In FIG. 4, the
horizontal axis represents power, and the vertical axis
represents current. As illustrated in FIG. 4, Ir_lim is
25 defined as a current value of the ripple tolerance of the
capacitor 33, and Pout_ac_lim is defined as the alternatingcurrent component Pout_ac of the output power Pout of the load
40 to be obtained when the ripple current Ir of the
capacitor 33 is equal to the ripple tolerance Ir_lim of the
30 capacitor 33. It is possible to cause the power converting
apparatus 100 to operate at a current value equal to or
less than the ripple tolerance Ir_lim of the capacitor 33 by
17
setting the alternating-current component Pout_ac of the
output power Pout of the load 40 within a range from
Pout_ac_lim to Pout_ac0. For example, when the ripple current
value Ir0 to be obtained in a case where the output power
5 Pout is not pulsated is a value twice as large as the ripple
tolerance Ir_lim, the power converting apparatus 100
controls the alternating-current component Pout_ac of the
output power Pout of the load 40 such that the alternatingcurrent component Pout_ac is 1/2 of the alternating-current
10 component Pout_ac0 of the output power Pout of the load 40
that allows the ripple current Ir to be controlled and kept
at substantially zero. As a result, the power converting
apparatus 100 can control the ripple current Ir of the
capacitor 33 such that the ripple current Ir falls within
15 an allowable range, and can be operated while minimizing
the effect on the load 40 due to a change in the output
power Pout of the load 40.
[0056] In addition, as illustrated in FIG. 5, when L0
denotes the inductance value L of the reactor 30, shown in
20 formula (18), for making the charging and discharging
current of the capacitor 33 substantially zero, and Ir_lim
is defined as a current value of the ripple tolerance of
the capacitor 33, the power converting apparatus 100 can be
operated at the current value equal to or less than the
25 ripple tolerance Ir_lim of the capacitor 33 by setting the
inductance value L of the reactor 30 within a range from
L_lim to L0. FIG. 5 is a diagram illustrating a
relationship between the inductance value L of the reactor
30 and the ripple current Ir of the capacitor 33 in the
30 power converting apparatus 100 according to the first
embodiment. In FIG. 5, the horizontal axis represents the
inductance value L of the reactor 30, and the vertical axis
represents the ripple current Ir of the capacitor 33. That
18
is, as shown in formula (20), the inductance value L of the
reactor 30 is set to a value obtained by multiplication of
formula (18) by a coefficient β that takes into
consideration a tolerance (Ir0-Ir_lim)/Ir0 with respect to the
5 ripple tolerance Ir_lim of the capacitor 33. Note that the
range of the coefficient β is shown in formula (21). As a
result, the power converting apparatus 100 can achieve both
of reduction in the size and weight of the reactor 30 and
prolongation of the life of the capacitor 33. Note that
10 the coefficients α and β do not need to be set separately,
and may be set in a range shown in formula (22) in
consideration of the coefficients α and β. A coefficient
αβ is a coefficient based on a load pulsation allowable
value and the ripple tolerance Ir_lim of the capacitor 33.
15 [0057] Formula 20:
[0058] Formula 21:
[0059] Formula 22:
20
[0060] As described above, in the power converting
apparatus 100, the range of the inductance value L of the
reactor 30 is defined by use of the maximum value Vmax of
the output voltage of the rectifier 20, the minimum value
25 Vmin of the output voltage of the rectifier 20, the directcurrent component Pout_dc of the output power Pout of the load
40, the number P of phases of the alternating-current power
supply 10, the angular frequency ω of the alternatingcurrent power supply 10, the ripple current value Ir0 of
30 the capacitor 33, which is a pulsating quantity to be
19
obtained when the output power Pout of the load 40 is not
pulsated, and the ripple tolerance Ir_lim of the capacitor
33. As described above, the power converting apparatus 100
can achieve both reduction of the fluctuation of the load
5 40 and reduction of the size and weight of the reactor 30
by considering the amount of change in the alternatingcurrent component Pout_ac of the output power Pout of the load
40, the inductance value L of the reactor 30, and the like
while considering the ripple tolerance Ir_lim of the
10 capacitor 33. Note that the range of the inductance value
L of the reactor 30 may be defined by use of the maximum
value Vmax of the output voltage of the rectifier 20, the
minimum value Vmin of the output voltage of the rectifier 20,
the direct-current component Pout_dc of the output power Pout
15 of the load 40, the number P of phases of the alternatingcurrent power supply 10, and the angular frequency ω of the
alternating-current power supply 10.
[0061] Actual operation will be described. FIG. 6 is a
diagram showing, as a comparative example, an example of
20 results of analysis performed when the power converting
apparatus 100 does not change the output power Pout of the
load 40. In FIG. 6, an analysis result in a first row
shows voltages output from the alternating-current power
supply 10 to the rectifier 20, that is, three-phase line
25 voltages Vuv, Vvw, and Vwu. Note that the three phases are
represented as a U phase, a V phase, and a W phase. An
analysis result in a second row shows the output voltage
Vdb of the rectifier 20 and the voltage Vdc across the
capacitor 33. An analysis result in a third row shows
30 output current of the rectifier 20, that is, the current
Idc flowing through the reactor 30, the current Ic flowing
through the capacitor 33, and the current Iz flowing
through the load 40. An analysis result in a fourth row
20
shows the output power Pout of the load 40. Note that the
horizontal axis represents time in the analysis results of
the first to fourth rows. When the output power Pout of the
load 40 is kept constant in the power converting apparatus
5 100, the current Ic of the capacitor 33 greatly pulsates
and charging and discharging are repeated, so that the
charging and discharging current of the capacitor 33, that
is, the ripple current Ir increases. Therefore, it is not
possible to achieve miniaturization and weight reduction of
10 the capacitor 33 by reducing the electrostatic capacitance
of the capacitor 33.
[0062] FIG. 7 is a diagram showing an example of results
of analysis performed when the power converting apparatus
100 according to the first embodiment changes the output
15 power Pout of the load 40 to reduce the charging and
discharging current of the capacitor 33. In FIG. 7,
respective items of analysis results shown in first to
fourth rows are the same as those in FIG. 6. FIG. 7
illustrates analysis results to be obtained in a case where
20 the inductance value L of the reactor 30 is set with the
coefficients α and β that have been set such that α=3 and
β=1, and the output power Pout of the load 40 is changed to
reduce the charging and discharging current of the
capacitor 33 in the power converting apparatus 100.
25 Looking at current waveforms as the analysis result in the
third row, it can be seen that the output current of the
rectifier 20, that is, the current Idc flowing through the
reactor 30, coincides with the current Iz flowing through
the load 40, and as a result, the current Ic of the
30 capacitor 33 becomes substantially zero. In the example of
FIG. 7, the coefficient α is adjusted such that the
alternating-current component, which is the pulsating
quantity of the load 40, is 1/3 of the direct-current
21
component. If it is desired to obtain the alternatingcurrent component that is 1/10 of the direct-current
component, the coefficient α just needs to be set such that
α=10.
5 [0063] FIG. 8 is a diagram illustrating a relationship
between the inductance value L of the reactor 30 and the
alternating-current component of the output power Pout of
the load 40 in the power converting apparatus 100 according
to the first embodiment. In FIG. 8, the horizontal axis
10 represents the inductance value L of the reactor 30, and
the vertical axis represents the alternating-current
component of the output power Pout of the load 40. As can
be seen from FIG. 8, the alternating-current component of
the output power Pout of the load 40 decreases as the
15 inductance value L of the reactor 30 increases in the power
converting apparatus 100. Note that since the inductance
value L of the reactor 30 increases, the charging and
discharging current of the capacitor 33 increases as a
result of selecting the coefficient β that falls within the
20 range shown in formula (21). However, it is possible to
achieve both miniaturization and weight reduction of the
reactor 30 and the capacitor 33 by adjusting the
coefficient β within a range of the ripple tolerance Ir_lim
of the capacitor 33.
25 [0064] In the power converting apparatus 100, current
flows directly from the alternating-current power supply 10
to the load 40, and charging of the capacitor 33 is avoided,
so that it is also possible to reduce current distortion
due to the conventional charging of the capacitor 33. As a
30 result, the power converting apparatus 100 can, for example,
ensure tolerance for a limit value of power line harmonics
defined by Japanese Industrial Standards (JIS),
International Electrotechnical Commission (IEC), or the
22
like, and improve a power factor.
[0065] Note that when the alternating-current power
supply 10 is a single-phase power supply, the conduction
state of the rectifier 20 changes according to the polarity
5 of the power supply voltage, but when the capacitor 33 is
not charged, the power converting apparatus 100 can be
approximated by an RL circuit, and power supply current has
retardation in phase with respect to the power supply
voltage. Here, in the power converting apparatus 100, when
10 the reactor 30 is disposed at a subsequent stage of the
rectifier 20, current cannot continuously flow depending on
the conduction state of the rectifier 20. Therefore, when
the alternating-current power supply 10 is a single-phase
power supply, the power converting apparatus 100 is
15 configured such that the reactor 30 is disposed between the
alternating-current power supply 10 and the rectifier 20.
As a result, current can continuously flow without being
affected by the rectifier 20, and harmonic components of
the current can be reduced.
20 [0066] In the power converting apparatus 100, the load
40 can be applied to any of a resistance load, a constant
current load, and a constant power load as long as power to
be consumed is variable. Examples of the constant power
load include an inverter that drives an inductive load. In
25 particular, when the inductive load is a motor, the work of
the motor is represented by the product of torque and
angular frequency. That is, the power converting apparatus
100 can control power based on formula (18) by making the
torque or the angular frequency variable.
30 [0067] FIG. 9 is a flowchart illustrating operation of
the power converting apparatus 100 according to the first
embodiment. In the power converting apparatus 100, the
rectifier 20 rectifies alternating-current power output
23
from the alternating-current power supply 10 (step S1).
The control unit 45 acquires a detection value indicating
an operation state of the power converting apparatus 100
from a detection unit (not illustrated) (step S2). In
5 order to reduce the charging and discharging current of the
capacitor 33, the control unit 45 controls the operation
state of the load 40 such that power pulsation occurs in
power to be consumed by the load 40 (step S3).
[0068] Next, a hardware configuration of the control
10 unit 45 included in the power converting apparatus 100 will
be described. FIG. 10 is a diagram showing an example of a
hardware configuration for implementing the control unit 45
included in the power converting apparatus 100 according to
the first embodiment. The control unit 45 is implemented
15 by a processor 91 and a memory 92.
[0069] The processor 91 is a central processing unit
(CPU, also referred to as a processing device, an
arithmetic device, a microprocessor, a microcomputer, a
processor, or a digital signal processor (DSP)) or a system
20 large-scale integration (LSI). Examples of the memory 92
include nonvolatile or volatile semiconductor memories such
as a random access memory (RAM), a read only memory (ROM),
a flash memory, an erasable programmable read only memory
(EPROM), and an electrically erasable programmable read
25 only memory (EEPROM (registered trademark)). Furthermore,
the memory 92 is not limited thereto, and may be a magnetic
disk, an optical disk, a compact disk, a mini disk, or a
digital versatile disc (DVD).
[0070] As described above, according to the present
30 embodiment, the power converting apparatus 100 reduces the
charging and discharging current of the capacitor 33 by
causing power pulsation in power to be consumed by the load
40, and uses the reactor 30 having an inductance value in a
24
prescribed range. As a result, the power converting
apparatus 100 can reduce the charging and discharging
current of the capacitor 33, and can prolong the life of
the capacitor 33 by reducing ripple current even when a
5 low-cost capacitor is used as the capacitor 33.
[0071] Second Embodiment.
In a second embodiment, a heat pump apparatus
including the power converting apparatus 100 and an air
conditioner including the heat pump apparatus will be
10 described.
[0072] FIG. 11 is a diagram showing a configuration
example of an air conditioner 70 according to the second
embodiment. The air conditioner 70 includes a heat pump
apparatus 50. The heat pump apparatus 50 includes the
15 power converting apparatus 100. Note that although only
the load 40 of the power converting apparatus 100 is
illustrated in FIG. 11 for the sake of simplicity, the
power converting apparatus 100 includes the rectifier 20
and the like as in FIG. 1. In the second embodiment, the
20 load 40 of the power converting apparatus 100 to be
installed in the heat pump apparatus 50 includes an
inverter 41 and a motor 44. The inverter 41 converts
direct-current power into alternating-current power. The
motor 44 is driven by alternating-current power output from
25 the inverter 41. The inverter 41 includes a switching
element 42 and a control unit 43. The switching element 42
converts direct-current power into alternating-current
power. The control unit 43 controls operation of the
switching element 42
30 [0073] FIG. 12 is a diagram illustrating a circuit
configuration of the heat pump apparatus 50 according to
the second embodiment. The heat pump apparatus 50 includes
a main refrigerant circuit 58 in which a compressor 51, a
25
heat exchanger 52, an expansion mechanism 53, a receiver 54,
an internal heat exchanger 55, an expansion mechanism 56,
and a heat exchanger 57 are sequentially connected by pipes
to circulate a refrigerant. In the main refrigerant
5 circuit 58, a four-way valve 59 is provided on a discharge
side of the compressor 51 so as to allow a direction of
circulation of the refrigerant to be switched. Furthermore,
a fan 60 that is a cooling fan is provided near the heat
exchanger 57. Although not illustrated in FIG. 12, the
10 compressor 51 includes the motor 44, which is driven by the
inverter 41, and a compression mechanism. The heat pump
apparatus 50 further includes an injection circuit 62 that
connects a point between the receiver 54 and the internal
heat exchanger 55 to an injection pipe of the compressor 51
15 by means of a pipe. An expansion mechanism 61 and the
internal heat exchanger 55 are sequentially connected to
the injection circuit 62. The heat exchanger 52 is
connected to a water circuit 63 through which water
circulates. Note that although not illustrated, the water
20 circuit 63 is connected to a device using water of a
radiator and the like of the heat exchanger 52, such as a
water heater, a radiator, or a floor heating device.
[0074] First, how the heat pump apparatus 50 works
during heating operation will be described. During the
25 heating operation, the four-way valve 59 is set in a
direction indicated by solid lines. Note that the heating
operation includes not only heating to be used in the air
conditioner 70 but also, for example, hot-water supply in
which heat is applied to water to produce hot water. FIG.
30 13 is a Mollier chart illustrating the state of the
refrigerant in the heat pump apparatus 50 according to the
second embodiment. In FIG. 13, the horizontal axis
represents specific enthalpy, and the vertical axis
26
represents refrigerant pressure.
[0075] A gas-phase refrigerant that has reached a high
temperature and a high pressure in the compressor 51 (point
1 in FIG. 13) is discharged from the compressor 51 and
5 subjected to heat exchange in the heat exchanger 52 serving
as a condenser and a radiator, to be liquefied (point 2 in
FIG. 13). At this time, water circulating through the
water circuit 63 is warmed by heat radiated from the
refrigerant, and is used for heating, hot-water supply, and
10 the like. The liquid-phase refrigerant liquefied in the
heat exchanger 52 is decompressed by the expansion
mechanism 53 to be in a gas-liquid two-phase state (point 3
in FIG. 13). The refrigerant brought into the gas-liquid
two-phase state by the expansion mechanism 53 exchanges
15 heat, in the receiver 54, with a refrigerant to be sucked
into the compressor 51, and is cooled to be liquefied
(point 4 in FIG. 13). The liquid-phase refrigerant
liquefied in the receiver 54 bifurcates and flows through
the main refrigerant circuit 58 and the injection circuit
20 62.
[0076] The liquid-phase refrigerant flowing through the
main refrigerant circuit 58 exchanges heat, in the internal
heat exchanger 55, with the refrigerant flowing through the
injection circuit 62 that has been decompressed by the
25 expansion mechanism 61 to be in the gas-liquid two-phase
state, and is further cooled (point 5 in FIG. 13). The
liquid-phase refrigerant cooled in the internal heat
exchanger 55 is decompressed by the expansion mechanism 56
to be in a gas-liquid two-phase state (point 6 in FIG. 13).
30 The refrigerant brought into the gas-liquid two-phase state
by the expansion mechanism 56 exchanges heat with outside
air in the heat exchanger 57 serving as an evaporator, and
is heated (point 7 in FIG. 13). Then, the refrigerant
27
heated by the heat exchanger 57 is further heated by the
receiver 54 (point 8 in FIG. 13), and is sucked into the
compressor 51.
[0077] Meanwhile, the refrigerant flowing through the
5 injection circuit 62 is decompressed by the expansion
mechanism 61 as described above (point 9 in FIG. 13) and
subjected to heat exchange in the internal heat exchanger
55 (point 10 in FIG. 13). An injection refrigerant, which
is the refrigerant in the gas-liquid two-phase state
10 subjected to the heat exchange in the internal heat
exchanger 55, flows into the compressor 51 from the
injection pipe of the compressor 51 while being kept in the
gas-liquid two-phase state. In the compressor 51, the
refrigerant sucked from the main refrigerant circuit 58
15 (point 8 in FIG. 13) is compressed to an intermediate
pressure and heated (point 11 in FIG. 13). The refrigerant
compressed to the intermediate pressure and heated (point
11 in FIG. 13) joins the injection refrigerant (point 10 in
FIG. 13), and decreases in temperature (point 12 in FIG.
20 13). Then, the refrigerant having decreased in temperature
(point 12 in FIG. 13) is further compressed and heated to
reach a high pressure and a high temperature, and is
discharged (point 1 in FIG. 3).
[0078] Note that when injection operation is not
25 performed, the opening degree of the expansion mechanism 61
is fully closed. That is, the opening degree of the
expansion mechanism 61 is larger than a prescribed opening
degree when the injection operation is performed, but the
opening degree of the expansion mechanism 61 is made
30 smaller than the prescribed opening degree when the
injection operation is not performed. As a result, the
refrigerant does not flow into the injection pipe of the
compressor 51. Here, the opening degree of the expansion
28
mechanism 61 may be electronically controlled by the
control unit 43 such as a microcomputer.
[0079] Next, how the heat pump apparatus 50 works during
cooling operation will be described. During the cooling
5 operation, the four-way valve 59 is set in a direction
indicated by broken lines. Note that the cooling operation
includes not only cooling to be used in the air conditioner
70 but also taking heat from water to produce cold water,
freezing, and the like.
10 [0080] A gas-phase refrigerant that has reached a high
temperature and a high pressure in the compressor 51 (point
1 in FIG. 13) is discharged from the compressor 51 and
subjected to heat exchange in the heat exchanger 57 serving
as a condenser and a radiator, to be liquefied (point 2 in
15 FIG. 13). The liquid-phase refrigerant liquefied in the
heat exchanger 57 is decompressed by the expansion
mechanism 56 to be in a gas-liquid two-phase state (point 3
in FIG. 13). The refrigerant brought into the gas-liquid
two-phase state by the expansion mechanism 56 is subjected
20 to heat exchange in the internal heat exchanger 55, and is
cooled to be liquefied (point 4 in FIG. 13). The internal
heat exchanger 55 causes the refrigerant brought into the
gas-liquid two-phase state by the expansion mechanism 56 to
exchange heat with a refrigerant resulting from the liquid25 phase refrigerant liquefied in the internal heat exchanger
55 and then decompressed by the expansion mechanism 61 to
be in a gas-liquid two-phase state (point 9 in FIG. 13).
The liquid-phase refrigerant (point 4 in FIG. 13) subjected
to the heat exchange in the internal heat exchanger 55
30 bifurcates and flows through the main refrigerant circuit
58 and the injection circuit 62.
[0081] The liquid-phase refrigerant flowing through the
main refrigerant circuit 58 exchanges heat, in the receiver
29
54, with a refrigerant to be sucked into the compressor 51,
and is further cooled (point 5 in FIG. 13). The liquidphase refrigerant cooled in the receiver 54 is decompressed
by the expansion mechanism 53 to be in a gas-liquid two5 phase state (point 6 in FIG. 13). The refrigerant brought
into the gas-liquid two-phase state by the expansion
mechanism 53 is subjected to heat exchange in the heat
exchanger 52 serving as an evaporator, and is heated (point
7 in FIG. 13). At this time, as the refrigerant absorbs
10 heat, water circulating through the water circuit 63 is
cooled and used for cooling, freezing, and the like. Then,
the refrigerant heated in the heat exchanger 52 is further
heated in the receiver 54 (point 8 in FIG. 13), and is
sucked into the compressor 51.
15 [0082] Meanwhile, the refrigerant flowing through the
injection circuit 62 is decompressed by the expansion
mechanism 61 as described above (point 9 in FIG. 13) and
subjected to heat exchange in the internal heat exchanger
55 (point 10 in FIG. 13). An injection refrigerant, which
20 is the refrigerant in the gas-liquid two-phase state
subjected to the heat exchange in the internal heat
exchanger 55, flows into the compressor 51 from the
injection pipe of the compressor 51 while being kept in the
gas-liquid two-phase state. Compression operation in the
25 compressor 51 is similar to that to be performed during the
heating operation.
[0083] Note that, as in the heating operation, when the
injection operation is not performed, the opening degree of
the expansion mechanism 61 is fully closed so that the
30 refrigerant does not flow into the injection pipe of the
compressor 51. Furthermore, the heat exchanger 52 has been
described above as a heat exchanger such as a plate-type
heat exchanger that causes the refrigerant to exchange heat
30
with water circulating through the water circuit 63. The
heat exchanger 52 is not limited thereto, and may be a heat
exchanger that causes the refrigerant to exchange heat with
air. In addition, the water circuit 63 need not be a
5 circuit through which water circulates, but may be a
circuit through which another fluid circulates.
[0084] Here, in order to reduce the charging and
discharging current of the capacitor 33, power to be
consumed by the load 40 just needs to be pulsated. In the
10 heat pump apparatus 50, most of power is consumed by the
compressor 51. The compressor 51 includes the motor 44 and
a compression mechanism, and power consumption is mainly
due to the product of torque generated in the motor 44 and
an angular frequency of the motor 44. Therefore, the heat
15 pump apparatus 50 can reduce the charging and discharging
current of the capacitor 33 by changing the torque of the
motor 44 or the angular frequency that is a rotational
frequency. That is, in the power converting apparatus 100,
the control unit 45 causes power pulsation in power to be
20 consumed by the load 40 by changing torque to be output to
the motor 44 or a rotation speed of the motor 44.
[0085] The torque of the motor 44 can be implemented by
use of control for making the torque variable during
rotation, which is a well-known technique. Specifically,
25 it is possible to implement the heat pump apparatus 50 by
decomposing current flowing through the motor 44 into a daxis current that is an excitation component and a q-axis
current that is a torque component, and controlling the qaxis current. Furthermore, it is possible to implement the
30 heat pump apparatus 50 by generating, with regard to the
angular frequency of the motor, a command value for the qaxis current from a speed command value of the motor 44 and
a speed detection value or estimation value.
31
[0086] Furthermore, when the compressor 51 has load
torque pulsation during one rotation as with a rotary
compressor, the heat pump apparatus 50 may make the angular
frequency, the output torque of the motor 44, and the like
5 variable so as to reduce the charging and discharging
current of the capacitor 33 in accordance with fluctuation
in load torque. In addition, needless to say, the heat
pump apparatus 50 may make the load torque to be applied to
the compressor 51 variable by adjusting the opening degree
10 of the expansion mechanism 61, or may make the load torque
variable by other methods.
[0087] As described above, the heat pump apparatus 50
can be used not only for the air conditioner 70 but also
for a heat pump apparatus using an inverter compressor,
15 such as a heat pump water heater, a refrigerator, or a
refrigeration machine.
[0088] Application of the power converting apparatus 100
to the heat pump apparatus 50 has been described.
Meanwhile, the power converting apparatus 100 can be
20 applied to any apparatus as long as the apparatus rectifies
alternating-current power from the alternating-current
power supply 10, stores the alternating-current power in
the capacitor 33, and supplies the alternating-current
power to the load 40. The power converting apparatus 100
25 can be applied not only to household appliances such as a
blower, an electric washing machine, an induction heating
(IH) cooking heater, a vacuum cleaner, and lighting, but
also to devices such as an electric vehicle and a power
conditioner.
30 [0089] The configurations set forth in the above
embodiments show examples, and it is possible to combine
the configurations with another known technique or combine
the embodiments with each other, and is also possible to
32
partially omit or change the configurations without
departing from the scope of the present disclosure.
Reference Signs List
5 [0090] 10 alternating-current power supply; 20
rectifier; 30 reactor; 31 inductance component; 32
resistance component; 33 capacitor; 40 load; 41 inverter;
42 switching element; 43, 45 control unit; 44 motor; 50
heat pump apparatus; 51 compressor; 52, 57 heat
10 exchanger; 53, 56, 61 expansion mechanism; 54 receiver;
55 internal heat exchanger; 58 main refrigerant circuit;
59 four-way valve; 60 fan; 62 injection circuit; 63
water circuit; 70 air conditioner; 100 power converting
apparatus.
15
33
WE CLAIM:
[Claim 1] A power converting apparatus comprising:
a rectifier that rectifies alternating-current power
output from an alternating-current power supply;
5 a capacitor provided at an output end of the
rectifier;
a reactor provided on a path from the alternatingcurrent power supply to the capacitor;
a load connected across the capacitor; and
10 a control unit that reduces a charging and discharging
current of the capacitor by controlling an operation state
of the load such that power pulsation occurs in power to be
consumed by the load, wherein
a range of an inductance value of the reactor is
15 defined by use of a maximum value of an output voltage of
the rectifier, a minimum value of the output voltage of the
rectifier, a direct-current component of output power of
the load, a number of phases of the alternating-current
power supply, and an angular frequency of the alternating20 current power supply.
[Claim 2] The power converting apparatus according to claim
1, wherein
the range of the inductance value of the reactor is
25 further defined by use of a pulsating quantity and a ripple
tolerance of the capacitor, the pulsating quantity
corresponding to a ripple current of the capacitor to be
obtained when the output power of the load is not pulsated.
30 [Claim 3] The power converting apparatus according to claim
2, wherein
the inductance value of the reactor is expressed by
following formulas:
34
Formula 1:
,
and
Formula 2:
5 ,
where L is the inductance value of the reactor, Vmax is
the maximum value of the output voltage of the rectifier,
Vmin is the minimum value of the output voltage of the
rectifier, Pout_dc is the direct-current component of the
10 output power of the load, P is the number of phases of the
alternating-current power supply, ω is the angular
frequency of the alternating-current power supply, Ir0 is a
ripple current value of the capacitor corresponding to the
pulsating quantity to be obtained when the output power of
15 the load is not pulsated, Ir_lim is the ripple tolerance of
the capacitor, and αβ is a coefficient based on a load
pulsation allowable value and the ripple tolerance of the
capacitor.
20 [Claim 4] The power converting apparatus according to claim
3, wherein
an alternating-current component of the output power
of the load corresponding to a pulsating quantity of the
power pulsation is equal to or less than a value of Pout_ac
25 expressed by a following formula:
Formula 3:
,
where Pout_ac is the alternating-current component of
the output power of the load.
35
[Claim 5] The power converting apparatus according to any
one of claims 1 to 4, wherein
the load includes an inverter and a motor, and
5 the control unit causes the power pulsation by
changing torque to be output to the motor or a rotation
speed of the motor.
[Claim 6] A heat pump apparatus comprising the power
10 converting apparatus according to any one of claims 1 to 5.
[Claim 7] An air conditioner comprising the heat pump
apparatus according to claim 6.