JP2019205305A - Active filter device, air conditioning system, ripple suppression method and program - Google Patents

Abstract

To provide an active filter device capable of suppressing ripples while maintaining harmonic restraint performance.SOLUTION: An active filter device comprises a command output section outputting an ON/OFF command to the switching element of an active filter circuit, on the basis of a converter current flowing to an outdoor apparatus, a duty ratio determination section for determining whether or not the duty ratio of the ON/OFF command goes below a prescribed lower limit value in a prescribed period, and a DC voltage adjustment unit for lowering a DC voltage outputted from the active filter circuit, when the duty ratio of the ON/OFF command goes below the prescribed lower limit value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an active filter device, an air conditioning system, a ripple suppression method, and a program.

  In an air conditioning system, it is known that a motor for a compressor of an outdoor unit is driven to rotate as desired using an inverter. The current flowing in the outdoor unit of such an air conditioning system is likely to generate harmonics due to the characteristics of a rectifier circuit that converts AC power into DC. Therefore, the active filter device is used to suppress harmonics of the current flowing through the outdoor unit.

  In relation to the active filter described above, Patent Document 1 discloses a current detection unit that detects an alternating current input to the outdoor power supply device and the indoor power supply device, and a harmonic of the alternating current based on the current detection result of the current detection unit. An air conditioner including a harmonic suppression unit that performs control to reduce a wave component is disclosed.

JP 2004-364491 A

  The active filter device detects a current for driving a compressor motor or the like of an outdoor unit (that is, a current including harmonics, hereinafter also referred to as “converter current”), and follows the steep change. By superimposing an appropriate current, the total current supplied from the power system (hereinafter also referred to as “system current”) is formed into a sine wave, and harmonics are suppressed. Hereinafter, the current output by the active filter device is also referred to as “active filter output current”.

  The active filter output current is controlled by ON / OFF control of a switching element (power transistor) of the active filter circuit. The active filter output current is smoothed by a reactor included in the active filter device. This reactor suppresses ripples that occur as the switching element is repeatedly turned ON / OFF. The higher the inductance value of the reactor, the higher the ripple suppression effect.

  However, if the inductance value of the reactor is too high, the active filter output current cannot follow the sharp change (harmonic) of the converter current, and the harmonic suppression effect, which is the original purpose, is reduced. Therefore, in general, an upper limit value of the inductance value is determined in the reactor so that harmonics can be suppressed (followed) with respect to the maximum converter current that flows during rated output operation of the outdoor unit.

  Thus, since the upper limit value of the inductance value of the reactor is regulated in accordance with the maximum converter current, the ripple suppressing effect is relatively insufficient when the converter current is low. Therefore, harmonic components due to ripple increase. Further, when the ripple width is relatively large with respect to the amplitude of the system current, the error of the zero cross detection is also increased, and the malfunction of the motor control by the inverter is likely to occur.

  An object of the present invention is to provide an active filter device, an air conditioning system, a ripple suppression method, and a program capable of suppressing ripple while maintaining harmonic suppression performance.

  According to the first aspect of the present invention, an active filter device includes a command output unit that outputs an ON / OFF command to a switching element of an active filter circuit based on a converter current flowing in an outdoor unit, and a predetermined period. A duty ratio determination unit for determining whether the duty ratio of the ON / OFF command is below a predetermined lower limit value, and the active ratio when the duty ratio of the ON / OFF command is lower than the predetermined lower limit value. A DC voltage adjusting unit that reduces the DC voltage output from the filter circuit.

  Further, according to the second aspect of the present invention, the duty ratio determination unit further determines whether or not the duty ratio of the ON / OFF command has reached a predetermined upper limit value, and the DC voltage adjustment unit When the duty ratio of the ON / OFF command reaches a predetermined upper limit value, the DC voltage output from the active filter circuit is increased.

  Moreover, according to the 3rd aspect of this invention, an air conditioning system is provided with the above-mentioned active filter apparatus and the said outdoor unit.

  Moreover, according to the 4th aspect of this invention, the said active filter apparatus is integrated in the inside of the said outdoor unit in the above-mentioned air conditioning system.

  According to the fifth aspect of the present invention, the ripple suppressing method includes the steps of outputting an ON / OFF command to the switching element of the active filter circuit based on the converter current flowing through the outdoor unit, and within a predetermined period. Determining whether the duty ratio of the ON / OFF command is below a predetermined lower limit value, and if the duty ratio of the ON / OFF command is below the predetermined lower limit value, from the active filter circuit Reducing the output DC voltage.

  According to the sixth aspect of the present invention, the program outputs to the computer of the active filter device an ON / OFF command to the switching element of the active filter circuit based on the converter current flowing in the outdoor unit; Determining whether the duty ratio of the ON / OFF command is below a predetermined lower limit value within a predetermined period, and when the duty ratio of the ON / OFF command is lower than the predetermined lower limit value, Reducing the DC voltage output from the active filter circuit.

  According to at least one of the above aspects, ripple can be suppressed while maintaining harmonic suppression performance.

It is a figure showing the whole air-conditioning system composition concerning a 1st embodiment. It is a figure which shows the function structure of the active filter control part which concerns on 1st Embodiment. It is a figure for demonstrating the function of the active filter apparatus which concerns on 1st Embodiment. It is a figure for demonstrating operation | movement of the active filter control part which concerns on 1st Embodiment. It is a figure which shows the processing flow of the active filter control part which concerns on 1st Embodiment. It is a figure for demonstrating the effect | action and effect based on the process of the active filter control part which concern on 1st Embodiment. It is a figure for demonstrating the effect | action and effect based on the process of the active filter control part which concern on 1st Embodiment. It is a figure which shows the whole structure of the air conditioning system which concerns on 2nd Embodiment.

<First Embodiment>
Hereinafter, the active filter device according to the first embodiment and an air conditioning system including the active filter device will be described with reference to FIGS.

(Overall configuration of in-vehicle air conditioner control device)
Drawing 1 is a figure showing the whole air-conditioning system composition concerning a 1st embodiment.
The air conditioning system 1 is an air conditioning system including an outdoor unit 1 </ b> A and an active filter device 3. The air conditioning system 1 also includes an indoor unit, which is not shown in FIG.
The outdoor unit 1 </ b> A of the air conditioning system 1 according to the present embodiment is connected to the AC power supply 2 via the power connection terminal T. The AC power supply 2 is a normal commercial power system that outputs three-phase AC power.
In the following description, in each configuration of the outdoor unit 1A and the active filter device 3, the side close to the AC power supply 2 is also referred to as “upstream side”, and the side close to the compressor motor 13 is referred to as “downstream side”. ".

The configuration of the outdoor unit 1A will be described.
As shown in FIG. 1, the outdoor unit 1A includes a noise filter 10, a rectifier circuit 11, an inverter circuit 12, a compressor motor 13, and an electrolytic capacitor C1.
The noise filter 10 removes noise from the three-phase AC power supplied from the AC power supply 2.
The rectifier circuit 11 rectifies the three-phase AC power from which noise has been removed by the noise filter 10. The rectifier circuit 11 may be, for example, a three-phase rectifier circuit using a diode element. The rectified high potential is output from the high potential output line α, which is the output line of the rectifier circuit 11, and the rectified low potential is output from the low potential output line β.
The electrolytic capacitor C1 is connected between the high potential output line α and the low potential output line β of the rectifier circuit 11. The electrolytic capacitor C1 smoothes the voltage after rectification by the rectifier circuit 11 and generates a DC voltage.
The inverter circuit 12 is a power conversion circuit for generating desired AC power based on a DC voltage rectified by the rectifier circuit 11 and smoothed by the electrolytic capacitor C1. The inverter circuit 12 generates AC power for driving the compressor motor 13 to rotate at a desired rotational speed.
The compressor motor 13 is a three-phase AC motor for rotationally driving the compressor provided in the outdoor unit 1A. The compressor motor 13 is driven to rotate based on the three-phase AC power generated by the inverter circuit 12.
Converter current detection sensor SE is a current sensor that detects a three-phase AC current flowing from AC power supply 2 to outdoor unit 1A. The converter current detection sensor SE may be, for example, a clamp type current sensor.

Next, the active filter device 3 will be described.
As shown in FIG. 1, the active filter device 3 is connected to the AC power supply 2 via the power supply connection terminal T of the outdoor unit 1A. The active filter device 3 includes an active filter control unit 30, an active filter circuit 31, and a reactor L3.

  The active filter control unit 30 is a so-called microcomputer and operates according to a program prepared in advance. The active filter control unit 30 controls ON / OFF of the switching element SW3 included in the active filter circuit 31 based on the detection result of the converter current I2 acquired from the converter current detection sensor SE described later. Specific functions and operations of the active filter control unit 30 will be described later.

The active filter circuit 31 includes a switching element SW3 that is turned ON / OFF in synchronization with the three-phase AC power input from the AC power supply 2. The active filter circuit 31 functions as a synchronous rectifier circuit, and outputs the rectified voltage generated thereby to the electrolytic capacitor C3. A predetermined DC voltage Vdc is applied to the electrolytic capacitor C3.
When the switching element SW3 is appropriately ON / OFF controlled, the active filter circuit 31 outputs a current (active filter output current I3) for suppressing harmonics of the converter current I2. Since the active filter output current I3 is superimposed on the converter current I2, the system current I1 is formed into a sine wave with reduced harmonics.

The reactor L3 is an element for smoothing the active filter output current I3, and mainly suppresses ripples that occur with ON / OFF control of the switching element SW3.
The higher the inductance value of the reactor L3, the higher the ripple suppression effect of the active filter output current I3. However, if the inductance value of the reactor L3 is too high, the active filter output current I3 cannot follow the steep change (harmonic) of the converter current I2, and the harmonic suppression effect is reduced. Therefore, the reactor L3 is designed to be able to suppress (follow) harmonics of the maximum converter current I2 that flows during the rated output operation of the outdoor unit 1A.

(Functional configuration of active filter controller)
FIG. 2 is a diagram illustrating a functional configuration of the active filter control unit according to the first embodiment.
As shown in FIG. 2, the active filter control unit 30 functions as a command output unit 300, a duty ratio determination unit 301, and a DC voltage adjustment unit 302 by operating according to a predetermined program.
Command output unit 300 outputs an ON / OFF command to switching element SW3 of active filter circuit 31 based on converter current I2 flowing from AC power supply 2 to outdoor unit 1A. The switching element SW3 is turned on / off according to this on / off command.
The duty ratio determination unit 301 acquires the duty ratio of the ON / OFF command within a predetermined period (for example, within one cycle of AC power). The duty ratio determination unit 301 according to the present embodiment determines whether or not the duty ratio of the ON / OFF command is below a predetermined lower limit value (for example, 80%). Further, the duty ratio determination unit 301 according to the present embodiment determines whether or not the duty ratio of the ON / OFF command has reached a predetermined upper limit value (for example, 100%) within a predetermined period.
The DC voltage adjustment unit 302 controls the switching element SW3 of the active filter circuit 31 to change the DC voltage Vdc applied to the electrolytic capacitor C3. Specifically, the DC voltage adjustment unit 302 can adjust the DC voltage Vdc, for example, by changing an ON / OFF pattern as a synchronous rectification circuit of the switching element SW3. In particular, the DC voltage adjustment unit 302 according to the present embodiment reduces the DC voltage Vdc output from the active filter circuit 31 to the electrolytic capacitor C3 when the duty ratio of the ON / OFF command is below a predetermined lower limit value. . Further, the DC voltage adjusting unit 302 according to the present embodiment increases the DC voltage Vdc output from the active filter circuit 31 to the electrolytic capacitor C3 when the duty ratio of the ON / OFF command reaches a predetermined upper limit value. .

(Function of active filter device)
FIG. 3 is a diagram for explaining the function of the active filter device according to the first embodiment.
Specifically, FIG. 3 shows an example of current waveforms of the system current I1, the converter current I2, and the active filter output current I3.

  The converter current I2 flowing through the outdoor unit 1A has a timing that changes sharply within one cycle, for example, as indicated by the circles in FIG. That is, the converter current I2 includes a harmonic component.

  The active filter output current I3 output from the active filter device 3 changes corresponding to the converter current I2. In particular, the active filter output current I3 changes following the steep change of the converter current I2 at a position indicated by a circle in FIG. As described above, the active filter output current I3 needs to change following the steep change of the converter current I2 as shown by a circle in FIG. 3, and therefore, the inductance value of the reactor L3 is increased without limit. I can't.

  The system current I1 is a current obtained by superimposing the active filter output current I3 on the converter current I2. As shown in FIG. 3, since the active filter output current I3 changes so as to compensate for a steep change in the converter current I2, the system current I1 is formed in a current waveform close to a sine wave.

(Operation of active filter controller)
FIG. 4 is a diagram for explaining the operation of the active filter control unit according to the first embodiment.
Hereinafter, specific processing of the command output unit 300 of the active filter control unit 30 will be described in detail with reference to FIG.

  First, when the command output unit 300 acquires the converter current I2 through the converter current detection sensor SE, the command output unit 300 calculates a current command indicating a current to be output in order to suppress harmonics of the converter current I2.

  Subsequently, the command output unit 300 superimposes the calculated current command on a comparison carrier that is a predefined triangular wave (see FIG. 4). Then, the command output unit 300 outputs an ON / OFF command (PWM signal) in which the period of the triangular wave that is lower than the current command is the ON period. Hereinafter, the ratio of the period (ON period) in which the ON / OFF command is “ON” with respect to one carrier cycle is also referred to as “duty ratio” (%). The carrier period of the comparison carrier is set to 20 kHz, for example.

The command output unit 300 outputs the ON / OFF command obtained as described above to the switching element SW3 of the active filter circuit 31. The switching element SW3 transitions to an ON state and an OFF state based on this ON / OFF command.
As shown in FIG. 4, the active filter output current I3 is instantaneously turned on / off by switching the switching element SW3 based on the duty ratio specified by the current command and the comparison carrier. On the average, the active filter output current I3 corresponding to the current command is output while repeating the increase / decrease according to OFF.

  As indicated by the circles in FIG. 3, when the active filter output current I3 is to be changed abruptly, the command output unit 300 increases the duty ratio of the ON / OFF command to the switching element SW3. For example, if the duty ratio is increased to the upper limit (100%), the command output unit 300 can increase the active filter output current I3 at the maximum increase rate (change rate ΔI). Here, the change rate ΔI is a change rate per unit time of the active filter output current I3 during the ON period of the switching element SW3, and is determined by the equation (1).

  In Expression (1), “Vdc” is a DC voltage Vdc applied to the electrolytic capacitor C3. “L” is an inductance value of the reactor L3. “DI / dt” is a change rate ΔI of the active filter output current I3.

  According to the equation (1), the change rate ΔI increases as the inductance value of the reactor L3 is smaller or the DC voltage Vdc applied to the electrolytic capacitor C3 is larger. Therefore, the active filter output current I3 changes more rapidly. Can be made.

  On the other hand, the ripple width R, which is a fine increase / decrease width of the active filter output current I3 according to ON / OFF of the switching element SW3, increases as the change rate ΔI of the active filter output current I3 increases. That is, the ripple width R increases as the inductance value of the reactor L3 decreases or as the DC voltage Vdc increases.

  Here, the ripple width R can be reduced by reducing the change rate ΔI of the active filter output current I3. However, if the rate of change ΔI is too small, it becomes impossible to follow the change in the converter current I2 even when the duty ratio of the ON / OFF command is set to the maximum value (100%), particularly at the timing indicated by the circles in FIG.

Therefore, when the duty ratio of the ON / OFF command is sufficiently low, the active filter control unit 30 according to the first embodiment dynamically reduces the rate of change ΔI to suppress ripples and When the peak (100%) is detected, the change rate ΔI is dynamically increased so that the change in the converter current I2 can be followed.
The inductance value of the reactor L3 is a fixed value and cannot be changed dynamically. Therefore, the active filter control unit 30 according to this embodiment changes the change rate ΔI of the active filter output current I3 by dynamically changing the DC voltage Vdc applied to the electrolytic capacitor C3.

(Processing flow of active filter controller)
FIG. 5 is a diagram illustrating a processing flow of the active filter control unit according to the first embodiment.
The process flow shown in FIG. 5 is continuously and repeatedly executed during the operation of the air conditioning system 1.

First, the duty ratio determination unit 301 of the active filter control unit 30 acquires the duty ratio for each carrier cycle (20 kHz) of the ON / OFF command for one cycle of the AC power supply cycle (50 Hz or 60 Hz) ( Step S01). In this process, for example, the duty ratio determination unit 301 may acquire the duty ratio by a predetermined number of samplings corresponding to one power cycle.
Subsequently, the duty ratio determination unit 301 determines whether or not the duty ratio is equal to or less than 80% in one power supply period (step S02). The fact that the duty ratio is 80% or less in one whole power supply cycle means that the converter current I2 is sufficiently changed at the timing when the converter current I2 changes sharply as shown by the circle in FIG. ) It seems that it is following. That is, since there is still room for increasing the duty ratio, the active filter output current I3 can follow the converter current I2 even if the change rate ΔI is reduced as compared with the current state. Therefore, when the duty ratio is 80% or less over the entire power cycle (step S02: YES), the DC voltage adjustment unit 302 of the active filter control unit 30 performs a process of reducing the DC voltage Vdc (step S03). ). By doing in this way, as shown in Formula (1), since change rate (DELTA) I falls with the fall of DC voltage Vdc, the ripple width | variety R is suppressed.

  On the other hand, when the duty ratio is not less than 80% in the entire power supply cycle (step S02: NO), the duty ratio determination unit 301 then reaches the peak duty ratio in a part of the power supply cycle (100). %) Is determined (step S04). Here, the fact that the duty ratio has reached its peak in a part of one power supply cycle can be followed sufficiently particularly at the timing when the converter current I2 changes sharply as indicated by the circles in FIG. There is no possibility. That is, the change rate ΔI should be increased from the current level so that the active filter output current I3 can sufficiently follow the converter current I2. Therefore, when the duty ratio reaches a peak in a part of one power cycle (step S04: YES), the DC voltage adjustment unit 302 performs a process of increasing the DC voltage Vdc (step S05). By doing in this way, since change rate (DELTA) I raises with the raise of DC voltage Vdc, the followability to converter current I2 increases and a duty ratio does not peak.

  When the duty ratio does not reach the peak in a part of the power cycle (step S04: NO), the DC voltage adjustment unit 302 ends the process without changing the DC voltage Vdc.

(Function, effect)
FIG. 6 and FIG. 7 are diagrams for explaining the action and effect based on the processing of the active filter control unit according to the first embodiment.
Hereinafter, the operations and effects obtained as a result of the processing flow described above will be described with reference to FIGS. 6 and 7.

First, it is assumed that the air conditioning system 1 is in the state shown in FIG. That is, as shown in FIG. 6, in the air conditioning system 1, the load of the compressor motor 13 is high, and the amplitude W of the system current I <b> 1 changes at a relatively high amplitude “W1”. It is assumed that the DC voltage Vdc at this time is “Vdc1” and the ripple width R is “R1”.
Next, it is assumed that the air conditioning system 1 has transitioned from the state illustrated in FIG. 6 to the state illustrated in FIG. That is, as shown in FIG. 7, in the air conditioning system 1, it is assumed that the load on the compressor motor 13 is reduced and the amplitude W of the system current I <b> 1 has changed to “W2” (W2 <W1). As the load (amplitude) decreases, the degree of abrupt change in the converter current I2 also decreases, so that the duty ratio of the ON / OFF command calculated by the command output unit 300 decreases as a whole.

  As the duty ratio of the ON / OFF command decreases as a whole, the active filter control unit 30 proceeds to the processing of Step S02 to Step S03 shown in FIG. 5 and decreases the DC voltage Vdc. As a result, the DC voltage Vdc decreases from “Vdc1” to “Vdc2” (Vdc2 <Vdc1). As a result, the ripple width R is suppressed from “R1” to “R2” (R2 <R1).

  It is assumed that the load (amplitude) increases again after the DC voltage Vdc is reduced to “Vdc2”. In this case, if the DC voltage Vdc is in the state of “Vdc2” (that is, the state in which the ripple width R is suppressed to “R2”), it becomes impossible to follow a sudden change in the converter current I2, and the ON / OFF command A period when the duty ratio reaches 100% occurs.

  When the duty ratio of the ON / OFF command reaches 100%, the active filter control unit 30 proceeds to the processing of step S04 to step S05 shown in FIG. 5 and increases the DC voltage Vdc. As a result, the DC voltage Vdc rises from “Vdc2” to “Vdc1”. Thereby, although the ripple width R increases from “R2” to “R1”, it becomes possible to sufficiently follow the steep change of the converter current I2, and the system current I1 can be shaped into a sine wave.

  As described above, according to the active filter device 3 according to the first embodiment, it is possible to suppress the ripple while maintaining the harmonic suppression performance.

<Second Embodiment>
Next, an active filter device according to a second embodiment and an air conditioning system including the active filter device will be described with reference to FIG.

(Overall configuration of in-vehicle air conditioner control device)
FIG. 8 is a diagram illustrating an overall configuration of an air conditioning system according to the second embodiment.
As shown in FIG. 8, the active filter device 3 according to the second embodiment is configured to be incorporated into the outdoor unit 1 </ b> A of the air conditioning system 1.
Specifically, the active filter circuit 31 of the active filter device 3 according to the second embodiment is provided between the rectifier circuit 11 and the inverter circuit 12 of the outdoor unit 1A. The active filter circuit 31 includes a switching element SW3, a reactor L3, a diode D3, an electrolytic capacitor C3, and a converter current detection sensor SE.
The electrolytic capacitor C3 of the active filter circuit 31 is connected between the high potential output line α and the low potential output line β of the rectifier circuit 11, and smoothes the voltage rectified by the rectifier circuit 11 to generate the DC voltage Vdc. .
The switching element SW3 of the active filter circuit 31 connects (short-circuits) between the high potential output line α and the low potential output line β of the rectifier circuit 11 when turned on. When the switching element SW3 is turned on, a current instantaneously flows from the high potential output line α to the low potential output line β, but the change in the current is suppressed by the reactor L3. By appropriately switching the switching element SW3 by the active filter control unit 30, the current flowing on the output side (downstream side) of the rectifier circuit 11 is formed as a sine wave as a whole. The diode D3 prevents a backflow of current from the downstream side when the switching element SW3 is turned on.

  Converter current detection sensor SE is a resistance element (shunt resistance) installed on the upstream side of switching element SW3 in low potential output line β. The voltage drop generated in this resistance element indicates the current flowing to the output side of the rectifier circuit 11 (the active filter circuit 31, the inverter circuit 12, the compressor motor 13, etc.).

  Since the specific operation of the active filter control unit 30 of the active filter device 3 according to the second embodiment is the same as that of the first embodiment (processing flow shown in FIG. 5), detailed description thereof is omitted.

  In the description of each of the above-described embodiments, the duty ratio determination threshold value related to the processing flow (FIG. 5) of the active filter control unit 30 is uniquely specified as 100%, 80%, and the like. The specific value of the determination threshold is not limited to these, and can be changed as appropriate according to the embodiment.

  As described above, several embodiments according to the present invention have been described. However, all these embodiments are presented as examples, and are not intended to limit the scope of the invention. The above-described embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. The above-described embodiments and modifications thereof are included in the invention described in the claims and the equivalents thereof as well as included in the scope and gist of the invention.

DESCRIPTION OF SYMBOLS 1 Air conditioning system 1A Outdoor unit 10 Noise filter 11 Rectifier circuit 12 Inverter circuit 13 Motor for compressor 2 AC power supply 3 Active filter device 30 Active filter control unit 31 Active filter circuit T Power supply connection terminal SW3 Switching element D3 Diode L3 Reactor C1, C3 Electrolytic capacitor SE Converter current detection sensor

Claims (6)

A command output unit for outputting an ON / OFF command to the switching element of the active filter circuit based on the converter current flowing in the outdoor unit;
A duty ratio determination unit that determines whether or not a duty ratio of the ON / OFF command is below a predetermined lower limit value within a predetermined period;
A DC voltage adjusting unit that reduces a DC voltage output from the active filter circuit when a duty ratio of the ON / OFF command is below the predetermined lower limit;
An active filter device comprising: The duty ratio determination unit further determines whether the duty ratio of the ON / OFF command has reached a predetermined upper limit value,
The active filter device according to claim 1, wherein the DC voltage adjustment unit increases the DC voltage output from the active filter circuit when the duty ratio of the ON / OFF command reaches a predetermined upper limit value. The active filter device according to claim 1 or 2,
The outdoor unit;
Air conditioning system equipped with. The active filter device includes:
The air conditioning system according to claim 3, wherein the air conditioning system is incorporated in the outdoor unit. Outputting an ON / OFF command to the switching element of the active filter circuit based on the converter current flowing in the outdoor unit;
Determining whether a duty ratio of the ON / OFF command is below a predetermined lower limit value within a predetermined period;
Reducing the DC voltage output from the active filter circuit when the duty ratio of the ON / OFF command is below the predetermined lower limit;
A method for suppressing ripples. In the computer of the active filter device,
Outputting an ON / OFF command to the switching element of the active filter circuit based on the converter current flowing in the outdoor unit;
Determining whether a duty ratio of the ON / OFF command is below a predetermined lower limit value within a predetermined period;
Reducing the DC voltage output from the active filter circuit when the duty ratio of the ON / OFF command is below the predetermined lower limit;
A program that executes

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