JP7141853B2 - Active filter device, air conditioning system, ripple suppression method and program - Google Patents

Description

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

2. Description of the Related Art In an air conditioning system, it is known to use an inverter to rotate a compressor motor of an outdoor unit or the like as desired. A current flowing through an 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 power. Therefore, an active filter device is used to suppress the 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 AC current input to an outdoor power supply device and an indoor power supply device, and a harmonic adjustment of the AC current based on the current detection result of the current detection unit. An air conditioner including a harmonic suppressor that performs control to reduce wave components is disclosed.

Japanese Patent Application Laid-Open No. 2004-364491

The active filter device detects a current (that is, a current containing harmonics, hereinafter also referred to as a "converter current") for driving a compressor motor of an outdoor unit, etc., and follows the sudden change. By superimposing an appropriate current on the power system, the total current supplied from the power system (hereinafter also referred to as "system current") is formed into a sinusoidal 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 the 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 caused by repeated ON/OFF of the switching element. 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 will not be able to follow a sharp change (harmonics) in the converter current, and the original purpose of suppressing harmonics will be reduced. For this reason, the reactor generally has an upper limit for the inductance value so that harmonics can be suppressed (followed) with respect to the maximum converter current that flows during rated output operation of the outdoor unit.

In this way, the reactor has an upper limit value for the inductance value according to the maximum converter current, so when the converter current is low, the ripple suppressing effect is relatively insufficient. Therefore, harmonic components due to ripples increase. In addition, when the ripple width becomes large relative to the amplitude of the system current, the error in zero-crossing detection becomes large, and the motor control by the inverter is likely to have problems.

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 that flows through an outdoor unit; a duty ratio determination unit for determining whether or not the duty ratio of the ON/OFF command is below a predetermined lower limit; a DC voltage adjustment unit that reduces the DC voltage output from the filter circuit.

Further, according to the second aspect of the present invention, the duty ratio determining section further determines whether or not the duty ratio of the ON/OFF command has reached a predetermined upper limit value, and the DC voltage adjusting section and increasing the DC voltage output from the active filter circuit when the duty ratio of the ON/OFF command reaches a predetermined upper limit value.

Further, according to a third aspect of the present invention, an air conditioning system includes the above active filter device and the outdoor unit.

Further, according to the fourth aspect of the present invention, in the air conditioning system described above, the active filter device is incorporated inside the outdoor unit.

Further, according to a fifth aspect of the present invention, a ripple suppression method includes the steps of: outputting an ON/OFF command to a switching element of an active filter circuit based on a converter current flowing in an outdoor unit; a step of determining whether or not 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, a and lowering the output DC voltage.

Further, according to the sixth aspect of the present invention, the program outputs an ON/OFF command to the switching element of the active filter circuit to the computer of the active filter device based on the converter current flowing through the outdoor unit. a step of determining whether the duty ratio of the ON/OFF command is below a predetermined lower limit value within a predetermined period; and if the duty ratio of the ON/OFF command is below the predetermined lower limit value, and reducing the DC voltage output from the active filter circuit.

According to at least one of the above aspects, it is possible to suppress ripple while maintaining harmonic suppression performance.

It is a figure showing the whole air-conditioning system composition concerning a 1st embodiment. 3 is a diagram showing the functional configuration of an active filter control section according to the first embodiment; FIG. FIG. 3 is a diagram for explaining functions of the active filter device according to the first embodiment; FIG. 4 is a diagram for explaining the operation of the active filter control section according to the first embodiment; FIG. It is a figure which shows the processing flow of the active filter control part which concerns on 1st Embodiment. FIG. 4 is a diagram for explaining actions and effects based on processing by an active filter control unit according to the first embodiment; FIG. 4 is a diagram for explaining actions and effects based on processing by an active filter control unit according to the first embodiment; It is a figure showing the whole air-conditioning system composition concerning a 2nd embodiment.

<First Embodiment>
An active filter device according to a first embodiment and an air conditioning system including the same will be described below with reference to FIGS. 1 to 7. FIG.

(Overall configuration of in-vehicle air conditioner control device)
FIG. 1 is a diagram showing the overall configuration of an air conditioning system according to the first embodiment.
The air-conditioning system 1 is an air-conditioning system having an outdoor unit 1A and an active filter device 3 . The air conditioning system 1 also includes an indoor unit, which is not shown in FIG.
An outdoor unit 1A of the air conditioning system 1 according to this embodiment is connected to an AC power supply 2 via a power connection terminal T. As shown in FIG. 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 closer to the AC power supply 2 is also referred to as the "upstream side", and the side closer to the compressor motor 13 is referred to as the "downstream side". ” is also written.

A 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 .
A 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 diode elements. A rectified high potential is output from the high potential output line α, which is the output line of the rectifier circuit 11, and a 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 to generate a DC voltage.
The inverter circuit 12 is a power conversion circuit for generating desired AC power based on the DC voltage rectified by the rectifier circuit 11 and smoothed by the electrolytic capacitor C1. The inverter circuit 12 generates AC power for rotationally driving the compressor motor 13 at a desired number of revolutions.
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 rotationally driven based on the three-phase AC power generated by the inverter circuit 12 .
The converter current detection sensor SE is a current sensor that detects a three-phase AC current flowing from the AC power supply 2 to the outdoor unit 1A. Converter current detection sensor SE may be, for example, a clamp-type current sensor or the like.

Next, the active filter device 3 will be explained.
As shown in FIG. 1, the active filter device 3 is connected to the AC power supply 2 via the power connection terminal T of the outdoor unit 1A. The active filter device 3 includes an active filter control section 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 provided in the active filter circuit 31 based on the detection result of the converter current I2 obtained 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 has 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 rectification 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.
By appropriately ON/OFF-controlling the switching element SW3, the active filter circuit 31 outputs a current (active filter output current I3) for suppressing harmonics of the converter current I2. By superimposing the active filter output current I3 on the converter current I2, the system current I1 is formed into a sine wave with reduced harmonics.

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

(Functional configuration of active filter control unit)
FIG. 2 is a diagram illustrating a functional configuration of an active filter control section according to the first embodiment;
As shown in FIG. 2, the active filter control section 30 functions as a command output section 300, a duty ratio determination section 301, and a DC voltage adjustment section 302 by operating according to a predetermined program.
The command output unit 300 outputs an ON/OFF command to the switching element SW3 of the active filter circuit 31 based on the converter current I2 flowing from the AC power supply 2 to the outdoor unit 1A. The switching element SW3 is turned ON/OFF according to this ON/OFF command.
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 this embodiment determines whether or not the duty ratio of the ON/OFF command is below a predetermined lower limit value (80%, for example). Further, the duty ratio determination unit 301 according to this 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 by changing the ON/OFF pattern of the switching element SW3 as a synchronous rectification circuit, for example. 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 adjustment 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 examples of current waveforms of system current I1, converter current I2, and active filter output current I3.

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

The active filter output current I3 output by the active filter device 3 changes according to the converter current I2. In particular, the active filter output current I3 changes in accordance with the sharp change in the converter current I2 at the locations indicated by the circles in FIG. As described above, the active filter output current I3 must change in accordance with the steep change in the converter current I2 as indicated by the circles in FIG. 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 the steep change in the converter current I2, the system current I1 is formed into a current waveform close to a sine wave.

(Operation of active filter control section)
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 command output unit 300 acquires converter current I2 through converter current detection sensor SE, it calculates a current command indicating a current to be output in order to suppress harmonics of converter current I2.

Subsequently, the command output unit 300 superimposes the calculated current command on a comparison carrier that is a predetermined triangular wave (see FIG. 4). Then, command output unit 300 outputs an ON/OFF command (PWM signal) whose ON period is a period in which the triangular wave is less than the current command. Hereinafter, the ratio of the period during which the ON/OFF command is "ON" (ON period) to one carrier period is also referred to as "duty ratio" (%). Note that the carrier period of the comparison carrier is, for example, 20 kHz.

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 between the ON state and the OFF state based on this ON/OFF command.
As shown in FIG. 4, the ON/OFF control of the switching element SW3 based on the duty ratio specified by the current command and the comparison carrier causes the active filter output current I3 to instantaneously change the ON/OFF state of the switching element SW3. The active filter output current I3 corresponding to the current command is output on average while repeating the increase/decrease according to the OFF state.

As indicated by the circle 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%), command output unit 300 can increase active filter output current I3 at the maximum rate of increase (rate of change ΔI). Here, the rate of change .DELTA.I is the rate of change per unit time of the active filter output current I3 during the ON period of the switching element SW3, and is determined by equation (1).

In equation (1), "Vdc" is the DC voltage Vdc applied to electrolytic capacitor C3. "L" is the inductance value of reactor L3. Also, "dI/dt" is the change rate ΔI of the active filter output current I3.

According to the equation (1), the smaller the inductance value of the reactor L3 or the larger the DC voltage Vdc applied to the electrolytic capacitor C3, the higher the rate of change ΔI. can be made

On the other hand, the ripple width R, which is the width of fine rise/fall of the active filter output current I3 corresponding to ON/OFF of the switching element SW3, increases as the rate of change 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, especially at the timing indicated by the circle in FIG. 3, even if the duty ratio of the ON/OFF command is set to the maximum value (100%), it will not be possible to follow the change in the converter current I2.

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 change rate ΔI to suppress the ripple, and at the same time, reduces the duty ratio. When the plateau (100%) is detected, the rate of change ΔI is dynamically increased to follow the change in converter current I2.
Note that 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 the present embodiment dynamically changes the DC voltage Vdc applied to the electrolytic capacitor C3 to change the change rate ΔI of the active filter output current I3.

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

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 for 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 80% or less over the entire power supply cycle (step S02). The fact that the duty ratio is 80% or less over the entire power supply cycle means that, for example, even at the timing when the converter current I2 changes sharply as indicated by the circle in FIG. ). 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 rate of change ΔI is reduced from the current level. Therefore, if the duty ratio is 80% or less for the entire power supply cycle (step S02: YES), the DC voltage adjustment unit 302 of the active filter control unit 30 performs processing to reduce the DC voltage Vdc (step S03). ). By doing so, as shown in equation (1), the rate of change ΔI decreases as the DC voltage Vdc decreases, so the ripple width R is suppressed.

On the other hand, if the duty ratio is not equal to or less than 80% throughout one power supply cycle (step S02: NO), then the duty ratio determination unit 301 determines that the duty ratio peaks out (100%) in part of one power supply cycle. %) (step S04). Here, the fact that the duty ratio hits a peak in a part of one cycle of the power supply means that the converter current I2 can sufficiently follow the timing at which the converter current I2 abruptly changes, as indicated by the circle in FIG. may not. That is, the rate of change ΔI should be increased from the current state so that the active filter output current I3 can sufficiently follow the converter current I2. Therefore, when the duty ratio peaks out in part of one cycle of the power supply (step S04: YES), the DC voltage adjustment unit 302 performs processing to increase the DC voltage Vdc (step S05). By doing so, the change rate ΔI increases as the DC voltage Vdc increases, so that the followability to the converter current I2 is improved and the duty ratio does not peak out.

Note that if the duty ratio does not peak out in part of one cycle of the power supply (step S04: NO), the DC voltage adjustment unit 302 terminates the process without changing the DC voltage Vdc.

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

First, assume 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 on the compressor motor 13 is high, and the amplitude W of the system current I1 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, assume that the air conditioning system 1 transitions from the state shown in FIG. 6 to the state shown in FIG. That is, as shown in FIG. 7, in the air conditioning system 1, the load on the compressor motor 13 is reduced and the amplitude W of the system current I1 changes to "W2"(W2<W1). As the load (amplitude) decreases, the degree of steep change in converter current I2 also decreases, so the duty ratio of the ON/OFF command calculated by 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 steps S02 and S03 shown in FIG. 5 to reduce the DC voltage Vdc. As a result, the DC voltage Vdc drops from "Vdc1" to "Vdc2" (Vdc2<Vdc1). As a result, the ripple width R is suppressed from "R1" to "R2" (R2<R1).

Assume that the load (amplitude) rises again after the DC voltage Vdc is reduced to "Vdc2". In this case, if the DC voltage Vdc remains in the state of "Vdc2" (that is, the state in which the ripple width R is suppressed to "R2"), it will not be possible to follow the steep change in the converter current I2, and the ON/OFF command will A period occurs when the duty ratio peaks out at 100%.

When the duty ratio of the ON/OFF command peaks out at 100%, the active filter control unit 30 proceeds to the processing of steps S04 and S05 shown in FIG. 5 to increase the DC voltage Vdc. As a result, the DC voltage Vdc rises from "Vdc2" to "Vdc1". As a result, although the ripple width R increases from "R2" to "R1", it can sufficiently follow a steep change in 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, the ripple can be suppressed 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 same will be described with reference to FIG.

(Overall configuration of in-vehicle air conditioner control device)
FIG. 8 is a diagram showing the 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 designed to be incorporated inside the outdoor unit 1A of the air conditioning system 1. As shown in FIG.
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. Active filter circuit 31 includes switching element SW3, reactor L3, diode D3, electrolytic capacitor C3, and 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, smoothes the voltage rectified by the rectifier circuit 11, and generates a DC voltage Vdc. .
The switching element SW3 of the active filter circuit 31 connects (short-circuits) 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, current momentarily 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 to the output side (downstream side) of the rectifier circuit 11 is formed into a sine wave as a whole. The diode D3 prevents reverse current flow from the downstream side when the switching element SW3 is turned on.

Converter current detection sensor SE is a resistive element (shunt resistor) installed upstream 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 will be 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%, or the like. Specific values of the determination threshold are not limited to these, and can be changed as appropriate according to the mode of implementation.

Although several embodiments of the present invention have been described above, all these embodiments are provided by way of example and are not intended to limit the scope of the invention. The above-described embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. The above-described embodiments and modifications thereof are included in the scope and spirit of the invention, as well as the invention described in the claims and equivalents thereof.

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

Claims (6)

a command output unit that outputs an ON/OFF command to the switching element of the active filter circuit based on the converter current flowing through the outdoor unit;
a duty ratio determination unit that determines whether or not the maximum value of the duty ratio of the ON/OFF command within a predetermined period is below a predetermined lower limit;
a DC voltage adjustment unit that reduces the DC voltage output from the active filter circuit when the 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,
2. The active filter device according to claim 1, wherein the DC voltage adjusting section 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. an active filter device according to claim 1 or claim 2;
the outdoor unit;
air conditioning system. The active filter device is
The air conditioning system according to claim 3, which is incorporated inside the outdoor unit. a step 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;
determining whether the maximum value of the duty ratio of the ON/OFF command within a predetermined period is below a predetermined lower limit;
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 ripple suppression method comprising: In the computer of the active filter device,
a step 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;
determining whether the maximum value of the duty ratio of the ON/OFF command within a predetermined period is below a predetermined lower limit;
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;
program to run.

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