JP2018148757A - Active filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active filter capable of quickly generating a compensation current without requiring a memory means for recording a waveform. An active filter of the present invention is connected to a three-phase AC power source in parallel with an electric motor as a load. The active filter 20 includes a main circuit 23 that generates a compensation current that cancels harmonic components, and a controller 21 that controls driving of the main circuit 23. The controller 21 obtains a current command that approximates the current waveform at the timing when the system voltage is commutated by the AC power supply 3 with a square parabola, and drives the main circuit 23 based on the obtained current command. [Selection diagram] Figure 1

Description

  The present invention relates to an active filter that generates a compensation current that cancels harmonic components.

  When a load current flows from an AC power supply to a load, generally a so-called harmonic component is generated in the load current. Since this harmonic component causes a so-called harmonic disturbance, a countermeasure using an active filter is taken. The active filter detects the current of the harmonic generation load connected to the AC power supply with a current sensor, and injects a compensation current that cancels the detected harmonic component into the AC power supply line. Reduce the harmonic component of.

  Regarding the control of the active filter, for example, Patent Document 1 stores the current waveform of the device to be compensated and uses it for the current command of the active filter. The waveform to be stored at this time is 1/6 cycle of the power supply and compensates for the current detection delay and control delay. Japanese Patent Application Laid-Open No. H10-228707 states that the memory capacity can be saved by setting the waveform to be stored to be 1/6 power cycle.

  In Patent Document 2, the phase of the current waveform of the device to be compensated is advanced and used for the current command of the active filter. As a result, Patent Document 2 states that current detection delay and control delay can be compensated.

  Patent Document 3 proposes to compensate for a dead time due to a current detection delay or a control delay and an output filter for a current command of an active filter calculated from a current waveform of a device to be compensated.

Japanese Patent Laying-Open No. 2015-111995 JP 2014-121145 A Japanese Patent Laid-Open No. 10-336897

However, Patent Document 1 still requires a memory means for storing a waveform even if the capacity can be saved. Further, in Patent Document 1, when the AC power supply or the load is unbalanced, the compensation performance may be deteriorated because the waveform is different every 1/6 period.
Further, in Patent Document 2, in order to advance the phase, the waveform is delayed by the amount obtained by removing only the phase advancement (power supply cycle-phase advance) from the power supply cycle, but this also records the waveform. A memory means is required.
Furthermore, Patent Document 3 does not describe specific means for compensating for dead time.

  In view of the above, an object of the present invention is to provide an active filter that can quickly generate a compensation current without requiring a memory means for recording a waveform.

The present invention is an active filter connected in parallel to a load for a three-phase AC power supply, the active filter generating a compensation current that cancels harmonic components, and driving the main circuit. And a controller for controlling.
The controller in the present invention obtains a current command that approximates a current waveform at the timing when the system voltage from the AC power supply is commutated by a square parabola, and drives the main circuit based on the obtained current command. And

The controller in the active filter of the present invention, to remove the fundamental wave component from the current waveform to obtain the harmonic component from the harmonic component obtained, the phase θ when a peak value I _P and the peak value I _P of the current detected, the phase θ does not hit either than the range of (the phase θ when a peak value I _P) phase ~θp the phase voltage of the system voltage is equal, corresponds to a predetermined commutation timing is advanced by the control delay of I can judge.

  The controller in the active filter of the present invention can obtain an AF current command (CC1) that is a compensation current for canceling the harmonic component.

The controller in the active filter of the present invention determines that corresponds to a predetermined commutation timing based on the phase θp and the peak value I _P, obtains the AF current command advanced by the control delay of the phase theta (CC2), AF Current control can be performed by replacing the value of the current command (CC1) with the value of the AF current command (CC2).

  Further, when the controller in the active filter of the present invention determines that the predetermined commutation timing is not reached, the controller can control the current so as to be the AF current command (CC1).

  According to the present invention, it is only necessary to measure the current value and timing when commutation ends, so that a compensation current can be generated without the need for memory means.

It is a figure which shows the structure of the inverter which concerns on embodiment of this invention. In an inverter of an embodiment of the present invention, it is a figure showing current which flows into a converter when commutating from R phase to S phase. (A) shows the voltage waveform of the system voltage according to the embodiment of the present invention, (b) shows the waveform of the DC current and R-phase current of the converter, and (c) shows the R-phase current command generated by the active filter. The waveform is shown. (A) compares and shows the R phase current (upper graph) of the converter, the Q-axis current command of the active filter, and the waveform (lower graph) of the P-axis current command of the active filter in the embodiment of the present invention. (B) is a figure which shows each current waveform of the R phase of a converter when it will be in a voltage unbalanced state, S phase, and T phase. It is a flowchart which shows the control procedure of 1st embodiment of this embodiment. It is a flowchart which shows the control procedure of 2nd embodiment of this embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
A power supply device 1 according to the present embodiment includes an inverter 10 disposed between an AC power supply 3 and a load, for example, an electric motor 5, and an active filter 20 connected in parallel between the power supply device 1 and the inverter 10. .
In the power supply device 1, the constant voltage and the constant frequency three-phase alternating current output from the alternating current power supply 3 are converted into direct current by the inverter 10 and then reversely converted into alternating current, so that the magnitude of the frequency and voltage is arbitrarily adjusted. An alternating current is supplied to the electric motor 5.
The power supply device 1 determines the current command of the active filter 20 by predicting the waveform of the DC current smoothing converter by limiting the compensation target to the DC current smoothing converter. By predicting the current to be compensated in this way, there is no need to provide memory means for recording the waveform.

[Inverter 10]
Inverter 10 includes a converter circuit 11 connected to AC power supply 3 and an inverter circuit 13 connected to the output terminal of converter circuit 11. Converter circuit 11 converts an alternating current from alternating current power supply 3 into a direct current, and inverter circuit 13 converts a direct current received from converter circuit 11 into an alternating current. The inverter circuit 13 performs power conversion using a semiconductor switching element, and generates harmonics during the power conversion.
The inverter 10 includes a smoothing circuit 15 on the output side of the converter circuit 11. The smoothing circuit 15 is a filter that combines the DC reactor DCL and the capacitor C1, and smoothes the voltage applied to the resistance load. That is, the inverter 10 includes a DC current smoothing converter circuit 11.

The specific contents of the converter circuit 11 and the inverter circuit 13 are arbitrary as long as they fulfill their functions.
For example, the converter circuit 11 is premised to include one or a plurality of diodes, and there are a transformer method and a switching method, either of which can be used.

  As the inverter circuit 13, there are a voltage type inverter and a current type inverter, either of which can be used. Here, the voltage source inverter switches a load and a DC power source with a semiconductor switch, and supplies a square wave AC current to the load. In the current type inverter, a reactor is inserted on the DC side, and the current waveform becomes a square wave. In this embodiment, a voltage source inverter is employed.

[Active filter 20]
The active filter 20 generates a current that cancels and compensates the detected harmonics, and injects the generated compensation current into the electric wires W _R, W _S , and W _T that connect the AC power supply 3 and the converter circuit 11 of the inverter 10. To do. The active filter 20 is connected to the AC power supply 3 in parallel with the inverter 10.

The active filter 20 includes a controller 21 that controls the operation of the active filter 20, and a main circuit 23 that generates a current that cancels and compensates for harmonics according to instructions from the controller 21.
In the active filter 20, a controller 21 and a main circuit 23 are connected to the AC power supply 3 via an AC reactor ACL and a harmonic filter 25. The main circuit 23 is connected to the capacitor C2. The harmonic filter 25 removes harmonics caused by pulse width modulation performed by the switching elements constituting the main circuit 23 of the active filter 20.

  The controller 21 supplies the system voltage (R phase, S phase, T phase) of the AC power source 3 and the three-phase AC current (iR, iS, iT) flowing from the AC power source 3 to the electric motor 5 via the first detection circuit DL1. To detect. In addition, the controller 21 detects a second detection circuit DL2 of a current flowing through the AC reactor ACL, that is, a three-phase AC current that compensates for harmonics. Based on the detected information, the controller 21 performs a control operation for generating a current for compensating the harmonics, and drives and controls the main circuit 23 of the active filter 20.

The main circuit 23 generates a current that cancels out the harmonics and compensates in accordance with an instruction from the controller 21. The main circuit 23 is composed of a switching element, and generates a compensation current by PWM modulation that changes the duty ratio of the pulse wave by controlling on and off of the switching element.
The compensation current generated by the main circuit 23 is supplied to the AC power supply 3 via the AC reactor ACL and the harmonic filter 25.

In Patent Documents 1 and 2, the waveform is recorded in the memory means. In the present embodiment, the converter circuit 11 is limited to the direct current smoothing type, whereby the current waveform of the converter is obtained by approximation.
In the case of a DC current smoothing type converter, the input current changes sharply in accordance with the timing at which the phase current commutates. The current waveform of the converter circuit 11 is shown in FIG.
In the graph of FIG. 3 (b), as an example, the R-phase current of the converter is equal to or not equal to the DC current of the converter at times other than the timing surrounded by an ellipse where the converter DC current changes sharply. small.
A current command of the active filter 20, that is, a compensation current, is obtained by removing the fundamental wave component from the converter (R-phase) current. Therefore, as shown in the graph of FIG. 3C, the current command of the active filter 20 is also small except that it changes sharply at the commutation timing surrounded by an ellipse. In other words, the compensation current is not required to have a quick follow-up property other than the commutation timing.
As described above, only the commutation timing needs to be compensated for the delay in detection and control, and if the current waveform at the time of commutation is known, the delay as a whole can be compensated.

In the commutation, when the phase voltage of the system voltage becomes equal, specifically, in the case of the current of R phase, when the R phase voltage and the T phase voltage become equal, the R phase voltage and the S phase voltage become equal. Occurs when. FIG. 3A shows an example of the phase voltage of the system voltage. The R phase is commutated at a timing surrounded by a circle.
FIG. 2 shows the current flowing through the converter circuit 11 when commutating from the R phase to the S phase, following FIG. Before commutation, during commutation, and after commutation, the following process is followed.
Before commutation: i _R = idc, i _S = 0
During commutation: i _R + i _S = idc
After the _{commutation: iR = 0, i S =} idc

During commutation, a short circuit occurs through the diode of the converter circuit 11, so that the R-phase received voltage V _R and the S-phase received voltage V _S become equal, and the system impedance Z _L has a difference between the system power supply voltages V _RG and V _SG . Will be loaded.
Since commutation is completed in a very short time, the resistance component can be ignored, and only the inductance component L _{L of the} system affects.
The difference between V _RG and V _SG is a line voltage and is exactly a sine wave, but since commutation is a short time, it can be approximated linearly (v _SG −v _RG = kt).
For this reason, the waveform in which the S-phase current during commutation changes from 0 can be approximated to a square parabola as shown in the following equation 1.

As described above, commutation is started when the phase voltages of the system voltage are equal (line voltage = 0). Therefore, the commutation start timing can be known by measuring the system voltage.
As the converter current used as the current command of the active filter 20, the commutation start timing and the commutation end timing are detected, and the control current is advanced by the control delay or the change in the command current is fed forward to the voltage command in advance. Therefore, the delay can be compensated.
In order to generate this compensation current, it is only necessary to measure the current value and timing when commutation is completed, so that no memory means is required. As an example, this current value is indicated by a solid line H in the horizontal direction in FIG. 3B, and the timing at which commutation ends is indicated by a vertical solid line V in FIG. 3B.

In the present embodiment, as shown in FIG. 4A, harmonics obtained by removing the fundamental component from the converter current for the current command of the active filter 20 are converted into an effective component (P axis) and an ineffective component (Q axis). Can be converted. Then, a steep current change due to commutation appears only on the Q axis every 1/6 period of the AC power supply period.
Since commutation ends in a sufficiently short time, this change in the Q-axis current can be approximated to a square parabola. At this time, the end of commutation takes a maximum value so as to be surrounded by a circle in the lower graph of FIG.

  Next, a procedure for supplying a compensation current to the AC power supply 3 by the active filter 20 of the power supply device 1 according to the present embodiment will be described with reference to FIG. This procedure is executed by the controller 21 of the active filter 20 acquiring the system voltage, the converter current, and the like.

[First Embodiment]
[System voltage phase update (S101 in FIG. 5)]
The controller 21 of the active filter 20 continuously calculates and updates the phase θ from the voltage waveform of the input voltage of the active filter 20 detected via the first detection circuit DL1. The voltage waveform of the system voltage is as illustrated in FIG.

[Converter current harmonic component calculation (FIG. 5, S103)]
Next, the controller 21 removes the fundamental wave component from the converter current waveform (R phase, S phase, T phase) detected via the first detection circuit DL1, and obtains the harmonic component of the converter current.

[Commutation detection (S105 in FIG. 5)]
Next, the controller 21 detects the phase θ when the peak value I _P and the peak value I _P of the current are indicated from the obtained harmonic component of the converter current. Note that the phase θ at this time is θp. During one power cycle, θp appears twice for each phase, that is, R phase, S phase, and T phase.

[AF current command calculation (S107 in FIG. 5)]
The controller 21 obtains the waveform of the current command (AF current command) of the active filter 20 that cancels the harmonic component of the converter current. This AF current command is referred to as AF current command (CC1).

[Commutation timing judgment (FIG. 5, S109)]
The controller 21 determines whether or not the phase θ corresponds to a predetermined commutation timing advanced by a control delay from the commutation timing. The commutation timing here is specified in the range of the phase to θp where the phase voltages of the system voltage are equal. θp is a phase θ indicating a peak value in the harmonic component. Since the control delay is determined by the hardware configuration, the control delay time is set in advance.

[AF current command compensation (S115 in FIG. 5)]
The controller 21 determines that corresponds to a predetermined commutation timing (FIG. 5 S109 Yes), based on the phase θp and the peak value I _P indicating the peak value, AF current command advanced by the control delay of the phase theta ( AF current command (CC2) is obtained. The controller 21 compensates for the control delay by replacing the previously obtained AF current command (CC1) value with the obtained AF current command (CC2) value.

[AF current control (FIG. 5, S111)]
When the controller 21 determines that the commutation timing is not reached (No in FIG. 5), the controller 21 performs current control so that the AF current command (CC1) obtained in S107 is obtained, and obtains a voltage command by the active filter 20 by calculation. .
On the other hand, if the controller 21 determines that the commutation timing is not reached (S109 No in FIG. 5) and obtains the AF current command (CC2) in S115, the current is set so as to be the AF current command (CC2). Control is performed to obtain a voltage command by the active filter 20 by calculation.

[Duty output (S113)]
The controller 21 converts the AF voltage command obtained by calculation into a switching duty of a switching element that constitutes the main circuit 23 of the active filter 20. The controller 21 controls driving of the switching elements constituting the main circuit 23 based on the converted switching duty and outputs a compensation current.

[Second Embodiment]
FIG. 6 shows a series of procedures for converting a harmonic into an effective component (P axis) and an ineffective component (Q axis).
As shown in FIG. 6, the procedure for converting three phases (R phase, S phase, T phase) into two phases (P axis, Q axis) and two phases (P axis, Q axis) into three phases (R The procedure shown in FIG. 5 is the same as that shown in FIG.

[Effect]
As described above, according to the present embodiment, it is only necessary to measure the current value and timing when commutation is completed, so that a compensation current can be generated without requiring memory means.

  The preferred embodiments have been described above. However, the configuration described in the above embodiments can be selected or changed to other configurations as appropriate without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Power supply device 3 AC power source 5 Electric motor 10 Inverter 11 Converter circuit 13 Inverter circuit 15 Smoothing circuit 20 Active filter 21 Controller 23 Main circuit 25 Harmonic filter DCL DC reactor ACL AC reactor C1, C2 Capacitor DL1 First detection circuit DL2 Second detection circuit _{W R, W S, W T} wire

Claims (5)

An active filter connected in parallel with a load for a three-phase AC power source,
The active filter is
A main circuit that generates a compensation current that cancels harmonic components;
A controller for controlling the driving of the main circuit,
The controller is
Obtain a current command that approximates the current waveform at the timing when the system voltage from the AC power supply is commutated by a square parabola,
Driving the main circuit based on the determined current command;
An active filter characterized by that. The controller is
The fundamental wave component is removed from the current waveform to obtain the harmonic component,
From the obtained harmonic component, the phase θ when the current peak value I _P and peak value I _P are detected,
The phase θ is than the range of (the phase θ when a peak value I _P) phase ~θp the phase voltages are equal to the system voltage, does not touch or strike the predetermined commutation timing is advanced by the control delay of To determine,
The active filter according to claim 1. The controller is
An AF current command (CC1) that is the compensation current that cancels the harmonic components is obtained.
The active filter according to claim 2. The controller is
Wherein when it is determined that corresponds to a predetermined commutation timing based on said phase θp and the peak value I _P, obtains the AF current command advanced by said control lag from the phase theta (CC2),
The current control is performed by replacing the value of the AF current command (CC1) with the value of the AF current command (CC2).
The active filter according to claim 3. The controller is
If it is determined that the predetermined commutation timing is not reached, current control is performed so that the AF current command (CC1) is obtained.
The active filter according to claim 3.

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