JPH1169629A - Control method for active filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method for an active filter, in which even if a temperature and a system condition are changed, the command value of an inverter circuit is automatically corrected, so as to follow their change and which prevents a compensation rate from being lowered. SOLUTION: An inverter current Ii is injected into an injection circuit part 2 connected to a system bus 1, and an active filter 10 which offsets a harmonic current ILh in a load 4 is controlled. At this time, an error Iah between a harmonic current IaH which is detected from an active-filter output current Ia in the injection circuit part 2 and the harmonic current ILh is detected, so as to be input to an FIR-type adaptive filter 11. While a filter factor is being updated, a filter characteristic is changed so as to become a minimum error. A command value Ir is sent out to an inverter 3 from the adaptive filter 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method of an injection circuit type active filter which is installed in a system bus having a load of a harmonic generation source and cancels a harmonic current included in a load current.

[0002]

2. Description of the Related Art In recent years, electric appliances having power conversion devices using semiconductor elements, such as inverter air conditioners, have become widespread. As a result, harmonic failures occur frequently, and active filters (hereinafter referred to as AF
) Are increasing. AF
As shown in FIG. 4, a capacitor (Ca) and a reactor (La) are connected in series to an injection circuit section (2) connected to a system bus (1), and a reverse-phase harmonic is supplied from an inverter (3). An injection circuit system that suppresses harmonics by injecting an inverter current (Ii) is frequently used because of its excellent operation efficiency and the ability to reduce the inverter capacity. An example is shown in the general connection system in FIG. The following shows

In FIG. 5, (1) is a system bus, (2) is an injection circuit, (3) is an inverter, and (4) is a harmonic connected to a commercial AC power supply (Vs) via the system bus (1). Load with wave generation, (5) AF installed in the system,
(Z) is system impedance, and AF (5) has an injection circuit section (2), an inverter (3), and an inverter control circuit section (6).

The injection circuit section (2) includes a capacitor (C
a) and the primary side of the reactor transformer (T) are connected in series and connected to the system bus (1), and the AF output current (I
A current transformer (CTa) for detecting a) is inserted. Then, by using the reactor transformer (T), which has a high resistance to the harmonic current, to carry the harmonic component, the inverter component (3) handles the harmonic component, and the inverter capacity can be reduced.

The inverter (3) has an output side connected to the secondary side of the transformer (T) via an AC reactor (Lb), and converts a DC current supplied from a DC power supply (Cb) into an AC having a predetermined frequency. This is a current control type that converts and outputs a current. A current transformer (CTb) inserted on the output side uses an inverter current (I
i) is detected, and the detected value is detected as an inverter current command value (hereinafter, referred to as a command value) sent from the inverter control circuit (6).
(Ir).

The inverter control circuit section (6) performs a Fourier transform on the harmonic current (IL) from the load current (IL) detected by the current transformer (CTc) inserted into the system bus (1).
h) and a harmonic current (I)
Lh), a correction circuit unit (8) for setting a command value (Ir) to output an AF output current (Ia) and an inverter current (Ii) having a high compensation rate, and an inverter current (Ii).
And a command value (Ir), and a comparator (9) for driving and controlling the inverter (3) so that the two values match.

According to the above configuration, the inverter (3) is drive-controlled so that the inverter current (Ii) follows the command value (Ir) sent from the inverter control circuit (6), and the inverter current (Ii) Is injected into the system from the injection circuit section (2) via the transformer (T) to cancel and compensate for the harmonic current (ILh).

At this time, since the AF output current (Ia) is shunted from the inverter (3) to the capacitor (Ca) side and the inverter current (Ii) is enlarged, the AF output current (Ia) is increased in the correction circuit section (8). A value obtained by multiplying (Ia) by the reciprocal of the enlargement ratio is set as a command value (Ir).

Further, since the switching speed of the inverter (3) is limited, the output frequency is limited. As the frequency becomes higher, the amplitude of the inverter current (Ii) decreases and the phase shifts. Therefore, first, the current transformer (CTb) (C
The amplitude and phase of the AF output current (Ia) and the load current (IL) detected by Tc) are measured by the measuring device (11). Based on the measured value, the harmonic current (IL
h) The correction circuit unit (8) corrects the amplitude and phase parameters together with the enlargement ratio with a manual volume so as to output the AF output current (Ia) and the inverter current (Ii) that have a high compensation ratio with respect to h). Set the command value (Ir).

[0010]

According to the above-mentioned AF (5), the AF which has a high compensation ratio with respect to the harmonic current (ILh) is obtained.
Once the enlargement ratio, amplitude and phase parameters are set in the correction circuit section (8) to output the output current (Ia) and the inverter current (Ii), the set values are fixed. For this reason, the system impedance (Z) fluctuates more greatly than at the time of setting due to fluctuations in temperature and system conditions, and the injection circuit capacitor (Ca) and the injection reactor {reactor transformer (T)} of the injection circuit (2) and the system impedance (Z). When the shunt ratio of Z) changes, the amplitude and phase of the AF output current (Ia) greatly deviate, and the command value (I
r) followed by the inverter current (Ii), the compensation rate is greatly reduced, and the harmonic current (IL) generated by the load (4)
h) cannot be compensated. In addition, since the characteristic values of the injection circuit capacitor (Ca) and the injection reactor slightly change depending on the temperature, the frequency, and the like, there is also a problem that the compensation rate similarly decreases even if the calculated enlargement ratio is used.

An object of the present invention is to provide an AF control method for automatically correcting a command value of an inverter current according to a change in a temperature or a system condition to prevent a reduction in a compensation rate even if the temperature or a system condition changes. It is to be.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a method of controlling an AF for injecting an inverter current into an injection circuit connected to a system bus by connecting a capacitor and a reactor in series to cancel a harmonic current of a load. An error between the harmonic current of the order to be compensated detected from the AF output current of the circuit unit and the harmonic current of the load is detected and input to the FIR adaptive filter so that the filter error is updated and the minimum error is obtained. It is characterized in that a command value is transmitted from the adaptive filter to the inverter by changing the filter characteristics.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an AF control method according to the present invention will be described below with reference to FIGS. First, the same parts as those shown in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted. The difference is that the AF according to the present invention
In (10), an FIR adaptive filter (ADF) (11) is used in place of the correction circuit (8). That is, in FIG. 1, reference numeral (12) denotes a compensation target order (for example, fifth, seventh, or eleventh order) from the AF output current (Ia) detected by the current transformer (CTa) of the injection circuit unit (2) by Fourier transform.
(13th) harmonic detector for extracting the higher harmonic current (Iah), (13) is a higher harmonic current (ILh) and (Iah)
Is a comparator which detects the error (ILa) between the two and inputs the error to the adaptive filter (11).

The operation (method) of the present invention based on the above configuration will now be described. First, as shown in FIG. 2, the adaptive filter (11) outputs the output of the system (14) and the adaptive filter (1).
The error of the output of 1) is detected by the comparator (15), and the filter coefficient is automatically and gradually changed by the adaptive algorithm, so that the filter characteristic is changed so as to minimize the error.

Therefore, the error (IL) of the harmonic current (ILh) (Iah) detected by the harmonic detectors (7) and (12).
a) is detected by the comparator (13) and the adaptive filter (11)
Is input to the calculation unit. Then, the adaptive filter (1
In 1), the filter coefficient is automatically and gradually changed by the error (ILa), and the filter characteristic is changed so that the error (ILa) is minimized. Then, the command value (Ir) is automatically corrected so as to minimize the error between the harmonic current (ILh) of the load (4) and the AF output current (Ia) and sent to the inverter (3). By controlling the drive of the inverter (3) by the command value (Ir), the command value (Ir) is corrected and the harmonic current (ILh) is corrected even when the system impedance (Z) fluctuates and the magnification or phase changes. )
The AF (10) can be operated so as to follow.

FIGS. 3A and 3B show harmonic orders (eg, fifth, seventh, eleventh, and thirteenth orders) compensated by the AF (10).
Next) is taken out at once and one adaptive filter (11)
Are control block diagrams showing an embodiment in the case of inputting to each of the orders and in the case of taking out each order, inputting each of the orders to a plurality of adaptive filters (11)... And synthesizing them by an adder (16). In the former case, the signal is synthesized and becomes complicated, so that the adaptive filter (11) has a higher order. On the other hand, in the latter case, since the same frequency of the harmonic current of the load and the same frequency of the AF output current are compared, the signal is simple and the adaptive filters (11)...

[0017]

According to the present invention, in a control method of an injection circuit type AF for injecting an inverter current into an injection circuit to compensate for a harmonic current of a load, a compensation target detected from an AF output current of the injection circuit is used. The error between the harmonic current of the order and the harmonic current of the load is detected and input to the FIR adaptive filter. The filter characteristic is changed so that the minimum error is obtained while updating the filter coefficient. Is sent to the inverter, the AF can be operated so as to follow the harmonic current of the load even if the system impedance changes, and the operation can always be performed with a high compensation rate. In addition, since the magnification and the phase are automatically corrected, a measuring instrument becomes unnecessary, and the equipment is simplified.

[Brief description of the drawings]

FIG. 1 is an AF circuit block diagram showing an embodiment of an AF control method according to the present invention.

FIG. 2 is a general explanatory block diagram of an adaptive filter according to the present invention.

FIG. 3A is a control block diagram in a case where harmonic orders to be compensated are collectively extracted and input to one adaptive filter. (B) is a control block diagram in a case where harmonic orders to be compensated are extracted for each order and input to a plurality of adaptive filters.

FIG. 4 is a circuit diagram showing a general configuration of an injection circuit type AF.

FIG. 5 is a circuit diagram of a general connection system showing a conventional example of a control method of an injection circuit type AF.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 system bus 2 injection circuit section 3 inverter 4 load 10 AF 11 adaptive filter Ca injection capacitor T reactor transformer

Claims (1)

[Claims] 1. An active filter output current of an injection circuit for controlling an active filter for injecting an inverter current into an injection circuit connected to a system bus by connecting a capacitor and a reactor in series to cancel a harmonic current of a load. An error between the harmonic current of the order to be compensated and the harmonic current of the load, which is detected from the above, is input to the FIR adaptive filter, and the filter characteristic is changed so as to minimize the error while updating the filter coefficient. A method for controlling an active filter, comprising sending an inverter current command value from an adaptive filter to an inverter.