JP3444011B2 - Active filter for electric power - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power active filter for removing harmonic components from distribution system power,
In particular, it relates to a compensation current command value computing means for computing a compensation current command value.

[0002]

2. Description of the Related Art Generally, a rectifier circuit in a power converter connected to a power distribution system is, from the viewpoint of the system, a load that consumes a fundamental wave active current and a source of a fundamental wave reactive current. Further, since it is also a source of harmonic current, in a power conversion device using a rectifier circuit, it is necessary to separate and remove the fundamental reactive current and the harmonic current that adversely affect the distribution system by some method. is there. Active filters are well known for separating and removing the harmonic currents.

FIG. 2 shows the basic principle of an active filter. The active filter 1 is a system power supply 2
Current i flowing from the load current to the load 3 which is the harmonic current source
The harmonic current detector 1A detects the harmonic current ih from r (ir = if + ih), and the compensation current command value ic * (ic * = ki) is supplied to the compensation current generation source (1B) such as an inverter.
h), and the compensation current ic (ic (ic) having the same magnitude and phase as the harmonic current ih in the compensation current generation source 1B.
= Ih) is sent to the system 2 to be canceled with the harmonic current ih, the system (load) current is (ir) is limited to the fundamental wave current if, and the harmonic current (power) is compensated.

Various proposals have been made for such an active filter 1, but the performance thereof is such that the compensation current command value i is detected by detecting the harmonic current ih from the load current ir.
harmonic current detector 1A for obtaining c * (ic * = kih),
And the compensation current ic (ic
= In), which is related to the characteristic of the compensation current generating source 1B.

FIG. 3 corresponds to the harmonic current detector 1A of the active filter 1 shown in FIG. 2 and shows a conventional example of a compensation current command value calculation circuit for obtaining the compensation current command value ic *.

In the conventional compensation current command value calculation circuit shown in FIG. 3, the load detection current ir detecting the load current ir (see FIG. 3) is converted from a three-phase signal to a two-phase signal by the three-phase / two-phase conversion circuit 12. Further, the coordinate converter 13 performs the rotational coordinate conversion by the voltage phase reference signal ωt of the fundamental frequency which is also the angular velocity reference of the system power supply 2 (see FIG. 3), and the fundamental wave current if ( (See FIG. 3) Active component current signal including positive phase active component current ip and positive phase reactive component current i
It is separated into a reactive current signal including q. As a result, the positive phase active component current ip and the positive phase reactive component current iq of the fundamental wave current if
Can be treated as a constant DC component and are not subject to compensation (removal) by the active filter, so they are detected by the low-pass filters 11 and 11 'of the next stage, and are respectively detected by the matching circuits 15 and 15'. It is subtracted from the load detection current ir (effective portion, ineffective portion) and removed from the load detection current ir.

In this case, the fundamental positive-phase reactive current iq is
If the active filter only performs high frequency compensation, it will be detected and removed by the low pass filter as described above.
When not only the harmonic current compensation but also the reactive current iq compensation, this DC component is not removed.

In this way, the fundamental phase positive phase current if
The load detection current ir from which the (effective component ip, the ineffective component iq) is removed becomes only the harmonic current component ih (effective component ihp, ineffective component ihq) compensated by the active filter.
If this harmonic current component ih is subjected to coordinate reverse conversion by the coordinate converter 13 'and further converted into a three-phase signal by the phase converter 12', the compensation current command value ic * of the active filter can be obtained.

Generally, in the active filter 1 (see FIG. 3), since there is a circuit loss, the DC side voltage of the compensation current generating source 1B changes, and the compensation current ic as the compensation current command value ic * is obtained. Since it cannot be obtained, a control loop for keeping the DC side voltage constant is provided, the DC side voltage set value Vs is compared with the DC side voltage detection value Vd, and the voltage controller 14 is controlled by the comparison deviation signal. The constant DC voltage control signal, which is an output, is added to the harmonic effective component current signal ihp in the matching circuit 16 to increase the compensation current command value ic * by the amount of circuit loss for compensation.

[0010]

In the conventional compensation current command value arithmetic circuit as described above, the active component current and the reactive component current of the fundamental phase positive phase can be treated as a DC component, and the separation thereof is easy. However, the fundamental anti-phase component current, which is the second harmonic component generated due to load imbalance, cannot be easily distinguished and separated from other harmonic currents. It will be calculated as a compensation current to be compensated by the active filter.

Therefore, since the active filter also compensates for the fundamental-phase reverse-phase current that occurs due to load imbalance, etc., when the harmonic current component to be compensated for increases, the output of the active filter device increases. There is a problem that the harmonic current component cannot be compensated due to the capacity limitation. That is, the ratio of the fundamental wave anti-phase component current (second harmonic component current) in the actual system is larger than that of the other harmonic currents, and the fundamental wave anti-phase component current is a subharmonic AC component. Therefore, when trying to compensate for all other harmonic current components including compensation of the reverse-phase component current of these fundamental waves, the equipment capacity increases and the equipment capacity (equipment cost)
Cause an adverse effect on.

As a method of separating the current of the opposite phase (second harmonic) of the fundamental wave, generally, a bandpass filter of the second harmonic can be inserted. It is not always a good method considering the influence of the phase difference.

Further, even if an attempt is made to limit the current of the fundamental wave anti-phase component (second harmonic component) due to the capacity of the active filter device, the fundamental wave anti-phase component current is an alternating current component, so that it is handled. It will be very difficult to achieve.

The present invention has been made in view of the above points, and in particular, the reverse-phase component current of the fundamental wave generated due to load imbalance is easily separated from the system (load) current and compensated. It is possible to select the compensation target current according to the load condition, such as being excluded from the target, and variably control the limit value of each compensation current so that the device capacity is always 1 regardless of the load condition.
An object of the present invention is to obtain an active filter having a compensation current command value calculation circuit capable of outputting up to 00%.

[0015]

In the present invention, the means for solving the above-mentioned problems and the function thereof are connected to a power source in parallel with a load, and a harmonic included in the load current from the load current. A compensation current command value calculation circuit for detecting a wave component and calculating a compensation current command value, and a compensation for canceling the harmonic component by inputting the compensation current command value calculated by the compensation current command value calculation circuit as a control signal. A compensating current generating means for outputting a current, which is an active filter for electric power, wherein the compensating current command value arithmetic circuit converts a load current into three phases and two phases to perform rotational coordinate conversion according to a power supply voltage phase. Rotational coordinate transformation separates the fundamental wave effective component and fundamental wave ineffective component to remove them, and then performs rotational coordinate transformation at a frequency twice the power source angular frequency to accompany load imbalance. The opposite phase component of the main wave is separated and removed to extract the harmonic component, and the separated opposite phase component is added again to enable compensation of the opposite phase component, and the current value of each of these components is set to a predetermined value. A harmonic component current limit circuit that limits the value and a fundamental wave antiphase current limit circuit are provided.
The harmonic component and anti-phase component limited to the specified value are returned by rotational coordinate conversion with a frequency twice the angular frequency of the power supply, and the fundamental reactive component separated earlier is added via the fundamental reactive current limit circuit. Then, after the rotational coordinate conversion of the power supply cycle is performed, the two-phase three-phase conversion is performed to obtain the three-phase compensation current value command value, and the currents of the harmonic component, the fundamental wave antiphase component, and the fundamental wave reactive component are input, A limit value variable control means for variably controlling the limit value of the harmonic component current limit circuit, the fundamental wave reverse phase current limit circuit, and the fundamental wave reactive current limit circuit is provided, and the current of either one of the limit circuits reaches the limit value. , If the current of the other limit circuit has not reached the limit value, change the limit value of the limit circuit that reached the limit value to match the device capacity regardless of the load condition. Characterized in that with the capability to force.

In addition, priority control can be performed by setting a priority for each component in advance in changing the limit value by the limit value variable control means.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a compensation current command value calculation circuit of the present invention will be described with reference to FIG.

In FIG. 1, low-pass filters 11 and 1
1 ', phase converters 12, 12', coordinate converters 13, 13 '
The voltage controller 14 indicates the same device having the same function as that used in the conventional compensation current command value calculation circuit shown in FIG.

In the embodiment of the present invention, the conventional compensation current command calculation circuit is added to the fundamental frequency 2 of the system 2 (see FIG. 3).
Coordinate converter 1 using voltage phase reference signal 2ωt of double frequency
9. A fundamental wave anti-phase component (second harmonic component) separation / removal circuit including low pass filters 18 and 18 'for detecting a second harmonic component (fundamental anti-phase component) and a matching circuit 20, 20', and coordinates For limiting the device capacity of the coordinate inverse converter 19 'and the active filter by the voltage phase reference signal 2ωt having the double frequency of the fundamental frequency of the system, that is, the fundamental reactive current limiting circuit 22. , A harmonic component limit circuit 23, a fundamental wave reverse phase current limit circuit 24, and a limit value variable control circuit 25 for variably controlling the limit values of these current limit circuits.
Is provided.

Therefore, the same or corresponding portions as those in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted, and the newly added embodiment of the present invention will be described in detail.

Reference numeral 22 in FIG. 1 is for making the active filter compensation target a minimum fundamental wave positive phase reactive current i1q 'from the fundamental wave positive phase reactive current i1q detected by the low-pass filter 11'. A fundamental wave reactive current limit circuit, 23 is a harmonic component current limit circuit for determining the upper limit of the harmonic component (active component, reactive component) current ih to be compensated, and 24 is detected by the low-pass filters 18, 18 '. A fundamental wave anti-phase current limit circuit for making a minimum fundamental wave anti-phase component current i2 from the fundamental wave anti-phase component current (active component, reactive component) i2 to be an active filter compensation target, 25-
Reference numerals 1, 25-2, 26-1, and 26-2 are limiters that allow currents below a predetermined value to pass through as they are and limit only currents above a predetermined value to the predetermined value.

Reference numeral 25 denotes a variable limit value control circuit, which takes in the respective compensation currents of the fundamental wave in-phase reactive component, the fundamental wave anti-phase component and the harmonic component, calculates the total output capacity from these compensation currents, and calculates the respective currents. If the limit values of the limit circuits 8, 9, 12 are variably controlled and the total compensation current does not exceed the device capacity, the upper limit of the limit value is changed and the device capacity is changed even if a certain component reaches the limit value. 100%
Up to output.

Next, the operation of the compensation current command value calculation circuit will be described.

The three-phase load detection current ir for detecting the system (load) current is converted from the three-phase signal to the two-phase signal by the phase number conversion circuit 12, and further, in the coordinate converter 13, the voltage phase of the fundamental frequency of the system. Rotational coordinate conversion is performed by the reference signal ωt, and an active component current including the positive phase active component current i1p of the fundamental wave positive phase active current i1 and a reactive component current including the positive phase reactive current i1q on the orthogonal coordinates of the fundamental frequency of the system. Is separated into The positive-phase effective component current i1p and the positive-phase reactive component current i1q on the Cartesian coordinates can be treated as constant DC components and are not covered by the active filter compensation. ′ Is detected and separated, and the matching circuits 15 and 15 ′ are subtracted from the two-phase load detection current ir to remove the two-phase load detection current ir.

In this case, the fundamental phase positive phase reactive current i1q
When the active filter performs only harmonic compensation, it is removed by the low-pass filter 11 'as described above and excluded from compensation. However, when performing not only harmonic current compensation but also reactive current compensation, this DC component Is not removed, that is, only the low-pass filter 11 is used.

Further, the two-phase load detection current ir from which the positive-phase active component current i1p and the positive-phase reactive component current i1q of the fundamental wave positive-phase component current i1 are removed by the matching circuits 15 and 15 'is the fundamental frequency of the system. The coordinate conversion unit 19 uses the voltage phase reference signal 2ωt having a frequency of 2 times the rotation frequency to perform the rotational coordinate conversion, and the effective phase current i2p of the fundamental wave on the Cartesian coordinates of the double frequency of the system and the effective phase current i2p of the reverse phase of i2 Component current and reverse-phase reactive component current i
The active component current i2p and the active component reactive current i2q that have been separated are separated into a reactive current containing 2q, and can be treated as constant DC components.

Therefore, in this embodiment, since the fundamental wave anti-phase component current i2 is also excluded from the compensation of the active filter, it is opposite to the anti-phase effective component current i2p of the fundamental wave anti-phase component current i2. The phase reactive current i2q is detected and separated by the low-pass filters 18 and 18 'of the next stage, and subtracted from the two-phase load detection current ir by the matching circuits 20 and 20', respectively. Similarly to the component current i1, the fundamental phase antiphase component (second harmonic component) current i2 is also equal to
It is removed from the phase load detection current ir.

The two-phase load detection current ir from which the fundamental wave positive-phase component current i1 and the fundamental wave anti-phase component current i2 are removed becomes only the harmonic component current which is the compensation target of the active filter, and the coordinates are restored. The coordinate inverse converter 19 'based on the voltage phase reference signal 2ωt of the double frequency of the fundamental frequency of the system, and the coordinate inverse transformer 1 based on the voltage phase reference signal ωt of the fundamental frequency
The three-phase compensation current command value ic * of the active filter is obtained through 3'and the phase converter 12 '.

The operation of the limit circuit will be described below.

Regarding the harmonic component current ih to be compensated by the active filter, the harmonic component current limit circuit 23 controls the harmonic component current i1 and the fundamental wave anti-phase component current i2. (Effective component ihp, reactive component ihd) Incorporating the current ih, its harmonic component current i
If h exceeds a predetermined value, the limiters 25-1, 25-2
Limit signal is output to the limiters 25-1, 25
-2 is activated to limit the harmonic component current ih to the predetermined value, thereby lowering the harmonic component current ih below the predetermined value.
Only the active filter is subject to compensation. Further, in the fundamental wave reactive current limit circuit 22, the low pass filter 11 ′ is applied to the fundamental wave positive phase reactive current i1q which is not subject to the compensation of the active filter.
Incorporating the fundamental wave positive phase reactive current i1q detected and separated by, the fundamental wave positive phase reactive current i1q ′ below a predetermined value
Is output and added to the two-phase load detection current ir from which the fundamental wave positive phase reactive current i1q has already been removed by the matching circuit 16 ', whereby the fundamental wave positive phase reactive current i1q' below the predetermined value is added. Are subject to compensation of the active filter. Further, even with respect to the fundamental wave anti-phase component current i2 that is not subject to compensation by the active filter, the fundamental wave anti-phase component current limit circuit 24 detects the fundamental wave anti-phase component current separated by the low-pass filters 18 and 18 '. (Effective part i2p, ineffective part i2q) Taking in current i2,
If the fundamental-phase antiphase current i2 exceeds a predetermined value, the limiter 2
A limit signal is output to 6-1 and 26-2, the limit circuits 26-1 and 26-2 are operated, and the fundamental wave antiphase current i
By limiting 2 to a certain predetermined value, a fundamental wave antiphase current i2 ′ that is less than the predetermined value is output to output the matching circuits 21 and 2.
At 1 ′, the fundamental wave antiphase current i2 has already been removed 2
By intentionally adding to the phase load detection current ir, the active filter compensation target is also applied to the fundamental wave reverse phase component current i2 ′ below the predetermined value.

Originally, the active filter compensates the harmonic component current ih, and the fundamental wave positive phase reactive current i1.
Although q and the fundamental wave anti-phase component current i2 are to be compensated, as described above, the fundamental wave positive phase reactive component current i1
Since q and the fundamental wave anti-phase component current i2 have an adverse effect on the system 2 (see FIG. 2), they must be removed from the system (load) current by some method.

Therefore, according to the circuit of this embodiment, by providing the limit circuits 22, 23, and 24 having a predetermined limit value for each component current that adversely affects the system, the active filter device capacity and the system ( load)
Depending on the magnitudes of the harmonic component current ih, the fundamental positive-phase reactive current i1q, and the fundamental anti-phase negative current i2 included in the current ir, if these component currents are to be compensated, the active filter All of the component currents that adversely affect the system 2 (see FIG. 2) only by applying the device are analyzed by the system load current i.
A compensation current command value ic * that can be removed from f is obtained.

As described above, when the current limit circuits are provided for the harmonic component, the fundamental wave anti-phase component and the fundamental wave ineffective component, respectively, and when these currents are controlled to be equal to or less than the fixed values, the total of the respective limit values becomes active. It becomes the upper limit value of the device capacity of the filter, and only when all of these components reach their respective limit values, the output of the device capacity of 100% can be output. Therefore, in the present invention, further,
If some components exceed the limit value and other components fall below the limit value depending on the load situation, and the device capacity has a margin, the limit value variable control circuit 25 judges it. The upper limit setting value of the current limit circuit that has reached the limit value is increased, and the compensation current values of all components are controlled so that the limit values reach the limit values. This makes the device capacity 100%
It is possible to output up to.

In the circuit of the embodiment shown in FIG. 1, a current source (FIG. 2,
1B) Compensation current command value ic * due to fluctuation of DC side voltage
In order to compensate for the above, a control loop for keeping the DC side voltage constant is provided, the DC side voltage set value Vs and the DC side voltage detection value Vd are compared, and the voltage controller 1 is based on the comparison deviation signal.
4 and adds the constant DC side voltage control signal, which is the output, to the harmonic effective current ihp of the load detection current ir in the matching circuit 16 to increase the compensation current command value ic * by the circuit loss. Compensating is shown in FIG.
This is the same as the conventional compensation current command value calculation circuit shown in FIG.

In the limit value variable control circuit,
If a certain guaranteed current component is compensated preferentially and there is a margin in the device capacity, priority control can be made possible by allocating that portion to other compensation components.

[0036]

As described above, according to the compensation current command value calculation circuit of the present invention, which is based on the fact that each component current such as the fundamental wave positive phase component current and the fundamental wave antiphase component current can be treated as a DC component. , It is possible to easily separate not only the positive-phase component current of the fundamental wave but also the negative-phase component current of the fundamental wave from the load detection current that has detected the load (system) current of the system. Of course, the compensation target currents such as the fundamental wave positive phase component current and the fundamental wave antiphase component current can be selected according to the load condition, and the compensation target currents can be removed from the load (system) current. Moreover, in order to separate each component current from the load detection current, it is sufficient to simply separate the direct current component, but it is sufficient to use a simple filter with a first-order lag element having a long time constant, but the transient stability against load fluctuation is sufficient. In addition, even if the system power supply frequency fluctuates, the separation operation by the low-pass filter having a good frequency stability that does not fluctuate the DC value of each component current can be obtained by the rotational coordinate conversion by the successive power supply frequency.

Further, since each component current can be treated as a DC component, the structure of the limit circuit for each component current can be simplified and can be easily installed. Therefore, by installing the limit circuit, the capacity of the active filter device can be reduced. Not only is the calculation easier, but the filter device is prevented from becoming overloaded during actual operation, and a certain amount of the fundamental wave positive-phase reactive current and fundamental wave anti-phase It is also possible to remove the current.

Further, a current limit circuit is provided for each of the harmonic component, the fundamental wave anti-phase component and the fundamental wave ineffective component,
When controlling within a fixed value, the total of the respective limit values becomes the upper limit value of the device capacity, and the device capacity 100% is output only when all these components reach their respective limit values.

As described above, the present invention makes it possible to individually variably control the limit value of each compensation current of the harmonic component, the fundamental wave anti-phase component and the fundamental wave reactive component, and the control in which each component reaches the limit value. Since this is done, it is possible to always output up to 100% of the device capacity of the active filter regardless of the load condition.

Further, there is an excellent effect that priority is given to the compensation current by giving priority to the changing process of each component limit value.

[Brief description of drawings]

FIG. 1 is an embodiment of a compensation current command value calculation circuit for an active filter according to the present invention.

FIG. 2 is a basic principle diagram of an active filter.

FIG. 3 shows a compensation current command value calculation circuit for a conventional active filter.

[Explanation of symbols]

1 ... Active filter 2 ... power distribution system 3 ... Grid load 11, 11 ', 18, 18' ... Low-pass filter 12, 12 '... Phase converter 13, 13 ', 19, 19' ... Coordinate converter 22 ... Basic wave reactive current limit circuit 23 ... Harmonic component current limit circuit 24 ... Basic wave reverse phase current limit circuit 25 ... Variable limit value control circuit.

Claims (2)

(57) [Claims] 1. A compensating current command value calculating circuit, which is connected to a power source in parallel with a load and detects a harmonic component contained in the load current from the load current to calculate a compensating current command value.
An active power filter comprising: a compensation current command value calculated by the compensation current command value calculation circuit as a control signal; and a compensation current generating means for outputting a compensation current for canceling the harmonic component, The compensation current command value calculation circuit converts the load current into three phases and two phases and performs rotation coordinate conversion according to the power supply voltage phase, and by this rotation coordinate conversion, the fundamental wave effective component and the fundamental wave ineffective component are separated and removed. Then, the rotational coordinate conversion at a frequency twice the angular frequency of the power source is performed to separate the reverse phase of the fundamental wave due to load imbalance,
A harmonic component current is obtained by removing the harmonic component, removing the harmonic component again, and adding the separated negative phase component again to enable compensation of the negative component, and limiting the current value of each component to a predetermined value. A limit circuit and a fundamental wave anti-phase component current limit circuit are provided, and the harmonic component and the anti-phase component limited to a predetermined value are returned by rotational coordinate conversion with a frequency twice the angular frequency of the power supply, and the fundamental wave separated first The reactive components are added through a fundamental wave reactive current limit circuit, the rotational coordinates of the power supply cycle are converted, and then the two-phase and three-phase conversion is performed to obtain a three-phase compensation current command value. Minute variable and fundamental wave reactive component currents are input, and a limit value variable control means is provided to variably control the limit values of the harmonic component current limit circuit, fundamental wave anti-phase component current limit circuit, and fundamental wave reactive current limit circuit. , If the current of one of the limit circuits reaches the limit value and the current of the other limit circuit does not reach the limit value, change the limit value of the limit circuit of the one that reached the limit value, An active filter for electric power, characterized in that an output suitable for the device capacity can be output regardless of the state. 2. The active filter for electric power according to claim 1, wherein priority is set in advance for each component in changing the limit value by the limit value variable control means.