JPH0919062A - Active filter - Google Patents

Abstract

PURPOSE: To control the generation of higher harmonics and unbalance by zero-phase current element of a multiphase circuit having a zero-phase circuit by detecting zero-phase element from a detected current of a 3-phase load current and distributing such zero-phase element for addition to a 3-phase compensating current instruction value. CONSTITUTION: A zero-phase current compensating circuit 20 adds each load current transforming signal of each phase R, S, T with an adding circuit 21 to obtain a zero-phase current element, obtains a zero-phase current compensating amount distributed to each phase by multiplying the coefficient 1/3 to the zero-phase current element in a coefficient arithmetic circuit 22, adds this zero- phase current compensating amount to each phase compensating current command value from a phase converter 12' in the addition circuits 23R, 23S, 23T to define each phase compensating current command value as an output current command value of the current control circuit 24 of the current generating source. Therefore, the zero-phase current in the power source side is set to zero by generating the particular zero-phase current to the 3-phase 4-wire circuit as a compensating current from an active filter. Thereby, the influence of higher harmonics component and unbalance included therein can be removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active filter (harmonic compensating device for electric power) for removing harmonic power from electric power of a distribution system, and more particularly to compensating for zero-phase current in a multi-phase circuit having a zero-phase circuit. It relates to an active filter to be performed.

[0002]

2. Description of the Related Art In general, a rectifier circuit in a power converter connected to a distribution system is a load that consumes a fundamental active current and at the same time is a source of a fundamental reactive current when viewed from the above system. 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. 5 shows the basic principle of an active filter. The active filter 1 is a system power supply 2
From the load current ir (= if + ih) flowing to the load 3 (rectifier circuit, etc.), which is the harmonic current generation source, detects the harmonic current ih by the harmonic current detector 1A, and the compensation current command value is supplied to the current generation source 1B. ic * (= kih) is sent, and the compensating current ic (= ih) having the same magnitude and phase as the harmonic current ih in the current source 1B is sent to the grid 2 to cancel the harmonic current ih. (load)
The current is is only the fundamental wave current if, and the harmonic current (power) is compensated.

Various proposals have been made for such an active filter 1. FIG. 6 corresponds to the harmonic current detector 1A of the active filter 1 in FIG. 5 and shows a compensation current command value calculation circuit for obtaining the compensation current command value ic *.

In this compensating current command value calculation circuit, the load detection current ir for detecting the load current (see FIG. 5) is converted from the three-phase signal to the two-phase signal by the phase number conversion circuit 12, and further the coordinate converter. In 13, the positive phase effective component of the fundamental wave current if (see FIG. 5) on the rectangular coordinates of the fundamental frequency is converted by the rotation 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. 5). The active component current signal including the current ip and the reactive component current signal including the positive-phase reactive component current iq are separated.

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 constant DC components, and are not subject to compensation (removal) by the active filter. , The low-pass filters 11 and 11 ′ of the next stage detect the matching circuit 1 respectively.
At 5 and 15 ', the load detection current ir (effective and ineffective) is subtracted and removed from the load detection current ir.

In this case, the fundamental wave positive-phase reactive current iq is
When the active filter performs only harmonic compensation, it is detected and removed by the low-pass filter as described above.
When compensating for the reactive current iq as well as the harmonic current compensation, the DC component is not removed.

In this way, the fundamental wave positive phase component 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. 5), 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]

As a problem of the conventional active filter as described above, when applied to a multi-phase circuit having a zero-phase circuit, the zero-phase current cannot be controlled.
That is, it is impossible to expect the suppression of the harmonic current flowing there.

FIG. 7 shows a three-phase three-wire active filter. When this active filter is applied as it is as an active filter of a three-phase four-wire system, the current component flowing between each phase can be controlled, but it is neutral. The zero-phase current component flowing in the line cannot be controlled.

Therefore, it becomes impossible to suppress or balance harmonics on the power supply side. In particular, when a single-phase rectifier or the like is unevenly connected as a load between each phase and the neutral line, the third harmonic component of the zero-phase current increases, and the power supply voltage is significantly distorted. Further, when the load capacities are very uneven, the fundamental wave component of the zero-phase current also increases, making it impossible to balance the power supply side.

The present invention has been made in view of the above points, and provides an active filter capable of suppressing generation of harmonics and imbalance due to zero-phase current components in a multi-phase circuit having a zero-phase circuit. With the goal.

[0014]

In order to solve the above-mentioned problems, the present invention phase-converts a detection current of a three-phase load current supplied from a system of a multi-phase circuit having a zero-phase circuit to a two-phase circuit. As a load detection current, a two-phase compensation target current including a harmonic current or a reactive current of the system is detected from the two-phase load detection current, and the two-phase compensation target current is phase-converted to generate a three-phase current generation source. An active filter that uses a phase compensation current command value and removes a current to be compensated from the load current detects a zero-phase component from the detected current of the three-phase load current, and sets the zero-phase component to the three-phase compensation current command value. It is characterized in that a zero-phase current compensation circuit for distributing and adding is provided.

Further, the present invention is characterized in that the compensation target current is detected by providing a circuit for removing the fundamental wave antiphase component current from the load current.

Further, the present invention is characterized in that a current limiter circuit for limiting the current amount of the current to be compensated is provided.

[0017]

[Function] The current to be compensated includes the harmonic current or the reactive current, and further, the current excluding the reverse phase component current of the fundamental wave and the active filter for limiting by the current limiter circuit, the zero generated in the zero phase circuit The zero-phase current on the power supply side is made zero by detecting the phase current and distributing and adding it to the compensation current command value.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the basic construction of an active filter of the present invention. As shown in the figure, in this embodiment, the active filter is a three-phase four-wire type, and the current flowing between the neutral line and each phase can be freely controlled.

That is, the zero-phase current component generated from the load side is circulated by the active filter, and the zero-phase current on the power source side is made zero to avoid the influence.

The active filter control circuit for this purpose is realized by the configuration shown in FIG. In the figure, the low pass filters 11 and 11 ', the phase converters 12 and 12', the coordinate converters 13 and 13 ', and the voltage controller 14 are used in the conventional compensation current command calculation circuit shown in FIG. It shows the same device having the same function.

In this embodiment, a zero-phase current compensating circuit 2 shown by a broken line block is added to the conventional compensating current command calculating circuit.
0 is added.

This zero-phase current compensating circuit 20 is provided for each phase R,
A zero-phase current component is obtained by adding the load current change signals of S and T to each other in the adder circuit 21, and this zero-phase current component is multiplied by the coefficient 1/3 in the coefficient calculation circuit 22 to obtain each phase component. The distributed zero-phase current compensation amount is obtained, these zero-phase current compensation amounts are added to the respective phase compensation current command values from the phase converter 12 ′ in the adders 23 _R , 23 _S , and 23 _T , and these phase compensation currents are added. The command value is used as the current control circuit 2 of the current source 1B.
4 output current command value.

According to this embodiment, the zero-phase current peculiar to the three-phase, four-wire circuit is generated as the compensated zero-phase current from the active filter, so that the zero-phase current on the power supply side is reduced to zero and the harmonics contained therein. The effects of wave components and unbalanced components can be eliminated.

FIG. 3 shows another embodiment of the present invention. In this embodiment, in the compensation current command calculation circuit of FIG. 6, the coordinate converter 31 based on the voltage phase reference signal 2ωt having the double frequency of the fundamental frequency of the system 2 (see FIG. 5) is used. Low-pass filter 32, 32 'for detecting the reverse phase component)
And the fundamental wave anti-phase component (2
Next harmonic component) Separation / removal circuit, and voltage phase reference signal 2ω having twice the fundamental frequency of the system for restoring the coordinates
This is a case where the zero-phase current compensation circuit is provided in the active filter to which the coordinate inverse converter 31 ′ based on t is added.

The compensation current command calculation circuit having this configuration excludes the component of the load current having the fundamental wave of opposite phase from the compensation target.
This will be described in detail below.

The compensating current command value calculating circuit of FIG. 5 can treat the active and reactive components of the positive phase of the fundamental wave as DC components and can easily separate them. Since it is not possible to easily distinguish and separate the fundamental anti-phase component current, which is the second harmonic component, from other harmonic currents, the compensation current of the target that the active filter also compensates for the fundamental anti-phase component current. Will be calculated as

Therefore, since the active filter also compensates the fundamental-phase reverse-phase current that occurs when the load is unbalanced, when the harmonic current component to be compensated is increased, the active filter device There is a problem that the harmonic current component cannot be compensated due to the limitation of the output capacitance.

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 low frequency alternating current. Since it is a component, if it is attempted to compensate all the other harmonic current components including the compensation component of the fundamental wave anti-phase component current, the device capacity increases, which causes an adverse effect on the equipment capacity (equipment cost).

As a method of separating the current of the opposite phase of the fundamental wave (second harmonic wave), it is generally considered to insert a band pass filter of the second harmonic wave. It is not always a good method considering the influence of the phase difference.

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 portions 31 to 33 are the portions where such a reverse phase component of the fundamental wave is excluded from compensation. This circuit operation will be described below.

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 orthogonal coordinates of the fundamental frequency of the system. The fundamental wave positive phase current i ₁ is separated into an active current containing a positive phase active current i _1p and a reactive current containing a positive phase reactive current i _1q . The positive phase active current i _1p and the positive phase reactive current i _1q on this rectangular coordinate are
Since each of them can be treated as a constant DC component and is not covered by the compensation of the active filter, they are detected and separated by the low-pass filters 11 and 11 'of the next stage, and are detected by the matching circuits 15 and 15'. Phase load detection current i
It is removed from the two-phase load detection current ir by subtracting from r.

The positive phase active current of the fundamental wave positive phase component of the current i ₁ in the butt circuit 15,15 'i _1P and positive-phase reactive current i _1q
The two-phase load detection current ir from which is removed is subjected to rotational coordinate conversion by the coordinate converter 31 using the voltage phase reference signal 2ωt having the double frequency of the system fundamental frequency, and the fundamental wave inverse on the orthogonal coordinate of the system double frequency is inverted. The active component current i _2p including the anti-phase active component current i _{2p of the} phase component current i ₂ and the reactive component current including the anti-phase reactive component current i _2q are separated, and the separated anti-phase active component current i _2p and anti-phase reactive component are separated. The divided current i _2q can be treated as a constant DC component.

Therefore, in this embodiment, since the fundamental wave anti-phase component current i ₂ is also excluded from the compensation of the active filter, the anti-phase effective component current i ₂ of the fundamental wave anti-phase component current i ₂ is _2p and the negative-phase reactive current i _2q are detected and separated by the low-pass filters 32 and 32 ′ of the next stage, and are subtracted from the two-phase load detection current ir by the matching circuits 33 and 33 ′, respectively. Similarly to the fundamental wave positive phase current i ₁ , the fundamental wave antiphase (second harmonic component) current i ₂ is also removed from the two-phase load detection current ir.

The two-phase load detection current ir from which the fundamental wave positive-phase component current i ₁ and the fundamental wave anti-phase component current i ₂ are removed is only the harmonic component current to be compensated for by the active filter, and the original coordinate is used. Inverter 31 'based on the voltage phase reference signal 2ωt of the fundamental frequency of the system for returning to 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 '.

As described above, even when the active filter for which the reverse phase component of the fundamental wave is excluded from the compensation target is applied to the multi-phase circuit having the zero-phase circuit, the zero-phase current cannot be controlled. It is not possible to expect suppression of flowing harmonics.

Therefore, also in the present embodiment, the zero-phase current compensating circuit 20 is provided, the zero-phase component of the load current is detected, and this is added as the increment of the compensation current command, so that the zero-phase current on the power supply side is reduced. Set to zero to avoid the effect.

The configuration shown in FIG. 4 may be added to the embodiment shown in FIG. 3 by adding a limit circuit for limiting the device capacity of the active filter.

In FIG. 4, the same reference numerals as those in FIG. 3 denote the same devices having the same functions as those shown in FIG.

In this embodiment, in the compensation current command value calculation circuit shown in FIG. 3, for each component (fundamental wave positive phase reactive component, fundamental wave antiphase component, harmonic component) current that adversely affects the system 2. Since the limit circuit is provided and the other circuit portions operate in the same manner as the compensation current command value calculation circuit shown in FIG. 3, only the limit circuit will be described.

In FIG. 4, 41 is the low-pass filter 1.
1 ', the fundamental reactive current limiting circuit for _{subjecting the} active positive filter to the minimum fundamental positive reactive current i _1q from the positive reactive current i _1q detected in 1',
Reference numeral 42 denotes a harmonic component current limit circuit for determining the upper limit of the harmonic component (effective component, reactive component) current i _h to be compensated, and 43 denotes a fundamental wave anti-phase component detected by the low-pass filters 18 and 18 ′ ( Active component, reactive component) fundamental wave anti-phase current limit circuit for subjecting a minimum amount of fundamental wave anti-phase current from current i ₂ to compensation of the active filter, 42 ₁ , 42 ₂ ,
Numerals 43 ₁ and 43 ₂ are limiters which allow currents of a predetermined value or less to pass through as they are and to limit the currents of a predetermined value or more to the predetermined value.

The operation of the limit circuit in this embodiment will be described below.

Regarding the harmonic component current i _{h to be} compensated by the active filter, the harmonic component current limit circuit 42 removes the basic positive phase component current i ₁ and the fundamental wave anti-phase component current i ₂ from each other. wave component (active ingredient i _hp, reactive component i _hq) incorporating current i _h, and outputs a limit signal to the limiter 42 _1, 42 ₂ exceeds a predetermined value where that harmonic component current i _h, the limiter 42 ₁ , 42 ₂ are activated to limit the harmonic component current i _h to the predetermined value so that only the harmonic component current i _h below the predetermined value is subject to compensation by the active filter.

Further, with respect to the fundamental wave positive phase reactive current i _1q which is not covered by the active filter compensation, the low pass filter 1 in the fundamental wave reactive current limit circuit 41 is used.
Incorporating the fundamental wave positive phase reactive current i _1q detected and separated by 1 ′, the fundamental wave positive phase reactive current i _1q 'below a predetermined value
Is output and is added to the two-phase load detection current ir from which the fundamental wave positive-phase reactive current i _1q has already been removed by the matching circuit 16 ′, whereby the fundamental-wave positive-phase reactive current i below the predetermined value is added. _{For 1q} ', it is the compensation target of the active filter.

Further, with respect to the fundamental wave anti-phase component current i ₂ which is excluded from the compensation of the active filter, the low-pass filter 1 in the fundamental wave anti-phase component current limit circuit 43 is used.
When the fundamental wave _{antiphase component} current (effective component i _2p , reactive component i _2p ) current i ₂ detected and separated by 8, 18 'is taken in and the fundamental wave antiphase component current i ₂ exceeds a predetermined value, the limiter 43 ₁ , 43 ₂ outputs a limit signal to, the limit circuit 43 _1, 43 ₂ fundamental wave negative-sequence current i ₂ below the predetermined value by limiting to a predetermined value is activated is the fundamental wave negative-sequence current i ₂ a 'Is output and the summing circuit 44, 44' intentionally adds to the two-phase load detection current ir from which the fundamental wave antiphase current i ₂ has already been removed. The current i ₂ 'is also an object of compensation by the active filter.

Originally, the active filter compensates the harmonic component current i _h , and the fundamental wave positive phase reactive current i _1q
And the fundamental wave anti-phase current i ₂ are excluded from compensation, but as mentioned above, the fundamental wave positive phase reactive current i _1q
Since the fundamental wave anti-phase component current i ₂ adversely affects the system 2, it is necessary to remove it from the system (load) current by some method.

Therefore, according to the circuit of this embodiment, by providing limit circuits 41, 42, and 43 having a predetermined limit value for each component current that adversely affects the system, the active filter device capacity and the system ( load)
Harmonic component current i _h contained in the current ir, the fundamental wave positive phase reactive current i _1q, in accordance with the magnitude of the fundamental wave negative-sequence current i _2, if their component current subject to compensation , A compensation current command value ic * that can remove all the component currents that adversely affect the system 2 from the system (load) current ir only by applying the active filter device is obtained.

In this case, the selection of the limit circuit and the limit value may be appropriately determined within the allowable capacity of the filter according to the load condition, and the fundamental wave reactive component current limit circuit 41 and the fundamental wave anti-phase component current limit may be selected. As a matter of course, the limit value of the circuit 44 ₃ can be set to “zero”.

[0049]

As described above, according to the present invention, the current to be compensated includes the harmonic current or the reactive current, and further, the current excluding the reverse-phase component current of the fundamental wave or the limitation by the current limiter circuit is applied. In the active filter to be performed, a zero-phase current compensating circuit that detects the zero-phase component from the detected current of the three-phase load current and distributes and adds the zero-phase component to the three-phase compensation current command value is provided. The zero-phase current peculiar to the multi-phase circuit can be compensated, and harmonics and imbalances on the power supply side can be eliminated.

In particular, when a single-phase rectifier or the like is connected as a load unevenly between each phase and the neutral line, the third harmonic component of the zero-phase current increases, and the power supply voltage is significantly distorted. This is effective when applied to the case where the load capacities are very uneven and the fundamental wave component of the zero-phase current increases to cause imbalance on the power supply side.

[Brief description of the drawings]

FIG. 1 is a basic configuration of an active filter of the present invention.

FIG. 2 is a control circuit of an active filter showing an embodiment of the present invention.

FIG. 3 is a control circuit of an active filter showing another embodiment of the present invention.

FIG. 4 is a control circuit of an active filter showing another embodiment of the present invention.

FIG. 5 is a principle diagram of an active filter.

FIG. 6 shows a compensation current command value calculation circuit for a conventional active filter.

FIG. 7 is a conventional 3-phase 3-wire active filter.

[Explanation of symbols]

1 ... Active filter 2 ... Distribution system 3 ... System load 11, 11 ', 32, 32' ... Low pass filter 12, 12 '... Phase converter 13, 13', 31, 31 '... Coordinate converter 20 ... Zero phase current Compensation circuit 21 ... Addition circuit 22 ... Coefficient calculation circuit 23 _R , 23 _S , 23 _T ... Adder 41 ... Fundamental wave reactive current limit circuit 42 ... Harmonic component current limit circuit 43 ... Fundamental wave anti-phase current limit circuit

Claims (3)

[Claims] 1. A two-phase load detection current is phase-converted from a detected current of a three-phase load current supplied from a multi-phase circuit system having a zero-phase circuit to a load, and a harmonic of the system is generated from the two-phase load detection current. The two-phase compensation target current including the current or the reactive current is detected, and the two-phase compensation target current is phase-converted into the three-phase compensation current command value of the current generation source, and the compensation target current is removed from the load current. In the active filter, a zero-phase current compensating circuit for detecting a zero-phase component from the detection current of the three-phase load current and distributing and adding the zero-phase component to the three-phase compensation current command value is provided. Active filter. 2. The active filter according to claim 1, wherein the compensation target current is detected by providing a circuit for removing a fundamental wave antiphase current from the load current. 3. The active filter according to claim 2, further comprising a current limiter circuit that limits a current amount of the current to be compensated.