CN107248743A - A kind of active electric filter device for specifying subharmonic - Google Patents

Abstract

The invention discloses an active power filter device for specified harmonics, which is suitable for a circuit including a system power supply and a harmonic load, including: a transformer, an inverter, and a modulation signal generation module; the primary side winding of the transformer and the The harmonic load is connected in series, connected to the loop formed by the system power supply and the harmonic load; the modulation signal generating module is used to generate the modulation signal of the inverter, and the modulation signal is composed of the primary side fundamental wave current and positive Specify nth harmonic current superposition generation to the amplified primary side; the inverter is used to convert the DC signal into an AC current signal with the same frequency as the modulation signal and inject it into the secondary side winding of the transformer, so that the The equivalent impedance of the fundamental wave on the primary side of the transformer is Z ₁ +(1‑α)Z _m , and the equivalent impedance of the nth harmonic on the primary side of the transformer is nZ ₁ +(1+β)nZ _m . The invention is based on the mixed control of the fundamental wave and the specified harmonic flux, so that the primary side of the transformer is short-circuited relative to the fundamental wave and open-circuited relative to the specified harmonic.

Description

An active power filter device for specified harmonics

technical field

The invention belongs to the technical field of active power filtering, and more specifically relates to an active power filtering device for specified harmonics.

Background technique

As power electronic nonlinear loads are more and more widely used in industrial and civil fields, the current waveform distortion in the power grid is more serious, and the problems of harmonics and reactive power are becoming more and more significant. For harmonics and power factor problems, the industry has proposed a variety of solutions, the main filtering solutions include traditional passive LC filter, traditional parallel active power filter, series hybrid active power filter, injection hybrid Active power filter and unified power quality conditioner.

Passive filters are large in size and weight, and can only filter out harmonics of specific frequencies; among all power filters, the series hybrid active power filter can greatly improve the harmonic impedance (playing the role of "harmonic isolation") device" role) has aroused widespread concern. However, at present, the method of full harmonic current compensation is adopted, and the required transformer capacity is relatively large, so there are a series of problems in protection strategy and stability, as follows:

1) The overall system of series active power filters requires a customized protection strategy. The inverter components are connected in series between the power supply and the load, and cannot be directly protected by devices such as power contactors, circuit breakers or fuses;

2) The filter performance of the device conflicts with the transformer capacity. The traditional series hybrid active power filter based on fundamental magnetic flux compensation only compensates the fundamental magnetic flux, which can only reduce the fundamental equivalent impedance. Impedance; the design of the rated capacity of the transformer depends on the magnitude of the excitation impedance under the consideration of the system protection strategy. Considering the extreme case where the fundamental magnetic flux of the transformer is not compensated at all, the design capacity of the series transformer is In order to reduce the rated capacity, the excitation impedance of the transformer must be reduced; in summary, better filtering performance requires a larger capacity transformer.

3) The protection strategy and reliability of the device conflict with the transformer capacity. In order to facilitate protection and improve the reliability of the device, the excitation impedance of the transformer should also be designed to be small, otherwise once the device is in an abnormal operating state, the output voltage of the inverter will be very high.

4) When the harmonic current is fully compensated, the system stability is reduced. Usually high-order harmonics and some low-order harmonics (determined according to specific application occasions) have low amplitudes. For the above-mentioned harmonics, more economical and simple methods such as passive filters can be used for filtering, and satisfactory results can be obtained. However, when full harmonic current compensation is used, it will not only occupy the capacity of the active power filter, increase the cost, but also seriously reduce the stability of the system.

To sum up, passive filters are large in size and weight, and can only filter out harmonics of specific frequencies; the existing series hybrid active power filter has caused widespread focus on. But on the one hand, it only compensates the fundamental magnetic flux, so it can only reduce the fundamental equivalent impedance. When the transformer used is determined, its harmonic equivalent impedance is a fixed value. In order to obtain a better filtering effect, a larger capacity transformer; on the other hand, the current series hybrid active power filter adopts the method of full current compensation, which greatly reduces the system stability, and increases the cost due to the increase of the capacity of the transformer and each switching device of the system.

Contents of the invention

Aiming at the defects of the prior art, the purpose of the present invention is to solve the problem that the existing active power filter only compensates the fundamental magnetic flux, so that it can only reduce the fundamental equivalent impedance. When the transformer used is determined, its harmonic equivalent Impedance is a fixed value. In order to obtain a better filtering effect, a large-capacity transformer is required; and the existing active power filter adopts the method of full current compensation, which greatly reduces the stability of the system. The capacity of each switching device increases the technical problem of cost.

To achieve the above purpose, the present invention provides an active power filter device for specified harmonics, which is suitable for circuits including system power supplies and harmonic loads. The device includes: a transformer, an inverter, and a modulation signal generating module. The primary side winding of the transformer is connected in series with the harmonic load, connected to the loop formed by the system power supply and the harmonic load, and the current flowing through the primary side winding of the transformer includes a fundamental wave current and a harmonic current; a modulation signal generation module Used to generate the modulation signal of the inverter, the modulation signal is generated by the superposition of the reverse amplified primary side fundamental current and the forward amplified primary side specified sub-harmonic current; the inverter is used to convert the DC signal Generate an AC current signal with the same frequency as the modulation signal and inject it into the secondary side winding of the transformer, so that the fundamental equivalent impedance of the primary side of the transformer is Z ₁ +(1-α)Z _m , and the primary side of the transformer is specified The sub-harmonic equivalent impedance is nZ ₁ +(1+β)nZ _m , where Z ₁ is the primary side leakage reactance of the transformer, Z _m is the excitation impedance of the transformer, n is the specified sub-harmonic order, α and β are respectively are the fundamental wave control coefficient and the specified sub-harmonic control coefficient, which are adjusted by the amplification factor of the primary side fundamental wave current and the amplification factor of the primary side specified sub-harmonic current in the modulation signal, respectively.

The present invention makes the fundamental wave and the designated sub-harmonic equivalent impedance of the primary side winding separately controllable through the mixed control based on the fundamental wave and the designated sub-harmonic magnetic flux of the primary side of the transformer. The fundamental equivalent impedance of the primary side of the transformer is Z ₁ +(1-α)Z _m , the equivalent impedance of the nth harmonic of the primary side of the transformer is nZ ₁ +(1+β)nZ _m , the active power provided by the present invention The filtering device can control α and β so that the equivalent impedance of the fundamental wave on the primary side of the transformer is 0 (short circuit relative to the fundamental wave) and the equivalent impedance of the specified sub-harmonic on the primary side is large (open circuit relative to the specified sub-harmonic). The specified sub-harmonic compensation is adopted, and the active filter part only compensates the specified sub-harmonic current with a larger amplitude, and the general higher-order harmonics and lower-amplitude low-order harmonics use passive filters, etc. Filter in a more economical way, increase system stability and reduce filtering costs.

Optionally, the modulation signal generation module includes: a fundamental current detection unit, a harmonic current detection unit, a fundamental current amplifier, a harmonic current amplifier and a superposition unit. The fundamental current detection unit is used to detect the fundamental current of the primary side from the current flowing through the primary winding of the transformer; the harmonic current detection unit is used to detect the fundamental current of the primary side from the current flowing through the primary winding of the transformer. Detecting the specified subharmonic current of the primary side; the fundamental current amplifier is used to inversely amplify the fundamental current of the primary side; the harmonic current amplifier is used to amplify the specified subharmonic current of the primary side The current is amplified in the forward direction; the superposition unit is used to superimpose the fundamental wave current of the primary side after the reverse amplification and the specified harmonic current of the primary side after the forward amplification to generate a modulation signal.

Optionally, the modulation signal I _ref is:

in, is the fundamental wave component in the transformer primary side current I ₁ , that is, the primary side fundamental wave current, is the nth harmonic component in the transformer primary side current I ₁ , k _i is the gain of the current transformer used to determine the current flowing through the transformer primary side winding, and -k ₁ is the amplification factor of the fundamental wave current amplifier, k ₂ is the amplification factor of the specified subharmonic current amplifier.

Optionally, the current I ₂ on the secondary side of the transformer is: K _PWM is the gain of the inverter; the secondary side winding current of the transformer is equivalent to the current I ₂ ' of the primary side of the transformer as:

Wherein, k _T is the coupling transformation ratio of the transformer,

Optionally, the fundamental equivalent impedance of the primary side of the transformer and the specified harmonic equivalent impedance of the primary side of the transformer are determined in the following manner: the phasor of the voltage equation of the transformer is: U ₁ =Z ₁ I ₁ +Z _m (I ₁ + I ₂ ′), U ₁ is the voltage across the primary side winding of the transformer; the fundamental equivalent impedance of the primary side of the transformer for:

Transformer primary side nth harmonic equivalent impedance for:

in, is the fundamental voltage across the primary winding of the transformer, is the nth harmonic voltage across the primary winding of the transformer,

U ₁ ⁽¹⁾ = Z ₁ ⁽¹⁾ I ₁ ⁽¹⁾ + Z _m ⁽¹⁾ (I ₁ ⁽¹⁾ + I ₂ ′ ⁽¹⁾ ), U ₁ ⁽ⁿ⁾ = Z ₁ ⁽ⁿ⁾ I ₁ ⁽ⁿ⁾ + Z _m ⁽ⁿ⁾ (I ₁ ⁽ⁿ⁾ + I ₂ ′ ⁽ⁿ⁾ );

I ₂ ′ ⁽¹⁾ and I ₂ ′ ⁽ⁿ⁾ are respectively the fundamental wave component and the nth harmonic component of the transformer secondary side winding current equivalent to the transformer primary side current, I ₂ ′ ⁽¹⁾ =- αI ₁ ⁽¹⁾ , I ₂ ′ ⁽ⁿ⁾ = βI ₁ ⁽ⁿ⁾ ;

Z ₁ ⁽¹⁾ is the leakage reactance of the primary side of the transformer relative to the fundamental wave, Z ₁ ⁽¹⁾ = Z ₁ , Z _m ⁽¹⁾ is the excitation impedance of the transformer relative to the fundamental wave, Z _m ⁽¹⁾ = Z _m , Z ₁ ⁽ⁿ⁾ is the leakage reactance of the primary side of the transformer relative to the nth harmonic, Z ₁ ⁽ⁿ⁾ = nZ ₁ , Z _m ⁽ⁿ⁾ is the excitation impedance of the transformer relative to the nth harmonic, Z _m ⁽ⁿ⁾ =nZ _m .

Optionally, if but At this time, the primary winding of the transformer is equivalent to a short circuit to the fundamental wave.

Optionally, by setting the value of β, the equivalent impedance of the nth harmonic on the primary side of the transformer is It is high resistance, and at this time the primary side winding of the transformer is equivalent to an open circuit for the nth harmonic.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

1) Based on the mixed control of the fundamental wave and the designated sub-harmonic flux, the equivalent impedance of the fundamental wave and the designated sub-harmonic of the primary winding of the series transformer can be controlled separately.

2) By controlling the specified sub-harmonic control coefficient to be large enough so that the equivalent impedance of the specified sub-harmonic remains unchanged, a transformer with a smaller excitation impedance can be selected, that is, through a reasonable design of the specified sub-harmonic control coefficient, the transformer once Under the condition that the side winding has the same harmonic equivalent impedance (the active filter has similar filtering performance), the required transformer excitation impedance (transformer capacity) is smaller; when the transformer with the same capacity is used, the filtering effect is better.

3) The present invention only compensates the specified sub-harmonic current with larger amplitude, and the general high-order harmonics and low-order harmonics with lower amplitudes (determined according to specific application occasions) use more passive filters, etc. Filter in an economical way, increase system stability and reduce filtering costs.

4) Simplified passive filter design, when the same transformer is used, the filtering performance is better, so the capacity and volume of the passive filter can be greatly reduced.

Description of drawings

Fig. 1 is a schematic diagram of the single-phase principle of connecting the active power filter device to the power grid provided by the embodiment of the present invention;

Fig. 2 is a schematic circuit diagram of an active power filter device connected to a three-phase system provided by an embodiment of the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

Fig. 1 is a schematic diagram of a single-phase principle of an active power filter device connected to a power grid provided by an embodiment of the present invention. As shown in FIG. 1 , the power grid may include an active power filter device and a passive power filter device 200 , wherein the active power filter device includes: a transformer 101 , an inverter 102 and a modulation signal generating module 103 .

In order to reduce the capacity of the active power filter device and improve its stability, the active power filter device can be specified to filter certain harmonics with higher amplitudes, and the passive power filter device to filter low-order harmonics and lower-amplitude harmonics. In the way of higher harmonics, active filtering and passive filtering work together to complete filtering. Specifically, the passive power filtering device 200 may include a plurality of harmonic filtering branches, for example, a 3rd harmonic filtering branch: an inductor L ₃ and a capacitor C ₃ connected in series, a 5th harmonic filtering branch: an inductor L ₅ and capacitor _C5 series branch. It can be understood that, according to actual needs, the passive filtering device may also include more or fewer filtering branches, which is not limited in this embodiment of the present invention, and is only used as an example to illustrate the present invention.

As shown in Figure 1, U _S represents the ideal system voltage source, U _h represents the harmonic source, representing various distortions of the system power supply (such as voltage drop, harmonics, etc.), and L _S represents the impedance of the system voltage source. The current on the primary side of the transformer is I ₁ . C _d and L _d form an LC filter current, which is used to filter harmonics at the switching frequency of the inverter 102 . The primary side port of the transformer 101 is an AX port, and the secondary side port is an ax port.

The inverter 102 uses the triangular wave as the carrier, adopts the sine pulse width modulation SPWM control strategy, controls the voltage source inverter to follow the modulation signal to generate a controllable current, and the controllable current is injected into the secondary side of the coupling transformer after being filtered by an LC filter winding, the transformer secondary side winding current contains both fundamental current and harmonic current with different control coefficients. The DC side voltage U _d of the inverter has three sources: 1) A capacitor is connected to the DC side, and the DC side voltage is stabilized by controlling the inverter; 2) A battery is connected to the DC side, and a stable DC side voltage is obtained by controlling the inverter. Voltage; 3) Take electricity through the induction of the power system, and obtain a stable DC side voltage after rectification.

The primary side winding of the transformer 101 is connected in series with the harmonic load, connected to the loop formed by the system power supply U _S and the harmonic load, and the current flowing through the primary side winding of the transformer includes the primary side fundamental wave current and primary side harmonic current k is the harmonic order, k>0, and k≠1.

The modulation signal generation module 103 is used to generate the modulation signal I _ref of the inverter 102, and the I _ref is the primary side fundamental wave current amplified by the reverse and the specified sub-harmonic current of the primary side after positive amplification Superposition generation, n is the specified harmonic order, n>0, and n≠1.

The inverter 102 is used to convert the DC signal provided by U _d into an AC current signal I ₂ with the same frequency as I _ref and inject it into the secondary side winding of the transformer, so that the fundamental equivalent impedance of the primary side of the transformer is Z ₁ + (1-α)Z _m , the equivalent impedance of the nth harmonic on the primary side of the transformer is nZ ₁ +(1+β)nZ _m , where Z ₁ is the leakage reactance of the primary side of the transformer, and Z _m is the excitation impedance of the transformer , α and β are the fundamental wave control coefficient and the specified sub-harmonic control coefficient, respectively, which are adjusted by the amplification factor of the primary side fundamental wave current and the primary side harmonic current amplification factor in the modulation signal, respectively.

The modulation signal generating module 103 includes: a fundamental current detection unit, a harmonic current detection unit, a fundamental current amplifier, a harmonic current amplifier and a superposition unit.

Fundamental wave current detection unit, used to detect the fundamental wave current on the primary side Harmonic current detection unit, used to detect the specified sub-harmonic current of the primary side Among them, the transfer functions of the fundamental current and the nth harmonic current detection link are G _fund (s) and G _hn (s), respectively,

In addition, the gain of the current transformer used to determine the current I ₁ flowing through the primary side winding of the transformer is _ki , and G _di (s) represents the filtering link after detecting the primary side current.

The fundamental wave current detection unit and the harmonic current detection unit include current transformers, fundamental waves and specified harmonic current detection links. In the detection link, the fundamental wave current detection link detects the required fundamental wave component from the system bus current; the specified sub-harmonic current detection link detects the required specified sub-harmonic current component from the system current.

The fundamental current amplifier is used to reversely amplify the fundamental current of the primary side; the harmonic current amplifier is used to forwardly amplify the specified sub-harmonic current of the primary side. The amplification factors (gains) of the fundamental amplifier and the harmonic amplifier are -k ₁ and k ₂ , respectively.

The superposition unit is used to superimpose the fundamental current of the primary side after reverse amplification and the specified subharmonic current of the primary side after forward amplification to generate a modulation signal I _ref ,

in, is the fundamental wave component in the transformer primary side current I ₁ , that is, the primary side fundamental wave current, is the nth harmonic component in the primary side current I ₁ of the transformer, -k ₁ is the amplification factor of the fundamental wave current amplifier, and k ₂ is the amplification factor of the specified harmonic current amplifier.

The inverter 102 is equivalent to a first-order small inertia link, and the transfer function G _PWM (s) of the voltage source inverter is K _PWM is the gain of the inverter, T _PWM is the delay of the inverter, and s is an operator in the s domain. In order to simplify the analysis, the delay of the inverter is ignored, and the inverter is equivalent to a proportional link with a gain of K _PWM .

The current I ₂ on the secondary side of the transformer 101 is: K _PWM is the gain of the inverter; the transformer secondary side winding current is equivalent to the current I ₂ ′ of the transformer primary side as:

Wherein, k _T is the coupling transformation ratio of the transformer,

Optionally, the fundamental equivalent impedance of the primary side of the transformer and the equivalent impedance of the harmonics of the primary side of the transformer are determined by the following methods:

The voltage equation phasor of the transformer is: U ₁ =Z ₁ I ₁ +Z _m (I ₁ +I ₂ ′), U ₂ ′=Z ₂ ′I ₂ ′+Z _m (I ₁ +I ₂ ′);

Among them, U ₁ is the voltage across the primary winding of the transformer, U ₂ ′ is the voltage equivalent to the primary side of the secondary winding of the transformer, and Z ₂ ′ is the leakage reactance equivalent to the primary side of the transformer.

Seen from the AX port, the fundamental equivalent impedance of the primary side of the transformer for:

Transformer primary side nth harmonic equivalent impedance for:

is the fundamental voltage across the primary winding of the transformer, It is the nth harmonic voltage across the primary side winding of the transformer:

U ₁ ⁽¹⁾ = Z ₁ ⁽¹⁾ I ₁ ⁽¹⁾ + Z _m ⁽¹⁾ (I ₁ ⁽¹⁾ + I ₂ ′ ⁽¹⁾ ), U ₁ ⁽ⁿ⁾ = Z ₁ ⁽ⁿ⁾ I ₁ ⁽ⁿ⁾ + Z _m ⁽ⁿ⁾ (I ₁ ⁽ⁿ⁾ + I ₂ ′ ⁽ⁿ⁾ );

I ₂ ′ ⁽¹⁾ and I ₂ ′ ⁽ⁿ⁾ are respectively the fundamental wave component and the nth harmonic component of the transformer secondary side winding current equivalent to the transformer primary side current, I ₂ ′ ⁽¹⁾ =- αI ₁ ⁽¹⁾ , I ₂ ′ ⁽ⁿ⁾ = βI ₁ ⁽ⁿ⁾ ;

Z ₁ ⁽¹⁾ is the leakage reactance of the primary side of the transformer relative to the fundamental wave, Z ₁ ⁽¹⁾ = Z ₁ , Z _m ⁽¹⁾ is the excitation impedance of the transformer relative to the fundamental wave, Z _m ⁽¹⁾ = Z _m , Z ₁ ⁽ⁿ⁾ is the leakage reactance of the primary side of the transformer relative to the nth harmonic, Z ₁ ⁽ⁿ⁾ = nZ ₁ , Z _m ⁽ⁿ⁾ is the excitation impedance of the transformer relative to the nth harmonic, Z _m ⁽ⁿ⁾ =nZ _m .

Optionally, if but At this time, the primary winding of the transformer is equivalent to a short circuit to the fundamental wave.

Optionally, by setting the value of β, the equivalent impedance of the nth harmonic on the primary side of the transformer is It is high resistance, and at this time the primary side winding of the transformer is equivalent to an open circuit for the nth harmonic.

If the harmonic control coefficient β is set reasonably, the primary side winding of the transformer is equivalent to a high impedance to the specified harmonic, and when used in conjunction with the passive filter branch (that is, applied to the series hybrid active power filter structure), it can control the specified Subharmonics play a very good attenuation role. In addition, compared to the series hybrid active power filter based on fundamental wave flux compensation (harmonic equivalent impedance is nZ ₁ +nZ _m ), the series hybrid active power filter based on fundamental wave and harmonic flux compensation The filter (specified sub-harmonic equivalent impedance is nZ ₁ + (1+β)nZ _m ) introduces a coefficient (1+β) in the harmonic equivalent impedance, so when using a transformer with the same capacity, the filtering performance is better (On the premise of satisfying the same filtering effect, a transformer with a smaller capacity can be selected). With specified subharmonic compensation, the active filter part only compensates the specified subharmonic current with a larger amplitude, and the general high-order harmonics and low-order harmonics with lower amplitudes (determined according to specific applications) More economical filtering methods such as passive filters are used to increase system stability and reduce filtering costs.

Therefore, the transformer can be a small-capacity coupling transformer, which connects the output current of the voltage source inverter in series between the system power supply and the harmonic load through an LC filter. Due to the bilateral excitation of the primary and secondary (primary side, secondary side) side windings of the transformer, the primary winding of the transformer is equivalent to two adjustable reactances with different control coefficients for the fundamental and harmonics. Control the fundamental and harmonic gain coefficients of the amplifier unit, and change the fundamental and harmonic flux compensation of the transformer unit. Make the primary side winding of the transformer short circuit to the fundamental wave (low resistance), and open circuit to the specified sub-harmonic (high resistance), and the specified sub-harmonic current is forced to flow into the passive branch circuit, which acts as an active filter.

When multiple harmonic currents are specified to be compensated, multiple specified harmonic current detection links can be used and integrated into one specified harmonic current detection unit. Under the three-phase system, the single-phase system can be referred to, and an active power filter with specified harmonic compensation using a small-capacity transformer is used separately on each phase. Each amplifier unit on the three-phase line is controlled independently, and does not affect each other when a fault occurs. For details, refer to the schematic circuit diagram of the active power filter device connected to the three-phase system shown in FIG. 2 .

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (7)

1. An active power filter device for a specified subharmonic, adapted for use in a circuit including a system power supply and a harmonic load, comprising: the device comprises a transformer, an inverter and a modulation signal generation module;

the primary side winding of the transformer is connected with the harmonic load in series and is connected into a loop formed by the system power supply and the harmonic load, and the current flowing through the primary side winding of the transformer comprises fundamental current and harmonic current;

the modulation signal generation module is used for generating a modulation signal of the inverter, and the modulation signal is generated by superposing a primary side fundamental current after reverse amplification and a primary side appointed subharmonic current after forward amplification;

the inverter is used for converting the direct current signal into an alternating current signal with the same frequency as the modulation signal and injecting the alternating current signal into the secondary side winding of the transformer, so that the primary side fundamental wave equivalent impedance of the transformer is Z₁+(1-α)Z_mThe primary side of the transformer is assigned subharmonic equivalent impedance as nZ₁+(1+β)nZ_mWherein Z is₁Is the primary side leakage reactance of the transformer, Z_mFor the excitation impedance of the transformer, n is a designated subharmonic number, and α and β are a fundamental wave control coefficient and a designated subharmonic control coefficient, respectively, which are adjusted by the amplification factor of the primary side fundamental wave current and the amplification factor of the primary side designated subharmonic current, respectively, in the modulation signal.

2. The active power filtering device of claim 1, wherein the modulation signal generation module comprises: the harmonic current detection circuit comprises a fundamental current detection unit, a specified subharmonic current detection unit, a fundamental current amplifier, a harmonic current amplifier and a superposition unit;

the fundamental current detection unit is configured to detect a fundamental current on the primary side from a current flowing through a primary winding of the transformer;

the specified subharmonic current detection unit is used for detecting the specified subharmonic current on the primary side from the current flowing through the primary side winding of the transformer;

the fundamental current amplifier is used for reversely amplifying the fundamental current on the primary side;

the harmonic current amplifier is used for carrying out positive amplification on the specified subharmonic current on the primary side;

the superposition unit is used for superposing the fundamental wave current on the primary side after reverse amplification and the appointed subharmonic current on the primary side after forward amplification to generate a modulation signal.

3. The method of claim 2Active power filter device, characterized in that the modulation signal I_refComprises the following steps:

<mrow> <msub> <mi>I</mi> <mrow> <mi>r</mi> <mi>e</mi> <mi>f</mi> </mrow> </msub> <mo>=</mo> <mo>-</mo> <msub> <mi>k</mi> <mi>i</mi> </msub> <msub> <mi>k</mi> <mn>1</mn> </msub> <msubsup> <mi>I</mi> <mn>1</mn> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msubsup> <mo>+</mo> <msub> <mi>k</mi> <mi>i</mi> </msub> <msub> <mi>k</mi> <mn>2</mn> </msub> <msubsup> <mi>I</mi> <mn>1</mn> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </msubsup> <mo>;</mo> </mrow>

wherein,for the primary side current I of the transformer₁The fundamental component in (1) is the primary side fundamental current,for the primary side current I of the transformer₁Of (b) the nth harmonic component, k_i-k gain of a current transformer for determining a current through a primary winding of said transformer₁Is the amplification factor, k, of a fundamental current amplifier₂To specify the amplification of the subharmonic current amplifier.

4. The active power filter of claim 3, wherein the current I on the secondary side of the transformer₂Comprises the following steps:K_PWMis the gain of the inverter; the current of the secondary side winding of the transformer is equivalent to the current I of the primary side of the transformer₂' is:

<mrow> <msup> <msub> <mi>I</mi> <mn>2</mn> </msub> <mo>&amp;prime;</mo> </msup> <mo>=</mo> <mfrac> <mn>1</mn> <msub> <mi>k</mi> <mi>T</mi> </msub> </mfrac> <msub> <mi>I</mi> <mn>2</mn> </msub> <mo>=</mo> <mo>-</mo> <msubsup> <mi>&amp;alpha;I</mi> <mn>1</mn> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msubsup> <mo>+</mo> <msubsup> <mi>&amp;beta;I</mi> <mn>1</mn> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </msubsup> <mo>;</mo> </mrow>

wherein k is_TFor the coupling transformation ratio of the transformer,

5. the active power filter arrangement of claim 4 wherein the transformer primary side fundamental equivalent impedance and transformer primary side specified subharmonic equivalent impedance are determined by:

the voltage equation phasors of the transformer are: u shape₁＝Z₁I₁+Z_m(I₁+I₂′)，U₁The voltage across the primary winding of the transformer;

primary side fundamental equivalent impedance of transformerComprises the following steps:

<mrow> <msubsup> <mi>Z</mi> <mrow> <mi>A</mi> <mi>X</mi> </mrow> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msubsup> <mo>=</mo> <mfrac> <msubsup> <mi>U</mi> <mn>1</mn> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msubsup> <msubsup> <mi>I</mi> <mn>1</mn> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msubsup> </mfrac> <mo>=</mo> <msubsup> <mi>Z</mi> <mn>1</mn> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msubsup> <mo>+</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>&amp;alpha;</mi> <mo>)</mo> </mrow> <msubsup> <mi>Z</mi> <mi>m</mi> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msubsup> <mo>=</mo> <msub> <mi>Z</mi> <mn>1</mn> </msub> <mo>+</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>-</mo> <mi>&amp;alpha;</mi> <mo>)</mo> </mrow> <msub> <mi>Z</mi> <mi>m</mi> </msub> <mo>;</mo> </mrow>

primary side nth harmonic equivalent impedance of transformerComprises the following steps:

<mrow> <msubsup> <mi>Z</mi> <mrow> <mi>A</mi> <mi>X</mi> </mrow> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </msubsup> <mo>=</mo> <mfrac> <msubsup> <mi>U</mi> <mn>1</mn> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </msubsup> <msubsup> <mi>I</mi> <mn>1</mn> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </msubsup> </mfrac> <mo>=</mo> <msubsup> <mi>Z</mi> <mn>1</mn> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </msubsup> <mo>+</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mi>&amp;beta;</mi> <mo>)</mo> </mrow> <msubsup> <mi>Z</mi> <mi>m</mi> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </msubsup> <mo>=</mo> <msub> <mi>nZ</mi> <mn>1</mn> </msub> <mo>+</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>+</mo> <mi>&amp;beta;</mi> <mo>)</mo> </mrow> <msub> <mi>nZ</mi> <mi>m</mi> </msub> </mrow>

wherein,is the fundamental voltage across the primary winding of the transformer,is the nth harmonic voltage across the primary winding of the transformer,

<mrow> <msup> <msub> <mi>U</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msup> <mo>=</mo> <msup> <msub> <mi>Z</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msup> <msup> <msub> <mi>I</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msup> <mo>+</mo> <msup> <msub> <mi>Z</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msup> <mrow> <mo>(</mo> <msup> <msub> <mi>I</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </msup> <mo>+</mo> <msup> <msub> <mi>I</mi> <mn>2</mn> </msub> <mrow> <mo>&amp;prime;</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> </msup> <mo>)</mo> </mrow> <mo>,</mo> <msup> <msub> <mi>U</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </msup> <mo>=</mo> <msup> <msub> <mi>Z</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </msup> <msup> <msub> <mi>I</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </msup> <mo>+</mo> <msup> <msub> <mi>Z</mi> <mi>m</mi> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </msup> <mrow> <mo>(</mo> <msup> <msub> <mi>I</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </msup> <mo>+</mo> <msup> <msub> <mi>I</mi> <mn>2</mn> </msub> <mrow> <mo>&amp;prime;</mo> <mrow> <mo>(</mo> <mi>n</mi> <mo>)</mo> </mrow> </mrow> </msup> <mo>)</mo> </mrow> <mo>;</mo> </mrow>

andrespectively a fundamental component and an nth harmonic component in the current equivalent to the primary side of the transformer for the secondary side winding current of the transformer,

Z₁ ⁽¹⁾is the leakage reactance, Z, of the primary side of the transformer with respect to the fundamental wave₁ ⁽¹⁾＝Z₁，Z_m ⁽¹⁾Is the excitation impedance of the transformer with respect to the fundamental wave, Z_m ⁽¹⁾＝Z_m，Z₁ ⁽ⁿ⁾Leakage reactance, Z, of the primary side of the transformer with respect to the nth harmonic₁ ⁽ⁿ⁾＝nZ₁，Z_m ⁽ⁿ⁾For the excitation impedance of the transformer with respect to the nth harmonic, Z_m ⁽ⁿ⁾＝nZ_m。

6. Active power filter device according to any of claims 1 to 5, characterized in that ifThenAt this time, the primary side winding of the transformer is equivalently short-circuited to the fundamental wave.

7. The active power filter device of any one of claims 1 to 5, wherein the value of β is set such that the nth harmonic equivalent impedance of the primary side of the transformer is setThe impedance is high, and the primary side winding of the transformer is equivalently open to the nth harmonic wave.