CN201282339Y - Series hybrid active electric filter device - Google Patents

Abstract

The utility model discloses a series connection combined-type active power filter comprising a harmonic current detecting unit, a harmonic compensation current generation unit, a series connection transformer and a passive power filter, wherein, the series connection transformer has a very small self-inductance per-unit value which is only 0.1-10%; the harmonic compensation current generation unit generates S identical harmonic currents which are injected to S identical secondary windings in the transformer; the harmonic currents are same as a primary side harmonic current in phase and are as large as (a multiplied by k)/S times, so that the series connection transformer manifests a larger inductance L1 plus a multiplied by M to the harmonic currents while manifesting a smaller self-inductance L1 to fundamental waves, and finally the harmonic currents are forced to flow into the passive power filer; if the active power part goes wrong, the active power part can be cut off through a switch without affecting power supply to load; and because of open-circuit entry of the series connection transformer, the system retains certain filtering effect even when impedance increases by 0.1-10%. The device can operate without an LC fundamental-wave resonance circuit and ensure that secondary side capacities of the active power part and the series connection transformer are extremely small, thereby reducing cost and achieving better filtering effect.

Description

Series hybrid active power filter device

Technical Field

The utility model belongs to the technical field of power filter, concretely relates to adopt low self-inductance series transformer's series hybrid active power filter device.

Background

The series hybrid filter is a combined power filter adopting series active and parallel passive, can better overcome the resonance problem when the passive filter is used alone, obviously improves the filtering effect of the passive filter, has small capacity of the active part and high cost performance, and has good application prospect. Heretofore, the following solutions are mainly used for the series hybrid active power filter:

the active part proposed by scheme 1(Peng fangZHeng; Akagi Hirofumi; Sabae Akira, A new early harmonic compensation in power systems- -A combined system of passive and passive filters, IEEE Transactions on Industrial Applications, vol.26, No.6, Nov-Dec, 1990, page 983 and 990) works in the form of harmonic voltage source, but the inverter still flows a large system fundamental current, and the capacity of the active part is large.

An active part provided by scheme 2 (Chenqiaofu; Lidayi; Wei-nan, series-type active filter based on fundamental wave magnetic flux compensation, college of China university, 2000, volume 28, phase 12, page number: 82-84) works in the form of a fundamental wave current source, and similarly, an inverter flows very large system fundamental wave current, the capacity of the active part is also larger, but the control is simpler, and the filtering effect is obviously better than that of scheme 1.

Scheme 3 (Wuweimin; Chunliqing; Qian illumination; Pengzang, research on topology of a high-performance series hybrid active power filter, journal of China Motor engineering, 2004, 24 vol., 12 th, page number: 108 + 112) proposes an improved resonant impedance type structure, an active part still works in a harmonic voltage source form, but a power frequency resonant LC circuit is connected in series on the alternating current output side of an inverter, so that the voltage level of a direct current bus of the inverter can be reduced, but the inverter still flows very large system fundamental current.

In the above 3 schemes, the first and second sides of the series transformer need to flow large system fundamental current, so the capacity of the series transformer is also large. If the active part has a fault or needs to be overhauled and quit the operation, the load in the above 3 schemes is powered off, so the power supply reliability is poor.

Disclosure of Invention

For overcoming the not enough of current scheme, the utility model provides a novel series connection mixed type active power filter device, the device have better filtering effect, and active part is capacious, and series transformer is capacious, and system reliability is high.

The utility model provides a series hybrid active power filter device, which comprises a harmonic current detection unit, a harmonic compensation current generation unit, a series transformer and a passive filter; the method is characterized in that:

harmonic current detecting unitThe element consists of three current transformers and a harmonic current extraction link; three current transformers are respectively connected in series on a three-phase bus of a power grid and used for detecting the current i of the three-phase bus of the system_1A、i_1BAnd i_1CThe output is a three-phase bus current signal i_1As、i_1BsAnd i_1CsTransmitting the harmonic current to a harmonic current extraction link; the harmonic current extraction link is used for extracting a harmonic current according to a received power grid three-phase bus current signal i_1As、i_1BsAnd i_1CsAnd calculating harmonic component i in three-phase bus current signals of the power grid_1Ahs、i_1BhsAnd i_1ChsAnd transmitted to the harmonic compensation current generating unit;

the harmonic compensation current generation unit comprises S identical harmonic compensation current generation subunits, and each harmonic compensation current generation subunit consists of a harmonic current generation link and a switch; the harmonic current generation link receives a power grid three-phase bus harmonic current signal i output by the harmonic current extraction link_1Ahs、i_1BhsAnd i_1ChsPerforming current closed-loop control to generate compensation harmonic current i_2A，i_2BAnd i_2CAnd compensate for harmonic current i_2A，i_2B，i_2CRespectively connected with three-phase bus harmonic current i of power grid_1Ah、i_1BhAnd i_1ChThe following conditions are satisfied; compensating for harmonic currents i when the switch is closed_2A，i_2B，i_2CThe output is output to the series transformer through the closed switch;

i_2A＝(α×k)i_1Ah/S，i_2B＝(α×k)i_1Bh/S，i_2C＝(α×k)i_1Ch/S ①

wherein alpha is a harmonic compensation multiple, 1< alpha <10, alpha is a real number, S is the number of secondary side windings of the series transformer, the value range is 1-500, and k is the transformation ratio of the series transformer;

the primary side winding of the series transformer is connected in series on a power grid bus, the impedance of a main transformer of a load user is taken as a basic value, and the per unit value of the self inductance of the primary side winding is taken as0.1-10%, the secondary side of the_2A，i_2BAnd i_2C(ii) a When the switch is disconnected, the series transformer is opened and connected in series with the system;

the passive filter is connected to a power grid bus in parallel and is arranged between the series transformer and the nonlinear load, and harmonic current of the nonlinear load flows into the passive filter.

The above structure is suitable for three-phase loads, and when applied to single-phase loads, the two structures are different in that:

the harmonic current detection unit consists of a current transformer and a harmonic current extraction link; the current transformer is connected in series on the power grid bus and is used for detecting the system bus current i_1AThe output of which is a bus current signal i_1AsTransmitting the harmonic current to a harmonic current extraction link; the harmonic current extraction link is used for extracting a harmonic current according to the received power grid bus current signal i_1AsCalculating harmonic component i in the current signal of the power grid bus_1AhsAnd transmitted to the harmonic compensation current generating unit;

the harmonic compensation current generation unit comprises S identical harmonic compensation current generation subunits, and each harmonic compensation current generation subunit consists of a harmonic current generation link and a switch; the harmonic current generation link receives a power grid bus harmonic current signal i output by the harmonic current extraction link_1AhsPerforming current closed-loop control to generate compensation harmonic current i_2AAnd compensate for harmonic current i_2AHarmonic current i with power grid bus_1AhThe following condition is satisfied, when the switch is closed, the harmonic current i is compensated_2AThe output is output to the series transformer through the closed switch;

i_2A＝(α×k)i_1Ah/S ②。

the utility model discloses the active part of device works with harmonic current source form, compares prior art scheme, the utility model has the advantages of following three aspect:

(1) the active part only flows small harmonic current (generally less than 15% of system fundamental current) and does not flow system fundamental current, so the capacity of the active part is small, and the cost and the volume of the device are reduced.

(2) The utility model discloses well series transformer's self-inductance is very little (with load user's main transformer impedance as the basic value, the per unit value is only 0.1 ~ 10%), and secondary side winding capacity is littleer. Because in the scheme, the secondary side winding is connected with the harmonic compensation current generating unit, only the harmonic current (generally less than 15% of the system fundamental current) output by the harmonic compensation current generating unit is received, and the fundamental current does not flow, the capacity of the secondary side winding of the transformer is smaller, and the cost is further reduced.

(3) Compared with the prior art, the utility model provides a filter device reliability is higher, once the active part breaks down, the disconnection switch can withdraw from work at any time, has no influence on load power supply; when the active part is out of working condition due to fault maintenance, the system impedance is increased due to the access of the series transformer, a certain filtering effect is still achieved, and the voltage loss and the power factor loss caused by the series transformer are very small.

Drawings

Fig. 1 is a schematic structural diagram of a series hybrid active power filter device in a three-phase system according to the present invention;

fig. 2 is a schematic structural view of the filtering apparatus of the present invention using a multi-winding transformer;

fig. 3 is a schematic diagram of a specific embodiment of the filtering apparatus of the present invention.

Detailed Description

The present invention will be described in further detail with reference to fig. 1.

As shown in fig. 1, the utility model provides a novel series hybrid active power filter device comprises harmonic current detection unit I, harmonic compensation current generation unit II, series transformer III and passive filter IV.

The harmonic current detection unit I consists of three Current Transformers (CT)_1A，CT_1B，CT_1C) And a harmonic current extraction link 2. Three current transformers CT_1A，CT_1BAnd CT_1CAre respectively connected in series on the power grid bus 1 and are used for detecting the three-phase bus current i of the system_1A，i_1B，i_1C(three-phase bus Current i_1A，i_1B，i_1CEach containing a fundamental component i_1Af，i_1Bf，i_1CfAnd harmonic component i_1Ah，i_1Bh，i_1Ch). The output of the three-phase bus current signal i_1As，i_1Bs，i_1CsAnd transmits it to the harmonic current extraction section 2.

The harmonic current extraction link 2 receives a three-phase bus current signal i of the power grid_1Bs，i_1Bs，i_1CsAnd calculating harmonic component i in three-phase bus current signals of the power grid_1Ahs，i_1Bhs，i_1ChsAnd transmitted to the harmonic compensation current generation unit II.

The harmonic compensation current generation unit II is composed of S identical harmonic compensation current generation subunits II ', and each subunit II' is also composed of a harmonic current generation link 3 and a switch 4. S is a positive integer and has a value range of 1-500. Fig. 1 shows the case where S is 1.

The harmonic current generation link 3 receives the harmonic current signal i of the three-phase bus of the power grid output by the harmonic current extraction link 2_1Ahs，i_1Bhs，i_1ChsPerforming current closed-loop control to output a compensation harmonic current i_2A，i_2B，i_2CAnd the output of the whole harmonic compensation current generation unit II is used as the output of the whole harmonic compensation current generation unit II and is transmitted to a series transformer III. As shown in FIG. 1Series transformer dotted terminal and current are assumed to be positive and downward to compensate harmonic current i_2A、i_2B、i_2CRespectively connected with three-phase bus harmonic current i of power grid_1Ah、i_1Bh、i_1ChThe waveforms are the same.

The switch 4 is connected after the harmonic current generation link 3 and is in a closed state during normal work; and when the harmonic current detection unit I or the harmonic compensation current generation unit II has faults or needs to be overhauled, the harmonic current detection unit I or the harmonic compensation current generation unit II is disconnected from the system.

The series transformer III is composed of three single-phase transformers ST_A，ST_B，ST_CThe structure and the connection mode are the same (when S is equal to 1, the secondary side of the transformer only comprises one winding). The primary side winding of the series transformer is connected in series on the power grid bus 1, and the number of turns is W₁Self-inductance L of primary side winding of series transformer₁The design is very small, the impedance of a main transformer of a load user is taken as a basic value, the per unit value is designed to be 0.1-10%, secondary side windings of three single-phase transformers are connected in a Y shape, the number of turns is W2, the mutual inductance of the secondary side windings and the primary side windings of each single-phase transformer is M, and the transformation ratio of the transformer is k-W₁/W₂. The harmonic compensation current generation unit II outputs a compensation harmonic current i_2A，i_2BAnd i_2CRespectively transmitted to the secondary windings of the transformers connected in series corresponding to each phase.

The passive filter IV can be realized by adopting the existing passive filter device, is used as an important component of a filter system, provides a low-impedance path for harmonic current, and simultaneously provides reactive power for a load, and is connected to a power grid bus 1 in parallel and is arranged between the series transformer III and the nonlinear load 5.

The working principle of the filtering device is as follows:

(1) through three current transformers CT arranged on a three-phase bus 1 of the system_1A，CT_1B，CT_1CRespectively detecting the three-phase bus current i of the system_1A，i_1B，i_1CThe output is the system three-phase bus current signalNumber i_1As，i_1Bs，i_1CsAnd transmits it to the harmonic current extraction section 2.

(2) Harmonic current extraction link 2 derives a bus current signal i from a bus current signal_1As、i_1Bs、i_1CsDetecting a harmonic current signal i therein_1Ahs、i_1Bhs、i_1Chs. The specific detection process can adopt the existing detection method based on the instantaneous reactive power theory.

(3) The harmonic current generation link 3 receives the harmonic current signal i detected by the harmonic current extraction link 2_1Ahs、i_1Bhs、i_1ChsPerforming current closed-loop control to generate harmonic compensation current i_2A，i_2B，i_2CCompensating for harmonic current i in the direction of the dotted terminal and current assumption of the series transformer shown in FIG. 1_2A、i_2B、i_2CRespectively connected with three-phase bus harmonic current i of power grid_1Ah、i_1Bh、i_1ChThe waveform is the same and the harmonic current generating unit 3 can be implemented using existing current tracking techniques.

(4) In the normal operating state, the switch 4 is closed. Harmonic compensation current i output by harmonic current generation unit 3_2A，i_2B，i_2CFlows through the switch 4 as the output of the entire harmonic compensation current generation unit II.

(5) Three-phase compensation harmonic current i output by harmonic compensation current generation unit II_2A，i_2B，i_2CRespectively transmitted to the secondary side windings of the series transformers of each phase.

When three-phase compensation harmonic current i_2A，i_2B，i_2CWhen the following conditions are satisfied:

i_2A＝(α×k)i_1Ah，i_2B＝(α×k)i_1Bh，i_2C＝(α×k)i_1Ch；

wherein α is a real number and 1< α < 10.

The series transformer III presents very small inductance L to the fundamental current₁And a large inductance (L) to harmonic currents₁+ α · M) forcing harmonic currents to flow into the passive filter IV. For example, when α is 4, neglecting smaller leakage inductance, L₁Approximately equals M, at this time, the series transformer presents very small inductance L to the fundamental current₁And a large inductance 5L for harmonic current₁Thereby forcing harmonic currents to flow into the passive filter IV.

(6) When the active part breaks down or needs to be overhauled, the active part can quit working at any time, and the switch 4 is disconnected, so that no influence is caused on the power supply of the load. At this time, the series transformer opens the system fundamental current and harmonic current, so the transformer original self-inductance L appears for both fundamental current and harmonic current₁. Because the open circuit access of the series transformer increases the system impedance, a certain filtering effect is still achieved.

The series transformer III may also be a three-phase transformer. The filter shown in fig. 1 is a series hybrid active filter of a three-phase system, and a single-phase inverter may be used to form a single-phase series hybrid active power filter.

When the required inverter capacity is large, a multi-winding transformer structure may be employed. Thus, the active power filter with higher voltage and larger capacity (for example, 10kV and thousands of kVA) can be realized by using the existing lower-voltage and smaller-current devices (for example, 1200V and 200A-500A IGBTs). Fig. 2 shows that the utility model discloses filter equipment adopts the schematic structure of multi-winding transformer, and S >1 this moment, and S is the positive integer.

In fig. 2, the primary windings of the transformers connected in series are also connected in series on the system bus 1, and the number of turns is still W₁Primary measurement of winding self-inductance L₁The design is also very small, and the per unit value is still designed to be 0.1-10%. The secondary side comprises a plurality of windings, and the number of turns of each winding is W₂And the mutual inductance of each secondary winding with the primary winding is still M.

Harmonic current extraction link2 according to the received power grid three-phase bus current signal i_1As、i_1Bs、i_1CsAnd calculating harmonic component i in three-phase bus current signals of the power grid_1Ahs、i_1Bhs、i_1ChsAnd transmitted to the harmonic current generation section 3. The harmonic current generation unit 3 extracts the harmonic current signal i detected by the unit 2 according to the harmonic current_1Ahs、i_1Bhs、i_1ChsOutputting compensated harmonic current i through current closed-loop control_2A、i_2B、i_2CAnd the output of the whole harmonic compensation current generation unit II is used as the output of the whole harmonic compensation current generation unit II and is transmitted to a series transformer III. Compensating for harmonic current i in the homonymous terminal and current assumption forward direction of the series transformer shown in fig. 2_2A、i_2B、i_2CRespectively connected with three-phase bus harmonic current i of power grid_1Ah、i_1Bh、i_1ChThe waveforms are the same.

When three-phase compensation harmonic current i_2A，i_2B，i_2CWhen the following conditions are satisfied:

i_2A＝(α×k)i_1Ah/S，i_2B＝(α×k)i_1Bh/S，i_2C＝(α×k)i_1Ch/S；

α is a real number, and 1< α < 10.

The series transformer III presents very small inductance L to the fundamental current₁And a large inductance (L) to harmonic currents₁+ α · M) forcing harmonic currents to flow into the passive filter IV. For example, when α is 4, neglecting smaller leakage inductance, L₁Approximately equals M, at this time, the series transformer presents very small inductance L to the fundamental current₁And a large inductance 5L for harmonic current₁Thereby forcing harmonic currents to flow into the passive filter IV.

Aiming at the utility model discloses filter equipment three-phase system uses structure figure 1, and figure 3 gives a concrete embodiment, and is shown to figure 2 the utility model discloses filter equipment adopts the schematic structure of multi-winding transformer, and concrete implementation is similar, only needs to found S the same harmonic compensation current take place subunit II' can.

As shown in fig. 3, the harmonic current extraction unit 2 extracts a three-phase bus current signal i from the power grid_1As、i_1Bs、i_1CsDetecting a harmonic current signal i therein_1Ahs、i_1Bhs、i_1Chs. The existing detection method based on the instantaneous reactive power theory is adopted in the detection process. The specific process is as follows:

a) transforming matrix C by three-phase stationary coordinate system/two-phase stationary coordinate system₃₂The three-phase current signals i of the three-phase stationary coordinate system_1As、i_1Bs、i_1CsTransforming to two-phase stationary coordinate system to obtain i_1αs、i_1βs. Wherein, $C_{32}=\sqrt{2/3}\left[\begin{array}{ccc}1& -1/2& -1/2\\ 0& \sqrt{3}/2& -\sqrt{3}/2\end{array}\right].$

b) transforming the i of the two-phase stationary coordinate system by the two-phase stationary coordinate system/two-phase rotating coordinate system transformation matrix C_1αs、i_1βsTransforming to two-phase rotating coordinate system to obtain i_1ds、i_1qs。

Wherein, <math> <mrow> <mi>C</mi> <mo>=</mo> <mrow> <mfenced open='[' close=']' separators=','> <mtable> <mtr> <mtd> <mi>sin</mi> <mi>&omega;t</mi> </mtd> <mtd> <mo>-</mo> <mi>cos</mi> <mi>&omega;t</mi> </mtd> </mtr> <mtr> <mtd> <mo>-</mo> <mi>cos</mi> <mi>&omega;t</mi> </mtd> <mtd> <mo>-</mo> <mi>sin</mi> <mi>&omega;t</mi> </mtd> </mtr> </mtable> </mfenced> <mo>,</mo> </mrow> </mrow></math> sin ω t and cos ω t may be generated by sine and cosine generating circuits.

c) Filtering i by a low-pass filter circuit_1ds、i_1qsThe alternating current component in the signal is obtained, and then the direct current component i is obtained_1ds、i_1qs。

d) Transforming the matrix C by a two-phase rotating coordinate system/a two-phase stationary coordinate system^-1(i.e., the inverse of the C matrix), rotate the two phases by i of the coordinate system_1ds、i_1qsTransforming to two-phase stationary coordinate system to obtain i_1αfs、i_1βfs。

e) Transforming matrices by means of a two-phase stationary frame/a three-phase stationary frame(i.e. C)₃₂Inverse of the matrix) of the first and second order_1αfs、i_1βfsConverting the current into a three-phase static coordinate system to obtain a fundamental current signal i_1Afs、i_1BfsAnd i_1Cfs。

Obtaining harmonic current signal i by a subtracter_1Ahs、i_1Bhs、i_1Chs. I.e. i_1Ahs＝i_1As-i_1Afs；i_1Bhs＝i_1Bs-i_1Bfs；i_1Chs＝i_1Cs-i_1Cfs。

The harmonic current generation section 3 includes a proportional operation section 3A, a current control section 3B, and an inverter section 3C. The proportion operation part 3A extracts the harmonic current signal i output by the link 2 according to the harmonic current_1Ahs、i_1Bhs、i_1ChsAnd harmonic compensation multiple alpha (alpha is real number and 1)<α<10) Obtaining harmonic current command signal i of three-phase inverter by transformation ratio k of transformer_Aref、i_Bref、i_CrefAnd has i_Aref＝(α×k)i_1Ahs，i_Bref＝(α×k)i_1Bhs，i_Cref＝(α×k)i_1Chs. The current control part 3B adopts a triangular wave comparison mode, and firstly detects a mutual inductor (namely CT) through feedback current_2A，CT_2B，CT_2C) Detecting an inverter output current i_A、i_BAnd i_CSignal i of_As、i_BsAnd i_CsThen respectively sending three-phase harmonic current command signals (i.e. i)_Aref、i_BrefAnd i_Cref) And a feedback signal (i.e. i)_As、i_BsAnd i_Cs) Comparing in real time to obtain error signal delta i_A、Δi_BAnd Δ i_CAnd transmitted to a PI regulator (with output limit saturation), the output of which is Deltai_PIA、Δi_PIBAnd Δ i_PICΔ i to_PIA、Δi_PIBAnd Δ i_PICComparing with a triangular wave electric signal with a fixed frequency (for example, 10kHz) and a certain amplitude output by a triangular wave generator, and finally outputting a series of amplitude values of +1 (when delta i is_PIA、Δi_PIBAnd Δ i_PICGreater than the triangular wave voltage portion) or 0 (when Δ i_iPIA、Δi_PIBAnd Δ i_PICLess than the triangular wave voltage portion), i.e. pulse signals

Pulse signal

Is transmitted to the PWM driving unit to output a driving signal S_pwmTo the switching devices of the inverter (typically IGBTs).

The inverter portion 3C is composed of an inverter, an output filter, a feedback current detection transformer (i.e., CT)_2A，CT_2B，CT_2C) And (4) forming. The output filter circuit is mainly used for filtering out switching frequency components in the output current of the inverter and finally outputting compensation harmonic i_2A、i_2BAnd i_2CInto the secondary winding of the series transformer III. Compensating for harmonic current i in the homonymous terminal and current assumption forward direction of the series transformer shown in FIG. 3_2A、i_2B、i_2CRespectively connected with three-phase bus harmonic current i of power grid_1Ah、i_1Bh、i_1ChThe waveforms are the same.

When three-phase compensation harmonic current i_2A，i_2B，i_2CWhen the following conditions are satisfied:

i_2A＝(α×k)i_1Ah/S，i_2B＝(α×k)i_1Bh/S，i_2C＝(α×k)i_1Ch(ii) S; (in FIG. 3, S is 1)

α is a real number, and 1< α < 10.

The series transformer III presents very small inductance L to the fundamental current₁And a large inductance (L) to harmonic currents₁+ α · M) forcing harmonic currents to flow into the passive filter IV. For example, when α is 4, neglecting smaller leakage inductance, L₁Approximately equals M, at this time, the series transformer presents very small inductance L to the fundamental current₁And a large inductance 5L for harmonic current₁Thereby forcing harmonic currents to flow into the passive filter IV.

In the three-phase three-wire system shown in fig. 3, the passive filter IV may be set as a plurality of filtering branches with 7% reactance rate for main harmonics 5 and 7 to filter the harmonics 5 and 7, and a high-pass filtering branch is added to provide a path for higher harmonic current and compensate reactive power.

Claims (2)

1. A series hybrid active power filter device comprises a harmonic current detection unit (I), a harmonic compensation current generation unit (II), a series transformer (III) and a passive filter (IV); the method is characterized in that:

the harmonic current detection unit (I) consists of three Current Transformers (CT)_1A，CT_1B，CT_1C) And a harmonic current extraction link (2); three Current Transformers (CT)_1A，CT_1B，CT_1C) Are respectively connected in series on a three-phase bus (1) of the power grid and are used for detecting the current i of the three-phase bus of the system_1A、i_1BAnd i_1CThe output is a three-phase bus current signal i_1As、i_1BsAnd i_1CsTransmitting the harmonic current to a harmonic current extraction link (2); the harmonic current extraction link (2) receives a three-phase bus current signal i of the power grid_1As、i_1BsAnd i_1CsAnd calculating harmonic component i in three-phase bus current signals of the power grid_1Ahs、i_1BhsAnd i_1ChsAnd transmitted to the harmonic compensation current generating unit (II);

the harmonic compensation current generation unit (II) comprises S identical harmonic compensation current generation subunits (II '), and each harmonic compensation current generation subunit (II') consists of a harmonic current generation link (3) and a switch (4); the harmonic current generation link (3) receives a power grid three-phase bus harmonic current signal i output by the harmonic current extraction link (2)_1Ahs、i_1BhsAnd i_1ChsPerforming current closed-loop control to generate compensation harmonic current i_2A，i_2BAnd i_2C(ii) a And compensating for harmonic currents i_2A，i_2B，i_2CRespectively connected with three-phase bus harmonic current i of power grid_1Ah、i_1Bh、i_1ChSatisfying the condition of (1); compensating for harmonic currents i when the switch (4) is closed_2A，i_2B，i_2CThe output is transmitted to a series transformer (III) through a closed switch (4);

i_2A＝(α×k)i_1Ah/S，i_2B＝(α×k)i_1Bh/S，i_2C＝(α×k)i_1Ch/S ①

wherein alpha is a harmonic compensation multiple, 1< alpha <10, alpha is a real number, S is the number of secondary side windings of the series transformer, the value range is 1-500, and k is the transformation ratio of the series transformer;

the primary side winding of the series transformer (III) is connected in series on the power grid bus (1), the primary transformer impedance of a load user is taken as a basic value, the per unit value of the self-inductance of the primary side winding is 0.1-10%, the secondary side of the series transformer comprises S windings, the S windings are connected with the switches (4) in the S identical harmonic compensation current generation subunits (II'), and the S windings respectively receive the output harmonic current i_2A，i_2BAnd i_2C(ii) a When the switch (4) is disconnected, the series transformer (III) is opened and connected in series with the system;

the passive filter (IV) is connected to the power grid bus (1) in parallel and is arranged between the series transformer (III) and the nonlinear load (5), and harmonic current of the nonlinear load (5) flows into the passive filter (IV).

2. A series hybrid active power filter device comprises a harmonic current detection unit (I), a harmonic compensation current generation unit (II), a series transformer (III) and a passive filter (IV); the method is characterized in that:

the harmonic current detection unit (I) is composed of a Current Transformer (CT)_1A) And a harmonic current extraction link (2); current Transformer (CT)_1A) Is connected in series on a power grid bus (1) and is used for detecting the system bus current i_1AThe output of which is a bus current signal i_1AsTransmitting the harmonic current to a harmonic current extraction link (2); the harmonic current extraction link (2) extracts a power grid bus current signal i according to the received power grid bus current signal i_1AsCalculating harmonic component i in the current signal of the power grid bus_1AhsAnd transmitted to the harmonic compensation current generating unit (II);

the harmonic compensation current generation unit (II) comprises S identical harmonic compensation current generation subunits (II '), and each harmonic compensation current generation subunit (II') consists of a harmonic current generation link (3) and a switch (4); the harmonic current generation link (3) receives a power grid bus harmonic current signal i output by the harmonic current extraction link (2)_1AhsPerforming current closed-loop control to generate compensation harmonic current i_2AAnd compensate for harmonic current i_2AHarmonic current i with power grid bus_1AhThe condition that when the switch (4) is closed, the harmonic current i is compensated_2AThe output is transmitted to a series transformer (III) through a closed switch (4);

i_2A＝(α×k)i_1Ah/S ②

wherein alpha is a harmonic compensation multiple, 1< alpha <10, alpha is a real number, S is the number of secondary side windings of the series transformer, the value range is 1-500, and k is the transformation ratio of the series transformer;

series transformer (III) the primary side winding of which is connected in series on the power grid bus (1) and takes the main transformer impedance of the load user as a basic value, the per unit value of the self-inductance of the primary side winding is 0.1-10%, the secondary side of which contains S windings, the S windings are connected with the switches (4) in the S same harmonic compensation current generation subunits (II') and respectively receive the output harmonic current i_2A(ii) a When the switch (4) is disconnected, the series transformer (III) is opened and connected in series with the system;

the passive filter (IV) is connected to the power grid bus (1) in parallel and is arranged between the series transformer (III) and the nonlinear load (5), and harmonic current of the nonlinear load (5) flows into the passive filter (IV).

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