CN202384764U

CN202384764U - Active electric power filter

Info

Publication number: CN202384764U
Application number: CN201120452333XU
Authority: CN
Inventors: 殷骏
Original assignee: ANHUI LEADZONE INTELLIGENT GRID TECHNOLOGY Co Ltd
Current assignee: ANHUI LEADZONE INTELLIGENT GRID TECHNOLOGY Co Ltd
Priority date: 2011-11-16
Filing date: 2011-11-16
Publication date: 2012-08-15
Anticipated expiration: 2021-11-16

Abstract

The utility model relates to an active electric power filter, comprising a main circuit and a control circuit used for controlling the main circuit, wherein the main circuit comprises two breakers S1 and S2, three power supply side voltage detectors SVA, SVB and SVC, three load end current detectors LCA, LCB and LCC, resistors R1A, R1B, R1C, R2, R3 and R4, four AC inlet wire reactance sets L1, L2, L3 and L4, four current Hall sensors FCA, FCB, FCC and FCN, two relays J1 and J2, a capacitor C, a voltage Hall sensor VDC, and eight power modules 12. The active electric power filter is a four-bridge-arm parallel type active electric power filter, and can resolve the current harmonic wave problem of a three-phase four-wire type power distribution system.

Description

A kind of Active Power Filter-APF

Technical field

The utility model relates to a kind of filter, relates in particular to a kind of Active Power Filter-APF.

Background technology

Since nearly half a century; Along with applying of power electronics; The increasing sharply of nonlinear-load (for example the transmission device of electric locomotive, industrial furnace, frequency control etc. application), the Harmonious Waves in Power Systems pollution becoming serious, and therefore receive people's common attention and attention.Reducing harmonic effects can start with from two aspects: the one, from harmonic source, reduce the generation of harmonic wave; The 2nd, filter is installed.

Common filter comprises passive filter, active filter and compound filter.Passive filter (PF:Passive Filter) is also referred to as the LC filter, is the filter that is formed by filtering capacitor, reactor and resistor appropriate combination.The commercial Application of passive filter has had quite long history; Its method for designing is reliable and stable, simple in structure; But its filter effect depends on system impedance characteristics, and receive temperature drift easily, the influence of the aging and nonlinear-load of harmonic pollution in electric power net degree, filter capacitor.Corresponding with passive filter is that (Active Power Filter, APF), it has the unrivaled technical advantage of passive filter to active filter, therefore more and more receives people's attention.

The thought of active filter comes across in the paper of B.M.Bird in 1969 and J.F.Marsh the earliest.Described in the literary composition through injecting triple harmonic current to AC power to reduce the harmonic wave of power supply, improved the new method of source current waveform, the method described in the literary composition is considered to active filter thought the earliest.The H.Sasaki and the complete basic principle of describing Active Power Filter-APF of T.Machida of Japan in 1971.The L.Gyugyi of U.S.'s Westinghouse Electrical Corp. in 1976 and E.C.Strycula have proposed to adopt the Active Power Filter-APF of pulse width modulation control; The basic topological structure and the control method of main circuit have been confirmed; Having illustrated Active Power Filter-APF from principle is a desirable harmonic current generator; And implementation method and control corresponding principle, the basis of having established Active Power Filter-APF be discussed.Yet owing to lack high-power turn-off device, Active Power Filter-APF almost has no progress except the laboratory research of minority in the seventies in 20th century.Got into since the eighties in 20th century; The appearance of novel semi-conductor device; The development of PWM technology; Especially the people such as H.Akagi of nineteen eighty-three Japan have proposed " three-phase circuit instantaneous reactive power theory ", and the harmonic wave and the reactive current detection method that are the basis with this theory have obtained successful application in three phase active electric power filter, greatly promoted the development of Active Power Filter-APF.

Compare with passive filter, active filter is a kind of active compensation arrangement, has the better dynamic performance.Active Power Filter-APF is the hot issue of field of power electronics in recent years.At present, the active power filtering technology is applied in minority industrially developed country such as Japan, the U.S., has commercial plant to put into operation; Domestic research to Active Power Filter-APF still is in the starting stage.

According to the mode that inserts electrical network, Active Power Filter-APF can be divided into tandem type, parallel connection type and mixed type three major types.The active power filter structure of each type is different, thereby its operation principle, characteristic are also variant.What flow through in the series connection type active electric power filter is the normal duty electric current, so loss is bigger; In addition, after the switching of series connection type active electric power filter, the fault withdraw from and various protection also complicated than parallel connection type active electric filter.Series-multiple connection type Active Power Filter-APF combines tandem type and two kinds of structures of parallel connection type, forms the global question that a complete custom power device solves the quality of power supply jointly.Wherein Series active power filter plays bucking voltage harmonic wave, elimination system imbalance, regulation voltage fluctuation or flickering and improves the stability of power distribution network or the effect of damped oscillation; The shunt active power filter plays that the offset current harmonic wave is uneven, idle, the effect of regulating the current transformer dc voltage of compensation load, but that its major defect is a cost is high quite complicated with control.

Can be applicable to that at present the active power filter structure that solves three-phase four-wire system distribution system current harmonics problem mainly contains the mid point extraction.Mid point extraction Active Power Filter-APF is drawn center line by two electric capacity mid points; Two electric capacity about the center line offset current will be flowed through; Because the center line offset current contains a large amount of harmonic components; Two capacitance voltages also must contain a large amount of harmonic components up and down, and capacitance voltage fluctuation is comparatively violent, and the runnability of inverter is had a negative impact.For suppressing voltage fluctuation, must increase capacitance, be the compensation current in middle wire; Two capacitance voltage values of mid point extraction Active Power Filter-APF certainly exist difference; Capacitance voltage is inevitable uneven up and down, and this also causes the inverter performance decrease, is the sustaining voltage balance; Must adopt certain control measure, also must increase the complicated and reduction system operating safety factor of system hardware cost and system control.

The utility model content

In view of this, the utility model provides a kind of Active Power Filter-APF, and it is intended to solve three-phase four-wire system distribution system current harmonics problem.

The utility model is achieved in that a kind of Active Power Filter-APF, the control circuit that it comprises main circuit and is used to control said main circuit.Said main circuit comprises: two circuit breaker S1, S2; Three mains side voltage detector SVA, SVB, SVC; Three load end current detector LCA, LCB, LCC; Resistance R 1A, R1B, R1C, R2, R3, R4; Four exchange inlet wire reactance group L1, L2, L3, L4; Four current Hall transducer FCA, FCB, FCC, FCN; Two relay J 1, J2; Capacitor C; Voltage hall sensor VDC and eight power models (12).The end of circuit breaker S1 with four mutually the three-phase A among A, B, C, the N, B, C electrically connect, its other end is electrically connected at the end of three mains side voltage detector SVA, SVB, SVC.The other end of three mains side voltage detector SVA, SVB, SVC is electrically connected at the end of three load end current detector LCA, LCB, LCC; The other end of three load end current detector LCA, LCB, LCC is electrically connected at nonlinear-load, and said nonlinear-load also is electrically connected at another phase N.The end of circuit breaker S2 is electrically connected between three mains side voltage detector SVA, SVB, SVC and three load end current detector LCA, LCB, the LCC, and its other end is electrically connected at the end of three resistance R 1A, R1B, R1C.Three normally opened contacts of relay J 1 are parallel to three resistance R 1A, R1B, R1C respectively, and the other end of three resistance R 1A, R1B, R1C is electrically connected at three ends that exchange inlet wire reactance group L1, L2, L3.Another end that exchanges inlet wire reactance group L4 is electrically connected between another phase N and the nonlinear-load, and its other end is electrically connected at another end that exchanges inlet wire reactance group L4.Four other ends that exchange inlet wire reactance group L1, L2, L3, L4 are electrically connected at the end of four current Hall transducer FCA, FCB, FCC, FCN, and the other end of four current Hall transducer FCA, FCB, FCC, FCN is electrically connected between per two power models (12).One end of per two power models (12) is electrically connected and is electrically connected at an end of resistance R 3; The other end of per two power models (12) also is electrically connected and is electrically connected at an end of resistance R 4, and the other end of resistance R 3 is connected to the other end of resistance R 4 via voltage hall sensor VDC.The two ends of capacitor C electrically connect two resistance R 3, R4 respectively, and relay J 2 is connected in parallel on the capacitor C after resistance R 2 series connection.

Compare with the traditional active electric-power filter, the Active Power Filter-APF that the utility model provides is the parallel Active Power Filter-APFs of four brachium pontis, and its beneficial effect is following:

(1) has adaptation function, realized dynamic compensation, can compensate, the object that compensates is had the response that is exceedingly fast frequency and the humorous reactive power that involves variation that size all changes;

(2) can compensate harmonic wave and reactive power simultaneously, not need energy-storage travelling wave tube during compensating power, required energy-storage travelling wave tube capacity is little during compensation harmonic, and the size of compensating power can be accomplished continuous adjusting;

(3) receive the influence of electric network impedance little, be not easy and electric network impedance generation resonance; And can follow the tracks of the variation of mains frequency, so the influence that compensation performance is not changed by mains frequency.

Description of drawings

Fig. 1 is the main circuit structure sketch map of the Active Power Filter-APF that provides of the utility model preferred embodiments.

Fig. 2 is the control circuit module structural representation of Active Power Filter-APF among Fig. 1.

Fig. 3 is the electrical block diagram of signal processing circuit among Fig. 2.

Fig. 4 is the electrical block diagram of current signal modulate circuit among Fig. 2.

Fig. 5 is the electrical block diagram of voltage signal modulate circuit among Fig. 2.

Fig. 6 is the electrical block diagram of current foldback circuit among Fig. 2.

Fig. 7 is the electrical block diagram of overvoltage crowbar among Fig. 2.

Fig. 8 is the electrical block diagram of drive circuit among Fig. 2.

Symbol description

Main circuit 10

Control circuit 20

Nonlinear load 30

Circuit breaker S1, S2, J2

Mains side voltage detector SVA, SVB, SVC

Load end current detector LCA, LCB, LCC

Resistance R 1A, R1B, R1C, R2, R3, R4, R5a5, R5a7, R5a8, R5a9, R5a10, R5a11, R3a1, R3a2, R3a3, R3a4, R3a5, R3a6, R3a7, R1a, R5a0, R5a1, R5a2, R5a3, R5a4, R5a5, R5a6, R5a, R3a0, R3a71, R3a8, R3a9, R3a10, R3a11, R12, R13, R14, R15, R16,

Relay J 1

Exchange inlet wire reactance L

Current Hall transducer FCA, FCB, FCC, FCN

Power model 12

Voltage hall sensor VDC

DC side filter capacitor c

Modulate circuit 21

Signal processing circuit 23

Drive circuit 25

Man-machine interface circuit 27

Current foldback circuit 28

Overvoltage crowbar 29

Single-chip microcomputer 270

Supervisory keyboard 271

Display 273

Current signal modulate circuit 213

Voltage signal modulate circuit 215

Comparator A5aB, A3aB

Diode D5a, Vd3a, D3a, D6, D7, D8

Voltage stabilizing didoe Vd5a1, Vd5a, Vd3a1

Capacitor C 5a2, C3a, C3a1, C5a, C5a1, C3a2, C11, C12

Operational amplifier A 3aA, A5aA

Triode Q2

Electrochemical capacitor E14, E15, E16, E17, E18

Four phase A, B, C, N

Embodiment

For the purpose, technical scheme and the advantage that make the utility model is clearer,, the utility model is further elaborated below in conjunction with accompanying drawing and embodiment.Should be appreciated that specific embodiment described herein only in order to explanation the utility model, and be not used in qualification the utility model.

Please consult Fig. 1 and Fig. 2 in the lump; The structural representation of the Active Power Filter-APF that it provides for the utility model preferred embodiments; It is applied in the Active Power Filter-APF (figure does not show); Active Power Filter-APF is the parallel Active Power Filter-APFs of four brachium pontis, the control circuit 20 (as shown in Figure 2) that it comprises main circuit 10 (as shown in Figure 1) and is used to control main circuit 10.

Main circuit 10 comprises two circuit breaker S1, S2; Three mains side voltage detector SVA, SVB, SVC; Three load end current detector LCA, LCB, LCC; Some resistance R 1A, R1B, R1C, R2, R3, R4; Four exchange inlet wire reactance group L1, L2, L3, L4; Individual current Hall transducer FCA, FCB, FCC, FCN; Relay J 1, J2; Capacitor C; Voltage hall sensor VDC; And eight power models 12.

The end of circuit breaker S1 with four mutually the three-phase A among A, B, C, the N, B, C electrically connect, its other end is electrically connected at the end of three mains side voltage detector SVA, SVB, SVC.The other end of three mains side voltage detector SVA, SVB, SVC is electrically connected at the end of three load end current detector LCA, LCB, LCC; The other end of three load end current detector LCA, LCB, LCC is electrically connected at nonlinear-load, and said nonlinear-load also is electrically connected at another phase N.The end of circuit breaker S2 is electrically connected between three mains side voltage detector SVA, SVB, SVC and three load end current detector LCA, LCB, the LCC, and its other end is electrically connected at the end of three resistance R 1A, R1B, R1C.Three normally opened contacts of relay J 1 are parallel to three resistance R 1A, R1B, R1C respectively, and the other end of three resistance R 1A, R1B, R1C is electrically connected at three ends that exchange inlet wire reactance group L1, L2, L3.Another end that exchanges inlet wire reactance group L4 is electrically connected between another phase N and the nonlinear-load, and its other end is electrically connected at another end that exchanges inlet wire reactance group L4.Four other ends that exchange inlet wire reactance group L1, L2, L3, L4 are electrically connected at the end of four current Hall transducer FCA, FCB, FCC, FCN, and the other end of four current Hall transducer FCA, FCB, FCC, FCN is electrically connected between per two power models 12.One end of per two power models 12 is electrically connected and is electrically connected at an end of resistance R 3; The other end of per two power models 12 also is electrically connected and is electrically connected at an end of resistance R 4, and the other end of resistance R 3 is connected to the other end of resistance R 4 via voltage hall sensor VDC.The two ends of capacitor C electrically connect two resistance R 3, R4 respectively, and relay J 2 is connected in parallel on the capacitor C after resistance R 2 series connection.

Current Hall transducer FCA, FCB, FCC, FCN use for inspection side offset current, are used to provide the anti-extensive signal of electric current of current tracking control usefulness; Exchanging inlet wire reactance L is the interchange inlet wire reactance of active electric power beach ripple device; Voltage Hall voltage transducer VDC is used for the feedback signal of system to its DC voltage control for detecting the Active Power Filter-APF dc voltage; Mains side voltage detector SVA, SVB, SVC are used to detect mains side voltage; Load end current detector LCA, LCB, LCC are used to detect the load end electric current to be changed.

See also Fig. 3, control circuit 20 comprises modulate circuit 21, signal processing circuit 23, drive circuit 25 and man-machine interface circuit 27.Modulate circuit 21, drive circuit 25 all electrically connect with signal processing circuit 23 with man-machine interface circuit 27, and in this execution mode, signal processing circuit 23 is that example is illustrated with the DSP2812 chip.Man-machine interface circuit 27 adopts single-chip microcomputer 270 supervisory keyboards 271 and display 273, and through CAN bus and DSP2812 chip communication display parameters, revises parameter.

Modulate circuit 21 comprises current signal modulate circuit 213, voltage signal modulate circuit 215, current foldback circuit 28 and overvoltage crowbar 29.By the current signal that current sensor (like load end current detector LCA, LCB, LCC, current Hall transducer FCA, FCB, FCC, FCN) detects, through overcurrent signal modulate circuit 21, the ADC sample conversion of sending in the DSP2812 chip becomes digital quantity.

Please consult Fig. 2 and Fig. 4 in the lump, current signal modulate circuit 213 comprises resistance R 5a5, R5a7, R5a8, R5a9, R5a10, R5a11; Comparator A5aB (in this execution mode, selecting the TL082 components and parts); Diode D5a; Voltage stabilizing didoe Vd5a1; Capacitor C 5a2.

The termination power of resistance R 5a7 (in this execution mode, connect+15V); The other end of resistance R 5a7 is via the electrical ground connection of resistance R 5a9; The end of resistance R 5a5 is connected between resistance R 5a9 and the resistance R 5a7, and the other end of resistance R 5a5 is connected in the end of oppisite phase of comparator A5aB.The in-phase end of comparator A5aB is connected in any among load end current detector LCA, LCB, LCC and current Hall transducer FCA, FCB, FCC, the FCN via resistance R 5a8, and the output of comparator A5aB is successively via diode D5a, resistance R 5a10, resistance R 5a11 and be connected in the ADC input (having eight port ADCINA0 ~ 7) of DSP2812 chip.The plus earth of voltage stabilizing didoe Vd5a1, the negative electrode of voltage stabilizing didoe Vd5a1 are connected between resistance R 5a10 and the resistance R 5a11, and capacitor C 5a2 is parallel to voltage stabilizing didoe Vd5a1.

Please consult Fig. 2 and Fig. 5 in the lump,,, send into ADC sampling the carrying out computing of DSP2812 chip through overvoltage signal modulate circuit 215 by the voltage signal that voltage sensor (voltage hall sensor VDC) detects.Voltage signal modulate circuit 215 comprises resistance R 3a1, R3a2, R3a3, R3a4, R3a5, R3a6, R3a7, R1a; Operational amplifier A 3aA; Utmost point pipe Vd3a (in this execution mode, is Schottky barrier diode SchottkyBarrierDiode, SBD); Capacitor C 3a, C3a1.

The end of resistance R 3a5 is connected in voltage Hall voltage transducer VDC; The other end of resistance R 3a5 is via the electrical ground connection of resistance R 3a1; The end of resistance R 3a2 is connected between resistance R 3a1 and the resistance R 3a5, and the other end of resistance R 3a2 is via the electrical ground connection of capacitor C 3a1.The end of resistance R 3a3 is connected between resistance R 3a2 and the capacitor C 3a1, and the other end of resistance R 3a3 is connected in the in-phase end of operational amplifier A 3aA, and the end of oppisite phase of operational amplifier A 3aA is connected in the output of operational amplifier A 3aA via resistance R 3a4.The end of resistance R 3a6 is connected in the output of operational amplifier A 3aA, and the other end of resistance R 3a6 is via resistance R 3a7 ground connection.The end of resistance R 1a is connected between resistance R 3a6 and the resistance R 3a7; The other end of resistance R 1a via diode Vd3a be connected to respectively and power supply; The other end of resistance R 1a also is connected in the ADC input of DSP2812 chip, and the other end of resistance R 1a is also via capacitor C 3a ground connection.

Please consult Fig. 2 and Fig. 6 in the lump, survey electric current greater than 35A if exchange, current foldback circuit 28 starts, and the DSP2812 chip receives over-current signal, then blocks the pulse of drive circuit 25.Current foldback circuit 28 comprises resistance R 5a0, R5a1, R5a2, R5a3, R5a4, R5a5, R5a6, R5a; Operational amplifier A 5aA; Diode Vd5a (in this execution mode, is Schottky barrier diode SchottkyBarrierDiode, SBD); Capacitor C 5a, C5a1.

The termination of resistance R 5a1 is received ac-side current, and the other end of resistance R 5a1 is via the electrical ground connection of resistance R 5a2, and the end of resistance R 5a0 is connected between resistance R 5a1 and the resistance R 5a2, and the other end of resistance R 5a0 is via the electrical ground connection of capacitor C 5a1.The end of resistance R 5a3 is connected between resistance R 5a0 and the capacitor C 5a1, and the other end of resistance R 5a3 is connected in the in-phase end of operational amplifier A 5aA, and the end of oppisite phase of operational amplifier A 5aA is connected in the output of operational amplifier A 5aA via resistance R 5a4.The end of resistance R 5a5 is connected in the output of operational amplifier A 5aA, the other end of resistance R 5a5 via resistance R 5a6 connect power supply (+3V).The end of resistance R 5a is connected between resistance R 5a6 and the resistance R 5a5; The other end of resistance R 5a via diode Vd5a be connected to respectively with power supply (+3V); The other end of resistance R 5a also is connected in the ADC input of DSP2812 chip, and the other end of resistance R 5a is also via capacitor C 5a ground connection.

Please consult Fig. 2 and Fig. 7 in the lump, when dc voltage during greater than 625V, overvoltage crowbar 29 starts, and the DSP2812 chip receives the overvoltage signal, blocks the pulse of drive circuit 25.Overvoltage crowbar 29 comprises resistance R 3a0, R3a71, R3a8, R3a9, R3a10, R3a11; Comparator A3aB (in this execution mode, selecting the TL082 components and parts); Diode D3a; Voltage stabilizing didoe Vd3a1; Capacitor C 3a2.

The termination power of resistance R 3a71 (in this execution mode, connect+15V); The other end of resistance R 3a71 is via the electrical ground connection of resistance R 3a9; The end of resistance R 3a0 is connected between resistance R 3a9 and the resistance R 3a71, and the other end of resistance R 3a0 is connected in the end of oppisite phase of comparator A3aB.The in-phase end of comparator A3aB is connected in voltage hall sensor VDC via resistance R 3a8, and the output of comparator A3aB is successively via diode D3a, resistance R 3a10, resistance R 3a11 and be connected in the DSP2812 chip.The plus earth of voltage stabilizing didoe Vd3a1, the negative electrode of voltage stabilizing didoe Vd3a1 are connected between resistance R 3a10 and the resistance R 3a11, and capacitor C 3a2 is parallel to voltage stabilizing didoe Vd3a1.

Please consult Fig. 2 and Fig. 8 in the lump; Drive circuit 25 is the IBGT drive circuit in this execution mode; It adopts the IPM module, and the control signal that the IGBT drive circuit sends the DSP2812 chip changes the IGBT drive signal of each brachium pontis into, guarantees that the IPM module can operate as normal.Drive circuit 25 comprises chip for driving (in this execution mode, being SG3525); Resistance R 12, R13, R14, R15, R16; Capacitor C 11, C12; Electrochemical capacitor E14, E15, E16, E17, E18; Diode D6, D7, D8; Triode Q2.

In sum; Control circuit 20 is a core with dsp chip 2812; 7 road current signals (load current and offset current) and 1 road dc voltage send the ADC of dsp chip to convert digital quantity to after current signal modulate circuit 213 conditionings of modulate circuit 21; One road alternating voltage becomes the CAP1 that square wave send dsp chip through the voltage signal modulate circuit 215 of modulate circuit 21, the zero crossing of catching square wave with the capturing unit of dsp chip realize with line voltage synchronously.Pwm signal produces Dead Time by IXDP630/631 after level translation, be added to drive circuit after the anti-phase.IXDP630/631 also has defencive function concurrently, and E_R, E_S, E_T block monophasic pulses if respectively, and OUT_E blocks three-phase pulse simultaneously.

The beneficial effect of said Active Power Filter-APF is following:

(3) receive the influence of electric network impedance little, be not easy and electric network impedance generation resonance; And can follow the tracks of the variation of mains frequency, so the influence that compensation performance is not changed by mains frequency;

The above is merely the preferred embodiment of the utility model; Not in order to restriction the utility model; Any modification of being done within all spirit and principles at the utility model, be equal to replacement and improvement etc., all should be included within the protection range of the utility model.

Claims

1. Active Power Filter-APF, the control circuit that it comprises main circuit and is used to control said main circuit is characterized in that, said main circuit comprises: two circuit breaker S1, S2; Three mains side voltage detector SVA, SVB, SVC; Three load end current detector LCA, LCB, LCC; Resistance R 1A, R1B, R1C, R2, R3, R4; Four exchange inlet wire reactance group L1, L2, L3, L4; Four current Hall transducer FCA, FCB, FCC, FCN; Two relay J 1, J2; Capacitor C; Voltage hall sensor VDC; And eight power models (12); Three-phase A among A, B, C, the N, B, C electrically connect the end of circuit breaker S1 mutually with four; Its other end is electrically connected at the end of three mains side voltage detector SVA, SVB, SVC; The other end of three mains side voltage detector SVA, SVB, SVC is electrically connected at the end of three load end current detector LCA, LCB, LCC; The other end of three load end current detector LCA, LCB, LCC is electrically connected at nonlinear-load; Said nonlinear-load also is electrically connected at another phase N; The end of circuit breaker S2 is electrically connected between three mains side voltage detector SVA, SVB, SVC and three load end current detector LCA, LCB, the LCC; Its other end is electrically connected at the end of three resistance R 1A, R1B, R1C; Three normally opened contacts of relay J 1 are parallel to three resistance R 1A, R1B, R1C respectively, and the other end of three resistance R 1A, R1B, R1C is electrically connected at three ends that exchange inlet wire reactance group L1, L2, L3, and another end that exchanges inlet wire reactance group L4 is electrically connected between another phase N and the nonlinear-load; Its other end is electrically connected at another end that exchanges inlet wire reactance group L4; Four other ends that exchange inlet wire reactance group L1, L2, L3, L4 are electrically connected at the end of four current Hall transducer FCA, FCB, FCC, FCN, and the other end of four current Hall transducer FCA, FCB, FCC, FCN is electrically connected between per two power models (12), and an end of per two power models (12) is electrically connected and is electrically connected at an end of resistance R 3; The other end of per two power models (12) also is electrically connected and is electrically connected at an end of resistance R 4; The other end of resistance R 3 is connected to the other end of resistance R 4 via voltage hall sensor VDC, and the two ends of capacitor C electrically connect two resistance R 3, R4 respectively, and relay J 2 is connected in parallel on the capacitor C after resistance R 2 series connection.