CN103346567A - Shunt active power filter - Google Patents

Abstract

The invention discloses a shunt active power filter belonging to the technical field of an active power filter technology. The filter comprises three level inverters, a filter body, a switch tube, a clamp diode, a voltage-dividing capacitor, and six IGBT (insulated gate bipolar translator) drive circuits with two paths of signal output. The drive circuit adopted by the shunt active power filter includes a high-speed optocoupler inside; and a pulse control signal is isolated with inside of the drive circuit, so that electric isolation is achieved by a digital control circuit and the drive circuit; interference caused by electrical coupling can be prevented; gate drive adopts bipolar control voltage; and high anti-interference performance can be obtained by using negative grid voltage.

Description

A kind of parallel connection type active electric filter

Technical field

The invention belongs to the active power filtering technical field, be specifically related to a kind of parallel connection type active electric filter.

Background technology

Electric energy is requisite important energy source in modern society's production and the people's lives, along with the development of society and the especially extensive use of power electronic equipment of progress of science and technology, on the one hand the harmonic pollution in the electric power system increases along with the quantity of nonlinear load and capacity and is on the rise, supplier of electricity and power system device thereof, user and electrical appliance thereof also improve day by day to the requirement of the quality of power supply on the other hand, and more serious harmonic pollution requires to have formed a pair of sharp-pointed contradiction with the more and more higher quality of power supply.Because power quality problem causes the harmonic wave severe overweight of enterprises such as metallurgy, railway, mine to China, also of common occurrence because of the accidents such as switch trip, large-area power-cuts even electric power system off-the-line that harmonic problem causes, therefore the harmonic pollution of electric power system is carried out the comprehensive regulation and become the research topic that have important practical significance of pendulum in face of the scientific worker.

Active Power Filter-APF is to provide one to be that infinitely-great parallel network or equiva lent impedance are infinitely-great series network in the equivalent admittance of resonance frequency place to harmonic current or harmonic voltage, and an Active Power Filter-APF has infinite a plurality of resonance frequency in theory.Owing to have high controllability and a fast-response, can follow the tracks of compensation to the harmonic wave that frequency and amplitude all change, thereby be paid attention to widely, become at present the focus that electric power system harmonic wave both at home and abroad suppresses research.

In recent years, requirement to the high-capacity power converting means in commercial Application increases day by day, as in the electric power system with high voltage direct current transmission (HVDC), static reactive (STATCOM) etc. is the flexible AC transmission technology (FACTS) of representative, is the heavy-duty motor speed governing of representative and large power, electrically source apparatus etc. with the high voltage converter.In these applications, the high power contravariant device often becomes the critical problem of a core of their application.Because device can bear the restriction of voltage and current ability, make the two-level inversion device be difficult to directly realize high-powerization on the one hand; In high-voltage applications, the dv/dt of two-level inversion device output voltage is very big on the other hand, and the insulation of harm motor is arranged in governing system, problems such as aggravation shaft current, the also unbalanced problem of zero sequence current potential of Cun Zaiing.

Summary of the invention

The present invention is directed to the zero sequence current potential imbalance that present Active Power Filter-APF exists, the problem of the electromagnetic interference that forceful electric power signal and weak electric signal coexistence are subjected to proposes a kind of parallel connection type active electric filter.

A kind of parallel connection type active electric filter, three-level inverter 1 links to each other with 6 IGBT drive circuits 6, IGBT drive circuit 6 links to each other with DSP control circuit 10, DSP control circuit 10 is leaded up to frequency multiplication phase-locking device 11 and is linked to each other with load 13 with zero crossing detection device 12, DSP control circuit 10 another roads link to each other with load 13 with current sensing means 15 by current regulating device 14, current regulating device 14 links to each other with three-level inverter 1 by filter 2, filter 2 also links to each other with load 13, be provided with the clamping diode 4 that connects successively in the three-level inverter 1, switching tube 3 and voltage-dividing capacitor 5, DSP control circuit 10 links to each other with three-level inverter 1 by mid-point voltage checkout gear 16.

The structure of described IGBT drive circuit is: drive circuit 17 links to each other with driving chip 7, logical circuit 9 and photoelectricity coupling 8 successively, and photoelectricity coupling 8 connects drive circuits 17 and forms loops.

Described driving chip 7 is for driving chip M57962L.

The structure of described drive circuit 17 is: photoelectricity coupling 8 links to each other with interface circuit, interface circuit with link to each other with testing circuit, timing reset circuit, a door breaking circuit respectively, testing circuit links to each other with measurement point, a breaking circuit links to each other with the fault output circuit.

The voltage endurance capability of described switching tube 3 is rated voltage 2-10 times.

The voltage endurance capability of described clamping diode 4 is rated voltage 2-10 times.

The voltage endurance capability of described voltage-dividing capacitor 5 is rated voltage 2-10 times.

Beneficial effect of the present invention: the drive circuit inside that the present invention adopts has high speed photo coupling, and with pulse control signal and drive circuit internal insulation, digital control circuit and drive circuit have been realized electrical isolation like this, can prevent the interference that produces because of electrical couplings; Grid drives and adopts bipolarity control voltage, uses negative grid voltage can obtain higher anti-interference.The present invention has adopted the midpoint potential balancing control algorithm that injects based on residual voltage;

Adopt active balancing factor control method at this, this control method can accurately calculate f, thus can make as far as possible that mid-point voltage does not produce skew, thus reach the effect of accurate control midpoint potential balance.At dc capacitor voltage control problem, it is constant to adopt PI control to keep dc voltage in outer voltage, detects each phase current and midpoint potential fluctuation direction in current inner loop, small vector is accepted or rejected realized the control of midpoint potential balance.

The basic thought of control is: prediction DC side mid point change in charge trend, and it is cheap to calculate the mid-point voltage of required compensation, and the PWM waveform is revised.According to PWM waveform and load current, calculate the influence of alignment current potential.Before this waveform is not applied to circuit, earlier it is revised, make it not produce mid-point potential offset.

If C1 stores charge Q 1, it is identical that C2 stores charge Q 2. hypothesis amount capacitance characteristics, and if C1=C2=C0. is Q1=Q2, the balance of voltage of two electric capacity then, this moment the C1 bottom crown with the C2 top crown between electric charge be zero.So can offset original electric charge between C1 bottom crown and C2 top crown by the electric charge that flows into DC side two electric capacity mid points, make that electric charge is zero between two-plate, and when (k-1) individual PWM end cycle, the electric charge when expecting k PWM end cycle between two capacitor plates equals zero.According to this thought, can get:

Q2-Q1+Q0＝0 (1)

In the formula: Q1=CUdc1; Q2=CUdc2; Q0 is the electric charge that flows into DC side two electric capacity in the switch periods Ta, $Q0={\&Integral;}_{(k-1)\mathrm{<figure-callout\; id="1"\; label="Ts\; kTs\; ic"\; filenames="HSA0000093201430000012.png"\; state="\{\{state\}\}">Ts</figure-callout>}}^{\mathrm{kTs}}\mathrm{ic}1\mathrm{dt}+{\&Integral;}_{(k-1)\mathrm{<figure-callout\; id="2"\; label="Ts\; kTs\; ic"\; filenames="HSA0000093201430000012.png"\; state="\{\{state\}\}">Ts</figure-callout>}}^{\mathrm{kTs}}\mathrm{ic}2\mathrm{dt}\&CenterDot;$

With the leg-of-mutton on off state substitution in reference vector place, can draw T1P, T2, the i0 of a T3 and T1n4 time period, Q0=ibT3+iafT1 then, the accurate expression formula that can be got f by above derivation is:

$f=\begin{array}{c}-\mathrm{Taib}+\mathrm{Cd}(\mathrm{Udc}1-\mathrm{Udc}2)\\ \mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HSA0000093201430000012.png"\; state="\{\{state\}\}">T</figure-callout>}1\mathrm{ia}\end{array}---\left(2\right)$

Midpoint potential control strategy after the improvement is exactly to have considered original voltage deviation value in real time, when Udc1=Udc2, namely need not to consider original deviation, just do not have yet Cd (Udc1-Udc2) this.So adopt this to improve one's methods to can be implemented under the situation that midpoint potential has been offset and also midpoint potential can be retracted balance point, realize precisely control.

By the correct division to the reference voltage symbol area, can calculate required injection residual voltage fast and accurately, be conducive to the realization of control in real time.

Description of drawings

Fig. 1 is the driving circuit structure schematic diagram;

Fig. 2 is the active power filter structure schematic diagram;

Fig. 3 is IGBT drive circuit schematic diagram;

Among the figure, 1-three-level inverter, 2-filter, 3-switching tube, 4-clamping diode, 5-voltage-dividing capacitor, 6-IGBT drive circuit, 7-driving chip M57962L, the coupling of 8-photoelectricity, 9-logical circuit, 10-DSP control circuit, 11-cross frequency multiplication phase-locking device, 12-zero crossing detection device, 13-load, 14-current regulating device, 15-current sensing means, 16-mid-point voltage checkout gear, 17-drive circuit.

Embodiment

The present invention will be further described below in conjunction with the drawings and specific embodiments.

Embodiment 1

A kind of parallel connection type active electric filter, as Figure 1-3, three-level inverter 1 links to each other with 6 IGBT drive circuits 6, IGBT drive circuit 6 links to each other with DSP control circuit 10, DSP control circuit 10 is leaded up to frequency multiplication phase-locking device 11 and is linked to each other with load 13 with zero crossing detection device 12, DSP control circuit 10 another roads link to each other with load 13 with current sensing means 15 by current regulating device 14, current regulating device 14 links to each other with three-level inverter 1 by filter 2, filter 2 also links to each other with load 13, be provided with the clamping diode 4 that connects successively in the three-level inverter 1, switching tube 3 and voltage-dividing capacitor 5, DSP control circuit 10 links to each other with three-level inverter 1 by mid-point voltage checkout gear 16.

The structure of IGBT drive circuit is: drive circuit 17 links to each other with driving chip 7, logical circuit 9 and photoelectricity coupling 8 successively, and photoelectricity coupling 8 connects drive circuits 17 and forms loops.Drive chip 7 for driving chip M57962L.

The structure of drive circuit 17 is: photoelectricity coupling 8 links to each other with interface circuit, interface circuit with link to each other with testing circuit, timing reset circuit, a door breaking circuit respectively, testing circuit links to each other with measurement point, a breaking circuit links to each other with the fault output circuit.

The voltage endurance capability of switching tube 3 is 5 times of rated voltages.

The voltage endurance capability of clamping diode 4 is 5 times of rated voltages.

The voltage endurance capability of voltage-dividing capacitor 5 is 5 times of rated voltages.

Drive chip and be to use photoelectrical coupler to isolate driving signal and driven insulated gate of input, adopt thick film or PCB technology to support, the part Resistor-Capacitor Unit is inserted by pin.This product is mainly used in the driving of IGBT, because IGBT has the current tail effect, turn-offs so the optocoupler driver all is negative pressure without exception.

M57962L is the thick film integrated circuit of driving IGBT design, and essence is the isolated form amplifier, adopts the photoelectricity coupling process to realize the electrical isolation of input and output, and has disposed short circuit/overload protecting circuit.

Photoelectrical coupler is to be an a kind of electric light one power conversion device of the media transmission signal of telecommunication with light.It is made up of light emitting source and light-receiving device two parts.Light emitting source and light-receiving device are assembled in the same airtight housing, isolate with transparent insulator to each other.The pin of light emitting source is input, and the pin of light-receiving device is output, and common light emitting source is light-emitting diode, and light-receiving device is photodiode, phototriode

During its operation principle: add the signal of telecommunication at the photoelectrical coupler input and make light emitting source luminous, light intensity depends on the size of exciting current, after this illumination is mapped on the light-receiving device that is packaged together, because photoelectric effect has produced photoelectric current, drawn by the light-receiving device output, so just can realize the conversion of an electric light one electricity.

When IGBT module overload (overvoltage, overcurrent), collector voltage rises to 15V when above, isolating diode VD1 ends, 1 pin of M57962L is the 15V high level, then 5 pin with M57962L are set to low level, and IGBT is ended, and simultaneously 8 pin are set to low level, make photoelectrical coupler work, to drive external circuits input 13 pin are set to high level.Voltage stabilizing didoe ZD1 is used for preventing that VD1 from puncturing and damage M57962L.Rext is current-limiting resistance.ZD2, ZD3 form amplitude limiter, and be not breakdown with the base stage of guaranteeing IGBT.

The three-level inverter main circuit is the system core, it mainly realizes the DC/AC conversion of electric energy, control circuit mainly is the generation of SVPWM, realize by drive circuit that main circuit is connected with signal between the control circuit main circuit is carried out suitable control, to realize the electrical isolation between main circuit and the control circuit, voltage detecting circuit is realized the detection to the main circuit dc capacitor voltage, and current detection circuit is realized the detection to output current.

Need accessory power supply that two kinds of different level signals are provided on each piece drive circuit board, namely drive chip M57962L required+15.8V/-8.2V, be respectively the IGBT that will drive positive and negative bias voltage signal is provided, other auxiliary circuit that also is required to be in addition on the drive plate provides+the 5V power supply, as optical fiber reception/transmitter, latch, optical coupler etc.Accessory power supply does not have meter use the input of 24V direct current, through exporting high frequency square wave voltage after the half-bridge inversion circuit module, again by transformer isolation, boost, the required voltage signal of output after the filtering.

The Active Power Filter-APF operation principle:

Active Power Filter-APF detects load current by current transformer, and by inner DSP calculating, extract the harmonic components in the load current, send to inner IGBT by pwm signal then, control inverter produces one and load harmonic current equal and opposite in direction, the harmonic current that direction is opposite is injected in the electrical network, reaches the purpose of filtering.

The function of instruction current testing circuit mainly is to isolate harmonic current components and fundamental reactive current from load current, will the command signal of offset current take place after its reversed polarity effect then.The function of current tracking control circuit is the offset current that produces according to main circuit, calculates the trigger impulse of each switching device of main circuit, and this pulse acts on main circuit behind drive circuit.Only contain the real component of first-harmonic like this in the source current, thereby reach harmonic carcellation and the purpose of carrying out reactive power compensation.According to same principle, the negative-sequence current component that active power filter can also right title three-phase circuit compensates.

The main circuit of Active Power Filter-APF generally is made of the PWM inverter.According to the difference of inverter direct-flow side energy-storage travelling wave tube, can be divided into voltage type active filter (energy-storage travelling wave tube is electric capacity) and current mode active filter (energy-storage travelling wave tube is inductance).The voltage type active filter needs when work dc capacitor voltage control, and dc voltage is remained unchanged, thereby inverter interchange side is output as the PWM voltage wave.And the current mode active filter needs the DC side inductive current is controlled when work, and the DC side electric current is remained unchanged, thereby inverter interchange side is output as the PWM current wave.The advantage of voltage type active filter is that loss is less, the efficient height, and this electric current will produce than lossy in the inductance internal resistance.

The basic thought of midpoint potential balancing control algorithm:

Prediction DC side mid point change in charge trend, and it is cheap to calculate the mid-point voltage of required compensation, and the PWM waveform is revised.According to PWM waveform and load current, calculate the influence of alignment current potential.Before this waveform is not applied to circuit, earlier it is revised, make it not produce mid-point potential offset.

If C1 stores charge Q 1, it is identical that C2 stores charge Q 2. hypothesis amount capacitance characteristics, and if C1=C2=C0. is Q1=Q2, the balance of voltage of two electric capacity then, this moment the C1 bottom crown with the C2 top crown between electric charge be zero.So can offset original electric charge between C1 bottom crown and C2 top crown by the electric charge that flows into DC side two electric capacity mid points, make that electric charge is zero between two-plate, and when (k-1) individual PWM end cycle, the electric charge when expecting k PWM end cycle between two capacitor plates equals zero.According to this thought, can get:

Q2-Q1+Q0＝0 (1)

In the formula: Q1=CUdc1; Q2=CUdc2; Q0 is the electric charge that flows into DC side two electric capacity in the switch periods Ta, $Q0={\&Integral;}_{(k-1)\mathrm{<figure-callout\; id="1"\; label="Ts\; kTs\; ic"\; filenames="HSA0000093201430000012.png"\; state="\{\{state\}\}">Ts</figure-callout>}}^{\mathrm{kTs}}\mathrm{ic}1\mathrm{dt}+{\&Integral;}_{(k-1)\mathrm{<figure-callout\; id="2"\; label="Ts\; kTs\; ic"\; filenames="HSA0000093201430000012.png"\; state="\{\{state\}\}">Ts</figure-callout>}}^{\mathrm{kTs}}\mathrm{ic}2\mathrm{dt}.$

With the leg-of-mutton on off state substitution in reference vector place, can draw T1P, T2, the i0 of a T3 and T1n4 time period, Q0=ibT3+iafT1 then, the accurate expression formula that can be got f by above derivation is:

$f=\frac{-\mathrm{<figure-callout\; id="3"\; label="T"\; filenames="HSA0000093201430000012.png"\; state="\{\{state\}\}">T</figure-callout>}3\mathrm{ib}+\mathrm{Cd}(\mathrm{Udc}1-\mathrm{Udc}2)}{\mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HSA0000093201430000012.png"\; state="\{\{state\}\}">T</figure-callout>}1\mathrm{ia}}---\left(2\right)$

Midpoint potential control strategy after the improvement is exactly to have considered original voltage deviation value in real time, when Udc1=Udc2, namely need not to consider original deviation, just do not have yet Cd (Udc1-Udc2) this.So adopt this to improve one's methods to can be implemented under the situation that midpoint potential has been offset and also midpoint potential can be retracted balance point, realize precisely control.

By the correct division to the reference voltage symbol area, can calculate required injection residual voltage fast and accurately, be conducive to the realization of control in real time.

By system optimizing control, can suppress the midpoint potential imbalance preferably.

Adopt optocoupler to realize electrical isolation, optocoupler is rakish, is fit to the HF switch operation, and the former limit of optocoupler is series limiting resistor (about 185 Ω), the voltage of 5V directly can be added to input side.Its adopts duplicate supply Drive Structure, the optical coupler that inside is integrated with the 2500V high-isolating and circuit overcurrent protection, overcurrent protection output signal terminal with Transistor-Transistor Logic level compatible input interface mutually, drive the signal of telecommunication and postpone to be to the maximum 1.5us.

Embodiment 2

A kind of parallel connection type active electric filter, as Figure 1-3, three-level inverter 1 links to each other with 6 IGBT drive circuits 6, IGBT drive circuit 6 links to each other with DSP control circuit 10, DSP control circuit 10 is leaded up to frequency multiplication phase-locking device 11 and is linked to each other with load 13 with zero crossing detection device 12, DSP control circuit 10 another roads link to each other with load 13 with current sensing means 15 by current regulating device 14, current regulating device 14 links to each other with three-level inverter 1 by filter 2, filter 2 also links to each other with load 13, be provided with the clamping diode 4 that connects successively in the three-level inverter 1, switching tube 3 and voltage-dividing capacitor 5, DSP control circuit 10 links to each other with three-level inverter 1 by mid-point voltage checkout gear 16.

The structure of IGBT drive circuit is: drive circuit 17 links to each other with driving chip 7, logical circuit 9 and photoelectricity coupling 8 successively, and photoelectricity coupling 8 connects drive circuits 17 and forms loops.Drive chip 7 for driving chip M57962L.

The structure of drive circuit 17 is: photoelectricity coupling 8 links to each other with interface circuit, interface circuit with link to each other with testing circuit, timing reset circuit, a door breaking circuit respectively, testing circuit links to each other with measurement point, a breaking circuit links to each other with the fault output circuit.

The voltage endurance capability of switching tube 3 is 3 times of rated voltages.

The voltage endurance capability of clamping diode 4 is 3 times of rated voltages.

The voltage endurance capability of voltage-dividing capacitor 5 is 3 times of rated voltages.

M57962L is the thick film integrated circuit of driving IGBT design, and essence is the isolated form amplifier, adopts the photoelectricity coupling process to realize the electrical isolation of input and output, and has disposed short circuit/overload protecting circuit.

Photoelectrical coupler is to be an a kind of electric light one power conversion device of the media transmission signal of telecommunication with light.It is made up of light emitting source and light-receiving device two parts.Light emitting source and light-receiving device are assembled in the same airtight housing, isolate with transparent insulator to each other.The pin of light emitting source is input, and the pin of light-receiving device is output, and common light emitting source is light-emitting diode, and light-receiving device is photodiode, phototriode

During its operation principle: add the signal of telecommunication at the photoelectrical coupler input and make light emitting source luminous, light intensity depends on the size of exciting current, after this illumination is mapped on the light-receiving device that is packaged together, because photoelectric effect has produced photoelectric current, drawn by the light-receiving device output, so just can realize the conversion of an electric light one electricity.

When IGBT module overload (overvoltage, overcurrent), collector voltage rises to 15V when above, isolating diode VD1 ends, 1 pin of M57962L is the 15V high level, then 5 pin with M57962L are set to low level, and IGBT is ended, and simultaneously 8 pin are set to low level, make photoelectrical coupler work, to drive external circuits input 13 pin are set to high level.Voltage stabilizing didoe ZD1 is used for preventing that VD1 from puncturing and damage M57962L.Rext is current-limiting resistance.ZD2, ZD3 form amplitude limiter, and be not breakdown with the base stage of guaranteeing IGBT.

The voltage endurance capability of described switching tube is 5 times of rated voltages.The voltage endurance capability of clamping diode is 5 times of rated voltages.The voltage endurance capability of voltage-dividing capacitor is 5 times of rated voltages.

The three-level inverter main circuit is the system core, it mainly realizes the DC/AC conversion of electric energy, control circuit mainly is the generation of SVPWM, realize by drive circuit that main circuit is connected with signal between the control circuit main circuit is carried out suitable control, to realize the electrical isolation between main circuit and the control circuit, voltage detecting circuit is realized the detection to the main circuit dc capacitor voltage, and current detection circuit is realized the detection to output current.

Need accessory power supply that two kinds of different level signals are provided on each piece drive circuit board, namely drive chip M57962L required+15.8V/-8.2V, be respectively the IGBT that will drive positive and negative bias voltage signal is provided, other auxiliary circuit that also is required to be in addition on the drive plate provides+the 5V power supply, as optical fiber reception/transmitter, latch, optical coupler etc.Accessory power supply does not have meter use the input of 24V direct current, through exporting high frequency square wave voltage after the half-bridge inversion circuit module, again by transformer isolation, boost, the required voltage signal of output after the filtering.

The Active Power Filter-APF operation principle:

Active Power Filter-APF detects load current by current transformer, and by inner DSP calculating, extract the harmonic components in the load current, send to inner IGBT by pwm signal then, control inverter produces one and load harmonic current equal and opposite in direction, the harmonic current that direction is opposite is injected in the electrical network, reaches the purpose of filtering.

The function of instruction current testing circuit mainly is to isolate harmonic current components and fundamental reactive current from load current, will the command signal of offset current take place after its reversed polarity effect then.The function of current tracking control circuit is the offset current that produces according to main circuit, calculates the trigger impulse of each switching device of main circuit, and this pulse acts on main circuit behind drive circuit.Only contain the real component of first-harmonic like this in the source current, thereby reach harmonic carcellation and the purpose of carrying out reactive power compensation.According to same principle, the negative-sequence current component that active power filter can also right title three-phase circuit compensates.

The main circuit of Active Power Filter-APF generally is made of the PWM inverter.According to the difference of inverter direct-flow side energy-storage travelling wave tube, can be divided into voltage type active filter (energy-storage travelling wave tube is electric capacity) and current mode active filter (energy-storage travelling wave tube is inductance).The voltage type active filter needs when work dc capacitor voltage control, and dc voltage is remained unchanged, thereby inverter interchange side is output as the PWM voltage wave.And the current mode active filter needs the DC side inductive current is controlled when work, and the DC side electric current is remained unchanged, thereby inverter interchange side is output as the PWM current wave.The advantage of voltage type active filter is that loss is less, the efficient height, and this electric current will produce than lossy in the inductance internal resistance.

The basic thought of midpoint potential balancing control algorithm:

Prediction DC side mid point change in charge trend, and it is cheap to calculate the mid-point voltage of required compensation, and the PWM waveform is revised.According to PWM waveform and load current, calculate the influence of alignment current potential.Before this waveform is not applied to circuit, earlier it is revised, make it not produce mid-point potential offset.

If C1 stores charge Q 1, it is identical that C2 stores charge Q 2. hypothesis amount capacitance characteristics, and if C1=C2=C0. is Q1=Q2, the balance of voltage of two electric capacity then, and this moment, the C1 bottom crown asked that with the C2 top crown electric charge is zero.So can offset original electric charge between C1 bottom crown and C2 top crown by the electric charge that flows into DC side two electric capacity mid points, make that electric charge is zero between two-plate, and when (k-1) individual PWM end cycle, the electric charge when expecting k PWM end cycle between two capacitor plates equals zero.According to this thought, can get:

Q2-Q1+Q0＝0(1)

In the formula: Q1=CUdc1; Q2=CUdc2; Q0 is the electric charge that flows into DC side two electric capacity in the switch periods Ta, $Q0={\&Integral;}_{(k-1)\mathrm{<figure-callout\; id="1"\; label="Ts\; kTs\; ic"\; filenames="HSA0000093201430000012.png"\; state="\{\{state\}\}">Ts</figure-callout>}}^{\mathrm{kTs}}\mathrm{ic}1\mathrm{dt}+{\&Integral;}_{(k-1)\mathrm{<figure-callout\; id="2"\; label="Ts\; kTs\; ic"\; filenames="HSA0000093201430000012.png"\; state="\{\{state\}\}">Ts</figure-callout>}}^{\mathrm{kTs}}\mathrm{ic}2\mathrm{dt}.$

With the leg-of-mutton on off state substitution in reference vector place, can draw T1P, T2, the i0 of a T3 and T1n4 time period, Q0=ibT3+iafI1 then, the accurate expression formula that can be got f by above derivation is:

$f=\begin{array}{c}-\mathrm{Taib}+\mathrm{Cd}(\mathrm{Udc}1-\mathrm{Udc}2)\\ \mathrm{<figure-callout\; id="1"\; label="T"\; filenames="HSA0000093201430000012.png"\; state="\{\{state\}\}">T</figure-callout>}1\mathrm{ia}\end{array}---\left(2\right)$

Midpoint potential control strategy after the improvement is exactly to have considered original voltage deviation value in real time, when Udc1=Udc2, namely need not to consider original deviation, just do not have yet Cd (Udc1-Udc2) this.So adopt this to improve one's methods to can be implemented under the situation that midpoint potential has been offset and also midpoint potential can be retracted balance point, realize precisely control.

By the correct division to the reference voltage symbol area, can calculate required injection residual voltage fast and accurately, be conducive to the realization of control in real time.

By system optimizing control, can suppress the midpoint potential imbalance preferably.

Adopt optocoupler to realize electrical isolation, optocoupler is rakish, is fit to the HF switch operation, and the former limit of optocoupler is series limiting resistor (about 185 Ω), the voltage of 5V directly can be added to input side.Its adopts duplicate supply Drive Structure, the optical coupler that inside is integrated with the 2500V high-isolating and circuit overcurrent protection, overcurrent protection output signal terminal with Transistor-Transistor Logic level compatible input interface mutually, drive the signal of telecommunication and postpone to be to the maximum 1.5us.

Claims (7)

1. parallel connection type active electric filter, it is characterized in that, three-level inverter (1) links to each other with 6 IGBT drive circuits (6), IGBT drive circuit (6) links to each other with DSP control circuit (10), DSP control circuit (10) is leaded up to frequency multiplication phase-locking device (11) and is linked to each other with load (13) with zero crossing detection device (12), another road of DSP control circuit (10) links to each other with load (13) with current sensing means (15) by current regulating device (14), current regulating device (14) links to each other with three-level inverter (1) by filter (2), filter (2) also links to each other with load (13), be provided with the clamping diode (4) that connects successively in the three-level inverter (1), switching tube (3) and voltage-dividing capacitor (5), DSP control circuit (10) links to each other with three-level inverter (1) by mid-point voltage checkout gear (16).

2. according to the described a kind of parallel connection type active electric filter of claim 1, it is characterized in that, the structure of described IGBT drive circuit is: drive circuit (17) links to each other with driving chip (7), logical circuit (9) and photoelectricity coupling (8) successively, and photoelectricity coupling (8) connects drive circuits (17) and forms loop.

3. according to the described a kind of parallel connection type active electric filter of claim 2, it is characterized in that described driving chip (7) is for driving chip M57962L.

4. according to the described a kind of parallel connection type active electric filter of claim 2, it is characterized in that, the structure of described drive circuit (17) is: photoelectricity coupling (8) links to each other with interface circuit, interface circuit with link to each other with testing circuit, timing reset circuit, a door breaking circuit respectively, testing circuit links to each other with measurement point, and the door breaking circuit links to each other with the fault output circuit.

5. according to the described a kind of parallel connection type active electric filter of claim 1, it is characterized in that the voltage endurance capability of described switching tube (3) is rated voltage 2-10 times.

6. according to the described a kind of parallel connection type active electric filter of claim 1, it is characterized in that the voltage endurance capability of described clamping diode (4) is rated voltage 2-10 times.

7. according to the described a kind of parallel connection type active electric filter of claim 1, it is characterized in that the voltage endurance capability of described voltage-dividing capacitor (5) is rated voltage 2-10 times.

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