CN1279673C - Method and system for feedback type active power filtering of output current with DC sourse - Google Patents

Abstract

The present invention relates to an output current feedback active power filtering method with a direct current source and a system, and belongs to the technical field of direct current transmission. The present invention is characterized in that the method is an active power filtering method in which equivalent impedance connected has the characteristics of positive resistance and the numerical value of the equivalent impedance is controlled by gain coefficients so as to reduce ripple voltage and a ripple current at an output end. A system provided by the method is characterized in that the output end of an active power filtering circuit is provided with a current transformer, and measured current signals pass through a band pass filtering part, a gain amplifying part, a pulse width modulating part and a pulse driving part to control a single-phase voltage inverter circuit provided with a direct current power supply for power supply. Voltage pulses generated by the single-phase voltage inverter circuit are connected to a circuit composed of a smoothing reactor and a passive filter through a coupling transformer to suppress ripples. The method of the present invention has the advantages of explicit physical significance, easy realization, good stability and good ripple suppressing effect.

Description

Active power filtering method and system with output current reaction type of DC source

Technical field:

The present invention relates to a kind of active power filtering method and system with output current reaction type of DC source, this method and system thereof can suppress the low-frequency ripple of d. c. voltage signal of input and eliminate, the low-frequency ripple voltage and current noise of reduction output loading.The invention belongs to the direct current transportation technical field.

Background technology:

The Ripple Noise that comprises a large amount of low-frequency ranges by direct-current transmission voltage that the AC signal rectification is obtained or DC power supply voltage.These Ripple Noise will increase facility load on the DC transmission line of electric power system, produce electric energy loss, and its electromagnetic radiation also can interference communications equipment.Useful signal in the Ripple Noise meeting interference load equipment in the DC power supply has a strong impact on the normal operation of equipment.The method of traditional inhibition and elimination Ripple Noise is to adopt the filter circuit that is made of passive devices such as some resistance, inductance and electric capacity, and this is called as the passive filtering method.Along with the development of power electronic technology, the various devices that comprise power electronic device are applied to electric filtering, and this filtering method is called as active power filtering.Active power filtering can overcome the traditional passive filtering parameter inaccurate, can't adapt to the variation of frequency and load, easily shortcomings such as resonance take place, have better filtering performance.And, adopt active electric filter device can also reduce floor space in the bigger occasion of power, reduce the filtering cost.

" the electric power system journal of Institute of Electrical and Electronics Engineers in May, 1998, (IEEE Transactions on PowerSystems) " the 13rd volume the 2nd interim delivered one piece of exercise question for " bank carries-this bank HVDC (High Voltage Direct Current) transmission system in the control principle analysis of the active dc filter that adopted of forest-road nurse current conversion station, (Analysis on the Control Principle of the Active DCFilter in the Lindome Converter Station of the Konti-Skan HVDC Link) " article.In this piece article, the author has described a kind of active electric filter device and control method thereof of the low-frequency ripple noise that can the filtering rectifier produces, and its theory diagram as shown in Figure 1.In existing this active electric filter device and control method thereof, after the direct voltage that comprises Ripple Noise inserts the input port of filter circuit, at first arrive output port through the smoothing reactor that seals in the circuit, the secondary of coupling transformer is inserted on the former limit of the coupling transformer that is connecting passive filtration unit between the two ends of output port and be in series with it, DC power supply by single-phase electricity die mould inverter circuit.The control method of existing this active electric filter device at first will measure current i on the output port by current transformer _Out, filtering i then _OutIn flip-flop and noise, extract ripple current i _lRipple current i _lObtain M signal i through comb filtering or the filtering of groove shape again _rRejection frequency is f if desired _iThe ripple composition, the transfer function F of selected comb filtering or the filtering of groove shape _α(s) should have approaching ± j2 π f _iTwo limits, thereby transfer function f _α(s) amplitude-frequency response is at frequency f _iLocate to level off to infinity.Then, M signal i _rHandle the reference wave signal u that obtains pulse-width modulation through system balance _α, reference wave signal u _αProduce control impuls through pulse-width modulation, control wave by power amplification after in order to drive single-phase electricity die mould inverter circuit.So, obtain reference wave signal u on the former limit of coupling transformer _αIn the voltage signal of low-frequency ac composition amplitude after amplifying.If supposing the input voltage ripple of whole filter is 0, and with reference wave signal u _αAs unique driving source, again with the current i that output port produced of filter _{L α}In response, then can obtain the transfer function G of this input-output system according to circuit parameter _hThe transfer function characteristics of designed system compensation deals need satisfy in the document $F_C=\frac{1}{G_h}.$ Existing this active power filtering system transter model is shown in Figure 2.Input signal i among Fig. 2 _LhBe as reference wave signal u _αBe 0, the ripple voltage of input port is done the time spent separately, at the ripple current of filter output port.The transfer function of whole filtering control is:

$F_S\left(s\right)=\frac{i_l}{i_{\mathrm{lh}}}=\frac{1}{1+F_a}$

Because F _α(s) limit is F _s(s) so zero point is if the transfer function F of comb filtering or the filtering of groove shape _α(s) have and approach ± j2 π f _iLimit, then | F _s(± j2 π f _i) | will level off to 0, promptly filtering control system can blanketing frequency be f _iLow-frequency ripple.

Existing this active electric filter device and controlling party ratio juris basis thereof are the controlling models of system.The design of system balance processing section wherein need depend on the various parameters of circuit.If load changes, then need system balance to handle also corresponding change.This has just strengthened the difficulty that system balance is handled, and causes the control vibration easily, also can reduce the effect that ripple suppresses simultaneously.The design of comb filtering or the filtering of groove shape also is difficult in the existing this active power filtering method, the transfer function F of Filtering Processing on the principle _α(s) limit approaches ± j2 π f more _iBe f then to frequency _iThe inhibition effect of ripple just good more, but this certainly will make the Filtering Processing instability.Simultaneously, this also can make M signal i _rWith reference wave signal u _αExcessive, if exceed the allowed band of pulse-width modulation input, control system can't be stablized, can not reach the effect that suppresses ripple.

Summary of the invention:

The objective of the invention is to propose a kind of active power filtering method and system thereof with output current reaction type of DC source, wish to overcome the deficiency of existing active electric filter device on control method, reduce the influence that control principle is subjected to load variations, the physical significance of clear and definite Control Parameter, it is simpler that design is realized, avoid the input signal of pulse-width modulation to exceed allowed band, strengthen the stability of control and treatment process.

The active power filtering method of the output current reaction type with DC source that the present invention proposes may further comprise the steps:

The 1st step: the output port current i of measuring the ripple current composition that comprises required filtering _Out

The 2nd step: with the output port current i that measures _OutBy the bandpass filtering treatment of phase-frequency characteristic in-90 °～90 ° scopes of a transfer function F (s), obtain filtering letter i _F

The 3rd step: with filtering signal i _FMultiply by gain coefficient A and obtain the reference signal i that pulse-width modulation is used _Ref, i.e. i _Ref=A * i _F, gain coefficient A is a positive number, its selected value will make reference signal i _RefAmplitude i when control system is stablized _Refmax＜1.2 * A _Δ, A _ΔBe that the modulation signal amplitude that adopts is handled in pulse-width modulation, get the positive count value;

The 4th step: with reference signal i _RefCarry out pulse-width modulation and handle back acquisition one prescription wave pulse signal, the way of square-wave pulse signal equals power electronic device number controlled in the single-phase electricity die mould inverter circuit, the pulse generation frequency that pulse-width modulation is handled should be greater than 2 times of the low-frequency ripple frequency band upper limit of required filtering, and the duty ratio of the potential pulse of being exported by the single-phase electricity die mould inverter circuit of this prescription wave pulse signal control should satisfy following formula:

The 5th step: will be above-mentioned the square-wave pulse signal of the 4th step acquisition carry out going to drive after the power amplification power electronic device in the single-phase electricity die mould inverter circuit, have the duty ratio of potential pulse of the single-phase electricity die mould inverter circuit output of DC power supply in order to change, and make the duty ratio of this potential pulse satisfy requirement in the 4th step;

The 6th step: above-mentioned potential pulse is loaded into the coupling transformer secondary, acts on the circuit that constitutes by smoothing reactor, passive filtration unit, in order to obtain the voltage and current output signal of low-frequency ripple after filtered at output port by the former limit of coupling transformer.

The active power filtering system that proposes according to aforesaid active power filtering method with output current reaction type of DC source consists of: active power filter circuit, it contains: the smoothing reactor on the end line of going into that is serially connected in the direct voltage input signal that comprises Ripple Noise, be serially connected in successively between this flat ripple reactance and the loop electrode in order to the passive filtration unit of bearing direct voltage and the former limit of coupling transformer, output is linked into the single-phase electricity die mould inverter circuit of coupling transformer secondary, and output is linked into the DC power supply of single-phase electricity die mould inverter circuit input; Be installed in the current transformer on the output loop of filtered voltage output signal; The bandpass filtering part, gain amplifier section and the pulse-width modulation part that are connected in series with the measurement output of this current transformer successively; Pulse driving circuit, its input is connected with the pulse signal that above-mentioned pulse-width modulation is partly exported, and its output then is connected with the trigger control end of single-phase electricity die mould inverter circuit.In this system, the no-load voltage ratio n of coupling transformer and DC power supply output voltage U _dSatisfy n * U _dThe maximum amplitude of the ripple voltage of output port in the frequency range of required filtering when being equal to or greater than the coupling transformer secondary short circuit; Bandpass filtering part, gain amplifier section and pulse-width modulation partly adopt circuit or software algorithm to realize.

The operation principle of active power filtering method of the present invention and system thereof can illustrate with simplification circuit model shown in Figure 4.Only consider the ripple in the frequency band of required filtering in Fig. 4, DC quantity is left in the basket, and circuit parameter adopts Laplce's form to represent that the Ripple Noise of input voltage is

The smoothing reactor parameter is L _sS, passive filtration unit add that the total impedance of coupling transformer short-circuit impedance is Z _C(s), the Ripple Noise electric current of output port is

The Ripple Noise electric current of output port is

So, active power filtering method of the present invention and system thereof be equivalent to produce one with passive filtration unit be in series by the output ripple electric current

The voltage source of control

Proportional K (s) wherein is by transfer function F (s), ride gain A, the pulse-width signal amplitude A of bandpass filtering treatment _Δ, coupling transformer no-load voltage ratio n and DC power supply voltage U _dCommon decision, its relational expression is:

$K\left(s\right)=\frac{F\left(s\right)\·A\·n\·U_d}{A_{\mathrm{\Δ}}}$

Circuit from the input voltage to the output port can carry out the Dai Weinan circuit equivalent, as shown in Figure 5.Equivalent voltage With equiva lent impedance Z _Eq(s) be:

${\tilde{U}}_{\mathrm{ineq}}=\frac{Z_C\left(s\right)}{L_s\·s+Z_C\left(s\right)}{\tilde{U}}_{\mathrm{in}}$

$Z_{\mathrm{eq}}\left(s\right)=\frac{(K\left(s\right)+Z_C\left(s\right))\·L_s\·s}{L_s\·s+Z_C\left(s\right)}$

Can see equivalent voltage thus Irrelevant with controlled variable K (s), and the inductance value L of smoothing reactor _sValue increases can reduce this equivalent ripple voltage, impedance Z _C(s) also can reduce equivalent ripple voltage in that the mould of the ripple frequency of required filtering is more little.Obviously, the reduction of equivalent ripple voltage can make the ripple voltage of output

And ripple current

Reduce.That active power filtering method of the present invention is regulated is the equiva lent impedance Z that seals in circuit _Eq(s).If K (s), L _sS and Z _C(s) at ripple frequency f _iSatisfy:

|K(j2πf _i)|＞＞|Z _C(j2πf _i)|

|j2πf _i·L _s|＞＞|Z _C(j2πf _i)|

Be similar to so following relation arranged:

Z _eq(j2πf _i)≈K(j2πf _i)

So, if fixedly the transfer function F of bandpass filtering treatment (s), pulse-width signal amplitude A _Δ, coupling transformer no-load voltage ratio n and DC power supply voltage U _dAfter, change the just equivalent equiva lent impedance Z that seals in circuit for control of ride gain A _Eq(s).In theory, in frequency f _iEquiva lent impedance Z _Eq(j2 π f _i) mould big more, then the output frequency is f _iRipple voltage

And ripple current

Just more little.So ride gain A is big more, then the inhibition effect of low-frequency ripple is just good more.But the increase of ride gain A also can make reference signal i _RefIn the noise signal of modulating frequency increase, so the value of ride gain A should be to make reference signal i _RefAmplitude when control system is stablized is no more than 1.2 * A _ΔBig positive.

Based on the analysis of above-mentioned operation principle to active power filtering method of the present invention as seen, the inventive method is not subjected to the particularly influence of load state of circuit parameter, need not the processing links of system balance in the control, can finish inhibition and elimination for ripple.So it is control method principle of the present invention is more clear, simpler on design realizes.Can prevent that by regulating gain coefficient A the input reference wave amplitude of pulse-width modulation from exceeding allowed band, thereby avoid the instability in the control.Seal in impedance Z based on changing the ripple voltage equivalence _Eq(s) operation principle, as long as the phase-frequency characteristic of the transfer function F (s) of bandpass filtering treatment part is in-90 °～90 ° scopes, i.e. equiva lent impedance Z _Eq(s) have positive resistance characteristic, active power filtering then of the present invention system just can stablize, and equiva lent impedance Z _Eq(s) positive resistance component is big more, and it is just good more that stability and ripple suppress effect.

Emulation experiment shows that the stability of active power filtering method of the present invention and system thereof and ripple suppress effect and all reach practical requirement.

Description of drawings:

Fig. 1 is the theory diagram of existing a kind of active electric filter device and control method thereof.

Fig. 2 is the transfer function model of existing a kind of active electric filter device and control method thereof.

Fig. 3 is the active power filtering method of the output current reaction type with DC source of the present invention and the theory diagram of system thereof.

Fig. 4 is the simplification circuit model of active power filtering method of the present invention and system thereof.

Fig. 5 is the thevenin equivalent circuit model of active power filtering method of the present invention and system thereof.

Fig. 6 is the rectification circuit that is used for producing 500 kilovolts of DC transmission system of the direct voltage input signal that comprises Ripple Noise in the embodiment of the invention.

Fig. 7 is as the circuit of active circuit filtering system output loading in the embodiment of the invention.

The circuit of the single tuning passive filtration unit that Fig. 8 is in the embodiment of the invention to be adopted.

Fig. 9 is the amplitude-versus-frequency curve of the bandpass filtering treatment that adopts in the embodiment of the invention.

Figure 10 is the phase-frequency characteristic curve of the bandpass filtering treatment that adopts in the embodiment of the invention.

Figure 11 is the reference wave waveform that the input pulse-width modulation when the coupling transformer secondary is opened a way from being shorted in the embodiment of the invention is handled.

Figure 12 is the output end voltage waveform when the coupling transformer secondary is opened a way from being shorted in the embodiment of the invention.

Figure 13 is the output end current waveform when the coupling transformer secondary is opened a way from being shorted in the embodiment of the invention.

Embodiment:

A specific embodiment of the present invention is to design for low-frequency ripple noise that the rectification circuit that reduces by 500 kilovolts of DC transmission system is loaded on the transmission line.From AC rectification be direct current circuit as shown in Figure 6, wherein three-phase alternating current bus frequency is 50Hz, line voltage is 382.9 kilovolts; The no-load voltage ratio of the transformer T2 of the transformer T1 of star/triangle type and star/star type is 345.0 kilovolts: 213.5 kilovolts, and rated capacity 603.7 megavolt-amperes, the per unit value of short-circuit impedance is 0.18; Adopt a rectifier bridge that is made of 12 controllable silicons to realize 12 impulse commutation circuit, the conducting pilot angle is got 5 degree, about 500 kilovolts of the direct voltage of output.The voltage of the input active power filtering of the present invention system that this rectification circuit produces mainly comprises 600,1200,1800,2400 hertz low-frequency ripple.

The output loading of the embodiment of active power filtering method of the present invention and system thereof as shown in Figure 7.Comprise one 250 kilometers transmission line in Fig. 7, power transmission line adopts the double bundle conductor apart from 0.46 meter of 50 meters spacing in ground, directly over high 8 meters are lightning protection ground wires, the earth is as loop electrode.The power transmission line other end has the smoothing reactor of L1=0.2 henry, R1=250 Europe load resistance, and by three electric capacity (C1=0.84 microfarads, the C2=3.0 microfarad, the C3=0.209 microfarad), two inductance (L2=0.84 milihenries, the L3=0.336 henry) and the passive filter circuit that constitutes of two resistance (R2=10 kilo-ohm, R3=6.3 Europe).

The circuit structure of the embodiment of active power filtering method of the present invention and system thereof as shown in Figure 3.Wherein the smoothing reactor Ls that seals in of incoming line one end gets 0.2 henry; After coupling transformer former limit series connection, be connected in parallel on the passive filtration unit employing single-tuned circuit as shown in Figure 8 of output port again, wherein capacitor C _C=1.0 microfarads, inductance L _C=0.0312 henry, resonance frequency are 900 hertz, and obviously the relative direct current of passive filtration unit is an open-circuit condition, and direct voltage will be loaded into capacitor C _COn; The no-load voltage ratio of coupling transformer is 20 kilovolts: 10 kilovolts, i.e. n=2, the short-circuit impedance of coupling transformer other circuit parameter relatively can ignore; An output U _d=10 kilovolts DC power supply is through inserting the secondary of coupling transformer by 4 IGBT and with the inverter circuit that 4 diodes of IGBT reverse parallel connection constitute voltage-type.The no-load voltage ratio n of coupling transformer and DC power supply voltage U _dProduct be nU _d=20 kilovolts, the maximum amplitude of the ripple voltage of filter circuit output port in the frequency range of required filtering (about 6 kilovolts) during greater than the coupling transformer secondary short circuit.

The first step of the control method of the embodiment of the invention is measured the output port current i by current transformer earlier _Out, kilo-ampere is got by unit.Bandpass filtering treatment is by four single tuned filters of corresponding 600,1200,1800,2400 hertz respectively, and the circuit of the output signal summation of these four filters is constituted, and its transfer function is:

$F\left(s\right)=\frac{0.04\·(2\mathrm{\π}\·600)\·s}{s^2+0.04\·(2\mathrm{\π}\·600)\·s+{(2\mathrm{\π}\·600)}^2}+\frac{0.04\·(2\mathrm{\π}\·1200)\·s}{s^2+0.04\·(2\mathrm{\π}\·1200)\·s+{(2\mathrm{\π}\·1200)}^2}$

$+\frac{0.04\·(2\mathrm{\π}\·1800)\·s}{s^2+0.04\·(2\mathrm{\π}\·1800)\·s+{(2\mathrm{\π}\·1800)}^2}+\frac{0.04\·(2\mathrm{\π}\·2400)\·s}{s^2+0.04\·(2\mathrm{\π}\·2400)\·s+{(2\mathrm{\π}\·2400)}^2}$

The amplitude-versus-frequency curve of bandpass filtering treatment and phase-frequency characteristic curve are respectively as Fig. 9 and shown in Figure 10.The filtering signal i that Filtering Processing output obtains _FBe input to gain amplifying circuit and obtain reference signal i in order to pulse-width modulation _Ref, the amplification coefficient of gain amplifying circuit is A=625, i.e. i _Ref=625i _FPulse-width modulation adopts the comparison circuit of reference wave and modulated triangular wave to realize.It is 10 KHz that modulated triangular wave generation circuit produces frequency, and maximum amplitude is A _Δ=1.0 modulated triangular wave.If reference signal i _RefAmplitude is greater than the current amplitude of modulated triangular wave, and then pulse-width modulated output signal will be controlled inverter circuit at coupling transformer secondary loading-U through behind the pulse driving circuit _dVoltage (to be labeled as the positive voltage direction among Fig. 3); If reference signal i _RefAmplitude is less than the current amplitude of modulated triangular wave, and then pulse-width modulated output signal will be controlled inverter circuit at coupling transformer secondary loading+U through behind the pulse driving circuit _dVoltage.

Embodiment to active power filtering method of the present invention and system thereof carries out simulation calculation.In 0.4 second of beginning, the coupling transformer secondary short circuit is controlled inoperative.After 0.4 second, voltage source type inverter inserts the coupling transformer secondary, and the inventive method is started working.Figure 11 has provided the reference signal i that handles from 0.38 second to 0.47 second input pulse-width modulation _RefWaveform.Active power filtering of the present invention system reaches control stabilization, reference signal i after this substantially starting 0.04 second _RefAmplitude does not have to surpass 1.2 times modulated triangular wave maximum amplitude, i.e. 1.2 * A _Δ=1.2.From the output end current waveform of the output end voltage waveform of Figure 12 and Figure 13 as seen, output end voltage and electric current comprise tangible low-frequency ripple during the coupling transformer secondary short circuit, and after method of the present invention started 0.04 second, low-frequency ripple was obviously eliminated.Further spectrum analysis also can illustrate the repressed effect of low-frequency ripple.It is worthy of note that active power filtering method of the present invention and system thereof are intended to eliminate low-frequency ripple, but can introduce the noise of the modulating frequency that the power electronic device switch causes simultaneously, Figure 11,12,13 also reflects this point.Certainly, behind the inhibition low-frequency ripple, the noise of high frequency can be eliminated by some simple filter circuits.

Claims (2)

1, the active power filtering method with output current reaction type of DC source contains the step of measurement, filtering, pulse-width modulation, pulsed drive, it is characterized in that: this method is that a kind of equiva lent impedance that seals in circuit that makes has positive resistance characteristic, and control the numerical value of equiva lent impedance by changing gain coefficient, thereby the output ripple voltage that the frequency range that reduces required filtering is interior and the active power filtering method of ripple current, this method comprises the steps:

The 1st step: the output port current i of measuring the ripple current composition that comprises required filtering _Out

The 2nd step: with the output port current i that measures _OutThe bandpass filtering treatment of phase-frequency characteristic in-90 °～90 ° scopes by a transfer function F (s) obtains filtering signal i _F

The 3rd step: with filtering signal i _FMultiply by gain coefficient A and obtain the reference signal i that pulse-width modulation is used _Ref, i.e. i _Ref=A * i _F, gain coefficient A is a positive number, its selected value will make reference signal i _RefAmplitude i when control system is stablized _Refmax＜1.2 * A _Δ, A _ΔBe that the modulation signal amplitude that adopts is handled in pulse-width modulation, get the positive count value;

The 4th step: with reference signal i _RefCarry out pulse-width modulation and handle back acquisition one prescription wave pulse signal, the way of square-wave pulse signal equals power electronic device number controlled in the single-phase electricity die mould inverter circuit, the pulse generation frequency that pulse-width modulation is handled should be greater than 2 times of the low-frequency ripple frequency band upper limit of required filtering, and the duty ratio of the potential pulse of being exported by the single-phase electricity die mould inverter circuit of this prescription wave pulse signal control should satisfy following formula:

The 5th step: will be above-mentioned the square-wave pulse signal of the 4th step acquisition carry out going to drive after the power amplification power electronic device in the single-phase electricity die mould inverter circuit, have the duty ratio of potential pulse of the single-phase electricity die mould inverter circuit output of DC power supply in order to change, and make the duty ratio of this potential pulse satisfy requirement in the 4th step;

The 6th step: above-mentioned potential pulse is loaded into the coupling transformer secondary, acts on the circuit that constitutes by smoothing reactor, passive filtration unit, in order to obtain the voltage and current output signal of low-frequency ripple after filtered at output port by the former limit of coupling transformer.

2, the active power filtering method of the output current reaction type with DC source according to claim 1 and active power filtering system that proposes is characterized in that this system comprises as the lower part:

Active power filter circuit, it contains: the smoothing reactor on the end line of going into that is serially connected in the direct voltage input signal that comprises Ripple Noise, be serially connected in successively between this flat ripple reactance and the loop electrode in order to the passive filtration unit of bearing direct voltage and the former limit of coupling transformer, output is linked into the single-phase electricity die mould inverter circuit of coupling transformer secondary, and output is linked into the DC power supply of single-phase electricity die mould inverter circuit input;

Current transformer: be installed on the output loop of filtered voltage output signal;

The bandpass filtering part, gain amplifier section and the pulse-width modulation part that are connected in series with the measurement output of this current transformer successively;

Pulse driving circuit: its input is connected with the pulse signal that above-mentioned pulse-width modulation is partly exported, and its output then is connected with the trigger control end of single-phase electricity die mould inverter circuit;

Wherein, the no-load voltage ratio n of coupling transformer and DC power supply output voltage U _dSatisfy n * U _dThe maximum amplitude of the ripple voltage of output port in the frequency range of required filtering when being equal to or greater than the coupling transformer secondary short circuit; Bandpass filtering part, gain amplifier section and pulse-width modulation partly adopt circuit or software algorithm to realize.

Images