CN102916572A - Control method and system for inhibiting secondary ripple current and improving dynamic characteristic - Google Patents

Abstract

The invention discloses a control method and a system for inhibiting a secondary ripple current and improving a dynamic characteristic. A voltage-current double closed-loop control is carried out on a front-stage direct-current (DC) converter, wherein the secondary ripple current in the front-stage DC converter is inhibited by lowering the cut-off frequency of a voltage loop greatly; a load current feed-forward is adopted on the basis of the double closed-loop control; and a wave trap is added to a feed-forward branch circuit to filter out a double frequency component in a feed-forward signal, thereby inhibiting the second ripple current in the front-stage DC converter and improving the dynamic characteristic of the front-stage DC converter in load hopping. As a result, the efficiency of the DC converter is improved.

Description

Suppress the secondary ripple current and improve control method and the system of dynamic characteristic

Technical field

The invention belongs to the power electronic equipment control field, more specifically, what relate to is the control method of prime DC converter in a kind of two-stage type inverter, the method both can be applied to the two-stage type single-phase inverter, two-stage type three-phase inverter when also can be applicable to unbalanced operation, secondary ripple current in the energy establishment DC converter significantly improves the dynamic characteristic of DC converter when the load saltus step simultaneously.

Background technology

The two-stage type inverter is widely used in electric power supply system of fuel cell, in the unmatched occasions of input and output voltage such as solar photovoltaic generation system and uninterruption power source UPS.Wherein, the prime DC converter realizes voltage matches and electrical isolation, and the rear class inverter is transformed to alternating current with the direct current that prime obtains.For single-phase inverter, its instantaneous output is with the pulsation of twice output voltage frequency, and this will make the pulsating current that produces the twice output voltage frequency in prime DC/DC converter and the input source, i.e. so-called secondary ripple current.In the two-stage type three-phase inverter, when load or unbalanced source voltage, prime DC/DC converter also will produce the secondary ripple current.The existence of secondary ripple current will reduce the efficient of DC converter, increase the current pulsation of input side, increase power loss and the capacity of input source, thereby increase system cost, reduce system effectiveness.

Fig. 1 is the circuit theory diagrams of two-stage type single-phase inverter.The two-stage type single-phase inverter comprises DC source, DC converter switching network, LC filter, single-phase inverter and output loading.Wherein, single-phase inverter both can be independent operating, also can be to be incorporated into the power networks.The instantaneous output voltage v of single-phase inverter when Fig. 2 has provided normal operation _o, instantaneous output current i _o, instantaneous output p _o, intermediate-bus voltage v _CfPart i with filtering switching harmonics in the input current of inverter _InvWaveform, wherein Be load power factor angle.Suppose the output voltage v of inverter _oBe desirable sine wave, i.e. v _o=V _oSin (ω _oT), V in the formula _oAnd ω _oBe respectively amplitude and the angular frequency of inverter output voltage.Then for linear load, the output current i of inverter _oBe desirable sinusoidal current,

I in the formula _oBe inverter output current amplitude.The instantaneous output that can get inverter according to electric current and voltage expression formula is As seen, the instantaneous output of single-phase inverter comprises two parts, and a part is steady state value, and a part changes with the output voltage frequency of twice.The conversion efficiency of supposing inverter is 100%, then its instantaneous input power p _InEqual instantaneous output p _oIn general, intermediate dc busbar voltage V _CfPulse less, then input current of inverter i _InvBe (ignoring high fdrequency component) Order

Then single-phase inverter can equivalence be DC current source I in parallel _DcWith secondary ripple current source i _2nd, as shown in Figure 3.

Secondary ripple current source i among Fig. 3 _2ndTo be transmitted in the filter inductance and input direct-current source of DC converter by main circuit and control loop, and reduce the efficient of DC converter, therefore the normal operation of harm direct current input source wishes to reduce as much as possible inductance L _FdcIn the secondary ripple current, make it as much as possible from middle bus capacitor C _FdcFlow through.There is the researcher to propose to adopt Double closed-loop of voltage and current for this reason and significantly reduces the outer voltage cut-off frequency and suppress secondary ripple current (C.Liu in the inductance, and J.S.Lai, " Low frequency current ripple reduction technique with active control in a fuel cell power system with inverter load; " IEEE Trans.Power Electron., vol.22, no.4, pp.1429 – 1436, Jul.2007), its circuit and control structure figure are as shown in Figure 4.Intermediate-bus voltage and voltage given V that sampling obtains _RefIt is poor by voltage regulator G to do _v(s) generate inductive current command value i _Ref(amplitude limit link wherein is used for restriction inductive current maximum), make difference by overcurrent adjuster G with the inductive current after the sampling _i(s) produce modulation signal after, then control DC converter through modulator and driving.For suppressing the secondary ripple current in the inductance, need to significantly reduce the cut-off frequency of outer voltage, thereby reduce inductive current instruction i _RefIn the secondary ripple component, as shown in Figure 5.Yet excessively low Voltage loop cut-off frequency will worsen the dynamic characteristic of converter when the load saltus step.When shock load, larger falling will appear in DC bus-bar voltage, as shown in Figure 6, even be lower than the required minimum direct voltage of inverter normal operation, thereby affect the normal operation of inverter; When the anticlimax load, larger overshoot will appear in DC bus-bar voltage, increase the voltage stress of inverter switching device pipe.

The DC converter load current i that sampling is obtained _FfIn the output of (the being the rear class input current of inverter) voltage regulator that is added to, thereby produce new inductive current command value i _Ref, can effectively improve the dynamic characteristic of converter when the load saltus step, load-current feedforward control that Here it is, its control structure figure is as shown in Figure 7.Yet, because feed-forward signal i _FfIn contain whole secondary ripple information, will cause inductive current instruction i _RefIn also contain whole secondary ripple information, thereby increase the secondary ripple current in the inductance.

Summary of the invention

In order both to suppress the secondary ripple current in the prime DC converter, improve simultaneously its dynamic characteristic when the load saltus step, the present invention improves existing Double closed-loop of voltage and current, proposes a kind of control method that suppresses DC converter secondary ripple current and improve dynamic characteristic.

Another object of the present invention is to provide a kind of control system that realizes described control method.

Suppress the secondary ripple current and improve the control method of dynamic characteristic, be specially:

(1) gathers intermediate-bus voltage feedback signal V _{Cf_s}, DC converter filter inductance current feedback signal i _{Lf_s}With DC converter load current feedback signal i _{Inv_s}

(2) according to intermediate-bus voltage feedback signal V _{Cf_s}And reference signal V _RefCalculate voltage error signal e ₁=V _Ref-V _{Cf_s}, to voltage error signal e ₁Process and obtain Voltage loop inductive current instruction i _v

(3) DC converter load current feedback signal i _{Inv_s}Pass through low-pass filtering, and obtain the load-current feedforward signal i of DC converter behind filtering two harmonics _Ff

(4) with Voltage loop inductive current instruction i _vWith load-current feedforward signal i _FfStack obtains the given signal i of inductive current _Ref1=i _v+ i _Ff

(5) to the given signal i of inductive current _Ref1Carry out amplitude limiting processing and obtain the actual given signal of inductive current $i_{\mathrm{<figure-callout\; id="2"\; label="ref"\; filenames="HDA00001756561300022.png,HDA00001756561300041.png"\; state="\{\{state\}\}">ref</figure-callout>}2}=\left\{\begin{array}{cc}{i}_{\mathrm{ref}1}& i_{\mathrm{<figure-callout\; id="1"\; label="ref"\; filenames="HDA00001756561300012.png,HDA00001756561300022.png"\; state="\{\{state\}\}">ref</figure-callout>}1}\&le;i_{\max }\\ i_{\max }& i_{\mathrm{<figure-callout\; id="1"\; label="ref"\; filenames="HDA00001756561300012.png,HDA00001756561300022.png"\; state="\{\{state\}\}">ref</figure-callout>}1}\&GreaterEqual;i_{\max }\end{array}\right.,$ i _MaxBe limiting threshold;

(6) with the given i of inductive current of reality _Ref2Deduct the inductor current feedback signal i that sampling obtains _{Lf_s}, obtain current error signal e ₂=i _Ref2-i _{Lf_s}, to current error signal e ₂Process and obtain modulation signal;

(7) utilize modulation signal to carry out pulse-width modulation, output duty cycle signal driver DC converter switching tube.

Realize the control system of described control method, comprise voltage sensor, input current of inverter transducer, inductive current transducer, first adder, second adder, the 3rd adder, voltage regulator, low pass filter, trapper, inductive current amplitude limiter, current regulator, pulse width modulator and DC converter switching network;

Two inputs of first adder are output and the voltage reference signal of voltage sensor respectively, and the output of first adder connects the input of voltage regulator;

Two inputs of second adder connect respectively the output of voltage regulator and the output of trapper, the input of trapper connects the output of input current of inverter transducer by low pass filter, the output of second adder connects the input of amplitude limiter;

Two inputs of the 3rd adder connect respectively the output of amplitude limiter and the output of inductive current transducer; The output of the 3rd adder connects the input of pulse width modulator by current regulator, the output of pulse width modulator connects the control end of DC converter switching network.

Technique effect of the present invention is embodied in:

The present invention adopts Double closed-loop of voltage and current to the prime DC converter, and suppresses wherein secondary ripple current by significantly reducing the Voltage loop cut-off frequency; A feedforward route load current sampling and two frequency multiplication trappers are composed in series feed-forward signal i _FfWith voltage regulator G _v(s) the signal i of output _vStack is rear as inductive current command value i _RefBecause the outer voltage cut-off frequency is lower, i _vIn substantially do not contain the secondary ripple component; In the feedforward branch road because the existence of trapper, i _FfIn substantially do not contain the secondary ripple component yet, thereby inductive current instruction i _RefIn substantially do not contain the secondary ripple component yet.Because the cut-off frequency of current inner loop is usually higher, tracking characteristics is good, so also will substantially not contain the secondary ripple component in the inductive current.And when the load saltus step, although G _v(s) response speed is slower, i _vHave little time to change, but since the existence on the road of load-current feedforward, i _FfTo change rapidly inductive current instruction i _RefAlso will change rapidly, and make inductive current follow the tracks of fast load current, guarantee intermediate-bus voltage V _CfLarge fluctuation can not appear.

The present invention can both suppress the secondary ripple current in the prime DC converter, thereby improved the efficient of converter, and protection direct current input source is not subjected to the impact of secondary ripple current; Improve again converter dynamic characteristic when the load saltus step, guarantee the normal operation of inverter, reduce the voltage stress of inverter switching device pipe; Because trapper is at the feedforward branch road but not in the control loop, the present invention also can not affect phase margin and the robustness of control system.

Description of drawings

Fig. 1 is two-stage type single-phase inverter schematic diagram.

Fig. 2 is two-stage type single-phase inverter secondary ripple current mechanism of production schematic diagram.

Fig. 3 is the circuit theory diagrams after the single-phase inverter equivalence.

Fig. 4 is DC converter Double closed-loop of voltage and current structure chart.

Inductive current and intermediate-bus voltage oscillogram when Fig. 5 is DC converter Double closed-loop of voltage and current steady operation.

Inductive current and intermediate-bus voltage oscillogram when Fig. 6 is the shock load of DC converter Double closed-loop of voltage and current.

Fig. 7 is DC converter voltage and current double closed-loop applied load current feed-forward control structure figure.

Fig. 8 is that the DC converter voltage and current double closed-loop adds and contains trapper load-current feedforward control structure chart.

Fig. 9 is that the DC converter voltage and current double closed-loop adds and contains under the trapper load-current feedforward control shock load inductive current and intermediate-bus voltage oscillogram.

1. intermediate-bus voltages samplings coefficient among the figure, 2. voltage regulator, 3. input current of inverter sampling coefficient, 4. low-pass filtering, 5. trapper, 6. inductive current amplitude limit, 7. inductive current sampling coefficient, 8. current regulator, 9. modulation with drive link.

Embodiment

In order to make purpose of the present invention, technical scheme and advantage clearer, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that embodiment described herein only in order to explain the present invention, is not intended to limit the present invention.

Control strategy of the present invention is: adopt Double closed-loop of voltage and current and significantly reduce the Voltage loop cut-off frequency and suppress secondary ripple current in inductance and the DC converter, adopt load-current feedforward to improve the dynamic characteristic of converter when the load saltus step, the trapper that seals in two frequencys multiplication simultaneously in the load-current feedforward branch road avoids increasing the secondary ripple current in the inductance.

Fig. 8 is that DC converter voltage and current double closed-loop of the present invention adds and contains trapper load-current feedforward control structure chart, comprises voltage sensor VH, current sensor CH1, current sensor CH2, first adder, second adder, the 3rd adder, voltage regulator 2, low pass filter 4, trapper 5, inductive current amplitude limiter 6, current regulator 8, pulse width modulator 9 and DC converter switching network.Wherein, H _v, H _I1, H _I2Be respectively intermediate-bus voltage sampling coefficient 1, inductive current sampling coefficient 7 and input current of inverter sampling coefficient 3.

The control method flow process of control system of the present invention is:

(1) utilize voltage sensor VH to detect intermediate-bus voltage V _Cf, collect intermediate-bus voltage feedback signal V _{Cf_s}Utilize current sensor CH1 to detect DC converter filter inductance current i _Lf, collect inductor current feedback signal i _{Lf_s}Utilize current sensor CH2 to detect input current of inverter feedback signal i _Inv, collect DC converter load current feedback signal i _{Inv_s}

(2) first adder is to middle busbar voltage feedback signal V _{Cf_s}And reference signal V _RefDo poor error signal e ₁, its formula is formula I.

e ₁=V _Ref-V _{Cf_s}Formula I

(3) voltage controller G _v(s) to error signal e ₁Process and obtain Voltage loop inductive current instruction i _vVoltage controller G _v(s) specifically can adopt the controllers such as PI, PID.

(4) the DC converter load current feedback signal i that samples and obtain _{Inv_s}Through behind the electric bandpass filter LPF filtering switching harmonics, send into two frequency multiplication trapper G _Notch(s) filtering two harmonics wherein obtain DC converter load-current feedforward signal i _Ff

(5) second adder is to Voltage loop inductive current instruction i _vWith load-current feedforward signal i _FfSummation obtains the given signal i of inductive current _Ref1, its formula is formula II.

i _Ref1=i _v+ i _FfFormula II

(6) the given i of inductive current that superposes and obtain _Ref1Through obtaining the actual given signal i of inductive current after the amplitude limit link _Ref2, in order to limit inductive current, damaging switching tube when preventing overload or short circuit, its formula is III.

$i_{\mathrm{<figure-callout\; id="2"\; label="ref"\; filenames="HDA00001756561300022.png,HDA00001756561300041.png"\; state="\{\{state\}\}">ref</figure-callout>}2}=\left\{\begin{array}{cc}{i}_{\mathrm{ref}1}& i_{\mathrm{<figure-callout\; id="1"\; label="ref"\; filenames="HDA00001756561300012.png,HDA00001756561300022.png"\; state="\{\{state\}\}">ref</figure-callout>}1}\&le;i_{\max }\\ i_{\max }& i_{\mathrm{<figure-callout\; id="1"\; label="ref"\; filenames="HDA00001756561300012.png,HDA00001756561300022.png"\; state="\{\{state\}\}">ref</figure-callout>}1}\&GreaterEqual;i_{\max }\end{array}\right.$ Formula III

Limiting threshold i _MaxCurrent limit according to the switching device in the switching network is determined.

(7) the 3rd adders are to the given i of the actual inductive current that obtains _Ref2The inductor current feedback signal i that obtains with sampling _{Lf_s}Ask the poor error signal e that obtains ₂, its formula is IV.

e ₂=i _Ref2-i _{Lf_s}Formula IV

(8) current controller G _i(s) to error signal e ₂Process obtaining modulation signal, through modulator and driving control switch pipe.Current controller G _i(s) specifically can adopt the controllers such as PI, PID.

Because the existence of trapper in the load-current feedforward branch road, the present invention can not affect Double closed-loop of voltage and current to the inhibitory action of secondary ripple current in the inductance, thereby guarantees that the prime DC converter does not have large secondary ripple current.Meanwhile, because the existence of load-current feedforward branch road, intermediate-bus voltage will large fluctuation can not occur when the load saltus step, as shown in Figure 9.

Control method provided by the invention can effectively be improved the dynamic characteristic of converter when the load saltus step by input current of inverter information is feedovered to controller by certain functional relation.In a word, this control method can significantly be improved the dynamic characteristic of converter when the load saltus step, suppresses simultaneously the secondary ripple current in the inductance.

Those skilled in the art will readily understand; the above only is preferred embodiment of the present invention; not in order to limiting the present invention, all any modifications of doing within the spirit and principles in the present invention, be equal to and replace and improvement etc., all should be included within protection scope of the present invention.

Claims (2)

1. suppress the secondary ripple current and improve the control method of dynamic characteristic, be specially:

(1) gathers intermediate-bus voltage feedback signal V _{Cf_s}, DC converter filter inductance current feedback signal i _{Lf_s}With DC converter load current feedback signal i _{Inv_s}

(2) according to intermediate-bus voltage feedback signal V _{Cf_s}And reference signal V _RefCalculate voltage error signal e ₁=V _Ref-V _{Cf_s}, to voltage error signal e ₁Process and obtain Voltage loop inductive current instruction i _v

(3) DC converter load current feedback signal i _{Inv_s}Pass through low-pass filtering, and obtain the load-current feedforward signal i of DC converter behind filtering two harmonics _Ff

(4) with Voltage loop inductive current instruction i _vWith load-current feedforward signal i _FfStack obtains the given signal i of inductive current _Ref1=i _v+ i _Ff

(5) to the given signal i of inductive current _Ref1Carry out amplitude limiting processing and obtain the actual given signal of inductive current $i_{\mathrm{ref}2}=\left\{\begin{array}{cc}{i}_{\mathrm{ref}1}& i_{\mathrm{ref}1}\&le;i_{\max }\\ i_{\max }& i_{\mathrm{ref}1}\&GreaterEqual;i_{\max }\end{array}\right.,$ i _MaxBe limiting threshold;

(6) with the given i of inductive current of reality _Ref2Deduct the inductor current feedback signal i that sampling obtains _{Lf_s}, obtain current error signal e ₂=i _Ref2-i _{Lf_s}, to current error signal e ₂Process and obtain modulation signal;

(7) utilize modulation signal to carry out pulse-width modulation, output duty cycle signal driver DC converter switching tube.

2. realize the control system of control method claimed in claim 1, comprise voltage sensor, input current of inverter transducer, inductive current transducer, first adder, second adder, the 3rd adder, voltage regulator, low pass filter, trapper, inductive current amplitude limiter, current regulator, pulse width modulator and DC converter switching network;

Two inputs of first adder are output and the voltage reference signal of voltage sensor respectively, and the output of first adder connects the input of voltage regulator;

Two inputs of second adder connect respectively the output of voltage regulator and the output of trapper, the input of trapper connects the output of input current of inverter transducer by low pass filter, the output of second adder connects the input of amplitude limiter;

Two inputs of the 3rd adder connect respectively the output of amplitude limiter and the output of inductive current transducer; The output of the 3rd adder connects the input of pulse width modulator by current regulator, the output of pulse width modulator connects the control end of DC converter switching network.

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