CN104037786A

CN104037786A - Cascading STATCOM steady-state zero-error control method

Info

Publication number: CN104037786A
Application number: CN201410316317.6A
Authority: CN
Inventors: 李圣清; 徐文祥; 栗伟周
Original assignee: Hunan University of Technology
Current assignee: Hunan University of Technology
Priority date: 2014-07-04
Filing date: 2014-07-04
Publication date: 2014-09-10

Abstract

The invention provides a steady-state zero-error control strategy of proportional feedback integral (PFI). The steady-state zero-error control strategy is used for analyzing the working principle of the PFI. In consideration of the disturbance of system voltage to output current, a control method of feedforward decoupling PFI is provided on the basis of the control strategy, the integral parameter ki is reasonably set, the alternating quantity amplitude of the PFI is 1 pu, phase deviation of the PFI is zero degree, the direct-current component amplitude is zero, and it shows that according to the control method, cascading STATCOM alternating-current quantity steady-state zero-error control can be achieved, and a direct-current component can also be effectively restrained. Effectiveness and practicability of the control method are verified according to the simulation and experiment result.

Description

Cascade STATCOM stable state zero error control method

Technical field

[0001] the present invention aims to provide the control method that a kind of cascade STATCOM eliminates alternating current component error and suppresses DC component in the time of stable state, can effectively ensure that cascade STATCOM safety and stability accurately moves, the method implements easily, has very high engineering practical value.

Background technology

In recent years, cascade STATCOM (static synchronous compensator, STATCOM) just can be accessed by mesohigh electrical network, is easy to expansion owing to having without transformer, is convenient to the advantages such as modularized design and has obtained application widely.Control precision to device output current directly has influence on entire system compensation effect, and Current Control performance index mainly contain stable state amplitude and phase error, dynamic response time, unity power factor, percent harmonic distortion and DC component etc. conventionally.Cascade STATCOM controls because great majority adopt PI, and it is difficult to of ac to play desirable effect, has the problem of steady-state error.Although can reduce to take up an area, reduce costs, raise the efficiency and device saves transformer, but also brought the grid-connected current DC component problem that exceeds standard simultaneously, to cause magnetic element Point Drifting in electrical network, and then causing the series of problems such as the harmonic wave, noise of transformer or motor, overheated and current spike, the DC component that IEEE Std.1547-2003 requires power electronic equipment to inject electrical network must not exceed 0.5% of output-current rating.

At present, STATCOM device control strategy has been carried out to many-sided research both at home and abroad.For Current Control, in the 4th phase of calendar year 2001 " Proceedings of the CSEE ", " Robust Adaptive Control of STATCOM reactive current " literary composition has proposed robust type direct adaptive control algorithm from device level level, controller has good Current Tracing ability and robust property, but controls relative complex.In the 6th phase in 2003 " Proceedings of the CSEE ", " Mathematical Modeling of chain type STATCOM " literary composition is on the basis of chain type STATCOM SWITCHING FUNCTION MATHEMATICAL MODEL, analyzed that fundamental current is meritorious, the variation relation of idle component and DC voltage average value, but be unfavorable for output current control algorithm design.In the 28th phase in 2010 " Proceedings of the CSEE ", " chain type D-STATCOM modeling and Decoupled State Variable Feedback Linearization control thereof " literary composition is by Using State Variable Feedback Linearization Method mode, realize meritorious, idle Decoupling Controller Design, and be applied in engineering." Hysteresis-band Current Tracking Control of Grid-connected Inverter research " stagnant ring control for a literary grace in the 9th phase in 2006 " Proceedings of the CSEE ", its feature is that principle is simple and dynamic response is fast, but it is larger that its maximum deficiency is that switching frequency is subject to hysteresis band to affect fluctuation range, cause design of filter difficulty, and then affect entire system performance." Vector current controlled voltage source converter:deadbeat control and saturation strategies " dead beat control and PREDICTIVE CONTROL for a literary grace in the 2nd phase in 2002 " IEEE Trans. on Power Electronics ", the validity of its control depends on the foundation of controlled device accurate model to a great extent.And the non-linear design that makes accurate model of cascade STATCOM system acquires a certain degree of difficulty, design improper meeting and cause system control unstable.In the 3rd phase of calendar year 2001 " IEEE Trans. on Power Electronics ", " Stationary frame current regulation of PWM inverters with zero steady-state error " literary grace has used ratio resonance PR based on internal model principle to control to solve of ac control to have the problem of steady-state error, but for the DC offset problem specifying in IEEE std.1547-2003, the method can not effectively suppress.

Summary of the invention

The present invention proposes the control method based on Feedforward Decoupling PFI, in realizing the control of cascade STATCOM device stable state zero error, can effectively suppress contained DC component in output current.Kp or ki value less (system stability nargin is larger) in the situation that, still can realize the control of stable state zero error, have principle simple, the feature such as implement easily, there is higher engineering practical value.

Embodiment is as follows:

The STATCOM output current that can release under PFI control according to Figure of description 1 is:

When only considering the impact of reference current.Clearly, when when establishment, the amplitude-frequency characteristic 1 at closed-loop system fundamental frequency place, phase-frequency characteristic is 0, realizes zero stable state amplitude phase error control of grid-connected output current first-harmonic, now grid-connected DC component is inhibited simultaneously.But while considering the affecting of line voltage Us, in situation about setting up, the disturbance of fundamental frequency place line voltage has decayed , illustrating that grid disturbances can not ignore, it can cause the steady-state error of grid-connected output current first-harmonic, and can accumulation DC component.

Traditional PI controls control grid-connected current and have stable state amplitude and phase error, its root is that its fundamental frequency place gain is , do not there is infinite gain characteristic.And Proportional Feedback integral control has infinitely-great gain at fundamental frequency place, the amplitude-frequency characteristic that makes closed-loop system fundamental frequency place is 1, and phase-frequency characteristic is 0, therefore can realize zero steady-state error control of grid-connected current.

Based on above-mentioned analysis, in order to eliminate grid disturbances impact, consider to introduce voltage feed-forward control decoupling zero scheme.As shown in Figure of description 2, now STATCOM output current is:

Remove thus the disturbance of line voltage for output current, system need only meet, and reasonable parameters ki, just can realize the stable state zero error control of output current.

Utilize matlab to carry out simulation analysis to the frequency domain of PI, PR, tri-kinds of controls of PFI, shown in presentation of results book accompanying drawing 3.Can find out, utilize conventional PI control device, its grid-connected current of ac amplitude is 1.36pu, and phase deviation 45 is spent, and has certain error, and DC component amplitude is 1, and unrestraint performance; Proportion of utilization resonance PR controller, its of ac amplitude is 1pu, phase deviation is 0, does not have steady-state error problem, but its DC component amplitude is 1, it does not suppress DC component ability as seen; And when proportion of utilization feedback integration PFI controller, its of ac amplitude is 1pu, and phase deviation 0 is spent, and its DC component amplitude is 0, known its not only can be realized the control of cascade STATCOM device of ac stable state zero error, can also effectively suppress DC component.

simulation and experiment interpretation of result:

Based on matlab7.0, carried control method is carried out to simulation analysis, simulation parameter is as follows: system line voltage us=311V, mains frequency fs=50Hz, connect inductance L=5.1mH, DC bus capacitor C=2200uF, capacitance voltage set-point udcref=200V, single-phase cascade module is counted N=5, output current is 36.75A, proportionality coefficient 0.0025, integral coefficient 0.74.

When PI controls, the simulation result of output current is as shown in accompanying drawing 4 and accompanying drawing 5.From accompanying drawing 4, its of ac amplitude is 49.96A, i.e. 1.36pu, 45 ° of phase differences; From accompanying drawing 5, after PI controls, its DC component is reflected in output by undamped, causes the DC component that contains suitable composition in output current.

PR control time output current simulation result accompanying drawing 6 and accompanying drawing 7 shown in.From accompanying drawing 6, its of ac amplitude is 36.75A, i.e. 1pu, and 0 ° of phase difference, it can realize the control of stable state zero error as seen; From accompanying drawing 7, after PR controls, its DC component also cannot be inhibited.

When Feedforward Decoupling PFI controls, the simulation result of output current as illustrated in Figure 8 and 9 reference.From accompanying drawing 8, its of ac amplitude is 36.75A, i.e. 1pu, and 0 ° of phase difference, it can realize the control of stable state zero error as seen; From accompanying drawing 9, after Feedforward Decoupling PFI controls, direct current amplitude-frequency characteristic is 0, and DC component will be by closed-loop system complete attenuation, and therefore the DC component of grid-connected current can be effectively suppressed.

Contrast accompanying drawing 6,7,8,9 is known, and it is 40ms that PR controls transient response time, and PFI controls after 20ms and enters stable state, and simulation result shows that PFI controls and compares PI, PR and control and have good steady-state behaviour and transient performance.

In order to verify the validity of the method, spy has carried out experimental study.Experiment parameter is: system voltage is 398V, and inductance is 25mH, and frequency is 50Hz, and electric capacity is 2000uF, and carrier frequency is 1000Hz, and devices switch frequency is 500Hz, and sample frequency is 3200 Hz, is often in series by 5 H bridge modules.Hardware platform is two many CPLD of DSP+FPGA+ combined systems, and DSP mainly realizes the functions such as first-harmonic line voltage is phase-locked, instruction current computing, DC voltage control, current transformer protection; FPGA is used for producing PWM and drives signal, and CPLD is used for each power tube to carry out pulse distribution.

Accompanying drawing 10 and accompanying drawing 11 are the voltage and current waveform of system output under PI controls, and result is basic consistent with emulation, just in waveform, contain a small amount of harmonic wave, and aberration rate is larger.

Accompanying drawing 12 and accompanying drawing 13 be lower system output voltage and electric current for Feedforward Decoupling PFI controls, and compares accompanying drawing 10,11, and except realizing the control of stable state zero error, waveform quality also slightly improves, and has proved thus the validity of the method.

brief description of the drawings:

Fig. 1 Proportional Feedback integration PFI schematic diagram

The control principle drawing of Fig. 2 Feedforward Decoupling PFI

Tri-kinds of controller frequency-domain analysiss of Fig. 3

Output current wave when Fig. 4 conventional PI control

Output current spectrum analysis when Fig. 5 conventional PI control

Output current wave when Fig. 6 ratio resonance PR controls

Output current spectrum analysis when Fig. 7 ratio resonance PR controls

Output current wave when Fig. 8 Feedforward Decoupling PFI controls

Output current spectrum analysis when Fig. 9 Feedforward Decoupling PFI controls

Figure 10 PI controls lower system output three-phase voltage current waveform

Figure 11 PI controls lower system output single-phase voltage current waveform

Figure 12 Feedforward Decoupling PFI controls lower system output three-phase voltage current waveform

Figure 13 Feedforward Decoupling PFI controls lower system output single-phase voltage current waveform.

Claims

1. the present invention aims to provide the control method that a kind of cascade STATCOM eliminates alternating current component error and suppresses DC component in the time of stable state, and concrete principle and step are as follows:

The first step, Proportional Feedback integral principle, the STATCOM output current under PFI controls is:

When only considering reference current impact, clearly, when when establishment, the amplitude-frequency characteristic 1 at closed-loop system fundamental frequency place, phase-frequency characteristic is 0, realizes zero stable state amplitude phase error control of grid-connected output current first-harmonic, now grid-connected DC component is inhibited simultaneously; But while considering the affecting of line voltage Us, in situation about setting up, the disturbance of fundamental frequency place line voltage has decayed , illustrating that grid disturbances can not ignore, it can cause the steady-state error of grid-connected output current first-harmonic, and can accumulation DC component;

Second step, Feedforward Decoupling PFI control principle, in order to eliminate grid disturbances impact, considers to introduce voltage feed-forward control decoupling zero scheme, and now STATCOM output current is:

Remove thus the disturbance of line voltage for output current, system need only meet , reasonable parameters ki, just can realize the stable state zero error control of output current;

The concrete visible Figure of description 1 of schematic diagram and accompanying drawing 2.