CN105071418A - Chain-type STATCOM control method under load unbalance - Google Patents

Abstract

The invention proposes a chain-type STATCOM double-ring superposing control method based on the combination of nonlinear decoupling and repeated control. A positive sequence current loop control device compensates reactive power needed by a load. A negative sequence current loop achieves the complete compensation of a negative sequence current under the condition of load unbalance, and low-order harmonics and disturbance, which are generated by a repeated control inhibition device, are introduced. Simulation and experiments indicate that the method can effectively solve a problem that a chain-type STATCOM achieves the compensation of an unbalanced load, and the method has a certain engineering reference value.

Description

The control method of chain type STATCOM under laod unbalance

Technical field

The present invention relates to the control method, particularly a kind of double ring stacking control method combined with Repetitive controller based on Nonlinear Decoupling of chain type STATCOM under a kind of laod unbalance.

Background technology

In recent years, along with a large amount of uses of the impact such as arc furnace, electric locomotive, asymmetric load, cause electric power system energy imbalance ubiquity in actual motion.Chain type STATCOM is due to without the need to accessing transformer, the plurality of advantages such as modularization can becoming study hotspot in recent years, and chain type STATCOM has phase-splitting adjustment and variable modulation than feature simultaneously, makes it possess the potentiality compensating unbalanced load.For STATCOM control problem in laod unbalance situation, " 38thAnnualConferenceonIEEEIndustrialElectronicsSociety.M ontreal in 2012, Canada:IEEE " in " ResearchonunbalanceloadcompensationbycascadedSTATCOMwith starconfiguration " one literary composition by introducing D/Y1 type transformer in chain type STATCOM, make that there is the ability compensating unbalanced load, but due to the introducing of transformer, its construction investment is strengthened." research based on the chain type STATCOM Dynamic Control Strategy of anti-Fault Control " literary composition in 4th phase " Proceedings of the CSEE " in 2005 proposes based on the meritorious of inverse system and idle decoupling zero pulse-width modulation (PWM) method, improve the reactive response speed of device, but need to carry out Fourier transform to electric current and voltage, calculate comparatively complicated." ControlofacascadeSTATCOMwithstarconfigurationunderunbala ncedconditions " literary composition in 1st phase " IEEETrans.onPowerElectronics " in 2009 proposes the control algolithm based on residual voltage superposition, but these residual voltage computational methods are more complicated, and the track with zero error strategy adopted needs to know the accurate parameter of main circuit passive device and sets up accurate Mathematical Modeling." the phase-splitting asymmetric control of STATCOM " literary composition in phase calendar year 2001 the 1st " Proceedings of the CSEE " proposes individual-phase control strategy, but this method referential current detection calculates more complicated, and compensation ability is limited.

Summary of the invention

The present invention is directed to chain static synchronous compensator (STATCOM) control problem in laod unbalance situation, propose the double ring stacking control method that a kind of Nonlinear Decoupling combines with Repetitive controller, idle needed for forward-order current ring control device compensating load; Negative-sequence current ring compensates the negative-sequence current in laod unbalance situation, introduces low-order harmonic and the disturbance of the generation of Repetitive controller restraining device itself simultaneously.Emulation and experiment show: the method can solve the compensation problem of chain type STATCOM to unbalanced load effectively, has higher project reference value.

Concrete implementation step is as follows:

The first step, introduces Current Decoupling in positive sequence control loop and voltage feed-forward control controls, and obtains positive sequence voltage instruction with ;

Second step, when laod unbalance, electrical network, to containing the meritorious and idle component of negative phase-sequence while load provides active power, causes three-phase voltage current asymmetric, reduces system power factor; Under negative phase-sequence environment, because line voltage is zero, only need introduce Current Decoupling link, idle component meritorious according to the negative-sequence current detected in real time and instruction electric current difference relatively sends into controller process, obtains negative sequence voltage instruction with ;

3rd step, because repetitive controller provides very high loop gain in feedback network, in order to improve the anti-interference of chain type STATCOM, reduces the low-order harmonic that switch produces, pIrepetitive controller is introduced on the basis controlled, wherein: r, ybe respectively the output signal of command signal, expectation; q (Z)for damping coefficient, usually get 0-1, the stability of system can be improved; s (Z)for correction link, be generally designed to second order filter, ensure the decay to high-frequency signal; z-Nfor cycle delay link, g (Z)for controlled device;

4th step, the positive sequence optimized through Repetitive controller, negative sequence voltage instruction are superposed as modulating wave, participate in the modulation of one pole frequency multiplication phase-shifting carrier wave, idle and the negative sequence component of system quick tracing compensation system load side is made, the low-order harmonic of effectively restraining device generation simultaneously itself and disturbance by the output voltage of adjusting device.

Simulation and experiment interpretation of result

For the validity of checking this paper institute extracting method, in MATLAB/Simulink environment, built the simulation model of chain type STATCOM, simulation parameter is as follows: system line voltage is 2KV, mains frequency is 50HZ, switching frequency is 2KHZ, and DC bus capacitor is 5mF, and single-phase cascade module number is 5.

Traditional positive sequence powerless control method and this paper institute extracting method are contrasted, verifies correctness and the validity of context of methods.Tradition reactive-load compensation method, as shown in accompanying drawing 4,5,6,7, is respectively line voltage, electric current, A phase power factor and chain type STATCOM output voltage frequency spectrum.From simulation waveform, due to the existence of unbalanced load, when only carrying out positive sequence compensation, due to the impact of negative sequence component, containing the meritorious of negative phase-sequence and idle component in electrical network, it is asymmetric that line voltage electric current there will be to a certain degree, now, electrical network A phase power factor about 0.8, the percent harmonic distortion THD=1.21% of chain type STATCOM output voltage.Visible, adopt conventional method cannot eliminate the imbalance of power network current, and power factor is on the low side.

Use the double ring stacking control method carried herein, to the positive sequence of unbalanced load, idle and negative sequence component compensates respectively.Simulation waveform after compensation, as shown in accompanying drawing 8,9,10,11, is respectively line voltage, electric current, A phase power factor and chain type STATCOM output voltage frequency spectrum after compensating.Can find out, after compensating, line voltage current unbalance factor improves obviously, and power factor of electric network is substantially close to 1, and owing to introducing Repetitive controller, the percent harmonic distortion of chain type STATCOM output voltage is reduced to THD=0.31%.Now STATCOM device fully compensate for that load positive sequence is idle, the meritorious and idle component of negative phase-sequence, system only provides positive sequence to gain merit, and output harmonic wave better performances.

In order to verify the effect of above-mentioned control method, spy has carried out experimental study.Chain type STATCOM main circuit adopts Y-connection, often to be in series by 5 H bridge power models, system voltage is 300V, connection reactance is 25mH, carrier frequency is 1000HZ, sample frequency is 3000HZ, and hardware platform is two CSTR+FPGA+ many CPLD combined system, 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 drive singal, and CPLD is used for carrying out pulse distribution to each power tube.Experimental verification is carried out respectively when only having positive sequence to control and positive-negative sequence controls simultaneously.Accompanying drawing 12,13 and accompanying drawing 14,15 are respectively system voltage current waveform in two kinds of situations.As can be seen from experiment, when only having positive sequence to control, system voltage is respectively 280V, 255V, 300V, and system power is respectively 50A, 50A, 63A, and positive-negative sequence controls rear three-phase voltage simultaneously and substantially maintains about 300V, and three-phase current maintains about 60A.Visible, after adding negative phase-sequence control, system voltage current unbalance factor obviously reduces.Experiment demonstrates the validity of context of methods.

Accompanying drawing explanation

Fig. 1 dicyclo superposing control block diagram

Fig. 2 Repetitive controller block diagram

Fig. 3 positive-negative sequence current detects block diagram

Grid voltage waveform during control that Fig. 4 positive sequence is idle

Power network current waveform during control that Fig. 5 positive sequence is idle

Electrical network A phase power factor during control that Fig. 6 positive sequence is idle

Chain type STATCOM output voltage frequency spectrum during control that Fig. 7 positive sequence is idle

Grid voltage waveform during Fig. 8 dicyclo superposing control

Power network current waveform during Fig. 9 dicyclo superposing control

Electrical network A phase power factor during Figure 10 dicyclo superposing control

Chain type STATCOM output voltage frequency spectrum during Figure 11 dicyclo superposing control

System voltage experimental waveform when Figure 12 positive sequence controls

System voltage experimental waveform during Figure 13 dicyclo superposing control

System power experimental waveform when Figure 14 positive sequence controls

System power experimental waveform during Figure 15 dicyclo superposing control.

Claims (1)

1. the present invention mainly proposes the control method of chain type STATCOM under a kind of laod unbalance, concrete principle and way as follows:

The first step, introduces Current Decoupling in positive sequence control loop and voltage feed-forward control controls, and obtains positive sequence voltage instruction with ;

Second step, when laod unbalance, electrical network, to containing the meritorious and idle component of negative phase-sequence while load provides active power, causes three-phase voltage current asymmetric, reduces system power factor; Under negative phase-sequence environment, because line voltage is zero, only need introduce Current Decoupling link, idle component meritorious according to the negative-sequence current detected in real time and instruction electric current difference relatively sends into controller process, obtains negative sequence voltage instruction with ;

3rd step, because repetitive controller provides very high loop gain in feedback network, in order to improve the anti-interference of chain type STATCOM, reduces the low-order harmonic that switch produces, pIrepetitive controller is introduced on the basis controlled, wherein: r, ybe respectively the output signal of command signal, expectation; q (Z)for damping coefficient, usually get 0-1, the stability of system can be improved; s (Z)for correction link, be generally designed to second order filter, ensure the decay to high-frequency signal; z-Nfor cycle delay link, g (Z)for controlled device;

4th step, the positive sequence optimized through Repetitive controller, negative sequence voltage instruction are superposed as modulating wave, participate in the modulation of one pole frequency multiplication phase-shifting carrier wave, idle and the negative sequence component of system quick tracing compensation system load side is made, the low-order harmonic of effectively restraining device generation simultaneously itself and disturbance by the output voltage of adjusting device.