CN104377714A - SVG-based compensation method for low-frequency oscillation of power grid - Google Patents

Abstract

An SVG-based compensation method for low-frequency oscillation of a power grid comprises the steps of measurement of system current oscillation frequencies, design correction of a band-pass filter (BPF) and control design of an SVG current loop. Low-frequency oscillation frequencies of network voltage or current are measured, and FFT analysis is performed, so that all the low-frequency oscillation frequencies are obtained. The low-frequency oscillation frequency of a system is set as the center frequency of the BPF, and the BPF is designed. According to the control design of the SVG current loop, in the DQ rotating coordinate system, the feedback quantity of active power of a power grid is added into a classic double loop feedforward decoupling strategy to serve as a given value of a reactive current component. The BPF is used for filtering out DC components and high-frequency components in the feedback quantity of the active power.

Description

A kind of compensation method of the electricity grid oscillating based on SVG

Technical field

The present invention relates to the reactive compensation system of electrical network, particularly relate to a kind of method using the low-frequency oscillation of SVG device compensation network.

Background technology

At present, along with the development of electric power system, electrical network scale is increasingly huge.But along with the increase of electrical network scale, while raising resource utilization, in electrical network, also there is a kind of low-frequency oscillation (0.1Hz ~ 2.5Hz).This low-frequency oscillation, once occur, understands the safe operation of serious threat electrical network.

Reactive power compensator is as conventional power system stability device, and in electrical network, Application comparison is extensive.Wherein the application of SVG is more flexible, and it can inject the electric current of assigned frequency in electrical network, improves the dynamic of system and steady-state characteristic.How research uses reactive power compensator (SVG) situation to electricity grid oscillating to suppress, increases system damping and have great importance.

The relative angular displacement that electricity grid oscillating shows as underdamping between generator amature and causes, frequency of oscillation is more large lower with electrical network scale, and with obvious active power oscillations.The solution of low-frequency oscillation normally adjusts generator control system field regulator (PSS) parameter, the selection of optimized parameter is difficult to analyze and quantize, but SVG itself can provide positive damping according to the frequency of oscillation of system, can ensure to play to characteristic frequency low-frequency oscillation the expansion that inhibitory action can not cause low-frequency oscillation amplitude and scope simultaneously.

Summary of the invention

Object of the present invention is just to provide a kind of method adopting reactive power compensator (SVG), carries out suppressing the low-frequency oscillation in electrical network, thus changes the stability of system, make system cloud gray model reliable.

For achieving the above object, the technical solution used in the present invention is as follows:

Based on a compensation method for the electricity grid oscillating of SVG, comprise the step such as design revise, the design of SVG current loop control of the measurement to network re-active power frequency of oscillation, band pass filter.Thus make SVG can provide effective positive damping effect for electricity grid oscillating while sending reactive current.

The described measurement to network re-active power frequency of oscillation, namely within the scope of 0.1Hz ~ 2.5Hz, measures the voltage of electrical network or the frequency of electric current, makes fft analysis, obtain the frequency of all low-frequency oscillations.

The design revise of described band pass filter, the low-frequency oscillation frequency by system is set to the centre frequency of band pass filter, design band pass filter BPF.

Described SVG current loop control design, namely be under DQ rotating coordinate system, in classical dicyclo Feedforward Decoupling strategy, add the set-point of feedback quantity as reactive current component of network re-active power, above-mentioned band pass filter BPF is for the direct current in filtering active power feedback amount and radio-frequency component.

Beneficial effect

Compared with prior art, advantage of the present invention is as follows:

1. using FACTS device to suppress electrical network low frequency oscillation problem, without the need to additionally increasing cost, having expanded the field that S walks G application.

2. compare the method for simulation calculation and the adjustment controller parameter theorized, avoid the system parameters problems such as research mode, the method for on-line measurement active power low-frequency oscillation frequency is more effectively simple.

3. in FACTS device, modulate idle output current impacts very little to electrical network, regulates active power flow can realize the fast and stable of low-frequency oscillation by reactive power.

Accompanying drawing explanation

Fig. 1 blower fan low-frequency oscillation frequency spectrum;

Fig. 2 overall system pie graph;

Fig. 3 traffic filter designs;

Fig. 4 current loop control structure;

Fig. 5 RTDS emulation experiment SVG current waveform;

Fig. 6 Matlab emulates the voltage waveform under low-frequency oscillation;

Fig. 7 Matlab emulates low-frequency oscillation voltage inhibition;

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further detail.

See Fig. 1 to Fig. 7.The method suppressing electricity grid oscillating based on SVG of the present invention, comprises the step such as design revise, the design of SVG current loop control of the measurement to active power oscillations frequency, band pass filter.Thus make SVG can provide effective positive damping effect for electricity grid oscillating while sending reactive current.

Suppress the concrete steps of electricity grid oscillating as follows:

The first step, measures the characteristic frequency of network re-active power low-frequency oscillation.Namely, within the scope of 0.1Hz ~ 2.5Hz, measure network re-active power fluctuation situation, make fft analysis, obtain the frequency curve of active power fluctuation, as system, near 0.2Hz, 1Hz, low-frequency oscillation occurs.0.2Hz, 2Hz are set to the centre frequency of band pass filter.

Second step, measure network re-active power fluctuation, System's composition comprises generator, burden with power, SVG, low-frequency oscillation suppression module.According to the characteristic frequency design band pass filter of network re-active power low-frequency oscillation.Band pass filter BPF1 and BPF2 is designed according to low-frequency oscillation frequency 0.2Hz, 1Hz.Wherein BPF is second-order bandpass filter, and passband is arranged on 0.2Hz, 1Hz place, and gain is set to-1, and the transfer function after filter parallel connection is as follows,

$F\left(s\right)=-\frac{{\mathrm{\ζ}}_1{w}_{n1}s}{s^2+{\mathrm{\ζ}}_1{w}_{n1}s+{w_{n1}}^2}-\frac{{\mathrm{\ζ}}_2{w}_{n2}s}{s^2+{\mathrm{\ζ}}_2{w}_{n2}s+{w_{n2}}^2}$

Wherein value ζ ₁=ζ ₂=0.7, w _n1=0.2*6.28, w _n2=1*6.28

3rd step, because band pass filter is different for the component phase characteristic of different frequency, the deviation of frequency will cause slight phase shift.Also the phase deviation that sampling keeps link to cause in power measurement link simultaneously, needs additive phase compensation tache, finely tunes for the phase place exported system, make the phase shift of filter at this Frequency point place be zero.Assuming that the sampling time is Ts, design phase shift all-pass filter PhaseShfiter afterwards, the angle corresponding to the mobile Ts/2 time, the transfer function corresponding to it is as follows,

$F\left(s\right)=\frac{1+T_{1}s}{1+T_{2}s}$

Finally by the output of PhaseShifter1 and PhaseShifter2, the Characteristics of Low Frequency Oscillations frequency that namely filtering obtains is added the referenced reactive current signal just obtaining SVG.

4th step, network re-active power signal is fed back through band pass filter and joins SVG current regulator, make SVG export reactive current and follow network re-active power signal fluctuation, to control the active current trend at electrical network PCC place, stablize the active power fluctuation of PCC point.The control mode of SVG power oscillation damping, Gc (s) is current controller transfer function, and Id, Iq are that SVG detects gained d-axis and quadrature axis current component, and Ed, Eq are voltage on line side feedforward, and signal finally generates pwm signal after Parker inverse transform block.

For generator G, because SVG inhibits active current to fluctuate by reactive current, and the active current of generator is relevant to machine torque, thus SVG inhibits the relative angular displacement between generator amature, so just reduce the intensity of electricity grid oscillating, add electrical network damping, the low-frequency oscillation suppression of the transient process of electric power system and the low-frequency oscillation of electrical network large-scale grid connection incidence stable state are suppressed significant.

Claims (4)

1. the compensation method based on the electricity grid oscillating of SVG, it is characterized in that: carry out the measurement to network re-active power frequency of oscillation, the design revise of band pass filter, the design of SVG current loop control, thus make SVG can provide effective positive damping effect for electricity grid oscillating while sending reactive current.

2. the compensation method of the electricity grid oscillating based on SVG according to claim 1, it is characterized in that: to the measurement of network re-active power frequency of oscillation, namely within the scope of 0.1Hz ~ 2.5Hz, measure the voltage of electrical network or the frequency of electric current, make fft analysis, obtain the frequency of all low-frequency oscillations.

3. the compensation method of the electricity grid oscillating based on SVG according to claim 1, is characterized in that: the design revise of band pass filter, the low-frequency oscillation frequency by system is set to the centre frequency of band pass filter, design band pass filter BPF.

4. the compensation method of the electricity grid oscillating based on SVG according to claim 1, it is characterized in that: described SVG current loop control design, namely be under DQ rotating coordinate system, in classical dicyclo Feedforward Decoupling strategy, add the set-point of feedback quantity as reactive current component of network re-active power, above-mentioned band pass filter BPF is for the direct current in filtering active power feedback amount and radio-frequency component.