Xiangning Xiao

Enhancement voltage stability of wind farm access to power grid by novel SVC

This paper studies the voltage stability problems of wind farm access to electric grid. Based on the equivalent circuit of asynchronous machine, it deduces the relationship of wind turbine angular velocity rotation with the induction generator terminal voltage. Aiming at wind power for 10kV distribution grid, a novel SVC is proposed to replace the fixed capacitors compensating devices. The reactive power can be detected based on the instantaneous reactive power theory and with this method the reactive power compensation is fast and continuous. The voltage level of wind farm access system is stable with a voltage feedback control strategy. The new SVC winding structure can achieve a multi-pulse, injecting the system small harmonic current component. Research results show that a corresponding control strategy of the novel SVC compensation device can be very good to improve voltage stability of wind farm access to the grid.

Compensation strategy of switching dead-time effect based on frequency domain model

The problem of current waveform distortion because of dead-time inserted in power electronic applications is analyzed and researched in this paper, and the equivalent voltage source model is set up in to analyze the low frequency harmonic voltage because of dead-time effect. The control strategy of harmonic injection is proposed to compensate the current distortion due to dead-time effect. Firstly, obtains the application output current amplitude and phase of mainly harmonic current by Fourier transform, then calculates the compensation instructive voltage according to the connected inductor and dc voltage. Based on H-bridges cascaded static synchronous compensator (STATCOM), the experiment on a STATCOM based on digital signal processor (DSP) and (Field Programmable Gate Array) FPGA is implemented. The simulation and experimental results show that the proposed method is feasible and efficient to compensate the current distortion.

A Novel Hybrid Dynamic Reactive Power Compensator

A novel dynamic reactive power compensation circuit topology suitable for low voltage distribution system was proposed. The efficient compensation of unbalanced load could be realized by the structure of three-phase four-leg inverter circuit. The sinusoidal pulse width modulation (SPWM) control of inverter could ensure the low distortion of voltage and current. Besides, by the regulation of the inverters output voltage, the compensation reactive power could be dynamically regulated and the aim of systems zero reactive power compensation could be realized. Combined with fixed capacitor compensator, small capacity of inverter is required to compensate dynamic reactive power. The novel dynamic static var compensator (SVC) could improve the systems power factor and voltage stability. Finally, simulations are carried on the platform of PSCAD/EMTDC. The results show that the proposed control strategy is feasible and efficient.

Research of method for voltage sag source location in power system

Four existing voltage sag source location methods based on reactive power variation, slope of the system trajectory, real current component and distance relay are analyzed and compared in this paper. The distance relay method takes advantage of measured impedance as judging criterion and shows the best performance among them. This paper proposes an improved impedance calculation method, which uses the change rate of impedance magnitude and increment of impedance angle before and during the voltage sag event to compare with a reasonable threshold. The improved method has been verified in simulated power systems with different structures, including single-supply, double-supply and ring system. Finally, an application case occurred in an actual city power system in P.R.China is given and good characteristics of the improved method are confirmed.

Research on a Novel Series-Connected Voltage Fluctuation Generator

A novel voltage fluctuation and flicker generating main circuit topology is proposed in this paper, combined with passive and active to realize voltage fluctuation and flicker. The fundamental frequency power is supplied by system source and the other frequency fluctuation power is supplied by active components, so the capacitor of generator is easy to realize larger because of lower active loss. Full-bridge diode rectifier is adopted to maintain the stable DC-bus voltage, the later inverter is controlled by instantaneous value voltage and current double closed-loop to make sure good static and dynamic performance. The inverter output two frequency voltage waveforms, and added to fundamental frequency sinusoidal voltage waveform by transformer so that the typical sinusoidal modulation voltage fluctuation and flicker waveform is obtained. The simulation model is set up on the platform of Matlab/Simulink. Finally, the simulation and experimental results show that the proposed main circuit and control strategy is feasible and efficient.

A novel low harmonic dynamic static var compensator resaerch

A novel SVC topology is proposed in this paper, firstly a multi-winding transformer is adopt to realize 12 ripple, secondly the 5th harmonic filter on system bus as the fundamental reactive power compensation, and control thyristor controlled reactor (TCR) to realize inflow system reactive power, thirdly modularization design is adopted, according to the compensation reactive power only one TCR module is phase controlled. Finally, the experimental result shows that the novel TCR without an additional filter has the advantages of low harmonic, good static and dynamic performance, small volume and etc, compared to traditional TCR.

Analysis on Parameters Selection of Injection Circuit of Differentiation Cascade type Controllable Custom Power Quality Disturbance-Generator

Theoretical and simulated analysis on the injection circuit parameters of the Controllable Custom Power Quality Disturbance-Generator which is designed as differentiation cascade type has been done. The topology has three modules: fundamental-frequency module, high-frequency module and rectifier module. The theoretical analysis results have shown that the regulation precision of output of the fundamental-frequency module, the voltage level of the high-frequency module, the current tracking performance and the harmonic current circumfluence in the high frequency module will be influenced by the linking inductor of the fundamental-frequency module. The harmonic current output of the high-frequency module will be influenced by the linking inductor of the high-frequency module. Furthermore, taking a capacitor in series with the inductor in the injection circuit of the high-frequency module is an effective method to reduce the voltage level of the high-frequency module. However, this method will influence the amount of the fundamental frequency current that generated by fundamental-frequency module. The simulations have been carried out to show the correctness of the theoretical analysis and provide a reference for parameters selection of the injection circuit and the design of the devices control methods.

Simulation Research on the Multiple Objective Voltage Quality Regulator

Due to the complexity of power systems combined with other factors such as increasing susceptibility of equipment, power quality (PQ) is apt to waver. With electricity in growing demand, low PQ is on the rise, the method of resolve those problem about power quality must be considered. In accordance with the familiar PQ problem, such as voltage sag, voltage swell, short interruption of supply voltage, harmonic suppression and short circuit fault. Basing on the H bridge cascade connection method, this paper design a new type regulator for the multiple objective control. Through the simulation software of PSCAD/EMTDC, the device can resume the voltage and restrain the harmonic dynamically and effectively, when there are voltage disturbances in the power system side. This device also could confine the short circuit current to a supportable level, when there is short circuit fault in the load side.

Multi-objective Voltage Quality Disturbance Generator with Cascade H-bridges

A novel main circuit topology of voltage quality disturbance generator is proposed in this paper, composed of PWM rectifier and cascade H bridge inverter. The three phase inverter is decoupling controlled. The main advantage of the topology is a hybrid structure, the mainly power of voltage quality disturbance generator is supplied by system source and the small power is supplied by inverter, so the capacitor generator is easy to realize larger because of lower active loss. PWM rectifier is adopted to maintain the dc-bus voltage stably, the later inverter is composed of cascade H-bridges. The inverter is controlled by carrier phase shifting with FPGA. The simulation model is set up on the platform of PSCAD/EMTDC, the problems of voltage fluctuation and flicker, sag and harmonic is researched by theoretical analysis and simulation. Finally, the simulation and experimental results show that the proposed main circuit topology and control strategy is feasible and efficient.

Self-recovery comepensation strategy for dynamic voltage regulator

A new self-recovery compensation and control strategy suitable for dynamic voltage regulator (DVR) supplied by DC-capacitor was proposed. Two compensation stages which were transient compensation stage and recovery compensation stage were included in the strategy. The maximum energy compensation strategy which could maximize the exchange active power between the equipments DC-capacitor and its outside system was proposed to the recovery stage. Moreover, the double closed-loop control strategy with load voltage and filter capacitor current was used. A stages switching control strategy which took both of the DC-capacitor voltage magnitude and source-side voltage magnitude as the criterion was applied. The simulation results of EMTDC/PSCAD show that the voltage of DC-capacitor could be recovered to the nominal value as soon as possible with the proposed strategy. And the strategy could be suitable for the compensation of several times transient voltage disturbances in short period flexibly.