Zhongdong Yin

Study on controllable reactor magnetic structure and loss based on ANSYS

Controllable reactor is an important voltage control and reactive power compensation device in power system which is wide range voltage application, high reliability, low harmonic and simple maintenance, etc. The reactor iron core magnetic field distribution directly affects the reactors loss and other properties. In this paper, aiming at six kinds of typical controllable reactor core structure, magnetic field is analyzed in theory and then the core magnetic field distribution analysis are compared for the first time by model building in the finite element analysis software ANSYS and imposing different exciting currents. Moreover, six kinds of core structures loss are compared by the use of the ANSYS inner set loss algorithm and the influence of excitation on the loss for a particular core is verified. The analysis results indicate that finite element analysis software can effectively analyze and compare the magnetic field distribution and the loss for different kinds of reactor core structure.

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.

Study on power factor through the similarity of waveform

With the rapid development of electric electronic technology, non-linear loads, large capacity converters, etc. increase mostly, which brings about the serious problems such as harmonics. Thus, the traditional power theory based on the average is unable to meet with the practical require. In this paper, the power definition in the sinusoidal and non-sinusoidal circuit is discussed and the waveform similarity between voltage and current is analyzed due to the criterion of minimum mean square deviation. Furthermore, the relationships among the waveform similarity factor, displacement power factor and real power factor are also discussed. The results show that power components are well analyzed in use of waveform similarity under the conditions of non-sinusoidal. At the same time, waveform similarity provides a simple but effective method for the calculation of power factor.

Design of voltage unbalance generating device based on negative sequence injection method

Single-phase large-capacity loads, such as electrified railways, electric arc furnaces, welding machines and so on, will exert influences on the power quality of the power system. As one important problem of them, three-phase unbalance may thereby endanger the safety of various types of electrical equipments. In this paper, reasons and hazards of three-phase unbalance are analyzed. According to the measurement method based on symmetrical components, the three-phase unbalanced generating device is designed. Its main circuit topology is electric power converter of AC-DC-AC with cascaded H-bridge units. The novel method of injecting the negative sequence components is used to simulate voltage unbalance disturbances. The correctness and effectiveness of the device and control algorithms are verified through experiments. This is of great significance for the development of three-phase unbalance compensation device and power quality control equipment and thus to improve the power quality.

A Survey on the Principle and Control of Dynamic Voltage Restorer

With the development of information and automation techniques, dynamic voltage problems are once again in the spotlight. Dynamic voltage restorer (DVR) is a modern and important custom power device used for mitigating voltage sags in power distribution systems. The operating principles, structures, and control strategies of DVR are surveyed and compared in the paper after investigating a large amount of DVR references in conferences and science periodicals. Meanwhile the application future of DVR in power system and several problems which need to solve are proposed.

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.

Series-Connected Hybrid Cascaded H-Bridge Voltage Disturbance Generator

A novel main circuit topology of voltage quality disturbance generator is proposed in this paper, mainly consisted by low-frequency cascaded H-bridge and high-frequency H-bridge modules. The topology is a hybrid structure, the mainly fundamental power of voltage quality disturbance generator is supplied by the system source and the small part of fundamental power is supplied by the inverter. The low frequency cascaded H-bridge inverter output fundamental waveform and voltage fluctuation and flicker waveforms, while the high-frequency H-bridge inverter output harmonic voltage waveforms, then the decoupled control of voltage disturbance is achieved in order to make sure the good dynamic and static performance. The low-frequency cascaded H-bridge is controlled by carrier phase shift and the high-frequency H-bridge is controlled by high-frequency SPWM with FPGA.

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.