The Main Circuit Topology Of Novel Unified Power Flow Controller And Its Application Study In Two Phases Operating

Unified power flow controller (UPFC) is one of the most powerful and most promising controllers of FACTS. If we use UPFC to control the transmission parameters, terminal voltage, line impedance and phase angle in normal situation and use it to compensate zero sequence and negative sequence currents when one of transmission lines is cut off, we can implement two phases operating in high voltage transmission lines, which can improve stability and reliability for the transmission system.There is no literature that discusses using UPFC to compensate zero sequence and negative sequence currents and conventional UPFC is three-phase three-wire, which cannot deal with zero sequence current, so we must improve the conventional UPFC in order to add a function of zero sequence and negative sequence currents compensation. The improved UPFC is called novel UPFC. The following is the main works and conclusions of this thesis.The novel UPFC needs high power rate because it is generally used in high voltage transmission lines. After studied high-power converters and the literatures of UPFC, the main circuit topology of novel UPFC base on diode-clamping multilevel inverter is presented and the principle of using novel UPFC to eliminate zero sequence and negative sequence currents is analyzed.The detecting techniques of harmful currents, the modulation methods of novel UPFC and the balancing control of capacitors voltage on DC link are studied thoroughly. In order to be fit for three-phase four-wire system, the method of balancing control using chopper presented in literature [29] is mended. The new standpoint that ip-iq detecting method based on three-phase three-wire system can be directly used in three-phase four-wire system is presented and proved. Generalized harmful currents compensation based on multilevel converter and multi-band hysteresis pulse width modulation with timer are presented. The validity and superiority of all these are proved by use the parallel converter of novel UPFC to implement reactive current compensation, zero sequence and negative sequence currents compensation, harmonic currents compensation and the mixed compensation of them.This thesis also studies that use novel UPFC to implement two phases operating in high-voltage transmission lines by theory analyze and simulation testify. The simulation models in MATLAB are established and the results of simulation testify the correctnessand the superiority such as equivalent switch frequency, EMI and energy dissipation are low, the performance of harmonics is fine, it suits to high-power application, etc.