The Control Method And Realization On Parallel Connected Compound Power Quality Disturbance And Compensation

Main circuit configurations and control strategies for compound power quality disturbance generation (PQDG) and compensation in shunt connection are the major research subjects of this dissertation. Analysis, simulations and experiments are all carried out, and major achievements of these researches are as followed.(1) Different from traditional power quality devices mainly aiming at reactive power problems such as harmonics and voltage fluctuations, a novel circuit topology based on back-to-back H-bridge modules is proposed for three-phase four-wire power quality devices, so that they have the capability of active power regulation. The pulse width modulation (PWM) rectifier modules are in shunt connection through a single-phase multi-winding transformer to increase the input current capacity. The inverter consists of N+1 H-bridges and N of them are cascaded in order to increase the voltage level, which is helpful for realizing modularization and larger capacity. The rest H-bridge is differently connected for decoupling control of fundamental and harmonic current controls.(2) A novel simulation system for three-phase four-wire large power controllable power electronic load (PEL) is proposed on the basis of the shunt-connected PQDG. An open loop control strategy based on orthogonal voltage vectors was realized for ac PEL, and then a closed loop control strategy based on d-q coordinates for power factor (PF) control is proposed, by which the PF can be accurately controlled from 0 to 1.0, either leading or lagging.(3) In the harmonic currents'generation, an open loop control strategy based on voltage source converter (VSC) model is proposed for cascaded main configuration. Harmonic voltage outputs by the inverter will cause harmonic currents injected into the power system through the connecting reactor, and the control may be realized easily in such simple structure. Hysteresis loop control of the reactor's current, another closed loop control strategy based on current source converter (CSI) model, is proposed for different connected circuit configuration, which allows decoupled control of fundamental and harmonic currents.(4) On the basis of sinusoidal waveform modulation analysis of current fluctuations, conclusion comes that the inner harmonic current is an intrinsic reason of current fluctuation. The mathematic relationship of inner harmonic frequency and fluctuation frequency is derived. The occurrence of low frequency fluctuation in a current may be checked by root mean squared (RMS) values of the current calculated by iteration. The Discrete Fourier Transform (DFT) using multi-cycle current data also used for output current analysis. Simulation and experimental results show the correctness of the theoretical analysis and mathematic derivation for the inner harmonic current and current fluctuation.(5) Use the research of PQDG for reference, a control strategy of power quality compensation (PQC) that intends to reduce the compound disturbance to zero is proposed, which is simple in detection and easy to be realized. To avoid the shifting of steady-state working point, some improvement is made. The introduction of closed loop control providing zero current in d-axis improves the compensation effect without increase difficulty to realize.(6) Simulation models of shunt-connected compound PQDG and PQC are established in PSCAD/EMTDC, and many kinds of problems in PQDG and PQC are examined. A 400V/100kVA prototype with DSP and FPGA digital control system is developed for experimental research of PQDG and PQC. The simulation and experimental results show that the proposed main circuit topology and control strategies are feasible and effective.