Study On The Parallel-processing Unified Power Quality Conditioner

With the rapid increase of electric power loads and capacity of unbalanced, impact, nonlinear loads, electric power quality problems in distribution systems have been more and more conspicuous. It exhibits broad prospect and very significance to improve the power quality. In this dissertation, one kind of unified power quality conditioner is analyzed and studied systematically.Parallel-processing topology of main circuit is determined according to the functional demands of the studied system. In the designed system, SMES coil is utilized as energy storage component, current source inverter (CSI) is used to accomplish DC-AC conversion. The main functions of the system are to eliminate the influences of source voltage sag and flicker on load voltage, and to restrain the influences of non-linear load and unsymmetrical load on supply current. The factors influencing the system performance are analyzed, according to which the parameters of the main circuit are designed.The operating principle of the system is established. According to the request of power quality standard, a system power regulating strategy is proposed, i.e. the load voltage is maintained by adjusting the reactive power of the inverter in the half main frequency cycle after the source voltage sag occurrence, the system operating performance is optimized. Direct current PWM control strategy is chosen to realize the DC-AC conversion of the current source inverter, which makes the system control more convenient.The system mathematic model is established, by which the system control strategy with decoupling and feedforward compensation of d/q components under synchronous rotating coordinate system is studied. Furthermore, after being extended and modified, the said control method is adapted to other functions of the system.The proposed system structure and control method are verified by simulation.