Study On Controllable Load In Power System Dynamic Simulation

Power system dynamic simulation, in which the models of power system with similar characters are studied in labs for relating principles in power system, is a kind of physical simulation for study of dynamic characteristics of power system.The existing models for power system load include non-synchronic motor load models, lamp box load model and so on. Load can be changed in a certain range by altering resistance in series circuit, changing the field excitation for motors or increasing and decreasing its additional wheels. However, some defects occur like its huge volume, numerous parts, high costs, no feedback of energy and uneasy alternation online. Nowadays, there are many studies on simulation load among which there is little model for power system dynamic simulation.In this paper, a novel design on controllable load based on PWM rectifiers is presented based on analysis of non-principle load model which focuses on the amplitude and phase of current sent by generators. In the design, PWM rectifier A, capacitor, and PWM rectifier B are paralleled and rectifier B is connected to power network by transformer. They are considered as the load of generators.As the main units of controllable load, the mathematics models of three phases PWM rectifier are analyzed in detail and design methods for double loops control systems of PWM rectifier are discussed in this paper.In this design, three phases bridge A with fixed switching frequency PWM with voltage feedforward control is in charge of changing character of load. Three phases bridge B with hysteresis loop control, which output pure active power to power network, is in charge of controlling resistance of load. The design is simulated by MATLAB Simulink, and some simulation waveforms in different conditions are gained to demonstrate its feasibility and availability.In addition, the hardware structure of the control unit in controllable load is presented in the paper.