A Study On Application Of Controllable Load Simulator In Power System Dynamic Simulation

Power system dynamic simulation,in which the models of power system based on Principle of Similarity are established in labs for testing the interrelated new theories, technologies and equipments,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, series-parallel capacitor load models and so on.Load can be changed in a certain range by changing the voltage,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.So time-varying power system load can't be simulated accurately, and it also caused a lot of inconvenience in dynamic model experiment.Considering the diversity and time-variation of power system load, a design of controllable load,which is applied to power system dynamic simulation, with dual three phases bridges structure and PWM control strategy is presented in th is paper. In this design, a hardware circuit of controllable load is constructed with a series of all-controlling power electronic devices (IGBT) and small storage devices (capacitance),and it realizes the desired characteristics of the load by real-time control algorithm to open and close the switch device.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 is in charge of adjusting the phase of current outputted by generator.Three phases bridge B with hysteresis loop control,which adjust active power to power network to adjust active power outputted by generator inndirectly,is in charge of changing the resistance of controllable load by coordinating with three phases bridge A.In the paper,its effectiveness and advantage are proved by simulation experiment using MATLAB/Simulink which got related simulation waveforms.