Research On Continuously Varying Capacitance Of Power Capacitors Based On PWM

The thesis presents a new method of continuously varying capacitance of power capacitors, which is based on the principle of PWM and power electronic device to solve the problem of capacitance discontinuity produced in switching the parallel-capacitors that is widely used in current power system. The principle of reactive power compensation and detection is introduced and the principle of continuously varying capacitance of power capacitors based on PWM is particularly analyzed. It can continuously vary the equivalent capacitance in the circuit through switching two capacitors under the control of two oppositional pulses in which duty cycle can be changed.The formulas of continuous varying the capacitance are deduced and the voltage of the capacitors, inductors and power electronic device used in the method is analyzed. The range of capacitance varying and the proportion of two capacitors are calculated. So the electrical criterion of choosing the devices in practice of reactive power compensation is provided.The simulation model is built with the SimPowerSystems in the MATLAB on the base of analysises in theory. The varying curve of the equivalent capacitance and the voltages of the capacitors, inductors and power electronic devices are simulated, and the method is proved.In this thesis, the hardware circuit of reactive power compensation controller is designed with the chip of TMS320VC33 of TI Corporation and CPLD of ALTERA Corporation on the base of theory analysis and simulation. The varying duty pulses for switching two capacitors are produced to compensate the resistive and inductive load. The experiments show that the method can compensate reactive power dynamically.