The Research And Design Of Three Phase Double PWM Variable-frequency Power Source

The variable-frequency power source can change voltage's magnitude, frequency and phase and the quality of power can be improved. But the common variable-frequency power source that uses uncontrolled rectifier leads low power factor, high harmonic and its application is limited. Double PWM variable-frequency power source uses controllable valve device and the rectifier is controlled by PWM technology, so the harmonic pollution to power system is decreased and the power factor is improved. And the regeneration power can be carried to the power system.The three-phase double PWM variable-frequency power source can be divided into the PWM rectifier and the PWM inversion two parts. In this article the three-phase PWM rectifier structure and its control method is analyzed deeply based on the introduction of the double PWM variable-frequency power source topology. The principle how the PWM rectifier is able to work in the rectification and the contrast is analyzed and the key to control the net side electric current is obtained. The switching functions are used to carry on mathematics modeling and the mathematic module of the PWM rectifier in d-q synchronization reference frame is obtained through the coordinate transformation. Then according to the systems control goal, the voltage and electric current double closed-loop control structure is used to carry on the control to the PWM rectifier. The PWM inversion uses the vector control to realize the electrical machinery velocity modulation and the torque control. The control structure constitutes by the speed outer ring and the electric current inner rim. The speed outer ring is used to control the speed and the electric current inner rim is used to control the electrical machinery's torque control.In the theoretical analysis foundation, the double PWM variable-frequency power source system simulation model is built by the MATLAB simulation toolbox and many simulation experiments are done. The simulation results show that the output DC voltage and the net side input alternating current can be controlled effectively. And performance of PWM inverter is acceptable.