Study On Control Strategy Of Three Phase PWM Rectifier

Power electronics, especially power supply, has found an increasingly wide application in real life. There is a growing demand for the power quality provided by the power source. For common rectifier, the most important performance is providing stable output voltage and having less effect for the power grid. Based on many references, this paper focuses on researching the control strategy of the rectifier. Taking three phase voltage source rectifier as the research object, this paper mainly studies on voltage senseless control strategy based on proportional resonant(PR) controller and direct power control strategy based on model predictive theory.Due to coordinate transformation and inverse transformation needed by PI controller for conventional PWM rectifier and complicated calculation process, proportional resonance control based on internal model control is adopted in this paper. The current is regulated in two-phase stationary reference frame, which omits the processes of phase lock, rotated coordinate transformation and feed-forward decoupling. Besides, the optimal control parameters are able to be obtained according to the impact on the system by each parameter of PR controller. Generally, PWM rectifier needs various voltage sensors and current sensors. However, the more the sensors are, the more the cost of the system will have. In addition, more sensors will bring about detection errors in communication. Thus, virtual flux which can omit voltage sensors of AC side is adopted. In order to eliminate the DC bias of virtual flux, the measure that simple integrator is replaced by the integrator of saturated amplitude limiting feedback loop is adopted. Through the combination of virtual flux and PR controller, the voltage senseless control strategy based on PR controller is obtained, which has been proved feasible through simulation.The traditional direct power control strategy contains hysteresis controller which has a high sampling frequency and results in unfixed switching frequency. These are the major disadvantages of direct power control. To eliminate these drawbacks, model predictive control is adopted in direct power control strategy. Model predictive control can predict the active power and reactive power of the next switching period based on the current collected data of the switching period and makes them close to the power reference. Based on these theories, AC side voltage can be calculated. Then through SVPWM modulation, fixed switching frequency can be achieved and sampling frequency can be reduced correspondingly. By simulation, the correctness of theoretical analysis is proved.Comparing the effectiveness of the two control strategies, direct power control strategy based on model predictive theory matches applications better. This control strategy is chosen to be experimented on. The experimental platform is set up and the control programs are compiled in DSP chip. The experimental results certify the validity of this control strategy.