Performance Improvement of Direct Power Control of PWM Rectifier With Simple Calculation

Conventional switching-table-based direct power control (STDPC) presents irregular power ripples and variable switching frequency, due to the use of predefined switching table and hysteresis comparators. This paper proposes an improved DPC for three-phase pulsewidth modulation (PWM) rectifier with simple calculation. The concept of duty cycle control is introduced in DPC to allocate only a fraction of control period to the voltage vector selected from conventional switching table in DPC, while a null vector is applied for the rest of time. The main advantages of the proposed duty cycle control are twofold. On one hand, it is independent of rectifier parameter such as line-side inductance, hence strong robustness against inductance variations is obtained. On the other hand, the principle to obtain the duty cycle is very simple and easy to implement. Compared to conventional DPC, significant power ripple reduction and more sinusoidal grid current can be observed in the improved DPC. The presented simulation results and laboratory tests validate the effectiveness of the proposed method.