Analysis of modulation strategy in six-phase synchronous wind generator vector control system

To determine the best modulation strategy in six-phase synchronous generator wind power system, the performances of three continuous modulation strategies are analyzed and compared. After analyzing switching voltage vectors distribution and the dwelling time determination for three continuous modulation strategy, namely, sine pulse width modulation (SPWM), dual three-phase space vector pulse width modulation (D3SVPWM), and maximum four vectors six-phase vector pulse width modulation (6SVPWM), the comparison results of switching times in one fundamental period and maximum modulation index are obtained. By analytical deducing and graph theory, the current ripple characteristics of three continuous modulation strategies are analyzed and compared. The comparison results show that the switching frequencies of SPWM and D3SVPWM are half of that of 6SVPWM when the sampling frequencies are equal; the DC voltage utilization rates of D3SVPWM and 6SVPWM are 1.155 times that of SPWM. When the equivalent inductance ratio of two sub-planes is no larger than 10, the current ripple of D3SVPWM is smaller than the other two modulation strategies. Overall, the performance of D3SVPWM is the best of all three continuous modulation strategies, which is verified by both simulation and experimental results. ©, 2014, Science Press. All right reserved.