A SVPWM/SHEPWM combined modulation strategy of starting inverter for a high speed generator power system

Recently more attention has been paid to the distributed power systems due to their high flexibility and reliability. The high speed permanent magnet (PM) generator driven by micro-turbine has been widely investigated since it has small size, high efficiency and power density. Since the micro-turbine cannot be self started, the PM generator has to operate as a motor for the system staring, which needs an inverter to drive the PM motor. The normal DC/AC conversion through normal inverter will generate harmonic currents in the generator winding which will cause additional loss and increase temperature rise of the generator. To reduce the current harmonics of high speed generator, a SVPWM and SHEPWM combined modulation strategy is adopted. Small signal model is analyzed and transfer function matrix is deduced. The structure and control strategy of a combined PWM inverter is introduced in this paper. The simulation and experimental results show the feasibility of the proposed design and control strategy.