Analytic Overmodulation Method and Application to IPMSM Current Control

An overmodulation (OVM) technique is proposed based on Fourier analysis. The OVM trajectory is a mixture of 6 arc segments of the inscribed circle and 6 vertices of the voltage hexagon. By adjusting the dwell time at each vertex, the modulation index is determined. The fundamental component is expressed as a function of the dwell time, and the linearity with the modulation index is obtained by the inverse relation. This algorithm guarantees seamless transitions from the space vector PWM (SVPWM) to OVM and finally to the six-step. Apart from the VVVF control, the proposed algorithm works well with the interior permanent magnet synchronous motor (IPMSM) current controller. By computer simulation and experimental evidences, the effectiveness is demonstrated.