| In order to obtain the maximum fundamental output voltage from a three phase inverter, a transition from PWM to six-step mode needs to be done. Because of the nonlinear behavior of this overmodulation range, different methods have been proposed to linearize it. Those methods use complex equations and look-up tables, limiting their application to powerful microprocessors with considerable amount of memory. In this thesis an overmodulation method is proposed, which has a perfect output linearity and requires only linear equations for implementation. This method can be applied to both sinusoidal and space vector PWM. A new method to calculate the modulation index from the instantaneous phase values is also proposed. Mathematical analysis, simulations, real microprocessor implementation, and a stand-alone digital design are presented here to demonstrate the effectiveness and simplicity of the proposed method. |
