Optimal surplus harmonic energy distribution [in PWM invertors]

A new optimal programmed PWM technique is described. The voltage total harmonic distortion at the output of an L-C filter connected to a PWM inverter is minimized. The proposed technique can be directly applied to constant frequency, constant amplitude sinusoidal power supplies such as uninterruptible power supplies. Without any hardware changes, the new method allows for more than 20 percent smaller THD than the general programmed PWM method. Other indexes that are functions of surplus harmonics, such as acoustic noise, heat losses, torque and speed ripples, can be optimized using the new method. A new model of nonconstraint optimization is developed for the proposed method. It is shown that this model includes both double-level and triple-level PWM waveforms. An energy conservation principle is applied to the model to prove and explain the optimization possibility. An energy conservation based algorithm for obtaining an optimization starting point is demonstrated. A numerical example of triple-level optimal programmed PWM waveforms for single-phase applications is presented.