A comparison based harmonic elimination method with digital control of fundamental amplitude

A common technique employed to eliminate switching harmonics is programmed SHE (Selective Harmonic Elimination) which requires the solution of a set of nonlinear equations. Typically, the method calculates the switching angles for each modulation depth offline using iterative computations and programmed into a digital processor. These values are recalled on a need basis for a particular application and the look up table has limited choice. Here we are proposing a comparison based method where a modified reference signal is compared against a sinusoidal carrier to generate a PWM (Pulse-width Modulation) signal which is free of the undesired harmonics. The modified reference intersects the carrier only at the desired switching angles. The distinguishing advantage of the method is that no digital processor is necessary and the fundamental amplitude can be varied continuously by inputting the desired modulation depth ratio. The present work has eliminated dc to 5th harmonic and research is continuing to expand the baseband floor. The new method has the potential in inverter applications where inverter power can be adjusted continuously to match the load power and thus perform the function of the MPPT controller in PV applications. Simulation and experimental results provide validity of the approach.