Closed loop operation of the harmonic cancellation technique

The proposed modulation technique, harmonic cancellation, aims to reduce the output voltage THD in AC power supplies generated by means of an inverter, when they are supplying non linear loads. Its operating principle is grounded in the proper pre-distortion of the inverter output voltage. It means that the inverter must generate a specified fundamental component and some controlled harmonics, which added to the ones across the filter inductance, they cancel each other out. The switching events are determined analytically for given operating conditions and stored within a control table. Along the present paper, the control strategy will be presented. The proposed final control scheme is able to select the proper switching pattern which guaranties the cancellation of the low frequency content due to the non linear load operation and the desired rms output voltage. The effect of considering the parasitic voltage drops within the calculus of the switching events is shown through simulation results. Additionally, the robustness of the overall system performance against non considered parasitic voltage drops and against load steps are also shown.