Distortion and regulation characterization of a Mapham inverter

Output-voltage total harmonic distortion (THD) of a 20 kHz, 6 kVA Mapham resonant inverter is characterized as a function of its switching-to-resonant frequency ratio, f_s/f _r, using the EASY5 Engineering Analysis System. EASY5 circuit simulation results are compared with hardware test results to verify the accuracy of the simulations. The effects of load on the THD versus f _s/f_r is investigated for resistive, leading, and lagging power factor load impedances. The effect of the series output capacitor on the Mapham inverter output-voltage distortion and inherent load regulation is characterized under loads of various power factors and magnitudes. An optimum series capacitor value which improves the inherent load regulation to better than 3% is identified. A fault protection and current limiting method which allows the Mapham inverter to operate into a short-circuit, even when the inverter resonant circuit becomes overdamped, is discussed