Improving the quality of the output quasi-sinusoidal voltage in a bridge inverter

Abstract

The possibility of decreasing the level of higher harmonics in the spectrum and improving the shape of the output quasi-sinusoidal voltage in a bridge inverter by deforming the shape curve of the trapezoidal voltage fronts of half-bridge converters is investigated. A generalized analytical expression for the function of the shape of the trapezoidal stress fronts is proposed, which has the ability to modify the function by the strain parameter. The influence of the deformation parameter and the duration of the fronts on the conditions for selective suppression of harmonics closest to the fundamental are analyzed. An optimal combination of the values of these parameters is determined, which makes it possible to achieve complete suppression of the higher harmonics and the formation of a theoretically ideal sinusoidal form in the output voltage of the inverter. Graphic dependencies are given that allow finding a compromise between the spectral composition of the output voltage of the inverter and the dynamic losses in the switching elements. The theoretical analysis is confirmed by the results of experimental verification. The theoretical results were verified experimentally on the layout of a bridge inverter with an output power of 1 kW. With a sinusoidal form of trapezoidal stress fronts with front edge duration of 0.94 radians, the minimum harmonic coefficient was 2.1%. In the transition to the optimally deformed shape of the fronts with a strain parameter of π/6 and a front duration of 1.05 radians, the harmonic level decreased to 0.8%.