Error Tolerance Analysis for SHE-PWM Calculation in a 3L-NPC Converter

Medium-voltage high-power converters are usually modulated using low switching frequency techniques such as Selective Harmonic Elimination - Pulse Width Modulation (SHE-PWM) in order to improve their efficiency. To calculate the firing angles, SHE-PWM transcendental equations are usually solved by offline calculation methods, whose computational burden depends on the number of firing angles or eliminated harmonics and the required accuracy in the solutions. Consequently, with the aim of reducing this computational burden, this paper presents an analysis that estimates the maximum accuracy required in the calculated SHE-PWM solutions considering the main non-idealities of the converter. In this sense, a systematic methodology to evaluate the error in the harmonic amplitudes due to control and dead time effects has been developed, providing an optimal error tolerance for the calculation methods that solve the SHE-PWM problem.