Fast SHEPWM Solution Method for Wind Power Converter Based on State Equations

Selective harmonic elimination pulse width modulation (SHEPWM) is a modulation strategy widely used for three-level wind power grid-connected converters. Its purpose is to eliminate specified sub-low frequency harmonics by controlling switching angle. Furthermore, it can reduce fluctuation of the microgrid system and improve system stability. Intelligent algorithms have been applied to the SHEPWM solution process to mitigate calculation complexity associated with the algebraic method, as well as the need to set the initial value. However, disorder of the optimization result causes difficulty in satisfying incremental constraint of the three-level NPC switching angles, and affects the success rate of the algorithm. To overcome this limitation, this paper proposes a fast SHEPWM strategy to optimize the result obtained by the intelligent algorithm. The SHEPWM can be realized by solving switching angles through a state equations-based mathematical model, which is constructed by using the initial variables randomly generated by the intelligent algorithm as the disturbance. This mathematical model improves the success rate of calculation by simplifying constraint representation of switching angles and solving the disorder problem of the optimization result. At the same time, a method based on the circle equation and the trigonometric function is applied to the initial variable assignment of the state equation, which further improves the speed and accuracy of the solution, realizes a more thorough filtering effect, and further reduces the impact of sub-low frequency harmonics on a wind power integrated system. Finally, simulation and experiment results have been used to prove the effectiveness of the proposed SHEPWM strategy when combined with intelligent algorithms.