Switching Frequency Minimized Harmonic Mitigation: A Multiobjective Optimized Modulation Strategy for High- Power Converters

In order to explore the minimum switching frequency required to regulate certain amount of harmonic components, a novel switching frequency minimized harmonic mitigation (SFMHM) model is proposed in this article, which can regulate $ {N}\mathbf{-1}$ harmonics with far less than N switching angles. By flexibly adjusting the threshold values, the proposed model can achieve both harmonic elimination and mitigation objectives. Based on pulsewidth modulation (PWM) discretization and supported by quadratic programming, the switching frequency in the proposed model is expressed as a quadratic objective function of the PWM waveform. The objectives as fundamental control and selected harmonic mitigations are realized by treating the numerical approximations of the Fourier coefficients as constraints, which are finally transformed into an optimization model with binary variables and can be easily solved by some optimization toolboxes, such as YALMIP. Some computing results show that, compared with the conventional selective harmonic elimination/mitigation (SHE/SHM) methods, the number of switching angles required to mitigate the same number of harmonics under the proposed method has been significantly reduced. The switching frequency can be reduced a lot compared with the conventional SHE/SHM methods, e.g., by 40% for some modulation indexes. Simulations and experiments verify the correctness of proposed SFMHM model.

I. Introduction

High-power converters play an indispensable role in modern industry [1], [2], [3], [4], [5]. For high-power applications, the switching frequency and the associated switching losses are crucial concerns, where a high switching loss can induce a number of problems, such as lower conversion efficiency and additional requirements for heat dissipations of the semiconductor devices [6]. Although a lower switching loss can be effectively achieved by reducing the switching frequency, it makes the output harmonics move to low-frequency range, which can reduce the output power quality, and increase the volume and weight of the output filters significantly. Therefore, the minimization of switching frequency and its associated switching loss, as well as the development of efficient and cost-effective solutions with good output waveform qualities remain a significant challenge for high-power converters.