Research on carrier modulation algorithm for a three level four-leg microgrid inverter based on zero sequence component injection

The inverter is a critical interface for microgrids, pivotal in the new power system amidst the push for “Carbon Neutrality.” The modulation strategy is essential for ensuring stable operation for power electronic inverters, significantly influencing performance metrics. In this article, a carrier based pulse width modulation (CBPWM) algorithm with zero-sequence component injected based on conventional SVPWM is proposed for a three level four-leg inverter. The method uses synthesized space vectors in SVPWM to compute the modulating waveforms required for CBPWM, which solves the complexity of sector condition determination and the tediousness of switching vector action time computation in the conventional four-leg inverter SVPWM algorithm where vectors space is three-dimensional space. The proposed algorithm simplifies the calculation. When the output frequency is 50 Hz and the TMS320F28335 DSP is used as the controller, compared to SVPWM, CBPWM remarkably reduces the computational time by approximately 95%. By eliminating the sector division in the proposed method, the THD of the output voltage of the inverter decreases to different degrees under different load conditions, especially for resistive-inductive loads, the proposed method reduces the THD of output voltage of the inverter exceed 2%. Finally, the feasibility and effectiveness of the method are verified by MATLAB/Simulink simulation and experimental results.