Research on Power Quality of Critical Loads of Single-phase Four-level Electric Spring

Aiming at the problems of the traditional Electric Spring (ES), which has a large harmonic content of the critical load voltage when the grid voltage fluctuates, as well as the low DC-side voltage utilization under the topology of the traditional H-bridge inverter, this paper proposes a topology structure of single-phase four-level ES, introduces the control strategy of ES based on this topology, and studies the modulation strategy of this topology. Based on this modulation strategy, four working principles of the topology are analyzed, Fourier series of inverter output voltage of the single-phase four-level Electric Spring is derived, and DC side voltage utilization rate is calculated, indicating that the DC side voltage utilization rate is increased by 42.5%. Finally, simulation results with MATLAB/Simulink show: Under the same control strategy, compared with the traditional ES-2, the Total Harmonic Distortion (THD) of the critical load voltage of the Single-phase Four-level Electric Spring decreases by 0.12% when the electrical grid voltage fluctuates. The effectiveness of Single-phase Four-level Electric Spring for improving power quality of critical loads is verified.