An optimized SVPWM switching strategy for three-level NPC VSI and a novel switching strategy for three-level two-quadrant chopper to stabilize the voltage of capacitors

This paper also presents a novel and optimized SS and control approach for a 3L two-quadrant (2Q) chopper in NPC VSI superconducting magnetic energy storage (SMES). Using the proposed SS, the voltage of the VSI capacitors in SMES can be independently controlled; also, the minimum power and switching losses - as well as the proper convection - can be achieved using this same strategy. The simulation results indicate that when combined with a proportional-integral (PI) control approach the proposed SS can be easily implemented in the power networks and can balance and stabilize the multi-level VSIs' capacitor voltage level. The voltage variation of the capacitors in the steady state condition is less than (0.062%) which is 15 times better than the IEEE standard requirement (1%). To investigate the effectiveness and reliability of the proposed approach in stabilizing capacitor voltage, SMES performance using the presented approach is compared with that of SMES when the capacitors of the 3L VSI are replaced with equal and ideal voltage sources. This comparison is carried out from the power quality point of view and it is shown that the proposed SS with a PI controller is highly reliable.