Neutral Point Voltage Balance Based on Space-Vector PWM with Five-Stage Sequence for Three-Level Voltage Inverter

The article proposes a new algorithm for space vector PWM (SVPWM) with a five-stage switching sequence (SS) providing a neutral point (NP) voltage balance for a three-level neutral point clamped voltage source inverter (3L NPC VSI). The proposed algorithm uses a five-stage SS to provide the lowest level of switching losses in the inverter power switches. The paper considers four combinations for building five-stage SS with different impacts on the NP voltage. In this case, the NP voltage control is done by switching between various five-stage SS combinations. The effectiveness of the proposed algorithm is confirmed on the basis of computer simulation in the MatLab & Simulink environment. Experimental dependences of the relative NP voltage error to the modulation coefficient and cosφ of the load for the proposed and well-known SVPWM algorithms with five-stage switching sequences are provided. The results showed that the proposed control algorithm 2.4 times reduces the maximum level of the relative NP voltage error. This makes it possible to balance the voltage of the three-level power supply and, as a result, improve the operational reliability of the 3L NPC VSI.