Optimizing DC Link Capacitors in Three-Level Voltage Inverter Based on Space-Vector PWM with Seven-Stage Switching Sequence

The voltage imbalance of the neutral point (NP) of the DC link is one of the key factors restricting the use of three-level autonomous voltage inverters with a fixed neutral point in electric drive systems. The NP voltage imbalance leads to reduced inverter output voltage (current) quality and increased voltage surges in DC link capacitors, which inevitably affects the reliability of the power elements of the inverter circuit. Reducing the NP voltage imbalance requires increasing the capacitance of capacitors, which, in turn, results in the greater weight and dimensions of the three-level inverters, as well as increased costs. To solve this problem, the authors of this paper suggest a new control algorithm for the three-level inverted based on space-vector PWM with a seven-stage switching sequence (SS) that facilitates a threefold reduction of DC capacitor capacitance compared to the conventional algorithm due to controlling the duty factor of distributed base vectors in each of the PWM period based on the displacement angle and load data. This article presents a calculation procedure for the operating time of the base vectors in the seven-stage SS, taking into account the impact of small and medium base vectors and load parameters. The efficiency of the proposed algorithm is confirmed with computer modeling in MatLab & Simulink. The proposed algorithm provides a significant improvement in the technical parameters of three-level voltage inverters, especially in high-power electric drive systems.