Research on Neutral Point Potential Balance of Three-phase Three-level Vienna Based on Improved Fuzzy Control

Abstract

The three-level VIENNA rectifier has been widely used and researched due to its relatively simple structure and superior performance. However, due to the design of its topology, the inconsistent charge and discharge of the upper and lower capacitors on the output side of the circuit causes the midpoint potential between the two capacitors to shift. As a result, the midpoint voltage fluctuates and is unstable, which makes the safe operation of the rectifier hidden danger. Aiming at the problem of instability of the midpoint potential, this article analyzes the influence of each vector on the midpoint potential during the adjustment process in the SVPWM control process to find out which vectors will cause the midpoint potential to shift, and then increase or reduce the control amount of the corresponding vector, so the calculation of the control amount will affect the final control effect. Therefore, by improving the fuzzy control, the proportion and integral terms of the output of the fuzzy controller are separated and adjusted according to the deviation to improve the accuracy of the control quantity. And perform MATLAB simulation, the simulation results verify that the control strategy can effectively improve the stability of the midpoint potential.