Research On Bridge Arm Current Equalization Scheme Of Multi-level Current Source Converter

Multilevel current source converters play an important role in new energy systems,but the current on the DC inductor will be unbalanced with modulation and control mode.This article aims to study the problem of the imbalance of the upper and lower bridge arm inductance current caused by circulating current in multi-level current source converter.The article improves the way of selecting zero vectors and then improves the control algorithm for the voltage magnitude of the center point in the upper and lower bridge arms to achieve the purpose of controlling the balance of the upper and lower bridge arm currents.First,the article analyzes the working principle of current source converter,establishes mathematical models of current source converter in three-phase stationary coordinate system,two-phase stationary coordinate system and two-phase rotating coordinate system,and makes extensions on this basis to model and analyze multi-level current source converter.Secondly,it analyzes the sine pulse width modulation and space vector modulation technology of current source converter,and accurately analyzes the change of switch loss caused by space vector offset caused by filter.Further discussion on circulating current phenomenon of multi-level current source under space vector modulation is carried out.Based on this phenomenon,a zero vector selection strategy for suppressing circulating current of multi-level current source converter is proposed,so as to balance the inductance current of upper and lower bridge arms and reduce the loss problem caused by inductance current imbalance.In this paper,a three-layer closed-loop control strategy for a single current source converter is designed under dq coordinate system,and feedforward control is added to each link in three closed loops.It is further extended to multi-level current source converter.Then,MATLAB software is used to simulate three-layer closed-loop control strategy and zero vector selection strategy for balancing upper and lower bridge arm currents of multi-level current source converter.On this basis,its dynamic and steady-state characteristics are analyzed.Finally,a single current source converter system is designed and built,and some experimental research is carried out on SVPWM modulation strategy and three-layer closed-loop control algorithm applied in single current source converter based on TMS320F28335 DSP and Xilinx XC6SLX9-2TQG144 C FPGA control circuit.