Balance Midpoint Potential Control of Three-Level Boost Converter for Rail Transit Application.

The application of the three-level boost converter (TLBC) in a high-frequency isolated auxiliary inverter system is able to reduce the voltage stress of power switches and diodes in the back-end circuit, reduce the volume and weight of energy storage components, and improve the overall power density of the converter system. However, the TLBC topology has its own disadvantage which is the capacitor midpoint potential offset problem. In order to solve this problem, this paper analyzes the limitations of the traditional independent duty control strategy first and then proposes the pulse phase delay control strategy to balance the midpoint potential of TLBC. After the relevant theoretical analysis based on the ac small-signal model of the TLBC, which is controlled by the pulse phase delay control strategy, this paper completes its modeling and simulation by using PSIM & Matlab. Finally, this paper presents some experimental results and combines with the waveforms of the simulation to verify that the proposed control strategy can effectively adjust the bias voltage without changing the TLBC output characteristics.