전압 밸런싱 기능을 갖는 바이폴라 타입 DC-DC 컨버터

Abstract

DC microgrid has no reactance components, so it does not generate reactive power, is easy to connect to the grid, and can maximize efficiency through fewer power conversion steps. The configuration of DC microgrid is classified into unipolar, bipolar, and multipolar. Bipolar consists of three lines and is classified into positive, neutral, and negative voltages, allowing three different voltage levels to be utilized. This structure can lower the rated voltage of semiconductor devices and prevent the spread of accidents by not affecting the other pole even if an accident occurs on one pole. However, compared to unipolar, the transmission capacity is low and there is a risk that power quality may be impaired due to voltage imbalance. As a way to resolve voltage imbalance, a power conversion device called a voltage balancer is connected to the DC side of the converter on the system side. However, the voltage balancer has the limitation that when the load is concentrated on one voltage pole, a large voltage difference occurs, which may cause the device to fail, and only serves to reduce voltage imbalance. Thus, this paper proposes a bipolar type DC-DC converter with voltage balancing function. The proposed converter can simultaneously perform bidirectional power transmission and voltage balancing without a separate voltage balancer circuit, so it can be applied to emergency power generation sources such as energy storage systems. To verify the proposed converter, the operating principle is analyzed under voltage imbalance conditions and the controller is designed using a mathematical model. Afterwards, it was confirmed that the designed controller operates stably through simulation analysis and experiments.