Research on DC Power Transformer

Abstract: With the development of high-power electrical and electronic components, the electrical electronic transformer formed by those components can serve as AC transformer and DC, so the dimension and cost of transformer will be reduced; in addition, with the development and broad application of DC grid, the DC transformer will be widely applied in the DC transmission. Consequently, the electrical electronic transformer attracts more and more attention. DC transformer based on full-bridge topology and its high frequency demagnetization mechanism is analyzed in details and the relation of input-output voltage is given. The simulation and test results show that the DC transformer can automatically use the output voltage to demagnetization and voltage transmission. Hence, the DC transformer will be extensively used in the DC transmission conditions.   

Key words:   DC transformer, electrical electronic transformer, full-bridge topology, zero voltage switch, automatic demagnetization, voltage clamping     

Introduction

Compared with AC transmission, the high voltage DC transmission has a broader application prospect due to the characteristics including large transmission power capacity, low loss, long transmission distance and good stability. At present, the connection between rectifier side & inverter side and AC grid still relies on power frequency transformer in the high voltage DC transmission system. The DC power transmission still serves as an auxiliary to AC transmission and is not directly used in the electrical equipment. If the high voltage DC transmission is directly applied in the electrical equipment in future, especially independent electrical system, the original proposal seems unworkable. The DC current conversion device, the function of which is similar to AC isolation transformer, is needed to convert high voltage DC into isolated low voltage DC. In recent years, with the development of high-power electrical components and control technologies, a new kind of transformer called PET have received more and more attention. The DC transformer was put forward by scholars headed by Fred C. Lee at the Virginia Electrical and Electronics Center. The DC transformer with simple structure runs at close to 100% equivalent duty ratio without filter inductance in the output; the open loop is used to control, which is easy to realize soft switch and further improves power density. The DC/DC transformer is applied between two DC systems by some scholars in order to improve the voltage adjustment modules of distributive and two-polarity structure and the efficiency and power density of power-supply system.