Bidirectional Isolation DC-DC Converter

Bidirectional DC/DC converter (BDC) can achieve the capacity of energy flowing bidirectional under the condition that both ends keep the constant voltage polarity. Compared to the traditional single-phase DC/DC converter, the BDC saves the device number, decreases the volume of the converter, and improves the system power factor. As the rapid development of fuel cell electric vehicle, uninterruptible power supply system (UPS), and green energy sources such as wind power, the BDC has been used more and more widely.The paper mainly introduces the working principle of the single-phase isolation bidirectional dual-active-bridge DC-DC converter (IBDC) and the three-phase isolation bidirectional dual-active-bridge DC-DC converter. Then the control methods are studied.The topology of single-phase IBDC is widely used in medium or high power occasion for the advantage of symmetric structure, capacity to achieve soft switch and energy bi-directional flow. In this topology, single-phase-shifting (SPS) control is adopted traditionally, because the strategy is easy to control and implement, and it has fast dynamic response, etc. However, when input and output voltage does not match, the backflow power and the current stress would incease, which lead to more losses and higher request to the switch tube. In order to deal with the disadvantages of SPS control, another two dual-phase-shifting (DPS) control are introduced and analyzed by establishing the mathematical models of transmission power and backflow power of the single-phase IBDC. This paper proposes a backflow-power-optimized dual-phase-shifting (DPS) control strategy to reduce backflow power and current strss. The optimal phase-shift ratios were calculated by using the segmentation optimization algorithm in different ranges of transmission power and input/output voltage conversion ratio. The backflow power curves under the proposed DPS and SPS control conditions were analyzed and compared which can prove that the proposed strategy could minimize the backflow power, reduce the current stress, improve the system power factor and increase system power capability. And the performances are particularly effective for operating conditions with high voltage conversion ratio or light load. Then an optimization control algorithm and system control scheme of the IBDC was presented, furthermore an experimental prototype was developed based on this strategy. The experimental results verify the effectiveness and feasibility of the proposed control strategy.The three-phase IBDC which can be used in high power applications has larger power capacity than the single-phase IBDC. The working principles of three-phase IBDC with YyO connection and Ydl connection are analyzed, and the condition to realize soft switching is deduced which has been verified by using PSIM simulation software. Furthermore, the power density of single-phase and three-phase IBDC with YyO connection and Yd1 connection has been calculated and analyzed.