Research on Distributed Energy Storage Devic

This dissertation investigates the key technologies for a distributed energy storage device including an isolated bidirectional DC--DC converter, their modulation, the application of gallium-nitride transistors in the converter and the technologies for a high power, ultra-high efficiency, low cost energy storage structure based on partial power process converter.;Most energy sources such as petroleum, natural gas and coal are nonrenewable or not environment-friendly. The associated energy shortage, green-house gas emission and energy security issues are gaining their severity. Wide spread adoption of renewable energy and transportation electrification are two potential solutions. Battery and bi-directional power converters play vital roles for both solutions. In Chapter 2, a high efficiency, low-cost bidirectional isolated DC--DC converter for distributed energy storage device is proposed. It consists of a half-bridge circuit at high voltage side and a push-pull circuit with active clamp at low voltage side. The proposed topology is attractive in low voltage and high current applications and it also reduces the number of switching transistors such that the cost and complexity are considerably reduced. With single phase-shift control strategy, all the switches operate in zero-voltage switching (ZVS) condition without increasing circuit complexity. A 400V to 12V DC, 500W DESD hardware prototype has been designed, fabricated, and tested. Experimental results verify the validity of the proposed bi-directional converter, which has 97.3% peak efficiency and maintains greater than 92% efficiency over a load range between 100W and 600W.;In Chapter 3, a novel isolated bidirectional DC-DC converter based on 650V GaN transistors is proposed. Two 650V enhancement mode GaN transistors are used at the high voltage side to solve the issues caused by 600V Si super junction MOSFET, extend the ZVS range and further improve the efficiency. Compared with Si device, fast reverse conduction feature, no reverse recovery and small output capacitance are the features we want This chapter describes a method to predict the power losses of the converter. Precise loss models are provided to calculate total component losses using the current and voltage information derived from the steady state inductor current calculator. Details of loss breakdown are given. The loss analysis provides valuable information for designing an efficiency optimized converters in the application. With the presented converter prototype, a top efficiency of 98.3% and an output power of 1 kW in a wide input/output voltage range (360-420V for high voltage side and 11.2-14.4V for love voltage side) is achieved. Experimental results verify the validity of the proposed DESD and the performance improved by using GaN transistors. In Chapter 4, three design considerations of the bidirectional dc-dc converter has been proposed in detail. They are the layout for minimum loop inductance and good heat dissipation, gate drive power supply for high side GaN device and high-resolution digital PWM control methodology. The PCB design considering both the loop inductance and thermal design shows good performance in terms of switching noise and thermal relief. Secondly, the isolated power with small inter-winding capacitance shows good resistance and reduction to high dv/dt of the switching mid-point. In the end, a wide range high resolution digital phase-shift modulation scheme to improve the resolution of the phase-shift angle is proposed. The experimental results verify the concepts on the bidirectional dc-dc converter with high performances.;In chapter 5, a low cost, high power, ultra-high efficiency energy storage system based on a fractional buck-boost converter is proposed. The system is based on a low voltage-ampere rating, high efficiency partial power converter concept with one extra low voltage battery pack. The performance of a family of non-isolated bidirectional fractional power converters is compared to traditional full power converter in terms of structure, conversion range, power ratings, switch stresses and efficiency. Simulation demonstrates the feasibility. Experimental results of a 100W GaN HEMT based prototype are presented to validate the analysis. The author verified it by experiment. Circuitry operational test, efficiency measurement, rating test and temperature rise test have been completed. New advanced topology retains a system efficiency > 99.0 %.;Chapter 6 concludes this work and presents an outlook regarding future research in the field of the DESD.