Research On The Storage Interface Unit Of Distributed DC Power Supply System

Distributed DC power supply system (DC micro-grid), with advantages of fewer powerconverters, higher efficiency and easy to control, can be used to build an efficient, friendly, reliableand intelligent power supply system for data centers, homes, buildings, schools, etc.. As an essentialcomponent of the distributed DC power supply system, the energy storage system plays a veryimportant role in supporting and stabilizing the voltage of the DC bus, which stabilizes powerfluctuations of distributed renewable energy generations such as photovoltaic panels and windturbines. Battery and super-capacitor hybrid energy storage system, integrating merits of energy-basedand power-based energy storage devices, greatly improves the performance of the storage system,which has attracted wide attention in recent years.Based on the storage interface unit of distributed DC power supply system, a novel “3+1”-portisolated bidirectional DC-DC converter is proposed, which can achieve ZVS for all switches in thewhole load range. The bidirectional power flow between any two of the ports is free. The accessionalinternal fourth port provides possibility for voltage matching when battery and super-capacitor areboth connected. No matter how the voltage of battery or super-capacitor changes, even the voltage ofDC bus changes, the voltage matching of transformer still maintains well. Moreover, the currentripples are greatly decreased by interleaved control, which is good for battery and super-capacitor.In this paper, the converter topology and the operating principle are introduced. Characteristicsof the converter under the voltage matching are analyzed in detail, including the power flowcalculation, soft-switching conditions and soft-switching operating range. The theoretical analysis hasprovided some advices for important parameters design of the converter. Based on the novel converter,a hybrid energy storage control strategy is presented, in which the power flow among three ports isrelied on the status of the DC bus and energy storage devices. According to the working status of thebattery, the energy storage system works in two cases: energy absorption and release, in which thereare several working modes of the converter depending on the current status of the DC bus and thesuper-capacitor. On the basis of the detailed analysis of various operating modes, control scheme isdesigned to achieve a smooth transition between operating modes. Simulation and experimentalresults verify the correctness and validity of the proposed converter and control strategy.