Research On Current-fed Half-bridge Based Bi-directional DC-DC Converter And Its Parallel/Series Control

In distributed power supply systems,due to the influence of some natural factors,such as light intensity,wind strength,the output power of new energy generation,including solar power,wind power and so on,will have the feature of randomness and uncertainty,which may cause power fluctuation in the DC bus and decline of the power quality.To restrain the fluctuation,energy storage devices are usually adopted in the systems,so that the impact caused by the new energy power can be reduced and the power quality can be improved.Batteries are widely used in storage systems,due to the advantages of low cost,high power density and high reliability.When batteries are adopted as the main energy storage devices,to realize the control of bus voltage and battery current,the interface converters are usually needed to connect the batteries with DC bus.When choosing the converters,compared with the single converter scheme,the modular design has the advantages of flexible configuration,high scalability and being helpful to redundancy design,which can meet the different requirements of power level and voltage level in different energy storage systems more easily.Aiming at the application of modular energy storage interfaces used in distributed power supply systems,a 48V/400 V modular bi-directional DC-DC converter based on current-fed half-bridge is investigated.The operation principle is analyzed and the power flow expression are derived.By theoretical calculation,the conditions of soft switching at full range of loads is determined.A master-slave control strategy based on digital communications for multi converters used in combination is proposed,by which the low voltage side of different modules can be used in parallel or series or independently,and the high voltage side of different modules can be used in parallel or series.With the auto-master-selected strategy,when the master module breaks down,a new master module will be generated immediately to replace the former one to ensure the whole system working normally,so that,the problem of system fail when the master module breaks down in traditional master-salve system can be solved.A prototype of 1.5kw bi-directional DC-DC converter module is developed.By simulations and experiments,the key waveforms of converter are demonstrated and the validity of the theory analysis is proved.The experiments of two modules running in parallel and series prove the validity of the proposed combination control strategy and the experiments of the master module switching verify the validity of the auto-master-selected strategy.