Research And Implementation Of A LCC Resonant Converter Based PFU Constant Current Charging System

The pulse power supply system is the core of the electromagnetic launcher, the research of which plays a vital role to the development of the electromagnetic launch technology. This paper studies the distributed PFU independent power supply structure of the capacitive energy storage electric launch system, and requires that the PFU power supply system can adjust both the charging voltage and the charging current. Therefore, it’s valuable in practice to study how to improve the current output capability of the charging power and supply power to multiple PFUs in a fast, efficient and different way, under the preconditions of not changing the output voltage level and increasing the capacity of the converter.Firstly, this paper analyzes the operation principles of the LCC resonant converter operating in discontinuous current mode. After discussing the expressions of the key variables in each stage, the design goal is determined, which is that the converter works in double pulse output mode during the whole process of charging. At the same time,this paper performs an in-depth analysis of the current output capability, the critical discontinuous switch frequency, soft switching and other features of the system under this mode. It is revealed that the current output capacity of the LCC resonant power supply has serious decay under the traditional control mode of fixed-width frequency modulation.Secondly, a digital control based pseudocritical constant current control scheme has been proposed, because the traditional PFM can’t compensate the attenuation of average output current with voltage rise. The resonant current critical discontinuous frequency function is equivalently fitted with the simplified linear function that can expand the upper frequency limit accurately.The control scheme can compensate the output current duty ratio loss maximumly and increase the charging current output capacity of the charging supply significantly. In addition, adopting the digital PI control algorithm to design the current loop can overcome the input and load disturbance and realize constant current charging.The hardware and software design of PFU constant current charging system has been completed. On the one hand, under the condition of using the transformer leakage inductance as the resonant inductance and gaining the equivalence of the parasitic capacitance, the resonant capacitance is designed, thus forming a complete set of design idea. A complete and fast protection system and the electromagnetic compatibility design are added to the internal of the power,owing to the problems of high output voltage and strong electromagnetic interference, etc. On the other hand, the monitoring and protection from the upper computer to the lower computer are realized through the CAN bus communication in the aspect of operation interface, and C++ language is utilized to write a user friendly human-computer interface in the PC.Finally, simulation and experimental results have been provided to verify the high voltage charging power supply system, and conclusions are derived as follows. Compared with the traditional constant current control scheme, the constant current output capacity of the power supply is increased by 23.7% with the pseudocritical constant current control scheme, without increasing the capacity of the main power switch and increasing the transformer turns ratio. The PFU charging power system designed in this paper has been successfully applied to a specific large device and its current running status is stable.