Resonant Capacitor Voltage Control Of LLC Resonant Converters

Distributed power systems with high reliability, anti-interference, and many other advantages have been widely adopted in the computer system. Its front-end converter often need to meet the high-frequency, high efficiency and high density requirements, which makes the traditional hard-switching PWM converter is limited in application. LLC resonant converter is one more representative of soft-switching topology, it can achieve the main switch soft switch in wide load range, and easily integrate magnetics, so it is widely used in distributed power systems.Currently voltage-mode control strategy is still the most common control strategy in LLC resonant converter, but with the wide application of the converter, in the dynamic response speed, overcurrent protection and short circuit protection, the control strategy shows great defects, to solve this problem, a secondary charge control used in LLC resonant converter is studied. Firstly, the working principle of the control methods are analyzed in detail, and its regulation about input response and load response is discussed. Secondly, the expression of the main parameters in the control loop is derived according to steady-state analysis, and a simulation circuit is builded to verify theoretical analysis.In addition, resonant capacitor voltage controlled LLC resonant converter is proposed in this paper. Compared with voltage controlled LLC resonant converter, this control eliminates oscillator and current sampling module, simplifies the control loop, reduces the overall volume of converter, and improves the dynamic response. The working principle> dynamic adjustment rule and critical design parameters of this control is analyzed in detail, and a simulation circuit is builded to verify theoretical analysis.Finally, an experiment platform is builded about a resonant capacitor voltage control used in LLC resonant converter. The paper gives the design of parameters in the main circuit of the experimental platform, selection of the main components in the main circuit and some PCB schematic in a control unit. Experimental results show that, compared voltage mode control, this control has better dynamic response effect.