Half-bridge LLC circuit with controllable resonant inductor and its control method

A half-bridge LLC circuit with controllable resonant inductor was proposed, which adjusts the inductance of the resonant inductor according to the output current to change the parameters of the resonant cavity, so that the switching frequency can be basically kept constant, and the light-load burst-mode range of LLC converter was reduced. This ensures that the converter has no noise when outputting in a wide power range, and has excellent output characteristics. The magnetic circuit of the variable inductor, the control method of the variable inductance, and the operating principle and operation process of the LLC converter were analyzed in detail, computer simulations were carried out on the proposed circuit and its control, and a prototype with an input of 740 V, an output of 420 V, a full load power of 1.8 kW, and an output power range of 10%~100% was designed and set up. Computer simulation and experimental results show that by adjusting the resonance parameters, the switching frequency is basically constant at 140 kHz, the converter does not enter the burst-mode in the entire power output range, and the output voltage characteristics are good. Moreover, compared with the traditional LLC circuit, the proposed circuit has a higher conversion efficiency. © 2021, Harbin University of Science and Technology Publication. All right reserved.