Abstract: A low-power series parallel induction heating power supply was designed based on specific operating conditions. Firstly, the electrostatic coupling characteristics of LLC resonant loads are utilized to replace traditional high-frequency transformers, in order to improve the stability and reliability of the power supply; secondly, regarding the specific phase relationship between the output voltage and compensation capacitor voltage of LLC type induction heating power supply operating in quasi resonant state, this paper proposes for the first time to apply the idea of vector transformation to the frequency tracking link, and adopts a frequency tracking control system based on second-order generalized integrator(SOGI). At the same time, second-order linear active disturbance rejection control technology(LADRC) is introduced to estimate and compensate for each state variable using its extended state observer to achieve phase locking, in order to improve the dynamic response speed of the induction heating power supply. Finally, to verify the effectiveness of the series parallel induction heating power supply, a Simulink simulation model was established. The simulation results show that the LLC resonant circuit can replace high-frequency transformers with reasonable parameter design, and verify the effectiveness and feasibility of applying the phase-locked loop based on second-order linear self disturbance rejection control to induction heating power supplies.