Design and implementation of a 10kV/2A LLC resonant converter with two-step soft-start PID control for industrial magnetron

This paper presents the design and implementation of a high-voltage direct current (HVDC) power supply rated for 10kV, 2A (20kW), developed to drive a 10kW, 2.45GHz industrial magnetron requiring approximately 8.8kV, 1.6–1.8A (16kW input) under nominal operation. Accordingly, the HVDC supply was rated at 20kW to allow margin for surges, efficiency variation, and future scaling. The converter core employs a full-bridge inductor-inductor-capacitor (LLC) resonant topology operating at a nominal switching frequency of 22kHz, chosen for its high power density, inherent soft switching, and effective use of transformer leakage inductance in the resonant tank. A two-step soft-start sequence is implemented: the output first stabilizes at 6.8kV in standby before smoothly rising to 8.8kV for full-power operation, with a transition time below 200ms and no overshoot. Closed-loop regulation is achieved through digital proportional–integral–derivative (PID) control on a Texas Instruments TMS320F280025C using pulses-frequency modulation (PFM). The prototype demonstrates stable voltage regulation with low output ripple (<1%) while maintaining zero-voltage and zero-current switching (ZVS/ZCS) across the operating range. All high-voltage magnetic components, including the resonant inductor and custom 20kVA transformer, were designed and built in-house to meet insulation and power-density requirements. Experimental validation confirms reliable startup, arc-free operation, and efficient power conversion under variable load conditions. In summary, the proposed digitally controlled LLC converter delivers a regulated 10kV/2A direct current (DC) output with controlled soft start, offering a compact, low-cost, and robust solution for industrial magnetron and plasma heating applications.