Multi-cell Operation of Class-PN at 6.78 MHz using GaN Devices for Industrial Dielectric Heating

Radio frequency (RF) dielectric heating is employed in industries like drying cross-laminated wood, baking food etc. Industries employ vacuum tube RF generators operating at 6.78 or 13.56 MHz to generate kVs range of RF output. High voltage at high frequency requirement is the reason for industry reliance on vacuum tubes, although they are only 60% efficient. Gallium nitride (GaN) devices have achieved multi-MHz operation, providing an opportunity to replace the inefficient vacuum tubes. However, the high voltage requirement is still a challenge as commercial GaN devices are only available at 650 V. This paper presents multi-cell operation of Class-PN to achieve the high voltage. Control design of Class-PN is provided. Three Class-PN cells are operated in multi-cell configuration to boost DC input of 185 V to peak-peak RF voltage of 1.1 kV at 6.78 MHz. Output power of 856 W at an efficiency of 80% from DC input to RF load is demonstrated.