From Vacuum Tubes to Modern Semiconductors: Opportunities for Industrial Heating Industry

Industrial heating plays a significant role in the modern society. It constitutes about 20% of the global energy consumption. Modern industrial heating plants (especially induction and dielectric heating) uses vacuum tube triode based radio frequency (RF) generator. The vacuum tube RF generator provides an efficiency of 60% or less. This is not optimum, as almost half of the energy is being wasted as heat. Modern semiconductor technology based on wide bandgap (WBG) materials such as silicon carbide (SiC) and gallium nitride (GaN) provides an opportunity to remove the ageing vacuum tube from industrial heating plants. However the industrial heating plants requires high voltage output from the RF generator to deliver high power which has been a technological barrier towards semiconductor implementation in industrial heating industry. In this paper a method is proposed to series connect multiple RF converters to scale-up the output voltage from semiconductor based RF generator. Class-PN is used as RF converter to demonstrate the proposed multi-cell series connection method. Furthermore a controller scheme is presented that allows individual Class-PN RF converter to maintain optimum operation without the need of communication between each cells. For the small-scale prototype three Class-PN cells are operated in multi-cell configuration to boost the 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.