Design of High-frequency, Paralleled Resonant Inverter to Control Output Power for Plasma Generation

This paper presents a discrete power control of a high-frequency power inverter system for plasma generation. Plasma generation requires a high-frequency dc-ac inverter to rapidly adjust the output power in step changes within a few microseconds such as the pulsed plasma in semiconductor processing. The parallel connection of single-ended resonant inverters such as class Φ2 inverters enlarges the output power and provides the step output by switching on/off some of the inverters. However, additional power combining networks is needed, which causes additional losses and complexity. To overcome the issue, we propose a new designing method for a class
$\Phi_{2}$
inverter by designing the second harmonic branch
$L_{MR}$
and
$C_{MR}$
to form a parallel resonance with the rest reactive elements to minimize the impact of the off inverters. We select the suitable ratio of the output series tank impedance
$X_{s}$
, consisting of
$L_{S}$
and
$C_{S}$
, to the actual load
$R_{L}$
to minimize the impact of the load variation. This designing method allows us to maintain high efficiency over the designed operation range thanks to zero-voltage switching (ZVS) and keep the linearity of the output power. The proposed inverter operating at 13.56 MHz with output power from 300 W to 1121 W was real-time controlled with step changes by an FPGA board. The step-change transition lasted less than 0.5 µS. The efficiencies in all the operation modes were over 90 %.