A method and firmware for controlling an inverter voltage includes steps of receiving as input a digitized feedback signal representative of an inverter voltage that varies with frequency according to a transfer function, calculating a frequency of a digital switch control signal in firmware in an inverter voltage microcontroller by the transfer function from the digitized feedback signal to adjust the inverter voltage to a set point value, and generating the digital switch control signal having the calculated frequency by firmware in the inverter voltage microcontroller as output to generate the inverter voltage at the set point value.