Tracking control of class E inverter for the duty cycle control

Class E resonant inverter is often applied to design a high frequency AC power source. Based on the zero voltage switching (ZVS) operation, the class E converter has high converting efficiency even the converter works at high frequency. In general, the output power needs to be controlled for practical application. The power output of class E inverter can be adjusted by regulating the duty ratio of the switch turn on. Unfortunately, the ZVS operation will fail while the operated duty ratio changes without adaptive tuning the switching frequency. Based on the Fourier series expansion, the fundamental component of load current is analyzed for the class E inverter while it is controlled by duty cycle and switching frequency. The phase shifting of the load current is an important message for ZVS examining. Without complicated mathematical model and numerical iteration, a close form formula has been proposed to calculate the phase shifting from the duty ratio and switching frequency. By the obtained phase shifting, a tracking controller is proposed to achieve the close loop control for keeping the class E inverter works on ZVS operation while the operated duty ratio is regulated. To illustrate the proposed method, both the examples of theoretical simulation and circuit simulation are given.