The present disclosure provides a control method, in which charge control is combined with input voltage feedforward control and output current feedforward control. It can be shown that the combination of the charge control with the feedforward control performs better than the combination of the direct frequency control (DFC) with the feedforward control. In particular, the combination of the charge control with the feedforward control has much better load transient response with respect to the load transient response of the combined direct frequency control and feedforward control.