The inputs of the mode control module are the mode output (mode_F) of the voltage monitoring module, the output Kslope of the slope calculation module and the calculation result V_PI of the PID module respectively. When the output mode_F of the voltage monitoring module is the dynamic mode (LTH mode or HTL mode), the module switches off the PID module through outputting a control signal PI_ctrl, and controls the PWM module to receive the switching period T_{s_LTH} or T_{s_HTL} of the dynamic mode, and duty ratio T_{on_LTH} or T_{on_HTL} (or current) information outputted by the module, and the PWM module generates a duty ratio waveform at the moment according to the two signals; when the mode control module jumps out of the dynamic mode to enter a first switch period of the normal working mode, the mode control module obtains the size of a corresponding output load according to the size of the slope Kslope of the slope calculation module at the moment, the PID module is started through the control signal PI_ctrl and V_PI0 is assigned to the current sampling result before PID calculation, V_PI0 is the output value of the PID module corresponding to the load in a stable state after change, the PID module conducts PID calculation according to the error outputted by the error module after the assignment, and a PID calculation result V_PI is fed back to the mode control module to conduct mode selection and control in the normal working mode; when the mode control module jumps out of the dynamic mode to enter a second switch period of the normal working mode and later, the control signal PI_ctrl is outputted to start the PID module to conduct calculation, the PID module conducts PID calculation according to the error outputted by the error module, the calculation result V_PI is fed back to the mode control module to conduct mode selection and control in the normal working mode, the PWM module receives a supplementary result V_PI outputted by the PID and the control mode (mode_ctrl) of the normal working mode given by the mode control module in the normal working mode, the switch period and the duty ratio (or current) information is obtained through calculation, and the PWM module generates the duty ratio waveform according to the two signals at the moment.