Systems and methods for voltage control and current control of power conversion systems with multiple operation modes

A system controller for regulating a power conversion system, the system controller comprising:

• an operation-mode-selection component configured to receive a first signal related to an output load of the power conversion system and a second signal related to an input signal received by the power conversion system and output a mode-selection signal based on at least information associated with the first signal and the second signal;
• and
• a driving component configured to receive the mode-selection signal and generate a drive signal based on at least information associated with the mode-selection signal, the driving signal corresponding to a switching frequency;
• wherein the operation-mode-selection component is further configured to:
• if the output load is determined to be larger than a first load threshold in magnitude and the input signal is determined to be larger than an input threshold, generate the mode-selection signal corresponding to a first mode if the switching frequency is determined to be smaller than a first frequency threshold and larger than a second frequency threshold;
• and
• if the output load is determined to be larger than the first load threshold in magnitude and the input signal is determined to be smaller than the input threshold, generate the mode-selection signal corresponding to a second mode if the switching frequency is determined to be equal to the second frequency threshold;
• wherein the operation-mode-selection controller includes a comparator configured to receive the second signal and a reference signal and output a comparison signal based on at least information associated with the second signal and the reference signal;
• wherein the operation-mode-selection controller includes a quasi-resonant-mode selector configured to:
• receive the first signal and the comparison signal;
• if the output load is determined to be larger than the first load threshold in magnitude and the input signal is determined to be larger than the input threshold, generate the mode-selection signal corresponding to the first mode;
• and
• if the output load is determined to be smaller than the first load threshold and larger than a second load threshold in magnitude, generate the mode-selection signal corresponding to the first mode;
• and
• wherein:
• the first mode is a valley switching mode;
• the second mode is a continuous conduction mode;
• and
• the first mode is different from the second mode;
• wherein the operation-mode-selection component is further configured to:
• process information associated with the first signal;
• detect an end of a demagnetization period based at least in part on the first signal;
• detect a first valley in the first signal, there being no other valley in the first signal between the end of the demagnetization period and the first valley;
• and
• under the valley switching mode, in response to the first valley being detected in the first signal, change the drive signal from a first logic level to a second logic level in order to trigger a switching cycle of the power conversion system.