Abstract: An energy conversion system, and a method and a device for controlling the energy conversion system at an overtemperature are provided. The energy conversion system includes at least one power conversion circuit each including at least two power modules that are cascaded. Respective operating temperatures of all the power modules are measured in real time, to determine the overheated power module that is operating at an overtemperature and the underheated power module that is operating at a normal temperature. Once an overheated power module is detected, a decreased power and a power difference for the overheated power module are acquired, and an increased power for the underheated power module is determined based on the power difference. The operating power of the overheated power module is decreased at the module level with the total operating power of the system remains constant or approximately constant.