POWER CONVERSION CIRCUIT AND CONTROL METHOD THEREOF, BATTERY PACK, AND ENERGY STORAGE SYSTEM

This application provides a power conversion circuit, an energy storage apparatus, and an energy storage system. The power conversion circuit includes a controller, a first-level DC/DC conversion circuit, a plurality of second-level DC/DC conversion circuits, a switching module, a first capacitor, a plurality of second capacitors, and a battery. When a voltage of the battery is less than a first voltage threshold and voltages at two ends of the first capacitor and the second capacitor are less than a third voltage threshold, the controller controls the switching module to be turned off or turned on, so that the plurality of second-level DC/DC conversion circuits are connected in series; or when the voltage of the battery is greater than a second voltage threshold and voltages at two ends of the first capacitor and the second capacitor are less than the third voltage threshold, the controller controls the switching module to be turned off or turned on, so that the plurality of second-level DC/DC conversion circuits are connected in parallel, so as to change a boost ratio between both sides of the first-level DC/DC conversion circuit. In addition, when a series/parallel connection manner between the plurality of second-level DC/DC conversion circuits is switched, voltages of the capacitors will not suddenly change, thereby ensuring safe switching, reducing costs, and improving electric energy conversion efficiency of a system.