An energy storage system includes one or more energy storage unit clusters, and the energy storage unit cluster includes at least two energy storage modules connected in series. The energy storage system further includes a first bus, a second bus, and a centralized monitoring system of the energy storage unit cluster, where the second bus is a direct current bus. The energy storage unit cluster is coupled to the first bus by using a first converter. One energy storage module includes one energy storage element group and one DC/DC converter, and the energy storage element group is coupled to the second bus by using the DC/DC converter. The centralized monitoring system is connected to the energy storage unit cluster through a control bus, and is configured to control a DC/DC converter in any energy storage module in the energy storage unit cluster.