CONTROL METHOD FOR AN OFF-GRID ENERGY STORAGE SYSTEM, CONTROL DEVICE AND ENERGY STORAGE SYSTEM

Control methods for an Energy Storage System (ESS) are provided which relates to the technical field of off-grid controlling and include: when the ESS operates in AC/DC parallel off-grid mode, obtaining given values of positive sequence voltage amplitude, positive sequence phase, D-axis and Q-axis negative sequence voltage of a present PCS to be controlled based on a current sharing control loop; determining target control amounts of D-axis and Q-axis according to the given values, an outer voltage loop and an inner current loop; determining a zero-axis target control amount based on a zero-sequence current loop; determining a midpoint target control amount of a master PCS based on a DC bus midpoint control loop; generating a target waveform according to the target control amounts; and controlling the present PCS according to the first target waveform. The present disclosure solves the problem of current imbalance of each PCS and zero-sequence circulating current.