Small battery energy storage system

A small battery energy storage (BES) system is proposed. The power circuit of this BES system is simple, since only one current-forced subharmonic PWM switching converter is used. The precise current control is achieved by applying feedforward control. If the utility power is off, the BES system operates in the inverter mode to supply power to the load. A sinusoidal output voltage with low distortion and good regulation is obtained by using instantaneous voltage control and average voltage control techniques. When the utility power recovers, the BES system minimises the power from the utility to the load in the peak load period. Conversely, the power from the BES system is minimised in the medium load period. During the off-peak load period, the utility supplies power to the load and also charges the battery bank. In addition to real power conditioning, the BES system can also compensate the load reactive and harmonic powers