Soft restarting of industrial power network using inverter-controlled energy storage system

We describe a process for using inverter-coupled local energy storage to softly-restart an industrial power network, and then bumplessly reclose the circuit breaker that has tripped the plant offline. The soft restart process eliminates a number of problems commonly associated with breaker reclosing such as large inrush currents, motor torque pulsations, and dipping of the line voltage feeding the plant. The soft restart is accomplished by pre-energizing the industrial power network with a voltage/frequency ramp while the network operates in islanded mode, then reclosing the circuit breaker when the industrial network is phase- and voltage-matched to the utility grid. Voltage and frequency acceleration of the industrial network are controlled by the inverter according to the characteristics of the connected loads. The performance of such a soft restart is characterized in terms of the plant load characteristics.