Short term energy storage for ASD ride-through

The need for a cost-effective short term energy storage system has arisen in the power quality market. This is a result of the increased sensitivity of modern electrical equipment to power system disturbances, of which voltage sags and momentary interruptions are the most disrupting. Some of the most sensitive equipment are adjustable speed drives (ASDs) which are prevalent in modern manufacturing facilities. Where continuous processes are interrupted due to the inability of ASDs to ride through sags or momentary interruptions, heavy financial losses can be incurred. When the speed and output torque of the machine need to be preserved throughout the disturbance and the power system cannot provide full power to the load, an energy storage system is required. Power quality surveys have shown that the majority of voltage sags and momentary interruptions last less than 3 seconds, therefore the energy storage system is required to effectively provide a short burst of power. In this paper, three promising energy storage technologies, batteries, ultra-capacitors and flywheels, are compared with regards to attributes required to fulfil this function. These include power density, cost, response time and maintenance.