A device for improving the voltage sag ride through capability of PCs

Voltage sags have emerged as one of the most serious power quality problem. Voltage sag disturbances which sometimes last less than a fraction of second, can cause sensitive equipment such as personal computers (PCs) to shut down and interrupt PC controlled systems and processes for considerable periods of time, which leads to loss of production and high costs. In order to overcome this problem, an electronic device to enhance the ride through capability of PCs during voltage sag is developed. The proposed device can be connected to the power supply unit of PC to add a new operational state to the PC's power supply, in which PC is supplied for one second by a capacitor bank in the events of voltage sags. It consists of sag detection circuit, control circuit, switching circuit and capacitor bank. The device is easy to use and can be built from cheap, commercially available components. Some of the salient features of the proposed device are that it does not require additional uninterruptible power supply for its operation, and it does not draw high levels of inrush currents from the mains. Furthermore, the proposed device can be adapted to other voltage sensitive devices such as lamps and ac contactors.