Uninterruptible power supply systems: nonlinear electrical load compatibility

The mass proliferation of computers and distributed control systems in process control rooms and solid-state device driven machines in plants has resulted in increased electrical spikes, over/under-voltages, outages, and higher rate of wear and tear on equipment. The underlying cause of these phenomena is that nonlinear electrical loads are being used more frequently in the control room and plant environment. The uninterruptible power supply (UPS) has been the mainstay of power solutions for conditioning and backup in the industrial environment. The traditional UPS design for high-performance, high-reliability applications has been the application of the double conversion topology, in single-phase output configuration, using passive output harmonic filters to mitigate the ill-effects of nonlinear loads on traditional UPS systems. Unfortunately, passive output harmonic filters are expensive, require additional foot-print and cannot adapt themselves to changing load environment. In the context of modern process control plants and current economic conditions, passive filters are ineffective in delivering the lowest cost, smallest footprint solution. This paper describes the latest advances in the design of single-phase UPS systems incorporating real-time, dynamic digital feedback control to accommodate nonlinear loads.