A low cost approach to provide ride-through for critical loads

In this paper a low cost approach to provide ride-through for critical loads connected in buildings and/or an industrial system is explored. In this approach a three-phase IGBT inverter with a built in DC-link voltage regulator, is suitably controlled along with static by-pass switches to provide continuous power to critical loads. During a disturbance, the input utility source is disconnected and the power from the inverter is connected to the load. After detecting normal utility conditions, power from the utility is restored to the critical load. The proposed approach does not require an external energy source (flywheel, fuel cell or battery) to protect against disturbances such as: voltage sags, voltage swells, flicker, etc. An external energy source can be incorporated in the DC link, to provide ride-through during short-term power interruptions. Since the inverter provides power only during a disturbance, the size and weight is small. Analysis, simulation and experimental results are presented on a 230 V, three-phase, three-wire, 3 kVA laboratory prototype.