Load bank elimination for UPS testing

A method for load testing AC and DC power supply equipment that minimizes harmonics and allows for control of the utility input power factor is presented. This testing method produces minimal losses in the load banks by recirculating the power back to the equipment input. Two types of recirculating load banks are presented: synchronized and nonsynchronized. In synchronized load banks, power flow from the output to the input of the unit is controlled by injecting the series voltage. Circulation of power in a nonsynchronized load is achieved by processing the load power through a utility interactive inverter which is synchronized with the utility. The theory of operation of quadrature voltage injection and the results of the experiments indicating the steady-state as well as the transient performance of the load banks are given. The financial benefits of using a recirculating load bank are analyzed, and the results are presented.<>