Abstract: First to n-th (n is an integer of 2 or more) power conversion devices are connected in parallel to a load. First to n-th fuses are provided in first to n-th wirings, respectively. Each of the first to n-th power conversion devices includes a converter, an inverter, and a DC bus supplying a DC voltage from the converter to the inverter, and capacitors connected to the DC bus. An i-th (1?i?n?1) wiring includes the DC bus of an i-th power conversion device and the DC bus of an (i+1)-th power conversion device. The n-th wiring is connected between the DC bus of the n-th power conversion device and the DC bus of the first power conversion device.

Abstract: A water injection controller and method usable in rolling lines using stored cooling water to cool a material. A cooling water usage predictor predicts, for a respective prescribed prediction cycle, usage of cooling water in a prescribed prediction target period. A constrained running condition predictor takes the predicted cooling water usage to predict a required running condition of a pump system in the prediction target period meeting a prescribed constraint condition. An energy consumption calculator takes the predicted running condition of the pump system to calculate an energy quantity to be consumed. An optimizer determines an optimal energy quantity to be consumed among plural energy quantities to be consumed under changed running conditions of the pump system. A pump system running controller controls running of the pump system having as a target value therefor a running condition of the pump system requiring the optimal quantity of energy to be consumed.