Patent ID: 8207632

Claim:
A control device for an uninterruptible power supply (UPS) comprising: a high-speed switch interposed in an electric passage connected between an electric power system and a load; an interconnection transformer having a primary winding side connected to a common junction between the high-speed switch and the load; an alternating current-and-direct current conversion device having an alternating current side connected to a secondary winding side of the interconnection transformer and a direct current side connected to an electric power storage section and configured to perform a change of an electric power between the alternating current and the direct current; the high-speed switch, the interconnection transformer and the alternating current-and-direct current conversion device, all provided in the UPS, the UPS operating in any one mode of the following three runs, as a normal operating mode in which system voltage is stable and instantaneous voltage drop or service interruption does not occur: (a) a charge run in which electric power of the electric power system is supplied to the load while charging the electric power storage section through the alternating current-and-direct current conversion device, (b) a stand-by run in which the electric power of the electric power system is supplied to the load while the alternating current-and-direct current conversion device is in a stand-by state, (c) a discharge run in which both the electric power of the electric power system and the electric power of the electric power storage section discharged through the alternating current-and-direct current conversion device are supplied to the load, the UPS also operating, when the instantaneous voltage drop or service interruption occurs, in a mode of (d) a self-contained run in which the high-speed switch is opened to separate the electric power system and the load, then the electric power of the electric power storage section is supplied to the load through the alternating current-and-direct current conversion device; and a controller which performs, before the normal operating mode of one of (a), (b) and (c) is changed to (d) the self-contained run upon the occurrence of the instantaneous voltage drop or the service interruption, a constant current discharge run in which the electric power of the power storage section is discharged at a predetermined constant current for a predetermined time to suppress an induced electromotive force due to a leakage inductance of the interconnection transformer which occurs upon the operating mode change from one of (a), (b) and (c) to (d), the self-contained run, and after performing the constant current discharge run, the normal operating mode being changed to (d) the self-contained run that supplies the electric power to the load.