GB1214646A - Improvements in or relating to standby power supply systems - Google Patents

Abstract

1,214,646. Converting; stand-by power supplies. PLESSEY CO. Ltd. 4 Oct., 1968 [13 Oct., 1967], No. 46728/67. Headings H2F and H2H. [Also in Division H3] In an emergency stand-by power supply system, Fig. 6, an inverter 26 is locked in phase quadrature with the mains input whereby it supplies no power to load 31 under normal conditions and takes over with no break in the event of a power failure. Thyristors 32 prevent power being fed back to the mains input. The inverter may have its frequency controlled by a unijunction transistor relaxation oscillator, Fig. 3 (not shown), the feedback signal adjusting the " aiming " potential of a CR circuit. In the phase locking system, Fig. 2, the inverter 4 is phase controlled by comparing its output with a reference signal to produce an error signal dependent on the phase difference, and combining the error signal with a control signal to produce a phase correction signal which controls the generator such that it is phase locked to the reference signal at a phase angle determined by the control signal. The reference signal and generator output signal are clipped and differentiated by units 4, 5 to produce pulses which switch bi-stable circuit 7. The resulting output, comprising pulses having a duration dependent on the phase difference, is then integrated at 8 to produce the error signal. The error signal and control signal are then fed to longtailed pair 9 to provide the required correction signal. The comparator and longtailed pair may be formed as transistor circuits, Fig. 4 (not shown).