GB1166196A - Improved System for Producing Alternating Current - Google Patents

Abstract

1,166,196. Standby supply systems. LICENTIA PATENT - VERWALTUNGS - G.m.b.H. 12 June, 1967 [23 June, 1966], No. 27015/67. Heading H2H. A system for producing alternating current of substantially constant frequency and voltage from a variable speed source, such as a ship's propeller shaft, comprises a synchronous machine 10 driven from the source 13 feeding load bus-bar 16 through a frequency changer, such as an uncontrolled rectifier 14 and inverter 15, and a synchronous condenser 17 normally supplying reactive current but which may supply active power on stoppage of the source 13 by being coupled to a prime mover 19 such as a diesel engine. The inverter may be controlled by known means for producing substantially constant frequency and voltage. The inverter firing angle may also be dependent on power output, rate of change of frequency or power output. The condenser 17 may be provided with automatic voltage control and the excitation of the machine 10 may be dependent on bus-bar frequency or rate of change of current. Combined power and frequency regulation may be provided. A capacitor 25 may be paralleled to the condenser through a choke 26, or through a tapping on a common choke (26a) (see Fig. 3, not shown). The machine 17 may be started in an asynchronous mode by a temporary direct connection from generator 10 and the choke 23 is shortcircuitable by a switch 24 when the condenser is being driven as a generator. For stable operation, the short-circuit current of the rectifier should be smaller than that of the condenser 17, also the voltage of generator 10 should fall more rapidly than that of condenser 17, e.g. due to a higher short-circuit reactance winding. A plurality of inverters may be employed having phase displaced outputs, and the resonant frequency of the capacitor choke combination is preferably tuned to the sixth harmonic where the inverter produces fifth and sixth harmonics. A plurality of systems may have their outputs paralleled to bus-bars 16, see Fig. 6 (not shown), and cross-coupled transformer windings may ensure satisfactory load division (see Fig. 7, not shown). The inverter 15 may include thyratrons or thyristors. Where the excitation of machine 10 exceeds a determined value, e.g. under short-circuit conditions, a means may be provided for automatically disconnecting unessential loads and reducing the retardation of the inverter firing angle. Speed control of the machine(s) 17 may control the bus-bar frequency.