DISPOSIZIONE DI COMANDO A MOTORE C.C.SENZA COLLETTORE

摘要

1481729 Frequency changing; control of inverters and A.C. motors WESTINGHOUSE ELECTRIC CORP 2 Sept 1974 [11 Sept 1973] 38262/74 Headings H2H and H2J An arrangement energizable by D.C. voltage for controlling an A.C. motor 151 comprises an inverter 231, having a plurality of selectively actuable switching devices A1 .. C2, arranged to couple the D.C. voltage 431 to the motor 151 and firing pulse generating means arranged to integrate the D.C. voltage 431 and produce firing pulses for the switching devices A1 ... C2 such that the frequency is proportional to the D.C. voltage 431. Automatic starting means is included for gradually increasing the D.C. voltage, together with over current sensing and restarting means. The D.C. voltage 431 is preferably derived by rectification of the supply mains 55, using a semi-controlled rectifier, the conduction angle of which is adjusted so as to determine the magnitude of the D.C. voltage and hence the frequency and voltage applied to the induction or synchronous motor 151. As described, the motor 151 is preferably 130 HP having a permanent magnet rotor and driving a centrifugal fan. The motor 151 is arranged to operate with leading power factor so that the inverter 231 may be naturally commutated. The D.C. voltage from semi-controlled rectifier 431 is integrated at 311, giving a ramp which rises until it reaches a reference voltage 331, when a crossover detector 361 operates a reset circuit 371. The circuit thus produces ramps the frequency of which is proportional to the D.C. voltage 431 and which are supplied to a firing pulse generator 251 for the thyristors A1 ... C2. Starting.-A start signal generator 61 initiates operation of a slow ramp generator 63 which is fed to phase-controlling circuits 59, 57 so that the D.C. output from semi-controlled rectifier 431 is gradually increased so that the voltage and frequency applied to the motor 151 is also gradually increased. Under starting conditions, the current from rectifier 431 may be discontinuous. A circuit comprising diodes 79 and resistors 81, 83 is therefore included to fill in the gaps from the voltage induced in the motor 151. The direct current is monitored at 511 and fed to a circuit 531 where it is compared with a reference 65 and arranges a restart if the current becomes excessive. A further reference 73 may be included to prevent inhibiting of the rectifier 431 in the event of load current being greater than the starting current. In Fig. 10 (not shown) the firing pulses for the rectifier 431 are produced by a phase-locked voltage-controlled oscillator. Figs. 8-11 relate to arrangements of integrated circuits (not described in the Specification) for the various firing pulse generators.