Patent GB-1290880-A (GB)
IPC: H02P6/14
Filed: 1969-10-24
Abstract: 1290880 Automatic current control JEUMONT SCHNEIDER 24 Oct 1969 [25 Oct 1968 10 June 1969 9 Oct 1969] 52241/69 Heading G3R [Also in Division H2] The windings of a synchronous or asynchronous motor are energized selectively with direct current, means being provided for controlling the mean value of the winding-current and for switching the current from one winding to another. The winding B1, for example, is energized through thyristor T1 until a line current threshold is reached whereupon switch H opens and thyristor t1 fires. The current through the winding B1 is maintained by an inductor S and flows through a freewheel circuit comprising a line L. When the freewheel current drops below a predetermined valve, switch H recloses, thyristor T1 fires, and thyristor t1 is switched-off. Constant current control is obtained by regulating the onoff periods of the switch H which is associated with a triggering unit P and current-sensitive device C. Alternatively, the switch H may be controlled to determine the speed of the motor directly. A rotor-position detector D is adapted to provide a signal to open switch H, cut-off the thyristor T1, and to fire the thyristor t1. The switch H is then re-closed and thyristor T2 fires to energize winding B2. If the motor has a squirrel cage rotor, the detector D2 is replaced by a timing device which enables operation at variable frequency. A pair of windings may occupy a single slot. A rheostat may be connected to the line L and the switch H for braking operation, the changeover from freewheel operation to braking being effected by means of the switch H, Fig.2 (not shown). The switch H may be dispensed with, and current interruption effected by thyristors T1-T4. A capacitor is connected to the line L to be charged through an oscillatory circuit to twice the line voltage. When the thyristor t1 is fired the thyristor T1 is quenched by the capacitor, Fig.3 (not shown). The capacitor-charging circuit may be separated from the freewheel circuit, surplus energy of the capacitor being returned to the supply through a transformer. A regenerative braking circuit may be completed through a pair of diodes, a smoothing choke, and any one of the thyristors t1-t4 and of the windings B1-B4. In another arrangement involving variable reluctance motors two windings are energized simultaneously and each winding is switched consecutively and alternately with other windings of the motor. For this purpose the thyristors T1-T4, together with the windings in series therewith, are formed in two parallel circuits, Fig.6 (not shown). The change-over from regeneration to freewheel effect is brought about by switching from one winding to another. Two freewheel circuits may be provided. In other modifications, the thyristors t1-t4 are replaced by diodes or the thyristors are replaced by transistors. The voltage across the quenching capacitor may be reversible, or two capacitors each having a separate charging circuit may be provided. In a further embodiment, each winding has its own control circuit and freewheel circuit. Rheostatic braking may be provided by a resistor associated with a special thyristor.