Switched Reluctance Drives Limited

Chloride Group Limited

Chloride Group Public Limited Company

Tasc Drives Limited

Rex Mountford Davis

William Frederick Ray

A method and apparatus for reducing winding failures in electric machines resulting from the application of high frequency or high dV/dt voltage pulses or voltage signals to the phase windings of the machine in which an inductive element is provided between the source of the high-frequency or high dV/dt pulses and the phase winding to absorb a portion of the voltage stresses on the phase windings that result from the application of the high-frequency or high dV/dt pulses to the machine.

Method and apparatus for reducing voltage stresses in electric machines

A method and apparatus for reducing winding failures in reluctance machines wherein winding coils for the switched reluctance motor are formed and positioned such that the turn-to-ground capacitance of the portion of the winding coil coupled to an electronic motor controller is reduced. Alternate embodiments are disclosed wherein additional insulation, and capacitive voltage distributors are provided to enable a switched reluctance motor to better handle the voltage stresses produced when high frequency or high dV/dt voltage pulses are provided to the motor.

Method and apparatus for reducing voltage stresses in electric machine

A switched reluctance generator is controlled such that flux growth in a phase winding occurs at a faster rate during the initial part of the phase inductance cycle and at a second, slower rate during the subsequent part of the phase inductance cycle. The difference between flux growth and decay may be achieved either by applying different voltages during the two parts of the phase inductance cycle or by applying the same voltage over only part of the phase winding during the initial part of the phase inductance cycle and then applying that voltage across the phase winding thereafter. It is advantageous to make the increase in flux more rapid than its decay because minimizing the length of time that the flux is present while the phase inductance is rising will minimize the production of unwanted (motoring) torque.

Switched reluctance generators

A polyphase switched reluctance machine has only n power cable connections for n phases. Each phase winding includes a series connected diode and the phase windings and their diodes are arranged in a conducting ring. Alternating currents are fed to the nodes of the conducting ring from an inverter. The nodal connections between the phases allows the alternating current to energize the windings where previously only a greater number of cables and a unidirectional current would have been required. Due to the presence of alternating current, a transformer may be interposed between the inverter and the nodes of the conducting ring to allow a boosted voltage to be delivered over long distances.

Power supply to a stator of a polyphase reluctance machine

A control circuit for an inductive load, such as a phase winding of a reluctance motor, includes a boost flyback converter. The controller includes a dc link capacitor switchable across the load by means of a control switch and a suppressor switch for controlling the application of rectified current to the dc link capacitor. The suppressor switch is operated independently of the control switch in order to control the rectified current so that it follows the sinusoidal input voltage waveform. By this technique, the harmonics generated by switching the rectified input current are substantially suppressed.

Control circuit for an inductive load

A switching circuit for a switched reluctance motor or generator comprises positive and negative power lines, a string of smoothing capacitors serially connected between them and two pairs of gate turn-off thyristors connected to either end of a phase winding of the motor or generator. Circulating diodes are connected between the ends of the winding and the opposite power line and further circulating diodes are connected between each pair of thyristors. A mid-point between the capacitors is connected between the further diodes. At switch-off one of the outer GTO's is first opened so that one of the diodes conducts and current in the winding is routed via the mid-point. Then the other outer GTO is opened so that current now circulates through both of the diodes and substantially no voltage is dropped across the winding. The first inner GTO is then opened causing one of the diodes to conduct. Thereafter the second inner GTO can be opened. Turn-on requires a progressive reversal of the turn-off sequence if winding current continues to flow. Otherwise, all but one outer GTO are turned on together followed by the omitted GTO after a delay. The GTO to be omitted initially at turn-on is chosen to provide the desired correction to the voltage at the midpoint.

Switching circuit

A regenerative ac to dc convertor includes a thyristor bridge invertor and a rectifier having a dc link capacitor. A second capacitor is connected across the invertor. In a regenerative braking mode of the motor the invertor is arranged to return energy from the second capacitor to the ac supply. Circulating currents are inhibited by diodes connecting the dc link and second capacitor. A first diode is arrange to conduct from the positive terminal of the second capacitor to the positive terminal of the dc link capacitor. A second diode is arranged so that it conducts from the negative terminal of the dc link capacitor to the negative terminal of the second capacitor.

Regenerative ac to dc converter

Power conversion circuit

Electric power converter circuit

Variable reluctance motor systems

Variable reluctance electric motor systems

In a variable reluctance electric drive system motor the fractions of a cycle during which the winding inductance of a phase increases with movement in either direction are such that the motor is self starting in either direction. The timing of the power converter in relation to the cycle of inductance is such that the current increases from its minimum value to substantially its maximum value while the winding inductance is substantially at its minimum value and thereafter substantially decreases before the power converter disconnects the winding from the supply. This can be achieved by making the switch-on and commutation of current occur at predetermined positions so related to the variation of inductance that the peak current ip at maximum power and maximum speed, is greater than I, where I=E/(R+dL/dt), E is the supply voltage, R the winding resistance and dL/dt is the maximum rate of increase of inductance before the commutation point.

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Loughborough, United Kingdom

Rex Mountford Davis