Abstract: A digital power factor correction circuit including a digital comparator that compares the actual DC bus voltage of an electric circuit with a desired DC bus voltage to produce a digital attenuation signal in the form of a pulse width modulated signal that is used to attenuate the voltage from a time-varying source. The attenuated source voltage is used as the current demand signal for a current controller that controls the current drawn from the line.

Abstract: An electric motor controller is disclosed that controls the torque of a switched reluctance motor with an angle controller that eliminates the need for a look-up table. In one example, the electric motor controller includes an angle controller that employs edge-triggered monostables to generate a single pulse firing signal which is synchronized with rotor position and whose pulse length varies with torque demand. An angle firing circuit utilizing freewheeling is also disclosed.

Abstract: A control circuit for a switched reluctance machine comprises a transistor connected with the machine winding across a rectified ac power supply. The transistor controls the flow of current through the winding in a primary current path. A silicon controlled rectifier and a capacitor are serially connected across the power supply and a diode is connected between the winding and the transistor and between the silicon controlled rectifier and the capacitor. In the steady state, the capacitor is charged each time the transistor is opened. The transistor and the silicon controlled rectifier are actuated together so that the capacitor discharges through the silicon controlled rectifier and the winding until the capacitor is discharged below the supply voltage. Thereafter, the silicon controlled rectifier ceases conduction and energy is drawn from the supply. The circuit avoids the need for a dc link capacitor across the power supply to smooth the supply voltage.

Abstract: A controller for a switched electric machine, especially a switched reluctance motor, takes timing information from a rotor position transducer to generate a switch-off output at a point near maximum phase inductance in a phase inductance cycle. A switch-on signal is generated after a delay but still within the phase inductance cycle. A simple form of single-pulse control is thereby achieved. A comparator is also provided which monitors phase winding current. A pulse generator is actuated by the comparator when the winding current exceeds a reference level and is used to control the motor in a chopping mode at low speeds and is disabled by the comparator at higher speeds when the single-pulse control is used.

Abstract: A rotor assembly for a reluctance machine is disclosed in which the rotor assembly comprises a stack of rotor laminations having a plurality of rotor poles defining interpole regions. The rotor assembly also comprises a cage including an end plate and support bars, which may be electrically conductive, that are axially aligned within the interpolar regions that lie between adjacent rotor poles. When the support bars are electrically conductive, the support bars can become transient "flux blockers" as the rotor assembly rotates past a stator pole, blocking the flow of flux through the interpole regions and improving the performance of the motor.

Abstract: A failure detector for a position encoder which uses a plurality of position sensors. The failure detector receives position signals from the plurality of position sensors. The position signals represent the rotor position for a switched reluctance machine, and the position signals have allowable states and allowable output state sequences that occur if the position encoder is operating properly. If one or more of the plurality of sensors fail or the rotating element of the position encoder is damaged, an illegal state occurs in the position signals from the position sensors. The failure detector produces a failure signal upon the occurrence of an illegal state. In addition, the failure detector monitors the sequence of the output states and generates a failure when the output states change in a sequence that is not one of the allowed sequences. The machine controller can respond to the failure signal to stop machine operation or trigger an alternate positioning scheme.

Abstract: The present invention employs digital circuitry to compensate for variations in DC link voltage transmitted to a switched reluctance machine. The digital voltage compensation system of the present invention periodically samples the DC link voltage and actual rotor speed, then supplies the samples in digital form to a microcontroller that derives a compensated speed signal to compensate for changes in DC link voltage.

Abstract: 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.

Abstract: 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.

Abstract: A temperature monitoring circuit comprises a thermistor which is connected with a power supply rail by means of a transistor. The transistor is pulsed to connect the thermistor intermittently in circuit with the power supply. The mean power drawn by the thermistor from the power supply is reduced, causing less drain on the power supply.

Abstract: A reluctance machine comprises a rotor, defining rotor poles and a stator defining stator poles. Each stator pole pair, creating a flux path through the rotor includes only one winding mounted on one of the stator poles. The invention is particularly applicable to a machine having a four-pole field pattern and an odd number of phases. The coils are placed on alternate stator poles such that the space between stator poles can be used exclusively for a single winding. The single winding is made larger to compensate for the lack of a winding on its associated pole.

Abstract: A circuit and method for controlling a switched reluctance drive having at least one phase winding and a rotor position encoder that provides a set of signals corresponding to the absolute position of the rotor relative to the stator. The circuit monitors the set of signals and generates a high frequency clock signal having a frequency substantially proportional to the frequency at which the set of signals changes state. The high frequency clock signal comprises a number of digital pulses for each rotor revolution that is an integral multiple of the number of digital pulses from the rotor position transducer for each rotor revolution and corresponds to the incremental position of the rotor. The high frequency clock signal is applied to a counter that is reset upon each change in state of the set of signals. The output of the counter is compared to predetermined values and the at least one phase winding is energized and de-energized in response to the results of the comparison.

Abstract: A single-phase variable reluctance motor is disclosed. The motor includes a stator having a pair of projecting poles defining a principal axis and a rotor mounted on a rotatable shaft co-axial with the principal axis of the stator. The stator may have inwardly extending poles that terminate in a central bore and the rotor may be rotatably disposed in the central bore. In such an embodiment, the stator poles are arranged generally diametrically opposed to one another. The rotor is mounted on a shaft and has a pair of poles generally diametrically opposed from each other. The stator and rotor may be formed from laminations of a ferromagnetic material. Energizing coils are wound around one or more of the stator poles. When energized, the energizing coil(s) impart a torque on the rotor causing it to rotate. One or more permanent magnets are inserted into the winding(s) forming the energizing coil(s) to park the rotor in a preferred starting position when the motor is turned off.

Abstract: A sensor failure detection circuit for a position encoder, the sensor failure detection circuit receiving from a first set of at least one position sensor position signals which change state at a high resolution and from a second set of at least one position sensor position signals which change state at a lower resolution, the detection circuit monitoring a count for the position signals at the high resolution between states of the position signals at the lower resolution and comparing the count with a predetermined range which represents an expected count for the position signals at the high resolution between the states of the position signals at the lower resolution.

Abstract: A rotor position encoder for an electric motor includes a discate member mounted to rotate with the rotor shaft. The encoder has a set of radially extending features formed with angularly evenly spaced leading edges and unevenly spaced trailing edges. The leading edges induce a signal in a sensor that corresponds to the relative timing of power switches for each motor phase, The trailing edges define a cyclical code by which motor controlling circuitry is able to determine the phase of rotation of the rotor and thus establish the correct power switch actuation sequence. An electric motor control system and methods of starting electric motors also provide significant advantages.

Abstract: A switched reluctance machine comprises a stator and a rotor and a winding for each phase of the stator. A single current sensor is arranged to sense current in the phase windings such that they are discriminated between according to the energization sequence of the windings by a controller, including a digital processor which counts the sensed currents and attributes the source of the currents counted among the phase windings according to a known phase winding energization sequence.

Abstract: 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.

Abstract: A control system for and method of controlling a switched reluctance generator to maintain stable control of the generator in the continuous current mode. This is achieved by sensing the load on the generator, the speed of the rotor and the position of the rotor with respect to each phase winding in order to derive switching command signals to maintain the volt-seconds applied to the winding in each phase period so as to inhibit progressive flux growth in the phase windings by actuation of the controller switches.

Abstract: An electric motor comprises a laminated stator core supporting windings to define similar adjacent poles. A rotor is mounted to rotate within the stator. The similar poles in a group define flux paths with adjacent pole groups. Thus the flux paths required are restricted to those between adjacent dissimilar pole groups. In this way the material of the core between the flux paths can be reduced as it is not required to carry flux itself. This redundant portion of the core can be shaped to accommodate neighbouring components or to reduce the material of the core laminations.