Abstract: Disclosed are a flux observer and a sensorless control system of a synchronous reluctance motor. The flux observer includes an estimated flux output unit, a measured flux output unit, and a fixed/rotational coordinate converter. The flux observer estimates a flux of a synchronous reluctance motor by removing higher harmonic components of a current in a rotational coordinate system which flows into the motor. The measured flux output unit measures a flux in a fixed coordinate system by combining a voltage in the fixed coordinate system, which is applied to the motor, and a current in the fixed coordinate system, from which higher harmonic components are removed, with the estimated flux outputted from the estimated flux output unit. The fixed/rotational coordinate converter converts the measured flux outputted from the measured flux output unit to a measured flux in the rotational coordinate system.

Abstract: A reactor (5) having a predetermined small capacity is connected to a rectifier (2), and a capacitor (6) having a predetermined small capacity which is connected between DC bus lines of the inverter (3). A PN voltage corrector (10) calculates a ratio of the DC voltage detection value of the inverter obtained by the PN voltage detector (9) to a predetermined DC voltage reference value of the inverter (3) to thereby generate a PN voltage correction factor. A beat amount corrector (16) calculates a fluctuation amount of the motor current from the motor current detection value obtained by the motor current detector (15) and generates a reverse phase component of the motor current fluctuation amount. Thus, a small, light and low-cost inverter controller can be implemented.

Abstract: A motor control apparatus having a fundamental wave current control circuit that implements feedback control on a fundamental wave component of a motor current in a dq coordinate system rotating in synchronization with the rotation of the motor and a higher harmonic current control circuit that implements feedback control on a higher harmonic components of the motor current in a dhqh coordinate system rotating with a frequency which is an integral multiple of the frequency of the fundamental wave component of the motor current, eliminates the higher harmonic component of the motor current from the control deviation between a fundamental wave current command value and a motor current feedback value.

Abstract: A circuit system that includes a sensor circuit for a sensor that detects the state of a motor is provided in an inverter unit for driving the motor. A 0V of the circuit system is connected with a shield braid of a shielded cable that connects the sensor circuit and the sensor. Further, the shield braid of the shielded cable is connected to an earth plate.

Abstract: A provide a position-sensorless motor control apparatus comprises a salient-pole AC motor 2, a PWM inverter 3 for applying voltage to the AC motor 2, and a controller 1 for controlling the PWM inverter 3 by means of PWM signals, wherein the controller 1 has a position estimation means 11 which detects motor inductance in the pre-determined direction to the vector direction of the current that flows through the AC motor 2 and estimates the AC motor's rotor position based on the motor inductance.

Abstract: A drive control apparatus and method drives an AC motor by applying a rectangular wave voltage thereto. The apparatus estimates the torque of a rotor of the AC motor, and detects a torque deviation which is the difference between the estimated torque and a required torque of the motor. A controller controls a state of the rectangular wave voltage applied to the AC motor, through torque feedback control based on the torque deviation, so that the torque approaches the torque command value. The controller detects a current rotation speed of the motor, and switches, in a predetermined order, a plurality of predetermined rectangular wave voltage states corresponding to different phase values of the rectangular wave voltage. The switching timing of the rectangular wave voltage states is set to a timing that deviates from a reference timing determined based on the current rotation speed, by a length of time corresponding to the torque deviation.

Abstract: A control system for an electric motor including an inverter for providing power to the electric motor, a controller for controlling the inverter, a first motor speed control block in the controller injecting a high frequency signal into the electric motor to determine the speed and position of the electric motor, where the first motor speed control block includes a tuned moving average filter to determine the magnitude of high frequency current in the electric motor.

Abstract: There are provided an inverter part having switching means for applying a three-phase AC voltage to a motor 3, lock detection means for detecting a lock state of the motor 3 and also generating a lock detection signal by the detection, and current control means for passing a d-shaft armature current id through the motor 3 so that an absolute value of a current of a phase with the largest current flowing through the motor 3 decreases based on the lock detection signal.

Abstract: A motor driving system for driving an induction motor with a rotation frequency detector. The induction motor drives a load, and the rotation frequency detector detects a rotation frequency of the induction motor. The motor driving system includes a variable speed driving unit and an inverter control unit. The variable speed driving unit is connected to the induction motor and has a capacitance at output. The variable speed driving unit rectifies first 3-phase AC power to produce DC power, and converts the DC power into second 3-phase AC power with a frequency, and drives the induction motor with the second 3-phase AC power. The inverter control unit generates a frequency instruction and a temporary current instruction based on the detected rotation frequency and a rotation frequency instruction at least.

Abstract: A microcomputer for performing an inverter control includes three AD converters provided therein. The first and second AD converters are used for a motor control, and each receive a motor position detection signal. The third AD converter is used for a power supply control, and receives an analog signal representing the state of the power supply. Therefore, a motor control and a power supply control are performed by using separate AD converters, whereby it is possible to optimally perform each control without an AD conversion having to wait for another AD conversion to be completed.

Abstract: A method to estimate motor speed for extended stabilized rotational control of an induction motor at all speeds including slow speeds. The speed estimator supplies real-time time motor control feedback information for a variable speed motor drive controller without a mechanical encoder. The speed estimator is based on an optimized fast orthogonal search algorithm with control of the carrier drive frequency to reduce computation time. The reduced processing time provides for an update rate to the motor controller sufficient to maintain motor stability to near zero the motor rated base speed.

Abstract: A method and apparatus for estimating flux angle position in an induction machine, the method including the steps of providing high frequency injection voltage signals to a three-phase motor, obtaining frequency feedback signals from machine supply lines, converting the feedback signals to two-phase stationary high frequency signals, converting the stationary signals to synchronous signals using a high frequency angle estimate, negating one of the resulting synchronous signals, stepping up the negated signal to generate a low frequency spectrum signal, adding the low frequency spectrum signal and the high frequency injection signal to generate a combined spectrum signal and integrating the combined spectrum signal to generate the high frequency angle estimate, dividing the low frequency spectrum by a system specific DHN to generate a stator frequency estimate and integrating the stator frequency estimate to generate the flux angle estimate.

Abstract: The invention is applied to the field of industrial controls for electric motors and more precisely refers to a process for measuring phase currents of an inverter or a DC controller consisting in detecting the temperature of a copper path made with IMS (Insulated Metal Substrate) technology and the like, used as shunt and that is the extension of a pre-existing adduction line towards a motor or towards the supply line or towards power devices, and in compensating through software the path drop in order to have an accurate measure of the current crossing it. A heat sensor is applied next to or over such copper path to detect its temperature. This latter one will also be assumed, with an acceptable degree of approximation, as the power transistors temperature.

Abstract: This invention relates to a system for limitation of the output current from a speed controller for three-phase asynchronous electric motors, comprising a PWM type converter in which the electronic switches are controlled by a microcontroller circuit (Mc), characterized by the fact that the microcontroller circuit comprises means (LIC) of calculating the modulus of the current vector using motor phase current measurements, and comparing it with a limitation set value in order to obtain a limitation error (y) and to calculate a correction voltage (&Dgr;V) that is added to the control voltage (V) applied to the motor.

Abstract: A motor driver having output circuits each including upper and lower side switching elements connected in series. The motor driver includes: a current detection resistance connected in series with the output circuits in common; a phase switch circuit for turning ON a switching element on one side of one of the output circuits for a time period corresponding to a predetermined electrical angle and switching switching elements on the other side of a plurality of output circuits among the remaining ones of the output circuits; and an ON-period control section for generating a signal for controlling the switching operation so that each of periods obtained by dividing the time period includes a first period in which a plurality of switching elements are turned ON and a second period in which one of the switching elements turned ON in the first period is kept ON.

Abstract: A direct current motor rotation control apparatus, a method and device for controlling a rotational speed of a direct current motor, and an apparatus having the direct current motor rotation control apparatus. The apparatus and device control rotational operations of a direct current motor such that the direct current motor rotation control apparatus includes at least one rotation detecting brush which detects a signal indicative of an operation of the direct current motor, a motor driving circuit which drives the direct current motor by applying the direct current drive voltage to the pair of electrode brushes, a reference voltage generating device which generates a reference voltage a comparator which compares a voltage detected by the rotation detecting brush with the reference voltage generated by the reference voltage generating device and produces an output comparison voltage, and a motor control circuit which adjusts the direct current drive voltage based on the output comparison voltage.

Abstract: A method of generating low voltage auxiliary power forms for electric or hybrid vehicle use by tapping power from the traction motor primary winding with a secondary winding and rectifier.

Abstract: PWM controlling means (4) for inputting PWM signals corresponding to PWM target values to electric power supplier (3) in order to servo-controlling DC motor (2) comprises synchronizing control part (41), PWM computing part (50), selecting part of PWM target value (45) and PWM commanding part (46). The synchronizing control part (41) instructs the commencement of the PWM computation, selection of PWM target value and PWM command allotted to some of the infinitesimal intervals obtained by dividing processing term, on which PWM signals regulating the electric power supplied to the motor (2) are allotted, into n equal parts, and terminates one cycle for a series of the process and/or computation predetermined within one processing term. PWM target values corresponding to plural control target values (DP0, DV0, DT0) are computed in parallel so that the servo-control of motor can be operated in quick response to the change of control mode.

Abstract: A N pulse variable frequency drive for driving two or more motors that is the combination of two or more variable frequency drives with each drive driving an associated one of the two or motors. One application is a decanter centrifuge which has a main motor to drive the bowl and a back motor to drive the conveyor. One of the two variable frequency drives drives the main motor and the other drive drives the back motor. The variable frequency drives are connected to a common buss and to a N pulse phase shifting transformer.

Abstract: A method and system for early detection of incipient faults in an electric motor are disclosed. First, current and voltage values for one or more phases of the electric motor are measured during motor operations. A set of current predictions is then determined via a neural network-based current predictor based on the measured voltage values and an estimate of motor speed values of the electric motor. Next, a set of residuals is generated by combining the set of current predictions with the measured current values. A set of fault indicators is subsequently computed from the set of residuals and the measured current values. Finally, a determination is made as to whether or not there is an incipient electrical, mechanical, and/or electromechanical fault occurring based on the comparison result of the set of fault indicators and a set of predetermined baseline values.

Abstract: A reluctance drive includes a stator, a phase winding (16) on the stator, a rotor (12) that is movable relative to the stator, a controller for applying a current to the phase winding (13), and a sensor for measuring the phase current in the winding (16). Aspects of the invention detect when the phase current has passed its peak, compute when the peak phase current occurred using information on when the phase current passed its peak, determine rotor position using the computed position of the peak phase current.

Abstract: A microcomputer for performing an inverter control includes three AD converters provided therein. The first and second AD converters are used for a motor control, and each receive a motor position detection signal. The third AD converter is used for a power supply control, and receives an analog signal representing the state of the power supply. Therefore, a motor control and a power supply control are performed by using separate AD converters, whereby it is possible to optimally perform each control without an AD conversion having to wait for another AD conversion to be completed.

Abstract: A method and apparatus for controlling flux in an induction motor. During initial start of an induction motor drive the motor flux has to be charged up. The method provides time optimal flux forcing under limited inverter ampere capability. Command stator flux and current are generated and coordinated through a motor flux model. Charging of the motor flux and flux current are accelerated up to nominal operating values in coordinated manner.

Abstract: A back EMF monopole motor and method using a rotor containing magnets all of the same polarity and in a monopole condition when in momentary apposition with a magnetized pole piece of a stator having the same polarity, said stator comprised of a coil with three windings: a power-coil winding, a trigger-coil winding, and a recovery-coil winding. The back EMF energy is rectified using a high voltage bridge, which transfers the back EMF energy to a high voltage capacitor for storage in a recovery battery. The stored energy can then be discharged across the recovery battery through the means of a contact rotor switch for further storage.

Abstract: The present invention provides a control algorithm which instantaneously detects magnetic pole positions in the inside of a motor including polarities of the motor. A controller 1 applies a minute voltage change vhd to a voltage command on a dc axis which constitutes an estimation magnetic pole axis of the motor 3, detects electric currents Idc, Iqc of a motor 3 and discriminates the polarities of the magnetic pole axes by making use of the difference between a cycle in which ripple components of the electric currents Idc, Iqc become positive and a cycle in which the ripple components become negative or the difference between positive-side and negative-side current change rates. Further, the minute voltage change vhd with respect to the above-mentioned voltage command is generated on both of the dc axis and the qc axis rectangular thereto, and the magnetic pole positions of the motor are directly estimated based on the current ripple components on the respective axes.

Abstract: An H-bridge motor driving circuit has, between a PWM comparator and a control circuit, first and second frequency dividers for frequency-dividing, by 2, an AND gate, OR gate, and first and second and second inverters. During a first period, the first and second MOS transistors are turned on, and the second and third MOS transistors are turned off, caused a current to flow through a motor. During a next second period, the third and fourth MOS transistors are turned on, and the first and second MOS transistors are turned off, causing a regenerative current to flow through the motor. During a next third period, the MOS transistors are turned on and off in the same manner as during the first period, causing a current to flow through the motor. During a final fourth period, the first and second MOS transistors are turned on, and the third and fourth MOS transistors are turned off, caused a regenerative current to flow through the motor.

Abstract: A system (10) for controlling the torque of an induction motor (12) utilizes a flux observer (14). The flux observer (14) receives stator current inputs (16, 18) and a rotor speed estimate (80) and then outputs a rotor flux estimate (20) that provides increased motor control stability at all speeds.

Abstract: The present invention overcomes the disadvantages of previously known motor controllers for centrifuge machines wherein a motor controller is provided for a centrifuge machine including a logic control module, one or more power cells, and one or more contactors. The logic control module is capable of interfacing with the main centrifuge controller and provides control over the power cells and contactors to provide a voltage ramp-up to accelerate the centrifuge basket. As such, the logic control module avoids the current draining problems associated with across the line starting of the centrifuge motor. The power cells receive a voltage from the main power supply, and output to the contactors variable power to control centrifuge motor speed. Further, the configuration of multiple contactors to reverse the power supplied to the centrifuge motor windings may eliminate the need for a second, reverse direction motor.

Abstract: A method and apparatus for achieving constant air flow rate economically utilizes an induction blower motor with control settings determining the motor excitation voltage. A memory stores, for a variety of motor speeds, a graph of the speeds plotted against a proportionality constant of flow rate to fan speed for the selected motor system on one axis and motor control settings on the other axis. The only monitoring necessary to achieve the constant flow rate is thus the sensing of fan rotational speed. The measured fan speed is compared against the proportionality constant needed for the selected constant air flow rate and a motor excitation voltage is derived to achieve that proportionality constant. When the system load changes significantly, thereby causing significant fan speed change, a cascaded control loop is used whereby the speed changed induced by each control voltage adjustment is monitored until the desired constant flow rate is again attained at the new load level.

Abstract: The present invention makes possible a safety function for speed monitoring in the case of all induction machines operated on an inverter without a sensor system, in that a determined setpoint stator frequency value (&phgr;5*) is limited and monitored in a two-channel mode in two systems with approximate redundancy, deriving from this in each system respective sets of control signals for the electrical valves of the inverter, which can be compared with one another in two systems of monitoring electronics. In the event of fault detection, two-channel switching off takes place. The circuit arrangement according to the invention can additionally be subjected to enforced dynamization.

Abstract: The temperature (25, 33, 43) of solid state switching devices in variable speed motor drives (11, 18), such as elevator motor drives, are utilized to reduce the load on the drive, by reducing the switching frequency (50) or the commanded load (110). The choice between the preferred non-switching zero state and an alternative zero state is determined (60) by temperature (28, 34, 56) of the switched transistor's anti-parallel diode. The rate of recognizing reduced temperatures is limited (33, 34) to avoid motor speed and/or load variations. The temperature may either be measured (24, 27) or determined (70) from models utilizing manufacturer product specification and normalized thermal transient response from the transistor/diode package to a heat sink.

Abstract: An apparatus and method for controlling a motor/blower system to provide a constant fluid flow by iteratively loading revised stator frequency values and stator voltage values to a variable frequency drive. Target DC bus current values corresponding to constant fluid flow rates are predetermined and stored as a function of the desired fluid flow rate, the operating frequency, and system specific constants or calculated by the controller as a function thereof during system operation. Actual DC bus current is measured with a current sensor and compared with the target DC bus current. Operating frequency is estimated using a PI controller based on the difference between measured and target DC bus current values. Operating voltage values corresponding to operating frequencies and system specific constants are predetermined and stored in memory or calculated by the controller during system operation. An updated target DC bus current, operating frequency and operating voltage are determined upon each iteration.

Abstract: A circuit and method for permitting uninterrupted operation of a motor, even in the event of an over temperature condition, by dynamically controlling the motor torque based on the temperature of switching devices in the motor controller circuit. The circuit limits the torque current to either a fixed limit value if the temperature of the switching devices (or a current feedback signal for estimating the temperature of the switching devices) is below a predetermined value, or to a variable limit value which is inversely proportional to the temperature signal if the temperature of the switching devices (or the current feedback signal) exceeds the predetermined value. Accordingly, in the event of an over temperature condition, the motor continues to operate, but at a reduced torque, allowing the switching devices to cool.

Abstract: A method of reconnecting a motor to a motor drive comprises controlling a current which flows through the motor using a current regulator. The current regulator produces a voltage command output based on a current command input. A current is commanded at the current command input of the current regulator. Back EMF measurements are acquired at different instants in time by monitoring the voltage command output of the current regulator. Back EMF phase angles are determined for a plurality of the instants in time based on a respective plurality of the back EMF measurements. A frequency of the back EMF is determined based on the back EMF angles determined for the plurality of instants in time. The motor drive is reconnected to the motor based on the frequency of the back EMF.

Abstract: A power electrical system is disclosed for a microturbine power generator. The invention permits the microturbine to be started using an external DC power source. The DC voltage is converted to a variable DC voltage by means of a bi-directional buck-boost circuit, DC bus and a DC-to-AC converter. The DC-to-AC converter produces at its output a fixed voltage pattern whose frequency is gradually increased in concert with the DC voltage, to accelerate the microturbine from standstill to startup speed. Once the microturbine is started, the excitation is discontinued, and the DC bus and DC-to-AC are used to produce output AC power at a voltage level and frequency to match an electrical load.

Abstract: In a valve timing control apparatus for an internal combustion engine using an oil pressure control, a feedback correction amount is calculated so as to have a linear term proportional to a deviation between a target value and an actual value of the valve timing control apparatus, and a non-linear term using a switching function by a sliding mode control. Further, a dither control is added to the feedback correction amount and a learning is performed for a basic control amount and a control gain. Therefore, a control can be executed with high robust, high accuracy and quick response.

Abstract: This monitoring apparatus for monitoring the adhesion of a motive power unit of an electric rail vehicle set comprises a power control stage for controlling the power supplied to the motor of the motive power unit, and an adhesion monitoring stage proper delivering to the power control stage a reference signal generated on the basis of at least one operating characteristic of the motor so as to keep the slip of the wheels of the motive power unit under control. The apparatus further comprises means for generating an activation signal for activating the monitoring apparatus and means for injecting the activation signal into the reference signal so as to cause it to deliver a modified reference signal.

Abstract: A control apparatus for an electrical power steering apparatus whereby a high output, small motor can be achieved, variation in the relative magnetization and coil positions and position detection precision requirements can be alleviated, steering feeling is improved, and apparatus cost is reduced. In a control apparatus for an electrical power steering apparatus for controlling a motor applying steering assistance force to a steering mechanism based on a current control value calculated from the current of a dc motor or brushless motor and a steering assistance control value calculated based on steering torque occurring at the steering shaft, torque ripple of the motor is suppressed to 10% or less.

Abstract: A motor current detection amplifier detects a motor current's areas in two phase periods with reference to a motor voltage. A controlling microcomputer computed the ratio of the motor current areas of the two phase periods and provides the same as phase difference information which is in turn used to control a motor drive voltage to apply a sine wave of a predetermined period to the motor's coil to allow 180°-driving including a sine wave conduction resistant to noise and achieving a reduced cost hike.

Abstract: A motor control system 16 for use within an electric vehicle 10 having an induction motor 12. Control system 16 utilizes a torque control module 18, a vector control module 20 and a space vector PWM module 22 to efficiently and accurately control the torque provided by motor 12.

Abstract: A method and apparatus for deriving characteristics of a utility signal for synchronizing the output of a motor drive with the utility for a transfer or capture operation. With the drive in idle, the voltage and phase angle of an input to the drive are detected by instrumentation of the drive. The voltage and phase angle of a signal from a utility are detected by instrumentation of the drive at the output of the drive. A phase angle difference and scaling factor are determined to correlate the input signal to the motor drive with the signal at the output of the motor drive. The phase angle difference and scaling factor are stored and subsequently used to derive the signal at the motor due to the utility at the time of the transfer or capture procedure.

Abstract: A control device for an alternating current motor includes: a target current generating unit which generates a current order value, based on a torque order, as a d-axis target current and a q-axis target current on dq coordinates; a current detection device which detects an alternating current supplied to each phase of a polyphase alternating current motor; a coordinate transforming unit which transforms the alternating current detected by the current detection device into a d-axis current and a q-axis current on the dq coordinates; and a vector control unit which carries out a current feedback control so that the d-axis current follows up the d-axis target current and the q-axis current follows up the q-axis target current.

Abstract: The present invention concerns a method for symmetrizing asymmetric faults occurring within a pull chain comprising a synchronous or asynchronous motor controlled by a two-level or multi-level inverter consisting of static switches using semiconductors such as IGBT or bipolar transistors. The invention comprises detecting whether the fault connects or may connect a motor phase with the top point or the bottom point of the inverter power supply, and short-circuiting only the half of the inverter affected by the fault on the basis of the detection.

Abstract: A refrigerator, having a motor for driving a compressor, an inverter for controlling the operation of the motor, a converter responsive to AC to perform a boosting function to supply DC of variable voltage to the inverter, converter control means for controlling the converter so that a plurality of DC voltages are outputted thereby and inverter control means for controlling the inverter in pulse width modulation each of the plurality of voltages. The lowest voltage among the plurality of voltages being a voltage which turns off the boosting function of the converter.

Abstract: A motor/generator has a stator provided with a plurality of coils (6), a first rotor (3) provided with a fixed number of magnetic poles, and a second rotor (4) provided with fewer magnetic poles than the first rotor (3). A current of the composite wave form is supplied from an inverter (12) to the coils (6) in response to a signal generated by a control unit (15). The control unit (15) is programmed to calculate a wave form of a first current flowing through the coils (6) which generates a rotating magnetic field which is synchronous with a magnetic field produced by the first rotor (3), and calculate a wave form of a second current flowing through the coils (6) which generates a rotating magnetic field which is synchronous with a magnetic field produced by the second rotor (4).

Abstract: A method and apparatus for actively controlling the energization of the stator windings of a rotating electromagnetic machine to actively overcome any tendency of the rotor of the machine to prefer certain angular positions with respect to the stator over other angular positions.

Abstract: A controller for electric vehicles comprising a vector control inverter for controlling motors, which drive wheels of the electric vehicles, by dividing the primary current of the motors into an exciting current component and a torque current component, and controlling respective of the current components based on a respectively designated command, characterized in further comprising a dectector for detecting a wheel velocity (including a rotor frequency of the motor proportional to the wheel velocity), a detector for detecting slipping and skidding of the wheel based on a differential value (a changing rate with time) of the detected wheel velocity, a dectector for detecting re-adhesion of the wheel based on the differential value and a twice differential value of the detected wheel velocity, and an adjuster for adjusting the designated command for the torque current component in response to the detectors.

Abstract: An electric power system for an electric vehicle includes an electric drive motor, a high voltage bus for supplying operating power to energize the drive motor, and an inverter including power switching devices and having an inverter output. The inverter is coupled between the high voltage bus and the electric drive motor and a controller is coupled to the inverter and provides motor control signals and high frequency injection signals to the inverter. An auxiliary power unit is coupled to the inverter output and has a DC output for supplying DC operating power. The auxiliary power unit supplies DC power in response to the high frequency injection signals. The electric drive motor operates in response to the motor control signals and is substantially unaffected by the high frequency injection signals.

Abstract: A more compact and light-weight drive unit is required for an electric vehicle in order to improve its mileage per charge, acceleration performance and overall efficiency. A control apparatus which generates drive signals to drive power devices in the power converter includes: a current reference generator calculates from a torque reference value a d-axis exciting current reference value on the basis of which the ac motor generates a magnetic flux, and a q-axis torque current reference value, the d-axis and the q-axis being orthogonal to each other; a current control circuit generates ac voltage reference values Vu*, Vv* and Vw* from the d-axis exciting current reference value and the q-axis torque current reference value; and a drive signal generator generates drive signals to drive power devices from the ac voltage reference values. Both the current reference generator and the current control circuit are processed digitally by the same arithmetic unit.

Abstract: A method and apparatus for controlling a motor. The apparatus includes a voltage input; a half-bridge inverter connected the voltage input and to the motor to provide low speed excitation to the motor; and a circuit for selectively electrically connecting the voltage input to the motor and for selectively electrically disconnecting the inverter from the motor.