Abstract: The invention relates to an assembly for adjusting mobile elements of furniture, comprising a motor, a control circuit which is provided with push-button switches, a current supply circuit, a mains connection, a mains supply circuit, a mains isolating relay and an auxiliary current source. The aim of the invention is to construct said assembly in a more cost-effective manner whilst at the same time retaining a safety isolation from the mains. To achieve this, the first push-button switch forms a direct electric circuit with the motor and the control input of the isolating relay is connected in parallel to the motor, or is connected to the latter via a Graetz bridge.

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: If a speed instruction value is less than a predetermined value, the output current of a power-conversion unit is controlled to be larger than a current value in an ordinary no-load operation, or a frequency instruction value is calculated based on a speed instruction value in place of an estimated speed.

Abstract: A method of AC induction motor speed control employing a rotor flux based MRAS (Model Reference Adaptive System) speed observer. Rotor flux-based MRAS speed observers develop two independent rotor flux estimates. The reference rotor flux estimate is based on the currents and voltages in the stator windings, and the adaptive estimate is based on the stator currents and the measured or estimated rotor speed. These two estimates are compared by taking the cross product between them, and this error signal is passed into a proportional-integral (PI) controller, which adjusts the speed until the flux estimates agree with one another. While this method is well-established, the estimator poles become lightly damped at high speeds and prone to stability problems. In this invention, the upper speed range of the rotor flux-based MRAS speed observer is extended by discretely or continuously modifying the gain/bandwidth parameters of the low-pass filter in the adaptive flux estimator as a function of estimated speed.

Abstract: Space vector modulation methods and structures are provided that reduce feedback errors which degrade motor control performance. In particular, the rotation of a reference voltage vector Vref is modified as it rotates with respect to voltage vectors that each represent a respective one of converter switch states in an electric-motor control system. One embodiment modifies the reference voltage vector Vref as it approaches various voltage vectors and another modifies the reference voltage vector Vref when its magnitude is less than a predetermined magnitude.

Abstract: A method for measuring three-phase alternating current using a current sensor and an apparatus therefore, which are capable of not changing an average voltage for a switching period by changing reference voltages for modulating pulse width in a switching period of an inverter and compensating for the changed reference voltages in the same switching period. It is possible to prevent current from being distorted, to detect three-phase output current in all of the switching periods, and to rapidly control instantaneous current by changing the reference voltages of arbitrary two phases in one switching period of an inverter, measuring current of each phase for the switching period using the current sensor, and compensating for the amounts of changes in the changed reference voltages of the two phase in the switching period.

Abstract: A switched reluctance drive is supplied from a power source and has a DC link capacitor. The phases of the machine are controlled by a current chopping controller which, during phase conduction overlap, controls the initiation of chopping in a second phase so as to minimize the current drawn from the capacitor, thereby allowing a reduction in the capacitor rating.

Abstract: A method and apparatus for generating stator and rotor resistance estimate, the method including the steps of providing high frequency injection voltage signals to a three phase motor, rotating three phase feedback current therefrom, converting the feedback currents to two phase currents that represent the high frequency component of the current vector wherein the d and q axis components are within a two phase voltage coordinate system and driving a regulator via one of the current components to generate a lag angle estimate, the lag angle estimate used to solve any of several different equations to calculate the stator and rotor resistance estimates.

Abstract: An induction motor control apparatus includes a first constant correction unit for correcting primary resistance based on quantity obtained by multiplying quantity of a voltage command from a frequency voltage control unit by the output of a correction unit, the quantity of the voltage command being a result of partial differentiation with the primary resistance; a second constant correction unit for correcting the inductance based on quantity obtained by multiplying quantity of the voltage command, the quantity of the voltage command being a result of partial differentiation with the inductance; and a third constant correction unit for correcting the inductance ratio based on quantity obtained by multiplying quantity of the voltage command, the quantity of the voltage command being a result of partial differentiation with the inductance ratio, suppressing the deterioration of control performance caused by the setting errors.

Abstract: A method and apparatus for monitoring voltage input to an appliance, such as a dryer, sensing when power input to the appliance is lost. In addition, a controller in the appliance pulses relay coils controlling motors and/or heating devices within the appliance to conserve energy on a backup capacitor that supplies the control circuit of the appliance in the event of power loss. Further, a voltage sense circuit outputting a square wave effects monitoring of the input voltage to the appliance by outputting the square wave signal whose cycle period is monitored to determine power outage. The controller stores current operation settings at the time of power outage in a memory device and ensures proper storage through the extra energy conserved from the capacitor by the pulsing of the relay coils.

Abstract: A method and apparatus for controlling power supplied to a motor comprising a power controller having a source of electrical power for providing the necessary power to operate the apparatus, an oscillator for generating gating signals at a relatively higher frequency than the electrical power supplied, circuitry responsive to the gating signals for gating the low frequency electrical power to generate a DC voltage, and an inhibitor for inhibiting the generating of gating signals by the oscillator to regulate the DC voltage generated so as to control the speed of any motor connected to the apparatus. The apparatus may be setup to inhibit the oscillator when certain circuit conditions such as an over current condition is detected. The apparatus may also be setup to keep the oscillator in an OFF state once inhibited until a specified amplitude or period of the input signal has been reached.

Abstract: Method and system for controlling an induction machine are provided. The method allows to sense rotor position of the induction machine using a relatively low-resolution rotor position sensor configured to supply a stream of pulses indicative of angular increments as the rotor position changes. A memory device is used for storing a synchronous angle boost function. The method further allows to retrieve from the memory device at least one function parameter for providing a synchronous angle boost during a start up mode of operation of the induction machine. Upon sensing a predetermined number of pulses from the rotor position sensor, the method allows to switch from the start up mode of operation to a normal mode of operation, wherein the boost provided to the synchronous angle is discontinued upon switching to the normal mode of operation.

Abstract: A fuel cell power plant (1) and a rechargeable battery (2) are connected in parallel to an electric motor (3) of a fuel cell powered vehicle, and the output voltage of the fuel cell power plant (1) is regulated by a converter (4). A temperature sensor (5) detects the temperature of the electric motor (3), and a controller (6) controlling the output voltage of the converter (4) to a predetermined high voltage value when the temperature of the electric motor (3) is greater than a predetermined temperature, thereby preventing the excessive rise of the temperature of the electric motor (3).

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 method for a frequency converter, when the frequency converter controls a motor and operates torque-controlled partly or entirely in a field weakening region. The method comprises the steps of defining the direction of travel and sector of a stator flux vector ({overscore (&psgr;)}s) in the motor, predicting a torque estimate (Tpred) produced by a voltage vector of the output of the frequency converter at the end of the voltage vector when a voltage vector change occurs at the instant of prediction, comparing the predicted torque estimate (Tpred) with a reference torque (Tref) of the frequency converter, and implementing the voltage vector change when the predicted torque estimate (Tpred) is smaller than the reference torque (Tref) and the stator flux vector ({overscore (&psgr;)}s) is moving in a positive direction of travel or when the torque estimate (Tpred) is greater than the reference torque (Tref) and the stator flux vector ({overscore (&psgr;)}s) is moving in a negative direction of travel.

Abstract: Method and apparatus for eliminating greater than twice motor overvoltage by altering modulating signals provided to a PWM controller which in turn provides firing pulses to a PWM inverter. The modulating waves are altered by either tying them to positive or negative DC buses or limiting the maximum magnitudes to a maximum magnitude value above which modulating waveforms are known to cause greater than twice overvoltage. Pass through modulating waveform angles at which waveforms have to be modified are determined as a function of modulating waveform symmetries and the first pass through angle within a waveform cycle.

Abstract: A brushless motor-generator has a stator with armature windings for polyphase operation and a rotor having at least one pair of permanent magnet poles. A controller varies the magnitude of the alternating-current voltage applied to the armature windings for controlling the operating motor power factor to permit the rotor magnetic field to operate at the optimum or at least at an improved torque angle with respect to the stator magnetic field in the motoring mode, with little or no torque pulsations at substantially all or at least most conditions of motor load.

Abstract: A variable output induction motor drive system for use with a polyphase variable output alternating current motor including a rotor and stator to drive an operating load such as an automotive vehicle, the variable output induction motor drive system comprises a sine wave current generator operatively coupled to a direct current power source to receive direct current therefrom and to generate a variable sine wave current and operatively coupled to the polyphase variable output alternating current motor to selectively feed the variable sine wave current thereto and a sine wave current control coupled between the sine wave power current generator and the polyphase variable output alternating current motor to monitor the operating parameters of the polyphase variable output alternating current motor and to control the amplitude and frequency of the variable sine wave current fed from the sine wave current generator to the polyphase variable output alternating current motor to control the output torque and speed t

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 motor speed control for controlling the speed of an electric induction motor by modulating the amplitude and frequency of the driving voltage. When the load increases the speed control controls the speed so as to be relatively constant with respect to the frequency of the driving voltage. Preferably, the speed control controls the amplitude of the driving voltage in proportion to the square of the frequency.

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: Disclosed is a three phase BLDC motor driving circuit which makes a BEMF voltage generated in a motor lower than a voltage source and makes a difference between the BEMF voltage and the voltage source greater than a saturation voltage of a transistor. An emitter is coupled to the voltage source and a collector is coupled to a three phase coil so that the voltage between the emitter and collector of the transistor supplying a current to the three phase coil attenuates to a first level so as not to saturate the transistor.

Abstract: A method for operating an actuating drive for controlling fittings. The actuating drive has an electric motor which is fed from a frequency converter and moves a fitting with a predetermined torque via a self-locking gearbox. In order to protect the actuating drive against unacceptable, destructive heating while maintaining operation in the surrounding process installation when an excess temperature occurs, the temperature of the actuating drive is measured during continuous operation, and the rotation speed of the electric motor is reduced as a function of the measured temperature while maintaining the torque. To this end, the amplitude and the frequency of the output voltage of the frequency converter are reduced in proportion to one another.

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: According to an aspect of the present invention, an induction motor driver includes a DC power supply having a selectively variable voltage. The driver also includes an inverter coupled to the DC power supply and coupleable to an induction motor, the inverter selectively actuateable to generate from the selectively variable voltage of the DC power supply a low-frequency series of square-shaped pulses, the series of square-shaped pulses having a frequency and each pulse having an amplitude related to the selectively variable voltage.

Abstract: An induction motor control system (10) for electric vehicles having a DC power supply (14), an inverter (16), an induction motor (12), a motor controller (26) and a vehicle-level controller (32). The method and system of the present invention optimizes the torque output for the induction motor and utilizes minimum power. The method and system of the present invention calculates the flux current such that the slip frequency is maintained at a nominal level, thereby producing peak torque.

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: The present invention provides a new limiting signal circuit configuration for the connection of a pulse-width modulation motor controller integrated circuit. This new circuit allows for increased control over the over-current protection scheme while increasing the maximum available current levels. The invention utilizes a resistor based voltage divider connected to an input power source to provide a sliding scale current limiting signal in proportion to the input voltage. This method provides protection in relationship to the incoming power signal.

Abstract: An apparatus and method for controlling an induction motor having a variable frequency drive in a blower system so that the blower system provides a specific fluid flow. A start-up program causes the motor to ramp up to approximately a predetermined steady state speed. A required blower torque is calculated by operating on a table of blower constants, a selected flow rate and a motor speed which is read from a speed sensor in the motor/blower system. A developed motor torque is calculated by operating on a table of motor specific constants, a voltage-frequency index and the motor speed taken from the speed sensor. The calculated required blower torque is repeatedly compared with the calculated developed motor torque. The voltage-frequency index to the variable frequency drive is modified to force the developed motor torque to converge with the required blower torque in a steady state.

Abstract: An apparatus and method for controlling an induction motor having a variable frequency drive in a blower system so that the blower system provides a specific fluid flow. A start-up program causes the motor to ramp up to approximately a predetermined steady state speed. A required blower torque is calculated by operating on a table of blower constants, a selected flow rate and a motor speed. The motor speed is calculated by operating on a table of motor specific constants, a voltage-frequency index and a measured direct current bus current. A developed motor torque is calculated by operating on a table of motor specific constants, a voltage-frequency index and the calculated motor speed. The calculated required blower torque is repeatedly compared with the calculated developed motor torque. The voltage-frequency index to the variable frequency drive is modified to force the developed motor torque to converge with the required blower torque in a steady state.

Abstract: If a speed instruction value is less than a predetermined value, the output current of a power-conversion unit is controlled to be larger than a current value in an ordinary no-load operation, or a frequency instruction value is calculated based on a speed instruction value in place of an estimated speed.

Abstract: A new series of portable electric tools using high frequency three-phase induction motors with built-in power electronic converter. The tools operate from a single phase AC mains and a built-in power electronic circuitry converts the input supply to a three-phase, higher frequency (200-400 Hz) supply, which is used to drive a three-phase induction motor connected to the gearbox. A microprocessor-based controller, with a novel algorithm, generates three-phase, sinusoidal output waveforms and also provides the soft-start feature for the inverter and the motor. The entire electronics is packaged in a novel way within the housing of the tool itself. The output shaft of the motor, either directly or through a gearbox, can be connected to a wide range of tools like Drills, Grinders, Nut Runners, Screw Drivers, Impact Wrenches, Shears, Nibblers, Saws, Sanders, polishers, etc.

Abstract: An objective of this invention is to provide a drive control device to control the drive applied to a high-speed rotor unit which would have no circuits in either its pump unit A or its power supply unit B that would limit the use of the device with various types of rotor units, which could easily be used with various types of rotor units, and whose power supply unit B could be used generally. The drive control device for controlling a high-speed rotor unit according to this invention has a power supply unit contains a set of tables of constants needed to control the various types of rotor units with which the drive control device might be used. These constants allow the rotation of the high-speed rotor unit to be adjusted or set according to the type of rotor unit. A signal intended to detect and indicate the type of rotor unit to be driven by the rotor is automatically detected and input before the motor is driven. Based on this signal, the appropriate table is selected.

Abstract: A system for starting synchronous motor from a pulse-width-modulated static inverter without using rotor position or speed measurements. The system monitors supply current to the stator and derives a relationship between that current and the magnetizing flux. The system utilizes a narrowband filter that is tuned to pass only the motor currents fundamental component and whose tuned frequency changes with variations in motor speed. Furthermore, the system reduces the excitation provided to the motor after a certain value of line voltage is sensed.

Abstract: In an induction motor drive system with/without a speed sensor, resistance values are stably and accurately estimated during the operation of the motor regardless of the operating conditions such as a speed, a load, etc. and of a particular combination of parameters. A suitable point Pr is taken inside a current locus on a stator current vector plane, and a measured current is and an observed current is′ are referenced from this point Pr. The difference between the magnitudes of two vectors is and is′ is associated with an error of a rotor resistance Rr, while the difference between phase shifts is associated with an error of a stator resistance Rs.

Abstract: The present invention relates to a control of an AC motor, and in particular to a control device for an AC motor which can prevent an overvoltage from being applied to the motor, and minimize voltage consumption of a reactor itself during the starting and accelerating operation of the motor, by restricting a sharp increase of a motor line voltage resulting from a high-speed switching of an inverter during a high-speed operation of the motor, and a voltage reflection phenomenon of input terminals of the motor generated due to non-matching of a characteristic impedance between a power line and the motor, by inserting the reactor having a bar shaped core between the inverter and the motor.

Abstract: A dual stator winding induction machine has two windings with input terminals which are supplied separately with drive power. The two stator windings have a different number of poles to essentially eliminate the magnetic coupling between the two windings and to decouple the torques produced by each set of windings. Power is supplied to the two windings by two separate variable frequency inverter drives to provide two independently controllably torque components. At low speed, the power supplied to one of the windings can produce torque which opposes the torque from the power applied to the other winding, so that very low speed and standstill operation can be achieved while the frequency of the power supplied by the inverters is always greater than the minimum frequency. At higher operating speeds, power is supplied to the two windings so that the torque from the windings adds. The dual stator machine can be built with minimal modifications to standard winding configurations.

Abstract: A control algorithm or method for use in controlling a voltage-fed induction machine. The control algorithm includes the following steps. The DC link voltage supplied to an inverter driving the induction machine is monitored. When the DC link voltage is high enough, the algorithm controls the amount of current supplied to the induction machine to provide current controlled operation of the induction machine. When the DC link voltage is not high enough to control the current under transient conditions, the induction machine is controlled by imposing the maximum possible phase voltage and optimal slip angle on the machine to provide maximal torque per ampere operation of the induction machine. The maximal torque per ampere operation is performed when either of the following conditions is met: a) the torque level required by the induction machine is such that efficiency optimization cannot be performed, or b) current regulators approach saturation.

Abstract: A method of controlling a reciprocating compressor comprising of starting the reciprocating compressor at a minimum speed in which a frequency of 45-52 Hz is applied, operating the reciprocating compressor at a frequency of 52˜60 Hz and operating the reciprocating compressor at a predetermined rotational speed. Therefore, an optimum amount of lubricating oil is supplied to a sliding part of the reciprocating compressor so that the reliability of parts thereof is secured.

Abstract: An induction motor control device includes a power conversion circuit, a current sensor, a current component calculation circuit for calculating first and second current components, a magnetic flux command calculation circuit for calculating a magnetic flux command value such that the amplitude ratio between a squared value of the first current component and a squared value of the second current component takes a preset value, a voltage component calculation circuit for calculating a primary voltage component command value, and a primary voltage component command calculation circuit. The current component calculation circuit calculates first and second current components in phase and 90° out of phase with the primary voltage component command value, respectively.

Abstract: A barrier operator moves a movable barrier using a motive source having a movable member, a station, and first and second flexible members. The station includes a drive system operatively coupled to the movable member of the motive source. The drive system includes input and output members. The first and second flexible members each have first and second ends and a portion extending from the station. The first ends of each flexible members are operatively coupled to the movable barrier and the second ends of each of the flexible members are operatively coupled to the output drive system member of the station. Aspects include the first and second flexible members being cable or wire. Other aspects include the output drive system member of the station being a spool. The drive system further includes a gear box operatively coupled to the spool. Other aspects include the movable barrier being a gate or door.

Abstract: A method and apparatus for correcting DC offset in a frequency to voltage converter. An analog frequency to voltage converter receives a frequency signal and outputs a voltage signal having a level that is indicative of the frequency of the frequency signal. The frequency signal is also input into a digital processor which converts the frequency signal into a reference signal that is fed back and summed with the voltage signal. The processor integrates the difference between the reference signal and the output signal to drive the output signal to be equal to the reference signal thereby nullifying DC offset in the output signal. The invention can be applied to controlling the DC bus voltage in a variable frequency AC drive.

Abstract: A method for detecting a change in motor load and/or motor speed is provided. The method includes the step of measuring the number of transitions (i.e., state changes) of a phase control signal in a motor phase of the motor. The method also includes the step of comparing the number of transitions to a predetermined number that is indicative of a predetermined motor load and/or motor speed. The predetermined number may comprise the number of transitions in a prior phase control signal of the motor. A method for controlling a motor responsive to a change in motor load and/or motor speed is also provided. The method includes the above-described steps for detecting a change in motor load and/or motor speed and further includes the step of selecting one of a plurality of operating modes for the motor responsive to a comparison value obtained by comparing the measured transition number with the predetermined transition number.

Abstract: A drive for controlling the speed of an AC induction motor from an inverter. The inverter applies a voltage to the stator winding of the motor in accordance with the magnitude of a first input signal. The inverter causes the voltage to be applied at a frequency determined by the magnitude of a second input signal to the inverter. The drive includes motor speed sensor and a motor speed reference signal source coupled to a speed regulating amplifier. A slip detector determines the slip of the motor from the speed of the rotor and the energization frequency of the stator winding. A slip regulating amplifier receives the output signal from the speed regulating amplifier and the slip signal and provides an output to a summing amplifier. The summing amplifier also receives a motor speed signal and provides an output. The output comprises the second input signal to the inverter. The output may be supplied through an absolute value circuit as the first input signal to the inverter.

Abstract: In vector control apparatus and method for a three-phase multiplex winding motor, a plurality of inverters are installed, each inverter operatively driving a corresponding one of multiplex windings of the motor and a plurality of inverter controllers are installed whose number corresponds to that of the inverters. Each controller includes: a decoupling voltage calculator for calculating d-axis and q-axis voltage setting values V.sub.1 d* and V.sub.1 q* on the basis of an excitation instruction value Io*, a torque instruction value I.sub.T *, d-axis-and-q-axis current instruction values i.sub.1 d* and i.sub.1 q* which are quotients of the excitation instruction value Io* and the torque instruction value I.sub.T * divided respectively by the multiplex number N of the windings of the motor, and a power supply frequency .omega. which is an addition of a slip frequency .omega.s to a rotor revolution frequency .omega.

Abstract: A method and apparatus for improving the efficiency of an induction motor used in fluid pump and blower applications including a controller that reduces the flux generated by the motor at less than maximum motor loads.

Abstract: In a process for controlling a rotating machine having n phases powered by a voltage inverter defining m.sup.n states of the stator phase voltage vector the electromagnetic torque .GAMMA. and the stator flux .vertline..phi..sub.s .vertline. of the machine are servocontrolled. A calculator calculates a succession of n states of the phase voltage vector to move the torque .GAMMA. and the flux .vertline..phi..sub.s .vertline. towards the set points .GAMMA..sub.ref, .vertline..phi..sub.s .vertline..sub.ref. On each sampling, the calculator calculates the remaining application time of the current state and the updated application times of the future states of the phase vector. Asynchronously with the sampling times and the calculation times, the calculator sends SPmLL switch control signals to switch from the current state to the next state.

Abstract: Converter-powered electric motors are often braked by electrical means. For this purpose the electronic converter that powers the motor is so controlled that the motor, when in generational operation, sends energy by way of the converter into an electrical braking resistor additionally connected to the converter, and this energy is there converted to heat. In order to avoid overloading the electrical braking resistor, an additional electronic or thermo-mechanical protective device is customarily provided. To simplify the arrangement, it is proposed in the present invention to provide as an electric braking resistor one made of a resistive material with a conductance that decreases progressively as the temperature rises through a certain range below the maximal acceptable operating temperature of the braking resistor. As a result, the power that can be accepted by the electrical braking resistor is made self-limiting, so that the braking resistor is protected against overheating.

Abstract: A motor driving power supplying section obtains an output voltage by switching-controlling a predetermined voltage outputted from a main power supply and smoothing a voltage thus switching-controlled. A driving transistor group includes a plurality of driving transistors, for supplying electric power based on the output voltage of the motor driving power supplying section to the motor driving coils of multiple phases. A commutation control section supplies conduction switching signals to the driving transistor group so as to switch successive conduction states of the motor driving coils. An output control section controls the output voltage of the motor driving power supplying section so that a collector-emitter voltage of at least one of the plurality of driving transistors included in the driving transistor group has a predetermined value.