Abstract: Systems and methods for compensating for a current measurement offset error in a permanent magnet synchronous motor (PMSM) drive are disclosed. The systems and methods include reading an output voltage command signal, extracting a signature of a current measurement offset error from the output voltage command signal, and compensating, based on the signature, for the current measurement offset error in a closed-loop using a feedback path.

Abstract: Stable current control is performed even at the time of occurrence of disturbance, while the steadily occurring current pulsation is suppressed. A motor drive device 100 includes a power conversion circuit 103 that drives an alternating-current motor 101, and a controller 102 that controls the power conversion circuit 103. The controller 102 includes a voltage command calculation unit 108, a control state judgement unit 112, and a control gain change unit 113.

Abstract: The disclosure relates to a method for controlling a synchronous three-phase electrical machine having a stator and a rotor. The method may include measuring currents of the first and second phases of the stator. The method may include measuring an angular position of the rotor. The method may include calculating the currents measured in a rotor reference frame. The method may include measuring the rotor current. The method may include calculating an automatic control error. The method may include calculating control voltages for the electrical machine. The method may further include applying the control voltages to said electrical machine. According to the disclosed method, the control voltages are calculated in the rotor reference frame in a recursive manner and as a function of a command update period value, a DC voltage value, and the angular electrical speed of the rotor.

Abstract: The invention concerns an electrical installation providing an apparatus, a three-phase inverter and a control device, the inverter being adapted for generating a three-phase current presenting a first frequency for operating the apparatus and an undesired frequency component presenting a second frequency. The control device is adapted for measuring a parameter of each phase of the current, the measured parameters forming a measurement vector, and for calculating a Clarke transform, providing a first vector represented in a first basis of a two-dimensional vector space, of the measurement vector. The control device is adapted for generating a representation of the first vector in a second basis of the vector space, the second basis rotating at the second frequency with respect to the first basis.

Abstract: According to one embodiment, a robotic control apparatus includes a physical parameter switching unit, an observer unit, and a state feedback unit. The physical parameter switching unit switches a physical parameter set in accordance with a value of a mass of an end effector load of a robotic arm. The observer unit estimates an angular velocity of a link based on a simulation model of a motor angular velocity control system which undergoes gain proportional-integral control equivalent to a proportional-integral control of the angular velocity control system. The state feedback unit calculates an axial torsional angular velocity based on a difference between the angular velocity of the motor, and the angular velocity of the link, and feed the calculated axial torsional angular velocity back to the angular velocity control system.

Abstract: A boost converter control apparatus for controlling a motor drive system which is provided with a boost converter disposed between an electric power converter and a direct current power supply, the boost converter boosting a direct current voltage of the direct current power supply and supplying it to the electric power converter, is provided with: an operating device provided with a proportional element, an integral element and a derivative element, the derivative element being configured as a bandpass filter, the operating device calculating a PID controlled variable corresponding to an electric current command value of the boost converter for maintaining an output voltage of the boost converter at a command value of an inter-terminal voltage VH of a smoothing condenser; and a controlling device which is configured to control the output voltage of the boost converter on the basis of the calculated PID controlled variable.

Abstract: An injection molding machine includes a motor; a driver circuit; a rectifying part; a capacitor provided between the driver circuit and the rectifying part; a bridge circuit that converts direct electric power between the driver circuit and the rectifying part into alternating electric power; a harmonics component reducing part connected to an alternating side of the bridge circuit; and a regenerative line connected to the rectifying part in parallel, wherein the bridge circuit and the harmonics component reducing part are provided in the regenerative line, and plural switching elements of the bridge circuit are turned on or off such that electric power of the motor is regenerated when a voltage of the capacitor is greater than or equal to a predetermined value, and all the switching elements are turned off when the voltage of the capacitor is less than the predetermined value.

Abstract: An injection molding machine according to the invention includes a motor, a driver circuit that drives the motor; and a rectifying part that supplies electric power to the driver circuit. A regenerative line for regenerative electric power of the motor is connected to the rectifying part in parallel. A converting part and a harmonics component reducing part are provided in the regenerative line. The converting part converts direct electric power between the driver circuit and the rectifying part into alternating electric power which is input to the harmonics component reducing part.

Abstract: Provided is a regenerative medium voltage inverter, the inverter being such that regenerative operation is enabled by changing structure of input terminal of a unit power cell at a series H-bridge medium voltage inverter, and a dynamic braking resistor is not required to reduce the size of a DC-link capacitor over that of a conventional medium voltage inverter.

Abstract: A drive signal for a motor-driven mechanical system has zero (or near zero) energy at an expected resonant frequency of the mechanical system. These techniques not only generate a drive signal with substantially no energy at the expected resonant frequency, they provide a zero-energy “notch” of sufficient width to tolerate systems in which the actual resonant frequency differs from the expected resonant frequencies.

Abstract: In a control apparatus for an AC electric motor, a dq axis current feedback control unit 44 and a qn axis current feedback control unit 46 execute a feedback control of higher harmonic components of actual currents id and iq flowing in an AC electric machine 10 to higher harmonic current instruction values ?idkr and ?iqkr. A d axis current instruction value adjusting unit 24 and a q axis current instruction value adjusting unit 26 add the higher harmonic current instruction values ?idkr and ?iqkr to fundamental current instruction values idr and iqr. Ad axis current feedback control unit 32 and a q axis current feedback control unit 34 execute a feedback control of a difference between the actual currents id and iq and the sum of the higher harmonic current instruction values ?idkr, ?iqkr and the fundamental current instruction values idr and iqr into zero.

Abstract: The motor control device includes: a vehicle control device (1) for generating a first torque command value Tref according to state quantities of the vehicle acquired from various sensors (7); a vehicle-resonance-compensation calculation unit (23) for extracting a frequency component generating a vehicle resonance from torque ripple components detected from an electrical angle ? of a motor for traveling (3) by a vehicle resonance component extraction filter (24), and generating a second torque command value Tcmp as a resonance compensation value for carrying out feedback control for the extracted frequency component; and an adder (20) for generating a torque command value Tref_cmp by subtracting the second torque command value Tcmp from the first torque command value Tref, and the motor (3) is controlled according to the torque command value. With this, it is possible to restrain the resonance of the vehicle caused by the torque ripple of the motor (3).

Abstract: A vibration control robot system of the present invention includes: a robot controller (101) transmitting an operation command value and receiving an output value of a pulse encoder of the servo motor, wherein the robot controller includes a controller-side communication unit (5) which transmits the operation command value and the output value of the pulse encoder to a robot vibration controller; and the robot vibration controller (11) including: an acceleration sensor interface (15); a corrected operation command value calculation unit (13) which calculates a corrected operation command value obtained so as to suppress vibration of the robot; and a vibration-controller-side communication unit (12) which transmits the corrected operation command value to the robot controller (101), wherein the robot vibration controller (11) is arranged independently of the robot controller (101).

Abstract: A boost control section for controlling a converter includes a PI control section and a resonance suppression section. The PI control section calculates a basic command value based on a deviation between a drive voltage generated by the converter and a target voltage to equalize the drive voltage and the target voltage. The resonance suppression section calculates, based on the state of variation of the drive voltage, a correction value for correcting the basic command value to suppress the variation. The basic command value is corrected by adding the correction value. First and second drive pulses corresponding to the corrected command value are outputted to the converter.

Abstract: An embodiment of a motor controller includes a motor driver and a signal conditioner. The motor driver is configured to generate a motor-coil drive signal having a first component at a first frequency, and the signal conditioner is coupled to the motor driver and is configured to alter the first component. For example, if the first component of the motor-coil drive signal causes the motor to audibly vibrate (e.g., “whine”), then the signal conditioner may alter the amplitude or phase of the first component to reduce the vibration noise to below a threshold level.

Abstract: A motor-drive circuit includes: a filter circuit to attenuate a frequency band including a resonance frequency of an actuator in a target-current signal, which is a digital signal indicating a target value of a driving current to be supplied to a voice-coil motor that drives the actuator; a digital-analog converter to convert an output signal of the filter circuit into an analog signal, to be outputted as a current-control signal; and a driving circuit to supply the driving current to the motor in accordance with the current-control signal, the filter circuit including: a digital-notch filter to attenuate a frequency band around the resonance frequency in the target-current signal; and a digital-low-pass filter to attenuate a frequency band greater than or equal to a predetermined frequency in the output signal of the digital-notch filter, the digital-low-pass filter having a sampling frequency higher than a sampling frequency of the digital-notch filter.

Abstract: The damping force of a damping force generation apparatus is controlled by operating an actuator on the basis of a control input u calculated by a state feedback controller K designed such that an L2 gain of a closed loop control system S which includes a generalized plant G designed by making use of a delay-approximated model M and the state feedback controller K therefor becomes less than a previously set positive constant ?. The delay-approximated model M is designed such that a delay element R representing operation delay of the actuator and a delay compensation element R* cancelling out the delay act on a mechanical motion model of the damping force generation apparatus. The delay-approximated model M is a bilinear system, and is designed to approximate a delay-considered model which is a control model designed on the basis of the mechanical motion model of the damping force generation apparatus and in consideration of the delay.

Abstract: An active motor damping system and method for dampening oscillations of a driveline in a vehicle includes generating a commanded torque indicative of an actual torque which would counteract the oscillations if delivered by a motor to the driveline. The commanded torque is adjusted as a function of a phase lag between the commanded torque and an actual torque which the motor would deliver in response to the commanded torque such that in response to the adjusted commanded torque the motor delivers the actual torque which counteracts the oscillations.

Abstract: A damping apparatus for an automobile is provided, capable of ensuring a high level of reliability while obtaining excellent damping effect with simple configuration. The damping apparatus for an automobile that reduces vibrations of an automobile body may include an actuator that is attached to the automobile body and drives an auxiliary mass; a current detector that detects a current flowing through an armature of the actuator; a section that detects a terminal voltage applied to the actuator; a calculation circuit that calculates an induced voltage of the actuator, and further calculates at least one of the relative velocity, relative displacement, and relative acceleration of the actuator, based on a current detected by the current detector and the terminal voltage; and a control circuit that drive-controls the actuator based on at least one of the relative velocity, relative displacement, and relative acceleration of the actuator calculated by the calculation circuit.

Abstract: The effect of chattering on the measurement of the pulse period is reduced. The pulse period representing the rise interval of target pulses appearing in a pulse signal PI is measured. The pulse signal PI is sampled in synchronization with a measurement clock CLK. Measurement of a designated inhibition period is started in synchronization with the fall of the signal PI. Measurement of the current pulse period is completed and measurement of a new pulse period is started if the inhibition period has elapsed at the rise of the signal PI. Counting of the current pulse period is continued if the inhibition period has not elapsed.

Abstract: A motor control device includes: a feedforward computing section for computing a motion reference value and a feedforward driving force based on a motion command; a deviation compensation computing section for outputting a deviation compensation driving force by a control computation for reducing a control deviation; a driving-force command synthesizing section for outputting a driving-force command based on the feedforward driving force and the deviation compensation driving force; a reaction-force compensation computing section for computing a motion correction value based on a predetermined reaction-force reference value and the deviation compensation driving force; and a control-deviation computing section for computing the control deviation based on a deviation between the motion reference value and a motor motion detection value, and the motion correction value.

Abstract: Embodiments of the present invention provide a drive signal for a motor-driven mechanical system whose frequency distribution has zero (or near zero) energy at the expected resonant frequency of the mechanical system. The drive signal may be provided as a pair of steps sufficient to activate movement of the mechanical system and then park the mechanical system at a destination position. The steps are spaced in time so as to have substantially zero energy at an expected resonant frequency fR of the mechanical system. The drive signal may be filtered to broaden a zero-energy notch at the expected resonant frequency fR.

Abstract: A drive signal for a motor-driven mechanical system has zero (or near zero) energy at an expected resonant frequency of the mechanical system. These techniques not only generate a drive signal with substantially no energy at the expected resonant frequency, they provide a zero-energy “notch” of sufficient width to tolerate systems in which the actual resonant frequency differs from the expected resonant frequencies.

Abstract: A motor control device includes a measurement unit, a speed control unit, a correction unit, a drive unit, and a disturbance suppressing unit. During a time period before a measurement value of speed of one of a motor and a driven object which is driven by the motor measured by the measurement unit becomes greater than zero the correction unit corrects a manipulated variable such that a reduced correction amount which is from zero percent to less than 100 percent of a correction amount determined by the disturbance suppressing unit, is added to the manipulated variable determined by the speed control unit corresponding to a target speed of the one of the motor and the driven object.

Abstract: A drive signal for a motor-driven mechanical system has zero (or near zero) energy at an expected resonant frequency of the mechanical system. The drive signal may be provided in a series of steps according to a selected row of Pascal's triangle, wherein the number of steps equals the number of entries from the selected row of Pascal's triangle, each step has a step size corresponding to a respective entry of the selected row of Pascal's triangle, and the steps are spaced from each other according to a time constant determined by an expected resonant frequency of the mechanical system.

Abstract: A motor control device of the present invention includes a correction input unit, a measurement unit, a first signal processing unit, and a second signal processing unit. The correction input unit corrects a control input signal outputted from a controller, and inputs a corrected control input signal into a motor. The measurement unit measures a physical quantity resulting from rotation of the motor corresponding to a control output. The first signal processing unit inputs a measurement signal representing the physical quantity inputted from the measurement unit into an inverse model 1/G of a transfer function G of a controlled object, and filters an output of the inverse model 1/G through a first low-pass filter. The second signal processing unit obtains a corrected control input signal to be inputted into the motor by the correction input unit, and filters the control input signal through a second low-pass filter.

Abstract: An electric machine provided with: a stator, equipped with a single stator winding; at least two shafts, which are independent of one another and are mounted so that they can turn; at least two rotors, which are independent of one another, are magnetically coupled to the stator, and are mounted on the shafts; and a single electronic power converter, which is connected to the stator winding for supplying the stator winding itself with a total electric current.

Abstract: A motor controller capable of detecting an oscillation of a feedback loop and performing gain adjustment while updating a gain value of a control unit is provided. The motor controller includes an electric motor, an operation-amount detector, a control unit, a machine, a disturbance signal generator which generates a sweep sine wave, a compensation-driving-force detector, a vibration calculator, an oscillation detector, a vibration storage, a simulated open-loop gain calculator, a gain changer, and an automatic gain changer, and detects an oscillation by processing a response signal in time series on the basis of a first threshold regarding to a magnitude of vibration and a second threshold regarding a frequency.

Abstract: A drive system for a compressor of a chiller system includes a variable speed drive. The variable speed drive is arranged to receive an input AC voltage at a fixed AC input voltage and provide an output AC power at a variable voltage and variable frequency. The variable speed drive includes a converter connected to an AC power source providing the input AC voltage. The converter is arranged to convert the input AC voltage to a DC voltage. A DC link is connected to the converter. The DC link filters and stores the DC voltage from the converter. An inverter is connected to the DC link. A motor connectable to the compressor for powering the compressor. An active filter connected in parallel with the motor. The active filter is arranged to generate high frequency currents having a magnitude and opposite polarity, with respect to the output AC power of the variable speed drive. The high frequency currents generated by active filter substantially cancel out high frequency currents flowing into the motor.

Abstract: A method of detecting a useful signal from a measurement signal that is overlaid by at least one interference signal for use in a control or regulating device, where the interference signal occurs with at least one known interference signal frequency. The method including the steps of detecting the measurement signal, performing a Fourier transformation on the measurement signal with reference to the interference signal frequency to detect the interference signal amplitude and phase, detecting the interference signal on the basis of the interference signal amplitude and phase, and removing the interference signal from the measurement signal to detect the useful signal. The Fourier transformation is performed only with reference to the known interference signal frequency to simplify the computation making it possible to detect the useful signal in real time.

Abstract: To reduce, in a power converting apparatus for an electric locomotive, a sixth-order harmonic noise induced by a torque ripple component equivalent to a sixth-order frequency of an inverter frequency. When a motor is driven in a three-pulse mode to drive the electric locomotive, three pulses included within a ½ cycle of the inverter frequency in a PWM waveform, which is used for controlling a switching element of an inverter unit that drives the motor, are set to satisfy Tq?T/8, Tp?Tq/2, and Tr?Tq/2 where, assuming that the three pulses include a first pulse, a second pulse, and a third pulse from an order of generation, Tp is a pulse width of the first pulse, Tq is ½ of a pulse width (full width at half maximum of a pulse) of the second pulse, Tr is a pulse width of the third pulse, and T is a cycle of the inverter frequency.

Abstract: An enhanced torque ripple mitigation algorithm for permanent magnet synchronous machines (PMSMs), the algorithm including compensation for sensor delay.

Abstract: An active vibration isolation support system includes an electronic control unit which supplies a target electric current to an actuator to periodically drive the actuator in an expansion and contraction manner with a target vibration waveform. The controller sets the target electric current by synthesizing a driving primary electric current waveform corresponding to the target vibration waveform for the actuator with higher-order (driving secondary and/or tertiary) electric current waveforms which eliminate higher-order vibration components of the actuator corresponding to the driving primary electric current waveform. It is possible to alleviate a calculating load in the electronic control unit by ignoring the quaternary and still higher-order vibration components which less affect the target vibration waveform for the actuator.

Abstract: An axial gap type motor/generator is provided with a stator, a rotor and an alternating current control device. The alternating current control device executes alternating current control of a single phase or multiple phase alternating current flowing in the coils. The alternating current control device includes a superpositioning control section and a frequency component control section. The superpositioning control section produces the alternating current by superpositioning a plurality of frequency components including a first order fundamental wave component and a plurality of higher harmonic wave components that have frequencies equal to integer multiples of a frequency of the fundamental wave components and are of orders that are equal to values of the integer multiples. The frequency component control section controls a relationship among the frequency components such that two pairs of the frequency components whose orders differ by two are aligned with respect to each other.

Abstract: In order to simultaneously realize an improvement in disturbance suppression force of an electric motor control apparatus and vibration suppression of a load machine, a velocity control circuit receives a velocity command signal as a target value of velocity of an electric motor and a corrected velocity signal, obtained by correcting a velocity signal with a velocity correction signal, and outputs a torque command signal specifying target torque of the electric motor driving the load machine. A vibration suppression circuit outputs a velocity correction signal, based on an acceleration signal, indicating acceleration of the load machine. A transfer function from the acceleration signal to the torque command signal is obtained by multiplying a transfer function from a position signal, indicating position of the electric motor to the torque command signal, by a proportion characteristic having a specified gain and integration characteristic.

Abstract: A motor control device of the present invention includes a correction input unit, a measurement unit, a first signal processing unit, and a second signal processing unit. The correction input unit corrects a control input signal outputted from a controller, and inputs a corrected control input signal into a motor. The measurement unit measures a physical quantity resulting from rotation of the motor corresponding to a control output. The first signal processing unit inputs a measurement signal representing the physical quantity inputted from the measurement unit into an inverse model 1/G of a transfer function G of a controlled object, and filters an output of the inverse model 1/G through a first low-pass filter. The second signal processing unit obtains a corrected control input signal to be inputted into the motor by the correction input unit, and filters the control input signal through a second low-pass filter.

Abstract: Presented is a harmonic regulator that regulates a plurality of individual harmonics in a system having periodic torque disturbances to commanded values, including zero. For each harmonic being regulated, a feedback signal having at least one harmonic component due to the harmonic being regulated is transformed from a source reference frame to a harmonic reference frame of the harmonic being regulated to form a qd feedback signal. The qd feedback signal is subtracted from the commanded value to form a qd signal and regulated. The regulated qd signal is transformed to a destination reference frame to form a compensation signal and the compensation signal is added to a control signal to form a qd control signal that drives each harmonic being regulated towards the commanded value.

Abstract: A drive signal for a motor-driven mechanical system has zero (or near zero) energy at an expected resonant frequency of the mechanical system. The drive signal may be provided in a series of steps according to a selected row of Pascal's triangle, wherein the number of steps equals the number of entries from the selected row of Pascal's triangle, each step has a step size corresponding to a respective entry of the selected row of Pascal's triangle, and the steps are spaced from each other according to a time constant determined by an expected resonant frequency of the mechanical system.

Abstract: Embodiments of the present invention provide a drive signal for a motor-driven mechanical system whose frequency distribution has zero (or near zero) energy at the expected resonant frequency of the mechanical system. The drive signal may be provided as a pair of steps sufficient to activate movement of the mechanical system and then park the mechanical system at a destination position. The steps are spaced in time so as to have substantially zero energy at an expected resonant frequency fR of the mechanical system. The drive signal may be filtered to broaden a zero-energy notch at the expected resonant frequency fR.

Abstract: Systems and methods for improved Variable Speed Drives having active inverters include an input filter for filtering common mode and differential mode currents. A three-phase inductor has three windings, each winding of the three-phase inductor having a center tap dividing each winding into a pair of inductor sections; and a three-phase input capacitor bank connected in a wye configuration to the three center taps at one end, and to a common point at the opposite end. The three-phase input capacitor bank provides a short circuit for frequencies above a predetermined fundamental frequency for shunting such frequencies through the three phase capacitor bank, while passing the predetermined fundamental frequency to an input AC power source.

Abstract: A method for damping vibrations in a stepper motor with micro-stepping control which comprises the steps of identifying the force amplitudes and phase shifts of multiple harmonic detent torques of the stepper motor, such as the first, second and fourth harmonic detent torques, and tuning the stepper motor with different current commands until minimum friction and resistive torque are obtained. Thereafter, a compensating harmonic current derived from said force amplitudes and phase shifts of the said multiple harmonic detent torques is injected into a current command during operation of the stepper motor to compensate for torque ripples.

Abstract: A method and system for operating a motor are provided. Power is provided to the motor through at least one switch operating at a first switching frequency. A pulse ratio of the motor is calculated based on the first switching frequency. The at least one switch is operated at a second switching frequency if the calculated pulse ratio is less than a first pulse ratio value and greater than a second pulse ratio value.

Abstract: Systems and methods that determine resonant frequencies of a motor system via employing an output of a velocity regulator. The velocity regulator enables the motor drive to command the rotation of the motor at predetermined rotations, by setting rotational speeds of the motor. The output of the velocity regulator can then be stored as a function of time, and a Fast Fourier Transform performed on such time data to obtain a frequency data and a signal power spectrum.

Abstract: The present invention provides a torque loop control method for servomotors utilizing discontinuous pulse width modulation that incorporates measuring the power factor in real time. Also included is a sine wave generator for software-based spectrum analysis.

Abstract: A load drive apparatus includes a noise filter, which includes a coil connected in series between a power source and a load, and a switching transistor connected in parallel across the coil, and a control circuit which is operated based on a drive signal. The control circuit turns on the switching transistor of the noise filter in case of subjecting the load to a full-on drive, thereby to short-circuit the coil and to form a power supply path including the switching transistor without the coil. The control circuit turns off the switching transistor of the noise filter in case of subjecting the load to a PWM drive, thereby to form a power supply path including the coil.

Abstract: A servo motor controller having: a frequency identification section that performs analysis based on a frequency response method and identifies the frequency of a disturbance exhibiting a specified phase lag; an input/output gain identification section that identifies the input/output gain at the frequency identified by the frequency identification section; and a magnification factor resetting section that resets an adjustment magnification factor by performing a specified operation on a ratio between the identified input/output gain and a specified target value of the input/output gain.

Abstract: Presented is a harmonic regulator that regulates a plurality of individual harmonics in a system having periodic torque disturbances to commanded values, including zero. For each harmonic being regulated, a feedback signal having at least one harmonic component due to the harmonic being regulated is transformed from a source reference frame to a harmonic reference frame of the harmonic being regulated to form a qd feedback signal. The qd feedback signal is subtracted from the commanded value to form a qd signal and regulated. The regulated qd signal is transformed to a destination reference frame to form a compensation signal and the compensation signal is added to a control signal to form a qd control signal that drives each harmonic being regulated towards the commanded value.

Abstract: Solving Means: A field coil current and a stator current are controlled by a controller. The stator current is controlled under vector control and is controlled so that the phase keeps an efficient motor zone. In a case of rated power generation, when the motor speed is low, the phase current and field coil current are increased to reserve the generated power. And, as the speed is increased, the phase current is decreased to reduce the copper loss, while in place of decreasing the phase current, the field coil current is kept high to reserve the generated power. Thereafter, as the speed is increased more, the field coil current is decreased to reduce the iron loss, while in place of decreasing the field coil current, the phase current is increased to reserve the generated power.

Abstract: In an apparatus to increase the service life of bearings in an electric machine, the bearing currents that act on the bearings of the rotor are reduced by the application of a corresponding negative field voltage to the rotor, obtained with the aid of a compensation unit. The reduction of the bearing currents prevents ripple formation in the bearing and increased ageing of the lubricant.

Abstract: A circuit and method for detecting an operating transition of a mechanical apparatus driven by a hydraulic prime mover comprising a hydraulic pump driven by an electric motor, the operating transition causing a change in the force applied by the mechanical apparatus on the prime mover. A motor current sensing circuit is connected in a motor power supply circuit to provide a motor current signal representing motor current. A bandpass filter receives the motor current signal and provides a filtered motor current signal consisting essentially of motor current signal components in the frequency range from a lower frequency boundary greater than zero Hz to an upper frequency boundary below substantially all the motor noise frequencies. A comparison circuit compares the filtered motor current signal to a first selected threshold level and outputs a signal representing the occurrence of the operating transition when the filtered motor current signal exceeds the selected threshold level.