Abstract: A method and apparatus for reducing parasitic distortion in terminal voltages connected to a PWM inverter, the method comprising the steps of receiving each of a command operating frequency and a command carrier frequency, comparing the command operating frequency to low and high threshold operating frequency values, and where the command operating frequency is less than the low threshold frequency, restricting the carrier frequency to a minimum carrier frequency, where the command operating frequency is greater than the high threshold frequency, setting the carrier frequency equal to the command carrier frequency and, where the operating frequency is between the low and high threshold frequencies, setting the carrier frequency to an intermediate value between the minimum carrier frequency and the commanded carrier frequency.

Abstract: A method and apparatus for reducing distortion at the outputs of an inverter system, the apparatus including a polarity discriminator for determining the polarity of a current passing through an output terminal to a load, a compensator programmed with different upper and lower compensation values and controlled by the discriminator to provide the upper compensation value as an output when the current polarity is positive and providing the lower compensation value when the polarity is negative and a combiner for receiving a modulating signal and the compensation value provided by the compensator and mathematically combining the two signals to generate a modified modulating signal.

Abstract: A method for mitigating current distortion on inverter supply lines that supply a load with power from a PWM inverter, the inverter including a switch and diode bridge constructed using devices that are characterized by losses that cause current distortion, the invert, lines and load together characterized by inductive and capacitive dynamics that also cause line current distortions, the method including identifying both a device drop error due to device operating characteristics and a system related dynamics error due to interaction of system components and using those errors along with a more conventional dead time compensation scheme to modify modulating waveforms used in PWM comparison by a controller.

Abstract: A method and apparatus for controlling a synchronous frame current regulator wherein the apparatus includes a current predictor and a current predictor adjuster, the current predictor predicting the current provided to a plant from both a forcing function and an actual current value and the adjuster adjusting the current prediction based on a difference between the current prediction and the actual current sampled thereby driving the actual current so as to conform with a commanded current value.

Abstract: A method and apparatus for selecting one of several different modulating signals for use with a system including a PWM controller and an inverter to generate low frequency alternating voltages on three motor supply lines, modulating signals selected as a function of a modulating index to minimize harmonic distortion in the alternating voltages, minimize switching losses, maximize overall system gain at high modulating index values and maximize the linear range of system operation.

Abstract: A method and apparatus for starting a motor drive into a rotating motor, the method including determining an initial search frequency and search current wherein the current is less than a rated drive current, providing a d-axis flux generating current to the motor at the search frequency and at a magnitude equal to the search current, monitoring a q-axis flux error, decreasing the search frequency until the d-axis flux error is less than a threshold value, thereafter increasing the search current to the rated drive current and, after a flux-up period, providing both q-axis torque producing current and d-axis flux producing current to the motor.

Abstract: A method and apparatus for determining the critical dwell time required between firing pulses generated by a PWM inverter to eliminate greater than twice overvoltage on motor supply lines. Critical dwell time is correlated with line parameters including inductance and resistance per unit length and is then provided to a controller to alter voltages provided to a motor to eliminate overvoltage.

Abstract: An apparatus for receiving and modifying a PWM trigger signal such that consecutive ON and OFF periods have durations at least as long as a critical dwell time where the critical dwell time is the minimum time required to avoid greater than twice overvoltage. The trigger signals are modified by, each time a trigger signal changes from low to high, providing a minimum pulse signal which remains high for the greater of a critical dwell time or the time over which the trigger signal remains high, when the minimum pulse signal changes from high to low, providing a maximum pulse signal which remains low for a critical dwell time, adding the maximum and minimum pulse times using a logical AND gate and providing the output of the AND gate as a modified trigger signal.

Abstract: A method and apparatus used with a field oriented motor controller for providing corrected transient inductance estimates during normal motor operation. The invention monitors q-axis feedback and command voltages and, based on an error therebetween, modifies a transient inductance estimate to compensate for the error and force the feedback voltage to equal the command voltage thereby facilitating field oriented control. The invention can be used either during a commissioning procedure to provide an inductance correction table for use during normal motor operation or can be used during normal motor operation to tune the inductance estimate.

Abstract: A method for generating electrical frequencies of a alternating current motor is disclosed wherein a torque current command signal, a d-axis voltage command signal and a d-axis voltage feedback signal are combined to generate the stator electrical frequency in the synchronous reference frame. The method also provides an estimate of the rotor electrical frequency as well as of the motor speed. The frequency generator is preferably incorporated in a variable frequency motor controller for driving a motor at desired speeds independent of changing load conditions. The generator permits the controller to maintain field oriented control without the need for speed sensing and feedback.

Abstract: A method and apparatus for compensating for deviations in the alternating voltage produced by a PWM inverter. The necessary sequence in which inverter components must be triggered results in voltage error pulses that accumulate over time and result in deviations from ideal voltage at motor terminals. By allowing the error pulses to continue and adjusting the trigger times to compensate for the error pulses, the effect of the error pulses is negated and the voltage deviations are eliminated.

Abstract: A method and apparatus for eliminating greater than twice motor over voltage 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 their maximum magnitudes when their instantaneous characteristics are known to cause greater than twice overvoltage. The modulating waveforms are altered in a symmetrical fashion so that the resulting fundamental terminal voltages remain essentially unchanged.

Abstract: A method and apparatus for controlling an AC motor are described wherein a frequency generator is configured to generate a signal representative of the stator electrical frequency and to estimate the rotor electrical frequency of the motor during operation. The generator operates on torque and flux current reference signals and on d-axis voltage reference and feedback signals to determine the electrical frequencies. The generator ramps up gain values applied to the torque current reference signals and to a voltage error signals representative of the difference between the d-axis voltage reference and feedback signals during a startup phase of operation to enhance performance and stability of the drive during this phase. The generator includes feedforward and feedback portions that contribute components of the final stator frequency signal. The components are filtered differently during startup and running phases of operation to provide the desired frequency signals.

Abstract: A method and apparatus used with a motor controller for determining transient inductance and rotor resistance upon commissioning of the motor. The estimator drives a single phase of the motor with an excitation current at an operating frequency, determines the d-q axis stator synchronous feedback voltages, divides the excitation current by 2 to produce a positive current signal, multiplies the operating frequency by the positive current signal to produce a current frequency signal and then divides the q-axis voltage feedback by the current frequency signal to produce the transient inductance estimate, divides the d-axis voltage feedback signal by the positive current signal and subtracts stator resistance estimate therefrom to obtain a rotor resistance estimate.

Abstract: A method and apparatus for eliminating greater than twice over voltage by altering firing signals provided to a PWM inverter. The signals are altered by either limiting their maximum and minimum on-times or eliminating signal changes in a symmetrical fashion so that the overall fundamental component and magnitude of a resulting low frequency alternating voltage is substantially unaltered.

Abstract: An apparatus reducing capacitive coupling between the stator and the rotor of an electromagnetic machine. The apparatus includes an electrically connective shield positionable between the stator and the rotor, the shield electrically separated from both the stator windings and the rotor when so positioned. A grounder electrically connects the shielder to ground thus substantially reducing capacitive coupling between the stator and the rotor.

Abstract: A method and apparatus for compensating for deviations in the alternating voltage produced by a PWM inverter. The necessary sequence in which inverter components must be triggered results in voltage error pulses that accumulate over time and result in deviations from ideal voltage at motor terminals. By allowing the error pulses to continue and adjusting the trigger times to compensate for the error pulses, the effect of the error pulses is negated and the voltage deviations are eliminated.

Abstract: A method and apparatus used with a motor controller having a PWM inverter for eliminating discontinuities in a stator current that are caused by noise, command signal discontinuities and feedback corrections. While noise, discontinuities, and correction can cause multiple crossings between a carrier signal and a command signal during a half cycle of a carrier signal, the present invention only allows a single crossing during any carrier signal half cycle to effect motor operation.

Abstract: A non-invasive system for accurately determining the stator resistance in an electric motor during motor operation. The system includes a mechanism for determining the phase angle of the stator current within the dq frame of reference and a mechanism for transforming feedback voltages into a new frame of reference defined by this phase angle. Counter EMFs are detected which are free of stator resistance and used to force the counter EMF components of the stator winding voltages to conform to desired values. The stator resistance is then derived using simple mathematical relationships between the resistance, stator current, feedback voltage and known counter EMF values.

Abstract: A motor controller for control of an AC motor which monitors the DC power provided to an inverter for synthesizing AC waveforms having the needed frequency and phase to power the motor. Information about variations in the DC power to the inverter are incorporated into the control strategy by adjusting a motor base frequency at which the motor moves from a constant torque to a constant horsepower mode of control. The change of control mode allows decrease in the field current, and hence a decrease in the required quadrature voltage while preserving the torque current. The torque current is ultimately limited by a user programmable direct voltage limit.