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 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 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 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.

Abstract: A non-invasive system for accurately determining the counter EMF or speed voltages 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. The speed voltage values thereby detected are free from stator resistance effects and represent parameters of improved accuracy which can be used in motor control functions.

Abstract: An open loop, volts/hertz motor drive for control of an induction motor adjusts the voltage command to a sine-triangle PWM inverter to compensate for reduction in PWM inverter gain and to compensate for variations in DC bus voltage in the pulse dropping transition region between PWM operation and six-step operation. The drive includes a microelectronic processor interfaces to DC bus voltage sensing circuitry and to the PWM inverter.

Abstract: A frequency control method is incorporated in a motor drive to prevent overcurrent trips when an induction motor is subjected to impact loads or reconnection under load. The drive includes a current regulator loop to control stator current and a voltage regulator loop to control the command to the current regulator. Motor voltage is sensed and a voltage error is developed. This voltage error is processed through a proportional-integral control loop which controls an operating frequency signal to the current regulator. The drive responds during current limit conditions to reduce operating frequency and speed until the current limit conditions subside. The motor can then be re-accelerated up to the desired operating speed.