Micro Linear Corporation

Mark R Vitunic

Daniel D Culmer

A controller for a switched reluctance motor that does not utilize a sensor for detecting the rotational position of the rotor. The inductance of each field winding changes according to the rotational position of the rotor. The rotational position of the rotor of the motor is determined by measuring the inductance of each phase during periods when a minimum level of inductance for the phase is expected to occur. A series of voltage pulses are applied to the appropriate field winding during the appropriate period while the current produced in response to the voltage pulses is measured. The relationship between applied voltage, measured current, and time, is utilized to determine the inductance value as it decreases and then increases between positions of rotor alignment. Commutation to a next phase is performed based upon the measured inductance values. More particularly, a first voltage pulse is applied to an appropriate field winding after a commutation and a level of current induced by the voltage pulse is stored across a capacitor. Then, subsequent current levels produced by subsequent voltage pulses are compared to a predetermined threshold. The predetermined threshold ensures that the rotor is not stationary during the measurements. Once a current level exceeds the predetermined threshold, subsequent current levels are compared to the stored level. Upon a subsequent measured value which does not exceed the stored value, commutation to a next phase is performed. The number of degrees of rotation between removing the excitation voltage from a phase and alignment of the rotor with the corresponding phase is the phase advance. The phase advance is adjusted by controlling an offset value utilized for comparing the current levels to the stored value.

Switched reluctance motor controller with sensorless rotor position

A circuit for driving a brushless dc motor includes an active deceleration circuit for rapidly slowing the motor. A phase locked loop senses a position of the rotor for commutating from a drive state to a next drive state in a sequence of drive states at an appropriate time for maintaining torque on the rotor in the direction of rotation. Thus, the rotor 'chases' the energized windings. A speed control loop controls current in the windings and, thus, motor speed. When the speed of the motor exceeds a desired speed by more than a threshold amount, rather than commutating to a next drive state in the sequence, the circuit skips a commutation. By skipping one commutation, the current drive state is maintained while the rotor continues to turn, due to its own inertia, such that the rotor 'passes up' the current drive state. This results in a torque on the rotor in a direction opposite rotation. When the phase locked loop indicates an appropriate time for commutating to a next drive state, the circuit transitions to the next drive state in the sequence. Therefore, the current drive state continues to remain one commutation behind the normally appropriate drive state, maintaining the reverse torque. Accordingly, during deceleration, the energized windings 'chase' the rotor. When the rotor slows sufficiently, the energized windings will 'catch up' to the rotor such that the current drive state will be the appropriate drive state for again inducing a torque on the rotor in the direction of rotation.

Active deceleration circuit for a brushless DC motor

A signal generator generates a reference signal, centered about a reference voltage and having a predetermined period. The signal generator also generates output signals P and Z. The output signal P is a squarewave which changes levels at the peaks of the reference signal. The output signal Z is a squarewave which changes levels at the reference voltage crossings of the reference signal. A phase-shifted signal generator generates a phase-shifted signal using the output signals P and Z by switching in appropriate signal levels from the signal generator. The output signals P and Z are input to a switch control circuit which controls a network of switches, depending on a current region of the reference signal, to couple appropriate signals to an amplifier circuit. The switch control circuit determines the current region based on the state of the output signals P and Z. The amplifier circuit provides the phase-shifted signal in response to the signals coupled to it by the network of switches. In an alternate embodiment, the output signal Z is generated by a hysteretic comparator and changes levels at positive and negative threshold levels above and below the reference voltage. The values of the positive and negative threshold values are variable and determine the degree of phase shift between the phase-shifted signal and the reference signal.

Phase-shifted triangle wave generator

A circuit for powering a three-phase AC induction motor. The circuit generates a first signal of the form Vdc+A sin (2.pi.ft-0.degree.) and a second signal of the form Vdc+A sin (2.pi.ft-90.degree.) as is done in conventional circuits for powering two-phase AC induction motors. A vector summation circuit is used to create a third signal from the first two signals. The third signal is of the form Vdc+A sin (2.pi.ft+60.degree.). The first signal is input to a first error amplifier along with a first sampled difference signal from the motor. The third signal is input to a second error amplifier along with a second sampled difference signal from the motor. The outputs from each of the first and second amplifiers is input into a first comparator and a second comparator along with a sawtooth waveform to create a first sinusoidally modulated square wave signal and a second sinusoidally modulated square wave signal. The first and second sinusoidally modulated square wave signals are fed to driver circuits which in turn control an H-bridge circuit for powering the motor from a DC bus. Therefore, the invention achieves two-phase control of a three-phase AC induction motor.

Two-phase electronic control of a three-phase induction motor

The invention is an active, hot insertable, SCSI terminator circuit having a bypass device that permits an initially unpowered active SCSI terminator to be coupled to a signal line of a powered SCSI bus such that no damage results to the SCSI terminator circuit itself or to other SCSI devices on the SCSI bus, and without having the effect of altering the existing state of the SCSI bus as a result of the coupling. Preferably, the terminating element of the SCSI terminator is a p-channel MOSFET. The SCSI terminator is prevented from being damaged during the coupling by using the bypass device to effectively short the gate of the p-channel MOSFET terminating element to its drain. When the drain of the p-channel MOSFET terminating element is shorted to its gate the amount of current the SCSI terminator may draw from any and all SCSI signal lines during the coupling is substantially limited to less than 50 .mu.A. The bypass device performs the shorting function until a SCSI terminator reference voltage powers up to its steady state value, after which the bypass device is disabled.

Hot insertable active SCSI terminator

The invention employs an active element, a p-channel MOSFET, between a regulated voltage and a SCSI terminating line. An 'ideal' current source terminator is most effective when a signal line is negated (low-to-high transition), whereas a resistive terminator is most effective when a signal line is asserted (high-to-low transition). The I-V characteristics of a p-channel MOSFET, wherein the relationship between the termination voltage and the termination current is characterized by a nonlinear and smooth voltage versus current curve, provide an optimized transient response for signal negations and signal assertions on a SCSI bus.

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San Jose, CA, United States of America

Mark R Vitunic