This paper addresses self-sensing ("sensorless") control of salient-pole permanent magnet synchronous motors (PMSMs). The major contribution of this work is the introduction of a simple-to-implement estimation technique that operates over a wide speed range, including zero speed. The technique achieves simplicity by decoupling the inherent cross-coupling in PMSMs. The technique utilizes the dependence of inductance on rotor position in interior permanent magnet machines to produce position and velocity estimates both for field orientation and for all motion control of the drives. The technique functions in a manner similar to a resolver and resolver-to-digital converter (RTDC) sensing system, whereby in the proposed technique the motor acts as the electromagnetic resolver and the power converter applies carrier-frequency voltages to the stator which produce high-frequency currents that vary with position. The sensed currents are then processed with a heterodyning technique that produces a signal that is approximately proportional to the difference between the actual rotor position and an estimated rotor position. This position error signal and a torque estimate are then used as inputs to a Luenberger style observer to produce parameter insensitive, zero lag, position and velocity estimates.

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Rotor position and velocity estimation for a salient-pole permanent magnet synchronous machine at standstill and high speeds

The operation of a brushless permanent-magnet machine requires rotor-position information, which is used to control the frequency and phase angle of the machine's winding currents. Sensorless techniques for estimating rotor position from measurements of voltage and current have been the subject of intensive research. This paper reviews the state of the art in these sensorless techniques, which are broadly classified into three types: motional electromotive force, inductance, and flux linkage.

Review of position-sensorless operation of brushless permanent-magnet machines

A simple control for a permanent motor drive is described which provides a wide speed range without the use of a shaft sensor. Two line-to-line voltages and two stator currents are sensed and processed in analog form to produce the stator flux linkage space vector. The angle of this vector is then used in a microcontroller to produce the appropriate stator current command signals for the hysteresis current controller of the inverter so that near unity power factor can be achieved over a wide range of torque and speed. A speed signal is derived from the rate of change of angle of the flux linkage. A drift compensation program is proposed to avoid calculation errors in the determination of angle position and speed. The control system has been implemented on a 5 kW motor using Nd-Fe-B magnets. The closed loop speed control has been shown to be effective down to a frequency of less than 1 Hz, thus providing a wide range of speed control. An open loop starting program is used to accelerate the motor up to this limit frequency with minimum speed oscillation. >

A permanent magnet motor drive without a shaft sensor

A brushless DC motor without a position sensor is described. Variable speed is achieved by adjusting the average motor voltage, just like chopper control of DC motors. The position-sensorless drive proposed is based on detection of the conducting interval of free wheeling diodes connected in antiparallel with power transistors. This approach makes it possible to detect the rotor position over a wide speed range, especially at a lower speed. Experimental results obtained from a prototype brushless DC motor with a rating of 300 W are shown to confirm the validity of the sensorless drive from 45 to 2300 r/min. The starting procedure of the motor is also discussed because it is impossible to detect the rotor position at a standstill. >

An approach to position sensorless drive for brushless DC motors

To control PM brushless DC motors, position and speed sensors are indispensable because the current should be controlled depending on the rotor position. However, these sensors are undesirable from standpoints of size, cost, maintenance, and reliability. There are different ways of approaching this problem, depending on the flux distribution. The paper presents the speed and position sensorless control of PM brushless DC motors with a sinusoidal flux distribution. Two approaches are presented and compared with each other; one is based on the voltage model of the motor and another is based on the current model. The starting procedure is also a very difficult problem under sensorless drives, because the sensorless drive algorithm uses voltage and current for estimation of rotor position, but no information is available before starting. A novel starting method is presented by using a salient-pole machine. Experimental results based on DSP-TMS320C25 controller are shown for comparisons, which demonstrate desired characteristics both in steady-state and starting conditions.

Sensorless PM brushless DC motor drives

The microcomputer control of a brushless motor without a shaft position sensor is studied. A method which permits the determination of the permanent magnet rotor position by the back electromotive force (EMF) induced in the stator windings and the starting technique which uses the motor as a synchronous motor at standstill are explained. The motor voltage is chopped by commutator transistors to change the motor speed. The control system consists of a 4-b single-chip microcomputer and two quad-comparators.

Microcomputer Control for Sensorless Brushless Motor

AC power supply is converted to DC by a rectifier circuit. The DC is stepped up by a step-up chopper circuit. The output of the step-up chopper circuit is smoothed by a smoothing circuit. The output of the smoothing circuit is input to an inverter via a current detecting circuit and a voltage detecting circuit. A synchronous motor is connected to the inverter. When the speed of the synchronous motor is judged to be in a high speed region based on the output signal of the voltage detecting circuit, the first speed control apparatus operates the interrupting control of the switching element of the step-up chopper circuit in such a manner that a deviation speed between an instruction speed signal to the motor and the detected speed of the motor reaches to zero. When the duty ratio of the inverter reaches to 100%, that is, when the speed of the motor reaches to a low speed region, the first control speed apparatus controls the switching element of the step-up chopper circuit based on the output signal of the current detecting circuit, and the second control speed apparatus carries out the pulse width modulation control of the inverter in such a manner that a deviation speed signal between an speed instruction signal to the motor and the detected speed of the motor reaches to zero.

Speed control apparatus for a brushless direct current motor

In speed control apparatus and method for a motor operable to drive a load whose magnitude varies over a predetermined period which use a unit for controlling voltage or current supplied to the motor such that the speed of the motor can coincide with a command speed, n pieces of data indicative of voltages or currents supplied to the motor and corresponding to n divisions of the predetermined period are independently stored in a read/write storage, at least one of the n pieces of data is corrected at the rate of each of the n divisions in accordance with a difference between the command speed and the speed of the motor, and the voltage or current supplied to the motor is controlled in accordance with at least the one of the n pieces of data, so that pulsation and noise occurring especially under low revolutions can be minimized.

Speed control apparatus and method for motors

The present invention continuously speed-controls an electric motor for driving a compressor for refrigerant compression such that the compressor is driven in its maximum rpm if the difference (temperature deviation) between a target cooling temperature and an actual temperature is greater than a first predetermined value, the compressor is stopped if the temperature deviation is less than a second predetermined value, and the compressor is speed-controlled by a digital control signal if the temperature deviation is between said first and second predetermined values.

System of controlling refrigerator temperature

A novel refrigerator control system is disclosed which comprises an inverter for driving a motor for a compressor, and a change-over device for driving the compressor directly with a commercial power supply when the compressor motor is not driven by the inverter.

Kenichi Iizuka

Papers

Microcomputer Control for Sensorless Brushless Motor

Speed control apparatus for a brushless direct current motor

Speed control apparatus and method for motors

System of controlling refrigerator temperature

Refrigerator control system