BRUSHLESS MOTORS - Elinco

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SMALL BRUSHLESS DC MOTORSPrinciples of OperationThe differences between a DC motor having a mechanical commutation system and a BLDC motor aremainly found in :• the product concept• the commutation of phase currents.From the user’s point of view, brushless DC motors follow the same equations as those with brushes:torque is proportional to current; speed depends on the voltage and the load torque.The commutation of brushless motorsIn the conventional DC motor commutation takes place mechanically through the commutator-and-brushsystem. In a BLDC motor, commutation is done by electronic means. In that case the instantaneous rotorposition must be known in order to determine the phases to be energized.The angular rotor position can be known by:• using a position sensor (Hall sensor, optical encoder, resolver)• electronically analyzing the back-EMF of a non-energized winding. This is called sensorless commutation.Use of Hall sensorsIn general, BLDC motors have three phase windings. The easiest way is to power two of them at a time,using Hall sensors to know the rotor position. A simple logic allows for optimal energizing of the phases asa function of rotor position, just like the commutator and brushes are doing in the conventional DC motor.Use of an encoder or resolverThe rotor position may also be known by use of an encoder or resolver. Commutation may be done verysimply, similar to the procedure with Hall sensors, or it may be more complex by modulating sinusoidalcurrents in the three phases. This is called vector control, and its advantage is to provide a torque ripple oftheoretically zero, as well as a high resolution for precise positioning.Use of Back-EMF analysisA third option requiring no position sensor is the use of a particular electronic circuit. The motor has onlythree hook-up wires, the three phase windings are connected in either triangle or star. In the latter case,resistors must be used to generate a zero reference voltage. With this solution the motor includes no sensorsor electronic components and it is therefore highly insensitive to hostile environments. For applicationssuch as hand-held tools, where the cable is constantly moved, the fact of just three wires is anotheradvantage.The functioning of a sensorless motor is easy to understand. In all motors, the relation of back-EMF andtorque versus rotor position is the same. Zero crossing of the voltage induced in the non-energized windingcorresponds to the position of maximum torque generated by the two energized phases. This pointof zero crossing therefore allows to determine the moment when the following commutation should takeplace depending on motor speed. This time interval is in fact equivalent to the time the motor takes tomove from the position of the preceding commutation to the back-EMF zero crossing position. Electroniccircuits designed for this commutation function allow for easy operation of sensorless motors.As the back-EMF information is necessary to know the rotor position, sensorless commutation doesn’twork with the motor at stall. The only way of starting is to pilot it at low speed like a stepper in open loop.8Elinco International Inc. 1525 Kings Highway East, Fairfield, Ct 06824Ph. (203) 275-8885 Fax (203) 334-7792 sales@elincoinc.com www.elincoinc.com
Remember:- for commutation, position sensors are necessary when operating in incremental mode-sensorless commutation is recommended only for applications running at constant speed and load.Operating principle of BLDC motors:It follows the same equations as the DC motor using mechanical commutation except that parameterslike iron losses and losses in the drive circuit are no longer negligible in applications where efficiency is ofprime importance.Iron lossesThey depend on speed and, in the torque formula, may be introduced as viscous friction. The equation foruseful motor torque becomes:M m= k·l m– k v·ω-M fWith M m= motor useful torquek = torque constantl m= motor currentk v= viscous coefficient for iron lossesω = angular velocityM f= bearing frictionLosses in the electronicsThe current and voltage required by the motor and the drive circuit to be operated at the desired speedand torque depend also on the drive circuit.As an example, a driver bridge in bipolar technique will reduce the voltage available at the motor terminalsby about 1.7V, and the total current must include the consumption of the circuitry.BLDC MOTORS SLOTLESS BLDCSTEPPING MOTORSElinco International Inc. 1525 Kings Highway East, Fairfield, Ct 06824Ph. (203) 275-8885 Fax (203) 334-7792 sales@elincoinc.com www.elincoinc.com9
Page 2 and 3: This catalog provides complete elec
Page 4 and 5: Elinco International OrganizationMo
Page 6 and 7: PART NUMBERING SYSTEMBrushless DC M
Page 10 and 11: Brushless DC Motor22mmELECTRICAL SP
Page 14 and 15: Brushless DC Motor42mm x 42mmELECTR
Page 18 and 19: SLOTLESS BRUSHLESS DC MOTORSWhat is
Page 20 and 21: STEPPING MOTORSFeatures of Stepping
Page 22 and 23: Basic Characteristics ofStepping Mo
Page 24 and 25: Actions for VibrationReduction of S
Page 26: High Torque Hybrid Stepping Motor 2
Page 29: SPEED/TORQUE CURVESKM2832L3-G095A P
Page 32 and 33: Hybrid Stepping Motor 39mm 1.8°•
Page 34 and 35: High Torque Hybrid Stepping Motor 4
Page 48 and 49: Round Hybrid Stepping Motor 86mm 1.
Page 54 and 55: Hybrid Stepping Motor110mm• NEMA
Page 56 and 57: Hybrid Stepping Motor 86mm 1.2°3 P
Page 58 and 59:
Hybrid Stepping Motor 110mm 1.2°3
Page 60:
ELINCO ENGINEERING AVAILABLEElinco
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BRUSHLESS MOTORS - Elinco

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