Presentation on theme: "VIEW ON THE CONTROL ASPECTS OF UNIVERSAL MOTOR"— Presentation transcript:
1VIEW ON THE CONTROL ASPECTS OF UNIVERSAL MOTOR SUBRAMANIAN.REdited BySarath S Nair
2SYNOPSIS Basics of universal motor Characteristics Control aspects Equivalent circuitAnalysisConclusionReferences
3UNIVERSAL MOTOR Can run on either dc or ac power A series wound dc motorA double-excited motorHigh starting torque and a variable speed characteristicsRuns at dangerously high speed on no loadInput range is few watts to 2000 watts
4PARTS Stator: field windings to generate the radial magnetic flux Rotor: armature winding supplied with current through the carbon brushes to generate magnetic fluxBrushes: mechanical linking of power supply and rotor windingsCommutator & a compensating winding
6CONSTRUCTIONPermanent magnets in dc motor is replaced by electromagnetsmanufactured in two typesConcentrated-pole, non-compensatedDistributed-field compensated
7Contd… Concentrated-pole, non-compensated low rating Stator: Two salient poles & like a two pole dc series motor except that whole of its magnetic path is laminatedRotor: wound type and a small dc motor with laminated core having straight slots having armature winding is connected to the commutator
8Contd… Distributed-field compensated high rating Stator: Similar to that of a split phase motorRotor: Wound type similar to that of a small d.c. motorCompensating winding is used to reduce the reactance voltage present in the armature when motor runs on ac supplyThe reactance of the field winding can be kept low by limiting the number of turns.
9OPERATIONWith input DC power, the stator coils as permanent magnets like a DC motor & continues to rotate in the same directionthe current through the rotor also reverses the current through the electromagnetsevery pole of the motor changes from north to south or from south to north
10Contd…With input AC power, it reverses the poles and thus the direction of rotation is obtained.experiences no torque during current reversal, but the average torque is sufficient to turn the motor as if it were connected to a DC power supply.different rotational speeds can be achieved by varying the amount of current reaching the electromagnets.The starting torque of a universal motor is determined by the current that flows through the armature
11ADVANTAGES Simple structure Robust Small size & compact Portable Good power density characteristicsRotates more than 3000 to rpm
12APPLICATIONS DISADVANTAGES Sparks occurring between brushes & commutator due to their imperfect electrical contact leads to loud noise while operatingAs a result life of brushes is reducedHigh maintenance requirementsHigh peak to peak current gains poor motor efficiencyHigh brush temperature results in limited motor lifetimeAPPLICATIONSSpeed control and high torque are requiredTypical applications are in the field of power tools and home appliances like mixers, washing machine.
14Contd…Torque is inversely proportional to speed & directly proportional to the currentMore current flows at high speed, torque increases as magnetic flux density also increaselow speed tends to cause magnetic saturation, deteriorates the characteristic of the motorRotation speed is determined by the no. of windings
15CONTROL ASPECTSIn domestic appliances, Electric motors the ability to control its speedTwo control methodsPhase angle controlChopper control
17Contd… Phase angle control is a simple and cost-effective solution The speed of a universal motor is controlled by using a triac.The gate of the triac can be controlled directly by the output ports of a microcontrollerThe whole circuitry is usually connected directly to the mains.
18Contd… Advantages Disadvantages simplicity cost effectiveness full speed controlDisadvantageshigh brush noiseshort lifetimehigh current ripple
19CHOPPER CONTROL PWM control The AC voltage from the mains is rectified and then switched at a high frequency by a Power MOSFET or an IGBTlower current ripple which reduces the harmonicsreduces the copper and iron losses
20Contd… Advantages 1. Higher motor efficiency 2. Lower acoustic noise 3. Smooth current behaviorDisadvantages1. More components needed2. Filtering of chopper frequency requiredTwo chopper control method is usedDC chopper speed controlDC chopper speed and current control
211. DC CHOPPER SPEED CONTROL The speed regulation is poor at low and medium speedsThe average error is largeThe speed regulation improves at high speedsThe speed dynamic response is slowControl system takes a long time to get back to a steady state when load changes
222. DC CHOPPER SPEED AND CURRENT CONTROL The current control loop is designed to be much faster than the speed controla fast dynamic response to load changes
23EQUIVALENT CIRCUITThe equivalent circuit of a proposed universal motor with speed and current control is shown in Figure
24Contd…The model of the proposed universal motor control can be described mathematically as:e the motor back emfk1 is the motor constant dependent on the motor characteristics.
25Contd… Lp =La+Lf V(t) = [R + Lp – k1w]i(t) Where R=Ra+Rf The mechanical equation can be written asa serial excitation motorthe motor torque is proportional to the square of the motor current
26MODEL OF UNIVERSAL MOTOR Dynamics of universal motor is governed by the equations:Term ωφ in (1) represents the Counter electromotive forceTerm iφ in (2) is the electromagnetic Torque produced by the motor.The flux φ is a function of the current I, a non-linear system of equations.The relation between Φ and I isΦ(i ) =k(| I |)I (3)Where the coefficient k is the mutual inductance Between the field and armature coils.
27CONCLUSIONThe basic outline of the universal motor & the dc chopper speed & current control are discussed hereEquivalent circuit & model of the universal motor are also explained briefly
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