1. VIEW ON THE CONTROL ASPECTS OF UNIVERSAL MOTOR
SUBRAMANIAN.R
Edited By
Sarath S Nair

2. SYNOPSIS Basics of universal motor Characteristics Control aspects
Equivalent circuit
Analysis
Conclusion
References

3. UNIVERSAL MOTOR Can run on either dc or ac power
A series wound dc motor
A double-excited motor
High starting torque and a variable speed characteristics
Runs at dangerously high speed on no load
Input range is few watts to 2000 watts

4. PARTS Stator: field windings to generate the radial magnetic flux
Rotor: armature winding supplied with current through the carbon brushes to generate magnetic flux
Brushes: mechanical linking of power supply and rotor windings
Commutator & a compensating winding

5. UNIVERSAL MOTOR FROM A BLENDER
Fig Fig.2

6. CONSTRUCTION
Permanent magnets in dc motor is replaced by electromagnets
manufactured in two types
Concentrated-pole, non-compensated
Distributed-field compensated

7. Contd… 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 laminated
Rotor: wound type and a small dc motor with laminated core having straight slots having armature winding is connected to the commutator

8. Contd… Distributed-field compensated high rating
Stator: Similar to that of a split phase motor
Rotor: Wound type similar to that of a small d.c. motor
Compensating winding is used to reduce the reactance voltage present in the armature when motor runs on ac supply
The reactance of the field winding can be kept low by limiting the number of turns.

9. OPERATION
With input DC power, the stator coils as permanent magnets like a DC motor & continues to rotate in the same direction
the current through the rotor also reverses the current through the electromagnets
every pole of the motor changes from north to south or from south to north

10. Contd…
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

11. ADVANTAGES Simple structure Robust Small size & compact Portable
Good power density characteristics
Rotates more than 3000 to rpm

12. APPLICATIONS DISADVANTAGES
Sparks occurring between brushes & commutator due to their imperfect electrical contact leads to loud noise while operating
As a result life of brushes is reduced
High maintenance requirements
High peak to peak current gains poor motor efficiency
High brush temperature results in limited motor lifetime
APPLICATIONS
Speed control and high torque are required
Typical applications are in the field of power tools and home appliances like mixers, washing machine.

13. CHARACTERISTICS

14. Contd…
Torque is inversely proportional to speed & directly proportional to the current
More current flows at high speed, torque increases as magnetic flux density also increase
low speed tends to cause magnetic saturation, deteriorates the characteristic of the motor
Rotation speed is determined by the no. of windings

15. CONTROL ASPECTS
In domestic appliances, Electric motors the ability to control its speed
Two control methods
Phase angle control
Chopper control

16. PHASE ANGLE CONTROL

17. Contd… 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 microcontroller
The whole circuitry is usually connected directly to the mains.

18. Contd… Advantages Disadvantages simplicity cost effectiveness
full speed control
Disadvantages
high brush noise
short lifetime
high current ripple

19. CHOPPER CONTROL PWM control
The AC voltage from the mains is rectified and then switched at a high frequency by a Power MOSFET or an IGBT
lower current ripple which reduces the harmonics
reduces the copper and iron losses

20. Contd… Advantages 1. Higher motor efficiency 2. Lower acoustic noise
3. Smooth current behavior
Disadvantages
1. More components needed
2. Filtering of chopper frequency required
Two chopper control method is used
DC chopper speed control
DC chopper speed and current control

21. 1. DC CHOPPER SPEED CONTROL
The speed regulation is poor at low and medium speeds
The average error is large
The speed regulation improves at high speeds
The speed dynamic response is slow
Control system takes a long time to get back to a steady state when load changes

22. 2. DC CHOPPER SPEED AND CURRENT CONTROL
The current control loop is designed to be much faster than the speed control
a fast dynamic response to load changes

23. EQUIVALENT CIRCUIT
The equivalent circuit of a proposed universal motor with speed and current control is shown in Figure

24. Contd…
The model of the proposed universal motor control can be described mathematically as:
e the motor back emf
k1 is the motor constant dependent on the motor characteristics.

25. Contd… Lp =La+Lf V(t) = [R + Lp – k1w]i(t) Where R=Ra+Rf
The mechanical equation can be written as
a serial excitation motor
the motor torque is proportional to the square of the motor current

26. MODEL OF UNIVERSAL MOTOR
Dynamics of universal motor is governed by the equations:
Term ωφ in (1) represents the Counter electromotive force
Term 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 is
Φ(i ) =k(| I |)I (3)
Where the coefficient k is the mutual inductance Between the field and armature coils.

27. CONCLUSION
The basic outline of the universal motor & the dc chopper speed & current control are discussed here
Equivalent circuit & model of the universal motor are also explained briefly

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29. REFERENCES
[1] Huangsheng Xu, Kevin King, and Yashvant Jani Renesas Technology America, Inc. 450 Holger Way, San Jose, CA “ High Performance DC Chopper Speed and Current Control of Universal Motors Using a Microcontroller” /07/$25.00 © 2007 IEEE
[2] Hac1 Bodur, A. Faruk Bakan, M. Hadi Sarul Yildiz Technical University, Dept. of Electrical Engineering Istanbul 80750, TURKEY “Universal Motor Speed Control with Current Controlled PWM AC Chopper by using a Microcontroller /00/$10.00~2000IE
[3] L. C. PACKER Associate. A. I. E. E. “Universal Type Motors” Westinghouse Electric & Mfg. Co., Springfieldl Mass.- Presented at the Regional Meeti,ng of the A. I. E. E., Swarmp- scott, Mass., May 7-9, 1925
[4] Rex Miller and Mark Richard Miller “Small Electric Motors” 2nd Edition Wiley-dreamtech India Pvt. Ltd
[5] Charles I. Hubert “Electrical Machines” 2nd Edition Pearson Education
[6] B.L.Theraja, A.K. Theraja “ A Textbook of Electrical Technology” Volume II AC &DC Machines S.Chand & Company Ltd.