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UNIT 1.Drive Characteristics

(1)ELECTRIC DRIVE SYSTEM:

              System employed for motion control are called as DRIVES and may employed any of the prime movers, diesel engine or petrol engine, hydraulic motor, electric motor for supply mechanical energy for motion control.

Electric Drives

 An electric drive is a system that (control to)converts electrical energy to mechanical energy

Parts:

  1.electric motor (or several)

  2.control system (including software)

Constant-speed drives

   Only a start/stop and protection system in addition to the electric motor

Variable-speed drives (VSDs)

   Include an electronic power converter

Types of Drives:

1. Group Drive
2. Individual Drive
3. Multi Motor Drive

Group Drive:

• Group drive is a single motor sufficient capacity.
• To drive an entire group of load used in a shaft and through the belts and pulleys.
• All the machines were driven.  
• This type of drive control is difficult to control and unsafe.  

Individual Drive:

• the individual drive is only one drive used for the total working system

Multi Motor Drive:

• More than one drive used for each machine
• each motor is used to driven
• good control
• EX: paper mills, rolling mills,etc.

(2)PART OF ELECTRICAL DRIVES:

POWER MODULATOR(CONVERTER):

1. controlled rectifier(AC to DC)
2. Inverters(DC to AC)
3. AC voltage controller(fixed ac to variable ac)
4. DC chopper
5. cyclo converted(frequency conversion)

FUNCTIONS OF POWER MODULATOR:

• It modulate the flow of power from source to motor
• During transient operation such as starting,breaking and speed reverser maintenance the motor current with in permissible values 
• It converts electrical energy of the source from suitable form to the motor

(3)CLASSIFICATION OF ELECTRIC DRIVES:

1. AC Drives
2. DC Drives

AC &DC Drives

                Using ac ,motor or other drives using this system is called AC Drives and the system using DC supply is called DC Drives.

ADVANTAGES OF ELECTRIC POWER SYSTEM:

• It provide feasible control characteristics
• Drives can be provided with automatic fault detection system
• PLC and Computers can be employed to automatically control the Drive operation 
• It is adaptable in almost any operation function such as explosive radio active employment it will operate all the four quadrants.

APPLICATION:

1. Paper mills
2. Cement mills
3. Rolling mills
4. Coal mills,etc.

DIFFERENT BETWEEN AC DRIVES & DC DRIVES:

DC DRIVE	AC DRIVE
1.Pullky, costly and heavy weight in the motor	These problems are not there
2.Power circuit and control circuit are simple and explosive	Power circuit and control circuit are coupled
3.It required frequency maintenance	Less maintenance
4.Power factor will be very poor	Power factor is better
5. It use in certain location	It use in alllocation

(4)DYNAMICS OF MOTOR LOAD SYSTEM:

Fundamental Torque Equation:

                                motor->load 

Change in torque will be rate of change of motion.

                   T-Tl=d/dt(jwm)

                   T-Tl=j(dwm/dt) +wm(dj/dt)

                   T-Tl=j(dwm/dt)(constant inertia drives)

                   T=Tl+ j dwm/dt

T->Torque developed by a motor(Nm)

Tl->Load torque(Nm)

J->moment of inertia of motor(kg m2)

Classification of load torque:

1. Active load torque
2. Passive load torque

Active load torque:

              The load torque which have a potential to drive the motor under equilibration condition are called active load torque.

Passive load torque:

               The load torque which always oppose the motion and change the sign an reversal of motion are called as passive load torque
COMPONENTS OF LOAD TORQUE:

1. Friction torque
2. Winding torque
3. Mechanical torque

Friction torque:
            The torque which develop due to friction is known as friction torque it is develop of soft of the motor
Winding torque:
            This torque is develop due to wind when a motor run the wind generate a torque opposing the notion this is known as winding torque
Mechanical torque:
             The torque which develop due to the mechanical work. It may be a constant line invariant and also it is varies with the change in the load mode of operation.

 

Syllabus

                        EE 62                            SOLID STATE DRIVES

1.         DRIVE CHARACTERISTICS

Equations  governing  motor  load  dynamics  -  Equilibrium  operating  point  and  its

steady  state  stability  -  Mathematical  condition  for  steady  state  stability  and

problems  -  Multi  quadrant  dynamics  in  the  speed  torque  plane  -  Basics  of

regenerative  braking  -  Typical  load  torque  characteristics  -  Acceleration,

deceleration, starting and stopping.

2.        CONVERTER / CHOPPER FED DC MOTOR DRIVE

Steady state analysis of  the single and three phase fully  controlled  converter fed

separately  excited  D.C  motor  drive:  Continuous  and  discontinuous  conduction

mode  -  Chopper  fed  D.C  drive:  Time  ratio  control  and  current  limit  control  -

Operation of four quadrant chopper.

3.        INDUCTION MOTOR DRIVES

Stator voltage control - Slip-power recovery drives - Adjustable frequency drives:

v/f control, constant slip-speed control and constant air-gap flux control – Basics

of voltage/current fed inverters - Block diagram of closed loop drive.

4.         SYNCHRONOUS MOTOR DRIVES

Open  loop  volts/hertz  control  and  self-control  of  synchronous  motor:  Marginal

angle control and power factor control - Permanent magnet synchronous motor.

5.        DESIGN OF CONTROLLERS FOR DRIVES

Transfer  function  for  dc  motor,  load  and  converter  –  Closed  loop  control  with

current and speed feedback - Armature voltage control and field weakening mode

control - Design of controllers: Current controller and speed controller - Converter

selection and characteristics.

TEXT BOOKS

1.         R. Krishnan, ‘Electric Motor & Drives: Modelling, Analysis and Control’,

Prentice Hall of India, 2001.

2.         Bimal K. Bose. ‘Modern Power Electronics and AC Drives’, Pearson Education,

2002.

REFERENCE BOOKS

1.         G.K. Dubey, ‘Power Semi-conductor Controlled Drives’, Prentice Hall of India,1989.