ELECTRIC DRIVER 1

Upon the completion of this topic, you should be able to:- 2.1 Study the Electrical driver in AC motor 2.1.1 Define an electrical driver 2.1.2 Compare types of AC driver2.2 Study four quadrant in AC motor operation 2.2.1 Draw the torque against speed axis 2.2.2 Justify the types of moto operation in each quadrant 2.3 Understand torque speed curve 2.3.1 Construct the torque-speed curve for the induction motor 2.3.2 Explain the operation and function of a motor in every quadrant 2.3.3 Draw the curve of torque versus speed if the stator connected in forward and reverse

Define an electrical driver

• a system that contains one or more electric motors and most electrical control equipment designed to control the motors achievement.

Overview of AC and DC drives

After vector control drives were introduced (1980s)

• AC motors used in high performance applications – elevators, tractions, servos

• AC motors favorable than DC motors – however control is complex hence expensive

• Cost of microprocessor/semiconductors decreasing –predicted 30 years ago AC motors would take over DC motors

Electrical Drives

Drives are systems employed for motion control

Require prime movers

Drives that employ electric motors as prime movers are known as Electrical Drives

Conventional electric drives

• Bulky• Inefficient• inflexible

Modern electric drives (With power electronic converters)

• Small• Efficient• Flexible

Modern electric drives

• Inter-disciplinary• Several research area• Expanding

Machine designSpeed sensorlessMachine Theory

Non-linear controlReal-time controlDSP applicationPFCSpeed sensorless Power electronic converters

Utility interfaceRenewable energy

INTRODUCTION TO ELECTRIC DRIVES - MODULE 1

Components in electric drives

e.g. Single drive - sensorless vector control from Hitachi

INTRODUCTION TO ELECTRIC DRIVES - MODULE 1

Components in electric drives

e.g. Multidrives system from ABB

INTRODUCTION TO ELECTRIC DRIVES - MODULE 1

Components in electric drives

Motors• DC motors - permanent magnet – wound field• AC motors – induction, synchronous (IPMSM, SMPSM), brushless DC• Applications, cost, environment

Power sources• DC – batteries, fuel cell, photovoltaic - unregulated• AC – Single- three- phase utility, wind generator - unregulated

Power processor• To provide a regulated power supply• Combination of power electronic converters

•More efficient •Flexible •Compact •AC-DC DC-DC DC-AC AC-AC

Components in electric drives

Control unit• Complexity depends on performance requirement• analog- noisy, inflexible, ideally has infinite bandwidth.• digital – immune to noise, configurable, bandwidth is smaller than the

analog controller’s • DSP/microprocessor – flexible, lower bandwidth - DSPs perform faster

operation than microprocessors (multiplication in single cycle), can perform complex estimations

Overview of AC and DC drives

DC motors: Regular maintenance, heavy, expensive, speed limit

Easy control, decouple control of torque and flux

AC motors: Less maintenance, light, less expensive, high speed

Coupling between torque and flux – variable spatial angle between rotor and stator flux

Overview of AC and DC drives

Before semiconductor devices were introduced (<1950)• AC motors for fixed speed applications• DC motors for variable speed applications

After semiconductor devices were introduced (1950s)• Variable frequency sources available – AC motors in variable speed

applications

• Coupling between flux and torque control• Application limited to medium performance applications – fans,

blowers, compressors – scalar control

• High performance applications dominated by DC motors – tractions, elevators, servos, etc

Overview of AC and DC drives

After vector control drives were introduced (1980s)

• AC motors used in high performance applications – elevators, tractions, servos

• AC motors favorable than DC motors – however control is complex hence expensive

• Cost of microprocessor/semiconductors decreasing –predicted 30 years ago AC motors would take over DC motors

Types of AC Driver

Static Frequency Changers• An electronic device that converts alternating

current (AC) of one frequency to alternating current of another frequency.

Static Voltage Controllers• An electrical device for providing fast-acting

reactive power on high-voltage electricity transmission networks.

Rectifier-inverter System with Line Commutation• A line communicated inverter is tied to a

power grid or line.• The commutation of power (conversion from

DC to AC) is controlled by the power line, so that, if there is a failure in the power grid, the photovoltaic system cannot feed power into the line.

Rectifier-inverter System with Self Commutation• Self-commutated Inverter an inverter that uses

switches and controls that may be turned on and off at anytime.

• Generally this inverter uses a PWM method to generate a synthesized waveform.

• Self-commutated inverters may be utility-interactive or stand-alone.

• They may be voltage controlled or current controlled

Torque speed curve

Four Quadrant in AC motor

QUADRAnt OPERATION

1 and 3 represent the motor applying torque in the direction of motionthe Flow of energy is from electrical to mechanicalThe servo motor is converting electrical power from the drive into motion in the system

2 and 4 represent applying torque opposite the direction of the motionmotor is actually acting as a generator. The motion of the system is being converted into electrical power, which is then absorbed by the drive

Curve of torque versus speed if the stator connected in reverse