01 basic drives

AC Drive Basics

AC Drives - Basics & Beyond…

Copyright © 2005 Rockwell Automation, Inc. All rights reserved

28th June’2005 1

AC Drive Basics

How Does A Motor Work?

1. Current flowing through a conductor

2. The direction of the current

flow

3. Pass a conductor through a magnetic field

Basic Rules:

Magnetic flux around the conductor

Polarity of the magnet

A voltage or current flow

AC Drive Basics

Stator Magnetic Field

Rotor Field Created by InducedCurrent Flow in Rotor Conductors

N S

Elastic Nature of Magnetic Lines of Force Rotor

Torque Generated in a motor

N S

F

AC Drive Basics

Workhorse of modern Industry Found in virtually every phase of Manufacturing One of the Most Common Forms of rotating power in the World• Consists of two sets of electromagnets – One set ,the stator, housed in motor Frame and other rotor, free to rotate and supported by bearings and motor end bells.

Squirrel Cage Induction Motor

Rotor

Fan BladesRotor BarEnd Rings

StatorPerforated Lamination disks stacked together and through careful die casting process Aluminum or Cu – Brass Alloy is filled in the channels and then End rings are formed.

AC Drive Basics

Issue with IM Motor

To change Speed below and above base speed Smoothly

AC Drive Basics

1. Starting Current - Very High 2. Power Factor - Poor at light load3. Efficiency - Not so good 4. Speed control - A big Problem5. Protection - additional Equipments Required

Operational Issues

AC Drive Basics

Mechanical

Constant SpeedMotor

ACMotor

VariableSpeedShaft

Vary Pitch Diameter

Eddy current

Constant Speed Motor

ACMotor

ExciterCoupling Field

Solid state DC

DC Motor

DC OutputAC Input

Rotating DCField Control

DC Motor

AC Motor

DC Gen

Solid state AC

AC Motor

Fixed DC Bus

InverterDiode AC OutputVariableFrequencyRectifier

LC

Hydraulic

Pump

Valve

Hydraulic Motor

ACMotor


Typesof

AdjustableSpeed

AC Drive BasicsConstant

Speed MotorAC

Motor

Vary Pitch Diameter

Mechanical Variable Speed

Pump

Valve

HydraulicACMotor


Hydraulic

Variable SpeedShaft

AC Drive Basics

Variable Speed Shaft


ACMotor

ExciterCoupling Field

Eddy Current Coupling

Benefits Initial cost Allows torque control Simple control

Limitations Heat generation Size Power consumption

AC Drive Basics

These Methods have numerous disadvantages Like –

- No ENERGY SAVING,- No smooth speed variation,

- No power factor improvement….. etc ……..

AC Drive Basics

Frequency Drives

AC Drive BasicsDrives Classification - Voltage basis

DC Drives : Not in much use due to Maintenance related problems associated with DC Motors.

AC drives : Market is zooming up to big targets and getting new fields of application

AC Drive BasicsDC Drives :Operation and Algorithm

Field

Cur. Reg.Speed

Reg.

SCR

Control

Field Bridge

High Bandwidth Current regulator

Armature

Cur. Reg.

Arm Bridge

M

PG

Ref

Voltage Fdbk

Current Fdbk

Current Fdbk

Speed Fdbk

AC Drive Basics AC Technology

Current Source Inverter

Variable Voltage Inverter

PWM Inverters� V/Hz Inverters� High Performance Vector Drive – Preferred over CSI & VVI

AC Drive BasicsCURRENT SOURCE INVERTER

Variable DC Bus

ControlledRectifier

AC Input

L Inverter

Benefits Regeneration Synchronous transfer

Limitations Limited speed range Poor input power factor is poor

varies with speed Poor multi-motor capability Limited ride through capability May require motor matching Increased Line Harmonics Poor Efficiency Sensitivity to line Transients

Uses Current Regulator

AC Drive BasicsCSI WAVEFORMS

0

0

Voltage(Line to Neutral)

Current(Line)

Unclipped voltage spikes can cause motor insulation breakdown Current wave shape creates cogging at low speeds

AC Drive Basics

Benefits Good speed range Multi-motor Simple regulator

Limitations Poor input power factor varies with speed Limited ride through Increased input harmonics Low speed cogging Poor efficiency (typically 95%) Sensitivity to line transients

VARIABLE VOLTAGE INPUT (VVI)

Variable DC Bus

ControlledRectifier

AC InputL InverterC

+

Uses Voltage Regulator

AC Drive BasicsVVI WAVEFORMS

0

0


Current(Line)

output voltage is frequently called a “six step” waveform cusps in the current waveform cause cogging at lower speeds

AC Drive BasicsPWM INVERTER

Fixed DC Bus

DiodeRectifier

AC InputL InverterC

+

Benefits Constant input P.F. Wide speed range High efficiency (97 - 98%) Ride through options Open circuit protection Common bus regeneration Smooth low speed operation Vector control performance (optional)

Limitations Extra hardware for regeneration to line Motor noise (solved with IGBT’s) Possible Cable length limitations (with IGBT’s)

AC Drive BasicsPower Circuit of PWM Drive

AC Drive BasicsRectifier Section - Conversion From AC to DC Positive Diodes

Negative Diodes

1

4

3

6

5

2

5&6

6&1

1&2

2&3

3&4

4&5

5&6

| One 360° Cycle of Power |

| |

| |

| |

| |

60°

| |

| |

| |

| |

| |

3 phase AC input to the converter

DC output

AC Drive Basics

To Filter Section

Precharging Arrangement - in low Rated Drives

AC Drive Basics

Rectified DC output

OV

Filtered DC output

Filter Section - Smoothing of Rippled DC

Vdc

Vdc = 1.35VL- L

Idc =(1.1 X 746 X Drive HP)/ Vdc

CRectified Input

FilteredOutput

DC Bus (+)

DC Bus(-)

OV

AC Drive BasicsInverter Section – Conversion From DC to AC

Positive DC Bus Line

Negative DC Bus Line

Filtered DCInput

PWM Output

IGBT fired in a sequence to produce a PWM output

AC Drive BasicsPWM WAVEFORMS

0

0


Current(Line)

AC Drive Basics

Triangle Generator

Modulation Generator

Generation of PWM WAVEFORMS

AC Drive BasicsSine Weighted PWM Pulses

AC Drive BasicsSine Weighted PWM

AC Drive Basics

RPM = 120 x Applied FrequencyNumber of Poles per Phase

e.g for a 4 POLE & 50 Hz FREQUENCY 120 X 50 RPM = ----------- = 1500 4

AC Motor

SPEED CONTROL

AC Drive Basics

Speed Speed

0 750 1440Base

1500Sync

60 RPMSlip

N

Rotor Speed = Synchronous Speed - Slip Speed

Slip

AC Drive Basics

T = K x x ILine

V

F

2

In an AC motor, torque varies by:

Where : V/F proportional to Motor Flux I is current drawn by the motor

PLAY WITH V/F RATIO TO GET HIGHER STARTING TORQUE

TORQUE Control

AC Drive BasicsWhy Voltage varies as frequency is changed

1). V/F proportional ФRated (Motor Rated Flux) If Ф > ФRated (What Happens?) If Ф < ФRated (What Happens?)

2). Impedance/Reactance Issue XL is dominant above 3-5

hertz

LZ XR Ss

22

Since I =V/Z; If we increase or decrease the applied frequency we must also increase or decrease the applied voltage accordingly.

fL 2XL

3). To keep the torque Constant as T α V/F Ratio

AC Drive Basics

0

% Currentand

% Torque

Speed (RPM)

Current

200

400

600

500 9001725

1800RPM

Torque

1750

100

Rated Torqueat rated FLA.

Synchronousspeed

Break down torque(peak Torque)

Basespeed

Motor Operating Characteristics

Starting torque(Break over Torque)

Starting Current

No LoadPull UP torque(DIP Torque)

AC Drive Basics

400

300

200

100

00 20 40 60 80 100

Perc

ent T

orqu

e

Percent Synchronous Speed

Breakdown Torque

Operating Range of Variable Frequency Drives

Torque & Speed Curve without Drive

AC Drive Basics

% Currentand

% Torque Current Rated Torqueat rated FLA.

Break down torque(peak Torque)

0

Speed (RPM)

200

500 900

17251800RPM

Torque

100

75RPM Slip75RPM Slip

Torque / Speed with drive applied

AC Drive Basics0 to Twice Base Speed Operation

Torque

Speed (Multiple of Base) Base

Peak

Rated

1.25 1.5 1.75 2

1 N2

.64

.44.33 .25

CT range CHP

Tpeak =

AC Drive Basics

Motor or Torque Control Technologies

AC Drive BasicsMotor Control Technologies

Conveyor MixerExtruder

Volts / Hertz SensorlessVector

FieldOriented

Speed Regulator Speed Regulator Torque RegulatorSpeed Regulator

Current LimitAdvanced

Current Limit

High BandwidthCurrent Regulator

Converting

FluxVector

Speed Regulator Torque Regulator

Current Regulatorbased on

Estimated Values

Converting

Parameter Selectable – (Application Based)

AC Drive Basics

MOTOR

INVERTER

Voltage Feedback

CURRENTLIMIT Frequency Ref

Electrical Frequency

+ VOLTAGECONTROL

V RefV/Hz Gate SignalsElec. Freq

Slip Frequency

+

SLIPESTIMATOR

V/Hz Control

Current Feedback

Speed RefCURRENT

LIMIT

Current Limit monitorsmotor current and altersfrequency command

Slip Compensation alters frequencyreference during load changes

takes a speed reference and varies Voltage and FrequencyVolts/Hertz Control

The drive monitors total current - no current resolver, Cannot distinguish between Id from Iq (Torque Capability limited)

AC Drive BasicsVolts/Hertz Control

Notice that the ability of the drive to maintain high torque output at low speeds drops off significantly below 3 Hz

AC Drive BasicsVolts/Hertz Control

Can not keep the shaft speed at desired level when subjected to shock loads.

However Drives with slip compensation feature correct for extra load but the dynamics are somewhat limited.

Shock Load

AC Drive BasicsVector Definition ?

To know the direction as well as magnitude of a certain quantity

Vector Drive DefinitionThe ability to independently identify and control the flux and

torque producing components of current in a motor for the purpose of accurate torque and power control.

ITotal = √ (IReal) 2 + (IReactive) 2

AC Drive Basics

Ia = Torque Producing Current (Armature Current)If = Flux Producing Current (Field Current)

DC

IaIa If

Z Z

DC

Ia

If

Load 1

Load 2

a*sin (d)

DC Motor Model

T = K X Ф X Ia X Sin (d)d = 900

AC Drive Basics

Iq = Torque Producing CurrentId = Flux Producing CurrentIs = Total Stator Current

ACIs

IdIq

Z

Z Z

AC

Id

Iq

Load 1

Load 2

Is

Is

K Id * Iq * sin(d)

T = K X Ф X Ia X Sin (d)d = Varies

AC Motor Model

AC Drive Basics



FieldOriented

Speed Regulator Speed Regulator Torque RegulatorSpeed Regulator


Current Limit


Converting

FluxVector



Estimated Values

Converting

AC Drive Basics

Voltage Feedback

MOTOR

INVERTER

VOLTAGECONTROL

V RefV/Hz Gate SignalsElec. Freq

Slip Frequency

+

SLIPESTIMATOR

Speed RefCURRENT

LIMIT+ Frequency Ref

V/Hz Control

CURRENTRESOLVER Current FeedbackTorque I Est.

Current Feedback - Total

FLUXVECTOR

CONTROLV Vector

Torque I E

st.

Torque I Est.

Sensorless Vector Control

A current resolver that separates flux producing current from torque producing currentProduces Tmax /Amps of motor Current keeping Flux Current Constant

AC Drive BasicsSensorless Vector Control

High Starting (Maximum) Torque about 250%

AC Drive BasicsSensorless Vector Control

Shock Load

Better Dynamic Response to shock loads

AC Drive Basics



FieldOriented

Speed Regulator Speed Regulator

Torque Regulator

Speed Regulator


Current Limit


Converting

FluxVector



Estimated Values

Converting

AC Drive Basics

MOTOR

INVERTER

Voltage Feedback

PG

CURRENTREG.

SPEEDREG.

Torque Current ReferenceSpeed Ref

Speed Feedback

Electrical Frequency

VOLTAGECONTROL

VOLTAGEVECTOR

Gate Signals

Auto TuneParameters

V/Hz Control

CURRENTRESOLVER

Flux I EstimateCurrent Feedback

Torque I Estimate

V Mag

V Angle

Flux Vector Control w/ Feedback

Uses Speed & Current Regulator ,Has a Current Resolver that separates Torque and Flux Currents Auto - tuning is a must

AC Drive BasicsFlux Vector Control w/ Feedback

2

1

Torq

ue

Speed (Hz)1 2 5 10 20 30 40 50 60

Flux Vector Control – Torque Vs Speed

Much better response at low speeds – 2Hz Torque is greater than 150%

AC Drive BasicsFlux Vector Control w/ Feedback

Shock Loads

Shock load dynamic Response much faster

Encoder FOCLoad Removed

Sensorless FOC Load Removed

FOC,FV & SVLoad applied

V/Hz Load

Applied

0.9

0.875

0.85

0.8250 1 2 3 4 5

Time (seconds)

Per U

nit Q

uant

ities

AC Drive Basics

AC Drive BasicsFORCE-FIELD ORIENTED CONTROL

Excellent Technology to produce as high as 400% Maximum torqueProduces 100% torque at zero speed – Key for Hoist Application

AC Drive BasicsFORCE-FIELD ORIENTED CONTROL

FORCE-FIELD ORIENTED CONTROL – Torque Vs Speed

Excellent response at low speeds – At 1Hz Torque is greater than 250%

AC Drive BasicsFORCE - FIELD ORIENTED CONTROL

Shock load dynamic Response is Excellent

Encoder FOCLoad Removed

Sensorless FOC Load Removed

FOC,FV & SVLoad applied

V/Hz Load

Applied

0.9

0.875

0.85

0.8250 1 2 3 4 5

Time (seconds)

Per U

nit Q

uant

ities

AC Drive BasicsVector Vs Field Oriented Control

Vector Control� Acknowledges that motor current is the vector sum of the torque and

flux currents and uses this information to provide better control of motor speed/torque.

Field Oriented Control� The ability to independently control the flux and torque in a motor for the

purpose of accurate torque and power control.

AC Drive Basics

Benefits from Drives What Benefits ?

AC Drive Basics

Saves Energy costsImproves Process operation by ‘Smooth’ speed control

Improves INPUT Power Factor

Increase Efficiency and Life of mechanical equipment (due to

‘soft starting’)

Lower chances of System disruptions (by lowering current

inrush from 600% to 100-150%)

Benefits of VFD

AC Drive Basics

275

15075

0

0120

240

360

480

600

%Torque

%Current

150%-260% 180%

115%

150%

600%

480%

600%

ACDrive

Full Voltage Starter

Reduced Voltage Starter

Solid State* (SMC)

ABC

C

B

A

* maximum shown,adjustable via digital switches

180%

Flexibility in Starting Current

Lower Investment in DG setsNo Penalty From Electricity Board

Benefits of VFD

AC Drive BasicsBenefits of VFD

ACCELERATION RANGE

0 15 3060 300Seconds

Full Voltage

AC Drive (Adjustable)

(Load Dependent)

(Not Adjustable)

Reduced Voltage

Solid State

600

Smooth Start and perfect Control

Acceleration Time =

Where:WK2 = Moment of inertia (lb-ft 2)

h N = Change in motor RPM T = Torque required308 = Constant

WK2 x hN 308 x T

AC Drive Basics

STOPPING CHOICES

CoastTime

Speed

SoftRamp Stop

Dynamic Braking

DC Injection

Coast Soft Ramp D.B. DC Inj.AC Drive X X X X XSolid StateX XR.V. XF.V. X

Benefits of VFD

AC Drive Basics

Complete Protection for motorAgainst Over voltageOverloadMotor StallingI2t Protection to Motor

& so on ……….Just Name….

Protections ??

Benefits of VFD

AC Drive Basics

Drives Save Energy ?

AC Drive Basics

Phase A

Phase B

Phase C

PWM VFDPWM VFDAC Input AC Input

PowerPowerAC Output AC Output

PowerPower

• IInput Current is less than Output since Source Voltage is Constantnput Current is less than Output since Source Voltage is Constant

• LLower demand on distribution systemower demand on distribution system

• PPower Consumption is proportional to motor speedower Consumption is proportional to motor speed

Real & Reactive Real & Reactive motor currentmotor current

Real Current OnlyReal Current Only

Energy Saving Concepts

AC Drive Basics

Auto-Economizer - Extra Saving

“Idle Mode” Energy Saver

Reduced Load

Automatically fold back Voltage to reduce motor flux


A key in Press Applications - 3-5% Saving

AC Drive Basics

Energy Savings

High Efficiency (>97% )Improves Power Factor to 0.98Payback within 12 to 24 months for reduced energy consumption

An investment which pays back immediately !


AC Drive BasicsTypes of Loads & Energy Savings

Constant Torque (CT)

Variable Torque (VT)

Constant Power (CHP)

AC Drive Basics

HP PRESSURE * FLOW

PRESSURE

SPEEDFLOW

HP SPEED3

SPEED2

Variable Torque

AFFINITY LAW

Power α (Speed)3

Torque α (Speed)2

AC Drive BasicsVariable Torque

P2 = P1 X (N2 / N1)3

P2 = 100HP X (1200 / 1440)3

P2 = 58HPPower Saved = P1 – P2 = 100-58 = 42HP

20 % REDUCTION IN SPEED REDUCES 45 % ENERGY CONSUMPTION

Multiply this quantity (42HP) by Time of operation and Cost/HP and get the energy saving on a variable torque applications Instantly.

AC Drive Basics

To reduce the flow from 100% to 60% , input power requirements are reduced from

100 % to 62 %

Variable Inlet Vane ID Fan application

Saves 38%

Variable Torque

AC Drive Basics

To reduce the flow from 100% to 60% , input power requirements are reduced only from

100 % to 86 %

Outlet Damper

Saves 14%

Variable Torque

ID Fan application

AC Drive Basics

Reduction of flow from 100% to 60% , results into Input power requirements reduction from

100% to 22%

The fan curve is changed by changing the motor speed

Variable Speed DriveEnergySaved

Saves 78% of Energy

ID Fan application

Variable Torque

AC Drive Basics

20 % SPEED REDUCTION SAVES 20 % ENERGY

Power α (Speed)Torque is Constant

P = 2 X Π X N X T

Constant Torque

AC Drive Basics

20 % SPEED REDUCTION SAVES 20 % ENERGY

Constant Torque

P2 = P1 X (N2 / N1)P2 = 100HP X (1200 / 1440)P2 = 84HPPower Saved = P1 – P2 = 100-84 = 16HP

Multiply this quantity (16HP) by Time of operation and Cost/HPand get the energy saving on a Constant torque applications Instantly.

AC Drive Basics

Compressors Application Operates at Lower Avg. Pressure

Proportional Savings No Unloading / Loading Cycles Less Leakages

Constant Lower Pressure Process Feedback

Better Motor EfficiencyHigher Power Factor

Controlled Accel / Decel TimeLower Starting Torque Lower Starting Current

Constant Torque

AC Drive Basics

Time

Reqd. Pr.

Pressure

Ksc

{

Savings Due to Pressure Reduction

6.1 6.0

With VFD6.5

Constant TorqueCompressors Application

AC Drive BasicsConstant Power

Power Remains Constant while Torque falls down as speed is exceeded base valueNo Energy SavingAttention needed for operation as greater speed can damage motor bearings and drive may not be able to generate required torque at high speed - may lead to motor cogging condition

AC Drive BasicsBest Features in our Drives

Ambient Temperature of 50 Degree C. Flexible performance for V/F, SVC or FVC Technology

with embedded ForceTM Feature 400% maximum torque can be achieved in closed loop As per IEEE 519 -1992 Built in DC Chokes to abate input Harmonics All Power Devices of 1600V PIV Built in Software to control the effect of reflected wave Built in EMC Filters Excellent Feature of Zero Stacking Internal family of communications modules Flexible Human Interface Module

AC Drive Basics

7th IGBT – Chopper is internally Provided Excellent Feature of Zero Stacking 6KV input transient protection 150% Overload for 60Seconds /200% for 3 Seconds Complete Output Short Circuit Protection Compact Size

Best Features in our Drives

AC Drive Basics

01 basic drives

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