AC DRIVE BASICS

MOTOR OUTPUT

LINE INPUT

All AC Drives convert fixed voltage and frequency into variable voltage and frequency, to run 3-phase induction motors.

Types of AC DrivesIn todays marketplace, there are 3 basic AC Drive categories: Open loop Volts / Hz DrivesV/Hz

Open loop Sensorless Vector Drives

SENSORLESS

VECTOR

Closed loop Flux Vector Drives All are Pulse-Width-Modulated (PWM) Some manufacturers offer 2-in-1 & 3-in-1 Drives, combining these attributes.

FLUX VECTOR

Open loop Volts / Hz Drives

V o l 230 t s460 0

Motor Nameplate V/Hz

t os Bo ue orq T

30 900

60 1800(Base)

HzRPM**( 4-pole motor)

Motor voltage is varied linearly with frequency No compensation for motor & load dynamics Poor shock load response characteristics

Sensorless & Flux Vector Drives

V o l 230 t s460 0 30 900 60 1800(Base)

Motor Nameplate V/Hz

HzRPM**( 4-pole motor)

Motor voltage is varied linearly with frequency, with dynamic self-adjustments V/Hz compensation for motor & load dynamics Excellent shock load response characteristics & high starting torque

AC Motor Torque & HP vs. Speed

T & HP50

%

100

Torque

HP

0

30 900

60 1800

Hz RPM

Motor Torque is constant to base speed HP varies proportionally to speed

Pulse-Width-Modulated Inverter Basic Power CircuitAC to DC Rectifier DC Filter DC to AC Inverter AC Output IGBTs

AC Input

DC Bus Caps

M

All PWM inverters (V/Hz, Vector & Sensorless Vector) share similar power circuit topologies. AC is converted to DC, filtered, and inverted to variable frequency, variable voltage AC.

PWM Power Circuit: AC to DC Converter SectionAC to DC Rectifier DC Filter

AC Input Input Reactor (option)

DC Bus Caps

+ -

The AC input is rectified and filtered into fixed-voltage DC Certain manufacturers units contain an integral DC reactor (choke)as part of the DC filter. Adding an external AC input reactor will yield similar benefits. Both reduce harmonics, smooth and lower peak current.

DC Reactor

Power Switches The IGBT: (Insulated Gate Bipolar Transistor)An IGBT is a hybrid between a MOSFET and a Bi-polar Darlington Transistor.COLLECTOR

GATE

=EMITTER

SWITCH

An IGBT can switch from OFF to ON in less than a microsecond. Amplified logic signals drive the high-impedance GATE. Application Issues: A 1 microsecond state-change will generate a 1 MHz RF pulse. Dv/dt (rapid voltage changes) can stress motor insulation systems.

PWM Power Circuit: DC to AC Inverter SectionDC Filter DC to AC Inverter Vu-v AC Output + IGBTsU V W

MImotor

IGBT Firing SignalsAn IGBT (Insulated Gate Bipolar Transistor) is a high-speed power semiconductor switch. IGBTs are pulse-width modulated with a specific firing pattern, chopping the DC voltage into 3phase AC voltage of the proper frequency and voltage. The resulting motor current is near-sinusoidal, due to motor inductance.

IGBT Switching IssuesCONDITIONController-to-motor lead length > 125 Reflected (standing) wave phenomena Carrier frequency in 2 to10Khz range

RESULT

SOLUTION

Nuisance trips from Output reactor installed capacitive coupling to near controller ground Nuisance trips; Motor insulation damage from voltage doubling Motor acoustic noise Output reactor; Improved motor insulation Higher carrier or quiet algorithm Improved motor insulation RFI/EMI input filter; shielded motor cable; separate ground conductor

High dV/dT from fast Motor insulation damage from voltage doubling switching R.F. & Electromagnetic interference Interference with other equipment; telecommunications

Basic V/HZ Control Circuit: Input, Feedback and Control Signals

VDC Bus current & voltage feedback Motor current & voltage feedback

IGBT Firing Signals

f

Operator InterfaceAC MOTOR DRIVE 0.75 KW HEALTH 200 V S E E Q v 1.3 LO CA REF L PROG L R JOG RUN F W RE D V STOP RESET RESET

Speed reference

M

PWM microprocessor controller

Flux Vector Control Elements Input, Feedback and Control Signals

Encoder Feedback Motor current & voltage feedback

DC Bus voltage feedback

Manmachine InterfaceAC MOTOR DRIVE 0.75 KW HEALTH 200 V S E E Q v 1.3 LO CA REF L PROG L R JOG RUN F W RE D V STOP RESET RESET

IGBT Gating Signals

Speed and / or Torque reference

M

PWM microprocessor controller with Vector algorithm

AC VECTOR CONTROL LOOPS AC Vector DriveSpeed LoopSpeed Error Speed Reference

Torque LoopTorque RegulatorFreq. & Voltage Reference

Encoder

Torque Ref.

Speed Regulator

PWM Firing

Torque Reference Actual Torque

Torque Calculator

Frequency Feedback

Speed Feedback

Typical AC Induction Motor Speed / Torque CurveAcross-the-line operation @ 60 Hz, NEMA B motor225Starting Torque Breakdown point: Maximum torque motor can produce before locking rotor

%T

175 150

Pull-Up Torque

Full load operating point (100% current & torque) 1750 RPM (nameplate)

LO AD

100Synchronous no-load speed 1800 RPM

Speed

(50 rpm)

SLIP

Typical AC Induction Motor Current & Torque CurvesAcross-the-line operation @ 60 Hz, NEMA B motor650

Starting (inrush) current

400

Breakdown current:maximum level when motor locks rotor (stalls)

225

%T %I

175 150 100

Linear range: 40-150% load (operating range in which current isproportional to torque)

Speed

AC Motor Speed / Torque Curve family on Inverter Power225

Motor base speed: 1750 RPMPeak Inverter Torque (150 -200%)

%T

175 150 100

100% load torque operating line

Slip (50 rpm)

Speed

Slip (50 rpm)

At any applied Frequency, an induction motor will slip a fixed RPM at rated load.

AC MOTOR FORMULASYNCHRONOUS SPEEDSYNC RPM = 120 x Frequency # of Poles

VOLTS / HERTZV/Hz = Motor Line Volts Motor Frequency

Example: 4-pole motor SYNC RPM = 120 x 60 / 4poles = 1800 RPM

Example: 460 V, 60 Hz motor V/Hz = 460/60 = 7.66 V/Hz

MOTOR SLIP%SLIP = SYNC RPM - FULL LOAD RPM X 100 SYNC RPM

VOLTS FREQUENCY V/Hz 460 345 230 115 7.66 60 45 30 15 1 7.66 7.66 7.66 7.66 7.66

Example: 1750 RPM motor % Slip = (1800 - 1750) / 1800 x 100 = 3% Slip

AC MOTOR SIZEFrame size is directly related to base RPM, for a given HorsepowerExample: 15 HP motors of different base speeds

Base RPM Frame Size Torque Amps

3600 (2-pole) 215 22.5 lb-ft 18.5

1800 (4-pole) 254 45 lb-ft 18.7

1200 (6-pole) 284 67.5 lb-ft 19.3

How Slip Compensation improves speed regulationExample: Motor under load at 30 Hz BEFORE30 Hz curveFull load 30 Hz operating point (100% current & torque) 850 RPM Sync. or no-load 30 Hz speed 900 RPM

AFTER

% 150 T

175

% 150 T

175

New 31.7 Hz curve900 RPM

100

100950 RPM

Speed

Slip (50 rpm)

Speed

Slip (50 rpm)

A motor will lose 50 rpm under full load with 30 Hz applied frequency, slipping from 900 to 850 RPM.

By sensing current and other variables, SLIP COMP will apply 31.7 Hz to the motor, restoring the speed to 900 RPM.

Induction Motor Advantages Low cost (compared with DC) Wide availability Low maintenance - no brushes or commutator Rugged design - can be used in harsh environments Low inertia rotor designs High electrical efficiency Wide speed ranges No separately-powered field windings Good open-loop performance

Elements of an Induction Motor: The RotorNo direct electrical connections are made to the rotor. All forces are magnetically induced by the stator, via the air gap.

Rotor Bar Current Cast aluminum rotor barsCarry induced current (skewed bars shown)

Cast aluminum end ringsElectrically joins rotor bars at both motor ends

Laminations of high-silicon content steelLow-eddy current loss magnetic medium

Elements of an Induction Motor: The StatorStator CoreLamination stack of notched steel plates

Elements of an Induction Motor: Stator Windings (4-pole)Steel Laminations

wye or delta connection types

Slots

Stator Windings

Elements of an Induction Motor: The Stator (4-pole)t Rotating magnetic field

The stator induces magnetic lines of flux across the air gap, into the rotor

Induction Motor SlipSLIP = (s - r ) / s

rotor

stator

Motor slip is proportional to load torque. Stator speed is known by frequency Rotor speed is measured with an encoder (Vector). Rotor speed can be approximated, knowing motor and bus current (Sensorless Vector algorithm)

Rotor Magnetic Field Dynamics: SLIP creates TORQUEMagnetic Flux Linesur r en t

When rotor speed is near stator speed (light load), few stator flux lines are cut . Rotor bar current and slip frequency are low.Magnetic Flux Lines Magnetic Flux Lines

R

ot or B

ar C

Light Load

Heavy Load

As the rotor slips, rotor bar current slip frequency increases, resulting in greater rotor field strength (more torque).

Induction Motor Equivalent CircuitAir Gap

StatorStator Resistance Leakage Reactance

RotorRotor Reactance

R1

XLR XMMagnetizing Reactance

XR RLOAD = R / Slip* 2*(R2 is rotor bar resistance)

V

Although there is no physical connection between rotor and stator, the induced field causes the motor model to behave as if there is.

Motor Current Vectorst rre n uTotal Current is the Vector sum of Magnetizing and Torque-producing current, which are at a right angle to each other.

Magnetizing Current

lC Tota

Torque-Producing Current

StatorStator Resistance Leakage Reactance

Air Gap

RotorRotor Reactance

Torque Current

R1 Total Current

XLRMagnetizing Current

XR XM RLOAD

Motor Current VectorsMagnetizing Current

l ta nt To re r CuTorqueProducing Current

LIGHT LOAD

High % of total current is magnetizing current Magnetizing current is reactive (low p.f.) Measured (total) motor current is not a good indicator of load level.

Magnetizing Current

lC Tota

t rre n u

MEDIUM LOAD & HEAVY LOAD

Most of total current istorque-producing Motors run at high power factor Total motor current is proportional to load level.

Torque-Producing Current

Magnetizing Current

T

nt Curre otal

Torque-Producing Current

Autotuning on Sensorless Vector DrivesFACT: Most motor electrical parameters are difficult to obtain from the manufacturer.ROTOR RESISTANCE ROTOR REACTANCE MAGNETIZING CURRENT STATOR RESISTANCE LEAKAGE REACTANCE

Not typically found on motor nameplate

?????

A Sensorless Vector AUTOTUNE function makes the job easy:1. Enter nameplate motor parameters (base speed, full load amps, voltage, frequency, power factor). 2. Run the AUTOTUNE function. The controller will pulse the motor & determine approximate motor electrical characteristics for SENSORLESS VECTOR Operation. 3. The S-V algorithm can now compute torque- and magnetizing current vectors for more precise motor control.

Facts about Induction MotorsMost AC motors are designed to be used in fixed speed (across-the-line) operation. Rotor bar design, cooling impellers, insulation systems have been designed for 60 Hz sine-wave power. When operated on an inverter, performance and reliability may be compromised: Insulation systems may break down from stresses of IGBT PWM power. Cooling efficiency from shaft-driven fan will limit low speed range Motor harmonics will reduce Service Factor rating. Peak running torque is less than optimum.

Inverter-Duty Induction MotorsMany motor manufacturers have introduced lines of motors they call Inverter Duty or Vector Duty. Features and characteristics vary between manufacturers.

Typical features found on Inverter-Duty Motors High Dielectric strength wire insulation - Thermal-ezeTM (one brand) resists pin-hole punctures caused by IGBT dV/dT switching stresses. Better Cooling - Efficient shaft-fan designs, constant-speed fans, and overframing. Optimized rotor design - Bar profile designs suited for inverter, not linestart duty. Tach-mounting provisions - Easy, non-drive end mounting of encoders for Vector Duty operation. Wider speed ranges - Designs for above-base speed operation and custom V / Hz ratios

AC Induction MotorsCommon Rotor Bar Shapes & EffectsAll have nearly the same performance at full load At locked rotor... Low resistance Low reactance High amps Average torque ACROSS-THE-LINE OPERATIONBest for Inverter

High resistance Average reactance Average amps Average torque High resistance High reactance Low amps Low torque

TORQUE & AMPS

SPEED

AC Induction MotorsEffecting Base Speed through Volts / Hz DesignMotors on inverters dont have to be wound for 60 Hz Optimal power delivery occurs if voltage peaks at base speed Lowest amps occur at peak voltage . Drive price / component cost is related to amps. Example of a 4-pole 550 RPM base speed motor: Stator is wound for 460V @ 20 Hz V/Hz = 460/20 = 233:1 CONSTANT HP460NAMEPLATE BASE SPEED

VOLTS

0

20 600

40 1200

60 1800

Hz RPM (sync.)

Motor Operation above Base SpeedMotor base speed: 1750 RPM (4-pole)22560 Hz curve

% 175 T 150100 501800 Base

120 Hz curve

Peak Inverter Torque (150 -200% current) 100% current operating line 3600 Slip (50 rpm)

Speed

Slip (50 rpm)

Above base speed, continuous torque declines to 50% at 2 x base. Peak Inverter (overload) torque declines even more rapidly. Motor slip increases, for a given torque level.

Motor Operation above Base SpeedConstant Voltage 460Field Weakened Range

Torque

V/Hz

V

Frequency increases above base speed, but voltage levels off. The result is increased speed with weakened torque, or constant HP operation. Above 2:1 , motor torque drops sharply & operation is not recommended.

60

120

Hz100 Constant Torque Constant Horsepower

%T & HP50OW EP RS HO

ER

Reduced Torque

Hz

60

120

AC V/Hz DrivesPros & ConsAdvantages Simple, look-up table control of voltage and frequency Good speed regulation (1-3%) No motor speed feedback needed Multi-motor capability

Limitations Low dynamic performance on sudden load changes Limited starting torque Lacks torque reference capability Overload limited to 150%

Best for General Purpose & Variable Torque Applications: Centrifugal Pumps & Fans Conveyors Mixers & Agitators Other light-duty non-dynamic loads

AC Sensorless Vector DrivesPros & ConsAdvantages High starting torque capability (150% @ 1 Hz) Improved speed regulation (< 1%) No motor speed feedback needed Self-tuning to motor Separate speed and torque reference inputs

Limitations Speed regulation may fall short in certain high performance applications Lacks zero-speed holding capability Multi-motor usage defaults to V/Hz operation Torque control in excess of 2 X base speed may be difficult

Suitable for all General Purpose, Variable Torque and moderate to high performance applications Extruders Winders and unwind stands Process lines

AC Closed-Loop VectorPros & ConsAdvantages Ultra-high torque and speed loop performance & response Excellent speed regulation to .01% Full torque to zero speed Extra-wide speed range control

Limitations Requires encoder feedback Single motor operation only May require premium vector motor for full performance benefits 4-quadrant (regenerative) operation requires additional hardware

Best for High Performance Applications: Converting applications Spindles & Lathes Extruders Other historically DC-applications

Variable Torque Applications: Centrifugal Pumps & Fans100%

Flow, Torque & Horsepower

80%e um

T = K x (RPM)2 HP = K x (RPM)3Load varies with the square of the speed HP varies with the cube of the speed Ideally suited for AC Drivesue rq To

50%

ow Fl

ol rV o

Energy savings benefits: only 50% power required at 80% flowe r we po

rs Ho

AC Drives replace inefficient dampers, guide vanes and valves

Speed

80%

100%

Variable Torque Applications: Centrifugal Fan Energy Savings100%Damper Control Power

Power Consumption

50%

Throttling air volume mechanically with dampers or inlet guide vanes is an inefficient control method.

AC Drive Power

Flow

100%

Variable Torque Applications: Centrifugal Pumps & Fans100%

Load Torque

Since load torque diminishes rapidly below base speed, the Drive always appears lightly loaded.

RPM100%E QU OR U RQ O

Base

Volts

CO

AN ST N

T

T

E

VA

LE AB RI

T

Most drive controllers have a special variable torque V/Hz profile selection that further cuts down on magnetizing current at light loads. Since magnetizing current is purely reactive, motor losses are reduced .

Hz

60

Regenerative Operation of AC MotorsExample: 1750 RPM motor on 60 Hz power Current

LOAD TORQUE & CURRENT

+100%

Motoring1750 -100%

Synchronous Speed 1800 RPM 1850

SPEED

Regenerating

Regen Breakdown

4-Quadrant Operation of AC Motors on Inverter PowerClockwise TORQUE

REVERSE REGENERATING- RPM

FORWARD MOTORING+ RPM

REVERSE MOTORING

FORWARD REGENERATING

CounterClockwise TORQUE

Conditions for Regenerating on an AC MotorAC Motors regenerate when pulled faster than their sync speed at the applied frequency. At 60 Hz, if a motor is pulled faster than 1800 RPM*, the motor will behave as an induction generator.

Regeneration conditions: Overhauling loads Fast deceleration of high inertial loads Stopping on a timed-ramp Cyclic loads or eccentric shaft loadingPULLROTATION

* 1750 RPM base speed at 60 Hz

WEIGHT

AC Drive RegenerationEnergy Flow:ONE - WAY TWO - WAY

AC Input

DC Bus Caps

+ _

IGBTs

M

Current flows back into the DC bus, via the IGBT switching & back diodes. AC Drive front-end rectifier is unidirectional; energy cannot flow back into the AC line. Some returned energy is dissipated in losses in the capacitors, switches, and motor windings (10-15%). Excessive regeneration can cause problems, such as DC Bus Overvoltage.

Dynamic Braking on AC DrivesV DC Feedback

AC Input

DC Bus Caps

+ _

DBR

M

SIGNAL

DB is ACTIVE when: Motor has an overhauling load Fast decel of high-inertial load Stopping in ramp-to-rest mode

DYNAMIC BRAKING CONTROL

DB is NOT ACTIVE when: Decelerating a frictional load Stopping in coast-to-rest mode Drive is disabled or if power is removed

DYNAMIC BRAKING is typically an option for AC DrivesA seventh IGBT, integrally mounted, is modulated when DC Bus voltage is excessive. Resistor Grids (external on ratings 5 HP & above) dissipate the excess energy. DB is duty-cycle limited to a set number of stopping operations

Dynamic Braking on AC Drives: Application ConsiderationsDB is not failsafe: if the drive faults or power is removed, DB will not function. DB only operates when the drive is running: in coast-rest or stand-by, DB is inactive. DB should not be used in EMERGENCY STOPPING: the drive will continue on a timed ramp, producing torque the entire time. DB is suitable for intermittent operation only: other regenerative solutions exist for long-term overhauling loads

Application of AC Drives on a Common DC Bus+ M

M

M

AC Drives on a Common DC Bus: Theory of Operation+AC DRIVE

REGEN

NET POWERNet power usage is minimal, due to the efficient use of returned energy.

AC DRIVEMOTORING

AC DRIVEREGEN

As individual drives regenerate, the returned energy is redistributed to motoring drives via the common DC bus.

AC DRIVEMOTORING

AC Drives on a Common DC Bus: Typical Connection DiagramTHERMAL- MAG BREAKER

INPUT LINE REACTOR

AC DRIVE

AC DRIVE

AC DRIVE

SEMICONDUCTOR FUSES INTERLOCKED DC CONTACTOR

Line Regenerative AC DrivesBI-DIRECTIONAL POWER FLOWV DC Feedback

LINE

M

LOAD

IGBT Firing SignalsCONVERTER

IGBT Firing SignalsINVERTER

PWM microprocessor controller Two sets of 6 - IGBT bridges Gating control for both sets Converter IGBTs modulate on when bus voltage is excessive. More complex regulator design More conducted noise to power line

Cost of drive is 1.8 times standard non-regen AC Drive

Multi-motor ApplicationsMotor amps must total less than controller amp capability Each motor must have its own overload Drive must be in the V/Hz control mode Motor speeds will be within slip-speed range, with respect to each other. Interlock output contactors to drive run logic, when used.

AC DRIVE(V/Hz mode) 30 HP 38 AmpsOVERLOAD CONTACTS

2 hp 2.8 amps

3 hp 3.9 amps

10 hp 12 amps

2 hp 2.8 amps

3 hp 3.9 amps

5 hp 7.2 amps

Total HP = 25 Total Amps = 32.6

Application of Contactor Bypass on AC DrivesProvides back-up, across-the-line operation of motor Single-speed operation on line only (must have mechanical control in place) Motor overloads are mandatory. Contactors are interlocked to prevent inverter back-feed. Popular in HVAC / VT applications. Not recommended on inverter duty only motors (high inrush current).OFF INVERTER BYPASS INVERTER CONTACTOR INVERTER DISCONNECT

MAIN CB

AC DRIVEBYPASS CONTACTOR

MOTOR OVERLOAD

TYPICAL 3-POSITION SELECTOR SWITCH

AC Drives and Power FactorMotor P.F. = .70 (Light Load)

AC INPUT P.F. = .96

REACTIVE FLOW

AC Input

M

AC Drives inherently correct motor Power Factor Reactive current bi-directionally flows between the inductive motor and bus capacitors. Input PF has no relationship to motor PF. Since input current is in-phase with voltage, input displacement PF is always near unity.

Never use power factor correction capacitors with AC Drives!!!

DC DRIVE BASICS

A1 A2 F1 F2

Armature

Field

LINE INPUT

MOTOR OUTPUT

DC Drives convert AC line voltage into variable DC voltage with an SCR phase-controlled bridge rectifier, to power the DC motor ARMATURE. A separate field supply provides the motor with DC FIELD excitation.

Inside the DC Motor(Shunt Field Design)The commutator & brushes keep armature flux in a fixed position relative to the field, which guarantees the torque force is always perpendicular to field magnetization.

F1

NF2

A1

A2

S

Typical DC Motor Armature Current & Torque Curves200NO LOAD

100

MOTORING RPM

%T % IDC

0

-100

REGENERATING

Armature current is directly proportional to torque throughout the loading range.

-200

DC Motor Torque & HP vs. SpeedMotor nameplate: 250 / 1000 RPM

TORQUE & HORSEPOWER

%100

FULL FIELDCONSTANT TORQUE

FIELD WEAKENED RANGE 4:1CONSTANT HORSEPOWER

75HO RS EP OW ER

50

TORQUE @ 100% ARMATURE AMPS2 : 1 FIELD WEAKENING 3 : 1 FIELD WEAKENING 4 : 1 FIELD WEAKENING

25

250 Base Speed

500

750

1000 Max.Speed

SPEED (RPM)

Power SwitchesThe SCR: (Silicon Controlled Rectifier) a.k.a. - ThyristorANODE CATHODE

GATE Extremely robust solid-state switch / 40+ year proven track record Key element in DC Drive power circuit Simple pulse gating turns on current flow Device has self-turn-off when reverse biased Stud-mount, hockey-puck and encapsulated 2-, 4- and 6-pack types available in certain sizes and ratings. +TRIGGER

Application Issues: AC Line Notching on DC DrivesAC Input

Commutation notches are caused by the transfer of current from one SCR to another.

V ph-ph

The notches can cause misfiring on drives common to the same power line.

Solution: Installation of a small (25-50 uH range), 3-phase reactor on each DC controller will prevent cross-talk and other related problems.

Elements of a DC Drive: Non-regenerative typeAC Input

A1

F1

F2Field Control Signals

Tachometer Feedback (closed-loop)

SCR Firing SignalsLine current feedback

A2Motor voltage feedback

AC MOTOR DRIVE 0.75 KW HEALTH 200 V S E E Q v 1.3 LO CA REF L PROG L R JOG RUN F W RE D V STOP RESET RESET

Speed or Torque Reference

Microprocessor controller

M

Operator Interface

Elements of a DC Drive: Regenerative typeAC Input F R F R F R

A1

F1

F

R

F

R

F

RField Control Signals

F2 A2Motor voltage feedback

Tachometer Feedback (closed-loop)

SCR Firing SignalsFWD/MOT Line current feedbackAC MOTOR DRIVE 0.75 KW HEALTH 200 V S E E Q v 1.3 LO CA REF L PROG L R JOG RUN F W RE D V STOP RESET RESET

REGEN/REV

Speed or Torque Reference

Microprocessor controller

M

Operator Interface

Dynamic Braking on DC DrivesM Braking Power A1 F1 M

F2 A2 M

DBR

time

Dynamic Braking Resistors are shunted across the motor armature in a STOP or ESTOP mode. Motor counter-EMF (back voltage from motor, acting as generator) appears across resistor grids. Voltage diminishes as resistors dissipate energy. Braking Power diminishes exponentially with motor slowdown: P = V2/R

Not failsafe: DB will not function if field supply is absent (i.e. - if power is lost)

DC Regenerative Drives vs. DC Dynamic Braking DC regen drives provide constant torque deceleration and stopping. DC dynamic braking power diminishes with speed reduction. Both require full field power / neither will work in power outage. DC regen requires drive to be fully operational (no faults) DB can be used in conjunction with a regen drive, for certain stopping conditions DC regen added benefits include full 4-quadrant torque control. DB may require an additional contactor, if the manufacturer uses an AC input contactor.

DC DRIVE MARKETMARKETPLACE FOR THE DC THYRISTOR DRIVE Most widely used drive in heavy industry Account for 40% of total variable speed drive market (much higher percentage in process industries). Estimate 0 - 5 % growth / annually to 2000 Very established mature product with continuing development.

AC DRIVE MARKETMARKETPLACE FOR THE V/Hz AC PWM DRIVE Accounts for 60% of total variable speed drive market (much lower percentage in process industries) Estimated 5 - 10% growth / annual to 2000 Mature product but due to limited performance used generally only on peripheral rather than process drives.

AC VECTOR DRIVE MARKETMARKETPLACE FOR THE AC FLUX VECTOR DRIVE

Introduced during last eight years Sensorless introduced during last three years Growing use in most process industries (very strong growth in elevators & hoists etc) Only AC drives currently available with similar or equivalent performance to DC

Measuring Bandwidth Response AC Vector DriveTESTSpeed Ref 1.0

Speed LoopSpeed Error

Torque LoopTorque RegulatorFreq. & Voltage Reference

Encoder

Torque Ref.

Speed Regulator

PWM Firing

45 degrees .7071 Speed Feedback

Actual Torque

Torque Calculator

Frequency Feedback

Speed Feedback

A sine-wave signal generator is applied to the reference input Feedback is monitored as reference frequency is increased. When feedback lags reference by 45 degrees, and amplitude is reduced to 71% of the input signal, this is defined as the BANDWIDTH RESPONSE.

Drive Performance ComparisonSpeed Regulation DC open loop DC closed loop AC V/Hz AC Sensorless Vector AC Flux Vector 2-3% .01 - 1% 1 - 5% .1- .5% .01 -.05% Speed Loop Response .5 - 2 Hz 10 - 20 Hz 1 - 2 Hz 15 - 25 Hz 20 - 100 Hz Torque Accuracy 5 - 10% 2 - 5% 10 - 20% 2 - 10% .5 - 1% Torque Response 10 - 20 Hz 20 - 100 Hz 5 - 10 Hz 75 - 200 Hz 200 - 1000 Hz

Performance varies widely, between drive manufacturers Speed regulation is dependent upon speed feedback device used. Open loop regulation is motor-dependent Response rates are rarely published & can be misleading.

Common Drive Formulas for AC & DCTORQUE AND HORSEPOWER Torque x RPM 5252 HP x 5252 RPMFor a 4-pole (1800 RPM) motor:

HP =

Torque (lb-ft) = 3 x HPFor a 6-pole (1200 RPM) motor:

Torque =

Torque (lb-ft) = 4.5 x HPFor a 2-pole (3600 RPM) motor:

Torque (lb-ft) = 1.5 x HP

Accelerating / Decelerating an inertial load:Wk2 x RPM Torque = 308 x tsec tsec = Wk2 x RPM 308 x Torque

*(Wk2 is inertia in lb-ft2)

Common Electrical Formulas for AC & DC DrivesAC line current and armature current (DC Drives)

IDC = IAC / .83AC line voltage and DC bus voltage (AC Drives)

VDC = VL-L x 1.41Horsepower and Kilowatts

HP = KW / .746 KW = HP x .746Three phase Power

KVA =

VL-L x I x 1.7321000

Pout % Efficiency = X 100 Pin

KVA = KW / P.F.

Power losses in AC & DC controllers(5 - 100 HP; excluding motor; full speed & load)

DC: AC:AC to DC SCR / Diode losses = 1%

AC to DC

98% 96%IGBT losses = 1.5%

SCR losses = 1% Fixed losses = 500 -1000W CONTROL & FANS DC to AC

EFFICIENCY

Cap losses = .5%

EFFICIENCY

CONTROL & FANS Fixed losses = 800 -1500W

Power Factor on AC and DC Drives.96 .85

AC

On AC Drives, input displacement power factor remains nearly constant with speed & load. On DC Drives, power factor varies directly with SCR phase-firing angle, peaking near .85 .

POWER FACTOR

DC.30

Since power increases linearly with speed, the effects of low power factor at low speed are negligible.20% 100%

SPEED

DC Drive Advantages over AC Simple Controller Design- only one power conversion stage, no power storage elements. Higher Controller Efficiency- 98%+ electrically efficient Simple, 4-quadrant line regeneration - with 6 reverse SCRs Efficient, inherent Torque control - Field & Armature flux always positioned optimally. Retrofit to existing DC motors - previously power by M-G set or older drive types. Most cost-effective drive package above 100HP High Controller reliability - Low maintenance due to simple power module design

more DC Drive Advantages over AC Lower power line harmonic contribution - less than 50% of AC Smaller line reactors- less costly More compact controller size per equivalent HP More robust power semiconductors - SCRs have better overload and peak voltage characteristics, vs. IGBTs. Low motor acoustical noise: no carrier noise. Fewer motor lead-length issues: no capacitive coupling, dV/dT or standing wave problems. Easier troubleshooting & serviceability

AC Drive Advantages over DC Simple, low-maintenance motor - no brushes or commutator. High dynamic performance - low rotor inertia, compared with DC armature. Motors are inexpensive & readily available Motors suitable for harsh, rugged environments : some explosionproof ratings available. Better open-loop speed regulation - with Sensorless Vector & slip compensation. Higher torque response bandwidth - on Vector-type; not limited by AC line frequency. More cost-effective drive package below 100HP Multi-motor & inherent load sharing on single controller Line-bypass option - permits single-speed motor operation during controller maintenance

more AC Drive Advantages over DC

No separate motor field - no field loss sensing required Wider speed ranges - motors available through 6000 RPM & higher. Contactor-free dynamic braking - linear braking power to zero speed. Retrofit onto existing single-speed AC applications Smaller motor frame sizes than equivalent DC. Longer power-dip ride-through capabilities Near unity power factor regardless of speed and load