TORQUE PRODUCTION WITH AC DRIVES MOTORS Understanding the

TORQUE PRODUCTION WITH AC DRIVES & MOTORS: Understanding the technology Developed by, Rockwell Automation Drives Business Reliance Electric Spring Update CD, May 2001

Presentation Abstract After 25 years of AC Drive acceptance, drive manufacturers offer the industry many types of control methods. We’ll review some motor & drive basics and then discuss the technologies offered in AC Drives along with the selection process. Spring Update CD, May 2001

AC & DC Motor Basics REVIEWING MOTOR FUNDAMENTALS Spring Update CD, May 2001

Motor Basics Motor nameplate HP is achieved at Base RPM: Constant Torque Constant Horsepower HP = Torque * Speed / 5252 Torque Range H or se po w er 100% Nameplate HP is only achieved at base speed, NOT BEFORE! Base Speed Spring Update CD, May 2001 RPM

Motor Basics - AC Motor Construction Motor Frame Assembly Stator Winding Assembly Rotor & Shaft Assembly 3 phase stator winding circuit w/ connections T 1, T 2 & T 3 Spring Update CD, May 2001

Motor Basics - AC Motor Operation 2 Pole Motor RPM is equal to: 120 * Frequency # Motor Poles Note that Frequency is the only variable to affect motor speed Rotating Magnetic Field of a 2 Pole AC Induction Motor Spring Update CD, May 2001

Motor Basics - DC Motor Construction Commutator & Brush Assembly Armature Assembly Field Poles Assemblies NOTE: The Armature & Field Circuits are mechanically fixed at 90° at all times Distinct Armature & Field Circuits are mechanically separated Spring Update CD, May 2001

Motor Basic - DC Motor Operation Simple Model S V V N Motor RPM is equal to: Voltage Arm - ( Voltage Drop ) Both Armature Terminal Voltage & Field Strength affect DC Motor speed Field Flux To create motor torque at the shaft, we increase Armature Current Rotating Magnetic Field of a 2 Pole AC Induction Motor Spring Update CD, May 2001

Motor Basics - AC & DC Summary Key Points of Understanding • AC Induction Motors have one circuit to connect • Connection to T 1, T 2 & T 3 for the stator • DC Motors have 2 separate circuits to connect • Connection to F 1 & F 2 for the Field • Connection to A 1 & A 2 for the Armature • To make AC Motors perform like DC Motors • Treat the AC motor like a 2 circuit machine Mechanical differences must be overcome mathematically Spring Update CD, May 2001

AC Drive Basics PWM AC DRIVE FUNDAMENTALS Spring Update CD, May 2001

Drive Basics - PWM AC Drive Construction Motor AC Line Diode Rectifier DC Bus Filter IGBT Inverter • Diode rectifier converts AC line voltage to fixed voltage DC. • DC voltage is filtered to reduce current ripple from rectification. Spring Update CD, May 2001

AC Drive Basics - PWM AC Waveforms VLL @ Drive 500 Volts / Div. + DC Bus 1 - DC Bus 3 Phase Current 10 Amps / Div. M 2. 00 s Ch 1 1. 18 V PWM waveform is a series of repetitive Voltage pulses Spring Update CD, May 2001

AC Drive Basics - V/Hz Operation At 100% of the motor’s base speed, the V/Hz ratio is determined: HP = 100% of motor nameplate Output Voltage Operation at Base Speed 460 Ratio @ 460 VAC = 7. 67 V/Hz 230 115 0 15 30 60 90 Output Hz Base Frequency Motor speed is controlled by ramping Voltage & Frequency Spring Update CD, May 2001

AC Drive Basics - V/Hz Operation At 50% of the motor’s base speed, the V/Hz ratio is maintained: HP = 50% of motor nameplate Output Voltage Operation at 50% Base Speed 460 Ratio @ 460 VAC = 7. 67 V/Hz 230 115 0 15 30 60 90 Output Hz Frequency Base Frequency At 50% of base speed, Voltage & Frequency decrease by 1/2 Spring Update CD, May 2001

AC Drive Basics - V/Hz Operation At 25% of the motor’s base speed, the V/Hz ratio is maintained: HP = 25% of motor nameplate Output Voltage Operation at 25% Base Speed 460 Ratio @ 460 VAC = 7. 67 V/Hz 230 115 0 15 30 60 90 Output Hz Frequency Base Frequency At 25% base speed, Voltage & Frequency decreases by 3/4’s Spring Update CD, May 2001

AC Drive Basics - V/Hz Operation To increase starting torque, V/Hz Drives use Voltage Boost to over-flux the motor to increase starting torque Output Voltage 460 Ratio @ 460 VAC = 7. 67 V/Hz + 248 % BOOST 138 Voltage Boost 0 15 30 60 90 Output Hz Frequency Base Frequency Offsetting the voltage ratio increases motor starting torque Spring Update CD, May 2001

AC Drive Basics - V/Hz Operation Voltage Boost over prolonged operating periods may result in overheating of the motor’s insulation system and result in damage or premature failure. CAUTION: Motor Insulation Life is decreased by 50% for every 10 C above the insulation’s temperature capacity Unable to perform like DC, the industry looks to Vector Control Spring Update CD, May 2001

AC Drive Basics - Vector Operation If we can de-couple and Regulate Current, the component that creates torque at the motor, we can regulate motor torque, not just motor speed! This is the premise for Vector Control Current Regulation allows Torque Control Spring Update CD, May 2001

AC Drive Basics AC VECTOR DRIVE FUNDAMENTALS Spring Update CD, May 2001

AC Drive Basics - Motor Modeling AC Drive Parameters create a “Motor Model” based on data entered in the drive parameters • Motor Magnetizing Current • Motor Full Load Amps • Motor Voltage • Motor Base Frequency • Motor Base (Slip) RPM • Motor Horsepower Correct Motor Data is the most important factor for success Spring Update CD, May 2001

AC Drive Basics - Motor Modeling AC Drive Parameters: “Magnetizing Current” Magnetizing Current is the current required to excite the motor laminations and copper winding w/o doing work. • Magnetizing Current is: NO LOAD AMP draw less friction and windage • Establishes the motor’s Flux • (FLA - Mag. Amps) = 100% Torque Current L Wrong data will reduce motor torque production Magnetizing Current will range from 35% to 50% of FLA value Spring Update CD, May 2001

AC Drive Basics - Vector Operation Torque is produced, as well as regulated even at “ 0” RPM Magnetizing Current = Motor No Load Amps 100% “a fixed value from “ 0” RPM to Motor Base RPM” Torque Current 90 Magnetizing Current is the equivalent of Field Current Spring Update CD, May 2001

AC Drive Basics - Motor Modeling AC Drive Parameters: “Full Load Amps” The motor FLA value may set the scaling for: • Motor Overload • Drive Overload • Torque Current Available • (FLA * %OL) - Mag. Amps = Max. Available Torque Current L Wrong data affects available torque current and may allow damage to the motor. Since every Vector algorithm is unique, check w/ manufacturer Spring Update CD, May 2001

AC Drive Basics - Motor Modeling AC Drive Parameters: “Voltage & Base Hz” Voltage & Base Hz values will: • Establish the motor V/Hz ratio for the drive output L Wrong data will cause motor heating and possibly reduce motor torque as well as shorten insulation life. Needed to assure proper motor operation w/o over-heating Spring Update CD, May 2001

AC Drive Basics - Motor Modeling AC Drive Parameters: “Base HZ & RPM” Base Hz & RPM values will set the scaling for: • Calculation of motor slip • Identifies expected motor RPM at Frequency • Allows for speed error detection & correction • Establishing the point of field weakening L Wrong data here can cause excessive current draw AC Drives regulate speed based upon motor slip Spring Update CD, May 2001

AC Drive Basics - Motor Modeling AC Drive Parameters: “Horsepower” The Horsepower value may be used to: • Estimate the expected motor impedance • Estimate the expected motor inductance • Calculate the torque loop gains L Wrong data here can cause poor speed and torque regulation Horsepower information gets us “in the Ballpark” Spring Update CD, May 2001

AC Drive Basics - Vector Operation Flux Vector Drives act very much like DC Drives Magnetizing Current is decreased above Motor Base RPM 100% Torque Current 90 Magnetizing Current Field Weakening occurs whenever we exceed Motor Base RPM Spring Update CD, May 2001

AC Drive Basics - Vector Operation Torque at the motor shaft based upon load Torque Current = Motor Load at the Shaft 100% “a variable value” during speed regulated operations Torque Current 10% 90 Magnetizing Current Torque Current increases or decreases dependent upon load Spring Update CD, May 2001

AC Drive Basics - Vector Operation Torque at the motor shaft based upon “Torque Reference” Torque Current = Reference setting 100% “a fixed value” during torque regulated operations Torque Current 10% 90 Magnetizing Current Torque Current can be commanded as a reference value Spring Update CD, May 2001

AC Drive Basics - Vector Operation Torque production suffers if 90° is not maintained 100% Improper tuning, incorrect motor parameters, problems with motor speed feedback or undersized drive applications will result in poor load (torque) regulation. Torque Current Optimized Torque Production Poor Torque Production & Regulation Torque Current ie: Impact Load 90 Magnetizing Current ? Magnetizing Current Motor torque is optimized ONLY when 90 is maintained Spring Update CD, May 2001

AC Drive Basics - Vector Operation Load Type: Forward Speed & Reverse Torque ? How a load becomes applied to the drive system can be critical to system success. A load where there is Forward Velocity & Reverse Torque is the most difficult load to handle. If the Nip Rolls are engaged during web travel, a condition with forward velocity and reverse torque can occur. Use either V/Hz or a closed loop system if inertia or speed is high. Time to find motor rpm & position is limited by inertia & speed Spring Update CD, May 2001

AC Drive Basics - Vector Operation Motor Current is = Vector Sum of Torque & Magnetizing This is where the term VECTOR DRIVE is derived 100% Torque Current Motor Current A² + B² = C² Torque Current Motor Current 90 Magnetizing Current Motor Current is what’s measured with a clamp-on meter Spring Update CD, May 2001

AC Drive Basics - Flux Vector Operation Flux Vector Drives regulate current & torque using rotor speed & position to optimize torque at the motor shaft along w/ current feedback from the motor. Current Feedback L 1 L 2 L 3 Motor E Micro P Encoders provide rotor speed & position information Spring Update CD, May 2001

AC Drive Basics - Rotor Temperature & Torque As motor temperature reaches nominal operating values, torque linearity and accuracy improves in FVC operation HOT Motor % Torque accuracy of 5% or better ! COLD Motor Inch - Lbs Spring Update CD, May 2001

AC Drive Basics - Field Oriented Control uses the same basic technology as Flux Vector Control, but adds Voltage Feedback to optimize / adapt to changes in motor temperature. Voltage Feedback L 1 L 2 L 3 Motor E Micro P The drive continuously adapts to motor temperature change Spring Update CD, May 2001

AC Drive Basics - Summary Key Points of Understanding • Errors in Encoder Feedback affect the Micro-Processor • Speed instability will occur • Encoder Feedback Signals must be NOISE FREE • Select an appropriate encoder for Vector Motor use • Proper grounding is very important • Motor Data programmed in the drive must be accurate Motor information, measured or programmed is key to success Spring Update CD, May 2001

AC Drive Basics - Sensorless Vector Operation There actually 2 types of drives advertised as Sensorless Vector; • Those with a V/Hz Core • Those with a Vector Core All Sensorless Vector Drives are NOT the same! Spring Update CD, May 2001

AC Drive Basics - Sensorless Vector Operation SVC with V/Hz Core Technology • Use sophisticated “Current Limiting” algorithms to improve constant torque & starting torque operation • Typically needs less motor information for setup adding some simplicity • Can operate multiple motors from one drive • ONLY regulates V/Hz output, clamps CURRENT • Can only operate as a Speed Regulator, NOT TORQUE V/Hz Core SVC Drives can operate multiple motors Spring Update CD, May 2001

AC Drive Basics - Sensorless Vector Operation SVC with Vector Core Technology • De-couples Torque & Magnetizing Currents to maintain 90 alignment • Typically needs more motor information for setup adding some complexity • Can operate only one motor per drive due to the information required to regulate current • Regulates SPEED and Regulates TORQUE Vector Core SVC Drives can operate only one motor at a time Spring Update CD, May 2001

AC Drive Basics - Sensorless Vector Operation SVC Drives w/ a Vector Core estimates rotor speed & position Current Sensors L 1 L 2 L 3 Motor Micro P ( FVC + Speed Estimator ) A “Speed Estimator” calculates rotor speed & position Spring Update CD, May 2001

AC Drive Basics - Control Loops There are 3 Basic Control Loops in High Performance Drives: POSITION SPEED 10 rad/sec 100 rad/sec Position Reference is optional in most Vector Controls, internal in some Speed Reference is typical of how we control motor operation TORQUE 1, 000 rad/sec Torque Reference can made directly, bypassing the speed loop as a reference for applications such as Winders & Test Stands Bandwidth ratio between loops ranges from 3: 1 to 10: 1 Spring Update CD, May 2001 MOTOR

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AC Motor Basics - Inverter Duty INVERTER DUTY MOTORS Spring Update CD, May 2001

AC Motor Basics - Inverter Duty Blowers may be added to motors to allow operation at low speed including “ 0” RPM with 100% Torque continuous Some motor frames are sized so that just the surface area is suitable to dissipate motor heat w/o the need of a fan or blower Spring Update CD, May 2001

AC Motor Basics - Inverter Duty Types of AC Motors Match Motor type to meet your needs! T-Frame Construction Motors allow commonality in footprint & shaft height. Definite purpose “laminated frame” designs provide higher power densities & improved torque to inertia performance. Spring Update CD, May 2001

AC Motor Basics - Inverter Duty Rotor Designs Vary by motor type: Rotor design affects torque production! Standard Industrial AC Motor “double squirrel cage” Rotor Design for improved across the line starting torque. Definite purpose “single squirrel cage” rotor design for Variable Frequency Drive use Spring Update CD, May 2001

AC Motor Basics - Equivalent Circuit Diagram of an AC Induction Motor Resistan ce Inductanc e Stator Rotor + AC Input Voltage Inductance Magnetizing Current Working Rotor heating affects torque production! Resistan ce Rotor - Spring Update CD, May 2001

AC Motor Basics - Drive Operating Region NEMA Design ‘B” Motor Breakdown Torque Full Load Torque Rule of Thumb: Approximately 80% of BDT (ft-lbs) is usable for PEAK Torque needs when current is available. Therefore, current headroom from the drive can improve recovery from sudden load changes. Peak Torque capacity is dependent upon the motor BDT % Spring Update CD, May 2001

AC Motor Basics - Drive Operating Region NEMA Design “B” Motors vary in Breakdown Torque capacity Breakdown Torque identifies Peak Torque capabilities Spring Update CD, May 2001

AC Motor Basics - Operating Range Speed / Torque Curve of an AC Drive & Inverter Duty Motor 100 Torque 90 % T O R Q U E 80 Torque 70 60 50 40 Acceptable Region for Continuous Operation 30 20 10 0 0 6 12 18 24 30 36 42 48 54 60 66 72 78 Inverter Duty Motors operate at 1/10 th Base RPM Spring Update CD, May 2001 84 90 HZ

AC Motor Basics - Operating Range Speed / Torque Curve of an AC Drive & Inverter Duty Motor 100 Torque 90 % T O R Q U E 80 Torque 70 60 Torque above base RPM = 50 40 100% % Above Base RPM 30 20 10 0 0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 CHp Operation above Base RPM is typically limited to 150% Spring Update CD, May 2001 HZ

AC Motor Basics - Operating Range Speed / Torque Curve of a Vector Drive & Vector Duty Motor 100 Torque 90 % T O R Q U E 80 Torque 70 60 50 40 Acceptable Region for Continuous Operation 30 20 10 0 0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 HZ Vector Duty Motors operate at “ 0” RPM w/ 100% Torque Cont. Spring Update CD, May 2001

AC Motor Basics - Operating Range Speed / Torque Curve of a Vector Drive & Vector Duty Motor 100 Torque 90 % T O R Q U E 80 Special motor & drive designs can allow operation up to 8 * Base RPM Torque 70 60 50 40 Vector Duty Motors may have CHP Ranges of 2 * Base Speed or more depending on their design 30 20 10 0 0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 102 108 114 120 HZ Some Vector Duty Motors can provide CHp ( 2 * Base RPM ) Spring Update CD, May 2001

AC Drive Performance COMPARING AC DRIVE PERFORMANCE Spring Update CD, May 2001

Control Selection • FVC operation is best since the position and velocity of the rotor is known and restarting is immediate. • V/Hz being a soft speed regulator is very forgiving for restarting into loads with high inertia. • SVC may be more difficult to implement due to limitations by manufacturer. Processor & algorithm dependent. Spring Update CD, May 2001

Control Selection • V/Hz operation inheriently controls multiple motors. • SVC or FVC operation with multiple motors is only possible when motor shafts are mechanically locked together and assumptions are made about “total” motor current values. Spring Update CD, May 2001

Control Selection • V/Hz is typically good for up to 10: 1 Constant Torque. • SVC is typically good for up to 40: 1 Constant Torque. • FVC is typically good for up to 1, 000: 1 which includes continuous operation at Zero Speed. Spring Update CD, May 2001

Control Selection • V/Hz has no quantifiable response time or bandwidth. • Typical SVC specifications may state 100 Radians/second. • Typical FVC specifications may state 1, 000 Radian/second. Spring Update CD, May 2001

Drive Selection Both AC & DC Drives have specific areas of merit to consider Spring Update CD, May 2001

Drive Selection Both AC & DC Drives have specific areas of merit to consider Spring Update CD, May 2001

Drive Selection - Speed Range Digital DC Drives & AC Vector Drives performance similarly Spring Update CD, May 2001

Thank You! Any Questions? Spring Update CD, May 2001