7154/7156 variable speed drives
DESCRIPTION
7154/7156 Variable Speed Drives. Paul Weingartner 569-1776. Overview. Variable Frequency drives (VFD) Application of VFDs Power quality issues Human Machine Interface (HMI). Standards organizations. NEMA IEEE IEC. NEMA. Enclosures Motor characteristic curves. - PowerPoint PPT PresentationTRANSCRIPT
7154/7156 Variable Speed Drives7154/7156 Variable Speed Drives
Paul WeingartnerPaul Weingartner
569-1776569-1776
OverviewOverview
Variable Frequency drives (VFD)Variable Frequency drives (VFD)
Application of VFDsApplication of VFDs
Power quality issuesPower quality issues
Human Machine Interface (HMI)Human Machine Interface (HMI)
Standards organizationsStandards organizations
NEMANEMA
IEEEIEEE
IECIEC
NEMANEMA
EnclosuresEnclosures
Motor characteristic curvesMotor characteristic curves
History of adjustable speed History of adjustable speed systemssystems
Variable pitch pulleyVariable pitch pulley
Motor-Generator (MG) setMotor-Generator (MG) set
Eddy current clutchEddy current clutch
Solid state drivesSolid state drives
ProblemsProblems
ExpensiveExpensive
Electrical (utility) issuesElectrical (utility) issues
Motor wear/tearMotor wear/tear
Solid State drivesSolid State drives
DC drivesDC drives
AC soft startAC soft start
AC Variable frequency drivesAC Variable frequency drives
AC vector drivesAC vector drives
DC drivesDC drives
High torqueHigh torque
Large speed ratiosLarge speed ratios
Regenerative brakingRegenerative braking
DC motors – high maintenanceDC motors – high maintenance
BasicsBasics
SpeedSpeed
TorqueTorque
HorsepowerHorsepower
EfficiencyEfficiency
Power factorPower factor
Real powerReal power
Apparent powerApparent power
Leading power factorLeading power factor
Inductive reactanceInductive reactance
Capacitive reactanceCapacitive reactance
Electric utilitiesElectric utilities
Commerical customers are defined as Commerical customers are defined as users above 15KVAusers above 15KVA
Electric chargeElectric charge
Demand chargeDemand charge
Power factor penaltiesPower factor penalties
BrakingBraking
None – let load coast to stopNone – let load coast to stop
Dynamic breaking – resistive load, uses Dynamic breaking – resistive load, uses generator effectgenerator effect
Plugging – reverse polarity across motorPlugging – reverse polarity across motor
DC injection – DC voltage is applied across two DC injection – DC voltage is applied across two phases of an AC induction motor. Current must phases of an AC induction motor. Current must be limited and timing is critical for proper usebe limited and timing is critical for proper use
RegenerativeRegenerative
Mechanical brakeMechanical brake
GoalsGoals
Ability to vary speedAbility to vary speed
Limit power factor issuesLimit power factor issues
Sensitive to electric demand issuesSensitive to electric demand issues
Often need “soft start”Often need “soft start”
Cost savingsCost savings
Ways to start a motorWays to start a motor
Full voltage – Across the line startingFull voltage – Across the line starting
Reduced voltage startingReduced voltage starting
Soft start – limit current and rate of startupSoft start – limit current and rate of startup
VFD – great latitude over motor controlVFD – great latitude over motor control
Relative cost difference for 1 HP Relative cost difference for 1 HP motormotor
Full voltage - $120Full voltage - $120
Reduced V - $200Reduced V - $200
Soft state - $250Soft state - $250
VFD - $400VFD - $400
MotorsMotors
3 phase squirrel cage induction motor3 phase squirrel cage induction motor
Principle of operationPrinciple of operation
Synchronous speedSynchronous speed
SlipSlip
Starting characteristicsStarting characteristics
NEMA classificationsNEMA classifications
Motor Insulation classMotor Insulation class
Motor VFD issuesMotor VFD issues
Volts/Hertz ratioVolts/Hertz ratio
Constant volts rangeConstant volts range
VFD principle of operationVFD principle of operation
3 phase rectifier3 phase rectifier
DC busDC bus
3 phase inverter3 phase inverter
VFDs – 1VFDs – 1stst Generation Generation
VVI – Variable Voltage InvertersVVI – Variable Voltage Inverters 6 step drive6 step drive Uses SCRs on rectifier front endUses SCRs on rectifier front end Variable voltage DC busVariable voltage DC bus
Problems with VVI drivesProblems with VVI drives
Motor signal – not very sinusoidal, causes Motor signal – not very sinusoidal, causes problemsproblemsSensitive to source voltage flucuations – Sensitive to source voltage flucuations – 5-10% change will fault the drive5-10% change will fault the driveAt low speed the drive will “cog” creating At low speed the drive will “cog” creating stresses on shafts, etc – freq should be stresses on shafts, etc – freq should be above 15 Hzabove 15 HzDrive will reflect harmonics back to the lineDrive will reflect harmonics back to the lineShort power loss is badShort power loss is bad
CSI – Current Source InverterCSI – Current Source Inverter
Similar to VVI, but adds a line reactor on Similar to VVI, but adds a line reactor on the DC busthe DC bus
Supports regenerative braking without Supports regenerative braking without needing extra hardwareneeding extra hardware
Creates harmonicsCreates harmonics
PWMPWM
Operating frequency – carrier frequencyOperating frequency – carrier frequency Increasing the carrier frequency decreases Increasing the carrier frequency decreases
the efficiency of the drive electronicsthe efficiency of the drive electronics
Duty cycleDuty cyclet-ont-ont-offt-offTransistor exampleTransistor example Linear operation vs. PWMLinear operation vs. PWM Power dissipationPower dissipation
PWM drivesPWM drives
Uses diodes for the rectifer, creating a Uses diodes for the rectifer, creating a Constant voltage DC busConstant voltage DC bus
Constant power factor – due to diode front Constant power factor – due to diode front endend
Full operating torque at near zero speedFull operating torque at near zero speed
No coggingNo cogging
Can ride thru a power loss from 2 Hz to 20 Can ride thru a power loss from 2 Hz to 20 secondsseconds
VFD drivesVFD drives
ScalarScalar
VectorVector
3 3 phase phase motormotor
NEMA NEMA Motor Motor
CurvesCurves
1336 picture1336 picture
1336 – Description of L7E option1336 – Description of L7E option
1336 Drive literature link1336 Drive literature link
http://www.ab.com/drives/1336PlusII/literathttp://www.ab.com/drives/1336PlusII/literature/index.htmlure/index.html
PWM PWM inverterinverter
Motor selection criteriaMotor selection criteria
Synchronous speedSynchronous speed
AC motors have a sync design speed that AC motors have a sync design speed that is a function of the number of poles and is a function of the number of poles and the line frequencythe line frequency
At sync speed ZERO torque is generatedAt sync speed ZERO torque is generated
Therefore, motors cannot run at sync Therefore, motors cannot run at sync speedspeed
Motor slipMotor slip
Since motors cannot run at sync speed, Since motors cannot run at sync speed, the will run at slightly less than this speed.the will run at slightly less than this speed.
““Slip” is the term used to describe the Slip” is the term used to describe the difference between the sync speed and difference between the sync speed and the maximum rated speed at full loadthe maximum rated speed at full load
Motor slip calcMotor slip calc
This formula includes a characteristic called slip. In a This formula includes a characteristic called slip. In a motor, slip is the difference between the rotating motor, slip is the difference between the rotating magnetic field in the stator and the actual rotor speed. magnetic field in the stator and the actual rotor speed. When a magnetic field passes through the rotor's When a magnetic field passes through the rotor's conductors, the rotor takes on magnetic fields of its own. conductors, the rotor takes on magnetic fields of its own. These induced rotor magnetic fields will try to catch up to These induced rotor magnetic fields will try to catch up to the rotating fields of the stator. However, there is always the rotating fields of the stator. However, there is always a slight speed lag, or slip. For a NEMA-B motor, slip is 3-a slight speed lag, or slip. For a NEMA-B motor, slip is 3-5% of its base speed, which is 1,800 rpm at full load. For 5% of its base speed, which is 1,800 rpm at full load. For example, example,
Volts/HertzVolts/Hertz
Drive frequencyDrive frequency
The speed at which IGBTs are switched on and The speed at which IGBTs are switched on and off is called the carrier frequency or switch off is called the carrier frequency or switch frequency. The higher the switch frequency, the frequency. The higher the switch frequency, the more resolution each PWM pulse contains. more resolution each PWM pulse contains. Typical switch frequencies are 3,000 to 4,000 Typical switch frequencies are 3,000 to 4,000 times per second (3-4 kHz). As you can imagine, times per second (3-4 kHz). As you can imagine, the higher the switch frequency, the smoother the higher the switch frequency, the smoother (higher resolution) the output waveform. (higher resolution) the output waveform. However, there is a disadvantage: Higher switch However, there is a disadvantage: Higher switch frequencies cause decreased drive efficiency. frequencies cause decreased drive efficiency. The faster the switching rate, the faster the The faster the switching rate, the faster the IGBTs turn on and off. This causes increased IGBTs turn on and off. This causes increased heat in the IGBTs. heat in the IGBTs.
High motor voltagesHigh motor voltages
http://www.mtecorp.com/solving.htmlhttp://www.mtecorp.com/solving.htmlHigh peak voltagesHigh peak voltagesFast rise timesFast rise timesStandard Motor Capabilities established by the National Standard Motor Capabilities established by the National Electrical Manufacturers Association (NEMA)and Electrical Manufacturers Association (NEMA)and expressed in the MG- I standard (part 30), indicate that expressed in the MG- I standard (part 30), indicate that standard NEMA type B motors can withstand standard NEMA type B motors can withstand 1000 volts 1000 volts peakpeak at a minimum rise time of 2 u-sec (microseconds). at a minimum rise time of 2 u-sec (microseconds). Therefore to protect standard NEMA Design B motors, Therefore to protect standard NEMA Design B motors, one should limit peak voltage to one should limit peak voltage to 1KV1KV and reduce the and reduce the voltage rise to less than 500 volts per micro-second. voltage rise to less than 500 volts per micro-second.
Constant torque loadsConstant torque loads
Conveyor systemsConveyor systems
Constant horsepower loadsConstant horsepower loads
grinders, winders, and lathes grinders, winders, and lathes
Variable torque loadsVariable torque loads
fans and pumps fans and pumps
Motor ventilationMotor ventilation
TENVTENV
TEFCTEFC
ODPODP
High Altitude considerationsHigh Altitude considerations
Motor soft startMotor soft start
Limit inrush currentLimit inrush current
Linear rampLinear ramp
S-curveS-curve
Skip freqSkip freq
Flux vector drivesFlux vector drives
http://www.mikrokontrol.co.yu/sysdrive/Whhttp://www.mikrokontrol.co.yu/sysdrive/WhatInv.htm#FVatInv.htm#FV