VFD Basics.pptx
- 1. VFD Basics Class Name: LS VFD Basics Version: 1.10 Date: 3/30/2020
- 2. Principles VFD Basics Wiring Connection Diagram ⢠I/O is used for the control and monitoring of the VFDs operation and status. ExamplesâŚ. ⢠Start/Stop ⢠Speed control (analog or digital) ⢠Analog meter (speed monitoring) ⢠Communications ⢠Output contacts for fault, run, speed status, etc. ⢠The I/O terminals typically consist of and interface with 24VDC, 4-20mA, 0-10VDC, and other low voltage signals.
- 3. Principles VFD Basics VFD Sections Inverter Voltage Controlled AC Input Voltage DC Voltage ⢠Variable Frequency ⢠Variable Voltage ⢠Constant V/f Input Output Converter Non-Regulated Rectifier ⢠The main power sections of the VFD are necessary to convert constant frequency and voltage to variable frequency and voltage. ⢠This allows us to control motor speed and torque! Hey, G100! Go faster!
- 4. Principles VFD Basics Principle 1 â Main Components ⢠The VFD changes (rectifies) AC power to DC power and then changes (inverts) it back to AC power. AC AC DC
- 5. Principles VFD Basics Converter Section ⢠The converter section is made up of diodes that convert the AC input voltage to DC voltage. + - Schematic diagram Anode (+) Cathode (-)
- 6. Principles VFD Basics DC Bus Section ⢠The DC bus consists of capacitors used to smooth and store DC voltage. ⢠DC Bus Voltage = Vin*1.414 + + AC to DC Conversion
- 7. Principles VFD Basics DC Bus Section ⢠The DC bus is protected by a soft charge circuit. The circuit utilizes a resistor and contactor to âsoftlyâ charge the DC bus capacitors on power up. + 3 phase input Input Diode DC Bus Capacitors Output Transistors Soft Charge Resistor Soft Charge Contactor Fuse Simplified VFD Circuit Soft Charge Sequence 1. Current flows through the resistor which limits inrush to the capacitors. 2. The undervoltage level is reached and the contactor closes. This bypasses flow through the contactor instead of the resistor.
- 8. Principles VFD Basics DC Bus Section ⢠Some VFDs have a DC bus fuse which is used to protect the power components when then output shorts or fails. + 3 phase input Input Diode DC Bus Capacitors Output Transistors Soft Charge Resistor Soft Charge Contactor Fuse Simplified VFD Circuit
- 9. Principles VFD Basics Inverter Section ⢠The inverter section consists of rapid firing insulated gate bipolar transistors (IGBTs). The IGBTs are utilized as switches to switch the voltage ON and OFF to the connected motor.
- 10. Principles VFD Basics Inverter Section ⢠The rapid firing IGBTs âchopâ up the DC bus voltage to reconstruct a pseudo sine wave. This is called Pulse Width Modulation (PWM) ⢠The rate at which the IGBTs switch is called the carrier frequency.
- 11. Principles VFD Basics Principle 2 - PWM ⢠The output voltage to the motor is adjusted by modulating the width of the output pulses which make up the output voltage waveform via PWM. ⢠The higher the ratio of ON time as compared to the switching time results in a higher voltage. Tc Ton Ton Tc = 50% Ton: Length of time the transistor is on Tc: Switching time
- 12. Principles VFD Basics Principle 2 - PWM ⢠More ON time means higher output voltage. Tc Ton Tc Ton Ton Tc Ton Tc = 50% Ton Tc = 75% Ton Tc = 90% Ton: Length of time the transistor is on Tc: Switching time
- 13. Principles VFD Basics Principle 2 - PWM Question: How can an AC motor possibly run on this PWM output? Answer: An induction motor isâŚan inductor! An inductor resists the change in current. Even though the output voltage waveform is a PWM square wave, the current is sinusoidal!
- 14. Principles VFD Basics Principle 3 â Speed Torque Curve ⢠Speed Torque Curve for an âacross the lineâ start. (600%) Locked Rotor Torque (150%) Full Load Torque (100%) Pull Up Torque (125%) Breakdown Torque (200-250%) Rated Speed Synch Speed SPEED TORQUE CURRENT No Load Current (30%) Slip (300%) (300%) (200%)
- 15. Principles VFD Basics Principle 3 â Speed Torque Curve ⢠Torque production when connected to an inverter. Locked Rotor Torque (150%) Full Load Torque (100%) TORQUE Fout (Hz) 60
- 16. Principles VFD Basics Principle 3 â Speed Torque Curve ⢠Torque can be controlled at any speed with an inverter to meet application demands! Locked Rotor Torque (150%) Full Load Torque (100%) TORQUE Fout (Hz) 60 3.0
- 17. General Topics VFD Basics Topics of Discussion ⢠MCCB Current Rating and Selection ⢠Single Phase Input ⢠Motor Overload Protection ⢠Operating Multiple Motors ⢠Input/Output Contactors ⢠High Altitude Derating ⢠Input/ Output Reactors ⢠DC Link Chokes ⢠NEMA Enclosure Ratings
- 18. MCCB Current Rating and Selection VFD Basics ⢠Rule of Thumb: MCCB ďł 150% of drive input current rating ⢠Iin= Where: Iin = Input fuse/MCCB Rating Vinv = Inverter rated output voltage Iinv = Inverter rated output current x 150% Vin = Nominal input voltage Pfs = Power system power factor Pfm = Motor power factor Vinv x Pfm x Iinv Vin x Pf Note: All sizing for MCCBs, Fuses and MMS paired with LS VFDs has been done by LS! See the document on www.LSElectricAmerica.com titled âFuse, CB, and MMS Sizing for LS VFDs Supplemental Bulletinâ
- 19. Single Phase Input VFD Basics ⢠All LS VFD series can operate off of a single-phase input. The VFD acts as a phase converter to run a three-phase motor. ⢠Some LS VFD series, with a â-1â in the model # are dedicated for single- phase input use. ⢠For standard three-phase input VFDs, a general 50% derate can be applied when sizing. LS has UL tested single-phase derate tables available! But why do we have to derate?
- 20. Motor Overload Protection VFD Basics ⢠VFDs include electronic thermal overload protection for the motor. ⢠The overload is adjusted to the motor current via parameters. ⢠This eliminates the need for an external overload for motor protection. 0 20 40 60 80 100 120 140 60% 85% 110% 135% 160% 185% Time/Minutes Percent Load Trip/minutes at 0Hz Trip/minutes at 6.7Hz Trip/minutes at 13.4Hz Trip/minutes at 20Hz Trip/minutes at 33.3Hz Trip/minutes at 46.6Hz Trip/minutes at 60Hz
- 21. Operating Multiple Motors VFD Basics ⢠When more than one motor is driven in parallel with a single VFD, select the capacity so that⌠⢠Operating multiple motors requires separate overloads for each motor and the VFD must be programmed for V/f. VFD Output Current ďł Total Motor FLA x 1.1 T1-Temp Proportional (PID) Control VFD OLR OLR OLR OLR
- 22. Excessive Switching VFD Basics The recommended maximum switching of the input of the VFD is 2 times per minute. Pre-charge circuits can heat up causing premature failure when exceeding this recommendation. Transformer
- 23. Input/Output Contactors VFD Basics Input Contactors ⢠A VFD can be operated without an input contactor. ⢠Do not use an input contactor to start and stop the drive. ⢠Instead use terminal run commands or alternative start/stop controls through the VFDs I/O. Output Contactors ⢠A VFD can also be used without an output contactor. ⢠Opening or closing an output contactor while the VFD is running can cause damage and failure to the VFD.
- 24. High Altitude Derate VFD Basics ⢠Power conversion equipment must be derated above a certain altitude. ⢠LS VFDs are rated to 3300 feet (1000 meters) in altitude and 40 degrees C. Derate is about 3% for every 1000ft (300M) above that. Hey! I hope you derated that drive!
- 25. Input Reactors VFD Basics Problem ⢠Stray voltages, spikes, and transients can damage a VFD. ⢠Imbalanced phases can also cause stress on filter capacitors or trigger various faults. ⢠The closer your application is to the maximum load of the VFD the more sensitive it becomes to a voltage imbalance. ⢠Current Harmonics. Solution ⢠Use a three-phase input reactor when the power source transformer (KVA) is very large compared VFD capacity (KVA). ⢠Also used when the power factor needs to be improved. ⢠Can reduce current harmonics from 85% down to 30-35%.
- 26. Output Reactors VFD Basics Problem ⢠Long lead lengths causing reflective (standing) waves. ⢠Low impedance motor is used. Solution ⢠Use a three-phase output reactor to filter the spikes on the output PWM waveform. And output reactor will also add additional impedance. M
- 27. DC Reactors VFD Basics ⢠DC Reactors (DC link chokes) are used when the power source transformer (KVA) is very large compared to the VFD capacity (KVA). ⢠DC Reactors improve VFD power factor and mitigate bus ripple caused by a single phase input. ⢠Larger VFDs tend to have built in DC reactors while smaller VFDs would need one installed. A 150HP H100 with two built-in DC link chokes.
- 28. NEMA Ratings VFD Basics Enclosure Rating Characteristics 1 Intended for indoor use primarily to provide a degree of protection against contact with the enclosed equipment or locations where unusual service conditions do not exist 3R Intended for outdoor use primarily to provide a degree of protection against falling rain and sleet; undamaged by the formation of ice on the enclosure 4 Intended for indoor or outdoor use primarily to provide a degree of protection against windblown dust and rain, splashing water and hose-directed water; undamaged by the formation of ice on the enclosure 4X Intended for indoor or outdoor use primarily to provide a degree of protection against corrosion, windblown dust and rain, splashing water and hose-directed water; undamaged by the formation of ice on the enclosure 12 Intended for indoor use primarily to provide a degree of protection against dust, falling dirt and dripping noncorrosive liquids S100 NEMA 4X iS7 with NEMA 1 Kit
- 29. Closing VFD Basics Thank You! For a copy of these slides or for any technical questions⌠Contact your local Gilson Sales person.