Switching Efficiency Losses occur during transition from Off to On - PDF document

Part 4: VFD Control (Voltage Source) Output Issues with VFDs Line Power DC Link Output AC Converter Inverter Section Section Motor (Sine Wave ) Siemens. Siemens.   Siemens. Global network of innovation .  Global network of innovation . 2004 2004 Global Network of innovation . AC Drives - Power Technology AC Drives - Power Technology a Why IGBT’s SCR’s a — Low losses — GTO’s Smaller Heatsinks Transistors a Smaller product packages — Mosfet — Economical control — Bi-polar On / off with low level signal (ma) — Darlingtons — More “ robust” — IGBT’s Faster turn-off after fault sensing = Easier protection — Relatively inexpensive Mainstream device Competitive supply Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Switching Efficiency Switching Efficiency Losses occur during transition from Off to On and from On to Off. Losses Losses The faster the turn-on time (turn – off time), the lower the losses. Transistor IGBT’s Current Voltage Current Current Current Voltage Voltage Voltage Off On Off On Off On Off On Time Time .1 to 5 Time .1 to 5 Time 0.1 Sec Sec Sec Ideal Switch Transistor Faster Switching = Lower Losses Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Part 4 Output issues with VFDs 1

Inverter - Current Wave Shape Transistor IGBT Carrier Frequency for Squirrel Cage Motors is 2-3 kHz Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Random and Form Wound IGBT - Voltage at Inverter Coils Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Stator Wiring, Random and Form wound Actual Pulse Voltage Graphically Pulse Voltage Single Pulse Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Part 4 Output issues with VFDs 2

dv/dt = Voltage Rise / Rise Time = ____Volts/microsecond dt Applying Pulses to Long Cables L L L Reflected PWM L Wave Pulse Output C C VFD R EMF d — Pulses generate reflected waves v — Shorter rise times = Higher reflected wave Motor Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 IGBT Inverter - Voltage at Motor Voltage at Motor Vs. Cable Length 12 ft. cable No Filter 824 V. peak Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Part 4 Output issues with VFDs 3

IGBT Inverter - Voltage at Motor Reflected Wave Facts a Higher impedance in motor “ reflects” Voltage back — Reflection adds to pulse voltage — Closer to step voltage rise = Greater reflection — Maximum can be 2 to 2.5 times 140 ft. cable Peak voltage (~ 1350V. On 460 VAC line) No Filter (~ 1700V. On 600 VAC line) 1360 V. peak Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Reflected Wave Facts AC Motors a Shorter cables = less reflection (For a given cable length) Line Voltage — Less transmission delay M otor Winding - One Phase Input — Lower impedance a Longer pulse rise-times are better — Longer propagation time — Windings in each phase are a series of coils (Sine wave is no problem) — Longer cables allowable Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Voltage Distribution in Motor Windings Sine Wave 34% 66% Input Pulse 70% 30% Input Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Part 4 Output issues with VFDs 4

Motor Insulation System Stress Protecting Against Winding Stress Winding a Phase-to-phase Phase — Winding enamel can be to Ground. enhanced Phase — Phase paper insulation to Phase Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Protecting Against Winding Stress Protecting Against Winding Stress a Phase-to-ground a Output reactors — Inductor — Winding enamel can be enhanced — At output terminals — Slot liner insulation + a Dv/dt filter Phase a Intra-winding — At inverter output To M otor — And DC bus - — Winding enamel can be a Sine wave filter enhanced L — Remove harmonics C — Form wound coils — Sinusoidal power R Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 IGBT Inverter - Voltage at Motor Output Reactor Effects (Rise Time) (12 Ft. Of Cable) Without Output Reactor With Output Reactor Without Output Reactor With Output Reactor 0 - 4 - 5 Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Part 4 Output issues with VFDs 5

dV/dt Output Filter IGBT Inverter - Voltage at Motor (12 Ft. Cable) Without dV/dt Filter With dV/dt Filter a Limits motor. dv / dt to < 500 V / micro second. a Reduces cable Charging currents. a Reduces motor transient voltages to approx. 1200 V. Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Sine Wave Output Filter IGBT Inverter - Voltage at Motor (140 Ft. Cable) L C Without Sine wave Filter With Sine wave Filter R Absolutely the best protection a a True sine wave at AC motor terminals a Cost and space must be considered a Motor parameters cannot be Measured Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Critical Cable Length Vs. Rise Time Inverters With Very Long Cables Long Cables Line to Motor Inverter Power Variable Sine Output AC Frequency Wave M otor Control Filter Transformer Sine wave is ~ 4000 micro seconds Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Part 4 Output issues with VFDs 6

Noise EMC - What is it? VSD Conducted Emissions Radiated Emissions Electrical noise is an unwanted and continuous signal on the steady state voltage and/or current waveforms. Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Differential mode noise Noise - two modes Differential mode (transverse) noise refers only to that case where the phase conductors only are polluted with noise. Common mode (longitudinal) noise refers to the case where the phase conductors and the ground conductors are polluted with noise. Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Electromagnetic Compatibility Electromagnetic Compatibility Electromagnetic Compatibility can be ensured by: The essential protection requirements of the EC directive - and Good Design: Good installation: common sense - demand that electrical equipment must be Careful component layout. constructed in such a way as to:- Solid Grounding. Controlling switching and Separation of power and Have sufficient inherent Oscillations. Have sufficient inherent signal cables. Not emit electromagnetic Not emit electromagnetic immunity to externally immunity to externally interference which disturbs Protection on inputs. interference which disturbs generated electromagnetic Suppression of contactors, generated electromagnetic the intended operation the intended operation disturbances to enable it relays. disturbances to enable it Good grounding and use of other apparatus of other apparatus to operate as intended to operate as intended of Ground-planes. Use of external filters. Internal RFI filters. Use of shielded cables. Emissions and Immunity Emissions and Immunity Good design is the responsibility of Siemens ; Good installation is the responsibility of the installer. Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Part 4 Output issues with VFDs 7

Common Mode Interference Differential Mode Interference Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Capacitive Coupling EMC: Installation Rules 1. Ground all metalwork together using thick solid straps. 2. Separate signal and power cables. 1/2 Z v 3. Suppress all coils, contactors, relays, solenoids I 1/2 etc. using RC suppressors. VS 4. Use shielded cable or twisted pairs where possible. I Z V 5. Avoid long cable runs or loops. Keep cables v close to grounded metalwork. developed across Z 6. Ground unused cables at both ends. Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 EMC: Good Grounding EMC: Principles of Grounding shielded motor cable. Inverter M Rectifier DC Link ? All Conductors have a finite impedance which 3 ~ increases with frequency . I. S ? Two physically separate ground points are not at the Z N same potential unless no current flows between them . Z E At high frequencies there is no such thing as a single ? This impedance must be low, point ground. otherwise interference voltage will build up. Siemens. Siemens.   Global network of innovation . Global network of innovation . 2004 2004 Part 4 Output issues with VFDs 8