1. 2010
ASHRAE Rocky Mountain Chapter VFD Fundamentals April 16, 2010 Jeff Miller - ABB
© ABB
Month DD, YYYY | Slide 1 1

2. What is a Drive / VFD/ AFD?
230
460
Volts
Hertz 30 60
460 V
60 Hz
= 7.67 V Hz
230 V
= 3.83
If 230 VAC Power Line:
230 V Motor
460 V Motor

3. What is a Drive? Motor L1 L2 L3 C L Input Converter (Diode Bridge)
Output Inverter
(IGBT’s)
DC Bus
(Filter) + _

4. What is a Drive?

5. VFD Fundamentals
A variable frequency drive converts incoming 60 Hz utility
power into DC, then converts to a simulated variable voltage,
variable frequency output AC DC AC
RECTIFIER
(AC - DC)
INVERTER
(DC - AC)
60 Hz Power
60 Hz
Zero Hz
VFD
ABB To
Motor
Zero Hz
Electrical Energy
VFD

6. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

7. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

8. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

9. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

10. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

11. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

12. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

13. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

14. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

15. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

16. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

17. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

18. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

19. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

20. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

21. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

22. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

23. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

24. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

25. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

26. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

27. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

28. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

29. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

30. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

31. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

32. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

33. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

34. +
Positive
DC Bus -
Negative
DC Bus
RECTIFIER
INVERTER

35. - + RECTIFIER INVERTER Area Under The Square-Wave Pulses
Approximates The Area Under A Sine Wave +
Positive
DC Bus
Voltage -
Negative
DC Bus
RECTIFIER
INVERTER
Frequency

37. - + RECTIFIER INVERTER How Often You Switch From Positive
Pulses To Negative Pulses Determines
The Frequency Of The Waveform +
Positive
DC Bus
Voltage -
Negative
DC Bus
RECTIFIER
INVERTER
Frequency

38. Frequency = 30Hz
Frequency = 60Hz

39. RECTIFIER
INVERTER +
Positive
DC Bus -
Negative
DC Bus
Motor

40. RECTIFIER
INVERTER +
Positive
DC Bus -
Negative
DC Bus
Motor

41. RECTIFIER
INVERTER +
Positive
DC Bus -
Negative
DC Bus
Motor

42. RECTIFIER
INVERTER +
Positive
DC Bus -
Negative
DC Bus
Motor

43. RECTIFIER
INVERTER +
Positive
DC Bus -
Negative
DC Bus
Motor

44. RECTIFIER
INVERTER +
Positive
DC Bus -
Negative
DC Bus
Motor

45. RECTIFIER
INVERTER +
Positive
DC Bus -
Negative
DC Bus
Motor

46. Non-Linear Loads?
Loads which draw non-sinusoidal current from the line:
Non-incandescent lighting
Computers
Uninterruptible power supplies
Telecommunications equipment
Copy machines
Battery chargers
Electronic variable speed drives
Any load with a solid state AC to DC power converter

47. Typical AC Drive ConfigurationM
460VAC 3-phase
Simulated AC
(PWM)
650VDC
All AC Drives rectify AC to DC, then convert to simulated AC (PWM) to provide the motor Variable voltage and Frequency. The AC to DC conversion generates harmonics.

48. Harmonics — Definitions
Non-linear loads draw current in a non-sinusoidal or distorted manner
Harmonics or harmonic content is a mathematical concept implemented to allow quantification and simplified analysis of non-linear waveforms
Harmonics are typically present in both network currents and network voltages
Non-linear current draw creates non-linear voltage as it flows through the electrical network
Current harmonics  Voltage harmonics

49. Harmonic Frequencies Fundamental 60 Hz 5th Harmonic 300 Hz
420 Hz 660 Hz
780 Hz
1020 Hz
1140 Hz

50. The Theory: Fundamental, 5th and 7th Harmonics
Components
7th
Summation

51. Harmonic Content, 6- Pulse Drive
PWM Drive Harmonic Input Spectrum
Fundamental
5th
7th
11th
13th

52. Harmonics — Why worry? Harmonic Current Distortion —
Added heating in transformers and cables, reduces available capacity
May stimulate a resonance condition with Power Factor Correction Capacitors
Excessive voltage
Overheating of PF correction capacitors
Tripping of PF protection equipment
Voltage Distortion interfering w/ sensitive equipment. Largest Concern!

53. Harmonics, Important Terminology
(Definitions per IEEE )
Harmonic - A sinusoidal component of a periodic wave or quantity having a frequency that is an integral multiple of the fundamental frequency.
Point of common coupling (PCC)
Def. 1 - “point of common coupling (PCC) with the consumer-utility interface.” (current harmonic emphasis) This is typically the primary of the main transformer(s). This is to protect the utility.
– Secondary of transformer for Voltage Distortion. This is to protect the USER.

54. PCC Example MV PWM M PCC1 (Harmonic Current Distortion) PCC2 (HarmonicLV
PWM
MV PWM
13.8 KV
4.16 KV
480 V
PCC1
(Harmonic Current Distortion)
PCC2
(Harmonic
Voltage Distortion)
Substation Transformer
To other utility customers

55. Harmonics, Important Terminology (cont.)
ISC/IL - The ratio of the short-circuit current available at the point of common coupling, to the maximum fundamental load current.
Total harmonic distortion (THD) or distortion factor - The ratio of the root-mean-square of the harmonic content to the root-mean-square value of the fundamental quantity, expressed as a percent of the fundamental.
Total demand distortion (TDD) - The root-sum-square harmonic current distortion, in percent of the maximum demand load current (15 or 30 min demand).

56. Effect of Short Circuit Ratio on Harmonics
ISC IL
~ 400
ISC IL
~ 8

57. Harmonics — A System Issue!
Harmonics produced by an individual load are only important to the extent that they represent a significant portion of the total connected load
Linear loads help reduce system harmonic levels
TDD equals the THD of the nonlinear load multiplied by the ratio of nonlinear load to the demand load:
Where
TDD = TDD of the system
THDNL = THD of the nonlinear loads
NL = kVA of nonlinear load
DL = kVA of demand load
(nonlinear + linear)

58. Harmonics — By the Numbers
IEEE

59. Harmonics — By the Numbers (cont.)
IEEE

60. Harmonics — Attenuation Options
Reactors (Chokes)
Passive Filters
Harmonic Trap
Hybrid
High Pulse Count Rectification
Active Filters
Drive Front End
Stand Alone

61. Reactors (Chokes)
Simplest and least expensive harmonic reduction technique
May be included in base drive package
Often meet harmonic needs provided drive load is a small portion of total connected load
May be implemented with AC line reactors or with DC link reactors
AC line reactors provide better input protection
DC link reactors provide load insensitive drive output voltage
Both types provide similar harmonic benefits
“Swinging” choke design provides enhanced light load harmonic performance

62. Reactors, AC Line or DC Link
Different design techniques
Equal harmonic reduction for same normalized % reactance
Typical full load THD (current) at drive input terminals 28%  46%

63. Hybrid Filter Installs in series with drive input
May feed multiple drives
Improves power factor (may go leading)
Typical full load THD (current) at filter input terminals 5%  8%
Relatively unaffected by line imbalance

64. High Pulse Count Rectification
Typical configurations are either 12 pulse or 18 pulse
Phase shifting transformer is required
Additional drive input bridge(s) is needed
Typical full load THD (current) at transformer primary 8%  12% (12 pulse), 4%  6% (18 pulse)
Performance severely reduced by line imbalance (voltage or phase)
Excellent choice if step-down transformer is already required

65. High Pulse Count Rectification (cont.)
6 pulse rectifier
Transformer and cabling simple
Current very distorted
Ithd typically 45% with 3% reactor
DC/AC
18 pulse rectifier
DC/AC
Transformer and cabling
complicated
Current wave form good
Ithd 4% to 6% (depending on network impedance)
DC/AC
Transformer and cabling
complicated
Current distorted
Ithd 8% to 12% (depending on network impedance)
12 pulse rectifier

66. Active Filter Front End with LCL Filter
Line
inverter
(rectifier)
Motor L C M
LCL Filter (Sine Filter) removes high frequencies >1 kHz. (Current and voltage)
Full output voltage is available with 80% input voltage (400VIn = 480VOut)
Full regenerative capability
No transformer required
Not affected by line imbalance

67. Harmonic Reduction Summary
Remember!
Even an 80% THD nonlinear load with a will result in only 8% TDD if the nonlinear load is 10% and the linear load is 90%.
(80%•(10%/(10%+90%))=8%)

68. Summary – Practical Advice
With a main distribution transformer, 20-30% of its load on non-linear loads will typically comply with IEEE
Voltage distortion causes interference with sensitive equipment, not current distortion!
5% reactors address 90+% of typical applications. They also provide protection against line transients and keep input currents low to avoid oversizing power wiring to comply with NEC.
Make VFD vendor perform a harmonic distortion calculation with the submittals.

69. PEAK: 1,040 volts

70. Peak Voltage all at 50’ of cable
Drive
Peak Voltage 1
1040 2
1110 3
1180 4
1290 5
1350 6
2454
Peak Voltage has many Contributing Factors
Inverter Rated Motors Help Minimize the Issue
Less dV/dT minimizes; problems with RFI/EMI Motor Insulation & Bearing Current

71. Recommendations Keep cable length short as possible
Use a NEMA MG1, Part 31 motor (not “inverter duty” or “inverter ready”
Ensure that grounding is sound