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

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**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

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**What is a Drive? Motor L1 L2 L3 C L Input Converter (Diode Bridge)**

Output Inverter (IGBT’s) DC Bus (Filter) + _

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What is a Drive?

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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

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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+ Positive DC Bus - Negative DC Bus RECTIFIER INVERTER

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**- + 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

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**- + 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

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Frequency = 30Hz Frequency = 60Hz

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RECTIFIER INVERTER + Positive DC Bus - Negative DC Bus Motor

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RECTIFIER INVERTER + Positive DC Bus - Negative DC Bus Motor

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RECTIFIER INVERTER + Positive DC Bus - Negative DC Bus Motor

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RECTIFIER INVERTER + Positive DC Bus - Negative DC Bus Motor

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RECTIFIER INVERTER + Positive DC Bus - Negative DC Bus Motor

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RECTIFIER INVERTER + Positive DC Bus - Negative DC Bus Motor

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RECTIFIER INVERTER + Positive DC Bus - Negative DC Bus Motor

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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

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**Typical AC Drive Configuration**

M 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.

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**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

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**Harmonic Frequencies Fundamental 60 Hz 5th Harmonic 300 Hz**

420 Hz 660 Hz 780 Hz 1020 Hz 1140 Hz

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**The Theory: Fundamental, 5th and 7th Harmonics**

Components 7th Summation

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**Harmonic Content, 6- Pulse Drive**

PWM Drive Harmonic Input Spectrum Fundamental 5th 7th 11th 13th

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**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!

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**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.

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**PCC Example MV PWM M PCC1 (Harmonic Current Distortion) PCC2 (Harmonic**

LV 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

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**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).

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**Effect of Short Circuit Ratio on Harmonics**

ISC IL ~ 400 ISC IL ~ 8

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**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)

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**Harmonics — By the Numbers**

IEEE

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**Harmonics — By the Numbers (cont.)**

IEEE

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**Harmonics — Attenuation Options**

Reactors (Chokes) Passive Filters Harmonic Trap Hybrid High Pulse Count Rectification Active Filters Drive Front End Stand Alone

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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

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**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%

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**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

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**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

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**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

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**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

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**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%)

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**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.

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PEAK: 1,040 volts

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**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

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**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

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