high frequency electromagnetic noise of modern pwm adjustable speed drives 2014-09-16 (final)...

8/10/2019 High Frequency Electromagnetic Noise of Modern PWM Adjustable Speed Drives 2014-09-16 (final) MF.pptx

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Harmonic and Energy Saving Solutions

Power Quality You Can Trust | Real World Experience | A History of Innovation


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Harmonic and Energy Saving Solutions

High Frequency Electromagnetic Noise ofModern PWM Adjustable Speed Drives

Marek Farbis


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Private and Confidential | Mirus International

Scope of Presentation

EMI Emissions PWM Adjustable Speed Drives Problems Associated with PWM Inverter Operation

Long leads/cables Overvoltage at motor terminals and reflective wave phenomenon Motor Anti-resonance issue Common-mode voltage issues, shaft voltage and bearing

currents Output Filters for AC Adjustable Speed Drives Summary


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The Federal Communications Commission (FCC)regulates the use of radio frequencies from 9 kHz to3000 GHz (FCC Part 15)

Any electronic system with digital circuits using clocksignals or other signals over 9 kHz must comply withthe FCC limits for radiated and conducted emissions

FCC Part 15 regulations on allowable EMI emissionsbecame Defacto Standard for all SMPS (Switch ModePower Supply) manufacturers

There is no North American EMI standard for Adjustable Speed Drives

Only CE standards cover ASDs

EMI Emissions


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Common Mode (CM) noise is a type of EMI noiseintroduced on signals with respect to a referenceground

Common Mode noise problems

Source of noise Means of coupling noise, by conduction or radiation Circuits / Equipment susceptible to the magnitude,

frequency, and repetition rate of the noise impressed

CM noise issues increase with susceptibleequipment present, high system-input voltage,large quantity of ASD, and long length of motorleads, also ground system and layout

2014 Mirus International | All Rights Reserved

What is Common Mode noise?


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Applications with potential EMI issues


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Higher system AC line voltages have higher DCbus voltages (V DC bus) Higher output switching dV/dt (change of voltage

with time) increases peak Common-Mode groundcurrent, =

Increasing drive quantity increases sum total oftransient CM noise current to ground

Higher drive carrier frequency (f c) increases thenumber of switch transitions and sum total of CMnoise current


Risk factors


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Motor cable lengths < 20 ft (6.1m) exhibit low cableline-to-ground capacitance and low Common-Moderisk from capacitive dV/dt ground currents

As cable lengths increase, cable capacitanceincreases and CM charging current to groundincreases

At long cable lengths, the high frequency

oscillations of reflected wave voltage transients (~2 x VDC bus) also appear on motor terminals, tocreate CM ground noise current through the statorwinding and cable capacitance


Risk factors cntd.


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PWM Adjustable Speed Drives



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Conventional ASD System

M


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Utilize Pulse Width Modulation (PWM)Inverters with high frequency switching ofInsulated Gate Bipolar Transistors (IGBTs) 2 to 8 kHz switching frequencies typical,

Voltage rise time (dV/dt) rates of 6,000 V/ s typical,(dV/dt of up to 20kV/ s is possible).

Motors are designed to withstand stress of1,000V/ s.


ASD Inverters and Generation of EMI

Reference: An Evaluation of Mitigation Techniques for Bearing Currents, EMI and Overvoltages in ASD Applications, IEEE IA Vol. 34, No.5 Sept/Oct . 1998


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200 HP ASD Normal Output Waveforms

2 ms/Div


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ASD Normal Mode Output Voltage:Typical PWM for 600V inverter at 2 kHz

Voltage rise time ratio (dV/dt) = 4,400 V/ s

Peak voltage = 853 V (603V AC supply)


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Pulse rise and fall time between pulses


VDC_bus

pulse width (T)

trise tfall

f c

f n= 1 / ( * trise )

V U-V

dV / dt magnitude (~ V DC_bus / t rise )


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Simplified drive-conduit-motor system


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ASD phase current

- Fundamental sinewave- Ripple current- Line-to-line cable charge current due to dV/dt (I_ll)- Line-to-ground transient current due to dV/dt (I_lg)


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Transient line-to-line cable charge current (I_ll) isdetermined by the DC bus voltage magnitude and surgeimpedance of the cable parameters Cable resistance (R_01) Self inductance (L_01)

Line-to-line capacitance (C_ll) R_02 L_02

I_ll is confined to the drive terminals and cable loop area I_ll does not interfere with other plant equipment,

interference possible only by radiated noise from the powerleads

I_ll may reach 12 Amps peak and become problems forsmall HP drives and current sensors used within them


Transient line-to-line cable charge current


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Transient line-to-ground current (I_lg) is determined by theDC bus voltage magnitude and surge impedance of thecable parameters Cable resistance (R_01) Self inductance (L_01) Line-to-ground wire (PE) capacitance (C_lg)

Line-to-conduit ground capacitance (C_lg-c) Motor stator winding capacitance to ground (C_lg-m)

I_lg is sourced from to the drive output terminals, but doesnot have a return path directly back to the output terminals

I_lg can interfere with other plant equipment referenced toground

I_lg is Common-mode or zero-sequence current I_lg may reach 20 Amps peak and is a predominant EMI

problems generator


Transient line-to-ground current


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Common-Mode Noise Current Path in aSolidly Grounded ASD System


Ilg ~(C lg-c + C lg-m )*(dv/dt)


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Noise source


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I_lg magnitudes are highest for: ASDs with long output cables (C_lg-c is greater) High HP ASDs with higher motor capacitance (C_lg-m is

greater) ASDs with faster output voltage rise times (dV/dt is greater) ASDs with higher system voltages (dV/dt is greater)

RMS magnitude of I_lg CM noise current increaseswith higher carrier frequency, since repetition rate isfaster

Higher quantities of ASD may increase the RMS

magnitude of CM noise and EMI, due to increased I_lgin the ground circuit I_lg current returns to ASD through lower impedance

path at the I_lg transient oscillation frequency


Induced line-to-gnd CM current


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ASD PWM Inverter


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Inverter zero-sequence switching patternand Common-Mode Voltage generation



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Switching state 1

GND

Vdc/2

Vdc/2

V(N-GND) = - Vdc/2

0 GND

-Vdc/6

-Vdc/2

Vdc/6

Vdc/2

Stator neutral toGround Voltage


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Switching state 2

Vdc/2

Vdc/2

V(N-GND) = - Vdc/6

- Vdc/2 x 1/3

-Vdc/6

-Vdc/2

Vdc/6

Vdc/2

GND

0 GND



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Switching state 3

Vdc/2

Vdc/2

V(N-GND) = Vdc/6

Vdc/2 x 1/3

-Vdc/6

-Vdc/2

Vdc/6

Vdc/2

GND

0 GND



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Switching state 4

Vdc/2

Vdc/2

V(N-GND) = Vdc/2

-Vdc/6

-Vdc/2

Vdc/6

Vdc/2

GND

0 GND



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Switching state 5

Vdc/2

Vdc/2

V(N-GND) = Vdc/6

Vdc/2 x 1/3

-Vdc/6

-Vdc/2

Vdc/6

Vdc/2

GND

0 GND



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Switching state 6

GND

Vdc/2

Vdc/2

V(N-GND) = - Vdc/6

- Vdc/2 x 1/3

-Vdc/6

-Vdc/2

Vdc/6

Vdc/2

GND

0 GND



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Switching state 1

GND

Vdc/2

Vdc/2

V(N-GND) = - Vdc/2

0 GND

-Vdc/6

-Vdc/2

Vdc/6

Vdc/2



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Switching state 7

Vdc/2

Vdc/2

V(N-GND) = - Vdc/6

- Vdc/2 x 1/3

-Vdc/6

-Vdc/2

Vdc/6

Vdc/2

GND

0 GND



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Switching state 8

Vdc/2

Vdc/2

V(N-GND) = Vdc/6

- Vdc/2 x 1/3

-Vdc/6

-Vdc/2

Vdc/6

Vdc/2

GND

0 GND



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Switching state 4 again

Vdc/2

Vdc/2

V(N-GND) = Vdc/2

-Vdc/6

-Vdc/2

Vdc/6

Vdc/2

GND

0 GND



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Common-Mode Voltage The motor neutral voltage on a balanced 60Hz or

50Hz utility sine-wave system is zero. The motor neutral on ASD due to rectangular

PWM pulses at high frequency is never zero. Although sum of average 3-ph voltages is zero an

instantaneous sum of 3-ph voltages is not zeroresulting in neutral point shift voltage (Common-ModeVoltage).

Common-Mode voltage induces shaft voltage and

generates bearing currents in motor. Common-mode currents cause motor bearing

failures and other motor issues. Reference: Inverter Driven Induction Motor Bearing Current Solutions IEEE PCIC -2002-08



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Measured ASD neutral-to-ground voltage

Vng neutral-to-groundvoltage

Ilg CMcurrent


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Expanded Neutral-to-GND Voltage


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Frequency Characteristics of theDifferential Mode (DM) Voltage Spectrum

Spectrum normalised to the DC bus voltage value

Duty cycle = 50%

Carrier frequencyf c=500 Hz

Pulse rise timet rise =200 ns

- 20 dB/decade

- 40 dB/decade


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IGBT rise times range from 50 ns to 200 ns,corresponding to noise coupling frequencies of 6.4MHz and 1.6 MHz, respectively

BJT trise range from 1 to 2 us, corresponding to320 kHz and 160kHz, respectively

Slow pulse rise time has a significant effect on thetotal noise energy coupled into a circuit, becausethe 40 dB/decade attenuation factor is occurringat a higher frequency


Rise times


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Frequency Characteristics of the CommonMode (CM) Voltage Spectrum

Spectrum normalised to the DC bus voltage value

Duty cycle = 50%

Carrier frequencyf c=500 Hz

Pulse rise timet rise =200 ns

- 20 dB/decade

- 40 dB/decade


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High EMI and RFI Motor problems:

Motor terminal overvoltage (spikes) due to reflected wave phenomenon, and

motor anti-resonance

Excessive harmonic losses

Excessive noise

Stressed insulation leading to failures Shaft voltage and Bearing currents leading to bearing

failures


Problems Associated with PWM InverterOperation


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What is it? Inverter section of adjustable speed drive does not

produce sinusoidal output voltage wave forms butgenerates a continuous series of pulses (PWM)


The reflected wave phenomenon


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PWM pulses travel betweeninverter and motor behaving liketraveling waves on transmissionlines

Lead to reflected wavephenomenon and result inovervoltage at motor terminals Can be up to 2 x DC bus voltage of

the drive (nearly 3 x system voltage)

Caused by high dV/dt of PWM

pulse and mismatch betweencable and motor surgeimpedance (characteristicimpedance Z 0)

Reflected Wave Phenomenon


Motor Terminal Voltage

Voltage Oscillation


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Characteristic impedanceZ0,

Ratio of the amplitudes ofvoltage and current of asingle wave propagatingalong the line

lossless

Surge Impedance


properly terminated, Z L = Z 0, the end of atransmission line produces no reflections

Transmission line model

Transmission line

Sending endReceiving end


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Reflected wave transients occur at every driveswitching instant determined by the ASD carrierfrequency

Reflected wave transients are independent of ASDfundamental output frequency

Determined by: dV/dt Magnitude of drive pulse (V DC bus) Voltage rise time of drive pulse

Cable transmission line characteristic impedance(surge impedance),

Motor surge impedance Spacing of PWM pulses (switching frequency) Cable length


Variables Affecting Reflected WavePhenomenon


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Motor and cable surge impedance mismatch areprimarily responsible for the magnitude of peak over-voltage

The rise time of the PWM pulse primarily determines acritical cable length where the peak over-voltagedevelops

Worse with long cable runs, PWM pulse rise time, andhigher switching frequency

Higher surge impedance of smaller HP (kW) motorsalso makes problem worse

Most of the excessive peak voltage is impressed uponthe first turns of the motor windings and can causepremature failure


Variables Affecting Reflected WavePhenomenon (cont.)


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IGBTs allow for higherswitching frequencies

Even relatively short cableruns can cause problems: Critical cable length for

dV/dt=500V/s is in the 100mrange (328 ft),

1000 V/s is in the 50m range(164 ft),

and for 10,000 V/s in the 5mrange (16 ft).

Reflected wave phenomenonappears at some cable lengthregardless of the type of outputswitching device used

Critical Cable length


Reference: AB App Note , Effective Motor Protection Against Reflected Wave Phenomenon


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0

20

40

60

80

100

120

140

3 6 9 12

m a x .

c a

b l e l e n g

t h [ f t ]

Carrier frequency [kHz]

Carrier frequency impact on

critical cable length

460V motors

575V motors

Causes insulation stress Voltages can be higher thanmagnetic wire insulationrating

Higher voltage at shorterrise time on the motor coilscreates higher volt/turnstress on the insulation

High dV/dt can ionize air in

insulation voids causingpartial discharges, coronaand lead to breakdown

Insulation stress


Reference: Eaton App Note , The Reflective WavePhenomena

A i


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When frequency ofvoltage oscillationmatches internal anti-resonance frequency

of motor Can cause overvoltages

within motor windingseven with relativelyshort cable runs

Motor Anti-ResonancePhenomenon


Reference: A Failure Mode for PWM Inverter-Fed ACMotors Due to the Anti-Resonance Phenomenon

Voltage Ratios withinMotor Windings

Motor Winding Measurement Points

P bl A i d i h PWM I


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High EMI and RFI Motor problems:

Motor terminal overvoltage (spikes) due to reflected wave phenomenon, and

motor anti-resonance

Excessive harmonic losses Excessive noise

Stressed insulation leading to failures

Shaft voltage and Bearing currents leading to bearing failures

Higher cost, inverter duty motors required NEMA MG-1 Part 31 Special cables required to reduce leakage currents, deal

with overvoltage, etc


Problems Associated with PWM InverterOperation

d d l


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Low pass filter with cutofffrequency well below thelowest harmonic frequencyof the inverter voltageresulting from PWM. Filters out high frequency currents

while allowing lower frequencyfundamental currents to pass

Prevents Transient overvoltages at motor

terminals

Additional motor losses

Excessive motor noise

INVERSINE Advanced Universal Sine-WaveFilter (AUSF)



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Motor does not have adequate insulation for ASD duty.

Number of parallel motors.

Motor cable length is long.

Step-up/Step-down transformer is used.

There are specific requirements for peak voltage level and dV/dtrise time ratio.

Motor noise needs to be reduced.

Maximum safety and reliability is needed in e.g. EX applications.

Submersible pumps with long motor cables e.g. in the oil & gasindustry.


INVERSINE (AUSF) Applications


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INVERSINE AUSF Performance (Voltage)VTHD = 1.9%< 3% VTHD Typical


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INVERSINE AUSF Performance (Current)ITHD = 2.3%


< 8% ITHD Typical


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The filter capacitorcompensates a part of thereactive power of the motor.

Power Factor improvedclose to 1.0

The resulting RMS currentof the inverter is smallerwith filter than without filter.

Voltage drop of the filterchoke is kept as low aspossible.

INVERSINE and the inverter current


Vinv

VL

Iinv

IC

I0

VM

IMN


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Low insertion loss< 2% of rated voltage.

(inverter voltage needs to be2% higher than normal todeliver the same shaft power)

No damping resistorsrequired

Much higher efficiency thancompetitors filters, > 98%.

Power delivered to themotor> 96%.

Standard LC filterinsertion loss is 10% ofrated voltage.

This translates to powerdelivered to the motor81%.

INVERSINE and the inverter power



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Rated for Full-Load Current of the motor as perNEC Table 430.250

For motors 5 HP to 500 HP (shaft power)

Rated for NEMA motors efficiency levels

Rated for power factor 0.8

Motor rated voltage 460V, or 575V, (660V alsoavailable)

Rated motor frequency 60Hz, max. 90Hz

Inverter carrier frequency > 1 kHz.


INVERSINE design criteria


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The use of PWM Drives can lead to motor problems, cable issuesand high EMI/RFI

Mirus I NVERSINE Advanced Universal Sine-Wave Filter willeliminate or reduce these problems by:

Substantially reducing voltage rise time (dV/dt)

Converting output voltage to near sinewave (


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Thank you

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high frequency electromagnetic noise of modern pwm adjustable speed drives 2014-09-16 (final)...

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