EMC Compatibility Considerations Charles Razzell Regulatory Limits Summary CISPR limits for the Conducted Disturbances of DC ports of PVGCPCs CISPR 11 201506 Quasipeak 74dBuV 500kHz linearly increasing to 84dBuV 150kHz ID: 599992
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SunSpecEMC Compatibility Considerations
Charles RazzellSlide2
Regulatory Limits Summary
CISPR limits for the Conducted Disturbances of DC ports of PV-GCPCs (
CISPR 11
2015-06)Quasi-peak: 74dBuV @ 500kHz linearly increasing to 84dBuV @150kHzAverage: 64dBuV @ 500kHz linearly increasing to 74dBuV @150kHzFCC rules in 47 CFR§15.109(e) Carrier current systems used as unintentional radiators or other unintentional radiators that are designed to conduct their radio frequency emissions via connecting wires or cables and that operate in the frequency range of 9 kHz to 30 MHz, including devices that deliver the radio frequency energy to transducers, such as ultrasonic devices not covered under part 18 of this chapter, shall comply with the radiated emission limits for intentional radiators provided in §15.209
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Regulatory Limits (FCC Radiated)
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Measurements in
frequency bands 9-90 kHz, 110-490
kHz employ an average detector.
Regulatory limits apply all the way down to 9kHz.Slide4
Conversion of E-field Limits to Current /Voltage
300m @480kHz/625m is in the radiative region of the near field (0.48λ)
Dimensions of DC string are typically electrically short (<
λ/10)Cannot use infinite-wire model to predict H field!Actual structure is similar to an electrically-short loop antennaCan compute E and H fields under idealistic assumptionsAssume area encompassed by PV string current flow: 50m2 (highly installation dependent)EM simulation needed for realistic results, but calculation was done anyway for 480kHz and 150kHz.
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E and H Fields Per Ampere of Current (480kHz)
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9.4mA allowable current for 5uV/mSlide6
E and H Fields Per Ampere of Current (150kHz)
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69.5mA allowable current for 5uV/mSlide7
Radiation Resistance
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Which is
very small, fortunately.Slide8
Ohmic Resistance
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For 12 AWG, resistance per km is tabulated as 5.1983 Ω
Radiation efficiency (valid in far field):Slide9
Conclusions
Electrically-short loop antennas are notoriously inefficient
Radiation resistance is <<
Ohmic resistance for practical wire gauges.This is good news, especially for far-field EMC issues and EMC ingressMoving from 480kHz to 150kHz increases allowable signal power by 17.4dB under FCC rules (from ~9 to ~69mA)Above analysis assumes differential mode excitation onlyFor common mode excitation, loop becomes a horizontal monopole (more efficient radiator, which is bad)Care should be taken to avoid differential to common mode conversion.EM simulations are needed to confirm simplified calculations.Moving below 150kHz for CISPR also benefits FCC compliance
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Backup
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Equations for E and H Fields For Short Loop
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Controlling Radiated Emissions by Design, Michel
Mardiguian, Springer; 3rd ed. 2014 edition (May 29, 2014)