SunSpec EMC Compatibility Considerations Charles Razzell

Regulatory Limits Summary CISPR limits for the Conducted Disturbances of DC ports of PV- GCPCs (CISPR ) >Quasi-peak: 500kHz linearly increasing to >Average: 500kHz linearly increasing to FCC 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 § | Maxim Integrated | Company Confidential2

Regulatory Limits (FCC Radiated) | Maxim Integrated | Company Confidential3 Measurements in frequency bands 9-90 kHz, kHz employ an average detector. Regulatory limits apply all the way down to 9kHz.

Conversion of E-field Limits to Current /Voltage 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 antenna Can compute E and H fields under idealistic assumptions >Assume area encompassed by PV string current flow: 50m 2 (highly installation dependent) EM simulation needed for realistic results, but calculation was done anyway for 480kHz and 150kHz. | Maxim Integrated | Company Confidential4

E and H Fields Per Ampere of Current (480kHz) | Maxim Integrated | Company Confidential5 9.4mA allowable current for 5uV/m

E and H Fields Per Ampere of Current (150kHz) | Maxim Integrated | Company Confidential6 69.5mA allowable current for 5uV/m

Radiation Resistance | Maxim Integrated | Company Confidential7 Which is very small, fortunately.

Ohmic Resistance | Maxim Integrated | Company Confidential8 For 12 AWG, resistance per km is tabulated as Ω Radiation efficiency (valid in far field):

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 ingress >Moving from 480kHz to 150kHz increases allowable signal power by 17.4dB under FCC rules (from ~9 to ~69mA) Above analysis assumes differential mode excitation only >For 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 | Maxim Integrated | Company Confidential9

Backup | Maxim Integrated | Company Confidential10

Equations for E and H Fields For Short Loop | Maxim Integrated | Company Confidential11 Controlling Radiated Emissions by Design, Michel Mardiguian, Springer; 3rd ed edition (May 29, 2014)