BOOSTXL-AFE031-DF1: AFE031

Hi Marco,

What if the target power line has a several capacitors across the power line? 

Are you referring to the capacitors circled in red? These capacitors are used to block DC components of transmitter and receiver parts signal. 

The BOOSTXL-AFE031-DF1 is designed for coupling transmitted signal onto AC powerline via transformer. Transformer does not work with DC power (transformer will be saturated in DC), thus the capacitors are used to block DC. 

Is this line coupling board has problem for transmitting PLC signal since the impedance of the power line is low? Do you have any suggestions for this situation?

Please specify that your powerline whether it is AC or DC on the right side of PLC application. Yes, AFE031 is able to drive and couple onto low impedance powerline without issues. Depending on the types of powerlines, the different coupling methods will be used. The schematic above is referenced to AC powerline. 

If you have additional questions, please let me know. 

Best,

Raymond 

Hi Raymond,

The powerline that we want to connect is DC, which is connected the DC input of PV inverter, 1000VDC max. There are RSD devices connected to PV panel and its output connected in-series to form at PV strings and connected to the DC input of PV inverter.

According to SunSpec, the impedance of the RSD devices is 1 to 8 ohm at mark (131.25kHz) and space (143.75kHz) frequency.

The problem is the DC input of the inverter has several microfarad capacitors and the impedance is low (e.g. 0.1ohm) at 131.25kHz and 143.75kHz. Most PLC signal will flow through those capacitors and RSD devices can't detect the PLC signal. Do you have any suggestion for this application?

Thanks,

Marco

Hi Marco,

The impedance of the RSD devices is 1 to 8 ohm

The impedance 1-8Ω you referring to is DC resistance at a load. The coupled inductance across transformer or coupled inductor should have up to 1mH at a Tx/Rx operating frequency. The coupled device will have impedance in sL or 2*pi*140kHz*800uH or ~104Ω impedance at 140kHz, and AFE031 should have no issues to drive the coupled load (see Wurth Electronik transformer's datasheet below).

Your application is coupling PLC signal onto DC powerline, you have to use coupled inductor to couple the PLC signal onto the powerline. If AC transformer is used, the transformer will be saturated instantly. 

Below is an example how to couple PLC signal onto DC powerline. You are unable to use the Wurth Electronik transformer specified for the AC powerline application mentioned in the application note. You have to get a high saturation current coupled inductor for the DC coupling application. It looks similar to AC transformer, but the internal construction is different. Transformer does not store magnetic energy during operation by definition, while coupled inductor will store the magnetic energy during operation without saturation.  

The coupled inductor is using a gaped inductor, where DC current will not be able to saturate the magnetic core easily. If a maximum current in the PV application, say 10Adc, the saturated DC current in the coupled inductor should be rated up to 5X-10X higher depending on your application. The magnetic core in the coupled inductor cannot be saturated during a nominal operation, say switching transients, on/off event of the power inverter or PV panels, pulse load requirements etc.. And you have to implement protection circuitries on the PLC side to prevent high voltage/current transients to damage the primary side of circuit. 

Tx Rx coupling onto DC PLC 11292021.TSC

You should be able to get the coupled inductors in HongKong/Shengzhen electronic market readily. Please make sure the coupled inductor is able to handle Tx/Rx frequency up to 200kHz range without significant core losses at the inductor. It is likely constructed from ferrite magnetic core materials.

If you have additional questions, please let me know. 

Best,

Raymond