Power Line Communication Modem

Design Considerations

 

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Power line communication (PLC) leverages the existing power line infrastructure and provides cost-effective approach for introducing intelligent monitoring and control to many industrial applications. It makes PLC one of the leading enabling technologies for Smart Grid applications ranging from smart metering, lighting control, solar, plug-in electrical vehicle home and building automation of heat and air conditioning, and security.
For these applications, implementing a Low Frequency NarrowBand PLC (LF NB PLC) technology provides an optimal fit in terms of bandwidth, power, and cost requirements. Operating in the narrowband domain (frequencies up to 500 kHz) ensures data integrity while minimizing system cost. Data rates that can vary from 1.2 kbps up to hundreds of kbps based on the existing standards.
Developing an efficient PLC implementation is not without its challenges. Power lines are inherently noisy and require a robust architecture to ensure data reliability. In addition, each application and operating environment is different, requiring developers to optimize designs across a variety of factors. With the many protocol standards and modulation schemes available, developers need a flexible development platform which simplifies design, allows for optimization to environmental conditions, supports local regulations, and can be easily adjusted to conform to evolving standards.
A Power Line Communication Modem system begins with a modulated signal entering the receiver stage, or active band pass filter where the op-amp selected for the filter should provide low noise, low harmonic distortion, and low input bias as seen in TI’s OPA365 or OPA353. Scaling the received signal by using a Programmable Gain Amplifier (PGA) such as the PGA112 allows for a wide dynamic range and optimal signal processing. It needs to connect to the input of an Analog to Digital Converter fast and accurate enough to properly convert to a digital form for processing. This is done thanks to the on–chip 12-bit ADC of the F28235 Delfino™ or F2802x/03x Piccolo™ microcontroller member of the scalable C2000™ 32-bit microcontroller (MCU) family. The 12-bit ADC operates at up to 12.5 MSPS and also includes triggering mechanisms for support of multi-frequency and phase sampling (2 sample and hold functions). The C2000™ MCU family then enables developers to support multiple modulations on the same hardware, thus eliminating the need to redesign the modem to support different modulation or standards. This makes the C2000™ 32-bit MCU family a smart and flexible platform for Power Line Communication implementation.
Processed signals are injected back into the power grid by the PLC transmitter stage that drives a high output current. The control can be done using the C2000 ePWMs support duty cycle resolution down to 150 ps to enable more control over harmonics and reduce sample-to-output delay. The transmitter stage must be carefully designed to take digital signals from the MCU, filter them to eliminate out of band emissions and drive the low impedance of the AC power line. The OPA564 is a 24V, 1.5A, 17 MHz power opamp designed for the rigorous demands of the PLC line driver. Further improvements in integration, performance and cost can be realized when combining the AFE031, a highly integrated PLC Analog Front End with the C20000TM. The AFE031 integrates the transmit filter, power amplifier, receive filter and PGA in a programmable integrated circuit designed just for PLC.
The resulting modem MCU + AFE can directly communicate with outside systems (both wired and wireless applications) via one of C2000TM serial interface options including CAN, I2C, LIN, SPI or UART.
TI PLC software is delivered in the plcSUITE library and enables developers to support several modulations and standards on one unique design. Developers can implement SFSK IEC61334, PRIME and G3 standards as well as FlexOFDM for custom OFDM implementation and is scalable for the incoming standards.
From the power management perspective, the PLC module can take its power from existing system DC rails or directly from the mains AC power it is communicating over. In the case of the latter, 115V, 60Hz in the U.S. (or 230V, 50Hz in Europe and Asia) needs to be filtered and converted to isolated DC power for the MCU, AFE and various support components. The UCC28600 or UCC28610 Flyback Green-Mode Controller is ideal for providing an isolated 12V or 15V DC rail that can be used directly for the power amplifier and into a DCDC module, such as the PTH08080W, or buck converter, such as the TPS54231, to provide low voltage (5V) PLC system rail. The addition of a linear regulator such as the TPS79533 LDO can provide a low-noise 3.3V rail for use by low power components such as the MCU, PGA, op amps, USB transceivers, and any additional digital or analog components.