Solar power generation and energy storage monitoring
For solar PV applications, RS-485 communications are used due to inherent noise immunity. Adding iCoupler isolated RS-485 transceivers provides a safe, reliable, and EMC robust solution for solar PV network communication interfaces.
RS-485 has several uses, the primary use being remote monitoring of power generation, power point trackers, and energy storage status (battery storage). For solar applications like energy storage communications is critical, as it alerts the user of power generation and consumption activities within their solar installation. Several systems strategies may be installed such as bill management, PV self-consumption, demand charge reduction, and backup power. Backup power is the most popular, especially in the U.S., due to the various hurricanes causing havoc in the states of Texas and Florida.
Solar generation, energy storage, and domestic consumption in a typical, 24-hour day is illustrated in figure 1. It is the primary reason why systems are designed for bill management in a solar system. During night time when there is no irradiation on the solar panel, energy consumed will be purchased from the grid where the grids are lowest. As soon as the sun rises irradiation appears on the solar panels, power is generated, and domestic self-consumption begins where any solar generation is either used in the household or is diverted to charge the energy storage unit. This allows bill costs to be controlled by reducing the energy drawn from the grid and using solar generated energy where low feed-in tariff areas are available from utility companies.
RS-485 is the communication application of choice for PC screen data updates such as current power, current consumption in the maximum power point trackers, battery charge and health, and CO2 reduction, etc., are available, as can be seen in figure 2.
Figure 3 illustrates a typical solar system with input-for-input dc strings, dc-to-ac conversion, energy charging and storage, and battery management and communications.
Analog Devices offers a complete power, communication, and control interface signal chain solution for solar PV and energy storage applications. iCoupler isolated gate driver solutions include the ADuM4135 and ADuM4223/ADuM3223; iCoupler isolated communication port solutions include the ADM2795E, ADM2587E, and ADM3054; and mixed signal processor solutions include the ADSP-CM419.
Why use RS-485 transceivers with iCoupler isolation?
iCoupler isolation provides a safe, reliable, and an EMC robust solution for solar PV network communication interfaces.
For solar PV networks the RS-485 or CAN communications interfaces often run over long cables in an electrically noisy environment. RS-485 communications are differential in nature and inherently noise immune. Adding iCoupler isolation increases noise immunity. The iCoupler family of digital isolation products has been tested and approved by various regulatory agencies, including UL, CSA, VDE, TÜV, CQC, ATEX, and IECEx. This regulatory agency testing provides a certified level of safety in the presence of high voltage transients and electrical surges that can occur in electrically harsh solar PV environments. The solar PV communications interface usually operates at low data rates—less than 500 kbps—which is an ideal operating range for RS-485 communications. Alternative implementations such as Ethernet operate at fixed data rates of 10 Mbps/100 Mbps or 1 Gbps, which are clearly overdesigned for the application requirement. iCoupler isolation has proven EMC robustness, which reduces field failures. Added EMC robustness reduces design and test time for interface circuits, allowing faster time to market for solar PV networks.
Drop-in iCoupler isolation solution for existing solar PV networks
For existing installations of solar inverters, which do not include iCoupler isolation robustness on the communications port, the iCoupler isolated RS-485 repeater is a powerful drop-in solution. The compact, signal, and power iCoupler isolated RS-485 repeater delivers robust isolation protection against electrical noise in electromagnetic capability (EMC) harsh solar environments.
The iCoupler isolated RS-485 repeater design consists of two RS-485 transceivers and two high speed ADCMP600 comparators. The ADM2587E is a fully integrated signal and power isolated data transceiver with ±15 kV ESD protection, and is suitable for high speed communication on multipoint transmission lines. The device includes an integrated, isolated dc-to-dc power supply, which eliminates the need for an external dc-to-dc isolation block. An RS-485 repeater requires flow control, which is essential for controlling the direction of communication on the RS-485 bus. Using the ADCMP600 high speed comparator allows high speed flow control and directionality on the ADM2587E logic pins, which results in a reliable communication system.
iCoupler signal isolated RS-485 with additional EMC robustness
When designing an EMC communications interface, the circuit designer is often faced with a design and test iterative cycle. The circuit needs to be designed to meet system-level EMC standards and customer requirements. System-level IEC standards, such as IEC 61131-2 for industrial automation, specify varying levels of protection against IEC ESD, EFT, and surge, as well as immunity to radiated, conducted, and magnetic disturbances.
Analog Devices’ iCoupler signal isolated RS-485 includes additional certified EMC protection against these noted disturbances, reducing time to market for designs that need to meet strict regulatory targets. In particular, the ADM2795E RS-485 transceiver integrates isolation robustness and EMC protection, which saves significant printed circuit board (PCB) board space for the solar PV communication port interface.
The ADM2795E is a 5 kV rms signal isolated RS-485 transceiver that features up to ±42 V of ac-to-dc, peak bus overvoltage fault protection on the RS-485 bus pins. The device integrates Analog Devices iCoupler technology to combine a 3-channel isolator, RS-485 transceiver, and IEC electromagnetic compatibility (EMC) transient protection in a single package.
About the authors
Richard Anslow works on new product definitions and customer-facing roles related to Analog Devices’ isolated communications portfolio – www.analog.com
Martin Murnane is a solar PV systems engineer in the Industrial and Instrumentation segment, focusing on energy/solar PV applications at Analog Devices – www.analog.com