This is the second article in a 5-part series exploring Energy Storage Systems (ESS) collaboratively written by Richard Anslow and Martin Murnane. The series will provide insight into emerging technologies, covering topics including battery manufacturing, testing, and application.

The articles were originally published in an e-magazine, and have been substantially edited by Wevolver to update them and make them available on the Wevolver platform. This series is sponsored by Mouser, an online distributor of electronic components. Through their sponsorship, Mouser Electronics supports the growth of a sustainable future fuelled by renewable and distributed generation technologies.

Introduction

New government policy combined with new regulation is driving renewable energy generation.  The current increase of power density in solar inverters and the demand for energy storage balancing generates the need to significantly monitor all elements of the latest generations of solar systems.

For solar photovoltaic (PV) applications, RS-485 communications are used because of 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 such as energy storage, communication is critical as it alerts the user of power generation and consumption activities within their solar installation. Several systems strategies can 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., because of 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. Figure 1 shows the primary reason why systems are designed for bill management in a solar system. When there is no irradiation on the solar panel during nighttime, 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.

Figure 1. Solar generation, energy storage, and domestic consumption in a typical 24-hour day. 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., as can be seen in Figure 2.

Figure 2. Typical PV monitoring system data from a PV solar system.

 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. 

Figure 3. Block diagram of a typical solar system with storage.

Why Use RS-485 Transceivers with iCoupler Isolation?

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. iCoupler isolation solutions from ADI are one option for providing a safe, reliable, and an EMC robust solution for solar PV network communication interfaces.

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 500kbps—which is an ideal operating range for RS-485 communications. Alternative implementations such as Ethernet operate at fixed data rates of 10 Mbps/100Mbps or 1Gbps, 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 (Figure 4) is a solid 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.

Figure 4. Signal and power iCoupler isolated RS-485 repeater.

The iCoupler isolated RS-485 repeater design consists of two RS-485 transceivers and two high-speed comparators.

The ADM2587E , from Analog Devices is a fully integrated signal and power isolated data transceiver with ±15kV ESD protection, and is suitable for high-speed communication on multipoint transmission lines. The ADM2587E includes an integrated, isolated DC-to-DC power supply eliminating 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. For complete design guidelines, refer to AN-1458 Application Note Isolated RS-485 Repeater with Automatic Direction Control.

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 5kV_rms signal isolated RS-485 transceiver that features up to ±42V 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.

The ADM2795E integrated iCoupler technology is certified by VDE0884-10, UL 1577, CSA, and CQC (pending).

• Working voltage: 849V_PEAK (600V_rms) reinforced approved by VDE 0884-10
• Withstand voltage: 5000V_rms approved by UL1577

The ADM2795E performs robustly in several system-level EMC tests, which are certified by an EMC compliance test house (certification is available on request):

• IEC 61000-4-5 surge
• IEC 61000-4-4 EFT
• IEC 61000-4-2 ESD
• IEC 61000-4-6 conducted RF immunity
• IEC 61000-4-3 radiated RF immunity
• IEC 61000-4-8 magnetic immunity

Conclusion

iCoupler isolation provides a safe, reliable, and EMC robust solution for solar PV network communication interfaces.

Analog Devices’ interface and isolation portfolio has several options for isolating your RS-485 interface. The ADM2795E provides a complete, system-level EMC solution with compliance to IEC 61000 surge, EFT, and ESD standards, as well as immunity to conducted, radiated, and magnetic disturbances, which are common in harsh solar PV environments. The ADM2795E reduces time to market for designs that need to meet strict regulatory targets.

Signal and power isolated RS-485 transceivers, such as the ADM2587E, provide the most integrated signal and power isolated solution available on the market today. The ADM2587E can be used in a RS-485 repeater design to provide a path to adding iCoupler isolation robustness in designs that are already completed.

This article was originally written by Richard Anslow and Martin Murnane for Mouser and substantially edited by the Wevolver team. It's the second article of a 5-part series exploring Energy Storgae Systems (ESS). Future articles will explore Communication Solutions for Essential Monitoring of Solar PV and Energy storage, electric vehicles production futures, and battery monitoring systems for lithium-ion solutions. 

Article one outlined the Energy Storage Systems in healthcare applications.  

Article two explained communication systems for energy storage.  

Article three gave an overview of battery stack monitoring systems for li-on batteries.

Article four provided a deep analysis of the critical design considerations in estimating the state of lithium-ion batteries.

Article five looked at solutions for scaling electric vehicle production. 

About the sponsor: Mouser

Mouser Electronics is a worldwide leading authorized distributor of semiconductors and electronic components for over 800 industry-leading manufacturers. They specialize in the rapid introduction of new products and technologies for design engineers and buyers. Their extensive product offering includes semiconductors, interconnects, passives, and electromechanical components.