Smart 3-Ph E-Meter

As a result of increasing law regulations, energy subscribers will be provided more freedom to choose between tariffs and utilities, optimizing their energy costs. However, with an increase of renewable energy generation, local utilities require a more efficient way to monitor the energy consumed on a subscriber level, in order to adjust the conventional electrical energy generation. The utility’s business model – pre-paid vs. after-paid – will mainly be driven by local consumption and payment habits. Consequently, future electricity meters will require reliable bidirectional communication paths to address these needs. The solutions that will be chosen will depend on local circumstances and will be either wired or wireless. Although the solution presented will address a 3-ph shunt E-Meter application, the same principles of operation are applicable to current transformer and Rogowski-coil based sensing approaches, with the intrinsic isolation provided by the inductive approach being the differentiator as compared to the shunt approach.

System Benefits:

• As an alternative to the suggested intelligent front-end, the RL78/I1C microcontroller (MCU), the final solution may use the cost-effective RL78/I1B MCU, a design variant of the I1C without hardware encryption; both devices integrate a 24-bit Sigma–Delta (ΣΔ) ADC.
• The calculated energy parameters will be digitized and transferred via UART to the application's controller through an optical isolator (PS9821).
• The digitized metrology data transferred through the optical isolator (PS9821) reaches the applications controller (RA6M1), a Cortex^®-M4 device with 512kB flash and 256kB RAM.
• The suggested LED and RS-485 interfaces (ISL3179E) address the capability of bidirectional serial connectivity in production and out in the field.
• For remote rural deployments with poor grid quality, 2G or 5G wireless connectivity is a must.
• The suggested mechanical switch is a common approach to detect tamper approaches, triggering a register flag upon case opening.
• For urban deployments, either Sub-1-GHz communication via a data logger or wired connectivity via power line communication (PLC) is a must; while the RAA6045S00 supports a proprietary frequency-shift keying (FSK) or the Wi-SUN protocol, the R9A06G037 supports the 3G-PLC and PRIME specification.
• The suggested two DC/DC bucks (ISL85412) independently provide the power to the wireless module as well as the application part of the meter; on the other hand, the three LDOs (ISL80410) independently supply the power for each metrology phase.
• Provided the RS-485 interface requires its own galvanic isolation, the same LDO (ISL80410) could be optionally used for the case of an existing additional flyback output.