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 – 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 addresses a 1-ph shunt E-Meter, the same principles of operation are applicable to current transformer and Rogowski-coil based sensing approaches with the intrinsic isolation provided by the inductive.

System Benefits:

  • As an alternative to the suggested intelligent analog 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 applications controller through an optical isolator (PS9821). Depending on the number of lines, the serial interface is based on “n” number of isolators that may be needed.
  • The selected applications controller (RA6M1) is a Cortex®-M4 device with 512kB flash and 256kB RAM.
  • The suggested LED/IrDA and RS-485 interfaces (ISL3179E) address the capability of bidirectional serial connectivity in production and/or 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 RAA604S00 supports a proprietary frequency-shift keying (FSK) or the Wi-SUN protocol, the R9A06G037 as well as the following line driver (ISL15102) support both the 3G-PLC and PRIME specification.
  • The PS2561FL optical isolator is a good choice for a device that complies with the G3 requirement of zero-crossing detection, which is required for both non-isolated and isolated coupling designs.
  • The wireless module’s nominal voltage is specified at 3.8V (min 3.3V). The supply will have to be supplied separately through its own DC/DC buck (ISL85412); yet, whether this system will have to be galvanically isolated from the rest of the system is a matter of discussion and cost.
  • The rest of the system (except metrology) can be supplied through a similar, separate DC/DC buck (ISL85412), as the other component’s nominal supply voltages are typically at 3.3V.
  • In order to guarantee galvanic isolation through the complete signal path, the metrology’s power will have to be supplied through a separate LDO (ISL80410); alternatively, an additional LDO could be used to power the RS-485 modem.

smart-1-ph-e-meter-block-diagram

 

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