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Activating electrical prepayment systems in homes

20 Jul 2015  | Hamed Sanogo

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This HDU demo platform was built to illustrate how the system works. Central to the HDU is the MAX66242 secure NFC tag authenticator. All the pieces of the demonstration unit are shown in figure 3. The LCD displays the kilowatts consumed and the amount of kilowatt credits remaining. A switch will enable or disable energy consumption. Operating this HDU requires a smartphone with NFC capability. A local Wi-Fi network connected to a laptop simulates the utility company's server. A travel router, MWR102 from ZyXEL, was used. The server runs a TCP/IP client-server app which handles the energy credit transactions. The server also has the meter's ROM ID, binding page data, partial secret, master secret (M-Secret), and page data (i.e., meter reading) so it can recreate each slave's secret (S-Secret). In this system, the HDU is the slave device while the server is the master.

Figure 3: The prepay utility demonstration platform presented here features the MAX66242 secure authenticator tag and a MAXQ610 microcontroller (not seen here).

The HDU displays customer energy consumption and expenditure information. Using the software app supplied by the utility, a customer can access their daily, hourly, or instant electricity consumption, thus giving them the opportunity to analyse and perhaps change their energy-consumption behaviour and even reduce their budget. Communication between the smart meter and the HDU can also be a hardwired connection through the existing electrical wiring from a power outlet using powerline carriers (i.e., powerline communication, PLC).

The utility can use the HDU to send the customer an audible alert when their account reaches a predetermined, low-balance amount. Customers can also choose to receive this notice by email, text message, phone call, or all three. A customer purchases additional credits at any time using the NFC-enabled smartphone/tablet. Replenished prepayment credits are then loaded onto the HDU. If a customer's prepaid balance is ever totally depleted, the HDU's display could be designed to turn red and service is disconnected shortly thereafter. After another prepayment, the account is remotely reconnected.

The HDU architecture and principles of operation
Figure 4 shows the actual demonstration HDU, front side and back, built on the MAX66242 evaluation (EV) kit board. This architecture uses a DeepCover secure, ISO/IEC 15693 tag authenticator IC, the MAX66242, to implement the energy prepayment system. The display panel was added to the EV kit board to facilitate the two-way communication.

Security is paramount in this energy prepay system. This HDU uses both the integrated SHA-256 crypto block technology in the MAX66242 secure tag and its memory protection features to ensure that the depletion and recharge of the energy prepayments do not expose the entire communication to counterfeiters and/or anyone who would exploit the exchange of private information.

Figure 4: HDU front-side PCB (top) with integrated NFC antenna and display; HDU back-side PCB (bottom) shows the NFC antenna coil connected to the MAX66242 secure tag authenticator.

Actual system operation is surprisingly uncomplicated. First, the customer prepays for energy credits with a smartphone using a utility-supplied software app (figure 5 in Steps 1 and 2). Second, the customer aligns the smartphone's NFC antenna with the octagonal shaped antenna of the HDU. A handshaking transaction occurs between the phone and HDU, transferring the purchased credits from the smartphone securely onto the HDU (Step #3). Third, now the customer's account is updated with the amount of electricity prepaid credits, and the total available credit is updated instantly on the HDU's display screen. The remote connect and disconnect switch is then activated in Step 4 for a customer who is adding energy credits to an already disconnected home.

While updates from the smart meter to the HDU are done via the link in Step 5, the meter data is synchronised to the utility's server via Step 6. Note that the current demo platform implementation does not allow the same smartphone to buy new energy credits unless the previously purchased credits have been transferred onto a HDU device.

Figure 5: Advanced prepaid metering infrastructure showing energy buying framework. In Step 1, the customer uses the custom app and buys credits with a financial data transfer to the utility back-office servers. The prepayment credits (data packet including the maximum meter value, or MMV) are transferred to the smartphone in Step 2. The customer then transfers these credits onto their HDU in Step 3.

Operates over a standard wireless network
This energy prepay system can be set up quickly without a full AMI deployment by using the ubiquitous wireless network around us (figure 6).

The customer would first need to register for the prepaid system with the utility by completing a short profile. The credentials entered into the short profile are then used to set up the account and activate the payment system framework. The utility stores a secret in a HDU (i.e., the S-Secret) and then sends the HDU to the customer. If the customer requests it, the utility can dispatch a technician to the customer's home to complete the hardware install.

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