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Near-field communications power utility transactions

Near-field communications power utility transactions

Technology News |
By eeNews Europe



There is an appreciable trend to transition from a fixed-rate billing to a time-of-use billing. Secure prepaid meters may be used for this purpose. These types of electricity meters give the customer a greater control over their electricity bills. The target regions for using the prepaid meters are mainly the UK, Eastern Europe, Latin America, South Africa and Asia. These types of meters are suitable for installation in landlords’ flats, in shops, stores and sporting facilities, etc.

The basic and common principle of prepayment in energy meters is to buy energy credit in advance and to inform the prepaid meter in some manner. This means that customers decide how much energy they need and want to consume. This solution gives the customer greater control over their energy usage. After the prepaid amount of electricity is consumed, the user is automatically disconnected from the mains unless he/she makes a further prepayment for electricity. This is the main difference in comparison to traditional power meters (based on fixed-rate billing transactions), where the customer consumes electricity continuously.

For the prepaid metering market, there is the need to build that payment infrastructure. Generally, a bank account, an ATM, vending stations or shops are required to reload the energy credit. The main parts of the typical prepaid meter are: the metering part that measures the accumulated energy, a contactor used for disconnecting the meter (consumer) from the mains, and a prepaid sensing element which is used for loading the energy balance onto the meter itself. According to the prepaid sensing element, we may differentiate several types of prepaid meter solutions:

  1. Based on an electromechanical system – prepayment is done simply by coins;
  2. Using a meter’s integrated keypad – users buy energy credit at the vendor company which generates a unique PIN which is assigned to the meter through the keypad;
  3. Using a token – plastic key or magnetic strip card (may be obtained from a vending machine);
  4. Using a memory card which is refreshed at a vending station and finally put into the prepaid meter by the user;
  5. Using a smart card which offers the same behavior as memory cards, but with improved security (mutual authentication, etc.) – these smart cards may be contact or contactless;
  6. Wirelessly (using a mobile phone) – mostly based on GPRS, ZigBee or NFC communication – these technologies may be used not only for loading the energy balance, but also for wirelessly reading the smart meters’ data or valuable information by authorized utilities in real-time.

The following text is focused on describing in detail the prepayment solution based on the Near Field Communication technology (NFC). NFC is a special, low range (a few centimeters), wireless technology that enables devices such as smartphones to securely connect with other NFC-enabled devices, such as prepaid meters. This technology has already been proven in the banking industry, combining it with a secure microcontroller. A typical prepaid meter reference design, based on this technology, has been jointly introduced by two companies, Freescale Semiconductor (U.S.) and Inside Secure (France). This reference design, which has been developed thanks to the cooperation between both companies, provides the NFC-based prepaid meter with the ability to securely reload energy balances. This reference design uses three key parts: the Freescale MK30X microcontroller (MCU), a part of the recently introduced Kinetis series, and the secure element, the ATVaultIC460, together with the NFC (Microread 3.4) chipset, both from the Freescale partner company, Inside Secure.

The meter is driven by the Freescale MK30X256 32-bit MCU, which is the heart of the metering engine. This MCU is built on the popular ARM Cortex-M4 core. The main function of this MCU, coupled with an integrated Analog Front-End (AFE), is to periodically read data from external voltage and current sensors and compute other values consecutively, mainly the powers and accumulated energies. As the main computing technique is based on the Fast Fourier Transform (FFT), the meter can measure energy precisely in all four quadrants (import/export energy, active/reactive energy). Thanks to this, the meter can perform a complete frequency analysis of the mains. The next MCU function is to communicate with on-board AMR communication interfaces, such as an optically-isolated RS232 interface, energy LEDs pulse output interface, an infrared IEC1107 interface, and an I2C/SPI interface for communication with RF/ZigBee daughter cards. The MCU also cooperates with on-board human-machine interfaces (HMI), such as an LCD, which is used for showing the demand values, and with a built-in push-button used for menu item selection.

The next important part of this reference design is a stand-alone RF daughter card, which incorporates two main functions: security and NFC communication. The secure element is the basis for implementing end-to-end security between the prepaid meter and the utility and its distributors who sell energy credits. The referred to RF daughter card features Inside Secure’s ATVaultIC460 and an NFC (Microread 3.4) chipset. The ATVaultIC460 security module provides comprehensive security functions, such as mutual authentication, verification and generation of certificates, encryption/decryption and managing the secure storage of cryptographic keys. Additionally, the controller is EAL4+ ready and can also support FIPS 140-2 Level 3 and other certification and standards.

Combining all these cryptographic services and an 8/16-bit RISC processor, the ATVaultIC460 delivers a secure control solution not only for metering applications. The NFC connectivity integrated in this design allows users to upload energy credits using contactless smart card technology or through an NFC phone. NFC connectivity on this daughter card is implemented using the Microread 3.4 controller and the Open NFC protocol stack. Both the RF/NFC daughter card with security functions and the MK30 MCU are connected through an I2C interface, with communication based on the standard Host Communication Interface (HCI) protocol.

The firmware for this reference design is based on Freescale’s MQX real-time operating system (RTOS), which helps to improve the code structure and is ideal for advanced markets. This RTOS is designed to allow the users to configure and balance code size with performance requirements. Freescale’s MQX RTOS provides the developer a faster development time by relieving engineers of the burden of creating or maintaining an efficient scheduling system and interrupt handling. This RTOS also provides a framework, with a simple API, to build and organize those features across Freescale’s broad portfolio of embedded processors.

The key benefits of the described MK30 single-phase secure, prepaid meter are:

  1. End-to-End security between the meter and the utility and its energy credit distributors;
  2. Physically secure – a sealed meter casing thanks to NFC technology (NFC energy balance reload);
  3. Metering engine based on the popular ARM Cortex–M4 Core;
  4. Fully 4-quadrant measurement – the ability to measure import/export, active/reactive energy;
  5. Ability to compute the Total Harmonics Distortion (THD) and frequency analysis of the mains;
  6. Secure data exchange between the meter and the utility through a smart phone – the ability to reload the meter’s balance and perform an anti-counterfeiting check;
  7. MQXTM RTOS enabled.

To better understand how this secure prepaid meter works in a real application, refer to the working scheme in Figure 1. Firstly, the user must recharge the energy balance inside the prepaid meter. To do that, the user must refresh the energy credit on his/her mobile phone by the vendor who debits an adequate amount of money from the user’s bank account. Alternatively, or for cost effective markets, the smartphones may simply be substituted by cheaper smart cards. Using an NFC enabled smart phone or contactless smart card doesn’t have any impact on the meter’s hardware or firmware. In this case, the users buy a smart card at vendors (shops, etc.). Then, the user must approach the smartphone or smart card to the meter. At that moment, the meter’s NFC interface recognizes a new balance request and after doing a mutual authentication it starts transferring the new energy credit from the smart card or smartphone to the meter. After that, the received data and digital signature of the whole message must be verified. After successful verification, the meter activates its contactor (power latch relay), which connects the meter (load) to the mains. The meter continuously measures the accumulated energy. The received credit is deducted depending on energy usage and when this credit reaches zero, the meter disconnects the load from the mains. If the user wants to use further energy from the mains, he/she must carry out a further prepayment.

Figure 1: Working scheme for secure prepaid working meters. Click on image to enlarge.

The end-to-end secure, prepaid meter reference design, described in this issue, provides a solid, safe and powerful solution for prepaid meter developers. For more information about this reference design, visit the link www.freescale.com/metering at Reference Designs section.


About the author

Ludek Slosarcik received his M.Sc. degree in electrical engineering from the VSB-Technical University of Ostrava in 1992 and 1997. His early career experience includes two different R&D companies focused on designing of equipment for measurement and control and power engineering. Since 2008, he has been employed by Freescale Semiconductor, Czech System Center (Roznov pR), as a Systems Application Engineer with a focus in sensor and metering applications.

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