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:
• End-to-End security between the meter and the utility and its energy credit distributors
• Physically secure – a sealed meter casing thanks to NFC technology (NFC energy balance reload)
• Metering engine based on the popular ARMCortex–M4 Core
• Fully 4-quadrant measurement – the ability to measure import/export, active/reactive energy
• Ability to compute the Total Harmonics Distortion (THD) and frequency analysis of the mains
• 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
• 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.
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.
See related links:
Modern power line communication for the smart grid
Open communications for the smart grid
How software and initiatives are fueling the growth of smart grid technology
Gov't mandates driving smart grid deployments
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