Todays electricity companies are demanding more information from meters in the residential sector, where metering has typically been limited to kilowatt hours. New features such as multi-tariff billing, reactive energy measurement and power quality monitoring, are desirable to improve generation, customer service, and billing.
The worldwide market for meter ICs is growing because these ICs make it easy for all-electronic energy meters to be designed. A set of complete solutions for energy metering and automatic meter reading (AMR) has been developed at STMicroelectronics.
The ST mono-phase reference design consists of two independent parts called the ‘measurement module’ and the ‘control board’ connected by a flat cable. It allows designers a quick and easy evaluation of the ST solution for energy meters.
Indeed, the measurement module is a simple but complete energy meter ready to use. The most innovative device is the new ASSP by ST, the STPM01.
The STPM01 device integrates the analogue front end, ADC, and a hardwired DSP. Produced in an advanced 0.35µm BCD6 technology and available in a TSSOP20 package, the device can be used as a single chip energy meter IC compliant with IEC 62052-11 and IEC 62053-22 specification for class 0.5s AC watt meters, with live and neutral anti-tampering features. On-chip information consists of active, reactive and apparent energies, voltage and current RMS, and momentary line frequency. The STPM01 performs an energy-to-pulse conversion for standalone applications. Because of the innovative, patented ripple-free computation algorithm, as well as the support of different types of current sensing principles (Rogowski coil or current transformer and shunt resistor) and fast digital calibration, the STPM01 lowers production costs of the entire energy meter.
The control board, the application management of the overall energy meter, is comprised of an 8-bit microcontroller belonging to the ST7 family. The microcontroller, the well-established ST72F324, is housed in a mid-range 32-pin TQFP package with two 16-bit timers available, SPI and SCI serial interfaces. It controls a real time clock – the M41ST87 serial I2C TIMEKEEPER®, a 256Kbit serial SPI bus – the EEPROM M95256, and a dedicated alphanumeric 32 character LCD display. Moreover, the ST72F324 is interfaced through SPI communication bus with the STPM01 analogue front-end.
Figure 2 – ST measurement module
Currently, ST is working to extend its portfolio of devices and reference designs to correspond with customers’ requirements. To this end, the STPM family portfolio will be
enlarged with the introduction of new low-end mono-phase devices, STPM1x, and a three-phase device. All devices within the STPM1x family are pin-to-pin compatible with the STPM01. Moreover, with the introduction of a dedicated monolithic ASSP, ST will address the three-phase market, which is currently covered by the STPM01
For the AMR solution, ST offers the ST7538P, a PLM that incorporates a frequency shifting key, modulation/ demodulation circuitry, and a low distortion, high-current power line driver. The modem can be integrated into an existing static meter main board by connecting it to a few general purpose I/Os of the microcontroller, as well as to the power line, through an inexpensive coupling network. While meeting the requirements set by international regulation bodies, such as IEC for electromagnetic compatibility, the ST7538 offers a broad range of settings to fit the specific requirements of the physical and media access control layer being used.
Furthermore, meter designers can count on ST’s broad MCU portfolio, which ranges from an 8-bit to a 32-bit core processor. These MCUs, with memory sizes from 1KB up to 256KB, come with a large set of integrated peripherals that make them versatile enough for a wide range of metering applications.
For example, ST’s ST7Lite series consists of entry level standard 8-bit Flash microcontroller devices, ideal for cost sensitive applications. Another series of general purpose microcontrollers, the ST7232x family, are ideal for applications requiring the most stringent standards, for medium to large memory capacities with various pin-count packages in Flash and ROM versions.
Finally, the STR7 microcontrollers are a new range of high performance 32-bit microcontrollers made by ST. Built on a leading ARM architecture, the STR7 family comprises highly integrated microcontrollers with embedded Flash, and flexible embedded processors with cache, MMU, and memory interfaces.