Functional Design and Demonstration Based on ARM Processor Smart Meter System

Electricity management fees have been used for many years in the traditional operation mode of electricity consumption, post-meter reading, and re-payment. The calculation of the electric quantity value cannot achieve higher precision and the deviation is large. In order to meet the needs of the society and ensure that users use electricity safely, reasonably and conveniently, it is necessary to redesign the traditional electricity meter and electricity to meet the needs of social development.

This article refers to the address: http://

1. The development prospects of smart meters:

The first stage 2000-2007

Gradually replace traditional electromechanical meters with electronic meters; promote the promotion of one-way communication networks in the United States and Europe;

The second stage 2008-2012

Electromechanical meters are being phased out globally; two-way communication networks based on automated metering infrastructure (AMI, an automatic two-way flow architecture between smart meters with IP addresses and power companies) are being promoted in Europe, America and China; As a simple home gateway, the meter can be used for automatic meter reading (AMR) and load management in a variety of utilities.

The third stage 2013-after

Smart meters become home gateways that enable a variety of residential control functions, such as security, alarms, etc.; intelligent power generation (solar and wind power generation) and distribution in homes and units.

From the above three stages, we can see that smart meters not only do not develop in the direction of small, single functions, but on the contrary, the future will give smart meters more functions, making them an indispensable part of the family.

The peak-to-valley time-of-use tariff and the avoidance of peak electricity prices have been introduced, and the market demand for multi-rate meters will be further increased. Especially for large industrial users, the demand for smart multi-rate meters will produce rapid growth. With the advancement of the information age and the development of technology, smart meters as the nerve endings of the smart grid, in the near future, smart meters will play a greater role in the information society, with a broader application prospects.

2, the introduction of ARM smart meter:

It is because of the above background that smart meters have emerged. The so-called smart meter is the application of computer technology and communication technology, etc., forming a power meter with intelligent chip as the core, with high-precision calculation of power, communication with the host computer, and power-related data display.

The electric energy meter is the only tool for electric power companies to collect electricity charges. The stability of performance, measurement accuracy and reliability are related to the settlement problem between the power sector and users. The electric energy metering technology of smart meters is particularly important. Most of the smart meter systems designed are generally controlled by 8-bit or 16-bit microcontrollers. The control functions are relatively simple, and it is difficult to achieve network and wireless transmission. The scalability of smart meter systems in the future is limited. Based on such limitations, we propose a smart meter system based on ARM processor.

At present, the smart meter we need to design mainly realizes the following functions:

1. Realize high-precision calculation and scalability of smart meters;

2. Realizing two-way transmission of data, including wireless meter reading, the meter sends the customer's power consumption to the power department, and the power department sends the customer account balance back to the meter and displays it on the meter;

3. Realize LED display of data, display of electricity last month, current month, and balance display;

Based on the functional design of the above smart meter, higher requirements are placed on the software and hardware of the meter. Obviously, it is difficult for the conventional meter to do this. ARM technology features high performance, low cost and low power consumption for a wide range of applications, such as embedded control, consumer/educational multimedia and mobile applications. So far, the application of ARM microprocessors and technologies has almost penetrated into various fields, and there are precedents for application on smart instruments and meters, so we use ARM technology to apply to smart meters.

The smart meter adds multiple functions based on the digital meter, making it more adaptable to the requirements of the residents. It is more intelligent, convenient and fast to read the user's power, making it possible to realize the power distribution and power conversion of individual users in the future. 3. Design of various functions of smart meter:

3.1, the realization of remote meter reading:

As far as the integrity of the system is concerned, the power system has basically realized network management from power generation, power distribution, transmission and regional substation, and only the user terminal is not connected to the network, resulting in incomplete system, directly or indirectly. The impact of the system's potential, so we designed this technology for smart meter remote meter reading.

The meter signals from the multi-way branch connection are collected by the collector in sequence and processed and stored. The collectors are connected by bus and finally connected to the computer. The typical feature is that each household meter is connected to the collector position through the household line, and then sent to the server subsystem by the collector through wireless transmission, so as to avoid installing a wireless RF module for each smart meter to save cost. The system is generally divided into four levels: front-end acquisition subsystem, server subsystem, communication subsystem, and management center subsystem.

The initial idea is to install a collector in each building, or install several collectors in one cell to realize the front-end acquisition subsystem of the entire meter reading system. The collector connects to each smart meter through the CAN bus; The data is sent to the street or a range of servers installed by radio frequency; finally, the server sends the data to the management center through the communication subsystem. The management center will also send the customer's information back to the meter according to the IP address of each meter. The path is only the reverse of the data collection mentioned above, so we will build an intelligent meter based on the automatic metering infrastructure, namely the AMI architecture. The so-called AMI architecture is an automatic two-way flow architecture between smart meters with IP addresses and power companies.

3.2, sampling filter:

The key part of the whole hardware design is signal acquisition. The signal acquisition is to convert 220V power frequency AC into a corresponding 0 to 3V AC signal. This is a problem related to the accuracy of the entire system. If the distortion is collected, not only the accuracy is lowered, but also serious errors may occur.

This technology selects the transformer to directly transform the transformer, and obtains the required AC signal. After the filter circuit, it is directly output to the A/D interface of the MCU for sampling.

The current is passed through a dedicated transformer to convert the voltage into a voltage Ui of 0.5V. After passing through the first-order low-pass filtering R1 and C1, the low-pass filtering is mainly to filter out the high-frequency signal, and the capacitor can pass the high-frequency signal and hinder the low-frequency. When the signal passes, the capacitor C1 is grounded, and the high frequency signal can be filtered out. Since the signal obtained after filtering is relatively weak, it is necessary to add a Ur through the resistor R2, and the Ur is a 0-3V DC signal, and finally a 0-3V AC signal U0.

3.3, smart meter hardware design method:

The smart meter is mainly composed of electronic components. Its working principle is: firstly, by real-time sampling of the user's power supply voltage and current, using the integrated circuit, the sampling voltage and current signal are transformed, and the analog signal of 0-3V is obtained by filtering. Then, through the four processes of sampling, holding, quantization and encoding of the A/D converter, the digital signal is converted, and the calculation is performed by a formula in the digital signal processing unit, and the power per second is obtained, accumulated, and finally obtained. The power value is processed and controlled by the control unit, and the power value is stored or output.

A 16/32-bit ARM7TDMI CPU with real-time emulation and embedded tracking, with embedded high-speed flash memory, a memory interface and a unique acceleration structure allow 32-bit code to run at maximum clock frequency.

Applications that have tight control over code size can use 16-bit Thumb mode to reduce code size by more than 30% with minimal performance loss. The A/D converter needs to satisfy the undistorted sampling of the three-phase power frequency AC. Multiple serial interfaces facilitate interface expansion.

The peripheral interface can be connected to a palm reader for staff debugging and maintenance. Data storage, output, and display all require different structures of data. Therefore, structural conversion of the power data is required, and conversion to the corresponding storage structure, output structure, and display structure are performed in the data conversion module of the MCU.

3.4, software design method of smart meter:

The software of the smart meter is mainly the calculation part of the power value. We use software programming to calculate the power value in the way of formula calculation, which is mainly performed in the digital signal processing unit module. U0, I0 obtained by A/D converter

To calculate the demonstration and design of ARM technology on smart meters, but the integral is too complicated in the binary calculation of the computer. Taking into account the cost problem, the accumulation method is used instead of the integral operation, and the accumulation formula is

. The demonstration and design of ARM technology applied on smart meters, if the value of N is 100000, the cycle of adding 100000 times is the value calculated by the smart meter in one second.

to sum up:

This design mainly discusses the application of ARM in smart meters. The main problem of ARM in smart meter application is cost. Therefore, the cost saving problem has been thought of many times in the design, including using as little as possible in wireless transmission. Wireless modules and can be considered to implement multi-user smart meters. ARM applications in smart meters mainly take into account the future development trend of smart meters, to achieve more scalability and compatibility of smart meters, in the future can add more practical functions in ARM-based smart meters.