At present, most of the power FTU products on the market use the MCU+MPU dual processor architecture to take advantage of the real-time performance of the MCU and the stable network protocols and file system resources running on the MPU. So, can we replace the structure of MCU+MPU with an MPU? The answer is ok, here we introduce a single processing core FTU implementation.
The full name of FTU is the feeder terminal equipment, which is an important monitoring equipment in the distribution automation system. It has remote control, remote signal, fault detection function, and communicates with the distribution automation master station to provide information about the operation of the power distribution system and various parameters, namely monitoring and control, including switch status, power parameters, phase-to-phase faults, ground faults and faults. The parameters of the time, and execute the commands issued by the power distribution main station to adjust and control the power distribution equipment to realize functions such as fault location, fault isolation and fast recovery of power in non-faulty areas. The FTU photo is shown in Figure 1.
Figure 1 FTU
The FTU hardware needs to comply with the "DL/T721-2000 Distribution Network Automation System Remote Terminal" standard, and the software needs to comply with the "IEC 60870-5-104:2009" transmission protocol. From the above two parts of the standards and protocols can be extracted FTU achieve three key technologies art point:
The remote SOE resolution needs to be within 1ms;
The software protocol requires that the data be stored in a file system, and the storage space requirement is on the order of 50 Mbytes;
A minimum of 2 Ethernet interfaces are required.
Among the above three points, there are real-time requirements, and there are relatively rich data processing and communication capability requirements. Therefore, the MCU+MPU scheme will be adopted in the conventional situation, and the block diagram of the conventional hardware scheme is shown in Figure 2.
Figure 2 FTU block diagram
Below we discuss the feasibility of replacing the FTU MCU+MPU with the AW280 single core solution on three key points.
First, 1ms SOE resolution
From the point of view of the power automation device event sequence recording process, the main factors affecting the SOE resolution of the device are event processing time and device time precision. The event processing time depends on the device state quantity processing mode and the hardware processing speed; the device time precision depends on the accuracy of the device clock chip and the device clock processing mode. Best way the amount of processing means in response to an interrupt mode, to ensure that the state quantity can be interrupted by other tasks with the highest priority immediately.
Conventional MPU running linux system because of the uncertainty of the workload, will cause an interrupt response time of uncertainty, this will cause the device state the amount of processing is not timely, conventional FTU program must have real-time operating system kernel to run a MCU To process the state quantity to achieve SOE resolution within 1ms.
AW280 core board mounted AWorks operating system real-time operating system interrupt handling and MCU commonly used RTOS approximation, so as to ensure the interrupt response time is not less than the conventional embodiment; Further AW280 an MPU core board running at 454MHZ It is more than twice the main frequency of the conventional MCU, which makes the AW280's interrupt response better than the conventional MCU processing scheme, and the performance can meet the SOE resolution that can be achieved by the previous MCU+MPU.
Second, the file system.
Different from ordinary MCU, AW280 can support NAND-type FLASH and realize high-capacity storage at low cost.
The AWorks operating system on the AW280 core board has a complete and stable file system;
Hardware and software performance AW280 determine the MCU + MPU file system services can be achieved before the meet;
The location of the file system in the AWorks system is shown in Figure 3.
Figure 3 Location of the file system in the AWorks system
Third, Ethernet needs.
The FTU needs at least 2 Ethernet networks to complete communication between different objects. In the conventional scheme, the MCU generally only has one network port, which requires an additional MPU to increase the network interface.
The IMX280 chip on the AW280 has 2 Ethernet ports, and the AWorks system supports dual network ports by default. This is not available on conventional MCUs, and dual Ethernet support is also rare on conventional RTOS. Therefore, the AW280 can meet the multi-network port function that can be realized by the previous MCU+MPU.
In addition, AW280 has SPI to connect to national grid encryption IC, AW280 has 5 UART to meet the communication needs of peripheral devices.
In summary, the AW280 core board is fully capable of FTU's functional requirements and can replace the traditional MCU+MPU solution.
Figure 4 Evaluation board of the AW280 series core board
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