Design of intelligent motor protector based on ARM LPC2132

1 Introduction

With the development of motor control center (MCC) technology, modular intelligent motor protectors have been more and more widely used, and higher requirements have been put forward for motor protection. In view of the development trend of higher and higher automation of electrical monitoring systems, using low-voltage intelligent motor protection controllers as protection and measurement and control of low-voltage motors in power plants is an important means to improve the operation and maintenance level of electrical monitoring systems.

At present, traditional 8/16-bit single-chip microcomputers are still widely used in electrical protection, but they only have basic measurement and control functions, and their human-machine interface, data query, and monitoring processing capabilities are relatively limited, and most of them lack network communication functions. In the field of automatic online monitoring, ARM chips have strong advantages in multi-target acquisition, multi-level monitoring, and networking. Since LPC2132 belongs to the ARM7 series processor, it can measure multiple sampling points simultaneously and has powerful data processing functions. At the same time, the protector includes powerful network functions and action protection recording functions, supports open communication protocols, and builds an effective protection measurement and control network.

2. Functional features of the system

The intelligent protector is mainly based on the LPC2132 microprocessor as the computing core, and contains functional modules such as analog digital quantity acquisition, relay protection, interface display and key control. The system is connected to the standard RS 485 communication interface to realize data transmission and communication with the monitoring system. LPC2132 is a 32-bit ARM7TDMI-S core microprocessor that supports real-time simulation and tracking, and has 64 kB of high-speed FLASH memory, 4 communication interfaces, 2 32-bit timers, 1 10-bit 8-way ADC, 2 hardware ferroelectric interfaces, 47 GPIOs and up to 9 edge or level triggered external interrupts.

In addition to completing the traditional measurement, control and protection functions, the protector has the following design features:

In view of the common false operation in relay protection, the sampling quantity measurement mutation instantaneous start and the static stability detection element are combined as the starting element mode of the protection device. A two-level locking channel is designed from the issuance of the warning signal to the generation of the protection action, so as to ensure the sensitivity of the starting element and the protector will not cause false operation when the static stability state is destroyed; [page]

By setting the function selection menu, users can remove unnecessary functional tasks according to their needs, reduce the amount of calculation, and improve the system operation speed and accuracy;

By utilizing the powerful network communication function of the ARM series of single-chip microcomputers, the number of data sampling channels is increased, and the sampling quantity information is tracked and displayed in real time, effectively solving the problem of information transmission delay in the distributed electrical monitoring and control system (ECS).

3. System Hardware Design

3.1 Overall hardware structure

The block diagram of the motor protector system is shown in Figure 1. The protector is mainly divided into six parts: main processor LPC2132, signal acquisition module, network communication module, interface display module, key control module and relay protection module.

At the front end of the device, the input circuit converts the collected three-phase current and voltage into a DC signal suitable for A/D conversion through a mutual inductor and an operational amplifier. The system integrates a successive approximation type 10-bit 8-channel A/D converter with a sampling speed of up to 400 kb/s, which fully meets the requirements of real-time monitoring of the system; in addition, an independent reference voltage source is added to the A/D conversion circuit to prevent external pressure fluctuations and improve the conversion accuracy of the device. Since the microprocessor LPC2132 has very high control and processing capabilities, the general main frequency operating speed can reach 60 MHz, and it can process multiple switch inputs and 4-channel relay outputs at the same time. Through the logical operation of the sampled signal, the communication protection and control functions of the system are realized.

The functional output and protection actions of the system device are mainly controlled by the chip pin enable, but the jitter of the external voltage often causes the reference voltage of the chip to change. In the case of external voltage drop, in order to quickly reset the chip and enter the normal working state, a power-off detection circuit is added to the system. The detection circuit is divided into two levels of detection, the front-stage warning and the back-stage action. The fast interrupt reset is used to prevent the FLASH content from changing. In addition, the anti-interference design is fully considered in the hardware circuit design. For example, optocouplers are added to all the input and output and communication parts of the system for isolation, ensuring the good reliability of the system in field applications.