Abstract: DSPs, with their high-speed clock frequency and fast processing speed, provide hardware support for online fault monitoring. This paper utilizes the data processing capabilities of DSPs by analyzing the stator apparent impedance to achieve online fault monitoring of a three-phase asynchronous motor.
Keywords: apparent impedance; online monitoring; DSP; stator current
Research on Fault On-line monitoring of Three-phase Induction Motor Based on DSP
ZHANG Dong-xia
Abstract: DSP has the high speed clock rate and the fast operating speed, was the breakdown online monitor has provided the hardware support. This article through the stator apparent impedance's analysis, displays DSP the data-handling capacity, has realized to the three-phase asynchronous motor's breakdown online monitor.
Key words: Apparent impedance; Online monitor; DSP; Stator current
0 Introduction
Three-phase asynchronous motors are widely used in industrial and agricultural production due to their simple structure, low cost, high reliability, long service life, and convenient maintenance. However, motors inevitably experience faults during long-term operation, requiring early detection and timely resolution to prevent losses. To detect faults early in their development, reliable monitoring and diagnostic methods are needed. Many monitoring methods exist, such as stator current signal monitoring, vibration signal monitoring, shaft voltage monitoring, and axial leakage flux monitoring. Stator current monitoring is the most widely used method due to its non-invasive nature. This paper monitors stator current and voltage to derive its apparent impedance, analyzes the spectrum of the apparent impedance, and utilizes a DSP to perform online fault monitoring.
1. Changes in stator current frequency when a motor malfunctions
2. Apparent impedance and the manifestation of faults within it.
3.1 Hardware System Design
This system uses a DSP as its core. A high-speed sampling module samples and converts the three-phase AC current and voltage, while the DSP performs calculations, processing, and spectrum analysis. A microcontroller handles display, keyboard input, and other expansion functions. Its block diagram is shown in Figure 1.
Figure 1 Hardware system design block diagram
(1) Features of TMS320LF2407A
The TMS320LF2407A chip, as a new member of the 24x DSP controller series, is currently the most integrated and highest-performing chip in the TMSC2000 family. It is code-compatible with existing 24x DSP controller chips, but has richer resources and more powerful functions. It has 32KB of Flash program memory, up to 1.5KB of data/program RAM, 544B of dual-port RAM (DRAM) and 2KB of single-port RAM (SARAM), a serial communication interface (SCI) module, a 16-bit SPI (Serial External Device Interface) module, a WD (watchdog) timer module, and two event manager modules, EVA and EVB.
(2) High-speed parallel A/D sampling MAX155 chip
The MAX155 chip is a high-speed, multi-channel analog-to-digital converter (ADC) with parallel sample-and-hold (T/H) functionality, eliminating time differences in input channel sampling. The MAX155 has eight analog input channels, each with its own T/H module, and all T/H modules sample synchronously. The A/D conversion time for each channel is 3.6 μs, and the results are stored in an internal 8×8 RAM register.
Outputting a negative pulse to the WR pin can start the conversion. Sending a negative pulse to the RD pin can read the conversion result stored in RAM. Data input and output can be achieved through the bidirectional data port of MAX155, or the chip can be made to work only in output mode through hardware connection.
(3) Keyboard/Display
The keyboard/display circuit is based on the AT89S51. We chose a general-purpose keyboard and a dot-matrix LCD with an interface chip T6963C. It can be directly connected to the AT89S51 and can display in graphic, text, and combined graphic and text modes. It has an internal character generator and can manage a 64K display buffer and character generator, allowing the microcontroller to access the display buffer at any time.
3.2 Software System Design
The software system can be programmed in C language. The control software mainly consists of control, signal processing, and display programs. Its software flowchart is shown in Figure 2.
4. Conclusion
Three-phase asynchronous motors are widely used, and many methods for online fault monitoring have been discussed. This article, based on monitoring stator current and voltage, analyzes the apparent impedance spectrum and utilizes DSP fast Fourier transform to detect motor faults in real time. This greatly facilitates future maintenance and has strong practical application value.
Figure 2 Software Flowchart
References
1 Liu Heping, Yan Liping, Zhang Xuefeng, et al. TMS320LF240x DSP Structure, Principle and Application [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 2002.
2 Zhang Yun, Xie Liping, Xiong Hongyan. DSP Controllers and Their Applications [M]. Beijing: Machinery Industry Press, 2001.
3 Wang Peng, Li Zhi, Li Jinghua, Xu Chuanpei. An 8-channel high-speed A/D parallel acquisition system based on TMS320LF2407 [J]. Microcomputer Information, 2006, No. 29.
4 Zhang Zhe, Yin Xianggen, Liu Zhenxing. Rotor fault detection method for squirrel-cage asynchronous motors [J]. Electric Power Automation Equipment, 2002, 10
5 Xu Xiaolai, Wang Li. Simulation study on short-circuit fault of stator winding of asynchronous motor [J]. Large Electric Machine Technology, 2006, 1.
