Research On Power Line Communication Key Technologies For Remote Monitoring Of The Motor Group

Data transmission system is an important part of the motor group remote monitoring.The system which transmit motor monitoring data using the power line has advantages such as low-cost equipment, easy installation, no cost of communication services and so on. But power line is not dedicated communication line, so there will be varieties of loads which produce interference noise run in the distribution network, and it's a harmful factor in the PLC signal demodulation.In this thesis, according to the geographical scope of the motor control management,the TWACS which can across the transformer area and the low voltage power line carrier-current communication is used to transmit motor monitoring information. Based on the research of the key technology of the two kinds of power lines of communication,a power line data transmission system which can adapt to industrial distribution network channel environment is developed to provide information channel for the motor remote monitoring. And the field experiment operation is taken in scale.The main work and achievements are as follows:(1) According to the demand of motor remote monitoring which has a wide regional distribution.Based on TWACS, a data transmission system is designed to realize the remote communication by the low frequency distortion signal which can through transformer.There is no need of adding coupling equipment in high voltage line.A signal detection scheme is designed according to the industrial distribution network channel environment and the characteristics of the motor remote monitoring.(2) The power frequency communication synchronization method is put forward based on pseudo-random code and time-frequency analysis. The modulation, synthesis and receiving of the information is carried through the pseudo-random code. According to the frequency domain features of the power frequency communication signal,the industrial frequency cycle of the coding is determine by the amplitude-frequency parameters provided by multitaper short-time Fourier transform analysis. The modulation time domain of the signal is confirmed through the amplitude-frequency parameters provided by STFT and Wagener distribution which is used to analysis synchronous synthesis signal.(3) Based on the confirming of the modulation time-domain, the grid interference in modulation time-domain is inhibited by the use of adaptive interference offset technology.The demodulation is carried out by skills such as cross-correlation or wavelet analysis,and the influence of phase difference of the voltage can be overcomed so that the communication performance can be improved.(4) The transmission of the motor monitoring information in low voltage power line is realized by the way of Multi-Carrier spread spectrum. According to the dynamicity of the low voltage power lines channel and the existing of random strong-narrow band interference. The carrier communication frequency and speed is automatic controlled by the channel condition obtained in signal demodulation. Channel condition parameters can also provide key basis for the path optimization of the carrier relay communications.Based on the research above,the motor remote monitoring data transmission system based on power line communication is developed. MCU and16-bit A/D converter as the core of the detection of the power frequency communication signal cross transformer area. The modulation and demodulation of the low voltage power line carrier signal is realized on a platform consist of AVR SCM and analog comparator. Through the massive field experiment in industrial distribution network,it is proved that the motor remote monitoring data can reliably across transformer and the transmission of the monitoring data in low voltage power lines is reliable.