Research On Wireless Channel Characteris-Tics And Noise Modeling In High Voltage Sub-Station Environment

With the continuous increase of social electricity consumption,the demand for power system is getting higher and higher.In order to reduce the operation energy consumption of power grid,it is urgent to develop smart power grid.Substation is not only the core link of power system,but also an important place to receive and distribute electric energy.To build a smart grid,we need to use advanced modern communication system in the substation to carry out automatic remote monitoring,control and diagnosis of the main high-voltage equipment in the substation,such as transformer,circuit breaker,high-voltage disconnector and other primary equipment,which can significantly improve the efficiency,reliability and safety of the power grid.However,in terms of wiring complexity,cost reduction and deployment convenience,the use of wireless sensor networks has more significant advantages than wired sensor networks.But,the electromagnetic environment in the substation area is bad,the wireless channel is complex,and the wireless communication system is vulnerable to noise interference,which seriously degrades the communication performance.In addition,wireless equipment should have a low output power when sending signals,so as to avoid impact on sensitive equipment in the substation,result in misoperation and cause security problems.Therefore,the research on wireless channel modeling and noise in substation environment and the construction of reliable communication system not only have very important theoretical significance,but also have practical application value in the future.The main work and innovations of this article are as follows:1.The conversion mechanism of power line carrier access line differential mode signal and common mode signal is studied,and the conversion formula of differential mode current and common mode current is deduced,and the unbalance coefficient is proposed,which represents the change of impedance factor.When the unbalance coefficient is not equal to zero,it will lead to the conversion of differential mode signal and common mode signal.For the measurement of broadband current,a measurement method is designed.The S parameter is measured by vector network analyzer,which avoids the traditional method of measuring the transmission impedance of current clamp.The measurement results are consistent with the theoretical values.Then,according to the principle of long conductor antenna,the power line carrier access line is equivalent to long conductor traveling wave antenna,the radiation models of power line carrier access line differential mode current and common mode current are established,the previously known differential mode current and deduced common mode current are brought into the radiation model,and the values of differential mode radiation and common mode radiation are calculated respectively.Finally,the total value of the two modes of power line carrier access line radiation are measured with a loop antenna.The results show that the change trend of the measured data is consistent with the calculated value,and the coincidence effect is good.2.A matching pursuit algorithm based on modulation gaussian pulse atomic library is proposed.The noise of high voltage substation is divided into three groups:a group of modulation gaussian pulse noise with long duration and large amplitude obeying poisson distribution,a group of pulse noise with short duration and small amplitude obeying gaussian distribution,and the rest noise is background white gaussian noise.Compared with the traditional matching pursuit algorithm based on gabor atomic library,it improves the operation speed and reduces the calculation time.Then,the three groups of noise are constructed into three systems,and the state transition matrix of markov chain is calculated according to its occurrence probability.It can be found by calculated that the proposed hybrid noise model has satisfactory results,and has higher accuracy than the traditional bernoulli-gaussian noise model,and can match the measurement data very much.3.Firstly,for the outdoor channel of high voltage substation,an extraction method for outdoor path loss parameters of high voltage substation based on maximum inner product fitting method is proposed.A range is preset within which the values of the loss index n and the standard deviation σ in the log-distance path loss model vary,and the received power is calculated.By solving the inner product of measurement received power and calculated received power,the maximum value of the inner product is found,and the corresponding loss index n and standard deviation σ are obtained.The proposed method traverses the loss index n and standard deviation σ in a certain range,and it ensures that the proposed loss index n and standard deviation σ are the optimal solutions,comparing with traditional methods such as minimum mean square deviation and accumulative method.Then,for the indoor corridor environment of high voltage substation,the path loss model in the indoor environment is optimized,the traditional Friis transmission formula is modified,and a new Friis extension model is deduced.According to the equivalent circuit of receiving antenna,considering the matching coefficient,polarization matching factor and normalized field intensity direction function,a new form of indoor path loss model is established.Comparing with the traditional path loss models such as ITU model,Chan model,attenuation factor model and single slope model.The results show that the error between the proposed Friis extension model and the measurement value is less than 7.5 dB,which is 5 dB higher than Chan model,which is better than other models.4.The wireless relay communication model of high voltage substation is established.Considering the statistical characteristics of high voltage substation noise and wireless channel,the theoretical formula of signal to interference and noise ratio with double hop amplification and forward relay is deduced.The important parameters affecting the signal to interference and noise ratio are studied,and the communication performance of cascade channel and single channel characteristics are analyzed.It is found that the outage probability of cascade channel is better than that of single channel communication,but the improvement of bit error rate performance is not very obvious.Aiming at the improvement of bit error rate performance,the biological growth function is introduced,and the companding transformation technology is adopted.Under the M-PSK modulation mode,the bit error rate and constellation are simulated.Compared with the traditional square root companding function,it is found that the proposed method can effectively suppress noise and improve bit error rate performance.