| Nowadays the wireless sensor networks have played an important role in many fields, but it is not smooth to apply the wireless sensor network to coal mine. An amount of research is still in the laboratory stage, whose main reason is the problem of energy supply that is showed in the following two aspects:(1) The way that electricity is supplied to the wireless sensor networks. The Battery, whose life is limited, can be used to provide the power for the wireless sensors, whereas the traditional method of wired power supply loses the flexibility of wireless sensors and increases the cost greatly; (2)The wireless sensor network nodes needs a large amount of energy. Because the nodes, whose own power consumption and required energy, are too much undertake the task of collecting and sending data, the limited energy of the sensor nodes becomes very important. This problem is becoming particularly serious when energy demand exceeds the wired power supply. Therefore, a system of self-supplied energy is needed to be designed, in which people can use micro-energy transformed by the rich natural resources in the pit to provide power for the optimized lower-cost wireless sensor nodes to ensure its normal work. So the above mentioned system can provide effective technical support for the mine’s safe production and management. There being no relative reports about the optimization of self-supplied power consumption of wireless sensor networks (WSNs)in the pit at home and abroad, the author mainly carries out the systematic studies from the aspects of finding new resources and reducing expenditure in face of three problems that are how to supply electricity to wireless sensors in the pit, how to match nodes-design with electromagnetic environment in the pit and how to operate and optimize nodes in the pit.Firstly, the rich ambient energy resources in the pits are analyzed, and wind and vibration energies are found that are suitable to provide power for the underground WSN nodes. That the characteristics and power of the ambient energy in the pit are tested shows that the ambient energy used in the pit mainly includes thermal energy, noisy energy, electromagnetic energy, vibration energy and wind energy. The thermoelectric generation is not acailable in the pits because the temperature difference is too small in the pits whose maximum difference is about 4 degrees Celsius. Because of the mechanical friction vibration etc in the process of production, the equipment in the pits will make some noise which is greater than 90 dB, exists in the process and meets the requirements of noisy generation. But it is impossible to produce noise when the production stopped because noise is produced with the production and the conversion and output of noise energy is immature. Therefore, the noise in the pit does not meet the requirements of the energy conversion. As far as electromagnetic radiation is concerned, electromagnetic field in the pits seems to meets the demand of power-generation, but because many cables are armored in the mature mine and most of the electromagnetic energy is blocked, electromagnetic energy cannot meet with the requirements of power. The equipment in the pits can vibrate when run, which is quite common in working surface and in the pit chamber. The analysis shows that this energy can meet the energy collection in the pit chamber and working face, meanwhile there are the requirements of forced aeration in the pits, and the structure of wind power is simple, so it is possible to provide power for the majority of the equipment in the pit.Secondly, On the basis of the above experiment, the author deeply studies the energy-supply unit of the wind self-powered wireless sensor nodes in the put. This section focuses on solving two problems, which are how to reduce the consumption of generator itself and how to reduce the load of WSN nodes at the back of matching. Specifically,in the WEH system operated at low wind-speed and limited space, the peak of the AC voltage generated by wind turbines is 1-3 V. which is an challenge for the conventional diode rectification. Therefore this dissertation puts forward that conventional diode should be replaced by MOSFET to enhance the conversion efficiency of AC to DC in a very low voltage. In order to improve the efficiency of generators, this dissertation proposes a new method of MPPT, whose principle is to control the effective load impedance and calculate source impedance inside the wind turbine in order to achieve good impedance match between the source and the load and make the collected power is at its greatest wind speed of operating. On the basis of the above experiments,, the control theory of improved self-adaptive sliding mode is proposed to improve the responding speed and quality of MPPT. Testing results show that the system can trace the maximum power point very well after converted into arithmetic of sliding-mode control. When the wind speed changes, the system can trace the new maximum power point very quickly. There is very little wave near the maximum power point after the system is stable. Meanwhile, the ULP management strategy of the self-adaptive voltage adjustment technology is proposed and closed-loop control method is used to adjust processing core’s voltage flexibly, which is to monitor and manage the entire circuit and reduce 64% of the nodes energy consumption approximately. Experimental results show that the active rectifier and MPPT based on simulated resistance will make electric-power collected by the wind turbines increase from 2.5% to 9.6%. The generated energy can meet the needs of driving wireless sensors, and battery-charging system, additional energy protection module, is working well to satisfy the design requirements for energy sources in the project.Thirdly, according to the vibration characteristics of the equipment in the pits, this dissertation constructs an electromechanical model of piezoelectric ceramic transducer which is available in the pits. On the basis of the existing research, the author derives the electric energy equation (obtained by piezoelectric ceramic plates under the pressure load) and the expressions for current and voltage under the specific boundary conditions, piezoelectric cover conditions and electrode conditions. In order to improve the transforming efficiency of the piezoelectric transducers, the method of impedance-matching is studied in this dissertation, which is simulated by changing the output impedance of transducers to control current. The simulation shows that if the best impedance of multilayer transducer is reduced by 40 times, the output power is twice as much as the generated power. Based on the above results, the acquisition circuit is optimized to make itself adjust the load impedance of transducers and strengthen the output power and current. Meanwhile, with the help of pressure power generation, the LED light array is lighten up and the super-battery recharged,which proves that 50% of energy is lost when in the incomplete matching of impedance. In view of this, the piezoelectric transducer circuit with maximum power is realized, in which no energy is lost in the conditions of ideal load. In the circuit, the assumed output-impedance is 50 Ω, and the input and output signals of the piezoelectric transducer are measured by using this parameter. The results show that the peak of the conversion efficiency is 95%. The above simulation experiment shows that the energy can be collected greatly in the pits,that is to say, this method of collecting energy can meet the needs of the power supply of wireless sensors in the pits.At the same time, the communication frequency channels, antenna parameters and communication efficiency are improved to reduce the load of self-supplied power module and achieve the purpose of cutting expenditure. The power consumption of WSN nodes is optimized in this dissertation, which shows that the power consumption of antenna makes up a sizeable proportion of the whole consumption of WSN nodes and choosing suitable frequency channel and antenna can reduce its power consumption. The transmission of electromagnetic waves in the pits is different from that on the ground because of the much electrical equipment in the pits, Firstly, the method of combined measurement of time and frequency domain is adopted and electromagnetic interference in the pits is studied in this dissertation. The results show that whether the electromagnetic radiation is high frequency, low frequency or transient interference, the electromagnetic radiation is lower than the I level of the existing terrestrial standards, and the electromagnetic interference is mainly lower than 500MHz. At the same time, Taking the advantage of the frequency resources in the pits, this author adopts the idea of using bandwidth for distance, which is realized by establishing the statistical model of the broadband electromagnetic wave propagation in the pits and tunnels. The broadband electromagnetic wave with different frequency points transmits along the pits whose characteristics of decline and delay spread are studied on which the influence of tunnel’s cross section and bend is also studied. The problem that needs solving is studied when using the finite element method to solve the theory of lossy media, and the concept of tunnel’s surface impedance is put forward. The boundary condition of the lossy media waveguide is solved according to the tunnel’s actual conditions. The figure of the lossy waveguide theory is used to modify the approximate error of the analytical solution of classic theory, and then the modified formula is proposed. The statistical channel model of the broadband electromagnetic wave propagation in the pits is established. In order to verify the channel characteristics and the influence of the modulation technology on the performance of wireless communication, the actual test in the pit is carried out in the non-coal mine, the Gold mine of Xiadian in Shangdong province. The specific test is carried out under WLAN communication standard of 802.11b/g and the communication performance of data packet of 2.4G carrier frequency. Based on the experimental results and theory, the optimal operating characteristics and antenna parameters of WSN nodes that are low power consumption in the pit are obtained.In order to further reduce the power consumption of wireless sensor nodes, the dissertation puts forward a special algorithm, which deals with the compression of the data collected by wireless sensor nodes. In the premise of keeping data features unchangeable, the transmitted byte length is reduced. This dissertation presents a new optimized -decoding scheme based on CS according to compressed sensing theory. The DCT at the encoding end is considered as the observations of the original signal that is thinned by using total variation (TV), and the quantized noise is seen as the measured noise, which transforms signal decoding into CS reconstruction that is used to replace anti-conversion of DCT. On this basis, we propose the CS’optimization and decoding based on block-combination to further improve the decoding quality. The experimental results show that the program has significantly improved the subjective and objective quality of the decoded signal in comparison with the conventional decoding. Finally, according to the requirements of monitoring mine tunnel environment parameter and the characteristics and structure of the designed wireless sensor networks, the author proposes the system of wireless sensor networks’ monitoring mine environment based on ambient energy, and gives the corresponding solution to the different circumstances of the mine tunnels.The application of the study in coal pits will realize wireless and intelligence of the sensor networks in the pit, which will provide technical support for the safe production and the precise management in the pit and has important economic and social benefit. At the same time, the above studies synthesizes many technologies such as green energy technology, information technology, safe-production technology in coal mine and automation technology, which are the technology field that nation supports and advocates in line with national industrial policy. |
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