Study Of Power Management System Based On Wireless Sensor Node

Wireless sensor network has the virtues of multi-hop, self-organization and infrastructureless, so it can offer many useful applications in military and civil field. However, so many tiny sensor nodes are distributed widely at the dangerous or complex topography, that there is no way to change batteries to supply energy. So,to solve energy problems in wireless sensor networks and to use energy fully and rationaly is the focus of our research.The main contents are listed as follows:1. Using low-power wireless RF transceiver chip nRF401 and AT89C2051-12PU single-chip microcomputer (SCM), there developed small, low-cost wireless sensor nodes, which carry a light sensor and temperature sensor that are able to obtain the information environment illumination and temperature information, and to test out the transmission distance under different conditions. Combined with the difficulties in the process of researching, some problems that should be paid attention in designing and producing the wireless sensor nodes have been concluded.2. After analyzing the characteristics of the solar cells and photovoltaic system, it is found that when around the point of maximum power, the photovoltaic shows best output characteristics. If possible to make the photovoltaic working around the point of the point of maximum power, it can supply energy to sensor nodes more efficiently. In the design maximum power point tracking algorithm has been introducted.3. The principle and characteristics of ultra-capacitors and lithium-ion batteries and the feasibility of using them together are analyzed. The results show that if the lithium-ion batteries and ultra-capacitors are mixed used, the frequency of the lithium-ion battery's'charging and discharging, the output current and the internal loss will be reduced, the discharge time will be extended, and the process of failure will slow down. The mix can avoid weaknesses, and complete each other to form a high-capacity, high power, long-life hybrid energy storage system. The application space of lithium-ion battery and ultracapacitor will be extended.4. The temperature effect of photovoltaic is analyzed. It was found that the solar cells convert 80% of light to heat, 20% of the light energy into electrical energy. The temperature of solar cells affects their own productivity. To utilize solar energy more fully, to reduce the temperature's affected to the solar cells. A photovoltaic - thermal hybrid power management system was constructed. The thermoelectric batteries absorb heat which are generated by photovoltaic cells and converted it into electricity; it will not only reduce the temperature of photovoltaic, but also increase the output voltage and the peak power to increase the power output of the system. Through the theoretical and experimental validation, compared to a single photovoltaic energy conversion subsystem, in the photovoltaic - thermal energy conversion subsystem, the back temperature of photovoltaic can decrease 13℃at most; the largest voltage in the open circuit of photovoltaic increase 304mV; the efficiency of photovoltaic are improved by 5.2% under the same conditions. The advantages of energy mix are fully embodied, the efficiency of photovoltaic are improved compared to the generate electricity and waste heat utilization is achieved. Therefore, the photovoltaic - thermal hybrid energy management system can bring more energy to the node. But the voltage that the thermoelectric battery produced is not high, unless in the summer, the output voltage of the battery temperature is difficult to achieve the step-up circuit voltage to start operating, so if the super capacitor charged by the thermoelectric battery directly, the super-capacitors will store a little power. In the design, the ultra-low-voltage boost technology was used in order to use the energy as much as possible.5. Through the analysis of the solar cells output characteristics, it is found that when in daily days, or at dawn and sunset of everyday, light intensity and output power are much lower. Although it's not possible to supply energy to the sensor nodes directly, this part of energy lasts quite long time. Without efficient usage, it is sure to cause a huge waste. An idea that solar cells use different power has been proposed. A circuit in which the solar cells collect energy efficiently has been designed. Experimental results show that the application of solar cells power sub-thought takes fuller advantages of environmental energy and improves the utilization efficiency of solar photovoltaic cells. 6. There exists a common problem of high energy consumption in the designed four-generation energy management system.. Aimed at this problem, an energy-saving energy management system is designed. Through controlling the SCM to make it start working within the discharge time of the ultracapacitor and stop as the the discharge is completed. Thus the energy consumption of energy management systems is successfully reduced.7. Aimed at the shortcomings of the thermotelecric battery's low output power, a energy management system which contains four photovoltaic to provide energy for wireless sensor nodes is designed. Thus making full use of the solar energy around the nodes.Under standard light intensity, tests of both the single and hybrid management systems'overfall performance have been made (both two systems are based on sensor nodes). Experimental results show that every part of the designed system coordinate the work, the system's output is stable, and the system can guarantee the sensor nodes work normally.