In the face of global energy shortage, climate warming and other serious problems, human beings turn to find and use clean energy technology for survival and development. Clean energy includes solar energy, wind energy, thermal energy, vibration energy, ocean energy, and other energy such as human kinetic energy and biochemical energy. With the development of science and technology, wireless sensor network technology has penetrated into all aspects of human production and life. Wireless communication network has gradually developed to the Internet of things, which can communicate with any person and object at any time and anywhere. The scale of the network is expanding rapidly, but at the same time, the overall stability and sustainable development of the Internet of things are becoming more and more prominent. At the same time, in order to meet the needs of human life, more and more sensors need to be placed in inaccessible or bad environment areas. The bad environment in these areas determines that people can not use chemical batteries to power wireless sensor nodes, because it is often impossible to replace chemical batteries in these areas. Because of these reasons, this paper proposes to use renewable energy (dynamic energy) to provide energy for wireless communication nodes to solve these problems.
A set of micro thermoelectric generator supply wireless sensor network system. The micro thermoelectric generator is used as the energy source of the system, and the ultra-low power energy management chip bq25504 of Texas Instruments is used as the energy source The DC-DC boost converter can collect energy from the energy source as low as 80 mV, and use the peripheral circuit to realize the maximum power point tracking control of the energy source. Combined with the energy buffer, it can store energy when necessary, and then through mic841n dual voltage comparator and tps78001 ultra-low dropout linear regulator, it can realize the effective collection and utilization of micro temperature difference energy. The system realizes the function of wireless sensor network through efficient energy collection and effective energy management, and becomes a real energy self supply wireless sensor system. At the same time, it also conforms to the development requirements of green radio in China’s communication industry.
Wireless sensor network node architecture model based on micro thermoelectric generator
In order to meet the requirements of wireless sensor network system supplied by micro thermoelectric generator, this paper designs the following system architecture of wireless sensor node transmitter, as shown in Figure 1.
Figure 1 wireless sensor network node transmitter architecture of micro thermoelectric generator
As can be seen from Figure 1, the transmitter structure of wireless sensor network node powered by micro thermoelectric generator is composed of thermoelectric energy collector, boost circuit with MPPT function, energy buffer and system load (wireless sensor node). Thermoelectric energy collector is composed of thermoelectric conversion chip, which can determine the surface area and the number of layers of thermoelectric conversion chip according to the size of the actual application site and the amount of electric energy required, so as to meet different application environments. The power management IC is mainly composed of maximum power point tracking module (MPPT), power output interface, charger (DC-DC boost module) and energy buffer. The energy buffer circuit is composed of energy storage capacitor, comparator circuit and voltage regulator circuit. The load mainly includes processing the data collected by the sensor and transmitting it through the wireless transmission module. As can be seen from Figure 1, in the wireless sensor network node powered by micro thermoelectric generator, power management integrated circuit (PMIC) is an extremely important part, which contains multiple and important circuit functions, and is the key to the energy acquisition system of micro thermoelectric generator.
Overall design of power management control circuit (PMIC)
In this paper, the power management control circuit mainly includes the following functions: maximum power point tracking, DC-DC boost conversion and energy buffering. As shown in Figure 2, the energy acquisition and tube circuit of wireless sensor system based on micro thermoelectric generator is mainly composed of chip bq25504, mic841n, tps78001, energy storage capacitor and their corresponding peripheral circuits. Ultra low voltage boost conversion and management chip bq25504, low-power multi-function voltage comparator mic841n and linear regulator output chip tps78001 together constitute the multi-function of temperature difference energy acquisition and management of wireless sensor network nodes supplied by micro thermoelectric generator.
Figure 2 Schematic diagram of system temperature difference energy acquisition and application circuit
In this paper, bq25504 power management chip is mainly used to absorb energy from heat energy conversion module with ultra-low power consumption. Bq25504 is a high efficiency energy management chip with 16 pins and 3mm * 3mm subpackage. The 16 pins are distributed counter clockwise in turn. In this paper, the corresponding functions of these pins are reasonably applied to realize the high efficiency micro energy management. In addition, a significant advantage of the chip is that it has ultra-low starting voltage, which enables it to extract energy from the energy source as low as 80 mV when it works stably, and boost the ultra-low voltage for subsequent circuit storage. In this circuit, with appropriate peripheral circuit, the maximum power point tracking of electric energy collected from ultra-low power energy source is realized, which plays an important role in the micro temperature difference energy self supply system. At the same time, the circuit protection of overvoltage and undervoltage is set through the peripheral circuit to ensure the stable operation of the chip.
Mic841n is an ultra-low power dual voltage comparator with internal reference voltage. In this paper, the linear regulator is driven by setting the upper and lower limits of voltage comparison. The working characteristic of tps78001 is to determine the output voltage (i.e. the output signal of pin out) by continuously detecting the voltage on the VDD pin and comparing it with the working voltage set on the lth and HTH pins, so as to control the working state of tps78001. Tps78001 is an ultra-low power regulator produced by Ti. It can stabilize the output voltage of the circuit. By setting the resistance parameters of the corresponding peripheral circuit, the output can get a stable voltage, which can stably drive the wireless sensor transmitting nodes behind. In order to better explain the circuit designed in Fig. 2, the chip and related electronic components contained in each module of the above circuit diagram, as well as the working mode and function are described in detail. The circuit in Figure 2 is the general circuit diagram of the self power supply system of the micro thermoelectric generator. According to the function of the actual circuit, it can be divided into three circuits, which are replaced by circuits a, B and C. Circuit a is a DC-DC boost converter circuit with MPPT function and energy storage circuit based on bq25504 chip; circuit B is a dual voltage comparator circuit based on mic841n chip; circuit C is a regulator output circuit based on tps78001 chip.
Design of DC-DC boost converter and energy storage circuit with MPPT function
As shown in Figure 3, circuit a is mainly composed of power management chip bq25504 and its peripheral circuits. First, connect the relevant electronic components of circuit a according to figure 3. TEG (thermoelectric generator) is a micro thermoelectric generator, which outputs the bare voltage of thermoelectric conversion. The main functions of circuit a are MPPT, DC-DC boost converter and energy storage circuit. How to realize these three functions is described in detail below.
Figure 3 Schematic diagram of DC-DC boost circuit and energy storage circuit with MPPT function