In recent years, people have paid more and more attention to energy and environmental issues, and solar energy, a representative clean energy, has received more and more attention. If we use solar energy reasonably, then we will have sufficient energy to use, and solar energy is the most direct and most common and cleanest energy on the planet. With the further development and advancement of solar photovoltaic technology, solar power has gained a good space for development in the field of street lighting. Thus, a new type of street lamp system with high efficiency and energy saving is formed. The street lamp system has various advantages such as safety, reliability, energy saving and environmental protection, simple installation and convenient maintenance, and is a new technology with great value. 1LED Photovoltaic Street Light Control System Photovoltaic LED Photovoltaic Street Lighting System utilizes the photovoltaic effect of solar cells. White light converts light energy into electrical energy and stores it in the battery. At night, the battery releases electrical energy and supplies LED street lights for night illumination. The block diagram of the photovoltaic LED street lighting system is shown. Sun 16 battery high power LED street light Reward Zhixiong rechargeable power storage ft PWM constant current board dynamic control M system LED photovoltaic street lighting basic frame. 1 Solar cell solar cell is the power source of the whole system. First, when there is sunlight during the day, it uses the light energy to generate photovoltaic effect, generate electric energy, and store the electric energy in the battery. At night, the stored energy stored in the day is released as LED. Street lights provide electrical energy. MCU control system It is the control center in the whole system, which provides the most suitable charging voltage and charging current for the battery, which can realize fast, safe, stable, stable and efficient charging. In the process of charging, it can be in the charging process. Reduce losses, maximize battery life, and prevent overcharging and overdischarging of batteries. Since the sun's illumination is not fixed, the output voltage is also unstable. Therefore, the DC/DC converter module is used to convert the unstable voltage into a stable DC voltage, and the battery is intelligently charged by adjusting the duty cycle of the PWM. 1.4 The battery stores the DC power converted by the solar panel and supplies power to the appliance when needed. The LED driving circuit still outputs a constant current to the LED street lamp when the battery voltage changes, thereby ensuring that the brightness of the LED is substantially unchanged. 1.6 High-power LED street light As the energy consumption of the solar street lamp system, the ideal lamp not only needs efficient illumination, but also reduces power loss as much as possible. The main problem of 2LED photovoltaic streetlights LED photovoltaic streetlight system is mainly composed of solar cells, controllers, lead-acid batteries and LED lights. When photovoltaic cells use solar energy to convert solar energy into electrical energy, they store electricity by direct current. The electric energy supply mode required for LED street lamps also needs to be supplied in the form of direct current. In the process of utilizing electric energy, the mutual cooperation degree is high, and the process of AC/DC conversion is reduced, so that the application is more convenient and direct. During the day, photovoltaic cells absorb solar energy to produce a photovoltaic effect, generate electricity, and then store electrical energy. At night, LED street lights convert electrical energy into light energy and emit light. In the whole system, the cost of solar cells is the highest. Under the same effect, solar cells should be applied as little as possible in design, which not only can maximize the efficiency of solar cells, but also save money. And cost. Another point is that the output current of solar energy changes with temperature and illumination, so we must ensure that the solar cell works under the same light and temperature conditions, so that the output power of the solar cell can be maximized, and finally in actual use. In the process, we must pay attention to the overcharge and over-discharge of solar cells to ensure the best results. 3 Maximum power point tracking principle and implementation method 3.1 Principle of maximum power tracking point The output characteristic curve of solar cell is as follows. The output curve of the solar cell From the output characteristic curve of the solar cell, we can know that there is a maximum power point on each characteristic curve, and the maximum power point increases as the light intensity increases, but decreases as the temperature rises. If the solar cell directly charges the battery, the tracking of the maximum power point cannot be achieved because the output voltage is constant. To achieve the maximum power point tracking, it is necessary to implant a DC converter between the solar cell and the battery, and regard the DC converter and the battery as the load of the solar cell, and adjust the DC converter to make the load and the solar cell. The resistance is matched so that the maximum power is obtained on the load. With the development of technology, the efficiency of DC converters can be made very high by electronic technology, so most of the power of solar cells can charge batteries. The output voltage of the DC converter can be regarded as equal to the voltage of the battery, which is constant. The duty ratio is adjusted to change its input voltage, that is, the output voltage of the photovoltaic cell. 3.2 Maximum power point tracking control method According to the current theory, the commonly used maximum power tracking methods are as follows: fuzzy logic control method, incremental conductance method, hysteresis comparison method, constant voltage control method, optimal gradient Law, disturbance observation method, etc. In general, these methods are based on the output curve of the solar cell, and the maximum power point is found by the change of the light intensity and the temperature, and then implemented by the corresponding circuit. These methods have both advantages and disadvantages. Among them, the constant voltage control method has the advantages of simple circuit and easy implementation, and is relatively applied in practice. Considering that the power of the system is not very large, a constant voltage control method is adopted. It can be seen from the characteristic curve that when the temperature is constant, the output voltage of the photovoltaic cell at the maximum power point is almost constant under different illumination intensities. Therefore, as long as we make the output voltage of the photovoltaic cell a certain value, we can Track the maximum power point. This is the principle of the constant voltage control method. However, the disadvantage is that the effects of temperature changes are not taken into account. In response to this problem, we can make the following improvements: Add a temperature compensation system so that different temperatures correspond to different maximum power point voltages, or press -3~-5mV/"C, which can solve the problem. 3.3 to achieve maximum power point tracking specific circuit In general, to achieve maximum power point tracking, the circuit used is more Buck circuit and Boost circuit. The input current of the Buck circuit is intermittent. If this current is applied to the photovoltaic cell, the output current of the photovoltaic cell will also be intermittent, and the photovoltaic cell cannot always be in the best working state. To solve this problem, we need to introduce a storage capacitor, which is to insert a storage capacitor between the Buck circuit and the photovoltaic cell. However, after adding the storage capacitor, although the previous problem is solved, external factors such as circuit reliability and volume will be affected to some extent. Compared with the Buck circuit, the input current of the Boost circuit is continuous. As long as the boost inductor in the Boost circuit is large enough, the output current of the photovoltaic cell can be basically prevented from fluctuating. In contrast, the Boost circuit is maximally realized. There are significant advantages to power point tracking as shown. 1 Photovoltaic battery r power storage his boost circuit is used to realize the structure of MPPT BiBoost-Buck application in the system From the perspective of the whole system, the energy of the battery needs to be transmitted in both directions. However, photovoltaic cells cannot directly charge the battery. To charge the battery, a DC converter is required, and when the LED is driven by a constant current, the battery also needs a DC converter. The two DC converters are shared in one main circuit, and the control circuits are made together, thus forming a bidirectional DC converter. The function of this bidirectional DC converter is the two-way transmission of energy, which is a typical dual-purpose device. It can reduce the number of circuit components, make the control more concentrated, and the circuit is smaller. Many unidirectional DC converters can turn a passive switch into an active switch and turn the original active switch back into a passive switch into a bidirectional DC/DC converter. The Boost converter described above constitutes a BiBoost-Buck bidirectional DC converter by the above-described conversion, as shown. Since the charging process and the discharging process of the battery are not performed at the same time, the energy is transmitted in one direction at any time. When the photovoltaic cell charges the battery, that is, the energy is transferred from left to right, operated by LiSD, and C, the operating circuit is equivalent to a Boost circuit; when the battery supplies power to the LED lamp, the energy is transmitted from right to left. Operated by S2, L, C2D1, its operating circuit is equivalent to the Buck circuit. By properly selecting the inductor L, the circuit can be placed in the Boost circuit, and the input current of the circuit is basically not fluctuated. When the circuit is in the working state of the Buck circuit, the constant current driving of the LED lamp is relatively easy to implement. At the same time, capacitor 02 can use a smaller capacitance value. 5 system design In the photovoltaic street lamp, the controller includes a bidirectional DC converter, as well as a charge controller with MPPT and discharge and LED drive control. The control part mainly includes two parts, discharge and LED drive and charge controller with MPPT, which are the core of system design. When the photovoltaic cell charges the battery and the battery is discharged, the LED lamp is driven by the bidirectional DC converter. The middle switches K, and K2 are not allowed to be turned on at the same time. When the light is good and the battery is not charging, K is turned on; when the light is poor and the battery is not discharged, K2 is closed, the system block diagram is as follows. The best working voltage of the photovoltaic cell selected by the system block diagram system is 20.4V, the rated power is 100W, the battery capacity is 100Ah/24V, and the LED lamp power is 60W. The design is about 6~8h per day. The system uses Microsoft's 16-bit single-chip microcomputer. . Table 1 shows the measured data without maximum power point tracking control and with maximum power point tracking control. It can be concluded from Table 1 that when the system is added to the MPPT control, the output power of the photovoltaic cell can be increased by about 13%. Table 1 Real drop data Light intensity Battery level MPPT control Charging current without MPPT control Charging current 6 Conclusion In the LED photovoltaic street lamp system designed in this paper, the photovoltaic circuit used is a constant voltage controlled Boost circuit. The system not only realizes the tracking of the maximum power point, but also forms a BiBoost-Buck converter, and realizes constant current driving of the LED lamp. It can be seen from the above research and analysis that the LED photovoltaic street lamp system has great feasibility and its simple installation method. The system has the advantages of simple circuit, low cost of implementing the same lighting effect, small circuit size, practical and high efficiency. In the context of the current energy crisis, it has a promotion value.
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