In order to quickly judge the faults of solar street lamp system and verify the rationality of its system design, a controller with state data acquisition and storage function is designed. Supporting software monitoring platform based on WINDOWS operating system, through the PC to achieve internal data access and download, to achieve intelligent management of solar street lighting system. Solar street lamp system is widely used in the field of solar power generation because of its advantages of simple installation, stable and reliable operation, no laying of cables, no consumption of conventional energy and long service life.
At present, the use of solar street lamps has become the largest branch of off grid photovoltaic power generation system, widely used in rural roads, urban landscape roads, thermostatic element squares and residential lighting. However, because the single solar street lamp system itself is an independent system, including power generation unit, energy storage unit and charge and discharge control unit, its power supply system structure is relatively complex, and the running environment of the street lamp system is more complex, which brings many difficulties to the design and operation management of the system. At present, the widely used solar street lamp system, operation and maintenance management only refers to the traditional management of street lamp, system failure rate is high. The energy storage equipment with the highest single cost in the system, which runs for about 3 to 5 years, is basically in the state of scrap. When the system fails, the only criterion to judge is whether the light source can still illuminate and how long the illumination time can last. In judging whether it can illuminate, the main way is to check the controller output, battery status, current and voltage of photovoltaic module and other parameters of the street lamp during the daytime when the light source is not on at night. In judging the performance of energy storage equipment, the main way is to check the continuous illumination time of the street lamp on rainy days and nights. For the daily operation of the street lamp system, the operation and management status of the PV module and the performance of the battery are not known to the operators. Therefore, the traditional operation and management methods of solar street lamp system are still very primitive, and can not track the running process of the street lamp system in real time and predict the fault points of the system.
Based on the above factors, a solar street lamp controller with data acquisition and storage function is developed. As a core component of the solar street lamp system, it has important practical significance for its research. The solar street lamp system is mainly composed of solar panels, storage batteries, controllers and loads. The controller plays a key role in the whole system.
During the day, the charging process of the solar panels depends on the whole process of the equipment. The working condition of the solar panels can also be analyzed through the charging process. At night, the controller collects the voltage of the solar panel terminal to judge the coming of night and turn on the output of the load terminal to realize the power supply of the light source. In the process of power supply, the lighting time and brightness of the light source can be adjusted automatically according to the pre-set. Solar street lamp controller sampled the parameters of charging voltage, charging current, battery terminal voltage, discharge current and ambient temperature of solar cells through single chip microprocessor, and realized the high-efficiency and high-accuracy control of discharge rate and temperature compensation correction, and charged the battery with high-efficiency PWM mode to ensure that the battery works in the best state and prolong the battery. The service life and the related charging and discharging data can be saved [1]. The controller has protective measures such as lightning protection, anti charging, anti reverse, overload, load short circuit and so on, and has indication of charge and discharge, battery state, load work, display and display time of various faults. Besides, the controller also has key setting function and data storage function. The stored data can be exported and viewed on the computer through serial port communication, and it can also be communicated through serial port. Monitoring charge and discharge data [2]. The structure of a photovoltaic street lamp controller for data storage is shown in Figure 1. Because the system requires the control of solar street lights, that is, the voltage adaptation of the 12 V/24 V system, the control of solar panels charging the battery, controlling the discharge of batteries to load, working in single time, dual time and fixed mode, with data storage function, and reading data to the computer conveniently through the serial port interface. At the same time, the controller itself is required to consume less power. After considering the above requirements and considering the writing mode of program memory, power supply range, working frequency, market price, compatibility, encryption function, anti-interference, longer burning life and other factors, the chip of STC Company is selected as the central controller of the system. This chip is a single-clock/machine cycle (1T) single-chip computer produced by MacroCrystal Technology. It is a new generation of 8051 single-chip computer with high speed/low power consumption/super anti-interference. Its instruction code is fully compatible with traditional 8051, but its speed is 8-12 times faster. Internal integration of MAX810 dedicated reset circuit, 2-way PWM, 8-way high-speed 10-bit A/D conversion (250K/s), anti-interference, Flash program memory 28K [3]. In Fig. 1, the MCU sampled the charging voltage, current, battery voltage and load output current through charge and discharge detection module, converted analog signal into digital signal through A/D conversion, and calculated the digital signal inside the chip to judge whether the charging or discharging conditions were met in real time. If the charging conditions were met, the charging state would be adjusted while charging and discharging. The relevant data are stored in Flash program memory in the process of electricity. Temperature acquisition module and key setting module also convert the sampled data into digital signal through A/D conversion and operate the digital signal inside the chip. Temperature is sampled to compensate for charging voltage (temperature changes will affect the charging characteristics of batteries) [4]. The key setting module is to set the mode and time of discharge.
The set value will be displayed on the digital tube. The controller is different from the traditional controller. It not only has all kinds of basic functions of the traditional controller, but also increases the function of serial communication and data storage. This makes the maintenance of PV street lamp more simple and convenient. As long as the computer can transfer the past charging and discharging data on the serial port software, we can know the problem of the street lamp system when we look at the data. Because of the function of data storage, designers can verify the rationality of their street lamp design scheme when looking at the data, which is very helpful for accumulating design experience and doing scientific experiments related to photovoltaic street lamp.
The basic principle of data storage is that the stored data is collected to the SCM through the collection of each module. After computing, the stored data is stored in Flash program memory in binary code. The single chip computer inspects the input voltage and current of the solar cell, and determines whether it is dark or not. During the day, the battery is charged, and at night, the output is turned on according to the set output time. Temperature detection is carried out while charging, and charging voltage is compensated to make the voltage value in a standard correction value. The daily charge and discharge data are captured and stored in on-chip memory. The flow chart is shown in Figure 2. Data acquisition and storage function for solar street lamp system, the components and equipment that affect the operation condition of street lamp include photovoltaic module, battery and controller. Therefore, the data collected and stored by the controller need to include the daily charge amount, discharge amount and the voltage status of the battery during some periods. According to the above data requirements, the data acquisition and storage functions of the designed photovoltaic controller need to have real-time monitoring of the working voltage, open circuit voltage, working current at the photovoltaic module end, on-line voltage at some time points of the storage battery, as well as statistics of daily charging and discharging power. By counting the daily charged and discharged electricity, we can analyze the optimum design scheme suitable for the local climate conditions.
Verify the rationality of the initial design and configuration of the project, so as to facilitate the actual adjustment of the later project plan. By analyzing the difference of charging and discharging capacity over a period of time, combined with the voltage situation when the battery turns on and off every day, if there are problems in configuration or when the region has special climate and low solar radiation in a certain year, the brightness or lighting time of lighting equipment can be adjusted artificially to avoid damage caused by long-term feeding of the battery. The operating conditions of photovoltaic modules are judged by analyzing the daily charging capacity and charging current, and combining with the local sunshine conditions. The operation status of storage battery was judged by analyzing the on-off voltage and off-off voltage of storage battery every day for a period of time. The software monitoring platform on PC connects with the controller through RS232 serial port, and collects the data stored in the controller. At the same time, the platform can also be used to adjust the operating parameters of the solar street lamp system, refer to the real-time charging and discharging status data (see Table 1). Although solar street lamp is a green and clean energy demonstration window, it has been widely used in urban and rural road lighting in recent years. However, due to the short service life of the energy storage equipment and the high cost, it has virtually increased the late operation management cost of the street lamp system. From the data analysis of street lamp controller with data acquisition and storage functions, it is found that the particularity of the installation location of street lamp system makes the problem of photovoltaic module being shaded by surrounding buildings and trees more prominent. There is a certain unscientificity in the traditional configuration scheme of photovoltaic system moving to street lamp system, which results in the premature failure of storage battery and increases the later operation cost. Serial communication and data storage functions are added to the solar street lamp controller to facilitate the fault detection of the street lamp system and to verify the rationality of the design and configuration of the system, which makes the function of the photovoltaic street lamp controller more perfect and the whole street lamp system more stable.