Discussion on the application and control strategy

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Discussion on the application and control strategy of independent photovoltaic system

Abstract: This paper analyzes the application of independent photovoltaic system in solving the power supply problems of border Island troops and the construction of Ecological Barracks, discusses the main problems of independent photovoltaic system, analyzes the current situation of energy control strategy and battery grouping control strategy, gives grouping principles, and studies the structure and principle of control circuit. Practice has proved that grouping charge and discharge has certain practical significance for improving power supply reliability and prolonging battery life

key words: photovoltaic system grouping strategy in solar Ecological Barracks

I. Introduction

in recent years, with the continuous intensification of environmental pollution and the continuous improvement of environmental awareness, people pay more and more attention to energy and environmental issues. The development and application of new energy have achieved rapid development, among which solar energy is the most widely used in military and civilian areas. Solar power generation has played a great role in solving the power supply problems of Companies in remote mountainous areas and border islands. Especially after the headquarters put forward the requirement of building "Ecological Barracks", solar energy has also played an important role in the construction of "Ecological Barracks" of the army, mainly photovoltaic power generation systems and solar water heating systems, including solar landscape lights, solar street lights, solar power generation systems, solar water heaters Solar desalination systems have been widely used

through extensive research on the application of photovoltaic system in the army, analyzing and sorting out data and suggestions, we get three enlightenments: first, photovoltaic system will be more and more widely used in the army, mainly to solve the power supply in remote camps, and other forms of applications are developing rapidly; Second, the energy control strategy in the independent photovoltaic system is too simple, and there is no specific design according to the capacity of the system, resulting in low efficiency of energy utilization, easy failure of energy storage batteries, and high operating costs; Third, the implementation of grouping charging and discharging of energy storage system can effectively improve the reliability of power supply

this paper will study and analyze the application of independent photovoltaic system in military barracks, and study the energy control strategy of the system, and propose a grouping charge and discharge control strategy, which provides a good reference for solving the problems existing in the application of photovoltaic system

II. Application of photovoltaic system in military barracks

with the continuous development of science and technology, the war now puts forward higher requirements for the support of logistics power, requiring us to expand a variety of power supply channels and study a variety of power supply support methods to meet the power supply requirements under various complex conditions; At the same time, due to the continuous improvement of social living standards, officers and soldiers also have higher requirements for the living environment. Environmental friendly and green military barracks can better create a positive and healthy lifestyle, and stimulate the awareness of officers and soldiers to love their posts and work hard. As a kind of green energy, solar energy meets the above requirements. As a clean, environment-friendly and green energy, solar energy plays an increasingly important role in military construction. Through the application research of photovoltaic system, the main application and significance of photovoltaic power generation in the military are as follows:

1. It solves the problem of power supply guarantee for border defense and Island companies. Many companies stationed in border defense and islands, as well as many army barracks far away from the power grid, basically have the problem of difficult power supply. Before engineering plastics are mainly divided into general-purpose and special types, their power consumption is mainly solved by self-contained generators (sets). Obviously, this scheme has the disadvantages of high power generation cost, high noise, environmental pollution and high fuel transportation cost. With the continuous development of new energy technology, it has become more and more important to improve the power supply conditions of these troops in peacetime and wartime, among which the independent photovoltaic power generation system and small-scale wind power generation system are the most widely used. Building a small independent photovoltaic power station can not only solve the problem of power supply, but also reduce the cost of transporting fuel oil and reduce the dependence on fuel oil

2. Power supply for outdoor independent work stations. For all kinds of outdoor independent working equipment such as microwave relay stations, outdoor detection points and navigation lighthouses, they are often far away from electricity, and the extension power supply of electricity is difficult. Photovoltaic system can well solve the power supply problem of such outdoor working stations

3. It is widely used in the construction of "Ecological Barracks" in the army. The reconstruction and construction of military barracks are aimed at Ecological Barracks, environmental protection barracks and green barracks. Generally, the demonstration of new energy projects will be carried out according to the natural environmental conditions of the barracks, mainly including solar street lamps, solar landscape lamps, photovoltaic power generation systems, wind power generation, etc., of which solar landscape lamps are the most widely used

4. it provides ideas for exploring new methods of logistics power supply support. Expand various power supply channels and study various power supply modes. Photovoltaic power generation system provides ideas for exploring new methods of logistics power supply guarantee at this stage. For example, the comprehensive application of thin-film solar cells and new energy storage devices (super capacitors) is of great significance to develop small capacity mobile solar power generation devices. At present, small solar digital chargers have been used in charging, digital cameras and notebooks, and become the first choice of auxiliary standby power supply for outdoor digital products

5. it provides a good reference for the development of other new energy systems. The investment and construction of photovoltaic power generation system has a good reference for the development and application of other multi energy sources, and can also continuously improve the awareness of environmental protection and resource conservation of officers and soldiers. At the same time, it can also provide a good application reference for the development and application of other new energy systems, such as wind solar complementary system

III. application analysis of independent photovoltaic system

1. main problems faced by independent photovoltaic system

the structural block diagram of a typical independent photovoltaic power generation system is shown in Figure 1, including solar array, dc/dc converter, controller, battery and inverter for AC load. The dotted line shows the alternative structure, which is selected when there is AC load. According to the voltage design requirements of the system, select the appropriate dc/dc conversion circuit, and can track the maximum power point to achieve load matching. The core component of the photovoltaic system is the controller, which has two main functions: first, to prevent the battery from overcharging and discharging, and to comprehensively monitor, manage, control and protect the power supply system; The second is to realize the energy control strategy of the system and control the operation of dc/dc conversion circuit [1]

at present, the independent photovoltaic power generation system faces the following two problems: first, the energy density is not high, the overall utilization efficiency is low, and the investment in the early stage is large; Second, the energy storage device of the independent power generation system is generally dominated by lead-acid batteries, whose cost accounts for about 25% of the initial equipment cost of the photovoltaic power station. However, the charging and discharging control of the batteries is relatively simple, which is easy to cause the batteries to fail in advance, increasing the operation cost of the system [2]. The battery accounts for 43% of the investment cost in the 20-year operation cycle. Most batteries cannot reach the designed service life. In addition to the defects of the battery itself and the inadequate management and maintenance, the unreasonable operation and management of the battery is an important reason for the premature failure of the battery [3]. Therefore, for independent power generation systems, improving energy utilization and studying scientific system energy control strategies can reduce the investment cost of independent photovoltaic systems

2. Analysis of the current situation of control strategy

in the development process of solar photovoltaic system, from direct connection to the application of electric energy converter, microprocessor and computer monitoring integrated control system, especially with the rapid development of microprocessor technology and power electronics technology, the efficiency of energy utilization is gradually improved. According to the relatively typical literature published at home and abroad in recent years [], it mainly studies the charging and discharging control strategy and energy management of photovoltaic system, among which there are many independent studies in the three aspects of battery charging and discharging control, power tracking control and controller design. The main problems are as follows: (1) the cooperative control relationship between the power tracking of photovoltaic modules and the battery charge state is simple, The commonly used phased control strategy needs to be improved; (2) There is a lack of detailed design for the grouping charge and discharge management of batteries; (3) There is no published comprehensive energy control strategy among the charge and discharge control, power tracking control and controller design of independent photovoltaic system batteries

this paper analyzes and studies the second problem raised above, mainly from the application of independent photovoltaic system in military camp power supply, and discusses the principle and control of grouping. The loads in the actual system are divided into important loads and general loads. The important loads have high requirements for the reliability of power supply, and the grouping charge and discharge strategy of battery has great practical significance for power load grading power supply

IV. analysis of grouping charge and discharge control strategy

1. proposal of grouping strategy

in order to strengthen the charge and discharge management of batteries and improve the reliability of power supply to loads, the batteries in photovoltaic system can be grouped and managed to turn into multiple battery packs with small capacity, mainly for the following reasons:

(1) improve the charging current and effectively use the energy of solar arrays, Reduce the adverse effects of long-term small current discharge and small current charging on the battery, and avoid large crystallization caused by small current discharge

(2) the battery has a strong ability to receive current after high current discharge, so grouping can appropriately increase the charging efficiency

(3) grouping can realize the maintenance charging of the battery pack, and the maintenance balanced charging of the battery can be carried out under the conditions of light conditions and battery capacity. Proper overcharge can avoid the stratification of battery electrolyte

(4) it can not only realize charging, but also discharge important loads that need to be guaranteed during the day

2. principle of grouping management

the design capacity of the whole system should be considered for battery grouping, and the relationship between the maximum output current of photovoltaic array under the maximum solar radiation mainly applicable to raw material particles passing through the grid and block material passing through the grid and the maximum chargeable current of battery group should be comprehensively considered. The main principles of grouping are as follows:

(1) the maximum output current of system photovoltaic array should be less than the maximum chargeable current of battery group. The acceptable charging current is slightly larger than the maximum output current of the array in terms of the charging reception capacity of the battery at a low state of charge

(2) grouping should consider the size of the load in the system. The discharge current is near the discharge rate specified by the manufacturer, and it is appropriate that the discharge capacity of a working day accounts for about 20% of the capacity of the battery group

(3) grouping should consider the design and implementation of the control system. It should not be too many. Generally, it should not exceed 3 groups, and 2~3 groups are appropriate

3. Structure analysis of grouping control circuit

taking two groups as an example, the control strategy is as follows: first predict the capacity, charge the battery group with small capacity first, and allow the other group to discharge at the same time; Judge the change of the capacity of the two groups. When the difference between the two groups reaches more than 30%, switch the charging and discharging (or static) states; Combine the control strategy of the system to achieve the purpose of balanced charge and discharge. At the same time, when the charge state of the system is low, the low charge state prompt should be output, combined with the load

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