The solar power generation system mainly includes: solar battery components (arrays), controllers, batteries, inverters, and users, ie, lighting loads. Among them, the solar battery module and the battery are the power supply system, the controller and the inverter are the control protection systems, and the load is the system terminal.
Solar power system
The solar battery and the battery constitute the power supply unit of the system, so the battery performance directly affects the system operating characteristics.
(1) Battery unit:
Due to technical and material reasons, the amount of electricity generated by a single battery is very limited. In practice, a solar battery is a battery system in which a single battery is composed of strings and parallels, and is called a battery module (array). The single cell is a silicon crystal diode. According to the electronic characteristics of the semiconductor material, when the sun shines on the pn junction made of p-type and n-type homogenous semiconductor materials of different conductivity types, under certain conditions Solar radiation is absorbed by the semiconductor material, resulting in non-equilibrium carriers, electrons and holes, in the conduction band and valence band. Similar to the PN junction barrier region, there is a strong built-in electrostatic field, so that the current density J, the short-circuit current Isc, and the open-circuit voltage Uoc can be formed under illumination. If the electrodes are drawn on both sides of the built-in electric field and connected to the load, theoretically, the circuit formed by the PN junction, the connecting circuit, and the load will have a "photocurrent" flowing therethrough, and the solar cell module will realize a power P to the load. Output.
Theoretical research shows that the peak power Pk of a solar cell module is determined by the local average solar radiation intensity and the end-use electrical load (electricity demand).
(2) Electrical energy storage unit:
The direct current generated by solar cells enters the battery first, and the characteristics of the battery affect the efficiency and characteristics of the system. The battery technology is very mature, but its capacity is affected by the amount of power required at the end of the day and the duration of the sunshine (power generation time). Therefore, the battery watt-hour capacity and ampere-hour capacity are determined by the predetermined continuous no-sunlight time.
Controller
The main function of the controller is to make the solar power system always in the vicinity of the maximum power point of power generation in order to obtain the highest efficiency. The charge control usually adopts pulse width modulation technology, ie, PWM control mode, so that the entire system always runs in the area near the maximum power point Pm. Discharge control mainly refers to the lack of electricity in the battery, system failure, such as the battery open or reversed switch off. Currently, Hitachi has developed a "sunflower" type controller that can both track the control point Pm and track the sun's movement parameters, which increases the efficiency of fixed battery modules by about 50%.
DC-AC inverter:
The inverter can be divided into self-excited oscillation inverter and he-excited oscillation inverter according to the excitation method. The main function is to reverse the direct current of the battery into alternating current. Through a full-bridge circuit, SPWM processors are generally used to modulate, filter, boost, etc., to obtain sinusoidal alternating-current power supply system end users that match the lighting load frequency f and rated voltage UN.
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