Circuit protection design in small solar photovoltaic power generation systems

　　With the increasing shortage of energy and the increasing pressure on environmental protection, humans are relying more on renewable energy. The development and utilization of solar energy has become the most promising, rewarding and readily available technology. Among them, solar power generation is the direct conversion and utilization of solar energy.

　　Solar cells use the photovoltaic effect of semiconductor devices to convert solar radiation energy into electrical energy, which is then utilized or stored through the conversion of electronic technology. The main components of the solar battery system are solar cells, batteries, controllers and inverters. The structural block diagram is shown in Figure 1. Solar power generation systems are divided into independent solar photovoltaic power generation systems and grid-connected solar photovoltaic power generation systems. Independent solar photovoltaic power generation refers to a power generation method in which solar photovoltaic power generation is not connected to the power grid. A typical feature is that batteries are required to store energy used at night. Independent solar photovoltaic power generation is mainly used in remote villages in the civil scope, such as home systems and village-level solar photovoltaic power stations; in the industrial scope, it is mainly used in telecommunications, satellite radio and television, solar water pumps, and in areas with wind power generation and small hydropower It can also form a hybrid power generation system, such as wind power generation/solar power generation complementary system, etc.

　　Lightning protection for small solar photovoltaic power generation systems

　　Since solar panels are located outdoors, they are usually set up in open areas or high places to ensure sunlight. According to the IEC61000-4-5 electrical environment classification, its power connection lines belong to Class 4 electrical environment, that is, the interconnection lines are laid along the power cables as outdoor cables and these cables are used as electronic and electrical circuits. According to IEC's lightning protection requirements for Class 4 electrical systems, the power input part of the solar power generation system needs to be lightning protected, including the AC power input circuit, charge and discharge circuit, and inverter circuit. The protection level is designed based on the requirements of 2KV between lines and 4KV between lines and ground. The form of protection may require one or more levels of protection based on different circuit locations. Due to the harsh working environment of solar power generation systems, long maintenance cycles, unattended operations, high service life requirements and other special requirements, it is necessary to consider the surge capacity of overvoltage protection devices in the design of overvoltage protection solutions. In addition, the working life and anti-aging capabilities of the entire protection solution need to be evaluated; if necessary, the 6KV protection level should be adopted.

　　Each solar panel cable in the solar power generation system is first connected to the combiner box of the solar system controller. Therefore, the overvoltage protection design shown in Figure 2 should be used at the input end of the combiner box and controller. Among them, A, B and C are overvoltage protection devices. For systems and equipment with higher voltage and high reliability requirements, a gas discharge tube (GDT) and a varistor (MOV) should be used in series as protection devices at positions A, B, and C to complete the lightning protection of outdoor cables. For low-power systems with voltages lower than 48VDC, GDT can be used directly for overvoltage protection. Considering the failure mode of overvoltage protection devices, overcurrent protection devices are required to cooperate with the protection. In unattended or difficult-to-maintain situations, self-recoverable overcurrent protection devices should be used. Tyco Electronics Circuit Protection Department has a variety of protection solutions for this type of lightning protection based on different application environments and protection requirements.

　　The above solution can also be used for lightning protection for the DC load of the solar power generation system. For lightning protection of AC loads (that is, the output end of the inverter), the protection circuit design shown in Figure 3 needs to be used. Tyco Electronics' circuit protection department also has profound experience and diverse solutions.

　　Figure 3 Solar power generation system AC load lightning protection circuit

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