Selection and maintenance of photovoltaic grid-connected inverters

1. Classification

Photovoltaic grid-connected inverter is a special device that converts the DC power generated by the photovoltaic effect (solar energy converted into electrical energy) of the photovoltaic array (photovoltaic cells/modules) into AC power and then connects it to the public power grid. Different from conventional inverter products, it can follow the changes in sunshine conditions to the greatest extent and maintain the best power conversion efficiency and power output characteristics. It can be divided into three categories: photovoltaic grid-connected micro-inverter, string inverter and centralized inverter. The application range covers large-scale ground photovoltaic power stations, wind-solar complementary street lighting, household rooftop photovoltaic power generation, photovoltaic agricultural irrigation and other fields. There are many product styles, which can be divided into indoor and outdoor products. To cope with different application environments, the product appearance varies. At the same time, its output power ranges from tens of watts to hundreds of kilowatts, or even megawatts, to meet different application needs.

2. Purchase

Photovoltaic grid-connected inverter is one of the essential core components in photovoltaic power generation applications. The efficiency of a single photovoltaic power generation project and the amount of annual power generation depend on this product. It is also the core component for the safe operation of photovoltaic power generation. Consumers (users) can choose products of different power levels and types according to different functions, which can meet the needs of household power generation, industrial and commercial distributed power generation, and dedicated photovoltaic power station power generation of power production enterprises.

When purchasing a photovoltaic grid-connected inverter, you should first pay attention to the labels on the packaging box and the product, and identify the photovoltaic grid-connected inverter's input voltage range, voltage type, maximum input current; output voltage level, voltage type, frequency; maximum continuous working current, maximum output power, and inverter efficiency, etc. Secondly, you should check that the random information of the product is complete, and the random information should at least include the following: detailed product introduction (including technical parameter description), product installation instructions, operation instructions and maintenance instructions, etc.

As a general industrial product, non-professionals are advised to use photovoltaic grid-connected inverters under the guidance of professional technicians. After purchasing the product, non-professionals need to carefully read the product manual and other accompanying documents, and install and use it strictly in accordance with the requirements of the accompanying documents. If there are any questions, they need to contact the manufacturer or manufacturer to ensure correct installation and use.

When purchasing imported products, you need to pay attention to whether the foreign products declare that they are applicable to the requirements of domestic standards. The current effective product standard in China is NB/T32004-2013 "Technical Specifications for Photovoltaic Grid-connected Inverters". In particular, you need to pay attention to the fact that the output voltage and frequency of foreign products should match the domestic public power grid point to which the product is connected. In addition, you need to pay attention to the fact that the over-voltage and under-voltage protection requirements implemented by foreign products are significantly different from domestic standards. When using foreign products, it will cause the product to malfunction or refuse to operate, posing a huge safety hazard. It is not recommended for non-professionals to purchase imported products.

When professionals purchase photovoltaic grid-connected inverters, in addition to paying attention to the maximum conversion efficiency marked on the product nameplate, they also need to pay attention to the maximum power point tracking efficiency of the product, as well as the power quality of the product when it is running at medium and low power (50% rated output power and below) (such as output harmonics, DC components, etc.), and its over/undervoltage protection parameters. And differentiate the purchase and use of products according to different use environments, such as: household products need to pay attention to the electromagnetic compatibility and noise indicators of the product; products used in high-altitude areas (the applicable altitude of conventional products does not exceed 1,000 meters) need to pay attention to capacity reduction; products used in extremely low and high temperature areas (the temperature range of conventional products is -25℃～+60℃) need to pay attention to the climate and environmental adaptability of the product, leaving enough safety margin for normal use of the product.

3. Maintenance

The service life of photovoltaic grid-connected inverters generally ranges from 10 to 20 years, and the quality levels of the products vary. If they are not used and maintained properly, the life of the photovoltaic grid-connected inverters will be seriously shortened, and even bring huge safety hazards.

First, professionals must determine the technical parameters of the products to be purchased based on usage requirements, and then they must be installed by professional technicians. Only after approval and acceptance by the local power department can the product be connected to the power grid and put into use.

During daily use, the input and output terminals of the product should be checked regularly. The connection should be firm, the input and output wires and cables should not be aged or damaged, and the grounding wire should be firm and not broken or detached. If any problems are found, a professional should be asked to replace it. Do not remove the input and output terminals at will. Dangerous voltage is generated at the input terminals during the day, and the output terminals are always energized before being disconnected from the power grid. The live parts of the terminals should be avoided from being exposed and not touched by people.

In daily use, if you find that the inverter is operating faulty, you should immediately disconnect the protection switch from the grid and ask professionals to troubleshoot the fault before turning on the inverter again.

Before any maintenance work is performed, the electrical connection between the photovoltaic grid-connected inverter and the grid should be disconnected first, and then the DC side electrical connection should be disconnected. Wait for at least 5 minutes until the internal components are fully discharged before performing maintenance work. Maintenance operations should be completed by professional technicians.

Non-professionals should not disassemble the product casing. Professionals should comply with the warning signs on the product during maintenance, wear anti-static gloves, avoid unnecessary contact with circuit boards, and be careful not to directly touch the inverter's power components and heat dissipation devices with bare hands. The product will still have a high temperature for a period of time after power failure, so avoid burns.

In daily use of the product, you can regularly use a clean, soft, dry cloth to clean the product surface and dust accumulation at the air inlet and outlet to maintain good heat dissipation of the product and keep the product in a well-ventilated environment. It is not recommended for non-technical professionals to perform maintenance on the product after removing the outer shell.