How to reduce (or eliminate) the maintenance of inverters

The photovoltaic inverter is the core equipment for energy conversion in photovoltaic power stations. It is responsible for converting the DC power of photovoltaic modules into AC power and incorporating it into the public grid. It also serves as the information collection center of the entire power station, acting as the "ears", "eyes" and "nose" of the power station. For such an important device, the owner certainly hopes that there will be as few problems as possible, and it would be best if it never needs maintenance after installation. To achieve this goal, we need to have a deeper understanding of the inverter and understand which characteristics of the inverter will cause failures and generate operation and maintenance. The author summarizes how to make the inverter less (free) in operation and maintenance, and believes that three factors should be considered: inverter selection, system design and on-site application environment.

1. Model selection

The standard warranty period for string inverters is 5 years. To ensure that the inverter does not fail due to its own reasons within 5 years, the following aspects should be paid attention to:

1. Outdoor application considerations

The protection level must be IP65 or above. The larger the number, the better. The larger the number, the better the protection performance.

The casing processing technology is divided into traditional sheet metal technology and die-casting technology, and the die-casting technology is superior to the sheet metal technology.

In terms of shell material, aluminum shell is better than iron shell.

(II) Maintenance-free design considerations

The inverter should avoid using vulnerable and consumable parts as much as possible. Common vulnerable parts are:

l Fan: Self-failure, loud noise, causing derating, regular maintenance is required.

lDC fuse: self-failure, increased losses, and fire.

lLCD screen: faulty.

lButton: Self-fault.

Based on this aspect, a more reliable inverter should adopt natural cooling, no DC fuse, and use Bluetooth, radio frequency and other methods to replace LCD screen and buttons. There are not many inverter manufacturers in the market that follow the above design considerations, and currently there are only a few manufacturers such as Huawei, Sungrow, and Shengnengjie.

(III) Considerations for component selection

l As a power electronic product, the inverter is composed of numerous electronic components. The reliability of the components directly determines the reliability of the inverter and is the cornerstone of the inverter's reliability. Well-known brands in the industry must be selected.

l Components that affect the service life of the product should be examined in detail, such as electrolytic capacitors, film capacitors, IGBTs, relays, connectors, spoiler fans, etc.

l Avoid using easily damaged and consumable parts as much as possible.

The following are suggestions for the selection of components:

(IV) AC and DC voltage adaptability considerations

The string inverter is located between the photovoltaic panels and the public power grid, and plays the role of power conversion. The front end must adapt to the DC input voltage of the components, and the back end must adapt to the AC reference voltage of the power grid. Only when both sides are adapted can the machine work normally. If either side is not adapted, the machine will report a fault and fail to work.

DC voltage adaptability considerations

1. The lower the DC starting voltage value, the stronger the adaptability

2. The wider the DC voltage range, the stronger the adaptability

AC voltage adaptability considerations

1. The wider the AC voltage range, the stronger the adaptability

2. Current harmonic THDI: <3%, the smaller the better

3. Output current DC component value: <0.5%ln, the smaller the better

4. Power factor: Normal PF=1, the wider the adjustable range, the better

2. System Design

Paying attention to the above matters regarding inverter selection can only ensure that the inverter's own reliability and adaptability are OK, and only solve "its own" problems. As one of the electrical equipment in the photovoltaic system, the inverter must be designed and applied in conjunction with the entire system. Whether it can work normally is not only due to its own reasons but also closely related to the system design and application environment. If the system design and on-site construction are not standardized, "external" factors that exceed the normal working conditions of the inverter will be introduced, causing the inverter to fail to operate normally, resulting in operation and maintenance. Regarding the precautions for optimizing the design of photovoltaic systems, the author has specifically discussed them in previous articles, so I will not repeat them here. Interested friends can look through the previous article "Precautions for Optimizing the Design of Photovoltaic Systems".

3. On-site application environment

1. Consideration of the natural environment

Recommended installation positions for string inverters:

1. Install the inverter as close as possible to avoid long-distance routing of DC cables.

2. Try to install it on the bracket below the component, under the eaves, or on the outer wall (it is recommended to install a sunshade cover on the top) to avoid excessive external ring temperature causing machine derating or even shutdown.

(II) Electrical environment considerations

1. The grid voltage should remain stable. For power consumption areas with weak rural grids or strong inductive loads in factories, you can contact the manufacturer to appropriately relax the inverter output voltage range to avoid machine shutdown due to overvoltage or undervoltage faults.

2. The distance from the inverter to the grid connection point should be as short as possible. If there are objective reasons for long-distance wiring, it is necessary to pay attention to the inverter output voltage being increased by the cable voltage, resulting in overvoltage and disconnection from the grid. You can also contact the manufacturer to appropriately relax the inverter output voltage range.

3. The number of inverters connected in parallel should not be too many. It is better to have a certain load usage in the same grid-connected point. Too many inverters connected in parallel at one grid-connected point can easily cause harmonic interference, leading to system instability and affecting the normal operation of the machine.

There are many factors that affect the normal operation of string inverters. The above are some factors that need to be considered for the normal operation of the inverter, which I analyzed from three aspects: the inverter itself, system design and application environment. Only by taking all these factors into consideration can we ensure the normal operation of the inverter for a long time and avoid unnecessary operation and maintenance investment.

About Shenzhen Shengnengjie Technology Co., Ltd.

Shenzhen Shengnengjie Technology Co., Ltd. focuses on the research and development, production, sales and service of photovoltaic inverter products. Relying on the strong supply chain and production strength of the parent company of the group, Asia Power Technology Co., Ltd., it brings together the top R&D talents in the industry at home and abroad, as well as senior marketing, product and sales teams. Adhering to the corporate spirit of "professionalism, integrity, innovation and win-win", it takes Shenzhen as the starting point, faces China and goes to the world. Shengnengjie's Shenzhen production base is equipped with highly automated production equipment, and its manufacturing capacity and production capacity are at the forefront of the industry, and it has been awarded the title of National High-tech Enterprise. ?

As the holding parent company of Shengnengjie Technology, Asian Power Devices Co., Ltd. is a world-renowned power electronics product design and manufacturing company with sales of approximately US$300 million in 2017. It ranks first in the world in the external power adapter market for network communications, printers, and storage devices. At the same time, it has been marketing its PrimeVOLT brand photovoltaic inverters in Taiwan, Europe and the United States for more than ten years, and has the second largest market share in Taiwan.