[Useful and informative] Safety first - essential knowledge for selecting medium-power string inverters

The doctrine of the mean that runs through the 5,000-year history of Chinese civilization emphasizes the pursuit of perfection on the basis of balanced development. Any new technological breakthrough in photovoltaic inverters should be based on the principle of moderate advancement and the goal of balanced development. Starting from reality, a combination of new and old technologies should be adopted. From the user's perspective, maximizing benefits within the life cycle is the doctrine of the mean in inverter design and selection. After launching the two articles "Moderate Advancement" and "Balanced Development", this article will explain in detail the doctrine of the mean in inverter design - safety first.

During the operation of the photovoltaic system, due to the quality of the components, the external environment or improper installation and construction operations, components may be damaged, circuit failures and other problems may occur. Photovoltaic power stations are generally installed in the wilderness or on rooftops. The natural environment is harsh and it is inevitable to encounter natural disasters and man-made disasters, such as typhoons, snowstorms, sandstorms and other natural disasters; or encounter other damages such as human cutting of cables, rats and other animals biting off cables, etc. Therefore, the safety of the power station is very important.

String monitoring: monitors the voltage and current of each photovoltaic input component. During the operation of the photovoltaic system, component quality, external environmental influences or improper installation and construction operations may cause component damage, circuit failure and other problems.

If there is no string monitoring function, some small problems cannot be detected in the early stage and will eventually cause big problems; some problems require specialized personnel to go on-site for investigation, which takes a long time and results in large power generation losses.

The full name of PID effect (Potential Induced Degradation) is potential induced degradation. The direct harm of PID is that a large amount of charge accumulates on the surface of the battery cell, causing the surface of the battery cell to passivate, resulting in component power attenuation, reduced power generation, and reduced power station revenue of the solar power station.

By integrating the PID protection module in the inverter, the PID phenomenon of the components can be effectively avoided and the power generation loss of the power station can be reduced. At the same time, the PID module has a repair function, which can repair the components that have PID problems and restore the various index parameters of the components to normal.

DC arc detection: Fire is the biggest accident that causes economic loss in photovoltaic power plants. If the photovoltaic power plants are installed on factory buildings or rooftops, it can easily endanger personal safety. Once a fire occurs in a photovoltaic power plant, water cannot be used directly to extinguish the fire. The power supply must be cut off as quickly as possible. There are many factors that cause fire accidents in photovoltaic power plants, and DC arcing is the main cause.

Growatt has launched a circuit protection device, AFCI, whose main function is to prevent fires caused by fault arcs. It has the ability to detect and distinguish between normal arcs and fault arcs generated when the inverter is started, stopped or switched, and cut off the circuit in time after detecting a fault arc.

DC fuses are indispensable: Due to improper device selection, incorrect installation methods, or fuse quality problems, over a period of time, photovoltaic power stations have experienced frequent fuse failures on the DC side, causing certain losses to customers. In fact, these problems are not caused by the fuse itself, and there are now solutions. However, some inverter manufacturers have cancelled the DC fuse protection and instead adopted only two series-parallel connections in each MPPT and used anti-reverse diodes as overcurrent protection. This practice itself is a greater hazard.

As an overcurrent protection device, the fuse can cut off the fault circuit as quickly as possible when a short circuit occurs in the system to avoid greater losses. Photovoltaic power stations are generally installed in the wilderness or on rooftops. The natural environment in these places is harsh, and the power station will inevitably be damaged. Therefore, the protection of DC fuses in photovoltaic systems is indispensable. It is irresponsible to completely cancel DC fuse protection.

The inverter system consists of multiple MPPT input circuits. Each MPPT is connected to two strings. The photovoltaic strings are connected in parallel after passing through the Boost circuit. The front-stage Boost circuit is generally connected in parallel with a bypass element. The purpose is to bypass the Boost circuit when the voltage rises to a certain value to improve the efficiency of the system. At this time, it is equivalent to having only one MPPT, and all the front-stage circuits are connected together. If a short circuit occurs in one circuit, the voltage will drop, and the current of other strings will flow to this circuit, causing the short-circuit circuit current to expand several times. If there is no fuse protection, it will cause a fire.

The following points should be noted when designing, selecting and installing the fuse of the inverter, which can effectively reduce the impact of the fuse blowing without any fault.

(1) Fuse should be a qualified product from a regular manufacturer with a suitable rated current. If the current is too small, it is easy to misjudge, and if the current is too large, it will not provide protection.

(2) The fuse should be installed at an air inlet, where the temperature is low.

(3) The fuse is not exposed and has an arc protection cover on the outside to prevent the fuse from generating arcs and catching fire

Shenzhen Growatt New Energy Co., Ltd. was established in May 2010 with a registered capital of RMB 100 million. It is a national high-tech enterprise specializing in providing new energy system solutions such as photovoltaic inverters, energy storage systems, and home smart energy management systems. Since its establishment, Growatt inverters have been exported to more than 100 countries and regions in six continents, including Europe, America, Australia, Asia, Africa, and Latin America, and have been recognized and favored by global customers. Growatt has always maintained its leading position in the Chinese home inverter market and has been committed to becoming the world's largest user-side smart energy solution provider.