Inverters play an important role in photovoltaic power plants (systems). How smart is an unattended and fully automatic photovoltaic inverter? Let's sort it out today.

1. Intelligent MPPT

MPPT (Maximum Power Point Tracker) technology is the core key technology of the inverter, which refers to the ability of the inverter to track and find the maximum output power of the components (square array) in real time. The output power of photovoltaic modules is affected by various factors such as radiation and temperature, and cannot always output the nominal rated power. increase power generation.

The inverter judges the positional relationship between the current operating point and the peak point by measuring the current, voltage, and power, and intelligently adjusts the voltage (or current) at the operating point to bring it closer to the peak power point, so that the photovoltaic system always operates at the peak value near the power point.

2. Smart anti-islanding

The inverter is equipped with an anti-islanding (Anti-Islanding) protection circuit, which intelligently detects the voltage (V) and frequency (f) of the grid to be connected in real time, and compares it with the preset voltage and frequency in real time, such as If the detected actual value is within a reasonable range, the inverter is working normally; otherwise, the current will be cut off within a corresponding time according to different measured values, the output will be stopped, and a fault will be reported.

Anti-islanding and low-voltage ride-through are inherently contradictory, but in some unattended power stations or large ground power stations, there is a certain necessity and reason for their simultaneous existence. The relevant regulations of the national standard have regulations on the time of anti-islanding protection and low voltage ride-through. When the power grid fails, the island will be generated. At this time, the photovoltaic system only needs to support the time for about 1S to wait for the power grid to recover. If it has not recovered after 2S, then Can be cut out. During this process, the inverter is always in the state of detecting grid information.

3. Intelligent string monitoring

With the development of technology, the inverter has already realized intelligent string-by-string monitoring on the basis of the original MPPT monitoring. Compared with MPPT monitoring, group string monitoring monitors the voltage and current accurately to each branch string, and users can clearly view the real-time operation data of each group string. The number of component blocks in a string is inconsistent, which is clear at a glance.

4. Intelligent I-V curve scanning diagnosis

The I/V curve of photovoltaic modules refers to a corresponding relationship between the output current and output voltage of photovoltaic modules, which is expressed by researchers in the form of curves.

Once the components are shaded, damaged, or poorly connected, the I/V curves of the components and strings will change significantly.

The I/V curve of traditional test components requires special testing tools (I/V curve tester, irradiance meter and other equipment), and the strings to be tested need to be removed from the inverter and measured one by one. It takes a long time and delays power generation.

At present, mainstream high-performance inverters already have intelligent I-V curve scanning and diagnosis functions. The main implementation principles are as follows:
(1) Measure the string open circuit voltage Voc and short circuit current Isc.

(2) Measure the maximum power point voltage Vmpp and current Impp, and the peak power Pmax.

⑶ Identify photovoltaic module/array defects, shadow occlusion, dust loss of photovoltaic modules, temperature rise loss, power attenuation, series-parallel configuration loss, etc.

5. Intelligent anti-PID effect

The PID (Potential Induced Degradation) effect of photovoltaic modules refers to a situation in which the performance of modules will gradually decay after working for a long time. The direct harm of the PID effect is that a large amount of charge accumulates on the surface of the battery sheet, causing the surface of the battery to passivate, which reduces the fill factor (FF), open circuit voltage, and short circuit current of the battery module. Reduce the output power of the solar power station, reduce the power generation, and reduce the income of the photovoltaic power station.

The PID effect is easy to occur in a humid environment, and the degree of activity is positively related to the degree of humidity. At the same time, the degree of contamination of the surface of the component by conductivity, acidity, alkalinity, and objects with ions is also related to the occurrence of attenuation.

At present, the mainstream components themselves have the function of anti-PID effect. In addition, the inverter can also add this function. By raising the N-line voltage on the AC output side, the PV negative voltage is indirectly raised, so that the PV negative pole-to-ground voltage of each inverter is close to 0 or slightly higher than 0 potential to achieve the purpose of suppressing the PID effect. The data collector in the system is connected and communicated with the inverter and the external anti-PID module, automatically collects the negative pole status information of the inverter, and automatically performs lifting adjustment, thereby realizing the intelligent anti-PID function.

6. Intelligent air cooling

Heat dissipation is an important issue for inverters. Thousands of power electronic components are integrated in an inverter. If the heat dissipation is not good, it will seriously affect the output capability and service life of the inverter. The 10-degree rule of electronic devices means that for every 10°C increase in temperature, the life of the device will be reduced by half. At present, the inverter generally adopts intelligent air cooling. The inverter has an external high-performance fan, and the protection level can reach IP67. The built-in temperature sensor and driving circuit monitor the temperature of the device in real time and set an appropriate threshold. When it is detected that the temperature exceeds the threshold, the circuit will automatically drive the fan to run. After the temperature returns to normal, the drive circuit will be turned off and the fan will gradually stop running.

7. Intelligent recovery and grid connection

The reason why the inverter can realize automatic operation is because it has the function of intelligent recovery grid connection. The normal operation of the power station depends on many factors, such as string voltage, grid voltage, frequency, etc. The inverter may appear in standby or shutdown due to the lack of grid-connected output conditions. Once it detects that the operating conditions are normal, it will automatically restore the grid-connected output after self-inspection (generally 20s~5min), and there is no need for manual operations such as re-commissioning and restarting.

8. Intelligent reactive power compensation

Photovoltaic inverters only generate active power under normal power generation conditions, but in actual application scenarios, especially in industrial and commercial photovoltaic self-consumption application scenarios, the power consumed by the load includes not only active power but also reactive power. Only the active power fee is charged at the time of settlement, but the power factor will be assessed at the same time. If the power factor is lower than the requirements of the grid company, the grid company will charge a punitive power adjustment fee. In order to avoid the generation of electricity charges for power regulation, industrial and commercial owners usually use reactive power compensation devices at the load end to ensure that the power factor meets the standard.

However, as the photovoltaic power station is put into operation, the compensation capacity of the original reactive power compensation device is not enough, and an additional reactive power compensation device needs to be purchased. , Intelligently adjust the power factor and send a part of reactive power for intelligent reactive power compensation at the same time, which can help users save the cost of reactive power compensation devices, and can also reduce the power loss of reactive power compensation devices without load.

It can be seen from the above that the inverter is indeed the center and brain of the photovoltaic power station. It is precisely because of the guarantee of these intelligent functions that the photovoltaic power station can operate stably and maximize revenue.