How to prevent backflow in photovoltaics system

When photovoltaic inverters convert the direct current generated by photovoltaic modules into alternating current, they may contain direct current components and harmonics, three-phase current imbalance, output power uncertainty, etc. Currently, effective measures have not been taken to control them. Therefore, when the generated power is sent to the public power grid, it will cause harmonic pollution to the grid, which can easily cause voltage fluctuations, flicker, etc. If many such power sources transmit power to the grid, it will lead to a serious decline in the power quality of the grid. So this type of photovoltaic power generation system must be equipped with anti backflow facilities to prevent the occurrence of reverse power.

When the photovoltaic power generation exceeds the load demand, reverse power will be generated. Therefore, we need anti-backflow devices to determine if the inverter has excessive power output, and then the instruments can exchange signals with the inverter data through RS485 communication to adjust the output power of the inverter and balance it with the power consumption.

Photovoltaic backflow prevention is mainly implemented through two core processes: 

firstly, real-time monitoring, which accurately collects the power flow and real-time values between the power grid and the photovoltaic system through anti backflow meters or power sensors deployed at the grid connection point; 

Secondly, there is the intelligent regulation process. When reverse power is detected (i.e. photovoltaic output is higher than the on-site load electricity consumption, there is a risk of electricity being transmitted back to the grid), the system will instantly trigger the regulation command. The most common operation is to control the photovoltaic inverter to reduce the output power or even shut down in stages until the photovoltaic output and load electricity demand reach dynamic balance, completely eliminating reverse power; If the system is equipped with energy storage devices, it can also actively charge and consume excess photovoltaic power through the energy storage system, without reducing the normal output of photovoltaics, achieving maximum energy utilization. The core significance of implementing anti backflow protection lies in two aspects: on the one hand, based on considerations of safe operation of the power grid, to avoid voltage and frequency fluctuations caused by reverse power transmission, and to prevent islanding operation of the photovoltaic system during power outages, which poses a safety hazard of electric shock to power grid maintenance personnel; On the other hand, it is in line with policy and measurement management requirements. Most distributed photovoltaic grid connection agreements explicitly prohibit private grid reverse transmission behavior, and the grid side meters only measure the power supply from the grid to users. The reverse transmission amount usually cannot obtain reasonable benefits, and in severe cases, it may trigger the tripping of the grid protection device, affecting the normal operation of the system.

Whether it is a household low-power solar energy storage system or a commercial high-power grid connected energy storage system, their core control units (energy storage PCS and photovoltaic inverters) are real-time linked with anti backflow meters through industrial standard protocols such as 485/Modbus, building a closed-loop power control system of photovoltaic energy storage load grid. The anti backflow function is enabled by default at the factory, and users can flexibly adjust key parameters such as anti backflow power threshold and response time according to actual electricity demand and grid connection protocol requirements, adapting to different application scenarios.