Rather than home solar power system, modular inverters are mainly used in photovoltaic power station projects with large power generation capacity. They are an alternative to centralized and string inverters.

The advancement of modular inverter is mainly reflected in its use of a combination method of multiple string to multiple inverter. When a single inverter module fails, other modules can quickly fill in, which avoids the waste of power generated by some photovoltaic power sources due to the failure of a single inverter module.

This article will introduce you to the advantages of modular inverter in detail, and also the technical difficulties and barriers to build a proper modular inverter.



1. Advantages of modular inverter

① Reliability

Modular inverter has certain advantages in terms of reliability compared to centralized and string inverter. When the power module of a traditional centralized or string inverter fails, it will cause the system to shut down, causing the corresponding system to lose all power generation. When a single inverter module fails in a modular inverter, the system will remove the faulty module from the system, and the rest will operate normally without the system shutting down, which will only cause a slight decrease in the rated peak power of the system.


Based on the specific conditions of daily sunshine, the photovoltaic power generation system only approaches the rated peak power for a small amount of time in a day. Therefore, a photovoltaic system equipped with a modular inverter will hardly cause a large power generation loss due to the failure of a single power module.

The distributed power conversion architecture composed of modular inverter can significantly enhance the reliability of the system. The modules have strong complementary capabilities when faults occur, which can effectively avoid the cut off of some photovoltaic power sources when a single module fails.


② Flexibility

The flexibility of modular inverter is similar to that of string inverters, and both have significantly improved flexibility compared to centralized inverters. Centralized inverters generally only use a single MPPI (maximum power point tracking). When coordinating different photovoltaic power sources at the same time, it is difficult to ensure that each photovoltaic power source is in the best working condition.

A single module or a single module group of a modular inverter can use one MPPT (correspondingly, a single string or a single string group of a string inverter can use one MPPT). Therefore, for photovoltaics with different orientations, the power supplies can be adjusted using different MPPTs to ensure the flexibility of the overall maximum power point tracking of the system.

The flexibility of modular inverter is mainly reflected in the fact that it has more MPPTs than centralized inverter, so they can flexibly allocate the power points of photovoltaic power sources in different directions in relatively complex terrain, improving the overall power generation efficiency.

In addition, the models of centralized inverters are relatively fixed, and the power differences between different models range from tens of kW to hundreds of kW. Modular and string inverters can more accurately match the appropriate power levels for different scales of photovoltaic power sources, and are therefore more flexible in precise adaptation to different scenarios. A schematic diagram of the modular inverter flexibility is shown in the figure below:


③ Easy maintenance

The easy maintenance of modular inverter is mainly reflected in the complementary structure between modules, which enables rapid replacement when a single module fails. The single-point failure rate of the power module of the modular inverter system is extremely low, so the timeliness requirements for maintenance are lower, the operation and maintenance is less difficult, and the operation and maintenance cost is saved.

In addition, the modular inverter supports rapid replacement within 5 minutes, and its inverter failure will hardly cause a loss of power generation. Correspondingly, the maintenance time for string inverters ranges from several hours to one day, and the maintenance time for centralized inverters ranges from one day to several days. So we can see that modular inverters are easier to maintain.

2. Disadvantages of modular inverters

Since the topology structure and control algorithm of modular inverter are more complex than string and centralized inverter, their price per watt is generally higher than that of string and centralized inverter.


3. Technical difficulties and barriers of modular inverter

The core difficulty for global top 10 best solar inverter brands to deal with modular inverter lies in the capability of coordinated decision-making and synchronous execution required to achieve the system architecture of multiple string to multiple inverter module.

  • Coordinated decision-making means that after multiple inverter modules are connected in parallel, the decision-making instructions used to adjust the operating status of each module will affect the operating status of other modules at the same time. Therefore, the execution sequence and specific parameters of the instructions need to be systematically considered;
  • Synchronous execution means that the execution of instructions to adjust the operating status of each module needs to occur at the same time, thereby avoiding time differences in the execution of the adjustment instructions that may cause current inequality, current distortion, poor power quality, or even equipment damage between modules.

Coordinated decision-making

Each inverter module is equipped with a series of complex dynamic algorithms that adjust the working state according to the environment, such as maximum power point tracking, islanding detection, and grid fluctuation ride-through, etc., which can ensure that each module always runs at the best amidst continuous changes in the external environment.

However, since the modules are connected in parallel, the dynamic algorithm instructions of a single module will affect other modules. Therefore, on the basis of its own dynamic algorithm, the central processor is also required to coordinate and communicate the operation results of different modules to ensure a single module adjustment instructions (such as changes in the operating points of certain modules, or even the input or removal of certain modules) will not adversely affect the operation of other modules. The module control diagram is as follows:


Synchronous execution

Synchronous execution is one of the key technologies that modular inverter needs to solve. Since photovoltaic power sources are always in a continuously changing external environment (such as light and temperature), modular inverters need to quickly adjust the operating status of each module according to changes in the external environment.

During the adjustment process, different modules must be able to synchronously execute the corresponding instructions for their respective status changes. If different modules execute instructions at different times, the synchronization conditions will not be fully achieved, and the outputs of multiple modules will have a greater mutual impact, which may lead to:

  • The currents output by multiple modules are not equal (i.e. uneven current state), affecting the performance and life of the equipment;
  • The current waveforms output by multiple modules are distorted, affecting power quality;
  • Resonance may even form between modules, causing serious failure or even shutdown damage.

In addition, since the output of the modular inverter is the sine wave of the power grid, there are many electrical parameters that need to be synchronized, including voltage, frequency, inverter waveform, phase and phase sequence, etc., which also greatly increases the difficulty of synchronization.


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