Solar inverters come in a wide variety of types, which can be categorized by type (centralized, string, micro) or end-use application scenarios (residential, commercial, utility). Currently, string inverters are the most widely used due to their high flexibility and ease of installation. With the continuous iteration and upgrading of power devices, the power level and power density of individual inverters continue to increase, while their unit price and size continue to decrease, making them the mainstream products in the solar inverter market.

Centralized solar inverters are typically employed in utility-scale power plants and boast immense capacity. However, due to constraints on installation locations, their newly installed capacity has been surpassed by string solar inverters in recent years. Micro solar inverters are primarily utilized for residential power generation, while also extensively serving urban infrastructure power supply, such as street lights, traffic signals, and other scenarios.

The core of a solar inverter lies in its power conversion section, specifically comprising a DC-DC boost converter and a DC-AC inverter. With the continuous advancement of power devices and the emergence of new demands from end products, numerous novel topology structures have emerged. A deep understanding of these topology structures and power products aids in a more thorough comprehension of the entire system and facilitates rapid design.

Block diagram - Photovoltaic inverter

The block diagram below illustrates the photovoltaic inverter solution crafted by ON Semiconductor. This diagram showcases the power management and power conversion technologies employed in the photovoltaic inverter. ON Semiconductor offers a comprehensive range of products, encompassing discrete silicon carbide (SiC) devices, insulated gate bipolar transistors (IGBTs), power modules, isolated gate drivers, and power management controllers, all of which contribute to achieving higher power density and efficiency in the system.

image.png 

Market information and trends

Silicon carbide substitutes

Silicon carbide (SiC) contributes to providing higher efficiency to advance current technology trends. Compared to traditional silicon-based MOSFETs/IGBTs, SiC devices exhibit particularly prominent advantages in high-voltage scenarios: high-voltage devices can simplify the topology structure, eliminating the need for multilevel converters; SiC inverter solutions exhibit lower losses than IGBT solutions; meanwhile, SiC MOSFETs have faster switching speeds, enabling the reduction in the size of passive devices, especially inductors. These two factors jointly enhance power density, allowing devices of the same size and weight to achieve higher power output.

However, in practical applications, it is necessary to strike a balance between cost and performance, and select the most suitable solution based on specific needs.

IGBT and SiC diode

The application of SiC diode alternatives is becoming increasingly prevalent, especially in DC-DC conversion stages, for three reasons: firstly, the cost has been reduced to a reasonable level; secondly, there is no need for significant modifications to circuit design; and thirdly, and most importantly, it can significantly enhance system performance. Furthermore, the increase in operating frequency can also reduce the size of passive components.

In high-power products (above approximately 200kW), IGBT remains the preferred choice. On the one hand, IGBT performs excellently in high-current scenarios, and such systems do not require high operating switching frequencies, so the slow turn-off speed of IGBT does not pose a significant impact. On the other hand, a fully SiC system requires a completely new design and is costly. For example, IGBT-based converter drive circuits are not compatible with SiC systems; since SiC components have a shorter short-circuit withstand time (SCWT) than IGBTs, protection schemes also need to be redesigned.

Higher bus voltage

The demand for high power continues to grow. Under the same power conditions, replacing 1100V strings with 1500V strings can reduce interconnection costs due to lower current. To comply with such trends, switching devices with higher voltage levels have emerged. Whether choosing high-voltage switching devices or adopting multi-level topology structures, both can significantly increase the operating power of photovoltaic inverters. For a detailed comparison between 1500V inverters and 1100V inverters, please refer to the following text.

image.png 

Table 1: Comparison between 1500V (Model-2) and 1100V Photovoltaic Inverters

Utility-level solution

300 kW+ Photovoltaic String Inverter - Utility-Grade Solution

ON Semiconductor has released a new Si/SiC hybrid power integrated module (PIM) in an F5BP package, which can increase the power output of utility-scale photovoltaic (PV) string inverters and energy storage systems by 15%. These modules enhance power density and efficiency, allowing the power of PV inverters to increase from 300kW to 350kW. This means that for a 1 GW PV power plant, nearly 2 MW of additional power can be saved per hour. Furthermore, the new modules, with their higher power density and efficiency, reduce the number of modules required, thereby lowering component costs by over 25%.

This series of modules integrates advanced components, including 1050V FS7 IGBTs and 1200V D3 EliteSiC diodes. Compared to previous generations, the power loss has been reduced by up to 8%, and the switching loss has been reduced by 15%. These PIM modules employ an innovative I-NPC topology in the inverter section and a flying capacitor topology in the boost section. Additionally, they utilize advanced direct bonded copper (DBC) substrates, which significantly reduce stray inductance and thermal resistance. This design reduces the thermal resistance of the heat sink by 9.3%, helping to maintain lower operating temperatures under high loads, thereby enhancing overall reliability.

image.png 

Figure 1: Schematic diagram of a 300 kW+ photovoltaic string inverter

image.png 

Figure 2: Thermal properties of F5BP and F5

Si/SiC hybrid module, F5BP NXH600N105H7F5P2HG

feature

       Type I neutral point clamped three-level inverter module

       1050V field-stop 7-type IGBT and 1200V SiC diode

       High efficiency, high power density, and excellent reliability

       Low thermal resistance base plate

       Low inductance layout, with built-in NTC thermistor

advantage

The system efficiency is as high as 99%

         Reduce the number of modules, simplify PCB design, and lower system costs

application

1500V string-type photovoltaic inverter for industrial and commercial use

About The Author

This is reported by Top Components, a leading supplier of electronic components in the semiconductor industry

They are committed to providing customers around the world with the most necessary, outdated, licensed, and hard-to-find parts.

Media Relations

Name: John Chen

Email: salesdept@topcomponents.ruThis is reported by Top Components, a leading supplier of electronic components in the semiconductor industry. They are committed to p with the most necessary, outdated, licensed, and hard-to-find parts.

Media Relations Name: John Chen

Email: salesdept@topcomponents.ru