Against the backdrop of global efforts to promote green energy and carbon reduction goals, solar power technology has rapidly advanced, becoming a key pillar of renewable energy. Among these technologies, solar inverters, as the critical core equipment that converts the direct current (DC) generated by solar panels into alternating current (AC), directly impact the efficiency and reliability of the entire power generation system. This article explores the latest development trends in solar inverters and the innovative solutions introduced by onsemi to address the challenges of future energy transition and smart grids.
Solar inverter systems as an effective pathway for environmental protection and carbon emission reduction
With the continuous growth of civilization and population density, the rate of CO₂ emissions has become increasingly difficult to control. Global warming caused by carbon emissions will lead to climate deterioration and inevitably harm our planet. Therefore, to address this issue, we need to adopt clean energy sources such as wind and solar power.
Renewable energy sources like solar and wind power are among the most efficient ways to reduce carbon emissions. Unlike wind power, solar inverters are widely used in various applications. Today, in conjunction with energy storage systems, people can control and store this free energy. The core of a solar inverter consists of high-power conversion stages, DC-DC boost converters, and DC-AC inverters. With advancements in power switches and new demands from end products, many new topologies have emerged.
The primary advantage of solar energy is that it is a "free" energy source as long as a solar inverter system is installed. This process is environmentally friendly, as it produces no emissions and relies on an abundant and sustainable resource - the sun. Utilizing solar energy helps combat climate change, reduces dependence on fossil fuels, and provides a reliable energy source. Additionally, it often leads to long-term cost savings for individuals and businesses by lowering electricity bills.
Solar inverters come in various categories, differentiated by type (central, string, micro) or end application (residential, commercial, utility-scale). Currently, string inverters are the most popular type due to their flexibility and ease of installation. With the continuous iteration of power devices, the power level/density of a single inverter is increasing while unit costs and sizes are decreasing, making them the mainstream choice in the solar inverter market.
Central solar inverters are typically installed in utility-scale stations with ultra-high capacity. However, due to installation location limitations, the newly installed capacity of central inverters has been surpassed by string inverters in recent years. Micro solar inverters, used for residential power generation, are also widely deployed to power urban infrastructure such as streetlights and traffic lights.
Energy conversion efficiency and high-power demands drive semiconductor application development
With increasing demands for energy conversion efficiency and high power, the trend of silicon carbide (SiC) replacing traditional semiconductors has emerged, as SiC helps improve efficiency. Compared to traditional silicon-based MOSFETs/IGBTs, SiC devices are more suitable for higher-voltage applications. Higher-voltage devices can simplify topologies, eliminating the need for multi-level converters. SiC inverter solutions exhibit lower losses than IGBT solutions, and SiC MOSFETs switch faster, reducing the size of passive devices, particularly the inductors. These two factors enhance power density, enabling higher power in equipment of the same size and weight. However, trade-offs between cost and performance must still be considered during product design, and actual requirements must be understood to determine the most suitable solution.
On the other hand, SiC diode replacement is becoming increasingly common, especially in DC-DC stages, due to their decreasing cost, minimal changes required in circuit design, and most importantly, significant improvements in system performance. Additionally, higher frequencies can reduce the size of passive devices.
For high-power products (above approximately 200 kW), IGBTs are the preferred choice because they perform well under high-current conditions, and the system does not require very high switching rates, meaning the slow turn-off of IGBTs does not pose significant issues. Conversely, a full SiC system requires a completely new system design, which incurs substantial costs. For example, the driving circuit of an IGBT-based converter is incompatible with a SiC-based system. New protection methods must also be considered, as SiC components have a shorter short-circuit withstand time (SCWT) compared to IGBTs.
With the growing demand for high power, using 1500 V instead of 1100 V strings reduces interconnection costs for a given power level due to lower current. To meet this trend, higher-voltage switches have been developed. Whether using high-voltage switches or multi-level topologies, the operating power of solar inverters can be significantly improved.
Furthermore, three-level solar inverters are often the preferred choice for high-power solar inverters due to their optimized EMI performance, switching losses, and inductor current ripple. However, they also introduce challenges for PCB design and switching schemes. With the development of SiC, power modules and discrete power devices with maximum operating voltages ≥ 2000 V have been developed and deployed. While there are still gaps (such as higher requirements for other components/accessories) before mass production, a two-level 1500 V system can significantly reduce design and control complexity while shrinking the size of end products.
Another emerging opportunity is hybrid solar inverters, typically used for residential cases, which feature an additional DC-DC converter connected to the solar inverter’s bus. The external DC-DC converter links to a battery pack, providing backup energy or enabling energy arbitrage. This new system is integrated into a case that resembles traditional residential solar inverters.
System implementation tips for solar inverter systems
In terms of system implementation, the main components of a string inverter system include the solar panel array, the DC-link capacitors, and the inverter (DC/AC converter). A DC-DC boost stage is often used between the PV strings and the DC link. These systems primarily serve two functions: elevating the output voltage of the PV strings to the DC link operating level and implementing the Maximum Power Point Tracking (MPPT) function to maximize power generation under varying environmental and sunlight conditions. When the PV string reaches the DC link operating voltage, the DC/DC converter is bypassed (via a low VF diode) to maximize efficiency.
Regarding power and voltage levels, the inverter stage is available in single-phase and three-phase configurations. The single-phase systems are rated from below 1 kW up to 10 kW (depending on the region), with DC links voltages typically ranging from 300 V to 600 V. Three-phase systems cover a broad power range, from 15 kW for light commercial applications to over 300 kW for utility-scale applications. The DC link voltage typically operates at 1100 V (residential, commercial, and utility) or 1500 V (commercial and utility).
In terms of topology design, power semiconductor solutions vary across the wide spectrum of power and voltage levels. For higher-power applications, Power Integrated Modules (PIMs) with IGBTs, SiC MOSFETs, and/or SiC/hybrid solutions are often preferred. Multi-level topologies must be considered for high bus-voltage systems. Two-level systems also offer advantages in terms of system and control complexity but place higher demands on power switches.
When choosing between discrete devices and power modules, many factors influence customer decisions. However, for high-power products, module solutions are highly recommended, especially when paralleling multiple discrete MOSFETs/IGBTs. Module solutions simplify issues such as long-term performance imbalances caused by uneven current and heat distribution, switching timing, and wiring connections.
High-quality solar inverter solutions optimized for performance
onsemi offers a range of solar inverter solutions, including discrete SiC and IGBT devices, power modules, isolated gate drivers, and power management controllers, to enhance system power density and efficiency.
Below are highlights of some of onsemi’s solutions. First, the new EliteSiC 1200 V M3S planar SiC MOSFET series is optimized for fast-switching applications and high-temperature operation. Planar technology ensures reliable performance under negative gate voltage drive and suppresses gate spikes. This series delivers optimal performance with an 18 V gate drive but also works well with 15 V. Improved parasitic capacitance makes it suitable for high-frequency operation, with RDS(ON) = 22 mΩ @ VGS = 18 V, ultra-low gate charge (QG(TOT) = 137 nC), low capacitance (COSS = 146 pF), and high-speed switching. It features a 4-pin TO-247-4L package with a Kelvin source, is 100% avalanche-tested, halogen-free, and RoHS-compliant.
The new 1200 V Trench Field Stop VII IGBT series features a trench narrow mesa and proton-implanted multi-buffer, offering fast-switching and low VCE(SAT) types. Improved parasitic capacitance supports high-frequency operation, and it comes in common packages. Target applications include energy infrastructure and factory automation.
onsemi’s extensive portfolio of full-SiC Power Integrated Modules (PIMs) includes half-bridge, full-bridge, and other larger topology configurations. These modules feature low thermal resistance, built-in NTC thermistors, lower RDS(ON) at higher voltages, higher efficiency and power density, and flexible, high-reliability thermal interface solutions.
Conclusion
As the global energy transition accelerates, solar inverter technology and applications continue to evolve toward higher efficiency, intelligence, and modularity. Faced with diverse application scenarios and demanding operating environments, manufacturers must continuously optimize design architectures, improve thermal management and protection mechanisms, and adopt advanced power semiconductors and control algorithms. onsemi’s solar inverter solutions can assist in developing more environmentally friendly and low-carbon energy conversion systems, playing a pivotal role in the future green energy ecosystem and driving the realization of sustainable development.