Manufacturers and consumers are trying to move away from their dependence on fossil fuel energy, and electrification solutions are becoming popular as a result. This is important for protecting the environment, limiting pollution and slowing the damaging trend of global warming. Electric vehicles (EVs) are becoming increasingly popular around the world, with companies entering the market to convert commercial and agricultural vehicles (CAVs) to be powered by electricity.
However, this shift has led to a rapid increase in the demand for electricity, putting a strain on the power grid. Despite their energy efficiency, applications such as electric vehicles, data centres, heat pumps and others still require significant amounts of energy to operate.
New renewable energy sources such as solar, wind, and wave energy are gaining popularity and are becoming more mainstream. Only applications that use exclusively renewable energy can be considered truly ‘clean’.
The solar energy market has been growing for many years and is relatively mature; according to a report by Fortune Business Insights, the current solar energy market size is estimated at $273 billion and is expected to grow to $436 billion by 2032; in 2023, North America accounted for more than 40 per cent of the solar energy market.
Power conversion challenges in renewable energy applications
Solar power is growing rapidly. According to the International Energy Agency (IEA), in 2022, solar-generated electricity will increase by 26 per cent over the previous year to 1,300 TWh, marking the passing of wind power as the largest renewable source of electricity.
Solar photovoltaic (PV) panels generate direct current (DC), and the grid requires alternating current (AC), so a central PV inverter is an integral part of a large grid-connected installation. All the energy generated by the PV panels passes through the inverter, so inverter efficiency has a significant impact. Although solar energy is inexhaustible, inefficient conversion results in very limited energy being delivered to the grid. The energy wasted in the process is converted into heat, which in turn poses a serious challenge, as many solar installations are often located in sunny, high-temperature environments such as deserts.
Cost is also a very important consideration, which can have a direct impact on the consumer's electricity bill and the profitability of the utility. To achieve higher power, many central inverters use multiple conversion modules in parallel, with the exact number determined by the power rating of each module. The higher the power capacity of each module, the fewer modules are required, which in turn reduces costs.
While electric vehicles have come a long way, CAVs have been slow to make the transition to electric drive; they are larger, consume more fuel and produce more emissions per trip, and although they account for only 2 per cent of the vehicle fleet in terms of numbers, they are responsible for 28 per cent of total transport emissions in terms of greenhouse gases. While the electrification of commercial passenger vehicles (e.g. buses) is beginning to take hold, most large trucks, construction machinery and agricultural vehicles (e.g. tractors) still rely on diesel power. Now, things are starting to change. In order to meet stringent zero-emission regulations in global markets such as the EU, China and California, the share of sales of electric trucks (purely electric and hybrid) is expected to increase from the current 5 per cent to 40-50 per cent by 2030.
Compared to fossil-fuelled commercial vehicles, electric commercial vehicles are simpler and have fewer moving parts. For the same load capacity, electric vehicles are smaller, more reliable and have lower maintenance-related costs. Battery costs are now so low that the total cost of ownership for electric CAVs is already lower than for internal combustion engine (ICE) vehicles.
Similar to solar applications, efficiency is a key requirement for electric CAVs. Each vehicle has a limited amount of battery power, and the more efficient the conversion process in the inverter, the longer the vehicle can travel. Or less power is required to travel the same distance.
Given our reliance on solar and electric CAVs in the future, reliability naturally becomes very important.
Advanced Power Technologies for Inverter Applications
In high power applications such as three-phase solar PV inverters, three-level active neutral point clamped (ANPC) converters are a relatively common topology. This multi-level topology is specifically designed to improve system performance and efficiency.
Normal Neutral Point Clamped (NPC) converters use a diode to connect the neutral point of the DC link capacitor to the output. In the ANPC configuration (Figure 1), the clamping is performed by a switch, which allows for improved control, reduced switching losses, and increased efficiency, with a corresponding reduction in the need for heat dissipation measures, thus contributing to a smaller, lower-cost solution.
The topology is arranged in such a way as to reduce the voltage stress on the individual switches, thus improving reliability. In addition, ANPC enables grid-friendly waveforms.
Figure 1: ANPC converters can be easily constructed from modules
Design engineers can create high-performance three-level active neutral clamping modules with system outputs of 1.6 MW to 1.8 MW by paralleling multiple power modules, such as ONSEMI's QDual 3 IGBT modules.
Figure 2: QDual3 IGBT Module
The QDual 3 module integrates a new generation of 1200 V field-stopping 7 (FS7) IGBT and diode technology to provide superior performance for high-power applications. The FS7 technology provides a significant improvement in conduction loss compared to previous generations.
Figure 3: FS7 Technology Enhances Key Performance Parameters
In the FS7 IGBT process, the trench-narrow table delivers low VCE(SAT) and high power density, while proton injection multi-buffering ensures robustness and soft-switching characteristics (Figure 2). With VCE(SAT) as low as 1.65V, ON Semiconductor's medium-speed FS7 devices are suitable for motion control applications, while its FS7 fast products have an EOFF of only 57 μJ/A, making them ideal for high-power applications such as solar inverters and CAVs.
Figure 4: FS7 IGBTs Smaller Size, Higher Power Density
The innovative FS7 technology enables the chip size in the new QDual3 modules to be reduced by 30 per cent compared to the previous generation (Figure 3). This miniaturisation, combined with the advanced packaging, allows a significant increase in maximum current rating. In motor control applications with operating temperatures up to 150 degrees Celsius, the QDual3 delivers output power from 100 kW to 340 kW, which is approximately 12 per cent higher than other products on the market today.
Reliability is key in solar and CAV applications, so how the modules are constructed and tested is critical. For example, while many similar solutions today use lead bonding to secure the terminals, ON chooses to ultrasonically weld the module. The latter helps increase current-carrying capacity, provides a better path for heat dissipation, and is more robust than the former (Figure 4).
Figure 5: Ultrasonic Welding Reduces Temperature and Increases Reliability
This approach improves conductivity, which reduces power losses and improves efficiency. It also reduces operating temperatures, increases mechanical stiffness, and improves the overall reliability of the module.
ON Semiconductor's New High Power QDual3 Technology
The dedicated QDual 3 half-bridge IGBT modules NXH800H120L7QDSG for central solar inverters, energy storage systems (ESS), uninterruptible power supplies (UPS), and SNXH800H120L7QDSG for CAVs are based on FS7 technology, with improved VCE (SAT) and EOFF for reduced losses and improved efficiency. Both devices are based on FS7 technology, with improved VCE(SAT) and EOFF, resulting in lower losses and improved efficiency.
Currently, to design a 1.725 MW inverter using 600 A IGBT modules in an ANPC/INPC architecture, a total of 36 modules would be required. However, using the new NXH800H120L7QDSG and SNXH800H120L7QDSG, which are rated at 800 A, the number of modules required for the design is reduced by nine. Accordingly, the design size, weight and cost savings are 25 per cent. This is valuable for both solar and CAV applications, as the reduced weight and increased efficiency will result in increased vehicle range.
Figure 6: Greater Current Capability Supports Building Systems with Fewer Modules
These modules include isolated backplanes and integrated NTC thermistors for thermal management, and support direct PCB mounting of the modules via solderable pins in an industry-standard layout that facilitates easy upgrade of existing designs to the new QDual3 technology.
All ON Semiconductor QDual3 modules undergo rigorous reliability testing that exceeds that of other comparable devices on the market. Our humidity testing requires the product to withstand 960V bias for up to 2000 hours, while comparable devices are only required to withstand 80V bias for 1000 hours. Vibration testing is critical for CAV applications, and our products are tested at 30 G peak/10 G RMS for 22 hours to meet AQG324 requirements. Other devices have been tested at vibration levels as low as 5 G for as little as 1 hour.
Summaries
Renewable energy use is increasing worldwide, and power grids are under enormous pressure. Solar power has matured and will overtake wind power as the main source of renewable electricity by 2022.
The electrification of CAVs is progressing steadily and is now bearing fruit, although fossil fuel-powered vehicles are still a major source of pollution.
New semiconductor technologies such as ON Semiconductor's FS7 support the development of low-loss, high-power devices to meet the efficiency and reliability needs of these segments. Based on this technology, ON Semiconductor's new QDual3 devices are available in compact packages for high power density and excellent energy efficiency. Well-soldered terminations and certification testing that exceeds that of other devices in the industry help ensure robust performance of QDual3 devices.
The new generation of NXH800H120L7QDSG and SNXH800H120L7QDSG modules, with a current capability of up to 800 A, reduces the number of modules required for an inverter design by up to 25 per cent and further simplifies the design, reducing its size, mass and cost.
This is a significant advancement, and ON Semiconductor will continue to explore the high-performance potential of FS7 technology, aiming to introduce more modules that go beyond the current standard to meet the growing needs of the solar industry and CAV manufacturers.
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