ELECTROMOBILITY How the rapid growth in e-mobility is driving the power electronics market
As EV manufacturers seek to improve their vehicles’ performance and competitiveness, they are being helped by improvements in power semiconductor technology. This article looks at these improvements and the underlying wide bandgap semiconductor technology.
Worldwide demand for electric vehicles (EVs) is growing dramatically, with battery electric vehicles (BEVs) being the dominant consumers: IDTechEx predicts a 15 % CAGR globally for BEVs over the next decade . And this growth in turn is driving demand for the EVs’ powertrain components, namely the batteries, traction motors, and power electronics - which can be further classified into on board chargers (OBCs), inverters, and DC-DC converters, which derive low 12 V or 48 V supplies from the 400 V or 800 V traction battery. This expanding market environment is still young, with plenty of room for improvement. This means that component technologies are continuously advancing as vehicle manufacturers and their suppliers enhance vehicle range, chargeability, safety, lifetime, and sustainability of travel to grow market share.
Below, we look at the power electronics components involved. Firstly, we look at wide bandgap semiconductor (WBG) technology as a major contributor to EV power semiconductor development, and then at how this technology is used by different power electronics devices to contribute to overall EV performance improvement.
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Wide bandgap semiconductor technology
The EV power electronics components are predominantly semiconductor devices. These have traditionally been based on silicon (Si), but designers are now increasingly exploiting the advantages of more advanced devices, based on wide bandgap (WBG) technologies, implemented as silicon carbide (SiC) or gallium nitride (GaN) devices.
Wide bandgap semiconductors, also known as WBG semiconductors, are a class of materials that have a higher bandgap than traditional semiconductors such as silicon. The bandgap is the energy required to move an electron from the valence band to the conduction band, and the wider the bandgap, the more a material is able to conduct electricity at higher temperatures, voltages, and frequencies. WBG semiconductors are typically made from materials such as silicon carbide (SiC) or gallium nitride (GaN).
So, how are WBG semiconductors helping to improve EV design? Firstly, they allow for higher efficiency in the conversion of electrical energy to mechanical energy. Traditional silicon-based semiconductors suffer from significant energy loss when used in high-power applications such as EVs. As WBG semiconductors can operate at higher voltages, frequencies, and temperatures, they operate with less energy loss and greater efficiency.
Secondly, WBG semiconductors are smaller and lighter than traditional silicon-based semiconductors. This means that they can be integrated into smaller, more compact power electronics modules, resulting in reduced weight and size of the overall EV system. This is particularly important for electric cars, where reducing weight is critical to improving performance and range.
Thirdly, WBG semiconductors offer greater reliability and durability. High-power applications such as EVs can put severe stress on electronic components, leading to potential failure and downtime. WBG semiconductors have been shown to be more reliable and durable than traditional silicon-based semiconductors, reducing the likelihood of failure and the need for maintenance.
Finally, WBG semiconductors offer greater design flexibility. As they can operate at higher frequencies and temperatures, they allow for the design of more compact and efficient power electronics systems. This, in turn, allows for greater design flexibility in the overall EV system, enabling more innovative and creative designs that can improve performance, range, and safety.
Silicon carbide costs much more than silicon, but for some manufacturers, the benefits more than justify the higher price. According to the New York Times , some automakers are planning to use silicon carbide not only in inverters, but also in other electrical components such as DC/DC converters and on-board chargers.
Silicon is expected to continue to dominate the half-trillion-dollar semiconductor industry, but SiC is finding an important niche in power electronics, which are critical for EVs, and currently make up a market of about USD20 billion per year. Yole Développement projects that the automotive market for silicon carbide will increase from USD1 billion to USD5 billion by 2027 .
Silicon carbide has been under development as a transistor material for decades. More recently, engineers have started using newer WBG materials such as gallium nitride, in power electronics. Yole Développement estimates that the gallium nitride market will grow from its current annual value of around USD200 million to USD2 billion by 2027.
On board chargers
Onboard battery chargers take AC current from the car owner’s home or public charging point and convert it to DC power to recharge the battery. They are also often capable of harvesting kinetic energy from the vehicle itself to provide additional charge when braking. Charging powers vary from less than 2 kW in applications such as electric scooters to 22 kW in high-end EVs. Traditional silicon has made these systems very limited in their output, size, and speed. And, OBCs are inevitably packed into confined spaces, creating thermal management and conversion efficiency issues. Also, while charging power is traditionally unidirectional, bi-directional charging has been gaining traction in recent years. This is because an EV equipped with sufficient battery capacity is potentially capable of acting as an energy-storage system, enabling a variety of vehicle-to-everything charging use cases: vehicle-to-home power generation, vehicle-to-grid opportunities, or vehicle-to-vehicle charging. As a result, the OBC is migrating from a unidirectional to a bidirectional topology. In fact, there is a general trend toward the employment of bidirectional OBCs for their higher system efficiency.
As EV designers move over to bidirectional OBCs, they can optimize performance by using SiC devices from a manufacturer like Wolfspeed. Wolfspeed SiC MOSFETs address many EV OBC power-design challenges by providing devices with low on-resistance, very low output capacitance, and low source inductance for an optimized blend of low switching losses and low conduction losses. Compared with Si-based solutions, Wolfspeed SiC power-device technology enables increased system power density, higher switching frequencies, reduced component count and size of components such as inductors, capacitors, filters, and transformers, and potential system cost reduction.
In a 22kW bidirectional OBC, for example, a detailed side-by-side comparison shows that a SiC-based solution requiring 14 power devices and 14 gate drivers can replace a Si-based design needing 22 of each type of device. When comparing performance, the SiC design achieves 97 % efficiency and a power density of 3 kW/L, versus silicon at 95 % efficiency and 2 kW/L. Finally, a system cost breakdown shows that the Si-based solution is approximately 18 % more than the SiC design.
Inverters are a critical part of the electric vehicle (EV) drivetrain. Put simply, their role is to use the direct current (DC) supplied by the onboard battery for three separate functions; creating an alternating current (AC) for the vehicle’s traction motor, converting it back into DC to enable regenerative braking and, finally, to control motor speed when the accelerator is depressed.
Given their vital role, it is no surprise that innovation around inverter technology is high on many stakeholders’ agendas. A key development area is 800-volt-compatible inverters, which are slowly nudging towards mass-market models such as Hyundai’s Ioniq 5. Such inverters support ultra-fast charging and lighter electric cabling, which is expected to become a feature in next-generation EVs. Meanwhile, the use of silicon carbide allows for the development of a faster, more efficient, and lightweight drivetrain.
SiC offers an improvement on today’s commonly used silicon semiconductors as it produces less heat and is less temperature-sensitive. McLaren, for example, claims that they have leveraged SiC to create an inverter that can switch power more efficiently than conventional inverters, while also generating less heat to allow customers to use smaller cooling systems and reduce weight and cost by extension. Battery size can also be reduced by the same logic.
McClaren also comments: “If OEMs want to remain competitive and deliver vehicles with greater ranges, faster charging times and better acceleration, they must make the transition to an 800V SiC architecture.”
"The next generation in power semiconductors will be driven by Silicon Carbide technology"
DC – DC converters
Electric vehicles (EV) use two different power systems; a high-voltage battery (200 to 450 VDC, now trending towards 800 V) for traction and a low-voltage (12 V or 48 V) one for supplying all the electric appliances in the vehicle. Traditionally the low-voltage battery was charged from the alternator, but in today's vehicles it obtains power from the high-voltage battery pack. Conversion from the battery’s high voltage down to the appliances’ lower voltages is handled by a DC-DC converter, sometimes known as an auxiliary power module (APM). These devices are also sometimes used to convert from one low voltage to another – between 48 V and 12 V, for example.
In specific electric car architectures, the low voltage battery should be available for recharging the high-voltage battery pack to provide energy for cranking the car. This means that the on-board DC-DC converter must be bi-directional and very efficient as well as highly reliable in order to run the complex control algorithms needed to ensure an energy-efficient solution. Power outputs range from 250 W to 3.5 kW. Critical loads on the low-voltage side, such as steering, are driving an increase in functional safety requirements for converters, while reliability demands are also growing because vehicle OEMs want to reduce the size of the low voltage battery. A modern step-down DC-DC converter contains electromagnetic devices such as transformers that reduce the voltage at the input, capacitors that store energy, semiconductor switches that regulate the output and capacitors that filter it. Digital control logic such as FPGAs implemented in devices is also included, because heavy computation is required to take full advantage of the increased switching frequencies enabled by new semiconductor technologies.
These all have to be integrated and packaged in a compact manner while still managing thermal losses to keep temperatures down. The smaller the converter the more concentrated the heat loads become and the greater the challenge involved in extracting that heat efficiently. Development challenges are the familiar interrelated ones of size, weight, efficiency, reliability, electromagnetic compatibility, high voltage isolation for safety, and robustness against the often harsh operating environments to which vehicles are subjected.
According to E-Mobility Engineering Magazine, EV manufacturers are pushing for greater power densities in particular, which means a move to much higher switching frequencies. With higher switching frequencies come shorter switching cycles, which means that other converter components, such as the magnetics in the transformer for example, do not have to hold power for so long and can therefore be made smaller.
DC-DC converter manufacturers’ technological response in recent years has come from two main areas – advanced topologies and advanced semiconductor materials. While there are many topologies in use, they fall into the two broad classes of fixed-frequency pulse width modulation (PWM) and variable frequency quasi-resonant zero-current switching (ZCS). The semiconductor materials in question are wide-bandgap semiconductors silicon carbide (SiC) and gallium nitride (GaN), out of which the solid-state switches are made, either in the form of IGBTs or MOSFETs. While more expensive than silicon, SiC is cost-effective because it enables higher efficiency, smaller size and higher switching frequencies than silicon, which in turn permits the magnetic components in the converter to be made smaller. GaN is expected to enable further performance improvements. The emergence of these new materials has been called game-changing, because they allow one of the most important components in any DC-DC converter – the heavy and bulky transformer – to be made smaller and lighter, while reducing losses.
However, increasing the switching frequency means everything else about the converter design has to be reconsidered, including the magnetics, integration, and digital control. The result is a dramatic fall in the volume of the converter compared with the best available a decade ago.
PCIM EUROPE 2023 with focus on E-Mobility & Energy Storage
This article has focused on wide bandgap semiconductor technology, especially SiC devices, as this presents major benefits to EV manufacturers seeking to improve their vehicles’ performance. However, many other devices, topologies, materials are becoming available all the time – especially when we consider that the EV power train comprises batteries and traction motors as well as the power electronics. There is also the external charging infrastructure to consider.
If you would like an up to date and comprehensive insight into what’s happening in today’s EV marketplace, you should visit the E-Mobility & Energy Storage Zone and Stage within PCIM Europe in Nuremberg, Germany, 9 – 11 May 23.
In addition to a networking area for exchanging ideas with experts, the stage will offer an exciting program of presentations on current topics and trends relating to the value chain of electromobility and energy storage. Here, new developments and challenges in power electronics for different applications (electric, hybrid and fuel cell vehicles, charging infrastructure, payment systems, etc.) will be considered. You can also learn about the products and services of specialized exhibitors at their booths during Live Product Presentations.
Experience the trends E-Mobility & Energy Storage for power electronics firsthand
Are you explicitly looking for power electronics products and systems for electromobility or energy storage? Then become part of the largest PCIM Europe ever from 9 – 11 May 2023 in Nuremberg, Germany. There, you can experience a special zone including a networking area and stage with top-class presentations as well as Live Product Presentations at the stand of specialized exhibitors.Learn more