Electric vehicles (EVs) are transportation vehicles that are powered by electric motors and rely on batteries or other energy storage systems. They are mainly classified into pure electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and fuel cell electric vehicles (FCEVs). In today's society, electric vehicles play a crucial role in reducing greenhouse gas emissions, promoting the transition to renewable energy, and improving urban noise and air quality.
The electric vehicle (EV) drive system typically consists of the battery pack, power electronic converters (including the inverter and DC-DC converter), electric motor, and control unit.
- On-Board Charger (OBC)
- Battery System
- Drive System
- DC-DC Converter
- Power Distribution Unit (PDU)
Power electronics technology
Since the 1980s, MOSFETs have been the preferred devices for low-voltage inverters, while IGBTs have been the preferred devices for voltages around 150V or higher. It wasn't until the mid-to-late 2010s, when wide-bandgap semiconductors like silicon carbide (SiC) MOSFETs were commercialized, that IGBTs remained the dominant choice in the high-voltage market.
IGBTs are efficient switching devices, but they also have limitations in certain areas. Although they can perform relatively fast switching operations, their switching speed is still slower compared to other devices like MOSFETs. The main issue with slow switching is that when the device transitions from the "on" state to the "off" state, or vice versa, it is still influenced by the voltage during conduction, resulting in significant power losses during the switching process. In other words, the device remains partially "on" during the switching moment, which is undesirable. The longer the switching time, the more heat is generated, which limits the switching frequency to prevent overheating and damage to the device's performance.
As silicon power IC (Si) technology begins to reach its limits, engineers are looking for alternatives to help them create smaller, lighter, and more efficient products.
Wide-bandgap (WBG) materials, such as GaN and SiC, are superior to silicon due to their inherent high electron mobility and higher bandgap energy. SiC power devices share some characteristics with Si devices, such as similar turn-on and turn-off voltage requirements. However, like GaN, SiC can operate at higher temperatures than Si, providing better thermal management, while also offering higher switching frequencies, lower switching losses, higher efficiency, and smaller sizes and weights.
Traction Inverter
The high-voltage direct current (DC) from the battery pack needs to be converted into three-phase alternating current (AC) suitable for the electric motor. This process is carried out by a key power electronic device—the inverter.
The traction inverter is a critical component in electric and hybrid vehicles, converting the DC power from the battery into the AC power required to drive the motor, enabling efficient and smooth vehicle operation. It plays an important role in vehicle performance, efficiency, and sustainability. The traction inverter is also commonly referred to as a motor driver, variable frequency drive (VFD), or motor controller, and is widely used in various types of electric land transportation vehicles. High-performance power devices, such as MOSFETs, are employed in these systems to ensure precise motor control and energy conversion, supporting both low-voltage and high-voltage system applications.
Inverter and Rectifier
In power electronics, inverters and rectifiers are two core devices. The primary function of an inverter is to convert DC power into AC output to drive loads such as motors, while a rectifier performs the opposite function, converting AC into DC. In electric vehicles, the traction inverter not only performs inversion but also acts as a rectifier during regenerative braking. It converts the AC energy generated by the motor into DC and recharges the battery. This bidirectional energy flow enhances the energy efficiency and driving range of electric vehicles.
In the field of power electronics, terms like rectifiers, inverters, and class D amplifiers, despite reflecting different primary functions in their names, share highly similar core circuit designs. This similarity arises from the half-bridge topology, which is widely used in various devices. Depending on the type of components used and the control methods employed, the half-bridge can perform rectification, inversion, and even signal amplification functions.
If a fixed diode is used as the switch in the half-bridge circuit, it can only perform rectification, converting AC to DC. In contrast, when the half-bridge uses controllable semiconductor switches, such as transistors or IGBTs, it can perform both inversion (converting DC to AC) and rectification, even supporting regenerative energy feedback functions.
Through optimized design, the half-bridge structure can be expanded into various topologies, such as single-phase rectifiers and H-bridge inverters. While their fundamental principles are similar, the control and connection of switches in the circuit are adjusted to adapt to different application scenarios.
In the electric vehicle (EV) field, the three-phase inverter is the most commonly used form. Its circuit consists of three half-bridges, each of which controls the current of one phase of the motor. For multi-phase motors, additional half-bridge units can be added to meet the control requirements of higher-phase systems.
Power Device Applications
The emergence of the IGBT (Insulated Gate Bipolar Transistor) was a key breakthrough in power electronics technology. As a semiconductor switching device that combines the characteristics of both MOSFETs and BJTs, the IGBT enables efficient switching in high-voltage, high-current scenarios while maintaining relatively low conduction losses. This feature makes it an ideal choice for driving high-power motors. Modern inverters typically integrate multiple half-bridges and associated circuit components into a complete motor drive system. Even though these systems also perform rectification, they are still widely referred to as "inverters" or "variable frequency drives" (VFDs). In industrial applications, these devices are commonly called motor drivers.
Large current power modules typically use IGBT-type devices, with Si IGBTs paired with Si fast recovery diodes (FRDs), forming the common configuration in automotive inverter modules. However, compared to existing Si IGBT devices, SiC (silicon carbide) devices offer higher operating temperatures and faster switching speeds. These features undoubtedly make SiC devices the best choice for traction inverters, as traction inverters require the transmission of large amounts of energy into and out of the battery.
As the first electric vehicle manufacturer to integrate full SiC power modules into its main inverter, Tesla has adopted this technology in its Model 3.
On-Board Charger (OBC)
The on-board charger (OBC) in electric vehicles is responsible for converting the alternating current (AC) from the power grid into direct current (DC) suitable for charging the battery. As user demand for fast charging continues to rise, modern OBCs need to support higher power levels while ensuring efficient energy conversion and compact design.
The design of the On-Board Charger (OBC) aims to maximize energy efficiency and reliability to ensure fast charging, while also meeting the space and weight constraints set by EV manufacturers. OBC designs using GaN (Gallium Nitride) technology can simplify the EV cooling system, reduce charging time, and lower power consumption.
The on-board charger (OBC) converts the AC power source into high-voltage DC, such as 400V or 800V (depending on the specific vehicle's battery voltage). The power range typically falls between 6.6 kW and 22 kW. While 800V battery systems require the use of 1,200V SiC MOSFETs and differential circuits to ensure sufficient safety margin, in 400V battery systems, OBCs, DC-DC converters, and traction inverters can utilize GaN-based devices rated at 650V or 700V.
The On-Board Charger (OBC) is one of the key technologies for future sustainable smart grid infrastructure. It allows electric vehicles to act as energy storage devices or power sources for other loads, helping to manage power demand and stabilize the grid. GaN and SiC devices can support advanced power topologies, reducing the size and integrating power converters, thereby improving the system's structure and efficiency.
In terms of market share, commercial GaN power devices are slightly behind SiC devices, but they are rapidly gaining ground due to their outstanding performance. Like SiC devices, GaN devices offer lower switching losses, faster switching speeds, higher power density, and the ability to reduce system size and weight, all while lowering overall costs.
DC/DC Converter
Electric vehicles (EVs) typically contain multiple electrical subsystems operating at different voltage levels. The DC/DC converter is responsible for converting electrical power between the high-voltage battery and low-voltage systems (such as lights, entertainment systems). Efficient converters help reduce energy losses and extend the vehicle's driving range.
IGBTs (Insulated Gate Bipolar Transistors), as traditional power semiconductor devices, offer advantages in terms of lower cost and mature technology. However, the switching losses of IGBTs lead to heat accumulation, requiring additional heat dissipation measures, which limits their performance in high-frequency, high-power applications. Nevertheless, IGBTs are still suitable for medium to low-power DC-DC converters, especially at lower switching frequencies, where they offer strong cost-effectiveness.
Silicon Carbide (SiC) devices have switching speeds fast enough to meet the power conversion needs in electric vehicles, and their overall higher durability is a significant advantage. GaN (Gallium Nitride) devices have zero reverse recovery, which results in very low switching power losses. For applications that require switching frequencies in the megahertz range, GaN may be the optimal choice. On-Board Chargers (OBCs) and high-voltage to low-voltage DC-DC converters with power ratings up to 25 kW are well-suited for GaN technology.
Applications and Development of SiC and GaN in Electric Vehicle (EV) Power Electronics
IDTechEx predicts that by 2035, SiC MOSFETs will contribute to more than 50% of the automotive power semiconductor market. SiC technology is progressively addressing key challenges in the electric vehicle (EV) market, such as range anxiety, charging speed, sustainability, and the widespread adoption of 800V architectures, especially in high-voltage charging and efficient energy management. SiC shows significant advantages in these areas.
While GaN (Gallium Nitride) is not yet ready for widespread use in high-voltage applications, it is expected to rapidly penetrate the EV power electronics market in the future. Initially, GaN will be mainly used in low-power, high-frequency applications such as On-Board Chargers (OBCs) and DC-DC converters, and gradually move toward higher-power systems such as power inverters. With investments and technological breakthroughs from major companies like ROHM, Infineon, and Renesas, GaN devices are expected to make exciting progress in areas like motherboard technology, vertical structure design, and multi-stage topologies. These technological innovations may allow GaN to become a crucial solution in the EV power electronics field within the next decade.
In the power electronics ecosystem of electric vehicles, Si (Silicon), SiC (Silicon Carbide), and GaN (Gallium Nitride) will coexist and complement each other, as each material has its unique advantages and optimal application scenarios. SiC will continue to play a leading role in high-power applications such as traction inverters and onboard chargers, particularly in 800V and higher voltage systems. In the near future, GaN is expected to play a key role in low-power, high-frequency applications such as DC-DC converters and onboard charging systems.
Hitachi Energy launches game-changing power semiconductor module globally for all types of electric vehicles:https://www.hitachienergy.com/products-and-solutions/semiconductors/e-mobility-modules
