By Omara Aziz
MOSFET vs. IGBT: The future of motor drive control
Electromechanical devices — switches, solenoids, encoders, generators, and electric motors — are the fundamental bridge from the digital world to the physical world. The magic of all these devices is their ability to convert electrical signals into mechanical actions.
As industries such as automated manufacturing, electronic vehicles, advanced building systems, and smart appliances advance, the demand for increased control, efficiency, and capabilities of these electromechanical devices also grows. This article explores how breakthroughs in silicon carbide MOSFETs (SiC MOSFET) are redefining the capabilities of electric motors that have historically utilized silicon IGBTs (Si IGBT) for power inversion. This innovation expands the capabilities of motor drive applications in nearly every industry.
What are Si IGBTs and SiC MOSFETs?
Si IGBT is shorthand for silicon-insulated-gate bipolar transistors. SiC MOSFET is short for silicon carbide metal-oxide-semiconductor field-effect transistor.
Si IGBTs are current-controlled devices that are toggled by a current applied to the gate terminal of the transistor, while MOSFETs are voltage-controlled by a voltage applied to the gate terminal.
The primary difference between Si IGBTs and SiC MOSFETs is the type of current that they can handle. Generally speaking, MOSFETs are suited for high frequency switching applications, while IGBTs are better suited for high-power applications.
Why silicon IGBTs and silicon carbide MOSFETs are essential in motor drive applications
Electric motors are ubiquitous in modern technology and often rely on battery systems as their power source. For example, electric vehicles utilize massive battery array systems that provide DC power to the vehicle, thereby creating physical motion via AC electric motors. Absolute control of these AC motors is essential to the performance and efficiency of the vehicle, as well as the safety of those inside. However, this powertrain system relies on inverters to convert the DC power from the battery into an AC signal that the motors can use to create motion.
These inverters precisely control the motor’s speed, torque, power, and efficiency and enable regenerative braking capabilities. Ultimately, the inverter is as valuable to the powertrain system as the motor. As is true with all devices in power applications, inverters can vary drastically in capabilities and design requirements and are essential to the overall system performance of DC power to AC motor system.
Two types of inverters are used in modern DC to AC motor drive applications: silicon IGBTs and silicon carbide MOSFETs. Historically, Si IGBTs are the most common, but SiC MOSFETs have multiplied in popularity given their various performance advantages and continually dropping costs. When SiC MOSFETs first came onto the market, they were widely cost-prohibitive for most motor drive applications. However, as the adoption of this superior technology increases, scaled manufacturing has dramatically reduced the cost of SiC MOSFETs.
Si IGBT advantages and disadvantages vs. SiC MOSFETs
Si IGBTs are historically utilized in DC to AC motor drive applications due to their high current handling capability, fast switching speed, and low cost. Most importantly, Si IGBTs have a high voltage rating with a low voltage drop, conductance losses, and thermal impedance, making them an obvious choice in high-power motor drive applications such as manufacturing systems. However, one considerable drawback to Si IGBTs is that they are highly susceptible to thermal runaway. Thermal runaway occurs when the device temperature rises uncontrollably, causing the device to malfunction and eventually fail. In motor drive applications where high current, voltage, and operating conditions are common, such as electric vehicles or manufacturing, thermal runaway can be a significant design risk.
As a solution to this design challenge, SiC MOSFETs are more resistant to thermal runaway. Silicon carbide is more thermally conductive, allowing for better device-level heat dissipation and stable operating temperatures. SiC MOSFETs are better suited for warmer ambient condition spaces such as automotive and industrial applications. Additionally, given their thermal conductivity, SiC MOSFETs can eliminate the need for additional cooling systems, potentially reducing the overall system size and potentially reducing system cost.
Because SiC MOSFETs operate at much higher switching frequencies than Si IGBTs, they are ideal for applications where accurate motor control is essential. High switching frequencies are paramount in automated manufacturing, where highly accurate servo motors are used for tool arm control, precision welding, and precise object placement.
In addition, a notable advantage of SiC MOSFET over Si IGBT motor driver systems is their ability to be embedded within motor assemblies, with a motor controller and inverter embedded within the same housing as the motor.
By moving the motor driver assembly to the local location of the motor, the cabling between the drive inverters and the motor driver can be drastically reduced, enabling significant savings. In the example from Image B, a traditional Si IGBT power cabinet may require 21 unique cables to power the seven motors (labeled ‘M’) of the robotic arm, which could amount to hundreds of meters of expensive and complex cabling infrastructure. With a SiC MOSFET motor drive system, the cable count can be reduced to two long cables that connect to each of the motor’s motor drives within the local motor assembly
Image 2: Comparison of a Silicon IGBT vs Silicon Carbide MOSFET system control of a robot arm.
Downsides of SiC MOSFETSs vs Si IGBT
However, there are downsides to SiC MOSFETs vs. Si IGBTs. First, SiC MOSFETs are still more expensive than Si IGBTs, making them potentially less suitable for cost-sensitive applications. Although, SiC MOSFETS themselves are more expensive, some applications may see price reduction in the overall motor driver system (by reduction of wiring, passive components, thermal management, etc.) and may be cheaper overall when compared to a Si IGBT system. This cost savings may require an involved design and cost-study analysis between the two application systems but could lead to increased efficiency and cost savings.
Another drawback of SiC MOSFETs is that they can feature more complex gate drive requirements that may make them less ideal than IGBTs in applications where other components in the system may limit gate drive resources.
Improved inverter technology with silicon carbide MOSFETs
Silicon carbide MOSFETs have drastically improved inverter technology for motor drive systems. As is true with all types of components, there are particular applications where IGBTs may still be better suited. However, SiC MOSFET inverters offer several distinct advantages over Si IGBTs, making them very attractive solutions for motor drive applications and a wide array of other applications.
Browse an assortment of MOSFETs and IGBTs from industry-leading manufacturers at Arrow.com. Find popular and top-selling MOSFET and IGBT transistor products below.
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