The Silicon Carbide Inverter

Inverters are an often-overlooked component of an electric vehicle (EV) powertrain. Their influence directly affects its efficiency, which in turn influences battery range and charging time.

Silicon carbide power semiconductors have quickly become the go-to choice for electric vehicle inverters due to their superior performance over traditional silicon devices. In this article we explore five key benefits associated with using silicon carbide inverters.

1. High Breakdown Voltage

Silicon carbide (SiC) is a compound semiconductor material composed of silicon and carbon that offers excellent thermal and chemical stability, boasting a wider bandgap energy of 3.2eV than that of silicon. Furthermore, SiC’s greater thermal efficiency means reduced power losses and extended operating lifetimes.

SiC inverters are devices used to transform direct current into alternating current, making them useful in solar power generation and electric vehicle charging, among other applications. Their greater efficiency compared to conventional inverters allows it to operate at higher voltages and currents while having smaller footprints and being lighter overall than traditional inverters.

SiC is an innovative wide bandgap semiconductor material with high breakdown voltages (VBR) and ultra-low drain-to-source on-resistance RonS, up to 300-400 times lower than silicon devices with similar VBR. SiC MOSFETs can be made by depositing silica onto silicon wafers, doping their substrate, and creating MOSFETs that feature thin drift layers ensuring reliability even at higher temperatures.

High gate current capabilities are an integral component of SiC switching devices, as this enables isolated gate drivers and thus lower total system costs, improve efficiency and performance, eliminate parasitic effects on gate drives, and decrease total system cost. ROHM gate drivers support all generations of SiC switches while operating at higher voltages than IGBTs with minimum gate current of 3A; IGBTs typically only achieve 1-2% current. Furthermore, their higher switching frequency enables compact, energy-efficient inverter designs.

2. Lower Switching Losses

SiC MOSFETs exhibit lower switching losses under partial load conditions than traditional silicon devices due to reduced conduction loss on their devices, which helps lower energy losses during switching processes and ultimately results in higher efficiency in power stages of silicon carbide inverters.

SiC has superior thermal conductivity compared to silicon, meaning it can withstand higher temperatures without degrading, giving designers more freedom in choosing when and at what temperatures to use silicon carbide inverters; even high temperature applications like electric vehicle traction inverters could benefit.

SiC MOSFETs are less susceptible to gate oxide damage from hot spots found in conventional silicon transistors, helping extend their lifespan and performance – an important consideration as power inverters must provide consistently high-performing power.

silicon carbide technology for inverters still faces several obstacles, chief among them cost. SiC power semiconductors tend to be more expensive than their silicon equivalents; however, as demand for silicon carbide inverters increases production costs are expected to decline accordingly.

ON Semiconductor is working closely with electric vehicle (EV) manufacturers to facilitate their transition to silicon carbide technology, including working closely with Mercedes EQ Formula E team on next-generation power inverters for electric vehicles. These will improve driving range and acceleration performance by optimizing power conversion efficiency in motor drive power stages.

The power inverter features a full-bridge module using CoolSiC automotive trench MOSFET technology that is specifically optimized for high voltage, low cost EV traction inverters. Each module boasts 1200 V blocking voltage required by big battery EVs with long driving range and fast charging times – this represents a significant upgrade over the 600-volt inverters used today in similar vehicles.

3. High Efficiency

Inverters convert direct current (DC) to alternating current (AC). They are widely used in power conversion systems ranging from renewable energy systems and electric vehicles, to industrial machinery. Over the past decade inverter technology has seen rapid development to meet demands for increased power density, higher efficiency, improved reliability, reduced component size and weight reductions as well as performance gains such as switching voltage frequency losses as well as reduced component size. SiC inverters offer significant performance enhancements with respect to switching voltage frequency losses as well as reduced component size and weight improvements over previous generation inverters.

Silicon carbide semiconductor field-effect transistors (MOSFETs), which can operate at much lower temperatures than their IGBT counterparts, offer higher current ratings that enable smaller magnetics and reduced circuit design complexity, while their more robust construction allows them to withstand thermal stress without failing.

SiC MOSFETs feature a trench structure which facilitates increased cell density and reduced gate oxide field strength for lower conduction loss, thus permitting a lower switching frequency thereby improving efficiency and decreasing system cost.

Silicon carbide’s superior thermal conductivity also assists in lowering internal parasitic resistance and stabilizing temperature stability of devices, thus significantly lowering energy loss compared with silicon devices, making them more energy-efficient under full load conditions.

Jing-Jin Electric developed its battery electric vehicle inverter independently using state-of-the-art wide band gap semiconductor silicon carbide technology. Featuring an auxiliary power supply feature powered by car batteries to maintain 24V low voltage when necessary.

ROHM provides an expansive portfolio of semiconductor devices for power electronics applications. Their products include silicon carbide diodes, Schottky diodes and super junction MOSFETs to meet varying voltage levels – each product designed to maximize performance by offering maximum current densities in small package sizes with minimal parasitic effects such as stray inductance.

4. High Reliability

SiC power semiconductors significantly enhance the reliability of PV inverter systems. Their use significantly decreases circuit complexity, size and weight while simultaneously offering higher efficiency, extended lifespan in harsh environments at higher voltages/currents, as well as better operation over a wider temperature range, thus saving money on cooling equipment costs.

Silicon carbide’s wide bandgap allows transistors to operate at higher temperatures and frequencies, leading to lower switching losses than with IGBTs or bipolar transistors, which have relatively narrow operating bands and are limited in frequency range. Schottky barrier diodes and MOSFETs made from SiC have significantly decreased switching losses at any frequency over IGBTs or bipolar transistors and can operate over a wider temperature range.

Designing a PV inverter using SiC power components requires taking into account many design parameters. When planning the PCB layout, power routing, noise reduction, efficient cooling and meeting industry requirements must also be prioritized. Furthermore, electromagnetic compatibility (EMC) standards must also be observed along with automotive regulations for compliance purposes. To ensure optimal results are reached it is also vital that extensive testing and quality inspection be conducted prior to final production.

SiC inverters provide the ideal solution for distributed PV system and energy storage applications that require two-way DC/AC power conversion. Solar panels link together in strings and send DC energy directly to one single inverter that converts it to AC electricity that can then power homes or businesses. A small and lightweight SiC inverter can easily be installed and moved around from location to location while being more eco-friendly than traditional inverters by reducing carbon footprint and energy requirements while saving installation costs and installation time.

5. Compact Size

Inverters are key components in electrical vehicle (EV) systems. They convert DC power from the vehicle battery into AC for feeding its motor. By doing this, inverters help reduce vehicle weight and size while improving acceleration, performance and driving range – not to mention more efficient cooling resulting in decreased carbon dioxide emissions.

Silicon carbide inverters are much smaller than their silicon counterparts due to the reduced switching losses and higher breakdown voltage of SiC devices, leading to shorter circuit lengths which in turn reduce size, cost and footprint of an inverter. Furthermore, their compact form factor enables seamless integration into small spaces.

Wolfspeed’s CoolSiC XM3 power modules offer several distinct advantages over silicon MOSFETs for power inverters at the same power rating, including being 60% smaller, with lower total volume and improved stray inductance performance owing to their integrated micro deformation liquid-cooled cold plate design.

Wolfspeed’s third generation SiC MOSFET technology is optimized in these modules by means of advanced design that maximizes its performance, including a trench MOSFET structure for greater cell density, increased device cell reliability and low switching losses that allow higher frequency operation with reduced gate oxide field strengths.

This combination has produced a highly efficient inverter that offers improved performance and reliability over traditional silicon-based solutions. ON Semiconductor’s technical collaboration with Mercedes-EQ’s Formula E car team has proven instrumental in developing their traction inverter using XM3 devices and increasing driving range of its electric powertrain. ON Semiconductor’s partnership has also enabled advancement of power conversion system while increasing performance on racecar.

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