Renesas Electronics rolled out a new generation of compact high-voltage IGBTs with withstand voltages of up to 1,200 V and current ratings of up to 300 A, in a bid to boost the power electronics at the heart of EVs.
IGBTs—insulated-gate bipolar transistors—are a class of power semiconductors that have been vital in getting electric vehicles (EVs) on the road. Renesas said that it is raising the bar for performance with a new generation of IGBTs that reduce power losses by 10% compared to its predecessor. The power savings in the company’s AE5 series of IGBTs will help automakers save battery power and boost the range of EVs.
The new chips deliver 10% higher current density than anything currently on the market in a form factor of 100 mm2 per 300 A. The new products also are approximately 10% smaller while retaining high robustness.
Targeted at a new generation of EV inverters, the AE5 IGBTs will be mass-produced starting in the first half of 2023 on 200- and 300-mm wafers at the company’s fab in Naka, Japan.
“Demand for automotive power semiconductors is rapidly growing, as EVs become more widely available," said Katsuya Konishi, head of the Power System Business at Renesas. IGBTs combine the high switching speeds and high impedance of the venerable MOSFET with the higher input resistance of a bipolar junction transistor (BJT).
Voltages Hit New Highs
The brushless-dc (BLDC) motors used in electric vehicles are controlled by inverters that convert dc from the car’s battery pack into ac. The range of the vehicle is affected by the performance (the amount of power lost when current is converted from one form to another) of the inverter. High-efficiency switches such as IGBTs are critical to extending the vehicle's range.
Today, most electric vehicles have internal architectures that can handle 400 V per battery pack. But auto manufacturers have plans to upgrade to 800-V batteries to increase EV ranges and reduce charging times.
Doubling the voltage in EV subsystems cuts the current in half for the same power, giving you the ability to boost range. This directly influences the cost of the battery and, as a result, the overall cost of the vehicle.
Upgrading from 400 V to 800 V also allows for the doubling of the charging rate with the same losses, said Renesas. That means no additional heat while charging. Heat dissipation is a limitation on the cables that pump electric current into the EV, as well as the charger’s inlet and internal wiring. If charging power is doubled, it will theoretically take half the time to top off the battery.
Reducing losses gives you the ability to cut the weight, space, and cost of everything from the power electronics to the electric motor. Saved space can be used to build bigger battery packs and extend range.
The upgrade from 400-V battery packs to 800-V systems is also triggering a shift from silicon IGBTs to silicon-carbide (SiC) MOSFETs. SiC devices deliver much higher switching speeds and thus lower switching losses.
While the SiC MOSFET is the top contender to take on IGBTs in high-voltage power supplies, not everyone is moving to the new technology yet. Moreover, the average IGBT generally costs less than its SiC counterpart.
Not Going Anywhere
The new family from Renesas signals that the IGBT will remain an important player in the world of power electronics for years to come, particularly when it concerns the high- to low-voltage power supplies in EVs.
The product family spans four high-voltage IGBTs targeted at 400- to 800-V inverters in EVs, including 220- and 300-A models with 750-V withstand voltage and 150- and 200-A models that tolerate up to 1200 V.
When it comes to 800-V battery packs, the IGBT or other switch at the core of the power supply must have significantly higher isolation and voltage ratings than the battery to keep it from overloading unsafely.
IGBTs typically suffer from conduction and switching losses. According to Renesas, the AE5 series focuses on conduction losses, improving them by 10% compared to its previous AE4 to further keep losses in check.
Another major characteristic of the IGBT is its saturation voltage, which influences conduction losses and, thus, overall losses and heat dissipation. Renesas said it sets a new standard for saturation voltage at 1.3 V.
The limitations of semiconductor equipment mean that IGBTs and other power switches frequently leave the fab with slight variations, which in some cases can hurt performance. High-power systems generally require you to connect several IGBTs in parallel to handle loads in the 10- and 100-kW range. This is usually done to obtain higher current ratings, improve thermal tolerance, and boost redundancy.
To address this, Renesas dialed in the production process to minimize fluctuations in the threshold voltage used to turn on the IGBTs—to within ±0.5 V—which is 50% better than it was in its previous generation.
The company said that this feature helps prevent current imbalance, reducing the load on the inverter.
Robustness Retention
Robustness is another area of improvement in the new IGBTs, which have to work in harsh automotive environments. The chips maintain stable performance through the operating junction temperature range of −40 to 175°C.
A 50% reduction in the temperature dependence of gate resistance (Rg) helps cut down on switching losses at hotter temperatures and suppress voltage spikes at colder temperatures, giving it better stability over variations. The chips support a reverse bias safe operating area (RBSOA) with a maximum IC current pulse of 600 A at 175°C junction temperatures, and a highly robust short-circuit withstand time of 4 µs at 400 V.
The AE5 series helps reduce inverter power losses, improving power efficiency by up to 6% compared to the last generation at the same current density. As a result, EVs with the IGBTs inside can last longer before having to be recharged.
Renesas said it plans to ramp up production starting in the first half of 2024 at its new 300-mm wafer fab in Kofu, Japan, which will double its supply capacity for power semiconductors and help it keep up with rising demand for electric car components.
The company will also roll out reference designs to give customers a blueprint to integrate the IGBTs into inverters with MCUs, power-management ICs (PMICs), gate-driver ICs, and fast recovery diodes (FRDs).
The IGBTs are available as bare die or in discrete packages. The 750-V, 300-A model is currently sampling.