Tesla’s New Hybrid Inverter Design Acts Like a Battery Gearbox

@minusYCore on X

Over the past decade, designers of traction inverters—the components that convert a battery's DC output into the AC used by electric motors—have had to choose between two semiconductor approaches. Silicon (Si) IGBTs are inexpensive and very rugged but relatively inefficient. Silicon Carbide (SiC) MOSFETs, by contrast, offer much higher efficiency at the cost of greater fragility and much higher price.

Many higher-end electric vehicles today, including the Model 3 and Model Y, employ SiC MOSFETs to maximize range, but that efficiency increases motor production costs.

A recently published patent application (WO 2026/010828-A1), titled "Hybrid Traction Inverters for Electric Traction Motors," describes an alternative: place both Si and SiC devices in the same inverter and actively switch which technology is used depending on driving conditions.

Variable Transmission

The patent outlines a controller that functions like an automatic transmission, routing electrical load to whichever semiconductor is best suited for the moment.

For steady-state cruising—when efficiency is most important—the controller favors the SiC MOSFETs. In a low-current mode, the system keeps these MOSFETs dominant to maximize range.

For high-demand situations such as hard acceleration or towing, the system switches to the Si IGBTs. In these high-current "power gear" scenarios, the rugged IGBTs are driven first so they absorb the heavy electrical stress and protect the more delicate SiC devices.

Cutting Costs

Cost is a major driver of the design. SiC devices are substantially more expensive than silicon IGBTs.

To address that, the patent describes a 2:1 physical ratio: two Si IGBTs for every SiC MOSFET. That lets the SiC portion be sized for the common case—highway cruising—rather than rare peak acceleration events. Because peak acceleration is a small fraction of real-world use, Tesla can downsize its SiC capacity and rely on the cheaper IGBTs to supply the peak currents, reducing overall module cost while retaining nearly the same driving range as an all‑SiC design.

Increased Durability and Backup

The design also improves robustness. Permanent magnet (PM) motors, such as those used in the Model 3 and Model Y, can generate a back-EMF voltage spike if the motor spins faster than the inverter or if the car is towed with wheels on the ground. That spike can stress inverter components.

The hybrid approach uses the more resilient IGBTs as a safeguard. A fault-management circuit can immediately override the normal efficiency-first logic if it senses a dangerous voltage spike or other fault, ensuring the heavy-duty IGBTs handle the load first and protect the SiC MOSFETs.

The Technical View

The patent details how the two device types are coordinated to avoid interfering with one another. They cannot be on at the same instant, so a timing protocol is used: the rising edge of the IGBT drive leads the SiC drive by roughly 100 nanoseconds to 10 microseconds. That brief lead time creates a protective window in which the Si device takes the stress.

To reduce parasitic inductance and magnetic interference, the described board layout places the SiC MOSFET centrally, flanked by Si IGBTs. That arrangement balances electrical fields and helps prevent unwanted interactions inside the motor inverter.

What This Means For You

Fundamentally, the patent aims to remove long-standing trade-offs in traction-inverter design. Until now, buyers and engineers have effectively had to choose between range, performance, and affordability; picking two typically meant sacrificing the third.

High-range, high-performance cars like the Model S are expensive in part because they require large amounts of silicon carbide. More affordable vehicles have historically sacrificed either range (smaller batteries) or efficiency (cheaper Si inverters).

A hybrid inverter that combines SiC for cruising efficiency and Si IGBTs for peak loads promises lower-cost motors without a meaningful range penalty, improved durability in fault scenarios, and the same on-road performance that drivers expect.