This decade is expected to be the decade of electric vehicles. The rise of electric vehicles is inevitable around the world and India alike. The Indian electric vehicle market is still in its infancy, but it is predicted to grow at more than 50% CAGR over the next two decades. The primary technology driver for e-mobility systems in Power Electronics. Building blocks for Electric Vehicles are Batteries, Traction Motor, and Power Electronic Converters. Technologies for these building blocks must improve to provide vehicle range, safety, reliability, life, and flawless operation. This article focuses on Power Electronics elements for Electric Automotive Vehicle applications.

Advanced semiconductor switches, new ferromagnetic material, improved embedded electronics hardware, and several other new technologies are propelling the increased performance of electrical power train systems in electric vehicles. While safety, reliability, and efficiency are mandatory requirements, the cost is the primary business driver for these products. Intelligent design to strike a suitable balance between performance and cost is key to business success. Above all, design decisions are driven by cost.

While battery technology is evolving as a reliable and safe power storage unit, researchers are also working on improving battery technology to enable their fast-charging capability. Standardization of battery voltage across various segments of vehicles is a key factor for the success of electric vehicle technology development. Most vehicle manufacturers (OEMs) are finalizing about 400V for passenger cars and about 800V for commercial vehicles. While two-wheeler and three-wheeler manufacturers are staying with 48V, 60V, and 72V batteries.

Few critical demands from all Power Electronic products in an electric vehicle are Efficiency (Output power as a percentage of Input Power drawn), Size, and Weight. The efficiency of all power electronic products, in turn, influences the size and weight of the products. Lower efficiency means higher power loss which results in increased heating. To dissipate the extra heat, the size and weight of the products get increased. Higher efficiency helps better thermal management and better “Range” (miles per charge). Thus, one of the most important factors that the engineers are trying to improve in these products is “efficiency.” The next important area of attention is “power density” (Power delivered per unit of volume of the product)

Power Semiconductor Switches are at the heart of any power electronic device. Power Semiconductor Switch technology is going through a rapid transition driven by the increased demand for power converters in Electric Transportation systems, be it Electric vehicles, Electric Rail engines, or More Electric Aircraft. Silicon-based IGBTs and MOSFETs are coming with better switching characteristics that enable higher power conversion efficiency.

Additionally, the technology of Silicon Carbide MOSFETs (SiC MOSFET) and Diodes are maturing and improving faster. SiC MOSFETs are helping to improve the efficiency and size of the power converter. Silicon Carbide (SiC) MOSFET as a wide bandgap device provides a lot of merits that are especially favored by the electrical vehicle (EV) industry. Compared with Silicon IGBT or MOSFET, SiC MOSFET has lower switching and conduction losses, which is important for EV mileage extension. Further, SiC switching devices can operate up to 175oC as compared 150oC for Silicon devices. The high junction temperature operation capability makes it possible to design an integrated powertrain with a reduced cooling requirement. The high switching frequency of the SiC device reduces the size of passive components in the powertrain system, including the DC-link capacitor, boost inductor, and EMI filter. Because of these features of the SiC device, the overall size of the powertrain can be reduced, which makes the SiC device a good candidate for achieving high power density for EV powertrain.

Semiconductor manufacturers are constantly working on bringing superior silicon technologies to the market. They are revamping the silicon die packaging technologies to address various automotive applications, thermal management being the most important and improving the semiconductor packages for challenging power densities in EV applications. IGBT and MOSFET solutions are constantly evolving to address the growing demands of the automotive market. Dual-Side Cooled compact 750V IGBT modules with Integrated chip-level temperature & current sensors are specially made for 400V traction inverter application. MOSFET packages evolved from through-hole packages to surface-mount devices (SMD) like the DPAK or D2PAK, and finally to the latest leadless packages with significantly improved silicon technologies inside. Innovative surface-mount packaging with top-side cooling MOSFETs is becoming available for compact converter packaging. In the traditional approach of bottom-side colling, the surface mount MOSFETs dissipate the heat through PCB to the heatsink. With top-side cooling, the hot-spot of MOSFET is exposed at the surface of the package, which allows 95 percent of the heat to be dissipated directly to the heatsink. These packages are specifically targeted for high thermal performance in EV applications.

There are three major Power Electronic elements in the electric vehicle: Traction Inverter, DC-DC Converters, and Onboard Chargers. 

The inverter is an AC to DC converter that converts the Battery voltage to supply an alternating voltage to the traction motor. The typical power rating of the Inverter ranges from 120kW to 250kW for a passenger car. Inverter controls the rotational speed of the traction motor and provides the required torque to propel the motor. Another significant feature the inverter brings to the vehicle is its ability to provide precise “Electric Braking.” Electric braking helps reduce the usage of mechanical braking and hence improves the life of the mechanical brake system by reducing mechanical wear and tear. The electric braking feature also transfers the motor kinetic energy to the battery every time the vehicle is braked. This, in turn, improves the vehicle range.

The power conversion efficiency of Traction Inverter directly influences the vehicle range (miles/charge). The typical efficiency of the inverter is more than 98%, which is expected to improve in the coming years further. The typical power density of the inverters is 20kW/Lit. In the coming years’ power density is expected to improve to 40kW/Lit, which means double the power in the same size. 

DC-DC Converter acts as a DC transformer that converts the high voltage from traction battery to low voltage to supply all low voltage electronics like power steering, power window, wiper control, dashboard multifunction display, and all other electronic control functions, including very critical “Vehicle Control Unit” (VCU). The typical efficiency of a DC-DC Converter is more than 96%. Typical power rating of a DC-DC Converter ranges from 1kW to 6kW for a passenger car. 

An onboard charger (OBC) is a Battery Charger that is operational only when the vehicle is stationary. OBC converts the AC voltage of the utility power source to DC voltage to charge the battery. OBC has its in-built control function to charge the battery at constant current, constant power, and constant voltage. Onboard chargers for passenger car are typically rated for 3.3kW for operation from a single-phase power source and goes all the way to 22kW for operation from the 3-phase power source. The typical efficiency of Onboard Chargers is more than 95%, which is expected to reach better than 97% in coming years. Typical power density of Onboard Chargers is less than 1kW/Lit. In the coming years, the power density of onboard chargers is expected to improve to 3kW/Lit. 

Most of the current Onboard Chargers support unidirectional power flow, namely AC grid to the battery. However, many OEMs are planning to install Bi-directional Onboard chargers. Bi-directional onboard chargers are futuristic technology. Bidirectional onboard chargers allow fully charged EV batteries to supply power to the utility grid. Discharging the EV batteries whenever available help improve their life while the burden on the grid reduces. It is expected that bi-directional onboard chargers will gain higher popularity, supporting Vehicle to Grid (V2G) and Vehicle to Home (V2H) power flow.

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