Increased electrification of the powertrain in the car – the how and why

What is all this electrification discussion about in the automotive world? There have been a lot of articles in the press on batteries, specifically 48V and 400V Li-ion, 12V lead-acid batteries and their challenge to co-existence in one vehicle with increased load requirements. It turns out that these loads such as traction motors, power steering, onboard charging, compressors and regenerative braking, all in the power train system require power above 1kW – much higher than previously.

Handling the load of a conventional 12V battery used in infotainment, cluster and safety applications is challenging because it is inefficient and heavy for a vehicle due to large wiring harnesses required to handle high currents. Operating these loads at the regulated voltages (higher than 12V) generated from a conventional 12V lead-acid battery, significantly reduces the power dissipation, wiring complexity and overall system weight. This is where a 48V Li-ion battery system comes into play for HEV and ICE vehicles and 400V for EVs. Higher voltage means lower current for the same energy transfer, which in turn implies lower power dissipation and hence alleviates the need for large wires. This is why both battery types need to co-exist while transferring power at a very high efficiency.

HEV charger system block diagram

The need for high efficiency, different batteries, and increased power make an efficient energy transfer conditioning system using switched-mode power supplies (SMPS) more compelling than linear regulators used in the past. SMPS enables the application to operate in both ON and OFF states, which, in theory, achieves 100% energy efficiency of energy transfer. With advances in power electronic switches, employing the SMPS concept enables automakers to work towards achieving these requirements.

So, how does SMPS work? The switches turn on or off using a technique known as pulse-width modulation (PWM). These switches can operate under high switching frequencies, making the power converters less bulky and smaller in size. PWM is achieved using a controller that can be analog or digital followed by a gate driver circuit that delivers the appropriate charge to switch the power devices and operate at the right operating voltage. Gate drivers enable power supply systems with superior performance and efficiency.

Picking a controller is highly dependent on the vehicle’s requirements - cost, flexibility, integration, reliability and availability to write firmware (for digital controllers) are all taken under consideration. Likewise, the choice of gate drivers is dependent on the drive current, maximum allowable operating voltage, speed (reduced propagation delays), along with cost reduced component count (single channel versus bridge drivers), and isolation, to name a few. Texas Instruments has several automotive qualified controllers, both analog and digital (read this article on when to choose analog versus digital), as well as industry’s fastest gate drivers to operate SMPS switches.

Also read a white paper I wrote on power electronics in Automotive.

If you have any questions on SMPS, please leave it in the comment section below.

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