How to Increase Hybrid Electric Vehicle Battery Utilization Efficiency

One of the major efforts to increasing Hybrid Vehicle/Electric Vehicle battery utilization efficiency in the automotive industry is focusing on the inverter. Current estimates of switching losses are in the range of 5-15%. Switching losses are inevitable, but we can address this by design and target how we want to mitigate it while weighing the factors of compactness, ease of design, ease of manufacturability, and cost.

Electric Vehicle Battery

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Magnitude of Loss and Wasted Heat

Even with the most efficient designs, the heat losses in the inverter can be in the kW range. This waste heat must be removed. Discrete switches generally have a single side to transfer heat. However, modules are now moving to double sided cooling where the silicon die has a set of heat transfer layers on both top and bottom sides. This allows for heat extraction on both sides of the module, allowing for more compact designs. Discrete components are screwed or clipped on to a heat sink with thermal grease, whereas modules are moving to a direct copper bonded baseplate which is connected to a pin fin heat sink with coolant flowing around the pins to remove heat.

Reducing Heat at the Source

Advances in switch technology have decreased losses. The progression has been from MOSFET to IGBT to SiC or GaN. Although it is easy to say, “I’ll just use the switch with the lowest power loss!”, there are other considerations. One example is cost: does it make sense in this application? Another example is that the more exotic switching technology requires careful design in the form of symmetrical component and trace layout as well as using best practices to eliminate stray inductance.

Reducing Heat Throughout the System

As the industry moves towards higher power applications, such as class 8 trucks, the need for higher voltage systems to reduce the I²R losses throughout the system increases. Higher voltages are permitted by advances in batteries and inverters. Battery packs are being designed for higher voltages and switches are being (or soon will be) introduced to the market to handle these increased voltages. Additionally, as the overall power increases, the industry is hitting a limit in the viability of very high current connectors. Higher voltages allow for the use of a much broader availability of suitable connectors as well as reduce the weight and cost of copper conductors in the vehicle.

While this is a high level overview of switching losses, it is still important to understand at an introductory level in order to start your investigation in how to deal with switching losses.

If you would like some additional help with increasing hybrid electric vehicle battery utilization, the staff at LHP Technology Solutions would love to help you develop a solution!