Innovation – Power Electronics

Novel Power Electronics for battery packs

A major innovation in the LiBat project is the use of a novel power electronics topology called Multi-Level Converter (MLC). Originally aimed at road vehicles, the BIPED (Battery Integrated Power Electronics for EV drive train) feasibility study showed significant weight savings that equally apply to electrically powered aircraft.

Two of the BIPED consortium Obrad Dordevic (Liverpool John Moores University) and Paul H. Riley (City University of London) both in the UK modified the original BIPED design for the LiBat aerospace application.

How it works

Conventional methods have a single high voltage battery connected to the power electronics that drives the motor (see Figure 1).

Figure 1: Conventional motor driver

Battery voltages are high and above the safe handling limit, so special precautions must be taken to handle them. The power electronics are bulky and heavy and usually there is a separate box needed to charge the battery.

An MLC segments the battery into smaller, safe groups (see right hand side of Figure 2). For LiBat this is 14 cells in series, 50.4V nominal. To meet the 110V three phase requirement of LiBat with depleted batteries, 5 modules are connected in series but only switched in when the motor needs power, Figure 3.

In the future, we expect to develop a special customised control chip (called an ASIC) that will combine the functions of MOSFET driver, battery management and communications in a topology we call M2LeC; Modified Multi-Level Converter. This configuration is about the same price as the 2035 Power Electronic predictions and when used with the innovative LiBat cooling system up to 20 times lighter (left and bottom of Figure 2).

Figure 2: final miniaturised M2LeC

A great benefit of MLC is that you can charge the batteries from a standard 3-phase supply using the same Power Electronics system, something we expect to demonstrate soon in LiBat.

Figure 3: Motor control