Better EV chargers through modular power electronics

Creating a new (power electronics) product is a very labor-intensive and expensive process. The journey from initial designs to various prototypes forms a very high proportion of the product’s cost. To tackle this, modular designs were introduced. Here, a higher power level can be achieved by using pre-designed blocks without the need for a complete re-design. However, in addition to ‘modularity in design’ and 'modularity in production’, there is also the concept of ‘modularity in use’. Our goal was to achieve all three types of modularity for power electronics used in high-power electric vehicle chargers.

Proposed solution

To achieve modularity in use, it is necessary to make each module functional. In our case, this means that each module is a fully operational power electronics converter with its own sensors and controllers that can operate as a standalone converter. Next, we connect multiple convertors into one smart system via data bus connections. This results in a higher power rating without altering the existing building blocks. Doing so, we utilize the benefits of modularity in use:

We can adjust the number of modules during operation resulting in higher efficiency.
We can handle failure during operation by isolating the failed module and keep operating at a lower capacity.
We simplify maintenance/reparations by only needing to replace the failed module instead of the whole system.

The biggest concern when using a modular approach is the cost of the components. A single converter of 200kW uses less components than 4 convertors of 50kW. To determine at which power levels modular designs are cost-effective, and result in higher efficiency or lifetime, we have developed a tool. Below is the example of 200kW AFE rectifier designs with a single module (non-modular) versus 2-5 modules (different levels of modularity) as shown in this figure:

costs and power losses

We conclude that for this specific case, the option using 5x40kW AFE rectifiers is the best, with 52% reduction in cost and 31% less power loss compared to the non-modular option (1x200kW). While the option of using 2x100kW modules has identical cost, but worse efficiency than the non-modular solution.

Validated solution

Once the ideal number of modules is identified, there are several other challenges in designing modular power electronics, and we have addressed them in our scaled-down modular AFE prototype as follows:

We have built 3 identical modules.
Each module is a complete stand-alone converter with hardware, sensors and controllers.

We have achieved equal current sharing between modules as shown in measured currents in the figure below, despite manufacturing inaccuracies (5-10% deviation in inductance values).
Adjusting the number of modules for higher efficiency requires a smooth turn-on and turn-off of modules during operation, which was achieved as shown in this figure:

modules

Conclusion

Modular approach to power electronics can be beneficial in many ways: increased reliability, efficiency, lower cost, more scalable and flexible design. However, the positive impact of using modular power electronics will vary depending on the use case: each power level and application will require a different number of modules.

Our tool can be used to identify the optimal number of modules and design of the Modular power electronics for the specific application and user preferences. Moreover, hardware validation of the solution provides tangible proof of concept and addresses potential challenges of modular systems.

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Kristof Vrancken, Communication Officer

14 December 2023

Kristof Vrancken is Digital Communication Officer at Flanders Make since 2019. As Digital Marketeer with experience in both B2B and B2C environments he writes with a fresh view on technological innovation, about what literally and figuratively moves within our research centre.