Executive Summary
To show the automotive industry the advantage of wide bandgap semiconductors (SiC and GaN), HiPERFORM project has been defined in which several tasks are defined in which the advantages of these materials can be shown/utilized. Especially by the increasing demand for Electric Vehicles (EV) SiC devices could stimulate that more. The advantages of SiC modules can be summarized by defining four goals to be realized:
1. increase of switching frequency,
2. increase of efficiency (decrease of conduction and switching losses),
3. decrease of volume and
4. increase of safety and reliability.
These goals are looked at by comparing the results with a state of art Si based solution.
One of the tasks (5.2.2) of HiPERFORM is to build an off-line charger of 175KW together with the required test equipment to test this charger according to different scenarios. This document describes the converter design which is used in the charger. To eventually get a fully-fledged charger it takes more than only designing a converter but that will not be treated here. The converter has three main functions:
1. to have galvanic isolation between suppling source (the mains) and the output
2. which can charge in constant voltage / c.q. constant current mode and
3. the input current has minor harmonics.
There are two major solutions, the most important one is depicted in Figure 5-1. The advantage of this converter is that it easily can be compared with a reference wherein the isolation is still done by a conventional LF transformer. In the second solution shown in Figure 5-2, the insulation is obtained by a high-frequency converter. However, this HF solution is not treated here.
Because of the lower dissipation per switching cycle the switching frequency can be increased. A part of the efficiency increasement will be scarified but despite this, other advantages will recover in return: the inductance of the sine filter can be lower (smaller volume, less losses). If the net result is that the ripple currents are lower this also leads to lower input and output capacities. Finally, lower semiconductor losses also result in smaller heat sinks. However, to achieve the set goals (volume reduction of 50% and 1% efficiency gain) remains a challenge.
Summarized, the use of SiC switches as described in this report results in higher efficiency due to lower switching losses and resistance losses in the sinus-filter. It also leads to smaller volume by smaller inductances and capacitances, and finally it yields reduction of sound by the higher switching frequency.