Advances in a power electronics system including improved power cycling capability have made it suitable for propelling heavier commercial vehicles.

The electrification trend in the on-road public transportation continues. Especially in China the plug-in-hybrid bus (PHEB) and the battery electric bus (BEB) take a significant part of new vehicle admissions covering more and more share of the small, medium and large city bus segments. According to Research Institute of Highway (RIOH), Ministry of Transportation (MOT) China plans to reduce the annual carbon emissions of city busses by as much as 10,7 million tons in 2020. The calculation has been done under the assumption that 200 000 PHEB and BEB city busses will reduce the fossil energy consumption by 5,84 * 10E9 liter Diesel. For usage in heavier busses a reinforced variant of Semikron´s field approved off-the-shelf motor controller SKAI2HV (Fig 1) has been developed which enables the increase of output torque by up to 30%. This has been achieved by a significant reduction of the existing thermal resistance. Furthermore the power cycling capability of the built-in power semi-conductors has been highly enhanced due to introduction of a new wire-bond alloy. The new variant allows now to propel heavier busses with a single electric drive.

Plug and play

Figure 2: Device Temperatures

As shown in main picture the new SKAI2HV variant is now alternatively available with a power connector interface. The connector features a high voltage interlock loop (“HVIL”) contact to enable safe shutdown of the high electrical voltage before the connection can be fully opened. Therefore the service staff is fully prevented from touching hazardous voltages. The built-in receptacle supports cable harnesses with 50mm^2 Cu cross section per line or 70mm^2, alternatively. Furthermore a straight or an angled plug can be attached. The power connector enables significantly faster and 100% process safe assembly of cable harness. As an example Fig 2 shows a part of the resulting power semiconductor temperature cycles of the new reinforced SKAI2HV motor controller driving a large city bus. The built-in motor control software QUASAR reduces the switching frequency before the inverter losses can lead to a critical high junction temperature of the implemented power semiconductors. This happens in real-time. Due to the significantly reduced thermal resistance of the power semiconductors together with the implementation of the improved bonding wire alloy the maximum overload current of the SKAI2HV motor controller during vehicle acceleration or deceleration can be increased by more than 20%.

Versatile applicability

The SKAI2HV product portfolio now covers a wide range of commercial vehicle applications. It fits for small, medium and large city busses, supports drivetrains with one or several traction motors fed by battery or internal combustion engine (ICE). In case of ICE it covers also the need for active rectifying of the generator output. The battery voltage can vary between 100Vdc and up to 800Vdc. The new reinforced variant supports an electrical output peak power of up to 250kW. The motor position can be sensed with a resolver or absolute encoder. Another variant supports motor speed measurement by means of incremental encoder.