A new generation of durable inverters that are able to measure and control temperature changes are enabling the expansion of electrified vehicle development.
In the wake of the electrification of the passenger car, multitudes of applications start to adopt the zero emission idea. Variety in applications also means variety in requirements for the respective motor and controller system. Solutions for full-electric driving, P0-P4 mild-hybrid systems or hydraulic pumps for example have vastly different requirements, which cannot simply be expressed by an overall kW value. The inverter-controller functionality must match with the overall vehicle-control structure. Power-ratings and lifetime must match the vehicle operating conditions.
Temperature is the key element to understand, predict, control and balance power and lifetime. Average temperatures and especially temperature changes and their repetition of the power-switches have the strongest impact on thermal stress and thus define product lifetime. Accurate thermal models that can simulate temperatures in a system are therefore necessary in the design-phase to optimize the integration of the inverter in the overall vehicle system – balancing output power against lifetime and cooling. The same models are later on in the regular operation needed to calculate critical system temperatures based on the measurable temperatures and load conditions.
For the SKAI3 LV a thermal model has been derived that can predict temperatures of the power switches and the capacitors, depending on the cooling conditions and the load conditions. Even with extreme steps in the output current, an accuracy of <2°C after 400 sec compared to the measurement is achieved. This allows for any kind of load cycle, the evaluation of required ambient and cooling conditions and a prediction of the achievable lifetime. With the same basic model, in-operation temperature calculation is possible even for highly dynamic conditions, such as load steps, where reference temperatures from a separate sensor would be too slow and inaccurate. The Foster-model approach is used to describe the mathematical formalism, making it easy for the user to implement a precise thermal calculation in the system control-loop.
The upcoming SKAI3 LV, 3rd generation of MOSFET based inverters, offers high power in a very small volume, while leaving maximum flexibility for system integration. Supported by models for power-loss and temperature calculation, a wide range of applications can be addressed. The SKAI3 LV is a compact powercore, which needs a control-board to be completed. With a power-density of more than 25 kVA/l and a total volume of less than 1.8l, the design fits into many applications with its standard case, already. For designs with special requirements regarding space, cooling or power-connectors, the design suits as a perfect starting point for a customer specific design.
The interface between customer controller and gate-driver has an easy-to-use structure and requires only a single 13V supply. Fed back control signals are already voltage-scaled. Current and temperature sensors are routed to a separate connector to maintain electrical isolation. To simplify controller and software design, a dedicated housing is available, providing easy access to the controller-PCB in design, while already using the power section in its full functionality and performance.
The SKAI3 LV product family is designed for battery voltages with a wide range of input voltages, ranging from nominal 48V up to 144VDC covering all typical batteries in industrial applications and most other vehicle applications.