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Isolated buck converter from KNESTEL – more than just a voltage transformer

A DC source sink that meets the many requirements in the field of electromobility? That is exactly what the Knestel company has succeeded in doing with the development of the isolated buck converter.

In the field of electromobility, there are numerous applications and a wide variety of requirements for a DC source sink. The product developed is a device that can be used flexibly. The first task to be solved was the realization of a galvanic isolation. The solution is a bidirectional resonant converter. With the efficient Zero-Current-Switching technology, an efficiency between 92 and 95% is achieved, depending on the operating point. The transformer is primary and secondary shielded, which means that no coupling capacitance can be measured. In order to fulfill as many applications as possible, the complete device is designed for 2-quadrant operation. This means that energy can flow in both directions. Electric vehicles can thus not only be charged, but also discharged. Currently, for example, the batteries of a vehicle can be discharged to a lower point for delivery. It can also be used as a DC sink for fuel cell tests. To enable an adjustable output voltage, the second part of the product consists of a microprocessor controlled 3-level buck converter bridge. This also functions as a boost converter bridge in bidirectional direction.
As a total product, a device has been created which has a continuous output power of 50kW. For 10 seconds, a limit output power of 80kW can be retrieved. In order to meet the output power required for each application, it is possible to cascade the overall device as often as desired. Thus small and also large battery outputs can be simulated. The max. output power can be configured according to the requirements. The complete product consists internally of two bidirectional resonant converters and a buck converter bridge in double design. Depending on the requirements, the buck converter bridges can be connected together in series or in parallel. For example, a total output voltage of 1000V at 640A is possible, which will enable fast charging for powerful vehicles in the future. The setpoint is currently transmitted to the control board via CAN-BUS and for time-critical applications via EtherCAT. The isolated buck converter is thus suitable for a wide variety of DC source-sink applications. Efficiency and flexibility are convincing when used in charging technology, e.g. for electric vehicles. The speed of the microprocessor comes into its own e.g. for simulation purposes, such as battery simulation, especially in combination with KNESTEL’s precision analog measurement module.