Johannes Pforr

Filter Optimization for multi-phase DC-DC converter in automotive energy backup system

Cascaded filters offer a possibility to minimize the size of the filter components due to their increased attenuation at high frequencies. A cost optimized design of a cascaded filter of a multi-phase converter for an automotive energy back-up system will be shown, that results in small values of the inductances. However, the decreasing inductance values results in increasing current ripples in the first filter stage. The implementation of coupled inductors helps to reduce the current ripples of the single phase currents significantly and achieves a cost optimized design with increased converter efficiency. The influence of tolerances on the ripple cancelation phenomenon in multi-phase converters and coupled inductors on the cascaded filter design will be analyzed. The theoretical predictions are in good correlation with the experimental results obtained from a full-size prototype converter.

Current-balancing controller requirements of automotive multi-phase converters with coupled inductors

Voltage perturbations at the input of automotive multi-phase converters with coupled inductors can lead to significant equalizing currents in the converter and perhaps to core saturation and system failure, if adequate balancing control is not adapted. Analyses have been performed to predict the equalizing currents in the coupled inductors dependent on the input perturbations and dependent on the design of the coupled inductor. Results of these analyses demonstrate the need of a current-balancing controller and show that the required performance of the controller and the current measurement devices is heavily dependent on the coupled inductor design. A full size automotive prototype converter with four interleaved phases and coupled inductors has been built and tested. Measurements with the four-phase prototype converter are in close correlation with theoretical predictions from the analyses.

Buck-boost converter topology for paralleling HB-LEDs using constant-power operation

A single switch multi-inductor buck-boost converter topology is presented for paralleling LED-networks. The proposed technique is based on discontinuous inductor currents to achieve a homogenous light-distribution of parallel connected high-brightness LEDs. In contrast to the common approach of driving LED-strings with constant-current, the proposed topology supplies the LEDs with constant-power. The topology has originally been developed for automotive low voltage applications; however applications with galvanic isolations and operating off-line from a 230V or 115V mains supply are also possible. A prototype converter has been built and tested to proof its performance for an automotive lighting application and to verify the constant-power operation of the LEDs. The converter drives 6 parallel strings with 4 high-brightness LEDs connected in series. Experimental results demonstrate a good performance when the converter is operated in its desired operation range of discontinuous conduction mode. Measurements confirm the good performance of the converters constant-power operation, with maximum power deviations below 2% in the LEDs. A comparison of the common constant-current drive of LEDs to the prototypes constant-power operation shows a slightly more homogenous light distribution between the LED strings for the constant-power approach. Furthermore, tests with different heatsink temperatures show a better brightness stability of single LEDs operated at the proposed constant-power compared to the constant-current drive.

Multi-Port Converter with bidirectional energy flow for automotive energy net applications

A novel family of multi-port converters with bidirectional energy flow has been investigated for low-voltage high-current automotive energy-net applications. An example is given of a three-port converter designed for the 14 V/42 V automotive energy net and providing the possibility to also connect a double-layer capacitor to relieve the battery from excessive current stress and to stabilize the energy net voltages. The proposed three-port converter requires only three MOSFETS as switching devices. Analyses have been performed to investigate the suitability of the multi-port converter for the given application and a prototype converter has been built and tested to prove theoretical predictions. Measurements are in good correlations with results from the analysis.

Comparison of multi-port converter topologies with bidirectional energy flow for automotive energy net applications

Three-port converters with bidirectional energy flow have been investigated for the 14V/42V automotive energy net. The three-port converters are designed to interlink the two energy nets and a double-layer capacitor to relieve the battery from current stress and to stabilize the energy net voltages. The investigated converter topologies include a three-port converter that requires only three MOSFETS as switching devices. Analyses of the converter topologies have been performed and a prototype converter of the most promising converter, the three-switch topology, has been built and tested to prove theoretical predictions. Measurements are in good correlations with results from the analyses.

Turn-on behavior of automotive multi-phase converters with coupled inductors

Multi-phase converters with coupled inductors achieve high power density and high efficiency and are therefore very suitable for automotive applications. A disadvantage of coupled inductors in comparison to uncoupled inductors is the increased sensitivity to rapid changes of the volt-time product across the windings. These conditions occur at converter turn-on if the converter links two energy nets with constant voltages. In this paper an analysis has been performed to calculate the magnetic flux in the core of coupled inductors during the turn-on of the converter. Results of the analysis show that the peak flux obtained is much higher than the flux under steady-state conditions. To prevent core saturation an optimized start-up switching pattern has been developed for multi-phase converters with coupled inductors and arbitrary number of phases. Measurements with a full-size prototype converter have been carried out that confirm theoretical predictions.

Comparison of different winding schemes of an asynchronous machine driven by a multi-functional converter system

A comparison between different winding schemes has been carried out to optimize an asynchronous machine for an automotive electrical power steering system. The machine is driven from a multi-functional converter that consists of an inverter with integrated converter. This integrated converter provides an increased dc-link voltage to the inverter, but forces additional dc currents to flow through the machine windings. A detailed analysis is performed to describe the influence of the dc currents to the behavior of the machine and four most suitable winding schemes have been selected for the investigation. Results of the analysis demonstrate the requirement to carefully select the winding scheme when an asynchronous machine is operated from a multi-functional converter system. FEM simulations verify the results of the analysis. Four machines with different winding schemes have been built and tested together with the multi-functional converter. Experimental results are in close correlation with theoretical predictions.

Application of a floating H-Bridge converter to stabilize the automotive energy net

A floating H-Bridge converter is proposed to stabilize the automotive energy net against undesired voltage spikes and to limit the voltage range for the electrical loads. In comparison to classical converter topologies the proposed floating H-Bridge converter with integrated energy storage device provides lower switch-voltage stress and allows therefore the implementation of high-current low-voltage switching devices with lowest on-state resistance and very simple drive circuits. This low cost topology, which is connected in series to the loads, is analyzed for different operating modes. A full-size prototype converter was build and tested to prove the converter performance for the given application. Theoretical predictions are in good correlation with experimental results.

Impact of input and output voltage perturbation on the behavior of automotive multi-phase converters with coupled inductors

The impact of input and output voltage perturbations on the behavior of automotive multi-phase converters with coupled inductors has been analyzed. Results have shown that voltage disturbances on the automotive energy net can lead to significant equalizing currents in the converter and perhaps to core saturation or even system failure, if adequate balancing control is not adapted. Analyses have been performed to predict the equalizing currents in the coupled inductors dependent on the input and output perturbations. A full size automotive prototype converter with four interleaved phases and coupled inductors has been built and tested. Measurements with the four-phase prototype converter are in close correlation with theoretical predictions.

Feed-forward control of non-linear inductors providing soft-switching of DC-DC-converters

A novel auxiliary circuit with a current controlled non-linear inductor has been developed to achieve soft-switching for different converter topologies. This paper outlines the operation principle of the auxiliary circuit and gives details about the control of the non-linear inductor. A model has been developed that allows the calculation of the control current dependent on the operating point of the converter. This model has been implemented into a digital controller. A prototype converter has been built and tested to verify theoretical predictions. Measurements have shown that the efficiency of the prototype converter is greatly improved by the auxiliary circuit. Experimental results are in good correlation with theoretical prediction.