K.H. Edelmoser and F.A. Himmelstoss (Austria)
DC-DC Converter, Solar Converter, Parallel Operation, Multiphase.
Especially in case of low voltage (e.g. battery powered solar) converter applications, normally very high primary current ratings will occur. This leads to a problematic design with efficiency restrictions. To improve the overall efficiency of the inverter and to reduce the input capacitor array, a possible solution is the parallel operation of several stages. The solution proposed in this paper is able to improve the parallel operation of power stages in conventional converters with modern current sharing techniques. Due to the reduced current in each of the paralleled output stages, the efficiency will increase significantly. The ripple of the input current is shared between the different stages, which helps to reduce the input capacitor in each string. In addition, the resulting frequency rises with the number of paralleled stages when multiphase operation is used. This leads to a more silent (EMV) design. Another big problem, the output rectifier operating at the high DC-link voltage, can be disburdened significantly by using the suggested current source inverter structure. In this paper a 12V / 500W solution realized by two 250W converters operating in parallel is described. Each output stage switches at 50kHz with a phase delay of 180° to the other one. The maximum peak current of each input stage is only about 25A. So very cheap mass products can be used as power switches. The concept is well suited for solar and renewable energy as well as aerospace applications.
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