New isolated converter for interfacing PMSG based wind turbine ...

Fig. 20. Output voltage and current of voltagedoubler rectifierSecond experiment was performed in conditions thatcorrespond to maximal wind speed. First DC linkvoltage U dc1 was set to 250 V, but load of voltagedoubler rectifier was 1250 W. Inverter input voltageU 1 have small ripple due to charge current of voltagedoubler rectifier, but qZS DC/DC converter inputcurrent I in have no ripple (Fig. 21).Fig. 23. Secondary voltage of isolation transformerat 1250 W loadOutput voltage of voltage doubler rectifier havebigger ripple than at rated conditions (Fig. 24) andcan be too high if load will be grid inverter insteadof pure active load.Fig. 21. Input voltage U 1 of inverter and inputcurrent I in of qZS networkTransformer primary and secondary voltagewaveforms have the same shapes as in simulations(Fig. 22, Fig. 23).Fig. 22. Primary voltage of isolation transformer at1250 W loadFig. 24. Output voltage and current of voltagedoubler rectifier at 1250 W loadConclusions and Future WorkThe study of the wind theory shows that a variablespeed wind turbine allows maximum power from airflow to be extracted. PMSG based VSWTcharacteristics and wind properties on the Balticcoastal regions were analyzed to define the converteroperation modes. Analysis of the convertertopologies studied earlier shows that they are notwell suited for VSWT applications due to the highcomplexity of the parallel LCL DC/AC converter orlow efficiency in the case of the isolated buck typeconverter.For these reasons the new topology of PMSG basedVSWT and grid interfacing converter is presented inthis paper. The converter consists of a fullycontrolled rectifier, a quasi-Z-source DC/DCconverter, a high frequency isolation transformerand a voltage doubler rectifier. Such topology offersgood input voltage boost properties and a relativelysimple power circuit.Simulations of the proposed topology wereperformed to verify its ability to ensure necessaryoutput voltage at all defined generator operationmodes.106