| According to the prospects and development of the wind power generation systems, this paperselects Boost Three-Level (Three-Level, TL) converter (referred to as the Boost-TL converter) anddiode neutral point clamped (neutral-point-clamped, NPC) three-level inverter cascaded topologywith control program among several typical converter topologies which are suitable for direct-drivewind power generation systems. The structure of the generator-side is a diode rectifier with Boost-TLconverter, the converter of the grid-side is NPC three-level inverter.The operation principle of the former Boost-TL converter is analyzed in detail, the input-outputrelationship of the converter is derived and the small signal model of the Boost-TL converter is alsoestablished. The voltage balance of the voltage divided capacitors is analyzed, a decoupling ideaabout the output-voltage control loop and the deviation-voltage control loop is introduced and a specificcontrol scheme is given. For NPC three-level inverter, this paper focuses on its neutral-point voltagebalance problem. The neutral-point voltage balance of the inverter is achieved by the Boost-TLconverter.On the basis of theoretical analysis, this paper builds Boost-TL converter and NPC three-levelinverter SVPWM simulation model. At the same time, for the issue of neutral-point potential balanceabout the NPC three-level inverter, a neutral-point voltage control module simulation model is alsoestablished. A simulation study of Boost-TL converter with resistive load and the load of the inverteris conducted respectively. The inverter load’s influence on the former Boost-TL converter is discussed.While using the former Boost-TL converter to balance the neutral-point voltage, THD of the grid-sidecurrent and the inverter’s AC output voltage are lower than that with other software algorithms.Finally, a5kW Boost-TL converter principle prototype is made. Experimental results verify thetheoretical analysis. |
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