Independent Control of Rotor and Grid Side Converters Using Cascaded and Incremental Hysteresis Controllers in DFIG Wind System

This paper presents an independent control of rotor side converter (RSC) and grid side converter (GSC) for a doubly fed induction generator (DFIG). A novel cascade feedback linearization (CFL) technique based on non-linear differential geometry is developed for design of RSC, which leads to decoupled currents. Here, the rotor DC link voltage can be regulated with respect to a square transform on its voltage reference and the d-axis current that satisfies conditions for zero dynamics. The controlled RSC has a capability to track DC link voltage reference faster and also attain global stability. The GSC controller has been designed by incorporating a new incremental hysteresis comparator (IHC) that utilizes the hysteresis band to produce the suitable switching signal to the GSC to get enhanced controllability during grid unbalance. The IHC produces higher duty-ratio linearity and larger fundamental GSC currents with lesser harmonics. The latter can thus achieve fast transient response for GSC. All these features are confirmed through time domain simulation on a 15 KW DFIG Wind Energy Conversion System.