Control of Brushless Doubly-Fed Reluctance Machines under Normal and Faulty Operating Conditions
The brushless doubly fed reluctance machine (BDFRM) is an attractive alternative technology to traditional slip-ring doubly fed induction machine (DFIM) for slip-power recovery applications with limited variable speed ranges such as wind turbines or pump-alike drives.\ud Owing to its favourable operational characteristics, the BDFRM has been receiving increasing attention by the research and industrial communities, foremost because of its brushless design and high reliability (these being the main DFIM limitations) as well as cost advantages of using a partially rated power electronics converter.\ud A comprehensive, largely or small scale lab model machine parameter independent control development and comparative performance analysis of this emerging machine topology have been done both by computer simulations and experimentally on a dSPACE platform using the\ud parameters of a small-scale laboratory prototype obtained by off-line testing. A Maximum Torque Per Inverter Ampere (MTPIA) strategy and scalar control method with voltage boost, which is rather suited to drive and generator systems under consideration where fast dynamic\ud response is not required, have been implemented and efficiency of the machine (e.g. copper losses) investigated in both motoring and generating modes. Such kind of work has not been reported in the literature available on the subject.\ud A large-scale BDFRG for grid-connected wind turbines with maximum power point tracking (MPPT) has also been examined by simulation studies under the same scalar control conditions referenced above. Comparisons with high-performance control algorithms as primary flux\ud (field) oriented control (FOC) have been made and associated trade-offs considered for typical ii wind profiles. A vector control (VC) scheme, similar to the FOC approach, has also been demonstrated on both the machine side converter (MSC) and grid side converter (GSC) in the BDFRM(motoring and generating)modes.\ud The BDFRG low-voltage fault-ride through capability has also been researched and a dedicated FOC scheme developed to allow the generator to stay on-line and provide the necessary reactive power support for the network voltage recovery under the faulty operating conditions. The\ud BDFRG has been shown to be able to safely ride through the fault without the crowbar circuitry this being difficult to achieve with a comparable DFIG. This desirable BDFRG property can be attributed to the relatively large leakage reactance’s and consequently lower fault current levels compared to the equivalent DFIG.
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