Characterising brushless doubly fed machine rotors

Abstract

The brushless doubly fed machine (BDFM) is a robust alternative to the doubly fed induction generator, currently widely used in wind turbines but prone to brush-gear and slip-ring failure. The rotor winding plays an important part in a BDFM, coupling the two stator windings. To date, nested-loop (NL) rotor windings have been exclusively used in practical BDFM. This approach may not be ideal for larger machines, in which form-wound series-loop rotor winding may be preferable to large section bars and end-rings. This study gives a comparative analytical and experimental study of two different brushless doubly fed 160 frame-size rotors, with NL or series-wound windings, mounted in identical rotor core laminations operating in the same stator tested at a limited voltage (200 V line). The rotors gave a performance which accords with theoretical predictions from two independent methods, giving insight into the design issues of the different rotor windings from both an electrical and manufacturing viewpoint. Nomenclature List of symbols X 1 , X 2 , X r indicating, respectively, stator1, stator 2 and rotor winding quantities p 1 , p 2 stator winding pole-pair numbers q phase number f 1 , f 2 supply frequencies s 1 , s 2 slips of different winding systems N shaft speed N eff1,2&r effective number of turns for the stator, 1&2 , and rotor, r , windings n 1,2&r turns ratios of stator, 1&2 , and rotor, r , windings k w winding factor k p pitch factor γ winding pitch angle R, L winding resistance and inductance Z impedance of a rotor loop www.ietdl.org

A Novel Wound Rotor Type for Brushless Doubly Fed Induction Generator

“…It is evident that, intermediate the stator two windings, the optimized winding arrangement (Case 5) owns a more sufficient ability for creating cross coupling. Before the proposed wound rotor type BDFIG construction, the most widely used type is the nested-loop cage rotor BDFIG which makes a great contribution to BDFIG analysis [2][3][4][5][6]. The nested-loop cage rotor contains multiple loops and can be regarded as a concentrated winding, thus, it is difficult to obtain high winding factors for both two pole pairs.…”

“…Compare with the conventional wound rotor windings, large cage-type rotor winding designs are deemed to create higher space harmonic contents. A comparison analysis of nested-loop rotor windings and series-loop wound rotor winding was presented in [6]. Focus on the electrical and manufacturing, it shows the latter may be preferable to large machines, but they did not propose methods to reduce harmonic content which cannot be ignored for BDFIG.…”

Experimental analysis of noise and vibration for large brushless doubly fed machines

“…Both stator windings were connected in delta. The rotor comprises six sets of nests each consisting of a number of concentric loops [13], the conductors being solid bars with one common end ring [14]. The magnetic properties for the iron were provided by the machine manufacturer.…”

Effects of Rotor Winding Structure on the BDFM Equivalent Circuit Parameters

“…2 [7]. R 1 and R 2 are the stator resistances, L m 1 and L m 2 are the stator magnetizing inductances and L 1 and L 2 are the stator leakage inductances.…”

“…The loops were connected in series resulting in a reduced rotor leakage inductance but increased rotor resistance. McMahon et al [7] characterized BDFM rotors with the winding factor method, a new analytical parameter calculation method. It was assumed that there is no coupling via harmonic fields and that the magnetizing inductances associated with harmonic fields were neglected.…”