Brushless Doubly Fed Machine Magnetic Field Distribution Characteristics and Their Impact on the Analysis and Design

Abstract

This paper contributes to the characterisation of the brushless doubly fed induction machine (BDFIM), which is attractive as a variable speed generator in applications (offshore wind turbine) with minimum maintenance requirements. The BDFIM has two three-phase stator windings of different pole numbers housed within the same stator slots and a shortcircuited rotor winding capable of coupling fields of different pole numbers. The stator windings and rotor winding create a magnetic field distribution with a range of characteristics different to those of conventional induction machines. This paper presents an analysis to identify the field characteristics and discusses their impact on the analysis and design of the BDFIM. The characteristics are determined from an analysis of the sum of two rotating sinusoidal field waveforms and confirmed by comparison with time-stepping finite element results and measured magnetic flux density data.Index Terms-Brushless doubly fed machine (BDFM), flux density, field distribution, rotor design, core loss, standing wave.

Parameter independent control of doubly-fed reluctance wind generators without a rotor position sensor

“…⋆ = 0) with the secondary winding taking over completely the machine magnetisation from the primary side as = 0 given (11). The and waveforms are essentially scaled replicas of the closely related and ones considering (10). They don't seem affected by the sudden variations instigated in the , and further reflected upon the and counterparts, to demonstrate the excellent disturbance rejection capabilities of the PI regulators.…”

“…This undesirable trend can be explained by the rising | | and | | levels in (26), according to Fig. 7 and (10). The corresponding Δ and Δ can be formulated by means of Fig.…”

“…Under the primary voltage alignment conditions (i.e = , = 0) depicted in Fig. 2, ignoring the winding resistance ( ), which is justified for MW range generators, and substituting (4) and ( 5) for ≈ = ∕ , ≈ 0, with = and = from (9), into ( 7) and ( 8), and the primary reactive power ( ) in terms of the controllable secondary − frame currents can be expressed as: (10) and (11) and can be realised as illustrated in Fig. 3.…”

“…The BDFRG has two stator windings of different pole numbers and frequencies: the grid-connected primary, and the back-to-back converter-fed secondary to enable a bi-directional power flow by analogy to the DFIG's rotor winding [9]. The magnetic coupling between them is achieved through a modern reluctance rotor having half the total number of the stator poles [10]. Such unusual design and operating principles make the BD-FRG's 'natural' synchronous speed half the DFIG's for the same number of rotor poles and line frequency.…”