Abstract
This article proposes a new differential-cascading-based dual-stator brushless doubly-fed induction machine with a staggered dual cage rotor. Conventional differential mode of the brushless doubly-fed machine with cage rotor suffers from the low number of rotor bars because of the low equivalent synchronous pole pairs of |p1-p2|, and thus, severe rotor flux leakage, low capacity of magnetic field conversion of the rotor and low efficiency. To overcome the obstacle of the excessive harmonics of the rotor, a design method based on the differential cascading is proposed which enables the cage rotor with a high number of conductor bars even in the case of low pole pairs of |p1-p2|, hence the greatly reduced rotor leakage inductance and enhanced performance of the machine. The rotating magneto-motive force theory is applied to derive the interconnection rule of the staggered dual cage rotor, and meanwhile, the corresponding examples are illustrated. The performance comparisons between the differential cascading and the sum cascading based on the proposed machine are carried out. The results show that the proposed machine based on the differential cascading obtains higher power densities comparing to the sum cascading at the region of sub-natural synchronous speed, while its drawback is the increment of the loss due to the high rotor frequency, gaining lower efficiencies at the region of super-natural synchronous speed.
Highlights
Brushless doubly-fed machines (BDFMs), as the alternative to the conventional doubly-fed induction machine (DFIM) (Yin, 2021; Zhang et al, 2021), offer increased reliability and low maintenance due to the elimination of the brushes and slip-rings (Okedu et al, 2021), showing the promising prospects in the fields of variable speed constant frequency system (VSCF) such as the on-shore and off-shore wind power generation system (Cheng and Zhu, 2014; Han et al, 2018; Xiong et al, 2020)
The number of conductor bars of DS-BDFIM-SDCR based on the differential cascading (DC) is in accordance with the sum cascading (SC) one which means the number of conductor bars large even with the pole pairs of |p1-p2|, the greatly reduced rotor leakage inductance and improved performance of the machine
The design method of the DC for the DS-BDFIMSDCR is proposed to solve the issues of high rotor leakage and low capacity of magnetic field conversion of the conventional differential-mode-based BDFM
Summary
Brushless doubly-fed machines (BDFMs), as the alternative to the conventional doubly-fed induction machine (DFIM) (Yin, 2021; Zhang et al, 2021), offer increased reliability and low maintenance due to the elimination of the brushes and slip-rings (Okedu et al, 2021), showing the promising prospects in the fields of variable speed constant frequency system (VSCF) such as the on-shore and off-shore wind power generation system (Cheng and Zhu, 2014; Han et al, 2018; Xiong et al, 2020). If a magnetic field of the rotor rotates in the same direction with respect to the other one, the natural synchronous speed of the BDFM is determined by 60f1/|p1-p2| and the pole pairs are equivalent to be |p1-p2| which has been pointed out in (Williamson et al, 1997), namely, the differential mode of the BDFM. In the early study (Williamson et al, 1997), the cage rotor is utilized for the differential-mode-based BDFM, but the number of rotor bars is too low owing to the low pole pairs of |p1-p2|, resulting in excessive harmonics and the large rotor leakage inductance. The number of conductor bars of DS-BDFIM-SDCR based on the DC is in accordance with the sum cascading (SC) one which means the number of conductor bars large even with the pole pairs of |p1-p2|, the greatly reduced rotor leakage inductance and improved performance of the machine.
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