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In this paper, a fast initial speed estimation method has been proposed for low rotational speed operation of speed sensorless induction motor drives based on the second-order differential of the secondary flux. The fast estimation can reduce an undesirable disturbance torque generation during the restart process. The effectiveness of the proposed method is confirmed by experiments. The estimation time has been compared with those in the literature and the benefit of the proposed method is confirmed.

This paper provides a theoretical and experimental discussion on ac-inductors design for a modular multilevel triple-star bridge-cell (TSBC) converter, or shortly a TSBC converter. This converter requires multiple ac inductors for controlling nine cluster currents. This paper proposes three three-legged, six-winding, "inter-zigzag" inductors for the TSBC converter. Since each leg of the individual inductor has two windings, the three inductors have 18 windings in total. The wire leads are zigzagged among the three inductors. This unique structure of the "inter-zigzag" windings leads to the following feature: Both three-phase supply and motor currents produce no magnetic flux in each of the nine legs. This feature makes each inductor smaller in size and lighter in weight. A specially-designed downscaled motor drive system rated at 400 V and 15 kW is constructed and tested to confirm the validity of a design of the proposed inductors, as well as to verify transient motor-drive performance during four-quadrant operation.

Experimental results are presented for three different low-speed flux-focusing magnetic gearboxes. The performance of the magnetic gearbox is compared when utilizing ferrite and NdFeB and also a hybrid design, in which ferrite magnets are used in the inner rotor and NdFeB magnets are used in the outer rotor. The peak torque and efficiency are measured. It is shown that the NdFeB magnetic gearbox has an active torque density of 151 Nm/L.

This paper presents the design of a sustainable wind generator system using redundant materials. The topology makes use of permanent magnets (PMs) from discarded computer hard disk drives. The challenges associated with these magnets are discussed in detail. An axial-flux machine topology is developed, which ensures balanced voltage production and eliminates the large proportion of coil interconnecting leads associated with direct-drive wind generators which operate at low speed and have many poles. The performance of the machine is first predicted using classical machine theory. Detailed 2-D and 3-D numerical analyses of the machine topology are then presented, and a sensitivity analysis is conducted with the help of the numerical analysis, in which the influence of the PM dimensions on the performance of the machine is investigated. Finally, the analytical and numerical results are verified using experimental results.

This paper describes an approach in improving the performance of the position sensorless control of an interior permanent-magnet synchronous motor using parameter identification. The model-based sensorless method requires accurate motor parameters. At low speed, the resistance variation degrades the accuracy of position estimation. The identified parameter is used in the sensorless drive system to improve the accuracy of position estimation. In this paper, the resistance is identified online, but the offline identified value of the q-axis inductance is used. The experimental results reveal the effectiveness of applying parameter identification to the sensorless drive system.

This paper analyzes the effects of fractional pitch and distributed winding stators on the self-sensing performance of permanent-magnet machines. Three rotor configurations (i.e., a flux-weakened interior permanent-magnet synchronous machine (IPMSM) and two flux-intensified IPMSMs) and two stator designs (i.e., distributed and concentrated windings) are presented to analyze the cross saturation, secondary saliencies, saturation-induced saliencies, and saliency ratio, depending on the possible rotor and stator configurations. Finite-element modeling has been used to obtain a detailed understanding of the self-sensing performance of these machines.

The focus of this paper is to improve the self-sensing performance of an interior permanent-magnet synchronous machine (IPMSM) by modifying the rotor configurations. A field-intensified IPMSM (FIIPMSM) is designed by adding flux barriers in the rotor of an IPMSM. In comparison with IPMSMs, FIIPMSMs have the advantage of decoupling saturation-induced saliency, cross-coupling effects, and also secondary saliencies, which reduce the estimation accuracy of self-sensing control for IPMSMs. A finite element analysis is used to design the FIIPMSM and assess the performance of the machine for self-sensing. The self-sensing capabilities of IPMSMs and FIIPMSMs are presented and compared. The results demonstrate the improved self-sensing performance of the new field-intensified machine.

The objective of this paper is to present a sensorless position estimation technique for switched reluctance machines (SRM) operating in constant dynamic mode over a wide speed range including zero speed. The technique combines two different methods to deliver high resolution position information over the wide speed range. At zero and low speeds, a voltage pulse injection method is used to estimate the rotor position in all four quadrants. For higher speeds, a sliding mode observer (SMO) based algorithm is used and combined to work with the low speed algorithm. Experimental results demonstrate the effectiveness of this new combined technique that has four-quadrant operation capability.

In this paper, a new current vector control method combined with an indirect field orientation feedforward algorithm is presented for shaft sensorless induction motor drives. The new current control technique is based on the concept that the angular speed and the magnitude of the stator current vector can be controlled by two stator voltage components relative to the stator current vector. In the proposed solution, the current regulators are working with DC quantities and are rotating together with the stator current vector. The new topology drive has improved low speed performance compared to the conventional solutions. Experimental results show the performance of the prototype drive system.

M. Depenbrock and A. Steimel comment on the paper by H. Kubota et al. (see ibid., vol.38, p.1081-6, 2002), pointing out that some of the problems to be solved have already had solutions published, one of which is protected by a German Patent. H. Kubota replies to the comments.