This paper investigates an induction machine using a novel concept of a converter-fed rotor. The stator is directly connected to the grid while the rotor is fed by a converter with a floating capacitor over the dc-link. In earlier work this topology has shown to be capable of improving the power factor and efficiency of a 4-pole induction machine. This paper explores the possibility to improve the power factor and efficiency of a squirrel-cage 12-pole 17.5 kW induction machine by redesigning the cage rotor to a wound rotor to enable connection of the rotor windings to the converter. A standard 12-pole squirrel-cage induction machine (SCIM) with an inherent low power factor is studied. A wound rotor induction machine (WRIM) is then analytically designed. The performance of the designed WRIM using the analytical model is shown to agree with the results from the finite element (FEM) simulations, thus verifying the correctness of the model. The analytical model is then further used to design different WRIMs with different dimensions and rotor slot numbers. Performances of these designed WRIMs show good potential for power factor and efficiency improvement. Particularly, an optimum efficiency improvement of 6.8%, compared with the original SCIM, has been achieved.

This paper investigates an induction machine with a novel concept of the rotor fed by a converter. The stator is Y-connected and directly connected to the grid, while the rotor windings are open-ended and fed by a back-to-back converter with a floating capacitor. Power factor and efficiency improvements of the induction motor are studied with different settings of phase-shift angle between the two converters. Moreover, the dynamic performance of the induction machine is explored in MATLAB/Simulink and verified experimentally on a 1.8-kW induction machine in the laboratory. The result shows good agreement between simulation and experiment. At a constant speed, variable load operation of the induction machine is obtained by setting the frequency of the rotor voltage.

This paper presents the synchronous operation of a novel generator termed as the rotating power electronic brushless doubly-fed induction generator (RPE-BDFIG). It is shown that the generator operates well at the synchronous speed of the main machine, delivering the desired power to the grid. Furthermore, it is illustrated that the RPE-BDFIG behaves similar to a synchronous generator in the synchronous mode. The closed-loop control of the generator is implemented in real-time, and the current and voltage waveforms of the stator and rotor of the RPE-BDFIG are experimentally analyzed. The paper highlights the stable operation and full control of the generator during synchronous mode.

A novel topology of induction machine with a rotor integrated converter with a floating capacitor is investigated in this paper. The stator windings of the induction machine are directly connected to the grid. While the rotor windings are connected to a converter with a floating capacitor. The steady state mathematical model is presented and used to predict the operating range of the induction machine. The result shows that the induction machine can operate in a wide torque and speed range instead of working on the original torque-speed curve. In addition, the relationship between capacitance and capacitor voltage is studied for the constant speed and variable load operation. It is shown that it is possible to choose a low volume and high capacitance capacitor since the average DC-link voltage is quite low.

This paper describes the construction of the rotating power electronic converter. By mounting the power electronics on the rotor of an induction machine, the rotor winding can be made easily accessible without the use of slip-rings and brushes. This offers certain advantages regarding motor control. However, it is evident that the rotating mass, communication with the converter and maintaining the mechanical stability and reliability of the system are huge challenges that must be overcome. This paper describes some solution that are partly investigated and some solutions that still needs to be investigated in more detail.

This paper explores a topology of induction machine drive with a novel concept of a wound rotor fed by a converter with a floating DC-link capacitor. The Y-connected stator windings are connected to the grid, while Y-connected rotor windings are connected to a three phase converter with a floating DC-link capacitor. By integrating the converter into the wound rotor, the slip-rings and the brushes becomes unneeded. Constant speed operation can be achieved at various loads by controlling the fundamental frequency of the converter. The stator power factor can be effectively improved over a wide range of load at constant speed. Particularly, unity power factor can be obtained within ±25% of the rated load. Moreover, harmonic spectra of the stator and rotor currents are presented.

A novel speed control strategy of an inductionmachine with RPEC (rotating power electronic converter) isinvestigated in this paper. The stator of the machine is directlyconnected to the power distribution network while the open-endedrotor windings are connected to a back-to-back converter. Adynamic model is developed in the three-phase reference frame.Dynamic performance of the starting process of the system isstudied, based on an 1.8kW induction machine in the laboratory.Experimental results have shown that constant speed control isachieved in a simple manner by controlling the rotor currentfrequency. Importantly the stator power factor can be improvedeffectively within a wide range of load variation including therated load. Moreover, the dc-link voltage over the capacitorbetween the two converters is considerably low which implies agreat reduction of the capacitor size.

The use of solid rotor and pole-plate synchronous machines has several advantages, among which is the fact that it provides a more robust rotor compared to laminated equivalents. This paper investigates the time and space harmonic losses in solid rotor synchronous machines. The work considers the use of copper coating on the pole-plates, studying the effect that this design modification has on the losses. A recommendation is given based on this study, which is considered to reduce the time harmonic losses without detrimental effects as far as the space harmonic losses are considered.

Impact of the different magnitudes of symmetrical voltage dip on the performance of a Rotating Power Electronic Brushless Doubly-Fed Induction Generator is presented. This type of topology consists of a doubly-fed induction generator with power electronic converter and an integrated exciter mounted on the shaft and rotating with it. The transient simulation study is carried out in order to investigate the magnitude of the voltage dip the rotor converters can withstand before a protection scheme is needed for Low Voltage Ride Through (LVRT) of the generator. Furthermore, successful LVRT under severe voltage dips is also performed using passive resistive network strategy.

A different configuration of brushless doubly-fed induction generator is presented. The power electronic converters are mounted on the rotor rotating with it. The slip rings and carbon brushes are replaced by a rotating exciter which serves as a slip recovery device as well as a means of providing excitation to the rotor of the induction generator. The dynamic model of the brushless topology is derived and analyzed. Furthermore, feedback control of the topology is also implemented and analyzed. It is shown that the generator shows stable operation in steady state as well as in dynamic state at variable speeds.