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This paper presents an instantaneous torque control method for cascaded doubly fed induction machines (CDFIMs) with a rated torque-sharing ratio feature under steady-state operation. A CDFIM includes two coupled main and auxiliary doubly fed induction machines, and the rated torque-sharing ratio herein means that the machine torques are proportional to the machine ratings. The proposed method is established based on transferring the torque equations of the two machines into the rotor-flux reference frame of the auxiliary machine. Then, the instantaneous torque and the rated torque-sharing ratio are controlled via the stator current components of the auxiliary machine, while machine fluxes are within allowable ranges. To verify the method and evaluate its capabilities, the suggested method is used for the speed control of a CDFIM experimental setup including two 4-kW doubly fed induction machines and a 4-kW dc machine to apply a sudden mechanical load change to the CDFIM. Further, a case study including 12-kW and 4-kW DFIMs is also simulated to evaluate the performance of the torque control method for a CDFIM with different machine ratings. The test results confirm that the proposed control schemes achieve the desired performances without exceeding the ratings of the machines under various test scenarios. [ABSTRACT FROM AUTHOR]

A fast and robust fixed switching frequency peak current controller for DC–AC converters is presented. The proposed method tends to mimic the switching behavior of pulse width modulation (PWM) techniques, so it features all the advantages of peak current controllers (such as simplicity, fast transient, and optimum dynamic response), with the superiority of fixed switching frequency and harmonic free output. The proposed method is a generalized approach that can be applied to different PWM schemes. The method is specifically elaborated for single-phase distributed generation applications, using various inverter topologies and mimicking different PWM schemes. Moreover, adaptive bands are proposed to provide active damping for the controller, to extend use of the proposed method for inverters with LCL output filters. Feasibility and performance of the controller is shown by means of simulations and experiments. [ABSTRACT FROM AUTHOR]

This paper presents a fast and robust $DQ$ current controller to regulate the output power of single-phase grid-connected inverters. The proposed method generates the grid current orthogonal component without introducing any additional dynamics or distortions to the control loop. Moreover, its operation does not depend on the system parameters. The proposed method exhibits improved steady-state and dynamic performances in comparison with the inverters equipped with the conventional orthogonal signal generation techniques. Its improved characteristics make the proposed controller suitable for smart inverter applications, to provide advanced grid functionalities as demanded by recently revised standards. Simulation and experimental results show the feasibility and performance of this control structure. [ABSTRACT FROM AUTHOR]

This article proposes and demonstrates a fault-detection method to locate interturn short circuits (ITSCs) in the stator windings of a brushless doubly fed induction machine (BDFIM). The detection of ITSC is important in machine health prognostics as ITSC is an early stage fault that may lead to other faults such as coil-to-coil and coil-to-ground. BDFIM consists of power and control windings in the stator that are magnetically coupled through a nested-loop rotor winding. Existing ITSC detection algorithms use rotor slot harmonics in stator current spectra as fault indicators for only conventional doubly fed induction machines. However, these algorithms cannot be applied to BDFIM due to its different stator/rotor winding structure. This article primarily proposes a new analytical formulation for the nested-loop rotor slot harmonics (NRSHs) as ITSC fault indicators in BDFIMs. Using NRSHs, a detection algorithm is also proposed to detect and locate ITSC in power/control windings of BDFIMs. The proposed algorithm is verified based on numerical analysis of a BDFIM using the finite-element method. The accuracy of the proposed fault-detection algorithm is also experimentally investigated and demonstrated using a BDFIM test rig. Both numerical and experimental test results confirm effectiveness of the proposed ITSC fault-detection algorithm. [ABSTRACT FROM AUTHOR]