Mohammad Farshadnia

Analysis of MMF and back-EMF waveforms for fractional-slot concentrated-wound permanent magnet machines

An analytical modelling technique to calculate the generated magneto-motive force (MMF) and back-EMF of fractional slot concentrated wound (FSCW) permanent magnet synchronous machines (PMSMs) is reported. The generated MMF of a FSCW stator is analyzed and modelled using a Fourier series technique. General expressions of the harmonic winding factors for FCSW stators with different slot-pole combinations are then obtained. A general expression for the generated back-EMF of FSCW PMSMs is then derived. The obtained analytical results are validated through finite-element analysis (FEA) and experimental tests on a prototype FSCW PMSM. A comparison between the generated voltages of various FSCW stator topologies is also performed.

Diagnosis of broken rotor bars in induction motors based on harmonic analysis of fault components using modified adaptive notch filter and discrete wavelet transform

Abstract This paper proposes a method for fast and accurate detection of broken rotor bars (BRBs) in a three-phase squirrel cage induction motor. The fundamental component of the stator current signal is extracted using a linear time-invariant filter. The resultant residual signal which contains the harmonic components of the current is then used to detect the BRBs, by means of discrete wavelet transform (DWT). Since in experiment it is not possible to break the rotor bars while the motor is under load, finite element method and MATLAB/Simulink are employed to accurately demonstrate the behavior of the running machine as the BRB happens. To get more accuracy, differential evolution (DE) optimization algorithm is used to obtain the corresponding fault impedance for the rotor external circuit of the MATLAB model. Detail coefficients (DCs) of the wavelet decomposition are employed as the new fault indicators. Simulation results show that using DCs of the harmonic component signal rather than the actual current signal, leads to more distinctive fault signatures in the wavelet decomposition. The obtained results suggest that the proposed fault detection scheme can be employed as a highly reliable technique for diagnosing rotor bar failures in running machines.

Optimal gain scheduling controller design of a pitch-controlled VS-WECS using DE optimization algorithm

This paper presents an optimal gain scheduling power controller for a variable-pitch variable-speed wind energy conversion system (VS-WECS). For this purpose a set of linear quadratic Gaussian (LQG) controllers are optimally designed using differential evolution (DE) optimization algorithm. These controllers are then used to form a gain scheduling controller (GSC), aiming to regulate the pitch angle and generator electromagnetic torque, and thus, controlling the VS-WECS output electrical power as well as the shaft speed in the above-rated wind speeds. The designed controller for this multi-input multi-output (MIMO) system also reduces destructive mechanical loads on the rotating parts of the wind turbine, while ensuring fast and accurate regulation of the systems variables within their operational constraints. Simulation results on a VS-WECS subjected to a realistic wind model are provided using MATLAB/SIMULINK, which are compared with those of conventional point design controllers. Results indicate that in addition to being robust against parametric uncertainties, the proposed GSC provides enhanced transient and steady-state performance, as well as reduced mechanical loads in a wide range of above-rated wind speed and turbulence variations.

Combined Speed and Direct Thrust Force Control of Linear Permanent-Magnet Synchronous Motors With Sensorless Speed Estimation Using a Sliding-Mode Control With Integral Action

A sliding-mode-based control scheme with integral action for combined speed and direct thrust force control of a linear permanent-magnet synchronous motor is proposed. A nonlinear state-space model for the combined dynamics of speed and thrust force as system states is utilized for the synthesis of the sliding-mode control law. Direct integral action is also included in the control law to eliminate the steady-state error in the speed tracking. The sensorless speed estimation is performed by using an adaptive flux observer with a modified dual boundary layer sliding-mode component. Lyapunov stability analysis to prove the global asymptotic stabilities of both the controller and observer is provided. The effectiveness of the proposed method is validated experimentally and demonstrates excellent transient and steady-state speed control performance.

Detailed Analytical Modeling of Fractional-Slot Concentrated-Wound Interior Permanent Magnet Machines for Prediction of Torque Ripple

Electromagnetic torque in interior permanent magnet machines is a function of their inductances and permanent magnet (PM) flux linkages, which are assumed sinusoidal in the standard dq model of the machine. This assumption is flawed when a fractional-slot concentrated-wound stator is utilized, because its nonsinusoidal winding function leads to harmonics in the machine parameters. In order to address this deficiency, the nonsinusoidal machine parameters are modeled in this paper, based on which, a modified extended dq model is proposed. The harmonics in the machine parameters are included in the proposed modified extended dq model and their effects on the machine operational characteristics are accounted for. Detailed equations for the average torque and torque ripple are then derived based on the proposed modified extended dq model. Experimental tests are also described for the measurement of the proposed modified extended dq model parameters. The estimated torque and torque ripple by the proposed model are validated through experimental tests on a prototype fractional-slot concentrated-wound interior permanent magnet machine.

Detailed analytical modelling of fractional-slot concentrated-wound interior permanent magnet machines for prediction of torque ripple

The standard dq model of interior permanent magnet machines is based on the assumption of sinusoidal machine parameters. This assumption is flawed especially when a fractional-slot concentrated-wound stator is utilized. In order to address this deficiency, in this paper the non-sinusoidal machine parameters are modelled in the abc-system. An extended dq-model is then proposed based on the derived non-sinusoidal machine parameters. New parameters are introduced in the proposed model and experimental tests are described for their determination. Based on the proposed extended dq-model, detailed equations for the average torque and torque ripple are proposed that specify the parameters involved in the production of different torque components. The proposed extended dq-model is used to predict the performance of a prototype fractional-slot concentrated-wound interior permanent magnet machine.

Analytical Modelling of Rotor Magnetic Characteristics in an Interior Permanent Magnet Rotor

This chapter proposes a technique for analytical modelling of the non-homogenous magnetic saturation in the IPM rotor iron, based on which an analytical model for calculation of the PM flux density is proposed. The principles of the magnetic equivalent circuit in electric machines are first explained. The flux paths in a V-shaped IPM rotor due to the magnet residual flux are then classified into five groups. Accordingly, geometrical relationships in the IPM rotor are derived and used in analytical modelling of the non-homogenous magnetic saturation in the rotor iron. The B-H curve of the rotor core material is taken into account in the proposed approach. The proposed model provides information regarding the flux density and relative permeability of the iron in different regions of the rotor. In the next step, the state of the art analytical model for the PM flux density in the airgap is briefed, for which, a novel model is then proposed that is based on the novel magnetic saturation map that was derived earlier in this chapter. A case-study was then investigated to evaluate the proposed techniques using FEA and experimental results from the prototype machine.

Design of Optimal Winding Layouts for Multiphase Fractional-Slot Concentrated-Wound Permanent Magnet Machines

This chapter proposes a heuristic algorithm for the design of optimal winding layouts for multiphase FSCW stators to achieve maximum torque density. The proposed heuristics algorithm is based on the analysis performed in Chapter 2 of this thesis for determining the harmonic winding factors for FSCW stators. A new indicator referred to as the “winding performance index” is proposed that evaluates the torque production ability of different winding layouts for FSCW stators. Multiple case-studies are investigated to evaluate the application of the proposed heuristic algorithm. The obtained results are validated through FEA and tests on a prototype FSCW machine.

Analytical Modelling of Stator Magnetic Characteristics in Fractional-Slot Concentrated-Wound Permanent Magnet Machines

This chapter lays the basis for the rest of this thesis. A thorough analysis is first performed on the MMF produced by different FSCW configurations, based on which, FSCW stators are classified into “classes” and “categories”, each of them with their own distinct features. Lumped equations are then proposed for different stator categories. The harmonic winding factors of the different FSCW stator categories are then formulated based on which the flux linkages and back-EMFs are calculated. A case-study is then investigated to evaluate the application of the proposed equations in the selection process for the most appropriate slot and pole combination for application-oriented FSCW stators.

Conclusions and Future Works

This chapter discusses the significance of the research reported in this thesis and concludes its contributions. Suggestions are also provided for future expansion of this work.