Electromagnetic Torque Ripple Research Articles

A novel speed control strategy for 3-phase induction motor drives with star-connected under single-phase open-circuit fault using modified RFOC strategy

In this research, a novel control method is proposed for 3-Phase Induction Motor (3-PIM) drives with star-connected under Single-Phase Open-Circuit (SPOC) fault using modified Rotor Field-Oriented Control (RFOC) strategy. The standard RFOC strategy is designed based on the d−q model of 3-PIM during normal mode. This strategy cannot be applied for a 3-PIM under SPOC fault as the model of a healthy 3-PIM is different from the model of a faulty 3-PIM. The use of standard RFOC strategy for Vector Control (VC) of a 3-PIM under SPOC fault increases the electromagnetic torque ripples during this fault. To overcome this problem, two unbalanced rotational transformations are used. A Current Transformation Matrix (CTM) is obtained based on the concept of maintaining value of Magnetic Motive Force (MMF) of the faulted machine like the healthy machine. Then, a Voltage Transformation Matrix (VTM) is introduced by using the presented CTM and according to the Single-Phase Induction Motor (SPIM) model. Based on the results, faulted machine RFOC equations were obtained similar to the healthy machine RFOC equations by using the CTM and VTM. The proposed technique was verified by simulations and experiments. Results indicated that the performances of the faulted machine under the proposed RFOC strategy are better than standard control techniques.

Five-Level Inverter Fed DTFC-SVM of Permanent Magnet Synchronous Motor Drive

In this paper, a five-level diode clamped inverter fed DTFC-SVM of Permanent Magnet Synchronous Motor (PMSM) drive is proposed for high power industrial applications. In Direct Torque and Flux Control with Space Vector Modulation (DTFC-SVM) technique, the speed of PMSM drive is regulated by controlling stator flux and electromagnetic torque directly and independently such that it abandons the use of direct torque control for PMSM Drive. The proposed multilevel inverter fed DTFC-SVM based PMSM drive gives very less ripples in stator flux and electromagnetic torque and also gives very less total harmonic distortion (THD) in the stator winding voltages and currents which consequences excellent dynamic and steady-state performance of drive. The five-level inverter switching pulses are designed using five-level space vector modulation (SVM) based on two-level SVM, so that it reduces the complexity of the SVM and also gives very good performance under all environmental conditions. The proposed model is simulated in MATLAB/SIMULINK software under various conditions, such as, No-load, load, reversal speed, and change in speed. In order to show the feasibility and effectiveness of the proposed model, it is also implemented in the experimental setup under various conditions.

Vector Control Applied to Mitigate the Electromagnetic Torque Ripple in Doubly Fed Induction Generator

This paper proposes a novel Vector Control topology for stator current harmonic mitigation, due to the grid voltage harmonic content, focusing on mitigating the torque undulations in the Doubly Fed Induction Generator. The Proposed Controller referred here as to HVC - Harmonic Vector Control, is capable of mitigating any desired current harmonic. Voltage grid fifth, seventh, eleventh and thirteenth harmonic components causes current harmonic components of the same order (5th, 7th, 11th and 13th) in the generator but of higher relative amplitudes, due to the low stator series impedance. Therefore, the HVC has been tested for the control of such current harmonic components. As an advantage, the proposed control does not require a harmonic filter to estimate the harmonic content present in the stator current due to the power grid, which are the main disadvantages found in literature for the existing controllers. Firstly, the control topology is described and explained in detail. Next, simulation and experimental data are shown and compared to prove the suitability and efficacy of the proposed control. In the cases studied, the steady state error of the proposed controller is close to zero. Furthermore, the HVC can be used as a harmonic filter in DFIG and the harmonics can be chosen according to the application requirements.

Feedforward Neural Network-DTC of Multi-phase Permanent Magnet Synchronous Motor Using Five-Phase Neural Space Vector Pulse Width Modulation Strategy

In this work, the direct torque control (DTC) is applied to the five-phase permanent magnet synchronous motor (FP-PMSM). The DTC method based on classical space vector pulse width modulation (SVPWM) is a common solution used to overcome traditional problems; such as stator flux ripple, electromagnetic torque ripple and gives more total harmonic distortion (THD) of the stator current. The actual paper is based on improving the performance of DTC-SVPWM by using the feedforward neural networks (FNNs) instead of the proportional-integral (PI) regulators and hysteresis comparators (HCs) of the conventional SVPWM strategy. This algorithm can solve the traditional PI regulators and HCs problems which are represented in responses dynamic and reduce the torque ripple, flux ripple, and the THD of stator current of FP-PMSM drives. The proposed strategy was tested in different tests with simulation using Matlab software.

Real-Time Implementation of Starting Current Limitation Method for Cereals Milling Systems Using dSPACE R&D Controller Board

In this paper, a starting current limitation method of a cereals milling system powered by a photovoltaic micro-grid is proposed. Today, the milling system consisting of a locally designed hammer mill driven by an induction motor is recognized as an innovative and efficient cereal milling solution. For this purpose, they are increasingly being developed in urban and rural areas. Although they offer many advantages, they have some limitations, such as the electromagnetic torque oscillations and the high inrush current at startup. A starting current limitation method based on soft starting technique is proposed to mitigate these negative effects in the transient state. To develop the proposed method, the scalar control principle is used. The scalar control is a simple technique, and it is operated to control the voltage magnitude and the supply frequency. The proposed method has been simulated and compared to conventional direct-on-line starting to evaluate its performance. Simulation results show that the method achieves a predominant performance over the conventional, providing a significant reduction in inrush current while having a lower electromagnetic torque ripple. To validate the method in real-time, an experimental test environment was developed using a dSPACE R&D 1104 controller board, an induction motor, and a SEMIKRON converter. Real-time experimental results show positive feedback on the proposed current limitation method's efficiency and effectiveness by corroborating the simulation results.

Fault-Tolerant Control of a Triple Redundant PMA-SynRM Driven Under Single-Phase Open-Circuit by Mono-Inverter

In this article, a new fault-tolerant control strategy for a triple redundant 3 × 3 phase permanent magnet assisted synchronous reluctance motor under a single-phase open-circuit fault has been proposed. In order to reduce the cost of the system, a two-level three-phase inverter is constructed to drive the parallel-connected motor under normal and fault-tolerant conditions. In normal operations, the current and torque are equally distributed to the three modules of the motor, while in a fault-tolerant state, they should be redistributed according to a specific ratio. The optimal ratio is obtained by investigating the control strategy of minimum copper loss and minimum torque ripple. The torque ripple of the normal module is increased to offset the torque ripple of the fault module, thereby reducing the total electromagnetic torque ripple after the failure. It means that no auxiliary switching devices need to be added even if the failure happened, which can significantly reduce the complexity and improve the reliability of the control system. To verify the theoretical analysis, simulations and experiments have been conducted. The results are in good agreement with that of theoretical analysis.

Development of Three-Phase Permanent-Magnet Synchronous Motor Drive with Strategy to Suppress Harmonic Current

This study aimed to develop a three-phase permanent-magnet synchronous motor drive system with improvement in current harmonics. Considering the harmonic components in the induced electromotive force of a permanent-magnet synchronous motor, the offline response of the induced electromotive force (EMF) was measured for fast Fourier analysis, the main harmonic components were obtained, and the voltage required to reduce the current harmonic components in the corresponding direct (d-axis) and quadrature (q-axis) axes was calculated. In the closed-loop control of the direct axis and quadrature axis current in the rotor reference frame, the compensation amount of the induced EMF with harmonic components was added. Compared with the online adjustment of current harmonic injection, this simplifies the control strategy. The drive system used a 32-bit digital signal processor (DSP) TMS320F28069 as the control core, the control strategies were implemented in software, and a resolver with a resolver-to-digital converter (RDC) was used for the feedback of angular position and speed. The actual measurement results of the current harmonic improvement control show that the total harmonic distortion of the three-phase current was reduced from 5.30% to 2.31%, and the electromagnetic torque ripple was reduced from 15.28% to 5.98%. The actual measurement results verify the feasibility of this method.

Frequency analysis in fault detection of dual‐channel BLDC motors with combined star–delta winding

This study compares the properties of dual-channel brushless DC motors with permanent magnets (DCBLDCMs) in three configurations of the stator windings of both channels. An analysis was performed of star-connected (Y), delta-connected (Δ), and combined star–delta (YΔ) channel windings. A proprietary mathematical model of a DCBLDCM machine with combined star–delta windings is presented. Each type of winding configuration was evaluated in terms of tolerance to the occurrence of a discontinuity in the channel. An Fast Fourier Transform (FFT) analysis of the selected voltage signal was used to diagnose the operating status of the DCBLDCM. It was demonstrated that it provides unambiguous information about the operating status of individual channels of the motor. In the case od 24/10 DCBLDCM design, the harmonic spectra of a selected voltage signal in relation to the artificial neutral point, are presented. The results of simulation tests were compared with the results of laboratory measurements. It was demonstrated that an FFT analysis of a voltage signal in relation to the artificial neutral point identifies a fault in a channel of the motor. When evaluating the characteristics of individual winding configurations, the value of electromagnetic torque, torque ripple, system efficiency, and emitted noise were taken into account. In the conclusions, the advantages of the combined star–delta winding compared to the traditional star and delta winding configurations are presented.

Model Predictive Torque Control for Dual Three-Phase PMSMs with Simplified Deadbeat Solution and Discrete Space-Vector Modulation

Unprecise voltage vectors applied in conventional model predictive control (MPC) would cause additional ripples in electromagnetic torque. To eliminate the problem, this article proposes an improved model predictive torque control (MPTC) based on deadbeat solution and discrete space-vector modulation (DSVM) for dual three-phase permanent magnet synchronous machines (PMSMs). First, deadbeat-direct torque and flux control (DB-DTFC) algorithm is applied and simplified, so that the computational burden can be reduced. Second, the virtual voltage vectors (VVVs) are adopted in dual three-phase voltage vector space to reduce voltage harmonics. Also, the DSVM is further proposed in this VVVs based vector space to generate more voltage vectors. After that, the simplified DB-DTFC and the DSVM scheme are artfully combined to select suitable voltage vector candidates for the MPTC, and the best one is then chosen to control the dual three-phase PMSMs. Finally, both simulation and experimental results are given to verify the effectiveness of the proposed method.

Minimization of the Electromagnetic Torque Ripple of a Synchronous Reluctance Generator Using External Rotor Excitation

This paper presents an approach to minimize the electromagnetic torque ripple of a synchronous reluctance generator (SynRG) with a magnetic field created by externally excited rotor coils. The synchronous reluctance machine is widely used in low and medium power systems such as wind power generation and new electric vehicle technologies. This paper proposes a rotor topology with flux barriers and direct current excited coils that reduce the torque ripple and replace the permanent magnets used in other reluctance rotor topologies. First, the initial rotor design, without excitation coils, is optimized to obtain a new rotor structure that reduces the electromagnetic torque ripple. In this work, the optimization of the rotor geometry was achieved by using genetic algorithms and the finite element method to optimize and parameterize the main components of the machine. In the optimized rotor model, an external electronic converter is included to feed the coils positioned between the magnetic flux barriers and the segments formed by the ferromagnetic material of the rotor. Finally, the electrical and magnetic machine variables obtained from implementing the coils into the optimized rotor are compared to the initial rotor structure operating under nominal load conditions to demonstrate the advantage of this topology in minimizing the electromagnetic torque ripple.

Two-level DPC strategy based on FNN algorithm of DFIG-DRWT systems using two-level hysteresis controllers for reactive and active powers

In this paper, a novel switching table (ST) of the twelve sectors direct power command (DPC) strategy of doubly-fed induction generator (DFIG) based dual rotor wind power (DRWP) is proposed using two-level hysteresis controllers for reactive and active power and feedforward neural networks (FNNs) algorithms. This intelligent technique was used to replace the conventional ST in order to reduce rotor flux ripple, active power ripple, total harmonic distortion (THD) of stator voltage, torque and reactive power undulations. The simulation and modeling of the proposed strategy were carried out in Matlab software. The DFIG is tested in association with a DRWP systems. The simulation results show that the DPC with FNN controller (DPC-FNN) reduced the THD value of stator voltage, rotor flux undulation, active/reactive power undulation, and electromagnetic torque ripple compared to conventional DPC strategy. It was found that the current waveform becomes purely sinusoidal with a reduction in the THD rate to 0.64%.

Electromagnetic Torque and Its Ripples in a Unipolar Brushless Torque Motor with Permanent Magnets

A physical and mathematical model is given, along with a computational and analytical description of physical processes in the electric motor and their relationship with the design of its equivalent electromagnetic circuit. The sources are determined and the relationships are investigated when the electromagnetic torque ripples occur. The analytical dependences of the ripples are obtained taking into account the nature of the air gap magnetic conductivity and the currents in the phase windings. It has been determined that the sources of these ripples are the higher harmonics of the air gap magnetic conduction function. The ripples contain three components: ripples of the main, additional and residual torques. It was determined that the amplitudes and phases of the ripple components of the main and additional electromagnetic torques are related to the lead angle of the windings current vector relative to the magnetic flux vector passing through the stator poles of the electric motor. The results were confirmed by numerical simulation of the electric motor electromagnetic system by the finite element method in ANSYS Maxwell. These results can be used to improve the designs of this type of electric motor, as well as in the development of circuit solutions and control algorithms for precision gearless electric drives of automatic control systems.

Influence of design parameters on flux‐weakening performance of interior permanent magnet machines with novel semi‐overlapping windings

This study performs a design and parametric study of interior permanent-magnet (IPM) machines equipped with novel semi-overlapping windings (NSWs). The influence of the key design parameters including; number of turns per phase, stack length, distance and angle between V-shaped magnets, rotor yoke thickness, magnetic bridge width and thickness and number of magnet segments on the flux-weakening (FW) performance characteristics are evaluated in detail. The influence of material of segmentation (material of bridge namely, air or iron) is also considered. A combination of analytical calculation-based program and a time-stepping 2D finite-element analysis based program are employed to evaluate the FW characteristics. The accuracy of the FW calculations, particularly the performance at high-speed regions, is verified over changes in torque components; namely reluctance and permanent magnet (PM), inductance components, PM flux coefficient and inverse saliency ratio due to the change in considered design parameter. The electromagnetic torque, torque ripple, output power and FW capability are investigated by parametric analyses. Moreover, the power losses and efficiency maps together FW curves are calculated for the optimal NSW IPM machine. The experimental measurements, taken from manufactured prototype, verify that the performed analyses and methods described in this study are accurate and reliable.

Analytical study of air-gap surface force – application to electrical machines

AbstractThe Maxwell stress tensor (MST) method is commonly used to accurately compute the global efforts, such as electromagnetic torque ripple and unbalanced electromagnetic forces in electrical machines. The MST has been extended to the estimation of local magnetic surface force for the vibroacoustic design of electrical machines under electromagnetic excitation. In particular, one common air-gap surface force (AGSF) method based on MST is to compute magnetic surface forces on a cylindrical shell in the air gap. However, the AGSF distribution depends on the radius of the cylindrical shell. The main contribution of this study is to demonstrate an analytic transfer law of the AGSF between the air gap and the stator bore radius. It allows us to quantify the error between the magnetic surface force calculated in the middle of the air gap and the magnetic force computed on the stator teeth. This study shows the strong influence of the transfer law on the computed tangential surface force distribution through numerical applications with induction and synchronous electrical machines. Finally, the surface force density at stator bore radius is more accurately estimated when applying the new transfer law on the AGSF.

Switching Sequence Model Predictive Direct Torque Control of IPMSMs for EVs in Switch Open-Circuit Fault-Tolerant Mode

A switching sequence model predictive direct torque control (MPDTC) of IPMSMs for EVs in switch open-circuit fault-tolerant mode is studied in this paper. Instead of selecting one space vector from the possible four space vectors, the proposed MPDTC method selects an optimized switching sequence from two well-designed switching sequences, including three space vectors, according to a new designed cost function of which the control objectives have been transferred to the dq-axes components of the stator flux-linkage under the maximum-torque-per-ampere control. The calculation method of the durations of the adopted space vectors in the optimized switching sequence is studied to realize the stator flux-linkage reference tracking. In addition, the capacitor voltage balance method, by injecting a dc offset to the current of fault phase, is given. Compared with the conventional MPDTC method, the complicated weighting factors designing process is avoided and the electromagnetic torque ripples can be greatly suppressed. The experimental results prove the effectiveness and advantages of the proposed scheme.

Performance analysis on direct torque controlled induction motor drive with varying hysteresis controller bandwidth

The fore most issue in DTC based induction motor drive is its torque ripples. The core objective of this paper is to reduce the electromagnetic torque ripples by varying the hysteresis controller bandwidth. Space Vector Modulation (SVM) based Direct Torque Controlled (DTC) induction motor drive is simulated in MATLAB/SIMULINK environment and its performance is studied with step change in load torque. The influence of hysteresis controller bandwidth on the performance of induction motor drive is analysed in terms of stator flux and electromagnetic torque ripples. The electromagnetic torque response and the stator flux trajectory for different values of hysteresis controller bandwidth are obtained and the results are presented.

Partitioned Stator Switched Flux Machine: Novel Winding Configurations

Torque density is one of the major limiting factors in machine design. In this paper, we propose the hybrid excited partitioned stator switched flux machine3 (HE-PSSFM3). In HE-PSSFM3, armature winding is positioned on the outer stator whereas the permanent magnet (PM) and field winding are placed at the inner stator, while the rotor is free from excitation sources and armature winding. Moreover, concentrated field winding is replaced by toroidal winding. The power splitting ratio between two stators/rotor pole combinations is analytically optimized and are validated through genetic algorithm (GA) in order to enhance average torque and flux regulation capability. The electromagnetic characteristics of the improved and initial design are evaluated and compared with existing designs, i.e., HE-PSSFM1 and HE-PSSFM2. The proposed HE-PSSFM3 has achieved high average torque, i.e., 2.0015 Nm, at same armature and field current densities of 5 A/mm. The results show that the average torques of the proposed design are 35% and 15% greater than HE-PSSFM1 and HE-PSSFM2, respectively. Furthermore, the analysis of various parameters such as flux linkage, flux regulation, electromagnetic performances, cogging torque, back EMF, electromagnetic torque, and torque ripples are investigated using two dimensional (2D) finite element analysis (FEA). Moreover, the simulation results of the proposed design are validated through GA and analytical modeling.

Improved DTC-SPWM strategy of induction motor by using five-level POD-PWM inverter and MRASSF estimator

This article presents an improved direct torque control strategy based on proportional-integral controllers applied to an asynchronous cage motor. The main objective of this study is to improve the system performance by reducing the electromagnetic torque and stator flux ripples while adjusting the currents shape by optimizing the total harmonic distortion, and this by supplying the motor with a diode clamped five-level inverter using the phase opposition disposition technique. Furthermore, the use of an observer employing the stator flux based model reference adaptive system allows improving the control performance by using a sensorless algorithm to obtain an accurate estimation, therefore, increase the system reliability. A comparative study between the five-level inverter installation with the same system and the same control strategy but another two different topologies of inverters; such as the NPC three-level inverter and the conventional two-level inverter has been made under MATLAB/SIMULINK to validate the efficiency of the proposed installation under various tracking and robustness tests.

Cost Function-Based Open-Phase Fault Diagnosis for PMSM Drive System With Model Predictive Current Control

Open-phase fault (OPF) in the permanent magnet synchronous machine (PMSM) drive system is one of the most prevalent failures due to the resulting large electromagnetic torque ripples and serious mechanical vibration. To improve the reliability of the PMSM drive system, several OPF diagnosis methods were studied and were mainly focused on vector control system. Recently, model predictive control (MPC) has been emerging as a popular control method for the PMSM drive system owing to its simple structure and excellent dynamic performance. However, so far, there are no special OPF diagnosis methods for the model predictive controlled PMSM drive system. Hence, this article first proposes a cost function-based OPF diagnosis method for the model predictive controlled PMSM drive system, considering the characteristics of MPC system. The dc component and second harmonic component in the cost function are used for the OPF diagnosis, and the initial phase angle differences are defined to locate the faulty phase. The experimental results show that, by the proposed fault diagnosis method, not only the OPF can be rapidly detected, but also the faulty phase can be effectively located. Moreover, the proposed method can be implemented simply and is robust against the operating point and parameter variations of the PMSM drive system. This article proposes an OPF diagnosis method for the model predictive controlled PMSM drive system based on cost function, taking into account the characteristics of the MPCC system. The experimental results verify the effectiveness of the proposed method. From the theoretical analysis and experimental results, the following works and conclusion are drawn.

A nonlinear time–frequency control based FOC for permanent magnet synchronous motors

PI control based field oriented control (FOC) scheme is the predominant method for the control of permanent magnet synchronous motors (PMSMs) in applications requiring high performance. A novel nonlinear time–frequency control based FOC design for the fast, accurate, and robust control of PMSMs is presented. Featuring a single nonlinear time–frequency controller and a PI controller as the 2 primary components in the control configuration, the new scheme is evaluated against a classic PI control based FOC design for performances in response to rapid speed-switching and abrupt external torque variation. The scheme displays significantly smaller steady-state tracking errors undergoing speed shifting and no high frequency current oscillations or electromagnetic torque ripple in the motor, as does the PI based scheme. The tracking errors corresponding to changes in torque are free of distortion and oscillation that would otherwise indicate instability and inaccuracy. Precision positioning control is also realized through incorporating a P controller into the controller configuration. When the motor reference position is briskly flipped between 360° and 1°, the novel controller design is shown to perform well with a rotor position error that is less than 0.13°.