Rotor Flux Research Articles

Predictive Power Control of PMSG based WECS: Development and Implementation for Smooth Grid Synchronisation, Balanced and Unbalanced Grid

In this paper, the distributed generation unit is controlled to operate in both stand-alone (SA) and grid-connected (GC) modes and offers a smooth transition between these modes using the model predictive control scheme. The permanent magnet synchronous generator (PMSG), along with a 2-level back-to-back converter, is named a DGU. A simple and intuitive approach using predictive control is presented in a stationary reference frame for a load-side converter (LSC). A voltage control loop is used during SA mode to fix the voltage and frequency at the load end. The smooth synchronization technique is developed without a phase-locked loop. During GC, a predictive power control regulates active and reactive power during the symmetry and unbalanced grid voltage conditions. The designed strategy makes the power factor improvement, reduction of grid current harmonics, and elimination of twice grid frequency ripple from power during grid unbalance possible. This work has proposed a solution to reduce the overall computational burden on the processor by eliminating the state prediction in each sampling period. The machine-end converter control is formulated in the rotor flux reference frame to keep the power flow across the dc-link capacitor constant. Comprehensive experiments are conducted with the designed scaled laboratory prototype to successfully validate the control’s theoretical claim.

An improved subdomain method for air gap flux density of interior permanent magnet machines based on rotor reconstruction and flux equivalence

AbstractThe aim of this article is to develop a rotor reconstruction method for the V‐shaped interior permanent magnet (IPM) machine so that the subdomain method to analytically calculate the air‐gap flux density can be applied. With the proposed method, the V‐shaped IPM rotor with rectangular magnets, magnetic barriers, and saturated iron bridges can be transformed into a U‐shaped equivalent analytical model. The geometry and material parameters of the magnets in the equivalent U‐shaped model can be determined according to the flux equivalence in the air‐gap of the motor. Then using the subdomain method on the U‐shaped equivalent rotor, the static magnetic field problem can be solved and the flux density distribution in the air‐gap be obtained. The validity of this method and accuracy of the solution is verified by the finite element method with case studies. Compared with existing methods, the improved subdomain method has higher accuracy in calculating flux density including radial and tangential components. The presented rotor reconstruction method is not only limited to single‐layer V‐shaped rotor, it can also be applied to other IPM rotors with more complex structures. It is valuable in the design, optimisation of IPM motors, and even development of new rotor topology.

Reduction of quadrature armature reaction in salient-pole synchronous generator by rotor flux barrier

Reduction of quadrature armature reaction in salient-pole synchronous generator by rotor flux barrier

High Fault-Tolerance Dual-Rotor Synchronous Machine With Hybrid Excitation Field Generated by Halbach Permanent Magnets and High Temperature Superconducting Magnets

Superconductors can help electric machines achieve extremely high torque and power densities. However, operational instability is still a severe challenge for most superconducting electric machines. This paper proposes a novel dual-rotor hybrid excitation variable flux synchronous motor (DRHE-VFPM) suitable for applications with high safety requirements. The primary characteristic is using series-connected permanent magnet (PM) and High-temperature superconducting (HTS) magnet as the rotor's flux sources. These two magnets are on different rotors and steadily excited by each other through armature slots, improving several critical characteristics of the superconducting motor. First, the new electromagnetic topology can avoid severe quench accidents. At normal operation, the PM and HTS rotors can produce a large total electromagnetic torque. When the HTS magnets are damaged by the overtemperature or the mechanical shocks, the motor can still use the PM rotor to generate continuous torque instead of sudden interruption. Secondly, because an excessively strong rotor field will limit the speed, the variable flux density of the HTS magnet allows fuller use of voltage to extend the speed range and improve the power density. Moreover, the main magnetic circuit of the motor changes significantly under different operating states, which is analyzed theoretically in detail.

A Double Rotor Flux Switching Machine With HTS Field Coils for All Electric Aircraft Applications

The increasing demand for high-power density motors in electric transport industries opens a new research opportunity to develop motor topologies with less weight and high efficiency. In particular, all-electric aircraft applications require very high power density motors. This paper shows the design of a new 1 MW 20-pole/15-slot double rotor flux switching machine with high-temperature superconducting field coils and thermal management system. The proposed motor features an air-core stator. Aluminum Litz wire is used for the armature conductors, and the YBCO- high-temperature superconducting material is used for the field coils. The armature winding and field coils operate at 95K and 65K, respectively. The active part power density including rotors, armature windings and field coils obtained with the proposed design is 29.3kW/kg. The specific power density of proposed motor considering mechanical, support structure and TMS is about 18.5 kW/kg. The efficiency can be higher than 98.7% which satisfies the requirement of electric aviation.

Enhanced Integrator with Drift Elimination for Accurate Flux Estimation in Sensorless Controlled Interior PMSM for High-Performance Full Speed Range Hybrid Electric Vehicles Applications

Interior Permanent Magnet Synchronous Motor (IPMSM) motion-sensorless speed control necessitates precise knowledge of rotor flux, speed, and position. Due to numerous non-ideal aspects, such as converter nonlinearities, detection errors, integral initial value, and parameter mismatches, the conventional first-order integrator’s estimated rotor flux experiences a DC offset (Doff). Low-pass filters (LPF) with a constant cut-off frequency yield accurate estimates only in the medium- and high-speed range; however, at the low-speed area, both magnitude and phase estimates are inaccurate. The presented technique resolves the aforementioned issue for a broad speed range. In order to achieve precise flux estimation, this article presents an improved technique of flux estimator with two distinct drift mitigation strategies for the motion-sensorless field-oriented control (FOC) system of IPMSM. Using the orthogonality of the α- and β-axes, the proposed drift elimination system can estimate drift in different situations while maintaining a high level of dynamic performance. The stator flux linkage (SFL) computation in the synchronous coordinate is established from the estimation of the rotating shaft’s permanent magnetic flux linkage orientation and the statistical equations model of the SFL. By comparing the calculated SFL vector to the SFL vector derived from the stator winding voltage and currents integral model with a drift PI compensation loop, a feedback loop is formed to neutralize integral drift, and the rotational speed and position of an IPMSM is estimated utilizing the vector product of the two flux linkages in a phase-locked loop. Theoretical interpretation is presented, and Matlab Simulink simulations, as well as experimental outcomes, consistently demonstrate that the suggested estimation techniques can eliminate the phenomenon of flux drift.

A novel control method for improving reliability of 3‐phase induction motor drives under the stator winding open‐circuit fault

AbstractPost‐fault control of a 3‐phase Induction Motor (IM) drive under the Stator winding Open‐Circuit Fault (SOCF) has gained significant importance in recent years especially for safety‐critical industrial applications. Nevertheless, most of proposed schemes suffer from low accuracy or high complexity. In this research, a novel control scheme for improving reliability of wye‐connected 3‐phase IM drives under the SOCF according to Direct Field‐Oriented Control (DFOC) is proposed and evaluated. In the proposed system, different transformations are presented and employed to control the faulty system. The controller is achieved by minor modifications in the traditional control scheme structure. In the proposed system, an Extended Kalman Filter (EKF) is also used to estimate the rotor flux. The designed EKF‐based DFOC (DFOCEKF) is verified using simulations and experimental tests conducted on a 0.75 kW 3‐phase IM drive. Based on the results it can be calculated that the torque ripple is decreased clearly after the proposed fault‐tolerant control approach is applied. The DFOCEKFstrategy can control the faulty motor accurately, which can further improve the reliability of IM drive systems. The results also confirmed that the proposed controller after the SOCF has faster dynamic response and higher accuracy compared to previous published papers.

Sliding Modes Control of the Asynchronous Motor with an Observer of a Special Class of the Non-linear Systems Interconnected to an Estimator

The present paper deals sliding modes control of the asynchronous motor, where the sensor mechanical speed, it replaced by a software sensor. It is an observer of a special class of the non-linear systems interconnected to an estimator. The performances of the sliding modes control of the asynchronous motor with an observer of a special class of the non-linear systems interconnected to an estimator proposed are shown by a simulation treating the evaluation of the rotor flux and rotating speed an asynchronous motor.

Harmonic Injection Strategy Considering Multiplane Iron Loss Impact With Optimal Magnetizing Flux Distribution for Multiphase Induction Machines

Lagging orientation error detuning induced by iron losses for multi-planes of multiphase IM under non-sinusoidal supply control triggers error in determination of calculated harmonic, fundamental air-gap flux advance angles and harmonic slip frequency. This in-turn leads to inaccurate harmonic injected currents, which are dependent on harmonic multiple of frequency for the corresponding plane with respect to fundamental plane frequency. This paper proposes the novel harmonic injection strategy considering the detuned impact of iron losses by keeping in view the complete iron loss modeling for both harmonic magnetizing flux orientation control (MFOC) and fundamental rotor flux orientation control (RFOC) planes. Furthermore, satisfaction of complete optimal flux distribution constraints for multiphase IM are taken into account which results in preserving optimal flux patterns throughout the mechanical loading particularly at low and medium load conditions. Contrary to other traditional orientation schemes, this paper adopts the MFOC and RFOC for harmonic and fundamental plane respectively for acquiring the aligned and synchronized control of harmonic and fundamental air-gap flux distribution. Detailed experimental results incorporating seven phase induction machine as prototype are utilized to evaluate the harmonic injected currents, advance angles, slip frequencies and induced EMF waveforms which validate the effectiveness of proposed scheme.

MTPA STRATEGY FOR THE ELECTRIC VEHICLE DRIVE

Abstract. When the vehicle is moving, the driving torque that the traction motor should develop can be very large. Therefore, to prevent over loading of the traction motor by current, it is necessary to limit the current in the stator winding to the nominal value. In this regard, it is necessary to develop a system of vector control of the stator current of an induction motor, in which, at the nominal value of the stator current, the induction motor will develop the largest possible electromagnetic moment. Today, the problem of obtaining the maximum electromagnetic moment per unit current stator decides the MTPA strategy. Therefore, the aim of the work is to develop a system for regulating the moment of induction motor using the MTPA strategy, which provides the maximum value of the electromagnetic moment per unit current in the stator winding, as well as conducting a comparative analysis of the traction properties of an asynchronous electric drive when applying the MTPA strategy and in its absence. It is also necessary to clarify the requirements that the MTPA strategy imposes on the technical parameters of the induction motor and the restrictions that the real parameters of the induction motor impose on the MTPA strategy. The study was conducted on the example of a traction asynchronous electric drive of a city bus. As a result of this work, it was found that with the same current value in the stator winding, the induction motor will develop the greatest electromagnetic moment if the angle between the stator current vector and the rotor flux vector is equal to 45 electric degrees. By limiting the current of the stator induction motor at the nominal level, the application of the MTPA strategy allows obtaining an electromagnetic moment 2.56 times greater than in the absence of an MTPA strategy. This is due to the fact that when applying the MTPA strategy, the rotor flux linkage should exceed 3.55 times the nominal flux coupling of induction motor. To get so big the flux coupling of the rotor must increase the value of the voltage on the stator winding by 3.57 times relative to the nominal voltage value. When applying the MTPA strategy, the flux linkage of the rotor will not exceed the nominal value only at stator current values 3.54 times less than the nominal value of the stator current. In this case, the maximum value of the electromagnetic moment that will develop induction motor will be 4.92 times less than the nominal value of the moment of induction motor. In developing the MTPA strategy, the saturation of the magnetic system AD was not taken into account. Keywords – induction motor, vehicle, electromagnetic moment, energy, MTPA strategy.

Robust Nonlinear Predictive Control Applied to Induction Motors

In this paper, a nonlinear predictive controller is proposed for a variable-speed induction motor. The research work is directed towards improving the trajectory tracking capability, stability guarantee, robustness to parameter variations, and disturbance rejection. The Generalized Predictive Control (GPC) without constraint and output-constrained controller to induction motor drive is illustrated. The variables to be controlled are rotor speed and flux trajectory. The load torque is considered an unknown disturbance. Finally, the tuning parameter of GPC is automatically determined. The simulation results show a good performance for the nonlinear dynamic system.

Reference Input Signals Formation for Induction Motor Control in Traction Drive

The purpose of this work is to build the analytical improved (with resistances estimation) real time computation of the reference inputs for rotor flux and torque in the vector control system of an induction motor of a traction electric drive. The reference inputs must maximize electromagnetic torque in conditions of voltage source instability, particularly in magnetic field weakening mode. The conventional way to control the field weakening mode is to form flux coupling task inversely proportional to the speed or inversely proportional to the square of the speed in second and third zones respectively. Such reference input signals are not able to provide the maximum torque capability over the entire speed range, and the improved torque capability is achieved in different ways. For instance, voltage feedback is useful for the torque capability enhancement in conditions of internal and external perturbations. A wide change in speed with the weakening of the flux reveals the nonlinear properties of an induction electric motor. However, in vector control systems, proportional-integrating (PI) regulators are usually used. Therefore, firstly, linear PI controllers must be robust, and secondly, the reference input signals for flux and torque must guaranty linear, not saturated state of each PI controller. The proposed expressions for calculating reference inputs for induction motor rotor flux and electromagnetic torque as functions of actual rotor speed are the approximate expressions. The estimation of the possible error shows that the error is acceptable. Simulation is performed for the vector control system of an induction motor and taking into account the calculation of the control signal by the microcontroller and the dynamics of the frequency invertor. The simulation of the resulting system validates the effectiveness of the control system using the proposed expressions for the formation of real-time reference input signals for setting the flux and torque.

Design and Enhanced Equivalent Magnetic Network Modeling of a Fractional-Slot Spoke-Array Vernier PM Machine With Rotor Flux Barriers

The spoke-type arrangement of permanent-magnets (PMs) in rotor of Vernier-PM (VPM) machines was first introduced in a dual-stator topology to overcome low power drawback of VPM machines. However, this special structure is mostly applicable for high-power motor drives. This paper presents a fractional-slot spoke-array VPM machine with a special rotor structure for small scale electric-vehicles. The leakage flux lines tend to be aligned with the main flux routes due to special design of flux barriers in end portion of PM housings. High torque-density, low weight, torque-speed curve with a wide constant torque region, promising efficiency and power-factor are the advantages of the proposed machine. An equivalent-magnetic-network (EMN) model is established for predicting the complex behavior of flux lines and operating quantities of the proposed structure with reasonable accuracy. The contribution of the modeling method includes a special mesh cell for the air-gap permeance network to more accurately capture the flux routes, continuous positioning method for omitting spikes on post-processing waveforms due to numerical errors and a stable solving flowchart with a high convergence rate. The validity of EMN model is proved by comparing its operating waveforms with the finite-element results and experimental measurements.

Power density improvement due to Rotor Flux screens in an SRM with a higher number of Rotor Poles than Stator Poles

Power density improvement due to Rotor Flux screens in an SRM with a higher number of Rotor Poles than Stator Poles

A comparison study between the optimal DFIG flux and speed control in presence of magnetic hysteresis and classical control strategies for wind systems

In the wind energy systems field, the most common control objective treated by authors is the speed and flux control of the doubly fed induction generator (DFIG). For computing complexity matter, the generator mathematical representation is generally modelled assuming a linear magnetic characteristic. Based on this assumption, the rotor flux control will aim to track a fixed flux reference, mostly its nominal value. The inconvenience with this strategy is that practically, neglecting the nonlinearity of the generator’s magnetic characteristic, optimal performance control cannot be performed. In this study, considering the magnetic flux hysteresis and saturation characteristic, new modelling of the DFIG is presented. Furthermore, a new speed and optimal flux Backstepping controller is designed based on the Lyapunov theory. To prove its performance, a comparison study with different control strategies will be conducted. Simulations considering a wide range of wind speed variations are illustrated in the Matlab/Simulink environment.

Power density improvement due to Rotor Flux screens in an SRM with a higher number of Rotor Poles than Stator Poles

Power density improvement due to Rotor Flux screens in an SRM with a higher number of Rotor Poles than Stator Poles

Discrete Sliding-Mode-Based MRAS for Speed-Sensorless Induction Motor Drives in the High-Speed Range

By combining the high robustness of sliding-mode observer (SMO) with the adaptability of model reference adaptive system (MRAS), the sliding-mode-based MRAS can improve the speed estimation performance of speed-sensorless induction motor (IM) drives. However, the analysis of this paper shows that there exists a mismatch problem between the fixed-value of SMO gains and the variable stability boundary which changes with IM operation speed, resulting in speed estimation performance degradation or even instability in high-speed range. To cope with this problem, a discrete SMO is proposed to expand the effective operation range of sliding-mode-based MRAS. First, a discrete terminal SMO with modified observer structure is designed for rotor flux estimation. Then, a variable gain is designed to ensure the SMO stability in high-speed range, and avoid the chattering caused by gain value overestimation. Compared with existing sliding-mode-based MRAS, the studied method can improve the stability and accuracy of speed estimation in high-speed range. Finally, the experimental results from a 3.7kW IM test bench can confirm the validness of studied speed estimation scheme.

Study on decoupling control of bearingless motorized spindle

Bearingless motorized spindle is a kind of spindle structure that combines a bearingless motor with a motorized spindle. It has the advantages of a motorized spindle and a bearingless motor, which can further improve the speed of the machine tool spindle. However, its complex electromechanical structure and the coupling relationship between the subsystems make it difficult to control its operation process accurately. In this paper, the voltage control decoupling method is used to decouple the torque and suspension system of a bearingless motorized spindle with an independent inverse system, then control the systems. Finally, the control of decoupled bearingless motorized spindle is simulated. The results show that when the speed, rotor radial displacement, and rotor flux change respectively, they will not influence each other. The speed and radial displacement are unaffected after the sudden load is applied. It proves the effectiveness of the decoupling control method.

Online estimations for electrical and mechanical parameters of the induction motor by extended Kalman filter

In this study, a novel extended Kalman filter (EKF)-based observer is designed to increase the number of estimated states and parameters of the induction motor (IM). To perform the online estimations of stationary axis components of stator currents and rotor fluxes ([Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]) as well as rotor mechanical speed ([Formula: see text]), which are required for direct vector control (DVC) systems along with the load torque ([Formula: see text]), rotor resistance ([Formula: see text]), magnetizing inductance ([Formula: see text]), and the reciprocal of the total inertia of the system ([Formula: see text]), the proposed EKF uses the measured phase currents and voltages together with the measured rotor speed. To estimate all of the five states ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]) plus four parameters ([Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]), the proposed EKF-based observer does not include a switching operation nor a hybrid structure, which is a common approach in the literature for online state and parameter estimations of IMs and results in design complexity and computational load increase. In simulation studies, the estimation performance of the proposed EKF is tested and verified under the variations of [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] in DVC systems that perform the speed and position controls of IM. The obtained results confirm the satisfying tracking performances and thus better control achievements of the speed and position controlled IM drives in this paper. Moreover, the proposed EKF and the EKF without [Formula: see text]-estimation are compared in the position control system to demonstrate the importance of the [Formula: see text] estimation. In the comparison, nearly 10 times less mean square error (MSE) is obtained in the estimations of [Formula: see text], [Formula: see text], [Formula: see text], and the magnitude of the rotor flux for the proposed EKF. Finally, the proposed EKF algorithm is tested and verified in real-time experiments with a challenging speed reversal scenario causing nonlinear variations in both [Formula: see text] and [Formula: see text].

An Improved Sensorless Nonlinear Control Based on SC-MRAS Estimator of Open-End Winding Five-Phase Induction Motor Fed by Dual NPC Inverter: Hardware-in-the-Loop Implementation

This paper introduces a sensorless nonlinear control scheme based on feedback linearization control (FLC) of an open-end winding five-phase induction motor (OeW-5PIM) topology fed by a dual neutral point clamped (NPC) inverter. The suggested sensorless control is combined with the sliding mode (SM) controller to improve the dynamic performance (i.e., rising time, overshoot, etc.) of the studied motor. Furthermore, a stator-current-based model reference adaptive system (SC-MRAS) estimator is designed for the estimation of the rotor flux and the motor speed. In parallel, to enhance the robustness of the designed sensorless control against motor parameter changes, an adaptive estimation method is suggested to estimate the rotor and stator resistances during low-speed ranges. The estimation method of motor resistances is associated with the suggested sensorless control to further improve the speed estimation accuracy and minimize the speed estimation error. Finally, the effectiveness and correctness of the suggested control with the examined estimators are validated in real-time implementation using a hardware-in-the-loop (HIL) based on the dSpace 1103 board.