Rotor Flux-oriented Control Research Articles

Minimum DC link Voltages for the Generator Bridge Converter of a SCIG Based Variable Speed Wind Turbine with Fully Rated Converters

Squirrel Cage Induction Generator (SCIG) based variable speed wind turbine with Fully Rated Converters (FRC) is a popular choice in the industry for the modern multi megawatt wind turbines. Typical FRC system uses a fixed DC link voltage that allows operation in all steady state and dynamic operating conditions while allowing the modulation index of the PWM scheme to vary. However, the analysis made in this paper shows that at steady state, in the maximum power point tracking region where the turbine is operated at variable speeds with generator controlled using Rotor Flux Oriented Control (RFOC), it is possible to operate the Generator Bridge (GB) converter with significantly lower DC link voltages than the fixed value used, by maintaining maximum modulation index in the PWM scheme. This paper presents a methodology of determining the minimum DC link voltages for such a system supported by simulation results showing the successful operation of a GB converter with minimum DC link voltages in the maximum power point tracking region.

On the Induction Motor Rotor Flux Estimation in the Electric Traction Systems with Rotor Flux-Oriented Control

Characterized by very good performance in both steady-state and dynamic regimes and also by a relatively simple control structure, the induction motor control with rotor flux orientation is frequently adopted in electric drive systems, especially in electric traction applications. This paper analyses the possibilities of rotor flux estimation in a real Romanian electric traction system of locomotives. Thus, to estimate the magnitude of rotor flux and the angu-lar position of the rotor flux vector, two possibilities are identified and discussed. First, the use of the sensed speed and stator currents is taken into consideration, and then the use of the measured supply voltages and the stator currents is the second alternative. Dedicated algorithms were designed for their related control. Both variants are analyzed through the results of the simulations obtained based on the specific models created in the Matlab/Simulink software. Four values of the imposed speed are taken into account in the performed analysis. It is highlighted that, in real conditions where the drive system is provided with speed sensor and there is no sine filter for the distorted motor supply voltage, the best option to estimate the rotor flux is to use the measured speed and the stator currents.

Experimental Validation of Different Control Techniques Applied to a Five-Phase Open-End Winding Induction Motor

Open-end winding five-phase induction motor (OeW-5PIM) configuration is used in industrial applications, where minimization in the total harmonic currents and high reliability are needed. The majority of the literature on OeW-5PIM topology discusses field-oriented control and direct torque control in addition to other robust control techniques such as the backstepping approach. This paper focuses on the mathematical and experimental approaches of backstepping control (BSC) and rotor-flux-oriented control (RFOC) for an OeW-5PIM topology. The space vector pulse width modulation (SVPWM) strategy is associated with the suggested control techniques to improve the dynamic performance (i.e., reducing ripple, fixed switching frequency, etc.) of the studied motor. Furthermore, the RFOC-SVPWM and BSC-SVPWM are comprehensively compared using experimental implementation under various situations such as load torque, open-phase fault, and high/low-speed operation.

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.

Analysis of the Stator Current Prediction Capabilities in Induction Motor Drive Using the LSTM Network

Abstract In modern areas of knowledge related to electric drive automation, there is often a need to predict the state variables of the drive system state variables, such as phase current and voltage, electromagnetic torque, stator and rotor flux, and others. This need arises mainly from the use of predictive control algorithms but also from the need to monitor the state of the drive to diagnose possible faults that have not yet occurred but may occur in the future. This paper presents a method for predicting stator phase current signals using a network composed of long-short-term memory units, allowing the simultaneous prediction of two signals. The developed network was trained on a set of current signals generated by software. Its operation was verified by simulation tests in a direct rotor flux-oriented control (DRFOC) structure for an induction motor drive in the Matlab/Simulink environment. An important property of this method is the possibility of obtaining a filtering action on the output of the network, whose intensity can be controlled by varying the sampling frequency of the training signals.

Harmonic and Fundamental Rotor Resistance Estimation Scheme for Multiphase Induction Motor Based on Nonsinusoidal Supply Control

In the absence of flux measurements, techniques of field orientations depend on motor parameters, particularly on rotor resistances. During operation in flux-oriented mode, online continuous estimation of harmonic and fundamental rotor resistances is important for multiphase IM. To limit the core saturation and to achieve the synchronous and aligned air-gap flux density distribution, the harmonic plane is based on magnetizing flux-oriented control (MFOC) whereas the fundamental plane is taken as rotor flux-oriented control (RFOC). Mismatch harmonic and fundamental resistances trigger deviations in the rotor and magnetizing flux and also cause misalignment in the resultant induced electromotive force (EMF) waveform which could, in turn, be the reason for over-excitation and under-excitation. This article formulates the simultaneous online identification of rotor resistances for particularly MFOC harmonic plane while the fundamental plane is RFOC based on the dot product of rotor flux and stator current for making a model reference adaptive system (MRAS). Mismatched stator resistance and dead time of inverter have a negligible effect on the reference model during steady state. Convergence and steady-state performance can be acquired for a variation of load conditions particularly at heavy loading. The validation of the proposed approach is verified through simulation and experiment results by incorporating a multiphase platform consisting of a seven-phase induction machine.

Self-Correcting Virtual Current Sensor Based on the Modified Luenberger Observer for Fault-Tolerant Induction Motor Drive

Fault-tolerant control (FTC) solutions are increasingly being used in modern drive systems with AC motors. Such systems provide a higher degree of security and solutions that allow the on-line detection and localization of failures, as well as the switching of the control mode to a mode that allows us to continue the operation or safely stop the drive system. As the current sensors (CSs) are necessary to ensure precise control of the AC motors, in the event of their failure, one of two strategies can be used—hardware or software redundancy. The first strategy requires the use of additional measuring sensors. For this reason, the algorithmic solution, based on the Luenberger Observer (LO), has been proposed in this article as one of the software redundancy methods. In contrast to methods presented in the literature, the proposed solution allows one not only to compensate the stator current in a phase with a faulty CS, but also to adjust the correction of current estimation based on a measured signal in the other phase with a healthy CS. Extensive simulation studies in the direct rotor flux-oriented control (DRFOC) structure with the induction motor (IM) confirm the effectiveness of the proposed method. In addition, the proposed solution allows the drive system to be controlled even if all CSs are damaged.

A comparative study of the speed control of an IM–based flywheel energy storage system using PI–DTC and RFOC strategies

Abstract This paper examines the modeling and speed–based control of an IM–based flywheel energy storage system (FESS) for integration with a variable wind generation system (VSWG) feeding an online isolated load at the DC bus level. Two traditional control strategies are considered for the FESS, rotor flux oriented control (RFOC) and direct torque control (DTC). Instead of controlling the IM torque directly, the proposed schemes control the measured speed of the FESS–IM to follow a reference value estimated from the required power compensation. Matlab/Simulink simulations show that the tracking performance of the two controllers is comparable.

Field Oriented Control of Doubly Fed Induction Motor using Speed Sliding Mode Controller

This article presents a modeling and control of the Doubly Fed Induction Motor (DFIM), associated with two inverters controlled through the Pulse Width Modulation technique (PWM), the control of the DFIM is carried out by the approach of Rotor Flux Oriented Control (RFOC) according to the direct axis. In this approach, regulation is done by classic PI regulators, the latter having undesirable overruns and static errors in non-linear systems, for that the introduction of the control by sliding mode in place of the classic PI speed regulator, that is in the form of a control law based on this type of controller since it is invariant to the non-linearity of the system and precise, stable, simple and has a good response time, in order to validate the objectives of improving the DFIM behavior in front of the reference parameters, such as the speed and the torque imposed on the machine. The results of the proposed approach are validated by its implementation on the Matlab/Simulink environment.

Identify magnetising inductance and rotor resistance to improve the performance of the induction motor through IRFOC

To get a high dynamic performance of AC machines, field-oriented control was used. The best method of field-oriented control is an indirect rotor flux-oriented control. When applied this method of ...

Phase Voltage-Oriented Control of a PMSG Wind Generator for Unity Power Factor Correction

This paper presents the power factor control of a permanent magnet synchronous wind generator (PMSG) wind turbine using a phase voltage-oriented control (PVOC) scheme, which is different from the conventional rotor flux-oriented control (RFOC) method and without using a rotor position sensor or sensorless estimator. The proposed control system is operated in two separately synchronously rotating d-q frames. One is for a phase-locked loop (PLL) and the other is for the PVOC current control loop. A PI controller functioned as a low-pass filter in the PLL loop is designed for extracting the phase voltage angle for the coordinate transformation between the stationary α-β frame and the synchronously rotating d-q frame in the PVOC control loop. The d-q modeling of the PMSG with the three-phase voltage vector aligned on the d-axis is then derived and based on which an another PI controller followed by decoupling control is designed, so that the three-phase currents are in phase with the three-phase output voltages of the wind generator for unity power factor correction. The simulation results in PSIM show the performance of the proposed control system which is also experimentally verified by using a TI TMS320F28335 digital control chip.

A Constrained Non-Linear Model Predictive Controller for the Rotor Flux-Oriented Control of an Induction Motor Drive

Predictive controllers have been extensively studied and applied to electrical drives, mainly because they provide fast dynamic responses and are suitable for multi-variable control and non-linear systems. Many approaches perform the prediction and optimization process on-line, which requires a high computational capacity for fast dynamics, such as, for example, the control of AC electric motors. Due to the complexity of embedding constraints in controller design, which demands a high computational capacity to solve the optimization problem, off-line approaches are one of the choices to overcome this problem. However, these strategies do not deal with the inherent constraints of the drive system, which significantly simplifies the design of the controller. This paper proposes a non-linear and multi-variable predictive controller to control the speed and rotor flux of an induction motor, where the constraints are treated after the controller design. Besides dealing with the constraints of the electric drive system, our proposal allows increasing the stability of the system when the model does not incorporate disturbances and when parameter incompatibilities occur. Several computer simulations and experimental tests were performed to evaluate the behavior of the proposed controller, showing good performance to track the controlled variables under normal operating conditions, under load disturbances, parametric incompatibility, and at a very low rotor speed.

Electromechanical Coupling Modelling of High Speed EMUs with Rotor Field Oriented Control

According to the theory of vehicle system dynamics and rotor flux-oriented control (RFOC), an electromechanical coupling simulation model of transmission system of high-speed EMUs is established considering the effect of mechanical and electrical characteristics. Firstly, an EMUs multi-body system (MBS) model including is developed by Simpack software based on the structure and parameters of a high-speed EMUs, and a RFOC simulation model of traction transmission system is also built by the Simulink platform. Then two types of models are linked by Simpack co-simulation interface model. Consequently, the electromechanical coupling model of EMUs is developed. The computer simulation method is adopted to simulate the coupling system with RFOC. Simulation results indicate that the proposed model can effectively reveal the change of electrical performance of the high-speed EMUs, the coupling system has a good anti interference performance and robustness.

A Simple Feedforward Approach to Stabilize VSI-Fed Induction Motor With Filter in RFOC

LC filters are used in between a pulsewidth modulated three-phase voltage source inverter and a squirrel cage induction motor (SQIM) to reduce the losses in the motor and the high dv/dt at the motor terminals by feeding the motor with three-phase sinusoidal voltages. However, it affects the rotor-flux oriented control (RFOC) of the SQIM drive because of the sustained resonant frequency oscillations. It also destabilizes the drive at some operating points if proper control action is not taken. This article proposes a simple feedforward (FF) technique where the FF terms are subtracted from the d- and q-axis stator-current references to damp out the resonant frequency oscillations. Additional sensors and controllers are not required except the sensors and controllers used in RFOC of SQIM without filter. It does not depend on the tedious calculation of damping gain like in any active damping method. The stability of the drive has been analyzed and verified through simulation as well as experimental results at different test conditions. It ensures good steady-state and dynamic performances of the SQIM with filter. There is no need to change the parameters of four proportional-integral controllers previously designed for the RFOC of SQIM without filter.

Stabilization of Rotor Flux-Oriented Control of Induction Motor With Filter by Active Damping

Sinusoidal LC filters are generally placed between the voltage source inverter (VSI) and squirrel cage induction motor (SQIM) to reduce the distortion in the output voltage of the VSI, voltage surges at the motor-terminals, core losses in the SQIM, bearing-current, and electromagnetic interferences. Rotor-flux oriented control (RFOC) of the SQIM is widely used in adjustable speed drives. However, the introduction of filter network may make the operating point of RFOC of SQIM drive unstable and may create sustained resonance frequency oscillations in the stator-current, stator-voltage of SQIM. This paper proposes a simple inverter-current-based active damping (AD) technique, which damps out the resonance frequency oscillation by emulating the virtual resistance connected in series with the filter inductor in its control structure. It also effectively stabilizes the unstable operating point of the closed-loop system without changing the parameters of the controllers used in RFOC. The idea of the proposed AD technique has been illustrated with mathematical expressions and justified through stability analysis. The instability of operating point and the impact of the AD technique are experimentally demonstrated on RFOC of VSI-fed SQIM with filters at different test conditions.

High-gain observer-based sensorless control of a flywheel energy storage system for integration with a grid-connected variable-speed wind generator

This paper introduces an induction machine-based flywheel energy storage system (FESS) for direct integration with a variable-speed wind generator (VSWG). The aim is to connect the FESS at the DC bus level of a permanent magnet synchronous generator-based VSWG in order to stabilize the DC bus voltage as well as the power flowing into the grid. A rotor flux-oriented control strategy is proposed for the FESS converter based on the actual speed of the flywheel rotor. Since mechanical speed sensors are prone to failure and increase the maintenance cost of the system, a sensorless technique is proposed to estimate the rotor speed through a specially synthesized high-gain observer (HGO). The proposed observer achieves accurate tracking of the flywheel speed and flux and reduces the adverse effects of variations in the rated rotor resistance. Simulation results obtained using the MATLAB-Simulink environment are presented to illustrate the theoretical synthesis and analysis of the proposed FOC and sensorless HGO control strategies.

Direct RFOC Strategies Aimed to Symmetrical Two-Phase IM Drives: Comparison Between B4- and B6-Inverters in the Stator

This paper deals with an investigation of the steady-state and transient performance of the direct rotor flux-oriented control (RFOC) strategies implemented in symmetrical two-phase induction motors (2PIMs). Such an investigation is structured within a comparison study considering: 1) the case of a two-leg voltage source inverter (B4-inverter), and 2) the case of a three-leg voltage source inverter (B6-inverter), in the stator of the 2PIM. Following a presentation of both drives, the principle of the RFOC is briefly recalled. Then, a special attention is paid to the implementation of the direct RFOC on current-regulated B4- and B6-inverters. The control of the power switches is achieved by two two-level hysteresis regulators in the B4-inverter rather than three in the B6-inverter. Initiated by a simulation-based analysis of the selected steady-state features of both 2PIM drives under direct RFOC strategies, the comparison study is then extended to a deep experimental investigation of the steady-state operation with emphasis on the dc-link capacitor voltages, the stator line-to-line and phase voltages, stator phase currents, the rotor flux, and the electromagnetic torque. The established results reveal three major limitations of the B4-inverter fed 2PIM drive, such as: 1) unbalanced dc-link capacitor voltages at low speeds; 2) a reduced speed range due to the low level of the phase voltages; and 3) an injection of harmonics due to the $d$ – $q$ transformation. While the B6-inverter exhibits balanced dc-link capacitor voltages in the total constant torque region with higher ripple of the stator phase currents and of the electromagnetic torque, the experiment-based comparison is achieved by an investigation of the dynamic behaviors of both drives under step- and ramp-shaped reversals of the reference speed. It highlights the poor dynamic behavior of the B4-inverter fed 2PIM drive under both shapes of speed reversal.

Solar powered sensorless induction motor drive with improved efficiency for water pumping

This study deals with a speed sensorless induction motor drive (IMD) with efficiency optimisation. This drive is driven by a solar photovoltaic array for water pumping. The elimination of speed sensor increases the robustness and decreases cost of the IMD. The speed estimation is achieved by rotor flux-oriented control in stationary reference frame. Moreover, the parameters, namely stator resistance adaptation, make the system parameters insensitive. The efficiency of the drive system is enhanced by optimising the excitation current by using a particle swarm optimisation technique. The smooth operation of overall system during starting and steady-state condition is simulated in MATLAB/Simulink environment and validated on a prototype developed in the laboratory. The efficiency of the system with loss minimisation technique is compared with the conventional IMD. Simulated results comply with the test results and a comprehensive comparison is made to validate the suitability of proposed system.

Enhancing Fault-Tolerant Ability of a Nine-Phase Induction Motor Drive System Using Fuzzy Logic Current Controllers

With distinct advantages over three-phase machines, multiphase machines are gaining increasing popularity in ship electric propulsion applications. Many fault-tolerant control strategies have been proposed for multiphase drive to suppress the torque ripples under faulty conditions; however, most of them depend heavily on the mathematical models and the need of the prefault to postfault transitions, which would increase the complexity of the control system. Because of high robustness, Fuzzy Logic controllers are suggested to substitute the proportion integration (PI) controllers in the current loops of rotor-flux oriented control (RFOC) for multiphase induction motors in this paper. The experimental results from a multiphase drive platform demonstrate that compared with the conventional RFOC with PI current controllers, Fuzzy logic-RFOC has significantly improved the fault-tolerant ability of the nine-phase drive system in various kinds of faulty conditions.

Current Balance Control for Symmetrical Multiphase Inverters

The current imbalance between stator phase windings could shorten the motor life and affect the drive performance, whereas in case of multiphase drive applications, there is not a general current balance control strategy that can apply to symmetrical inverters with any phase number m . Based on the generalized symmetrical component theory, this letter analyzed the values of relative symmetrical components of the multiphase systems in balanced and unbalanced cases. Then, developed from the conventional rotor-flux oriented control (RFOC), the current-balance RFOC is proposed to compensate the current imbalance for symmetrical m -phase inverters. Finally, the experimental results from the five-phase and nine-phase drive systems confirm the validity of the control strategy in eliminating current imbalance.