Rotor Flux Vector Research Articles

Rotor Flux and EEMF Observer for Interior Permanent Magnet Synchronous Machine

In recent years, the use of the Interior Permanent Magnet Synchronous Machine (IPMSM) in various applications has grown significantly due to numerous benefits. Sensors are used to achieve high efficiency and good dynamic response in IPMSM drives but due to their high cost and reduce overall size of system,sensorless control techniques are preferred. Non-sinusoidal distribution of rotor flux and slot harmonics are present in the considered IPMSM. In this article, these problems are considered as control system disturbances. With the above-mentioned problems, the classical observer structure based on (d-q) fails to estimate at low-speed ranges. This article proposes an observer structure based on a rotor flux vector in (α-β) stationary reference frame, which works using the adaptive control law to estimate speed and position, and a non-adaptive EEMF-based observer to estimate speed and position. Moreover, a comparative analysis between both observer structures at the different speed ranges is also considered in this article. The effectiveness of the observer structure is validated by simulation tests and experimental tests using the sensorless control system with a field-oriented control scheme for 3.5 kW IPMSM drive system.

Rotor-Flux Vector Based Observer of Interior Permanent Synchronous Machine

The sensorless control system of the interior permanent magnet machine (IPMSM) is considered in this paper. The control system is based on classical linear controllers. In IPMSM, there occurs non-sinusoidal distribution of rotor flux together with the slot harmonics, these are treated as control system disturbances. In this case, the classical observer structure in the (d-q) is unstable for the low range of rotor speed resulting in disturbances. This negative effect can be minimized by using the observer structure which is based on the rotor flux vector in (α-β) stationary frame together with the classical rotor speed and position law of estimation. The performance of the observer structure is validated by simulation and experimental results in the sensorless control system with field-oriented control.

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.

Implementation of Indirect Field Oriented Control Using Space Vector Pulse Width Modulation for the Control of Induction Motor

For the efficient speed control of three phase Induction motor, the Vector control or Field oriented control (FOC) technique is used for the Voltage source inverter. In implementing FOC the angular position of the rotor flux vector is to be determined. There are two methods (direct and indirect) of vector control for the evaluation of rotor angle. In an Indirect field-oriented control (IFOC) method rotor angle is estimated from slip frequency and rotor frequency without using a sensor (sensors are used in direct FOC) which are achieved in a synchronously rotating frame. IFOC produces high performance in induction motor drives by decoupling rotor flux and torque, so it can be separately controlled by stator direct-axis current and quadrature-axis current respectively, like in a DC motor. The rotor flux orientation method is used for incorporating PI control system using the Space Vector Pulse Width Modulation (SVPWM) technique. The Induction motor drive control generally involves three different PI controllers for torque, speed, and flux respectively. Through the simulation result, varying the load torque, and reference speed is achieved within a few milliseconds, and the behavior of the separately excited DC motor is observed.

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.

Synthesizing the Optimal Control of an Induction Motor-Based Traction Electric Drive with Taking into Account Magnetic Saturation and Core Losses

Traction electric drives based on an induction motor often employ vector control with orienting along the rotor flux vector, with which it becomes possible to achieve high performance indicators of the motor and drive as a whole in both static and dynamic operation modes. However, to achieve high energy efficiency of the drive, the use of optimal control strategies becomes of issue. This implies the need to set up, given a specified electromagnetic torque, the stator current flux-forming and torque-forming components according to a certain law to achieve the motor operation optimized with respect to the selected criterion. In the context of a traction electric drive, such criteria are stator current to be maximized or power losses to be minimized. In doing so, it is important to take into account the motor magnetic system saturation and core losses, which have a significant impact on the synthesis of optimal control strategies. The article gives the equations of electromagnetic processes in a cage induction motor with field-oriented control and with taking into account the above-mentioned specific features. A procedure for synthesizing optimal control strategies while minimizing power losses and stator current is also given. Differences in approaches to the synthesis of optimal strategies with and without taking the magnetic system saturation into account are shown.

An Approach of Position and Torque Estimation for Induction Motor based Sensor-less Drive

This paper presents a new approach with stability analysis, simulation and experimental investigation of a sliding mode based estimator for rotor-position and torque-load calculation in high performance speed-sensor-less AC motor drive. The proposed algorithm is built based on the induction motor (IM) fluxes equations for two rotationg referential frames. The First equation calculates the stator flux vector while the second gives the rotor flux vector. Moreover, the stator flux equation is linked to a stator-flux rotating referential frame and the rotor flux equation is linked to a rotor-flux rotating referential frame. Among merits of the proposed technique is no necessity to rotor-speed measurement and adaptation. Thus, it is well suitable to the fully speed-sensorless scheme. The whole observer stability is verified by using of Lyapunov’s principle. Simulations are done by using Matlab-Simulink and experimental implementation is performed in order to prove the feasibility of proposed algorithm. The illustrated results are shown by using a DS1104 controller board.

Robust Finite Control Set Model Predictive Current Control for Induction Motor Using Deadbeat Approach in Stationary Frame

The model predictive control increased its prominence in the field of induction machine drives. However, the performance of this strategy depends on the accuracy of the machine model parameters. In order to overcome this deficiency, this paper proposes a robust model predictive current control employing indirect field-oriented control in stationary reference frame using the stator current and the rotor flux vectors as state and stator voltage vector as the input. The control algorithm combines the classical model predictive control with the deadbeat approach in order to calculate the applied stator voltage vector in two components: one element considers the stator current reference, and another employs the disturbances caused due to the parameter errors, which allows to compensate the parameter mismatches in the plant model. The minimized cost function employs the predicted stator voltage vector to select the voltage vector to be applied to the stator terminals of the motor. The control method performance was verified using an experimental test bench analyzing the system steady-state and dynamic actions. In this way, the results corroborate the proposed controller robustness against parametric variations.

Control Strategy of a Five-Phase Induction Machine Supplied by the Current Source Inverter With the Third Harmonic Injection

In the five-phase induction machine (IM), it is possible to better use the electromagnetic circuit than in the three-phase IM. This requires the use of an adequate converter system which will be supplied by an induction machine. The electric drive system described, in this article, includes the five-phase induction machine supplied by the current source inverter (CSI). The proposed novelty—not presented previously—is the control system structures for the five-phase IM, which is supplied by CSI. The proposed control systems allow for independent control of IM state variables in the first and the second system plane to inject the third harmonic. However, the third harmonic must be suitably associated with the fundamental harmonic. In the proposed solution, the machine vector model is not transformed into the ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d–q</i> ) coordinate system that is connected to the rotor flux vector but utilizes the stationary system ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α–β</i> ). The nonlinear model linearization is based on the demonstrated nonlinear variables transformation for i-orthogonal ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α–β</i> ) (i) planes. Voltage control is applied to the control system structure. The control variables of the five-phase IM are the voltage in the dc link and the angular speed of the output current vector. In the control strategy, the control variables are determined for both system planes. Therefore, the transformation of these control variables to the dc link of CSI is proposed. The proposed control structure allows for independent control of variables in the first and second system planes. It leads to the possibility to increase the value of electromagnetic torque up to 12% for the five-phase IM, which has not been used before in the case of the machine supplied by the CSI. All theoretical issues are confirmed by experimental tests in the 5.5 kW five-phase IM.

Parameter Estimation and Online Adaptation of Rotor Time Constant for Induction Motor Drive

The performance of a sensor-based rotor flux-oriented vector control induction machine drive is highly influenced by the estimated value of the rotor time constant/rotor resistance which varies continuously with temperature when it is driven with the variable loads. Therefore, to achieve accurate torque control, online tunning of the rotor time constant is necessary. This article proposes a novel and simple adaption technique to estimate the rotor time constant. In this proposed method, the reference model of the rotor flux vector is derived using the voltage model of the induction machine, which is independent of the rotor time constant. The current controller uses the model of the rotor flux vector that is derived using the current model of the induction machine. This current model is dependent on the rotor time constant. The error between the rotor flux vectors derived using the current model and the voltage model is minimized using the least-squares method. In this process, the rotor time constant is always tuned to its actual value. The article also presents a simple approach to estimate the parameters of induction machine like the stator resistance, the net leakage inductance, and the initial value of the rotor time constant in an offline mode at a standstill condition. To validate the proposed algorithm, two experimental prototypes are developed for two different power ratings of 3.7 and 67 kW. Experimental results from these prototypes confirm the effectiveness, reliability, and stability of the proposed algorithm both in the motoring and regenerative modes of operation. This method of the adaptation of the rotor time constant is simple and, therefore, useful for practicing engineers.

Analysis and Performance Evaluation of Three-Phase Induction Motor Model with Zero Quadrature Axis Flux Component

Modeling of three phase induction motor has been extensively discussed in literature. Several models have been developed and applied by different authors to solve different problems. This paper presents a differentmodel of the symmetrical three phase induction motor in which there is an alignment of the direct axis component of the rotor flux vector to direct axis of the reference frame. The alignment reduces the quadrature axis flux component to zero, removes the dependencies associated with the d-q components of the stator current and simplifies the rotor dynamics. The model is not commonly used in literature to study motor behavior when vector control is not the objective. The model is analyzed in the synchronous reference frame and simulated. Simulation results for torque, speed and flux in the motor are presented. Also presented are the waveforms of stator voltages and currents in both the d – q and a-b-c reference frames and the rotor d-q axis currents. These results provide a correct description of the three phase induction motor behavior under load and no-load conditions.

THE IDENTIFICATION OF INDUCTION MOTOR INTERNAL QUANTITIES

In the presented work a new identification method of difficult measured internal quantities of IM, such as components of magnetic flux vector and electromagnetic torque, is proposed. Commonly measurable quantities of IM like stator currents, stator voltage frequency and mechanical angular speed are used for identification to determine a feedback effect of the rotor flux vector on vector of stator currents of IM. Based on this feedback it is also possible to identify actual value of the rotor resistance, which can alter during IM operation. This has a significant impact on precision of identified quantities as well as on master control of IM. Stability of the identification structure is guaranteed by position of roots of characteristic equation of its linear transfer function. Results obtained from simulation measurements confirm quality, effectivity, feasibility, and robustness of the proposed identification method.

Enhanced control technique for a sensor-less wind driven doubly fed induction generator for energy conversion purpose

The current paper is concerned with introducing a predictive polar flux control (PPFC) scheme for a variable speed wind driven doubly fed induction generator (DFIG) without speed sensor. The operation of the designed PPFC is based on the power angle regulation. The adaptation process is performed through studying the relation between the generator’s torque and the power angle between the stator and rotor flux vectors. A robust observer is designed based on the back-stepping theory to estimate the rotor speed, stator currents, rotor flux and stator and rotor resistances. Furthermore, an effective maximum power point tracking (MPPT) scheme is designed to achieve the optimal wind power exploitation. To recognize the operation of the schemed PPFC, a discursive performance evaluation is performed for the modeled control scheme and the classic predictive torque control (PTC) scheme. The achieved results report that the DFIG’s performance is effectively enhanced with the proposed PPFC in comparison with the PTC technique. The improved dynamics are observed through the ripples reduction and reduced switching frequency. In addition, the designed observer has successfully managed in estimating the specified variables with high precision.

Dual direct torque control of doubly fed induction machine using second order sliding mode control

In this paper a dual direct torque control (DDTC) strategy with second-order sliding mode control (SOSMC) controller of the doubly fed Induction motor (DFIM) is presented in order to overcome some drawback such as ripples in torque, flux and to improve dual direct torque control (DDTC) performance toward the electrical parameters variations. This control strategy used in the doubly fed induction machine supplied, coupled by two voltage source inverters in rotor and stator sides witches are linked to two switching tables in order to determined the rotor and stator flux vector control. This controller based on super-twisting algorithm (STA). Comparative results between a classical controller (PI) and the proposed controller can prove the very satisfactory performance and robustness of this new controller.

Position-sensorless direct torque control of grid-connected DFIG with reduced current sensors

Direct torque control (DTC) of a grid-connected doubly fed induction generator (DFIG) necessitates at least 2 stator current sensors, 2 rotor current sensors and a rotor position sensor. This letter presents a position-sensorless DTC scheme of DFIG without rotor current sensors. The elimination of two rotor current sensors and position sensors improves hardware reliability by reducing the redundancy of physical components to be used. In the proposed scheme, the rotor flux vector magnitude and torque are estimated using measurable stator quantities. The effectiveness of proposed position-sensorless DTC scheme is validated using MATLAB/Simulink for a 2-MW DFIG-based wind energy conversion system (WECS).

Dynamic Identification of Rotor Magnetic Flux, Torque and Rotor Resistance of Induction Motor

In the modern high-performance drive applications, a high-precision and efficient control of the induction motor depends on the accuracy of parameter values. However, the motor parameters may change due to the winding temperature fluctuations, flux saturation and skin effect. Any discrepancy between the values of the motor’s actual parameters and the ones used for the design of the controllers may result in degradation of the drive performance. In this work, a new identification method of hardly measurable internal quantities of the induction motor, such as components of the magnetic flux vector and electromagnetic torque, is outlined. Commonly, the measurable quantities of the induction motor like stator currents, stator voltage frequency and mechanical angular speed are used to determine a feedback effect of the rotor flux vector on the vector of the stator currents of induction motor. Based on this feedback, it is also possible to identify the actual value of the rotor resistance, which may alter during the induction motor operation. This has a significant impact on the precision of the identified quantities as well as on the master control of the induction motor. Stability of the identification structure is guaranteed by the position of roots of characteristic equation of its linear transfer function. Simulation and experimental results are given to highlight the quality, effectivity, feasibility, and robustness of the proposed identification method, which is working reliably within the whole range of the motor angular speed.

Sensorless Closed-Loop Voltage and Frequency Control of Stand-Alone DFIGs Introducing Direct Flux-Vector Control

In this article, an innovative control method, termed direct flux-vector control, is proposed for the stand-alone doubly fed induction generators (DFIGs) feeding local ac loads. In these systems, both the amplitude and frequency of the stator voltage must be precisely controlled. The proposed method, instead of controlling the rotor currents or voltages, directly controls the rotor flux vector, including magnitude and angle. To achieve an accurate control, two separate closed-loop hysteresis controllers are employed in which the stator-voltage amplitude and frequency are adjusted through the rotor-flux magnitude and angle, respectively. The proposed control method is performed in the rotor reference frame, thus it does not require the rotor speed/position sensors or any reference-frame transformation. As an outstanding feature, the method works for both sub and supersynchronous speed modes without changing the switching table. Hence, no need to detect the operation mode of DFIG. Besides, the method consists of a simple implementation and is almost parameter independent, as it only requires the rotor resistance. The proposed method is implemented on a 3-kW laboratory scale DFIG and its performance, effectiveness, robustness, and correctness are evaluated and discussed for a series of experimental tests.

Feedback Control of Multiphase Induction Machines With Backstepping Technique

This article presents the control possibility of five-phase induction machines. In the proposed solution, the machine model vector form is not transformed to the ( dq )-coordinate system, that is connected to the rotor flux vector, but utilizes the stationary system (α β ). Moreover, the nonlinear model linearization is based on demonstrated nonlinear variables transformation for i -orthogonal $(\alpha \beta)_{(n)}$ planes. By introducing the backstepping approach, the independent stabilization of electromagnetic torque and rotor flux in each plane is obtained. A practical stability analysis of the proposed controller for a multiphase machine is illustrated as well. Finally, experimental test results are demonstrated for a specific speed sensorless five-phase induction motor test setup.

Improved Direct Torque Control for a DFIG under Symmetrical Voltage Dip With Transient Flux Damping

This paper proposes a new reference-generation-strategy for direct torque control (DTC) of doubly fed induction generator (DFIG), under symmetrical voltage-dips. Since DTC has no current-control loop, it cannot prevent overcurrent during voltage-dips. The proposed method prevents overcurrent in the rotor side converter, by damping the transient-flux and modifying the references of rotor-flux and torque, during voltage dip and recovery. The analysis of DTC for DFIG is presented by a λ-i equivalent circuit, which is decomposed into forced and natural circuits. Based on the natural λ-i circuit, the method adds a transient compensation term to the rotor-flux reference, which is obtained by multiplying the stator-natural-flux with a proposed decaying-ramp function. Moreover, this method reduces the forced component of rotor-flux proportional to the grid voltage. As a result, this method adjusts the transient-flux damping time and ensures overcurrent prevention in the rotor and stator windings. The torque reference is modified to maintain the torque-angle (between rotor and stator flux vectors) constant, which results in stable control of the DFIG during grid faults. The effectiveness of the proposed method is confirmed by experimental results of a 3-kW test set-up and simulation results of a 2-MW DFIG.

An Improved Rotor Flux Space Vector Based MRAS for Field-Oriented Control of Induction Motor Drives

The paper proposes an improved low speed performance of classical rotor flux (RF)-based model reference adaptive system (MRAS) for field oriented controlled induction motor (IM) drives. The improved performance of the RF-MRAS estimator is obtained by using voltage reference vector to compute the rotor flux vector in the reference model instead of actual voltage signal vector in the process of speed estimation. The voltage reference vector is estimated by using proportional integral controller over the error signal vectors obtained from the difference between the reference and the measured current vectors. This modification allows satisfactory low or zero speed estimation of IM drive using RF-MRAS-based estimator. The proposed drive's performance is compared with classical RF-MRAS and its performance for the low-speed operation is also authenticated with ${\vec{V}^ * } \times \vec{I}$ based MRAS in MATLAB/ Simulink. Stability and sensitivity studies are further carried out to ensure the robustness of the drive system. Experimental results as obtained by a dSPACE-1104 based IM laboratory prototype are also presented to validate the simulation study.