Stator Current Components Research Articles

Rapid Prototyping and Hardware-In-the-Loop Verification of Enhanced Sliding Mode Control of an Asynchronous Machine Using a Xilinx System Generator and an FPGA-Zynq Board

This article describes rapid prototyping using the Xilinx system generator (XSG) of a direct field oriented control (DFOC) strategy based on improved super twisting sliding mode controllers (ISTSMCs) of an asynchronous machine to succeed a hardware implementation on a field programmable gate array (FPGA) board. The main goal is to enhance regulation loops governing rotor speed, rotor flux, and stator current components within the classical DFOC structure. These ISTSMCs replace integral proportional controllers, resulting in improved system dynamics, faster speed and torque responses, and heightened robustness against load and rotor resistance variations, surpassing other control methods. Additionally, the article aims to implement this DFOC-ISTSMC method on an FPGA board to reduce control system sampling time and loop delays, leveraging the FPGA’s parallel processing capabilities. The hardware architecture is designed using XSG in the MATLAB/Simulink environment, enabling effective simulation, testing, discrete algorithm creation, and VHDL code generation for FPGA implementation via the hardware-in-the-loop (HIL) process. Assessment involves digital simulation studies and HIL processes using XSG with a Xilinx FPGA Zynq 7000 under MATLAB/Simulink, demonstrating improved system performance, reduced time delays, and efficient FPGA utilization. This approach validates the effectiveness of the proposed DFOC-ISTSMC algorithm in enhancing control strategy for asynchronous machines.

SPEED CONTROL OF PERMANENT MAGNET SYNCHRONOUS MOTOR IN SLIDING MODE

The paper examines a series of speed control algorithms for a synchronous permanent magnet motor in sliding mode, providing asymptotic stability of the first, second, and third order. In the sliding mode, the control system exhibits properties that are unattainable with classical continuous control algorithms. The control algorithms are developed based on the inverse dynamics method combined with the minimization of local instantaneous energy functionals. The key idea of the method lies in the reversibility of the direct Lyapunov method for stability analysis. The closed-loop control system has a predefined Lyapunov function, represented by the instantaneous energy. Notably, the control algorithms do not require knowledge of the object's parameters or differentiation operations, which facilitates their practical implementation. The regulator parameters consist solely of coefficients used to specify the desired duration and shape of current and motor speed transient processes. The vector speed control system comprises two controllers for the stator current components and the motor speed controller. All regulators operate in sliding mode. The output signals of the stator current component controllers and speed vary discontinuously from maximum to minimum values. Simulation results demonstrate the effectiveness and high-quality performance of the control algorithms. To determine the control performance indicators for the three synthesized speed controllers, the motor startup trajectory is formed from characteristic segments of constant, linearly increasing, and parabolic signals. The speed control algorithm with a first-order asymptote ensures zero tracking error only for a constant reference signal. With a linearly increasing reference signal, the steady-state relative tracking error is 2,5 %, while for a parabolic reference signal, the error varies between zero and 2,5 %. The second-order asymptotic speed control algorithm ensures zero steady-state tracking error for constant and linearly increasing reference signals, and for a parabolic reference signal, the steady-state relative tracking error is 0,125 %. The third-order asymptotic speed control algorithm ensures zero steady-state tracking error for constant, linearly increasing, and parabolic reference signals, with a maximum dynamic relative tracking error of 0,05 %.

Model Predictive Control of Counter-Rotating Motors for Underwater Vehicles Considering Unbalanced Load Variation

The propulsion system for underwater vehicles, driven by a counter-rotating permanent magnet synchronous motor (CRPMSM), can enhance the operational stability and efficiency of the vehicle. Due to the influence of complex underwater flows, the load imbalance of CRPMSM’s dual counter-rotating rotors may lead to severe issues of dual-rotor desynchronization rotation. Combining traditional vector control (VC) with master-slave control strategies can address the desynchronization problem when CRPMSM’s load changes. However, it results in significant speed fluctuations and a long transition time during the transition from load disturbance to synchronous rotation. This paper introduces a model predictive control (MPC) strategy to effectively resolve this issue. The incremental MPC model is established based on the mathematical model of CRPMSM in the dq coordinate system. The predictive control system forecasts the d- and q-axis components of stator currents for the next four control cycles. It selects the optimal control increments to minimize the cost function based on current predictions and different inverter voltage states. The obtained optimal d- and q-axis components of stator voltage are used to control CRPMSM under unbalanced load disturbances. Simulation results demonstrate that, compared to the VC strategy, CRPMSM utilizing the MPC strategy exhibits better dynamic performance with faster speed response and reduced torque fluctuations during load and speed variations.

Single open‐phase fault detection and tolerant control for wye‐connected three‐phase induction machine drives

SummaryThis paper proposes open‐phase fault detection (FD) and tolerant control strategies for wye‐connected three‐phase induction machines (WCTPIMs). The FD mechanism is based on the comparison between predicted and actual values of stator currents, and the control approach is derived from the field‐oriented control (FOC). In the proposed fault‐tolerant control (FTC) method, an asymmetrical current transformation is used for stator current components, and the conventional symmetrical voltage transformation is employed for stator voltage components. It is shown that using these transformations, a modified FOC can be employed for the faulty WCTPIM. The suggested scheme is able to control WCTPIM drives under normal and single open‐phase fault (SOPF) modes with minor adjustments. Experimental results achieved from a laboratory prototype confirm the possibility and good performance of the proposed open‐phase FD and tolerant control for the WCTPIM under different operating conditions.

A novel vector control strategy for sensorless 3φ induction machines under single‐phase fault

AbstractSafety and reliability are very important in machine driving systems for many industries. A novel rotor flux‐based Vector Control (VC) strategy for Y‐connected 3φ Induction Machines (IMs) without speed sensor under the Single‐Phase Fault (SPF) is proposed. The sensorless VC technique is based on using Asymmetrical Transformation Matrices (ATMs) for stator voltage and current components as well as an Extended Kalman Filter (EKF) for estimation of the speed and d‐q fluxes. Furthermore, a simple model‐based SPF detection mechanism based on the EKF is suggested. The performance of the proposed control scheme for a 1 HP sensorless Y‐connected 3φ IM prototype is validated by several experiments. According to the experimental results, the designed scheme during the SPF has several advantages of improved phase currents and low speed, flux, and torque ripples.

Improving the Efficiency of Electric Rolling Stock Operation Through the Use of Adaptive Filtering Methods for High Harmonic Current Components in Traction Drive Systems

The aim of this work is to investigate the efficiency of various adaptive filtering methods for higher harmonic components of stator currents in a vector-controlled traction drive system to improve the operation efficiency of electric rolling stock. The set goal was achieved by implementing an adaptive filtering block into the basic vector control system, which sequentially employs various adaptive filtering methods. The first harmonic component of stator currents was proposed to be used as the desired signal. An algorithm for determining the first harmonic component under conditions of varying supply voltage frequency was developed. Based on the simulation results, filtration efficiency metrics were established, indicating that the Wiener filter is the most effective for filtering higher harmonic components of stator currents. The most significant results include the algorithm for determining the first harmonic component of the stator phase current and the determination of an adaptive filtering algorithm with the highest convergence rate. The importance of these results lies in identifying the most effective adaptive filtering algorithm for traction drive operation, taking into account the operating modes of electric rolling stock. This will help reduce losses from higher harmonic components in the traction drive and, consequently, increase its energy efficiency.

Revamped System Performance of Grid-Interactive Hybrid DFIG-PV System Using WSO Based Dual Layer MRFKMP Adaptive Control

Due to the stochastic characteristicsof wind, keeping high-quality power into the grid-dependent hybrid wind energy systems is important for effective energy utilization, especially when there are non-linear loads involved. In this paper, a dual layer random features kernel mean p-power (MRFKMP) adaptive control for the grid interfaced converter of a DFIG-PV based hybrid energy system is implemented for the purpose of maintaining power balances and quality power at both the source and grid ends while operating at unity power factor. The introduced control extracts the weight of stator and load current components with finer convergence and lower computational complexity, excluding complex reference transformations. The dual layer adaptive control improves grid side converter functionality by improving power quality, interruption of loads, taking into account reactive power and harmonic remediation under steady-state and dynamic scenarios.In the secondary step, to achieve optimal DFIG-PV control response, the stability of the DC-link, which is themain coupling element for power transfer between DFIG, solar PV, and battery energy storage (BES), is reinforced by tuning the DC link voltage controller with the white shark optimization (WSO) algorithm. Under the worst-case scenario of large step wind change, the primacy of the envisaged WSO algorithm for tuning DC-link PI controller has been evidenced. It is discovered that WSO tuning positively affects the settling time and oscillatory response of the DC-link voltage not just at the outset, but also throughout the subjugated dynamic wind speedchange.Power flow to the grid is stable due to optimized DC-link voltage performance. WSO parameter tuning improved efficiency is validated using MATLAB simulation results and compared to GA and PSO techniques in this study.

Adaptive control of DFIG-based wind turbines for fault ride-through and reactive power support based on stator current transient component

The fault ride-through performance is improved through the control of the transient components of the stator current. The reactive power provided by the DFIG within the margin of the converter can significantly enhance the grid-connected safety of the DFIG. Firstly, the reasons for the fault overcurrent of the DFIG’s rotor are analyzed. Secondly, according to the operating conditions of the wind turbine, the reactive power support limit of the DFIG-based wind turbines based on the stator current transient component control is analyzed, and an adaptive reactive power support control suitable for fault ride-through is proposed to maximize its support potential for grid-connected voltage. Finally, the DFIG can not only suppress the rotor overcurrent through the transient component of the stator current but also have a reactive power support capability that is superior to the grid-connected standard.

DC-Link Current Minimization Scheme for IM Drive System Fed by Bidirectional DC Chopper-Based CSI

Compared to a voltage source inverter, a current source inverter (CSI) retains the advantages of inherent boost capacity, friendly output voltage waveforms, and high reliability in motor drive systems. As the motor drive usually operates on variable speed and torque occasions, the CSI needs a pre-stage circuit and control scheme to generate a proper DC-link current. Because the DC-link current minimization can reduce the losses of semiconductor devices and the THD of stator current, a DC-link current minimization scheme for CSI fed induction motor (IM) drive system fed by bidirectional DC chopper-based CSI is proposed in this paper. Firstly, the calculation method for the reference of the minimum DC-link current and the optimal exciting component of stator current is derived. Secondly, the hysteresis control scheme based on the bidirectional DC chopper is designed to regulate the DC-link current tracking to the reference under different operation modes. Thirdly, the influence of the parameters mismatch in the steady-state is discussed. Finally, the correctness and feasibility of the DC-link current minimization scheme proposed in this paper are verified by simulation and experimental results.

A simple fault-tolerant control method for open-phase three-phase induction motor drives

Fault-Tolerant Control (FTC) strategies for Three-Phase Induction Motors (TPIMs) against an open-phase fault have attracted considerable interest in safety-critical applications. In the available literature, open-phase FTC methods for TPIMs are typically implemented using suitable Current Transformation (CT) and Voltage Transformation (VT) matrices. However, the controller design becomes complicated due to different transformations. In addition, the model based on CT and VT suffers from slow dynamics due to several Proportional–Integral (PI) controllers. This paper proposes an open-phase FTC technique for TPIM drives with proof of its asymptotic stability. It is designed based on a new CT for stator current components. Using this CT, the traditional vector control method can be used for Open-Phase TPIMs (OPTPIMs). Furthermore, considering that parameters of the PI controller have an important effect on the OPTPIM drive performance, a design technique is presented to achieve the best values of PI controller parameters. Additionally, an open-phase fault detection technique is presented based on the third-difference operator. The proposed FTC has a simple structure and fast dynamic responses. Matlab simulation and experimental results using DSP/TMS320F28335 approve the ability and good performance of the introduced FTC technique for TPIM drive systems under different conditions.

Dynamic Addition of Common Mode Voltage in Post Fault Operation of Cascaded H-Bridge Converter Fed Induction Motor Drive

In this article, a postfault control technique is proposed for a rotor field-oriented induction motor (RFO-IM) drive fed from a cascaded H-bridge multilevel (CHB-ML) converter. The control strategy is to vary the magnitude and phase shift of the injected fundamental common mode voltage (FCMV) according to the motor’s operating condition. The addition of the proposed FCMV with the reference phase voltages, not only ensures maximum line voltage in the postfault operating condition but also shares equal power among the remaining healthy cells of the converter. Moreover, in the postfault operation, a detailed analysis is performed on both motor and converter, and an integrated control is presented to maintain the command speed and load torque of the RFO-IM. This includes the mathematical equation explaining the new operating point of the motor for different fault configurations, traversal of operating point, and the variation in power factor of each leg of the converter in postfault conditions. From the above analysis, the dynamic FCMV is calculated from the new operating point of the stator current components in the current <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dq</i> -plane and the fault configuration of the CHB-ML converter. The proposed control technique is validated using simulation and experimental results conducted on a 3-hp IM.

An Improved Angular Stator Flux Frequency Computation Method for Robust MPPT Operation of DFIG Under Unbalanced Grid Voltage

Maximum power extraction and constant power generation in a smooth and uninterrupted manner are challenging control tasks for the robust operation of DFIG under grid voltage dips, owing to severe power and torque pulsations. Thus, necessitating tailored power control strategies while curtailing the undesirable effects on DFIG performance under voltage dips. The crux of this paper is to compute the angular stator flux frequency for precise reference power generation and control of DFIG subjected to grid voltage unbalance especially during MPPT operation. The angular frequency of stator flux is computed with the stator voltage and current components in the positive sequence stationary <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α-β</i> reference frame without the need for a PLL and differentiation of stator voltage vector. Further, the computed stator flux frequency signal is employed for rotor speed computation, and reference power generation for maximum power extraction from DFIG. The efficacy of the proposed method in enabling precise power control of DFIG under unbalanced grid voltage is demonstrated using simulations in PSCAD/EMTDC and further through test results on a 3 hp DFIG test set up. The overall results show enhanced performance of DFIG under MPPT with the proposed scheme.

Design and Analysis of Novel Three-Phase PFC for IM Drives

Induction motor drives (IMDs) can achieve high performance levels comparable to dc motor drives. A major problem in getting high dynamic performance in an IMD is the coupling between the flux and torque producing components of stator current. This is successfully overcome in FOC (Field-Oriented Control) IM, making it to the industry standard control. The performance of an IMD with an improved power quality converter at the front end is presented in this study. In the IMD, boost converter is employed to reduce power quality difficulties at the utility interface. As the boost converter contains only one switch, it results in a low processing time and cost. To ensure sinusoidal supply currents with high PF (Power Factor) and minimal THD (Total Harmonic Distortion), a novel PFC (Power Factor Corrector) control technique is proposed. To enhance the performance of the converter and to lower distortions at the motor side, PI (Proportional Integral) controller is incorporated at the PFC side. Thus it controls the DC bus voltage. The proposed boost converter improves power quality by lowering overall harmonic distortion of AC mains current, improving power factor correction, and regulating dc-link voltage. It is designed, modelled, and simulated in the MATLAB/simulink platform. Using a DSP (Digital Signal Processor), the suggested system’s performance is experimentally validated. The system’s performance is evaluated for speed and load torque, and the power quality indices are determined to meet IEEE-519 standards under all operating conditions. From the obtained results, it is evident that the proposed system mitigates the power quality issues effectively.

Sampling error‐based model‐free predictive current control of open‐end winding induction motor with simplified vector selection

AbstractA sampling error‐based finite‐set predictive current control (FS‐PCC) is proposed in this article for the open‐end winding induction motor (OEWIM) drive. The proposed scheme controls the zero‐sequence current (ZSC) alongside the stator currents. In a model‐free approach, this method predicts the future of ZSC and stator current components by the stator current and voltage sampling errors. In this way, the parameters of the OEWIM are not utilised in the prediction algorithm of the FS‐PCC. So, the proposed method is robust against the variation of the parameter. Moreover, this article presents a simple vector selection technique for the FS‐PCC of the OEWIM. The proposed technique has two cost functions and a simple algebraic equation to put the voltage vectors (VVs) in the prediction algorithm. The first cost function uses VVs that do not have the zero‐sequence voltage component. Then, the algebraic equation determines VVs that must be utilised in the second cost function. Finally, the optimum VV is selected by the second cost function. In the proposed scheme, the prediction algorithm is iterated 14 times instead of 27 iterations of the conventional predictive algorithm. So, besides establishing a novel model‐free prediction algorithm, the proposed method has almost 50% fewer calculations. The validity of the proposed sampling error‐based FS‐PCC and the simplified vector selection technique has been verified through experimental tests.

Speed Tracking for IFOC Induction Motor Speed Control Using Hybrid Sensorless Speed Estimator Based on Flux Error for Electric Vehicles Application

This paper presents hybrid sensorless speed tracking by an indirect field-oriented control (IFOC) for an induction motor (IM). The sensorless model is based on an improved virtual estimation topology model to predict the virtual speed and flux of the IM using stator current components. The hybrid sensorless model, defined as a modification of voltage with a rotor flux-oriented current model, was also implemented with proportional-integral (PI) control for comparison with the conventional voltage model (CVM). The suggested adaptive mechanism for PI control in the hybrid estimator was able to compensate for the back-EMF error from the rotor flux-oriented current model into the voltage model and change the air gap flux of the IM. An accurate rotor flux position was estimated and used to estimate the speed with low speed error. This IFOC model, with various speed change references, was tested in a simulation environment by using the MATLAB/Simulink program. The proposed hybrid estimator was tested in two different EV operations, which were reverse and forward operations. The effectiveness of the proposed estimator was analyzed for its transient and steady-state performances based on settling time, recovery time and the overshoot and speed error percentages. All the results were in good agreement in terms of the stability of the speed and current controller with minimum speed error obtained, where the average errors were 0.08% and 0.16% for high speed and lower speed, respectively.

An Integral Sliding Mode Stator Current Control for Industrial Induction Motor

An integral sliding mode control (ISMC) for stator currents of the induction motor (IM) is developed in this work. The proposed controller is developed in the d-q synchronous reference frame, by using the indirect field-oriented control (FOC) method. Robust asymptotic tracking of stator current components in the presence of model uncertainties and current coupling disturbance terms has been guaranteed by using an enhanced ISMC surface. More precisely, the stationary error of stator currents has been eliminated, and the accuracy of the regulators has been enhanced. According to the Lyapunov approach, it has been proven that the stator currents tracking happens asymptotically, and consequently, the stability of each loop has been demonstrated. Simulation and experimental results show the capability of the new controller in diminishing system chattering and increasing the robustness of the designed scheme, considering the variation of the plant parameters and current disturbance terms. It has been illustrated that compared with the conventional ISMC and PI regulators, the proposed current controllers provide smoother control actions and excellent dynamics. In addition, because of the precise control over the rotor flux, the rotor flux weakening method is employed to run the motor at a higher speed than the rated value.

Improved Slight Fault Diagnosis Strategy for Induction Motor Considering Even and Triple Harmonics

This article proposes an improved fault diagnosis strategy to enhance the diagnosis accuracy for the induction motor under the slight fault situation. The additional even and triple harmonics, caused by the faulty asymmetric structure, are taken into account. As a result, the stator current faulty characteristic frequency components, caused by faults from the stator side, the rotor side and the air-gap side, are enlarged. The Hilbert transform and the support vector machine (SVM) multiclassification method are applied to improve the sensitivity of fault identification. To increase the diagnosis accuracy and speediness in different applications, the grid search method, the genetic algorithm and the particle swarm algorithm are employed for the parameter optimization of the SVM classification prediction model. Finally, compared with the traditional strategy, the diagnosis accuracy can be increased by 6%–10% based on the proposed strategy. Comprehensive simulation and experimental results have fully verified the proposed diagnosis method in this article.

A Novel Experimental Method for Identifying the Flux Linkage Map of a High-Power Medium-Voltage Electrically Excited Synchronous Machine with Double Stator Winding

Accurate knowledge of the magnitude and position of the magnetic flux is essential for implementing field-oriented control (FOC) and achieving high-performance behaviour of AC drives. For estimating the flux in a wide range of speeds, so-called hybrid flux estimators, which are a combination of current-model and voltage-model based estimators, are usually used. Since the inductances are used as parameters in the current model, knowledge of the actual flux–current relationship, i.e., of the actual flux linkage map, is inevitable. In this paper, a novel experimental method for identifying the flux linkage map of an electrically excited synchronous machine (EESM) with double stator winding is proposed, which, unlike most existing experimental methods, does not require an additional machine to be used as a load. The flux is determined for different operating points to which the unloaded and sped-up machine is brought to by injecting d- and q-axis stator current components, whereby the current controllers are used to keep them constant for a certain operating point. The proposed method has been used to identify the flux linkage map of a medium-voltage EESM with double stator winding. A more than acceptable accuracy confirmed by comparison with three different analytical methods, together with the fact that it does not require a complex experimental setup, makes the proposed method suitable for the identification of a machine’s flux linkage map in an industrial environment.

Стійкість систем векторного керування напругою асинхронного генератора

The paper presents an analysis of the stability properties of typical structures of induction generators-based vector control systems with linear proportional-integral currents and DC-link voltage controllers. The study is based on the mathematical model of an induction machine taking into account the magnetization curve. It provides the modification of the typical voltage-flux vector control algorithm by considering the saturation of the magnetic system. The stability proof problem of an induction generator-based generation system is that its model is nonlinear and nonminimal-phase, and that the dynamics of the DC-link voltage is nonlinear even for a constant flux linkage and speed due to the presence of nonlinear components which are proportional to active losses. The conditions which provide consideration of the reduced-order system dynamics are formulated and properties of local asymptotic stability of the generation system with typical vector control algorithms are proven based on the singular perturbation theory. It is shown that the local asymptotic stability is ensured when the regulation processes of the DC-link voltage and the torque-forming stator current component are decoupled, which is achieved due to the proposed special adjustment of the voltage and current controllers. A modified vector control algorithm of induction generator is studied in simulation and experimentally. At the first stage, the system dynamics is investigated when the flux subsystem is in equilibrium point. As a result, the possibility of the reduced-order system consideration for the design and analysis of the voltage regulation subsystem was confirmed. At the second stage, the dynamic behavior of the voltage control loop for different settings of the controllers was experimentally investigated. It is shown that the configuration of the voltage control algorithm proposed in the work provides the timescale separation of the current and DC-link voltage regulation processes, as well as their quasi-decoupling.

Improving the energy efficiency of electric drives for auxiliary units of traction rolling stock

The review of technical solutions and schematic characteristics of auxiliary drives for traction vehicles has shown that the most rational variant is an electric drive with an induction machine. Given the operating modes of the auxiliary drives and the share of their power consumption in the total locomotive power, the task of using scalar control systems for induction machines becomes relevant. Based on a mathematical model describing the dynamic energy conversion processes in the T-shape substitution circuit of an induction motor, taking into account stator steel losses and current displacement effects in the rotor winding and saturation along the main magnetic path, possibilities for reducing stator current have been investigated. In order to improve the energy efficiency of electric drives two variants of control system have been proposed. One based on search method of self-tuning to the stator current minimum and the other - on maintaining the power factor of induction motor at the level that ensures equality of active and reactive components of stator current. The hardware and software requirements for implementing control systems have been analysed. Modelling using Matlab has shown that both control systems work - power loss reduction can be as low as 50% and as high as 60% in certain modes.