Flux-oriented Control Research Articles

Robust vector control strategy for variable speed wind turbines

The efficiency of the wind power conversions systems can be greatly improved using an appropriate control algorithm. In this work, a robust control for variable speed wind power generation that incorporates a doubly feed induction generator is described. The electrical systems incorporate a wound rotor induction machine with back-to-back three phase power converter bridges between its rotor and the grid. In the presented design, it is applied the so called vector control theory. The proposed control scheme uses stator flux-oriented vector control for the rotor-side converter bridge control and grid voltage vector control for the grid-side converter bridge control. The proposed robust control law is based on a sliding mode control theory that, as it is well-known, presents a good performance under system uncertainties. The stability analysis of the proposed controller under disturbances and parameter uncertainties is provided using the Lyapunov stability theory. Finally, simulated results show, on the one hand, that the proposed controller provides high-performance dynamic characteristics, and on the other hand, that this scheme is robust with respect to the uncertainties that usually appear in the real systems.

Study on Control System of Bearingless Induction Motor Based on Modified Internal Model Control

Bearingless induction motor is a multi-variable, nonlinear and strong coupled system. On the basis of working principle of bearingless induction motor, independent control of suspension control windings is combined with rotor flux-oriented control of torque control windings in the paper. Meanwhile, in order to improve robustness and decoupling performance of system, the modified internal model control (MIMC) is applied in the control of two sets of windings to realize the dynamic decoupling of currents and stable control of radial displacement. The results of simulation experiments show that the proposed strategy has good ability of disturbance rejection and robustness, so the stable operation of motor can be achieved effectively.

A Novel Control Scheme for Maximum Power Operation of Synchronous Reluctance Motors Including Maximum Torque Per Flux Control

This paper proposes a novel control scheme for maximum power operation of synchronous reluctance motors. The proposed scheme consists of a combination of maximum torque per ampere control, maximum torque per flux control, flux-weakening control, and torque limiting. The first three control methods are based on a mathematical model in a rotating reference frame that is synchronized with the stator flux linkage. The final method utilizes a reactive torque calculated as the inner product of the flux and current vectors. The proposed control scheme is suitable for direct torque control (DTC) or flux-oriented control. In this paper, the scheme is applied to a DTC-based motor-drive system. The validity of the control scheme is verified by simulation and experimental results.

Speed Control of a Doubly Fed Induction Motor using Fuzzy Logic Techniques

This paper presents a comparison between a fuzzy logic controller and a conventional IP controller used for speed control with a direct stator flux orientation control of a doubly fed induction motor. The effectiveness of the proposed control strategy is evaluated under different operating conditions such as of reference speed and for load torque step changes at nominal parameters and in the presence of parameter variation. Simulation results show that the fuzzy logic controller is more robust than a conventional IP controller against parameter variation and uncertainty, and is less sensitive to external load torque disturbance with a fast dynamic response.

약계자영역에서 유도전동기 고정자자속기준제어의 파라미터 비동조 영향 분석

The selection of flux level in the maximum torque control of stator flux-oriented induction motor drives in the field weakening region is dependent on stator resistance and inductances. This paper presents parameter detuning effects of stator flux-oriented control drives in the field weakening region. The detuning effects of stator resistance and rotor leakage inductance are analyzed. The decrease of torque and the flux control lost by the detuning of inductance are shown in the simulation results.

Dynamically Reconfigurable Control Structure for Induction Motor Drives on FPGA Control Platform

The concept of dynamic reconfiguration of controls is commonly known in Fault Tolerant Control (FTC) systems. The general idea of this concept is highlighted and that can be extended to achieve the optimal performance from a plant in its whole operating region. Today, many industrial standard drives provide more than one control scheme for the drive control. The customer may chose between, e.g., flux-oriented control (FOC) and constant voltage frequency ratio control (v/f). However, the dynamic (on-the fly) change-over between these control schemes is usually not available as a feature, although it may be essential e.g. in cases of handling different operating modes optimally or as a fallback strategy in case of faults. The main emphasis of this contribution is to present the detailed concept, implementation and the experimental validation of dynamic reconfiguration between the well known control schemes for the induction machine. The idea is not only to show the switch-over between different control schemes, but also to utilize field-programmable gate arrays (FPGA) as basis for controller implementation. The inherent parallel execution of FPGA makes it easy to implement such dynamically reconfigurable control structure on a single control platform.

A novel dual stator-winding induction generator system applied in wind power generation

This paper presents a novel usage of 6/3-phase dual stator-winding induction generator (DWIG) with a static excitation power controller (SEC) as a wind power generator. This generator is composed of a standard squirrel-cage rotor and two sets of winding housed in the stator slots. One is referred to as the 6-phase power winding, and the other is defined as the 3-phase control winding. On the basis of the instantaneous power theory, the control mechanism of DWIG wind power system is analysed, and the control winding flux orientation control strategy is obtained consequently. The simulation and experimental results from a prototype of 18 kW 6/3-phase DWIG wind power system are presented to verify the correctness and feasibility of control strategy, and a desirable performance is implemented.

A High-Performance Drive for the Rotary Coal Breaker Application

This paper considers recent advances made within the field of electric drives and how this new technology might be best applied within the mining industry. A case study is presented showing simulated results of the performance of the electric drives in a coal preparation plant. The various starting methodologies (resistance starting, fluid coupling, V / f = const, and vector control) are compared within this application. The merits of each method are then discussed with regard to the specific application and other more generic applications within the mining industry. Application of a rotor flux orientation control drive is substantiated, and its superior performance under start and stall conditions to that of the currently implemented system is confirmed by theoretical analysis and simulations. Experimental results for a scale model of the candidate system are presented, which agree with the main conclusions of this paper.

Performance Evaluation of Rotor Flux-Oriented Control on FPGA for Advanced AC Drives

Hardware implementation of mechatronic systems become more and more feasible with the constant development of simulation software tools and more performing computer hardware. The work presented here explains the use of Matlab/Simulink and Xilinx System Generator tools and FPGA hardware in designing, simulating and evaluating control laws for mechatronic systems. Particularly, this paper reports improved results for FPGA implementation and hardware/software co-simulation of a rotor flux-oriented control loop for three-phase AC induction motors. On FPGA, the computation time achieved for the complete control loop proves to be short enough that many enhancements proposed in theory become possible, including the use of neural networks, matrix calculations, on-line monitoring, advanced control of PWM inverter-fed AC machines, and multiple hybrid controls, without affecting system performance or sacrificing precision.

Rotor position estimator for stator flux-oriented sensorless control of slip ring induction machine

A rotor position estimation scheme for stator flux-oriented speed sensorless control of slip ring induction machine (SRIM) is presented in this paper. Position of the rotor is estimated by integrating the rotor back-electromotive force. The problem of DC drift during integration is eliminated using an error-decaying mechanism in the estimator. This estimation scheme reduces the propagation of noise in the sensed current to the estimated rotor side unit vectors. This scheme also eliminates the need for differentiating the unit vectors for estimating slip frequency. The proposed scheme is simulated and experimentally verified.

유도전동기 고정자자속기준제어의 개선된 최대효율제어

유도전동기 고정자자속 기준제어의 최대효율제어를 위한 초기자속값의 계산방법을 제안한다. 3개의 자속에 대한 입력을 계산한 후 3점을 2차 보간하여 2차 함수의 최소점, 즉 입력이 최소가 되는 자속을 구하고, 이 자속을 초기값으로 하여 최대효율제어를 수행한다. 시뮬레이션 결과 기존의 방법에 비해서 제안한 방법에 의하여 최대효율점으로의 수렴시간이 단축됨을 보인다.

Modelling Analysis in Power System Small Signal Stability with Grid-Connected Wind Farms of DFIG Type

In this paper, the modelling and small signal stability analysis of grid-connected wind farms of doubly-fed induction generator (DFIG) type are conducted. A simplified and practical DFIG model is presented firstly. The stator flux-oriented vector control based method is utilized to implement stator active and reactive powers control in modelling rotor-side converter control strategy. The power system small signal stability analysis is then carried out to explore and exploit the essential impacts on the existing power grid due to the high penetration of grid-connected wind farms of DFIG type. Finally, numerical results illustrate the effectiveness and validity of the proposed model and method.

Sensorless direct vector control of an induction motor

In high-performance variable speed AC drive systems it is often important to accurately determine machine parameters and rotor speed values. An extended complex Kalman filter (ECKF) is used to estimate rotor resistance and mutual inductance without the use of a speed sensor. Such estimates are important in air gap flux orientation control. The ECKF is chosen over the more common extended Kalman filter based on the real-valued model as it is not as computationally intensive. The model of an induction machine obtained by the spiral vector theory and the ECKF are used to develop a new adaptive direct air gap flux orientation control with two sensors: one for the stator voltage and one for the stator current without Park transformation. The simulation tests show the effectiveness of the proposed adaptive direct air gap flux orientation control method.

유도전동기 고정자자속 기준제어의 최대효율제어에서 부하증가로 인한 문제 해결방법

유도전동기 고정자자속 기준제어의 최대효율제어에서 경부하시 자속은 작은 값이 된다. 이러한 상태에서 갑자기 부하가 증가하였을 경우 전동기는 부하토크에 대응하는 토크를 발생시켜야 하지만, 낮은 자속 때문에 토크제한조건에 의한 토크성분전류는 작은 값으로 제한되며, 부하토크에 대응하는 토크를 발생시키지 못해서 속도제어가 안 되는 문제가 발생한다. 본 논문에서는 이러한 문제를 해결하기 위한 방법을 제안한다.

Evaluation and Modeling of Cross Saturation Due to Leakage Flux in Vector-Controlled Induction Machines

A detailed magnetic reluctance-based computational model of an induction machine, into which a traditional rotor-flux-orientated vector control scheme has been grafted, is used to examine the influence of saturation of both main and leakage flux paths upon vector-controlled drive performance. Individual machine teeth, windings, and conductors are incorporated, as is pseudo-3-D modeling of skew. The cross-saturation effect is therefore determined from the basic dimensional and winding design data of the machine. Effective compensation methods can then be derived for practical implementation. Direct rotor flux orientation and magnitude control is used to ensure that inaccuracies in a machine-parameter-based vector control scheme are not reflected in the results for cross saturation. Results for a 15-kW four-pole induction motor with rotor skewed one stator slot pitch show that skew leakage flux is predominantly responsible for cross saturation. The skew leakage flux is shown to heavily saturate one end of the machine and to reduce the air gap flux density at the other. At 200% rated load current, this equates to an 11% reduction in direct axis flux if isd is kept constant. To compensate for this reduction, a 27% increase in isd would be required

Flux pinning and orientation control of large grain LREBa2Cu3Oy

The ternary high-Tc superconductor (Nd0.33, Eu0.39, Gd0.27)Ba2Cu3Oy ‘‘NEG-123’’ doped by 5 mol% of the nonsuperconducting secondary phase (Nd0.33, Eu0.33, Gd0.33)2BaCuO5 ‘‘NEG-211’’ was prepared by oxygen controlled melt growth (OCMG) process using MgO seeds. Various contents of ZnO up to 0.07 mol% were added. At the ZnO concentration around 0.035 mol%, a substantial reduction of liquid phase loss was observed, accompanied with a perfect facet line up to the bottom of the sample, with c-axis reflection plane. Magnetization measurements showed that at this optimum ZnO addition the superconducting transition temperature was slightly depressed. On the other hand, flux pinning performance around the secondary peak, observed at liquid nitrogen temperature, was continually improved with increasing ZnO content up to 0.035 mol%. It was found that the optimum content of ZnO is crucial for flux pining enhancement and orientation control of MgO seeded melt-textured NEG-123 system.

A control strategy for stand-alone wound rotor induction machine

A control strategy to regulate the frequency and voltage of a stand-alone wound rotor induction machine is presented. This strategy allows the machine to work as a generator in stand-alone systems (without grid connection) with variable rotor speed. A stator flux-oriented control is proposed using the rotor voltages as actuation variables. Two cascade control loops are used to regulate the stator flux and the rotor currents. A closed loop observer is designed to estimate the machine flux which is necessary to implement these control loops. The proposed control strategy is validated through simulations with satisfactory results.

A high-performance sensorless indirect stator flux orientation control of induction motor drive

A new method for the implementation of a sensorless indirect stator-flux-oriented control (ISFOC) of induction motor drives with stator resistance tuning is proposed in this paper. The proposed method for the estimation of speed and stator resistance is based only on measurement of stator currents. The error of the measured q-axis current from its reference value feeds the proportional plus integral (PI) controller, the output of which is the estimated slip frequency. It is subtracted from the synchronous angular frequency, which is obtained from the output integral plus proportional (IP) rotor speed controller, to have the estimated rotor speed. For current regulation, this paper proposes a conventional PI controller with feedforward compensation terms in the synchronous frame. Owing to its advantages, an IP controller is used for rotor speed regulation. Stator resistance updating is based on the measured and reference d-axis stator current of an induction motor on d-q frame synchronously rotating with the stator flux vector. Experimental results for a 3-kW induction motor are presented and analyzed by using a dSpace system with DS1102 controller board based on the digital signal processor (DSP) TMS320C31. Digital simulation and experimental results are presented to show the improvement in performance of the proposed method.

Direct torque control with an optimized observer for multi-machine systems

The first purpose of this work is to design a new observation technique for the Direct Torque Control (DTC). We put emphasis on robustness especially at very low speed, which represents the basic problem of the DTC operating, and on the optimization of the time computing. The reduced order observer is defined by decoupling the full order one in and axis. The second basic aim of this paper is to apply the DTC strategy to multi-machine multi-inverter industrial systems. Speed and tension controls are designed; their performances and parameter robustness are analyzed and compared with those obtained with a Flux Oriented Control (FOC). Mechanical and electrical couplings constitute the principal operation difficulty of these systems mainly when one of the machines is perturbed.

Double-fed induction generator control for variable speed wind power generation

Vector control of a doubly fed induction generator drive for variable speed wind power generation is described. A wound rotor induction machine with back-to-back three phase power converter bridges between its rotor and the grid forms the electrical system. The control scheme uses stator flux-oriented control for the rotor side converter bridge control and grid voltage vector control for the grid side converter bridge. A complete simulation model is developed for the control of the active and reactive powers of the doubly fed generator under variable speed operation. Several studies are performed to test its operation under different wind conditions. A laboratory test setup consisting of a wound rotor induction machine driven by a variable speed dc motor is used to validate the software simulations.