Stator Flux Oriented Vector Control Research Articles

A Simple Yet Parameter-Less and Cost-Effective Rotor Speed-Cum-Position Estimator for Encoder-Free Control of Doubly-Fed Induction Generator

A hybrid process for estimating rotor speed and position is proposed for the doubly-fed induction generator (DFIG) in connection with its stator flux-oriented vector control. The improved characteristics of the proposed method are: (i) unlike existing schemes, this method does not exhibit error due to discrepancy in the machine’s parameters, and (ii) The number of sensors is reduced in comparison with the other estimators. As a result, the estimation model achieves parameter independence while also using fewer sensors, i.e., a cost-effective, reliable, and compact scheme is suggested due to the reduction of physical element and parameter dependency. In the proposed case, it is not necessary to calculate fluxes or intermediate variables, as well as to use fewer measured input quantities, which reduces the calculation burden. Differentiation and integration of variables are absent. This prevents the magnification of noise and low-frequency signals on the primary signal. The operations of the proposed estimator under diverse conditions are tested by means of a real-time working prototype. The performances here support the theoretical conclusions. The comparisons with other state-of-art techniques indicate the superiority of the proposed estimation scheme.

Steady State Modeling and Performance Analysis of a Wind Turbine-Based Doubly Fed Induction Generator System with Rotor Control

The utilization of renewable energy sources aids in the economic development of a country. Among the various renewable energy sources, wind energy is more effective for electricity production. The doubly fed induction generator is an extensively known wind turbine generator for its partially rated power converters and dynamic performance. The doubly fed induction generator assists the wind turbine to function with a wide speed range. Hence, the steady-state performance analysis of a doubly fed induction generator helps enable it to operate efficiently at a specific wind turbine speed. In this paper, a 2 MW variable speed pitch regulated doubly fed induction generator with a speed range of 900—2000 rpm was opted for steady-state analysis. This was followed by the design and modelling of a doubly fed induction generator in Matlab/Simulink environment, and the analyses were performed using mathematical equations computed via Matlab coding. The steady-state magnitudes were calculated with rotor magnetization idr = 0. The closed-loop stator flux-oriented vector control is applied to the rotor side converter for controlling the designed doubly fed induction generator model. The simulation results were compared with computational values to establish a workable model with less than 10% error. The simulation model can be used for predicting the performance of the machine, fault analysis, and validation of existing DFIG at a steady state.

Impact Analysis of Increased Penetration of Variable Speed Constant Frequency Wind Power Generation on Power System Stability

Wind energy has the characteristics of randomness and intermittency. The simulation of the dynamic process on the medium and long-term time scale caused by this is of great significance to the planning and operation of power systems containing wind power. The paper discusses the operating principle of AC-excited variable-speed constant-frequency wind power generation system, analyzes the operating characteristics and control objectives of doubly-fed asynchronous wind generators before and after grid connection, and studies the grid connection of generators based on stator flux-oriented vector control technology Control and tracking control of maximum wind energy. The simulation analysis of the fault disturbance process of the power grid system with variable speed and constant frequency wind turbines, the results verify the correctness of the modeling.

Dynamic Analysis of DFIG Fault Detection and Its Suppression Using Sliding Mode Control

In this article, a fault detection method based on chaos is proposed for doubly fed induction generator (DFIG). First, the nonlinear differential equation of the DFIG is established by the stator flux-oriented vector control method, and then, the motion state of the DFIG is proved by the 0–1 test algorithm. Second, the motion state of the DFIG is analyzed under normal and fault conditions. Due to some failures that may occur in the normal operation of the DFIG, the motion state of the DFIG system may enter chaos from the cycle, which is mainly manifested by the violent oscillation of the rotor current and speed. At this time, the system is in an extremely unstable operating condition. Thereby, a new sliding mode control rate is mentioned to suppress chaotic behavior. Its stability is analyzed by constructing the Lyapunov function to ensure that the system state can quickly and stably converge to the given value. After that, the simulation model of the system is built. The simulation results show that sliding mode control can make the DFIG get out of the chaotic state quickly. And, the sliding mode control has the characteristics of fast fault elimination and high control accuracy. In addition, the traditional sliding mode approach rate is compared with the proposed new sliding mode approach rate. It proves that the proposed new approach rate can achieve better control effect.

Neural Speed Estimation Applied to Stator Flux-Oriented Control Drives

The induction motor speed is an important quantity in an industrial process and can be used indirectly in flow, pressure, and drive control. However, the direct measurement of speed compromises the driver system and control, increasing the implementation cost. Speed estimators are usually based on a mathematical model of the induction motor, but it is typically necessary to obtain the parameters of the motors. Thus, this work proposes an artificial neural network approach to estimate the mechanical speed of induction motors in a stator flux-oriented vector control by direct current control and direct torque control. In this proposed strategy, no machine parameters adaptation is needed. The neural speed estimators, without weight change, are tested in two different motors to evaluate its robustness. First, by simulation, the neural networks are trained with constant machine parameters and then the estimator performance is evaluated under stator and rotor resistance variation. After that, the same neural estimators are experimentally tested, with another machine, under the variation of motor load torque and speed reference operating point.

Effect of Doubly Fed Induction Generator on Transient Stability Analysis under Fault Conditions

Wind is one of the most widely used non-conventional sources of energy. The majority of wind farms use a variable speed Wind Turbines Generator (WTGs) equipped with Doubly-Fed Induction Generator (DFIG) due to their advantages over other WTGs. The analysis of Wind Energy (WE) dynamics with the DFIG – Wind Turbines (WTs) has become an interesting research issue during transient faults. This paper investigates the effects of the different faults on transient stability. The analysis is performed on a 6-bus test system during transient faults and loss of excitation in synchronous generators. The stator-flux oriented vector control approach used for both stator and Rotor Side Converter (RSC) is proposed to mitigate DFIGs impacts on the system stability. The dynamic performance of DFIG variable speed WT under faults conditions are simulated using Neplan® program, considering different disturbance natures.

Stator flux‐oriented vector control of dual stator induction generator with time optimised 11‐zone hybrid PWM for grid connected wind energy generation system

This work presents a novel stator flux-oriented vector control (SFOVC) of a dual stator induction generator (DSIG) used for a grid connected, variable speed wind energy generation system. The DSIG consists of two stator windings electrically separated by an angle of 30° with dissimilar pole numbers, which are in the ratio of 1:3. In conventional vector control, the rotor flux is oriented along the d-axis of the rotor winding. However, the rotor variables are not easily accessible. So, in the SFOVC, the total flux is made to be oriented along the d-axis of the stator winding. SFOVC is advantageous as compared to conventional vector control because the stator variables are easily accessible and do not require any special arrangement for the measurement of variables which increases the robustness of the system. Here, two separate converters are used for the two stator windings of the machine and the converter switching is being controlled by a novel space vector based 11-zone hybrid pulse-width modulation (PWM). This special PWM results in better harmonic performance, reduced torque pulsation and minimal switching loss. The overall simulation is being performed in MATLAB Simulink environment and the simulated results are also being validated experimentally.

DFIG stator flux‐oriented control scheme execution for test facilities utilising commercial converters

The utilisation of conventional industrial converters for development of doubly-fed induction generator (DFIG) test facilities poses an attractive prospect as it would provide proprietary commercial protection and functionality. However, standard commercial converters present significant challenges in attainable DFIG operational capability. This is due to the fact that they are designed for execution of a limited set of pre-programmed common control modes. They typically do not cater for execution of complicated stator flux-oriented vector control (SFOC) schemes required for DFIG drive control. The research work presented in this study reports a methodology that enables effective implementation of SFOC on industrial converters through a dedicated external real-time platform and a velocity/position communication module. The reported scheme is validated in laboratory experiments on an experimental DFIG test-rig facility. The presented principles are general and are therefore applicable to conventional DFIG drive architectures utilising standard industrial converters.

Neural network–based improved active and reactive power control of wind-driven double fed induction generator under varying operating conditions

Artificial neural network–based power controllers are trained using back propagation algorithm for controlling the active and reactive power of a wind-driven double fed induction generator under varying wind speed conditions and fault conditions. Vector control scheme is used for control of the double fed induction generator. Here stator flux–oriented vector control scheme is implemented for the rotor side converter and grid voltage vector scheme is used for control of grid side converter using tuned proportional–integral active and reactive power controllers, which is later replaced by artificial neural network–based controllers. The artificial neural network controllers are trained using the data obtained from simulation of conventional proportional–integral controllers under varying operating conditions. The intelligent controller makes the generated stator active power to track the reference active power more precisely at specified power factor in both sub-synchronous and super-synchronous modes of operations. Simulation results reveal that the neural network–based controller significantly improves the performance of variable speed wind power generating double fed induction generator under various conditions.

Establishment and Parameter Allocation of DFIG Wind Turbine Control Model of PSCAD

At present, PSCAD simulation analysis of wind turbine model is not perfect, and with the increasing capacity of wind turbine assembly machine, the simulation model put forward higher requirements. This paper firstly established the wind turbine model, generator and converter model, transmission line and system model of doubly fed wind power generation system using PSCAD simulation software. The wind energy generation system can capture wind energy with the highest efficiency by using the stator flux oriented vector control method. Through the PSCAD model simulation analysis, the wind turbine model established in this paper realizes the MPPT control, voltage control, power factor control and so on. Simulation analysis of fault, depend on the output characteristic of the wind turbine, it is proved that the stable output of active and reactive power depends on the stability of the control system of the turbine side and the network side.

Open Switch Fault Detection and Fault Tolerant of Power Converter Fed DFIG in WECS

This paper work addresses the detection of converter open switch faults and the fault tolerant of power converters fed Doubly Fed Induction Generator (DFIG) in Wind Energy Conversion Systems (WECS). The stator flux-oriented vector control algorithm is used to control active and reactive power supplied by the stator windings. The mean value of the rotor current diagnosis technique is adopted for fault detection. The fault tolerant topology used for service continuity is that with a redundant leg. The simulations are performed using the Matlab / Simulink environment and Sim power. The fault operation is analyzed and the detection method and fault-tolerant topology used are tested with encouraging results.

Research on Simulation and Control Strategy of Doubly - fed Wind Power Generation System

The new energy research and development of the development and utilization of wind power system is the focus and hot spots of the world. DFIG (Double-fed Induction Generator) has become the main object of wind power research with its unique operating characteristics. Decoupling Control of Active Power and Reactive Power of Doubly-Fed Machines is a Key Issue in the Research and Development of Wind Power Generation Technology. In this paper, the dual-PWM converter controlled variable speed constant frequency power generation system, the use of wind energy under different wind speeds, combined with the maximum wind energy tracking, to improve the traditional controller performance[1]. The stator flux-oriented DFIG generation vector control strategy with adaptive proportional resonance (PR) is proposed. The power decoupling regulation is realized by controlling the frequency, phase and amplitude of rotor current. The modeling and simulations of the DFIG power generation operation control system are carried out by Matlab. The results verify the correctness and effectiveness of the strategy and control method.

Modeling of Wind Power Plant with Doubly-Fed Induction Generato

This paper presents the modeling and simulation of wind turbine driven by doubly-fed induction generator which feeds ac power to the distribution network. A stator flux oriented vector control is used for the variable speed doubly-fed induction generator operation. By controlling the generator excitation current the amplitude of the stator EMF is adjusted equal to the amplitude of the grid voltage. To set the generator frequency equal to the grid one, the turbine pitch angle controller accelerates the turbine/generator until it reaches the synchronous speed. The system is modeled and simulated in the Matlab Simulink environment in such a way that it can be suited for modeling of all types of induction generator configurations. The model makes use of rotor reference frame using dynamic vector approach for machine model. The system is also simulated when a fault occurs in 25 kV grid of distribution system. The results of a single line to ground fault and a symmetrical three-phase ground fault is analyzed. The results show that the wind energy conversion system can normally operate in fault conditions.

Terminal voltage build-up and control of a DFIG based stand-alone wind energy conversion system

The paper presents the voltage build-up process and the terminal voltage control of a doubly-fed induction generator (DFIG) driven by a pitch controlled wind turbine for the supply of autonomous system without any auxiliary source. A control strategy for the complete system including voltage build-up phase is developed with a view to provide as well as possible the required power for load. Indirect stator flux-oriented vector control is proposed to keep the stator voltage constant by means of a back-to-back converter connected to the rotor side, while the management system is supported by the pitch angle and the load shedding controllers. A novel scheme for voltage build-up is presented, which requires no additional hardware support, and physical interpretation of how self-excitation can occur from residual magnetism in the machine core is examined. A reliable start-up process is accomplished by using an appropriate voltage reference ramp which enables minimizing energy loss during the starting. The proposed system is modeled and simulated using Matlab/Simulink software program to examine the dynamic characteristics of the system with proposed control strategy. Dynamic simulation results for different transient conditions demonstrate the effectiveness of the proposed control strategy.

Reactive power control strategy for a wind farm with DFIG

Reactive power control strategy for a wind farm with a doubly fed induction generator (DFIG) is investigated. Under stator flux-oriented (SFO) vector control, the real power of the DFIG is controlled by the q-axis rotor current Iqr and the reactive power is mainly affected by the d-axis rotor current Idr. To examine the effect of Idr on stator reactive power Qs and rotor reactive power Qr, the DFIG is operated under five different operating modes, i.e, the maximum Qs absorption mode, the rotor unity power factor mode, the minimum DFIG loss mode, the stator unity power factor mode, and the maximum Qs generation mode. In pervious works, stator resistance Rs was usually neglected in deriving the d-axis rotor currents Idr for different DFIG reactive power operating modes. In the present work, an iterative algorithm is presented to compute the d-axis rotor currents Idr for the five reactive power control modes. To demonstrate the effectiveness of the proposed iterative algorithm, the rotor current, rotor voltage, stator current, real power and reactive power of a 2.5 MW DFIG operated under the five different operating modes are computed.

An Effective Reference Generation Scheme for DFIG With Unbalanced Grid Voltage

This paper presents a reference current generation scheme for improved dynamic performance of a doubly fed induction generator (DFIG) subjected to unbalanced grid voltage. The power and torque oscillations induced due to the unbalance in grid voltage are minimized using additional compensatory terms in the reference currents. The focus is on estimating the reference currents and control implementation without the need for dual vector control. Real and reactive power control is implemented in the positive ${\mbi {d - q}}$ reference frame using stator flux-oriented vector control. The rotor-side converter (RSC) is controlled to enable effective reduction of oscillations in torque and active and reactive power. The dc-link voltage oscillation is minimized and the grid-side power factor is maintained unity using the grid-side converter (GSC). Unlike the previously reported techniques, the proposed scheme enables effective reduction of oscillations in torque, active, and reactive power, and the dc-link voltage, all in a single target. The performance of DFIG is investigated in consideration with the Indian Electricity Grid Code (IEGC). Numerical simulations are carried out in power system computer aided design/electromagnetic transients including direct current (PSCAD/EMTDC) for the laboratory 3-hp DFIG test setup. The results establish that the performance of DFIG is notably enhanced with the proposed scheme.

Study of Hoist Control System Based on Dual Three-Level Inverter

The double-fed control strategy for AC hoist motor is discussed in this paper. The AC/DC/AC power converter is adopted as main circuit. Three-phase neutral-point-clamped three-level rectifier is used as AC/DC link to realize unity power factor at grid-side, which reduces harmonic distortions. For the DC/AC inverter, three-level topology is used, which is controlled by stator-flux oriented vector control method. Meanwhile, energy flows in bidirectional way by back to back three-level power converter. The hoist motor control system obtains a high dynamic performance when stator side operating in unity power factor condition. The reliability and safety of hoist system is improved based on double PLC. The control system mentioned in this paper is being used to control a shaft hoist with a capacity of 260kW, and the power saving is remarkable.

Application of Fuzzy Adaptive PID Control for Rotor Side Converter of DFIG Based WPGS

PI control strategy was introduced into rotor side converter of DFIG control with the mathematical models and the structure of stator flux-oriented vector control. As the main problem of conventional PID controller with parameters fixed in the whole control process, and influence of three PID control parameters can not be distinguished between different stages, so, the adaptive fuzzy PID control was introduced into RSC control system. The parameters were tuned by adaptive fuzzy control, the design of membership was designed and the control feature was verified with simulation.

Modeling and Optimum Power Control Based DFIG Wind Energy Conversion System

This paper proposes the modeling and control of Wind Energy Conversion System (WECS) based on the Double Fed Induction Generator (DFIG). In order to improve the effectiveness of the WECS, two independent control objectives can be stated. Therefore, a control is designed to capture a maximum energy at certain wind speed range and to regulate the stator reactive power, contributing to the compensation of the power factor according to grid requirements. A cascade control structure based on Fuzzy Logic Controller (FLC) has been applied to perform these two main objectives. The control algorithm tracks the maximum power for wind speeds at rated speed of wind turbines and ensures that the power will not go over the rated power for wind speeds over the rated value. Then, the Rotor Side Converter (RSC) is controlled to follow the optimal torque for a given maximum wind power, based on stator flux-oriented vector control. The control algorithm employs fuzzy logic controller to effectively achieve a smooth control of both stator active and reactive powers quantities under fault conditions. Some simulation results are presented to show the effectiveness of the WECS based on DFIG with the proposed control strategy.

NN-IMC Control for DFIG Based Wind Power Generation System RSC

The rotor side converter of DFIG with stator flux-oriented vector control was presented with the mathematical model created and the control structure analyzed. The neural networks internal model control was proposed in this control system which composed of NNC and NNM, the NNC was the inverse model of neural networks, which serve as controller, NNM was the positive model of neural networks, the control feature was verified with simulation.