Variable Speed Wind Power Generation Research Articles

Formula omitted]-Synthesis robust coordinated control of variable speed wind power generators and electric vehicles to regulate frequency

Variable speed wind power generators (VSWPGs) can inevitably introduce power fluctuations and reduce the system inertia in modern power systems. On the other hand, VSWPGs also have certain frequency support ability due to the fast control characteristics of the power electronics in the converters. Therefore, it is urgently required for VSWPGs to regulate the frequency of the power system. Taking into consideration the internal and external uncertainty in the power systems and that frequent regulation actions of VSWPGs might lead to mechanical failures and aggravate the aging process of the wind power generators, a coordinated control method of VSWPGs and electric vehicles (EVs) for frequency regulation on the basis of μ-synthesis control is proposed in this paper. The EVs are modeled as energy aggregators, the VSWPGs are modeled under the derating control using the small-signal analysis method, and the dynamic frequency response model for the system with uncertainty is then built. Considering the power system parametric uncertainty, a μ-synthesis controller is implemented to tackle the coordinated control problem of VSWPGs and EVs regulating system frequency by means of the D-K iterative method. Then the comparisons through time-domain simulations are conducted to verify the presented coordinated strategy is able to overcome influence of uncertainty on system frequency and also has better dynamic frequency performance.

Design, analysis, and adaptive maximum power point tracking control of small‐scale wind turbine system

SummaryDue to the stochastic and unpredictable nature of wind speed, extraction of maximum power from the wind turbine system becomes an attractive control objective. Therefore, to capture more wind power, various conventional maximum power point tracking (MPPT) schemes are developed for standalone small‐scale variable speed wind power generation system (VSWPGS). This manuscript proposes novel adaptive step size (ASS) and drift‐free ASS (DF‐ASS) MPPT methods for a permanent magnet synchronous generator (PMSG)‐based VSWPGS. The control schemes achieve maximum power point (MPP) without using mechanical sensors like speed encoder and anemometer. The proposed MPPT controllers are implemented on a laboratory‐scale DC motor‐PMSG‐based wind power generation system (WPGS) using OPAL‐RT real‐time digital platform. The ASS and DF‐ASS methods capture more power, reduce the steady‐state power oscillation around MPP, and improve the tracking speed. Also, the proposed DF‐ASS control scheme avoids drift phenomenon during wind speed increase condition. The comparative experimental results of proposed ASS and DF‐ASS methods with respect to the fixed step size MPPT schemes show better dynamic and steady‐state performance, making it pertinent for small‐scale WPGS.

Predictive direct torque control of a rotor-side matrix converter driven grid connected DFIG with torque and flux ripples minimisation criterion

The doubly fed induction generator (DFIG) is the most commonly used machine for variable speed wind power generation, and the single stage matrix converter (MC) can potentially replace the conventional back-to-back voltage source converters (VSCs) for rotor to grid inter connection. In this research work, the performance of grid connected DFIG with rotor side MC is analysed with predictive direct torque control (P-DTC) technique incorporating a criterion for minimising the torque and rotor flux ripples at a fixed switching frequency. Space vector modulation (SVM) is utilised for MC side control. The system exhibits better transient and steady-state behaviour over conventional configurations, for both sub and super-synchronous operating modes, as evaluated by simulation based on a 2 MW DFIG model in MATLAB-Simulink environment.

Lyapunov Function Based Flux and Speed Observer Using Advanced Non-linear Backstepping DVC for PWM-Rectifier Connected Wind-turbine-driven PM Generator

In this paper, modeling, and speed/position sensor-less designed Direct Voltage Control (DVC) approach based on the Lyapunov function are studied for three-phase voltage source Space Vector Pulse Width Modulation (SVPWM) Rectifier Connected to a Permanent Magnet Synchronous Generator (PMSG) Variable Speed Wind Power Generation System (VS-WPGS). This control strategy is based on voltage orientation technique without mechanical speed sensor. Advanced Non-linear Integral Backstepping Control (IBSC) of the Generator Side Converter (GSC) has the ability to have a good regulation of the DC link voltage to meet the requirements necessary to achieve optimal system operation, regardless of the disturbances caused by the characteristics of the drive train or some changes into the DC load. The estimation of the speed is based on Model Reference Adaptive System (MRAS) method. This method consists in developing two models one of reference and the other adjustable for the estimation of the two d-q axis components of the stator flux from the measurement of currents, the speed estimated is obtained by canceling the difference between the reference stator flux and the adjustable one using Lyapunov criterion of hyper-stability. Some results of simulation using Matlab/Simulink® are presented, discussed to prove the efficiency and robustness of the system control policy for WPGS against external and internal perturbations.

Self‐stabilising speed regulating differential mechanism for continuously variable speed wind power generation system

Self‐stabilising speed regulating differential mechanism for continuously variable speed wind power generation system

Voltage and Frequency control in Wind Turbine Using Sparse Matrix Converter

Due to the sudden exploitation of conventional resources such as fuel impart to the increase in necessity of power generation through renewable energy resources. So, extraction of energy from wind at a quantity became a well known industry. In this described system, variable-speed wind power generation system using Permanent Magnet Synchronous Generator (PMSG). In PMSG, required voltage induced is not enough to synchronize with the system at lower speed of wind. Also the variations in the wind speed causes the system become oscillatory. In case of maintaining the system stable, Sparse Matrix Converter (SMC) is used. The real time application of large capacity at variable speed providing system by the Pulse Width Modulation (PWM) technique. Because, it can use the vector control and realize torque control. In this analysis, the voltage and the frequency of the given system are taken into account. Simulation output explains the steadiness of the proposed system to maintain the voltage and frequency when desegregated to PMSG wind turbine using Sparse Matrix Converter.

Active and Reactive Power Control of Doubly Fed-Induction Generator Based on Variable Speed Wind Power Generation

This paper deals with the control of Doubly Fed Induction Generator (DFIG) in wind energy conversion system (WECS), to regulate the real and reactive power exchanged with the grid. The control architecture consists of two pulse width modulation converters allowing the generator to work in both sub-synchronous and super-synchronous mode. The real power is controlled by the energy maximization strategy, while the reactive power is controlled to operate the system under the unity power factor. The dynamic behavior of DFIG and its control are modelled based on the stator flux orientation (SFO) strategy. The control algorithm design based on anti-windup integration is developed in Matlab-Simulink.

Improved E&S Model for Core Loss Calculation of Brushless Doubly Fed Machine With Hybrid Rotor

Brushless doubly fed machine (BDFM), is a new type of machine with special structure, shows promising features for the field of variable frequency speed regulation and wind power generation due to its inherent characteristics, which has the advantages of reliable operation, adjustable power factor, lower operation and maintenance costs as well as requiring a smaller capacity converter [1], [2]. Since core loss has an important effect on efficiency and temperature distribution, it is vital to accurately calculate such component in an optimal design procedure. Furthermore, rotor core loss is also a significant factor which can affect the performance characteristics of BDFM due to the complex magnetic field distribution and relatively high value of slip. Specifically, a novel hybrid rotor structure which is combined with magnetic barrier and assisted cage has better coupling ability than the commonly used rotor structures such as cage rotor and reluctance rotor is presented but it also increases the difficulty of core loss calculation. E&S model is a vector magnetic hysteresis property model [3], [4], in which H (magnetic field intensity) is dependent not only on B (magnetic flux density) but also on time derivative of B. Increase of core loss when the phase difference between B and H occurs, is well expressed in this method, while the conventional analysis was not able to consider the phase difference between B and H. Furthermore, the total core loss including both alternating and rotational losses can be directly calculated from the fundamental terms of obtained $B_{x}$, $B_{y}$, $H_{x}$ and $H_{y}$ without other fitting data, which can improve the core loss computation accuracy of BDFM with hybrid rotor in contrast with conventional core models. In this paper, an improved E&S model based on a 2-D rotational magnetic property analysis for core loss of BDFM with hybrid rotor is proposed by considering the high-order harmonic magnetic field. The finite element analysis model of BDFM with hybrid rotor is established. The core loss calculation results are compared with the simulation results to verify the correctness and feasibility of the proposed E&S model. Fig. 1 shows the finite element model, hybrid rotor of prototype and special points distribution diagram of BDFM with hybrid rotor. As shown in Fig. 1 (a)-(b), the cage bars are added on the non-magnetic layer of the radial magnetic barrier rotor, and the cage bars are respectively divided into concentric cage bar and common cage bar. There are two kinds of rotating magnetic fields with different poles and frequencies in the air-gap of BDFM, which renders that the air-gap magnetic density harmonic contents are rich and the magnetic properties of each part of core are different. According to the basic principle, structure characteristics and magnetic field distribution of BDFM with hybrid rotor, some special points of stator and rotor are analyzed and calculated. The relationship between B vector and H vector, and the relationship between the waveform of $B_{x}$, $B_{y}$ and the waveform of $H_{x}$, $H_{y}$, obtained by the combination of the improved E&S model and finite element analysis, is shown in Fig. 1 (c), which is seen that the phase between B and H is different. The improved E&S model can consider higher order harmonic magnetic field than the conventional E&S model. As shown in Fig. 2 (a), the stator and rotor core loss calculation process of BDFM with hybrid rotor is described by the flow diagram. The datum of $B_{x}$, $B_{y}$, $H_{x}$, $H_{y}$ are obtained by the combination of the improved E&S model and finite element method, and all order harmonic of $B_{x}$, $B_{y}$, $H_{x}$, $H_{y}$ are computed by fourier series expansion. Therefore, the total core loss of BDFM with hybrid rotor can be calculated by the formula in the flow diagram, where, $\rho$ is the magnetic material density, T is the period, $m$ is the amount of the special points, $n$ is the harmonic order, and $M_{i}$ is the mass. In addition, in order to verify the accuracy of the core loss calculation, the 2-D finite element model of BDFM with hybrid rotor is established, and the simulation results are shown in Fig. 2 (b). The validity and feasibility of the improved E&S model is verified by comparing with the simulation results. In addition, the full paper will present the detailed calculation procedure and analysis.

Design, Modeling, and Control of a Novel Hybrid-Excited Flux-Bidirectional-Modulated Generator-Based Wind Power Generation System

This paper proposes a novel hybrid excited generator, which is suitable for a variable-speed wind power generation system. Two sets of excitation sources are employed, which are permanent magnets (PMs) on the rotor and the field windings on the stator. The rotor is design with PM-iron structure, namely the PMs and iron poles are alternatively located in rotor, which can provide PM excitation and flux modulating simultaneously. Meanwhile, the adjacent stator teeth are designed with different height, which enables the stator with flux modulating effect, and, therefore, bidirectional flux modulating can be achieved. Some specific harmonics excited by the rotor PMs can be effectively adjusted by the field current, and the back electromotive force and electromagnetic torque can be regulated accordingly. Therefore, the proposed generator can achieve constant voltage control and maximum power point tracking control by controlling the field current. The design considerations and field regulating principle are analytically investigated. An improved Tabu search algorithm is used to optimize the proposed generator, and finite-element method is used to realize preliminary study of the electromagnetic performances. A prototype is manufactured and experimental tests are conducted to verify the theoretical analysis and control strategies.

Direct control of active and reactive power of a doubly fed

This paper proposes a direct power control for doubly fed induction machine for variable speed wind power generation. It provides decoupled regulation of the primary side active and reactive power and is suitable for both electric energy generation and drive applications. In order to control the power flowing between the stator of the doubly fed induction generator and the network, a decoupled control of active and reactive power is synthesised using PI controllers. The obtained simulation results show the feasibility and effectiveness of the suggested method.
 Keywords: Doubly fed induction machine, decoupled power control, vector control, active and reactive power, PWM inverter.

Characterisation of long‐term voltage stability with variable‐speed wind power generation

Voltage stability in general is of paramount importance with increasing penetration levels of variable-speed wind power generators (VSWGs) in power systems. Limited knowledge exists considering the impact of VSWGs on long-term voltage stability (LTVS) of power systems, focusing on doubly fed induction generators and full-converter wind generators. This paper presents the results of a comprehensive study on the impact of VSWGs on LTVS. Integration of wind generators while operating the existing synchronous generators improves the LTVS. However, it is unlikely that power systems will retain all existing synchronous generators operating, with high wind penetration levels. Therefore, this study compares the capability of the synchronous generators and VSWGs on LTVS by considering the dynamic reactive power capabilities. The significance of overload capability of synchronous generators on LTVS is highlighted. It is also illustrated that integrating wind farms at remote and local locations from load centres has distinct impacts on LTVS. Replacement of synchronous generators located in close proximity to load centres has a detrimental effect on LTVS. Furthermore, this study demonstrates the impact of different wind generator loading levels on LTVS. The study outcomes highlight several distinct factors which influence the LTVS of power systems with high wind penetration levels.

可変速風力発電機のオンライン出力帯域制御による電力系統周波数変動抑制

可変速風力発電機のオンライン出力帯域制御による電力系統周波数変動抑制

Multi-objective control of direct-driven wind power generation system with frequency separation

Variable-speed wind power generation system usually adopts maximum power point tracking (MPPT) below the rated wind speed or constant power control above the rated wind speed. However, single objective control has large dynamic loads on transmission systems. This paper presents a multi-objective control scheme for wind turbine in low wind speed, which achieves not only high power capture efficiency but also low fatigue load on mechanical parts. Input wind speed is separated into two components: a slowly varying seasonal component and a rapidly varying turbulent component. Correspondingly, the machine-side converter controller is divided into low frequency loop and high frequency loops. The low frequency loop implements MPPT control, the high frequency loop reduces the fluctuations of torque, and both loops together suppress the variations of output power. Simulation was conducted in Matlab/Simulink and FAST code was used to further verify the correctness of the multi-objective control strategy.

Design of an Electrical Continuously Variable Transmission Based Wind Energy Conversion System

The electrical continuously variable transmission system is a very promising concept for variable-speed constant-frequency wind power generation due to its ability of seamless speed adjustment. In this paper, a novel wind energy conversion system based on electrical continuously variable transmission is proposed. This system combines the merits of two popular wind generation concepts: It enjoys high torque density like the permanent-magnet synchronous generator system and, also, it needs only a partial-scale converter like a doubly fed induction generator system. With a special doubly fed dual rotor structure, the system realizes both speed variation and power generation within one single machine, which makes it very compact. Besides introducing its structure and working principle, the design and performance analysis of the machine are presented in this paper. A prototype is made and tested for validation.

Sensorless fuzzy‐logic‐based maximum power point tracking control for a small‐scale wind power generation systems with a switched‐mode rectifier

This study proposes a sensorless maximum power point tracking (MPPT) control using an improved variable-speed small-scale wind power generation system (WPGS) with a permanent magnet synchronous generator. The passive elements of a small-scale WPGS that use a conventional boost converter suffer from disadvantages that result in power losses, increased costs, and increased system size. Therefore, to eliminate the passive elements, the proposed system performs MPPT control to vary the duty ratio of a switched-mode rectifier. To evaluate the MPPT algorithms, a comparison was made between a fuzzy-logic-based perturb-and-observe (P&O) control with variable step size and a conventional P&O control with fixed-step size. A wind turbine model is investigated using a squirrel-cage induction motor, and the variable torque is controlled by varying the generator speed. The presented system and algorithm are verified by the simulations and experiments.

Stand Alone Performance of Permanent Magnet Synchronous Wind Power Generator with Current Source Matrix Converter

—A matrix converter is a voltage/current source AC/AC frequency converter. In grid-connected operation of a variable-speed permanent magnet synchronous wind power generator, the matrix converter is normally controlled as a voltage source converter. In this control method, the generator-side voltage is synthesized from the grid-side voltage source. However, in the stand-alone mode of operation, the grid-side stiff voltage source is not available, and the input filter of the matrix converter is unstable. In this article, a new control method is presented that controls a permanent magnet synchronous wind generator in a stand-alone mode with a matrix converter as a current source converter. The proposed method is so fast that it can control the matrix converter small capacitor voltage despite the generator large inductance and without any input filter instability. A multi-pole permanent magnet synchronous wind generator is simulated to prove the performance of the proposed control strategy.

Experimental Assessment with Wind Turbine Emulator of Variable-Speed Wind Power Generation System using Boost Chopper Circuit of Permanent Magnet Synchronous Generator

This paper presents experimental results and its assessment of a variable-speed wind power generation system (VSWPGS) using permanent magnet synchronous generator (PMSG) and boost chopper circuit (BCC). Experimental results are obtained by a test bench with a wind turbine emulator (WTE). WTE reproduces the behaviors of a windmill by using servo motor drives. The mechanical torque references to drive the servo motor are calculated from the windmill wing profile, wind velocity, and windmill rotational speed. VSWPGS using PMSG and BCC has three speed control modes for the level of wind velocity to control the rotational speed of the wind turbine. The control mode for low wind velocity regulates an armature current of generator with BCC. The control mode for middle wind velocity regulates a DC link voltage with a vector-controlled inverter. The control mode for high wind velocity regulates a pitch angle of the wind turbine with a pitch angle control system. The hybrid of three control modes extends the variable-speed range. BCC simplifies the maintenance of VSWPGS while improving reliability. In addition, VSWPGS using PMSG and BCC saves cost compared with VSWPGS using a PWM converter.

Development of a Novel Brushless Power Split Transmission System for Wind Power Generation Application

This paper presents a novel gearless and brushless power split transmission system for variable-speed constant-frequency wind power generation application. The core element of this system is a novel axial-flux doubly fed dual-rotor permanent magnet machine. The key of the design is to utilize the flux modulation principle to modulate the magnetic flux in an axial-flux machine and use doubly fed stator winding to control the rotor rotation. This design combines the merits of direct-drive machines and doubly fed generators. As the mechanical problems related to brushes, slip rings, and gear boxes are successfully overcome, the operational reliability of the system is improved. The stator winding of the proposed system can be directly connected to the power grid, and the power rating of its associated frequency converter is reduced. Time-stepping finite-element method is used to analyze the dynamic performance of the proposed system.

DFIG sliding mode control fed by back-to-back PWM converter with DC-link voltage control for variable speed wind turbine

This paper proposes an indirect power control of doubly fed induction generator (DFIG) with the rotor connected to the electric grid through a back-to-back pulse width modulation (PWM) converter for variable speed wind power generation. Appropriate state space model of the DFIG is deduced. An original control strategy based on a variable structure control theory, also called sliding mode control, is applied to achieve the control of the active and reactive power exchanged between the stator of the DFIG and the grid. A proportional-integral-(PI) controller is used to keep the DC-link voltage constant for a back-to-back PWM converter. Simulations are conducted for validation of the digital controller operation using Matlab/Simulink software.

A Space-Vector-Modulated Sensorless Direct-Torque Control for Direct-Drive PMSG Wind Turbines

This paper proposes a space-vector modulation (SVM)-based direct-torque control (DTC) scheme for a permanent-magnet synchronous generator (PMSG) used in a variable-speed direct-drive wind power generation system. A quasi-sliding-mode observer that uses a relatively low sampling frequency, e.g., 5 or 10 kHz, is proposed to estimate the rotor position and stator flux linkage based on the current model of the PMSG over a wide operating range. The optimal torque command is directly obtained from the estimated rotor speed for the DTC by which the maximum power point tracking control of the wind turbine generator is achieved without the need for wind speed or rotor position sensors. Compared with the conventional DTC, the proposed SVM-DTC achieves a fixed switching frequency and greatly reduces the flux and torque ripples, while retaining the fast dynamic response of the system. The effectiveness of the proposed SVM-DTC scheme is verified by simulation studies on a 1.5-MW PMSG wind turbine and is further verified by experimental results on a 2.4-kW PMSG with a 10-kHz sampling frequency.