High performance control of a permanent magnet wind power generation system using an adaptive sliding observer

This paper presents a Space-Vector Modulated (SVM) Direct-Torque-Control (DTC) scheme for a direct-drive permanent magnet synchronous generator (PMSG) and a gird converter for wind energy without any position sensor. Direct control of the rotating velocity and amplitude of the stator flux vector allows very fast torque response of the PMSG according to the generator speed. Fixed switching frequency and very low torque ripple are obtained with space vector modulation. SVM-DTC can also be implemented into the grid converter in which nearly sinusoidal input current and fast dc link voltage regulation can be achieved. Experimental results verify the effectiveness of the proposed control technique for the PMSG and grid converter other than the widely used field orientated control.

—This article presents an enhanced control strategy for a direct-driven permanent synchronous generator based wind-power generation system with a flywheel energy storage unit. The behaviors of the direct-driven permanent magnet synchronous generator system with a flywheel energy storage unit under unbalanced grid fault conditions are investigated. Three control targets for the grid-side converter during network unbalance conditions are identified, including eliminating the oscillations in the total active power or reactive power or no negative-sequence current injecting into the grid. Meanwhile, the DC-link voltage oscillations can be effectively suppressed during the unbalanced grid fault by controlling the flywheel energy storage unit. Furthermore, a proportional–integral-resonant controller is designed for the flywheel motor to eliminate the oscillations in the DC-link voltage. Finally, the proposed coordinated control strategy for the direct-driven permanent magnet synchronous generator system with a flywheel energy storage unit has been validated by the simulation results of a 1-MW direct-driven permanent magnet synchronous generator wind power generation system with a flywheel energy storage unit under unbalanced grid fault.

With the advance of power electronics, direct-driven permanent magnet synchronous generators have drawn increased interest to wind turbine manufacturers due to its advantages over other variable-speed wind turbines. This article studies permanent magnet synchronous generator characteristics under the general d-q control strategy in the rotor-flux-oriented frame so as to benefit the development of advanced permanent magnet synchronous generator control technology. Compared to traditional approaches, the specific features of the article are (1) a steady-state permanent magnet synchronous generator model in a d-q reference frame, (2) a simulation mechanism that reflects the general permanent magnet synchronous generator d-q control strategy, (3) an integrative study that combines generator-converted power with extracted wind power characteristics, and (4) a joint investigation incorporating both steady-state and transient evaluations. Extensive simulation-based analysis is conducted to study how permanent magnet synchronous generator characteristics are affected by different d-q control conditions and are interacted with wind power drive characteristics in power generation and speed regulation of a permanent magnet synchronous generator wind turbine.

Recurrent modified Elman neural network control of PM synchronous generator system using wind turbine emulator of PM synchronous servo motor drive

With the integration of large-scale wind farm of direct-driven permanent magnet synchronous generator (PMSG) type into power systems, the impacts on the existing power system have to be evaluated elaborately and systematically. This paper will discuss the impact of grid-connected wind farm of PMSG type on power system small signal stability. First, a simplified practical model of wind farm of PMSG type is derived for analyzing small signal stability in this paper. The rotor-flux-oriented control strategy is applied in the modelling of PMSG. Second, the simulation scenario involving replacing synchronous generator with wind farm of PMSG type based on the IEEE 3-generator-9-bus test system as benchmark is carried out to conduct the eigenvalue analysis and to assess the effect of wind farm of PMSG type on power system small signal stability. Finally, some preliminary conclusions and comments are drawn according to the simulation results.

The direct-drive Permanent Magnet Synchronous Generator (PMSG) wind power imitation platform is an essential requirement for its research, development and product test. It's more efficient and flexible to demonstrate control strategies including the wind turbine's Maximum Power Point Tracking (MPPT). Conventionally, many control strategies of the motor's speed or torque are used to implement the turbine MPPT imitation, which, however, much depend on the motor parameters and are only for the Double Feed Induction Generator (DFIG) system, but rarely for direct-drive PMSG one. Thus, a novel control strategy for the wind turbine MPPT implementation is proposed, which provides a direct power control method of DC motor together with decoupled vector control of PMSG without the speed sensor. Using this control strategy, the system less depends on either parameters of the DC motor or the PMSG, and has excellent dynamic performance and high steady-state precision. The analysis, simulation and experimental results have verified its feasibility and validity.

In recent years, the sub-synchronous oscillation (SSO) accidents of the power system caused by wind power have received extensive attention. This paper focuses on the self-sustained oscillation problem caused by the control limit of the grid-following direct-driven permanent magnet synchronous generator (PMSG) wind farms. When one PMSG in a multi-machine system oscillates, whether the removal of other PMSGs can affect its oscillation conditions is studied. In this paper, the generator tripping problem in the oscillation scene of the wind farm with grid-following PMSGs is transformed into the influence of the equivalent parameter change of a two-machine coupling system on the self-sustained oscillation conditions. Considering the synchronization stability condition of the phase-locked loop (PLL), the influence of the generator tripping strategy on the self-sustained oscillation condition caused by the hard limit in the control system is analyzed. Since the fundamental and harmonic currents of the self-sustained oscillation frequency can all be monitored at the terminal of each PMSG when nonlinear oscillation occurs in the wind farm, this paper proves that cutting off the part of the wind farm without the oscillating ones does not help the oscillation suppression. The necessity of accurately locating nonlinear oscillation sources is thus demonstrated.

With the advance of power electronic technology, direct-driven permanent magnet synchronous generators (PMSG) have increasingly drawn interests to wind turbine manufacturers. Unlike a fixed-speed wind turbine, the maximum power extraction of a PMSG wind turbine is affected by (1) electrical characteristics of the generator, (2) aerodynamic characteristics of the turbine blades, and (3) maximum power extraction strategies. In an environment integrating all the three characteristics, it is found in this paper that the existing commercial lookup-table maximum power extraction mechanism suitable to a DFIG wind turbine is not suitable to a PMSG wind turbine. Through the integrative study of all the three characteristics, this paper proposes a novel PMSG maximum power extraction design. The special features of the proposed strategy include (i) an adaptive virtual lookup-table approach for PMSG maximum power extraction and (ii) an implementation of the peak power-tracking scheme based on a novel direct-current vector control configuration. The proposed maximum power extraction mechanism with a nested speed- and current-loop control structure is built by using MatLab SimPowerSystems. Simulation studies demonstrate that the proposed PMSG peak power-tracking strategy has superior performance in various aspects under both stable and gust wind conditions. Copyright © 2010 John Wiley & Sons, Ltd.

A new practical way of modelling direct-driven permanent magnet synchronous generator (PMSG) wind turbines is proposed. The model emphasizes on the wind-rotor-to-PMSG-to-converter-to-grid system, which is the main energy flow system of the direct-driven wind turbine. In this article, a new wind-rotor back propagation neural network is proposed, which consists of a four-layer network and is used to describe the wind-rotor aerodynamic characteristics. According to the orthogonal experimental method, 1200 sets of wind-rotor aerodynamic data, which are calculated based on combining blade element momentum-modified theory with a dynamic stall model, are adopted as the sample data; and the wind-rotor neural network is trained using the Levenberg–Marquardt algorithm. Then, the coupling dynamic models of the wind-rotor and PMSG, and AC–DC–AC converter model are established, respectively; the control strategies for the generator-side and grid-side converters are constructed, too. The mechanical model, electric model, and control model are integrated into the whole simulation model, and the numerical simulation are carried out. The research results show that all the wind-rotor aerodynamic characteristics, electrical characteristics, and control characteristics can be obtained quickly and efficiently from the constructed model, and are helpful for optimization design and control for large-scale direct-direct PMSG wind turbines.

A brief review of permanent magnet (PM) synchronous generators with hybrid field excitation systems and output voltage regulation capabilities has been presented. Both series and parallel hybrid field excitation systems have been discussed. The review emphasizes the construction, advantages, drawbacks and basic characteristics of PM synchronous generators with additional field excitation winding placed either on the stator or rotor.

This paper presents power quality issues of a grid connected wind generation system with a MW-class direct-driven permanent magnet synchronous generator (PMSG). A variable speed wind turbine model was simulated and developed with the simulation tool of PSCAD/EMTDC. The model includes a wind turbine with one mass-model drive train model, a PMSG model and a full-scale voltage source back to back PWM converter. The converter controller model is employed in the dq-synchronous rotating reference frame and applied to both generator and grid sides. To achieve maximum power point tracking, a tip speed ratio method is applied in machine side, whereas DC voltage control is applied in grid side to achieve constant DC voltage. Due to wind fluctuation and power oscillation as a result of wind shear and tower shadow effects (3p), there will be a fluctuation in the output power and voltage. The concerned power quality issues in this work are Harmonics, power fluctuation and flicker emission. The measurements will be carried out under different wind speed and circumstances.

A high performance rectifier with a novel structural and wide speed range for direct-drive wind energy system has been investigated and design. The utilization rate and efficiency of low wind are critical focus for wind energy system, in the form of ultimate output dc voltage as the optimum object, a traditional full- bridge PWM rectifier and a boost circuit for the direct-drive permanent magnet synchronous generator (PMSG) compose the novel rectifier in order to achieve the satisfying demands of high performance and low-wind speed. The design can feasible realize the maximum power point tracking (MPPT) with a modified strategy and unit power factor (UPF) control, and improve the ability greatly of full-speed operation especially. The analysis and investigation results all have been confirmed that the excellent dynamic states and steady states performances of the rectifier.

In this paper a cascaded multilevel converter with reduced number of switches is proposed for grid connection of a direct-drive Permanent magnet synchronous generator (PMSG) based variable speed wind turbine to improve the waveform quality of the converter output voltage and current. Therefore, the bulky passive grid filters can be reduced or even removed. The basic topology and control strategy of the proposed converter are presented in detail. The generator is connected to the grid by means of a diode rectifier, an intermediate buck-boost dc-dc converter, and a multilevel converter with reduced number switches. The grid side multilevel converter is controlled to obtain high efficiency under different load conditions. Vector control of the grid-side multilevel converter featured with output voltage and frequency controller that is capable of handling variable load conditions. The operation and performance of the proposed system have been evaluated by Matlab/simulink. Simulation results shows that the controller regulate magnitude and frequency of voltage to match with the grid under varying wind and load conditions.

Mechanical interactions between a wind turbine and a direct-driven permanent-magnet synchronous generator (PMSG) are studied, and a model to analyze the system behavior is suggested. The proposed model can be applied to analyze the mechanical vibrations of direct-driven wind turbine installations both in steady state and in dynamic cases. The cogging torque and torque ripple of the PMSG are used as excitation sources in the mechanical model. Four different permanent-magnet rotor constructions are analyzed. It is shown that the maximum allowable value of the cogging torque of the direct-driven permanent-magnet wind generator in this case is 1.5%-2% of the rated torque even when the corresponding resonance frequency does not occur in the operational speed range of the wind turbine. Furthermore, it was noticed that the resonance caused by the excitation torque should occur at the lowest possible speed.

In order to improve the dynamic response speed and the steady-state performance of the DC side bus voltage of the wind power grid-connected inverter, a mathematical model of a typical three-phase voltage type PWM (Pulse Width Modulation, PWM) grid-connected inverter was established, and its traditional voltage-current double closed loop with proportional-integral control method was analyzed. Then a second-order linear active disturbance rejection controller that does not depend on system model information was designed to replace the traditional voltage outer loop proportional-integral controller, thus a new double closed-loop control structure was formed to control it. The frequency domain theory was used to analyze the convergence of the third-order linear extended state observer and the influence of the total disturbance on the performance of the third-order linear extended state observer. The parameter tuning scheme of the designed controller was given. Finally, the 1.5 MW direct-driven permanent magnet wind power generation system was built in the Matlab/Simulink software and the control effects of the two control modes under different working conditions are compared. The simulation results show that the control scheme designed in this paper is superior to the traditional proportional-integral controller which has good anti-interference characteristics and robustness. Especially it has a good stability effect on DC side bus voltage fluctuations.