René Wamkeue

Condition Monitoring and ault Diagnosis in Wind Energy Conversion Systems: A Review

There is a constant need for the reduction of operational and maintenance costs of wind energy conversion systems (WECS). The most efficient way of reducing these costs would be to continuously monitor the condition of these systems. This allows for early detection of the degeneration of the generator health, facilitating a proactive response, minimizing downtime, and maximizing productivity. Wind generators are also inaccessible since they are situated on extremely high towers, which are normally 20 m or greater in height. There are also plans to increase the number of offshore sites increasing the need for a remote means of WECS monitoring that eliminates some of the difficulties faced due to accessibility problems. Therefore and due to the importance of condition monitoring and fault diagnosis in WECS (blades, drive trains, and generators); and keeping in mind the need for future research, this paper is intended as a tutorial overview based on a review of the state of the art, describing different type of faults, their generated signatures, and their diagnostic schemes.

Unbalanced transient-based finite-element modeling of large generators

Abstract Finite-element modeling is used to study the steady-state and transient performance of a large synchronous machine. In the present paper, we carry out a two-dimensional, non-linear, time-stepped finite-element simulation of a line-to-line short circuit on a large salient-pole synchronous generator with multiple rotor circuits under no-load conditions. The work is validated for performance prediction using a Hydro-Quebec network generator.

Hybrid-State-Model-Based Time-Domain Identification of Synchronous Machine Parameters From Saturated Load Rejection Test Records

This paper presents a suitable method for time-domain identification of synchronous machine parameters from the hybrid state model recently introduced by the authors in a compact matrix form. The saturated version of this model is developed in terms of generator equivalent-circuit parameters. The load rejection test of a combined resistive/inductive load is performed for the parameter identification while the online symmetrical three-phase short-circuit test is carried out for the model cross-validation. For weak power factor initial loads connected to the generator, the rotor speed is quite constant during the full load rejection test. Thus, the mechanical transients do not have any influence on estimated electrical parameters since they are decoupled from the electrical model of the machine. The method is successfully applied for the parameter identification of 380 V, 3 kVmiddotA, four-pole, 50 Hz saturated synchronous generator.

Line-to-Line Short-Circuit-Based Finite-Element Performance and Parameter Predictions of Large Hydro Generators

A two-dimensional time-stepped finite-element (FE) method is used to model and successfully replicate saturated line-to-line and three-phase short-circuit test responses recorded on a 40-pole 13.75 MVA hydro generator at Hydro-Quebecs Rapides-des-Quinze generating station. Three levels of line-to-line and sudden three-phase short-circuit tests (0.13, 0.25, and 0.48 p.u.) are simulated numerically using the FE-based model. While symmetrical faults are only used for parameter determination, the computed line-to-line waveforms are thoroughly compared to real data, with a special attention given to field current responses. According to IEEE Standard 115-1995, the d-axis dynamic reactances and time constants are computed from three-phase short-circuit tests, while the negative-sequence reactance is derived from the line-to-line short-circuit test resulting in a rated armature current. The obtained simulated test responses and parameter values, from both symmetrical and asymmetrical faults, support the effectiveness of the proposed FE-based model in incorporating the saturation phenomenon, large number of poles, and detailed damper representation to achieve an accurate dynamic performance assessment together with negative-sequence reactance and dynamic constants prediction.

Two-Step Method for Identification of Nonlinear Model of Induction Machine

A two-step method is applied for parameter identification of a saturated electromechanical model of an induction machine (IM). The k-factor cross saturation technique is used to account for iron saturation. Balanced and unbalanced short-circuits armature current waveforms of this machine are less sensitive to variations in the mechanical parameters. Conversely, any change in these parameters has a strong impact on the start-up test. Accordingly, in the proposed estimation method, the online double-line-to-neutral short-circuit test is performed to estimate the electrical parameters of the machine and the results obtained are then used to compute the mechanical parameters from the starting test. The good agreement of the estimated results with actual data attests to the effectiveness and suitability of the proposed algorithm in computing the electromechanical parameters of these machines.

Cross-Identification of Synchronous Generator Parameters From RTDR Test Time-Domain Analytical Responses

In a recent work, the authors computed generator parameters from a load-rejection test based on what they called hybrid state model of the synchronous machine. The state matrices were presented in compact numerical form and may prove tedious to implement. Such a model is a complicated function of the unknown machine parameter vector to be computed which is not always easy to comprehend in an identification process for engineering applications. In this paper, therefore, the decoupled property of the so-called hybrid model along with the application of the complete well-known solution of the linear control systems theory is used to derive time-variant analytical waveforms of the phase voltages and the field current following a generator tripping (load rejection) and an open stator field short-circuit tests in terms of the generator parameters. In the cross-identification approach, the field short-circuit test is used to compute the generator d-axis parameters while the q-axis parameters are obtained from the load-rejection test q-axis data. The proposed identification technique is successfully applied for the parameter identification of a 4-pole 1.5-kVA, 208-V, and 60-Hz saturated laboratory synchronous generator.

Sliding mode control of DFIG based variable speed WECS with flywheel energy storage

In this paper a so-called sliding mode control (SMC) technique is applied for variable speed wind energy conversion system (WECS) control with doubly-fed induction generator (DFIG). The paper also points out interesting performances of the double-fed induction machine (DFIM) used as flywheel energy storage system (FESS). In fact, adjusting the rotor speed can allow the induction machine to release the kinetic energy to the power system or to absorb this energy from the utility grid. The DFIM enables the decoupled control of system active and reactive powers in both steady and transient states. The effectiveness of the proposed DFIG based WECS control approach along with FESS is proved throughout computer simulations results.

A review of concepts and methods for wind turbines condition monitoring

As the demand for wind energy continues to grow at exponential rates, reducing operation and maintenance costs and increasing reliability is now a top priority. Aside from developing more advanced wind turbines designs to improve the availability, an effective way to achieve this improvement is to apply reliable and cost-effective condition monitoring techniques. This paper is a general review and classification of methods and techniques for wind turbine condition monitoring. After highlighting on condition monitoring, diagnosis and maintenance theories, it outlines the relationship between these theories and related technical concepts.

Dynamic model of diesel generator set for hybrid wind-diesel small grids applications

In order to reduce the carbon gas emissions, wind energy conversion systems are currently more and more connected to actual diesel power plants to provide electricity to small remote communities where the power grids are not available. As for classical power systems, the stability analysis, prediction, identification, control and diagnostic of hybrid wind-diesel small grids need accurate modelling of its main components. The state space representation is known as the more suitable system representation for simulation, identification/diagnostic and stability studies purposes. In this paper a linear state modelling of a diesel generator is proposed. The global diesel generator model obtained from the superposition principle of its components is applied for stability analysis using the eigenvalues calculation. Furthermore, the effectiveness of the model is assessed through numerical simulations of large transient tests such as load rejections and the synchronous generator automatic voltage regulation action is carried out. field transients during a Field short-circuit test with the stator in open circuit is also simulated.

Selection of Gearbox Ratio and Power Converters Ratings for Wind Turbines Equipped With Doubly-Fed Induction Generators

This paper presents a methodology for the optimal selection of the gearbox ratio and the power converters ratings of a doubly-fed induction generator (DFIG) drive associated to a wind turbine. The design process of such an electromechanical system needs suitable compromises between the performances of the wind turbine on the whole speed range and the respective characteristics of the induction machine, the gearbox and the static converters. The optimal solution in terms of performance and cost must be derived from a global design approach. For a given turbine, a given DFIG and a given annual wind distribution, a suitable compromise must be found between the gearbox ratio and the sizing of the power converters to maximize the annual energy yield. This paper presents a methodology that can be used for the optimal determination of these two important variables of the design process, in terms of annual energy yield and initial cost. The proposed approach is applied to a 2MW wind turbine.