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This paper proposes an analytical time and frequency domains evaluation of torque harmonics produced by high-power load-commutated-inverters (LCIs) and pulsewidth-modulated (PWM) voltage-source inverters for adjustable speed applications. These drive systems are used in petrochemical and mining industries, where driven loads have multi-inertia or long shafts that are potentially subject to torsional mode excitation. Such excitation may lead to accelerated fatigue, system failure, and loss of production, and in turbine-generator sets, to system blackout. The investigated power conversion topologies are multi-pulse LCIs (6/6 and 12/12-pulse systems), parallel connected three-level neutral-clamped-converters with non-interleaved and interleaved PWM signals, as well as series-connected H-bridge multi-level inverters, single thread and four threads supplying a 12-phase machine and parallel connection of four threads converter systems with interleaved PWM commands. They are the most used variable frequency drives in the megawatt range, both with synchronous and induction machines, in the petrochemical industry. The time and frequency domains of the machine's air-gap torque is calculated from the motor's voltage and stator's current waveforms, this proven method is independent from the type of ac machine. More than 50 simulated operating points are discussed and experimental results for NPC and cascaded inverters are also presented.

In this paper, review on modeling photovoltaic (PV) generator is established first; next, the combination of the optimization method of maximum likelihood estimator (MLE) and Newton Raphson (NR) resolution for identifying unknown parameters of single diode PV module at different test conditions is proposed. This predicted method is compared with generalized least square estimator (LSE) known also as optimization method. The results are also compared with popular predictive methods as Villalva's and Lambert solution. The proposed method is applied for polycrystalline silicon photovoltaic MSX60 solar module at standard test conditions (STC) and at 1000 W/m2, 75 °C. Two types of comparison are made: first, the dynamic variations of parameters values are carried out by graphs and compared in tables with the values found with the other methods (mentioned above); the parameters have converged after up to 150 iterations at STC and the accuracy of estimated parameters is sensitive to the initial parameters of trust region. Secondly, the (I-V) or (P-V) curves are superposed, justifying the accuracy of the proposed method. The comparative errors graphs are also carried out. The results proved the effectiveness of the maximum likelihood estimator, by accuracy parameters of the PV module. An extended study is done for the recent mono-crystalline module CSK6-280M known as Canadian Solar's module. This last study reveals the accuracy for the proposed method during irradiation variation.

This paper analytically investigates expressions of an oscillating motor's air-gap torque resulting simultaneously from dynamic electromagnetic and dynamic mechanical components. The electromagnetic torque is generated in the air gap when the motor is supplied by variable frequency drives (VFDs), such as pulsewidth modulated voltage source inverters or load commutated inverters. Whereas, the mechanical torque components might result from dynamic mechanical processes, such as wind turbine blades, oil and gas fluid fluctuation, and, for emulating dynamic mechanical loads, a load-side VFD. Simple and straightforward analytical relationships between electrical and mechanical harmonics are developed to understand the propagation of mechanical dynamics to the electric side and vice versa. Intensive numerical simulations have been carried out to support the theoretical analysis. Time and frequency domain results confirm the robustness of the proposed relationships. Finally, laboratory experimental test results also confirm the accuracy of the proposed relationships.

A synchronous current controller for field-oriented control is a popular control scheme that is used in industry to separately control the synchronous current of an induction motor in steady state. However, in some transient states such as during start-up and variation of the mechanical load, the synchronous current along the d -axis remains coupled to the q -axis current. Conventional decoupling current control considers only the model of an induction motor to compensate these coupling terms, but the motor is often powered by an inverter, which also influences the current, voltage, and torque behavior. Thus, a novel decoupling current control method is proposed to consider the coupling terms of both the motor and power converter in a synchronous current controller. Existing approaches assume that the motor is directly connected to the power supply, so a model is also suggested for a pulse width modulation (PWM) inverter. Analytical equations with simulation and experimental results prove that the coupling terms are still present when not considering the PWM inverter in the decoupling network. The proposed method shows good performance, and the d -axis current is always separated from the q -axis current during variation of the mechanical load.

Models are crucial in the engineering design process because they can be used for both the optimization of design parameters and the prediction of performance. Thus, models can significantly reduce design, development and optimization costs. This paper proposes a novel equivalent electrical model for Darrieus-type vertical axis wind turbines (DTVAWTs). The proposed model was built from the mechanical description given by the Paraschivoiu double-multiple streamtube model and is based on the analogy between mechanical and electrical circuits. This work addresses the physical concepts and theoretical formulations underpinning the development of the model. After highlighting the working principle of the DTVAWT, the step-by-step development of the model is presented. For assessment purposes, simulations of aerodynamic characteristics and those of corresponding electrical components are performed and compared.

As the demand for wind energy continues to grow at exponential rates, reducing operation and maintenance (OM) costs and improving reliability have become top priorities in wind turbine (WT) maintenance strategies. In addition to the development of more highly evolved WT designs intended to improve availability, the application of reliable and cost-effective condition-monitoring (CM) techniques offers an efficient approach to achieve this goal. This paper provides a general review and classification of wind turbine condition monitoring (WTCM) methods and techniques with a focus on trends and future challenges. After highlighting the relevant CM, diagnosis, and maintenance analysis, this work outlines the relationship between these concepts and related theories, and examines new trends and future challenges in the WTCM industry. Interesting insights from this research are used to point out strengths and weaknesses in today’s WTCM industry and define research priorities needed for the industry to meet the challenges in wind industry technological evolution and market growth.

The complex and unsteady aerodynamics of vertical axis wind turbines (VAWTs) pose significant challenges for simulation tools. Recently, significant research efforts have focused on the development of new methods for analysing and optimising the aerodynamic performance of VAWTs. This paper presents an electric circuit model for Darrieus-type vertical axis wind turbine (DT-VAWT) rotors. The novel Tchakoua model is based on the mechanical description given by the Paraschivoiu double-multiple streamtube model using a mechanical-electrical analogy. Model simulations were conducted using MATLAB for a three-blade NACA0012 aerofoil with an average Reynolds number of 40000 for the blade and a tip speed ratio of 5. The results obtained show strong agreement with findings from both aerodynamic and CFD models in the literature.

Models are crucial in the engineering design process because they can be used for both the optimisation of design parameters and the prediction of performance. Thus, models can significantly reduce design, development and optimisation costs. This paper establishes bases that can underlie the development of a novel equivalent electrical model for Darrieus-type vertical axis wind turbines (DTVAWTs). A brief review of existing models underscores the necessity of a new approach in modelling of DTVAWT. This work also addresses the physical concepts and theoretical formulations that can underpin the development of the model. After highlighting the working principle of the DTVAWT, the mechanic-electric analogy approach for the new model is presented. The paper ends with presentation of key lines of the theoretical formulation for the development of the new model.

Models are crucial in the engineering design process because they can be used for both the optimisation of design parameters and the prediction of performance. Thus, models can significantly reduce design, development and optimisation costs. This paper presents the construction process of a novel equivalent electrical model for Darrieus-type vertical axis wind turbines (DTVAWTs). Physical concepts and theoretical formulations underpinning the development of the model are addressed. The proposed model was built from the mechanical description given by the Paraschivoiu double-multiple streamtube model and is based on the analogy between mechanical and electrical circuits. After highlighting the working principle of the DTVAWT, the step-by-step development of the model is presented. For assessment purposes, simulations of aerodynamic characteristics and those of corresponding electrical components are performed and compared.

Mechanical damage of rotating shafts has been reported for several years from various high-power applications. This paper shows that the variable frequency drive incorporated in a rotating shaft is one of the main root causes of mechanical-shaft failures. Simple analytical relationships show that the frequencies of the motor air-gap torque have a more significant impact on the mechanical-shaft failure than their magnitudes. Effects of mechanical damping are analytically derived and analyzed. Motor air-gap torque is successfully reconstructed using only the motor's voltage and current, thus avoiding torque sensors, which are subject to failure and errors. Simple relationships between frequencies of current harmonics and frequencies of motor pulsating torques are proposed. For pulsewidth-modulated inverters (two and multilevel), possible drive operating points that might excite the shaft's eigenmodes are predicted. Simulation results of four interleaved three-level neutral-point-clamped converters are analyzed for validation purposes. Experimental tests up to 35 MW are performed on a compressor test bed. The presented results confirm the accuracy of the proposed approach, which is particularly valuable for multimegawatt drive applications.

This paper proposes a new approach to ensure the torque decoupled to the rotor flux of an induction machine based on the Field Oriented Control (FOC). The suggested method consists of inserting into the conventional d-q synchronous current controller, coupling terms of motor and multi-level inverter models. Making, the dynamic response of stator current components decoupled as well as the rotor flux and torque. In this paper, the mathematic model of an induction motor and multi-level inverter are first derived. Then, the synchronous current controller and modulation strategy for high power inverters are investigated. Finally, the validation through implementation and simulation of a 4.16 kV electric drive with MATLAB/Simulink and SimPowerSystems is performed. The model simulated in this paper includes an induction motor, nine-level cascaded H-bridge inverter and a carrier based space vector pulse-width-modulation.The results of the simulations of each method has been recorded and the comparison results reveal that the proposed method effectively maintains the rotor flux decoupled to the torque.

This paper presents new, simple, and linear mathematical relationships to predict pulsating torque frequencies in industrial multi-megawatt pulse width-modulated (PWM) drives. The proposed relationships provide direct definition of possible drive operating points where the torsional resonance modes of the mechanical shaft assembly might be excited. The calculation accuracy of natural frequencies and the induction motor slip have been taken into account in the definition of a critical excitation band. Variable switching frequency PWM strategies have also been analyzed. Pulsating torque frequencies of complex load-commutated-inverter configurations have been proposed as complementary results. Several tests have been performed on an integrated-motor-compressor system operating at high-speed (3.3 kV, 6 MW at 10 000 r/min). Intensive simulation results of a higher power PWM drive for compressor applications are shown to validate the suggested approach. This paper is a key tool for electrical engineers involved in the design of multi-megawatt drive systems such as in liquefied natural gas compression and transportation, mining, or cements.

This paper proposes an analytical approach to reconstruct the air gap torque waveform of an electrical motor from its stator voltages and currents. This approach is consistent with practical implementation requirements of large variable frequency drives, where a direct measurement of the air gap torque is generally not possible. The method is based on an analytical reconstruction of the air gap torque in stationary and orthogonal coordinates. The proposed approach can be used as a design tool to accurately predict the frequencies of torque harmonics along with their magnitudes and phases. The results can be used to predict the shaft's torsional behavior and they can help assessing shear stresses of the shaft, thus providing a better understanding of the shaft's design life time. Moreover, the proposed approach is a tool for root cause analysis of drive failures. By reconstructing the air gap torque one can accurately prove whether or not one of the shaft's eigenmodes was excited. The proposed technique is applied to a 35 MW drive system based on the parallel connection of four back-to-back neutral point clamped converters. Through simulations, the pulse-width modulated voltage source inverters are analyzed for different switching frequencies and over a wide operating range. The results confirm the accuracy of the proposed method.

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.

Mechanical damage of rotating shafts has been reported for several years from various high-power applications. This paper shows that the variable frequency drive incorporated in a rotating shaft is one of the main root causes of mechanical shaft failures. Simple analytical relationships show that the frequencies of the motor airgap torque have a more significant impact on the mechanical shaft failure than their magnitudes. Effects of mechanical damping are analytically derived and analyzed.