Showing papers in "IEEE Transactions on Energy Conversion in 2012"

A Particle Swarm Optimization-Based Maximum Power Point Tracking Algorithm for PV Systems Operating Under Partially Shaded Conditions

Abstract: A photovoltaic (PV) generation system (PGS) is becoming increasingly important as renewable energy sources due to its advantages such as absence of fuel cost, low maintenance requirement, and environmental friendliness. For large PGS, the probability for partially shaded condition (PSC) to occur is also high. Under PSC, the P-V curve of PGS exhibits multiple peaks, which reduces the effectiveness of conventional maximum power point tracking (MPPT) methods. In this paper, a particle swarm optimization (PSO)-based MPPT algorithm for PGS operating under PSC is proposed. The standard version of PSO is modified to meet the practical consideration of PGS operating under PSC. The problem formulation, design procedure, and parameter setting method which takes the hardware limitation into account are described and explained in detail. The proposed method boasts the advantages such as easy to implement, system-independent, and high tracking efficiency. To validate the correctness of the proposed method, simulation, and experimental results of a 500-W PGS will also be provided to demonstrate the effectiveness of the proposed technique.

Power Losses in Long String and Parallel-Connected Short Strings of Series-Connected Silicon-Based Photovoltaic Modules Due to Partial Shading Conditions

Abstract: Configuration of a photovoltaic (PV) power generator has influence on the operation of the generator, especially if it is prone to partial shading. In this paper, the mismatch losses and the power losses due to failure in tracking of the global maximum power point of a long string of 18 series-connected PV modules and three short strings of six series-connected PV modules connected in parallel are investigated under different partial shading conditions by using a MATLAB Simulink simulation model. The generators with parallel-connected short strings are studied in case when they have the same operating voltage and when they operate as separate strings. The results show that long series connection of modules and parallel connections of strings via a single inverter to the electrical grid should be minimized to avoid losses in case of partial shading conditions. Under partial shading conditions, short strings operating separately have the lowest power losses.

Second-Order Sliding Mode Control of a Doubly Fed Induction Generator Driven Wind Turbine

Abstract: This paper deals with power extraction maximization of a doubly fed induction generator (DFIG)-based wind turbine. These variable speed systems have several advantages over the traditional wind turbine operating methods, such as the reduction of the mechanical stress and an increase in the energy capture. To fully exploit this latest advantage, many control schemes have been developed for maximum power point tracking (MPPT) control schemes. In this context, this paper proposes a second-order sliding mode to control the wind turbine DFIG according to references given by an MPPT. Traditionally, the desired DFIG torque is tracked using control currents. However, the estimations used to define current references drive some inaccuracies mainly leading to nonoptimal power extraction. Therefore, using robust control, such as the second-order sliding mode, will allow one to directly track the DFIG torque leading to maximum power extraction. Moreover, the proposed control strategy presents attractive features such as chattering-free behavior (no extra mechanical stress), finite reaching time, and robustness with respect to external disturbances (grid) and unmodeled dynamics (generator and turbine). Simulations using the wind turbine simulator FAST and experiments on a 7.5-kW real-time simulator are carried out for the validation of the proposed high-order sliding mode control approach.

Impedance-Model-Based SSR Analysis for Type 3 Wind Generator and Series-Compensated Network

Abstract: Interaction between doubly fed induction generator (DFIG) Type 3 wind generators and series-compensated networks can lead to subsynchronous resonance (SSR) oscillations-a phenomenon observed in the real world. In this paper, impedance-based Nyquist stability criterion is applied to analyze the SSR phenomena. Impedance models of a DFIG along with its rotor-side converter (RSC) and grid-side converter, and a series-compensated network are derived in terms of space vectors. The DFIG impedance and the network impedance are analyzed to show the impact of wind speed, compensation level, and RSC current controller gain on SSR stability. Nyquist maps are also used to demonstrate the impact on SSR stability. Simulation studies are carried out to show SSR controller interaction. This paper successfully demonstrates that the interaction between the electric network and the converter controller is a leading cause of the SSR phenomena recently observed in wind generation grid integration.

A MATLAB-Simulink-Based PV Module Model and Its Application Under Conditions of Nonuniform Irradiance

Abstract: The performance of a photovoltaic (PV) module is mostly affected by array configuration, irradiance, and module temperature. It is important to understand the relationship between these effects and the output power of the PV array. This paper presents a MATLAB-Simulink-based PV module model which includes a controlled current source and an S-Function builder. The modeling scheme in S-Function builder is deduced by some predigested functions. Under the conditions of nonuniform irradiance, the model is practically validated by using different array configurations in testing platform. The comparison experiments indicate that I-V and P-V characteristic curves of simulation match the measurements from outdoor experiment well. Under the conditions of nonuniform irradiance, both simulation and experiment show that the output power of a PV array gets more complicated due to multiple peaks. Moreover, the proposed model can also simulate electric circuit and its maximum power point tracking (MPPT) in the environment of MATLAB-Simulink. The experiments show that the proposed model has good predictability in the general behaviors of MPPT under the conditions of both nonuniform and uniform irradiance.

Evaluation of the “Hill Climbing” and the “Incremental Conductance” Maximum Power Point Trackers for Photovoltaic Power Systems

Abstract: Maximum power point tracking (MPPT) is an important function in all photovoltaic (PV) power systems. The classical “hill climbing” and “incremental conductance” MPPT algorithms are widely applied in many papers and applications. Both algorithms perturb the operating conditions of the PV array and detect the changes in generated power. Since the detected change in generated power also could be a result of changes in irradiance, both algorithms are prone to failure in case of large changes in irradiance. This paper starts to discuss the size of the perturbation of the operating conditions for both algorithms, based on the single-diode model. The result is used to select the updating frequency for the two algorithms, in order not to run away under certain dynamic conditions. Both algorithms are implemented in an inverter and tested over 16 days of simultaneous operation. Basic statistical procedures, the paired t-test, have been applied to the data with the conclusion that the two algorithms perform equally good.

Comparison of Interior and Surface PM Machines Equipped With Fractional-Slot Concentrated Windings for Hybrid Traction Applications

Abstract: Electric drive systems, which include electric machines and power electronics, are a key enabling technology for advanced vehicle propulsion systems that reduce the petroleum dependence of the ground transportation sector. To have significant effect, electric drive technologies must be economical in terms of cost, weight, and size while meeting performance and reliability expectations. This paper will provide details of the design, analysis, and testing of two permanent magnet (PM) machines that were developed to meet the FreedomCar 2020 specifications. The first machine is an interior PM (IPM) machine and the second machine is a surface PM (SPM) machine. Both machines are equipped with fractional-slot concentrated windings (FSCW). The goal of this paper is to provide a quantitative assessment of how achievable this set of specifications is, as well as a comparison with the state of the art. This paper will also quantitatively highlight the tradeoffs between IPM and SPM FSCW machines especially in the context of traction applications.

Reliability-Centered Maintenance for Wind Turbines Based on Statistical Analysis and Practical Experience

Abstract: The concept of reliability-centered maintenance (RCM) is applied to the two wind-turbine models Vestas V44-600 kW and V90-2MW. The executing RCM workgroup includes an owner and operator of the analyzed wind turbines, a maintenance service provider, a provider of condition-monitoring services, and wind-turbine component supplier as well as researchers at academia. Combining the results of failure statistics and assessment of expert judgement, the analysis is focused on the most critical subsystems with respect to failure frequencies and consequences: the gearbox, the generator, the electrical system, and the hydraulic system. This study provides the most relevant functional failures, reveals their causes and underlying mechanisms, and identifies remedial measures to prevent either the failure itself or critical secondary damage. This study forms the basis for the development of quantitative models for maintenance strategy selection and optimization, but may also provide a feedback of field experience for further improvement of wind-turbine design.

Thermal Analysis of a PMaSRM Using Partial FEA and Lumped Parameter Modeling

Abstract: This paper presents an advanced lumped parameter (LP) thermal model for a permanent-magnet assisted synchronous reluctance machine (PMaSRM) developed for propulsion in a hybrid electric vehicle. Particular focus is put on the stator winding and a thermal model is proposed that divides the stator slot into a number of elliptical copper and impregnation layers. The model is enabled by the derivation of an approximate analytical expression for the thermal resistance of an elliptical cylinder with constant thickness. The approach is attractive due to its simplicity and the fact that it closely models the actual temperature distribution for common slot geometries. Additionally, an analysis, using results from a proposed simplified thermal finite element model representing only one slot of the stator and its corresponding end winding, is presented in which the number of layers and the proper connection between the parts of the LP thermal model representing the end winding and the active part of winding is determined. The presented thermal model is evaluated experimentally on a PMaSRM equipped with a water cooling jacket, and a good correspondence between the predicted and measured temperatures is obtained.

Fault Analysis and Condition Monitoring of the Wind Turbine Gearbox

Abstract: Data mining algorithms and statistical methods are applied to analyze the jerk data obtained from monitoring the gearbox of a wind turbine. Two types of analyses are performed-failure component identification and monitoring vibration excitement. In failure component identification, the failed stages of the gearbox are identified in time-domain analysis and frequency-domain analysis. In the time domain, correlation coefficient and clustering analysis are applied. The fast Fourier transformation with time windows is utilized to analyze the frequency data. To monitor the vibration excitement of the gearbox in its high-speed stage, data mining algorithms and statistical quality control theory are combined to develop a monitoring model. The capability of the monitoring model to detect changes in the gearbox vibration excitement is validated by the collected data.

Enhancing Low-Voltage Ride-Through Capability and Smoothing Output Power of DFIG With a Superconducting Fault-Current Limiter–Magnetic Energy Storage System

Abstract: Two major problems that are faced by doubly fed induction generators are: weak low-voltage ride-through capability and fluctuating output power. To solve these problems, a superconducting fault-current limiter-magnetic energy storage system is presented. The superconducting coil (SC) is utilized as the energy storage device for output power smoothing control during normal operation and as a fault-current limiting inductor to limit the surge current in the stator or rotor during the grid fault. The SC can also weaken the rotor back electromotive force voltage, and thus enhance the controllability of the rotor-side converter (RSC), which helps to protect both the RSC and the gearbox. Simulation results verify the efficacy of the proposed approaches.

Sliding-Mode-Based Direct Power Control of Grid-Connected Wind-Turbine-Driven Doubly Fed Induction Generators Under Unbalanced Grid Voltage Conditions

Abstract: This paper proposes an improved direct power control (DPC) strategy of grid-connected wind-turbine-driven doubly fed induction generators (DFIGs) when the grid voltage is unbalanced. The DPC scheme is based on the sliding mode control (SMC) approach, which directly regulates the instantaneous active and reactive powers in the stator stationary reference frame without the requirement of either synchronous coordinate transformation or phase angle tracking of grid voltage. The behavior of DFIGs by the conventional SMC-DPC, which takes no negative-sequence voltage into consideration, is analyzed under unbalanced grid voltage conditions. A novel power compensation method is proposed for the SMC-based DPC during network unbalance to achieve three selective control targets, i.e., obtaining sinusoidal and symmetrical stator current, removing stator interchanging reactive power ripples and canceling stator output active power oscillations, respectively. The active and reactive power compensation components are calculated via a simple method and the proposed three control targets can be achieved, respectively, without the need of extracting negative-sequence stator current components. Experimental results on a 2 kW DFIG prototype are presented to verify the correctness and validity of the proposed control strategy and power compensation method.

Parameter Identification of Multiphase Induction Machines With Distributed Windings—Part 1: Sinusoidal Excitation Methods

Abstract: Multiphase induction machines (IMs) are gaining increasing interest in industry due to their numerous advantages over the conventional three-phase ones. A lot of different parameter estimation methods have been developed for three-phase IMs, but the existing literature regarding specific identification techniques for multiphase IMs is almost nonexistent at this point. This paper proposes simple offline methods to estimate the stator resistance and stator leakage inductance of multiphase IMs with distributed windings, under different conditions, utilizing the machine's degrees of freedom associated with the nonflux/torque producing current components. Once these parameters are identified, the rotor ones can be easily calculated by combination with the total values obtained from locked-rotor tests. The procedure enables segregation of the stator and rotor parameters in a simple manner, something that is very difficult to achieve in three-phase IMs where, usually, equality of leakage inductances and a constant stator resistance are assumed. In this manner, the magnetizing inductance can be then also more accurately assessed from no-load tests, because the error in its estimation that would be caused by assuming both leakage inductances to be equal is avoided. The proposed methods are experimentally tested on two different five-phase IMs.

Detection of Demagnetization Faults in Surface-Mounted Permanent Magnet Synchronous Motors by Means of the Zero-Sequence Voltage Component

Abstract: This paper develops and analyzes an online methodology to detect demagnetization faults in surface-mounted permanent magnet synchronous motors. The proposed methodology, which takes into account the effect of the inverter that feeds the machine, is based on monitoring the zero-sequence voltage component of the stator phase voltages. The theoretical basis of the proposed method has been established. Attributes of the method presented here include simplicity, very low computational burden, and high sensibility. Since the proposed method requires access to the neutral point of the stator windings, it is especially useful when dealing with fault tolerant systems. A simple expression of the zero-sequence voltage component is deduced, which is proposed as a fault indicator parameter. Both simulation and experimental results presented in this paper show the potential of the proposed method to provide helpful and reliable data to carry out an online diagnosis of demagnetization failures in the rotor permanent magnets.

Sliding-Mode Control for DFIG Rotor- and Grid-Side Converters Under Unbalanced and Harmonically Distorted Grid Voltage

Abstract: Regarding doubly fed induction generator (DFIG) operation, unbalanced and harmonically distorted grid voltage conditions have been treated as two separate control problems. This paper reports a solution for the rotor- and grid-side power converters, which allows one to keep the DFIG successfully in operation under both grid voltage conditions. The proposed solution is based on sliding-mode control (SMC). The rotor-side converter is commanded so that the electromagnetic torque and the stator reactive power remain free of fluctuations that arise during grid voltage disturbances. Meanwhile, the grid-side converter ensures both constant DC-link voltage and steady active power output from the overall system. The developed algorithms turn out being robust against parameter variations and of fast dynamic response. In addition, none of the converters need either voltage or current positive and negative sequences extraction. The simulation results presented demonstrate the appropriateness of SMC to face such disturbed scenarios. Finally, the stability proof of both converters' control algorithms is provided in the appendices.

Modeling of a Complementary and Modular Linear Flux-Switching Permanent Magnet Motor for Urban Rail Transit Applications

Abstract: In this paper, a complementary and modular linear flux-switching permanent magnet (MLFSPM) motor is investigated, in which both the magnets and armature windings are placed in the short mover, while the long stator consists of iron core only. The proposed MLFSPM motor incorporates the high power density of a linear permanent magnet synchronous motor and the simple structure of a linear induction motor. It is especially suitable for long stator applications such as urban rail transit. The objective of this paper is to build the mathematical model for the purpose of control of this motor. The simulation results by means of finite-element analysis (FEA) verified the theoretical analysis and the effectiveness of this model. Both the analytical model and the FEA results are validated by experiments based on a prototype motor.

Standalone Operation of Wind Turbine-Based Variable Speed Generators With Maximum Power Extraction Capability

Abstract: The application of variable speed wind generators in hybrid remote area power supply (RAPS) systems provides opportunities for improved voltage and frequency control together with maximum power point tracking (MPPT), where limited research outcomes exist. The study presented in this paper covers two such hybrid systems: 1) permanent magnet synchronous generator (PMSG) and 2) doubly fed induction generator (DFIG) as wind turbine technologies together with a battery storage and a dump load. The battery storage system and dump load are able to assist in maintaining the active power balance during over and under generation conditions as well as sudden load changes. Through simulation studies, it has been demonstrated that both RAPS systems are able to regulate the load side voltage and frequency within the acceptable limits while extracting the maximum power from wind, which is an inherent capability of variable speed generators. The two RAPS systems and their associated control strategies have been developed and their performance is investigated using SimPowerSystems blocksets in MATLAB.

A Space-Vector Modulation Scheme for Multilevel Open-End Winding Five-Phase Drives

Abstract: Open-end winding three-phase variable speed drives with dual-inverter supply have been extensively investigated for various applications, including series hybrid powertrains and propulsion motors. The topology is simple to realize while offering a higher number of switching states without the need for capacitor voltage balancing algorithms, when compared to the standard multilevel converters. This paper extends the open-end winding concept to a five-phase drive. A relatively simple space-vector modulation (SVM) algorithm, based on the already well-understood five-phase two-level drive SVM method, is developed. The proposed modulation technique has the advantage of being straightforward to implement and, like its two-level counterpart, is able to generate output voltages with minimum low-order harmonic content. The method generates up to 17-level output phase voltage and, therefore, offers superior harmonic performance when compared to the two-level five-phase modulation. The developed scheme is verified via detailed simulations and experiments, using a five-phase induction machine operating under open-loop V/f control.

Simple Analytical Expressions for the Force and Torque of Axial Magnetic Couplings

Abstract: In this paper, a theoretical analysis of an axial magnetic coupling is presented, leading to new closed-form expressions for the magnetic axial force and torque. These expressions are obtained by using a 2-D approximation of the magnetic coupling geometry (mean radius model). The analytical method is based on the solution of Laplace's and Poisson's equations by the separation of variables method. The influence of geometrical parameters such as number of pole pairs and air-gap length is studied. Magnetic field distribution, axial force, and torque computed with the proposed 2-D analytical model are compared with those obtained from 3-D finite elements simulations and experimental results.

Imbalance Fault Detection of Direct-Drive Wind Turbines Using Generator Current Signals

Abstract: Imbalance faults constitute a significant portion of all faults in wind turbine generators (WTGs) WTG imbalance fault detection using generator current measurements has advantages over traditional vibration-based methods in terms of cost, implementation, and system reliability However, there are challenges in using current signals for imbalance fault detection due to low signal-to-noise ratio of the useful information in current signals and nonstationary characteristic frequencies of imbalance faults This paper proposes a method of using generator stator currents for imbalance fault detection of direct-drive WTGs In the proposed method, the variable shaft rotating frequency of a WTG is estimated from one phase stator current measured from the generator terminal by using a phase-locked loop method The estimated shaft rotating frequency is then processed by using appropriate upsampling and variable-rate downsampling algorithms Consequently, the variable characteristic frequencies of imbalance faults in the spectrum of the estimated shaft rotating frequency are converted to constant values Therefore, the signatures of wind turbine imbalance faults can be clearly identified from power spectral density analysis of the converted shaft rotating frequency signal Simulation and experimental results show that the proposed method is effective to detect various imbalance faults in direct-drive WTGs

Effect of Wind Speed on Wind Turbine Power Converter Reliability

Abstract: Wind turbine power converter system (WTPCS) is a crucial device in a wind energy conversion system. This paper presents the new failure rate models and a reliability evaluation technique for the (WTPCS) considering effects of wind speeds, which can be named by the multistate probability analysis method. The case studies on the WTPCS of a 2 MW wind turbine with a permanent magnet synchronous generator are conducted using wind speed data at Lauwersoog and Valkenburg wind sites in Holland. The results indicate that reliability of the WTPCS is affected significantly by variations of wind speed and the rated wind speed of wind turbine. The effectiveness of the proposed method is demonstrated by examples.

Nyquist-Stability-Criterion-Based SSR Explanation for Type-3 Wind Generators

Abstract: Type-3 wind generators in series-compensated networks could lead to subsynchronous resonance (SSR) oscillations- a phenomenon observed recently. In this letter, impedance-based Nyquist stability criterion is applied to explain the phenomenon. The resonance is not due to the shaft's torsional characteristics, but rather due to its slip related impedance, which can give rise to equivalent negative resistance. The explanation corroborates the authors' previous explanation of self-excitation using net negative resistance concept. Nyquist map is also able to demonstrate the impact of wind speed on SSR.

Parameter Identification of Multiphase Induction Machines With Distributed Windings—Part 2: Time-Domain Techniques

Abstract: Multiphase drives are advantageous when high overall system reliability and the reduction in the total power per phase are required. The control strategies for these applications require a good knowledge of the machine parameters to ensure a high quality of the dynamic and steady-state drive performance. Multiphase machines are still not common in industry and it appears that very little work has been done so far in relation to parameter identification techniques. This paper presents and implements a procedure to estimate the parameters of a five-phase induction machine, which can be also extended to other multiphase machines with higher phase numbers. The method is based on standstill time-domain tests and recursive least-squares algorithms. Experimental results are provided to illustrate the developed identification method using tests on two different five-phase induction machines. Correlation with corresponding parameters obtained in Part 1 of this paper is established, where electrical parameters of the same two five-phase inverter-fed induction motor drives were identified using various procedures, based on sinusoidal excitation of the machine.

Integrated Modeling and Enhanced Control of DFIG Under Unbalanced and Distorted Grid Voltage Conditions

Abstract: This paper focuses on the enhanced control and improved fault-ride-through capability of a doubly fed induction generator (DFIG)-based wind turbine system under both unbalanced and distorted grid voltage conditions. A more integrated mathematical model of DFIG is first set up with both the negative-sequence and the low-order harmonic grid voltages considered. Based on the developed model, the instantaneous active/reactive powers and electromagnetic toque are redefined in detail. Besides, four alternative control targets and their corresponding rotor current references are calculated and assigned. A novel current controller, consisting of a conventional PI regulator and a dual-frequency resonant (DFR) compensator, tuned at twice and six times the grid frequency, named PI-DFR controller, is designed to regulate the fundamental and the fifth- and seventh-order harmonic components simultaneously. Experiment studies verify the correctness of the developed model and the effectiveness of the suggested control strategies in improving the fault-ride-through capability of a DFIG system under such adverse grid conditions.

Design Optimization and Analysis of Single-Sided Linear Induction Motor, Considering All Phenomena

Abstract: Regarding the different capabilities, linear motors have been employed in many applications in industry. Among different linear motors, single-sided linear induction motors (SLIMs) have been widely used due to their simplicity and low construction cost. However, these types of motors suffer from low efficiency and power factor and also, existence of so called end effect. The end effect produces braking force that deteriorates the performance of the motor, especially at high speeds. In this paper, analytical equations are derived for end effect braking force, efficiency, power factor, and output thrust. Employing the derived equations and considering all phenomena involved in the single-sided SLIM, a simple design procedure is presented and the effect of different design variables on the performance of the motor is analyzed. A multiobjective optimization method based on genetic algorithm is introduced to maximize efficiency and power factor, as well as to reduce primary weight and end effect braking force, simultaneously. All effective design variables are considered in optimization. The results show significant improvements in the objective function. Finally, the 2-D and 3-D finite element method is employed to validate the results obtained by the analytical method.

High-Efficiency Control for a Wind Energy Conversion System With Induction Generator

Abstract: In this paper, an improved efficiency control scheme for wind energy conversion systems (WECSs) with squirrel cage induction generators is proposed. Thus, the power harvesting from the WECS is increased and additionally expansion of the exploitable wind speed region toward the lower speed range is accomplished. The generator is connected to the power grid by means of two space-vector-controlled back-to-back converters. A minimum ohmic loss (MOL) controller is introduced in order to minimize the generator resistive loss that is accomplished by adjusting the d-axis stator current according to torque conditions. The implementation of the proposed controller is easy and cost effective because neither additional control signals nor the knowledge of the generator loss model is required. The effectiveness of MOL controller and its successful cooperation with two types of maximum power point tracking (MPPT) controllers, which are employed to maximize the wind turbine output power, are experimentally verified. The MPPT controller is implemented by using an adaptive search control and a fuzzy-logic-based control technique, since both are independent of wind turbine characteristics and widely used. Selective experimental results are presented to demonstrate the resulting improvements of the suggested control scheme.

An Induction Machine Emulator for High-Power Applications Utilizing Advanced Simulation Tools With Graphical User Interfaces

Abstract: In this paper, a method is presented for removing the risk associated with the testing and development of novel drive system topologies, prototype electrical machines, advanced control system strategies, or a combination of the aforementioned without using any real motors/generators. The test platforms for low-power machines are relatively inexpensive and accessible; however, as power levels increase into the upper kilowatt and megawatt range, validation of prototype machines and drives becomes costly. The proposed induction machine emulator (IME) platform utilizes the power hardware-in-the-loop concept in conjunction with a high-fidelity machine model and load dynamics. The electrical machine and its load dynamics are simulated with a real-time digital simulator, which generates appropriate control commands to a power electronics-based voltage amplifier that interfaces to a variable speed drive (VSD). Specifically, the current draw is recreated by altering the phase and magnitude of a voltage amplifier connected to a VSD under test via a unique transformer-based LCL-type coupling network. Based on the proposed concept, the use of a multiwinding, tap-changing transformer establishes a truly versatile and universal test platform for a wide range of power levels. In addition, this paper presents a control strategy in the synchronously rotating reference frame in dq coordinates for the power electronic converters in IME operation. Experimental results at the 25-kVA power level validate the feasibility and highly dynamic performance of the proposed test platform.

Diagnosis of Output Power Lowering in a PV Array by Using the Kalman-Filter Algorithm

Abstract: The number of photovoltaic (PV) generators has been significantly increased worldwide as a main renewable energy resource. The output power of PV generators mainly depends on the solar irradiance, module temperature, and field conditions. Therefore, the maintenance of the PV system is necessary to improve the reliability in its use. In this paper, a novel method to diagnose output power lowering in a PV array is proposed to keep the good performance of its output power based on the relationships between PV module temperature, current, and voltage under maximum power point conditions. In particular, the proposed method does not require the accurate information in specification on PV module and sensors for measuring irradiation levels, which are required in conventional monitoring systems. This results in the reduction of cost. Then, it is effectively applied to a practical PV system by using the Kalman-filter algorithm. The performances of the proposed diagnosis method are evaluated and verified with the laboratory experiment and field tests as well as the PSCAD/EMTDC-based simulation test.

An Active–Reactive Power Method for the Diagnosis of Rotor Faults in Three-Phase Induction Motors Operating Under Time-Varying Load Conditions

Abstract: This paper presents a new method to diagnose rotor faults in operating three-phase induction motors under the presence of time-varying loads. The proposed diagnostic strategy relies on a combined analysis of the amplitude and phase spectra of the instantaneous active and reactive powers of the motor, and allows to discriminate the effects introduced by a rotor fault from the ones caused by an oscillating load torque, even when these phenomena occur simultaneously. A theoretical analysis carried out using a linearized model of the induction motor in a synchronous reference frame, complemented with several simulation and experimental results, confirms the validity of the proposed diagnostic approach.

Modeling of Different Winding Configurations for Fault-Tolerant Permanent Magnet Machines to Restrain Interturn Short-Circuit Current

Abstract: This paper describes an analytical model to evaluate the short-circuit (SC) current resulting from an interturn fault by computing the self and mutual inductances under SC fault condition. Two different concentrated winding configurations, i.e., horizontally and vertically placed conductors in the slot of a fault-tolerant permanent magnet synchronous machine are considered. By computing the associated slot-leakage and air-gap fluxes, the self inductance of both healthy and faulty windings as well as the mutual inductance between them, the SC current can be determined for any position and number of shorted turns. The proposed model is verified with finite-element analysis and validated experimentally. It will be shown that the magnitude of an interturn SC current depends on both the number of shorted turns and their position in the slot. The measured SC inductance shows that a new proposed concentrated vertical winding configuration can inherently limit the SC current and reduce its dependence on the position within the slot.