Nuno M. A. Freire

Open-Circuit Fault Diagnosis in PMSG Drives for Wind Turbine Applications

Condition monitoring and fault diagnosis are currently considered crucial means to increase the reliability and availability of wind turbines and, consequently, to reduce the wind energy cost. With similar goals, direct-drive wind turbines based on permanent magnet synchronous generators (PMSGs) with full-scale power converters are an emerging and promising technology. Numerous studies show that power converters are a significant contributor to the overall failure rate of modern wind turbines. In this context, open-circuit fault diagnosis in the two power converters of a PMSG drive for wind turbine applications is addressed in this paper. A diagnostic method is proposed for each power converter, allowing real-time detection and localization of multiple open-circuit faults. The proposed methods are suitable for integration into the drive controller and triggering remedial actions. In order to prove the reliability and effectiveness of the proposed fault diagnostic methods, several simulation and experimental results are presented.

A Fault-Tolerant Direct Controlled PMSG Drive for Wind Energy Conversion Systems

Reliability and availability levels are crucial aspects for assessing the economic viability of wind energy conversion systems. Therefore, fault-tolerant systems can make a valuable contribution. This paper presents a fault-tolerant permanent-magnet synchronous generator (PMSG) drive employing new direct control techniques. For postfault operation, a direct power control (DPC) of a four-switch three-phase converter and a direct torque control of a three-switch three-phase rectifier are proposed. Switching tables are theoretically formulated for both control techniques. Two alternative tables are obtained for the DPC of the grid-side converter, permitting the choice between implementation simplicity and enhanced performance. All necessary reconfigurations to handle open-circuit faults are triggered by a reliable fault diagnostic method, which has a low computational demand, without requiring additional measurements. Experimental results are presented, demonstrating the feasibility of the proposed fault-tolerant PMSG drive.

A Voltage-Based Approach Without Extra Hardware for Open-Circuit Fault Diagnosis in Closed-Loop PWM AC Regenerative Drives

The widespread use of electric drives has led to an increasing interest in their condition monitoring and fault diagnostics. With respect to power-switch open-circuit fault diagnosis, the majority of the proposed voltage-based approaches require additional hardware, increasing the system cost. As a result, industry acceptance may be low. This paper proposes a new voltage-based approach-without additional sensors-for open-circuit fault diagnosis in closed-loop controlled pulsewidth-modulation (PWM) ac voltage source converters, by using the information contained in the reference voltages available from the control system. The robustness against false alarms of the proposed technique is improved by employing a voltage observer, in order to estimate the actual converter voltages. It has been proven that the algorithm is insensitive to parameter errors; thus, its effectiveness is not compromised. In order to assess the applicability of the diagnostic technique, it is integrated into the control system of a permanent-magnet-synchronous-machine drive, with regenerative capabilities, together with three of the most widely used PWM control strategies: hysteresis current control, direct torque control, and space vector modulation. The technique performance is analyzed in detail by means of several experimental results.

Recent advances in fault diagnosis by Park's vector approach

This paper addresses recent advances in fault diagnosis by Parks Vector Approach, with special emphasis being given to the most recent developments concerning power converter fault diagnosis in variable speed ac drives. With the aim to demonstrate the suitability of such approach for power converters self-diagnostic, a detailed comparison of four algorithms intended for real-time diagnosis is also included. Their performance evaluation is accomplished by means of experimental results, analyzing some key features such as effectiveness, robustness against false alarms, detection speed, implementation effort, tuning effort and computational burden.

A New Approach for Current Sensor Fault Diagnosis in PMSG Drives for Wind Energy Conversion Systems

Fault diagnosis is a mandatory feature in fault-tolerant systems, since it provides the information necessary for the fault isolation and system reconfiguration. Recently, permanent-magnet synchronous generator (PMSG) drives have achieved prominence in wind energy conversion systems (WECSs), due to their reliability and availability. In this paper, a new approach is proposed for current sensor fault diagnosis in PMSG drives for WECSs. As opposed to the conventional state-observer-based methods for current sensor faults, which require a system model and the respective parameters, the proposed diagnostic method uses the measured phase currents only. Thus, its main merits are simplicity and reliability in the diagnosis, making it suitable for real-time implementation and to trigger remedial procedures. In addition, current sensor and open-circuit faults can be distinguished, and the affected phase is effectively identified in both cases. The proposed diagnostic technique is applied to the two power converters of a conventional back-to-back topology, and its performance is analyzed by means of several experimental results.

Fault-Tolerant PMSG Drive With Reduced DC-Link Ratings for Wind Turbine Applications

Fault-tolerant permanent magnet synchronous generator drives might play an important role in improving the reliability and availability levels of the modern wind turbines. However, the acceptance by the wind turbine industry will be low if its implementation cannot be accomplished in a cost-effective way. In this paper, a low-cost fully integrated fault-tolerant converter with the ability to handle power switch open-circuit faults is proposed. The two topologies proposed for post-fault operation of the grid- and PMSG-side converters are a five-leg converter with a shared leg connected to a phase of the generator and to the transformer neutral point and a three-switch three-phase rectifier, respectively. Both do not require the oversizing of any component of the conventional system in order to operate within a limited range. Moreover, the fault diagnostic technique does not require additional measurements, and the integration into the drive controller of all diagnostic and control algorithms can be performed without great increase of the computational effort. Control strategies are proposed for the considered converter topologies, and their performance is analyzed by means of experimental results.

A Fault-Tolerant PMSG Drive for Wind Turbine Applications With Minimal Increase of the Hardware Requirements

Fault-tolerant permanent magnet synchronous generator (PMSG) drives for wind turbine applications play a major role in improving reliability and availability levels, since power converters are very prone to fail. In this paper, a fault-tolerant converter with the ability to handle power switch open-circuit faults is addressed. The main concern of the proposed converter topology is the minimization of the hardware requirements, leading to a low increase of the system cost. First, the employed fault diagnostic technique does not require additional measurements, nor high computational effort. Secondly, the circuit topology reconfiguration implies a minimum number of extra components as well as minimal oversizing of the standard ones. Accordingly, a four-switch three-phase converter with the dc bus midpoint connected to the transformer neutral point and a three-switch three-phase rectifier are adopted for post-fault operation of the grid- and PMSG-side converters, respectively. Vector control strategies are proposed for both converters under analysis, focusing the issues of capacitor voltages balancing and torque ripple minimization. The performance of the proposed fault-tolerant PMSG drive is analyzed by means of experimental results.

Converters fault-diagnosis in PMSG drives for wind turbine applications

In order to compensate the worldwide energy consumption that is still rising, the wind energy is becoming more and more important. For this reason, the analysis of wind energy conversion systems, in which the occurrence of faults has a high negative impact, becomes a very important issue. Considering this, the aim of this paper is to present some diagnostic methods for open-circuit faults in the two power converters of a permanent magnet synchronous generator (PMSG) drive for wind turbine applications. To achieve this goal, fault analysis is the first step, in order to know which parameters can be used for the diagnosis. The following step is the development of reliable diagnostic methods. Various simulation results, considering multiple faults in the grid-side converter and a single fault in the PMSG-side converter, are presented.

Multiple open-circuit fault diagnosis in voltage-fed PWM motor drives using the current Park's Vector phase and the currents polarity

Presently, condition monitoring and fault diagnostics in electric drives are already considered essential to optimize maintenance operations and increase reliability levels. Regarding fault-tolerant inverters, it is well known that reliable fault diagnostic methods are mandatory to trigger remedial actions. This paper presents a diagnostic method for multiple open-circuit faults in pulse-width-modulation (PWM) voltage source inverters (VSI) feeding ac motors, with a special focus on the issue of false alarms during transients, such as load or speed changes. The diagnostic method combines a detection method based on derivative of the current Parks Vector phase, which guarantees robustness to transients, with a localization method based on the currents polarity, which allows for multiple faults diagnosis. In order to prove the reliability and effectiveness of the proposed fault diagnostic method, several simulation and experimental results are presented, using a permanent magnet synchronous motor (PMSM) drive.

A new approach for current sensor fault diagnosis in PMSG drives for wind energy conversion systems

Fault diagnosis is a mandatory feature in fault tolerant systems, since it provides the information necessary for the fault isolation and system reconfiguration. Recently, permanent magnet synchronous generator (PMSG) drives have achieved prominence in wind energy conversion systems (WECS), due to their reliability and availability. Therefore, in this paper a new approach is proposed for current sensor fault diagnosis in PMSG drives for WECS. As opposed to the conventional state observer-based methods for current sensor faults, which require a system model and the respective parameters, the proposed diagnostic method uses the measured phase currents only. Thus, its main merits are simplicity and reliability in the diagnosis, making it suitable for real-time implementation and to trigger remedial procedures. Additionally, current sensor and open-circuit faults can be distinguished and the affected phase is effectively identified in both cases. The proposed diagnostic technique is applied to the two power converters of a conventional back-to-back topology, and its performance is analyzed by means of several experimental results.