Mike Barnes

Junction-temperature cycling and the associated thermo-mechanical stresses strongly affect the reliability of power electronic (PE) devices, but conventional sensors are challenged in providing accurate measurement of related localized stresses due to limited electrical insulation, size limitations and poor electromagnetic interference (EMI) immunity. Fiber Bragg grating (FBG) sensors have emerged as a promising solution because of their miniature size, excellent insulation, high bandwidth, and multiplexing capability. This review summarizes recent progress in applying FBG sensing to the condition monitoring of PE devices, detailing bonding strategies, sensor placement, and strain–temperature decoupling across different monitoring schemes, while also examining the effect of airgaps, residual stress, and grating length on the measurement accuracy and dynamic response. Building on the reviewed state of the art, the FBG-based approaches for device ageing assessment and the remaining challenges in this area are discussed.

Frequent failures of converters in individual wind turbines (WTs) of modern wind farms (WFs) means sub-optimal operation, loss of generation, as well as increased operation and maintenance (O&M) costs. Improving sub-system and component reliability, including that of converters, is a key element in maintaining technical confidence and consequently minimizing losses for operators and energy cost for consumers. In this paper one dominating cause of failures in WT converters is studied: the thermo-mechanical stress of IGBT modules. Using a lifetime and stress evaluation methodology, the reliability of different subcomponents of a converter module is evaluated. The torque control of the generator, as well as the control of real and reactive power transfer to the grid, are considered. A detail sensitivity analysis and model order reduction of the whole methodology is undertaken. This addresses the need to maximize computational efficiency if such models are to be applied practically, for example in WT digital twins. A novel current control strategy that reduces the IGBT thermal stress without impacting the torque control of the PMSG WT is suggested and successfully applied to a test case.

Accurate measurement and real-time monitoring of the junction temperature is vital for reliability and performance of insulated-gate bipolar transistor (IGBT) power modules and is a continuously developing area. This study presents a performance comparison of the recent advances in fibre Bragg grating (FBG) sensor application for direct on IGBT chip temperature measurement, with the leading conventional methods for junction temperature acquisition: the chip’s on-state voltage ( V _CE ) based temperature evaluation and the non-contact temperature measurement using a thermal camera. The implementation features, accuracy, limitations and potential error sources for each method are evaluated and compared based on practical tests on a commercial IGBT module. The results expose the V _CE based temperature evaluation’s susceptibility to voltage noise and disparities in voltage drops across IGBT terminals and bond wires, with limited and challenging to implement practical methods available to mitigate these. In contrast, the in-situ FBG sensors offer accurate localized real-time IGBT temperature monitoring at a cost of being intrusive to the power module’s geometry. The thermal camera based measurements of IGBT die temperature are found to be limited in practical application by the requirement of a clear line of sight and relatively low response rate of most commercial cameras. The presented analysis aids the understanding of the IGBT temperature measurement method selection and capability based on particular application needs.

This paper investigates the application of adhesive bonded FBG sensors for insulated gate bipolar transistor (IGBT) direct on-chip thermal sensing. The influence of physical properties of different adhesives on the sensor’s calibrated wavelength to temperature characteristic is first investigated. The thermal sensing performance of the bonded FBG sensor is then tested under various current levels in laboratory experiments on a commercial IGBT module. It is found that the bonding adhesive’s curing temperature, glass transition temperature, coefficient of thermal expansion, and hardness can modify the sensor’s calibration characteristic. The adhesive’s glass transition temperature needs careful consideration to ensure an effective match to the IGBT’s thermal operating range of interest and the hardness of the solid bond required for a given application. Operation within the adhesive’s linear working region is shown to be sufficient to provide accurate sensing performance while ensuring the retention of a solid physical bond between the sensor and the chip.

Due to the increasing number of power electronics-based devices in modern power systems, there are concerns about the impact of higher-frequency interactions on system stability. The typically-used algebraic representation of networks fails to capture these newly emergent issues, but dynamically modelling the entire network with differential equations will lead to a prohibitively long simulation time. This paper proposes a computationally-efficient analysis framework to determine the system loadability in power electronics-rich, large networks with the consideration of multiple types of stabilities. The framework developed in this paper identifies the critical network elements based on the eigenvalue sensitivity in order to exploit a hybrid modelling approach. Within the hybrid model, only the critical network portion is modelled dynamically with the rest of the network represented by algebraic equations. Bifurcation theory is used to simultaneously analyze both small-disturbance rotor angle and small-disturbance voltage stability. The results obtained show that the high-frequency interactions are accurately captured with the proposed framework. Additionally, applying this methodology results in a small dimension for the system matrix and a reduction in the computational burden. Two test networks, a three-bus system and the IEEE 39-bus system, are used to illustrate and verify the analysis framework.

This paper studies the influence of Fiber Bragg Grating (FBG) head length on insulated gate bipolar transistor (IGBT) direct on-chip thermal sensing performance of FBG sensors. To this end the surface of a commercial IGBT chip is thermally simulated and experimentally characterized. Uniform FBG sensors with three head sizes are then tested in two promising thermal sensing locations. The study has found that the large thermal gradients in this application create an additional constraint when using longer head lengths. A distortion in the reflected spectrum of the 5 mm FBG sensor is used to illustrate the underlying physical effect which causes this limitation for IGBT junction temperature measurement. This additionally affects the length of head sizes providing accurate temperature readings of the IGBT surface hotspots, and significantly this limit is location dependent in a given IGBT geometry.

It is anticipated that a large number of voltage source converters (VSCs) will be integrated into future power systems, which can potentially be detrimental to system stability. Previous work has utilized an impedance-based approach to analyze the stability boundaries of power systems with multiple VSCs. However, impedance-based modeling limits the analysis of the system feasibility region to just two or three dimensions. Hence, this paper develops a methodology based on bifurcation theory that enables the system multi-dimensional feasibility region to be identified efficiently with consideration of multiple different varying parameters. The developed methodology is generalized so that it can be applied to identify system stability boundaries in other power systems with multiple varying parameters. The partial Spearman correlation coefficient is adopted in this paper to identify the key parameters that affect the stability boundary. Additionally, the calculated correlation indices quantify the interactions between the control loops VSCs in the system. The proposed methodology is verified against other analytical methods and the impact of key parameter variation on the system stability boundaries is discussed.

Enhancing power electronics (PE) converter reliability is crucial for ensuring a reliable operation of current and future operating Wind Turbines (WTs). Achieving high reliability of variable speed WT PE systems requires careful consideration of their operation, and particularly their thermal cycling. This paper presents a methodology for evaluating and reconsidering operational strategies of WTs with relation to the thermal loading and lifetime consumption of the converter. The methodology is applied to compare control strategies for the WT generator and evaluate their impact on the converter reliability by observation of the thermal cycles and by calculating the resultant lifetime consumption of those stress cycles. The thermal stress on both the Machine Side Converter (MSC) and the Grid Side Converter (GSC) is examined and compared. It is shown that the least reliable of the three evaluated control strategies is the one that tracks the power curve below rated speed most closely. This paper suggests that dynamic transients associated with the WT control largely influence the IGBT module wear-out and their modelling needs to be prioritized for lifetime studies. These dynamic transients are captured by the improved model whose value is confirmed for the comparisons in the case study of the paper.