Cristian Busca

An overview of the reliability prediction related aspects of high power IGBTs in wind power applications

Abstract Reliability is becoming more and more important as the size and number of installed Wind Turbines (WTs) increases. Very high reliability is especially important for offshore WTs because the maintenance and repair of such WTs in case of failures can be very expensive. WT manufacturers need to consider the reliability aspect when they design new power converters. By designing the power converter considering the reliability aspect the manufacturer can guarantee that the end product will ensure high availability. This paper represents an overview of the various aspects of reliability prediction of high power Insulated Gate Bipolar Transistors (IGBTs) in the context of wind power applications. At first the latest developments and future predictions about wind energy are briefly discussed. Next the dominant failure mechanisms of high power IGBTs are described and the most commonly used lifetime prediction models are reviewed. Also the concept of Accelerated Life Testing (ALT) is briefly reviewed.

Control of Permanent Magnet Synchronous Generator for large wind turbines

Direct Torque Control (DTC) and Field Oriented Control (FOC) are the most dominant control strategies used in generators for wind turbines. In this paper both control methods were implemented on a Permanent Magnet Synchronous Generator (PMSG). The variable speed wind turbine with full scale power converter topology was chosen for design. Parameters from a 2 MW wind turbine were used for system modeling. All the components of the wind turbine system (WTS), except the DC-link and the grid site converter were implemented in MATLAB/Simulink. The pitch controller was used to limit the output power produced by the turbine. DTC and FOC strategies, using SVM were used to control the generator rotor speed. The performance of the two control strategies were compared after different tests have been carried out.

Modeling lifetime of high power IGBTs in wind power applications - An overview

The wind power industry is continuously developing bringing to the market larger and larger wind turbines. Nowadays reliability is more of a concern than in the past especially for the offshore wind turbines since the access to offshore wind turbines in case of failures is both costly and difficult. Lifetime modeling of future large wind turbines is needed in order to make reliability predictions about these new wind turbines early in the design phase. By doing reliability prediction in the design phase the manufacturer can ensure that the new wind turbines will live long enough. This paper represents an overview of the different aspects of lifetime modeling of high power IGBTs in wind power applications. In the beginning, wind turbine reliability survey results are briefly reviewed in order to gain an insight into wind turbine subassembly failure rates and associated downtimes. After that the most common high power IGBT failure mechanisms and lifetime prediction models are reviewed in more detail.

Harmonic Interaction Analysis in a Grid-Connected Converter Using Harmonic State-Space (HSS) Modeling

An increasing number of power-electronic-based distributed generation systems and loads generate not only characteristic harmonics but also unexpected harmonics. Several methods, such as impedance-based analysis, which are derived from the conventional average model, are introduced to perform research about the harmonic interaction. However, it is found that the linear-time-invariant-based model analysis makes it difficult to analyze these phenomena because of the time-varying properties of the power-electronic-based systems. This paper investigates a grid-connected converter by using the harmonic state-space (HSS) small-signal model, which is based on a linear time-varying periodically theory. The proposed model can include the switching behavior of the model, where it makes the model possible to analyze how harmonics are transferred into both the ac-side and dc-side circuits. Furthermore, a harmonic matrix of the grid-connected converter is developed to analyze the harmonic interaction at the steady-state behavior. Besides, the frequency-domain results are compared with time-domain simulation results by using the HSS modeling to verify the theoretical analysis. Experimental results are finally discussed to verify the proposed model and study.

Dynamic thermal modelling and analysis of press-pack IGBTs both at component-level and chip-level

Thermal models are needed when designing power converters for Wind Turbines (WTs) in order to carry out thermal and reliability assessment of certain designs. Usually the thermal models of Insulated Gate Bipolar Transistors (IGBTs) are given in the datasheet in various forms at component-level, not taking into account the thermal distribution among the chips. This is especially relevant in the case of Press-Pack (PP) IGBTs because any non-uniformity of the clamping pressure can affect the chip-level thermal impedances. This happens because the contact thermal resistances in the thermal impedance chains are clamping pressure dependent. In this paper both component-level and chip-level dynamic thermal models for the PP IGBT under investigation are developed. Both models are developed using geometric parameters and material properties of the device. Using the thermal models, the thermal impedance curves under various mechanical clamping conditions are derived. Moreover, the deformation of the internal components of the PP IGBT under operating-like conditions is investigated with the help of the thermal models and the coefficient of thermal expansion (CTE) information.

Efficiency improvement of pumped storage system for MW scale off-grid PV plants

The photovoltaic market has been growing at a fast rate in the last two decades, and in 2014 reached a global capacity of about 180GW. Due to the increasing penetration level, large-scale energy storage systems that can compensate for its fluctuations become increasingly important. In case of off-grid systems, suitable energy storage is naturally a necessity. In areas with favorable geographical properties, pumped storage has an excellent potential to be applied with large-scale PV plants. The performance of a pumped storage system at MW power level, connected with an off-grid PV plant, is analyzed in this paper, considering the variable character of the PV power. An efficiency increase of the pumped storage system is obtained by means of an improved control of the motor for pumps drive. The system is tested and validated on a RTDS (Real Time Digital Simulator) platform.

Induction motors most efficient operation points in pumped storage systems

A clear focus is nowadays on developing and improving the energy storage technologies. Pumped storage is a well-established one, and is capable of enhancing the integration of renewable energy sources. Pumped storage has an efficiency between 70-80%, and each of its elements affects it. Increased efficiency is desired especially when operating with renewable energy systems, which present low energy conversion factor (up to 50% - performance coefficient for wind turbines, and efficiency up to 40% for photovoltaic systems). In this paper the most efficient operation points of the induction motors in pumped storage systems are established. The variable speed operation of the pumped storage systems and motor loading conditions for pump applications have been the key factors for achieving the purpose of the paper.