Dawei Xiang

An Industry-Based Survey of Reliability in Power Electronic Converters

A questionnaire survey was carried out to determine the industrial requirements and expectations of reliability in power electronic converters. The survey was subjective and conducted with a number of high-profile semiconductor manufacturers, integrators, and users in the aerospace, automation, motor drive, utility power, and other industry sectors. According to the survey, power semiconductor devices ranked the most fragile components. It was concluded that main stresses were from the environment, transients, and heavy loads, which should be considered during power electronic system design and normal operation. This paper has also highlighted that there is a significant need identified by the responders for better reliability-monitoring methods and indicators.

Condition Monitoring for Device Reliability in Power Electronic Converters: A Review

Condition monitoring (CM) has already been proven to be a cost effective means of enhancing reliability and improving customer service in power equipment, such as transformers and rotating electrical machinery. CM for power semiconductor devices in power electronic converters is at a more embryonic stage; however, as progress is made in understanding semiconductor device failure modes, appropriate sensor technologies, and signal processing techniques, this situation will rapidly improve. This technical review is carried out with the aim of describing the current state of the art in CM research for power electronics. Reliability models for power electronics, including dominant failure mechanisms of devices are described first. This is followed by a description of recently proposed CM techniques. The benefits and limitations of these techniques are then discussed. It is intended that this review will provide the basis for future developments in power electronics CM.

Coordinated control of an HVDC link and doubly fed induction generators in a large offshore wind farm

Doubly fed induction generators (DFIGs) are an economic variable-speed solution for large wind turbines while high-voltage dc (HVdc) transmission is being considered for the grid connection of some offshore wind farms. This paper analyzes the need for coordinating the control of the DFIGs and the HVdc link so that the two topologies can work together, giving system designers and operators a choice that may be useful in some applications. It is desired that individual generators be controlled for power tracking in a way similar to that used when they are connected directly to an ac grid, although a grid voltage reference for the DFIG control is no longer available as an independent source in this case. The study shows that machine control should explicitly maintain the flux level, which then allows the HVdc link to regulate the local system frequency and, indirectly, voltage amplitude. Interactions between DFIGs and the HVdc link are investigated and simulations performed to verify the proposed control strategy.

An industry-based survey of reliability in power electronic converters

A questionnaire survey was carried out to determine the industrial requirements and expectations of reliability in power electronic converters. According to the survey, power semiconductor devices ranked the most fragile components. It was concluded that main stresses were from the environment, transients and heavy loads, which should be considered during power electronic system design and normal operation. Further analyses suggest that power device reliability is a key issue and power electronic converter design is correlated with failure costs.

Investigation Into IGBT dV/dt During Turn-Off and Its Temperature Dependence

In many power converter applications, particularly those with high variable loads, such as traction and wind power, condition monitoring of the power semiconductor devices in the converter is considered desirable. Monitoring the device junction temperature in such converters is an essential part of this process. In this paper, a method for measuring the insulated gate bipolar transistor (IGBT) junction temperature using the collector voltage dV/dt at turn-OFF is outlined. A theoretical closed-form expression for the dV/dt at turn-OFF is derived, closely agreeing with experimental measurements. The role of dV/dt in dynamic avalanche in high-voltage IGBTs is also discussed. Finally, the implications of the temperature dependence of the dV/dt are discussed, including implementation of such a temperature measurement technique.

Monitoring Solder Fatigue in a Power Module Using Case-Above-Ambient Temperature Rise

Condition monitoring is needed in power electronic systems as a cost-effective means of improving reliability. Packaging-related solder fatigue has been identified as one of the main root causes of power electronic module failures. This paper presents a method to monitor solder fatigue inside a module by identifying the increase of internal thermal resistance due to that solder fatigue, taking account of the masking effect of the variable operating point. It is assumed that the total loss in the module increases as junction temperature rises, causing an increase in case-above-ambient temperature rise, which can be measured. A dynamic thermal model of the heat sink is utilized to estimate the power loss from temperature measurements, while a device power loss model is developed to estimate the internal thermal resistance by considering the converter electrical loading. Experiment and simulation are used to demonstrate the concept and verify the method.

Condition Monitoring Power Module Solder Fatigue Using Inverter Harmonic Identification

Condition monitoring power semiconductor devices can inform converter maintenance and reduce damage. This paper presents a method to monitor solder fatigue in a voltage source inverter insulated gate bipolar transistor power module by detecting the change of an inverter output harmonic. It is shown that low-order harmonics, caused by nonideal switching, are affected by the device junction temperature, which in turn depends upon module solder condition. To improve the detection accuracy of the phenomenon, the inverter controller is set to cause harmonic resonance at the target harmonic frequency. The would-be resonance is suppressed by an outer control loop where the control action can be used as the condition monitoring signal. Simulation and experiment are presented to validate the method and evaluate its performance in operation.

Analysis of Electromechanical Interactions in a Flywheel System with a Doubly Fed Induction Machine

This paper analyzes the electromechanical inter-action in a flywheel system with a doubly fed induction machine, used for wind farm power smoothing or grid frequency response control. The grid-connected electrical machine is subject to power control and this can cause it to produce negative damping to the shaft torsional vibration. Resonance must be prevented and the study proposes a solution by coordinating the design of the electrical controller and mechanical shaft. Computer simulations are used to demonstrate the problem and the proposed solution.

Monitoring solder fatigue in a power module using the rise of case-above-ambient temperature

Condition monitoring is desired by power electronic system designers as a cost effective means of improving reliability. This paper presents a method to monitor solder fatigue inside a power module by identifying internal thermal resistance increases due to solder fatigue, taking account of the masking effects of a variable operating condition. It is assumed that the total power loss increases as junction temperature rises, causing an increase in the case temperature above ambient, which can be measured. A dynamic thermal model of the heat sink is established, to estimate power loss by measurement, while a device power loss model is developed to estimate internal thermal resistance by further considering the converter electrical loading. Experiment and simulation using validated models are used to characterise the proposed method and verify the concept.

Control of a doubly fed induction generator in a wind turbine during grid fault ride-through

This paper analyzes the ability of a doubly fed induction generator (DFIG) in a wind turbine to ride through a grid fault and the limitations to its performance. The fundamental difficulty for the DFIG in ride-through is the electromotive force (EMF) induced in the machine rotor during the fault, which depends on the dc and negative sequence components in the stator-flux linkage and the rotor speed. The investigation develops a control method to increase the probability of successful grid fault ride-through, given the current and voltage capabilities of the rotor-side converter. A time-domain computer simulation model is developed and laboratory experiments are conducted to verify the model and a control method is proposed. Case studies are then performed on a representatively sized system to define the feasibility regions of successful ride-through for different types of grid faults