Emerging Multiport Electrical Machines and Systems: Past Developments, Current Challenges, and Future Prospects

Distinct from the conventional machines with only one electrical and one mechanical port, electrical machines featuring multiple electrical/mechanical ports (the so-called multiport electrical machines) provide a compact, flexible, and highly efficient manner to convert and/or transfer energies among different ports. This paper attempts to make a comprehensive overview of the existing multiport topologies, from fundamental characteristics to advanced modeling, analysis, and control, with particular emphasis on the extensively investigated brushless doubly fed machines for highly reliable wind turbines and power split devices for hybrid electric vehicles. A qualitative review approach is mainly adopted, but strong efforts are also made to quantitatively highlight the electromagnetic and control performance. Research challenges are identified, and future trends are discussed

Fault analysis and protection for wind power generation systems

Wind power is growing rapidly around the world as a means of dealing with the world energy shortage and associated environmental problems. Ambitious plans concerning renewable energy applications around European countries require a reliable yet economic system to generate, collect and transmit electrical power from renewable resources. In populous Europe, collective offshore large-scale wind farms are efficient and have the potential to reach this sustainable goal. This means that an even more reliable collection and transmission system is sought. However, this relatively new area of offshore wind power generation lacks systematic fault transient analysis and operational experience to enhance further development. At the same time, appropriate fault protection schemes are required. This thesis focuses on the analysis of fault conditions and investigates effective fault ride-through and protection schemes in the electrical systems of wind farms, for both small-scale land and large-scale offshore systems. Two variable-speed generation systems are considered: doubly-fed induction generators (DFIGs) and permanent magnet synchronous generators (PMSGs) because of their popularity nowadays for wind turbines scaling to several-MW systems. The main content of the thesis is as follows. The protection issues of DFIGs are discussed, with a novel protection scheme proposed. Then the analysis of protection scheme options for the fully rated converter, direct-driven PMSGs are examined and performed with simulation comparisons. Further, the protection schemes for wind farm collection and transmission systems are studied in terms of voltage level, collection level wind farm collection grids and high-voltage transmission systems for multi-terminal DC connected transmission systems, the so-called “Supergrid”. Throughout the thesis, theoretical analyses of fault transient performances are detailed with PSCAD/EMTDC simulation results for verification. Finally, the economic aspect for possible redundant design of wind farm electrical systems is investigated based on operational and economic statistics from an example wind farm project

Electric Generators Fitted to Wind Turbine Systems: An Up-to-Date Comparative Study

International audienceThis paper describes a comparative study allowing the selection of the most appropriate innovative structures for electrical machines for a wind turbine system. This study is based on an exhaustive review of the state of the art and on an effective comparison of the performances of the three main conventional electric generator in wind energy application system that are the Doubly-Fed Induction Generator (DFIG), the Squirrel-Cage Induction Generator (SCIG), the Permanent Magnet Synchronous Generator (PMSG), and an innovative machine that is the Switched Reluctance Generator (SRG). The main conclusion drawn by the proposed comparative study is that the innovative switched reluctance generator is able fulfills the major requirements of a wind energy system

Modeling and Linearization of DFIG Based Wind Turbine

Usage level of wind units in power systems is increasing rapidly. There are different kinds of wind turbine generator. The Doubly-Fed Induction Generator (DFIG), is one of the most widely used electrical machines in the megawatt-class wind turbines. In a DFIG-based wind turbine, the stator is connected to grid directly while the rotor is connected a back-to-back converter via slip rings. Current sensor fault diagnosis for renewable power of wind turbine based on DFIG has gained serious importance. In this work, mathematical modeling of DFIG is presented. Nonlinear state equations are linearized with Takagi-Sugeno (T-S) Local Models for current sensor fault diagnosis. Modelling error between linear and nonlinear model is minimized by heuristic approach on membership functions. A bank of observer-based residual generator system for fault diagnosis is created, so additive and gain faults of stator current sensors can be detected and isolated

Performance Analysis of a Four-Switch Three-Phase Grid-Side Converter with Modulation Simplification in a Doubly-Fed Induction Generator-Based Wind Turbine (DFIG-WT) with Different External Disturbances

This paper investigates the performance of a fault-tolerant four-switch three-phase (FSTP) grid-side converter (GSC) in a doubly-fed induction generator-based wind turbine (DFIG-WT). The space vector pulse width modulation (SVPWM) technique is simplified and unified duty ratios are used for controlling the FSTP GSC. Steady DC-bus voltage, sinusoidal three-phase grid currents and unity power factor are obtained. In addition, the balance of capacitor voltages is accomplished based on the analysis of current flows at the midpoint of DC bus in different operational modes. Besides, external disturbances such as fluctuating wind speed and grid voltage sag are considered to test its fault-tolerant ability. Furthermore, the effects of fluctuating wind speed on the performance of DFIG-WT system are explained according to an approximate expression of the turbine torque. The performance of the proposed FSTP GSC is simulated in Matlab/Simulink 2016a based on a detailed 1.5 MW DFIG-WT Simulink model. Experiments are carried out on a 2 kW platform by using a discrete signal processor (DSP) TMS320F28335 controller to validate the reliability of DFIG-WT for the cases with step change of the stator active power and grid voltage sag, respectively

Solid state transformers topologies, controllers, and applications: State-of-the-art literature review

With the global trend to produce clean electrical energy, the penetration of renewable energy sources in existing electricity infrastructure is expected to increase significantly within the next few years. The solid state transformer (SST) is expected to play an essential role in future smart grid topologies. Unlike traditional magnetic transformer, SST is flexible enough to be of modular construction, enabling bi-directional power flow and can be employed for AC and DC grids. Moreover, SSTs can control the voltage level and modulate both active and reactive power at the point of common coupling without the need to external flexible AC transmission system device as per the current practice in conventional electricity grids. The rapid advancement in power semiconductors switching speed and power handling capacity will soon allow for the commercialisation of grid-rated SSTs. This paper is aimed at introducing a state-of-the-art review for SST proposed topologies, controllers, and applications. Additionally, strengths, weaknesses, opportunities, and threats (SWOT) analysis along with a brief review of market drivers for prospective commercialisation are elaborated

Converter fault diagnosis and post-fault operation of a doubly-fed induction generator for a wind turbine

Wind energy has become one of the most important alternative energy resources because of the global warming crisis. Wind turbines are often erected off-shore because of favourable wind conditions, requiring lower towers than on-shore. The doubly-fed induction generator is one of the most widely used generators with wind turbines. In such a wind turbine the power converters are less robust than the generator and other mechanical parts. If any switch failure occurs in the converters, the wind turbine may be seriously damaged and have to stop. Therefore, converter health monitoring and fault diagnosis are important to improve system reliability. Moreover, to avoid shutting down the wind turbine, converter fault diagnosis may permit a change in control strategy and/or reconfigure the power converters to permit post-fault operation. This research focuses on switch fault diagnosis and post-fault operation for the converters of the doubly-fed induction generator. The effects of an open-switch fault and a short-circuit switch fault are analysed. Several existing open-switch fault diagnosis methods are examined but are found to be unsuitable for the doubly-fed induction generator. The causes of false alarms with these methods are investigated. A proposed diagnosis method, with false alarm suppression, has the fault detection capability equivalent to the best of the existing methods, but improves system reliability. After any open-switch fault is detected, reconfiguration to a four-switch topology is activated to avoid shutting down the system. Short-circuit switch faults are also investigated. Possible methods to deal with this fault are discussed and demonstrated in simulation. Operating the doubly-fed induction generator as a squirrel cage generator with aerodynamic power control of turbine blades is suggested if this fault occurs in the machine-side converter, while constant dc voltage control is suitable for a short-circuit switch fault in the grid-side converter.Wind energy has become one of the most important alternative energy resources because of the global warming crisis. Wind turbines are often erected off-shore because of favourable wind conditions, requiring lower towers than on-shore. The doubly-fed induction generator is one of the most widely used generators with wind turbines. In such a wind turbine the power converters are less robust than the generator and other mechanical parts. If any switch failure occurs in the converters, the wind turbine may be seriously damaged and have to stop. Therefore, converter health monitoring and fault diagnosis are important to improve system reliability. Moreover, to avoid shutting down the wind turbine, converter fault diagnosis may permit a change in control strategy and/or reconfigure the power converters to permit post-fault operation. This research focuses on switch fault diagnosis and post-fault operation for the converters of the doubly-fed induction generator. The effects of an open-switch fault and a short-circuit switch fault are analysed. Several existing open-switch fault diagnosis methods are examined but are found to be unsuitable for the doubly-fed induction generator. The causes of false alarms with these methods are investigated. A proposed diagnosis method, with false alarm suppression, has the fault detection capability equivalent to the best of the existing methods, but improves system reliability. After any open-switch fault is detected, reconfiguration to a four-switch topology is activated to avoid shutting down the system. Short-circuit switch faults are also investigated. Possible methods to deal with this fault are discussed and demonstrated in simulation. Operating the doubly-fed induction generator as a squirrel cage generator with aerodynamic power control of turbine blades is suggested if this fault occurs in the machine-side converter, while constant dc voltage control is suitable for a short-circuit switch fault in the grid-side converter