Full- & Reduced-Order State-Space Modeling of Wind Turbine Systems with Permanent-Magnet Synchronous Generator

Wind energy is an integral part of nowadays energy supply and one of the fastest growing sources of electricity in the world today. Accurate models for wind energy conversion systems (WECSs) are of key interest for the analysis and control design of present and future energy systems. Existing control-oriented WECSs models are subject to unstructured simplifications, which have not been discussed in literature so far. Thus, this technical note presents are thorough derivation of a physical state-space model for permanent magnet synchronous generator WECSs. The physical model considers all dynamic effects that significantly influence the system's power output, including the switching of the power electronics. Alternatively, the model is formulated in the $(a,b,c)$- and $(d,q)$-reference frame. Secondly, a complete control and operation management system for the wind regimes II and III and the transition between the regimes is presented. The control takes practical effects such as input saturation and integral windup into account. Thirdly, by a structured model reduction procedure, two state-space models of WECS with reduced complexity are derived: a non-switching model and a non-switching reduced-order model. The validity of the models is illustrated and compared through a numerical simulation study.Comment: 23 pages, 11 figure

Study of Novel Power Electronic Converters for Small Scale Wind Energy Conversion Systems

This chapter proposes a study of novel power electronic converters for small scale wind energy conversion systems. In this chapter major topologies of power electronic converters that used in wind energy converter systems have been analysed. Various topologies of DC/AC single stage converters such as high boost Z-source inverters (ZSI) have been investigated. New proposed schemes for inverters such as multilevel and Z-source inverters have been studied in this proposed chapter. Multilevel converters are categorized into three major groups according to their topologies which are diode clamped multilevel converters (DCM), cascade multilevel converters (CMC) with multiple isolated dc voltage sources and flying capacitor based multilevel converters (FCMC). Z-source inverters are divided to ZSI, qZSI and trans-ZSI types. Trans-ZSI is mostly used for high step-up single stage conversions

Multilevel Converters: An Enabling Technology for High-Power Applications

| Multilevel converters are considered today as the state-of-the-art power-conversion systems for high-power and power-quality demanding applications. This paper presents a tutorial on this technology, covering the operating principle and the different power circuit topologies, modulation methods, technical issues and industry applications. Special attention is given to established technology already found in industry with more in-depth and self-contained information, while recent advances and state-of-the-art contributions are addressed with useful references. This paper serves as an introduction to the subject for the not-familiarized reader, as well as an update or reference for academics and practicing engineers working in the field of industrial and power electronics.Ministerio de Ciencia y Tecnología DPI2001-3089Ministerio de Eduación y Ciencia d TEC2006-0386

An Evaluation of the Cascaded H-Bridge Multilevel Inverter Topology For Direct-Drive Synchronous Wind Farm Applications

A key driver in the recent success of wind has been engineering advances that have lead to improved economics. Many of these advances have centered on power electronic converters, which feature a rectifier that converts the uncontrolled alternating current output of a wind generator to direct current, and an inverter, which converts that direct current back to a controlled alternating current synchronized with the power grid to which the wind generator is connected. Most of the inverters on today’s market use the full-bridge topology, which features six power electronic switches per wind turbine. The purpose of this thesis is to investigate if the cascaded H-bridge multilevel inverter offers benefit in terms of improved economics. Potential advantages of the cascaded H-bridge inverter include reduced switch count, improved converter efficiency, and simplified interconnection to the utility. Potential drawbacks include an increase in required power electronic switch ratings and a reduced ability to withstand transient wind conditions. This thesis concludes that certain control schemes can address performance under transient wind (and thus power production) conditions and that improvements in converter efficiency and reduction in switch counts are offset by increased switch requirements. Therefore, any benefit to justify the use of the cascaded H-bridge inverter in wind farms will arise from a simplified point of common connection to the utility

Modeling and control strategies of fuzzy logic controlled inverter system for grid interconnected variable speed wind generator

Today, variable speed operation of a permanent magnet synchronous generator (PMSG) is becoming popular in the wind power industry (PI). A variable speed wind turbine (VSWT)-driven PMSG, in general, is connected to the grid using a fully controlled frequency converter (FC). Along with the generator side converter, the FC necessitates the grid side inverter system that has a great impact on the stability issue of the VSWT-PMSG, especially in the case of network disturbance. The well-known cascaded-controlled inverter system has widely been reported in much of the literature, where multiple PI controllers are used in inner and outer loops. However, a fuzzy logic controller deals well with the nonlinearity of the power system, compared to a PI controller. This paper presents a simple fuzzy logic controlled inverter system for the control of a grid side inverter system, which suits well for VSWT-PMSG operation in a wide operating range. This is one of the salient features of this paper. Detailed modeling and control strategies of the overall system are demonstrated. Both dynamic and transient performances of VSWT-driven PMSG are analyzed to show the effectiveness of the control strategy, where simulation has been done using PSCAD/EMTDC

Energy Storage Systems for Traction and Renewable Energy Applications

Energy storage systems are the set of technologies used to store various forms of energy, and by necessity, can be discharged. Energy storage technologies have a wide range of characteristics and specifications. Like any other technology, each type of energy storage has its pros and cons. Depending on the application, it is crucial to perform a tradeoff study between the various energy storage options to choose the optimal solution based on the key performance objectives and various aspects of those technologies. The purpose of this thesis is to present a thorough literature review of the various energy storage options highlighting the key tradeoffs involved. This thesis focuses on evaluating energy storage options for traction and renewable energy applicationsHybrid Electric Vehicles (HEVs) is one key application space driving breakthroughs in energy storage technologies. The focus though has been typically on using one type of energy storage systems. This thesis investigates the impact of combining several types of batteries with ultracapacitor. A case study of integrating two energy storage systems in a series-parallel hybrid electric vehicle is simulated by using MATLAB-SIMULINK software.The other key application space is renewable energy especially wind and solar. Due to the intermittent nature of renewable energy sources, energy storage is a must to achieve the required power quality. Therefore, this thesis aims to investigate different cases of combining different types of energy storage with wind and solar. Hybrid Optimization Model for Electric Renewables (HOMER) software is utilized to study the economic and sizing aspects in each case

A review on DC collection grids for offshore wind farms with HVDC transmission system

Abstract: Traditionally, the internal network composition of offshore wind farms consists of alternating current (AC) collection grid; all outputs of wind energy conversion units (WECUs) on a wind farm are aggregated to an AC bus. Each WECU includes: a wind-turbine plus mechanical parts, a generator including electronic controller, and a huge 50-or 60-Hz power transformer. For a DC collection grid, all outputs of WECUs are aggregated to a DC bus; consequently, the transformer in each WECU is replaced by a power converter or rectifier. The converter is more compact and smaller in size compared to the transformer. Thus reducing the size and weight of the WECUs, and also simplifying the wind farm structure. Actually, the use of offshore AC collection grids instead of offshore DC collection grids is mainly motivated by the availability of control and protection devices. However, efficient solutions to control and protect DC grids including HVDC transmission systems have already been addressed. Presently, there are no operational wind farms with DC collection grids, only theoretical and small-scale prototypes are being investigated worldwide. Therefore, a suitable configuration of the DC collection grid, which has been practically verified, is not available yet. This paper discussed some of the main components required for a DC collection grid including: the wind-turbine-generator models, the control and protection methods, the offshore platform structure, and the DC-grid feeder configurations. The key component of a DC collection grid is the power converter; therefore, the paper also reviews some topologies of power converter suitable for DC grid applications

Soft-Switched Step-Up Medium Voltage Power Converters

With a ten-year average annual growth rate of 19 percent, wind energy has been the largest source of new electricity generation for the past decade. Typically, an offshore wind farm has a medium voltage ac (MVac) grid that collects power from individual wind turbines. Since the output voltage of a wind turbine is too low (i.e., typically 400 690 V) to be connected to the MVac grid (i.e., 20 40 kV), a heavy line-frequency transformer is used to step up the individual turbines output voltage to the MV level. To eliminate the need for bulky MVac transformers, researchers are gravitating towards the idea of replacing the MVac grid with a medium voltage dc (MVdc) grid, so that MV step-up transformers are replaced by MV step-up power electronic converters that operate at the medium frequency range with much lower size and weight. This dissertation proposes a class of modular step-up transformerless MV SiC-based power converters with soft-switching capability for wind energy conversion systems with MVdc grid. This dissertation consists of two parts: the first part focuses on the development of two novel groups of step-up isolated dc-dc MV converters that utilize various step-up resonant circuits and soft-switched high voltage gain rectifier modules. An integrated magnetic design approach is also presented to combine several magnetic components together in the modular high voltage gain rectifiers. The second part of this dissertation focuses on the development of several three-phase ac-dc step-up converters with integrated active power factor correction. In particular, a bridgeless input ac-dc rectifier is also proposed to combine with the devised step-up transformerless dc-dc converters (presented in the first part) to form the three-phase soft-switched ac-dc step-up voltage conversion unit. In each of the presented modular step-up converter configurations, variable frequency control is used to regulate the output dc voltage of each converter module. The operating principles and characteristics of each presented converter are provided in detail. The feasibility and performance of all the power converter concepts presented in this dissertation are verified through simulation results on megawatts (MW) design examples, as well as experimental results on SiC-based laboratory-scale proof-of-concept prototypes

Soft-Switched Step-Up Medium Voltage Power Converters

With a ten-year average annual growth rate of 19 percent, wind energy has been the largest source of new electricity generation for the past decade. Typically, an offshore wind farm has a medium voltage ac (MVac) grid that collects power from individual wind turbines. Since the output voltage of a wind turbine is too low (i.e., typically 400 690 V) to be connected to the MVac grid (i.e., 20 40 kV), a heavy line-frequency transformer is used to step up the individual turbines output voltage to the MV level. To eliminate the need for bulky MVac transformers, researchers are gravitating towards the idea of replacing the MVac grid with a medium voltage dc (MVdc) grid, so that MV step-up transformers are replaced by MV step-up power electronic converters that operate at the medium frequency range with much lower size and weight. This dissertation proposes a class of modular step-up transformerless MV SiC-based power converters with soft-switching capability for wind energy conversion systems with MVdc grid. This dissertation consists of two parts: the first part focuses on the development of two novel groups of step-up isolated dc-dc MV converters that utilize various step-up resonant circuits and soft-switched high voltage gain rectifier modules. An integrated magnetic design approach is also presented to combine several magnetic components together in the modular high voltage gain rectifiers. The second part of this dissertation focuses on the development of several three-phase ac-dc step-up converters with integrated active power factor correction. In particular, a bridgeless input ac-dc rectifier is also proposed to combine with the devised step-up transformerless dc-dc converters (presented in the first part) to form the three-phase soft-switched ac-dc step-up voltage conversion unit. In each of the presented modular step-up converter configurations, variable frequency control is used to regulate the output dc voltage of each converter module. The operating principles and characteristics of each presented converter are provided in detail. The feasibility and performance of all the power converter concepts presented in this dissertation are verified through simulation results on megawatts (MW) design examples, as well as experimental results on SiC-based laboratory-scale proof-of-concept prototypes