Types Of Wind Turbine Generators Research Articles

Power system stability improvement considering drive train oscillations of virtual synchronous generator‐regulated type‐4 wind turbines

The type-4 wind turbine generators (WTGs) can provide inertial frequency response by implementing the virtual synchronous generator (VSG) concept. However, unstable torsional oscillations (TOs) would be induced in the multi-mass-spring drive-train which can destabilize the entire power system. In this study, participation factor analyses are performed for a power system inclusive of a thermal unit and aggregated WTG system. The system's eigenvalues are characterized and the possible detrimental impacts of TOs on the inertia provision process and overall power system stability are demonstrated and the related stability limits are identified. A comprehensive active torsional oscillations damper (CA-TOD) and a supercapacitor-based energy storage system (ESS) are presented and discussed to implement the CA-TOD. A state of charge (SoC) regulator is also employed to set the reference speed difference for the turbine-generator. Small-signal studies and electro-magnetic transient (EMT) simulations are performed to evaluate the functionality of the CA-TOD and SoC controller and estimate their impacts on the system's dynamics. The robust performance of the CA-TOD is compared to the band-pass filter-based TOD by sweeping key control parameters of the VSG and emulating drive-train parameter uncertainty. Key results are cross-verified by EMT simulations of a multimachine power system.

Sustainability assessment of products - Case study of wind turbine generator types

This study proposes a product sustainability assessment tool (PSAT) that addresses the environmental, health and safety, social, and economic sustainability aspects from a life cycle perspective. The proposed PSAT uses the principles of Green Chemistry, Industrial Ecology, and Green Engineering as guidelines in the development of its assessment criteria. The developed assessment criteria are expressed as easy-to-answer questions covering the environmental, social, health and safety and economic aspects of sustainability. PSAT also incorporates life cycle assessment impact categories and the Circular Economy approach. PSAT comprises an Excel checklist of a questionnaire with a drop-down list of answers to select from describing the sustainability impact of the assessed product. PSAT serves to highlight the sustainability hotspots in a product's life cycle. The questionnaire consists of qualitative and quantitative assessment criteria and contains a total of 97 questions, out of which there are 11 design questions, 22 materials selection questions, 31 manufacturing questions, 24 use questions, and 9 end-of-life questions. The PSAT scoring system enables users to compare the sustainability performance of their products. PSAT aims to aid users in making informed decisions before purchasing a product based on the information on how the product is designed and what materials it contains, how it was manufactured, how it will perform during its use, and what will happen at the end of its useful life. It also aims to aid product manufacturers and designers in incorporating sustainability into all stages of the product life cycle. The PSAT methodology promotes a holistic view of a product life cycle, including the design, materials selection, manufacturing, use, and end-of-life stage.As a case study, PSAT was used to perform a comparative sustainability assessment of two types of 3 MW rated power wind turbines: a direct-drive permanent magnet synchronous generator (PMSG) and a doubly-fed induction generator with a gearbox (DFIG). The results from the sustainability assessment reveal that the DFIG wind turbine had a better sustainability impact than the direct-drive PMSG in the materials selection, manufacturing, and end-of-life life cycle stages. On the other hand, the direct-drive PMSG had a better sustainability impact than DFIG in the life cycle stages design and use. Overall, DFIG demonstrated a better sustainability impact than the direct-drive PMSG.

A new differential protection algorithm for transmission lines connected to large-scale wind farms

The fluctuated output power of the large-scale wind farms (WF) and their fault transient characteristics have an adverse effect on the current differential protection systems of the transmission lines. With increased transmission line length and in the case of weak output power from the WF, the differential current between both line ends increases in normal conditions since the capacitive current is comparable to the load current. This paper proposes a new differential protection algorithm for transmission lines connected to large-scale wind farms. The proposed current differential protection algorithm is developed based on the signs of the phase current samples at both line ends, instead of utilizing directly the current magnitudes. The similarity between the signs of the phase current samples at both line ends is evaluated utilizing the signed correlation criterion, and the fault detection index is calculated to discriminate the internal faults from other events. In addition, a new online technique is introduced to adjust the protection settings considering the different output power levels of the WF. The conducted PSCAD/EMTDC simulation studies confirm the acceptable performance of the proposed protection algorithm for numerous normal and fault scenarios, including different fault resistances and inception angles as well as all fault types. The effect of line length, type of wind turbine generator, and different values of WF output power are also considered.

Optimization study of the main parameters of different types of wind turbine generators * * This work was supported in part by the National Natural Science Fund under Grant 52071090, in part by the Doctoral Start-up and Postgraduate Fund under Grant R17062, and in part by the Young Innovative Talents in Colleges and Universities of Guangdong Province under Grant 2019KQNCX046.

The research and development of large-scale wind turbine generators have become a future trend in green renewable energy field from the dual perspectives of the environment and economics. In this work, an electrical design method is first proposed and applied to different types of wind turbine generators, including the high-temperature superconducting (HTS), the permanent magnet, and the traditional copper generators. The optimal electrical designs of the three types of 10 MW wind turbine generators are then created based on the developed design program. Second, the influences of the rated revolution on the basic performance parameters of the HTS generator are investigated, and the results are compared with those of the other two types of generators. It is found that the generator weight decreases with the increases of the rated revolution and the stator outer diameter, and the optimal rated revolution for a generator with a large stator outer diameter is determined to be 40 min−1. Moreover, the weight of the field parts is found to have the same regulation rule as the generator weight. Finally, the design results of the three types of wind turbine generators are comparatively discussed, and it is found that the HTS wind turbine generator is superior to its two counterparts.

Sustainability Assessment of Products - Case Study of Wind Turbine Generator Types

Sustainability Assessment of Products - Case Study of Wind Turbine Generator Types

Adaptive MPPT control applied to virtual synchronous generator to extend the inertial response of type-4 wind turbine generators

The increasing penetration level of wind generation in power systems has resulted in the degradation of the system frequency response and stability issues, where the decrease of the system equivalent inertia is one of the main causes of these problems. In this context, this work proposes an operational and control approach to provide emulated inertial response to wind turbine generators based on fully rated converter that operate at the maximum power point. The inertial response of the wind turbine generator is extended by a control strategy that combines an adaptive MPPT control with an adaptive inertia control based on virtual synchronous generator. The proposed approach mitigates the antagonistic interaction between the traditional MPPT control and inertia control. The impact of the MPPT control and inertia control on the dynamics of the wind turbine and system frequency is comprehensively addressed. The results have shown that the proposed strategy is effective in extending the inertial response of the wind turbine generator and mitigating the amplitude of the second frequency dip and electromechanical oscillations caused by the conventional MPPT control. The adaptive inertia control also prevents the violation of the minimum speed limit of the wind turbine

Generic EMT modeling method of Type-4 wind turbine generators based on detailed FRT studies

Developing effective electromagnetic transient (EMT) models of wind turbine generators (WTGs) is essential for power system transient analysis. However, manufacturer-specific EMT models are usually available as black boxes, which is not easy to be used in practical applications. To address this issue, a four-step generic EMT modeling method is proposed for type-4 WTGs based on detailed fault ride-through (FRT) studies. Step one, massive FRT field tests are conducted on type-4 WTGs, and generic FRT responses of active and reactive power are extracted and parameterized to characterize a wide variety of controller strategies of various vendors; Step two, piecewise expressions of active and reactive power responses are derived to formulate the detailed FRT processes, including the FRT control process during a fault, post-fault recovery control process, and their switching transients; Step three, a generic controller, to emulate the FRT responses, is implemented in the WTG model by automatically updating current references utilizing the derived analytical formulation; Step four, a stepwise identification method is proposed to identify the FRT control parameters, proportional-integral controller parameters, and circuit parameters. The proposed modeling method is verified by field tests, and the results show that the developed model can accurately capture the FRT behaviors of practical type-4 WTGs.

Voltage stability analysis of wind power plant integration into transmission network of Nepal

Government of Nepal has realized that wind energy could become a major source of alternative energy to solve energy crisis in the country as well as serve the purpose of energy mix. Various studies have identified several locations with potential for wind power generation in Nepal. The integration of wind power plant to the national grid, however, raises concerns regarding the power system stability. The voltage stability of the grid is a key issue, the effect on which increases with the increase in wind power penetration in the grid. This study performs voltage stability analysis due to high penetration of wind power in Integrated Nepalese Power System (INPS). Both steady state and dynamic stability study is performed using the power system simulation software DigSILENT/PowerFactory for different types of wind turbine generators.

Review on Dynamic Simulation of Wind Diesel Isolated Microgrids

Wind diesel isolated microgrids (WDIMs) combine wind turbine generators (WTGs) with diesel generators (DGs) to supply electricity to remote consumers. WDIMs are low-inertia isolated power systems where large system frequency and voltage variations occur. WDIM dynamic modeling allows short-term simulations to be performed and detailed electrical variable transients to be obtained so that the WDIM power quality and stability can be tested. This paper presents a literature review about WDIM dynamic simulation. The review classifies articles according to factors such as the different WDIM operation modes (diesel only, wind–diesel and wind only) simulated, the types of WTGs used in the WDIM (constant- and variable-speed types), or the use of different short-term energy storage technologies (batteries, ultracapacitors, flywheels) to improve the WDIM power quality, stability and reliability. Papers about the dynamic simulation of related isolated microgrids are also reviewed. Finally, as an example of WDIM dynamic simulation, a WDIM with one WTG, one DG, load and a discrete dump load (DL) is modeled and simulated. The WDIM response to variations of wind speed and load consumption is shown by graphs of the main electrical variables. The simulations show how the DL is used to improve the WDIM stability and reliability.

Direct method for transient stability assessment of a single wind turbine generator subject to LVRT requirements

The authors report on a step towards the development of direct methods for transient stability assessment of power systems with integrated wind turbine generators subject to low voltage ride-through constraints. In this study, they propose an approach to assess transient stability of a single wind turbine generator against an infinite bus using an energy function along with an extension of the potential energy boundary surface method. The proposed approach exploits the theory of constrained dynamical systems and the concept of constrained stability region to efficiently estimate critical clearing times taking into account not only the issue of stability due to rotor acceleration but also the issue of operational limit violations, such as low-voltage ride-through curve violations. Very often, wind turbine generators are disconnected due to violation of operational limits, such as under-voltage limits, instead of rotor acceleration. The proposed approach correctly estimates the critical clearing times to avoid operational limit violations, such as the low-voltage ride-through constraint violation, while traditional direct methods would fail to appropriately estimate such clearing times. They illustrate the effectiveness of the proposed approach by means of case studies considering two types of wind turbine generators, the fixed- and limited-variable-speed wind turbine generators.

Modeling and Simulation of Zafarana Wind Farm (Dept.E)

The wind turbines are classified according to their control strategy to fixed speed and variable speed turbines. The most common control strategies are stall, pitch and active stall. Each control strategy is coupled to either squirrel cage induction generator, doubly fed induction generator or direct drive synchronous generator. Zafarana wind farm which has already reached a capacity of 425 MW is the largest installed wind farm in the Middle East and Africa. Both fixed and variable speed wind turbines are used in Zafarana wind farm. This paper introduces steady state models of different types of Wind Turbine Generators (WTGs) used in Zafarana wind farm in terms of calculated performance coefficient, active power, and reactive power. The derived models are verified using actual data measured from the site as a very good approximation. So, they are used for further analysis. A complete power flow analysis of the Egyptian grid portion that contains Zafarana wind farm (Canal Zone that is represented by 34 bus system) is performed. Also the impact of interconnecting Zafarana wind farm on the Canal Zone voltage stability is evaluated by obtaining the expected voltage stability margin at each wind speed and accumulating for all expected wind speed values on the site.

Developing a Mathematical Model for Wind Power Plant Siting and Sizing in Distribution Networks

Wind Power Plants (WPPs) are generally located in remote areas with weak distribution connections. Hence, the value of Short Circuit Capacity (SCC), WPP size and the short circuit impedance angle ratio (X/R) are all very critical in the voltage stability of a distribution system connected WPP. This paper presents a new voltage stability model based on the mathematical relations between voltage, the level of wind power penetration, SCC and X/R at a given Point of Common Coupling (PCC) of a distribution network connected WPP. The proposed model introduces six equations based on the SCC and X/R values seen from a particular PCC point. The equations were developed for two common types of Wind Turbine Generators (WTGs), including: the Induction Generator (IG) and the Double Fed Induction Generator (DFIG). Taking advantage of the proposed equations, design engineers can predict how the steady-state PCC voltage will behave in response to different penetrations of IG- and DFIG-based WPPs. In addition, the proposed equations enable computing the maximum size of the WPP, ensuring grid code requirements at the given PCC without the need to carry out complex and time-consuming computational tasks or modelling of the system, which is a significant advantage over existing WPP sizing approaches.

Operating point optimization of wind turbine generators for provision of inertial response and frequency control

Inertial and frequency control approaches for wind turbine generators have proven to be effective in mitigating the frequency control and stability problems inherent to power systems and microgrids with high penetration levels of wind generation. This paper proposes an optimization formulation to determine the operating point of de-loaded wind turbines in order to improve the mechanical dynamics of the wind turbine-generator set. Such operating point optimization reduces the speed deviation magnitude and settling time of the wind turbine caused by the action of inertial and frequency control. The optimization approach is integrated into a combined inertial and frequency control approach for type-4 wind turbine generators. The optimized control approach, based on the concept of virtual synchronous generator, may extend the inertial response and frequency control capabilities of type-4 wind turbine generators, thus improving the transient and steady-state frequency performance of high wind penetrated power systems.

Identifying the Source of Subsynchronous Control Interaction via Wide-Area Monitoring of Sub/Super-Synchronous Power Flows

With the increasing penetration of converter based renewable generators into the modern power systems, subsynchronous control interaction (SSCI) phenomenon is jeopardizing the equipment safety and system stability. For the analysis and prevention, it is critically important to identify the source of such sub/super-synchronous oscillation caused by the SSCI. This article first develops three criteria for determining the SSCI sources based on sub/super-synchronous powers and impedances. One of the criteria takes into account the coupling effects between sub- and super-synchronous frequencies. Then, a general framework for the SSCI source identification is established, which is based on wide-area monitoring of the sub/super-synchronous power flows obtained from measured voltage and current phasors. Finally, the proposed identification criterion and framework are verified on the electromagnetic transient model of the Hami wind power system, which has experienced an actual SSCI incident. The results indicated that the wind farms based on type-4 wind turbine generators were the main sources of oscillation, while nearby thermal power plants were the sinks.

Assessment of subsynchronous oscillations in AC grid‐connected VSC systems with type‐4 wind turbines

Converters are the key for increasing the development of renewable energy generation but their dynamic interaction with the grid has an important impact on stability. Oscillatory instabilities in different grid-connected converter systems at several frequency ranges are reported. In particular, sub and supersynchronous oscillatory instabilities in AC power systems with type-3 and type-4 wind turbine generators (WTGs) were recently registered at several wind farm areas. A number of works based on eigenvalue analysis and frequency domain approaches are carried out to analyse this new stability issue and more research is going on to analyse in detail the electric and control parameters that may affect this phenomenon. This study contributes analysing in detail the influence of system parameters on the subsynchronous oscillations (SSOs) in AC power systems with type-4 WTGs. This study is based on a new approach for subsynchronous stability assessment which could also be used for analysing other types of SSOs (e.g. subsynchronous control interactions between doubly-fed induction generators and series-compensated networks) as well as supersynchronous oscillations. A representative example of weak AC grids with type-4 WTGs is used to illustrate the contributions of the study. Results are validated with PSCAD/EMTDC time-domain simulations.

Impacts of Grid Frequency Variation on Dynamic Performance of DFIG Based Wind Turbine

Wind energy is one of popular sources of renewable energy that massively used to generate electric power nowadays. Among wind generator technologies, Doubly Fed Induction Generator (DFIG) is placed as the first dominant wind generator type that is installed worldwide since 2004. Its popularity is due to the advantages of its capability to extract more energy compare to the fixed speed type. Moreover, it uses only one-third converter size which reduced the total construction cost compared to its closest rival, Full Converter Wind Turbine Generator Type. Although DFIG widely installed worldwide, it is in fact, very sensitive to the grid disturbances such as frequency variation. Based on IEEE standard for 60 Hz system, a power system should not be allowed to work in less than 59.3 Hz or more than 60.5 Hz. In this paper, DFIG-grid connected is extensively simulated in the condition of frequency variation that is carried out using Matlab/Simulink. The results show that some important parameters such as power output of the generator, voltage at point of common coupling, voltage at DC link and generator speed are experiencing significant rise/drop which in turn might damage the wind turbine generator.

Frequency-Coupling Admittance Modeling of Converter-Based Wind Turbine Generators and the Control-Hardware-in-the-Loop Validation

Recently, sub- and super-synchronous oscillation (SSO) associated with converter-based wind turbine generators (WTGs) has been attracting wide attentions. To investigate such SSO incidents, impedance or admittance-based modeling and analysis were widely used. It was discovered that coupling effects exist between impedances or admittances at complementary (i.e., sub and super-synchronous) frequencies. However, there is a lack of experimental validation on the coupling effects of different WTGs. In this paper, the frequency-coupling admittance models (FCAMs) of two types of widely adopted WTGs, i.e., direct-drive and doubly-fed WTGs, are presented at first. Secondly, a perturbation based identification method is proposed to obtain the FCAMs. Next, the method is implemented in a control-hardware-in-the-loop (CHIL) platform based on RTDS. Then with extensive CHIL tests, the FCAMs of both types of WTGs are obtained, and the impacts of frequency-coupling effects on SSO are validated. Finally, the characteristics of frequency-coupling effects and the root causes are further examined. This study is of important reference value to select appropriate models for oscillatory stability analysis.

Impact of Superconducting Magnetic Energy Storage Unit on Doubly Fed Induction Generator Performance During Various Levels of Grid Faults

Since 2004, Doubly Fed Induction Generator (DFIG) has become the most admired wind turbine generator type that is widely installed worldwide. The popularity of DFIG is due to its capability to extract more energy than fixed speed wind turbine generator type. Moreover, a DFIG requires only one-third of the full converter size used by type-4 wind turbine generator which in turn reduces the total cost of DFIG installation. The main weakness of DFIG is its vulnerability to grid faults such as voltage dip and swell. Grid faults may have adverse impacts on the overall performance of the DFIG including the voltage at the point of common coupling that, at certain fault levels, may violate the permissible margins of the grid codes established by the transmission line operators. This paper investigates the application of Superconducting Magnetic Energy Storage (SMES) unit to improve the fault ride-through capability of a DFIG during grid faults. Results show that the connection of a SMES unit at the point of common coupling between the DFIG and the grid can enhance the overall performance of the DFIG during such faults events.

Dynamic performance comparison of DFIG and FCWECS during grid faults

Among several types, variable speed-based wind turbine generator (WTG) is the most popular type installed worldwide. This type of WTG is able to extract 5% more energy from wind speed compared to the fixed speed WTG. There are two kinds of variable speed based WTG; Doubly Fed Induction Generator (DFIG) and Full Converter Wind Energy Conversion System (FCWECS). DFIG and FCWECS are placed at the first and second topWTG installation worldwide since 2004. However, both of them are very sensitive to the grid dip fault and may violate the allowable margins identified by various international Fault Ride Through (FRT) codes. This paper aims to investigate the responses of DFIG and FCWECS during certain level of grid dips and compare their performanceunder such event. Results show some differences of the performance of DFIG and FCWECS during voltage sag event, however the voltage profile at the point of common coupling is much better in case of DFIG. Results also recommend that DFIG can be effective when connected to weak grids whilst FCWECS is preferably to be connected to strong grids.

Phase\u2013amplitude model for doubly fed induction generators

The doubly fed induction generator (DFIG) is major type of wind turbine generator used in grid-connected wind farms. Practical models of DFIG have been built to study the influence of wind power generation on power system dynamics. However, most existing practical models of the DFIG are based on rectangular coordinates, in which frequency variation is neglected. In this paper, a phase–amplitude (P–A) model is proposed for a DFIG based on phase and amplitude of the internal voltage. The model structure is much like that of the synchronous generator, and the rotor voltage can manipulate both the amplitude and the phase of the internal voltage. Comparisons have been made between the new P–A model of the DFIG and the synchronous generator model, as well as the asynchronous motor model. The contributions of the new P–A model of the DFIG are discussed and it is demonstrated that the proposed model has better ability in describing power system dynamic phenomena such as voltage dynamics and structural dynamics in general. Simulation results and a field test validate these contributions.