Full-scale Power Converter Research Articles

Electronic Emulator of a Wind Energy System with Full-Scale Power Converter and Permanent Magnet Synchronous Generator

Electronic Emulator of a Wind Energy System with Full-Scale Power Converter and Permanent Magnet Synchronous Generator

A novel structure of magnetic geared generator in dual-rotor wind turbine

Variable-speed constant-frequency generating systems are commonly employed in wind turbines to enhance efficiency and minimize losses. Additionally, the utilization of dual-rotor wind turbines enables the capture of a greater amount of wind energy, leading to a significant increase in efficiency. Traditionally, dual-rotor wind turbines are managed by a full-scale power converter, and the rotor current is transmitted through brushes, which substantially raises the system's cost. To address these challenges, this study introduces a novel configuration that enables power control with a smaller power converter. In contrast to conventional dual-rotor wind turbines that generate power using both rotors, the proposed structure designates one rotor as a system controller. Apart from these benefits, the proposed structure greatly enhances conversion performance by notably improving the power factor. A comparison with existing configurations described in literature is conducted to demonstrate the superiority of the proposed structure.

Investigation of a converter fault for a DFIG wind turbine and analysis of the resulting gearbox component loads

Abstract Doubly fed induction generators are widely used in wind turbines in the field. The main advantage is the significantly lower cost of the partial scale power converter compared to the full scale power converter. Converter faults in wind turbines lead to significant generator torque excitations that lead to dynamic loads in the drivetrain. Dynamic loads and changing rotational speeds can lead to gearbox damages. The generator torque excitations have the highest influence on the high speed shaft torque due to the coupling to the generator. Gearbox damages occur mainly on the components of the high speed shaft. Thus, in this paper the influence of a converter fault in a wind turbine with doubly fed induction generator on the high speed shaft component damages is investigated. It is shown that the converter fault can induce dynamic torque excitations with a maximum increase to around 2.5 times rated torque. Due to the resulting dynamic gearbox loading the safety against scuffing in the high speed gear stage decreases by maximum 19 percent. The smearing risk in the high speed shaft bearings increases to around 2 times the value during rated power production.

A dynamic equivalent aggregation method of wind turbine systems with a full‐scale power converter for electromagnetic transient simulations

With the increasing exploitation of wind energy, the dynamic performances of large-scale wind farms (WFs) are vital for the system design and stability analysis. However, a detailed WF model considering every wind turbine system (WTS) makes the electromagnetic transient simulation time-consuming and computational-demanding. Therefore, a dynamic equivalent aggregation method is proposed for WTS with a full-scale power converter (WTS-FSPC) in this paper, in order to reduce the computational complexity meanwhile maintaining the same accuracy as the detailed model. To improve the accuracy of the equivalent collector system, the collecting strings are decoupled based on the power flow distribution. Then the WTSs are clustered according to the output AC voltage distributions using a Louvain K-means (LKM) algorithm, which innovatively determines the optimal solution automatically. Additionally, a centralized capacitor is set to represent the distributed capacitance of the collector system. Furthermore, to enhance the model adaptability during asymmetric short-circuit faults, the equivalent method for the zero-sequence collector system is introduced. Time-domain simulation results demonstrate the effectiveness and robustness of the proposed method in reflecting the WF dynamics. The case study in a 2-area system further verifies the superiority of the proposed method for the WF integrated power system stability analysis.

Grid Side Inverter Control for a Grid Connected Synchronous Generator Based Wind Turbine Experimental Emulator

This paper describes the real time implementation and control of a wind energy conversion chain emulator based on a synchronous generator (SG) using a full-scale power converter configuration. The proposed structure consists of the mechanical coupling of two 1.5 kW machines, a DC motor which emulates the static-dynamic behaviors of a three-blade wind turbine with a horizontal axis including an ideal gearbox, and a synchronous generator that ensures the electromechanical conversion and manages the different operating modes. The aim of the first part in this work is the design and the implementation of the control of the grid side converter in order to control the flow of the produced/consumed active and reactive power (PGSC / QGSC) in both directions between the generator and the grid. An improved experimental grid voltage vector-orientation control algorithm (VOC) is investigated and applied to the grid inverter to control the GSC powers independently and instantly. The control algorithms are implanted in C, using dSPACE DS1104 control board to drive the 6-IGBT’s inverter. The experimental results validate the effectiveness of the proposed control scheme of the GSC.

Accelerated Real-Time Simulations for Testing a Reactive Power Flow Controller in Long-Term Case Studies

This paper presents the development of an accelerated real-time cosimulation and testing platform, especially for long-term simulations of power systems. The platform is planned to be utilized in the development and testing of active network management functions for microgrids and smart grids. Long-term simulations are needed in order to study, for example, the potential weekly, monthly, or yearly usage of distribution-network-connected distributed energy resources for different technical flexibility services. In order to test new algorithms in long-term study cases, real-time simulations or hardware-in-the-loop tests should be accelerated. This paper analyzes the possibilities and challenges of accelerated long-term simulations in studying the potential use of a large-scale wind turbine for reactive power flow control between distribution system operator (DSO) and transmission system operator (TSO) networks. To this end, the reactive power flow control is studied for different voltage levels (HV and MV) in the Sundom Smart Grid in Vaasa, Finland. The control of reactive power flow between HV and MV networks is realized with a reactive power window control algorithm for a 3.6 MW MV-network-connected wind turbine with a full-scale power converter. The behaviour of the reactive power controller during long-term simulations is studied by offline and real-time simulations. Moreover, the real-time simulations are performed with both software-in-the-loop and controller-hardware-in-the-loop.

Evaluation of Reactive Power Support Capability of Wind Turbines

Reactive power plays an important role in the operation of power systems, especially in the case of wind energy integration. This paper aims to evaluate the reactive power support capability of wind turbines in both normal and voltage sag conditions. The three 2MW wind turbines studied are a fixed speed wind turbine and two variable speed wind turbines with full-scale and power-scale power converters. Comparison results indicate that at normal operation, the fixed speed wind turbine with a static synchronous compensator is able to consume the highest reactive power, while the variable speed wind turbine with full-scale power converter can supply the highest reactive power. In case of low voltage, the fixed speed wind turbine with the static synchronous compensator can support the highest reactive power if the static synchronous compensator’s capacity is similar to the wind turbine’s capacity, while if its capacity is equal to 25% of the generator’s capacity, the variable speed wind turbine with full-scale power converter has the best performance.

Control of Reactive Power for Stabilized Junction Temperature in Power Electronic Devices Serving to a 250-MW Asynchronous Hydrogenerating Unit

In order to enable a variable-speed operation in existing synchronous-machine-based fixed-speed pumped-storage power plant (PSPP), full-scale power converters are required. But it is not economical in case of large-size PSPP. Furthermore, full-scale power converters lead to increase the complexity of civil construction in case of underground powerhouses. Therefore, a doubly fed induction machine (DFIM) with a slip power rated power converter is an acceptable option for the storage dams with wide variation in water head (for e.g., Tehri Dam, India). In view of the reliability of converters used in such projects, thermal stress across the power semiconductor devices is a major cause for the failure of power converters. It is reported that 55% of failures in electric drives are due to thermal cycling or temperature rise in semiconductor devices. In consideration of this issue, this paper analyses active-thermal-control-based reactive power circulation in a five-channel parallel-connected back-to-back power converter fed 250-MW DFIM system (data collected from a 4 × 250 MW PSPP under construction at Tehri dam, India). The allowable limit of reactive power range is calculated in consideration of an operational strategy to be adopted, and the reactive power among the converters is circulated using the vector control technique. It is concluded that because of reactive power circulation among parallel-connected converters, temperature fluctuation is effectively stabilized. PLECS Blockset in MATLAB/Simulink software is used for this analysis. Experimental validation is carried out through a 2.2-kW scale-down DFIM laboratory prototype.

Control of variable-speed pumps used as turbines for flexible grid-connected power generation

The increasing accommodation of intermittent renewable energies into power grids creates needs for additional flexibility in power generation. In the field of hydropower research, this has translated into significant attention paid to the larger control possibilities brought by power electronics converters. Through theoretical analysis and transient simulations, the present paper investigates the power control of a pump-as-turbine fed by a reservoir, and driving an induction machine, itself connected to the grid through a full-scale power converter. The modelling of each part of the system is thoroughly discussed and two control strategies are considered, namely the direct control of power through the electromagnetic torque, and the indirect control of power through the rotational speed. Theoretical analysis and transient simulations show that the first control strategy may lead to unstable operation, depending on the system and control parameters, while the second ensures the system stability.

Modelling and simulation of variable speed pico hydel energy storage system for microgrid applications

Abstract The scheduling and dispatch of stochastic renewable energy sources can be difficult in a Microgrid (MG). Renewable energy sources can power the MG reliably if supported by energy storage systems, via hierarchical control of the MG. In this work, a sustainable energy storage system is modelled with the existing resources in an agricultural farm. The resource is a downscaled pumped hydro storage system called Pico Hydel Energy Storage System (PHESS). The PHESS is numerically modelled with the governing equations of various components in the system. The proposed configuration caters for the water demand of crops and the energy storage requirement in a renewable energy powered microgrid. A full scale power converter topology is employed for variable speed operation of the proposed energy storage system. The power absorbed from the microgrid and injected into the microgrid is controlled by adjusting the speed of PHESS. An adaptive perturb and observe algorithm is developed to control the storage system in the generating mode, thus enabling the maximum extraction of power at various discharge rates and hydraulic head. A relationship between the power and speed of the turbine is deduced through regression analysis to control the storage system in pumping mode. The proposed model of PHESS is optimized to accept power commands directly from the MG controller for various levels of controls in the MG thus ensuring plug and play feature. The results obtained from MATLAB/Simulink software justify the effectiveness of the control strategies in both modes of operation.

Guest Editorial

Guest Editorial

Real-Time Power-Hardware-in-the-Loop Implementation of Variable-Speed Wind Turbines

This paper presents the real-time (RT) power-hardware-in-the-loop (PHIL) emulation of the two most popular variable-speed wind turbines (WT): the doubly-fed induction generator WT with partial-scale power converter and the permanent-magnet synchronous machine WT with full-scale power converter. RT-PHIL emulation offers a realistic, controlled, and easily reconfigurable test environment for analyzing grid integration problems, in which classic tools frequently show a lack of capacity. The proposed discrete-time models and implementation methodology result in creation of platform-independent models suitable for application on any RT platform. A voltage-source converter is used as PHIL power interface between the RT simulation and a microgrid testbed. This test environment is of interest for verification of high-level control strategies for wind farms and for evaluation of the response of hardware systems, such as active filters or static synchronous compensators (STATCOMs) connected to a grid (or microgrid) in presence of wind power generation. The RT discrete models of both WTs are demonstrated in a grid-connection experiment.

Control strategy of wind turbine based on permanent magnet synchronous generator and energy storage for stand-alone systems

This paper investigates a variable speed wind turbine based on permanent magnet synchronous generator and a full-scale power converter in a stand-alone system. An energy storage system(ESS) including battery and fuel cell-electrolyzer combination is connected to the DC link of the full-scale power converter through the power electronics interface. Wind is the primary power source of the system, the battery and FC-electrolyzer combination is used as a backup and a long-term storage system to provide or absorb power in the stand-alone system, respectively. In this paper, a control strategy is proposed for the operation of this variable speed wind turbine in a stand-alone system, where the generator-side converter and the ESS operate together to meet the demand of the loads. This control strategy is competent for supporting the variation of the loads or wind speed and limiting the DC-link voltage of the full-scale power converter in a small range. A simulation model of a variable speed wind turbine in a stand-alone system is developed using the simulation tool of PSCAD/EMTDC. The dynamic performance of the stand-alone wind turbine system and the proposed control strategy is assessed and emphasized with the simulation results.

Analysis of Dynamic Interactions between Different Drivetrain Components with a Detailed Wind Turbine Model

The presented work describes a detailed analysis of the dynamic interactions among mechanical and electrical drivetrain components of a modern wind turbine under the influence of parameter variations, different control mechanisms and transient excitations. For this study, a detailed model of a 2MW wind turbine with a gearbox, a permanent magnet synchronous generator and a full power converter has been developed which considers all relevant characteristics of the mechanical and electrical subsystems. This model includes an accurate representation of the aerodynamics and the mechanical properties of the rotor and the complete mechanical drivetrain. Furthermore, a detailed electrical modelling of the generator, the full scale power converter with discrete switching devices, its filters, the transformer and the grid as well as the control structure is considered. The analysis shows that, considering control measures based on active torsional damping, interactions between mechanical and electrical subsystems can significantly affect the loads and thus the individual lifetime of the components.

Physical Concepts Related to Harmonics Produced by Wind Turbines Operation

The increasing demand for low environmental impact energy resources has intensified the importance of wind farms in many countries. However, several technical discussions about the integration of these generators to electrical networks are motivated by the harmonic distortion impacts on the coupling bus. In fact, power electronics devices play an important role in different wind generation schemes, although its harmonic emission affect directly the voltage quality standards. In this context, this work aims at reviewing the operational characteristics of wind turbines with synchronous machines and full-scale power converters, regarding the main factors responsible for harmonic generation. The theoretical concepts presented throughout the paper are supported by computer modelling and simulation, as well as field measurements on a real wind power plant.

Multiple Open-Circuit Faults Diagnosis in Back-to-Back Converters of PMSG Drives for Wind Turbine Systems

In order to increase the reliability and availability of wind turbines, condition monitoring and fault diagnosis are considered crucial means to achieve these goals. In this context, direct drives wind turbines based on permanent-magnet synchronous generators (PMSGs) with full-scale power converters are an emerging and promising technology. However, several statistical studies point out that power converters are a significant contributor to the overall failure rate of modern wind turbines. Accordingly, this paper presents a new algorithm for multiple open-circuit faults diagnosis in full-scale back-to-back converters, applied in PMSG drives used for wind turbine systems. The proposed method is based on a Luenberger observer and on an adaptive threshold, which can guarantee a reliable diagnosis independently of the drive operating conditions. Several simulation and experimental results using a PMSG drive with a full-scale converter are presented, showing the diagnostic algorithm effectiveness and robustness against false alarms for both generator- and grid-side converters.

Backup Control of Wind Power Generation System Based on Voltage-Sensorless and LCL Active Damping Scheme

Under the fault condition of voltage sensors, the wind power generation system requests an effective backup control scheme without voltage sensors. In order to save sensors for the grid-connected inverter (GCI) with LCL-filter in the full-scale wind power converter, a grid-side voltage-sensorless solution scheme is presented in this paper. A frequency-adaptive SOGI (FA-SOGI) is introduced to realize the virtual flux (VF) estimation. A grid-side voltage observer is thus designed to acquire the phase angle and amplitude, which can realize voltage orientation control (VOC) for the GCI system. With an improved feedback damping method for LCL filter, a full control strategy of the full-scale wind power generation system is given and explained in detail. All theoretical results have been validated by the simulation, followed by analysis and discussion.

Dynamics and Control of Lateral Tower Vibrations in Offshore Wind Turbines by Means of Active Generator Torque

Lateral tower vibrations of offshore wind turbines are normally lightly damped, and large amplitude vibrations induced by wind and wave loads in this direction may significantly shorten the fatigue life of the tower. This paper proposes the modeling and control of lateral tower vibrations in offshore wind turbines using active generator torque. To implement the active control algorithm, both the mechanical and power electronic aspects have been taken into consideration. A 13-degrees-of-freedom aeroelastic wind turbine model with generator and pitch controllers is derived using the Euler–Lagrangian approach. The model displays important features of wind turbines, such as mixed moving frame and fixed frame-defined degrees-of-freedom, couplings of the tower-blade-drivetrain vibrations, as well as aerodynamic damping present in different modes of motions. The load transfer mechanisms from the drivetrain and the generator to the nacelle are derived, and the interaction between the generator torque and the lateral tower vibration are presented in a generalized manner. A three-dimensional rotational sampled turbulence field is generated and applied to the rotor, and the tower is excited by a first order wave load in the lateral direction. Next, a simple active control algorithm is proposed based on active generator torques with feedback from the measured lateral tower vibrations. A full-scale power converter configuration with a cascaded loop control structure is also introduced to produce the feedback control torque in real time. Numerical simulations have been carried out using data calibrated to the referential 5-MW NREL (National Renewable Energy Laboratory) offshore wind turbine. Cases of drivetrains with a gearbox and direct drive to the generator are considered using the same time series for the wave and turbulence loadings. Results show that by using active generator torque control, lateral tower vibrations can be significantly mitigated for both gear-driven and direct-driven wind turbines, with modest influence on the smoothness of the power output from the generator.

Modelling of a synchronous offshore pumping mode airborne wind energy farm

A wind farm for the deployment of pumping mode AWE (airborne wind energy) systems is presented in this paper. The topology presented is suitable for the deployment of such systems in a marine or similarly inaccessible environment. A brief technical description of AWE is provided, outlining the background, motivation and approaches taken by this emerging technology. A method of providing a continuous power supply from a cluster of AWE systems whose individual operation produces a periodic power supply is outlined. This method employs direct drive, directly interconnected permanent magnet synchronous generators on a local bus. A full-scale power converter is located at the point of grid connection, providing compliant power output for the remote cluster. In the case of a marine environment deployment, the power electronics are located onshore where maintenance and repair can be readily performed without the delays and costs associated with offshore maintenance and repair. The direct interconnection of synchronous generators introduces the requirement for a control system to control the connection of offline machines to the energised bus. A mathematical model of the system is outlined and the implementation of this model in Simulink is detailed. Simulation results under varied operating conditions are presented and discussed.

Analysis of the short-term overproduction capability of variable speed wind turbines

Emphasis in this article is on variable speed wind turbines (VSWTs) capability to provide short-term overproduction and better understanding of VSWTs' mechanical and electrical limits to deliver such support. VSWTs' short-term overproduction capability is of primary concern for the transmission system operators (TSOs) in the process of restoring critical situations during large frequency excursions in power systems with high wind power penetration.This study is conducted on a simplified generic model for VSWTs with full scale power converter (Type IV), which includes several adjustments and extensions of the Type IV standard wind turbine model proposed by the IEC Committee in IEC 61400-27-1. This modified standard model is able to account for dynamic features relevant for integrating active power ancillary services in wind power plants, such as frequency support capabilities.The performance of VSWTs during short-term overproduction is assessed and discussed by means of simulations for different wind speed levels, overproduction percentages and durations. The results show that the capability of VSWTs providing short-term overproduction to the grid strongly depends on the initial pre-overproduction conditions.