Wind Turbine Converter Research Articles

MPC based fault tolerance control of AC–DC power converters for offshore wind turbines

MPC based fault tolerance control of AC–DC power converters for offshore wind turbines

Virtual impedance optimization control strategy for wind turbine grid-forming converters in weak grid

Abstract Grid forming(GFM) technology is key to the effective consumption and grid-friendly integration of large-scale wind power. However, as the new type of power system sees a high penetration of new energy sources and a decrease in circuit capacity, leading to systems exhibiting weak grid characteristics, this paper studies the adaptive characteristics of grid-forming wind turbine converters under weak grid conditions. It investigates the dynamic relationship between power coupling characteristics and the system impedance ratio based on the virtual impedance method and proposes an impedance optimization method to improve the power decoupling accuracy and dynamic response capability of grid-forming converters. The research results show that the grid-forming controller can operate stably under weak grid conditions, an increase in grid impedance ratio leads to stronger power coupling intensity, and the voltage support capability of grid-forming converters weakens. The simulation verifies that the virtual impedance optimization strategy proposed in this paper can effectively improve the power coupling characteristics of the grid-forming converter and enhance the converter’s dynamic response performance under weak grid conditions.

Understanding wind turbine power converter reliability under realistic wind conditions

AbstractThe reliability of wind turbine power converters is crucial for analyzing wind energy project costs, and for estimating maintenance and downtime. The published literature in this field relies on evaluating the reliability effect of wind speed to estimate the converter lifetime. However, this paper demonstrates that wind turbulence intensity, which has not been widely considered in similar reliability analyses, shows a significant impact on converter lifetime. This paper uses 821 10‐min wind speed time series sampled at 1 Hz on the two most commonly deployed wind turbine converter topologies: the two‐level voltage source and the three‐level neutral point clamped. Electromechanical and thermal modelling, combined with statistical analysis shows that mean wind speed and turbulence intensity both impact the lifetime of both converter topologies. However, the paper estimates that the three‐level converter can operate 2.4 to 4.0 times longer than the two‐level converter depending on the operating wind speed and turbulence intensity.

МАТЕМАТИЧЕСКОЕ И КОМПЬЮТЕРНОЕ МОДЕЛИРОВАНИЕ ПРЕОБРАЗОВАТЕЛЯ ДЛЯ МАЛОЙ ВЕТРОУСТАНОВКИ

Relevance The importance of using non-traditional energy sources is evidenced by the decision to provide subsidies from the federal budget for state support for technological connection of generating facilities operating on the basis of the use of renewable energy sources (RES). As part of the state policy aimed at improving energy efficiency and developing the use of renewable energy sources, mechanisms are provided to support the stimulation of electric energy production by generating facilities operating on the basis of the use of renewable energy sources. Aim of research In this paper, the development and research of a power converter for wind energy that meets the requirements of highly efficient alternative energy sources is carried out. The developed converter can be used by models. The article is devoted to the analysis of the weaknesses of traditional power converters and the development of solutions to improve their efficiency and reliability. Research methods This work consists in creating a computer model for the wind energy system in the Matlab/Simulink program. The model is focused on the characteristics of a specific wind turbine and includes elements for converting and controlling electricity, such as a generator, rectifier and inverter, as well as a component that simulates the physical operation of a windmill. The selected components make it possible to accurately simulate both the electrical and mechanical parts of the wind power system. Results The authors consider the possibility of developing a power converter for wind energy that meets the requirements of highly efficient alternative energy sources. Mathematical and computer modeling of a converter for a small wind turbine has been performed. The novelty of the work consists in the development of a model in the Simulink program of the Matlab converter software package for a small wind turbine, taking into account the parameters of a WH8-10000W type wind generator and consisting of a virtual PMGM, a rectifier, a pulse inverting stabilizer, an inverter, which were taken from the Specialized Power Systems library, as well as a system simulating the mechanical part of a wind generator. This article presents the results of the calculation and selection of the elements of the electrical schematic diagram of the developed and investigated converter of a small wind turbine. Based on the results of a study performed using computer simulation of a converter for a small wind turbine with a power source from a wind generator, graphs of converter currents and voltages were constructed and analyzed. Acknowledgments: The research was carried out using a grant from the President of the Russian Federation in 2022-2024 for young scientists and graduate students carrying out promising scientific research and development in priority areas of modernization of the Russian economy. Grant recipient is Regina Tagirovna Khazieva. The priority direction of modernization of the Russian economy (direction of competition No. SP-2022 of the Grant Council of the President of the Russian Federation) is «Energy Efficiency and Energy Saving, Including Issues of Developing New Types of Fuel». Research topic: «Development and Research of a Filter Compensating Device to Improve the Quality of Electricity».

Impact of LVRT Control on Transient Synchronizing Stability of PLL-Based Wind Turbine Converter Connected to High Impedance AC Grid

With large scale of wind turbines connected to high impedance AC grid, transient synchronizing stability of PLL (phase locked loop) based WTC (wind turbine converter) during LVRT (low voltage ride through) is increasing concerned. However, the existing research is usually carried out at the assumption of constant current injection. The influence of dynamic current injection adjusted by LVRT control is neglected. Yet, in high impedance AC grid, the dynamic current injection significantly affects the terminal voltage tracked by PLL. Then LVRT control has much impact on the transient synchronizing stability, which is concerned especially in this paper. First, an novel equivalent motion model is developed, in which PLL is modelled in the form of rotor motion and LVRT control adjusts its equivalent driving force similar as governor in synchronous generator. Then based on the developed model, accelerating-decelerating area method is employed to reveal the transient stability mechanism from energy's transformation and dissipation. Transient stability region method is employed to present the visualized stability region. Furtherly, the influence of K-factor, grid impedance and grid voltage sag are studied from the influence of them on accelerating-decelerating area and stability region. Finally, simulated results are presented to verify the analytical results.

Rotor Voltage Compensation Control Strategy of Double-fed Wind Turbine Considering Stator Flux Transient Characteristics

The stability of the grid voltage is directly related to the stability of the DFIG operation, which is related to the topology of the DFIGURE After the grid failure, the rotor current will be too large if the stability threshold is exceeded continuously. The current low voltage control uses additional hardware measures to make the wind turbines survive under the impact of grid voltage drop. Because additional hardware measures will increase the investment of the system, this paper proposes an additional control of the rotor-side converter of the double-fed wind turbine considering the stator flux linkage. The output voltage of the converter is increased through the compensation of additional control to suppress the excessive rotor current. Firstly, the dynamic process of the double-fed wind turbine can be obtained from the relationship between stator flux linkage and rotor voltage of the circuit before and after the fault, and the rotor equivalent circuit is obtained. Combined with the actual control of the rotor converter, the rotor current composition in different coordinate systems is obtained. Compared with the two current components, the equivalent relationship can be obtained to get the transient voltage to be compensated. The rotor converter increases the corresponding output voltage to prevent excessive rotor currents from affecting wind power systems. The simulation proves that the proposed additional control can limit the transient current of the fan rotor in a safe range when the grid voltage drops, which enhances the anti-interference ability of the double-fed wind turbine.

Fault detection and localization method for modular multilevel converters in offshore DC wind turbines

The offshore DC wind turbine, consisting of direct-drive permanent magnet synchronous generator (PMSG) and modular multilevel converter (MMC), has become a promising candidate for the large-capacity wind energy conversion system. Submodule (SM) failure detection and localization are crucial for reliable operation of the MMC. However, existing techniques mainly focus on the rated operation condition, which may not be suitable for the MMC in wind turbine due to varying wind speed. Moreover, proper injection of second-order harmonic circulating current (SHCC) is desirable to reduce capacitor voltage ripple and power loss, which may also affect the accuracy of fault detection. This paper proposes a fault-tolerant strategy immune to variable operation conditions, as well as SHCC injection, for the MMC with phase-shifted carrier modulation. Firstly, the inherent switching harmonics of circulating current with SM failure are analyzed, based on which the fault detection method is developed. Then, the localization approach is presented by measuring the difference of SM capacitor voltages. Compared with existing techniques, the proposed strategy requires neither estimator nor additional sensor, which is robust, simple, and economical. Finally, both simulation and experimental results demonstrate the effectiveness of the proposed method, which is not influenced by SHCC and varying wind speed.

Impact of DC link brake chopper design on the LVRT behavior of full-scale converter wind turbines

Wind turbines (WTs) are loaded by the wind and by the electrical grid. A low voltage ride through (LVRT) is a special load case for WTs, which can be critical for their drivetrain. They are usually less severe for WTs with a full-scale converter (FSC); however, in some cases there are still loads observable in the mechanical drivetrains of WTs with FSCs. Different aspects like the brake chopper design, the control and specifications of the grid side converter (GSC) as well as the grid and fault parameters affect these loads. In this paper, three different LVRT behaviors of a WT with a squirrel-cage induction generator (SCIG) and a FSC were investigated via simulations. In the worst case, a sharp peak in the electromagnetic torque of the generator after fault clearance is possible. The cause lies in the GSC control, especially the phase-locked loop (PLL), and can also be influenced by adjusting the control parameters, brake chopper and filter design. The resulting mechanical drivetrain torque, on the other hand, is increased by only 2.9% for a very short time. Thus, the loading of the mechanical drivetrain components is only slightly increased. Therefore, the risk of damage to the mechanical components of the FSC WT due to grid faults is relatively low.

Hybrid AC/DC Microgrid Energy Management Strategy Based on Two-Step ANN

In grid-connected operations, a microgrid can solve the problem of surplus power through regeneration; however, in the case of standalone operations, the only method to solve the surplus power problem is charging the energy storage system (ESS). However, because there is a limit to the capacity that can be charged in an ESS, a separate energy management strategy (EMS) is required for stable microgrid operation. This paper proposes an EMS for a hybrid AC/DC microgrid based on an artificial neural network (ANN). The ANN is composed of a two-step process that operates the microgrid by outputting the operation mode and charging and discharging the ESS. The microgrid consists of an interlinking converter to link with the AC distributed system, a photovoltaic converter, a wind turbine converter, and an ESS. The control method of each converter was determined according to the mode selection of the ANN. The proposed ANN-based EMS was verified using a laboratory-scale hybrid AC/DC microgrid. The experimental results reveal that the microgrid operation performed stably through control of individual converters via mode selection and reference to ESS power, which is the result of ANN integration.

ABNORMAL DETECTION OF WIND TURBINE CONVERTER BASED ON CWGANGP-CSSVM

Abnormal detection of wind turbine converter (WT) is one of the key technologies to ensure long-term stable operation and safe power generation of WT. The number of normal samples in the SCADA data of WT converter operation is much larger than the number of abnormal samples. In order to solve the problem of low abnormal data and low recognition rate of WTs, we propose a sample enhancement method for WT abnormality detection based on an improved conditional Wasserstein generative adversarial network. Since the anomaly samples of WT converters are few and difficult to obtain, the CWGANGP oversampling method is constructed to increase the anomaly samples in the WT converter dataset. The method adds additional category labels to the inputs of the generative and discriminative models of the generative adversarial network, constrains the generative model to generate few types of anomalous samples, and enhances the generative model’s ability to generate few types of anomalous samples, enabling data generation in a prescribed direction. The smooth continuous Wasserstein distance is used instead of JS divergence as a distance metric to measure the probability distribution of real and generated data in the conditional generative response network and reduce pattern collapse. The gradient constraint is added to the CWGANGP model to enhance the convergence of the WGAN model, so that the generative model can synthesize minority class anomalous samples more effectively and accurately under the condition of unbalanced sample data categories. The quality of anomalous sample generation is also improved. Finally, the anomaly detection is made on the actual operating variator dataset for the unbalanced dataset and the dataset after reaching Nash equilibrium. The experimental results show that the method used in this paper has lower MAR and FAR in WT converter anomaly detection compared with other oversampling data balance optimization methods such as SMOTE, RandomOverSampler, GAN, etc. The method can be well implemented for anomaly detection of large wind turbines and can be better applied in WT intelligent systems.

Field‐data‐based reliability analysis of power converters in wind turbines: Assessing the effect of explanatory variables

AbstractFrequent failures of power converters affect the availability of wind turbines and cause considerable maintenance costs. To enhance the reliability of power converters in wind turbines, the prevailing causes and modes of failures have to be identified. This publication contributes to root‐cause analysis of the power‐converter failures in wind turbines from a statistical point of view. For this purpose, the failure behavior of power‐converters is modeled via lifetime models as well as repairable‐system models. By means of regression models, covariates are incorporated, including both design‐related and site‐specific covariates. The analysis is based on a worldwide extensive field‐data collection covering more than 9000 turbines, including different turbine designs, sites, and ages. The results obtained by means of the applied regression models indicate that the location of the power converter within the turbine, the cooling system, the converter rated power, the DC‐link voltage, the IGBT‐module manufacturer, and the commissioning date of the turbine as design‐related covariates have a significant effect on the phase‐module failure behavior and with that on converter reliability. Among the site‐specific covariates, the analysis results confirm humidity as a likely significant driver of failures.

Design and Control of Series Resonant DC-DC Converter for DC Wind Turbines

High power reliability and high energy density are always in demand, and this is driving the evolution of power conversion technologies. People have begun to examine the potential positions of dc systems in both current and future power equipment due to the rise in the use of renewable energy and the implementation of energy storage in recent decades. Because of its efficiency and power density, dc voltage representation has found use in a wide range of fields, including data centres, the aerospace industry, and dc micro-grids. Resonant DC-DC converters, with their gentle switching and minimal EMI, provide a promising solution to these problems. Finding and examining the various modes of operation of the converter while employing the pulse-removal approach is the primary objective of this study. The new method of operation utilises variable frequency and variable phase displacement in sub-resonant mode, which promises to reduce the transformer size while also facilitating the soft-switching change of the insulated gate bipolar transistors (IGBTs) and line frequency diodes on the rectifier side. The pulse elimination approach, a revolutionary mode of operation for the converter, involves phase and frequency shift modulation at varying rates. Using the results of MATLAB/SIMULINK simulations, the suggested control technique may be utilised to establish the baseline switching function configuration necessary to attain high power efficiency.

Design and Control of Series Resonant DC-DC Converter for DC Wind Turbines

High power reliability and high energy density are always in demand, and this is driving the evolution of power conversion technologies. People have begun to examine the potential positions of dc systems in both current and future power equipment due to the rise in the use of renewable energy and the implementation of energy storage in recent decades. Because of its efficiency and power density, dc voltage representation has found use in a wide range of fields, including data centres, the aerospace industry, and dc micro-grids. Resonant DC-DC converters, with their gentle switching and minimal EMI, provide a promising solution to these problems. Finding and examining the various modes of operation of the converter while employing the pulse-removal approach is the primary objective of this study. The new method of operation utilises variable frequency and variable phase displacement in sub-resonant mode, which promises to reduce the transformer size while also facilitating the soft-switching change of the insulated gate bipolar transistors (IGBTs) and line frequency diodes on the rectifier side. The pulse elimination approach, a revolutionary mode of operation for the converter, involves phase and frequency shift modulation at varying rates. Using the results of MATLAB/SIMULINK simulations, the suggested control technique may be utilised to establish the baseline switching function configuration necessary to attain high power efficiency.

Power absorption of combined wind turbine and wave energy converter mounted on braceless floating platform

This work investigates the dynamic response and power absorption of a combined wind turbine and wave energy converter (WEC) mounted on a braceless semisubmersible floating platform. The floating platform consists of a Semi-submersible Wind turbine, a Wave energy converter Combination (SWWC) and a NREL 5-MW Current Source Converter (CSC) wind turbine. In this study, ANSYS/AQWA software is used in cooperation with a potential-based boundary element method (BEM) approach. The main targeted results include average power output and response amplitude of surge, heave and pitch motions of the combined concept at various wave and wind directions plus operational conditions. The numerical results are compared with experimental data, suggesting that the current numerical model predicts heave amplitude, average power, power take-off (PTO) damping force and response amplitude operator (RAO) of the platform motions with an acceptable agreement. Meanwhile, six environmental conditions (ECs) and five PTO damping coefficients are considered to optimize energy production. An optimal damping coefficient of 4000 kN s/m was found for the maximum average power generation for all the ECs. In addition, the effect of the wave/wind directions on the response motions and power absorption are obtained and presented.

A Review of Generators and Power Converters for Multi-MW Wind Energy Conversion Systems

The rated power of wind turbines has consistently enlarged as large installations can reduce energy production costs. Multi-megawatt wind turbines are frequently used in offshore and onshore facilities, and today is possible to find wind turbines rated over 15 MW. New developments in generators and power converters for multi-MW wind turbines are needed, as the trend toward upscaling the dimensions of wind turbines is expected to continue. Therefore, this paper provides a detailed review of commercially available and recently proposed multi-MW wind turbine generators and power converters. Furthermore, comparative analyses indicate the advantages and disadvantages of commercially available and promising technologies for generators and power converters at the multi-MW target.

Overcurrent Suppression Method for Multiple Wind Farms Connected to MMC-HVDC

To achieve asymmetric fault ride-through (FRT), it is crucial to limit the overcurrent for both the grid-forming modular multilevel converter (MMC) and the grid side converters (GSCs) of wind turbines. Compared with the MMC, GSCs enable better system stability when providing negative sequence paths, while the overcurrent can occur due to the negative sequence current. To address this issue, a negative sequence overcurrent suppression method is proposed, which introduces a negative sequence voltage proportional current control in each GSC. The redistribution of negative sequence currents is achieved in the manner that each GSC (filter included) is equivalent to a resistor with resistance determined by the proportional coefficient. Through this control, the negative sequence current can be evenly distributed so that the overcurrent can be effectively suppressed. Finally, simulations are performed in MATLAB/Simulink to verify the validity of the proposed negative sequence overcurrent suppression method.

A Health-Oriented Control Strategy for DC-Link Capacitor in Direct Drive Wind Turbine Converter

As the weakest components of wind turbine converters, dc-link capacitor withstands high-frequency ripple currents from both rectifier and inverter. Traditional wind turbine control strategy does not consider the influence of the harmonic current generated by both side converters on the dc-link capacitor, and ignores the restriction on the reliability of direct-drive wind turbine converter. For the reason, this paper synthesized the wind turbine model and dc-link capacitor harmonic spectrum analytical approach to derive the connection between mission profile and harmonic spectrum. Regarding with the capacitor lifetime model, the optimal mapping from control strategy to mission profile, maximizing the service life of capacitor, was solved. With the proposed health-oriented control strategy, the core temperature of dc-link capacitor can be effectively reduced, which can increase the service life of capacitor, making the dc-link capacitor no longer the most fragile component in wind turbine converter and ultimately improving the reliability of converters.

A novel methodology for effective short-circuit calculation in offshore wind power plants considering converter limitations

This paper deals with the short-circuit calculation of offshore wind power plants (OWPPs). The short-circuit calculation presented in this paper assumes the studied system achieves a new equilibrium state during the fault. The studied system is modeled with an element-based steady-state formulation where the grid-support control and potential current-saturated operation of wind turbine (WT) converters are included. In particular, the current-saturation modifies the converter control and represents various potential operation states of the converter. Then, an iterative methodology is proposed to identify the short-circuit equilibrium point that satisfies converters’ limitations and to obtain the current-saturation states of all power converters with a specific fault scenario in the studied system. The numerical case studies indicate that the WT converters operation has a significant influence to the system equilibrium point during the fault. In addition, the presented methodology is efficient for short-circuit calculation of a large-scale OWPP.

Virtual Resistance Control for Sequential Green-Start of Offshore Wind Power Plants

The changing energy landscape due to the large scale integration of renewable energy and shutting down of conventional thermal plants has opened up the potential of alternate sources in the blackstart services market. Grid forming wind turbines can do controlled islanded operation independent of an external grid voltage and thus participate in network restoration from the start. However, it is necessary to study the capability of wind turbines to deal with the demanding energization transients in a controlled and stable manner. This work investigates the feasibility of using virtual resistance in the wind turbine converter control to reduce transients during self-transformer inrush and sympathetic interaction from downstream string transformers. This can eliminate the need for pre-insertion resistors during sequential energization. The sensitivity of the AC current and voltage output along with DC link transient to the virtual resistance parameters has also been analyzed using PSCAD simulations. Finally the effectiveness of the proposed method for offshore network energization by a grid forming wind power plant has been tested by comparing to results for a pre-insertion resistor.

Power Curtailment Analysis of DC Series–Parallel Offshore Wind Farms

This paper analyzes one of the most important power capture challenges of the DC series–parallel collection system, called the power curtailment losses. The wind speed difference between the series-connected turbines causes over- and under-voltage conditions in the output voltage of the MVDC (medium-voltage DC) converters of the wind turbine. The power curtailment losses caused by the upper-voltage tolerance levels of the MVDC converters of the wind turbines are analyzed considering a redundancy-based upper-voltage limiting condition. This analysis emphasizes the importance of choosing suitable voltage tolerance levels for the MVDC converters of wind turbines based on the wind farm configuration. The annual energy curtailment losses are quantified and evaluated by a comparative case study performed on a DC series–parallel-connected wind farm rated at 200 MW with the redundancy-based upper-voltage limiting condition.