Dynamic equivalent method of PMSG‐based wind farm for power system stability analysis

A new practical way of modelling direct-driven permanent magnet synchronous generator (PMSG) wind turbines is proposed. The model emphasizes on the wind-rotor-to-PMSG-to-converter-to-grid system, which is the main energy flow system of the direct-driven wind turbine. In this article, a new wind-rotor back propagation neural network is proposed, which consists of a four-layer network and is used to describe the wind-rotor aerodynamic characteristics. According to the orthogonal experimental method, 1200 sets of wind-rotor aerodynamic data, which are calculated based on combining blade element momentum-modified theory with a dynamic stall model, are adopted as the sample data; and the wind-rotor neural network is trained using the Levenberg–Marquardt algorithm. Then, the coupling dynamic models of the wind-rotor and PMSG, and AC–DC–AC converter model are established, respectively; the control strategies for the generator-side and grid-side converters are constructed, too. The mechanical model, electric model, and control model are integrated into the whole simulation model, and the numerical simulation are carried out. The research results show that all the wind-rotor aerodynamic characteristics, electrical characteristics, and control characteristics can be obtained quickly and efficiently from the constructed model, and are helpful for optimization design and control for large-scale direct-direct PMSG wind turbines.

Wind energy is consistently attracting great research effort and actively developed in many countries. As a result, the penetration level of wind power in the power grid is increasing as well as the size of wind farms. A large-scale wind farm may consist of hundreds of wind turbines and its total installed capacity could be at a level of 1000MW or even more. Consequently, the large-scale wind farm could seriously impact the operation and control of the grid. To represent a large-scale wind farm, aggregated modelling takes advantage of fast computation and simplified implementation compared to detailed modelling that models every wind turbines individually and the interconnections among them. In this paper, three aggregated modelling techniques, namely, multi-machine equivalent aggregation, full aggregation and semi-aggregation are presented for power system transient stability studies based on a wind farm with permanent magnet synchronous generator (PMSG) wind turbines. Simulation results of the aggregated models and the detailed model are compared and analyzed respectively to prove the effectiveness of the aggregating techniques.

In practical engineering, large-scale wind power integration typically requires long-distance transmission lines to deliver power to load centers. The resulting weak sending-end systems lack support from synchronous power sources. Under extreme weather conditions, the rapid increase in active power output caused by high wind power generation may lead to voltage instability. In existing projects, a phenomenon of repeated voltage fluctuations has been observed under fault-free system conditions. This phenomenon is induced by the coupling of the characteristics of weak sending-end systems and low-voltage ride-through (LVRT) discrimination mechanisms, posing a serious threat to the safe and stable operation of power grids. However, most existing studies focus on the analysis of voltage instability mechanisms and the optimization of control strategies for single devices, with insufficient consideration given to voltage fluctuation suppression methods under the coordinated operation of wind power and energy storage systems. Based on the actual scenario of energy storage configuration in wind farms, this paper improves the traditional LVRT discrimination mechanism and develops a coordinated voltage ride-through control strategy for permanent magnet synchronous generator (PMSG) wind turbines and energy storage batteries. It can effectively cope with unconventional operating conditions, such as repeated voltage ride-through and deep voltage ride-through that may occur under extreme meteorological conditions, and improve the safe and stable operation capability of wind farms. Using a hardware-in-the-loop (HIL) test platform, the coordinated voltage ride-through control strategy is verified. The test results indicate that it effectively enhances the wind–storage system’s voltage ride-through reliability and suppresses repeated voltage fluctuations.

<p>With the increase in the development of offshore wind farm (OWF) around the world, this paper describes OWF consisting of permanent magnet synchronous generator (PMSG) wind turbines connected to Active network (AC grid) and Passive network (loads) through Multi Terminal High voltage direct current(MT-HVDC) transmission system. This paper discusses the effect of using a Superconducting Magnetic Energy Storage (SMES) unit in a hybrid power system that contains OWF. In this paper, we have aggregated 300 wind turbines of 1.5 MW PMSG using an aggregation technique (multi full aggregated model using equivalent wind speed (MFAM_EWS)). Furthermore, we have used a detector to detect any tripping of any wind turbine and substitute the shortage of power due to this loss of wind turbines immediately through SMES. The Active network in this paper should have a minimum of 150 MW power to be supplied by controlling the SMES unit (absorbing or providing power according to the system requirement). Simulation has been carried out by MATLAB/Simulink program to test the effectiveness of the SMES unit during tripping some of the wind turbines, fluctuation in wind speeds, load change and voltage dips. </p>

In recent years, the sub-synchronous oscillation (SSO) accidents of the power system caused by wind power have received extensive attention. This paper focuses on the self-sustained oscillation problem caused by the control limit of the grid-following direct-driven permanent magnet synchronous generator (PMSG) wind farms. When one PMSG in a multi-machine system oscillates, whether the removal of other PMSGs can affect its oscillation conditions is studied. In this paper, the generator tripping problem in the oscillation scene of the wind farm with grid-following PMSGs is transformed into the influence of the equivalent parameter change of a two-machine coupling system on the self-sustained oscillation conditions. Considering the synchronization stability condition of the phase-locked loop (PLL), the influence of the generator tripping strategy on the self-sustained oscillation condition caused by the hard limit in the control system is analyzed. Since the fundamental and harmonic currents of the self-sustained oscillation frequency can all be monitored at the terminal of each PMSG when nonlinear oscillation occurs in the wind farm, this paper proves that cutting off the part of the wind farm without the oscillating ones does not help the oscillation suppression. The necessity of accurately locating nonlinear oscillation sources is thus demonstrated.

With the advance of power electronics, direct-driven permanent magnet synchronous generators have drawn increased interest to wind turbine manufacturers due to its advantages over other variable-speed wind turbines. This article studies permanent magnet synchronous generator characteristics under the general d-q control strategy in the rotor-flux-oriented frame so as to benefit the development of advanced permanent magnet synchronous generator control technology. Compared to traditional approaches, the specific features of the article are (1) a steady-state permanent magnet synchronous generator model in a d-q reference frame, (2) a simulation mechanism that reflects the general permanent magnet synchronous generator d-q control strategy, (3) an integrative study that combines generator-converted power with extracted wind power characteristics, and (4) a joint investigation incorporating both steady-state and transient evaluations. Extensive simulation-based analysis is conducted to study how permanent magnet synchronous generator characteristics are affected by different d-q control conditions and are interacted with wind power drive characteristics in power generation and speed regulation of a permanent magnet synchronous generator wind turbine.

Aggregated models of permanent magnet synchronous generators wind farms

This paper is focused on the propagation of supraharmonics into power transmission grids introduced by wind power plants (WPP) based on permanent magnet synchronous generator (PMSG) wind turbines. The methodology is based in steady state and time domain simulations performed by MATLAB Simulink®. As results steady state power flow and time domain voltages and currents are obtained and supraharmonic indicators are proposed for analysis. In order to simulate the electrical power system, transmission lines are modelled by Pi equivalent circuit based on distributed parameters and linear models of transformers are considered. Furthermore, wind power plants are modelled as aggregations of several wind turbines. A study case based on the west side of the Brazilian state of Rio Grande do Sul is proposed to validate the modelling and simulation methodology. Results show that the level of supraharmonics emission from WPP is straightly related to the PWM modulation of power inverters. Furthermore, the propagation of supraharmonics into transmission grids follows a linear tendency of decreasing according to the distance in transmission lines to the point of common coupling (PCC) of the wind power plants. Anyway, intrinsic characteristics at each point of the grid such as load profile, generation and presence of capacitor banks also influence the behavior of supraharmonic propagation.

Considering the growing rate of global wind power and overall benefits of the permanent magnet synchronous generator (PMSG) wind turbines, the future demand for high-performing NdFeB magnet and its constituent elements is likely to increase. Future deployment of wind power generation may be affected by potential disruptions in supply and price rises of critical rare earth elements. By evaluating the substitution options for the rare earths permanent magnet-based wind turbines at the material and component levels, this paper shows that substitution has a real potential to alleviate the pressure on the supply of rare earths in the wind industry. Rare earth-free turbines with good efficiency levels were already developed and could be further adopted. Alternatively, the future demand for rare earths, in particular for dysprosium, could be reduced by improving material efficiency. The future market share of rare earth-based wind turbines will most likely depend on the evolution of the price of rare earths and the techno-economic advantages of PMSG in comparison to alternative technologies that use no rare earths elements.

In this paper, a nonlinear power transfer matrix model is presented for power control of Permanent Magnet Synchronous Generator (PMSG) wind turbines, incorporating the DC link dynamics to account for transient stability, thereby clarifying the technical aspect and purpose. The rising penetration of wind turbines (WTs) into the power grid necessitates that they remain connected during and after faults to ensure system reliability. During voltage dips, the stator and grid-side converter (GSC) of a permanent magnet synchronous generator (PMSG) system are directly impacted by the sudden voltage changes. These disturbances can induce large transient voltages and currents in the stator, which in turn may lead to uncontrolled current flow in the rotor circuit and stress the converter components. Moreover, Low Voltage Ride-Through (LVRT) is a critical requirement for grid connection to Wind Energy Conversion Systems (WECS). It ensures that WTs remain connected and operational during short periods of grid voltage dips (faults), instead of disconnecting immediately. This capability is essential for maintaining grid stability. However, in this paper, the authors propose an LVRT scheme for a grid-connected PMSG-based WECS. A sequence of attempts was performed to validate the effectiveness of the proposed control scheme under fault conditions and to improve its overall performance.

This paper presents an idea of utilizing the rotor kinetic energy of the wind turbine to smooth the output power. The mathematical expressions of the idea are developed based on the energy balance of the system. A control algorithm is presented to control the speed of the wind turbine based on the presented method. The control algorithm is applied to a Permanent Magnet Synchronous Generator (PMSG) wind turbine to evaluate the performance of the algorithm.

To prevent fossil resources from being depleted and protect the natural balance, renewable resources come to the forefront as an alternative to fossil resources. Wind energy resources, among the renewable energy resources, are important in terms of ensuring the reliability of energy and the use of their resources. Generators are the most important components for the conversion of wind power. Permanent magnet synchronous generators (PMSGs) are preferred in wind turbines since they have high efficiency and high volume/torque densities, thereby optimization of the PMSGs is an important topic for the wind energy community. On the one hand, these machines can cause problems due to overheating and mechanical friction during their long-time operation. To identify the performance lack of the machines due to the de-magnetization faults, systematic work has been performed. When a magnet of a PMSG is de-magnetized at different rates (i.e. 33%, 50%, and 100%), we have explored the artifacts in the electric generation. Besides, the torque performances of the generator at rated load are examined and the flux density distributions are revealed. The rated torque decreased substantially when the demagnetization rate of the magnet increased.

Magnetic gearboxes (MGs) are increasingly explored in wind turbines as a reliable alternative to mechanical gearboxes, which suffer failures and costly maintenance. By integrating MG with Permanent Magnet Synchronous Generator, an Integrated Pseudo-Direct-Drive PMSG (IPDD-PMSG) is achieved, offering higher efficiency, contact-free operation, and improved system reliability. The proposed design improved the performance of the IPDD-PMSG systems in torque and efficiency for 2MW wind turbines. A multi-objective optimization is implemented to achieve maximum volumetric torque density (VTD) as well as minimum cost. Both Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) heuristics methods of optimization are investigated in order to reach the best algorithm. Results showed that GA offers better convergence and higher-performing solutions, while PSO ensures a greater diversity of cost/VTD trade-offs. Thus, the proposed methodology enables optimized and balanced design systems and offers a significant improvement in VTD and cost of the system. The finite element approach verifies the geometry using the variables found by optimization.

The population growth demands a greater generation of energy, an alternative is the use of small wind turbines, however, obtaining maximum wind power becomes the main challenge when there are drastic changes in wind speed. The angle of the blades rotates around its longitudinal axis to control the effect of the wind on the rotation of the turbine, a proportional-integral controller (PI) for this angle achieves stability and precision in a stable state but is not functional with severe alterations in wind speed, a different response time is necessary in both cases. This article proposes a novel pitch angle controller based on auto-tuning of PI gains, for which it uses a teaching–learning based optimization (TLBO) algorithm. The wind speed and the value of the magnitude of the change are used by the algorithm to determine the appropriate PI gains at different wind speeds, so it can adapt to any sudden change in wind speed. The effectiveness of the proposed method is verified by experimental results for a 14 KW permanent magnet synchronous generator (PMSG) wind turbine located at the Universidad Autónoma de Querétaro (UAQ), Mexico.

Permanent magnet synchronous generator (PMSG) wind turbines with full‐scale back‐to‐back pulse‐width modulated (PWM) converters are being widely adopted in industry. This chapter presents a control strategy based on the synchronverter technology for back‐to‐back PWM converters. Both converters are operated as synchronverters, which are mathematically equivalent to the conventional synchronous generators. In contrast to common practice, the rotor‐side converter (RSC) is responsible for maintaining the DC link voltage and the grid‐side converter (GSC) is responsible for injecting the maximum power available to the grid. The RSC is operated as a virtual synchronous motor and the GSC as a virtual synchronous generator. The chapter also presents extensive real‐time digital simulation results to verify the effectiveness of the presented method under normal and abnormal grid conditions.