Long term dynamic simulation for power system including wind farms

Generation and transmission expansion planning with high penetration of wind farms considering spatial distribution of wind speed

Nowadays actual scientific problem of renewable energy is the problem of developing control systems, that ensure the generation of stable voltage in a changing environment. This paper presents a structure and methods of synthesis of control system development, which allow to decide the indicated problem. An electric subsystem of wind power plant is a well-known structure with well-known advantages, consisting mainly of double-fed induction generator (DFIG) and power converter in the circuit of rotor. Operation of the control system based on the original nonlinear mathematical model of DFIG in rotational dq coordinates, taking into account the nonlinear external and internal DFIG disturbances, such as inductances of coil winding, changes of coil winding resistances from temperature, etc. The study received mathematical model, adaptive control algorithms and its computer simulation of the wind turbine with DFIG. Introduction An increasing requirement in energy resources at unstable oil prices stimulate to search the alternative decisions of power problems. One of the most successfully developed types of alternative energy is wind power. Its rapid growth observed in the world, proofing an attractiveness of this technology. It is expressed in the purity, reliability and input speed. So, according to Global Wind Energy Council (GWEC), to the end of 2015 global wind power capacity will reach 609 GW, compared to 237. 4 gigawatts at the end of 2011. The three leading world markets remain the China, U. S. and Europe. In recent years, the rapid growth of installed wind power capacity turned out to be possible through the development and implementation of new technological solutions, one of which is DFIG used as generator in wind power plants(WPP). Such DFIG are widely used in powerful WPP, as they allow to convert the available wind energy more efficiently, especially in periods of weak winds. It is known that the parameters of the generated voltage depends on terms of environment. At the same time, the necessity of quality stable voltage generation sets the problem of technological decisions development, allowing to minimize influence of different factors on output voltage quality. Such a technological solution is adaptive control system (CS) of a WPP with DFIG , permitting high speed reaction to wind speed changes and the rate of the connected electrical load, thus maintaining the stability of the generator output voltage. Synthesizing an adaptive high-speed CS and using the structure of WPP with DFIG it becomes possible to design and build these types of wind turbines. Synthesis of nonlinear CS Nonlinear CS control law. The solution of the indicated problem, offered in this paper, is based on the nonlinear model of DFIG in rotational dq coordinates, as in the conditions of different disturbances, linearizing appears uneffective [1]. Because, coming from the structure of WPP, control circuit is a rotor circuit, then primary control objective is feed on it control voltage of some parameters, at that DFIG output voltage remains unchanging and corresponds to set, without depending on influences. As it applies to a model, it is necessary to get the control values of voltages International Conference on Advances in Energy, Environment and Chemical Engineering (AEECE-2015) © 2015. The authors Published by Atlantis Press 1 on the dq rotor axes dr V and qr V , at the well-known required stator voltages ref ds V and ref qs V . The classic mathematical model of DFIG does not take into account the nonlinear changes of its parameters, such as winding inductances, changes of winding resistances from temperatures etc., accepting their permanent, that is not quite right. Meantime, in real DFIG such changes have an influence on control quality, so the synthesis of control system, which is taking into account such nonlinear disturbances, is an actual task. The disturbances arising up from nonlinear character of the control object are difficult to mathematical description, however valuation of these disturbances with the subsequent bringing of adjustments in work of CS on the basis of such estimation is a fully solvable task. For this purpose, in the standard mathematical model of DFIG we will add some functions of immeasurable disturbances, and (Eq.1), accordingly for the stator d and q axes currents, and next we synthesize control laws.

With large wind energy integration into power systems, wind farms begin to influence power systems in a much more significant manner. As wind energy systems utilize different generator technologies from the one utilized in the conventional power plants, the steady-state, transient and small-signal dynamics, as well as, power system stability will thus be significantly affected. The impact of wind energy systems on the power system dynamics and stability is thus of practical importance. As there is a significant increase in installation of wind turbines equipped with doubly-fed induction generator (DFIG) in recent years, a dynamic model of the DFIG wind turbine is firstly developed in this thesis. The model is validated against field measurement data, and the validation gives confidence about the accuracy and applicability of the developed model. DFIG wind farms consist of tens to hundreds of identical DFIG wind turbines increasing the complexity of the wind farm model and simulation time. A novel aggregation technique is developed in this thesis that incorporates a multiplication factor, namely mechanical torque compensation factor (MTCF), to the mechanical torque of the full aggregated wind farm model. The MTCF is initially constructed to approximate a Gaussian function by using fuzzy logic method. By optimizing the MTCF on a trial and error basis, less than 10 percent discrepancy is then achieved between the proposed aggregated model and the complete model. The proposed aggregation technique is then applied to a 120 MVA offshore wind farm comprising of 72 DFIG wind turbines and shows higher accuracy in approximating the wind farm dynamics as it appears at the point of common coupling (PCC) as compared to the full aggregated model. The proposed aggregated model computes faster than the complete wind farm model by 90.3 percent during normal operations and 87 percent during grid disturbances. To overcome the adverse effects due to the fluctuating nature of wind, two wind power smoothing methods are proposed using a fuzzy logic pitch angle controller for a smooth performance with a minimum drop in output power. One method performs partial smoothing with only 4.74 percent drop in the output power while the other method offers complete smoothing with a 8.28 percent drop in output power. The impact of wind energy integration on power system transient stability (PSTS) is studied quantitatively with the transient energy margin (TEM), which is calculated through the evaluation of the transient energy function (TEF). This study is carried out in two ways in the thesis. One is to analyse the impact of transient fault on the DFIG wind turbine as compared to SGs for different factors, like the fault clearing time, the grid coupling, the inertia constant and the voltage sag. The study reveals that transient stability of the DFIG wind turbine is hardly affected by the grid coupling, the inertia constant and the generator terminal voltage sag variations indicating its consistent transient performance within a wide range of these factors. The fault clearing time should be almost 11 percent faster for the system with the DFIG than the synchronous generator (SG). The other is to investigate the impact of the DFIG wind farm on the PSTS with the variation of different factors, which are the voltage sag, the fault clearing time, the load and the wind power penetration level. The study reveals that power systems integrated with DFIG wind farms are sensitive to transient events with high voltage sag, high fault clearing time, low load operation and high wind power penetration level. Machines at different locations individually possess distinct fault response and suffer from a large-scale power imbalance. As a result, reliable operation of DFIG wind farm integrated power systems demands upgraded equipment, such as advanced switchgear, fast breakers/isolators, efficient power reserve systems and advanced reactive power compensating device, etc.

Designing of wide-area damping controller for stability improvement in a large-scale power system in presence of wind farms and SMES compensator

Penetration of renewable energy sources, such as wind power generation and PV power generation, into the power systems has been increasing significantly. Especially, wind power generation has attracted attention due to their superior characteristics such as low cost and high energy conversion efficiency. However, the power system including large-scale wind farm (WF) can become unstable during a fault condition because WF can be decoupled due to the instantaneous voltage drop in accordance with the grid code of Fault Ride Through (FRT) requirement. This paper proposes a new two-step control strategy using High Voltage Direct Current (HVDC) interconnection line. The proposed system controls the active power and the reactive power delivered to the grid from the HVDC interconnection line during a fault condition. The effectiveness of the proposed method is confirmed by simulation analyses on PSCAD/EMTDC software.

The integration of uncertain photovoltaics (PVs) and flexible loads leads to uncertainties in the power system dynamic simulation results. Furthermore, geographically close PV farms are correlated and may exhibit nonlinear correlations. This article proposes a copula-based sparse polynomial chaos expansion (PCE) framework for quantifying the impacts of uncertain dynamic PVs and loads on power system dynamic simulations and stability. The dynamics include both PV and load stochasticity and those governed by differential and algebraic equations. The copula statistics are utilized to accurately characterize the dependence structure of PVs and further used to develop the copula-PCE for quantifying the impacts of uncertain PVs and loads. A probabilistic TSI is also developed to assess the uncertainties from PVs and loads on the system stability. To address the cases, where both stable and unstable conditions coexist, a preprocessing step via sample classification is proposed. The effects of different dependence structures of PVs and different numbers of uncertain sources are investigated. Comparison results with other methods on the modified IEEE 39- and 118-bus systems, including the Monte Carlo method, Latin hypercube sampling, and traditional PCE without consideration of uncertain input correlations show that the proposed method is able to accurately quantify the uncertain dynamic simulations and transient system stability while being computationally efficient.

The adverse effects resulting from the intermittent nature of wind energy on power generation and stability is well documented in the literature. More specifically, the impact of power oscillations on doubly fed induction generator (DFIG)-based wind turbines can have drastic effects and even lead to large area blackouts, if not addressed properly. This paper deals with the design and implementation of a probabilistic coordinated approach for power systems with synchronous generators (SGs), DFIGs, and facts devices. The parameters of the power system stabilizers (PSSs) of the SG, power oscillation dampers (POD) of the DFIGs and STATCOM controllers were optimally coordinated using a modified Imperialist Competitive Algorithm (MICA) combined with a probabilistic eigenvalue approach. The proposed approach was implemented to a modified 39-bus New England power system. Its effectiveness in guaranteeing power system's dynamic stability was assessed using time domain analysis, eigenvalue mapping, and robustness analysis under various wind conditions. DFIG's realistic modes of operation, including normal, synchronous, and sub-synchronous modes were considered in the performance analysis. The obtained results were further compared to those of deterministic and uncoordinated approaches. A comparison of the MCA algorithm to other optimization approaches such as particle swarm optimization (PSO), genetic algorithm (GA), and imperialist competitive algorithm (ICA) is also carried out. The simulation results and robustness analysis confirmed the superiority of the proposed probabilistic approach over various other approaches.

Enhancing stability via coordinated control of generators, wind farms, and energy storage: Optimizing system parameters

Wang, G. and Zhang, Y., 2020. Dynamic simulation analysis of port economic throughput difference in marine environment. In: Yang, Y.; Mi, C.; Zhao, L., and Lam, S. (eds.), Global Topics and New Trends in Coastal Research: Port, Coastal and Ocean Engineering. Journal of Coastal Research, Special Issue No. 103, pp. 268–272. Coconut Creek (Florida), ISSN 0749-0208.A large number of sample data are needed in the dynamic simulation analysis of port economic throughput difference in the marine environment. In the traditional dynamic simulation method, the distribution of sample data is unbalanced, which affects the reliability of the simulation results. Therefore, the dynamic simulation analysis of port economic throughput difference in the marine environment is proposed. This paper analyzes the influencing factors of port economic throughput, determines the appropriate influencing factors by calculating the correlation coefficient, constructs the port economic throughput difference model, takes the predicted value and the original number series obtained by the model as the input, uses the trend extrapolation method and the linear regression model to realize the dynamic simulation of port economic throughput difference. The experimental results show that: compared with the traditional dynamic simulation method, the sample data of the dynamic simulation method of port economic throughput difference under the designed marine environment is evenly distributed, and this method is suitable for practical projects.

The growth rate of penetration of wind energy has addressed many challenges and impacts related to the power quality and power system stability because of its intermittent nature. Once a doubly fed induction generator (DFIG) is connected to a power system, it absorbs lagging reactive power during the grid operation causing instability issues to the grid voltages. In this research paper, a DFIG based wind turbine is being modeled considering the optimal power coefficient and reactive power control strategy. The optimal power coefficient correlates the power law exponent with the respect of velocity and elevation. The reactive power control strategy is modeled using back-to-back converter system. The paper also investigates the voltage improvement of a large distribution network connected with DFIG system. By using steady state analysis, the voltage magnitude profiles are determined during DFIG at point of common coupling. The proposed control shows that DFIG based wind-turbine integration to the large distribution network enhances the weak bus voltage.

ABSTRACTHigh penetration level of wind power has significant impact on the dynamic performance of power system. Power system with existing high-voltage direct current (HVDC) link may influence the stability of power system at high penetration level of wind power. This article investigates the stability issues of power system with existing HVDC link for different penetration level of doubly fed induction generator (DFIG) and direct drive synchronous generator (DDSG) based wind farms. The small signal stability analysis shows that power system with HVDC link has improved the stability of the power system for increased penetration of DFIG- and DDSG-based wind farms.

Much attention has been continuously paid on the model development and stability analysis of the doubly fed induction generator (DFIG) widely applied in wind power generation. Similarly, this study develops the form-standardised state-space model in the dq reference frame of the DFIG with stator winding inter-turn fault (SWITF). Compared with those previously developed, it is definitely preferable for the simulation and stability analysis of the DFIG with SWITF due to its standard form. Moreover, for the DFIG with SWITF working in stator-voltage-oriented control frame, the small-signal stability analysis is conducted using MATLAB simulation, yielding the conclusion that SWITF will never eradicate the DFIG's small-signal stability but deteriorate it to some extent. This conclusion is further validated by means of the Lyapunov stability theory. As a kind of contribution of this study, the analytical expressions of the eigenvalues of the DFIG with SWITF are derived. Case study based on an MATLAB/Simulink demo routine is completed to demonstrate the validity of the model development and small-signal stability analysis of the DFIG with SWITF.

Wind energy is considered to be the most technically and economically viable among all renewable energy sources. Recent technologies related to wind energy are mostly equipped with doubly fed induction generator (DFIG) because of its several advantages. In this paper a study on the impacts of DFIGs on large multi-machine system on aspects of small signal stability is presented. It is shown that improvement in small signal stability of a large multi machine system is location dependent. Also the optimum loading of DFIG is determined in terms of some sensitivity analysis.

Distributed power (DP) generation through solar and wind energy holds immense potential in meeting future energy demands. Recent advancements in grid technology enable efficient utilization of local energy sources, minimizing transmission line losses and facilitating enhanced power distribution capabilities. This study focuses on examining the impacts of disturbances and faults within a four-area system linked to a Doubly Fed Induction Generator (DFIG) using discrete-time modeling. The primary control approach within the four-area system involving the DFIG incorporates various discrete-time Power System Stabilizers (PSSs). A comparative analysis of time-domain responses is conducted across various scenarios, including systems without controllers (no PSS), systems equipped with traditional PSSs such as Delta Omega, Multi-Band, Delta Pa and Fuzzy Logic (FL) based PSSs. A discrete-time mode PSS is specifically tailored for the silent-pole synchronous generator associated with the DFIG system. To assess the performance of the Fuzzy Logic (FL) controller in ensuring power system stability, a test DFIG model is employed. Time-domain simulations of the test DFIG model are carried out using the MATLAB/Simulink (R2015a) environment.

In this paper, heuristic dynamic programming (HDP) based supplementary control is compared with the power system stabilizer (PSS) based supplementary control for doubly-fed induction generators (DFIG), namely, the active power damping control. The traditional design of PSS control on DFIG damping is based on eigenvalue analysis. For such analysis, disturbances are considered sufficiently small to permit the nonlinear model representing the power system to be linearized and expressed in state space form. When the disturbance or the system configuration changes, this kind of design is easy to become entrapped in local minimal and the robust ability of the controller is not guaranteed. On the other side, the HDP based supplementary damping controller analyzed in this paper is “model-free” with on-line learning capability: once a system state is observed, an action will be subsequently produced based on the performance index function. The obtained results by such a HDP supplementary controller on a benchmark power system are compared with the traditional PSS controller, demonstrating the improved control performance and robustness.