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Summary: The unstable operation of a direct‐drive permanent magnet synchronous generator (DPMSG) is exacerbated by periodic oscillation, having a significant impact on the safe and stable functioning of wind energy generation systems. This paper proposes an approximate solution method for analyzing the periodic oscillation of the Hopf bifurcation and a method for suppressing its bifurcation through H∞ robust control. Firstly, a three‐dimensional nonlinear dynamic model of the DPMSG is constructed. Secondly, the Hopf bifurcation of the system with changes in internal parameters is solved using the time domain and frequency domain methods, and the harmonic balancing method is used to approximate the periodic solution at the point of Hopf bifurcation. The order of the Hopf bifurcation neighborhood is then decreased using the central manifold theorem. Finally, this study suggests a H∞ output feedback control employing bifurcation parameters. The Nyquist criteria are used for evaluating small signal stability and convergence speed of the response system in DPMSG before and after dimensionality reduction. The simulation results suggest that the proposed strategy helps to tackle the periodic solution expression and instability difficulties caused by Hopf bifurcation. This paper provides theoretical suggestions for the future reliable operation of new energy generation systems. [ABSTRACT FROM AUTHOR]

Considering the dynamic behavior of doubly‐fed induction generators (DFIGs) under the influence of random factors, this paper not only analyzes the phenomenon of stochastic instability and bifurcation of a DFIG dynamic variable in its random space when they are affected by environmental noise, but also proposes a method based on the Tkagi–Sugneo (T–S) fuzzy control strategy to control its stochastic bifurcation. First, a four‐dimensional stochastic dynamic DFIG model is established by using multiplicative white noise to simulate the influence of environmental noise on electrical variables, and stochastic central manifold theory is used to reduce the dimensionality of a planar model in the bifurcation neighborhood. Then, the stochastic stability of the model is investigated based on singular boundary theory, while the steady‐state probability density of the stochastic DFIG is determined using the Fokker–Plank–Kolmogorov equation to obtain the location and probability density of its stochastic P‐bifurcation. Finally, the influence of stochastic bifurcation behavior is eliminated by H∞‐fuzzy output feedback control. The numerical simulation results indicate that the location and probability of stochastic bifurcation in a DFIG will vary with the change in noise intensity, and the bifurcation parameter values and stochastic stability domain are obtained. The harm caused by random factors can be solved based on H∞‐fuzzy output feedback, which provides a theoretical basis for the stable operation of the DFIG system. [ABSTRACT FROM AUTHOR]

To promote the efficient use of energy storage and renewable energy consumption in the integrated energy system (IES), an economic dispatch strategy for the concentrating solar power (CSP)-IES with generalized energy storage and a conditional value-at-risk (CVaR) model is proposed. First, considering the characteristics of energy storage and distributed power supply timing, a CSP-IES configuration is established by using a CSP plant to achieve thermal decoupling of the combined heat and power unit and by defining the thermal storage system of the CSP plant and the battery as the actual energy storage. Second, the fuzzy response of the logistic function is used to optimize the time-of-use tariff to guide load shifting, and the load shifting is defined as virtual energy storage. Third, the CSP-IES economic dispatch model is established to consider the carbon emission allowance model. Finally, considering the system uncertainty, a fuzzy chance constraint is used to relax the system power balance constraint, and then the trapezoidal fuzzy number is transformed into a deterministic equivalence class, and the CVaR model is used as a risk assessment index to quantify the risk cost of the system due to uncertainty. The CSP-IES economic dispatch model with CVaR is constructed. The feasibility and effectiveness of the proposed optimization model are verified by comparing various scenarios. [ABSTRACT FROM AUTHOR]

These days, the harmonic problem of wind power grid‐connected systems is becoming increasingly prominent due to the increase in the number of large‐scale centralized grid‐connected wind farms and the gradual trend of high‐proportion power electronics for source‐grid loads. The harmonic oscillation caused by power electronic equipment provides large‐scale propagating in the system, and the harmonic interaction makes the harmonic propagation more complex. First, the harmonic interaction of the system is simplified into the radiation relationship between the wind farm and each branch to solve the harmonic current propagation problem caused by the interaction in the multiple wind farms. Then, the branch harmonic current propagation analysis method is used to transfer harmonic impedance and generate the branch harmonic current decoupling. Second, a harmonic current propagation coefficient is proposed to quantitatively analyze the relationship between the harmonic current of the wind farm and the branch. Thereby, the quantitative analysis of the propagation characteristics for the wind farm harmonic current in the system branch is obtained. Finally, abundant simulations verify the effectiveness and feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

Summary To address the grid stability problem caused by random changes in cable impedance when an offshore wind power generation system is sent out via a power cable, this study proposes a stochastic stability analysis method for an offshore doubly‐fed wind power generation system considering the frequency variation of the power cable parameters based on the polynomial approximation theory, which can be analyzed by equating the problem of the random change in the impedance of the offshore wind power public coupling point as a deterministic problem. First, a stochastic dynamics model of doubly‐fed wind farm is established by considering variation impedance variation. Second, using the polynomial approximation theory, the wind farm model containing stochastic parameters is approximated for analysis as an equivalent deterministic model. Finally, based on the approximated deterministic model, the grid‐connected stability of wind farms with different impedance fluctuation strengths is investigated, and the stable operation interval of the wind farms affected by the impedance is determined. The simulation results show that when the stochastic intensity exceeds a certain threshold, Hopf bifurcation occurs during the voltage and turndown, and the system is destabilized. This study provides a theoretical basis for the stability of offshore wind power. [ABSTRACT FROM AUTHOR]