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In order to solve the frequency modulation (FM) problem caused by load in the virtual synchronous generator (VSG) system under an islanding state, this paper proposes a frequency modulation method based on active disturbance rejection control (ADRC). Firstly, design a nonlinear function using the design rules of nonlinear functions. Then, the extended state observer (ESO) and nonlinear feedback control law (NLSEF) of ADRC are designed based on the nonlinear function. By introducing ADRC into the power–frequency control loop of VSG, error-free frequency modulation of VSG is achieved. Finally, the superiority of the proposed method was verified through experimental comparison. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) power generation is considered to be a clean energy source. Solar modules suffer from nonlinear behavior, which makes the maximum power point tracking (MPPT) technique for efficient PV systems particularly important. Conventional MPPT techniques are easy to implement but require fine tuning of their fixed step size. Unlike conventional MPPT, the MPPT based on reinforcement learning (RL-MPPT) has the potential to self-learn to tune step size, which is more adaptable to changing environments. As one of the typical RL algorithms, the Q-learning algorithm can find the optimal control strategy through the learned experiences stored in a Q-table. Thus, as the cornerstone of this algorithm, the Q-table has a significant impact on control ability. In this paper, a novel Q-table of reinforcement learning is proposed to maximize tracking efficiency with improved Q-table update technology. The proposed method discards the traditional MPPT idea and makes full use of the inherent characteristics of the Q-learning algorithm such as its fast dynamic response and simple algorithm principle. By establishing six kinds of Q-tables based on the RL-MPPT method, the optimal discretized state of a photovoltaic system is found to make full use of the energy of the photovoltaic system and reduce power loss. Therefore, under the En50530 dynamic test standard, this work compares the simulation and experimental results and their tracking efficiency using six kinds of Q-table, individually. [ABSTRACT FROM AUTHOR]

A new partitioned stator field modulation machine (PSFMM) with H-shape permanent magnet (HPM) excitation (HPM-PSFMM) is proposed, which is evolved from the conventional flux-switching machine (FSM) and flux-reversal machine (FRM). The proposed HPM-PSFMM combines the merits of high reliability and good heat dissipation characteristic. In addition, it exhibits high torque production with low torque ripple. Based on the theory of electrical machine operation, the FSM and FRM can be transformed into PSFMM with interior permanent magnet (IPM) and surface-mounted PM (SPM) excitation by changing the position of PM excitation, respectively. It benefits to improve space utilization and increase slot area for a large number of armature windings. For reducing the flux leakage and enhancing the flux density in air gaps, the IPM and SPM excitation are combined into HPM excitation. The iron-pole rotor between the inner and outer stators acts the role of modulator to modulate the magnetic field excited by HPM excitation to couple with the armature reaction for converting electromechanical energy. The evolution process, operating principle, and key design parameters of the proposed HPM-PSFMM are presented. Finally, using the finite element analysis (FEA), it can be proven that the proposed HPM-PSFMM has the merits of high torque production, low flux leakage, low total harmonic distortion (THD), and low torque ripple when compared to other stator-PM machines, which is a desirable choice for high stability applications. [ABSTRACT FROM AUTHOR]

A new type of hybrid magnet dual stator field modulation machine with different split ratios of stators (DSR-HMDSFMM) is proposed in this article, which has the merit of high torque density. The split teeth of stator sever as modulators to modulate air gap flux density based on the magnetic gearing effect for high torque production. The total split tooth number of inner stator is equal to that of outer stator because the pole pair numbers of armature reaction and permanent magnet (PM) excitation on rotor are equal. Furtherly, the inner and outer stators with different split ratios and same split tooth number are employed to increase torque production because armature windings with high winding factor and high turn number can be used. In addition, the employment of hybrid magnet excitation can increase space utilization and enhance the air gap flux density with low harmonic distortion. Therefore, the proposed DSR-HMDSFMM can achieve high torque production with the same volume and PM usage. In order to find the optimal split ratio match of stators, several DSR-HMDSFMMs with different combinations of split ratios are proposed and calculated. The configuration and operating principle are illustrated, together with electromagnetic performances of the proposed machines analyzed using finite element analysis (FEA). The FEA-predicted results show that the proposed HMDSFMM exhibits high air-gap flux density with low harmonic distortion and high torque density, which is promising for the direct-drive applications. [ABSTRACT FROM AUTHOR]

The continuous operation of 1000 MW large hydro generators in China is of great value to the implementation of "double carbon strategy" and power grid safety. However, with the continuous increase of single unit capacity of the hydro generator, the problems of unit fault grounding current and neutral point voltage drift become more and more prominent, and the traditional analysis methods cannot accurately obtain the fault dynamic data. Therefore, starting from the neutral point grounding mode of the large hydro generator, taking a 1000 MW hydro generator as the research object, this paper establishes the single-phase grounding fault model under the condition of three-phase parameter asymmetry of stator winding and analyzes the dynamic characteristics of fault current, transient overvoltage, and neutral point voltage drift under different grounding modes by using transient analysis method; the influence of frequency offset on neutral voltage drift and the dynamic characteristics of single-phase grounding fault of the large hydro generator under different grounding modes are also obtained. Finally, according to the analysis results, the selection and optimization method of neutral grounding parameters are proposed, which provides a reference for the selection of neutral grounding mode and the research of protection strategy of the large hydro generator. [ABSTRACT FROM AUTHOR]

The effect of gas compressibility on the fluid flow characteristics of a 350 MW air‐cooled turbo‐generator is investigated in this paper. Two gas models taking gas compressibility and incompressibility into account are established for numerical calculation. Then, a one‐fourth physical model based on the practical ventilation structure and basic assumption is built to analyse the flow velocity and flow rate using the finite volume method (FVM). The FVM‐predicted flow rate and flow velocity of cooling medium in the air cavity, stator and rotor of the generator show the distribution characteristics of flow rate and velocity in the generator is affected by the gas compressibility model selection. The comparison of FVM‐predicted flow rate and experimental value shows that the FVM‐predicted results using the gas compressibility model is more accurate when comparing to those using the incompressible model. Therefore, the gas compressibility model is an appealing approach to analyse the flow fluid characteristics of the air‐cooled turbo‐generator. [ABSTRACT FROM AUTHOR]

The physical fields of synchronous generator are very complicated because of the coupling of electromagnetic field, fluid field, and thermal field. In this paper, a large synchronous generator is taken for an example and the three types of fields are calculated. First, the mathematical model and physical model of the 2-D electromagnetic field are determined by which the losses in each part of the generator are calculated. Second, the fluid kinetic differential equations in stator radial ventilation duct are built. After determining the solved region and boundary conditions, the 2-D fluid field is computed and the different distributions of fluid field are compared and analyzed when the fluid has different entrance angles. Finally, the 3-D stator temperature fields are solved under different inlet angles respectively. The results of the coupled fields are analyzed, and some useful conclusions are presented. Index Terms--Coupled fields, finite element method (FEM), finite volume method (FVM), numerical calculation.

Maximum power point tracking (MPPT) is required in PV power systems for the highest solar energy harvest. This article proposes a self-tuning scheme to improve the MPPT performance in terms of high accuracy and speed. The scheme adopts the reinforcement learning (RL) and Beta parameter for the highest MPPT performance. The tracking speed and accuracy are significantly improved since the RL algorithm is enhanced for high convergence speed, meanwhile, the guiding variable $\beta$ is introduced to constrain the exploration space. Simulation and experimental test are applied to validate the superior performance of the proposed solution following the EN50530 dynamic test procedure. [ABSTRACT FROM AUTHOR]

This article proposes new dual-stator field modulation machines with multiple magnetic excitations (MME-DSFMMs), i.e., NdFeB magnet excitation for rotor, ferrite magnet excitation for outer stator, and direct current (dc) excitation for inner stator. The open-slot stator teeth performs the role of modulator to modulate the magnetic field excited by NdFeB magnets. DC field windings with dc in the same direction are used to regulate the magnetic field. The ferrite magnets embedded at the top of outer stator slot are used to suppress the harmonic distortion. Therefore, the proposed machines have the merits of high torque production at low speed, wide speed range, and low torque ripple in full operation range. The configuration, operation principle, and design consideration of the proposed MME-DSFMMs are described. The electromagnetic performances of new topologies with different number of ferrite magnets, including back-electromagnetic force, torque characteristics, and power factor, are analyzed using finite-element analysis to show the merits of the proposed machines. [ABSTRACT FROM AUTHOR]

The 3D stator temperature fields of a SF300-48/1230 hydro-generator are calculated, using the isoparametric element method of hexahedron and eight nodes. The wires insulation aging and shelling in the generator is taken into account, and the fluid similarity theory is applied to calculate temperature fields. The computed results show good agreement with the measured results. Based on the results, some useful conclusions are drawn that provide a theoretical basis for real-time temperature monitoring and fault diagnosing for generators. [ABSTRACT FROM AUTHOR]