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Sub-synchronous resonance (SSR) phenomenon occurs due to the interaction between wind turbine generators and series-compensated transmission lines. A doubly-fed induction generator (DFIG) is considered one of the most widely implemented generators in wind energy conversion systems. SSR analysis based on the eigenvalue method is the most important among the used methods. The accuracy of the eigenvalue method depends on the initial values of state variables. Previously, the initial values of the state variables were calculated based on the iterative approach which is suffering from convergence problem, lacking accuracy, and requiring a long computation time. Moreover, many steps and details haven’t been provided. Consequently, it is urgent to fill this gap and show how can implement the SSR analysis model in detail. In this paper, a new application of a recent analytical approach is proposed for SSR analysis. All information is provided, and the SSR analysis model of a DFIG-based series compensated wind farm is built step-by-step. In order to prove the effectiveness and accuracy of the proposed method, the eigenvalue analysis based on the proposed and iterative methods is compared with the time-domain simulation results at different wind speeds and variable compensation levels. The results prove that the eigenvalue analysis based on the proposed method is more precise, where it is consistent with the simulation results in all studied cases. MATLAB software is used to validate the results.

Distributed energy resources are often connected to low-voltage distribution networks where the grid voltages may be unbalanced. This leads to an unwanted ripple in the output active power at twice the fundamental grid frequency. In this article, a new model predictive current controller is proposed for unbalanced grids. The variable switching frequency of existing model predictive controllers is fixed and the power quality is improved. A Kalman filter estimator is used to extract the positive and negative sequence components. A new calculation time compensation technique is proposed, which offers superior accuracy to existing approaches. A grid voltage discretization compensation strategy is outlined, and its effectiveness is demonstrated. Finally, the system stability is verified theoretically. Simulation and laboratory results are included to prove the robustness of the proposed controller and support the theoretical analysis. [ABSTRACT FROM AUTHOR]

Due to the scalability and flexibility of various modular power electronic converters, integrating split energy storage components (such as batteries and supercapacitors) is feasible and attractive. This paper investigates the operational and economic characteristics of different ac/dc fault-resilient schemes using energy storage integrated modular converters in ac-dc conversion applications. Based on the topological features between the energy storage system (ESS) and the ac and/or dc system, four energy storage based modular converter deployment schemes are presented. Through a case study, operational performance including fault isolation and power compensation under extreme ac/dc fault conditions are verified using time-domain simulation. System losses are evaluated, whereas detailed design considerations, major component usage and estimated capital costs are articulated. The four schemes are compared and selection guidelines are presented. In general, the schemes with independent ESSs would be preferable for such ac-dc conversion applications due to their high operational flexibility. [ABSTRACT FROM AUTHOR]

This article proposes a new active power flow controller for dc–dc multiactive bridge (MAB) converters with minimum current point tracking (MCPT) to minimize conductive losses. Unlike recent efforts in this area, the proposed controller does not require look-up table for implementation nor complex nonlinear converter modeling and is not circuit parameter dependent. The proposed control scheme is also generalized for MAB converters with any number of ports and is derived in per unit form to enable standard implementation for buck/boost/unity-gain operating modes. The proposed MCPT algorithm is based on an innovative adaptive perturb and observe tracking of the minimum current point (MCP) on the MAB converter current characteristic plane. This MCP is tracked while active power regulation is simultaneously achieved based on a new phase shift decoupler to enable direct regulation of individual port active power. Detailed design procedure of the proposed controller is presented and extensive simulation is carried out to validate the effectiveness of the proposed MCPT closed loop controller. Experimental implementation is also provided to substantiate the simulation results. [ABSTRACT FROM AUTHOR]

This article proposes a new asymmetric neutral-point diode-clamped (NPC) multilevel converter for a four-phase switched reluctance motor drive. The inbuilt NPC clamping capacitors are used for both voltage level clamping and also as dc rail voltage-boosting capacitors to increase the output power of the motor, particularly for high-speed electric vehicle applications. The new converter allows regenerative energy to be recovered back to the dc supply for rapid machine braking, thus increasing overall drive efficiency. Analysis of the different modes of converter operation, along with design equations for sizing the voltage-boosting capacitors, is detailed. The effect of capacitance on boost voltage and increased motor base speed is presented. Simulation and experimental results confirm the effectiveness of the proposed converter. [ABSTRACT FROM AUTHOR]

In an effort to minimize the power disruption between a dc grid and ac grids that host power converters during ac and dc network faults, this paper proposes a novel converter station structure to improve ac and dc fault ride-through performance of the multiterminal HVdc grid. The proposed structure consists of two independent ac and dc interfacing circuits, which are a half-bridge modular multilevel converter and a cascaded H-bridge (CHB) based energy storage system. Taking the advantages of high controllability and flexibility of the independent CHB converter and ease of integrating energy modules, a decoupled power relationship between the ac and dc sides is achieved, which is important for enhancing ac and dc fault performance. Operation of the proposed converter station under normal conditions and during ac and dc faults is explained, with the control system presented. Simulation validation of the proposed structure on a three-terminal HVdc grid confirms the enhanced performance, including the continuous operation during ac and dc faults with negligible power transfer disruption. [ABSTRACT FROM AUTHOR]