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In modern power systems with increasing penetration of wind turbines (WTs), improvement of low voltage ride through (LVRT) capability of WTs equipped with doubly-fed induction generators (DFIGs) is an important topic. Thus, this paper proposes an LVRT strategy and compares its performance with a widely used conventional LVRT strategy. The proposed strategy is designed with a capacitor connected in series with an inductor and both are connected in parallel to a resistor. This configuration is then connected to the ac side of the rotor side converter (RSC) via an R-L circuit. To validate the performance of the proposed scheme, three phase fault condition is simulated and analysed. Based on simulation results obtained in MATLAB/Simulink, there is significant improvement achieved in the stated objectives compared to the conventional LVRT scheme. Index Terms-Conventional crowbar scheme, doubly-fed induction generator (DFIG), fault ride through (FRT), low voltage ride through (LVRT), and wind turbines (WTs). I.

The future grid will include a high penetration of distributed generation, which will have an impact on its security. This paper discusses the latest trends, components, tools, and frameworks aimed at 100% renewable energy generation for the emerging grid. The technical and economic impacts of renewable energy sources (RES)-based distributed generation (DG) on the emerging grid security are also discussed. Moreover, the latest approaches and techniques for allocating RES-DG into the distribution networks using specific performance indices based on recent literature were reviewed. Most of the methods in recent literature are based on metaheuristic optimization algorithms that can optimally allocate the RES-DGs based on the identified network variables. However, there is a need to extend these methods in terms of parameters considered, objectives, and possible ancillary support to the upstream network. The limitations of existing methods in recent literature aimed at ensuring the security of the integrated transmission-active distribution network under high RES-DG penetration were identified. Lastly, the existing coordination methods for voltage and frequency control at the transmission and active distribution system interface were also investigated. Relevant future research areas with a focus on ensuring the security of the emerging grid with high RES-DG penetration into the distribution networks are also recommended.

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Low and time-changing inertia values due to the high percentage of renewable energy sources (RESs) can cause stability problems in power systems due to rapid frequency instabilities. Inertia monitoring will assist operators to apply suitable actions and more proper control methods to alleviate stability issues. Therefore, this paper proposes an online method to estimate the total inertia of a network using a recursive least-squares approach. The proposed method uses network measurements with a non-recursive system identification approach to initially estimate the network hypothesis model. Then, the recursive method is used together with time changing measurements to recursively estimate model parameters and extract online inertia estimates of the network. During the estimation, the method does not need to store previous data after each sample step; therefore, the computation burden is significantly reduced. More importantly, the technique incorporates the use of available electromechanical oscillation modes in the system, which are linked with system parameters, to determine the network inertia estimates. The applicability of the proposed method has been validated by numerical simulations of the IEEE 39-bus network and the aggregated New Zealand network with its actual inertia data.

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