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Many distribution system operators are installing PQ monitoring systems in their medium-voltage networks. Installation of PQ monitors in all the nodes of the network is uneconomical, and power quality monitors are rather expensive. Therefore, the optimal placement of PQ monitors has to be found, while minimising cost and maximising observability. Researches published so far have presented PQ placement algorithms, but only from the aspect of one PQ disturbance (either dips or harmonics). In this paper, an algorithm for PQ monitor placement is presented, and its novelty is that it is the first research work accounting for several key PQ disturbances at once: harmonics, flicker, unbalance and dips. The chosen PQ disturbances are also modelled using novel modelling techniques, with the PQ disturbance behaviour modelled for a longer time period of one week or month. PQ disturbance behaviour is modelled for a real study case, where known real network topology, customer structure and measurements are used to develop a model validated by PQ measurements. Obtained synthetic PQ data, which are validated by PQ measurements, are used to optimise the PQ monitor locations. To choose the optimal PQ monitor locations, multiple linear regression was used, with the coefficient of determination R2 being the selection criterion. The results show that only two PQ monitors are necessary to monitor the analysed large real medium-voltage distribution grid, with high confidence. The methodology is straightforward and relatively easy to apply, and can be implemented for other medium-voltage distribution networks. [ABSTRACT FROM AUTHOR]

In the transition from non-renewable to renewable energy sources, wind and solar power plants have emerged as primary sources for reducing atmospheric emissions. However, ensuring grid stability remains a challenge in the absence of traditional power plants. Renewable energy sources are often referred to as "inertia-less," highlighting their vulnerability in transient stability scenarios in which system inertia is crucial. This paper introduces the concept of "synthetic inertia estimation" using an Extended Kalman Filter as a novel solution. Using the synthetic inertia estimation from a wind power plant, one can use the residual kinetic energy, and through the DC/AC converter, inject it into the system during times of stability disturbances. This paper offers practical insights into synthetic inertia estimation and its implementation for enhancing grid stability in a sustainable energy landscape. [ABSTRACT FROM AUTHOR]

The increasing share of converter-based renewable energy sources in the power system has forced the system operators to demand voltage support from the converters in case of faults. In the case of symmetric faults, all the phases have equal voltage support, but in the case of asymmetric faults, selective voltage support is required. The grid codes define the voltage support required in the case of symmetric/asymmetric faults, which is the reactive current injection in the respective sequence proportional to its voltage dip, but studies confirm that it does not result in a minimum unbalance factor in the case of asymmetric faults. The unbalance factor is an indication of the level of imbalance voltage among the phases. Moreover, it also results in fluctuated active power injection in the case of asymmetric faults, which causes dc link voltage fluctuations, and the power reversal may also occur due to such fluctuations, which leads to higher protection costs for the dc link. In order to (1) enhance the uniformity of voltage among different phases in the case of asymmetric faults and (2) minimize the real power fluctuations in such conditions, a novel control scheme is presented in this paper. It optimally distributes the negative sequence current phasor into its active and reactive components to achieve the minimum voltage unbalance factor. It also confirms the minimum real power fluctuations by adjusting the positive and negative sequence current phasors. The proposed scheme also ensures the current limit of the converter. The proposed scheme is developed in Matlab/Simulink and tested under different faulty conditions. The results confirm the better performance of the proposed scheme against the grid code recommendation under different faulty conditions. [ABSTRACT FROM AUTHOR]

This paper examines how the combined use of hydro governors and a wide‐area damping controller (WADC) can improve the damping of inter‐area oscillations in power systems. Such oscillations can endanger the stability of power grids, thus damping them is a high priority for transmission system operators (TSO). To ensure that low‐frequency oscillations decay as fast as possible, a modal linear quadratic Gaussian (LQG) is proposed as a wide‐area controller approach. Using the 10‐machine New England Test System, the combined application of the WADC in hydropower plants via generator excitation as well as via the hydro governor is examined for their effectiveness in terms of damping capability. In order to minimize the number of essential PMUs in power systems for the model‐based WADC, the residue‐based input/output signal selection method is applied. To increase the robustness against large disturbance faults, the generator voltage as additional signal is utilized for the WADC. For controller performance and robustness, the verification has been done under various operating points, tie‐line failures as well as different PMU delays. The successful damping of the inter‐area oscillation by means of wide‐area controlled hydropower plants has been also demonstrated through a nonlinear time domain simulation. [ABSTRACT FROM AUTHOR]