Power grids with high integration of power electronic converters face new issues that have not existed before. The frequency in the power system is highly related to the inertia and the rotational speed of the operational synchronous machines. This is now changing, as the converter-based generation units are contributing increasingly to the balancing of active power in the modern power grid. Several frequency control designs for the power electronic-based generation units have been presented in the past. However, optimal control structures and settings are dependent on the current power grid parameters and operation. The converter-based units allow the transmission system operators to change their behaviour according to their grid requirements much more dynamical than ever before. The paper proposes a new analysis framework that can be utilized to find the best-suited control settings in converter-based units to enhance the system frequency reliability. The proposed framework is demonstrated in a study case by varying the settings of one frequency control scheme currently used in wind power plants in the Danish grid codes and validated on the IEEE 24-Bus reliability test system with additional wind power integration.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

The transition to renewable energy-based power systems is fast progressing. One of the main challenges in keeping a power system with high operational reliability is to maintain the system frequency. As synchronous generator units are being replaced with powerelectronic converters, the rotating mass and the system inertia are decreasing. Virtual synchronous machine (VSM) control is a modern control technique that aims to compensate for the reduction in inertia. The usage of power electronic-based converter units equipped with VSM control has to be managed and scheduled by system operators. An assessment of the operational frequency reliability is used to evaluate different service usages. A method is proposed that allows the comparison of different frequency management strategies. The proposed method uses fuzzy logic to evaluate the system risk for abnormal frequency and the system effort in the form of frequency control usage. This allows to quickly compare different frequency management strategies whilst keeping in mind many different reliability indices. The proposed method is validated with a modified IEEE Reliability Test System with integrated wind power capacity.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Power grids all over the world are nowadays facing high penetrations of renewable power generation. The converterbased generation units play a major role in system behaviour and operation. Thereby, also the reliability of the power system is impacted in many different aspects. It has to be verified whether the frequency reliability assessment, which is often studied by simulations, is still accurate, every time a new control structure is considered. For this, the number of simulations should not be further increased if possible, in order to keep the computational efforts low. In this study, the authors verify that the assessment outcome will be accurate when the load duration curve (LDC) and wind power curve (WPC) of a system are described well enough. This is shown to be true for different frequency controls, implemented in wind power plants in the system. Besides, the effects of different LDCs and WPCs are analysed, as they can change over time. The used methodology is validated on the IEEE reliability test system (IEEE RTS).

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STATCOMs with voltage control are known for their fast reaction time to stabilize the grid voltage. For optimal dynamic performance it is essential to use the correct gain settings for the PI voltage regulation controller, adapted for different states of operation. This paper shows the equation to calculate the accurate value for the gain setting in the voltage controller. The inner control behavior with enabled droop control is considered as well as the strength of the grid. After this the influences between STATCOMs installed in parallel in one bus is shown and the adaption of the gain to take this into account is calculated. The equations are validated by analytic aspects as well as by simulations. This enhances the existing control solution in industry and allows constant dynamic performance under various system changes in future grids.