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The main control loop of the synchronizer of the Grid Forming inverter can be synchronized with the voltage of the grid without using a phase-locked loop. However, in order to enable the inverter to realize the frequency regulation function accurately, a phase-locked loop is still required to obtain the grid's frequency information. Since the time constants of the phase-locked loop and P-f loop of grid forming control are at the same order of magnitude, the introduction of the phase-locked loop will affect the original dynamic performance of P-f loop. In this paper, small-signal modelling is performed on the P-f loop of the grid forming with considering phase-locked loop to obtain the transfer function of the system. The influence of the cutoff frequency of phase-locked loop on the system dynamics is mainly related to the expected damping of the P-f loop. When the P-f loop of the system is designed to be underdamped, decreasing the cutoff frequency of the phaselocked loop can increase the system damping, which increases the adjustment time and reduces the overshoot. The paper uses controller hardware-in-the-loop to verify the analysis results. [ABSTRACT FROM AUTHOR]

Wind field layout optimization concerning various parameters is a major point in planning and will influence the revenue for the whole life of the installation. Besides the obvious impact of wind distribution also other parameters like connection costs and levelized costs of energy influence the optimum layout and have to be included in a realistic optimization algorithm. In this paper the sophisticated optimization of wind field layout with of two fundamentally different heuristic algorithms is investigated. To do so, detailed real-world data from an existing wind field in Bogdanci, Macedonia is utilized by employing real wind field data we are able to calibrate model adequacy and ascertain a model that will serve as a referent guidance in the planning of future onshore wind fields. Different layouts were designed using sophisticated algorithms for handling the resulting highdimensional, highly nonlinear optimization problem. In particular, a nondominated sorting genetic algorithm (NSGA) and a mixed discrete particle swarm optimization algorithm (MD-PSO) were applied. Both optimization algorithms established bi-objective fitness functions, in particularminimizing the levelized cost of energy and maximizing the capacity factor. By comparing the results obtained with the existing layout, it is established that both optimization algorithms are adequate in determination of wind power plant layouts. It is proven that the implementation of sophisticated optimization methods can results in essential savings during the whole lifetime of the wind field. [ABSTRACT FROM AUTHOR]

In the practical application of PV grid-connected inverters, the failure of low voltage ride through has repeatedly occurred. Even if inverter model passed the grid compliance testing in test laboratories, multiple cases been observed where inverters lost stability during voltage dips in practice. The reason for this behavior were stability problems of the PLL (phase-locked-loop) circuit implemented in the converter control. This circuit is needed to set the phase reference for the inverter control. In this article, a detailed mathematical modeling of the inverter phase-locked loop system is carried out and analyzed. Based on the second order nonlinear differential equation, an intuitive graphical method is used to analyze the system. This analysis concludes that during and after low voltage ride through, stability of inverter depends on interaction of several control loops in the inverter. This interaction can lead to instability after fault clearing, since the phase-locked loop has left its area of stability. Through a power hardware-in-the-loop test system, this article reproduces this phenomenon in laboratory. [ABSTRACT FROM AUTHOR]