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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]

The increased use of distributed energy generation and storage systems for electrical, heat and cooling systems in households, industry and the Low- (LV) and Medium-Voltage (MV) networks makes an intelligent coupling of the electrical and thermals systems into a so-called hybrid energy system meaningful and necessary. In addition to the economic and ecological aspects, this coupling can be used to increase comfort and to reduce dependencies on fossil fuels and fluctuating energy price. The aim of the presented work is to investigate the effects of various influences on the economically optimal operation of a hybrid energy system (e.g. single-family house) and thus to show the interdependencies and drivers of the hybrid energy system, whereby these are graphically displayed for easier interpretation. [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]