In this study, a novel voltage droop scheme for the parallel operation of voltage source converters (VSCs) in an islanded multibus microgrid is proposed. In this scheme, the voltage droop coefficient is defined as a function of respective VSC active and reactive power outputs. Thus, each VSCs voltage reference is adaptively drooped as a non-linear function of its active and reactive power outputs. This approach leads to reduction in the reactive power sharing dependence on real power control and system parameters such as mismatched connecting and line impedances. A multiobjective index is introduced for evaluating the scheme performance. The index is used as an objective function in an optimisation problem that is employed to obtain optimal parameters of the scheme. The detailed analysis shows that this scheme has a superior behaviour compared to the conventional voltage droop method, in view of the reactive power sharing and loads voltage control under all loading conditions. Simulation and experimental results show the good performance of the method for three paralleled VSCs in a multibus microgrid system.

In this paper, a novel metaheuristic optimization algorithm inspired by General Relativity Theory (GRT) is presented. In this method that we named General Relativity Search Algorithm (GRSA), a population of particles is considered in a space free from all external non-gravitational fields and propel toward a position with least action. Based on GRT, particles have conserved masses and move along geodesic trajectories in a curved space. Step length and step direction for updating the particles are separately computed using particles velocity and geodesics, respectively. Velocity of particles is obtained by their energy–momentums. According to physical action principle, a population of particles goes to the position with minimum action. By inspiring this physical principle, GRSA will lead variables of an optimization problem move toward the optimal point. Performance of the proposed optimization algorithm is investigated by using several standard test functions and optimal Power System Stabilizers (PSSs) design in a multi-machine power system as a real-world application. Numerical simulations results demonstrate the efficiency, robustness and convergence speed of GRSA in solving various problems.

An asymptotically stable controller for solid-state transformers (SSTs) based on Lyapunov direct stability (LDS) method is presented in this study. The proposed controller has four control objectives for the SST application, which includes unity power factor at medium-voltage AC (VAC) side of the SST, constant DC-link voltage and constant output voltage magnitude and frequency at low-VAC side of the SST. To fulfil the above-mentioned objectives four control laws are derived from the Lyapunov function, directly. The proposed LDS-based controller is simulated using MATLAB/Simulink software. The obtained results indicate the fast and superior dynamic characteristics of the proposed controller. The LDS-based controller is comprehensive and can be adopted for the SST applications.

Dual-Active-Bridge (DAB) converters are able to step up/down DC voltage in a wide range by adopting medium frequency transformer (MFT) for isolating and converting voltage level. Increase in switching frequency of Si IGBTs reduces the MFT size instead it intensifies the semiconductor switching losses which leads to increase in the heatsink size. In this paper variation of heatsink volume versus frequency is compared versus MFT. MFT and heatsink volume of a 5 kW 600 to 400 V DAB converter are optimized. Obtained results show that variation of switching frequency in range 1-10 kHz increases the size of optimal heatsink by 3 times, i.e

This study aims at proposing an original single‐end protection scheme for the compensated transmission line using traveling waves and game theory. To this end, this paper initially investigates the effects of static synchronous compensator (STATCOM) on traveling waves passing through STATCOM installation point. Furthermore, based on the traveling wave theory, it evaluates the impacts of STATCOM's harmonic on conventional protections. A single‐end method will be proposed in the next stage for fault protection on the compensated transmission lines with STATCOM. The extracted traveling waves in this study will be discriminated using the game theory, and discrete wavelet transform will be utilized to process the signals and assess the sensitivity of the proposed scheme considering the extraction techniques of the traveling wave. According to the obtained results, the proposed protection scheme is a reliable and accurate method for all possible faults type on compensated transmission lines at the various locations of the line and with different fault inception angles.