The problem of control of parallel-connected photovoltaic (PV) based distributed generation (DG) units in an AC distribution system is studied in this work. Firstly, a new robust back-stepping sliding mode based maximum power point tracking (MPPT) strategy is designed for each PV system. Then, a new control scheme is presented for power management of parallel-connected inverters of PV systems. The proposed control technique is an improvement to the instantaneous average current sharing control scheme (IACS) and uses adaptive fuzzy controllers to adjust the gains of the controllers of each inverter module. The fuzzy inference system is optimized using the H$\infty$ optimal theory to reduce the error in the fuzzy system. This adaptive fuzzy gain scheduling is then introduced to the IACS controller to improve the current and power sharing for a condition in which the system parameters change. Simulation results are presented to show the effectiveness of the proposed control strategy in improving the load sharing among parallel-connected PV systems.

There are many important trade-offs and constraints on cost, volume, weight, conduction losses, switching losses, microcontrollers, isolation, voltage and current levels, voltage and current ripples, battery specifications, charging–discharging algorithms, control system, switch gate drivers, and efficiency of battery chargers in electric vehicles. In this paper, a well-known power electronic topology commonly used in recent relevant studies is considered, and some important technical considerations with regard to the mentioned trade-offs and constraints are discussed in detail for the first time. The discussion concerns the practical and theoretical experiences in implementation of battery chargers and charging stations of electric vehicles exclusively, and it can be extended to various other power electronic topologies.

The inappropriate mechanism designs for demand response (DR) in the community of microgirds (CoMGs) may cause massive problems, such as increase of consumers’ costs, rebound peaks, and thereby lack of optimality in the network. In this article, a bilevel energy management system (EMS) is proposed to tackle the challenges associated with DR programs for CoMGs. The current structure successfully models users’ behavior and dissatisfaction in the first level of optimization to develop best DR program for each of them. Moreover, in the second level, power system constraints are taken into account to prevent voltage and current deviation from their statutory limits. Each user is assumed to be part of a microgrid (MG) whose operation is controlled and optimized through its local EMS in the first level. On the other hand, the overall operation of all MGs is delegated to the whole system operator, which acts as the central EMS (CEMS) in the second level. An iterative transactive energy management method is proposed by CEMS to fairly limit the excess power of the MGs one day ahead for voltage and current regulation. The obtained results indicate the effectiveness of the proposed structure in preventing discomfort issues, voltage deviation and creation of the rebound peaks in the system.

Offshore wind generators are connected to the ac power grid through high-voltage direct current (HVDC) transmission systems. However, when a short-circuit fault occurs in a transmission line, which is connected to the point of common coupling (PCC) of the HVDC system, the performance of distance relays on the ac grid is affected. This is due to rapid response of reactive power control of the grid-side voltage source converter (GVSC) of the HVDC system to compensate the voltage drop of the PCC bus. In other words, during the fault, the GVSC injects the reactive power to the ac grid to restore the PCC bus voltage. This in turn causes to interfere with the distance protection scheme by affecting the viewed impedance of distance relays. To overcome this problem, based on robust control theory, the present paper introduces a robust control approach for voltage source converter of HVDC system using μ synthesis analysis. The proposed strategy controls the reactive power injected to the PCC bus by trying to keep the defined current ratio $\alpha $ constant. The effectiveness of the proposed approach was validated through simulation using MATLAB/Simulink.