Current control strategy of grid-connected inverter for distributed generation under nonliner load conditions

Distributed generation (DG) has become more important in recent years for supplementing traditional fossil energy resources for power generation. The DGs include microturbine (MT), fuel cell, photovoltaic (PV) arrays, wind turbine and storage devices. The DG units can operate in parallel to the main grid or in a microgrid (MG) mode. The MG is a discrete energy system consisting of DG and loads that are capable of operating in parallel with, or independently from the main grid. Meanwhile, Grid-Connected Inverters (GCIs) are typically used as the interfaces to connect each DG to the common bus in an MG mode. In the ongoing effort to improve the performance of MG, control strategy of three-phase GCI under nonlinear load conditions has become a mature and well-developed research topic, and some control strategies have been implemented in several countries. A new approach is proposed to control the GCI of DG in an MG under nonlinear and unbalanced load conditions. The proposed control strategy features the synchronous reference frame method. The primary advantage of this method is its ability to effectively compensate for the harmonic current content of the system currents and MG without using any compensation devices, such as an Active Power Filter (APF) or passive filter. In this system, the control strategy is designed to eliminate the main harmonics as well as to cancel the remaining harmonics. Furthermore, correction of the system unbalance is another key feature of the proposed strategy. Fast dynamic response, simple design, stability, and fast transient response are other key features of the presented strategy. The current total harmonic distortions were reduced from above 37.8% to less than 1% with the proposed control strategy under nonlinear load conditions. The proposed control method can be used on the GCI of MT and PV; and has the ability to reduce the complexity, size and cost of the control method in comparison with APFs

Techno-Economic Analysis of Stand-Alone Hybrid Energy System for the Electrification of Iran Drilling Oil Rigs

This paper explores the potential of use of stand-alone hybrid wind/solar energy system in electrification of calibrating equipment of drilling oil rig in Iran. To achieve this, different hybrid energy system configurations based on calibration equipment demand are proposed. This study puts emphasis on the energy production and cost of energy from both wind turbine and photovoltaic (PV) in the hybrid system. In addition, to make conditions more realistic, the real meteorological data is used for HOMER software to perform the technical and economic analysis of the hybrid system. Results indicate that the PV array shares more electricity production than the wind turbine generator if both wind turbine and PV array are utilized in the wind/solar hybrid system. Moreover, results show that the operational cost will be reduced by the suggested hybrid system

Optimal SSSC-based power damping inter-area oscillations using firefly and harmony search algorithms

The static synchronous series compensator (SSSC) can add a series reactance to the transmission line, and when it is fed using auxiliary signals, it can participate in damping inter-area oscillations by changing the series reactance. In this paper, the effect of the SSSC on small-signal stability is investigated. The design of a controller for damping oscillations is designed and discussed. Moreover, using the firefly and the harmony search algorithms, the optimal parameters controlling SSSC are addressed. The effectiveness of these two algorithms and the rate of SSSC participation in damping inter-area oscillation are also discussed. MATLAB software was used to analyse the models and to perform simulations in the time domain. The simulation results on the sample system, in two areas, indicated the optimal accuracy and precision of the proposed controller

Spotted hyena optimizer algorithm for capacitor allocation in radial distribution system with distributed generation and microgrid operation considering different load types

In this paper, the optimal allocation of constant and switchable capacitors is presented simultaneously in two operation modes, grid-connected and islanded, for a microgrid. Different load levels are considered by employing non-dispatchable distributed generations. The objective function includes minimising the energy losses cost, the cost of peak power losses, and the cost of the capacitor. The optimization problem is solved using the spotted hyena optimizer (SHO) algorithm to determine the optimal size and location of capacitors, considering different loading levels and the two operation modes. In this study, a three-level load and various types of loads, including constant power, constant current, and constant impedance are considered. The proposed method is implemented on a 24-bus radial distribution network. To evaluate the performance of the SHO, the results are compared with GWO and the genetic algorithm (GA). The simulation results demonstrate the superior performance of the SHO in reducing the cost of losses and improving the voltage profile during injection and non-injection of reactive power by distributed generations in two operation modes. The total cost and net saving values for DGs only with the capability of active power injection is achieved 105,780 $and 100,560.54$, respectively and for DGs with the capability of active and reactive power injection is obtained 89,568 $and 76,850.46$, respectively using the SHO. The proposed method has achieved more annual net savings due to the lower cost of losses than other optimization methods

A Multi-Objective Optimization Problem for Optimal Site Selection of Wind Turbines for Reduce Losses and Improve Voltage Profile of Distribution Grids

In this paper, the optimal site and size selection of wind turbines (WTs) is presented considering the maximum allowable capacity constraint with the objective of loss reduction and voltage profile improvement of distribution grids based on particle swarm optimization (PSO as a multi-objective problem using weighted coefficients method. The optimal site, size, and power factor of the WTs are determined using PSO. The proposed method is implemented on 84- and 32-bus standard grids. In this study, PSO algorithm is applied to determine the size, site, and power factor of WTs considering their maximum size constraint (with constraint, variant size) and also not considering their maximum size constraint (without constraint, constant size). The simulation results showed that the PSO is effective to find the site, size, and power factor of WTs optimally in the single and multi-objective problem. The results of this method showed that the power loss is reduced more and voltage profile improved more considering WTs maximum allowable size versus not considering this constraint. Additionally, the multi-objective results showed that there is a compromise between the objectives in the multi-objective WTs site selection and the multi-objective problem solution is a more realistic and accurate approach in comparison with the single-objective problem solution

Control active power filter for improving power quality in the micro-grid

This paper aims at improving the power quality with controlling method shunt active power filter in Microgrid System. A hybrid compensation system consisting of an active filter and passive filters in the Micro-grid is discussed. Passive filter is connected to a distortion source and designed to eliminate main harmonics and supply reactive power for the distortion source, while the active filter is applied to the correction of the unbalance condition a system and cancellation of the remaining harmonics. In order to examine the proposed method, simulations are carried out in the case of the distribution system with dynamic nonlinear loads and Micro turbine. Several dynamic nonlinear loads without any filters using just shunt active filter, passive filter and the proposed hybrid structure. The performance of the proposed system was analyzed and simulated via MATLAB software. The results confirm the validity of the proposed approach to eliminate undesired harmonic and distortion