In this paper, a new approach is proposed for voltage and current harmonics compensation in grid-connected microgrids (MGs). If sensitive loads are connected to the point of common coupling (PCC), compensation is carried out in order to reduce PCC voltage harmonics. In absence of sensitive loads at PCC, current harmonics compensation scenario is selected in order to avoid excessive injection of harmonics by the main grid. In both scenarios, compensation is performed by the interface converters of distributed generation (DG) units. Also, to decrease the asymmetry among phase impedances of MG, a novel structure is proposed to generate virtual impedance. At fundamental frequency, the proposed structure for the virtual impedance improves the control of the fundamental component of power, and at harmonic frequencies, it acts to adaptively improve nonlinear load sharing among DG units. In the structures of the proposed harmonics compensator and the proposed virtual impedance, a self-tuning filter (STF) is used for separating the fundamental component from the harmonic components. This STF decreases the number of phase locked loops (PLLs). Simulation results in MATLAB/SIMULINK environment show the efficiency of the proposed approach in improving load sharing and decreasing voltage and current harmonics.

Existing generators used in renewable wind Turbines (WT) that are connected to the power system at the distribution level need a sound power grid for proper operation. The purpose of this article is to simultaneously use Unified Power Quality Conditioner (UPQC), wind turbine and appropriate control system to achieve the lowest harmonic distortion and voltage drop during network faults. Also, in this article, in order to check the efficiency of different fact tools when there is a fault in the network, a comparison between UPQC performance with static VAR compensator (SVC) and distribution synchronous static compensator (D-STATCOM) was made and the obtained results were presented. The performed simulations are based on compensation of voltage decrease and increase as well as compensation of harmonic distortion caused by nonlinear loads. The results obtained in this article show that Using UPQC in the network was able to compensate for 100% of voltage drop and voltage increase in the network, while svc and D-Statcom equipment in the best case compensated for 98\% of voltage increase and 90\% of voltage decrease. UPQC also can be the best tool to eliminate network flow harmonics.  In the previous papers, the best value for harmonic current distortion was 1.67%, but our results showed that the harmonic distortion of the network current when using UPQC is 1.47%. Also the harmonic distortion of network current with SVC and D-Statcom is 5.67 and 4.87 percent, respectively. The capability of the equipment in compensating for short circuit fault current and protection of wind power plant is also evaluated. There was no change in wind turbine voltage during the use of UPQC and faults, and 1 P.U remained constant, but when using svc and D-Statcom equipment, the wind turbine voltage during the fault decreased by 0.3 and 0.5 P.U respectively.

The paper proposes an algorithm to calculate the switching angles using harmonic elimination PWM (HEPWM) scheme for voltage source inverter. The algorithm is based on curve fittings of a certain polynomials functions. The resulting equations require only the addition and multiplication processes; therefore, it can be implemented efficiently on a microprocessor. An extensive angle error analysis is carried out to determine the accuracy of the algorithm in comparison to the exact solution. To verify the workability of the technique, an experimental voltage source inerter was constructed. Since the proposed HEPWM algorithm is simple and fast, it is implemented using a low cost, 16-bit microprocessor.

This paper presents a new method based on the wavelet packet transform for the analysis of harmonics in power systems. The algorithm can simultaneously measure the rms value of current, voltage and power using wavelet packets transform. The advantage of the wavelet packets transform is that it can decompose a power signal into uniform frequency bands. This decomposition into uniform frequency bands helps for the identification of harmonic components and measure of harmonic parameters. The algorithm is validated using simulated waveforms from the full wave inverter bridge circuit.

The progressive application of non-linear loads in distribution systems (DS) increases current harmonics flow in DS's apparatuses, especially distribution transformers (DTs). Since DTs' operating temperature rises due to the harmonics flow, their loading should be reduced such that the hot spot temperature (HST) is preserved under its permissible value. This means that DTs' available capacity is influenced by load harmonic content. In this paper, a novel formulation for DTs' failure rate in the presence of harmonics is presented as a function of load harmonic contents. Using the suggested equivalent failure rate, DTs' available capacity in harmonic polluted DS is mathematically formulated. Additionally, the presence of the harmonic increases the HST, leading to DTs' aging acceleration. Therefore, the impact of harmonic components on DTs' aging is arithmetically modeled. To evaluate the efficacy of the suggested reliability model, it is applied to three distinct DTs having respectively industrial, commercial, and residential loads. The obtained results indicate that the available capacity of DTs with the same rated capacity would be different regarding to their load harmonic contents. On the other hand, it is comprehended from the achieved results that the aging acceleration factor (Faa) of the DTs increases owing to their load harmonic contents.

Penetration of harmonics from downstream low voltage networks and resonance phenomenon has caused the level of harmonics to increase in transmission networks. Compensation of these harmonics at high voltage levels is neither recommended nor cost effective. This is due to the fact that there is no single large non-linear load which is causing these harmonics, yet filtering at low voltage non-linear load sites cannot completely compensate the harmonics and the remaining harmonic at standard levels still flow into the upstream networks. The idea of controlling harmonics at a medium/high voltage level caused by the remaining harmonics flown from low voltage networks and possibly amplified by resonance conditions with the use of series active power filters has been proposed by the authors in a published work. Since, this application of a series active filter was new, it was preferred to assign a new name for such device, i.e. harmonic power flow controller or simply HPFC. This work looks into the control strategies applicable to a HPFC in more details. The shortcomings of the previous methods are now removed resulting in better performance of a HPFC.