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.

The use of distributed generation resources (grid-connected or islanded) such as solar systems and wind turbines in the form of microgrids can solve problems related to traditional power systems. On the other hand, the monitoring of power quality disturbances in microgrids is an important issue for compensating these problems. Among the various types of power quality disturbances, harmonic distortions are important. Accordingly, in this paper, a computational method has been used based on the recursive least squares with the variable forgetting factor (VFF-RLS). The prominent features of the proposed method are its high accuracy and speed, as well as identification with a low rate of signal samples. The main aim of the proposed method is to identify the contribution and extent of Harmonics and unbalanced in a microgrid equipped with Advanced Metering Infrastructure (AMI). In the proposed method, the identification is based on real-time estimation and using measured data with high computational speed and accuracy. The results of simulation by MATLAB software, and as well as the experimental results using the TMS320F2812 digital signal processor (DSP) show the validity of the proposed method.

This paper presents a new control method for simultaneous compensation of instantaneous reactive power and Current Harmonics by parallel active filters (PAFs). Reference compensating Currents of PAF are calculated using the subtraction of instantaneous power from its average value. In this way, it is possible omitting high/low pass filter(s) from the control circuit of PAF, which usually results in phase shift and magnitude change of alternating components of instantaneous power. It is possible regulating the DC side voltage of PAF using a closed loop control circuit, easily. The presented method is compared with the classical p-q theory method through simulation results. A simple model for controlling the switches of power electronic converters is offered that is usable in PSCAD/EMTDC simulation package. Experimental results verify the validity of presented control strategy in generating of reference compensation Currents.

The increased use of nonlinear devices in the industry has resulted in the direct increase of harmonic distortion in power systems during these last years. Active filter systems are proposed to mitigate Current Harmonics generated by nonlinear loads. The conventional scheme based on a two-level voltage source inverter controlled by a hysteresis controller has several disadvantages and cannot be used for medium or high-power applications. To overcome these drawbacks and improve the APF performance, there’s a great tendency to use multilevel inverters controlled by intelligent controllers. Three level (NPC) inverter is one of the most widely used topologies in various industrial applications such as machine drives and power factor compensators. On the other hand, artificial neural networks are under study and investigation in other power electronics applications. In order to gain the advantages of the three-level inverter and artificial neural networks and to reduce the complexity of classical control schemes, a new active power filter configuration controlled by two MLPNN (Multi-Layer Perceptron Neural Network) is proposed in this paper.The first ANN is used to replace the PWM Current controller, and the second one to maintain a constant dc link voltage across the capacitors and compensate the inverter power losses. The performance of the global system, including power and control circuits is evaluated by Matlab-Simulink and SimPowerSystem Toolbox simulation. The obtained results confirm the effectiveness of the proposed control scheme.

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 development of a simulation platform for the study and conception of Current injection technique to improve power factor, to reduce Current Harmonics generated by a DC drive in high power application is discussed. This work proposes the simultaneous Current injection in all the three phases. Two Current shaping networks and Current injection devices are applied for harmonic reduction and power factor improvement. Based on the simulated results, optimal Current shaping network, Current injection device, and firing angle are recommended. The work is carried out for converter at different firing angles and is simulated using MATLAB.

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.

Dynamic capacitor (DCAP), as a shunt power quality device, corrects the power factor of the load and reduces the total harmonic distortion (THD) of the source Current. A novel control method was presented based on the model predictive control (MPC) to control a three-phase three-wire buck-type DCAP. The injected Current of DCAP is the control variable, which must be controlled by two power electronic switches of DCAP. MPC controller minimized the absolute value of the difference between a reference Current and a DCAP Current in the prediction horizon. The reference Current consisted of two distinct parts, i. e., reactive power compensator (RPC), and harmonic Current eliminator (HCE), based on the fundamental component of the load Current. Also, a prediction model (PM) was proposed to calculate state variables of the DCAP based on their previous values, state of the switches, and prediction values of the grid voltage. The proposed PM was extracted from the linearized differential equations of the DCAP. All DCAP components, such as capacitors and inductors of the inner and outer filters, were modeled in the proposed PM. Unlike the PI controller, the proposed MPC has fewer control parameters and can use in extensive operational conditions. The simulation results in MATLAB software showed the superiority of the proposed method compared with the even harmonic modulation (EHM) method on a three-phase DCAP.