Inverter-Based Distributed Generation (IBDG) units are typically coupled to the grid via three-phase Voltage Source Converters (VSCs). The IBDGs may pollute utility with the injected harmonic currents. In order to meet the standards' requirements, the necessity of grid-integration through passive filters supports a reduction of harmonic currents. This paper presents a performance assessment for the harmonic reduction introduced on the grid-side inductor when using LLCL filter with a single LC-trap, and LLCL filter with a dual LC-trap, named here L-2LC-L filter. Moreover, it can be deduced theoretically, that the higher the number of the LC parallel branches, the lower the grid-side inductor. When connected between the VSC and the grid, these types of filters may introduce resonance. Therefore, a passive or active damping technique may be applied to suppress the resonance. This paper presents also through simulation, analysis, and experiment, an active damping approach for LCL filter as well as for a filter with single trap (LLCL) and for a filter with dual LC trap (L-2LC-L) with grid-interfaced three-phase VSC.

In inverter-based distributed generation (IBDG) and similar to the conventional third order LCL filter, the high order LLCL filter is difficult to stabilize, and may cause a resonance between the inverter and the grid. Passive damping techniques were explored in literature by connecting a resistor in different locations of the LLCL filter. This paper presents the performance of the high-order LLCL-filter with RC passive damping circuit through evaluating the system stability using dual-loop control strategy that has been applied to the LCLfilter. Comparative analysis regarding PI and PR controllers used in the proposed control strategy is offered. Simulation results using Matlab are conducted, presented, and discussed.

For the grid connection of voltage source inverters (VSIs), the power passive filters are a standard solution for grid-current harmonic attenuation. However, these types of filters may cause resonance between the inverter and the grid. Passive and active damping techniques are employed for resonance attenuation. Efficiency concerns have set active damping techniques as a promising solution for the resonance problem compared to the passive damping techniques. Characteristics, performance, effect of different active damping schemes, and stability analysis were investigated for the LLCL passive filter in literature. In this paper, the characteristics and performance, of active damping technique applied to an LLCL passive power filter interfacing a three-phase VSI to the grid are investigated. Stability analysis is conducted for the LLCL-based grid-connected VSI. The presented concept has been elucidated by simulation results using Matlab/Simulink platform and validated through experimental results.

The use of the Voltage Source Inverter (VSI) in Distributed Power Generation Systems (DPGS) and their connection to the utility network requires low pass filters which are typically used for grid current harmonic suppression. The first-order L-filter limits the harmonic current injection generated by the DC-AC converter, but at the expenses of high inverter switching frequency in addition to a bulky and expensive filter inductor. The L-filter may also lead to an increased loss due to a large voltage drop and to a poor dynamic response. For a better performance, the second-order LC filter can be used. The most common solution is to use the third-order LCL filter which reduces the filter size and introduces better dynamics with improved switching harmonic attenuation compared to a simple L-filter. However, this type of filter can be a source of resonance between inverter and grid if no damping method is adopted. Passive and active damping techniques are employed in order to reduce the resonance. Efficiency concerns established active damping technique as a promising solution for the resonance problem compared to the passive damping technique and thus has become of increasing interest. In this paper, the deployment of an additional control loop for active damping technique is investigated through simulation and demonstrated experimentally.

In inverter-based distributed generation (IBDG) and similar to the conventional third order LCL filter, the high order LLCL filter is difficult to stabilize, and may cause a resonance between the inverter and the grid. Passive damping techniques were explored in literature by connecting a resistor in different locations of the LLCL filter. This paper presents the performance of the high-order LLCL-filter with RC passive damping circuit through evaluating the system stability using dual-loop control strategy that has been applied to the LCL-filter. Comparative analysis regarding PI and PR controllers used in the proposed control strategy is offered. Simulation results using Matlab are conducted, presented, and discussed.

Power converters in grid connection applications commonly employ Sinusoidal Pulse-Width Modulation (SPWM) technique. Passive filters are employed in order to attenuate the generated switching current ripples and reduces resonances between the grid and the inverter. The first-order (L), the second-order (LC), and the third-order (LCL) filters topologies are typical filters for grid connected Voltage Source Inverters (VSI). Practically, due to the system size, weight, and cost requirements, the LCL filter is the most commonly used among others for the integration of the three phase VSI into the grid. However, the control system stability is affected by the underdamping characteristic of the LCL filter therefore, it introduces to challenges to the control problem. Numerous control strategies such as repetitive, predictive, multiloop control, and hysteresis regulation have been proposed in order to improve the stability of the grid-connected VSIs. In this paper, the performance of the third order LCL filter-based grid-connected three-phase VSI is evaluated and the system stability is investigated using a two-loop control approach with both passive and active damping. The two-loop control considers the grid current as the outer loop while for the inner loop, different variables are considered such as capacitor voltage, capacitor current, and inductor current.

Cooperative Learning is one of the most successful strategies used to develop class performance [1]. This procedure involves groups of students working together to complete a given task. The presented strategy helps students with low level (weak students) of abilities to increase their understanding of a topic and then improve their grades in the exam. The purpose of this study is to explore the use of face-to-face and e-learning (Blackboard) environments used by students to communicate and collaborate with each other. Clear instructions were providing to all students in order to be part of this study. During the achievement of this strategy, students realized that each person's work benefits not only that individual but the member of the same group as well.