In this study a new technique of Direct Power Control (DPC) is proposed to connect distributed generation sources to the nationwide grid. This technique not only adds power of distributed generation sources to the grid, but also is capable to compensate the reactive and harmonic power of non-linear loads as well. In this study, converters’ voltage references for generating compensation current are directly calculated in synchronous rotating coordinate system in each period of sampling; then, a proper pulse width modulation (PWM) generates the used voltages. The proposed DPC technique has some advantages including simple algorithm of fast dynamic as well as fixed switching frequency and small sampling frequency. The performance of the proposed direct control technique is confirmed by simulation results.

This paper presents a new control method based on Lyapunov function approach for simultaneous control of grid currents, circulating currents and modules voltages of a modular multilevel converter. Unlike existing methods that use nested and multi-loop control structures, the proposed method has a single-loop structure and ensures the global asymptotic stability of the closed-loop system. In this regard, first, the dynamic equations of the converter and the grid are extracted using the averaging technique, and then the coordinates of the steady-state operating point are calculated. Next, using the obtained operating point coordinates and the dynamic equations of the main system, the error dynamics are computed. Finally, these equations and the Lyapunov function, based on the error signals, are used for the analytic calculation of the control inputs. The simulation results confirm the efficiency of the proposed control method.

With the rise in the penetration of inverter based distributed energy sources, grid codes say that converters should not be disconnected during the fault. These sources should also help the grid by reactive power injection. Power system grids are resistive inductive and the converter may be unstable during the fault. converters use phase locked loop (PLL) to synchronize with the grid. PLL is not able to be stable during severe voltage drop, so converters cannot ride through the fault and should be disconnected. In this paper a novel method based on virtual impedance is proposed to maintain the synchronization during severe voltage drop. This method needs grid impedance estimation and virtually connects the converter to a point that has a stronger connection. By this novel method, during voltage drop, the converter stays connected to the grid and injects reactive power. Simulation results in MATLAB verify the ability of proposed method in improving the transient stability of converter.

Parabolic carrier PWM method is considered as one of the direct current control methods which has been proposed for the voltage-source converters (VSCs). This method has an excellent dynamic response. Besides, it proposes a constant switching frequency by employing a pair of parabolic PWM carriers. However, it suffers from some drawbacks and limitations. The major drawback of this method is its sensitivity to the inductance variations. In other words, in grid-connected applications the exact value of grid inductance should be exactly known to achieve a proper performance from this method. Moreover, it is essential that during each switching cycle the voltage at the point of common coupling remains constant. In grid connected applications such as active power filter these drawbacks may lead to operate at variable or non-expected frequencies. Therefore, this paper concerns the suggestions to deal with the situation. In this paper, by applying the conventional method the aforementioned problems are examined in a grid-connected active power filter. It is shown analytically that by using the proposed method, problems of sensitivity to inductance changes and also necessity to constant voltage at point of common coupling in a switching period will be solved. Finally, simulation and experimental results are presented.

Nowadays, LCL filters utilization to suppress the grid-connected inverter switching harmonics is expanding and various methods such as capacitor current active damping scheme could be investigated to damp out these harmonics. However, the computational delays including control system, and PWM switching delays have significant effect on damping system stability. In most of LCL filter parameter designing schemes, the try and error methods are used, and the complicated calculations are needed for system stability considering grid impedance variation and delay effect. In this paper, at first a systematic method is provided for filter parameters designing by which better dynamic response and lower filter volume size are resulted and then, the step-by-step design procedure of grid-connected converter controller parameters with LCL filter by reducing the computational delay in inner (capacitor current feedback)- and outer control loop (grid current) is proposed for LCL filter resonance damping which is stable in case of severe variations in grid impedance. The simulation results by MATLAB/Simulink illustrate appropriate system operation.

In the grid-tied PV inverter systems, the design of a proper power conditioning system is an important issue to ensure high-quality power injection to the grid. Among various control methods for a grid-interfacing inverter with LCL filter, converter-side current feedback (CCF) method has been widely used due to its inherent resonance damping feature. Applying the CCF method requires extra attention to the delay effect of the control system. In such systems, the delay narrows stability region of the resonance frequency of the CCF control method, especially, in the presence of wide variations of the grid inductance. Adequate tuning of the LCL filter and consequently, the proper choice of the resonance frequency can remarkably affect the performance of the CCF control. In this paper, a tuning procedure for the LCL filter has been proposed. Mathematical tuning of the Proportional Resonant (PR) controller parameters has also been included to avoid typical trial and error procedures of tuning. Simulation of the overall system also includes solar panels, maximum power point tracking algorithm, Modified-Y-Source inverter, and LCL filter to model the grid-tied PV system with the most possible details. Simulations are carried out in MATLAB/Simulink, and it has been proved that the proposed control system maintains its stability against grid parameters variations.

A critical protection requirement for grid connected distributed generators (DG) is antiislanding protection. In this paper, a new islanding detection method for any possible network loading is proposed based on utilizing and combining various system parameter indices. In order to secure the detection of islanding, eight intentional disturbances are imposed to the system under study in which two sets of them simulate the islanding condition. The proposed technique uses the adaptive notch filters for extracting the frequency of oscillation of generator’s output waveform as one of the output parameter indices. An advantage of this technique is that it does not necessitate varying the islanding detection boundaries under various system loading conditions.

The primary objective of this paper is to address the adverse effects of active power fluctuations on grid-connected converters. One of the challenges in integrating high levels of solar photovoltaic power into the utility grid is the lack of inertia from converter-based resources. This paper proposes a solution to this challenge by synthesizing additional inertia and damping properties using power electronics converters. They emulate the inertia and damping properties of synchronous generators. The paper discusses different approaches to achieving effective damping control in grid-connected converters. It proposes a genetic algorithm optimization tool to optimize virtual damping and inertia parameters. The goal is to suppress oscillations and ensure stable grid operation. The proposed method is evaluated in both time-domain and frequency-domain analyses. The simulation results demonstrate the validity of the optimization technique and implementation procedure. Using virtual inertia and damping properties ensures stable grid operation and improves the integration of solar photovoltaic power into the utility grid. The paper provides a detailed discussion of the approach, optimization tool, and simulation results, highlighting the effectiveness of the proposed method.