The integration of distributed generations (DGs) can disrupt the distribution system's radial configuration, leading to potential coordination issues with the existing protection scheme. Disparate operating modes of microgrids render traditional protection schemes ineffective and insecure. This highlights the need for alternative approaches to ensure the reliability and security of microgrids. To mitigate the relay coordination problem in microgrids, this paper puts forth a solution in the form of an adaptive protection scheme. The proposed method is based on fault current and integrates the use of adaptive numerical directional overcurrent relays (ANDOCRs). The proposed adaptive protection strategy encompasses a microgrid central protection controller (MCPC) equipped with communication capabilities. This feature enables MCPC to communicate with intelligent field electronics devices (IFEDs). The MCPC receives data from the IFEDs and updates the ANDOCRs' settings according to the operation mode. This paper suggests a modified objective function specifically tailored to tackle the nonlinear optimization problem for relay coordination in microgrids to strengthen the coordination between primary and backup relays. The proposed adaptive protection scheme also incorporates a quick online fault detection algorithm to identify the faulty feeder precisely. The proposed method is assessed for its performance using a highly unbalanced IEEE-13 node distribution system in MATLAB/Simulink.

Background and Objectives: Cascaded doubly fed induction generators (CDFIGs) can directly connected to isolated load or power grid without any brushes which are needed in conventional DFIGs. Output control targets before grid connection of CDFIGs are voltage and frequency control and after that are active and reactive power control. In control aspect, output control of CDFIG is a multi-input multi-output (MIMO) subject. In this paper, Relative Gain Array (RGA) methodology, as a MIMO interaction index, is used to show the degree of relevance between the control inputs and output targets, in both voltage control mode (before grid connection) and active-reactive power control mode (after grid connection). Based on RGA results, conventional PI controllers cannot be used to decouple control of generator outputs in grid connected mode. So, a powerful method based on sliding mode approach is proposed to generate the proper control voltages for output control of CDFIG in both islanded and grid connected mode. Simulation and experimental results using Matlab and TMS320F28335 based prototype of CDFIG are provided to demonstrate the effectiveness and robustness of the proposed method. Methods: A mathematical method based on RGA matrix is used to evaluate the amount of interactions between output targets and input control variables in CDFIGs in islanded and grid connected mode. Results: Conventional PI controller is a proper method to control the output voltage of Power Machine (PM) in CDFIG but is not a suitable technique for active and reactive power control in grid-tied mode. Conclusion: Sliding mode control can be used to decouple control of CDFIGs in both before and after grid connection. As well as, robustness against the wind speed variation and parameters uncertainties is proved via both simulation and experimental tests.

As the penetration of distributed generation sources increases at the distribution level, the necessity of designing microgrids is highlighted. Microgrids can operate in either islanded (separated from the utility grid) or grid-connected mode. Apart from the technical and economic bene ts of microgrids, they may cause some protection issues in distribution systems. The most important of these issues is the di erence between the short circuit levels in islanded and grid-connected operation modes. In this paper, an intelligent overcurrent relay that can adapt to the microgrid operation mode is proposed; that is, the relay detects the microgrid operation mode by means of an adaptive algorithm. The proposed adaptive method optimizes the accuracy and speed of the algorithm for detecting the microgrid operation mode. Then, the optimal settings that have been already stored in the relay are activated according to the microgrid operation mode. All internal processes of the relay use the voltage and current sampled at the relay location. As a result, the relay can be used in all networks without communication infrastructures. Finally, the proposed method is implemented in a sample microgrid. The superiority of the intelligent relay performance over conventional overcurrent relays is shown by numerical results.

This paper proposes a new adaptive controller for the robust control of a grid-connected multi-DG microgrid (MG) with the main aim of output active power and reactive power regulation as well as busbar voltage regulation of DGs. In addition, this paper proposes a simple systematic method for the dynamic analysis including the shunt and series faults that are assumed to occur in the MG. The presented approach is based on the application of the slowly time-variant or quasi-steady-state sequence networks of the MG. At each time step, the connections among the MG and DGs are shown by injecting positive and negative current sources obtained by controlling the DGs upon the sliding mode control in the normal and abnormal operating conditions of the MG. Performance of the proposed adaptive sliding mode controller (ASMC) is compared to that of a proportional-integral (PI)-based power controller and SMC current controller. The validation and effectiveness of the presented method are supported by simulation results in MATLAB-Simulink.

This study investigates a new double-stage single-phase Grid-Connected (GC) Photo-Voltaic (PV) system. This PV system includes a DC-DC Positive Output Super Lift Luo Converter (POSLLC) and a single-phase inverter connected to a grid through an RL filter. Due to its advantages, the POSLLC was used between PV panel and inverter instead of the conventional boost converter. The state space equations of the system were solved. By using two Sliding Mode Controls (SMCs), PV panel voltage and POSLLC inductor current were controlled and the designed controls were compared. Two of these SMCs included a simple Sign Function Control (SFC) and a conventional SMC. To control the power injected into the grid with a unity power factor, an SMC was used. Perturb and Observe (P&O) method was employed to reach maximum power of the PV panel. The Maximum Power Point Tracking (MPPT) control generated the voltage reference of the PV panel. Similar controls were used for the boost converter instead of POSLLC. The obtained results were compared.

SoC-based control unit for B4 inverters in a cheap grid-connected Photovoltaic (PV) system is proposed in this paper. Because the inverter is the main element of Photovoltaic module, we utilized the B4 one here for decrement of entire expenditure of Photovoltaic system. This paper also coupled the Photovoltaic system to the main grid via IGBT switches for removing the bulky transformers. Besides, in order to inject the real energy to the main grid, this kind of inverter is able to compensate the real power and mitigate the harmonics related to the non-linear loads. Instead of the conventional PV systems on which a DSP processor is used to control the B4 inverter, we applied a zynq-7020 SoC-base control unit to effective control of the B4 inverter. Several characteristics of such control units such as dedicated low power and fast 32bit×32bit multipliers, with modified algorithm, enable the application of the required control methods. The operation of the proposed control unit in a PV system is implemented on zynq-7020. Implementation of the control unit in the SoC zync-7020 is the main contribution of this paper. Comparison with the conventional DSP-based control systems, TMS320F28335 DSP processor, demonstrated the high efficiency of the proposed SoC-based control unit for B4 inverters.

Background and Objectives: In this paper, a novel approach for regulation of the output current in the grid-connected three-level flying capacitor inverter is presented by using the sliding mode (SM) method. In the proposed method, it is possible to control the active and reactive components of the inverter output current independently, and therefore it can be employed for grid connection of the renewable energy resources or for harmonic and reactive power compensation of the local loads. The designed controller uses an external loop to control the voltage of the inverter DC link and has a constant switching frequency. The stability of the proposed method has also been proved by using the Lyapunov stability theory. The simulation results show that in different operating conditions, the proposed controller has a stable and robust response. Methods: Grid-connected three-level flying capacitor inverter is modeled by using averaged state space technique. Considering nonlinearity of the obtained model, an equivalent SM controller is developed for output current control of the multilevel grid connected inverter. To improve robustness and stability of the system against uncertainty of model parameters, a nonlinear component is added to the equivalent controller. Results: The proposed controller enjoys very fast dynamic response, so it can be employed in wide ranges of application e. g. reactive compensation and harmonic mitigation modes. In active power filtering operation, it is able to eliminate harmonic components of the grid from 20. 61% to 1. 34% which is compatible with IEEE and IEC standards. Conclusion: The stability of the proposed method has also been proved by using the Lyapunov stability theory. The simulation results show that in different operating conditions, the proposed controller has a stable and robust response.