Utility intertie multi‐photovoltaic‐inverters‐based microgrid control for solar rooftop

This paper presents a real-time simulation of a photovoltaic-based distribution static compensator (PV-DSTATCOM) using the Typhoon HIL 604 simulator, demonstrating its effectiveness in reactive power compensation, harmonic mitigation, and active power injection. The system seamlessly transitions between pure DSTATCOM mode, operating during night-time or when PV generation is zero, and PV-DSTATCOM mode, where it injects PV power while enhancing the power quality. A voltage source converter (VSC) regulated by an indirect current control strategy ensures improved power quality at the point of common coupling (PCC). Real-time simulation results under both balanced and unbalanced PCC voltage conditions validate the ability of the PV-DSTATCOM to mitigate power quality disturbances. Notably, the PV-DSTATCOM effectively reduces total harmonic distortion (THD), maintaining levels between 3.03%–5.58% under balanced PCC voltage and 3.95%–5.93% under unbalanced PCC voltage conditions, generally adhering to or remaining near the acceptable limit of IEEE-519 standards across varying solar irradiance levels and non-linear load conditions. Additionally, it maintains a near-unity power factor operation at PCC and stabilizes the DC-link voltage at 900 V (± 5%), ensuring reliable operation.

This paper presents a three-phase four wire grid interactive multiple solar photovoltaic (PV) and a battery based microgrid system. The DC links for the main voltage source converter (VSC) and the ancillary VSC are interfaced individually, to two solar PV arrays using a different maximum power point (MPP) tracking control i.e. incremental conductance (InC) method, in an inexpensive and effectual single stage topology. These VSCs are interfaced in parallel linkage to the point of common coupling (PCC) with distinct nonlinear loads, to enhance microgrid rating for distributing the active power on grid side and the system is reliable in an islanded mode. In normal situations, the current control is used for the main VSC in the grid intertied mode and at the disconnection from the grid, this system operates with the voltage control. The main VSC's mode transition performance is free from transitory and is obtained by a power electronic switch (PES). At the main VSC DC link, a DC-DC converter with the buck-boost operation is linked in series with the battery, manages the load network demand and sustains the DC link's voltage to MPP. At the PCC, frequency and voltage are regulated via voltage control and gives incessant power to the loads and good quality voltage is provided to the ancillary VSC to perform through the current control. The current control is utilized for power factor correction, harmonics eradication and enhancement of system's dynamics with PV feed-forward part. The microgrid operation is found satisfactory for scenarios like, grid outage, solar irradiance alteration, load unbalance and neutral current compensation and authenticated through simulated results obtained in MATLAB / SIMULINK platform.

Brushless doubly-fed induction generators have higher reliability, making them an attractive choice for not only offshore applications but also for remote locations. These generators are composed of two back-to-back voltage source converters, a grid side converter and a rotor side converter. Existing techniques use the rotor side converter for reactive current control; however, it is more suitable for stabilizing steady state behavior. In order to stabilize the voltage fluctuations at the point of common coupling (PCC) due to sudden inductive load introduction, the grid side converter may be a better choice due to faster response and higher control bandwidth. Therefore, this paper proposes a control scheme for the grid side converter to suppress the PCC voltage fluctuations when a large inductive load is suddenly connected. The proposed technique is based on an analytical model of the transient behavior of the voltage drop at the PCC. The analysis shows that reactive current control using the grid side converter introduces a double fundamental frequency component to the PCC voltage. To block this harmonic, we designed a notch filter. The simulation results in Matlab/Simulink show that the proposed technique can not only significantly reduce the voltage drop but also results in an 82% reduction in voltage distortion at the PCC.

<p><span lang="EN-US">This work proposes an adaptive filter based on a new least mean sixth control approach with incremental conductance method of MPP for 3-phase grid-incorporated photovoltaic (PV) system. The proposed system comprises a PV array, 3-phase DC to AC converter, maximum power point tracker (MPPT), three-phase electronic load, and a 3-phase grid. The combination of solar PV array and the voltage source converter (VSC) supplies power to the grid. The 3-phase inverter as a distribution static synchronous compensator (D-STATCOM) improves the quality of the system performance in case of zero solar irradiation. D-STATCOM also reduces total harmonic distortion (THD) in grid currents, improves power factor, and maintainsa constant voltage at the point of common coupling (PCC). The system modelling and simulation is achieved on MATLAB/Simulink. The proposed system performance has been found satisfactory and conform to IEEE-519 standards.</span></p>

In this work, a novel control of single‐phase solar photovoltaic (PV) fed unified active power filter (PV‐UAPF) is proposed for use in low‐voltage distribution system. The shunt voltage source converter (VSC) of PV‐UAPF mitigates current power quality issues such as current harmonics, reactive current etc. while the series VSC of PV‐UAPF protects the sensitive load against point of common coupling (PCC) voltage disturbances. The shunt VSC control is based on extraction of fundamental load active current using recursive least squares with a variable forgetting factor. The proposed method improves the dynamic response of the system without sacrificing the steady‐state performance. The series VSC is controlled using a proportional‐resonant controller and it injects voltage in/out phase with PCC voltage during voltage sags/swells, respectively. The PV array which is integrated at the DC link of the PV‐UAPF through a reverse blocking diode, provides the load power demand and also supplies remaining power into PCC. The system performance is evaluated using Matlab‐Simulink software and is then experimentally verified on a prototype developed in the laboratory under steady‐state and dynamic conditions such as irradiation variation, PCC voltage fluctuations and load disturbances to validate the performance of the system.

This paper proposes a robust design for a standalone Distributed Generation (DG) system based on wind, solar photovoltaic (PV), and battery storage to serve isolated or off-grid applications. The system employs an Adaptive Normalized Least Mean Absolute Third (ANLMAT) algorithm to construct an adaptive controller that optimises synchronisation between Renewable Energy Sources (RESs) and the load, enhancing the overall reliability and Power Quality (PQ) of the system. The ANLMAT algorithm with a Voltage Source Converter (VSC) provides support at the Point of Common Coupling (PCC) by balancing loads, reducing harmonics, and improving PQ. The results confirmed the proposed system achieved a Total Harmonic Distortion (THD) of 3.29%, well below the IEEE-519 standard limit of 5%, confirming its capability to maintain PQ standards. The system architecture integrates a battery and a Maximum Power Point Tracking (MPPT)-enabled PV system at the VSC's DC link. The battery storage manages power by absorbing excess energy during periods of low demand and supplying additional power during peak demand. Under dynamic conditions, such as fluctuations in unbalanced loads, solar irradiance, and wind speeds, the ANLMAT-based control shows superior stability, synchronisation, and energy management compared to existing control approaches, including SRF-PLL and LMS algorithms.

This paper deals with the adaptive estimation of frequency observation (AEFO) based technique for compensating the harmonics component of two-stage grid-connected solar photovoltaic (PV) system. The maximum PV power is extracted using maximum power point tracking (MPPT) algorithm. Moreover, the input DC voltage of the voltage source converter (VSC) is maintained at desired level using a proportional integral (PI) controller. The AEFO control injects the required reactive component, which shapes the balanced grid currents. Moreover, the active power is injected in to the grid, which eliminates the harmonics in the grid currents. Using this controller, the fundamental reference currents are estimated using nonlinear load currents. This system maintains the grid current total harmonic distortion (THD) in accordance to the IEEE 519 standard. The dynamic response is improved by adding the PV feed-forward term with the estimated magnitude of i eα and i eβ current quantities. This control improves the dynamic response when insolation is changed and also provided a good response when switched from PV array to DSTATCOM and vice versa. Moreover, the power quality issues such as load unbalancing, power factor correction and reduced the grid side currents harmonics. Test results has shown the reactive power compensation of balanced and unbalanced nonlinear loads and the steady-state and dynamic performances of the system and PV array to DSTATCOM and vice-versa.

In the last decade, grid-connected photovoltaic systems were studied and developed due to advance in the technology of solar panels, their price drop and the climatic crisis. This work will study, analyze and design a low power solar inverter. The most important design constraints for a solar inverter are: efficiency, maximum power point tracking (MPPT) performance and synchronization with the utility grid. The objective of this project is to find a solution for each (minimization of power losses, precise tracking of grid frequency). To achieve a satisfying efficiency, a current mode control loop in a two-dimensional control frame was implemented, with an enhanced phase-lock loop (EPLL) as the synchronization mechanism with the utility grid. For tracking the maximum point on the power curve of the solar cell, a classical hill climbing method was improved and integrated into the system. For simulations, Matlab Simulink software was used and input power versus output power was examined along with total harmonic distortion (THD) of the inverter's output current, while for experimental testing a dSPACE controller board and two Suntec Power solar panel. The paper is focused on the current mode control loop mathematical equations providing a simplified step by step design process.

A single phase Grid Connected Current Source Converter (GCCSC) for photovoltaic (PV) systems with sinusoidal grid current injection control is presented in this paper. The Voltage Source Converter (VSC) topologies are extensively used for connecting Renewable Energy Sources (RES) to the utility grid. The grid current injection control structure is quite tough or dependent on outerloop in case of VSC based PV compared with current source converter (CSC) based PV. The presented control structure and overall system achieves following functionalities (i) Always PV panel is operating at Maximum Power Point (MPP) mode by using Perturbation and Observation (P&O) algorithm (ii) Ripple current in the DC link is very less (iii) Unity Power Factor (UPF) (iv) Very less Total Harmonic Distortion (THD) of grid currents. To verify the effectiveness of control structure and overall system, simulation studies were done in MATLAB/SIMULINK environment.

This paper presents the concept of interconnection of Solar Photovoltaic (SPV) power generating system using Synchronous Reference Frame (SRF) theory based control in indirect current control mode of operation. This proposed theory improves the power factor and voltage at point of common coupling (PCC). Voltage at PCC is maintained through reactive power compensation. The whole power generating system consists of SPV system, dc-dc boost converter, maximum power point tracking (MPPT), voltage source converter (VSC), ripple filter, different types of loads, interfacing inductor and three phase grid. This system eliminates harmonic currents and load balancing is also possible using it. The grid-interconnected SPV system is tested for two modes i.e. unity power factor mode of operation and voltage regulation mode, with load balancing problems of linear loads.

Voltage source converters (VSC)-based high voltage direct current (HVDC) link is an economical option for the long distance bulk power transmission, and it can be used to interconnect the offshore wind farms with an AC grid. Due to the penetration of VSC-HVDC system into the AC grid, the performance of the distance relay gets affected when a transmission line close to the point of common coupling (PCC) subjected to power system disturbances. In such condition, the PCC voltage is increased due to the VSC-HVDC control action, that causes the Zone-2 fault can be seen as a Zone-3 fault. As a result, the miscoordination of Zone-2 protection can occur in the distance relays. This paper presents both the analytical and simulation studies carried out on a VSC-HVDC system influence on the distance relay performance under fault conditions using PSCAD/EMTDC. Simulation results show that the presence of VSC-HVDC system greatly affects the performance of the Zone-2 and Zone-3 relay in an AC transmission line. Besides, the maloperation of the Zone-2 and Zone-3 relay is mitigated by varying the AC voltage reference input of the decoupled d-q controller of VSC-HVDC. Also, the effect of fault resistance on Zone-1 ground relay performance is analyzed.

This paper proposes a point of common coupling (PCC) voltage compensation method for islanding microgrids using an improved power sharing control scheme among distributed generators (DGs) without communication. The PCC voltage compensation algorithm is implemented in the droop control scheme to reduce the PCC voltage deviation produced by the droop controller itself and the voltage drop on the line impedance. The control scheme of each individual DG unit is designed to use only locally measured feedback variables and an obtained line impedance to calculate the PCC voltage. Therefore, traditional voltage measurement devices installed at the PCC as well as communication between the PCC and the DGs are not required. The proposed control scheme can maintain the PCC voltage amplitude within an allowed range even to some extent assuming inaccurate line impedance parameters. In addition, it can achieve proper power sharing in islanding microgrids. Experimental results obtained under accurate and inaccurate line impedances are presented to show the performance of the proposed control scheme in islanding microgrids.

Due to the Randomness and fluctuation of the photovoltaic (PV) system, Maximum Power Point Tracking (MPPT) algorithm is employed to ensure the maximum power extraction from PV arrays, when it is connected to the grid. The previous studies have indicated that the MPPT algorithm is one of the main causes of interharmonics emission in PV systems. The MPPT algorithm parameters such as perturbation step size inevitably have a strong impact on the interharmonics in the current injected to the grid. In general, a smaller MPPT perturbation step size will reduce the interharmonics emission level, but it will result in poor tracking performance of the MPPT algorithm. Thus, there is a trade-off between the MPPT efficiency and the interharmonics emission in PV system. In this paper, an interharmonics suppression scheme with variable step size MPPT algorithm was proposed. In the suppression scheme, two voltage values near by the MPPT voltage and two tracking step size are preset. When the dc-link voltage of PV is between the two preset voltage values, it means that the PV power near its MPP and the smaller perturbation step size implemented in the MPPT algorithm. Otherwise, the bigger perturbation step size is employed. It can greatly reduce interharmonics emission level and maintain the MPPT efficiency. Simulations have been carried out to verify the effectiveness of the suppression scheme.

Solar Photovoltaic (SPV) offers alternative sources of energy which is in general pollution free, environment friendly, sustainable and unlimited in nature. The concerns of environment due to green house gases and global warming force research communities to develop a smart power system that has capability to integrate Solar Photovoltaic with the power grid. There are many challenges in integrating SPV generation with the grid like efficiency, power quality, stability, cost of the energy conversion, load management, reliability etc. Moreover, power quality problems at distribution level like harmonics, unbalanced supply, unbalanced loads, reactive power, load management etc. affect the operation of grid connected SPV systems. Single stage grid connected PV systems has the advantage of use of a single VSC for MPPT (Maximum Power Point Tracking) and inverter operation. The proposed grid interfaced SPV generating system consists of a SPV array, VSC (Voltage Source Converter), three-phase grid and linear/nonlinear loads. The SPV energy is injected in to the DC bus of VSC during sunshine hours. The DC bus voltage of a three- phase VSC is regulated for MPPT from the PV array. Secondly, this system serves to provide harmonics elimination, load balancing, power factor correction (PFC) and regulating the terminal voltage at the PCC (Point of Common Coupling). In this paper, a SRF (Synchronous Reference Frame) based control of a single stage dual purpose grid connected SPV system is proposed and simulation based on MATLAB and Simpower System Blockset demonstrates the dual purpose of the system.

In future low voltage grids, with multiple inverter interfaced sources connected, voltage regulation may become a necessary task. The potential exists for inverter interfaced sources to be deployed to regulate the voltage at the point of common coupling (PCC) of each inverter interfaced sources. The PCC voltage regulation is attainable with inverter interfaced sources by dynamically controlling the amount of reactive power injected to the power distribution grid by individual systems. In the current research, a closed-loop controller is proposed to regulate the PCC voltage of a solar photovoltaic (PV) system that is connected to a single-phase power distribution feeder (with R to X ratio greater than 1). The plant model of the PCC voltage controller of the PV system is derived considering both reactance and resistance of the network to which the PV system is connected. Three different compensators are evaluated to identify a suitable compensator for the closed-loop PCC voltage controller to regulate the PCC voltage at a given reference voltage. Simulation studies and experimental verification confirm that the theoretical approach taken to derive the control plant model of the PCC voltage controller is accurate and the procedure that is followed to design the controller is robust. The control design procedures illustrated in the current research leads to a PCC voltage control system with acceptable dynamic and steady state performance.