The paper discusses load compensation using a distribution static compensator (DSTATCOM). It is assumed that the DSTATCOM is associated with a load that is remote from the supply. It is shown that the operation of a DSTATCOM assuming that it is connected to a stiff source in such situations will result in distortions in source current and voltage at the point of common coupling. To avoid this, the DSTATCOM is connected in parallel with a filter capacitor that allows the high frequency component of the current to pass. However, this generates control issues in tracking, as standard controls such as a hysteresis control are not suitable in these circumstances. This paper proposes a new switching control scheme and demonstrates its suitability for this problem. It also proposes a scheme in which the fundamental sequence components of a three-phase signal can be computed from its samples. The overall performance of the proposed scheme is verified using digital computer simulation studies.

Load compensating DSTATCOM in weak AC systems

The power system is experiencing an ever-increasing integration of photovoltaic power plants (PVPPs), which leads to the demand on the power system operators to force new requirements in order to sustain quality and reliability of the grid. Subsequently, a significant quantity of flexible power point tracking (FPPT) algorithms have been proposed in the literature to enhance functionalities of PVPPs. The intention of FPPT algorithms is to regulate the PV power to a specific value imposed by the grid codes and operational conditions. This will inevitably interfere the maximum power point tracking (MPPT) operation of PV systems. Nevertheless, the FPPT control makes PVPPs much more grid-friendly. The main contribution of this article is to comprehensively compare available FPPT algorithms in the literature from different aspects and provide a benchmark for researchers and engineers to select suitable FPPT algorithms for specific applications. A classification and short description of them are provided in this article. The dynamic performances of the investigated algorithms are compared with experimental tests on a scaled-down prototype. Directions for future studies in this area are also presented.

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Extended Functionalities of Photovoltaic Systems With Flexible Power Point Tracking: Recent Advances

Rapid industrialization and its automation on the globe demands increased generation of electrical energy with more reliability and quality. Renewable energy (RE) sources are considered as a green form of energy and extensively used as an alternative source of energy for conventional energy sources to meet the increased demand for electrical power. However, these sources, when integrated to the utility grid, pose challenges in maintaining the power quality (PQ) and stability of the power system network. This is due to the unpredictable and variable nature of generation by these sources. The distributed flexible AC transmission system (DFACTS) devices such as distributed static compensator (DSTATCOM) and dynamic voltage restorer (DVR) play an active role in mitigating PQ issues associated with RE penetration. The performance of DFACTS devices is mostly dependent on the type of control algorithms employed for switching of these devices. This paper presents a comprehensive review of various conventional and adaptive algorithms used to control DFACTS devices for improvement of power quality in utility grids with RE penetration. This review intends to provide a summary of the design, experimental hardware, performance and feasibility aspects of these algorithms reported in the literature. More than 170 research publications are critically reviewed, classified, and listed for quick reference for the advantage of engineers and academician working in this area.

/pdf/comprehensive-review-of-distributed-facts-control-algorithms-3abt9977a4.pdf

Comprehensive Review of Distributed FACTS Control Algorithms for Power Quality Enhancement in Utility Grid With Renewable Energy Penetration

This article presents a two-stage adaptive robust optimization (ARO) for optimal sizing and operation of residential solar photovoltaic (PV) systems coupled with battery units. Uncertainties of PV generation and load are modeled by user-defined bounded intervals through polyhedral uncertainty sets. The proposed model determines the optimal size of PV–battery system while minimizing operating costs under the worst-case realization of uncertainties. The ARO model is proposed as a trilevel min–max–min optimization problem. The outer min problem characterizes sizing variables as “here-and-now” decisions to be obtained prior to uncertainty realization. The inner max–min problem, however, determines the operation variables in place of “wait-and-see” decisions to be obtained after uncertainty realization. An iterative decomposition methodology is developed by means of the column-and-constraint technique to recast the trilevel problem into a single-level master problem (the outer min problem) and a bilevel subproblem (the inner max–min problem). The duality theory and the Big-M linearization technique are used to transform the bilevel subproblem into a solvable single-level max problem. The immunization of the model against uncertainties is justified by testing the obtained solutions against 36 500 trial uncertainty scenarios in a postevent analysis. The proposed postevent analysis also determines the optimum robustness level of the ARO model to avoid over/under conservative solutions.

Two-Stage Robust Sizing and Operation Co-Optimization for Residential PV–Battery Systems Considering the Uncertainty of PV Generation and Load

In this work, a simple phase-locked loop - less control is presented for a single-stage solar photovoltaic (PV) - battery-grid-tied system. As compared to traditional solar PV systems, the system has reduced losses due to the absence of boost converter and a flexible power flow due to the inclusion of a storage source (battery). The synchronous reference frame theory is used to generate the pulses for switching the voltage-source converter (VSC), while maximum power is extracted from the solar PV array by using perturb and observe-based maximum power point tracking technique. The inherent feature of shunt active filtering by the VSC has also been incorporated in this system. Test results for the system operation under fixed power and variable power mode are studied on a prototype developed in the laboratory. During fixed power mode, a fixed amount of power is fed to the grid, whereas in variable power mode the power fed to the grid varies. Test results obtained are in accordance with the IEEE-519 standard. This work is a basis for the upcoming power market, where solar PV consumers can manage the generated electricity and maximise their profit by selling the power to the grid judiciously.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-gtd.2017.1095

Control and operation of a solar PV-battery-grid-tied system in fixed and variable power mode

This study presents a solar photovoltaic distribution static compensator (SPV-DSTATCOM) system feeding a non-linear load connected at point of common coupling. A hybrid variable step size-least mean square-least mean fourth (VSS-LMS-LMF) algorithm is proposed for the control of voltage source converter, which acts as DSTATCOM. A weighing factor is used so that LMS and LMF work simultaneously, and a varying step-size helps in obtaining an adaptable system. The proposed control shows high convergence rate and low value of mean square error. The SPV array uses perturb and observe technique for maximum power extraction. The transition of SPV-DSTATCOM to DSTATCOM and vice-versa is also studied. In SPV-DSTATCOM mode, the SPV feeds power to the load and the grid, resolving the power quality issues of the system, whereas in DSTATCOM mode, the grid feeds power to the load at unity power factor. The system is first simulated in MATLAB environment and then these results are experimentally verified on the developed prototype in the laboratory. The system is studied for both power factor correction and zero voltage regulation modes and under distorted grid conditions. The obtained results adhere to an IEEE-519 standard.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-rpg.2016.0868

Hybrid VSS–LMS–LMF based adaptive control of SPV-DSTATCOM system under distorted grid conditions

This paper deals with the use of a distribution static compensator (DSTATCOM) to the system constituted by a nonlinear load fed from a distorted grid. Moreover, an improved proportionate normalized least mean square (i-PNLMS) control algorithm is proposed for the DSTATCOM. The system is first modeled on a MATLAB/Simulink platform and its performance is analyzed under steady state and load increment cases. The frequency response of the compensated system is also obtained. Tests are conducted on a laboratory prototype to analyze the system's performance under steady state and load unbalancing. This algorithm helps in achieving the desired grid currents easily and efficiently, and it shows an inherent tendency to adapt to the system's requirements. The obtained total harmonic distortion of grid currents and point of common coupling voltages are within the limits defined in the IEEE-519 standard.

Implementation of the DSTATCOM With an i-PNLMS-Based Control Algorithm Under Abnormal Grid Conditions

In this paper, a Volterra-filter-based control algorithm is developed to generate reference currents for a solar photovoltaic-distribution static compensator (PV-DSTATCOM) system in the distribution network The developed control is analyzed for being stable under Lyapunov stability criterion; consequently, the error function of the system converges to zero asymptotically The PV-DSTATCOM system is integrated to the grid to compensate the nonlinear load, while supplying solar PV array active power to the grid The system is modeled in MATLAB and is executed on a developed prototype in the laboratory, under balanced, unbalanced loading conditions, and variable insolation conditions Moreover, the harmonic distortion of the grid currents is observed under the IEEE-519 standard

Second-Order Volterra-Filter-Based Control of a Solar PV-DSTATCOM System to Achieve Lyapunov's Stability

In this paper, a vector-based synchronization technique is proposed for the synchronization of a solar photovoltaic (PV)-battery system to the grid. In this technique, the three-phase grid and point of common coupling voltages are transformed into two vectors in the α – β plane. Due to the absence of a phase-locked loop and feedback, the proposed technique is simple, and also instantaneous changes in the voltages are considered here. The grid-connected solar PV-battery system operates in the current control mode, while the islanded system operates in a voltage control. Experimental results are obtained on a grid-solar PV-battery system in grid-connected and islanded modes. The two transitions between these operating modes are also studied in detail. All these test results of harmonics in grid voltages and currents are found satisfactory and in accordance to the IEEE-519 and 1547 Standards.

Neha Beniwal

Papers

Control and operation of a solar PV-battery-grid-tied system in fixed and variable power mode

Hybrid VSS–LMS–LMF based adaptive control of SPV-DSTATCOM system under distorted grid conditions

Implementation of the DSTATCOM With an i-PNLMS-Based Control Algorithm Under Abnormal Grid Conditions

Second-Order Volterra-Filter-Based Control of a Solar PV-DSTATCOM System to Achieve Lyapunov's Stability

Vector-Based Synchronization Method for Grid Integration of Solar PV-Battery System