Grid Connected Two Stage PV-Battery System with PV Intermittency Mitigation and Improved Power Quality

In this paper, a maximum power point tracking (MPPT) technique based on extension neural network (ENN) was proposed to make full utilization of photovoltaic (PV) array output power which depends on solar insolation and ambient temperature. The proposed ENN MPPT algorithm can automatically adjust the step size to track the PV array maximum power point (MPP). Compared with the conventional fixed step size perturbation and observation (P&O) and incremental conductance (INC) methods, the presented method is able to effectively improve the dynamic response and steady state performance of the PV systems simultaneously. A theoretical analysis and the designed principle of the proposed method are described in detail. And some simulation results are made to demonstrate the effectiveness of the proposed MPPT method.

Power Quality has always been a major concern ever since the increase in the usage of many power electronic loads such as Personal Computers (PCs), TVs, variable frequency drives in nearly every household. These loads are a major source of harmonics into the distribution system. Unbalanced Three-phase loads or different single-phase loads result in unbalance in the three-phase voltages and currents in the grid. Equipment damage, Loss of data, nuisance tripping, overheating of wires, relay tripping are few of the major issues caused due to power quality. Also, there is an increase in the awareness about the various power quality issues as well as its ill-effects amongst the consumers. Hence, it is essential to improve the quality of the power supplied. Active and Passive filters play a huge role in the mitigation of power quality issues. In recent years, usage of active filters has increased because tuning is possible for various harmonic elimination and active filters when combined with a storage system can provide active as well as reactive power compensation. The fast depletion of non-renewable sources of energy and its effect on the environment has shifted the focus on the usage of non-renewable energy sources such as solar energy, wind energy, etc for the production of electricity. In this research work, solar energy is combined with shunt active filter for the mitigation of various power quality issues occurring in a grid-connected non-linear and unbalanced three-phase load. The active power filter will provide reactive power compensation to the non-linear load and active power delivery for unbalanced loads such the grid current and voltage will remain balanced and the stress on the grid is reduced while meeting the load demand. A battery system is also integrated to store the excess energy that may be generated by the Photo-Voltaic(PV) array and acts as a source of energy when PV array output is low or nil. Conservative Power Theory is used for controlling the power injection into the system by the Voltage Source Converter(VSC). The proposed system is verified using MATLAB/SIMULINK.

Purpose Silicon photovoltaics technology has drawbacks of high cost and power conversion efficiency. In order to extract the maximum output power of the module, maximum power point (MPP) is used by implying the nonlinear behavior of I-V characteristics. Different techniques are used regarding maximum power point tracking (MPPT). The paper aims to review the techniques of MPPT used in PV systems and review the comparison between Perturb and Observe (P&O) method and incremental conductance (IC) method that are used to track the maximum power and gives a comparative review of all those techniques. Design/methodology/approach A study of MPPT techniques for photovoltaic (PV) systems is presented. Matlab Simulink is used to find the MPP using P&O simulation along with IC simulation at a steady temperature and irradiance. Findings MATLAB simulations are used to implement the P&O method and IC method, which includes a PV cell connected to an MPPT-controlled boost converter. The simulation results demonstrate the accuracy of the PV model as well as the functional value of the algorithms, which has improved tracking efficiency and dynamic characteristics. P&O solution gave 94% performance when configured. P&O controller has a better time response process. As compared to the P&O method of tracking, the incremental conductance response rate was significantly slower. Originality/value In PV systems, MPPT techniques are used to optimize the PV array output power by continuously tracking the MPP under a variety of operating conditions, including cell temperature and irradiation level.

Solar photovoltaic (PV) technology has the versatility and flexibility for developing off-grid electricity system for different regions, especially in remote rural areas. While conventionally straight forward designs were used to set up off-grid PV-based system in many areas for wide range of applications, it is now possible to adapt a smart design approach for the off-grid solar PV hybrid system. A range of off-grid system configurations are possible, depending upon load requirements and their electrical properties as well as on site-specific available energy resources. The overall goal of the off-gird system design should be such that it should provide maximum efficiency, reliability and flexibility at an affordable price. In this chapter, three basic PV systems, i.e. stand-alone, grid-connected and hybrid systems, are briefly described. These systems consider different load profiles and available solar radiations. A systematic approach has then been presented regarding sizing and designing of these systems. Guidelines for selection of PV components and system sizing are provided. Battery energy storage is the important component in the off-grid solar PV system. Due to load and PV output variations, battery energy storage is going to have frequent charging and discharging. So the type of battery used in a PV system is not the same as in an automobile application. Detailed guidelines for selection of battery are therefore also provided. At present, most of the world-wide PV systems are operating at maximum power points and not contributing effectively towards the energy management in the network. Unless properly managed and controlled, large-scale deployment of PV generators in off-grid system may create problems such as voltage fluctuations, frequency deviations, power quality problems in the network, changes in fault currents and protections settings, and congestion in the network. A possible solution to these problems is the concept of active generator. The active generator will be very flexible and able to manage the power delivery as in a conventional generator system. This active generator includes the PV array with combination of energy storage technologies with proper power conditioning devices. The PV array output is weather dependent, and therefore the PV power output predictability is important for operational planning of the off-grid system. Many manufacturers of PV system power condition devices are designing and developing new type of inverters, which can work for delivering the power from PV system in coordination with energy storage batteries as conventional power plant.

A single-stage single-phase grid interfaced solar photovoltaic (SPV)-battery energy storage (BES) system with seamless multimode transition capability, is presented in this work, to reliably supply local loads. A bidirectional DC-DC converter (BDDC) control facilitates effective regulation of DC link voltage by matching it with peak power voltage of SPV array. In normal grid condition, extra power generated by the SPV array after feeding the local loads, is transferred to the grid and the load demand is fed by the grid during the SPV power insufficiency. In abnormal faulty grid as well as grid outage condition, the system isolates itself from the grid and operates in standalone mode (SAM) continuing the SPV array power generation, without disrupting the local loads. On arrival of healthy grid, the on-line resynchronization of system takes place. The BES provides backup for local loads when both grid and SPV array become incapable to fulfill the load demand. The BES also consumes the extra SPV array power during SAM. Effective control of multifunctional voltage source converter (VSC) facilitates reactive power and harmonics compensation of local nonlinear loads, maintaining sinusoidal grid current. Estimation of oscillation attenuated real time fundamental frequency as well as enhanced harmonics and DC offset rejection capability of improved adaptive generalized integrator (IAGI) filter presented in this paper, enables grid power quality enhancement as per IEEE-519 standard. The system behavior is observed at various operating scenarios, using a model of the system in Simulink environment.

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.

This paper presents the operational control strategy of multi-string photovoltaic (PV) systems in a dc microgrid by using model predictive control (MPC). Due to the intermittent nature of solar energy, battery energy storage system with unify-controlled charger is integrated to the dc microgrid to compensate the fluctuating generated PV power and to regulate the dc-bus voltage. A two-string PV system is considered in this paper to evaluate the performance of the proposed controller. The proposed MPC for the dc microgrid consists: maximum power point tracking (MPPT) of PV arrays and control of a bidirectional dc-dc converter for charging/discharging the battery energy storage system. The controller tracks the maximum power point (MPP) of each PV string under dynamic weather condition and ensures to deliver the required power by the load using the battery system in case of insufficient power generated by the PV systems. The MPC of the battery system stabilizes the bus voltage by considering the state of charge (SoC) of battery and evaluating the direction of power flow from battery system to the dc bus and vice versa. By using the characteristics of MPC with ability to add design constraints, the proposed system ensures power distribution among PV arrays and evaluates the battery SoC for changing the mode of operation to achieve a reliable energy source for the local loads. The practical feasibility of the proposed controller is studied for several case studies and verified experimentally by implementing the controller using dSPACE 1007 platform.

Photovoltaic (PV) system uses maximum power point tracking (MPPT) technique to maximize its power output. This paper presents a swarm inspired optimization based control method for the MPPT of a PV system. In particular, control methods of perturb and observe (P&O)-proportional integral (PI) and optimisation of this controllers using spider monkey optimisation (SMO) for MPPT control of PV generator are proposed. A well known PI controller is tuned using spider monkey algorithm and tested on a simulated stand alone PV system with local load. The proposed SMO based PI controller enhances the P&O MPPT technique to track the maximum power point (MPP) more rapidly and accurately. The design algorithm of this controller is presented with its simulation results. Simulation results under different environmental conditions are presented and discussed to verify the satisfactory performance of the proposed control, in which the optimised P&O-PI controller by SMO algorithms gives the better performance technique over the traditional control methods.

Partial shading conditions (PSCs) can significantly reduce the output energy produced by photovoltaic (PV) systems. Moreover, when such conditions occur, conventional and advanced maximum power point tracking (MPPT) systems fail to operate the PV system at its peak because the bypassing diodes may cause the PV system to become trapped at a low power point when they are in conduction mode. The PV system can be operated at the global maximum power point (MPP) with the help of global peak searching tools. However, the frequent use of these tools will reduce the output of PV systems since they force the PV system to operate outside its power region while scanning the I-V curve in order to determine the global MPP. Thus, the global peak searching tools should be deployed only when a PSC occurs. In this paper, a simple and accurate method is proposed for detecting PSCs by means of monitoring the sign of voltage changes (positive or negative). The method predicts a PSC if the sign of successive voltage changes is the same for a certain number of successive changes. The proposed method was tested on two types of PV array configurations (series and series–parallel) with several shading patterns emulated on-site. The proposed method correctly and timely identified all emulated shading patterns. It can be used to trigger the global MPP searching techniques for improving the PV system’s output under PSCs; furthermore, it can be used to notify the PV system’s operator of the occurrence of PSCs.

Conventional LC filters cannot compensate effectively harmonics due to non-linear loads in a grid-connected photovoltaic (PV) system. Thus, active power filters (APF) are introduced due to its characteristics and performances, for compensation of harmonics from non-linear loads in the grid-connected photovoltaic (PV) system. This work presents a three-phase voltage-fed shunt active power filter implementation to mitigate the harmonics in which the filter control system focuses on generating reference source current for compensating harmonic effects from non-linear loads. Furthermore, the developed model is verified with an experimental data from a nonlinear load.

Remote areas in India are still not connected to the power grid. But they have mobile network connectivity. The people face problems in charging their cell phones. They are forced to travel a long distances to get access to electrical outlets. The use of new efficient photovoltaic solar cells (PVSCs) has emerged as an alternative measure of renewable green power, energy conservation and demand-side management. The manufacturing of solar cells and photovoltaic arrays has advanced dramatically in recent years. But they have two inherent major problems the first is low conversion efficiency (10to16%for commercially available amorphous silicon solar cells), second is high capital cost [1]. Solar powered systems consist of different parts to be controlled separately. Since the generated power is a function of uncontrollable environmental conditions, it requires extra caution to design controllers that handle unpredictable events and maintain efficient load matching power. In this study, a photovoltaic (PV) solar array model was developed and analyzed using Matlab/Simulink. The model includes converter circuits, a controller using fuzzy logic control (FLC), and a maximum Power point (MPP) tracking control which is used to operate the PVA at its maximum power. The MPP point is tracked using four algorithms perturbation & Observation, Incremental conductance method, Constant Voltage method and Constant current method. Later a comparative performance analysis of the model for MPP algorithms is done.

Distributed generation units with small energy sources, such as fuel cells, micro-turbines, and photovoltaic devices, can be connected to utility grid as alternative energy sources besides providing power to their local loads. The distributed generation units are interfaced with utility grid using three phase inverters. With inverter control, both active and reactive power pumped into the utility grid from the distributed generation units can be controlled. Reactive power flow control allows the distributed generation units to be used as static VAr compensation units besides energy sources. This work presents a distributed generation unit control technique which provides robust voltage regulation with harmonic elimination under island running mode and decoupled active and reactive power flow control under grid-connected mode. The control technique, which combines discrete-time sliding mode current control, robust servomechanism voltage control, and integral power control, enables seamless switching between island mode and grid-connected mode and guarantees sinusoidal line current waveform such nonlinear local load. The P Q coupling issue is addressed and the stability of the power control loop is proved using Lyapunov direct method.

Solar photovoltaic (PV) energy production is important in reducing global energy crises since it is transportable, scalable, and highly customizable dependent on the needs of the industry or end-user. In addition, compared to other renewable resources, photovoltaic systems can produce electricity without moving parts and have a long lifespan. Nevertheless, solar photovoltaic (PV) systems provide intermittent output electricity with a nonlinear output voltage. Due to this intermittent availability, PV installations are facing significant challenges. As a result, in PV power systems, a Maximum Power Point Tracker (MPPT), a power extraction mechanism, is required to assure maximum power delivery at any given moment. The main objective of this work is to study the MPPT method of extracting the maximum power from photovoltaic modules under different solar irradiation and temperatures. Several MPPT methods have been developed for photovoltaic systems to achieve MPP, depending on weather conditions and applications, ranging from simple to more complex methods. Among these methods, five techniques have been presented and compared that are P&O perturbation and observation method, INC incremental conductance method, the ANN neural network method, the open circuit voltage based neural network method FVCO, and the neural network method at the base of FCC (short circuit current).

The proposed work deals with the implementation of a control approach for an active power transfer between solar photovoltaic (PV) array and grid/ load alongwith power quality improvement by eliminating harmonics and compensating reactive power required by the load in the distribution system. The PV array is directly connected across the DC link of a voltage source converter (VSC). The power is transferred to the grid/ load through VSC, which performs the function of distribution static compensator (DSTATCOM) by injecting compensating currents in the proposed system. The PV array is operated at maximum power by employing the usage of perturb and observe (P&O) maximum power point tracking (MPPT) approach in order to extract the available maximum power from the solar PV array. A feed-forward term for the solar PV array power, is incorporated for the enhancement of dynamic response. The prominence of the control algorithm lies in the efficient switching of VSC, by generating reference grid currents, which are obtained through indirect current control technique. The recursive digital filter is utilized for processing the load currents and extracting the active power component of the load currents. Therefore, the active power component of load currents obtained, are used for generating the reference grid currents in the proposed system. A prototype of the system is developed in the laboratory and its performance is studied for varying loads, changing solar insolation, and voltage swell and voltage sag conditions.

Currently, Photovoltaic (PV) energy is the most important energy resource in electrical power applications around the world since it is inexhaustible, clean and pollution free. As the output power from the PV arrays changing with solar irradiance and temperature, so it is necessary to operate the photovoltaic (PV) system at the maximum power point (MPP) to increase the power extraction from the solar panel. For this effective operation and maximum power extraction from a PV system, Maximum power point tracking (MPPT) algorithm plays a vital role by operating the PV energy system near the MPP. In this work, amongst several existing well established MPPT algorithms, the open voltage (OV) based algorithm is chosen for simulation of a PV system using Matlab / Simscape. As maximum power point (MPP) can be attained with a certain amount of load from the PV power system, so load matching is an important concept of MPPT algorithms. Here, the performances of this open voltage (OV) based algorithm method is evaluated for different values of solar radiation and battery was used as load to see the charging performance for the algorithm.