An adaptive control of voltage source converter based scheme for grid connected solar PV - battery system

This paper presents a path-finder algorithm (PFA) of meta-heuristic optimization for the performance enhancement of the bias compensated normalized maximum correntropy criteria (BCNMCC) based voltage source converter (VSC) control for a three-phase three-wire grid-tied dual-stage PV system. The DC link voltage variations during induced dynamic conditions are minimized by PFA optimized PI controller which also generates an accurate loss component of current for enhancing the VSC control performance. The BCNMCC algorithm effectively performs the system identification and echo cancellation in the presence of Gaussian noises. An accurate improves the VSC ability to accurately extract the fundamental load current component and to produce precise weight signals. The BCNMCC performs multifunctional operations, i.e., reactive power compensation, harmonics elimination, load balancing, and power balancing at point of common coupling during steady-state and various dynamic conditions, i.e., grid-islanding & re-synchronization, irradiation variation, unbalanced load and fixed power mode. The proposed system is capable of operating under grid-tied and isolated mode due to the seamless transition of a VSC control from grid current control (GCC) to voltage control. The seamless transition of VSC control does not induce any major transients at the source and on the load side of the system. The hybrid energy storage system (HESS) with a battery, fuel-cell and ultra-capacitor further improves the reliability of the PV system and the stability of the overall system during both grid-tied and isolated operations. The proposed system performs satisfactorily under steady-state and diverse dynamic states as per IEEE519 standards.

A control algorithm for a standalone solar photovoltaic (PV)-diesel-battery hybrid system is implemented in this paper. The proposed system deals with the intermittent nature of the energy generated by the PV array and it also provides power quality improvement. The PV array is integrated through a dc–dc boost converter and is controlled using a maximum power point tracking algorithm to obtain the maximum power under varying operating conditions. The battery energy storage system (BESS) is integrated into the diesel engine generator set for the coordinated load management and power flow within the system. The admittance-based control algorithm is used for load balancing, harmonics elimination, and reactive power compensation under three-phase four-wire linear and nonlinear loads. A four-leg voltage-source converter with BESS also provides neutral current compensation. The performance of the proposed standalone hybrid system is studied under different loading conditions experimentally on a developed prototype of the system.

This paper presents a grid connected photovoltaic (PV)-battery system. The PV array maximum power point (MPP) is traced using an incremental conductance method. A boost converter increases the PV array voltage level to the battery voltage level, which is coupled at the DC link of a voltage source converter, which also performs grid currents equalization, power factor correction, and mitigation of harmonics introduced in the grid current due to local nonlinear loads. The integrated battery is utilized to achieve smoothening of the erratic PV array output. Thus, the desired power output is injected into the grid, irrespective of the PV current output. In case the battery is unavailable, or excess local loads are connected, the system switches over to an alternative control, in which the PV power is distributed between the local loads and the grid. If the PV power is absent or unavailable, the system continues to perform as an active shunt filter. For quick estimation of the active power component of the nonlinear load, a modified version of variable step size normalized least mean square (VSS-NLMS) is utilized. The above capabilities are validated using test results, under varying PV array output and changing local nonlinear loads.

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.

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 work presents an improved phase-locked loop (IPLL)-based control for grid-integrated photovoltaic (PV) system (GIPVS). It is used to extract amplitude, frequency, and phase angle of distorted load currents to control PV-grid-interfaced voltage source converter (VSC). The VSC controls active and reactive powers at unbalances and distortions in the grid voltages. The control algorithm of VSC includes power feed-forward term, DC-link voltage, and grid voltages. The feed-forward term improves the dynamic performance of a GIPVS and enhances the utilisation of VSC. Three-phase IPLLs extract the in-phase components of three-phase load currents at utility frequency. Further, these in-phase components of load currents are used for estimation of reference-grid currents. The proposed IPLL-based control algorithm offers good dynamic response even under unbalanced load condition. The efficient working of IPLL-based control algorithm is realised by extracting maximum power from PV-grid system and through its power-quality improvement. The perturb and observe (P & O) control algorithm is used for optimum utilisation of a PV array. A developed prototype of PV-grid system is used to implement an IPLL-based control algorithm under different operating conditions.

The Distribution Static Compensator (DSTATCOM) provides active and reactive powers to enable harmonic current elimination, voltage and frequency mitigation, load compensation, and flicker mitigation. In this paper, investigation on power quality improvement in the presence of non linear and unbalanced load is done. The control algorithm provided for DSTAT-COM is p-q algorithm, anti-hebbian algorithm, and Synchronous reference frame algorithm. Comparison among various control algorithm is done on the basis of performance under non-linear and unbalanced load, Total Harmonic Distortion (THD), dynamic performance, complexity and reactive power compensation. The study has been carried out using real time simulator OPAL-RT. OP4510 is used for analysis and validation of results.

This work proposes a new model predictive control for three-phase four-wire voltage source converters operated at standalone mode. The proposed solution uses single cost function to deal with output filter voltage and current to improve output voltage quality, meanwhile, resonant energy oscillation between inductance and capacitance is effectively suppressed. Enhanced performance in both steady state and transient has been demonstrated by simulation data under nonlinear and unbalanced load condition.

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.

In this article, a fuzzy logiccontroller (FLC) tuned DC-link controller is presented. This controller is utilized to enhance the power quality characteristic of grid-integrated PV systems with power backup in comparison to the PI controller, without any filter at PCC (point of common coupling). The primary purpose of these controllers is to maintain power to the DC/AC sides by maintaining the DC-link voltage under transient conditions. The proposed system is tested with a non-linear load; hence, the proposed system requires power quality enhancements on PCC. By using both controller power flow control, reactive power compensation and harmonic mitigation is done on PCC, after that grid current becomes sinusoidal. For the power quality improvement, no filter/shunt active power filter (SAPF) is connected to PCC, only proposed inverter current controller improves the power quality at PCC by using these controllers. Using the MPPT (maximum power point tracking) Controller, the maximum power extraction feature is also included in this paper to extract maximum power from the PV module under varying atmospheric circumstances. The power backup unit is also connected with this system, power backup unit includes a battery controller which works as a boost and buck converter according to system requirements, along with a battery. On the MATLAB/Simulink platform, the control scheme and functioning of both controllers are tested, and the results are validated as satisfactory. According to IEEE 519, the grid current THD is below 5% when the suggested control system is implemented.

A standalone solar photovoltaic (PV)- battery energy storage (BES)- diesel generator (DG) based microgrid system is presented in this paper. The BES is integrated directly to the DC link of the voltage source converter (VSC). This system functions PV array maximum power extraction along with improvement of power quality such as harmonics elimination, reactive power compensation and balancing of DG currents. The PV array is integrated to the DC link of the VSC through a DC-DC boost converter. An automatic voltage regulator (AVR) is used to regulate the output voltage of the DG to the desired value. The performance of the standalone hybrid microgrid is studied under various operating conditions in the laboratory environment.

This paper presents a study for active power filters’ (APFs) application in a typical offshore O&G platform, where reactive power compensation and current harmonic mitigation are often needed to meet minimum power quality requirements. As size and weight are critical constraints in offshore installations, possible benefits of using Silicon Carbide (SiC) switches for the APF implementation are also investigated. Different compensation strategies have been compared, varying the connection point of the APF between two different voltage levels and assigning the APFs different compensation targets. Improvements in Power Quality (PQ) indexes as well as APFs rating, efficiency and design complexity have been considered for both SiC and Silicon-based solutions to identify trade-offs suitable for the considered application.

This paper deals with a three phase multifunctional grid connected SECS (Solar Energy Conversion system). A two stage power circuit topology is used in this work, in which the first stage is a boost converter, which serves the purpose of MPPT (Maximum Power Point Tracking) and the second stage is a 4-leg VSC (Voltage Source Converter) which serves the purpose of feeding extracted energy along with power quality improvement in the distribution system. The SECS not only feeds solar PV (Photo-Voltaic) energy into the grid but also serves purpose of grid currents balancing, reactive power compensation, harmonics elimination and neutral current mitigation. A feed-forward term for the solar contribution is used to improve the dynamic response for climatic changes. The PV array voltage is continuously adjusted with the help of boost converter to achieve MPPT whereas the DC link voltage of VSC is kept constant with the help of a PI (Proportional-Integral) controller. A SOGI-Q (Second Order Generalized Integrator - Quadrature) based algorithm is proposed for control of four-leg VSC. The system is modeled and simulated on MATLAB based platform. A wide range of simulation results are shown to demonstrate all features of proposed system. The simulation results show the feasibility of the proposed control algorithm. The THD (Total Harmonics Distortion) of grid current has been found well under IEEE-519 standard.

This work investigates the performance of a single-phase grid-connected photovoltaic (PV) system under non-ideal source voltage conditions using a fuzzy logic controller. The single-phase instantaneous reactive power theory has been modified to explore the harmonic and reactive power compensation with distorted grid voltage excitation while transferring active and reactive power to the grid and the non-linear load. Instead of a traditional Proportional-Integral (PI) controller, the proposed method implements a fuzzy logic controller for the extraction of the reference compensating current. This method is compared with the traditional single-phase instantaneous reactive power theory. The advantage associated with a fuzzy logic controller is that it does not need accurate mathematical modeling of the system, instead, it is based upon the linguistic characterization of the input and output variables. Besides, care has been taken to provide uninterrupted compensation throughout the variation of the solar irradiation level. The proposed method has also been verified through a laboratory-developed prototype using a DS1103 processor.

Experimental implementation of a fast dynamic response finite set control–model predictive control for voltage source converter in standalone microgrid