Grid Interface Inverter Research Articles

Frequency-adaptive DLIA–PLL-based current harmonic compensation for single-phase grid-interfaced inverters

Frequency-adaptive DLIA–PLL-based current harmonic compensation for single-phase grid-interfaced inverters

Delay-Tracking Loop for Frequency Estimation of Grid-Interfaced Inverter Under Distorted Conditions

Fast and accurate frequency estimation is difficult for grid-interfaced inverter under distorted grid conditions with off-nominal frequency. A popular solution considers the multiple second-order generalized integrator-based frequency-locked loop yet can hardly achieve a fast dynamic response under significant phase jump and voltage sag. Another solution uses an adaptive sliding window filter with an additional frequency estimator. However, it is challenging to handle numerical instability due to the adjusting marginally-stable resonator and the accumulation error. This letter proposes a delay-tracking loop to overcome these problems. This loop allows the delay length to track the frequency with an inherent harmonics rejection at off-nominal frequency. At the same time, the fast response speed is maintained, and the marginally stable resonator is avoided. Comparative experimental results validate the above claims.

Optimization of energy storage capacity using distributionally robust optimization for converter-based grids

As the penetration of converters into the grid continues to increase, converter-based power sources are replacing synchronous machine-based power sources, leading to the establishment of a converter-based grid (CBG) for regulating grid frequency and voltage. At this stage, energy storage becomes a necessity to support the operation of the CBG. The grid-interfacing inverters are transitioning from the conventional grid-following (GFL) control to the grid-forming (GFM) control. within the context of this research paper, considering the premise that energy storage capacity must meet CBG stability constraints and accommodate the integration of renewable energy sources, a capacity optimization model is constructed based on distributional robust optimization. The primary objective of this model is to minimize the overall cost with the allocation of energy storage capacity as the central focus. The study includes case analyses conducted within an IEEE-14 node CBG. The results of the case analyses confirm that the determined energy storage capacity can ensure the stable operation of the CBG and meet the demands for integrating renewable energy sources.

Energy Management For Renewable Hybrid System Based On Artificial Neural Networks (ANN)

Abstract: It has become necessary in recent years to use renewable energy sources, such as wind and solar energy, to meet the load demand. Because of their endless existence and environmentally friendly nature, they are useful for power generation. The management of energy in hybrid wind-solar power sources is the topic of this article. Using a common current source interface multiple-input DC-DC converter, the photovoltaic (PV) array, wind turbine, and battery storage are all connected. The power control between intermittent renewable energy generation, energy storage, and the grid is maintained by the artificial neural network (ANN) controller. For wind turbines to produce the most electricity, variable speed control can be used. For solar systems, the Maximum Power Point Tracking (MPPT) algorithm is used. By keeping the common DC voltage constant, the grid interface inverter sends the energy drawn from the PV array and wind turbine into the grid. Using MATLAB Simulink, the complete control strategy is subjected to a simulation study. The results of the simulation show the photovoltaic/wind hybrid system's dynamic behavior and control effectiveness

Development and Validation of an Integrated EV Charging Station With Grid Interfacing Inverter for Residential Application

Development and Validation of an Integrated EV Charging Station With Grid Interfacing Inverter for Residential Application

Lyapunov-Krasovskii passivity based stability analysis of grid-tied inverters

The non-linear dynamics of a grid-interfaced inverter (GII) in a distributed generation system results in dynamic instability and power quality issues. The conventional linear methods depend on parametric variations in controller parameters hence, tuning should be proper. Also, linearization of dynamical states around steady-state operating point works only if the controllers operate around a fixed operating point thus, only ensuring local stability. The feedback and feedforward damping methods can address some of the above challenges but requires additional sensors and also incapable of maintaining robustness against grid impedance variations and system parametric changes. To address aforementioned issues, this journal presents a non-linear Lyapunov Krasovskii Passivity (LK-PBC) based dynamic controller for Grid-interfaced Voltage Source Converters (VSCs). A generalized admittance model is derived which is used to calculate Non-passive regions of the VSC where the output admittance will have a negative real part. The damping provided by the proposed controller also eliminates the resonance instability issues in the concerned frequency scale regardless of the admittance seen at the inverter terminals. It also takes care of time delay and norm-bounded state uncertainties. The evaluation of the theoretical studies and efficacy of the proposed LK-PBC controller is confirmed by hardware in loop analysis on a laboratory experimental setup.

Two-Stage Control for Small-Signal Modeling and Power Conditioning of Grid-Connected Quasi-Z-Source Inverter with LCL Filter for Photovoltaic Generation

Grid-connected inverter-based photovoltaic (PV) systems play an important role in Distributed Power Generation (DPG). For this application, quasi impedance source inverter is very suitable due to its ability to increase or decrease the output voltage of the inverter in a single-stage and high reliable condition. Conventionally, to remove the harmonics, which are yielded by switching the grid-connected inverter, LCL filters are utilized at the inverter output. These filters can cause some problems at the Point of Common Coupling (PCC). The aim of this paper is to improve the quality of the injected power of the photovoltaic array, which is connected to the low voltage grid by quasi-Z-source inverter (QZSI). For this purpose, a two-stage control procedure containing DC and AC stages is performed. In the DC stage, the dynamic characteristics of the quasi-Z-source network are investigated by small-signal analysis. Using the transfer functions obtained from the dynamic model, the capacitor voltage of the quasi-Z-source network is suitably controlled to generate the appropriate voltage to the grid interface inverter. In the AC stage, in order to inject high-quality current into the grid as well as eliminating the resonance peak caused by the LCL filter, a systematic procedure is used to design the PR controller parameters and active damping coefficient. Simulation of the overall system includes solar panels, maximum power point tracking algorithm, quasi-Z-source inverter, and LCL filter to model the grid-tied PV system with the possible details. Simulations are carried out in MATLAB/Simulink environment, and results depict suitable performance of the studied power conditioning system with designed parameters.

Grid Integration of Renewable Energy Sources using GA Technique for Improving Power Quality

Hybrid Renewable energy sources (HRES) are rapidly increasingly compared to the traditional system since they are less effective to the environment and meet the huge demand required by the utilities. In the proposed paper the modelling, control and design analysis is implemented with PV, wind and battery as an energy storing device. The grid-interfacing inverter is regulated with a single-stage, three-phase RES-based distributed generation (DG) system. A genetic algorithm (GA) based shunt active power filter (SHAPF) is used to mitigate the power quality issues under nonlinear and unbalanced load conditions. The DG is grid-connected through a current-controlled –voltage source inverter (CC-VSI) via a DC link capacitor. Here the VSI is utilized to transfer the power from DG to the point of common coupling (PCC), SAPF to compensate for load current harmonics, under distorted supply voltage conditions, reactive power demand and load current imbalance. Both of these functions are important either individually or concurrently. As a result, the proposed controller regulates the power flow, controls it and acts as a SHAPF or does both at the same time. The proposed method is employed in the MATLAB/Simulink platform and performances were analysed.

Dynamic Modeling and Control of a Single-Phase Grid-Connected photovoltaic System

Designing control strategies to connect a photovoltaic (PV) system to the grid has been significantly challenging. This paper focuses on developing a controller for a single-phase PV system connected to the grid and its implementation to modify the power factor in the distribution power system. To design a grid-connected PV system, its components are modeled, such as PV panels, Maximum Power Point tracking (MPPT) algorithm, the grid interface inverter with the appropriate filter, and the DC link capacitor. SIMULINK / MATLAB is used for simulation in this study. The proposed control strategy is designed to track the maximum power point of The PV panels and control the PV active and reactive output power. In this paper, the presented reactive power control provides the PV system with power factor correction (PFC) capability. The proposed technique for checking controller validity is tested, and the results prove that the proposed controller is good and provides the required performance.

An integrated rule-based power management and dynamic feed-forward low voltage ride through scheme for a grid-connected hybrid energy system

Power generation from a grid-integrated renewable energy generator embedded with backup sources to form a hybrid energy system possesses convincing features of high efficiency and zero emissions. Control for felicitating apt power sharing and for providing ancillary services such as low voltage ride through (LVRT) is necessary for the compliance of grid codes. However, the simultaneous control coordination for meeting these control objectives is challenging due to the dynamic nature of renewable generators and utility grid. Hence, this paper proposes an integrated power management strategy (PMS) and LVRT control scheme for such systems. A wind energy conversion system backed up by a battery energy storage system, proton exchange fuel cell, and electrolyzer is considered in this work. A reduced rule-based power management control scheme is proposed for the considered system where the request made by the grid operator is kept in priority. Further, a dynamic current feed-forward based LVRT control scheme based on negative sequence current minimization is presented for the grid-interfaced inverter. The inverter control is coupled with an inherent mode selection capability between the grid feeding mode and LVRT mode in order to realize the proposed integrated control objectives. The validation of the proposed PMS and LVRT control is justified by detailing relevant mathematical control models and also by realizing practical case scenarios such as variable wind speed, load demand, grid power request, and occurrences of balanced and unbalanced voltage sag. The obtained simulation results show the cordial response of the system with the proposed control strategies.

RETRACTED ARTICLE: An ANN-based harmonic mitigation and power injection technique for solar-fed distributed generation system

In this article, a fifteen-level cascaded H-bridge multilevel inverter with active power filtering capability is suggested to increase the power quality in a single-phase distributed generation (DG) system. Integrating renewable power sources in the distribution line becomes easier with advancements in power electronic converters. At the same time, increase in usage of nonlinear loads leads to electronic pollutions like harmonics and power factor issues. Since most of the DG systems have interfacing inverters, it can be utilized for power quality improvement. This proposed work presents a control scheme to gain maximum utilization of these grid interfacing inverters with artificial neural network (ANN). An instantaneous p-q theory in a-s-0 reference frame-based control algorithm is derived to control the inverter in the single-phase distribution system. In the ANN-based approach, the control algorithm is solved and the ANN is trained based on the switching angles obtained. The trained system is integrated with DG system to operate as a multitasking circuit by adding active power filter (APF) operation. It is proposed to utilize the interfacing inverter as: (1) interfacing inverter to add power produced from renewable sources and (2) APF to mitigate the harmonics. Both functions are accomplished simultaneously. The proposed work is verified with extensive MATLAB/Simulink, and the obtained results demonstrate that the proposed approach delivers a notable improvement in power quality concerning reduction in total harmonic distortion and injection of real power generated through RES into the distribution line. A 3-kWp photovoltaic panel with multifunctioning inverter designed utilizing ANN is executed in an experimental setup to prove the efficiency of the proposed approach.

RETRACTED: Performance enhancement of grid-interfaced inverter using intelligent controller

The high-performance grid-interfaced inverters are in demand as they are rapidly used in renewable energy systems. The main objective of grid-interfaced inverters is to inject high-quality active and reactive power with sinusoidal current. Many control schemes have been proposed earlier in the literature, but the operation under parametric uncertainties has not been given much attention. In this article, an adaptive network–based fuzzy inference control algorithm for a three-phase grid-interfaced inverter under parametric uncertainties is proposed. The main purpose of the proposed technique is to enhance the response time, decrease the steady-state oscillation in the injected active and reactive power and enhance the power quality even with parametric uncertainties. For assessment and evaluation reason, the conventional proportional–integral control is compared with the proposed controller. For a fair comparison, the gain setting for the proportional–integral control is obtained by Particle swarm optimization algorithm. The suggested system is developed and simulated in MATLAB/Simulink. Simulation results demonstrate that both the controllers work well to regulate the powers to required values, even with parametric variations. However, the proposed control demonstrates superiority in comparison to conventional proportional–integral control in terms of speedy response, decreased steady-state fluctuations, better power quality and increased robustness. The rise time and fluctuations in the per-unit active and reactive power are much less with the proposed control. Total harmonic distortion of the injected current and grid current are significantly better than the conventional proportional–integral control.

Reconfigurable Real-Time Power Grid Emulator for Systems With High Penetration of Renewables

Novel power system control and new utility devices need to be tested before their actual deployment to the power grid. To assist with such a testing need, real-time digital emulators such as RTDS and Opal-RT can be used to connect to the physical world and form a hardware in the loop (HIL) emulation. However, due to the limitations of today’s computational resources, the accuracy and fidelity suffer from different levels of model reductions in purely digital simulations. CURENT has developed a reconfigurable electric grid hardware testbed (HTB) to overcome the limitations of digital emulators. The HTB has been used to develop measurement, control, modeling, and actuation techniques for a national grid with a high penetration of renewables. The power electronic-based system includes emulators for synchronous generators; photovoltaics with grid-interfacing inverter; wind turbines; induction motor loads, ZIP loads, power electronic loads; batteries; ac and dc transmission lines; short circuit faults and grid relay protection; and a multiterminal HVDC overlay including power electronics interfaces. The system contains real elements of power flow, measurement, communication, protection, and control that mimic what would be seen in an actual electric grid. This paper presents an overview of the HTB and several scenarios that have been run to determine control and actions needed for the future power grid.

An Interaction-Admittance Model for Multi-Inverter Grid-Connected Systems

In modern power systems, the increasing penetration of renewables and power electronics, particularly inverter-based wind and solar power generation, is altering power system dynamics and bringing new stability concerns. One challenging issue that is attracting considerable attention is the wide range of power oscillations associated with multiple parallel grid-connected inverters. In such systems, the characteristics in terms of resonance and oscillation are significantly different from single-inverter systems. This paper investigates the mutual interaction and stability issues of multiple grid-interfacing inverters with LCL -filters in power-electronics-based power systems under various grid conditions. The investigation reveals that such interactions between power inverters and the grid may excite multiple resonances at various frequencies under certain grid conditions. The nodal admittance matrix concept, which was originally from power systems engineering, is adopted here. Moreover, this paper further develops an Interaction-Admittance model that can effectively describe these mutual interactions in terms of a physical network admittance. We apply our model to various scenarios such as stiff grid conditions and inductive grids with/without power factor correction capacitors. The results with the proposed framework demonstrate an intuitive interpretation of multi-inverter system resonance and instabilities. Finally, simulations and experiments on a lab-scale system are provided to verify the theoretical analysis.

Benchmarking of Stability and Robustness Against Grid Impedance Variation for <italic>LCL</italic> -Filtered Grid-Interfacing Inverters

This paper comprehensively analyzes the stability of a grid-interfacing inverter with the LCL -filter in the discrete domain, where the LCL-filter, along with the controller, is modeled in a polar coordinate. System open-loop and closed-loop poles are analytically studied and expressed in the z -domain. Through the poles movement and distribution analysis, the relationship between system stability and the ratio of resonance frequency over sampling frequency is mathematically revealed and calculated as well as the system control gain limit. Moreover, this paper demonstrates that a grid-voltage feedforward regulator would significantly alter the inverter stability in a weak power system. By means of Jury stability criterion, the stability status under different filter resonance frequency is given. The selection of resonance frequency and filter parameters makes a considerable difference on system behavior. Finally, to improve the robustness against grid inductance variation, a conservative design recommendation of filter parameters and control gain is given. Through the tests on a laboratory-scale prototype, the theoretical analysis is validated by experimental results.

Bidirectional Power Converter for Solar Grid Interface Applications: An Experimental Investigation

Switching control of a current controlled grid integrated inverter using three-level neutral point clamped (NPC) inverter is investigated in this paper. The proposed scheme uses both the hysteresis current control (HCC) and carrier based switching schemes to improve the low switching frequency operation. To overcome the problems associated with current control techniques a simple carrier injection method is proposed in this paper. This current control method uses a high frequency triangular carrier injected to the current tracking error. The triangular carriers are chosen with minute amplitude comparable with current tracking error. This will enhance the switching frequency and stabilize the NPC inverter. This will ensure constant switching frequency operation of the grid interface inverter (GII). A comprehensive modeling of GII is carried out to study the stability of the system. A comparative study of switching frequency stabilization is presented. To verify the proposed current controller a prototype setup is developed. Analytical studies with experimental results of the proposed techniques are presented to show the superiority of results.

Nonlinear control of a grid connected hybrid energetic systems (HES) based on photovoltaic- fuel cells distributed power generation systems

This paper presents a discrete-time integral sliding mode control for a grid connectedhybrid energetic systems (HES) based on photovoltaic-Solid oxide fuel cell (SOFC) for distributedpower generation systems. The proposed HES systems employ solid oxide fuel cell (SOFC) andphotovoltaic panels as main sources, supercapacitors as complementary sources, and controlledDC-DC boost converter and three levels NPC inverter. A maximum power point tracking (MPPT)control is used in order to maximize the power of the photovoltaic system. The proposed controlconsists of a power management grid interface inverter transferring the energy from the hybridsources into the grid by controlling the main utility grid and the common DC voltage active andreactive power. The obtained simulation results show the effectiveness and robustness of theproposed control strategy. Keywords: Hybrid Energetic Systems (HES), Solid Oxide Fuel Cell (SOFC),Photovoltaic (PV), Sliding Mode Control, Maximum Power Point Tracking (MPPT), Grid powermanagement.

Modelling and Simulation of Grid Connected SPV System with Active Power Filtering Features

In this paper, the detailed simulation studies for a grid connected solar photovoltaic system (SPV) have been presented. The power electronics devices like DC–DC boost converter and grid interfacing inverter are most important components of proposed system. Here, the DC–DC boost converter is controlled to extract maximum power out of SPV under different irradiation levels, while the grid interfacing inverter is utilized to evacuate the active power and feed it into grid at synchronized voltage and frequency. Moreover, the grid interfacing inverter is also controlled to sort out the issues related to power quality by compensating the reactive power and harmonics current component of nearby load at point of common coupling. Besides, detailed modeling of various component utilized in proposed system is also presented. Finally, extensive simulations have been performed under different irradiation levels with various kinds of load to validate the aforementioned claims. The overall system design and simulation have been performed by using Sim Power System toolbox available in the library of MATLAB.

Performance and Efficiency Simulation Study of a Smart-Grid Connected Photovoltaic System

The availability of non-renewable energy sources such as crude oil, natural gas, coal etc., is fast diminishing. So the renewable energy sources such as solar, hydropower, geothermal, wind, tidal energy, are gaining more and more importance. Many new developments to convert these renewable energy sources into usable forms are taking place. Most renewable energy sources are used to produce electricity. In this paper, a performance and efficiency simulation study of a smart-grid connected photovoltaic system using Chroma DC programmable power supply, AC programmable source and an Aurora Inverter is proposed. The simulation is performed in MATLAB environment where the Current-Voltage (I-V) and Power-Voltage (P-V) curves from the solar array simulator are generated and plotted. The proposed topology has been verified with satisfactory results. In addition, temperature and irradiance effects on I-V and P-V characteristic curves are verified. Also, the efficiency curves of the photovoltaic grid interface inverter are generated in the study. The MATLAB code developed in this paper is a valuable tool for design engineers comparing different inverters, calculating the optimum efficiency of a given inverter type.

Stability Analysis of Grid-Interfacing Inverter Control in Distribution Systems With Multiple Photovoltaic-Based Distributed Generators

A stability-enhancement inverter controller is proposed and its impact on the small-signal stability of distribution systems with multiple photovoltaic-based distributed generators (PV-DGs) is investigated. In specific, the random variation of the power output from multiple PV-DGs is considered. Being different from a single grid-connected PV system, the spatial correlation between PV-DGs and the system stability sensitivity with respect to different PV-DGs among the feeder are also taken into account. The small-signal stability analysis of the distribution system is performed using a probabilistic approach. As the PV-DG power output is randomly variable, the distribution system is not operating in a fixed mode. Consequently, the critical eigenvalues of the system move randomly. Through the Gram–Charlier expansion method, the probability density function of the critical eigenvalues of the distribution system is approximated and the probabilities of the system stability and instability are calculated. Taking the probability of the system instability as the performance metric, the effects of different system parameter settings of the grid-interfacing inverter controller on the distribution system are analyzed. The verification of the analytical results is carried out through Monte-Carlo time-domain simulations of the distribution system. The results suggest several methods to reduce the probability of system instability, including installation of the proposed inverter controller, choosing a large substation capacitor and/or choosing large capacity load and substation transformers.