Grid Current Distortion Research Articles

Integrated Control Design for Hybrid Grid-Photovoltaic Systems in Distillation Applications: A Reference Model and Fuzzy Logic Approach

This paper presents a novel hybrid structural control solution designed for distillation systems that utilize a solar source alongside an electrical grid. The power conversion architecture incorporates a reversible bridge rectifier and a quadratic boost converter. The hybrid photovoltaic grid configuration offers several benefits, including source complementarity, enhanced dependability, and energy availability aligned with power requirements. Leveraging a photovoltaic source operating at maximum power facilitates energy conservation. On the control front, an adaptive technique based on a reference model is proposed. Fuzzy logic governs the quadratic boost converter, simplifying the management of its complex nonlinear nature. The control strategy aims to maximize solar power utilization, minimize harmonic components in the grid current, synthesize an adaptive controller, and achieve a near-unit power factor on the grid. The simulation results for a steady distillation system demonstrate promising findings. Despite variations in irradiation, load power, and grid drops, the system maintains a minimal bus voltage ripple, remaining close to the intended value. Optimization of the panel-generated power leads to improved PV source utilization and enhanced system efficiency. Furthermore, the combination with an electrical grid achieves a low rate of grid current distortion and a unitary power factor.

Sensorless control using single current sensor with PFC assisted SRM drive for cost-effective domestic appliances

This paper presents a sensorless control designed for low to medium speed operation of an 8/6 pole switched reluctance motor (SRM) drive, utilizing only a single current and voltage sensor while ensuring grid-side power quality. It emphasizes a cost-effective solution suitable for low-power applications in both domestic and industrial appliances, employing SRM drive technology. In this, AC input is fed to Cuk converter that suppresses grid current total harmonic distortion (THD). Using symmetrical structural properties of SRM allows for a cost-friendly sensorless control approach. Position estimation for four-phase SRM is achieved by comparing two-position reference fluxes with running flux. In case of four-phase SRM, phases A and C are conducted sequentially, enabling a single voltage and current sensor to estimate flux for both phases. This method contrasts with lookup table-based rotor position estimation, requiring only two sets of position flux data, thus reducing memory usage, controller complexity, and speeding up response. A laboratory prototype of a four-phase 8/6 SRM is used to estimate rotor position in sensorless control. Finally, test results are used to validate effectiveness of presented PFC assisted sensorless control approach.

Robust control for improving performance of grid-synchronized solar PV-BES-wind based microgrid

An integration of hybrid renewable energy systems (HRESs) to the grid results in power quality issues at the point of interconnection. This paper proposes an approach to investigate and mitigate power quality issues and uncertainties associated with integration of a HRES that includes a solar photovoltaic (PV) array, a wind generator, and battery energy storage (BES). The system functions in grid tied mode, standalone mode and seamless mode transition between these modes. Primary objective of proposed control approach is to ensure stable and reliable operation while mitigating effects of power quality issues. To achieve this objective, proposed control approach employs advanced control strategies, including generalized fourth order filter (GFOF) for grid tied mode and phase angle estimation. An off-grid mode uncertainty and disturbances are overcome by proportional resonant based control. GFOF addresses multiple power quality issues associated with grid-connected mode, including robust performance during voltage unbalance, harmonics suppression, DC offset removal, weak grid conditions, and evaluation of unit templates. GFOF extracts fundamental load currents and voltages for evaluation of reference grid currents and phase angle. This precisely estimates frequency and phase angle for seamless synchronization. It provides adaptive mode transition. Power quality of currents is enhanced in both islanded and grid-connected modes through utilization of GFOF control, ensuring that total harmonic distortions (THDs) of grid currents remain below 5% (simulated THD is 1.77% and experimental THD is 3.80%), as specified by the IEEE-1547and 519 standards. A comparative analysis has justified efficacy of control. Simulated and experimental results confirm effectiveness of proposed controllers in various scenarios, demonstrating their ability to provide a favourable solution for controlling unfavourable grid conditions with technical strength and precision.

PV System based on Active Power Filters for Energy Quality Improvement in EV Charging Station

The rapid expansion of electric vehicle (EV) charging stations leads to significant power quality issues and an increased demand for real power. Photovoltaic (PV) generators combined with active power filters (APF) can provide a solution to these problems and support the electricity grid to meet the needs of electrical loads. In this paper, a shunt APF powered by photovoltaic panels is designed to solve both the problems of the produced electrical energy quality and the preservation of the environment, while supplying charging stations for electric vehicles. The control objectives are: to make up for the harmonics and the reactive currents absorbed by the charging stations; to cancel the neutral current; and to regulate the voltage across the PV generator to extract the maximum power. To meet this purpose, a non linear controller based on the system model is developed, using a sliding-mode technique. Furthermore, a feedforward Artificial Neural Network (ANN) technique is designed to reach the PV optimum voltage to extract the maximum power. It combines the Particle Swarm Optimisation (PSO) algorithm to compute the optimum ANN’s initial weights for improving the accuracy search of this maximum. This theoretical result is confirmed by simulations involving wide range variations of solar irradiation. The simulation results show that with the SAPF, the grid current harmonic distortion is about 0.35% while the neutral current is practically zero. However, in the absence of this filter, the THD increases to 37.85% and the neutral current takes on an amplitude of 50 A.

Passivity Enhancement and Grid-Current Distortion Mitigation for Inverter-Side Current Controlled LCL-Type Grid-Connected Inverters

Passivity Enhancement and Grid-Current Distortion Mitigation for Inverter-Side Current Controlled <i>LCL</i>-Type Grid-Connected Inverters

Adaptability enhancement of fractional‐order LLCL‐type grid‐connected inverter to weak grid based on grid voltage weighted feedforward scheme

SummaryGrid‐connected inverter with a novel fractional‐order LLCL filter has the advantage of high grid current tracking accuracy and low total harmonic distortion without passive or active dampers, and the grid voltage full feedforward scheme is an effective method to improve the quality of grid current. However, due to the digital control delay, the suppression of the grid current harmonics is weakened, and the inverter output impedance has an additional negative phase shift, which deteriorates the stability of grid‐connected systems under weak grid. In this paper, a weighted grid voltage fractional‐order feedforward control scheme is proposed based on a quasi‐proportional resonant (QPR) controller, which introduces two weighting factors in the full feedforward path of the grid voltage and compensates the phase lag of the output impedance by designing appropriate weighting factors. Then, an improved scheme combining the QPR controller with a phase compensator is presented. As a result, the suppression ability of grid current harmonics and the adaptability to grid impedance variations are enhanced. Simulation and experimental results verify the effectiveness of the proposed grid voltage fractional‐order weighted feedforward scheme.

Grid integrated multifunctional EV charging infrastructure with improved power quality

This paper presents a grid integrated multifunctional electric vehicle (EV) charging infrastructure to power the EV batteries and simultaneously improve grid power quality. The EV charger control function is designed to operate the charger in grid-to-vehicle (G2V), vehicle-to-grid (V2G), and proposed active-filtering-mode (AFM) operating modes. In AFM mode, the proposed self-tuning filter (STF) based control algorithm effectively compensates the grid current harmonic distortions arising from nonlinear charging station load. Furthermore, the charger controller uses STF to estimate the synchronizing voltage templates for reference current generation instead of conventional phase-locked-loop (PLL) and second-order generalized integrator (SOGI) to address the nonideal grid voltage conditions. The charger controller is designed to operate in AFM operating mode simultaneously with G2V and V2G operating modes. Furthermore, to achieve these multifunctional operations in a single charger, the power electronics circuitry of the charger is developed by using an AC/DC voltage source converter and a DC/DC dual active bridge (DAB) converter. The embedded isolation in the DAB converter ensures the safety of the EV batteries from the disturbance in the AC and DC side of the charger. Furthermore, a 3.6 kVA EV charger prototype is developed in the laboratory to show the effectiveness of the control techniques.

A Robust High-Quality Current Control With Fast Convergence for Three-Level NPC Converters in Microenergy Systems

Three-level neutral-point-clamped (3L-NPC) power converters are necessary interfaces to form micro-energy systems. Naturally, designing a suitable control scheme, featuring superior dynamics, strong robustness, and simple structure, is a promising solution to guarantee more efficient operation of converter. This paper proposes a robust high-quality current control strategy for the 3L-NPC power converter in the stationary <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\alpha \beta$</tex-math></inline-formula> frame. A super-twisting algorithm coupled with a Luenberger observer current controller is proposed to deal with the poor sinusoidal current tracking issue due to the existing inductance/grid frequency deviations and the disturbance of the sinusoidal dynamic nature. Additionally, an extended sliding mode disturbance observer based proportional control is built to dramatically enhance voltage regulation performance, in the case of capacitance deviations and unknown dc-loads. Experimental data confirm the effectiveness of the proposed solution outperforms the conventional proportional-resonant/-integral control in terms of accurate tracking current/voltage, anti-disturbance, and grid current total harmonic distortion.

A Novel Approach for Power Quality Enhancement of Three-Phase Grid Integrated Solar PV System Using an Adaptive ZA-QLMS-Based Algorithm

This article incorporates grid-interfaced dual-stage solar photovoltaic (SPV) three-phase topology. Also, it employs an incremental conductance (INC) approach to extract the required maximum power from the PV array with the assistance of a DC-DC boost converter. In the next stage, an optimal control algorithm that exercises adaptive-based zero-attracting quaternion-valued sparse least mean square (ZA-QLMS) to control the voltage source converter (VSC). The proposed control technique enhances the convergence rate by including sparsity knowledge about the system in the weight-updation process. Thus, it allows the successful withdrawal of the fundamental current components that match the sensed grid current to produce requisite switching pulses for VSC. A 100 KW SPV system has been integrated with the utility grid through a VSC in MATLAB/Simulink environment. The feasibility of the ZA-QLMS-based control algorithm dictates that under variable irradiances and constant temperatures considering linear and non-linear loading situations, the generated power is effortlessly fed to the utility grid with the advantage of unity power factor operation. Thus, ensuring improved power quality performance with the total harmonic distortion of utility grid current is maintained well below the desired grid code (IEEE-519).

A variable step size robust normalized least mean absolute third‐based control scheme for a grid‐tied multifunctional photovoltaic system

SummaryThis paper develops a variable step size robust normalized least mean absolute third (VSSRNLMAT)‐based control scheme for a three‐phase grid‐tied multifunctional photovoltaic system (GTMPVS). The GTMPVS delivers PV power to grid‐connected loads and feeds excess power to the grid through a voltage source converter (VSC) when PV power is available. It enhances power quality (PQ) by mitigating current harmonics and compensating for an unbalanced load and reactive power simultaneously. The proposed control scheme accurately extracts the fundamental active and reactive weight components of nonlinear load current. The power exchange at the grid side occurs with balanced and sinusoidal grid currents. During the absence of PV power, the VSC continues its operation as a distribution static compensator (DSTATCOM), thus increasing the effective utilization of the power electronic switches employed in the VSC. The GTMPVS model is created in MATLAB/Simulink. The response of GTMPVS is observed under steady‐state and dynamic operating conditions while feeding power to a nonlinear load. The dynamic operating conditions are created by a change in solar irradiation and an unbalanced nonlinear load. Further, the proposed VSSRNLMAT control scheme is compared with some of the other adaptive filtering‐based control schemes, including least mean square (LMS), least mean fourth (LMF), least mean absolute third (LMAT), and normalized LMAT (NLMAT) in terms of convergence, oscillations, mean square deviation (MSD), computational complexity, and grid current total harmonic distortion (THD). It is found that the VSSRNLMAT control scheme offers THD of grid current as per IEEE‐519 standard. The proposed control scheme is implemented to operate the laboratory‐developed GTMPVS to verify the simulation results.

Analysis of Grid Current Distortion and Waveform Improvement Methods of Dual-Active-Bridge Microinverter

Due to its merits of fewer power switches, a wide zero-voltage switching range, and high efficiency, the dual-active-bridge (DAB) microinverter is drawing growing interest. However, it has an inherent issue of grid current distortion and spikes, which deteriorate the total current distortion. Existing literature mainly focuses on modulation strategies and barely analyzes the underlying causes, let alone the methods to improve grid current quality. This article fills this blank by revealing the dead-time effect on grid current distortion from two aspects. Several methods are proposed to improve the grid current quality and are compared in detail. Besides, a complete set of grid current closed-loop control methods is proposed based on the DAB microinverter modeling. The control method not only provides the correct control logic but also eliminates the immanent time-varying and condition-dependent features of the control loop, making the proposed current control method self-adaptive and universal. The analyses and the proposed control method are all validated by experimental results.

공통 모드 전압 및 THD를 고려한 계통연계형 3레벨 NPC 인버터의 운용 알고리즘 연구

A grid-connected 3-level NPC inverter is a power conversion device that connects renewable energy generators, such as photovoltaic or wind turbines to the grid. Although many studies have focused on this inverter, commercializing it requires strictly satisfying various safety and power quality-related standards. Among many standards, leakage current and grid current total harmonic distortion(THD) can be affected by external factors such as installation environment, aging, and grid conditions. Hence, inverter operations that can satisfy these standards need to be explored. In this study a 3-level NPC inverter operation algorithm using the Phase Opposition Disposition-PWM method that can effectively reduce leakage current and switching frequency adjustment to reduce THD effectively has been proposed.

Online Inductance Identification and FPGA-Based Real-Time Digital Control Design for APF

The harmonic suppression performance of active power filter (APF) under model predictive current control is obviously reduced, when the parameter exists a mismatch between the actual value in system and the nominal value adopted in the control. To suppress the influence of parameter mismatching, a model predictive control based on parameter identification with forgetting factor recursive least square (FFRLS) method is proposed for APF. The digital processing procedure of the FFRLS-based APF controller is detailed analyzed and designed. The identification error of inductance between identification value and the actual value is less to 6%, and the total harmonic distortion of grid current is significantly improved, especially a lower value of actual inductance. Simulation and experimental results show that the proposed method can not only effectively eliminate the influence of parameter mismatch on the control, but also result in better steady-state performance while retaining fast dynamic response.

Performance Investigation of Grid Connected DFIG Based Wind Energy System

The paper realizes the investigation of control operation and performance in grid integrated Doubly Fed Induction Generator (DFIG) system. Battery Energy Storage (BES), coupled at the DC link of DFIG is controlled by bidirectional power converter to compensate for utility/load demand. Rotor side converter (RSC) uses tip-speed ratio maximum power point tracking (MPPT) algorithm to harness maximum power from the wind turbine. An adjustable step size least mean square (LMS) based adaptive control is implemented for the grid side converter (GSC) of DFIG system that besides managing power balance at the Point of Common Coupling (PCC) also addresses power quality issues encountered in the system due to the presence of non-linear, unbalanced loads. The step size changes with the mean square error enabling the adaptive filter to detect system changes while producing a small steady state error. Performance of the system is exhibited and validated through simulated results in a developed Simulink model for steady state and dynamic conditions. The Total Harmonic Distortion (THD) in grid currents and voltage is within IEEE 519 standard guidelines.

An Adaptive DC-Link Voltage Control of a Multifunctional SPV Grid-Connected VSI for Switching Loss Reduction

In the proposed method in this article, to minimize the burden on the switches of the multifunctional grid-connected voltage-source inverter (MFGCVSI), the voltages of dc-link split capacitors are adjusted according to power injection from the MFGCVSI. The MFGCVSI is used to control the active power injection from solar photovoltaic (SPV) power generation to the main grid and loads, load reactive power compensation, harmonic mitigation, and main grid current total harmonic distortion within 5 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> . In such a case, the voltages of split capacitors depend on the rated power injection from the MFGCVSI. The power generated from the SPV system and the loads that are connected at the point of common coupling vary with respect to time. It is observed that the selection of rated dc-link voltages during low power injection from the MFGCVSI leads to additional switching stress and higher switching losses. Therefore, to reduce the burden on inverter switches and switching losses, the reference dc voltage is reduced under low power injection from the MFGCVSI. A model predictive controller with a multiconstraint technique is used in the proposed method for balancing the dc-link capacitor voltages and average switching frequency reduction. The proposed method is validated through simulation and hardware setup.

Sliding-Mode Control for Interleaved Operation of Parallel-Connected Three-Phase Active Front-Ends

A converter system is considered that consists of parallel-connected two-level voltage source converters that share the same ac and dc terminals. A controller design is proposed that, in a first stage, controls the grid currents using hysteresis controllers. To this end, augmented grid currents are introduced, which feature decoupling between the phases. As a consequence, a switching action in one phase does not affect the derivatives of these currents in the other phases. In a second stage, the converter currents are controlled using hysteresis controllers such that a desired current distribution among the parallel converters may be ensured. This implicitly sets the circulating currents. The proposed approach is verified by measurements on an industrial megawatt-scale testbench with ten parallel converters. The results are compared with a benchmark approach, with the proposed approach showing lower semiconductor losses and grid current harmonic distortion.

Design and analysis of Hermite function‐based artificial neural network controller for performance enhancement of photovoltaic‐integrated grid system

AbstractThis article proposes a Hermite function‐based artificial neural network (HeANN) controller for shunt compensation in photovoltaic (PV) interfaced grid system. Various power quality (PQ) issues such as load change, poor power factor, reactive power demand and current harmonics are experienced by distribution system. The proposed HeANN algorithm is utilized to improve the PQ issues of the distribution system. Shunt active power filter (SAPF) is operated in current control mode and injects the compensating current at the point of common coupling (PCC). The inverter is connected with the green energy resource, that is, PV at its direct current terminals and contributes its power to fulfil the load active power demand. The parameters of HeANN are trained in real time. A prototype hardware of SAPF is developed using sensor circuits and space 1104. The simulation results are validated by experimental results. The comparative analysis of the results establishes the superiority of the proposed control technique to other control techniques such as synchronous reference frame, second order generalized integrator and back propagation neural network in terms of convergence, computational burden and total harmonic distortion of grid current.

Performance Analysis of an Optimized Asymmetric Multilevel Inverter on Grid Connected SPV System

The purpose of this research is to develop an efficient single-phase grid-connected PV system using a better performing asymmetrical multilevel inverter (AMI). Circuit component reduction, harmonic reduction, and grid integration are critical criteria for better inverter efficiency. The proposed inverter’s optimized topology requires seven unidirectional switches, three symmetric dc sources, and three diodes to produce an asymmetric fifteen level output; whereas, the same configuration will generate 7, 11, and 15-level output with an appropriate choice of dc source magnitudes. It is possible to reduce inverter losses and boost efficiency by decreasing the number of switches used. The integration of an asymmetric 15-level inverter with a grid-connected solar photovoltaic system is discussed in this article. A grid-connected solar photovoltaic (GCSPV) system is modelled and simulated using an asymmetric 15-level inverter. The dc sources of the 15-level inverter are replaced with PV sources. The results were analyzed with different operating temperatures and solar irradiance conditions. The GCSPV system is controlled by a closed-loop control system using Particle Swarm Optimization (PSO), Harris Hawk Optimization (HHO), and Hybrid Particle Swarm Optimization-Genetic Algorithm (PSOGA) based Proportional plus Integral (PI) controllers. Grid voltage, grid current, grid power, and total harmonic distortion (THD) of grid currents were analyzed. The performance of the 15-level asymmetric inverter was evaluated by comparing the THD of the grid current and the efficiency of the grid-connected photovoltaic system.

Optimal Sector-Based Sequential Model Predictive Control for Current Source Rectifier

Conventional model predictive control (MPC) methods for current source rectifier (CSR) use either a PI controller or weight factor-based methods, which require time-consuming tuning methods to develop an efficient controller. Moreover, the limitations on the bandwidth requirements of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> filter cause resonances and grid current distortions if a variable switching frequency-based predictive control is used. So, a new fixed switching frequency-based MPC algorithm has been developed to control the load and source current simultaneously, thereby facilitating the weight factor less operation and applying a predefined space vector sequence. Unlike the conventional single cost function methods applied to CSR, the proposed method uses separate cost function for each control variable. Simultaneously, to provide fixed frequency operation, duty ratio-based modulation of grid current control has been applied. A virtual impedance-based active damping has been embedded into the supply current control to suppress the oscillations caused by the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$LC$ </tex-math></inline-formula> filter and grid current harmonics. Simulation and experimental results have been supported to validate the improvements in terms of supply current total harmonic distortion (THD), steady state, and transient switching performance.

A Simple Modulation Strategy for Full ZVS of Single-Stage Electrolytic Capacitor-Less EV Charger With Universal Input

The single-stage electrolytic capacitor-less on-board charger (OBC) is attracting attention with the possibility of achieving high efficiency, high power density, and low component count. However, under universal input and wide battery voltage, the single-stage OBC has a difficulty in achieving ZVS turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> while maintaining unity power factor. In order to achieve ZVS under wide voltage range, the conventional single-stage OBC uses multiple control variables including switching frequency where the switching frequency usually varies widely, which complicates the converter design and optimization. In this regard, a totem-pole based single-stage electrolytic capacitor-less OBC was introduced in [36]. It uses one control variable and fixed switching frequency. However, this topology is not able to achieve full ZVS under wide voltage range and has high grid current total harmonic distortion (THD). This article proposes a simple modulation strategy that uses an adaptive duty-cycle and phase-shift modulation to achieve full ZVS under universal input and wide battery voltage. In addition, the fourth-harmonic injection method greatly reduces the grid current THD. The effectiveness of the proposed modulation was validated on a 3.84-kW prototype with 100–240 V ac input and 460–800 V battery voltage. The efficiency is also increased up to 2.3%p under low-voltage grid compared to the previous work.