Grid Current THD Research Articles

Incorporation of multiple random features kernel mean p‐power controller to elevate power quality in reconfigurable grid‐connected residential solar photovoltaic systems

SummaryProblems like intermittent photovoltaic (PV) power, disconnected PV arrays, etc. are brought on by the extensive integration of PV generation. In this article, a single‐stage PV‐integrated grid‐tethered system is controlled using a reconfigurative multiple random features kernel mean p‐power (MRFKMP) control algorithm. The algorithm circumvents the dependence of kernel parameter in the classic random Fourier features mapping and lower the computing complexity in the traditional multiple kernel learning adaptive filter. MRFKMP algorithm with a linear filter structure can reduce both the computational and storage cost. This is the novel application of MRFKMP algorithm to extract fundamental component of nonlinear load currents in PV‐integrated grid‐tied system. Furthermore, to increase the reliability of the system, a reconfigurable control is developed, which adaptive regulates DC link voltage from PV mode (PVM) during PV hours to active power filtering mode (AFM) during PV nonavailability/PV disconnection. On a created laboratory testbed, the applied control's practical feasibility for numerous scenarios is evaluated. Comparison with existing control algorithms reveals that the MRFKMP controller outperforms the LMF based PV system by 79% less peak‐to‐peak load current ripple and 60% less than the best performing SRF control algorithm. The grid current THD is 2.60%, which is 30% low than that presented by SRF technique.

Design of Z source converter with the genetic-based chicken swarm algorithm for closed loop control of PV integrated grid

A single-phase grid coupled PV system with a switched Z-source boost converter is analysed on the basis of closed-loop control using a novel hybrid algorithm. As PV results in low-voltage DC, it is vital to step up this low-voltage DC and so a suitable DC-DC converter is needed. A switched Z-source boost converter is utilized for the step-up process as this converter uses minimum passive components, thereby reducing the cost with improved power density. Control of the converter is carried out by a closed loop control using a PI controller tuned with a novel genetic-based chicken swarm (GBCS) algorithm which combines the merits of both genetic and chicken swarm able to deal with complex problems, simple with fast convergence. The output of the converter is then given to the grid through a single-phase VSI in which DC–AC conversion takes place. While connecting PV to the grid, another factor to be taken care of is grid synchronization which is accomplished by a PI controller in which the actual and reference power are analogized. The proposed control scheme is simulated in a MATLAB environment and the outcomes are observed. The grid current THD of 1.6% and reactive power compensation is accomplished.

Mitigation of electric vehicles impact on grid current harmonics using DERs

ABSTRACT The power quality (PQ) variations due to the introduction of electric vehicles (EVs) and Electric Vehicle Charging Stations (EVCS) into the power system network is the foremost limitation which is holding back the push for a complete overhaul of fossil fuel-based internal combustion (IC) engine vehicles by EVs. With the emergence of EVs into the mainstream in the automobile sector, this research article proposes a system wherein distributed energy resources (DERs) like Fuel-Cells (FCs) are integrated to grid in order to supply for the additional power demand created by the EVs such that the current injected from FC compensates the grid current harmonics maintain the grid current THD ≤ 5% as per IEEE519 standards. A Particle Swarm Optimized (PSO) based PI current controller and a Fuzzy-logic-based controller are proposed for a grid connected fuel cell so as to mitigate the grid current deterioration caused due to the presence of existing nonlinear loads as well as EVCS. In addition, the parameters like grid voltage distortion and frequency variance are considered simultaneously to ascertain the capability of proposed controllers. This work is carried out in the MATLAB/SIMULINK environment.

Power Quality Improvement Grid Integrated Photovoltaic with LCL Filter Using DQ Controller

Grid-interactive solar photovoltaic (PV) systems are necessary for the current global scenario owing to their low cost and pollution-free energy source. The integration of PV systems in the power grid needs to be stabilized. To address this, this paper presents a composite controller that can synchronize Photovoltaic (PV) to the Grid, with bidirectional power flow in Grid. The proposed technique is explored with both RL and LCL filters. With grid synchronization of PV power generation, a control loop for power quality disturbance mitigation is simulated. The multicarrier SVPWM with DQ controller is used on the Grid Connected converter to mitigate Power Quality disturbances. MATLAB Simulink model is developed for the PV Grid setup and the validity of the composite controller is evaluated. The PI controllers are applied in the DQ-controlled PV integrated with the grid. Power quality parameters THD are found to be intact for both RL and LCL filters. The MATLAB simulation developed showed that the LCL filter has an incremental performance progression than using the RL filter. There is around a 3 to 4% improvement in the grid current THD while using the LCL filters instead RL filter for PV integration.

Implementation of artificial neural network based control for power quality enhancement of proton exchange membrane fuel cell powered distributed generation system

In this paper, a fuel cell and battery-based distributed generation system is demonstrated. A proton exchange membrane fuel cell is the primary power generator in this decentralized system, with a lead-acid battery providing backup power. A boost converter regulates the fuel cell’s output power to ensure its optimal performance. A bidirectional buck-boost converter has been employed to integrate battery using slope compensated current control. 5-level cascaded H-Bridge inverter is used to convert available DC power into AC power while integrating DG systems with the grid and improving power quality. The artificial neural network has been trained and used to generate the estimated reference current for sinusoidal pulse width modulation techniques. The artificial neural network has been fine-tuned using the scaled conjugate gradient with the performance value 0.094056. The THD of grid current has been reduced by 12.5% and 8.14% approximately for 30 Ω resistive, 30 mH inductive load and 20 Ω resistive, 15 mH inductive load respectively. The system has been simulated in Matlab/Simulink, and the findings have been validated. The results demonstrate the effectiveness of the methodology.

A comparative analysis of PI & FLC based grid connected PV system with power backup to improve power quality

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.

Control Method of Electrolytic Capacitor-Less Dual Inverter-Fed IPMSM under Periodic Load Torque Fluctuations

This paper proposes a control method for an electrolytic capacitor-less dual inverter for compressors. Single-phase motor drive systems are required to minimize vibrations, maintain a high power factor, and meet the limit for harmonic current emissions. The proposed control method achieves the harmonic reduction of the dq-axis currents, a high power factor, and a low grid current THD under periodic load torque fluctuations. The effectiveness of the proposed method is demonstrated via experimental results, using an open-end winding IPMSM and an electrolytic capacitor-less dual inverter. The proposed method reduced the 100Hz harmonic components of dq-axis currents up to 98% under periodic load torque fluctuations compared with an electrolytic capacitor-less single inverter. The results of FFT analysis of the input current show that the power factor and input current THD of the proposed method are equivalent to or superior to those of conventional methods. Therefore, the proposed control method can effectively achieve vibration reduction, a high power factor, and a reduction in the input current THD under periodic load torque fluctuations.

6-phase DFIG for wind energy conversion system: A hybrid approach

This research presents a novel wind power system based on a six-phase doubly-fed induction generator (DFIG). Optimization approaches are required to improve the efficiency of the traditional controllers. This study introduces a blended method for DFIG-based wind power transformation systems that combines quantum process and deep reinforcement learning (QPDRL) to improve control efficiency. It will be driven by using online control algorithms to eliminate the optimizing step and upgrade online control strategies. The proposed QPDRL can prevent local optimum solutions, forecast the future essential phase, and update DFIG-based wind power plants' regulation methods online. For two distinct scenarios, the QPDRL was contrasted with the proportional integral derivative (PID) controller, fractional-order PID, and reinforcement learning (for changeable air velocity, there are two types of arbitrary and step amplitudes). Matlab software was used to experiment. As air velocity variations exist, the findings revealed a 62% reduction in the DC link voltage ripples and a 99% reduction in speed overshoot with wind velocities overrun. Finally, comparing PID controls revealed a 42.15 percent reduction in grid current THD and an 11.38 percent reduction in the generator current.

Analysis of Grid-Interactive PV-Fed BLDC Pump Using Optimized MPPT in DC–DC Converters

In solar photovoltaic (PV) system-based Brushless DC (BLDC) motors for water pumping application, the role of DC/DC converters is very important. In order to extract the maximum power from the PV array, an efficient DC/DC converter is essential at the intermediate stage. In this work, different DC/DC converter topologies suitable for BLDC motors are proposed. The converters are supported by an optimized maximum power point tracking system to provide a reliable operation. Recent optimization algorithms such as fuzzy logic, perturb and observe, grey wolf, and whale optimization are implemented with the PI controller in maximum power point tracking to maximize the conversion efficiency. The obtained results using SEPIC, LUO, and interleaved LUO converters provide a comparative study in the case of converter output, motor parameters, and grid output. The performance analysis on three different converters and multiple optimization methods are carried out. By analyzing the performance of different converter topologies, the interleaved LUO converter outperforms the other two converters with the results of a voltage gain ratio of 1:22, conversion efficiency of 98.3%, and grid current THD of 2.9%. Moreover, regarding the power quality aspect, the total harmonic distortion of the grid current is maintained below the IEEE-519 standard. In addition, the developed system has an advantage of operating both in stand-alone and grid-connected operation modes.

A new five-level inverter with reduced leakage current for photovoltaic system applications

A general growth is being seen in the use of renewable energy resources, and photovoltaic cells are becoming increasingly popular for converting green renewable solar energy into electricity. Since the voltage produced by photovoltaic cells is DC, an inverter is required to connect them to the grid with or without transformers. Transformerless inverters are often used for their low cost and low power loss, and light weight. However, these inverters suffer from leakage current in the system, a challenge that needs to be addressed. In this paper, a topology with two alternative connection models is presented to stabilize the common mode voltage and reduce the leakage current. The output voltage characteristic of the proposed inverter is five-level, which reduces the harmonic distortion in the output current compared to the two- and three-level inverters. The operation modes and output of the proposed topology are described and analyzed. The structures of the proposed inverter are simulated in MATLAB/Simulink and are compared with some well-known structures. Results show that the proposed structure with both connection models effectively reduces leakage current and improves grid current THD.

A Variable Step Size Robust Least Mean Logarithmic Square-Based Control Scheme for Improved Power Quality of Grid-Interfaced PV System

Power Quality (PQ) issue has always been a challenge for Grid-Interfaced PV Systems (GIPS). A novel Variable Step Size Robust Least Mean Logarithmic Square (VSS-RLMLS)-based control scheme is thus presented for a GIPS. In the proposed control scheme, the VSS-RLMLS algorithm extracts the fundamental components of the nonlinear load currents accurately even during dynamic conditions which results in generation of accurate reference grid current thus allowing efficient functioning of the Voltage Source Converter (VSC) and delivering high quality power to the grid by mitigating the harmonics of the loads. The performance of the proposed control scheme is validated both in simulation and laboratory developed prototype system with different load and environmental conditions. This VSS-RLMLS control scheme is compared with LMF and variable leaky LMS. It is found that the proposed control exhibits superior PQ performance with least grid current THD.

Renewable energy based charging station with power quality features for multi EV spots using maximum correntropy sub-band adaptive technique

ABSTRACT Here, a photovoltaic (PV)-based multi-spots electric vehicles (EVs) charging station (CS) is presented by using maximum correntropy criteria with affine projection sub-band adaptive filter (MCC-APSAF). The presented CS also includes the features of power quality at nonlinear loads connected at the point of common coupling (PCC). This CS comprises a battery bank, multi-EV batteries, and ultra-capacitor (UC) charging spots. However, a dramatic increase of EVs and charging stations in the existing grid has raised the issues related to the harmonics, voltage fluctuations, reactive power, and burden on the grid. These issues are addressed in the presented charging station. Moreover, the ultra-capacitor can provide fast charging, which minimizes the high inrush current of the CS. Therefore, the batteries during the high EVs load at the CS are protected by the ultra-capacitor spots. To stabilize the DC bus voltage, separate cascaded controllers for ultra-capacitor and battery spots are used. The CS shows the multifunctional capabilities, which include PV array to grid (PV2G), PV array to the EV battery (S2EVB), EV battery to grid (EVB2G), and PV array to home (PV2H) when PV source is present. The various EVB2G, G2EVB, battery to home (EVB2H), and grid to home (G2H) behaviors are also presented. This CS shows good dynamic efficacy under insolation variation, EVB2G, G2EVB modes, load throw, and load reconnection operations. The grid current THD using the proposed current control is 1.44%, which is in accordance with the IEEE-519 standard. Moreover, the maximum power obtained from the PV generation is 63 kW, which is successfully distributed in the battery bank and six EV batteries (30 kW), in nonlinear load (14 kW), and the rest of the power is injected to the grid (29 kW). This CS is simulated in the MATLAB/Simulink library and test results are obtained using the experimental workbench with OPAL-RT (OP5600) in the laboratory.

Modular Single-Stage Three-Phase Flyback Differential Inverter for Medium/High-Power Grid Integrated Applications.

This paper proposes a single-stage three-phase modular flyback differential inverter (MFBDI) for medium/high power solar PV grid-integrated applications. The proposed inverter structure consists of parallel modules of flyback DC-DC converters based on the required power level. The MFBDI offers many features for renewable energy applications, such as reduced components, single-stage power processing, high-power density, voltage-boosting property, improved footprint, flexibility with modular extension capability, and galvanic isolation. The proposed inverter has been modelled, designed, and scaled up to the required application rating. A new mathematical model of the proposed MFBDI is presented and analyzed with a time-varying duty-cycle, wide-range of frequency variation, and power balancing in order to display its grid current harmonic orders for grid-tied applications. In addition, an LPF-based harmonic compensation strategy is used for second-order harmonic component (SOHC) compensation. With the help of the compensation technique, the grid current THD is reduced from 36% to 4.6% by diminishing the SOHC from 51% to 0.8%. Moreover, the SOHC compensation technique eliminates third-order harmonic components from the DC input current. In addition, a 15% parameters mismatch has been applied between the flyback parallel modules to confirm the modular operation of the proposed MFBDI under modules divergence. In addition, SiC MOSFETs are used for inverter switches implementation, which decrease the inverter switching losses at high-switching frequency. The proposed MFBDI is verified by using three flyback parallel modules/phase using PSIM/Simulink software, with a rating of 5 kW, 200 V, and 50 kHz switching frequency, as well as experimental environments.

In depth mathematical-analysis and experimentation of high-power SiC-FET based single-stage three-phase differential-based flyback inverter with practical design issues for grid-tied applications

This paper presents a detailed mathematical loss-modelling, design, hardware implementation issues, and experimental verification of high-power isolated single-stage three-phase differential-based flyback inverter (DBFI) for grid-tied photovoltaic applications. In addition, this paper studies the loss-modelling analysis of the DBFI components in terms of time and system parameters, which describes the power loss distribution over the circuit components for efficiency enhancement possibility. Also, it studies the practical design issues of DBFI; power stage design, HFT-based F3CC Nano-Crystalline C-Core design, passive elements selection effects on harmonics compensation of grid current waveforms, and the input DC current ripple for PV applications propriety. In addition, the input DC-voltage variation impact on the grid-current THD, system efficiency, and operational power factor are investigated. Also, continuous modulation scheme (CMS) is used to control the proposed DBFI for low-order harmonic components mitigation. The system is simulated by PSIM computer-aided simulator. Then, the proposed system is verified experimentally using a laboratory prototype controlled by TMS320C6713 DSP controller.

A new control scheme for limiting the compensation current and prioritizing power injection in multifunctional grid-connected photovoltaic systems

Several recent studies have demonstrated the benefits of incorporating auxiliary functions such as power quality enhancement services in the control strategy of grid-connected photovoltaic (PV) systems. However, most studies ignore the necessity to prioritize the PV power injection into the grid, the primary role of grid-connected PV systems, and limit the compensation (the achievement of the auxiliary functions) according to the available capacity of the PV inverter. Limiting the inverter's rated capacity in terms of maximal current is crucial not only for preserving the life of the semiconductors but also for ensuring the inverter's principal role of injecting active power into the network. This paper proposes a control technique in abc reference frame that incorporates a current harmonics filtering function for two-stage grid-connected PV systems. The proposed strategy inherently prioritizes the PV power injection over current harmonics filtering. It also considers the PV inverter's rated capacity by characterizing it by its peak rated current to fulfil its two functions without exceeding the inverter limit by optimally limiting the current for harmonics compensation. In addition, a fuzzy logic-based control scheme was proposed for the need to limit the generated PV power regardless of environmental conditions. Furthermore, A comparison between the proposed control sheme and a traditional shunt active power filter (APF) in terms of grid current THD improvement was conducted under two scenarios using MATLAB/Simulink. The simulation of the first investigated scenario, where the local load demand power is less than the PV power generation, results in a grid current THD of 3.41% vs. 3.53% when applying the proposed technique and the shunt APF, respectively. In the second scenario, When the load is supplied by the grid and the PV generator, A grid current THD of 2.04% vs 5.54% are obtained using the proposed method and the shunt APF, respectively.

Online Filter Parameters Estimation in a Double Conversion UPS System for Real-Time Model Predictive Control Performance Optimization

Uninterruptible Power Supplies (UPS) represent the key technology to continuously feed and protect a wide range of critical applications in electric power systems. Due to their continuous operation, UPS components degrade over time, including their filtering elements, leading to decreased filtering capabilities. With these deviations, UPS performance is typically reduced. Moreover, if filter parameter deviations are not considered in the control system, performance degradation can be further increased and the critical load can be seriously compromised. This is especially important with Model Predictive Control (MPC), which heavily relies on system parameters accuracy. Thus, control performance optimization using estimated filter parameters in UPS systems can be extremely important. Nevertheless, this has not yet been covered in the literature for UPS systems. In light of these facts, this paper proposes a new mechanism that, by using online estimated filter parameters, optimizes the performance of an MPC strategy, in a UPS system. In the scope of this optimization mechanism, an estimation method that enables parameter identification and control optimization not only in balanced but also in highly unbalanced filter conditions (rarely studied in the literature) is proposed. Experimental results demonstrate the accuracy of the proposed estimators and the effectiveness of the proposed control performance optimization mechanism. Under severe filter parameter variations, the proposed performance optimization scheme enabled to reduce the degradation (caused by filter variation) of the grid current and load voltage THD by 29.41% and 91.60%, respectively. Furthermore, the degradation of the RMS load voltage value was also significantly reduced by 97.89%.

Three-Phase PWM Inverter for Isolated Grid-Connected Renewable Energy Applications

This paper proposes a three-phase isolated flyback inverter (IFBI) for single-stage grid-tied solar PV applications, considering a simple sinusoidal pulse-width modulation (SPWM) scheme. The proposed single-stage inverter employs a reduced passive elements count by considering three input-parallel output-differential (IPOD) flyback converter modules. Additionally, a single small size LC-input low-pass filter is utilized at the input paralleling point for ripple-free input current operation, which is essential in grid-connected renewable energy applications. In addition, a mathematical model of the IFBI is presented to confirm the existence of its low-order harmonic components. A simple PI controller-based control scheme, considering only two loops and five sensors, is used to control the proposed grid-tied IFBI. Continuous modulation scheme (CMS) combined with SPWM is used to diminish the low-frequency harmonic components. Moreover, a simple selective harmonic elimination (SHE) loop is used for second-order harmonic components (SOHC) elimination from grid-injected currents. The SHE has decreased the SOHC from 43% to 0.96%, which improves the grid current THD from 39% to 3.65%, to follow the IEEE harmonic standard limits. Additionally, the harmonic elimination technique decreases the circulating power between the inverter paralleled modules, which enhances the grid currents power factor. The proposed inverter is verified through a grid-connected 200 V, 1.6 kW, 60 Hz experimental prototype, and the switching frequency is 50 kHz. TMS-based DSP controller is used to control the grid-injected power to follow the reference power set-point.

Electric vehicle operation modes with reactive power support using SMC in distribution generation

In this work, a single phase 120 V rms, 60 Hz on-board Electric Vehicle (EV) battery charger with capacity 100 Ah for operation in Grid to Vehicle (G2V) and Vehicle to Grid (V2G) with Reactive Power Support using Sliding Mode Controller (SMC) is presented. The controller is chosen for its robustness and steady tracking precision. State space models of G2V and V2G of EV are derived and good stability margins are obtained using frequency response characteristics. SMC is found to be good in tracking the dc voltage in G2V and grid current in V2G with less steady state error. THD in grid current is 0.645 % during G2V and 1.95 % in V2G which are comparatively less than in Proportional plus Integral (PI) and Proportional plus Resonant (PR) controllers. Dynamic nature of SMC is found to be robust during grid frequency variations. It delivers less steady state error of 1.52 % and settling time of 0.1 s during charging and discharging operations. Phase planes are presented to understand finite convergence of SMC. Reactive power support to the grid operation is presented without affecting the state of charge (SOC) of the battery. Solar based charging circuit is discussed for EV charging. The SOC depicts changeover state from normal to solar charging reaching 100% within short period. SMC was designed to be robust against bounded perturbations and also guarantee stability and finite convergence. PSCAD v4.6 software is used.

Modified grid side converter control technique for DFIG connected to nonlinear loads

ABSTRACT In this work, a grid side converter (GSC) control with integrated shunt active filtering function using space vector pulse width modulation (SVPWM) technique is proposed to mitigate harmonics produced by the nonlinear loads. This method is focused on removal of harmonics from the grid currents by supplying compensating currents through GSC of DFIG. The proposed control technique improves power quality and reduces Total Harmonic Distortion of the grid current. Simultaneously, it is also capable to control active power and regulate DC link voltage during variable wind speeds in the presence of nonlinear loads. Performance of the proposed technique is compared with the conventional technique considering grid-connected 2.6 MW DFIG-based wind energy conversion system using MATLAB Simulink. Performance analysis has been carried out to check the behavior of the proposed SVPWM-based modified GSC control technique to mitigate the grid current harmonics considering wide variations in various parameters. The simulation results validate the effectiveness of the proposed scheme since it achieved grid current THD within limits of 5% as per IEEE-519 standards for all wind speeds.

Harmonic elimination and dc-link voltage balancing in bipolar hybrid microgrid using Space vector modulation for Interlinking Converter (ILC)

The modernization of distribution grids developed the power systems towards the smart grid. The microgrid plays a vital role in an improving power systems area, which refers to the loads operated under an organized and synchronized way and the distributed energy resources. The microgrid, which is operated in “islanded” mode, should be connected to the main power grid, or it must be entirely off-grid. Bipolar hybrid microgrid feeds local loads with local resources because it consists of both DC and AC bus simultaneously. The converter, which is used for microgrid application, plays an important role, which is said to be Interlinking Converter (ILC). The lower order harmonics can be eliminated by these ILCs. By reducing the THD and increasing the dc-link voltage utilization SVM is used. In this paper, there will be an increase in system performance and great reliability with a fully automated system. There will be a decrease in switching losses, current ripple and THD of grid current by the use of a new switching modulation method, which is validated by the Matlab simulation results.