Grid Current Research Articles

Control Method of Four Wire Active Power Filter Based on Three-Phase Neutral Point Clamped T-Type Converter

An active power filter based on a three-level neutral point clamped T-type converter with LCL input filter is presented in the paper. The main goal of the paper is the analysis of a control system that ensures independent control of a current in each phase. The presented control method of the filter allows reactive power compensation and/or a higher harmonics reduction to be achieved in each phase independently, with the possibility of control tan (φ) coefficient. This allows the power flow between the phases to be minimalized and reduces the RMS values of filter currents without the need to balance grid currents. The analysis presents the possibility of an operation in different modes, which was verified by experimental results. The results have been obtained in a 20 ARMS laboratory system described in the paper. The results reveal relatively low power losses, which are a feature of the selected three-level T-type topology. Additionally, that topology, when compared to a two-level one, ensures the reduction in current ripples with the same parameters of passive components.

Efficient maximum power point tracking in grid connected switched reluctance generator in wind energy conversion system: an enhanced Mayfly Algorithm transient search optimization

ABSTRACT This manuscript proposes an efficient hybrid technique for efficient maximum power point tracking (MPPT) in wind energy conversion system (WECS). The system has MPPT-based control of Switched Reluctance Generator (SRG) is a hybrid Meta-heuristic algorithm. The proposed technique is the combination of Mayfly Algorithm (MA) and Transient Search Optimization (TSO), hence it is called enhanced MATSO (EMATSO) method. The main aim of the proposed method is to the reduction of speed error. Based on direct variation and Quadrature current parameters, the MA algorithm is proposed to stimulate the maximum proportional integral (PI) gain parameters controller with least error function. Here, the MA search behavior is enhanced using the efficient TSO algorithm. Based on speed variation of generator using MPPT method and loss reduction method, the direct axis set point is created with the Quadrature axis current parameters of WECS. The proposed EMATSO method has enhanced the efficiency of the WECS with this proper control. The proposed technique is carried out in MATLAB/Simulink platform, and then the efficiency is compared with other existing techniques, viz GA, ALO, and TSA, MA. Here, the current, voltage, power, grid current, flux, speed, theta, torque and reference speed are analyzed. By then, the statistical parameters, time domain parameters and elapsed time are also evaluated. In all the analysis, the proposed technique has superiority over other existing techniques.

Adjoint least mean square control for solar photovoltaic array grid‐connected energy generating system

This study deals with a new control for a double-stage grid-integrated solar photovoltaic array (SPVA)-based energy generation system, which is based on adjoint least mean square (ALMS) control. This ALMS control algorithm has some new features: (1) it provides a fast rate of convergence, (2) harmonics mitigation ability, and (3) ease of implementation. The solar PV energy generating system includes a DC–DC boost converter, a voltage source converter (VSC), a ripple filter, a three-phase grid, and local non-linear loads. The VSC is controlled for feeding the active power from the solar array to the grid and three-phase non-linear loads. Moreover, VSC control is used to improve the grid current quality. A DC–DC boost converter is coupled between the photovoltaic array and the DC-link capacitor, which tracks the maximum SPVA power from the SPV array by using perturb & observe algorithm. Here, the main goals of SPVA generating system are to eradicate power quality problems caused by unbalanced and non-linear loads and to provide sinusoidal grid currents at solar PV array irradiance variation. Moreover, a comparison of ALMS control is made with other control algorithms. Performance of this ALMS control is studied at varying non-linear loads and under different environmental conditions on a developed prototype in the laboratory. The simulated results of the system are validated with test results. Detailed behaviour of the grid-integrated SPV system and harmonics spectrum of grid currents are given here while meeting the IEEE 519 Standard.

Noninvasive Model-Based Open-Circuit Switch Fault Detection of AC-Bypass Leg Switches in Transformerless PV Inverter

Transformerless inverters are being used for integrating photovoltaic (PV) sources into the grid. Highly efficient and reliable inverter concept (HERIC) inverter is one such topology, which is derived from an H-bridge by adding a bypass leg on the ac side using two back-to-back insulated gate bipolar transistors (IGBTs). Open-circuit fault in the bypass leg would result in conduction of current through antiparallel diodes of the main switches of the inverter, effectively making the inverter operate in bipolar mode. As a result of the fault, there would not be an issue of leakage current, and the operation would continue at the expense of increased conduction losses and dc-offset in the grid current. This article proposes an online noninvasive model-based technique to detect switch faults in the bypass leg of the HERIC inverter. The grid current at the peak of the carrier signal is predicted based on the measured grid current at the start of the zero states. By comparing the estimated and measured grid currents at the peak of the carrier signal, the faulty switch in the bypass leg is localized. Once the fault is localized, the inverter’s modulation scheme is changed to conventional bipolar mode to improve the performance of the converter during the post-fault stage. A detailed simulation study is carried out to verify the effectiveness of the proposed approach. Experimental tests on the prototype converter show that the proposed algorithm can reliably detect the open-circuit fault in switches of the bypass leg, and once a fault is detected, the algorithm would change the modulation scheme to bipolar mode to minimize the inverter loss and dc-offset in the grid current.

Least mean sixth control approach for three-phase three-wire grid-integrated PV system

<p><span lang="EN-US">This work proposes an adaptive filter based on a new least mean sixth control approach with incremental conductance method of MPP for 3-phase grid-incorporated photovoltaic (PV) system. The proposed system comprises a PV array, 3-phase DC to AC converter, maximum power point tracker (MPPT), three-phase electronic load, and a 3-phase grid. The combination of solar PV array and the voltage source converter (VSC) supplies power to the grid. The 3-phase inverter as a distribution static synchronous compensator (D-STATCOM) improves the quality of the system performance in case of zero solar irradiation. D-STATCOM also reduces total harmonic distortion (THD) in grid currents, improves power factor, and maintainsa constant voltage at the point of common coupling (PCC). The system modelling and simulation is achieved on MATLAB/Simulink. The proposed system performance has been found satisfactory and conform to IEEE-519 standards.</span></p>

An Ignored Culprit of Harmonic Oscillation in LCL-Type Grid-Connected Inverter: Resonant Pole Cancelation

Resonant pole cancelation is usually adopted in the current control or active damping to tackle the filter resonance in the LCL-type grid-connected inverter. However, its potential impact on the system stability has not been adequately assessed. This article provides a comprehensive investigation on three typical control schemes that utilize resonant pole cancelation. An important finding is drawn that the resonant pole cancelation violates the so-called internal stability, which can give rise to the undesired harmonic oscillation in grid current. From the physical insights, it is revealed that the resonant pole cancelation does not essentially eliminate the LCL resonance but merely “hide” it in the system, which can still be triggered and, thereby, turns into the culprit of the harmonic oscillation. The theoretical expectation is validated by the simulation and experimental results.

A simple control strategy and dynamic energy management for the operation of combined grid-connected and standalone solar photovoltaic applications

There is an increased focus on energy savings in low-voltage DC (LVDC) loads for home appliances. The use of LVDC for the local distribution system enables easier integration with renewable sources. This work presents the control and management of power flow to DC loads in grid-tied photovoltaic (GPV) systems. This system provides bi-directional flow of power from the DC load to the AC grid, using a pulse width modulation (PWM) technique, employing a voltage source inverter between the DC nano grid and the AC main grid. The bidirectional converter controls the active power transferred in both directions while operating at unity power factor (UPF). The modified three-level hysteresis current controller and the voltage controller are designed as the inner loop and the outer loop, respectively, to control the bi-directional power flow. The corresponding grid voltages and currents are used to generate the reference currents. The proposed system has been validated through MATLAB/Simulink simulations and experimentation on a prototype system developed in the laboratory controlled by the dSPACE 1103 real-time digital controller board. The results show that a regulated DC voltage is obtained for dynamic changes of source and load like in a real-time environment. The control strategy with its validation shows the efficacy of the proposed system.

A Cascaded Generalized Integral Control for Multiobjective Grid-Connected Solar Energy Transfer System

A cascaded generalized integral control algorithm is presented in this article for a solar energy transfer system (SETS), connected to the grid. The control algorithm introduces a two part fundamental component extraction such as, primary harmonics filter with higher order harmonic reduction and dc-offset rejection, and secondary fine fundamental component tuning with fractional order and lower harmonics rejection property. This SETS transfers electrical energy converted from solar radiant energy, efficiently to the three-phase distribution grid. The two-stage system consists of a boost type dc–dc converter on the primary side. Moreover, the incremental conductance algorithm-based operation of the boost converter ensures maximum power output from the photovoltaic (PV) array. This system is designed to meet load demands and feeds remaining power to the grid. It mitigates the reactive power and harmonics requirements of the load at any irradiance level, and thereby keeps the balanced sinusoidal grid currents, in-phase with the respective grid voltages. As the PV array power and load power are varying, performance of SETS with adverse operating conditions is validated in this work. A prototype is developed and tested under varying irradiance conditions as well as nonlinear unbalanced load. The steady-state and dynamic behaviors of the system during transient operating conditions are expressed to substantiate the acceptability of the control technique for multiobjective grid-connected SETS.

Single phase multifunctional integrated converter for electric vehicles

In this paper, a single phase multifunctional integrated converter is proposed for electric vehicles (EVs) with single stage power conversion. The main objective of the proposed topology is to reduce the weight, size, and cost of the power electronic converter system used in EVs compared to the existing topologies that are already available in the industries. The novelty of the proposed topology includes: (i) single converter for charging, propulsion and regenerative braking; (ii) reduction of number of switches to reduce the switching and conduction losses; (iii) improving the efficiency by reducing the value of inductor; (iv) power factor correction for AC grid; and (v) improving the total harmonic distortion of the grid current. The complete analysis of the various modes of operation of the proposed topology is analyzed and implemented through MATLAB/Simulink software simulation and a power factor of 0.9999 and a current total harmonic distortion (THD) of 2.16% is achieved. The proposed topology is also compared with the existing topologies in terms of number of switches, diodes, inductors and capacitors used.

Buck-Boost Single-Stage Microinverter for Building Integrated Photovoltaic Systems

Microinverters for Building Integrated Photovoltaic (BIPV) systems must have had a small number of components, be efficient, and be reliable. In this context, a single-phase Buck-Boost Single-stage Microinverter (BBSM) for grid-connected BIPV systems is presented. The concept of topology is extracted from the buck-boost converter. The leakage current in the system is kept under control. It uses an optimal number of active and passive components to function at a high-efficiency level. The suggested topology provides a high level of reliability due to the absence of shoot-through problems. To validate the findings, a simulation in combination with an experimental system for a 70 W system is developed with the design approach. The efficiency of the microinverter, total harmonic distortion of the grid current are measured as 96.4% and 4.09% respectively. Finally, a comparison study has indicated the advantages and disadvantages of the suggested inverter.

AES-FLL control of RES powered microgrid for power quality improvement with synchronization control

In this paper, AES-FLL (Advanced Extremum-Seeking Frequency Locked Loop) control with DC-offset-rejection capability for power quality improvement is proposed. The attributes of the AES-FLL are a precise estimation of fundamental load current with low steady-state oscillations, fast dynamic response, DC-offset rejection capability and low THD. Further, the AES-FLL is capable of extracting the fundamental component of grid voltages and generates harmonic free reference grid current under weak grid conditions. Moreover, reactive power compensation, harmonics mitigation, unity power factor and coordinated power flow operation are accomplished using the AES-FLL control approach. A seamless transition is achieved from the grid-connected operating mode to the standalone operating mode during the grid outage to ensure power continuity. The grid synchronization is achieved through the LPN-PLL (Low-Pass Notch Filter Phase Locked Loop) control approach. Comparative analysis of the VSC (Voltage Source Converter) control approach AES-FLL and grid synchronization approach LPN-PLL with the conventional methods is presented. The performance of the microgrid is demonstrated by simulation and then presented a prototype experimental validation under nonlinear loads.

Control of grid-connected residential solar-PV system using novel adaptive linear combiner filter for power quality improvement

ABSTRACT A grid-connected residential photovoltaic (PV) system has been proposed using novel adaptive linear combiner filter-based control for power quality (PQ) improvement. In the present work, novel adaptive linear combiner (ALC) filter-based control-based control has been proposed to generate reference current. MATLAB/Simulink software is used to develop the two-stage grid-connected residential PV. The proposed control is tested in MATLAB/Simulink2018(a) under nonlinear, linear load and variable input and validated experimentally on prototype hardware. The performance of the proposed ALC filter-based control has been analyzed and compared with that of conventional synchronous d-q control. It has been observed from results that THD in grid current using proposed control is 3.74% whereas using conventional d-q control THD is 4.75%. Proposed control provides more efficient performance by improving the PQ of the system by compensating the harmonics and reactive load demand. Harmonic distortion in the grid current is within the limits as per IEEE-1547. Furthermore, proposed control has better transient response viz. settling time, under shoot and overshoot in DC link voltage during grid connection of rooftop PV system and provides, reduced complexity due to absence of phase lock loop (PLL), thus less sampling time, better accuracy, ease of implementation, and adaptability.

Analysis and Simulation of Current-source Flyback Inverter with Efficient BCM Control Strategy

The Flyback inverter is a single-stage power inverter which represent an attractive solution for photovoltaic (PV) grid-tied inverter application. The main advantages of a current-source flyback inverter are high power density and high efficiency due to its small, as well as low total harmonic distortion (THD) operation. However, a flyback topology works with Discontinuous Conduction Mode (DCM) control strategy has lower efficiency and poor THD values. In this paper, an efficient current-source flyback inverter topology works with Boundary Conduction Mode (BCM) control strategy is presented. Besides, an efficient incremental conductance (IC) maximum power point tracking (MPPT) is used to extract the maximum power from the PV module. To verify the proposed control a power simulator (PSIM) software is used. As a result, the simulation results indicates that the BCM control is more efficient than the DCM method for various weather conditions. Finally, the proposed BCM strategy is compared with DCM control in terms of THD and thus it is achieved lower THD contain in the injection current of grid.

Fault Protection of Urban Distribution Network Using a Superconducting Cable Joint

To enhance the operating security and stability of the cross-linked polyethylene power cable based urban distribution network due to conventional cable joint (CCJ) faults, this paper presents a novel superconducting fault current limitation scheme by using a superconducting cable joint (SCJ). The basic principle, circuit modeling, conceptual design and distribution network integrated with the SCJ are presented in detail. The comparative study without and with the proposed SCJ scheme and comprehensive evaluation are carried out. The simulation results obtained under symmetrical and asymmetrical CCJ faults show that the harmful large fault grid currents can be limited effectively and the fault grid voltage can be well improved. Thus the high temperature electric arc in the fault location caused by CCJ faults can be safely controlled. And large area power failure in actual power system can be avoided.

Power Quality Improvement of a Solar Energy Conversion System by a Coordinated Active and LCL Filtering

Power converters play an essential role in Photovoltaic (PV) system to maximize the power transfer to the electrical grid. However, the generated harmonics in the grids due to these power converters and nonlinear loads are considered one of the encountered problems to overcome. This paper presents a decoupled control of PV field real power and reactive power injected to the high voltage network via a PWM inverter by using fuzzy logic controllers. Elsewhere, a procedure based on a coordinated active and LCL filtering is proposed to mitigate the harmonic current introduced by a nonlinear load and the inverter itself in such a way to enhance the power quality injected into the grid. The results obtained in the present study show the good performance of the suggested hybrid filtering approach and demonstrate that almost all harmonics orders of the grid current are well mitigated; the current Total Harmonic Distortion (THD) meets its standard and consequently the power quality is considerably enhanced.

Modified incremental conductance MPPT algorithm for SPV‐based grid‐tied and stand‐alone systems

This paper deals with power generation through solar photovoltaic (SPV) system and its implementation as grid-tied and stand-alone systems. The major setbacks of SPV system of low conversion efficacy, that can be enhanced through the maximum power point tracking (MPPT) algorithm. A modified incremental conductance (MIC), termed as error based incremental conductance MPPT, has been proposed, and its behaviour is comprehensively compared with classical perturb and observe (P&O) and incremental conductance (IC) techniques. Dealing with the on-grid application of SPV system, maximum power obtained through MIC is fed to a three-phase grid operating at unity power factor (UPF), and the quality of grid current is monitored. Further, the power obtained through MIC finds its application in designing an SPV-diesel generator (DG) based hybrid renewable energy system (HRES) for areas either not connected to the grid or have insufficient fossils. The stochastic nature of source or uncertain load demand leads to deviation in system frequency. This paper proposes an intelligent, comprehensive supervisory optimal-fuzzy-proportional-integral-derivative (O-F-PID) controller for load frequency control (LFC). The performance of proposed O-F-PID controller has been vividly compared with the designed optimal-PID (O-PID) and conventional PID (C-PID) controllers under varying source and load demand conditions.

Control Methods for Performance Improvement of an Integrated On-Board Battery Charger in Hybrid Electric Vehicles

This paper presents control methods for performance improvement of an integrated on-board battery charger (OBC) in hybrid electric vehicles (HEVs). HEVs generally consist of an OBC and a starter generator system (SGS). Since these each have a power conversion device for independent operation, such as battery charging and starter generator driving for engine starting, it necessarily increases the number of components, weight, and volume of the HEV. In order to overcome these disadvantages, recent research concerning the integrated OBC has progressed. Although it demands installation of power relays and an additional circuit, the integrated OBC is effectively operated for battery charging and starter generator driving. This paper proposes not only a harmonic reduction method of grid current, but also a feed-forward control method for performance improvement of the integrated OBC in HEVs. The effectiveness of the proposed control methods is verified by simulation and experimental results.

Active filter for multi-pulse rectifiers with magnetically coupled reactor

The article presents the simulation and laboratory tests of multi-pulse rectifiers with magnetically coupled reactors, connected to the power grid and cooperating with an active parallel filter (APF). In the study, two types of multi-pulse AC/DC rectifiers were compared, namely 12- and 24-pulse rectifiers. It presents the operating principle and the results of the simulation and laboratory tests. The considered systems enable the reduction of undesired high harmonics in the power supply grid current. For the manufacture of multi-pulse rectifiers, assemblies of magnetically coupled spring reactors configured in the TDSλ system were used.

Third-Order Sliding Mode Applied to the Direct Field-Oriented Control of the Asynchronous Generator for Variable-Speed Contra-Rotating Wind Turbine Generation Systems

Traditional direct field-oriented control (DFOC) techniques with integral-proportional (PI) controllers have undesirable effects on the power quality and performance of variable speed contra-rotating wind power (CRWP) plants based on asynchronous generators (ASGs). In this work, a commanding technique based on the DFOC technique for ASG is presented on variable speed conditions to minimize the output power ripples and the total harmonic distortion (THD) of the grid current. A new DFOC strategy was designed based on third-order sliding mode (TOSM) control to minimize oscillations and the THD value of the current and active power of the ASG; the designed technique decreases the current THD from ASG and does not impose any additional undulations in different parts of ASG. The designed technique is simply implemented on traditional DFOC techniques in variable speed DRWP systems to ameliorate its effectiveness. Also, the results show that by using the designed TOSM controllers, in addition to regulating the active and reactive powers of the ASG-based variable speed CRWP system, the THD current and active power undulations of the traditional inverters can be minimized simultaneously, and the stator current became more like a sinusoidal form.

Feedback Linearization-Based Control Strategy for Interlinking Inverters of Hybrid AC/DC Microgrids with Seamless Operation Mode Transition

This study proposes an advanced control scheme for the interlinking inverters of the hybrid AC/DC microgrids, which facilitates a seamless transition between grid-connected and stand-alone/islanding modes for the microgrid. Due to a nonlinear relationship between the terminal voltages of the voltage-source inverter (VSI) interfacing through inductor–capacitor (LC) filters with the grid voltages and currents, a feedback linearization technique (FLT) is employed to control the interlinking VSI under both grid-connected and islanding operations. The FLT-based current controllers are applied in the grid-connected mode, in which they adjust the power exchange between the DC and AC subgrids and mitigate the distortion of the grid currents produced by nonlinear loads. Under the stand-alone operation, the AC bus voltages are directly regulated by the FLT-voltage controllers of the interlinking VSI. In order to reduce the inrush currents and voltage overshot at the instant of mode switching, the FLT-based controllers are performed all the time regardless of the operating modes, where the voltage references for the VSI are not changed abruptly. The control performance of the VSI is highly satisfactory with low-transient overshoot values of the voltages and currents and low total harmonic distortion (THD) values of the grid currents and AC bus voltages are about 3.5% and 2.7%, respectively, under the nonlinear load condition. The validity of the new control strategy is verified by the simulation work, which investigates the operation of a hybrid AC/DC microgrid.