Presence Of Nonlinear Loads Research Articles

A New Algorithm for Harmonic Impacts with Renewable DG and Non-linear Loads in Smart Distribution Networks

With the development of renewable energy sources (RECs), distributed generation (DG), micro-grid, electric vehicles, etc., in traditional distribution network which was earlier supply-side driven, single power supply, one-way service and basic reliance on manual management of business model turns into the direction of user interaction, the trend of two-way flow and highly automated these changes gradually formed the smart distribution networks (SDN). The rapid advancement in power electronic devices increases the fast growth of RECs into SDN and also increases the non-linear portion of loads. Due to this, harmonic currents will be injected into SDN. This paper proposed a new power flow algorithms (PFAs) for fundamental and harmonic impacts in SDN with integration of renewable energy based DG and presence of non-linear loads. The proposed methodology completely exploits the radial feature in distribution networks and developed the matrix of bus numbers (BUS_NUM) and matrix of branch numbers (BRANCH_NUM). These matrices make the implementation of PFAs simple. The accuracy of fundamental and harmonic PFAs is tested on IEEE-13 bus test feeder and they are found to be accurate with the literature. Different case studies are carried on IEEE-13 bus test feeder for analyzing the impacts of integration of synchronous based-renewable DG and power electronic based-renewable DG.

Integrated Renewable Smart Grid System Using Fuzzy Based Intelligent Controller

In high power medium voltage applications, the utilization of 5-H Bridge Multi-Level Inverter (MLI) has grown vastly in recent years. The 5-H Bridge MLI can effectively control link voltage as well as power factor. However, the inverter imparts harmonics owing to the high switching frequency. Hence Inductance Capacitance Inductance (LCL) filter is implemented at its output to mitigate harmonics in presence of non-linear load. It’s of highly important to choose LCL parameters wisely in order to attain good filtering effect. This work investigates the application of 5-H Bridge MLI with LCL filter at the output for efficient integration of renewable energy sources on to the grid. A modified fuzzy heuristic approach is used to solve LCL power filter optimization problem at output of 5-H Bridge Multi-Level Inverter. Subject to the constraint’s harmonic distortion and losses of the inverter, multi objective optimization problem is solved to obtain LCL filter optimal values. The optimized LCL filter design was applied to a grid connected cascaded H-bridge MLI of rating 4.5 MW, 11 kV. MATLAB-Simulink is utilized for modelling and simulating the system. The results showed that the system is more efficient and generic. dSPACE Hardware in Loop (HIL) test system was used to verify the efficacy of the prototype system.

An EAFOGI-FLL Based Adaptive Control for Seamless Operation of a Solar Photovoltaic System

This paper presents an enhanced adaptive fourth order generalized integrator with frequency locked loop (EAFOGI-FLL) based control that improves the power quality of a solar photovoltaic system (SPVS) in grid-connected mode (GCM) and standalone mode (SAM), ensures seamless operation, makes the grid currents sinusoidal and, also eliminates DC offset. It ensures unity power factor (UPF) operation of the grid to minimize line losses. The control maintains the point of common coupling (PCC) voltages sinusoidal in GCM and SAM even in the presence of nonlinear loads. The FLL enables effective frequency tracking with grid frequency variations and makes the system adaptive. The SPVS is run in maximum power point tracking (MPPT) mode in GCM and, with an improved control in SAM to ensure power balance. The system is analyzed using a developed simulink model in different conditions.

Nonlinear control of active power filter connected to photovoltaic system

The paper presents a nonlinear control of shunt active power filter operating in presence of nonlinear loads. The said filter is connected to PV system in order to deliver the active power to load. The main control objectives are: (i) compensation of harmonic currents and the reactive power caused by the nonlinear load; (ii) regulation the DC bus voltage of inverter. The control problem is dealt with a nonlinear controller that is developed by using the Lyapunov technique to cope with the harmonic’s issue. The outer-loop regulates the DC bus voltage of the static converter. The controller performances are validated by simulation in MATLAB\\Simulink.

Advanced Control and Observation of Shunt Active Power Filter Connected to PV System

We consider the problem of controlling single-phase shunt active power filter operating in presence of nonlinear loads. The filter is connected to PV system; this latter provides the active power to load. The main control objectives are: (i) compensation of harmonics current and the reactive power caused by the nonlinear load; (ii) regulation of the output voltage of PV system to track its reference provided by the MPPT block. The problem is dealt with a nonlinear controller involving two regulators in cascade. The PFC regulator is developed by using the Lyapunov technique to cope with the compensation issue based on the estimated grid voltage values provided by an observer. The outer-loop regulates the output voltage of PV system. The proposed controller performances are confirmed by simulation in MATLAB\\Simulink.

Improved Trans-Z-source inverter based dynamic voltage restorer

ABSTRACT This paper presents an improved Trans-Z-source inverter-based DVR to enhance the quality of power and to compensate the voltage abnormalities seen in the industrial and consumer premises. The proposed improved impedance structure of the inverter performs buck/boost inversion in a single stage with improved voltage gain featuring minimal component count. Constant maximum boost control logic for the inverter switches is implemented in this paper to minimise the size, cost of the passive components, accomplishment of maximum voltage boost for the given modulation index which in turn relieves the stress of the dc voltage source. Closed loop operation of DVR is carried out using synchronous reference frame control with PI controller to regulate the load terminal voltage at the point of common coupling (PCC). The voltage injected by the proposed inverter structure is able to mitigate balanced and unbalanced with dynamically occurring multiple voltage sag and swell conditions. It features fault ride through capability at the event of fault and ensures harmonic mitigation capability in the presence of non-linear loads. Simulation model developed using Matlab/Simulink is presented to validate the performance of improved Trans-Z-Source inverter based DVR and to indicate the effectiveness of the proposed modulation strategy for the inverter. The FFT spectral analysis obtained for the inverter output voltage is well below the IEEE harmonic limits.

Power quality improvement using model predictive control based shunt connected custom power device in a single phase system

Abstract The performance evaluation of a single-phase shunt-connected custom power device (SC-CPD) for current quality improvement is discussed in this paper. The SC-CPD performance is compared based on the linear triangle-comparison pulse width modulation (TC-PWM) control, hysteresis current control (HCC), and the predictive non-linear switching control strategies. The predictive switching control is implemented using the finite control set-model predictive control (FCS-MPC). The switching control techniques’ operational and implementation features are discussed for the given control objectives of the SC-CPD for a particular nonlinear load. Basic functional case studies with sinusoidal and non-sinusoidal supply mains in the presence of non-linear loads are presented to illustrate the appropriateness of the switching techniques. The SC-CPD model and control methodologies are developed in the MATLAB/Simulink environment, including designing of various circuit components. Finally, performance simulation results using the switching techniques have been compared and validated using OPAL-RT 4510-based real-time simulations.

Optimal Power Dispatch of Dispersed Sources in Direct-Current Networks with Nonlinear Loads

The problem of the optimal power dispatch of dispersed generators in direct-current networks under the presence of nonlinear loads (constant power terminals) is addressed through a combinatorial optimization strategy by using a master-slave solution methodology. The optimal power generation in the dispersed is solved in the master optimization stage through the application of the vortex-search algorithm. Each combination of the power outputs at the dispersed generation sources is provided to a power flow methodology known as the hyperbolic power flow approach for direct current networks. The main advantage of the proposed optimization method corresponds to the possibility of solving a complex nonlinear programming problem via sequential quadratic programming, which can be easily implemented at any programming language with low computational effort and high-quality results. The computational tests of the master-slave optimization proposal are evaluated in a 21-bus system, and the numerical results are compared with the implementation of the exact nonlinear programming model in the General Algebraic Modeling System (i.e., GAMS). All the computational results are conducted through the MATLAB programming environment licensed by Universidad Tecnologica de Pereira for academic usage.

An investigation of solar active power filter based on direct power control for voltage quality and energy transfer in grid-tied photovoltaic system under unbalanced and distorted conditions

This paper discusses a renewable energy system connected to a dual-function power grid through a shunt active power filter to improve the power quality and inject photovoltaic (PV) energy to the power grid in the presence of nonlinear loads. Disturbance rejection for this electrical network is provided by the proposed direct power control (DPC) command. The DPC strategy combines a fractional order PID controller for the regulation of the DC bus voltage with an intelligent method of tracking the maximum power point articulated on the fuzzy logic, reserved to address dynamic weather conditions. The quality of energy is offered by the improved DPC resides in the elimination of the undesirable harmonics of the source currents. Thus, the studied system operates under a power factor near unity with acceptable harmonic distortion, in agreement with the international standard IEEE-519. The overall control of the presented system is assessed under different states of the power source behavior—balanced, unbalanced, and distorted—through simulation using MATLAB/Simulink software. The results demonstrate the performance, robustness, and feasibility of the proposed methods compared to the existing techniques in the literature.

High impedance fault detection method for distribution networks under non-linear conditions

This paper presents a new high impedance fault (HIF) detection method considering the presence of non-linear loads in the distribution network. It adopts a cumulative error-based index to monitor the third harmonic phase angle, which is extracted with Stockwell transform and compared to a self-adaptive threshold for fault detection and classification. The proposed method requires only a single measurement device on the substation. Results show that the proposed method is able to quickly detect HIF in all simulated cases, considering several fault locations and different contact surfaces, not being affected by conditions such as fault inception angle, system loading percentage, or fault location. Additionally, results suggest that it can distinguish HIF from capacitor banks switching, low impedance faults, transformer energizing, and feeder energizing along with linear and non-linear loads switching. HIF real oscillographic records are also used for validation. The proposed method achieved a fast detection, in less than 11 cycles for most cases, and a high detection rate, over 99%, with no false positives.

Hybrid automaton-fuzzy control of single phase dual buck half bridge shunt active power filter for shoot through elimination and power quality improvement

This paper addresses the problem of controlling a single phase shunt active power filter (SAPF) in presence of nonlinear loads. The considered SAPF is based on a Dual Buck Half Bridge converter (DBHB), which has the ability to eliminate the shoot-through problem arising in the conventional inverter circuit. The aim is to design a controller that is able to achieve the following three control objectives: (i) simple and indirect estimation of harmonic components, (ii) compensating for the harmonic and reactive currents generated by the nonlinear load for assuring a satisfactory power factor correction (PFC) in the grid side, (iii) regulating the DC capacitor voltage of the DBHB converter. In order to meet these control objectives, a new controller based on multi-loop structure is proposed. In the inner loop, a hybrid automaton representation of the DBHB-SAPF is used for the purpose of designing an appropriate control law so that to ensure a unity power factor. In the outer loop, a fuzzy logic controller is developed to guarantee a tight regulation of the converter DC voltage to a desired value. The effectiveness of the proposed controller is verified and validated by numerical simulation using MATLAB/Simulink environment. From the obtained results, the designed controller shows significant performance in terms of robustness and tracking compared to the standard strategy based on PI regulator.

Economical High Frequency Voltage Source Inverter System.(Dept.E)

High-performance high-frequency inverter systems for voltage source applications such as UPS represent a demanding application that cannot be easily realized using conventional PWM inverter modes. New controller structures are necessary to cope with stringent voltage regulation and distortion constraints in the presence of nonlinear loads. This paper presents a simple but intelligent hysteresis controller. It utilizes all possible inverter topologies in addition to feed-forward strategy to achieve low output ripple, minimum switching frequency and excellent transient performance. These features were not available until now. The result verifying the concept, using pspice program for practical electronic control circuit and power devices, are presented Although this paper explains the implementation of the 3-phase control and power circuits that can adapt itself in case of nonlinear and unbalanced loads.

Dual Two-Level Voltage Source Inverter Virtual Inertia Emulation: A Comparative Study

In this paper, the virtual synchronous generator (VSG) concept is utilized in the controller of the grid-connected dual two-level voltage source inverter (DTL VSI). First, the topology of the VSG and the DTL VSI are presented. Then, the state-space equations of the DTL VSI and the grid-connected two-level voltage source inverter (TL VSI), regarding the presence of the phase-locked loop (PLL) and the VSG, are given. Next, the small-signal modeling of the DTL VSI and the TL VSI is realized. Eventually, the stability enhancement in the DTL VSI compared with the TL VSI is demonstrated. In the TL VSI, large values of virtual inertia could result in oscillations in the power system. However, the ability of the DTL VSI in damping oscillations is deduced. Furthermore, in the presence of nonlinear loads, the potentiality of the DTL VSI in reducing grid current Total Harmonic Distortion (THD) is evaluated. Finally, by using a proper reference current command signal, the abilities of the DTL VSI and the TL VSI in supplying nonlinear loads and providing virtual inertia are assessed simultaneously. The simulation results prove the advantages of the DTL VSI compared with the TL VSI in virtual inertia emulation and oscillation damping, which are realized by small-signal analysis.

An optimal transmission line power control under non‐sinusoidal conditions using static synchronous series compensator

In view of the growing load demand in developing countries, overloading in existing transmission lines is a major concern. In addition to the voltage drop due to overloading, the proliferation of non-linear loads in recent years distort the shape of sinusoidal voltage. Stable transmission of power through a transmission line under such condition is a challenge. In the presence of harmonics, control of transmittable power using static synchronous series compensator needs additional efforts, where increased power demand can be fulfilled by taking into consideration various other parameters. If an attempt is made to increase transmittable power through a transmission line using SSSC, power loss, the magnitude of voltage and its shape deteriorate in the presence of non-linear loads. Thus, the trade-off between transmittable power, transmission loss and voltage quality is tackled by optimal control of the compensator. In this study, a novel optimal control of SSSC is proposed with the objective of minimising transmission loss by maintaining the voltage within the limits while enhancing the transmittable power under non-sinusoidal conditions. A two-machine model of power system with 400 kV transmission line with parameters as per standards issued by the Central Electricity Authority is considered for validation of the algorithm using MATLAB platform and results are presented.

Simulation and Analysis of a Three-phase Shunt Active Power Filter

This paper presents the simulation-based study and results of a three-phase shunt active power filter (SAPF) for power quality improvement. The power quality of the power systems is degraded because of the presence of non-linear loads at the consumer end. The SAPF can reduce the impact of harmonics caused by the non-linear loads. The analyzed SAPF system is modeled and simulated using MATLAB-Simulink workspace. The ultimate goal of this study is to improve the total harmonic distortion of the system as per the standards defined by IEEE-519.

Protection of Converter-Interfaced Microgrids Using Modified Short-Time Correlation Transform

The limited and bidirectional fault current of inverter interfaced islanded microgrids make the fault detection and faulty feeder identification the major challenges for conventional overcurrent-based protection systems. To address the first challenge, this article proposes a fault detection strategy based on the modified short-time correlation transform (MSTCT) of feeder current. Using the superimposed component of MSTCT, a new directional element is defined to address the second challenge. The developed strategy relies on an intelligent electronic device in each feeder, making it a cost-effective scheme. The proposed scheme is effective for all types of fault and can differentiate normal switching events from the fault conditions. Also, it properly operates in the presence of nonlinear loads and measurement noises. The reliable performance of the proposed protection scheme is assessed on the MATLAB/Simulink simulation model of the CIGRE benchmark low-voltage microgrid network.

ANALYSIS OF HARMONIC DISTORTION SOURCES IDENTIFICATION METHODS IN DISTRIBUTION SYSTEMS

The presence of non-linear loads and the increase in the number of systems of distributed generation of electricity lead to a distortion of the voltage and current waveform in distribution systems (DS), that is, to the appearance of harmonics of current and voltage. In this case, the power system is obliged to supply electricity only to the fundamental frequency of 50 Hz with constant amplitude. Power supply organizations usually disclaim responsibility for the causes of harmonics by introducing standards or recommendations for limiting the levels of harmonic components in the points of common connection of consumers. These documents do not take into account the composition of DS equipment and, accordingly, the damage from these harmonics for network equipment and consumer equipment. The urgency of the work is due to the need to reliably identify the sources of harmonic distortion in the supply system for the effective functioning of the system of penalties and fines and to more effectively determine the list of measures to improve the electric power quality. The paper reviews the existing methods for distortion sources identification in supply systems. Their basic principles and application features are considered.

Optimal Planning of Distributed Generators and Shunt Capacitors in Isolated Microgrids With Nonlinear Loads

This article presents a comprehensive design procedure for isolated microgrids with a high penetration of nonlinear loads. The proposed microgrid planning approach simultaneously determines the sizes, locations and types of distributed generators (DGs) and shunt capacitor banks (CBs). The presence of nonlinear loads along with the capacitors of CBs or DGs’ output filters may cause severe voltage distortions. To consider this issue, a harmonic power flow tool tailored for planning applications is developed that takes into account the specific features of isolated microgrids. Given the necessity of supply continuity for isolated microgrids after a contingency, the proposed planning approach takes into consideration the reliability to increase the probability of building successful islands. Unlike previous methods, the proposed approach does not rely merely on supply adequacy, and takes into account the fact that the voltage provision requirement can only be fulfilled through dispatchable DGs. The intermittent natures of loads and renewable DGs are modelled probabilistically. The effectiveness of the proposed planning approach has been validated using the PG&E 69-bus system, and the followings are observed: 1) the significance of applying suitable fundamental-power-flow and harmonic-power-flow algorithms for isolated microgrids, and 2) the possibility of avoiding a severe voltage distortion by utilizing an appropriate planning method and only small increase in the cost.

Harmonics mitigation and non‐ideal voltage compensation utilising active power filter based on predictive current control

It is well-known that the presence of non-linear loads in the distribution system can impair the power quality. The problem becomes worse in microgrids and power electronic-based power systems as the increasing penetration of single-phase distributed generation may result in a more unbalanced grid voltage. Shunt active power filters (SAPFs) are used for improving the power quality and compensating for the unbalance grid voltage. This study presents a modification of the classical control structure based on the finite control set model predictive control (FCS-MPC). The proposed control structure can retain all the advantages of FCS-MPC, while improving the input current quality. Furthermore, a computationally efficient cost function based on only a single objective is introduced, and its effect on reducing the current ripple is demonstrated. The presented solution provides a fast response to the transients as well as compensates for the unbalanced grid voltage conditions. A straightforward single loop controller is compared to the conventional way of realising the active power filters, which is based on space vector pulse width modulation. The simulation results have been obtained from MATLAB/SIMULINK environment, while the obtained experimental results, utilising a 15 kVA power converter, highlight the effective performance of the proposed control scheme and verifies the introduced MPC-based method as a viable control solution for SAPFs.

Off-Grid System Configurations for Coordinated Control of Renewable Energy Sources

Configurations, coordinated controller design and applications of various off-grid systems with distributed energy resources (DERs) for an uninterrupted supply, are presented in this paper. The performances for the optimal operation of a diesel generator (DG) in the presence of nonlinear loads, fuel-savings, voltage and frequency regulation, a soft and secure transition among different operating modes, an optimization, and power management control, are validated through simulated results and test results on the prototype to demonstrate the suitability of these configurations with natural energy resources (NERs) for continuous development in remote as well as in isolated locations.