Analysis and Power Quality Improvement in Hybrid Distributed Generation System with Utilization of Unified Power Quality Conditioner

This paper presents a comprehensive study that includes the sizing and power flow by series and parallel inverters in a distributed generation system(DGs)that integrates the system of hybrid wind photovoltaic with a unified power quality conditioner(UPQC).In addition to supplying active power to the utility grid,the system of hybrid wind photovoltaic functions as a UPQC,compensating reactive power and suppressing the harmonic load currents.Additionally,the load is supplied with harmonic-free,balanced and regulated output voltages.Since PVWind-UPQC is established on a dual compensation scheme,the series inverter works like a sinusoidal current source,while the parallel inverter works like a sinusoidal voltage source.Consequently,a smooth alteration from interconnected operating modes to island operating modes and vice versa can be achieved without load voltage transients.Since PV-Wind-UPQC inverters handle the energy generated through the hybrid wind photovoltaic system and the energy demanded through the load,the converters should be sized cautiously.A detailed study of the flow of power via the PV-Wind-UPQC is imperative to gain a complete understanding of the system operation and the proper design of the converters.Thus,curves that allow the sizing of the power converters according to the power flow via the converters are presented and discussed.Simulation results are presented to assess both steady state and dynamic performances of the grid connected hybrid system of PV-Wind-UPQC.This investigation is verified by simulating and analyzing the results with Matlab/Simulink.

Optimal Power Flow Using Firefly Algorithm with Unified Power Flow Controller

Firefly algorithm is the new intelligent algorithm used for all complex engineering optimization problems. Power system has many complex optimization problems one of which is the optimal power flow (OPF). Basically, it is minimizing optimization problem and subjected to many complex objective functions and constraints. Hence, firefly algorithm is used to solve OPF in this paper. The aim of the firefly is to optimize the control variables, namely generated real power, voltage magnitude and tap setting of transformers. Flexible AC Transmission system (FACTS) devices may used in the power system to improve the quality of the power supply and to reduce the cost of the generation. FACTS devices are classified into series, shunt, shunt-series and series-series connected devices. Unified power flow controller (UPFC) is shunt-series type device that posses all capabilities to control real, reactive powers, voltage and reactance of the connected line in the power system. Hence, UPFC is included in the considered IEEE 30 bus for the OPF solution.

A multi-objective gravitational search algorithm based approach of power system stability enhancement with UPFC

On the basis of the theoretical analysis of a single-machine infinite-bus （SMIB）, using the modified linearized Phil- lips-Heffron model installed with unified power flow controller （UPFC）, the potential of the UPFC supplementary controller to enhance the dynamic stability of a power system is evaluated by measuring the electromechanical controllability through singular value decomposition （SVD） analysis. This controller is tuned to simultaneously shift the undamped electromeehanical modes to a prescribed zone in the s-plane. The problem of robust UPFC based damping controller is formulated as an optimization problem according to the eigenvalue-based multi-objective function comprising the damping factor, and the damping ratio of the undamped electromechanical modes to be solved using gravitational search algorithm （GSA） that has a strong ability to find the most optimistic results. The different loading conditions are simulated on a SMIB system and the rotor speed deviation, internal voltage deviation, DC voltage deviation and electrical power deviation responses are studied with the effect of this flexible AC transmission systems （FACTS） controller. The results reveal that the tuned GSA based UPFC controller using the proposed multi-objective function has an excellent capability in damping power system with low frequency oscillations and greatly enhances the dynamic stability of the power systems.

A Data Driven Security Correction Method for Power Systems with UPFC

The access of unified power flow controllers(UPFC)has changed the structure and operation mode of power grids all across the world,and it has brought severe challenges to the traditional real-time calculation of security correction based on traditionalmodels.Considering the limitation of computational efficiency regarding complex,physical models,a data-driven power system security correction method with UPFC is,in this paper,proposed.Based on the complex mapping relationship between the operation state data and the security correction strategy,a two-stage deep neural network(DNN)learning framework is proposed,which divides the offline training task of security correction into two stages:in the first stage,the stacked auto-encoder(SAE)classification model is established,and the node correction state(0/1)output based on the fault information;in the second stage,the DNN learningmodel is established,and the correction amount of each action node is obtained based on the action nodes output in the previous stage.In this paper,the UPFC demonstration project of NanjingWest Ring Network is taken as a case study to validate the proposed method.The results show that the proposed method can fully meet the real-time security correction time requirements of power grids,and avoid the inherent defects of the traditional model method without an iterative solution and can also provide reasonable security correction strategies for N-1 and N-2 faults.

Investigation of Real Power Flow Control of AI Based MC-UPFC in FACTS Controllers

The power consumption is rapidly increased due to ASD(Adjustable Speed Drives)and automation in industries and large consumption of electricity in domestic regions increased the concern of the power quality.The quality of the power received in the distribution system is altered because of the losses in the transmission system.The losses in the transmission system are mitigated using the FACTS(Flexible AC Transmission System)controller,among these controllers UPFC(Unified Power Flow Controller)plays a vital role in controlling the shunt and series reactive powers in the bus of the power system.The conventional topology of the UPFC consists of AC-DC converter and energy stored in the DC link and DC-AC converter injected a voltage in series to the bus which is to be controlled.Whereas a new topology based on matrix converter can replace the dual converters and perform the required task.The construction of 2-bus,7-bus and IEEE-14-bus power system is designed and modeled.MC-UPFC(Matrix Converter Based Unified Power Flow Controller)is designed and constructed.The MC-UPFC is the rich topology in the FACTS which is capable of controlling both the transmission parameters simultaneously with the switching technique of direct power control by the smooth sliding control which gives less ripple in the injecting control parameters such as control voltage(Vc)and voltage angle(α).By implementing MC-UPFC the real and reactive power can be controlled simultaneously and independently.The control techniques were designed based on the PID(Proportional Integral Derivative)with sliding surface power control,FLC(Fuzzy Logic Controller)and ANN(Artificial Neural Network)and the performances of Vc andαof the controllers are investigated.Hence the sliding surface and relevant control switching state of the MC can be controlled by the FLC which gives the robust and autonomous decision made in the selection of the appropriate switching state for the effective real power control in the power system.The work has been carried out in the MATLAB Simulink simulator which gives the finest controlling features and simple design procedures and monitoring of the output.

Harmonic influence analysis of unified power flow controller based on modular multilevel converter

The unified power flow controller(UPFC)based on modular multilevel converter(MMC) is the most creative flexible ac transmission system(FACTS) device. In theory, the output voltage of the series MMC in MMCUPFC can be regulated from 0 to the rated value. However,there would be relatively large harmonics in the output voltage if the voltage modulation ratio is small. In order to analyze the influence of MMC-UPFC on the harmonics of the power grid, the theoretical calculation method and spectra of the output voltage harmonics of MMC are presented. Subsequently, the calculation formulas of the harmonics in the power grid with UPFC are proposed. Based on it, the influence of UPFC on the grid voltage harmonics is evaluated, when MMC-UPFC is operated with different submodular numbers and voltage modular ratios. Eventually, the proposed analysis method is validated using digital simulation. The study results would provide guideline for the design and operation of MMC-UPFC project.

Voltage sag compensation strategy for unified power quality conditioner with simultaneous reactive power injection

Unified power quality conditioner(UPQC)holds the capability of solving power quality problems,especially shows good performance in the voltage sag compensation. In this paper, a compensation strategy based on simultaneous reactive power injection for UPQC(namely UPQC-SRI) is proposed to address the issue of voltage sag. The proposed UPQC-SRI determines the injection angle of compensation voltage with consideration of optimal configuration of UPQC current-carrying.Moreover, the compensation strategy also considers the current-carrying limit of UPQC, and then the zero active power injection region of UPQC-SRI(also called UPQCSRI region) is obtained. Under the conditions which exceed the UPQC-SRI region, the limit value of shunt current is determined by this proposed strategy. Finally, the proposed strategy and the corresponding algorithm are verified under the PSCAD/EMTDC platform. The result indicates the proposed UPQC-SRI strategy in this paper can provide more persistent voltage sag compensation than the previous strategies for the sensitive load.

Unified power quality conditioner based on a three-level NPC inverter using fuzzy control techniques for all voltage disturbances compensation

This paper presents a novel and efficient control scheme for unified power quality conditioner （UPQC） based on three-level neutral point clamped （NPC） inverter using fuzzy logic techniques. The proposed UPQC is capable of mitigating source current harmonics and compensate all voltage disturbances such as voltage sags, swells, unbalances and harmonics. It is designed by the integration of series and shunt active filters （AFs） sharing a common DC bus capacitor. The DC voltage is maintained constant using proportional integral voltage controller. The synchronous reference frame （SRF） theory is used to get the reference signals for shunt active power filters （APFs） and the power reactive theory （p-q theory） for series APFs. The shunt and series APF reference signals derived from the control algorithm and sensed signals are injected in two controllers to generate switching signals. To improve the UPQC capability, fuzzy logic techniques are introduced to control the series APF. The performances of the proposed UPQC system are evaluated in terms of power factor correction, mitigation of voltage or current harmonics and all other voltage disturbances compensation using Matlab-Simulink software and SimPowerSystem toolbox. The simulation results illustrate the performance of the proposed UPQC at the common connection point of the nonlinear load to improve the power energy quality.

Evaluation of optimal UPFC allocation for improving transmission capacity

A unified power flow controller(UPFC)combines the advantages of various flexible alternating current transmission system(FACTS)devices into a powerful format.Using a 500 kV power grid,this study evaluates the selection and use of a UPFC to improve transmission capacity.The"UPFC unit capacity control proportionality coefficient"is introduced to quantify the control effect of the UPFC,and an optimal calculation method for the UPFC capacity is presented.Following the proposal of a UPFC site selection process,the data of an existing power grid is used to conduct simulations.The simulation results show that the UPFC has a strong ability to improve transmission capacity,and its use is greatly advantageous.Additionally,by applying the proposed selection method,the control effect and economic benefits of the UPFC can be comprehensively considered during project site selection.These findings have a guiding significance for UPFC site selection in ultra-high voltage power grids.

Intelligent Controller for UPQC Using Combined Neural Network

The Unified Power Quality Conditioner (UPQC) plays an important role in the constrained delivery of electrical power from the source to an isolated pool of load or from a source to the grid. The proposed system can compensate voltage sag/swell, reactive power compensation and harmonics in the linear and nonlinear loads. In this work, the off line drained data from conventional fuzzy logic controller. A novel control system with a Combined Neural Network (CNN) is used instead of the traditionally four fuzzy logic controllers. The performance of combined neural network controller compared with Proportional Integral (PI) controller and Fuzzy Logic Controller (FLC). The system performance is also verified experimentally.

Comprehensive control for unified power quality conditioners

This paper presents a comprehensive control strategy for unified power quality conditioners(UPQCs) to compensate for both voltage and current quality problems.The controllers for the series and shunt components of the UPQC are, equally, divided into three blocks: à main controller, which deals with the fundamental-frequency issues such as active and reactive power flow;` harmonic controller, which ensures zero-error tracking while compensating voltage and current harmonics;′ the set-point generation block, which handles the different control objectives of the UPQC. The controller design procedure has been simplified to the selection of three parameters for each converter. Furthermore, the proposed strategy can be implemented measuring only four variables, which represents a reasonable number of sensors. In addition, a pulse width modulation(PWM)-based modulation with fixed switching frequency is used for both converters. The proposed control strategy has been validated experimentally under different conditions, including grid-frequency variations.

Superconducting Magnetic Energy Storage Based DC Unified Power Quality Conditioner with Advanced Dual Control for DC-DFIG

The development of DC custom power protection devices is still in infancy that confines the sensitive loads integrated into medium-voltage(MV) and low-voltage(LV) DC networks. Considering the DC doubly-fed induction generator(DCDFIG) based wind energy conversion system(WECS), this paper proposes a dual active bridge(DAB) based DC unified power quality conditioner(DC-UPQC) with the integration of superconducting magnetic energy storage(SMES) to maintain the terminal voltage of DC-DFIG and regulate the current flow. The principle of the proposed DC-UPQC has three parts, i.e., parallel-side DAB(PDAB), series-side DAB(SDAB), and SMES,used for the voltage compensation, current and power regulation, and energy storage, respectively. The circuit principle of the PDAB and SDAB and the modeling of SMES are analyzed in this paper. A DC dual control strategy is also proposed to deal with the DC voltage oscillation generated by the AC-side asymmetrical fault. A case study of DC-DFIG interfaced with DC power grid is carried out, integrated with the proposed SMES-based DC-UPQC to verify the high-power applications of the proposed structure. Finally, an experiment is implemented, and the results demonstrate the correctness of the theoretical analysis and the feasibility of the proposed structure.

EV charging station with cascaded low-pass filtering scheme-based control of unified power quality conditioner

This paper proposes a cascaded low-pass filter(CLPF)scheme for the control of a unified power quality conditioner(UPQC)installed for enhancing the power quality of an electric vehicle(EV)charging station.With the incorporation of UPQC,the EV charging station draws sinusoidal currents at unity power factor and the supply voltage is maintained at the nominal value at the charger input.In the CLPF scheme,theα-βcomponents of the load current are individually processed through a cascade connection of two LPFs to determine the corresponding fundamental orthogonal components.Based on thus determined components,the instantaneous and peak value and phase angle of the fundamental positive sequence component(FPSC)of the load current are computed.Similarly,the corresponding quantities related to the load and supply voltages are also computed with the CLPF scheme.With the computations related to the load current and supply voltage,the unit voltage templates(UVTs),power factor and fundamental active component(FAC)of the load current are calculated.For the control of shunt compensation,reference currents are generated based on the FAC of the load current and UVTs.Alternately,the control of series compensation is employed with the help of UVTs and peak amplitude of the FPSC of the load voltage.The performance of CLPF scheme-based extraction is compared with that of the earlier reported schemes through simulation and experimental studies.The performance comparison reveals a faster dynamic and more accurate steady-state response with the proposed scheme.The performance analysis of the proposed CLPF scheme-based control of a UPQC deployed at the EV charging station for different operating conditions demonstrates station operation with requisite reactive power compensation and mitigation of voltage sag/swell,and prevention of propagation of harmonic and unbalanced currents into the grid.This results in increased reliability of charger operation,energy savings and increased efficiency of the distribution network.

Multi-Level Inverter Linear Predictive Phase Composition Strategy for UPQC

The power system is facing numerous issues when the distributed gen-eration is added to the existing system.The existing power system has not been planned with flawless power quality control.These restrictions in the power trans-mission generation system are compensated by the use of devices such as the Static Synchronous Compensator(STATCOM),the Unified Power Quality Con-ditioner(UPQC)series/shunt compensators,etc.In this work,UPQC’s plan with the joint activity of photovoltaic(PV)exhibits is proposed.The proposed system is made out of series and shunt regulators and PV.A boost converter connects the DC link to the PV source,allowing it to compensate for voltage sags,swells,vol-tage interferences,harmonics,and reactive power issues.In this paper,the fea-tures of a seven-level Cascaded H-Bridge Multi-Level idea are applied to shunt and series active filter changeovers to reduce Total Harmonic Distortion and com-pensate for voltage issues.Despite its power quality capacity for common cou-pling,the proposed system can inject the grid’s dynamic power.During voltage interference,it can also provide a piece of delicate burden power.The simulation is carried out with the help of MATLAB/SIMULINK programming,and the results are compared to those of other conventional methods.

The Full Load Voltage Compensation Strategy in Capacity Configuration of UPQC Integrated PV-BESS

Unified power quality conditioner(UPQC)with energy storage is commonly based on conventional capacity configuration strategy with power angle control.It has problems such as phase jumping before and after compensation.DC-link cannot continuously emit active power externally.Therefore,this paper presents the compensation strategy of full load voltage magnitude and phase in capacity configuration of UPQC.The topology of UPQC is integrated a series active power filter(SAPF),a shunt active power filter(PAPF)and a photovoltaic-battery energy storage system(PV-BESS).The principle of full load voltage compensation is analyzed based on the PV-BESS-UPQC topology.Themagnitude constant of load voltage ismaintained by controlling the appropriate shunt compensation current.Then the UPQC capacity configuration is carried out using the full load voltage compensation strategy.The compensation capacity of UPQC series and shunt units are reduced.Finally,the simulation results show that the proposed compensation strategy reduces the capacity configuration by 5.11 kVA(36.4%)compared to the conventional compensation strategy.The proposed strategy can achieve full compensation of the load voltage,which can effectively reduce the capacity allocation and improve the economy of UPQC.It also has the PV-BESS units’ability of providing active power and can stabilize the DC-link voltage.

Machine Learning for Hybrid Line Stability Ranking Index in Polynomial Load Modeling under Contingency Conditions

In the conventional technique,in the evaluation of the severity index,clustering and loading suffer from more iteration leading to more com-putational delay.Hence this research article identifies,a novel progression for fast predicting the severity of the line and clustering by incorporating machine learning aspects.The polynomial load modelling or ZIP(constant impedances(Z),Constant Current(I)and Constant active power(P))is developed in the IEEE-14 and Indian 118 bus systems considered for analysis of power system security.The process of finding the severity of the line using a Hybrid Line Stability Ranking Index(HLSRI)is used for assisting the concepts of machine learning with J48 algorithm,infers the superior affected lines by adopting the IEEE standards in concern to be compensated in maintaining the power system stability.The simulation is performed in the WEKA environment and deals with the supervisor learning in order based on severity to ensure the safety of power system.The Unified Power Flow Controller(UPFC),facts devices for the purpose of compensating the losses by maintaining the voltage characteristics.The finite element analysis findings are compared with the existing procedures and numerical equations for authentications.

Performance Analysis and Technical Feasibility of an iUPQC in Industrial Grids

The iUPQC is a Unified Power Quality Conditioner in which the series converter emulates a sinusoidal current source and the shunt converter emulates a sinusoidal voltage source. This approach provides indirect power quality compensation of the load voltage and the source current. Recent studies have suggested that the iUPQC has technical advantages in comparison with the conventional UPQC due to its reduced switching frequency characteristic. In this paper, these technical advantages are investigated. Thus, the iUPQC performance is verified through a 150 kVA industrial equipment and technical design specifications are discussed: the iUPQC power circuit design, the converters arrangement and the driver configuration. Experimental results are provided to validate the technical feasibility and power quality compensation performance.

Adaptive fractional integral terminal sliding mode power control of UPFC in DFIG wind farm penetrated multimachine power system

With an aim to improve the transient stability of a DFIG wind farm penetrated multimachine power system(MPN),an adaptive fractional integral terminal sliding mode power control(AFITSMPC)strategy has been proposed for the unified power flow controller(UPFC),which is compensating the MPN.The proposed AFITSMPC controls the dq-axis series injected voltage,which controls the admittance model(AM)of the UPFC.As a result the power output of the DFIG stabilizes which helps in maintaining the equilibrium between the electrical and mechanical power of the nearby generators.Subsequently the rotor angular deviation of the respective generators gets recovered,which significantly stabilizes the MPN.The proposed AFITSMPC for the admittance model of the UPFC has been validated in a DFIG wind farm penetrated 2 area 4 machine power system in the MATLAB environment.The robustness and efficacy of the proposed control strategy of the UPFC,in contrast to the conventional PI control is vindicated under a number of intrinsic operating conditions,and the results analyzed are satisfactory.

UPFC setting to avoid active power flow loop considering wind power uncertainty

The active power loop flow(APLF)may be caused by impropriate network configuration,impropriate parameter settings,and/or stochastic bus powers.The power flow controllers,e.g.,the unified power flow controller(UPFC),may be the reason and the solution to the loop flows.In this paper,the critical existence condition of the APLF is newly integrated into the simultaneous power flow model for the system and UPFC.Compared with the existing method of alternatively solving the simultaneous power flow and sensitivity-based approaching to the critical existing condition,the integrated power flow needs less iterations and calculation time.Besides,with wind power fluctuation,the interval power flow(IPF)is introduced into the integrated power flow,and solved with the affine Krawcyzk iteration to make sure that the range of active power setting of the UPFC not yielding the APLF.Compared with Monte Carlo simulation,the IPF has the similar accuracy but less time.

Security-constrained line loss minimization in distribution systems with high penetration of renewable energy using UPFC

Focused on the challenges raised by the largescale integration of renewable energy resources and the urgent goal of energy saving,a novel control scheme for the unified power flow controller(UPFC)series converter is proposed to achieve line loss reduction and security enhancement in distribution systems with a high penetration of renewable energy.Firstly,the line loss minimum conditions of a general distribution system with loop configurations are deduced.Secondly,security constraints including the permissible voltage range,the line loading limits and the UPFC ratings are considered.System security enhancement with the least increase in line loss is tackled by solving a much reduced optimal power flow(OPF)problem.The computational task of the OPF problem is reduced by deducing the security-constrained line loss minimum conditions and removing the equality constraints.Thirdly,a hybrid control scheme is proposed.Line loss minimization is achieved through a dynamic controller,while an OPF calculator is integrated to generate corrective action for the dynamic controller when the security constraints are violated.The validity of the proposed control strategies is verified in a modified IEEE 33 bus test system.