Series Voltage Source Converter Research Articles

Control Strategies for Enhancing Power Quality with Unified Power Quality Conditioner in a Solar-PV Integrated Utility System

The electrical utility systems are well-liked as local energy systems because of their capacity to incorporate renewable energy, enhance energy effectiveness and strengthen the resilience of the power system. These benefits do, however, come with specific complications regarding control and power quality (PQ). PQ within a utility system is paramount to ensure the appropriate operation of connected devices and the well-being of the overall system. As a result, both voltage quality & current quality are significant. Control strategies in conjunction with cutting-edge power electronics devices (PED) offer a solid framework to handle PQ challenges. Hence, this paper’s proposed work discusses the application of a Solar-Photovoltaic (PV) fed Unified Power Quality Conditioner (UPQC) for power quality enhancement towards the supply grid network. The Solar-PV fed UPQC enhances PQ and maximizes solar energy utilisation, leading to an eco-friendly and cost-effective solution while injecting clean, renewable energy into the grid. In this paper, the control strategies for UPQC are based primarily on the Adaptive Leaky Least Mean Square (AL_LMS) algorithm as compared with the Synchronous Reference Frame (SRF) based theory for switching of series and shunt active converters of UPQC. This AL_LMS approach extracts reference signals to switch UPQC’s shunt and series voltage source converters (VSCs) by iteratively updating the weights. Thus, the control strategy applied to Solar-PV fed UPQC mitigates voltage problems like voltage sag and swell, current harmonic distortions and other PQ issues. The work is done in MATLAB/ Simulation software and simulation outcomes show the effectiveness of Solar-PV fed UPQC in improving power quality by maintaining within the IEEE-519 Standards.

Multi-Converter UPQC Optimization for Power Quality Improvement Using Beetle Swarm-Based Butterfly Optimization Algorithm

The primary goal of this paper is to design a Multi-Converter Unified Power Quality Conditioner (MC-UPQC). The proposed method is solved based on the Synchronous Reference Frame (SRF) theory. The MC-UPQC involves two series Voltage Source Converters (VSCs) for power transfer between feeders to eliminate voltage sag, swell, interruption, and transient response in the system. The proposed model adopts control strategies based on an optimized Fuzzy Logic Controller (FLC) in SRF, utilizing a hybrid metaheuristic algorithm called Beetle Swarm-based Butterfly Optimization Algorithm (BS-BOA), which combines Beetle Swarm Optimization (BSO) and Butterfly Optimization Algorithm (BOA) for membership limit optimization and control rule generation. The major benefit of the optimized FLC-based MC-UPQC is its quick behavior in minimizing Total Harmonic Distortion (THD) in source and load side voltages and currents. Simulation and MATLAB environment are used for the entire system implementation. The comparative analysis of the proposed controller for MC-UPQC is performed against conventional controllers to validate its effectiveness. Quantitative data related to the main research outcomes, such as THD of source voltage and current, and dynamic behavior of the system, are included. The main benefit of the study is the significant reduction in THD and improved dynamic performance of the system.

Power Quality Improvement in Multifeeder Using MC-UPQC

Power Quality (PQ) issues have been a major concern as there is increased load demand and usage of variety of nonlinear loads. The innovation of Flexible AC Transmission System (FACTS) devices is a great way of solving PQ issues. Many devices like UPFC, D-STATCOM, and TCPST are emerging and are widely used for PQ improvement. In this paper, the Multi Converter Unified Power Quality Conditioning (MC-UPQC) System will be used for improving PQ in multi-bus systems. The system of MC-UPQC contains one shunt and two series Voltage Source Converter (VSCs). The conventional methodology contains one shunt and one series static devices. In the proposed methodology, two series VSCs will be used for further reduction of overall THD value. The simulation results of a reduction in THD and an improvement in PQ are compared with and without the proposed using MATLAB. Keywords—PQ, MC-UPQC, series VSC, shunt VSC, MATLAB.

Transformer‐less unified power flow controller in medium voltage distribution networks

AbstractA transformer‐less unified power flow controller (UPFC) is a power electronic device consisting of series and shunt voltage source converters (VSCs) that are not connected to a common DC bus. It can control power flow in medium voltage (MV) distribution networks without the need for interfacing transformers. Hence there is a significant reduction in size and cost compared to a conventional UPFC. This paper investigates the operating range of a transformer‐less UPFC in an MV distribution network and the required power ratings of the series and shunt converters. The results showed that a transformer‐less UPFC is able to provide active power control using partially rated converters. However, its ability to control reactive power is limited by the current ratings of the converters. The analysis was verified using software simulation and hardware experiment.

Power Flow Control Using Series Voltage Source Converters in Distribution Grids

This study presents an application for a series VSC (voltage source converter) in distribution grids for power flow management. Series devices have been widely studied for FACTS (flexible AC transmission systems), however, more recently these devices have gained increased interest in applications for loading balance in medium voltage distribution grids. As the number of distributed generation (DG) units increases, increasing the capacity and reliability of distribution grids while maximizing the benefits of installed DGs and loading behavior is an ever more important task. In this paper, we describe a test system and control proposals for a practical application of series converters interconnecting two distribution feeders at 13.8 kV under load variation disturbances. This approach provides solutions when installed at the end of distribution lines by interconnecting two feeders, resulting in capacity increases in the feeders without needing grid reconfigurations using a small-rated series VSC.

Power Quality Enhancement and Power Flow Analysis of a PV Integrated UPQC System in a Distribution Network

Increasing awareness for green energy and sustainable energy management has accelerated the popularity for the incorporation of distributed energy resources and distributed energy storage into the distribution network and microgrid. This has proliferated the use of power electronic-based devices giving rise to a serious issue of deteriorating power quality (PQ) in the distribution system. In this context, this article presents a photovoltaic (PV) integrated unified power quality conditioner (UPQC) operating with an adaptive compensating technique based on variable leaky least mean square (VLLMS) algorithm. It is a soft computing-oriented method that offers quicker convergence to the desired condition in an iterative approach keeping the weight of the updating parameters within the specified limit. The VLLMS-based algorithm eliminates the use of low pass or moving average filter for the extraction of fundamental components from polluted source voltage and load current to generate reference signal for the switching of shunt as well as series voltage source converters (VSC) of the UPQC. Due to the involvement of feed-forward component of PV in the compensating technique of shunt VSC, it efficiently and smoothly manages power balance between grid, load, and PV besides resolving the PQ issues of current harmonics and poor power factor at PCC. It also ensures the regulation of dc-link voltage. The series converter maintains pure sinusoidal voltage at the load terminal irrespective of sag/swell and harmonics present in the grid voltage. The effectiveness of the proposed system is verified through simulation as well as hardware implementation under different static and dynamic operating conditions.

Research on power flow calculation method of true bipolar VSC-HVDC grids with different operation modes and control strategies

Compared with the pseudo bipolar Voltage Source Converter (VSC) based High Voltage Direct Current (HVDC) (VSC-HVDC) grid, the true bipolar VSC-HVDC grid with series voltage source converters is more flexible and reliable. Based on the analysis of structure and power distribution in the true bipolar VSC-HVDC grid, the node admittance matrices and a representation method of the converter station losses are first derived. Then, with various station-level control strategies of VSC taken into account, a layer-based power flow calculation method suitable for true bipolar VSC-HVDC grids in both symmetric and asymmetric operation is proposed. Finally, the applicability and accuracy of the proposed power flow calculation method are verified by a true bipolar VSC-HVDC grid model built in PSCAD.

Simultaneous Placements of TCSC and VSCDG for Congestion Management

Relieving congestion is a major technical issue in power transmission systems. In this paper, simultaneous placement of Thyristor controlled series capacitors (TCSC) and Voltage source converter based distribution generators (VSC-DG) are used for relieving congestion, minimize system cost and maintain the system in secure state. The system has been analyzed in three stages: (i) first stage, the congestions are made in different transmission network by overload and line outages, (ii) second stage, relieving congestion of transmission lines by using TCSC and VSCDG, where these devices are placed simultaneously at their optimal locations, (iii) comparative cost analysis is done between normal and congested systems. The proposed approach is tested on the 62-bus Indian power system network. The optimal solution of the test systems are obtained by genetic algorithm method and its solutions are compared with primal linear programming. All the results are validated through Power World Simulator and GA toolbox in MATLAB.

Implementation and Experimental Verification of a Novel Control Strategy for a UPFC-Based Interphase Power Controller

Replacing the phase shifting transformers of interphase power controller with a reduced rating dual unified power flow controller (UPFC) results in a unified interphase power controller (UIPC) with potential for enhanced performance. However, in most cases, the UPFC is controlled as a static phase shifter (SPS), producing marginal improvements. A control approach that allows the minimization of the power ratings of the series voltage source converters (VSCs) of the UIPC was recently proposed. For that, one has to define four control parameters, as opposed to only two in the SPS-based UIPC. This can be done off-line, by means of an optimization procedure that splits the desired transmission line current among the capacitive and inductive branches of the UIPC. In this paper, a control scheme is presented for the implementation of the novel technique. The current sharing factors obtained from the optimization are stored in a lookup table. The gating signals for the VSCs are generated using Park's transformation so as to synthesize the optimal UIPC inductive and capacitive branch currents with proportional resonant controllers and sinusoidal pulse width modulation. The transmission line angle, as well as the magnitude and phase of the desired transmission line current with respect to the voltage at the receiving end voltage, is assumed to be provided by a transmission system operator. Experimental results that include steady state and transient conditions are provided to prove its feasibility.

Power Quality Improvement of AC Distribution System using 3 Phase PV Integrated UPQC with Advanced Control Strategy

Renewable energy sources are used to accommodate the ongoing increasing power demand. So, the integration of PV system controlled by the revised p-q concept which is revealed from instantaneous active reactive power concept and a suitable choice to meet the energy demand. Enormous utilization of power electronic converters deviates the quality of power. Series voltage compensation and shunt current compensation is done by the p-q theory. Revised p-q conceptstates the single instantaneous active power and the imaginary powers for active and reactive power compensation. This paper presents the revised p-q concept to generate the reference signals for integrated unified power quality conditioner (PV-UPQC-S). This proposed method enables the process of PV-UPQC-S under unbalanced voltage circumstances at the point of common coupling (PCC). This system incorporates the series voltage source converter (VSC) to control the unbalanced voltage by sharing the part of the reactive power of the load, which in turn reduces the rating of the shunt VSC. The integration of the PV system at the DC bus of UPQC serves the purpose of load sharing as well as power quality improvement to maintain the healthy grid condition. This concept is approved by simulating the proposed model in MATLAB/Simulink. The proposed model comprises of both linear and non-linear loads. The experimental results validates the perfect dynamical response of the given model.

A review of series voltage source converter with fault current limiting function

The series voltage source converter(SVSC) is widely used in the power electronic equipment, such as series active power filter, dynamic voltage restorer, unified power flow controller and so on. However, while the SVSC is more vulnerable to the impact of fault current, its applications are increasing, bringing huge challenges to the safe operation of the grid. In recent years, the topology and control strategy of the series voltage source converter with fault current limiting(SVSC-FCL) are a research hotspot. In this paper, it suggests classifying SVSC-FCL based SVSC into two groups: the control scheme optimization group and the existing topology improvement group. The research challenges and perspectives of the SVSC-FCL are introduced in detail. This paper aims to illustrate current research progress on SVSC-FCL and enrich the available pool of the multi-functional power electronic equipment.

Performance of generalised unified power flow controller in transmission system

This paper focuses on innovative dynamic performance of power electronics based on generalised unified power flow controller (PFC). The GUPFC is a voltage source converter (VSC) based flexible AC transmission system (FACTS) controller used to provide series and shunt compensation among the multi transmission line systems of a substation. GUPFC improves the performance of power quality issues, active and reactive power oscillations in multiple transmission lines. This paper proposes a complete replica comprising of 48-pulse gate turn-off (GTO) thyristor based VSC which examines the dynamic operation of control scheme for shunt and two series VSC for voltage stabilisation and active and reactive power compensation by using POD controller among the transmission lines of the grid network. It is able to control injected voltage, at the same time as keeping injected voltage in quadrature with current within the power system is completely modelled in MATLAB/SIMULINK.

Modified <italic>pq</italic>-Theory-Based Control of Solar-PV-Integrated UPQC-S

This paper proposes a modified pq-theory-based control of a solar photovoltaic (PV)-array-integrated unified power quality conditioner (PV-UPQC-S). The system incorporates clean energy generation along with power quality improvement, thus increasing functionality of the system. The fundamental-frequency positive-sequence components of voltages at the point of common coupling (PCC) are extracted using the generalized cascaded delay signal cancellation technique, which are then used in pq-theory-based control to estimate reference signals for the PV-UPQC-S. This modification in pq theory enables its application for PV-UPQC-S control under conditions of distorted PCC voltages. The series voltage-source converter (VSC) of the PV-UPQC-S operates such that it shares a part of the reactive power of the load even under nominal grid conditions. This increases the utilization of the series VSC while reducing the rating of shunt VSC. The PV array is integrated at the dc bus of the UPQC and provides a part of active load power, thus reducing demand on the supply system. The dynamic performance of the modified pq-theory-based PV-UPQC-S is verified by simulating the system in MATLAB-Simulink with a combination of linear and nonlinear loads. The steady-state and dynamic performances of the system are then experimentally validated through extensive testing on a scaled-down laboratory prototype.

Performance analysis of proportional resonant and ADALINE‐based solar photovoltaic‐integrated unified active power filter

In this work, a novel control of single-phase solar photovoltaic (PV) fed unified active power filter (PV-UAPF) is proposed for use in low-voltage distribution system. The shunt voltage source converter (VSC) of PV-UAPF mitigates current power quality issues such as current harmonics, reactive current etc. while the series VSC of PV-UAPF protects the sensitive load against point of common coupling (PCC) voltage disturbances. The shunt VSC control is based on extraction of fundamental load active current using recursive least squares with a variable forgetting factor. The proposed method improves the dynamic response of the system without sacrificing the steady-state performance. The series VSC is controlled using a proportional-resonant controller and it injects voltage in/out phase with PCC voltage during voltage sags/swells, respectively. The PV array which is integrated at the DC link of the PV-UAPF through a reverse blocking diode, provides the load power demand and also supplies remaining power into PCC. The system performance is evaluated using Matlab-Simulink software and is then experimentally verified on a prototype developed in the laboratory under steady-state and dynamic conditions such as irradiation variation, PCC voltage fluctuations and load disturbances to validate the performance of the system.

Adaptive Non‐Linear Control of UPFC for Stability Enhancement in a Multimachine Power System Operating with a DFIG Based Wind Farm

AbstractAn instantaneous converter power based adaptive second order sliding mode control for the Unified Power Flow Controller (UPFC) in a multimachine power system penetrated with a doubly fed induction generator (DFIG) based wind farm is proposed in this paper. Instead of controlling the direct and quadrature‐axis currents of the series voltage source converter (VSC) of the UPFC, the instantaneous active and reactive power outputs are used as control variables. This mode of control dispenses the unmodelled dynamics of the VSC phase‐locked loop (PLL) system and produces a robust control for the active–reactive power, and DC voltage excursions. However, the PLL is used only to obtain the frequency component needed to generate the Pulse Width Modulation (PWM) signal. In comparison to the first order sliding surface, the second order sliding surface provides very good robustness features, finite reaching time, and chattering free sliding mode behavior. Further, the proposed controller gains of the UPFC are chosen in accordance with the various constraints imposed by the second order sliding mode approach to provide significantly superior and robust performance for a number of diverse operating conditions of the network in comparison to the conventional sliding mode controller.

Damping interarea oscillations in power systems using finite time terminal sliding mode control of the unified power flow controller

This paper presents a new nonlinear controller for unified power flow controller (UPFC) based on the Lyapunov's finite time terminal sliding mode concept. Further instead of controlling the direct and quadrature-axis currents of the series voltage source converter (VSC), the instantaneous real-and reactive power components are used as control variables. This mode of control dispenses the unmodelled dynamics of the VSC phase-locked loop system and produces a robust control for the active-reactive power, and dc voltage excursions. Computer simulation results are obtained for a variety of operating conditions for 3-machine 6-bus power system using the finite time terminal sliding mode control and the results are compared with a standard input-output feedback linearisation approach to validate the superiority of the proposed controller.

Algorithm for power angle control to improve power quality in distribution system using unified power quality conditioner

A novel algorithm is proposed for power angle control (PAC) to improve power quality (PQ) in distribution system. This algorithm reduces mathematical complication and its response time. It has aimed to make the designs of controller. The new concept is incorporates on triangle rules of vector addition/subtraction. The mathematical approach makes the algorithm efficient and comprehensive. The shunt voltage source converter (VSC) of unified power quality conditioner (UPQC) is controlled using instantaneous symmetrical component theory (ISCT). The ISCT enables UPQC to handle unbalanced and non-linear loads. The complete phaser diagram has been shown for various voltage conditions. A vector addition and subtraction-based mathematical calculation has been derived for estimation of different parameters of the proposed system. Proposed PAC can improve PQ in four wire distribution system with maximum utilisation of series VSC of UPQC. A simulation study for voltage sag/swell with the new algorithm for PAC verifies the improved performance of the system. Results have been discussed in detail.

A New Control Strategy Based Multi Converter UPQC Using Fuzzy Logic Controller to Improve the Power Quality Issues

A design of multiconverter unified power quality conditioner to improve the power quality issues is presents in this paper. Modified SRF theory and fuzzy logic controller technique are incorporated in this modelling. This newly designed controller is connected to a source in order to compensate voltage and current in the two feeders. The expanded concept of UPQC is multi converter-UPQC; this system has two series voltage source converter (VSC) and one shunt VSC connected back to back. In the proposed system, the power can be conveyed from one feeder to another in order to mitigate the voltage sag, swell, interruption and transient response of the system. The control strategies of multi converter-UPQC are designed based on the modified synchronous reference frame theory with fuzzy logic controller. The transient response of the fuzzy logic controller in dc-link voltage controller will be very fast. The relevant simulation and compensation performance analysis of multi converter-UPQC with fuzzy logic controller is performed using MATLAB/Simulink software.

Improving Power Quality in a Multi bus Multi Feeder System Using MC-UPQC

A b s t r a c t : This paper presents a new Unified Power-Quality Conditioning System (MC-UPQC), capable of simultaneous compensation for voltage and current in multi-bus/multi-feeder systems. By using one shunt Voltage-Source Converter (VSC) and two or more series VSCs the configuration is made. The system can be applied to adjacent feeders to compensate for supply-voltage and load current imperfections on the main feeder and full compensation of supply voltage imperfections on the other feeders. The configuration will be designed as all converters are connected back to back on the dc side and share a common dc-link capacitor. The system is also capable of compensating for interruptions without the need for a battery storage system and consequently without storage capacity limitations. By the simulation the performance of MC-UPQC as well as the adopted control algorithm will be illustrated. Index- terms: Voltage-Source Converter (VSC), Interline Power Flow Controller (IPFC), Unified PowerQuality Conditioning System (UPQC), I. Introduction When the power flows of two lines starting in one substation need to be controlled, an Interline Power Flow Controller (IPFC) can be used. An IPFC consists of two series VSCs whose dc capacitors are coupled. This allows active power to circulate between the VSCs. With this configuration, two lines can be controlled simultaneously to optimize the network utilization. The GUPFC combines three or more shunt and series converters. It extends the concept of voltage and power-flow control beyond what is achievable with the known two-converter UPFC. The simplest GUPFC consists of three converters—one connected in shunt and the other two in series with two transmission lines in a substation. The basic GUPFC can control total five power system quantities, such as a bus as well. By using GUPFC devices, the transfer capability of transmission lines can be increased significantly. Furthermore, by using the multiline-management capability of the GUPFC, active power flow on lines cannot only be increased, but also be decreased with respect to operating and market transaction requirements. In general, the GUPFC can be used to increase the transfer capability and relieve congestions in a flexible way. This concept can be extended to design multiconverter configurations for PQ improvement in adjacent feeders. For example, the interline unified power-quality conditioner (IUPQC), which is the extension of the IPFC concept at the distribution level, has been proposed in the IUPQC consists of one series and one shunt converter. It is connected between two feeders to regulate the bus voltage of one of the feeders, while regulating the voltage across a sensitive load in the other feeder. In this configuration, the voltage regulation in one of the feeders is performed by the shunt-VSC. However, since the source impedance is very low, a high amount of current would be needed to boost the bus voltage in case of a voltage sag/swell which is not feasible. It also has low dynamic performance because the dc-link capacitor voltage is not regulated. In this paper, a new configuration of a UPQC called the multiconverter unified power-quality conditioner (MC-UPQC) is presented. The system is extended by adding a series-VSC in an adjacent feeder. The proposed topology can be used for simultaneous compensation of voltage and current imperfections in both feeders by sharing power compensation capabilities between two adjacent feeders which are not connected. The system is also capable of compensating for interruptions without the need for a battery storage system and consequently without storage capacity limitations.

Digital Simulation of the Generalized Unified Power Flow Controller System with 60-Pulse GTO-Based Voltage Source Converter

The Generalized Unified Power Flow Controller (GUPFC) is a Voltage Source Converter (VSC) based Flexible AC Transmission System (FACTS) controller for shunt and series compensation among the multiline transmission systems of a substation. The paper proposes a full model comprising of 60-pulse Gate Turn-Off thyristor VSC that is constructed becomes the GUPFC in digital simulation system and investigates the dynamic operation of control scheme for shunt and two series VSC for active and reactive power compensation and voltage stabilization of the electric grid network. The complete digital simulation of the shunt VSC operating as a Static Synchronous Compensator (STATCOM) controlling voltage at bus and two series VSC operating as a Static Synchronous Series Capacitor (SSSC) controlling injected voltage, while keeping injected voltage in quadrature with current within the power system is performed in the MATLAB/Simulink environment using the Power System Block set (PSB). The GUPFC, control system scheme and the electric grid network are modelled by specific electric blocks from the power system block set. The controllers for the shunt VSC and two series VSCs are pre- sented in this paper based on the decoupled current control strategy. The performance of GUPFC scheme connected to the 500-kV grid is evaluated. The proposed GUPFC controller scheme is fully validated by digital simulation.