Voltage Source In Series 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.

Direct Adaptive SSDV Circuit for Piezoelectric Shunt Damping

Piezoelectric shunt damping is widely studied to suppress vibration of thin structures via shunting an attached piezoelectric transducer with an electrical impedance. The SSDV (synchronized switch damping on voltage) technique can be used to enhance the damping effect. However, SSDV is not stable in the weak excitation. Although some adaptive SSDV circuits have been developed to tackle the stability problems, additional monitoring devices are required to feed back the vibration strength signal for adjusting the series voltage sources. We here present a new direct adaptive SSDV (DA-SSDV) method without additional excitation level monitoring module, based on the ratio of the maximum piezovoltage and the value of the series voltage sources. A compact DA-SSDV circuit is designed with low-cost off-the-shelf discrete components. The close-loop control of the series voltage sources is realized simply through a passive envelope detector and a resistive voltage divider. Experimental results show the DA-SSDV circuit avoids the stability problems and possesses a good displacement transmissibility around 6.2, a fast voltage adjustment response speed above 5 V/s and a high operation sensitivity with the open-circuit piezovoltage of 540 mV. The DA-SSDV shows great application value in the compact and low-power vibration control systems.

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.

Reliability Improvement of Voltage Regulator Modules by a Virtual Series Voltage Source

Output voltage deviation is a key performance index of voltage regulator modules (VRMs) with consecutive load transients. Usually, a large-capacity filter capacitor bank is used in VRMs to reduce the voltage deviation and stabilize the output voltage during transients. However, capacitors are one of the most vulnerable links in power electronic converters. For reliability reasons, it is essential to reduce the capacitance requirement while guaranteeing the transient performances of VRMs. Focusing on this, many efforts have been made to optimize the design of VRMs, where the transient auxiliary circuit-based scheme is a popular one. Unfortunately, there exists a large number of additional components in the existing auxiliary circuits. Considering this issue, in this article, we present a virtual series voltage source (VSVS) based auxiliary circuit scheme, which has minimum component counts. By using a controlled coupled inductor as the VSVS, the proposed scheme enables VRMs to have a relatively small transient voltage overshoot and without needing large bulk capacitance. Moreover, considering different control schemes with the same designing aim, the number and the electrothermal stress of critical components (e.g., capacitors) of VRMs are different; it is difficult to compare directly their advantages and disadvantages. Regarding this issue, this article investigates the converter-level reliability of VRMs with different control schemes. Taking a 12–3.3 V VRM as a case study, the reliability benchmarking results illustrate that the proposed scheme can significantly improve the reliability of VRMs.

Wideband Series Harmonic Voltage Compensator for Enhancing Stability of Microgrids

A wideband series harmonicvoltage compensator (WSHVC) for mitigating the adverse effect of unknown grid impedance and load condition on the stability of microgrids with multiple grid-connected inverters (GCIs) is presented. The concept is based on extending the concept of series active power filter. A wideband series voltage source inverter is used to compensate for the high-frequency harmonic voltage caused by the impedance at the point of common coupling, thereby creating a virtually zero high-frequency impedance at the output of the GCIs. The system stability is then assured under any operating condition. The bandwidth of the WSHVC ranges from the second harmonic of the grid frequency to 8 kHz, which is sufficiently higher than the cut-off frequency of typical GCIs. Such fast dynamic behavior is realized by a novel fixed-frequency predictive control scheme with nonlinear switching surfaces. Since the WSHVC handles harmonic power only, its volt-ampere rating is lower than that of the entire system. A 500 VA prototype for a 6.5 kVA testbed with three commercial GCIs, nonlinear load, and adjustable grid impedance has been evaluated. The power dissipation of the WSHVC is less than 1% of the VA rating of the testbed. The effectiveness of the WSHVC on improving system stability is studied.

Double-layer balance system of voltage source series energy storage battery pack for electric vehicles

Inconsistent material properties or structural composition of batteries may occur in the process of battery manufacturing, storage, and operation. The resulting inconsistency in the battery cells will make the series battery packs in electric vehicles have the hidden danger of accidents. This paper designs a two-layer combination balance system with fast speed and simple structure based on the analysis of graph theory. On the one hand, the system is based on a distributed topology to provide a direct energy transmission path for non-adjacent battery cells in the battery pack to fully improve the balancing speed. On the other hand, it takes full advantage of the fast speed of centralized topology to avoid the increase in control complexity caused by too many balancing paths. Finally, a suitable switching frequency and a balancing capacitor were selected based on the simulation experiment. The prototype of the double-layer combined balance system was designed and built to verify its faster speed and good effect.

A Low-Power Direct Adaptive SSDV Piezoelectric Vibration Control Circuit

Piezoelectric shunt damping is promising in vibration suppression of thin structures. A Low-power direct adaptive synchronized switch damping on voltage (LDA-SSDV) circuit is designed to solve the stability problem of the SSDV without additional vibration strength monitoring devices. Based on the linear relationship between the maximum piezovoltage and the values of series voltage sources, we use simple envelope detectors and resistive voltage dividers to control the voltage sources. And the voltage sources are activated during the switching events for saving energy. The experimental results show that the LDA-SSDV circuit has a stable operation and similar vibration suppression level compared to SSDV.

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.

Formal Chaos Existing Conditions on a Transmission Line Circuit with a Piecewise Linear Resistor

By using one-dimensional (1-D) map methods, some lossless transmission line circuits with a short at one side terminal have been actively studied. Bifurcation results or chaotic states in the circuits have been reported. On the other hand, many weak or strong definitions such that a 1-D map is mathematically chaotic are still being studied. In such definitions, the definition of formal chaos is well known as being the most traditional and most definite. However, formal chaos existences have not been rigorously proven in such circuits. In this paper, a general lossless transmission circuit is considered first with a dc bias voltage source in series with a load resistor at one side terminal and with a three-segment piecewise linear resistor at another side terminal. Secondly, the method for deriving a 1-D map describing the behavior of the circuit is summarized. Thirdly, to provide a basis of chaotic application for the 1-D map, the mathematical definition of formal chaos and the sufficient conditions of the existence of formal chaos are discussed. Furthermore, by using Maple, formal chaos existences and bifurcation behavior of 1-D maps are presented. By using the Lyapunov exponent, the observability of formal chaos in such bifurcation processes is outlined. Finally, the principal results and the future works are summarized.

A Current Allocation Strategy Based Balancing Technique of Voltage Source String in Switch-Ladder Inverter and Its Switched-Capacitor Variety

A charge balancing method for series voltage source feeding multilevel inverters (MLI) based on current allocation control is presented. Unlike those MLIs based on isolated dc sources, the series-connected elements in a voltage source string, such as a battery or supercapacitor stack, cannot be by-passed individually. This brings the problems of source imbalance and limited redundant switching states for current allocation control at high modulation index. In this article, the source balance in the switch-ladder inverter is achieved by allocating the current distribution. Furthermore, the balancing effectiveness is enhanced by a novel configuration combining a switched-capacitor (SC) circuit. The working principle and modulation index limit for the current allocation method is elucidated with a flow diagram and mathematical representation. The feasibility and operation of the proposed method and topology are successfully validated by a simulation study and the experimental results.

Analysis of Transmission Line with Distributed Series Voltage Sources Using Green’s Function

In this article, the authors have made an attempt to promote the analysis of transmission lines containing distributed series voltage sources using Green’s function. Authors believe that this tutorial article can enrich a traditional course on transmission line theory due to the following two major value additions. Firstly, it extends the traditional transmission line theory by incorporating distributed voltage sources. Secondly, it acts as an excellent introduction to the concept of Green’s function. In this article, Green’s function for the point series voltage source is systematically derived. The 3D Electro-Magnetic tool is used to validate the analysis. A basic understanding of transmission line theory is a sufficient pre-requisite to dive into this journey.

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.

Multiport Interline Current Flow Controller for Meshed HVDC Grids

In meshed high voltage direct current grids, the current of each line cannot be controlled independently, since it depends on the resistances between nodes. Additional devices, such as current flow controllers (CFCs), may be needed to avoid bottlenecks or line overloads. This work presents a multiport dc-dc-based CFC topology to be connected to n lines with unidirectional current flows. The device is able to control the dc lines' currents to the desired value by inserting variable voltage sources in series. First, the modeling of the generic n-port topology is presented and then, its modulation and control strategy are described. In the first case study, the concept is validated considering a 5-port CFC by means of dynamic simulations using different control methods. Finally, in the second case study, a 3-port CFC prototype is built and tested in an experimental platform in the laboratory considering different control modes.

Enerji Dönüştürücüler için Ara Devresi

This paper presents an efficient self-startup interface circuit for ambient energy sources. The proposed circuit consists of a charge pump, a boost converter, a charge transfer control circuit and some passive components. The charge pump boosts the low voltage at the output of the energy source to store the charge into a super capacitor. Once enough charge is stored into the super capacitor, the charge transfer control circuit has been active (i.e. being on) to bridge the super capacitor to the boost converter. Thus, the load receives power supply in a short period of time i.e., operates in the burst mode since the generated power at the energy source is lower than the power required by the load. The boost converter is used for providing a constant voltage level (e.g. 3.3 V) to the load. The proposed circuit has been evaluated using off-the-shelf components and connects to emulate the energy source. A voltage source in series with a resistor can be modeled to emulate the energy source. The proposed circuit can start the operation as low as 0.3 V input voltage and up-convert to 3.3 V. The proposed interface circuit has been tested for various loads in order to indicate the effectiveness of the circuit. The proposed circuit has a peak overall efficiency of 11.56 %, which is higher than the conventional interface circuit achieves. As compared to conventional interface circuit, the proposed circuit enhances the efficiency by 1.8 X. The measured results indicate that the proposed circuit achieves a high efficiency without the need of external supply.

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.

An Improved Multiport DC Power Flow Controller for VSC-MTDC Grids

As a key device to facilitate power flow in the multi-terminal direct current (MTDC) transmission system, DC power flow controller (DCPFC) can effectively expand the power flow regulation area by implementing its multiport output functionality. In order to solve the coupling issue between the transmission line current and the capacitor voltage of the inter-line multiport DCPFC (M-DCPFC), an improved M-DCPFC with a partial power rated auxiliary DC/DC converter unit is proposed in this paper. It provides the advantages of power flow reversal, high adjustment flexibility and low port-expansion cost. Meanwhile, a generic control strategy is developed for the M-DCPFC with random number of the ports. Moreover, from the perspective of the transmission system, the proposed M-DCPFC is modeled as the equivalent series voltage source. Its power flow adjustment capability and its impact on the local voltage source converter (VSC) stations are investigated in detail in this paper. Lastly, to validate the effectiveness of the proposed M-DCPFC, it is first tested in the simulations of the MATLAB/Simulink and then deployed on an experiment platform. Both simulation and experimental results show that the proposed M-DCPFC can achieve stable power flow control in different conditions.

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.