Zigzag Transformer Research Articles

Technique for Mitigating Voltage Ripple of DC-Link Capacitors in a Three-Level NPC Utilizing a Zigzag Transformer

Technique for Mitigating Voltage Ripple of DC-Link Capacitors in a Three-Level NPC Utilizing a Zigzag Transformer

Investigation of the usage of zigzag transformers to reduce harmonics distortion in distribution systems

The increasing use of power electronics in various sectors leads to harmonic distortion in electric power systems, affecting power quality and equipment longevity. While harmonic filters have been used to address this issue, they are limited in effectiveness, particularly in reducing distortion across the entire distribution system. This study aims to reduce harmonic distortion using a zigzag transformer as a more comprehensive solution in mitigating harmonic distortion throughout the entire distribution system. In this research, the zigzag transformer was placed at point common coupling to reduce harmonic distortion in the distribution system as a whole. A zigzag transformer connection was configured by connecting either three windings of a single-phase transformer or one winding of a three-phase transformer. Based on the results of this research, the total harmonic distortion (THD) value has decreased from 25.26 % to 2.48 % following the implementation of the zigzag transformer. This substantial decrease in THD concludes the zigzag transformer's effectiveness as a solution for improving power quality in electrical distribution systems.

Improved dynamics of DC bus control with a zig-zag transformer for bipolar DC distribution systems

Improved dynamics of DC bus control with a zig-zag transformer for bipolar DC distribution systems

Power quality improvement of microgrid fed electric ship using fuzzy controlled multi-pulse/multi-level converter-based VFD

This paper investigates a harmonic mitigation technique for modern electrical propulsion ships (EPS) microgrids (MG) using a fuzzy controlled multi-pulse rectifier (MPR) and multi-level inverter (MLI)-based variable frequency drive (VFD). In this paper, the proposed MPR-MLI-VFD system is studied using different-pulses rectifiers and different-level inverter-based VFD to achieve proper mitigation of the harmonics in the main generating power system of the ships within the marine classification society's limitations for harmonics. This is achieved using a proposed low harmonic multi-pulse rectifier based on zigzag transformers. Moreover, the voltage harmonic distortions at propulsion motor feeder buses are minimised using the proposed MLI. A simple fuzzy logic control system is proposed for the VFD speed control. The voltage balancing control system for the diode clamped multi-level inverters is implemented using a fuzzy control system. MATLAB/Simulink is used for the simulation and validation process.

철도 전력계통 불평형 보상을 위한 지그재그 변압기 개발

According to the government’s energy policy, distributed generation is likely to be operated in connection with the railway system in the future. Circulating current may occur under unbalanced conditions when using the existing non-standard interconnected transformer for the distributed generation, and this circulating current problem must be solved from the perspective of a distributed power provider in order to accommodate the needs of the power utility. In addition, as the load connected to the power system through the rectifier increases, the harmonic current caused in the neutral wire is also increasing, and there is a need to solve various relevant problems. Therefore, it is necessary to develop an auxiliary transformer (grounding transformer), which has multiple auxiliary roles (reduction of excessive circulating current, protection of non-grounding systems by providing effective grounding). The developed zigzag transformer has been verified its performance through a characteristic test and an accredited agency certification test after manufacture. In this paper, the design of the zigzag transformer and the modeling of it by using Power System Computer Aided Design (PSCAD) are described. Simple compensation verification of unbalance situation has been also shown.

EPLL Control Technique Optimum Controller Gains to Control Voltage and Frequency in Standalone Wind Energy Conversion System

This study describes how to regulate the frequency and terminal voltage of a freestanding wind energy conversion system using an Enhanced Phase Locked Loop (EPLL)-based strategy to supply power to varied loads regardless of wind speed. In a standalone wind turbine energy conversion system, the EPLL control scheme extracts the reference source currents (SWECS). The control algorithm employs two proportional-integral (PI) controllers to create the active and reactive power components of the consumers' load currents, estimate reference source currents, and connect the zigzag transformer to PCC with VSC for neutral current compensation. To obtain optimal PI controller gains and most-suited settings to apply to SWECS, optimization approaches are used. The control algorithm is the most significant aspect of the system, and the speed with which it calculates, evaluates, and guesstimates determines the generation of source currents based on the algorithm's ideal controller PI gains. By properly estimating source currents, the EPLL control method improves dynamics and power quality issues, and the optimization technique is employed to acquire the gains of PI controllers. The proposed system employs the EPLL algorithm on a three-phase, four-wire system with changing loads to achieve ideal total harmonic distortion of source currents and voltages on the PCC, as defined by IEEE-519 standards. A battery energy storage device coupled to the VSC dc link keeps the load's necessary power constant. If the generator output exceeds the consumer demand, the excess power is delivered to BESS for temporary storage. When consumer demand exceeds generated power, a BESS delivers deficit power to the load, which adjusts and the frequency under various load conditions. The suggested system simulated results were tested with 3-phase 4-wire for harmonics reduction, load balancing, neutral wire current compensation, frequency and voltage control using MATLAB / Simulink.

Comparison of Analytical Method and Different Finite Element Models for the Calculation of Leakage Inductance in Zigzag Transformers

A zigzag transformer is a key segment of the electric power system. The optimal design of the zigzag transformer is important for transformer designers to provide a required return path for earth faults and to ensure proper operation of a power system. The two most important parameters of the zigzag transformers are no-load losses and leakage impedance. The accurate calculation of both factors helps to minimize the overall cost of the transformer. Therefore, the prediction of leakage reactance in the zigzag transformer using analytical or numerical methods is an essential part of the early designing stages of the transformer. This paper provides several two- and three-dimensional finite element models. The main purpose of these models is to evaluate the accuracy of the different models for the calculation of the leakage reactance. An analytical formula and a complete procedure for the calculation of the leakage reactance in the zigzag transformer are also provided, which will help the researchers and transformer designer to optimize this type of transformer. The prototype is also manufactured and tested to verify the accuracy of the analytical method and finite element models for the calculation of the leakage reactance. The simulation and experimental results show that the finite element calculation cannot only obtain accurate leakage reactance values (magnetostatic analysis), but also provides better accuracy in the no-load losses (transient analysis).

The Possibility of Enhanced Power Transfer in a Multi-Terminal Power System through Simultaneous AC–DC Power Transmission

The feasibility of power transfer enhancement, through simultaneous AC–DC power transmission in a two-terminal transmission network, has been proposed earlier by the authors, and the concept is well established. To meet the increase in demand for electricity, a new technique is proposed in this article to increase the use of existing transmission lines in addition to independent control of AC and DC power flow. This paper extends the concept to a three-terminal transmission network by considering a power tapping from the middle of the line. DC is also superimposed in the already existing three-terminal AC transmission system. In the proposed topology, a multi-terminal simultaneous AC–DC system is used, which is integrated with a zig-zag transformer and more than two voltage source converter (VSC) stations. Each terminal may represent an area of the power system. Anyone/two-terminal(s) may act as sending end, whereas the remaining two/one terminal(s) may act as receiving end. Power can flow in either direction through each segment of the transmission system. At sending end, VSC converts a part of AC to DC and injects it into the neutral of the zig-zag transformer. On receiving terminal, DC power is tapped from neutral of zig-zag transformer and fed to VSC for conversion back to AC. The concept is verified in the digital simulation software PSCAD/EMTDC.

Optimization of controller gains to enhance power quality of standalone wind energy conversion system

Abstract This article presents optimized gains for regulation of frequency and terminal voltage irrespective of the varying wind speeds in an autonomous wind power generation feeding linear and non-linear loads. Icosφ control algorithm is used to calculate and estimate reference source currents in a remote area wind energy conversion system (WECS) using an Induction Generator (IG). The Icosφ control algorithm do not have any phase locked loop or any conversions from one reference frame to other, which improves the dynamics and power system quality issues. The heart of the control algorithm is how quickly it estimates the reference source currents; this in turn depends on values of proportional and integral controller gains in the control algorithm. Here we are applying three optimization techniques to find the optimal proportional-integral (PI) controller output gains, the best convergence values are taken from optimization technique and applied for WECS. Battery energy storage system (BESS) connected to the direct current (DC) link of voltage source converter (VSC) manages the power of WECS. When load useful power level is less than the generated power level, the excess will be diverted and stored in the battery. But when generated power level is less than the load applied on WECS then the excess power requirement of the load is met by the battery, thus regulating the frequency under varying wind speeds. An isolated zigzag transformer is connected between point of common coupling and controller for neutral line current compensation. The controller is used for load balancing, current harmonic suppression, voltage and frequency regulation.

Multiple three-phase induction motors connected to a zigzag transformer

Many experiments have been conducted in this research work which is (i) connecting a zigzag transformer with an induction motor, (ii) connecting a zigzag transformer with multiple induction motors, and (iii) connecting multiple zigzag transformers with multiple induction motors. These experiments provide a thorough understanding of the sequence network connections under the single-phasing condition of a three-phase induction motor. Moreover, these experiments protect the three-phase induction motors from unbalancing voltage supply and allow the induction motor to start under unbalance voltage supply. Additionally, they keep the three-phase induction motor running even any one of the three phases disconnected from the power supply without creating excessive heat in the motor winding.

Principle and Control Design of a Novel Hybrid Arc Suppression Device in Distribution Networks

A single line-to-ground (SLG) fault may lead to a more severe line-to-line fault and power supply interruption if the ground-fault current exceeds a certain value. Arc suppression device (ASD) is a good solution to eliminate the ground-fault current. A novel hybrid ASD is proposed in this article, which consists of a passive device and an active one. The passive device utilizes multiterminal breakers and an isolation transformer to couple a secondary voltage of a zig-zag grounding transformer to the neutral point to compensate the majority of the ground-fault current. The active device uses a single-phase voltage source inverter to eliminate the residual fault current due to the leakage inductance of the zig-zag grounding transformer in the passive device. A dual-loop voltage and current control method for the active device is designed for the accurate residual current compensation. Results of simulation and prototype experiment validate the effectiveness of the proposed hybrid ASD. The proposed hybrid ASD does not need to detect distributed line-to-ground parameters, and it has lower cost, less control complexity, higher reliability, and better performance, compared to other ASDs.

Real-Time Implementation of CLMS Algorithm in 3P4W Solar PV-BES-Based Microgrid System

A solar photovoltaic (PV)—battery energy storage (BES) involved the microgrid (MG) system is presented in this article. It contains a bidirectional dc–dc converter (BDDC), which is responsible for extracting the maximum power output from the PV array by regulating the dc-link voltage to the maximum power point (MPP) voltage of the PV array. Whenever the PV array is not delivering any power, then the control of the BDDC is automatically shifted to regulate the dc-link voltage to a constant dc voltage. Thus, the BDDC regulates the dc-link voltage to the desired voltage in the presence of BES in the MG. Whenever the BES is disconnected from the MG, then the voltage source converter (VSC) regulates the dc-link voltage to the desired value. Thus, it enhances the reliability of the system. The neutral current compensation is performed by the zig-zag transformer, which is connected at the load end. The VSC performs different functions such as mitigation of harmonics and reactive power, balancing of grid currents, and the regulation of the dc-link voltage in the absence of BES. The system behavior is analyzed under different operating conditions in the simulation platform and in the laboratory conditions on a prototype.

Enhancement of Power Quality Utilizing Photovoltaic fed D-STATCOM Based on Zig-Zag Transformer and Fuzzy Controller

Distribution Static Synchronous Compensator (D-STATCOM) is a shunt compensator in the distribution systems that one of the most important tasks is to improve the imbalance, reduce and eliminate the nonlinear loads harmonics. Distributed generation resources such as photovoltaic (PV) array can be used as the DC input of D-STATCOM. In this paper, PV array and DC/DC boost convertor are used to stabilize the DC link voltage of D-STATCOM. The main advantage of the proposed method is that for all time provides continuous compensation. Another power quality issues are neutral current in four-wire systems that are created due to the harmonics and system imbalance. Zig-Zag transformer is one of the ways for compensating neutral current and providing isolation between the convertor and flow of the fundamental zero sequence component which contains harmonic neutral current. Role and performance of the distribution shunt compensator in the improvement of power quality indices depends on the performance of its control system. In this paper, the control scheme of synchronous reference frame theory based on fuzzy controller is used for D-STATCOM based on PV and Zig-Zag transformer. Performance and behaviour of the proposed system examined using Matlab/Simulink software and the results will be presented.

A fault-tolerant grid-forming converter applied to AC microgrids

A crucial converter for the islanded operation of AC microgrids is the grid-forming converter. This central converter supplies electrical loads, and assures the distributed generators operation, since the malfunctioning of grid-forming converter can jeopardize the whole microgrid. This paper proposes a bidirectional grid-forming converter with a fault-tolerant functionality applied to islanded AC microgrids using a centralized control architecture. The converter is based on a delta connection of three single-phase voltage source inverters (VSIs) using an H-bridge topology for three-phase three- or four-wire systems. For this latter case, a zigzag transformer is used to provide the neutral conductor for the system. In addition to establishing voltage and frequency references for the microgrid, the converter is capable of changing its configuration from delta to open-delta, and vice-versa, in a smooth mode and without interrupting the microgrid operation. Thus, in case of failure of one of the grid-forming VSIs, the system can keep supplying the microgrid. A control strategy is developed to allow a stable operation in all operating modes. Experimental results are presented with a converter prototype to validate the proposed topology, control and mode of connection.

Lorentzian adaptive filter for controlling shunt compensator to mitigate power quality problems of solar PV interconnected with grid

The proposed system deals with Lorentzian norm-based Lorentzian adaptive control algorithm, grid interconnected photovoltaic (PV) system which consists of solar photovoltaic, boost converter, maximum power point tracking (MPPT) controlling PV system, ripple filter, voltage source converter (VSC), interfacing inductor and three phase nonlinear/linear loads. The reference grid current for voltage source converter section is estimated using Lorentzian adaptive control algorithm. The Lorentzian norm based on sliding window objective function with gain factor matrix to eliminate the impulsive effect. Neutral current compensation is achieved by three phase zig-zag transformer connected to PCC of solar grid. The proposed Lorentzian adaptive filter maintains unit power factor at grid, harmonic elimination, load balancing, reactive and neutral current power compensation for zero voltage regulation. In the proposed system maximum power point tracking technique using incremental conductance's algorithm is used for maintaining constant DC bus voltage. The Lorentzian adaptive filter algorithm is modelled in MATLAB along with Simulink.

Lorentzian adaptive filter for controlling shunt compensator to mitigate power quality problems of solar PV interconnected with grid

The proposed system deals with Lorentzian norm-based Lorentzian adaptive control algorithm, grid interconnected photovoltaic (PV) system which consists of solar photovoltaic, boost converter, maximum power point tracking (MPPT) controlling PV system, ripple filter, voltage source converter (VSC), interfacing inductor and three phase nonlinear/linear loads. The reference grid current for voltage source converter section is estimated using Lorentzian adaptive control algorithm. The Lorentzian norm based on sliding window objective function with gain factor matrix to eliminate the impulsive effect. Neutral current compensation is achieved by three phase zig-zag transformer connected to PCC of solar grid. The proposed Lorentzian adaptive filter maintains unit power factor at grid, harmonic elimination, load balancing, reactive and neutral current power compensation for zero voltage regulation. In the proposed system maximum power point tracking technique using incremental conductance's algorithm is used for maintaining constant DC bus voltage. The Lorentzian adaptive filter algorithm is modelled in MATLAB along with Simulink.

Modelling of Transformerless Upfc Toimprovepower System Stability using Optimization Technique

Generally, power system faces the problem to transfer power from one system to another system without any fluctuations, with minimal of system losses. To overcome this problems, a flexible ac transmission system is implemented in this paper. In present scenario, facts devices are used to reduce the transmission losses for improvising transmission capacity and also to improve the system capability. Unified Power Flow Controller plays a most prominent role in FACTS controller to improve the system stability. The structure of UPFC is combination of back-back converters with boosting and zigzag transformer. This type of UPFC system consists of high losses due to presence of magnetic properties in this transformer. With this, a transformer-less multilevel inverter based UPFC topology is proposed in this paper. This paper focuses on the modulation of transformerless UPFC with PSO, which controlsfundamental frequency for better controlling of active and reactive power, harmonic minimization, and improvement in efficiency of system by controlling DC link voltage.

V f Controlled Autonomous Wind Energy Conversion System Using Z2 Transformer Connected DSTATCOM

Distributed generation and renewable energy sources are hot research topics from past 10 years or so due to various reasons. The sudden load variation leads to change in voltage and frequency, and if nonlinearity presents, the T.H.D. variations will be more. Power quality controlled devices like DSTATCOM with battery energy storage system (B.E.S.S.) that controlled by pulse width modulation (P.W.M.) based voltage source converter (V.S.C.) in the distribution system would control the voltage, frequency and THD, indirectly power control. This paper presents an autonomous W.E.C.S. with zig-zag (Z2) transformer connected V.S.C. controlled DSTATCOM with BESS and its control scheme. It also shows the various MATLAB simulated results. It also contemplates the various performance parameters from previous methodology. It strategically concludes that the proposed system is effective in controlling voltage and frequency (V-f) and T.H.D. in voltage and current.

Adaptive static synchronous compensation techniques with the transmission system for optimum voltage control

Abstract Static Synchronous Compensation (STATCOM) is considered as one of the famous modules of the Flexible AC Transmission Systems (FACTS) devices. This paper discusses the optimum voltage control technique using the STATCOM module with the transmission system to overcome the drop and the influence factors for the voltage in the power system. In addition, this paper discusses the impact of using the zigzag transformers with the STATCOM control system to prevent the combination between the STATCOM injection voltage and the harmonics to reach pure voltage compensation. The simulation in this paper uses the MATLAB/Simulink software to introduce the STATCOM operation steps, also the proposed analysis of the distribution system network has been validated with IEEE-14 busbar system as a case study to test the increasing loadability by using STATCOM module for enhancing the power system quality.

Power Quality Enhancement Using Euclidean Direction Search Based Control Technique

This paper proposes the design and control of a three-phase four-wire distribution static compensator (DSTATCOM) for elimination of several power quality (PQ) issues, namely harmonics, reactive power, load unbalancing, and neutral current. A three-phase voltage source converter (VSC) and a zigzag transformer based configuration are utilized as a DSTATCOM. The zigzag transformer is operated to provide a suitable path for load neutral current and other PQ problems are mitigated by designing a suitable control for VSC. The control of VSC is developed using Euclidean direction search (EDS) technique based adaptive control theory. This control algorithm is designed to extricate fundamental constituents from the load current and used to generate switching pulses for VSC. The improved behavior of the proposed EDS-based control is observed by comparing it with other existing controllers. Real-time performance of the EDS control is verified on a developed prototype in the laboratory using VSC and DSP (dSPACE1104 R&D controller).