Three-phase Three-wire System Research Articles

CHBMLI based DSTATCOM for power quality improvemt in a three-phase three-wire distribution system with PI controller

This paper presents a cascaded h-bridge (CHB) multilevel inverter (MLI) based MLI based distribution static synchronous compensator (DSTATCOM). The main objective of this paper is to reduce source current harmonics in the distribution system by using a cascade H-bridge multilevel inverter (CHBMLI) as DSTATCOM with a proportional-integral (PI) controller. The PI controller compensates reactive power, reduces source current harmonics, and maintains the unity power factor in the distribution system. The conventional two-level inverter-based DSTATCOM has many disadvantages such as high total harmonic distortion (THD), and high switching stress power semi-conductor devices, suitable for only low-power applications. This paper to overcome these drawbacks by using MLI-based DSTATCOM. The proposed system simulations are verified in MATLAB/Simulink software. The verified results are source current, load current, and compensating current.

Parallel active power filter based on single-phase independent control

With the rapid development of high-voltage power grids and power electronics technology, the integration of numerous power electronic devices has led to a significant increase in harmonic pollution in power grids. Consequently, the demand for high-voltage and large-capacity active power filters has become increasingly urgent. This article introduces a novel approach using single-phase independent control and proposes a parallel active power filter based on magnetic flux compensation. This filter not only enhances power quality but also achieves three-phase decoupling control. It is specifically designed for medium and high-voltage three-phase three-wire power systems. Simulation experiments were conducted to validate the efficacy of the proposed active power filter, demonstrating its ability to effectively reduce the total harmonic distortion rate at the grid connection point and subsequently improve power quality.

Strategies of Energy-Efficient Active Filtering in the Two Wattmeter Reference Frame

Such basic concepts of power theory as apparent power, active current and minimum power losses in the transmission line are defined for a three-phase three-wire system in the shortened two wattmeter reference frame. On the basis of these concepts, two energy-efficient active filtration strategies were developed and verified by virtual experiments. The first of them minimizes the power losses of a three-phase three-wire transmission line with different values of its resistances and ensures a unit value of the power factor. The second strategy follows the recommendation of IEEE Std. 1459-2010 ensures the minimum power loss of the transmission line with symmetrical sinusoidal currents of a three-phase source.

Research on flexible uninterrupted neutral section passing system based on V-clamp multilevel converter

This paper proposes a novel flexible uninterrupted neutral section passing system based on four-leg V-clamp multilevel converter (VMC). It can better solve a series of problems such as overvoltage, overcurrent and speed loss caused by the interruptible over-phase scheme used in electrified railway, and compensate the negative sequence and reactive current in traction power supply system at the same time. VMC is a new type of multilevel converter with common DC-link capacitors. VMC has advantages in the number of devices to some extent, and its expansion from odd level to even level is very simple. Compared with schemes based on modular multilevel converter (MMC), this system has the advantages of low converter hardware cost and no energy loss resulting from hot backup. The system configuration, working process and operating principle are analyzed in detail, and a control strategy for the whole process of neutral section passing is designed. Next, the method based on zero-sequence voltage component injection is used to solve the voltage-balancing problem existed in multilevel converter with common DC-link capacitors, which does not need additional switching times and is easy to realize in three-phase three-wire system. Finally, the simulation results are given to verify the feasibility and effectiveness of the system.

Per-Phase Power Controller for Smooth Islanded Transitions in Three-Phase Three-Wire Systems

This manuscript describes the operation of a droop-based controller for three-phase converters in the case of the absence of a neutral connection to the grid. The controller is capable of output power tracking and smooth transitions into the islanded operation. While independent per-phase control of the converter output power is possible if a neutral connection is present, its absence implies additional constraints to be considered. Focusing on this latter case, the controller described herein allows the independent control of the active power at the output of each phase of the converter and a smooth transition to the islanded operation. These features are paramount in future smart power systems, such as smart microgrids, for implementing demand–response, power-flow management, and uninterrupted power operation.

Power definitions for three-phase systems in terms of instantaneous symmetrical components

This paper considers power definitions for three-phase power systems with non-sinusoidal and unbalanced voltages and currents. By applying the Lyon transformation to three-phase voltages and currents, instantaneous symmetrical components are obtained and used to define powers. Definitions of instantaneous apparent and reactive powers are derived, as well as definitions of well-known quantities based on rms values, such as apparent and reactive powers. The introduced set of power definitions based on the same mathematical framework could be used for time-instantaneous and time-average compensation types. To provide correct calculation of powers for unbalanced three-phase four-wire systems, all wires and related quantities of the three-phase four-wire system are treated equally. The instantaneous apparent and reactive powers are also expressed in terms of instantaneous symmetrical components derived from the Clarke transformation. The proposed definitions are compared with other power definitions. In the case of a three-phase three-wire system, the proposed definitions give the same values of powers as the most known power definitions. In the case of a three-phase four-wire system, the proposed definitions give the same value of the apparent power as the DIN 40110 Standard and the same value of reactive power as the Currents' Physical Component theory.© 2017 Elsevier Inc. All rights reserved.

Multi-Objective Spotted Hyena Optimization-Based Control of Grid-Tied PV System

This article describes the multi-objective spotted hyena optimization (MOSHO) based control of a three-phase three-wire grid-tied dual-stage PV system. The MOSHO delivers an optimized step size ( δ ) for the incremental conductance (InC) based maximum power point tracking (MPPT) algorithm, as well as optimizes the PI controller gains for DC bus voltage ( V d c ) regulation. The δ optimized MPPT facilitates the faster and more accurate tracking of maximum power point with fewer fluctuations at steady-state. The MOSHO optimized PI controller regulates the V dc and delivers better stability with reduced V dc variations in DC bus voltage during steady-state and dynamic states, i.e. irradiation variation, abnormal and unbalanced grid voltage. The optimized DC bus generates an accurate loss component of current, which further enhances the voltage source converter (VSC) performance in terms of precise reference currents generation and power quality improvement. The proposed system performs satisfactorily in a MATLAB simulation environment as per IEEE519 standards.

CONTROL STRATEGY OF PHOTOVOLTAIC GENERATION INVERTER GRID-CONNECTED OPERATING AND HARMONIC ELIMINATION HYBRID SYSTEM

This paper proposes a three-phase three-wire photovoltaic generation inverter grid-connected operating and harmonic elimination hybrid system. The hybrid system mainly consists of photovoltaic array battery, photovoltaic output filter, three-phase voltage-type inverter, inverter output filter and passive filters. Based on working principle and working characteristics of the proposed hybrid system, the composite control strategy about active power, reactive power and harmonic suppression is proposed. The composite control strategy mainly consists of a single closed-loop control slip of active power and reactive power, double closed-loop control slip of harmonics. Simulation results show the correctly of this paper’s contents, the hybrid system have an effective to improve power factor, supply active power for loads and suppress Key words - Micro grid; harmonic restraint; active power control; reactive power control; photovoltaic generation.

THE UNIFIED POWER QUALITY CONDITIONER: A REVIEW

This thesis addresses the Unified Power Quality Conditioner (UPQC) which is a major custom power solutions capable for load balancing, power factor-correction, voltage regulation, voltage and current harmonics mitigation in a three-phase three-wire distribution system for different combinations of linear, non-linear and dynamic loads. The unit template technique (UTT) is used to get the reference signals for series active power filter and shunt active power filter which utilizes two closed loop PI controllers. The design of three- phase three-wire UPQC includes the design of shunt controller (SHUC) and series controller (SERC).

Least mean sixth control approach for three-phase three-wire grid-integrated PV system

<p><span lang="EN-US">This work proposes an adaptive filter based on a new least mean sixth control approach with incremental conductance method of MPP for 3-phase grid-incorporated photovoltaic (PV) system. The proposed system comprises a PV array, 3-phase DC to AC converter, maximum power point tracker (MPPT), three-phase electronic load, and a 3-phase grid. The combination of solar PV array and the voltage source converter (VSC) supplies power to the grid. The 3-phase inverter as a distribution static synchronous compensator (D-STATCOM) improves the quality of the system performance in case of zero solar irradiation. D-STATCOM also reduces total harmonic distortion (THD) in grid currents, improves power factor, and maintainsa constant voltage at the point of common coupling (PCC). The system modelling and simulation is achieved on MATLAB/Simulink. The proposed system performance has been found satisfactory and conform to IEEE-519 standards.</span></p>

Multi-Objective Grasshopper Optimization Based MPPT and VSC Control of Grid-Tied PV-Battery System

This article presents the control of a three-phase three-wire (3P-3W) dual-stage grid-tied PV-battery storage system using a multi-objective grass-hopper optimization (MOGHO) algorithm. The voltage source converter (VSC) control of the presented system is implemented with adaptive kernel width sixth-order maximum correntropy criteria (AKWSOMCC) and maximum power point tracking (MPPT) control is accomplished using the variable step-size incremental conductance (VSS-InC) technique. The proposed VSC control offers lower mean square error and better accuracy, convergence rate and speed as compared to peer adaptive algorithms, i.e., least mean square (LMS), least mean fourth (LMF), maximum correntropy criteria (MCC), etc. The adaptive Gaussian kernel width is a function of the error signal, which changes to accommodate and filter Gaussian and non-Gaussian noise signals in each iteration. The VSS-InC based MPPT is provided with a MOGHO based modulation factor for better and faster tracking of the maximum power point during changing solar irradiation. Similarly, an optimized gain conventional PI controller regulates the DC bus to improve the power quality, and DC link stability during dynamic conditions. The optimized DC-link generates an accurate loss component of current, which further improves the VSC capability of fundamental load current component extraction. The VSC is designed to perform multi-functional operations, i.e., harmonics elimination, reactive power compensation, load balancing and power balancing at point of common coupling during diverse dynamic conditions. The MOSHO based VSS-InC, and DC bus performance is compared to particle swarm optimization (PSO) and genetic algorithm (GA). The proposed system operates satisfactorily as per IEEE519 standards in the MATLAB simulation environment.

Path-Finder Optimization Based Control of Grid-Tied PV Hybrid Energy Storage System

This paper presents a path-finder algorithm (PFA) of meta-heuristic optimization for the performance enhancement of the bias compensated normalized maximum correntropy criteria (BCNMCC) based voltage source converter (VSC) control for a three-phase three-wire grid-tied dual-stage PV system. The DC link voltage variations during induced dynamic conditions are minimized by PFA optimized PI controller which also generates an accurate loss component of current for enhancing the VSC control performance. The BCNMCC algorithm effectively performs the system identification and echo cancellation in the presence of Gaussian noises. An accurate improves the VSC ability to accurately extract the fundamental load current component and to produce precise weight signals. The BCNMCC performs multifunctional operations, i.e., reactive power compensation, harmonics elimination, load balancing, and power balancing at point of common coupling during steady-state and various dynamic conditions, i.e., grid-islanding & re-synchronization, irradiation variation, unbalanced load and fixed power mode. The proposed system is capable of operating under grid-tied and isolated mode due to the seamless transition of a VSC control from grid current control (GCC) to voltage control. The seamless transition of VSC control does not induce any major transients at the source and on the load side of the system. The hybrid energy storage system (HESS) with a battery, fuel-cell and ultra-capacitor further improves the reliability of the PV system and the stability of the overall system during both grid-tied and isolated operations. The proposed system performs satisfactorily under steady-state and diverse dynamic states as per IEEE519 standards.

Sliding mode control of a dynamic voltage restorer based on PWM AC chopper in three-phase three-wire systems

In this paper, a control system is presented based on sliding mode control (SMC) for a three-phase three-wire dynamic voltage restorer to compensate for voltage sag and swell. This dynamic voltage restorer (DVR) system includes an AC/AC converter in each phase without energy storage and DC link. The proposed controller has advantages such as robustness against parameter variations, guaranteed stability, implementation simplicity and fast dynamic response. The second-order generalized integrator (SOGI) based phase-locked-loop (PLL) is implemented in this controller to remove the voltage harmonics. It is worth mentioning that the SOGI-PLL operates independently for each phase that the variation of voltage asymmetric can be identified. The proposed control method can compensate the power quality problems such as voltage sag, swell, under voltage, and overvoltage at balanced and unbalanced conditions. The performance of the proposed method has been evaluated by simulations and experimental results.

Adaptive Control Scheme for Grid Tied SPV System with DSTATCOM Capabilities: Review

This study provides an adaptive control approach of VSC (voltage source converter) coupled with SPV (solar photovoltaic array), in a 3P3W (three-phase three-wire) system with three single-phase non-linear loads having Distributed Static Compensator (DSTATCOM) abilities using P and O (perturb & observe) methodology. The adaptive control technique converges quickly and has a low mean square error. For the correction of power factor and zero voltage regulation modes, the system is studied and simulated. The system’s great efficacy at high voltages is due to its one-stage structure. Grid current harmonics are significantly below the IEEE-519 norm. The suggested system is modeled and simulated with the available sim power system toolbox in MATLAB/Simulink, and the system’s behavior under different loads and environmental circumstances is confirmed.

Constrained optimised flexible power control for grid‐connected converters under unbalanced faults

This paper presents a constrained multi-objective optimisation scheme for a grid-connected voltage source converter operating under unbalanced voltage conditions in a three-phase three-wire system. The scheme is aimed at evaluating the converter reference currents required to supply all the power generated by the connected source to the grid, whilst simultaneously suppressing oscillations of both real and reactive powers. The trade-off between these two conflicting requirements is achieved by setting a single cost function with variable weightings. Two constraints are set to restrict the converter instantaneous phase current and maintain low DC-bus voltage percentage ripple. A genetic algorithm is applied to search for the optimal solution. Simulation results are presented and confirm the effectiveness of the proposed method.

A Novel Switched-Capacitor Inverter with Reduced Capacitance and Balanced Neutral-Point Voltage

A novel three-phase switched-capacitor multilevel inverter (SCMLI) with reduced capacitance and balanced neutral-point voltage is proposed in this paper. Applying only one DC source, the three-phase seven-level topology possessing voltage-boosting capability is accomplished without the high-voltage stress of power switches. Owing to the inherent redundant switching states of the proposed topology, two charging approaches that can effectively limit the voltage ripples and path selection for capacitors can be realized. This provides the presented topology with reduced capacitance, balanced neutral-point voltage, good performance in not only the three-phase four-wire system but also the three-phase three-wire system, and low total harmonic distortion (THD) of the output voltage. A comprehensive comparison with previous SCMLIs in various aspects is conducted to validate the merits mentioned above. The simulation results accord with theoretical analyses, confirming the feasibility of the proposed three-phase SCMLI.

Impedance Modeling and Stability Analysis of Three-Phase Four-Leg Grid-Connected Inverter Considering Zero-Sequence

With the increasing applications of grid-connected voltage source converters, it is important to analyze the impedance characteristic of the grid-connected system to implement the stability analysis of the grid connection operation. Compared with the three-phase three-wire system, an additional zero-sequence path exists in the three-phase four-wire system. Therefore, it is necessary to consider the influence of the zero sequence when analyzing the stability of the system. In this paper, an impedance model including positive-sequence, negative-sequence and zero-sequence impedance of the three-phase four-leg grid-connected inverter is established. Through impedance characteristic analysis, the relationships between zero-sequence impedance and positive-sequence, negative-sequence impedance can be found which are decupled. Based on the developed zero-sequence impedance model, the main factors affecting the zero-sequence impedance model are revealed. Then, the system stability consisting of the grid and three-phase four-wire inverter is investigated, and the experimental results validate the theoretical analysis.

CPT-Based Multi-Objective Strategy for Power Quality Enhancement in Three-Phase Three-Wire Systems Under Distorted and Unbalanced Voltage Conditions

This paper explores the application of multifunctional inverters connected to the electrical network, to propose an adaptable system to individually control reactive power, load imbalance, and harmonic currents. Based on Conservative Power Theory (CPT), the dynamic compensation of Power Quality (PQ) indices is carried out under different conditions of demand and energy generation. First, a set of global factors for reactive power, imbalances, and current harmonics is introduced, which are effective even for bidirectional power flows in systems with harmonic voltage distortion and/or voltage unbalance. This set of factors gives rise to a multiobjective decision-making algorithm to estimate coefficients of proportionality, which instantly considers the reference signals linked to the disturbances, enabling to individually keep track of the target values of each of the PQ indices, as customarily established through standards or electricity utility criteria. As a result, this proposed approach allows a multiobjective operation of the inverter connected to the network, thereby allowing maximum use of energy generated, as well as limiting energy losses of distribution networks, and enhancement of the PQ of a prosumer. Finally, to illustrate the effectiveness of the proposed approach, different case studies were simulated with this set of case studies, including one representative real case containing a PV system connected to the network and a non-linear unbalanced load with variable demand.

Voltage Source Inverter Filter with Improved Proportional Gain for Dynamic Power and Melodies Mitigation in Three-Phase Three-Wire Distribution Systems

Voltage Source Inverter Filter with Improved Proportional Gain for Dynamic Power and Melodies Mitigation in Three-Phase Three-Wire Distribution Systems

Potential for Increased Rural Electrification Rate in Sub-Saharan Africa using SWER Power Distribution Networks

Rural electrification rate (RER) in Africa is still low to date. Several countries in Sub-Saharan Africa have tried to address this problem using conventional single- phase two-wire or three-phase three-wire systems, however at large costs due to the nature of dispersed rural load centres, low load demand, and low population density. Another solution of off-grid generation creates associated health problems. Therefore, this paper undertakes a review of a single wire earth return (SWER) network as a RER improvement solution. The paper undertakes intensive literature review to elucidate challenges and solutions to the implementation of SWER technology. Advantages of SWER technology discussed make it the choice for RER improvement in Sub-Saharan African countries. After that, a case study is selected in rural Tanzania, and a preliminary SWER network design is undertaken.