Three-phase Four-wire Distribution Network Research Articles

Three-phase four-wire shunt hybrid active power filter model with model predictive control in imbalance distribution networks

<span lang="EN-US">This paper presents a harmonic reduction and load imbalance model in a three-phase four-wire distribution network. This model uses a hybrid active power filter, a passive inductor and capacitor filter, and an active power filter in the form of a three-phase, four-leg connected grid inverter. The switching of the voltage source converter on this filter uses finite control set model predictive control (FCS-MPC). Control of this hybrid active power filter uses model predictive control (MPC) with a cost function, comparing the reference current and prediction current with mathematical modelling of the circuit. The reference current is taken from the load current by extracting dq, and the predicted current is obtained from the iteration of the voltage source converter (VSC) switching pattern. Each combination is compared with the reference current in the cost function to get the smallest error used as a power switching signal. Modelling was validated by using MATLAB Simulink. The simulation results prove a decrease in harmonics at a balanced load from 22.16% to 4.2% and at an unbalanced load, reducing the average harmonics to 4.74%. The simulation also decreases the load current imbalance in the distribution network. Reducing the current in the neutral wire from 62.01%-0.42% and 11.29-0.3 A.</span>

Mitigation of power quality problems using voltage-controlled based modified DSTATCOM

ABSTRACT This paper proposes a modified distribution static compensator (DSTATCOM) with the voltage controller. The modified DSTATCOM is incorporated in a three-phase four-wire distribution network. The design criteria of the modified DSTATCOM parameters is introduced. The Hysteresis Voltage Controller (HVC) is used to drive the Voltage Source Converter (VSC) and its reference voltage signal is generated based on the Instantaneous Symmetrical Components Theory (ISCT) to provide the proper compensation to stabilise the system voltage, improve the power factor and mitigate the harmonic distortion. Matlab/Simulink software is used to verify the performance of the modified DSTATCOM with the used controller under different load types and supply voltage conditions. The control algorithm ensures that the bus voltage is maintained at its rated value during different connected loads and supply conditions. Also, it compensates the non-linear and unbalanced supply currents and reducing the Total Harmonic Distortion (THD) of both current and voltage. The proposed modified DSTATCOM gives better results in comparison with the conventional DSTATCOM.

Voltage violation in four‐wire distribution networks integrated with rooftop PV systems

Integration of rooftop photovoltaic (PV) systems in a three-phase four-wire distribution network cause voltage-violations namely voltage-rise and voltage unbalance. This study investigates the factors that affect both the voltage-rise and voltage unbalance in low voltage distribution network integrated with the rooftop PV systems. The concerning factors are classified into active factors such as; loads active powers, PV active powers, and bus reactive powers, and passive factors such as; numbers of feeder buses and neutral-grounded resistances. The study also determines the factors conditions at which the highest values of both voltage-rise and voltage unbalance occurred. Moreover, the most and least significant effects of individual factors on both voltage-rise and voltage unbalance are studied. The studied system is simulated and implemented in MATLAB software environment and the feeder loads are modelled based on Back–Forward Sweep method. The simulation results identify that the conditions of the worst voltage-rise and voltage unbalance cases depend on the collective influence of the studied factors.

A control scheme for voltage unbalance mitigation in distribution network with rooftop PV systems based on distributed batteries

Unbalanced loads create unacceptable voltage unbalance (VU) in low voltage (LV) three-phase four-wire distribution networks with unbalanced rooftop photovoltaic (PV) systems. This paper proposes a mitigation strategy for restricting the VU depending on the distributed batteries that included in grid interfaced rooftop PV systems. Moreover, it introduces a dynamic control model based on two PI-controllers for determining the required batteries’ compensating currents and ensuring equality resultant stress current on each bus. It overcomes three existing challenges; the inequality stresses currents on the distributed batteries along the feeder, the insufficient size or non-existing of the distributed batteries, and satisfies the same stress among batteries on the same bus. For investigating the influence of equal phase magnitude batteries’ compensating current at the same bus on the whole distribution network (DN). Particle Swarm Optimization (PSO) and Bat optimization techniques are used to determine the optimum self and mutual sharing co-efficients of each battery. The limits of the distributed batteries' size are taken into consideration in the optimization process. The proposed dynamic model is implemented using MATLAB software. The simulation results show the effectiveness of the proposed control scheme for mitigating the VU on the distribution feeder’s buses at three scenarios; different loads, PVs, and states of charge of batteries. Moreover, the batteries’ compensating currents are presented to examine the implementation feasibility.

Сomprehensive provision of standard power quality parameters in three-phase networks by the use of hybrid filter-compensating converters

In this work the conditions of the most effective use of the developed perspective means for the solution of the actual problem of complex providing of electromagnetic compatibility in modern distribution public electricity networks are considered. This is achieved by improvement of a number of voltage quality characteristics (harmonics, asymmetry and voltage fluctuations). The simulation model of a three-phase four-wire distribution network is proposed, which allows estimating voltage quality characteristics when connecting non-linear and asymmetric loads. The simulation modeling of the operation of the specified network with certain characteristics, with different values of the power of single- and three-phase nonlinear load (rectifiers) is carried out. The simulation results showed that in modern conditions, with a high concentration of electronic equipment in the distribution network, it is not enough for each separate unit of equipment to have a built-in individual means for reducing the emission of disturbances, which ensures compliance with the requirements of the European Harmonized Standards for Electromagnetic Compatibility. Therefore, in order to solve this problem in the electricity networks it is suggested for consumers to additionally apply group electromagnetic compatibility means, including hybrid filter-compensating converters that combine functional capabilities of a regulated filter balancing device which based on an autotransformer with the zig-zag connection of windings and an active parallel power filter. The analysis of simulation results of a three-phase electric network with standard characteristics of a distribution transformer allowed to determine the ratio of power of one- and three-phase nonlinear load of consumers and linear load asymmetries in network, for which a hybrid filter-compensating converter has an advantage over the known passive group means of improving the quality of voltage and allows you to provide the quality of voltage in accordance with the norms of the international standards.

New method for calculating the susceptances of a balancing capacitive compensator for a three-phase four-wire distribution network

Nowadays, there is an increasing development of equipment type Custom Power Devices (CPDs) designed to ensure a high level of electrical power quality at the Point of Common Coupling (PCC). Most of these devices are built as advanced power electronics applications, such as the Switching Power Converters (SPCs) category. However, for a wide range of applications in consumer installations and electricity distribution operators, such as power factor correction, load balancing, voltage regulation, or flicker mitigation, the reactive power compensators based on passive circuit elements, Reactive Power Compensators (RPCs) are successfully used. The most efficient RPCs are those built so that they may adapt to variable regimes, known as Static Var Compensators (SVCs). Two of the usual functions of a SVC, namely power factor improvement and load balancing in a three-phase distribution network, can be achieved simultaneously by using an unbalanced SVC built in the version of Adaptive Balancing Reactive Compensator (ABRC). The paper briefly–outlines the mathematical model and operation of a Balancing Reactive Compensator (BRC) for a three-phase four-wire network. Then, moves on to develop a direct method of sizing based on equations that directly link the susceptances’ values of the compensator with the real and imaginary components of load sequence currents. The problem is to determine the weight of these components, meaning their degree of compensation, by requiring only capacitive or null susceptances and avoiding capacitive over-compensation of positive sequence currents. Thus, a particular case of BRC, i.e. a Balancing Capacitive Compensator (BCC) is obtained, which keeps the same functions, but has the advantage of reducing costs by eliminating high-power single-phase coils and by simplifying the compensation control system. The paper also presents the numerical results and the conclusions of a case study on the application of the method, performed using two computational and modeling software tools. Experimental laboratory determinations and modeling under nonsinusoidal conditions complete the analysis. The results demonstrate the correctness of the new method of solving the sizing problem and once again validate the unbalanced capacitive compensation as an efficient method of power factor improvement and load balancing at a PCC belonging to a three-phase four-wire distribution network.

A system optimization method for mitigating three-phase imbalance in distribution network

Three-phase imbalance is a common phenomenon in three-phase four-wire distribution network systems (DNSs), which may cause power quality deterioration, increase power losses, and can even damage appliances as well. The situation is becoming even worse because of the increasing integration of the distributed generations (DGs) and storage-capable loads into DNSs. In this paper, a joint optimization model based on the Y-connected and Δ-connected static reactive power compensation devices are proposed to mitigate the three-phase imbalance and minimize the active power losses in DNSs. The model is formulated to optimize the operation of all the devices in order to mitigate the imbalance of the whole DNS rather than a single feeder or a particular area. Meanwhile, the current imbalance of the transformer and the voltage imbalance of all three-phase nodes are simultaneously considered in the model according to the practical requirements. Several linearization techniques are applied to simplify the computation and accelerate the solving speed. These techniques convert the non-linear and non-convex model into a mixed-integer linear programming model, which can be effectively solved by off-the-shelf solvers. The effectiveness and scalability of the proposed method are verified by the test results obtained from the modified IEEE 34 and IEEE 123 test systems.

Source Current Control Strategy of Active Power Filters for Unbalanced Load Compensation in Three-Phase Four-Wire Distribution Networks

Source Current Control Strategy of Active Power Filters for Unbalanced Load Compensation in Three-Phase Four-Wire Distribution Networks

Identification of lines of electric lines of three-phase distribution networks in the composition of ASMAE

The problem of protection of a three-phase four-wire distribution network (DEN) with a voltage of 0.4 kV from the interruption of electric power lines is considered. On the basis of the analysis of the values of complex resistances of interpersonal sections of the main line of the network, criteria are proposed that allow detecting critical situations associated with discontinuities in power transmission lines. Using these criteria makes it possible to localize the places of breaks of phase and neutral wires. Mathematical models and methods that are used to evaluate the complex resistances of interpersonal sections of a three-phase network are briefly considered. The obtained results are oriented for use in the automated system of electricity control and accounting (ASMAE).

Comparative analysis of voltage and current source inverter based DSTATCOM systems

This paper presents a comparative performance evaluation of voltage source inverter (VSI) as well as current source inverter (CSI) based DSTATCOM systems in terms of power quality improvement in a three-phase four-wire distribution network. Due to increasing use of high-performance semiconductor based power electronic switches, the CSI based DSTATCOM is developed as a suitable option in high power applications. However, the VSI based DSTATCOM system is the best suited for medium power applications. The VSI based DSTATCOM offers advantages over the CSI based DSTATCOM in terms of current harmonic compensation, power factor correction, lower losses (both conduction and power losses), and simplicity in both power and control circuits. The control strategies of both the DSTATCOM systems are based on conventional PI and synchronous reference frame (SRF) theory. The performance of the VSI and CSI based DSTATCOM systems is tested under unbalanced and nonlinear load conditions. Analytical expectations of complete DSTATCOM systems are veried using simulations in the MATLAB/Simulink environment.

Power flow in PME distribution systems during an open neutral condition

The open neutral condition, in distribution networks, can cause significant damage to customer installations. Due to this, the continuity of the neutral conductor is important to the power utilities. In this paper, a power flow algorithm for three-phase four-wire distribution networks with protective multiple earthing (PME), during an open neutral condition, is presented. This algorithm is based on a modified backwards-forwards technique. Additionally, the return current flow is explicitly modeled. Results from three different distribution feeders with different load unbalance and topology are presented and discussed. Furthermore, the effects of the grounding resistances, the load model (constant admittance or constant power), and the neutral breakage point (abruption point) on the voltage levels, are investigated.

Fault analysis in four-wire distribution networks

The neutral wire in most existing power flow and fault analysis software is usually merged into phase wires using Kron's reduction method. In some applications, such as fault analysis, fault location, power quality studies, safety analysis, loss analysis etc., knowledge of the neutral wire and ground currents and voltages could be of particular interest. A general short-circuit analysis algorithm for three-phase four-wire distribution networks, based on the hybrid compensation method, is presented. In this novel use of the technique, the neutral wire and assumed ground conductor are explicitly represented. A generalised fault analysis method is applied to the distribution network for conditions with and without embedded generation. Results obtained from several case studies on medium- and low-voltage test networks with unbalanced loads, for isolated and multi-grounded neutral scenarios, are presented and discussed. Simulation results show the effects of neutrals and system grounding on the operation of the distribution feeders.