Three-phase Power Distribution System Research Articles

Application of Deep Learning Gated Recurrent Unit in Hybrid Shunt Active Power Filter for Power Quality Enhancement

This research work aims at providing power quality improvement for the nonlinear load to improve the system performance indices by eliminating maximum total harmonic distortion (THD) and reducing neutral wire current. The idea is to integrate a shunt hybrid active power filter (SHAPF) with the system using machine learning control techniques. The system proposed has been evaluated under an artificial neural network (ANN), gated recurrent unit, and long short-term memory for the optimization of the SHAPF. The method is based on the detection of harmonic presence in the power system by testing and comparison of traditional pq0 theory and deep learning neural networks. The results obtained through the proposed methodology meet all the suggested international standards of THD. The results also satisfy the current removal from the neutral wire and deal efficiently with minor DC voltage variations occurring in the voltage-regulating current. The proposed algorithms have been evaluated on the performance indices of accuracy and computational complexities, which show effective results in terms of 99% accuracy and computational complexities. deep learning-based findings are compared based on their root-mean-square error (RMSE) and loss function. The proposed system can be applied for domestic and industrial load conditions in a four-wire three-phase power distribution system for harmonic mitigation.

Estimate Three-Phase Distribution Line Parameters With Physics-Informed Graphical Learning Method

Accurate estimates of network parameters are essential for modeling, monitoring, and control in power distribution systems. In this paper, we develop a physics-informed graphical learning algorithm to estimate network parameters of three-phase power distribution systems. Our proposed algorithm uses only readily available smart meter data to estimate the three-phase series resistance and reactance of the primary distribution line segments. We first develop a parametric physics-based model to replace the black-box deep neural networks in the conventional graphical neural network (GNN). Then we derive the gradient of the loss function with respect to the network parameters and use stochastic gradient descent (SGD) to estimate the physical parameters. Prior knowledge of network parameters is also considered to further improve the accuracy of estimation. Comprehensive numerical study results show that our proposed algorithm yields high accuracy and outperforms existing methods.

A Distributed Optimization Model for Mitigating Three-phase Power Imbalance with Electric Vehicles and Grid Battery

Three-phase power imbalances may occur in the distribution network due to high electric vehicle (EV) charging demand. The imbalances become severe with the increasing number of EVs in the future and may be addressed with coordinated charging strategies. In this paper, we propose a phase-balancing and peak-shaving scheme for a community in the three-phase power distribution system by managing the charging and discharging strategies for EVs and grid battery energy storage systems (BESS). The proposed scheme includes energy transactions and distributed optimization models. In the transaction model, vehicle-to-vehicle (V2V) energy trading is considered. In the optimization model, the distribution system operator (DSO) optimizes the energy management strategy of the grid BESS while the EV owners optimize their charging strategies. Financial incentives are introduced to encourage the EV owners to assist the distribution system operator in reducing the phase imbalance. Simulation results show that the proposed scheme could mitigate the phase imbalance and reduce the difference between peak and valley load of the load curves in the three-phase distribution system. Both EV owners and the distribution system benefit financially. Moreover, the power quality and system reliability of the distribution network can also be improved.

Three-Phase Unbalance Improvement for Distribution Systems Based on the Particle Swarm Current Injection Algorithm

The aim of this study is to improve the three-phase unbalanced voltage at the secondary side of a distribution transformer. The proposed method involves compensation sources injecting three different single-phase currents into the connected point of a grid. The computations of optimal single-phase currents are performed using the circuit analysis method and particle swarm optimization algorithm. An unbalanced three-phase power distribution system model is constructed, including a transformer Δ–Δ connection, V–V connection, load balance, load unbalance combination, and three single-phase compensation current sources. The results show that the voltage unbalance rate of the electricity user side is improved to less than 1%, and the three-phase total compensation apparent power is approximately 0 VA. In the future, the application of the model as an auxiliary service could be achieved by adding an energy storage system.

Design and simulation of dynamic voltage restorer (DVR) for power quality improvement

Power quality (PQ) is one of the main issues faced in the present era. The PQ issues such as voltage sags, swells, harmonics, and unbalance as well as the impact on sensitive loads are often occurred in any power distribution system. To tackle the issues, a powerful dynamic voltage restorer (DVR) is commonly installed. However, the existing control algorithms for DVR are found to be complex, potentially increases computational burden to the controller. Therefore, in this paper, a new simplified control algorithm which utilizes the strengths of synchronous rotating frame (SRF) and phase-locked loop (PLL) concepts, is proposed to better manage operation of DVR. The DVR system is modelled and simulated by using MATLAB/Simulink platform. Performance of the newly proposed algorithm for DVR is tested in three-phase system with voltage sags, swells, harmonics and unbalances conditions. From the findings, it can be concluded that the proposed algorithm for DVR which installed in a three-phase power distribution system effectively mitigated the voltage sags, swells and unbalances conditions and, for harmonics condition, it is found to be able to minimize and contain the harmonic contents within the acceptable level.

Linear active disturbance rejection control for a dual unified power quality conditioner

In this paper, a linear active disturbance rejection control (LADRC) method is presented for a dual unified power quality conditioner (iUPQC). Compared with the traditional PI controller that requires double closed-loop control and decoupling design, the presented LADRC control method with Quasi-resonant (QR) feedforward has the benefits to simplify controller structure, and improve system steady-state, dynamic and anti-interference performance under the conditions with system uncertainty and external disturbances. By considering the unfavorable factors as control disturbances, the LADRC control method is able to obtain ideal performance through utilizing linear error state feedback (LESF) and dynamic disturbances compensation. In addition, in order to reduce DC link voltage fluctuation and eliminate double frequency ripple, a super capacitor is connected to DC link through a bidirectional DC/DC converter. By controlling the PWM signal of converter, the DC link capacitor can be charged or discharged to keep its voltage stable. Finally, the feasibility and effectiveness of this method are verified by MATLAB/SIMULINK simulation on a three-phase power distribution system.

Multi-objective Evolutionary Algorithms for Power Distribution System Optimal Reconfiguration

In this paper two reconfiguration methodologies for three-phase electric power distribution systems based on multi-objective optimization algorithms are developed in order to simultaneously optimize two objective functions, (1) power losses and (2) three-phase unbalanced voltage minimization. The proposed optimization involves only radial topology configurations which is the most common configuration in electric distribution systems. The formulation of the problem considers the radiality as a constraint, increasing the computational complexity. The Prim and Kruskal algorithms are tested to fix infeasible configurations. In distribution systems, the three-phase unbalanced voltage and power losses limit the power supply to the loads and may even cause overheating in distribution lines, transformers and other equipment. An alternative to solve this problem is through a reconfiguration process, by opening and/or closing switches altering the distribution system configuration under operation. Hence, in this work the three-phase unbalanced voltage and power losses in radial distribution systems are addressed as a multi-objective optimization problem, firstly, using a method based on weighted sum; and, secondly, implementing NSGA-II algorithm. An example of distribution system is presented to prove the effectiveness of the proposed method.

Bayesian Learning-Based Harmonic State Estimation in Distribution Systems With Smart Meter and DPMU Data

This paper studies the problem of locating harmonic sources and estimating the distribution of harmonic voltages in unbalanced three-phase power distribution systems. We develop an approach for harmonic state estimation utilizing two types of measurements from smart meters and distribution-level phasor measurement units (DPMUs). It involves regression analysis for power flow calculation, prediction of demands using recurrent neural networks, and sparse Bayesian learning for state estimation. The proposed approach requires fewer DPMUs than nodes, making it more applicable to existing distribution grids. We show the effectiveness of the proposed estimator through extensive numerical simulations on an IEEE test feeder. We also investigate how the increased penetration of distributed energy resources could affect the performance of our state estimator.

Leveraging Sparsity in Distribution Grids

Power distribution grids are sparse networks. The admittance matrix of a (radial or non-radial) power distribution grid is sparse, safety-critical events are relatively sparse at any given time compared with the number of nodes, and loads that produce significant harmonics at a specific order are also sparse. In this highlight talk, we define different types of sparsity in unbalanced three-phase power distribution systems, and explain how sparsity can be leveraged to address three increasingly important problems:

Generalised neural network‐based control algorithm for DSTATCOM in distribution systems

This study presents a new concept to control a distribution static compensator (DSTATCOM) based on generalised neural network in a three-phase power distribution system. Artificial neural network (ANN)-based controllers play the vital role in the performance improvement of DSTATCOM. However, their application is limited by the increase in complexity as well as the computational time. The proposed generalised neural network algorithm is a combination of Gaussian, sigmoidal and linear transfer functions within a layer to improve the DSTATCOM control strategy. This algorithm estimates the amplitude of the wattful and wattless current components of the load currents for harmonics elimination and reactive power compensation by the DSTATCOM. The algorithm is developed in MATLAB. The case studies validate its superiority over ANN-based control algorithms. The proposed method needs a less number of training patterns and unknown weights compared to other algorithms which reduces the complexity and the computational time. It also improves the performance of DSTATCOM estimating the weights and its learning online which is of the main merits of this algorithm. Its other inherent advantages are ease in design, robustness and its adaptivity with dynamics of load at utility end.

A Linear Three-Phase Load Flow for Power Distribution Systems

This letter proposes a linear load flow for three-phase power distribution systems. Balanced and unbalanced operation are considered as well as the ZIP models of the loads. The methodology does not require any assumption related to the $R/X$ ratio. Despite its simplicity, it is very accurate compared to the conventional back-forward sweep algorithm.

Partial Power Conversion Device Without Large Electrolytic Capacitors for Power Flow Control and Voltage Compensation

A novel partial power conversion device (PPCD) is proposed to realize power flow control and voltage compensation in a three-phase power distribution system in this paper. The PPCD circuit, which is derived from the conventional push-pull forward converter, can achieve arbitrary voltage output without any large electrolytic capacitors. Thus, the system reliability can be enhanced. Furthermore, the converter has no full-rated components, which reduces the cost. In this paper, an injection model for power flow control is derived. A minimum power transfer control strategy is proposed to minimize the power losses during the operation. A closed-loop control method employing the synchronous reference frame theory for voltage compensation is also developed to enable the precise control. The systems with PPCD are simulated by MATLAB/Simulink to verify the functions. The experiments for voltage compensation are carried out based on a 30-kW prototype, which shows the effectiveness.

An approach for the integration of renewable distributed generation in hybrid DC/AC microgrids

This paper presents an investigation of a hybrid DC/AC integration paradigm to establish microgrids (MGs) by using a conventional three-phase local power delivery system. This approach adds an additional DC power line to the local power distribution system in order to collect energy generated by distributed domestic renewable sources. The local renewable distributed generation (DG) works in conjunction with the conventional grid utility to reduce the power draw from the grid. Researchers designed an energy conversion station to mix energy from the local DGs with energy from the grid utility. This approach, therefore, uses a continuous energy mixing strategy for DC integration of local generation and grid energy to supply energy to MG consumers via the conventional three-phase power distribution system. Thus, local distributed renewable generators do not have to contend with AC integration problems, such as AC stability and line synchronization. This approach can facilitate the transformation of conventional local power distribution systems into reliable MGs in an affordable way for stakeholders and it is a step towards construction of future smart grids.

Current Distribution and Losses of Grouped Underground Cables

To fulfill installation requirements, sometimes two or more cables have to be connected in parallel in a three-phase power distribution system. The division of the current and power among the adjacent cables is governed by several factors, such as position, phase order, and the grounding method of the metal screen. This study demonstrates this effect and compares three solution methods of grouped single-core underground cables with their screens bonded at both ends. These three methods are: 1) an analytical one provided by international standards, and two 2-D finite-element approaches. One of the FE methods takes the twists of the wire screens into account.

Design of Delta Primary - Transposed zigzag Secondary (DTz) Transformer to Minimize Harmonic Currents on the Three-phase Electric Power Distribution System

The delta primary - transposed zigzag secondary (DTz) transformer has been designed and used to reduce the bad impacts of the harmonic in the distribution power system. The DTz transformer is constructed with delta connection in primary winding and the three transposed windings at the different core legs of secondary winding. The harmonic reduction method of the DTz transformer applies two basic principles. The first principle is to inhibit electromagnetic energy of the harmonic currents by cancelling the phase polarity on the secondary winding. The second is to insulate the remaining of the mmf induction from harmonic current loads and minimize to circulate in the delta windings on the primary side. The triplen harmonics currents generated on the primary and secondary winding of DTz transformer are simulated in this paper. Both balanced and unbalanced loads of the three-phase distribution system are examined. The experiment shows that the total THD current in the secondary winding when balanced loads are applied is about 70.8 %, and in the primary side is 24.3 %. While for unbalanced loads, the average THD in secondary winding is 68.44 % and in delta winding is 26.4 %. It means the DTz transformer has a filter-ability to reduce about 42 - 46 % THD for both balanced and unbalanced loads. By comparing the computer simulation results and data measurements through experiment in the laboratory, it is proved that the use of the proposed DTz transformer is one of the methods to reduce harmonic currents and inhibit them to enter to the supply system.

DSTATCOM topologies for three-phase high power applications

This paper proposes distribution static compensator topologies for application in three-phase high power distribution systems. These topologies overcome both the voltage and current rating constraints imposed by the semiconductor switches by the use of three single-phase multi-secondary transformers. Five topologies, namely, four leg-group, three leg-group split-capacitor, H bridge-group, three leg-group and two leg-group are suggested. These can effectively compensate unbalance, harmonics and low power factor of the load currents. Apart from the use of minimum number of current sensors and a single capacitor, the control circuit is very simple. It provides the electrical isolation and security deemed essential for high voltage systems. A detailed comparison is made for these topologies. Based on the hardware requirement and compensation quality, the four leg-group and three leg-group topologies are shown to be superior than the other structures for application in three phase four-wire and three-wire systems respectively. They are validated through extensive simulation studies using PSCAD in a three-phase four-wire power network with non-linear unbalanced load. Experimental verification is conducted for H bridge-group topology on a single phase system using a DSP-based prototype laboratory model.

H∞ Static Control Law for a Three-phase Shunt Active Power Filter

The aim of this work is to design a static feedback gain used to force a three-phase shunt active power filter to act as a current source capable of delivering the appropriate harmonics demanded by non-linear loads. This filter is connected in parallel to a three-phase power distribution system in order to keep the current supplied by the latter almost sinusoidal. The control design is performed using the H ∞ suboptimal control theory based on linear matrix inequalities (LMIs), with both partial and full state feedback. Numerical simulations will be presented in order to investigate the advantages of the full state feedback structure over the partial state feedback one, and to compare the performances of the corresponding H ∞ static control laws.

Steady State Analysis of Resin Molded Type Voltage-Current Sensor for Real-Time Observation of Power Factor in Power Distribution System

We have proposed the voltage-current sensor embedded in a ceramic insulator for the real-time observation of the power factor in three-phase power distribution systems and carried out the finite element analysis to investigate its characteristics and verify its feasibility. However, the ceramic sensor has problems in cost and a burning process in manufacturing to result in the deformation from the designed form. In the paper, we propose a resin molded type of voltage-current sensor with dual search coils for the current sensor part based on the finite element analysis and discuss its steady state electromagnetic behaviors theoretically and experimentally.

Monocyclic power: a novel but short-lived power distribution system

This paper provides a brief history of the monocyclic power system, which was rendered obsolete because of its technical complexity and by the development of the three-phase power distribution system. Primarily developed for the General Electric Company as a means of avoiding possible infringement of the Tesla patents, the monocyclic power system was decidedly inferior to the power transmission efficiency of the three-phase system, which eventually became universal for power delivery purposes. Nevertheless, the Steinmetz monocyclic circuit, which converts constant voltage into constant current and vice versa, remains a basic electrical circuit concept that may still have applications in various types of today's electronic circuitry.

Mini-Scale Power Distribution Network Feeding Trapezoidal-Wave Voltages to Power Electronic Loads with Diode Rectifiers

This paper proposes a novel three-phase power distribution system feeding trapezoidal voltages to various power electronic loads with diode rectifier front-ends. The network distributes trapezoidal voltages generated by synchronous superposition of wave-shaping voltages onto sinusoidal voltages available from a utility power grid. The power distribution by the trapezoidal voltages allows reducing harmonics of the line currents without electronic switching devices because of a spontaneously widened conduction period of the current waveforms. The reduction of the harmonic currents also contributes to improve total power factor at the load input terminals and efficiency of the power transmission cables. Since the diodes of the rectifiers successively commutate the trapezoidal waves during periods of their flat parts, not only total harmonic distortion of the currents is improved, but also voltage ripple across the dc-buses of the rectifiers can effectively be reduced with less filter capacitors. In addition, the system offers an uninterruptible power supply function by immediately changing its outputs from the wave-shaping voltages to the trapezoidal voltages when interruption occurs in the power grid. In this paper, a prototype of the system is experimentally examined from various angles of operating characteristics and test results are presented to prove feasibility of the proposed system.