Three-wire Distribution 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.

Field Programmable Gate Array-Based Execution on a Distributed Energy Resource Supported Electrical Distribution System for Enhanced Power Quality with Optimal Active Power Flow Control

This paper explains the experimental study of a distributed energy resource (DER) integrated three-phase, three-wire electrical distribution system (EDS) under power quality (PQ) and optimal active power flow control (OAPFC). In this research, a back-to-back connected two-level VSI (BTB-TVSI) based distribution static compensator (DSTATCOM) for unbalanced non-linear load is designed. The aim is to provide better OAPFC in EDS with shunt compensation to maintain a round-the-clock quality power supply for end users. The improved neural network-based adaptive least mean square (ALMS) control algorithms are employed for DSTATCOM. The ALMS control strategy is realized using the SPARTAN-6 field programmable gate array (FPGA) evaluation kit. This research involves the comparative study of a two-level voltage source inverter (VSI) and a BTB-TVSI in terms of their OAPFC capability and robustness in mitigating power quality (PQ) against source current disturbances, low power factor (PF), poor voltage regulation, unbalanced voltage at the point of common coupling (PCC), high switching stress, and issues in the EDS operation. The experimental results demonstrate that the BTB-TVSI using an ALMS controller is able to achieve better dynamic performance and lower total harmonic distortion (THD) under selected/permissible limits in comparison to a conventional VSI.

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).

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

Voltage Regulation using Probabilistic and Fuzzy Controlled Dynamic Voltage Restorer for Oil and Gas Industry

In a power distribution system, faults occurring can cause voltage sag that can affect critical loads connected in the power network which can cause serious effects in the oil and gas industry. The objective of this paper is to design and implement an efficient and economical dynamic voltage restorer (DVR) to compensate for voltage sag conditions in the oil and gas industry. Due to the complexity and sensitivity of loads, a short voltage sag duration can still cause severe power quality problems to the entire system. Dynamic Voltage Restorer (DVR) is a static series compensating type custom power device. The overall efficiency of the DVR largely relies on the effectiveness of the control strategy governing the switching of the inverters. It can be said that the heart of the DVR control strategy is the derivation of reference currents. This paper deals with the extraction of reference current values using a controller based on a combination of probabilistic and fuzzy set theory. The basis of the proposed controller is that Gaussian Mixture Model (GMM) which is a probabilistic approach can be translated to an additive fuzzy interface system i.e. Generalized Fuzzy Model (GFM). The proposed controller (GMM-GFM) initially optimizes the membership functions using GMM and the final output is calculated using GFM in a single iteration i.e. with no recursions. In the control scheme two control loops are used: a feed-forward loop that uses the Proportional and Integral (PI) controller and the feedback loop uses GMM-GFM based controller. The controller is implemented and respective simulations are performed in the MATLAB SIMULINK environment for three-phase, three-wire distribution system with various issues. A comparative analysis is then done amongst all the three controllers which are based on the T-S, ML, and GMM-GFM modes respectively. The simulation results of this comparison rank the DVR with the GMM-GFM controller first, followed by the fuzzy logic Mamdani model and then with the fuzzy logic T-S model.

Design and analysis of Levenberg–Marquardt‐based adaptive SOGI

This study presents the design and analysis of an adaptive second-order generalised integrator (SOGI) technique for controlling voltage source inverter in a three-phase three-wire distribution system. The function of the proposed shunt active power filter involves compensation of reactive power for power factor correction, harmonic elimination, load balancing, voltage regulation under non-linear load condition. In this study, an effective approach for load compensation is proposed by designing an adaptive SOGI trained using Levenberg–Marquardt technique and compared with conventional techniques which ensure smooth operation under normal and distorted grid condition. An experimental setup is developed and its performance is analysed during different loading conditions. The experimental results are in line with the expected simulation results. Experimental and simulation results are verified and analysed using Bode plot.

Adaptive spline‐based PLL for synchronisation and power quality improvement in distribution system

A new type of non-linear adaptive phase-locked loop (PLL) has been proposed here, which is based on spline interpolation. The study discusses the method of cubic spline, which is used to extract the fundamental voltage component, its phase angle and frequency. Test results under varying grid conditions viz. normal and distorted conditions such as the presence of harmonics, noise, phase and frequency variations etc. are presented for the developed PLL. An application of the proposed PLL to power quality improvement of grid current using shunt active power filter is further discussed here. The study demonstrates that the spline-based controller can be effectively employed as a PLL and to achieve improvement in the power quality of a three-phase, three-wire power distribution system.

High Performance of Unified Power Quality Conditioner and Battery Energy Storage Supplied by Photovoltaic Using Artificial Intelligent Controller

This paper proposes the use a of Battery Energy Storage (BES) on an Unified Power Quality Conditioner (UPQC) supplied by Photovoltaic (PV) through DC link to improve power quality on a three-phase three-wire (3P3W) distribution system. The BES serves to store the excess of power resulted by PV and to transfer it to load if necessary, preventing voltage interruption, and adjusting charging and discharging energy in battery. Power quality analysis is carried out in two conditions i.e. PV connected to DC link without and with BES. Fuzzy Logic Controller (FLC) is implemented to maintain DC voltage across the capacitor under disturbance scenarios of source and load as well as to compare the results with Proportional Intergral (PI) controller. The number of disturbance scenarios is six for each UPQC controller, so the total number of disturbances is 12. The six disturbances are: non-linear load (NL), unbalance and nonlinear load (Unba-NL), distortion supply and non-linear load (Dis-NL), sag and non-linear load (Sag-NL), swell and non-linear load (Swell-NL), and interruption and non-linear load (Inter-NL). FLC method on UPQC supplied by PV with BES is able to result in an average THD of load voltage slightly better than PI controller. In disturbance scenario 1 to 5, nominal of average THD of load voltage have met IEEE 519. FLC method on UPQC supplied by PV with BES is also capable to give average THD of source current better than PI controller. Under scenario 6 (Inter-NL), FLC is able to reduce the average THD of load voltage and source current significantly than PI controller. With the same disturbance, the combination of PV and BES is able to generate power to UPQC DC link and to inject full average compensation voltage through injection transformer on series active filter so that average load voltage remains stable. This simulations prove that the proposed artificial intelligent (AI) controller for UPQC with BES is able to improve power quality significantly under varying disturbances especially for interruption disturbance. The performance of the proposed model is validated and investigated through simulations using Matlab/Simulink.

Performance evaluation of digital filters in distribution static compensator for non‐linear loads

This study deals with the performance analysis of three digital filters viz. multiple complex coefficient filter (MCCF), moving average (MA) and Butterworth in distribution static compensator (DSTATCOM) for non-linear loads. The filters are designed to extract the fundamental component of load current and tested in the closed-loop control of DSTATCOM. The filters are used to extract fundamental signal from the non-linear distorted source/load currents and all the lower-order harmonics present in the non-linear current drawn by the load. The performance of MCCF filter is compared to conventional filters such as Butterworth and MA filter. The detailed frequency response of MCCF is analysed. The magnitude and phase response plot of the MCCF suggest that this filter has unity gain and zero phase shift at fundamental frequency. All the three filters are implemented on a DSTATCOM for three-phase, three-wire distribution system. The DSTATCOM is implemented using a three-phase voltage source converter controlled using dSPACE 1104 controller. The closed-loop operation of DSTATCOM designed using MCCF is tested under steady state and dynamic system conditions. Simulation and experimental results are demonstrated with relevant waveforms under different load conditions.

Design and Implementation of a STATCOM Based on a Multilevel FHB Converter with Delta-Connected Configuration for Unbalanced Load Compensation

A delta-connected STATCOM with cascade multilevel full H-bridge (FHB) converter has been applied for phase balancing and power factor correction of unbalanced load in a three-phase, three-wire power distribution system. In this paper, a feedforward compensation formula is presented for the STATCOM by using the symmetrical components method to compensate unbalanced load. Computer simulation is performed for preliminary verification. Accordingly, a hardware prototype employing a TMS320F2812 DSP-based system is built for final verification test. Experimental results show that the proposed STATCOM is very effective for real-time unbalanced load compensation.

A Versatile Unified Power Quality Conditioner Applied to Three-Phase Four-Wire Distribution Systems Using a Dual Control Strategy

This paper presents the study, analysis, and practical implementation of a versatile unified power quality conditioner (UPQC), which can be connected in both three-phase three-wire (3P3W) or three-phase four-wire distribution systems for performing the series–parallel power-line conditioning. Thus, even when only a 3P3W power system is available at a plant site, the UPQC is able to carry out power-line compensation for installed loads that require a neutral conductor to operate. Different from the control strategies used in the most of UPQC applications in which the controlled quantities are nonsinusoidal, this UPQC employs a dual compensation strategy such that the controlled quantities are always sinusoidal. Thereby, the series converter is controlled to act as a sinusoidal current source, whereas the parallel converter operates as a sinusoidal voltage source. Thus, because the controlled quantities are sinusoidal, it is possible to reduce the complexity of the algorithms used to calculate the compensation references. Therefore, since the voltage and current controllers are implemented into the synchronous reference frame, their control references are continuous, decreasing the steady-state errors when traditional proportional–integral controllers are employed. Static and dynamic performances, as well as the effectiveness, of the dual UPQC are evaluated by means of experimental results.

PSO and Improved BSFS Based Sequential Comprehensive Placement and Real-Time Multi-Objective Control of Delta-Connected Switched Capacitors in Unbalanced Radial MV Distribution Networks

Delta-connected switched capacitors are common in three-wire MV distribution systems as found in Europe and Australia but the majority of past studies focus on star-connected capacitors as applied in North America. This study presents a comprehensive optimization based sequential strategy and a multi-objective optimization based real-time strategy for the optimal placement and control of delta-connected switched capacitors. Considering load variations, a comprehensive optimization for capacitor placement is formulated to maximize the net annual returns from network loss reduction and capacity release. A sequential strategy based on loss sensitivity analysis is presented for efficient capacitor placement on large-scale unbalanced distribution networks. Then a capacitor control strategy is proposed to simultaneously minimize network losses, voltage deviations and voltage unbalance factor (VUF) while a weighted sum method reflects the preferences on the mutually conflicting control objectives. For the mixed integer programming (MIP) problems of capacitor placement and control, an improved backward/forward sweep (BSFS) load flow based particle swarm optimization (PSO) method is used. Finally, the robustness of the proposed capacitor placement and control strategies are verified by comparison against existing popular schemes through detailed simulations over 24 h on a real unbalanced Australian MV network.

Transferred Potential—A Hidden Killer of Many Linemen

The causes of electrical accidents which occur during maintenance of power lines are sometimes not traceable. Unfortunately, a grounding practice which has been widely adopted in the utility industry in India, U.K., and some other countries unintentionally causes so many fatal accidents every year. The conclusion was arrived after analyzing some fatal accidents. This practice of protective grounding is still continued by many distribution companies without realizing the hazards involved. For de-energized line maintenance, grounding the line at source end is commonly practiced for the purpose of personal protection. This paper explains how this safety practice turns into hazard by transferring the substation ground grid potential to the worksite and why this transferred potential cannot be controlled by any means in three-wire overhead distribution systems which run with no separated ground wire. This paper suggests the solution to avoid the transferred potential and to describe it in IEEE Std. 1048-Guide for Protective Grounding of Power Lines, IEEE Std. 80-2000-Guide for Safety in AC Substation Grounding, British Std. 7430-Code of Practice for Earthing, and Indian Std. 3043-Code of Practice for Earthing to bring an end to the accidents caused by this safety practice.

Smart Charger for Electric Vehicles With Power-Quality Compensator on Single-Phase Three-Wire Distribution Feeders

In this paper, we propose a smart charger for electric vehicles with a power-quality compensator. The proposed smart charger consists of four-leg insulated-gate bipolar transistors (IGBTs). Three legs are used for a single-phase full-bridge-based pulsewidth-modulated (PWM) rectifier, which converts power from ac to dc during the battery-charging operation or from dc to ac during the battery-discharging operation. This PWM rectifier can compensate reactive and unbalanced active currents on single-phase three-wire distribution systems because the third leg is connected to the neutral line of single-phase three-wire distribution feeders. The fourth leg is used as a bidirectional dc-dc converter for battery-charging and battery-discharging operations. The three-leg PWM rectifier uses only constant dc-capacitor voltage control, which is commonly used in active power line conditioners. Thus, the authors have developed the simplest possible control method for a single-phase power-quality compensator. The basic principle of the proposed smart charger is discussed in detail and then confirmed by digital computer simulation using PSIM software. A prototype experimental model is constructed and tested. Experimental results demonstrate that balanced source currents are obtained on the secondary side of the pole-mounted distribution transformer for battery-charging and battery-discharging operations.

Control strategies for harmonic mitigation and power factor correction using shunt active filter under various source voltage conditions

This paper gives a new insight into the concept of load compensation using shunt active filter (SAF) under ideal and non-ideal source voltage conditions. A novel approach based on an improved instantaneous active and reactive current component method is proposed. The performance of the proposed control strategy has been compared with instantaneous reactive power theory, symmetrical component theory and dq theory. SAF has been realized by three-phase voltage source converter. Reference currents generated by control strategies has been tracked by a SAF in a hysteresis band control scheme. The performance of the proposed scheme is evaluated in terms of reactive power compensation, reduction in magnitude of source currents, compensator currents, and harmonic compensation as per IEEE-519 standard. To ascertain the viability of the proposed control algorithm, the performance is evaluated under different source voltage conditions with the IEEE Standard-1459 power definitions. Variation in magnitude as well as harmonic content of source voltage has been considered. Under balanced sinusoidal source voltage condition, all control strategies congregate to similar results. Under unbalanced sinusoidal source voltage condition, dq theory and proposed theory have shown similar performance. However, under distorted source voltage conditions, an improved instantaneous active and reactive current component theory presents superior performance. A three-phase, three-wire distribution system supplying non-linear load is considered for simulation study. Simulation results from a complete model of SAF are presented to validate and compare the control strategies.

Load compensation using DSTATCOM in three-phase, three-wire distribution system under various source voltage and delta connected load conditions

This paper deals with a Distribution STATic COMpensator (DSTATCOM) for balancing of source currents, power factor correction and harmonic mitigation in three-phase, three-wire distribution system supplying delta connected load under various source voltage conditions. The control strategy applied to the DSTATCOM play a major role in its performance. A novel approach based on an improved instantaneous active and reactive current component (IARCC) theory is proposed for generation of three-phase reference currents for DSTATCOM. A three-phase voltage source converter with a dc bus capacitor is employed as DSTACOM which will track the reference currents in a hysteresis band scheme. The performance of DSTATCOM is evaluated under sinusoidal, unbalanced sinusoidal and unbalanced distorted source voltage conditions. Variation in load current, variation in magnitude and harmonic content in source voltage has been considered. Delta connected linear as well as non-linear load conditions have been considered. The performance of the DSTATCOM using the proposed control strategy is demonstrated using simulation results in MATLAB/SIMULINK software. Simulation results demonstrate the feasibility of proposed scheme for the control of DSTACOM.

A Constant DC-Capacitor Voltage Control Based Strategy for Current Balancer in Single-Phase Three-Wire Distribution Systems

This paper proposes a constant dc-capacitor voltage control based strategy for a current balancer in single-phase three-wire distribution systems. The proposed control strategy only uses the constant dc-capacitor voltage control block commonly used in active power conditioners to calculate the compensation current. No calculation blocks to obtain the reactive and unbalanced-active components are necessary. Thus, we provide the simplest possible control strategy for the current balancer. The basic principle of the proposed control method is discussed in detail then its validity is confirmed by digital computer simulation using PSIM software. A prototype experimental model is constructed and tested. Experimental results demonstrate that balanced source currents with a power factor of unity are obtained on the secondary side of a pole-mounted distribution transformer while retaining unbalanced load current conditions with a lagging power factor.

A novel approach of reference current generation for power quality improvement in three-phase, three-wire distribution system using DSTATCOM

This paper presents a novel approach based on an improved instantaneous active and reactive current component theory for generating reference currents for distribution static compensator (DSTATCOM). Three-phase reference current waveforms generated by proposed scheme are tracked by the three-phase voltage source converter in a hysteresis band control scheme. The performance of the DSTATCOM using the proposed control strategy has been evaluated under various source and load conditions. The performance of the proposed control strategy has been evaluated in terms of load balancing, reactive power compensation, compensator rating and harmonic mitigation. A three-phase, three-wire distribution system supplying star connected linear as well as non-linear unbalanced load is considered for simulation study. The detailed simulation results using MATLAB/SIMULINK software are presented to support the feasibility of proposed control strategy.

直流電圧平衡化回路を有するハーフブリッジインバータを用いた単相三線式配電用電流バランサ

This paper proposes a new topology for a current balancer with half-bridge inverters in single-phase three-wire distribution systems. Two half-bridge inverters are connected to the sources. The midpoint of the two capacitors on the DC-side is connected to a neutral line. The two half-bridge inverters function as a current balancer for single-phase three-wire distribution systems by exchanging the active and reactive power on each feeder through the two DC capacitors. The third leg functions as a DC-capacitor-voltage balancer for two DC capacitors connected to the half-bridge inverters. Thus, balanced source voltages and currents are obtained on the secondary side on the pole- mounted distribution transformer with balanced DC-capacitor voltages. The basic principle of the proposed current balancer is discussed in detail, and then confirmed by digital computer simulation using PSIM software. A prototype experimental model is constructed and tested. Experimental results show that balanced source voltages and currents are obtained on the secondary side on the pole-mounted distribution transformer with balanced DC-capacitor voltages. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 180(4): 38–46, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22277

A Constant DC Voltage Control Based Strategy for the Current Balancer in Single-Phase Three-Wire Secondary Distribution Systems

This paper deals with applying the constant dc voltage control based algorithm to the current balancer in single-phase three-wire secondary distribution systems. The power flows into a three-leg inverter, which performs the current balancer, are discussed, and then we show that only the reactive power flows into the three-leg inverter. This demonstrates that the required-capacity of the dc capacitor can be reduced as compared to that of the active power quality compensator used in the electrified railways. This reduced-capacity dc capacitor results in the rapid and stable balancing. The basic principle of the proposed method is discussed in detail, and then confirmed by digital computer simulation. Digital computer simulation results demonstrate that the balanced source currents with unity power factor are obtained remaining the unbalanced load currents conditions.