A Critical Evaluation Of Power-Quality Features In Multi-Feeder Power Distribution Network Using MF-UPQC Device

A Critical Evaluation Of Power-Quality Features

In Multi-Feeder Power Distribution Network Using

MF-UPQC Device

Abstract: At present, unique load demand characteristics are achieved by maintaining appropriate voltage and current perfections at common coupling point of power distribution network. This network faces critical power-quality concerns due to usage of massive non-linear power-electronic loads and sudden interruptions, voltage unbalancing, short-circuit fault, so on. Over the several mitigation schemes, a Multi-Functional Unified Power-Quality Compensator is integrated in multi-feeder distribution network for power-quality enrichment. In this work, a multi-functional UPQC is used to mitigate all current/voltage related PQ concerns and also provides load-sharing between the multi-feeders, maximizing the stable energy demand to reduce the power shortages by using reliable control methodology. The design of reliable control method is inevitable due to more transformations, mathematical functions, and low computational delays for feasible operation of MF-UPQC device. To alleviate the above-mentioned issues, a novel universal controller has been proposed for feasible operation of MF-UPQC. A critical evaluation of proposed universal controller fed MF-UPQC is verified by using Matlab/Simulink tool; Simulink results are illustrated with enhanced features.

Index Terms: Harmonic Elimination, Multi-Feeder Distribution System, Multi-Functional UPQC, Power-Quality Enrichment, Short-Circuit Fault, Voltage Interruptions, Voltage Unbalancing.

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1 INTRODUCTION

Now-a-days, the electric power system demoralizes the medium and small-scale industrial sectors among large-scale industries which lead to unstable power demand, partial interruptions, power-shortages, low quality power, scheduled block-outs, and so on [1]. To alleviate these concerns, multi-feeder distribution system is installed in power distribution system which conducts the energy sharing between near-by feeders [2]. But, the multi-feeder system is faced serious Power-Quality (PQ) concerns, at present these are regular issues in distribution system, realization of PQ is increased by consumer level. The PQ is mainly intensified basically on two factors like performance and reliability, subjected to voltage/current quality, supply/consume quality. In ideal manner, PQ is defined as, ―electric power with ideal sinusoidal constant voltage wave-shape with fundamental frequency‖, various economic-technical impacts relies on well-recognized voltage/current imperfections at Common-Coupling Point (PCC) level. The massive power-electronic loads like switch-mode converters, adjustable speed drives generates the current harmonics which affects the loads integrated near to PCC level of distribution networks. As well as, various utility side concerns accumulates on voltage related PQ issues such as voltage harmonics, voltage unbalancing, voltage interruptions, short circuit faults, voltage sag-swell, so on [3], [4]. In past, various passive elements are used but it has limited mitigation characteristics clearly explored in [5], an affective active-mitigation scheme is pre-requisite to attain

enriched PQ features. At current situation, emerging mitigation objectives are explored as Custom-Power Technologies (CPTs) contributes the unique results related to enrich PQ features. These CPTs employs power-converters for PQ enrichment as well as, provides continuity power, reliable operation, and so on. The well-organized element in CPTs utilizes the Voltage-Source Inverters (VSIs) are active device integrated as single or more as back-to-back manner [6]-[8]. The Unified Power-Quality Compensator (UPQC) is best suited for regulating both voltage/current related PQ concerns. It consists of dual-VSIs integrated as shunt/series combination near to PCC side of 3-wire three-phase distribution system controlled by reference voltage/current sequences. But, UPQC is insignificant in multi-feeder network, a relative choice of multi-feeder CPTs has been proposed for mitigating PQ concerns in main and adjacent multi-feeder networks. The relative selection of multi-feeder CPTs requires multiple-VSI modules interconnect as series-series, shunt-series, and series-shunt in between the multi-feeders via common DC-link source. In recent, several MF-CPTs are reviewed such as IDVR [9], IPFC [10], IUPQC [11], so forth for providing significant PQ features. Based on various reviews, the MF-UPQC is constituted for mitigation of all voltage-current related PQ issues in main and adjacent feeders and satisfies additional functions like load-sharing between feeders, maintain stable operations, and regulate sudden interruptions, so on.

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 N. Srinivasa Rao, Research Scholar, Department of Electrical & Electronics Engineering, Acharaya Nagarjuna University, Guntur, Andhra Pradesh, India. E-mail: [email protected]  P. V. Ramana Rao, Professor & HOD, Department of Electrical &

Fig.1 Schematic Diagram of Proposed MF-UPQC Device

The proposed MF-UPQC device pre-requisites well-recognized control method to attain effective performance to regulate power system dynamics in multi-feeder distribution network. Several control methods are explored from various literatures, Instantaneous Real-Reactive Power (IRP) theory, [12], Synchronous Reference-Frame (SRF) theory [13], Symmetrical Power Component (SPC) theory [14], so forth. In spite of that, these methods are inevitable due to presence of harmonic or high frequencies in reference current, complex transformations, more mathematical functions and high computational delay. In this work, a novel universal controller has been proposed for feasible operation of both multiple shunt-series VSIs of MF-UPQC. A critical evaluation of proposed universal controller fed MF-UPQC is verified by using Matlab/Simulink tool; Simulink results are illustrated with enhanced features.

2

PROPOSED

MULTI-FUNCTIONAL

UPQC

DEVICE

The proposed MF-UPQC device comprises of three-VSI modules employed as VSI-1 integrated as shunt for mitigating all current-related PQ concerns in feeder-2 and VSI-2 and VSI-3 are connected in between two feeders as series-series

Fig.2 Schematic Diagram of Proposed Universal Control Methodology for PQ Enhancement in Multi-Feeder Distribution Network Using MF-UPQC Device

3 PROPOSED

UNIVERSAL

CONTROL

METHOD

FOR

BOTH

SHUNT-SERIES

VSIS

OF

MF-UPQC

DEVICE

Generally, control method of MF-UPQC device plays significant role in compensation strategy for generation of reference voltage/current sequences through sensing elements. Harmonic distortions are sensed by harmonic analyzer and Potential Transformer (PTs) has been used for sensing voltage-related issues for sending required information to shunt-series VSIs of MF-UPQC. Based on sensor outcomes, respective control method generates the feasible switching pattern to respective VSIs of MF-UPQC through gate-pulse generation circuit. The main importance of controllers is providing respective information to compensator as well as regulating power-loss and maintains constant DC-link voltage at common DC-DC-link source. Various control methods are mainly functioning by transformation processes which require many calculations, mathematical functions and high computational delays, also inevitable due to presence of harmonic or high frequencies in reference current. To alleviate above-mentioned issues, a novel universal controller has been proposed for feasible operation of both shunt-series VSIs of MF-UPQC device in multi-feeder distribution system. The proposed universal control method is administered based on formation of unit vector analysis. These are developed in pre-synchronization mode angle (θ) by using discrete phase-locked loop from balanced RL-load voltage sequence. These load voltage is sensed from PTs, then deliver to unit-value vector which generates the unit values in simple notations as described in Eqn. (1), Eqn. (2), The three-phase balanced RL-load voltage is represented as below,

𝑉 = 𝑉 𝑠𝑖𝑛 (𝜃 − 2𝜋 3⁄ )

𝑉 = 𝑉 𝑠𝑖𝑛 (𝜃 + 2𝜋 3⁄ ) (1)

The unit-vector value is described as below

𝑉 = { (𝑉 + 𝑉 + 𝑉 )} ⁄

(2) The unit-vector voltages are extracted as in-phase sequences as represented in below Eqn. (3),

𝑈𝑉 = 𝑉

𝑉 = 𝑠𝑖𝑛𝜃 𝑈𝑉 =

𝑉

𝑉 = 𝑠𝑖𝑛 (𝜃 − 2𝜋 3⁄ ) 𝑈𝑉 =

= 𝑠𝑖𝑛 (𝜃 + 2𝜋 3⁄ ) (3) The extracted unit phase values (𝑈𝑉 ) are multiplied by a

reference voltage value (𝑉 ) for generation of feasible

reference voltages (𝑉 ) to series VSIs of MF-UPQC device

as described in below Eqn. (4),

𝑉 = 𝑈𝑉 𝑉 𝑉 = 𝑈𝑉 𝑉

𝑉 = 𝑈𝑉 𝑉 (4)

The extracted unit phase values (𝑈𝑉 ) are multiplied by a

reference current (𝐼 ) value from DC-link control loop for

generation of feasible reference currents (𝐼 ) to shunt

VSIs of Mf-UPQC device as described in below Eqn. (5),

𝐼 = 𝑈𝑉 𝐼 𝐼 = 𝑈𝑉 𝐼

𝐼 = 𝑈𝑉 𝐼 (5)

The reference current value (𝐼 ) is received from DC-link

to Sinusoidal Pulse-Width Modulation (S-PWM) for generation of feasible switching states to series VSIs of MF-UPQC. As well as reference current (𝐼 ) signals from universal

controller (𝐼 ) is compared to actual line currents for

generation of feasible switching states to shunt VSIs of MF-UPQC by using Hysteresis Current Control Loop (HCCL). These loops defines the regulation of compensation current through pre-defined upper and/or lower limitations and the compensation current is sequentially swinging inside these hysteresis loop followed by reference current signals generated by universal control method. The schematic diagram of proposed universal control method of MF-UPQC is depicted in Fig.2.

4 RESULTS

&

DISCUSSION

The critical evaluation of MF-UPQC is verified under several concerns for validating the achievement of enhanced PQ features by using Matlab/Simulink platform, simulation results are presented. As coming to individual feeders, the Feeder-1 is proliferated due to short-circuit LLLG fault, voltage unbalancing, voltage interruptions and these issues has been mitigated by using series VSIs of MF-UPQC device. The Feeder-2 is proliferated due to harmonic distortions in current/voltage, power-factor correction, reactive power regulation, voltage sag-swell, voltage interruptions. Both voltage-current related PQ concerns in Feeder-2 have been counteracted by shunt-series VSIs of MF-UPQC device with proposed universal control methodology. The system specifications of proposed MF-UPQC are considered from various review papers for PQ enrichment illustrated in Table.1.

Table.1 System Specifications of Multi-Feeder System

S. No

Parameters Values

Feeder-1 Feeder-2 1 Main Line Voltage

(Vrms)

Vs1- Vs2-415V, 50Hz

2 Main Line

Impedance

Rs=0.15Ω, Ls-0.9mH

3

Load Ratings

Sensitive Linear Load

RL=30 Ω, LL-20 mH

Non-Linear Critical Load VLrms=415V, 50Hz,

PLoad=10KW, QLoad=5KVar

4 Line Interfacing Transformer

((1:1-Linear Type)

Linear Model, 5KVA, 415V, 50Hz, 10% Leakage Reactance

Fig.3 Performance Evaluation of Shunt-VSI in Feeder-2 using

MF-UPQC driven by Proposed Universal Controller

(a)THD Spectrum of Non-Linear Load Current

(c) Source Voltage & Current In-Phase Condition

Fig.4 Harmonic Spectrum Analysis and In-Phase Condition of

Source Voltage & Current Represented as Source Power-Factor

The performance evaluation of shunt-VSI in Feeder-2 by using MF-UPQC driven by proposed universal controller under current harmonics coming from non-linear load is depicted in Fig.3. This multi-feeder is powered by three-phase balanced 415V, 50Hz driving the non-linear DBR fed RL-load. Due to this critical NL-DBR load, the PCC/source currents are distorted from sinusoidal creates harmonized shape, which produces more current flow towards the loads connected near to PCC attains a high heat loss which damages the entire distribution network. The presence of current harmonics in PCC/source currents are counteracted by adopting shunt-VSI of MF-UPQC based on in-phase opposition working principle. This shunt-VSI of MF-UPQC counteracts the harmonic distortions, reactive power regulation and mitigates all current-related PQ concerns which maintain the balanced sinusoidal characteristics in feeder-2. The harmonic spectrum analysis and power-factor representation at source/PCC is depicted in Fig.4. The THD spectrum analysis of Non-linear load driving DBR load is 30.05% and the source current (after mitigation) is 2.71% which is comply with IEEE-519/1992 limitations achieved by shunt-VSI of MF-UPQC. As well as, the effective shunt-VSI maintains source current is in-phase with source voltage which represents the ideal source power factor of entire feeder-2 in multi-feeder system.

Fig.5 Performance Evaluation of Series-VSI in Feeder-2 using

MF-UPQC driven by Proposed Universal Controller

(a)THD Spectrum of Source Voltage

(b)THD Spectrum of Load Voltage

Fig.6 Harmonic Spectrum Analysis of Source and Load

Voltage in Feeder-2 of Multi-Feeder Distribution System

340V to maintain balanced and constant load voltage with a value of 340V. During voltage swell in source voltage at a time period of 0.75 sec<t<0.85 sec, in this instant source voltage is slightly raised to 510V. In this period the series-VSI of MF-UPQC injects/absorbs pre-requisite load voltage as 170V to maintain balanced and constant load voltage with a value of 340V. The harmonic spectrum analysis of source and load voltages is depicted in Fig.6. The THD spectrum analysis of source voltage consisted of harmonic distortions is 20.62% and the load voltage (after mitigation) is 0.12% which is comply with IEEE-519/1992 limitations achieved by series-VSI of MF-UPQC. Similarly, all other current/voltage-related PQ issues in feeder-1 of multi-feeder distribution system are mitigated by utilizing shunt-series VSIs of MF-UPQC by using effective universal controller.

(a) Active Power of Source, Compensator, Load Parameters

(b) Reactive Power of Source, Compensator, Load Parameters

(c) Common DC-Link Voltage

Fig.7 Active & Reactive Power of Source, Compensator, Load in Feeder-2 and Common Dc-Link Voltage of Multi-Feeder Distribution System using MF-UPQC fed Universal Controller

4.2 Performance Evaluation of Series VSI of MF-UPQC in Feeder-1

Fig.8 Performance Analysis of Source and Load Voltage in

Feeder-1 of Multi-Feeder Distribution System

(a) Refernce Current of Traditional IRP Controller

(b)THD Spectrum of Reference Current of Traditional IRP Controller

(c) Refernce Current of Proposed Universal Controller

(d) THD Spectrum of Reference Current of Proposed Universal Controller

Fig.9 Performance Analysis of Traditional IRP and Proposed

Universal Controller fed MF-UPQC Device in Multi-Feeder Distribution Network

In this paper, a novel effective universal control methodology is proposed for driving the MF-UPQC in a multi-feeder distribution network under various conditions. The proposed universal controller reduces complex transformation, mathematical functions; furnish the low complex control circuitry, low computation time, so on. As well as produces a sinusoidal reference voltage-current signal which minimizes the dv/dt switches stress, switching loss and attains high efficiency features over traditional control methods. The proposed universal controller fed MF-UPQC mitigates all voltage-current related PQ concerns, active-reactive power regulation, and load sharing between feeders, regulate sudden interruptions, maintains high stability factor so on. The critical evaluation of proposed universal controller fed MF-UPQC is verified by using Matlab/Simulink platform, simulations results are presented. The harmonic spectrum of load voltage and source currents is comply within IEEE-519 limitations to achieve enriched PQ features. The further recommendations are carried on development of novel MF-UPQC device providing enhanced PQ features in multi-feeder distribution network.

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