Vinod Khadkikar

Enhancing Electric Power Quality Using UPQC: A Comprehensive Overview

This paper presents a comprehensive review on the unified power quality conditioner (UPQC) to enhance the electric power quality at distribution levels. This is intended to present a broad overview on the different possible UPQC system configurations for single-phase (two-wire) and three-phase (three-wire and four-wire) networks, different compensation approaches, and recent developments in the field. It is noticed that several researchers have used different names for the UPQC based on the unique function, task, application, or topology under consideration. Therefore, an acronymic list is developed and presented to highlight the distinguishing feature offered by a particular UPQC. In all 12 acronyms are listed, namely, UPQC-D, UPQC-DG, UPQC-I, UPQC-L, UPQC-MC, UPQC-MD, UPQC-ML, UPQC-P, UPQC-Q, UPQC-R, UPQC-S, and UPQC-VA. More than 150 papers on the topic are rigorously studied and meticulously classified to form these acronyms and are discussed in the paper.

Grid Interconnection of Renewable Energy Sources at the Distribution Level With Power-Quality Improvement Features

Renewable energy resources (RES) are being increasingly connected in distribution systems utilizing power electronic converters. This paper presents a novel control strategy for achieving maximum benefits from these grid-interfacing inverters when installed in 3-phase 4-wire distribution systems. The inverter is controlled to perform as a multi-function device by incorporating active power filter functionality. The inverter can thus be utilized as: 1) power converter to inject power generated from RES to the grid, and 2) shunt APF to compensate current unbalance, load current harmonics, load reactive power demand and load neutral current. All of these functions may be accomplished either individually or simultaneously. With such a control, the combination of grid-interfacing inverter and the 3-phase 4-wire linear/non-linear unbalanced load at point of common coupling appears as balanced linear load to the grid. This new control concept is demonstrated with extensive MATLAB/Simulink simulation studies and validated through digital signal processor-based laboratory experimental results.

A New Control Philosophy for a Unified Power Quality Conditioner (UPQC) to Coordinate Load-Reactive Power Demand Between Shunt and Series Inverters

This paper presents a novel philosophy to compensate the load-reactive power demand through a three-phase unified power quality conditioner (UPQC). Most of the UPQC-based applications show the dependency on shunt inverter for load-reactive power compensation, whereas the series inverter is always looked as controlled voltage source to handle all voltage-related problems. This paper proposes a new functionality of UPQC in which both the shunt and series APFs supply the load-reactive power demand. This feature not only helps to share the load-reactive power demand, but also helps to reduce the shunt APF rating, and hence, the overall cost of UPQC. This results in better utilization of the existing series inverter. The theory and complete mathematical analysis termed as ldquopower angle control (PAC)rdquo is presented. The simulation results based on MATLAB/Simulink are discussed in detail to support the concept developed in the paper. The proposed approach is also validated through experimental study.

Nighttime Application of PV Solar Farm as STATCOM to Regulate Grid Voltage

This letter presents a novel concept of utilizing photovoltaic (PV) solar farm (SF) as a flexible ac transmission systems controller-static synchronous compensator, to regulate the point of common coupling voltage during nighttime when the SF is not producing any active power. This concept, although general, is presented for the scenario of a distribution feeder, which has both PV solar and wind farms connected to it. The proposed control will enable increased connections of renewable energy sources in the grid. A MATLAB/Simulink-based simulation study is presented under variable wind power generation and fault condition to validate the proposed concept.

UPQC-S: A Novel Concept of Simultaneous Voltage Sag/Swell and Load Reactive Power Compensations Utilizing Series Inverter of UPQC

This paper introduces a new concept of optimal utilization of a unified power quality conditioner (UPQC). The series inverter of UPQC is controlled to perform simultaneous 1) voltage sag/swell compensation and 2) load reactive power sharing with the shunt inverter. The active power control approach is used to compensate voltage sag/swell and is integrated with theory of power angle control (PAC) of UPQC to coordinate the load reactive power between the two inverters. Since the series inverter simultaneously delivers active and reactive powers, this concept is named as UPQC-S (S for complex power). A detailed mathematical analysis, to extend the PAC approach for UPQC-S, is presented in this paper. MATLAB/SIMULINK-based simulation results are discussed to support the developed concept. Finally, the proposed concept is validated with a digital signal processor-based experimental study.

Two Degrees of Freedom Active Damping Technique for

In grid connected photovoltaic (PV) systems, lowpass filters are utilized to reduce injected current harmonics. LCL filters have recently drawn attention for PV system grid interfaces due to their small size and they have shown better attenuation to switching harmonics than simple L filters. However, the LCL filter causes resonance resulting in oscillation and instability issues. This paper proposes an effective active damping technique by introducing a two-degree-of-freedom (2DOF) PID control structure. The 2DOF control structure allows the independent action of PI and D terms giving two degrees of freedom. The design is based on a typical three-phase grid-tied PV system. The active damping control loop is formed by using the existing grid side inductor currents and thus eliminating the need of additional sensors. The relative stability is illustrated in frequency domain by using bode plots. A real-time hardware-in-loop study is performed to validate the performance of the proposed 2DOF technique to damp out the LCL filter resonance.

LCL

Summary form only given: Planning distribution systems without considering the operation status of multiple Distributed Generation (DG) units could result in constraining the network, lowering the utilization of its assets and minimizing the total DG capacity that can be accommodated. In this paper, the impact of multiple DG configurations on the potential of Active Network Management (ANM) schemes is firstly investigated. Secondly, the paper proposes a multi-configuration multi-period optimal power flow (OPF)-based technique (MMOPF) for assessing the maximum DG capacity under ANM schemes considering 1) variability of demand and generation profiles (multi-period scenarios), and 2) different operational status of DG units (multi-configurations). The results show that the availability of DGs at certain locations could critically impact the amount of DG capacity at other locations. If DGs are properly allocated and sized at certain locations up to the optimal limits, even with a “fit-and-forget” approach, the total connected DG capacity can be maximized, with minimum utilization of ANM schemes. However, exceeding these optimal limits may lead to minimizing the total DG penetration in the long term, impacting the system reliability due to the operational status of multiple DG units, and consequently, imposing more investments on ANM schemes to increase the amount of connected DG capacity.

Filter-Based Grid Connected PV Systems

Photovoltaic modules have a single operating point where the output of the voltage and current results in the maximum power output. In most photovoltaic power systems, a particular control algorithm, namely, maximum power point tracking (MPPT) is utilized to take full advantage of the available solar energy. The operation of maximum power point tracking is to adjust the power interfaces so that the operating characteristics of the load and the photovoltaic array match at the maximum power points. This study reviews the latest techniques and provides background knowledge about the recent development in MPPT techniques. The paper can be used as a reference for future research related to optimizing the solar power generation.

Planning Active Distribution Networks Considering Multi-DG Configurations

For photovoltaic applications, the interleaved flyback module-integrated converters (MICs) (IFMICs) operating in continuous conduction mode (CCM) show the advantages of high power density, low voltage and current stresses, and low electromagnetic interference but demonstrate a difficult control problem compared to the discontinuous conduction mode. This paper concentrates on the control issues and presents detailed modeling, in-depth dynamic analysis, and a two-step controller design approach for IFMIC systems operating in CCM. The proposed modeling approach is based on the fourth-order system considering the dynamics of the output CL filter. This realistic fourth-order system modeling shows the presence of a resonant peak at a certain frequency, which can cause phase loss and constraints of system bandwidth. A decoupled two-step controller design approach is thus proposed to simplify the modeling and control synthesis in the IFMIC development. The decoupled controller consists of a proportional-integral controller (based on the simplified model), followed by a lag term for mitigating the effect of the resonant peak. A 200-W digitally controlled MIC prototype is constructed for evaluation purposes. The simulation and experimental results verify the effectiveness of the proposed modeling and control approaches.

Overview of maximum power point tracking technologies for photovoltaic power systems

The application of active power conditioners to tackle power quality problems has become a matured subject. This paper is based on a unified approach for load and source compensation using unified power quality conditioner (UPQC). Performance of this UPQC has been evaluated with a typical industrial load with realistic parameters supplied by a polluted distribution network. The system performance for current harmonics, voltage harmonics, voltage sag and voltage swell has been evaluated. The MATLAB / Simulink based simulations are provided which support the functionality of the UPQC