Voltage Related Problems Research Articles

Proactive control to mitigate voltage violations after DER disconnection

During the last few decades, extensive research has been conducted to mitigate potential voltage-related problems that high penetration of Distributed Energy Resources (DERs) may cause. One of these problems is the voltage variation caused by the disconnection of the DERs due to their anti-islanding protection action after a temporary fault. This issue has not been deeply studied so far and it may pose severe voltage variations to distribution systems’ consumers. In this context, this paper proposes a new formulation aiming at the preventive voltage regulation strategy for step voltage regulators considering the impacts triggered by a sudden disconnection of DERs. The voltage control is accomplished by a specialized Particle Swarm Optimization that selects control actions predicting the possibility of the DERs being disconnected. Results show that voltage violations were minimized after the disconnection of DERs, keeping the nodal voltages within statutory limits.

MPC-Based Decentralized Voltage Control in Power Distribution Systems With EV and PV Coordination

Distribution systems are growing rapidly in size and complexity with increased penetrations of distributed energy resources (DER) and electric vehicles (EVs), leading to operational challenges. Reactive power compensation from photovoltaic (PV) inverters and active power curtailment of PV output are commonly used to mitigate voltage-related problems. However, the charging/discharging flexibility of EVs can be used to avoid PV output curtailment and save energy motivating methods to coordinate EV charging with PVs. Unfortunately, a large number of control variables makes the centralized voltage control computationally expensive. In this work, a decentralized voltage control algorithm which considers the active and reactive power compensation from PV inverters and EVs is presented. The proposed approach helps to solve the voltage issues in a more effective way. The approach involves clustering of the distribution network based on modified modularity, an index that considers EV flexibility and prediction time period. A model predictive control (MPC)-based algorithm is proposed for each cluster to solve the voltage problem using the respective PVs and EVs, while ensuring that the EV charging demand is satisfied while contributing to the voltage regulation. The proposed algorithm is validated using the IEEE 123 node test systems under two PV and EV penetration levels and shown to be effective in solving the voltage regulation problem.

A coordinated management scheme for power quality and load consumption improvement in smart grids based on sustainable energy exchange based model

This paper presents a contrived framework that accompanies the power quality improvement (PQI) and demand-side management (DSM) in the case of recurring voltage-related problems. The illustrative implementation of the proposed framework necessitates two antecedents. First, a comprehensive mathematical formulation of the electrical power for a dynamic voltage restorer (DVR) is presented. Second, a model is developed to analyze the energy exchange during the voltage disturbances. Afterwards, the performance of a DVR system is simulated and a scrutinization is accomplished about the effect of power exchanged by a DVR with distribution system on the load factor. Meanwhile, a modified mathematical model of demand response (DR) is developed to derive the different DR methods with the purpose of load profile improvement (LPI). The simulation results reveal that the DVR operation may decrease the load factor from +3.56% to −3.20% of the usual load factor. Furthermore, in some situations, the DR outcomes might be obliterated by PQI. The implementation of proposed framework demonstrates the load factor can be enhanced up to 7.46% by proper DR strategy adoption.

Performance Validation of PV System Incorporated ZSI-Dynamic Voltage Restorer for Long-Lasting Power Quality Improvement

Abstract A power distribution system’s main challenge is to provide consistent, reliable electricity to fulfill high demand. The incorporation of renewable energy sources into the utility grid system can be accomplished. However, renewable sources are intermittent in nature, and the loads work dynamically and cause imbalances to the system voltage within an immediate time frame. Intermittent renewable sources affect the voltage of the power grid system. Photovoltaic (PV) power generation with Z-source inverter (ZSI)–based dynamic voltage restorer (DVR) is used to avoid negative effects on the voltage. For step-up low direct current (dc) voltage to require alternating current voltage for the compensation of the voltage disturbance, ZSI with an energy storage impedance network is used. dc-dc converters connect the PV cell and the battery storage to the impedance source network. This article also incorporates an improved second-order generalized integrator (I-SOGI) control system for the generation of reference voltage signals. The I-SOGI control reference voltage generation approach greatly improves system performance and decreases the harmonic voltage. The voltage-related problems in the system connected to the utility grid are mitigated with DVR. In different load and source conditions, the PV generation with DVR performance is verified by the experimental prototype.

A detailed power flow analysis of the dual unified power quality conditioner (iUPQC) using power angle control (PAC)

In this paper, a detailed mathematical analysis of the power flow through the two converters of the Unified Power Quality Conditioner (UPQC) using its dual control strategy (iUPQC) is developed. Unlike previous power flow analyses, the proposed approach considers the power processed due to load current harmonics and grid voltage related problems, such as harmonic distortion, unbalance and fundamental frequency long-duration disturbances. Such analysis considers the unified conditioner under its conventional operation and with the implementation of the power angle control (PAC), which usually provides load reactive power demand sharing between the converters. The presented power flow analysis results in a better understanding on how the PAC can be used to equalize the powers processed by each of the iUPQC converters under general abnormal conditions. Besides, it contributes to clarify how such control can be used to provide active power cancelation or loss reduction. Finally, a three-phase four-wire prototype of an iUPQC was built to experimentally validate the proposed approach.

Implementation of solar PV system unified ZSI-based dynamic voltage restorer with U-SOGI control scheme for power quality improvement

The main challenge in today's power system is to supply continuous, reliable power and satisfy the high demand. The incorporation of renewable energy sources into the utility grid system can be accomplished. However, the renewable sources are intermittent in nature and the loads work dynamically and cause imbalances to the system voltage within an immediate time. Intermittent renewable sources affect the voltage of the power grid system. Photovoltaic (PV) power generation with Z-source inverter (ZSI)-based dynamic voltage restorer (DVR) is used to avoid that. For step-up low DC voltage to required AC voltage for the compensation of the voltage disturbance, ZSI with the energy storage impedance network is used. DC-DC converters connect the PV cell and the battery storage to the impedance source network. This article also incorporates an upgraded second-order generalized integrator (U-SOGI) control system for the generation of reference voltage signals. The U-SOGI control reference voltage generation approach greatly improves system performance and decreases the harmonic voltage. The voltage-related problems in the system connected to the utility grid are mitigated with DVR. In different load and source conditions, the PV generation with DVR performance is verified by the digital simulation and experimental prototype.

Implementation of Single Phase SRF based Dynamic Voltage Restorer in Distribution System for Power Quality Improvement.

Power Quality (PQ) is becoming an important issue as the increase in electricity use continues. Reduction in the quality of electrical power is due to various kinds of voltage related problems such as voltage sag, voltage swell, short-lived interruptions, harmonic distortions, notches, flickers, spikes and transients. The major power quality problems in single phase system are voltage sag and harmonics. The Mitigation of voltage sag and harmonics in single phase system under the distorted power supply situations was effectively eliminated with Dynamic Voltage Restorer (DVR). The single-phase SRFT (Synchronous Reference Frame Theory) was implemented in the controller design for DVR. DVR will produce required amount of instantaneous voltage to be injected. Designed controller technique will utilize the function of Moving Average Filter (MAF) for getting the fundamental quantity of positive sequence component from the disturbed supply voltage. Experimental results of DVR prove its effectiveness to mitigate voltage sag and harmonics during disturbed power supply condition.

A New Approach to Compensating Voltage Unbalance by UPQC-Based PAC

This paper proposes a novel algorithm for power angle control (PAC) which aims to simplify the control algorithm and obtain a fast dynamic response. It also extends the capability of PAC to compensate voltage unbalance with or without phase angle jump in a simple way. Using this control strategy, unified power quality conditioner (UPQC) can improve power quality problems such as sag, swell, and unbalances of source voltage, load reactive power and harmonics in distribution systems. The series converter in UPQC is responsible for compensation for voltage-related problems. In PAC method, the series converter also participates in load reactive power compensation which is the superiority of this control strategy. The proposed method uses triangular rules of vector addition/subtraction to determine phase and magnitude of voltage that should be injected by series converter. It reduces the required calculations and hence raises the velocity of compensation. For achieving a better dynamic response, a sliding mode control is used to control DC link voltage instead of conventional PI control. This makes the control algorithm faster and more robust. Simulation results obtained through MATLAB/SIMULINK verify the effectiveness of the proposed method.

Single-Phase Inverter-Control Techniques for Interfacing Renewable Energy Sources With Microgrid—Part II: Series-Connected Inverter Topology to Mitigate Voltage-Related Problems Along With Active Power Flow Control

In this paper (Part II), a control strategy for a single-phase series-connected inverter with the microgrid is proposed to interface ac loads not only to regulate the load voltage under voltage disturbances, but also to control the load power drawn from the microgrid. The inverter compensating voltage works in such a way that, irrespective of any type of disturbances in the microgrid voltage (such as sag, swell, or harmonic distortions), the load voltage is maintained at its rated voltage level with low total harmonic distortion (THD) in voltage. The proposed control strategy also facilitates a specific amount of active power flow (from renewable energy source) to the load irrespective of the microgrid voltage condition. The rest of the load power is supplied by the microgrid. To facilitate this control strategy, a spatial repetitive controller (SRC) is proposed and implemented in microgrid phase ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\theta$</tex> </formula> ) domain to make the controller independent of the microgrid frequency. The proposed controller ensures dynamic stability of the system even if there is a sudden change in the microgrid frequency. Detailed experimental results are presented to show the efficacy of the proposed series inverter system along with the controller under different operating conditions.

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.

A Series Active Filter Controlled by Personal Computer

This paper describes work that is being done in the design and implementation of a series active power filter for electrical power quality purposes. This type of filter is able to compensate for the following voltage related problems in the power grid: short blackouts for a few cycles, voltage distortion due to harmonics on a repetitive basis, voltage unbalance in three-phase systems, voltage flicker (subharmonics) and momentary over or under voltages. The main objective of the work described in the paper is to build a series active filter controlled by a personal computer with a standard multifunction data acquisition PCI bus card, because of its relative low cost and versatility. This PC based solution presents some difficulties since the control of a series active filter is a kind of application which requires a fast controller which that does not miss samples and where all real-time deadlines must be met each and every time, or the system will not operate properly. These characteristics imply that this application falls in the “hard real-time” control category. In the paper, some results are presented and some conclusions are taken using two different operating systems. Furthermore, a comparison with a microcontroller based implementation will be made.

Classification of voltage problems in electric power systems

In this paper sufficient mathematical and operating conditions are defined for distinguishing between voltage problems with insignificant frequency changes and voltage problems accompanied by frequency instabilities. With this as the main classification, additional conditions are introduced under which voltage related problems are either of a steady state character, or they evolve as the mid-/long-term phenomena only (in contrast to very fast, transient stability type phenomena). Within the first class (insignificant frequency changes) two distinct groups of voltage problems could arise, the most common of which is the existence of post-contigency voltage outside of operating limits. The other group of voltage problems within the first class is reflected in a small signal instability of an existing load flow solution. Assuming that a post-contingency load flow solution exists, mathematical and operating conditions are reviewed under which these problems occur. New conditions are established for preventing the second group of voltage problems from this class, i.e. small signal voltage instabilities. As a result, voltage related problems in this class are guaranteed to be, at worst, mid-/long-term type phenomena. Within the second class (accompanied by frequency instabilities), two groups of voltage-related problems occur. The first group is reflected in persistent but bounded terminal voltage oscillations, primarily contributed by the unstable mode associated with the rotor angle. The second group is characterized by unbounded changes of terminal voltages, primarily contributed by the unstable mode in field-flux voltage E q ′. In this paper, conditions are derived under which persistent but bounded voltage oscillations take place, as opposed to unbounded changes of state representing voltage dynamics, such as field-flux voltage E q ′ of the machine and its terminal voltage V t.

New approaches to voltage monitoring and control

Voltage-related problems evolving in interconnected electric power systems are examined. Reasons for these problems are introduced, and their potential importance for system operation is discussed. This physical phenomenon poses problems covering the entire spectrum from proper modeling to control design and communications. Consequences of novel control designs are discussed in the context of the improvement of system operation and the results benefits. >

The Control of Large Wind-Farm-Induced Voltage Fluctuations

The contemplated use of large sources of intermittent generation such as wind in concert with conventional utility generation poses special operational problems. These problems include the propensity of the wind-driven source for upsetting the voltage regulation systems. Related to voltage depression is the often excessive VAR requirements which lead to large network losses if not controlled. This paper explores the use of an AC/DC/AC interface designed to control these voltage related problems. An extinction angle control algorithm is proposed and simulation results are used to show the advantage of such control.

The Control of Large Wind-Farm-Induced Voltage Fluctuations

The contemplated use of large sources of intermittent generation such as wind in concert with conventional utility generation poses special operational problems. These problems include the propensity of the wind-driven source for upsetting the voltage regulation systems. Related to voltage depression is the often excessive VAR requirements which lead to large network losses if not controlled. This paper explores the use of an AC/DC/AC interface designed to control these voltage related problems. An extinction angle control algorithm is proposed and simulation results are used to show the advantage of such control.