Power Flow Controller Research Articles

Mitigating Low-Frequency Oscillations and Enhancing the Dynamic Stability of Power System Using Optimal Coordination of Power System Stabilizer and Unified Power Flow Controller

The integration of a flexible alternating current transmission system (FACTS) and a power system stabilizer (PSS) can increase dynamic stability. This paper presents the enhancement of power system dynamic stability through the optimal design of a power system stabilizer and UPFC using an ant lion optimization (ALO) technique to enhance transmission line capacity. The gained damping ratio, eigenvalue and time domain results of the suggested ALO technique were compared with a base case system, ALO-based PSS and ALO-based PSS-UPFC to test the effectiveness of the proposed system in different loading cases. Eigenvalues gained from an ant lion approach-based UPFC with a PSS and a base case system are compared to examine the robustness of the ALO method for various loading conditions. Thus, this paper addresses the mechanism regarding the power system dynamic stability of transmission lines by integrating the optimal size of a PSS and UPFC into the power system. Therefore, the main contribution of this manuscript is the optimal coordination of a power system stabilizer, power oscillation damper and unified power flow using ant lion optimization for the mitigation of low-frequency oscillation.

Sustainable development and applications of variable frequency transformer (VFT)

Power system interconnection is achieved by incorporating phase shifting transformers (PST) and back-to-back high voltage direct current (B2B HVDC) systems. Incorporating PSTs in an electrical power system is highly undesirable owing to its step wise variation of power transition. On the other hand, B2B HVDC systems are rarely employed in weak grids, due to their massive consumption of reactive power for device commutation. The variable frequency transformer (VFT) is capable of resolving the concerns described above by delivering improved performance on account of lower reactive power consumption besides providing smooth controllable power. This paper presents a critical review of VFT depicting its sustainable development for power system interconnection. To start with, an overview of VFT is presented followed by a brief description of other power flow controllers. These power flow controllers are compared with VFT to highlight its advantages over other conventional power flow controllers. This paper further identifies role of VFT in improving system stability and suppressing low frequency oscillations. This study also identifies the possible gaps for incorporation of VFT in power systems that have not been reported in literature and intends to serve as a useful reference for researchers working in the field of power system interconnection.

Optimal control for a photovoltaic integrated grid system using PSO and modified whale optimization to enhance power quality

The paper proposes a modified & optimized controller for PV-integrated grid-connected PV systems. As the solar power output depends on the environmental conditions, i.e., irradiation and atmospheric temperature, the maximum power from the photovoltaic (PV) module is extracted using perturb and observe (P & O) algorithm. With a variety of controllers, such as conventional proportional and integral (PI) controllers, particle swarm optimization (PSO), and the modified Whale optimization algorithm (MWOA) method based on optimum control, the power as compared to extracted from PV panels using MWOA-based controllers. A complete simulation and implementation of a single-phase grid-connected inverter are shown to verify the proposed PV controller. The power flow control and grid synchronization are also presented when the above controllers act as MPPT controllers in the proposed system. The performance of proposed system is evaluated and compared among conventional and optimal controllers under a MATLAB-Simulink environment.

Optimal Power Flow Using a Hybrid Improved Harris Hawks Optimization Algorithm-Pattern Search Method

The optimal power flow (OPF) problems for effective power system planning and operations are solved using a hybrid Improved Harris Hawks Optimization and Pattern Search (PS) (hIHHO-PS) algorithm in this research. The OPF problem is considered minimization of non-convex active power generation fuel cost (NAPGFC), total active power losses (TPL), shunt capacitor cost (SCC), voltage variation (VD), and maximization of social welfare (SW) and loadability factor (LF) objective functions. The proposed hIHHO-PS algorithm was tested on different benchmark test functions (unimodal (UM), multi-modal (MM), and fixed-dimension MM functions) and IEEE 30 bus test system, and obtained results are validated with existing algorithms. These results show the proposed hIHHO-PS algorithm outperformed the others. Further, to enhance the OPF results, optimally place the multi-line Flexible Alternating Current Transmission System (FACTS) devices (unified power flow controller (UPFC) and generalized unified power flow controller (GUPFC)) using severity index. Furthermore, test the effects of control modes of multi-line UPFC and GUPFC devices on OPF results. These results show the multi-line FACTS devices with control mode enhance the OPF results, especially GUPFC in control mode operation.

Power flow control and power oscillation damping in a 2-machine system using SSSC during faults

Abstract With the rapidly growing population, energy demand is increasing. The power supply to consumers must be free from distortions. By injecting voltage in quadrature with line current and varying the magnitude, the SSSC offers series compensation to the line. The injected voltage, which offers the effect of inserting an inductive or else capacitive reactance in series with the transmission line, is in quadrature with the line current. Using MATLAB/Simulink software, a phasor model of a 2-machine device with SSSC integration and POD as a subsidiary controller is simulated in this paper to evaluate efficient power flow regulation. The simulation has been used to study the time domain behavior of SSSC under normal and faulty conditions. The SSSC is implemented for correcting the voltage and analyzing power responses during a low voltage fault in the power system, whereas in normal conditions, the power system’s voltage stability for maintaining steady acceptable voltages at every bus is analyzed. It has been revealed that POD controller assists SSSC by supplying the reference voltage signal to damp out the low frequency power oscillations. The objective of this study is to reduce the crest outreach and clearing time during the fault thus improving the transient stability.

Impedance Modeling and Mechanism Analysis of Low-Frequency Oscillations in Single-Phase MMC-RPC Integrated Vehicle-Grid Coupling System

The single-phase modular multilevel converter-based railway static power conditioner (MMC-RPC) has significant advantages in governing the power quality problems in the traction power supply system. The mechanism analysis of low-frequency oscillations (LFOs) in the MMC-RPC integrated vehicle-grid coupling system when electric multiple units are put into operation is a critical issue, which has been investigated in this article. The third-order ac admittance models of single-phase MMC-RPC and vehicle rectifiers are developed for the first time. To comprehensively study the small-signal stability of the MMC-RPC integrated vehicle-grid coupling system, this article proposes a modal analysis method based on modal phase margin and parameter sensitivity and combined with the generalized Nyquist stability criterion. It is found that LFOs around 10 Hz or 48 Hz are prone to occur due to the interactions of MMC-RPC or vehicle rectifiers with the traction power grid. To reveal the LFO mechanism, dominant modes and key parameters leading to LFOs in different working scenarios are clarified, and a series of guidelines are proposed for LFO elimination. Furthermore, the effects of control loops and power flow of MMC-RPC on system stability are revealed in detail. Finally, real-time hardware-in-the-loop experimental results validate the theoretical analysis.

Unlocking the Hidden Capacity of the Electrical Grid Through Smart Transformer and Smart Transmission

Power systems are experiencing a rapid and dramatic transformation driven by the massive integration of nondispatchable renewable energy sources, such as wind and solar, and highly variable loads, such as electric vehicles and air conditioning. This challenges existing grid assets, eventually leading to updating them, which, in turn, increases significantly the costs of sustainable technologies. Power electronics is a pivotal technology for electrical power processing for renewable energies and sustainable transportation. By means of “smart” functionalities, power electronics converters already embedded in such applications can also contribute to guaranteeing the overall system’s stable operation. Anyway, this cooperative contribution from distributed devices may be not enough leading to the need for the voltage transformation and power transmission of “system-level” power electronics solutions. In the case of large charging stations, a smart transformer (ST), while, in the case of large solar and wind parks, integration medium- or high-voltage direct current (HVdc) transmissions are system-level solutions. This article wants to review the potential of using such infrastructures to increase the capacity of existing grid assets, avoiding or deferring their upgrade and, hence, reducing the overall costs of renewables integration and the electrification of the transport sector. In fact, the power converters embedded in ST and HVdc can provide fast frequency and voltage response, and precise control of power flow acting at the system level much more effectively and feasibly for system operators as the distributed power converters embedded in several small sources and users. This article reviews, for the first time, these two key power electronics “system-level” solutions together—ST and HVdc—starting from their basic functionalities and showings how they can go beyond them, showing how, with grid-forming functionalities, they can offer new “smart grid” tools to enhance the capability of the existing electric grid infrastructures.

Optimal UPFC Placement for Voltage Stability Enhancement

The Unified Power Flow Controller is a versatile and important device for improving the operational efficiency of power systems in the flexible AC transmission systems family. It finds applications in improving voltage stability in addition to provide a better voltage profile and reducing transmission loss. This paper presents a Chemical Reaction Inspired Optimization based method for placement of unified power flow controllers with the objective of raising the voltage stability. Most of the existing methods place all the given unified power flow controllers without analysing whether each of the given unified power flow controllers is actually needed to improve voltage stability or other selected performances. The proposed method tries to place only the essential unified power flow controllers from the allocated number of devices, besides providing optimal line locations and unified power flow controller parameters. It also includes the results of the proposed method for three standard test systems and compares them with existing methods to depict the dominance of the proposed method.

State-of-the-Art Literature Review of Power Flow Control Methods for Low-Voltage AC and AC-DC Microgrids

The development of AC distribution systems provides for the seamless integration of low-voltage microgrids with distributed energy resources (DERs). This poses new challenges for the control of normal, emergency, and post-emergency states of microgrids, calling for the creation and development of information and communications technology infrastructure. Power converters/inverters that are used to integrate renewable DERs lack inertia. Along with them, fossil fuel-fired generation units are also being integrated into microgrids. These include gas generator sets, diesel generator sets, and microturbines, having small (up to 1–2 s) values of mechanical inertia constants—Tj. This leads to an increase in the rate of transients by a factor of 5–10. Under these conditions, the technical requirements for the speed of automatic power flow control systems, as well as the methods they rely on, have to be reconsidered. Microgrids include DC microgrids, AC microgrids, and hybrid (AC-DC) microgrids. In the case of hybrid microgrids, DERs are connected to the DC grid and are integrated into the AC grid through a common inverter. The complexity of the task of microgrid control is due to the need to choose properly the type and extent of control actions so as to prevent the emergence and development of accidents. The employed control methods must ensure the reliable power supply to consumers and the quality of power in microgrids, as well as the reliable operation of the external distribution systems into which they are integrated. The article gives an overview of control methods for low-voltage AC and AC-DC microgrids, which allow one to tackle effectively solve the tasks.

Development of a Bidirectional DC/DC Converter with Dual-Battery Energy Storage for a Hybrid Electric Vehicle System

Abstract: This study develops a newly designed, patented, bidirectional DC/DC converter (BDC) that interfaces a main energy storage (ES1), an auxiliary energy storage (ES2), and a DC-bus of different voltage levels, for application in hybrid electric vehicle systems. The proposed converter can operate in a step-up mode (i.e., low-voltage dual-source-powering mode) and a stepdown (i.e., high-voltage dc-link energy-regenerating mode), both with bidirectional power flow control. In addition, the model can independently control power flow between any two low-voltage sources (i.e., low-voltage dual-source buck/boost mode). Herein, the circuit configuration, operation, steady-state analysis, and closed-loop control of the proposed BDC are discussed according to its three modes of power transfer.

Optimal location of FACTs devices in LFC studies considering the application of RT-Lab studies and emperor penguin optimization algorithm

The application of Real-time lab (RT-Lab) software in Load frequency control studies of a multi-area-source system under deregulation is demonstrated. It is provided with thermal systems accompanying renewable sources like Precise wind turbine systems (PWTS) in area-1, 2 and Realistic dish stirling solar thermal system (RDSTS) in area-3. FACTs devices like accurate HVDC (AHVDC) transmission, Interline power flow controller (IPFC) and Thrysitor controlled series capacitor (TCSC) are provided. A maiden effort has been made to utilize a new cascade controller called TI-FOIDN as a supplementary controller. A recent meta-heuristic algorithm called emperor penguin optimizer (EPO) is used for controller, RDSTS and PWTS parameter optimization considering a new perfromance index named Hybrid peak area-integral squared error (HPA-ISE). It is also observed that dynamics of the system with optimum values of the parameters obtained with HPA-ISE are better. Moreover, when the system is simulated in RT-Lab software, system performance is found somewhat better than Matlab. Further, the use of renewable, AHVDC parallel with AC tie-line, IPFC and TCSC improve system responses.

DE-Based Design of an Intelligent and Conventional Hybrid Control System with IPFC for AGC of Interconnected Power System

In this study, a fuzzy proportional integral derivative controller (FPID) was adjusted using the differential evolution (DE) method to enhance the automated generation control (AGC) of a three-zone reheat-type power system. The objective function used in this study was an integral of the time-weighted absolute error (ITAE). In the optimization, the gain control parameters of the proportional integral (PI), the integral (I), and FPID were optimized and compared to improve the limitations drawn by the controller over a few parameters. To demonstrate that FPID controllers with IPFC produce better and more accurate optimization results than integral and PI controllers optimized by DE, the interline power flow control (IPFC) of a flexible AC transmission system (FACTS) device with suitable connections and control parameter optimization was used. Also, the particle swarm optimization (PSO) PID with IPFC was compared with the proposed DEFPID + IPFC, and better results were achieved by using the DE technique. Similarly, to demonstrate the suggested technology’s strong control capacity, random load changes were applied to the system in various conditions, and it was demonstrated that the suggested control unit easily tolerated random load perturbations and returned the system to a stable functioning state.

Comparison of Control Techniques for Harmonic Isolation in Series VSC-Based Power Flow Controller in Distribution Grids

The application of power electronics equipment in medium voltage (MV) distribution grids can provide new management solutions for power flow control, load balancing and voltage problems. A series MV VSC-based power flow controller has recently been presented to interconnect two radial distribution feeders performing active and reactive power transfers to improve the flexibility and utilization of these circuits in a controlled and secure way. Although not previously explored, this power flow controller can integrate the functionality of a series power filter, accomplishing independent control of the fundamental power flow while isolating the harmonic content between the two interconnected feeders. This prevents harmonic pollution from one feeder from propagating to the other, improving the voltage quality. To implement the harmonic isolation, several control strategies can be used. Therefore, this paper provides a comparative analysis between two of the main harmonic control techniques found in the literature: the Synchronous Reference Frame (SRF) controller and the Proportional Resonant (PR) controller. Assessments are conducted both through simulations and experimental results in a meshed network at 13.8 kV with different types of non-linear loads. In the simulation cases, both algorithms showed similar results; however, in the experimental cases, the PR-based solution exhibited better performance in isolating the harmonics from one feeder to the other.

Optimal allocation of UPFC based on healthy and stressed zones for critical power systems

A unified power flow controller (UPFC) is a versatile compensator providing multi-variable control for the critical power systems (CPS). In an attempt to reduce the search space for optimal allocation of UPFC thereby standardizing the deliberation over UPFC placement, zone-wise segregation of the network into weak and healthy zones is logically executed by an advanced network power stability indicator (NPSI). The UPFC performance is ascertained by a new line flow margin index (LFMI), power loss index and its economic benefit. The latter is derived by the cash outflow reduction (COR) and the internal rate of return (IRR), calculated by practical aspects like installation and maintenance cost, considering inflation and interest on amortization. For optimization, an improved version of the wind-driven optimization algorithm is proposed with finite-mass air parcels and intra-particle forces. An improved normalization technique is adopted for the multi-ranged, multi-objective problem. To simulate the CPS, the 57-bus test system with enhanced arbitrary load is considered. A significant reduction in power losses is observed when optimizing in reduced search space and the optimal location of G-UPFC is found to be in bus 13–15, which is also a part of the weaker zone. Several other results confirmatively approve the proposed approach of isolating the most appropriate zone for UPFC allocation based on the healthy and weak regions along with the proposed techno-economical evaluators.

Performance amelioration of concerted voltage‐frequency regulation of multiarea hybrid power systems under restructured pattern using electric vehicles and interline power flow controller

AbstractElectric power consumers need a stable and reliable electricity supply for their appliances. Voltage and frequency fluctuate owing to the gain in intermittent renewable energy sources in hybrid power systems (PSs). To mitigate these issues, this article proposed a new cascade controller named proportional‐derivative with filter and fractional‐order tilt‐integral‐derivative with filter (CPDN‐FOTIDN), controller for combined voltage and frequency control of three areas hybrid PS under deregulated environment. Hybrid PS comprises hydro, thermal, and geothermal power plant, modern electric vehicles (EVs), and interline power flow controller (IPFC). To make the analysis more realistic of the hybrid PS, more appropriate nonlinearities are considered. The artificial flora algorithm is employed for tuning controller parameters with several studies to obtain the desired response. Comparative analysis of dynamics responses reveals the superiority of the CPDN‐FOTIDN controller relative to PIDN and FOTIDN controllers under the three different power transactions. Investigations exhibited the performance enhancement of combined voltage and frequency control of hybrid PS after the integration of EVs into the considered system. Simulation results show that the EVs are a quick response in the presence of a CPDN‐FOTIDN controller compared to TID, and FOTID controllers during the system disturbance. Inter‐area oscillations improve after integration of IPFC into the system and the optimal location was found between area 1 and 2. Sensitivity studies demonstrated the sturdiness of the proposed controller against a wide variation of the system loading.

Application of whale algorithm optimizer for unified power flow controller optimization with consideration of renewable energy sources uncertainty

Purpose. In this paper an allocation methodology of Flexible Alternating Current Transmission Systems (FACTS) controllers, more specifically, the Unified Power Flow Controller (UPFC) is proposed. As the penetration of Renewable Energy Sources (RESs) into the conventional electric grid increases, its effect on this location must be investigated. Research studies have shown that the uncertainty of RESs in power generation influences the reactive power of a power system network and consequently its overall transmission losses. The novelty of the proposed work consists in the improvement of voltage profile and the minimization of active power loss by considering renewable energy sources intermittency in the network via optimal location of UPFC device. The allocation strategy associates the steady-state analysis of the electrical network, with the location and adjustment of controller parameters using the Whale Optimization Algorithm (WOA) technique. Methodology. In order to determine the location of UPFC, approaches are proposed based on identification of a line which is the most sensitive and effective with respect to voltage security enhancement, congestion alleviation as well as direct optimization approach. The optimum location of UPFC in the power system is discussed in this paper using line loading index, line stability index and optimization method. The objective function is solved using the WOA algorithm and its performance is evaluated by comparison with Particle Swarm Optimization (PSO) algorithm. Results. The effectiveness of the proposed allocation methodology is verified through the analysis of simulations performed on standard IEEE 30 bus test system considering different load conditions. The obtained results demonstrate that feasible and effective solutions are obtained using the proposed approach and can be used to overcome the optimum location issue. Additionally, the results show that when UPFC device is strategically positioned in the electrical network and uncertainty of RES is considered, there is a significant influence on the overall transmission loss and voltage profile enhancements of the network.

Novel Isolated Multiple-Input, Multiple-Output Multidirectional Converter for Modern Low-Voltage DC Power Distribution Architectures

This work introduces a multiple-input, multiple-output (MIMO) isolated converter for low-power applications involving residential DC nanogrids and nanogrids. The topology has a multiport characteristic that allows for the integration of loads and sources with distinct ratings, e.g., photovoltaic (PV) modules, battery banks, DC loads, and the AC grid. The structure relies on a DC-DC multi-winding multidirectional flyback converter that operates as power interface and can minimize the number of power conversion stages while enabling flexible power flow control. Owing to its multidirectional characteristic, a port can be responsible for supplying or absorbing energy using duty cycle control or phase-shift control, respectively. Since the operating modes of the converter are decoupled, a predictive controller is capable of managing the power flow among the ports independently. Simulation results are presented and discussed to evaluate the control system robustness and its performance in power flow management.

Power flow control: Solutions for a modern grid [Book review

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Power flow control solutions for a Modern Grid Using SMART Power Flow Controllers</i> provides students and practicing engineers with a good understanding of the difficulties within congested power system networks and provides solutions to mitigate power flow problems.

Performance Characterization of T-Type Multilevel Dual Active Bridge DC-DC Converter

Conventionally, single phase shift control technique is used for controlling dual active bridge (DAB) performance, which works efficiently at unity voltage conversion ratio and full load. However, when there is mismatch between primary voltage and reflected secondary voltage on primary side at light load, its efficiency reduces because of increased current stress and reactive power. Moreover, due to single control variable, its power flow controllability is confined. In this paper, analysis, implementation and performance characterization of isolated bi-directional T-type multilevel dual active bridge DC-DC converter topology is presented. It has five level voltages on both the primary and secondary side of high frequency transformer, which reduces the current stress and reactive power over wide operating range. It also has five control variables which gives extra edge for enhancing power flow controllability. Comparative analysis reveals that the proposed converter has high efficiency over wide operating range, due to reduced reactive power and current stress. Performance of the proposed T- type multilevel dual active bridge DC-DC converter topology has been verified via simulation and experimental prototype developed in the laboratory.

Low-Voltage dc System Building Blocks: Integrated Power Flow Control and Short Circuit Protection

Low-voltage direct current (LVdc) systems are a promising technology for systems with a high penetration of renewable sources and storage that operate with bidirectional power flow. In this article, a fundamental building block for LVdc is presented for different applications, such as charge controllers, voltage regulation in street-lighting systems, and current limiters in meshed dc grids. The developed building block integrates a solid-state circuit breaker (SSCB) and partially rated power flow control converter (PFCC) capable of achieving the given control objectives with extremely high system efficiency and full short circuit protection.