Voltage Control Of Generators Research Articles

Fuzzy Switched Active Disturbance Rejection Voltage Control of Generators With Load Switchings

Fuzzy Switched Active Disturbance Rejection Voltage Control of Generators With Load Switchings

Power Compatibility of Induction Motors in Industrial Grids Containing Synchronous Generators

Starting an induction motor causes voltage sag in the industrial grid that may disturb the operation of grid equipment. Direct-on-line starting is the simplest and most cost-effective method for starting induction motors, but also the most problematic. Large industries often use internal power plants with synchronous generators and starting powerful motors may impact the generator operations. The synchronous generators could be operated with the automatic or manual mode of voltage control. As the operation experience proves, the generator voltage control mode has a significant impact on the transient behaviours in the industrial power grid when starting a large induction motor. This article presents a case study of the synchronous generator tripping within a true medium-voltage industrial grid during the direct-on-line starting of a large induction motor driving the feed water pump. An analysis of the generator protection logs after the tripping showed that the synchronous generator was controlled in manual mode and its protection relay settings were exceeded. The transients initiated by induction motor starts were studied for possible configurations and operating conditions of the grid using a model developed on the Matlab/Simulink Software platform. The simulations have shown that concern about starting large motors in industrial grids containing internal synchronous generators needs to be solved considering the grid configurations and the coordination of generator protection and control devices.

Enhanced DC-link voltage control of PMSG-based wind turbine generators by machine-side converter during asymmetrical grid faults

Under asymmetrical grid fault conditions, oscillating active power can occur on the grid-side converter (GSC) of permanent magnet synchronous generator (PMSG)-based wind turbine generators. The oscillating active power flows into the DC-link, causing voltage oscillations that can lead to a shortened lifetime of DC-link capacitors and additional harmonics injected into the grid. While conventional methods can mitigate the oscillating active power through negative sequence current injection by the GSC, this hinders the grid support of the GSC regarding negative sequence reactive current during grid fault. To address this issue, a novel control scheme is proposed that uses the machine-side converter (MSC) to transfer the oscillating power to the motor. Firstly, the active power capacity of the MSC is analyzed and compared with that of GSC, and the results show that MSC has enough capacity to accommodate the oscillating active power. On this basis, a novel MSC control scheme is proposed to transfer the oscillating active power on the DC-link to the motor, which has a much larger inertia to buffer the power oscillation. Compared with conventional methods, the proposed control scheme relieves the GSC from mitigating the power oscillation to support the grid. Simulation studies using DIgSILENT PowerFactory are presented to verify the effectiveness of the proposed control scheme for PMSG-based wind turbine generators.

A review of modeling and simulation tools for microgrids based on solar photovoltaics

Solar Photo Voltaic (PV) powered community microgrids are a promising sustainable solution for neighborhoods, residential quarters, and cities in sub-Saharan Africa (SSA) to meet their energy demands locally and to increase energy independence and resilience. This review provides a comprehensive study on the nature of solar PV community microgrids. Through their capacity to operate in both grid-connected and island modes, community microgrids improve utility system resiliency while also boosting energy security in local states and towns. The integration of solar PV microgrids with the electricity utility grid requires control strategies to facilitate the load sharing between distributed generation units, voltage and frequency control, as well as emergency islanding. Control strategies such as hierarchical control and droop are discussed in the review article. To identify the effectiveness of control strategies through system simulation, a review of various modeling designs of individual components in a solar PV microgrid system is discussed. The article goes on to talk about energy optimization approaches and their economic impact on microgrid systems. Finally, the review concludes with an overview of the technical challenges encountered in the integration of solar PV systems in microgrids.

Dynamic and Steady-State Power-Sharing Control of High-Efficiency DC Shipboard Microgrid Supplied by Diesel Generators

The integration of dc power distributed systems in modern shipboard microgrids is receiving much attention recently due to their high efficiency and grid connection flexibility. These dc shipboard microgrids (dc-SMGs) are characterized by having different operating modes and large proportion of electric propulsion, some of which involves severe dynamic/transient conditions. Considering various operation modes of actual ships, this paper proposes a hierarchical coordinated control, which includes primary control level (PCL) and power management system (PMS) for the coordinated operation of the power sources in dc-SMGs. The coordination between the PCL and the PMS provides the following features: First, the PCL includes primary speed regulation (PSR) of diesel generator (DG) and primary voltage control (PVC) of dc bus. The PVC can realize the dynamic/steady load power sharing by adding the virtual impedance loop, and the PSR of DG performs the rotation speed to follow the reference. Second, the PMS includes optimal speed reference setting and secondary voltage recovery control that can realize variable-speed operation of DG according to its optimal energy efficiency characteristic and improve the power quality. The simulation results are carried out under MATLAB/Simulink to verify the effectiveness and robustness of the proposed control.

Cooperative Markov Decision Process for Voltage Control of Grid-Tied Photovoltaic Generators With Reactive Power Support

The problem of voltage control (VC) by means of inverter reactive support in distribution grids with photovoltaic (PV) generation is addressed. A novel decentralized approach for VC is proposed, which consists in heuristic specification of a distributed reactive support cooperative partially observable Markov decision process (DRS-C-POMDP) whose agents control groups of PV nodes clustered according to voltage correlation. The proposed method employs offline policy optimization, which yields closed-form reactive power setpoint control laws. Hence, the online processing time required by most VC methods is avoided and controller implementation is simplified. The method is validated via simulation on a 123-bus feeder, in which it is compared to other decentralized heuristic methods from the literature. The results indicate that, for identical local inverter controls, the proposed method yields superior performance.

Voltage Control of Multiphase Cage Induction Generators at a Speed Varying over a Wide Range

The subject of this publication is a method of controlling the DC voltage of a PWM rectifier supplied by a multiphase cage induction generator with the number of stator phases greater than three operating in a wide range of driving speeds. Voltage regulation is performed by changing the frequency and amplitude of the stator voltages with simultaneous switching of the phase sequence of these voltages. The step change of the voltage sequence is made in the designated ranges of the generator speed, which enables the stabilization of the output voltage in a wide range from the minimum speed of about 25% of the rated speed. Such sequence switching changes the number of pole pairs produced by the winding for each supply sequence. The difference compared to multi-speed induction machines is that, in the presented solution, there is only one winding, not a few, which enables good use of the machine’s magnetic core in the same dimensions as for the three-phase machine of a similar power. Steady-state characteristics and dynamic operation were obtained using laboratory measurements of a standalone nine-phase induction generator. The automatic control system maintained the output voltage at the set level, regardless of the generator load and driving power.

Voltage Constrained Reactive Power Planning Problem for Reactive Loading Variation Using Hybrid Harris Hawk Particle Swarm Optimizer

This study proposes the application of an efficient and hybrid meta-heuristic algorithm of Harris Hawk-Particle Swarm Optimizer (HHOPSO) for solving voltage constrained reactive power planning (VCRPP) problem. The prime objective of present work is diminishing the transmission loss and overall operating cost coupled with retention of voltage consistency and enhanced congestion management in transmission lines. The efficacy of the proposed algorithm is tested on standard IEEE 57 bus test system with optimal transformer tap settings, reactive generation control, generator voltage control and optimal control of Var sources. The best location of Var sources is determined by Voltage Collapse Proximity Indicator (VCPI) method. Simulation results are generated under normal and variable reactive power loading condition which makes the reactive power planning problem more challenging and validates the robustness of the proposed algorithm. The results of proposed algorithm when compared with the other optimization algorithms surfaced in contemporary state of art literature yields superior solution in maintaining diversity and solution optimality.

Power-Sensitivities-Based Indirect Voltage Control of Renewable Energy Generators With Power Constraints

Recently, renewable energy has received considerable attention worldwide due to environmental problems such as climate change. However, there are still many problems to be solved to increase the penetration level of renewable energy sources in a power system. Above all, a power system with a high renewable penetration level requires an entirely novel operational strategy and control approach to achieve reliable operation by considering the intermittency of variable renewable energy sources. This paper proposes power-sensitivities-based indirect voltage control of renewable energy generators with power constraints. The proposed method realizes seamless control of the voltage by compensating with the reactive power if the real power of the distributed generator (DG) is insufficient due to its intermittency. To achieve the proposed method, the real and reactive power references of DGs are initially operated based on the power sensitivities between generation and loads if all the DGs operate within the power constraints. However, if at least one of the DGs reaches its constraint limit, the references can be modified using other sensitivities between real and reactive power generation enabling indirect voltage control of DGs. Therefore, a high level of renewable penetration in power systems can be accomplished with the proposed method. The proposed method is verified with several case studies that are based on a microgrid with practical data from a real island power system. Verification is carried out using the power system computer aided design and electromagnetic transient including DC (PSCAD/EMTDC™) simulation software.

Оптимизация тихоходного синхронного генератора модульного типа и принцип реализации системы управления напряжением генератора на основе нейронной сети

A method for optimizing the parameters of a modular half-speed synchronous generator with permanent magnets (PMSG) and the generator voltage control system with a neural network-based algorithm are proposed. The basic design scheme of the modular half-speed PMSG is considered, which features a compact layout of the generator main parts, thereby ensuring the optimal use of the working volume, smaller sizes of the magnetic system, and smaller mass of the active materials used in manufacturing the machine. Owing to the simple and reliable design of the generator, its output parameters can be varied in a wide range with using standard electrical circuits for voltage stabilization and current rectification along with an additional voltage regulation unit. Owing to this feature, the design scheme of the considered generator has essential advantages over the existing analogs with a common cylindrical magnetic core. In view of these circumstances, the development of a high-efficient modular half-speed PMSG as an autonomous DC power source is of both scientific and practical interest; this generator can be used to supply power to a large range of electricity consumers located in rural areas, low-rise residential areas, military communities, allotments etc. In solving the problem of optimizing the generator’s magnetic system, the main electrical machine analysis equation is obtained. The optimal ratios of the winding wire mass to the mass of permanent magnets and of the PM height to the air gap value for achieving the maximum specific useful power output have been determined. An analytical correlation between the optimal design parameters of a half-speed modular PMSG and its power performance parameters has been established. The expediency to develop a neural network-based control system is shown. The number of load-bearing modules of the half-speed PMSG is determined depending on the wind velocity, load factor and the required output voltage. The neural network was trained on the examples of a training sample using a laboratory test bench. The neural network was implemented in the MatLab 2019b environment by constructing a synchronous generator simulation model in the Simulink software extension. The possibility of using the voltage control system of a half-speed modular PMSG with a microcontroller for operation of the neural network platform of the Arduino family (ArduinoDue) independently of the PC is shown.

A Novel Approximation of Security-Constrained Optimal Power Flow With Incorporation of Generator Frequency and Voltage Control Response

This paper tackles key industry needs in the scope of the AC Security-Constrained Optimal Power Flow (SCOPF) framework, specifically two major challenging requirements regarding generators' post-contingency behavior: the (droop-based) frequency response and the voltage control mechanism (including PV/PQ switching). To this end, and to obtain a sufficiently accurate solution with a reasonable computational burden, we propose an approximation approach to SCOPF which extends significantly an existing algorithm with novel modelling elements: a continuous formulation to model generators' post-contingency responses based on successive approximations, a technique to evaluate the viability of contingencies with respect to the base case set-points, and the complexity reduction of all post-contingency states through network compression and power flow piecewise linearization. All new features are validated both separately and in unison, to monitor the improvement of the solution time and the potential degradation of the solution's quality. The proposed approach is successfully applied to three power system network models, the largest of which consists of 2,000 buses and more than 3,000 contingencies. Finally, the trade-off between the limitations in terms of solution quality and the benefits in terms of computational effort are assessed for all proposed approximations.

Robust position observer for sensorless direct voltage control of stand-alone ship shaft brushless doubly-fed induction generators

Robust position observer for sensorless direct voltage control of stand-alone ship shaft brushless doubly-fed induction generators

Self-Excitation of a Synchronous Generator During Power System Restoration

This paper analyzes synchronous generator self-excitation during power system restoration, caused by a large capacitive load and the impact of generator voltage control on the voltage rise. The paper analyzes measurements from a recent self-excitation incident in the Finnish 400-kV transmission system, models the system using an electromagnetic transient model and a linear d -axis generator model, validates the models using the measurements and analyzes the impact of generator voltage control during self-excitation. Self-excitation is rare during a normal system operation but may occur in a weak system during system restoration after a blackout. Since high voltages caused by the self-excitation may delay the restoration or even damage the equipment, self-excitation should be taken into account in restoration planning. This paper shows that the voltage controller and especially the under-excitation limiter settings of the generator have significant impact on the voltage during self-excitation. This paper also shows that details in the excitation system response influence the simulations significantly and reference measurements from the specific generator are required for detailed modeling. However, all measured incidents with digital static excitation systems are important references for simulations. In addition, special attention should be given to protection relays during the restoration.

Voltage Control of DC Generators Using Load Characteristic

The DC generators find much utilization in the devices that are used in application systems. This article describes the new voltage control of DC generators based on load characteristic. The DC generator load characteristic is important to identify the DC generator ability to provide the suitable load current. This paper proposed the performance of load characteristic of self-excited DC generator with the condition of voltage build up. The proposal allows for improvement of the more important factor in generation process which results in the voltage drop due to the losses and armature reaction. The field resistance, critical speed, and residual flux are very important factors in voltage build up process.

A Cost-Effective Redundant Digital Excitation Control System and Test Bed Experiment for Safe Power Supply for Process Industry 4.0

Recently, the energy demand and supply situation in the Republic of Korea (ROK) has been largely affected by the fluctuations in the energy markets around the world. Such a situation has provided a basis for requiring improvements to power plant facilities. The automatic generator voltage control systems in large-scale power plants are adopting a rapid-response static excitation method to improve the transient stability. A domestic commercially developed large-scale triple-redundant excitation system is currently operated by the 1000 MW-class nuclear power plant and its efficiency has been verified at the same site. However, such a system is too costly for smaller power plants so that a reliable and low-cost redundant digital excitation control system was developed and introduced in this study to resolve the cost problem. The system has improved its stability and reliability at the same time through double (redundant) configuration. Additionally, the system’s performance was put to the test by conducting a series of control function tests after applying it to the gas turbine used in a thermal power station. This study includes the development of system hardware, simulations as well as on-site experiments and each element was validated as a result. Also, the study discusses and validates the method used for replacing the protective relays at the Kanudi power plant operating in Papua New Guinea. The replacement of 27 and 81 protective relays at the existing power plant was carried out as they did not function properly. New relays were installed after removing the power supply in the existing panel. The individual power output sections of new relays were connected in parallel with the existing properly functioning relays, as previous protective relays had only allowed monitoring without outputting the contents. Thus, the new protective system was designed to enable both existing and new relays to carry out the detection function. It was validated that the replacement was successful. The new system with the new relays is performing properly by protecting its power generator and preventing further accidents.

Design Guidelines for Multiloop Perturbative Maximum Power Point Tracking Algorithms

Due to relatively good performance and simple implementation, fixed-step direct maximum power point tracking (MPPT) techniques such as perturb and observe and incremental conductance are the most popular algorithms aimed to maximize the energy yield of photovoltaic energy conversion systems. In order to optimize the MPPT process performance, two design parameters—perturbation frequency and perturbation step size—need to be set a priori , taking into account the properties of both interfacing power converter and photovoltaic generator. While perturbation frequency is limited by the combined energy conversion system settling time, perturbation step size must be high enough to differentiate system response from that caused by irradiation variation. Recent studies have provided explicit design guidelines for single-loop MPPT structures only, where the algorithm directly sets the interfacing converter duty cycle. It was shown that dynamic resistance of the photovoltaic generator, which is both operation point and environmental conditions dependent, significantly affects the combined energy conversion system settling time. On the other hand, no design guidelines were explicitly given for multiloop MPPT structures, where the algorithm sets the reference signal for photovoltaic generator (PVG) voltage and inner-voltage controller performs the regulation task. This paper introduces perturbation frequency and perturbation step size design guidelines for such systems. It is shown that while perturbation step size design is similar to that of single-loop structures, perturbation frequency design is quite different. It is revealed that once the inner-voltage loop is properly closed, the influence of PVG dynamic resistance on settling time (and thus on perturbation frequency design) is negligible. Experimental results are provided to verify the proposed guidelines validity.

A Steady State Voltage Stability Analysis of Wind Power Centralized System

It is significant to research the voltage stability of the wind power centralized system (WPCS) for the effective development of the large scale clustering wind energy resources. A steady state voltage stability analysis of the WPCS by employing the PV curve and model analysis is proposed to reveal the voltage stability influence from different aspects. The PV curve is utilized to trace and indicate the voltage collapse point of the WPCS when the small disturbance of wind power is increased gradually. Then the steady state voltage instability modes of the WPCS are analyzed by calculating the bus participation factors of the minimum eigenvalue model at the collapse point. The simulation results of an actual WPCS in North China show that the static state voltage instability mode of the WPCS is closely related to the operating features and control strategies of different reactive power sources. In addition, the implementation of the doubly-fed induction generator wind turbine generator voltage control is beneficial to improve the WPCS voltage stability.

Small Signal Stability of DFIG Connected Power System and Identification of Oscillatory Modes Using Prony Analysis

This paper investigates the impact of wind power on small signal stability of power system using parameters like; wind power penetration level and Doubly Fed Induction Generator (DFIG) voltage controller gain. The impact of wind penetration has been analysed by replacing conventional synchronous generator with DFIG based wind turbines. For this purpose, standard IEEE 14 Bus system has been selected. Time tested modal analysis has been used to compute the oscillatory modes that occur due to small disturbances. Further, the identification of low frequency oscillations has been done using prony analysis. Prony analysis has been performed in time as well as in frequency domain, and used for extracting hidden frequency information from the waveform of the signal.

Comparison among Series Compensators for Fault Ride through Capability Enhancement of Wind Generator Systems

Abstract —A comparison among series connected auxiliary devices, such as Superconducting Fault Current Limiter (SFCL), Dynamic Voltage Restorer (DVR), Thyristor Switched Series Capacitor (TCSC), and Series Dynamic Braking Resistor (SDBR), is performed in terms of fault ride through capability improvement, harmonics suppression, controller complexity, and cost of a fixed speed wind generator system. The tested system consists of one synchronous generator and one squirrel cage induction machine based wind generator, which feed an infinite bus through a double circuit transmission line. Simulation results show that all the devices perform well during symmetrical faults, however, in spite of its controller complexity, the DVR has the best performance among all devices in terms of voltage and speed control of wind generators. The SFCL is the costliest among all devices, however, it is the most efficient in reducing the fluctuations of active power and stator current of the wind generators. The SDBR is the cheapest, and shows a better enhancement in damping active power and limiting fault current as compared to the DVR and TCSC. Despite the ability of TCSC to compensate the reactive power for power quality improvement, it is less desirable to achieve a better performance under transient conditions.

Solving practical power system problems using hierarchical interactive PSO strategy considering SVC controllers

This paper presents a hierarchical interactive particle swarm optimization (HIPSO) for solving the static multi objective optimal power flow (OPF) considering multi SVC controllers and dynamic economic dispatch (DED). This study introduces a variant of PSO using new mechanism search based dynamic adjustment of PSO parameters coordinated with a hierarchical strategy for reactive power planning stage to improve the performances of the original PSO in terms of solution quality and convergence characteristics. The HIPSO algorithm optimizes a combined control variables such as: active power generations, voltage control of generators, tap transformer and the reactive power of multi SVC Controllers installed at a specified buses to minimize fuel cost, total power loss and voltage deviation while satisfying the generators constraints and power system security. The proposed approach examined and applied to many practical test systems: IEEE 57-Bus, IEEE 118-Bus, 40 generating units and 10 generating units to solving; the static multi objective OPF with quadratic fuel cost function, the economic dispatch considering valve point effects and the dynamic economic dispatch considering both valve point effects and ramp rate limits. Simulation results compared to Matpower, to the standard PSO and others recent metaheuristic methods confirm the effectiveness of the proposed combined approach.