Improved Voltage Regulation Research Articles

Improved Voltage Regulation of PV System With Current-Sensorless Active Damping Technique

Due to changing environmental conditions, mainly irradiance, photovoltaic (PV)-interfaced converters inevitably switch between continuous conduction mode and discontinuous conduction mode. Two modes present significantly different characteristics. Moreover, the dynamics in each mode is also dependent on the operating point. This article focuses on the system dynamics and proposes a new control scheme in the voltage-mode framework that enables the mixed conduction mode operation with consistently fast and null overshoot performance. A single control law is made possible for the entire operating range without complex adaptive mechanisms owning to the PV voltage feedback active damping technique. The controller tuning is designed to meet the desired settling time specified by the MPPT requirement. The advantages are validated with numeral simulations and experimental results in comparison to various available control proposals.

Optimal Location of Electric Vehicles in a Wind Integrated Distribution System Using Reptile Search Algorithm

Distributed generation (DG) has been employed over the years in distribution systems to enhance system voltage profile, improve voltage regulation and minimise power losses leading to improved stability besides economic benefits. This work addresses an application of reptile search algorithm (RSA) based optimization technique to determine the optimal placement of electric vehicles (EVs) in distribution systems. A matrix approach based radial distribution load flow method is adopted to determine the optimal location of DGs with the heuristic intelligent search approach of RSA looking after the optimal placement of EV loads. This work presents a standard IEEE-33 and 69 bus system integrated with a wind turbine generating system (WTGS). The system is modeled for optimal placement of EV loads such that the system voltage is maintained within allowable limits by reducing overall system losses. The optimal placement of EV loads in a radial distribution network (RDN) implies establishing an efficient active distribution network satisfying several operating parameters like bus voltage limits and current capacity of feeders while maintaining network radiality with minimal system losses. The proposed technique is investigated on the benchmark IEEE-33 and 69 bus test systems. The simulated results depict a substantial improvement in convergence characteristics and reduction in system losses.

An Improved Voltage Regulation Performance of Floating Interleaved Boost Converters for Fuel Cell Applications Subject to Input Variation and Load Change

This paper aims to provide a novel control framework for exactly regulating the output voltage of floating interleaved boost converters (FIBCs), which have been widely employed in fuel cell applications in recent years. Firstly, a mathematical model of the FIBC is constructed according to Kirchhoff’s current and voltage loop principles. Then a cascade control structure with a current inner loop and voltage outer loop is developed to achieve the desired voltage regulation performance. The current controller is established based on the generalized super-twisting algorithm (GSTA) to ensure that the inductor current exactly follows the current reference, which is generated by the outer loop. Meanwhile, an active disturbance rejection control (ADRC) framework is utilized for robustly regulating the output voltage despite the presence of input variation and load change in the voltage control loop based on a nonlinear continuous GSTA-based extended state observer (GSTA-based ESO). The stability of a closed loop system based on the GSTA controller and the GSTA-based ESO is conclusively proven using the Lyapunov theory. The Simscape model of the FIBC is developed, which is used to verify the feasibility and the appropriateness of the recommended control algorithm. Finally, numerical simulations are carried out to demonstrate the effectiveness of the proposed method compared to several previous works.

Hybrid multi-objective method based on ant colony optimization and firefly algorithm for renewable energy sources

This work presents a hybrid multi-objective optimization technique (HMO-ACO/FA) based on ant colony optimization (ACO) and firefly algorithm to address multi-objective optimum power flow (MOOPF) difficulties (FA) by eliminating certain operating restraints. In HMO-ACO/FA, an objective function (OF) vector with a vector of colonies has been modelled to be solved by an ACO, but the spare solutions in the search space have been projected to be found using a local search technique. Besides, FA has been projected to enhance the enactment and to obstacle the unfeasible solutions directly by presenting two moves for the fireflies. HMO-ACO/ The IEEE 30-bus standard and the Indian technical 62-bus scheme are both used in India have started FA to address three bi-objective characteristics: energy lower cost and power reducing losses; energy cost and power reduction; and power cost and energy loss reduction and L-index, as well as reductions in energy costs and pollutant emissions, as well as a tri-objective function that simultaneously reduces energy costs, reduces power losses, and improves voltage regulation. The findings were obtained by introducing two renewable energy sources (RES) into the test program, such as solar photovoltaic (PV) and wind farms. The findings show that HMO-ACO/FA can generate precise, MOOPF-free solutions with a well-distributed Pareto optimal distribution. The results of other published techniques in the literature were similar to those of the HMO-ACO/FA algorithms. The analysis' results show that HMO-ACO/FA performs better than other strategies in terms of discrete and compromise responses.

Integral sliding mode based direct power control of isolated DC‐DC converter for improved voltage regulation

AbstractThis article presents an isolated bidirectional DC‐DC dual active bridge (DAB) converter with an integral sliding mode‐based direct power control (SM‐DPC). Maintaining the dc‐link stability and obtaining a robust control for the converter during sudden load change is a significant challenge. The sliding mode control is well known for its robustness, stability, and tracking performance. The sliding surface based on output voltage error is selected, while the proposed method utilizes the equivalent control approach to generate the power reference for the DAB converter. The direct power control provides an easy control method for the DAB converter as the output voltage depends on the transmitted power, governed by the phase shift angle of two H‐bridges of the converter. The proposed method enhances the steady‐state performance and renders a fast transient response under load change and input voltage variation. Moreover, the method avoids complicated converter modeling and utilizes the voltage dynamic equation and power transfer equation for the controller design. The controller performance and effectiveness are validated with experimental results for a 2‐kW DAB converter.

Weak Grid-Induced Stability Problems and Solutions of Distributed Static Compensators with Voltage Droop Support

Distributed static compensators (DSTATCOMs) are grid-connected power electronic equipment dedicated to compensating reactive power as well as improving voltage regulation in distribution networks. They eclipse conventional compensation approaches, such as capacitor banks, in terms of flexibility and effectiveness. Despite their identified advantages, STATCOMs with voltage droop are subject to weak grid-induced stability problems, as first revealed by this paper. Specifically, the voltage droop controller that couples the amplitude of point of common coupling (PCC) voltages to the reactive current reference creates a local control loop. Such a loop greatly deteriorates system stability in weak grids, which feature large and variable grid impedances. To address such stability problems, we propose a novel virtual resistance control scheme, which improves system stability through mitigation of local control loop gains in the low-frequency band. Experimental results obtained from a DSTATCOM prototype clearly demonstrate the correctness of stability analysis and the effectiveness of stability improvement.

Design of Modified Luo Converter for Electric Vehicle Battery Charger

Higher energy and battery efficiency are now major concerns for Electric Vehicle (EV) manufacturers and consumers. The main component of the two-stage EV on-board charger is the DC-DC converter. The phase displacement of full-bridge to operate the switch at either zero voltage or zero current in a power switch DC-DC converter, currently has issues such as voltage variation on the consequent side, which is secondary of the transformer, and it implies poor performances. Power Factor Correction (PFC) converters used in modern EV chargers achieve high performance and adequacy throughout charging. A modified luo converter is designed to achieve high efficiency in EV charging. A luo converter is a type of PFC that is commonly used as a converter of DC to DC with improved voltage regulation in the presence of rapidly changing line voltages. In this aimed work, a reformed separate Luo converter-based electric vehicle charger is developed. To suppress voltage oscillations, two devices which means switches and two clipping diodes are connected at the elementary side in the detachment of High Frequency Transformer (HFT). The Luo converter handles Discontinuous Conduction Mode (DCM) of operation, decreases control complexity, and keeps converter's output constant. In the feedback system, the Constant Current and Constant Voltage (CC-CV) mode technique is used in conjunction with the PI controller to improve competence and reduce transmission leakage. The proposed system's performance is evaluated by applying in MATLAB/SIMULINK software, and the outcomes are promising.

An Improved Voltage Regulation and Effective Power Management by Coordinated Control Scheme in Multibus DC Microgrid

The available power is not always constant in renewable energy sources (RESs). It varies depending on the environmental conditions and time interval. These raise the problems of mismatch in power-sharing among the RESs and bus voltage regulation. The novelty of this article is that it presents a new control scheme for a multibus DC microgrid, in which it improves voltage regulation at the load bus under different network topologies and various system operating conditions. The proposed control method achieves adequate power-sharing proportional to the available power in RESs connected to the DC microgrid. Therefore, it accomplishes effectual power management and reduces the burden on the energy storage system (ESS) in the DC microgrids. It adapts to the inclusion and removal of sources under different network topologies. This control scheme is tested experimentally for various network topologies under diverse operating conditions. The results prove the feasibility of the proposed method.

A Comparative Study of Dual Stator With Novel Dual Rotor Permanent Magnet Flux Switching Generator for Counter Rotating Wind Turbine Applications

Compared with the single rotor wind turbine, a counter-rotating (CR) wind turbine with two rotor sets leads to twice power density. In this regard, dual stator CR (DSCR) permanent magnet flux switching generator (DSCR-PMFSG) is employed. However, in DSCR-PMFSG both rotor and armature parts are rotating and require slip rings for power transmission. These slip rings associate demerits of constant maintenance, poor speed regulation, increased cost, and additional slip ring losses, whereas DSCR-PMFSG offer lower flux and lesser power density. To overcome the demerits of DSCR-PMFSG as mentioned earlier, this paper proposed a novel dual rotor counter-rotating permanent magnet flux switching generator (DRCR-PMFSG) for wind turbine applications that eliminate the requirements of slip rings and retain brushless operation. The proposed DRCR-PMFSG share one stator connected back-to-back through a flux bridge that provides an alternate flux path between two mechanical ports associated with the inner rotor and outer rotor, contributing to the cumulative output. A detailed comparative analysis of DSCR-PMFSG and DRCR-PMFSG is performed under static characteristics, overload, and wide speed range to generate output power, voltage, current, power density, and efficiency. Quantitative comparative analysis under static analysis evident that proposed DRCR-PMFSG exhibits 33.29% higher flux, suppressed cogging torque and torque ripples up to 53.48% and 67.45%, respectively. Furthermore, a comprehensive quantitative analysis is performed under coupled overload and over-speed capability. Analysis exposes that in comparison with DSCRP-PMFSG, the proposed DRCR-PMFSG improves voltage regulation factor by 55.88%, output current enhanced by 67.9%, raise output voltage to 2.01 times, and power density to 1.72 times while maintaining the efficiency of 90.195% and achieving stable voltage profile with load variation. Finally, a detailed comparative analysis with conventional designs is performed and comprehensive mathematical modelling based on sub-domain model is developed accounting stator slot and rotor pole combinations, magnetic saturation, and winding configuration to validates finite element analysis (FEA) of JMAG Designer v.20.1.

A Modified Control Method for Grid Connected Multiple Rooftop Solar Power Plants

This article proposes an enhanced control strategy for a microgrid consisting of multiple rooftop solar photovoltaic sources. These sources are of different power ratings and intermittent in nature. The microgrid is flexible to function either in islanded mode or in grid connected mode. It affects power management and hampers the power quality in microgrid. The proposed control scheme enhances the power quality of the microgrid by providing reactive power compensation to local loads. Thus, it reduces the burden on utility grid. The proposed control technique establishes a priority-based policy for reactive and active power compensation under local demand variance. A smooth and automated transition of microgrid between islanded and grid connected modes is achieved. This seamless transition of the system between two modes avoids the transient in the system. In islanded mode, the proposed control scheme ensures improved voltage regulation under dynamic load demand. It also ensures a minimum burden on the voltage source. Also, the proposed control scheme maintains the power factor of the system near to unity. The system performance is validated experimentally under a number of various operating conditions such as dynamic load variation, grid condition, automated transition, intermittent power generation in real time simulator.

Cost-Based Interlinking Converter Droop Control Strategy for Load Management with Improved Voltage Regulation in AC–DC Microgrid

Cost-Based Interlinking Converter Droop Control Strategy for Load Management with Improved Voltage Regulation in AC–DC Microgrid

Improving the Transient Response of Hybrid Energy Storage System for Voltage Stability in DC Microgrids Using an Autonomous Control Strategy

In renewable microgrid systems, energy storage system (ESS) plays an important role, as an energy buffer, to stabilize the system by compensating the demand-generation mismatch. Battery energy storage system serves as a decisive and critical component. However, due to low power density and consequently slow dynamic response the lifetime of BESS is observably reduced due to high current stress, specifically experienced during abrupt/transient power variations. Hence, hybridization with supercapacitor storage system is conferred. Additionally, the controllers designed for energy storage systems should substantially respond for compensating the transient requirement of the system. In this article, we propose a decoupled control strategy for batteries and supercapacitors based on k - Type compensators and a nonlinear PI controller (NPIC) respectively. The formulated control design is tested for voltage regulation in a standalone microgrid. Furthermore, a comparative analysis is presented with benchmark low-pass-filter (LPF) based controller. The results obtained shows the proposed control technique possess a faster response with improved voltage regulation capabilities. For the test system regulated at 48 V for various abrupt load-generation various case studies presented, the proposed methodology maintains a significantly reduced voltage deviation between 47 V - 51 V in contrast to 45 V - 56 V observed in the LPF methodology. Furthermore, the complexity is simpler in comparison to LPF based control strategy and a comparative obviation of additional sensing devices is achieved, that inherently reduces the detrimental effect on ESS response during transient condition.

Optimal Planning and Operation of Multi-Frequency HVac Transmission Systems

Low-frequency high-voltage alternating-current (LF-HVac) transmission scheme has been recently proposed as an alternative solution to conventional 50/60-Hz HVac and high-voltage direct-current (HVdc) schemes for bulk power transfer. This paper proposes an optimal planning and operation for loss minimization in a multi-frequency HVac transmission system. In such a system, conventional HVac and LF-HVac grids are interconnected using back-to-back (BTB) converters. The dependence of system MW losses on converter dispatch as well as the operating voltage and frequency in the LF-HVac is discussed and compared with that of HVdc transmission. Based on the results of the loss analysis, multi-objective optimization formulations for both planning and operation stages are proposed. The planning phase decides a suitable voltage level for the LF-HVac grid, while the operation phase determines the optimal operating frequency and power dispatch of BTB converters, generators, and shunt capacitors. A solution approach that effectively handles the variations of transmission line parameters with the rated voltage and operating frequency in the LF-HVac grid is proposed. The proposed solutions of the planning and operation stages are evaluated using a multi-frequency HVac system. The results show a significant loss reduction and improved voltage regulation during a 24-hour simulation.

Voltage Source Inverter based Static Synchronous Compensator

Distribution static synchronous compensator is used to reduce the losses and improvement of voltage regulation in Multi Bus systems.The DSSC introduces a current into the system to lower the losses. The DSSC can enhance the reliability and quality in power flow of a less voltage distribution network. A DSSC is one of the new generation FACTSdevices with a promising feature of applications in power system. This work deals with the modeling and simulation of 50 Bus systems with Distribution static synchronous compensator and the voltage sag is created by involving a heavy load. The sag is mitigated with Distribution static synchronous compensator.

RETRACTED ARTICLE: Modified flower pollination algorithm for optimizing FOPID controller and its application with the programmable n-level inverter using fuzzy logic

Ann-level multilevel inverter for PV connected systems is proposed in this paper. The proposed inverter is the combination of a buck–boost converter and an H-bridge inverter (B2H multilevel inverter). This system produces a constant AC output voltage with multilevels for a PV connected system with few number of switches. With the proposed inverter, the constant output voltage level is obtained from the PV system irrespective of the variable irradiance. Any number of levels is achieved by varying the duty cycle of the buck–boost converter over a wide range using an n-level generation algorithm. Thus, many numbers of levels can be attained in the output voltage which reduces the THD significantly. The voltage regulation process is performed by designing an optimized fractional-order proportional integral and derivative (FOPID) controller. The FOPID controller provides improved voltage regulation characteristics through the optimization of parameters of controller with the use of modified flower pollination algorithm. The proposed configuration is designed and implemented in MATLAB Simulink. The quality of output, their harmonics and the output resolution time are evaluated for various input voltages and for various numbers of output levels.

Integrated control scheme for dynamic power management with improved voltage regulation in DC microgrid

This article presents an integrated control scheme to improve power sharing for power management and voltage regulation in DC microgrids. The proposed scheme considers the available power and the stochastic nature of sources to achieve adequate power sharing among them. Therefore, it achieves effective utilization of each source. In addition, the effective use of energy storage systems (ESSs) is also achieved by reducing their charging/discharging cycles. The proposed control scheme improves voltage regulation under various operating conditions. It enhances the stability of microgrids and improves their dynamic response. The proposed control scheme is adaptive to changes in the source or load. It operates without historical/previous data, which reduces the computational burden. The proposed control scheme is experimentally validated under diverse operating conditions.

Distributed droop control of dc microgrid for improved voltage regulation and current sharing

DC microgrid is becoming popular because of its high efficiency, high reliability and connection of distributed generation with energy storage devices and dc loads. The main objective in the dc microgrid is to keep the dc bus voltage constant and equalise per unit current sharing among converters. The conventional droop control is used to equalise per unit current sharing similar to reactive power sharing in an ac microgrid. Nevertheless, the problem in conventional droop control is that equal current leads to a reduction of dc bus reference voltage and voltage regulation becoming unequal across each node due to unequal line resistance drop. The proposed controller works on adaptive droop and voltage shifting technique, which equalises the current sharing whether line resistances are similar or not and controls each output voltage to follow the respective bus reference voltage. The isolated dc–dc converters are used to simulate and validate the proposed control technique.

Application of demand response to improve voltage regulation with high DG penetration

The ability of a consumer friendly demand response based voltage control (DR-VC) program to improve the voltage regulation in a low voltage distribution network (LVDN) with high penetration of DG is investigated. The use of active and reactive power management to regulate the nodal voltage in a distribution network with simple incremental reduction algorithm, in conjunction with DR, is proposed as a solution for over voltage and undervoltage issues in the LVDN. The algorithm micromanages the load and generation in the network enabling the operator to utilize grid resources economically and efficiently while maintaining fairness between consumers with minimum inconvenience. The algorithm is tested on a representative.74-load radial urban distribution network (Dublin, Ireland) using consumer load and DG generation profiles. The system is modelled and analysed using COM interface between OpenDSS and MATLAB. The DR is modelled through a mixed integer linear programming (MILP), implemented in CVX, such that consumer inconvenience is prioritized. The DR-VC algorithm is capable of regulating load and generation within normal operation limits during undervoltage and overvoltage scenarios.

Smoothing control of solar photovoltaic generation using building thermal loads

Distributed energy resources such as solar photovoltaic (PV) systems are seeing significant expansion in power grids worldwide. However, serious system integration issues have arisen including voltage fluctuations and accelerated aging of voltage regulation devices, when adopting mass amounts of volatile energy resources onto legacy distribution networks originally designed for unidirectional power flow. Building heating, ventilation and air-conditioning (HVAC) systems, collocated with the distributed generation, can be considered as flexible loads due to the inherent building thermal inertia. HVAC systems can be proactively controlled to improve voltage regulation of distribution networks with high PV penetrations. This paper presents a smoothing solution that modulates HVAC power in response to volatile PV generation as a means to mitigate fluctuations in the net demand and generation. To demonstrate the effectiveness and evaluate performance gains, hardware-in-the-loop (HIL) tests were carried out using a 3-ton variable-speed heat pump. The HIL tests leveraged a building thermal dynamic model and a steady-state power flow model for a 33-bus distribution network to capture realistic indoor thermal responses and distribution voltage variations during PV smoothing control. Test results showed that the developed strategy was effective in reducing variations of net demand and generation with negligible impact on indoor comfort. More than 55% reductions of voltage fluctuation were achieved and tap operations of voltage regulators could be fully or partially eliminated with proactive PV smoothing.

Hybrid photovoltaic/small-hydropower microgrid in smart distribution network with grid isolated electric vehicle charging system.

The increasing integration of renewable generation and power system innovations toward smartness have made microgrid a platform through which sources of energy could be annexed for efficient network operation. However, the sources must be carefully selected for a synergy to minimize intermittent challenges for productive output. This paper presents a grid-connected load-following hybrid solar photovoltaic and small-hydro microgrid with a grid isolated electric vehicle charging system. A decentralized multi-agent smart voltage network reactive power compensation dynamically regulates and monitors the network limits based on nodes' local measurements. The solar system supports hydropower during the peak load demand and solar storage is charged up by hydropower when irradiation is at the lowest threshold. The energy balance during excess production is configured for individual electric vehicle charging as load points. The photovoltaic-hydropower/electric vehicle microgrid is incorporated with maximum power point tracking and excitation control respectively as a means of control. The detail performance analysis using a time series evaluation over a 24 h daily simulation period is done on standard IEEE 33 and 118-bus radial distribution networks. Consequently, improved voltage regulation, dynamic energy reserve for electric vehicle’ charging and a better reduction in power loss are ensured in the research work.