Grid Voltage Research Articles

Grid Connection of a Squirrel-Cage Induction Generator Excited by a Partial Power Converter

This article concerns the connection process of a squirrel-cage induction generator to the grid/microgrid. Typically, the generator is unexcited, and its connection to the grid is made directly via a switch. This connection causes a high inrush current and grid voltage drop, which local consumers notice. This article proposes a robust power system consisting of the squirrel-cage induction generator, a power electronic converter, and a capacitor bank, all connected in parallel. The proposed configuration and a dedicated control system eliminate the inrush current and compensate for the generator’s reactive power during grid-tied operation. The converter controls the generator voltage build-up to adjust the generator voltage to the grid voltage (controlled excitation) and connects the generator to the grid, minimising distortions. Moreover, the system is robust because the failure of the converter does not stop the power generation, unlike a system with a back-to-back converter, where the converter links the generator and the grid. Furthermore, the parallel-connected converter has a significantly reduced power rating because it is only rated for a part of the reactive generator power. The rest of the reactive generator power is delivered by the fixed capacitor bank. The article presents the system configuration, the control method, and laboratory results confirming the system’s effectiveness in maintaining high-quality grid voltage during generator-to-grid connection and high-quality power supplied to the grid.

Dynamic inverter station current control of HVDC system integrated offshore DFIG wind farm under onshore grid voltage distortions

A power control method for an HVDC system integrating a DFIG-based offshore wind farm supplying a weak onshore grid is the prime focus of this work. The real power generated by the wind farm is regulated by the LCC-based rectifier station and transmitted to the VSC-based inverter station through the HVDC line. The work proposes a control mechanism to integrate these two stations with better power quality management. The inverter station facilitates the effective transmission of generated power to the onshore grid under nominal onshore grid voltages. Nevertheless, the abnormalities in onshore grid voltage lead to converter failures due to huge harmonic grid currents and power pulsations beyond permissible limits; uninterrupted power transfer without compromising power quality is the target. The proposed method utilises a dynamic current control technique at the inverter station to inject compensating current. This enables independent regulation of active and reactive power, mitigating power oscillations and minimising grid current THD induced by onshore grid voltage deviations. The simulations in PSCAD/EMTDC and hardware-in-loop (HIL) experiments using OPAL-RT demonstrate that the proposed control strategy significantly reduces power oscillations while maintaining a grid current THD of 1.47% up to 50% unbalance in onshore grid voltage.

Methodology for Determining the Optimal Location and Capacity of STATCOM Based on Grid Clustering for Grid Voltage Stability

Methodology for Determining the Optimal Location and Capacity of STATCOM Based on Grid Clustering for Grid Voltage Stability

Electron emission performance analysis and application of carbon nanotube cold cathode prepared by cold pressing process

In this work, a carbon nanotube (CNT) cold cathode electron emitter fabricated by the cold pressing process was developed and studied. The electron emission performance was investigated and the application of pulse x-ray emission and imaging was explored by this cold cathode. The results indicated that the electron emission performance was excellent with electric intensities of turn-on and threshold of 0.47 and 1.17 V/μm@1 mA/cm2, respectively, and the field enhancement factor reached 17 514. The application research results showed that the pulse x-ray waveform has a great corresponding well with the grid voltage, and the imaging of a screw was clear, whose thread and pitch could be seen clearly. This article proposed a cold pressing process prepared for the CNT cold cathode, providing a new technical approach for the development of field emission cold cathode preparation processes.

Experimental investigations on the trigger characteristics of a cold-cathode plasma discharge switch with grid voltage control

Experimental investigations on the trigger characteristics of a cold-cathode plasma discharge switch with grid voltage control

Design and Analysis of a Photovoltaic Power Conditioning System Using Grid Voltage Feedforward Procedure in Weak Grid Condition

Design and Analysis of a Photovoltaic Power Conditioning System Using Grid Voltage Feedforward Procedure in Weak Grid Condition

Study on Grid Stability of Electric Vehicle Bidirectional Charging Device Based on Bidirectional Power Electronic Converter

With the increasing number of electric vehicles (EVs), V2G (Vehicle-to-Grid) and G2V (Grid-to-Vehicle) technologies have garnered growing attention as essential methods for energy flow between EVs and the power grid. This study examines the impact of EV charging devices, based on bidirectional power electronic converters, on grid stability. As EVs become more widely adopted, V2G and G2V technologies are extensively applied to enable bidirectional energy flow between EVs and the grid. This study analyzes different topologies of power electronic converters and explores how optimized control strategies can enhance grid voltage and frequency stability. The research shows that bidirectional charging devices provide significant advantages in addressing voltage fluctuations and frequency instability, especially in peak shaving and valley filling, effectively easing grid load. Furthermore, future developments in bidirectional charging devices will focus on intelligent control and synergistic optimization with renewable energy to improve grid stability and power quality. The research methods include analysis and comparison of different converter topologies. Results indicate that bidirectional charging devices have a significant effect in resolving grid instability issues, supporting the further advancement of smart grids).

Multi-Fault-Tolerant Operation of Grid-Interfaced Photovoltaic Inverters Using Twin Delayed Deep Deterministic Policy Gradient Agent

The elevated penetration of renewable energy has seen a significant increase in the integration of inverter-based resources (IBRs) into the electricity network. According to various industrial standards on interconnection and interoperability, IBRs should be able to withstand variability in grid conditions. Positive sequence voltage-oriented control (PSVOC) with a feed-forward decoupling approach is often adopted to ensure closed-loop control of inverters. However, the dynamic response of this control scheme deteriorates during fluctuations in the grid voltage due to the sensitivity of proportional–integral controllers, the presence of the direct- and quadrature-axis voltage terms in the cross-coupling, and predefined saturation limits. As such, a twin delayed deep deterministic policy gradient-based voltage-oriented control (TD3VOC) is formulated and trained to provide effective current control of inverter-based resources under various dynamic conditions of the grid through transfer learning. The actor–critic-based reinforcement learning agent is designed and trained using the model-free Markov decision process through interaction with a grid-connected photovoltaic inverter environment developed in MATLAB/Simulink® 2023b. Using the standard PSVOC method results in inverter input voltage overshoots of up to 2.50 p.u., with post-fault current restoration times of as high as 0.55 s during asymmetrical faults. The designed TD3VOC technique confines the DC link voltage overshoot to 1.05 p.u. and achieves a low current recovery duration of 0.01 s after fault clearance. In the event of a severe symmetric fault, the conventional control method is unable to restore the inverter operation, leading to integral-time absolute errors of 0.60 and 0.32 for the currents of the d and q axes, respectively. The newly proposed agent-based control strategy restricts cumulative errors to 0.03 and 0.09 for the d and q axes, respectively, thus improving inverter regulation. The results indicate the superior performance of the proposed control scheme in maintaining the stability of the inverter DC link bus voltage, reducing post-fault system recovery time, and limiting negative sequence currents during severe asymmetrical and symmetrical grid faults compared with the conventional PSVOC approach.

Stability and Fault Detection Algorithm of Grid-Connected Inverter in Complex Power Grid Environment

In order to improve the stability, this paper designs a control strategy based on adaptive grid impedance. By monitoring the grid impedance in real time and dynamically adjusting the inverter control parameters, the influence of grid impedance change on inverter stability is effectively reduced. At the same time, LCL filter is introduced, which significantly filters out the higher harmonics in the inverter output current and improves the output waveform quality. In addition, a voltage compensation device is applied to quickly generate a compensation voltage signal when the grid voltage fluctuates to ensure the stability of the inverter output voltage. In the aspect of fault detection, a data-driven fault detection algorithm is proposed, which combines machine learning and real-time monitoring technology to realize early detection and accurate diagnosis of inverter faults by collecting and analyzing inverter operation data. The experimental results show that the algorithm performs well in the detection of power switch device faults, sensor faults and other types, and has high classification accuracy. The research shows that the control strategy based on adaptive grid impedance, the addition of LCL filter and the application of voltage compensation device have significantly improved the stability of grid-connected inverter in complex grid environment. The proposed data-driven fault detection algorithm provides strong support for rapid fault location and accurate treatment of inverter.

A Novel Synchronization Strategy for Distributed Energy Resources in Weak Grids Using Remote Strong Grid Sensing

This paper proposes a novel strategy for the current injection-based control of distributed energy resources connected to weak grids via a voltage source converter. The current injection controller is no longer synchronized with the point of common coupling but with the strong grid point voltage. The strong grid synchronization control strategy improves the output dynamics of the voltage source converter and recovery after faults in weak grids. The phase difference between the voltage source converter and the strong grid voltages caused by the long power lines does not affect the power control. Furthermore, a time delay-compensation method is proposed which tolerates the communication time delay introduced by the transmission of the synchronization signal from the strong grid point. The performance of the proposed control strategy is verified in detail using MATLAB 2023b simulations and real-time digital simulations on a medium voltage model and also validated in an experiment on a low-voltage grid-feeding inverter setup.

Power Flow Control with a Single Stage Grid Connected Pv Mechanism with a Multilevel Inverter

There is potential to feed excess electricity to the grid for more efficient and cost-effective power utilization when solar PV arrays are installed widely in comparison to other renewable power output. The primary objective of this article is to use a multilevel inverter to operate autonomously regulate the active and reactive power flow. A vector control system that rotates synchronously with the grid frequency has been devised in both direct and quadrature reference frames. Two current control loops have been implemented to control the current delivered to the grid so that it will has low total harmonic distortion and is in phase with the grid voltage. To run the inverter at a suitable DC link voltage which corresponds to maximum power-which is established by the MPPT algorithm, a DC voltage control loop has also been implemented. Inverters that are connected to the grid are commonly utilized to enhance dispersed generation and power eminence.

Power quality enhancement of three-phase solar photovoltaic system-based generalized integrator controlled UPQC

Abstract As distributed generation becomes increasingly prevalent, providing reliable and stable electrical energy to the grid is of paramount importance. Therefore, precise monitoring of grid voltage is necessary in order to synchronize compensating current and voltage with the grid. The Dual Second-Order Generalized Integrator (DSOGI) can extract the fundamental positive sequence component from three-phase grid signals, enabling accurate determination of grid phase and current signals for rapid and precise grid compensation. This paper presents a control algorithm for extracting and compensating UPQC reference signals based on the Second-Order Generalized Integrator (SOGI). The improved photovoltaic-fed Unified Power Quality Conditioner System (PV-UPQC) is verified and analyzed under conditions of unbalanced grid voltage, current harmonics, as well as voltage sags and swells. It can be demonstrated that the enhanced system exhibits superior adaptability to the grid.

Optimized control strategy for a three-phase grid connected inverter using PI controller and DQ frame

This paper provides a proportional-integral (PI) controller and direct-quadrature (DQ) frame transformation-based optimum control method for a three-phase grid-connected inverter. In terms of grid synchronization, voltage regulation, and harmonic abatement, the proposed control technique attempts to improve the inverter's performance. By separating the control of active and reactive power, the control structure is made simpler and independent regulation of these parameters is possible. This improves the inverter's capacity to quickly react to grid disruptions and track reference values accurately. In order to lower carbon emissions and improve grid dependability, it has become vital to integrate renewable energy sources into the current power grid. Grid-connected inverters are essential in this situation because they transform DC electricity from renewable sources into grid-safe AC power. This abstract outline a proportional-integral (PI) controller and direct-quadrature (DQ) frame-based optimal control method for a three-phase grid-connected inverter using a MATLAB simulation.

Grid-connected double-stage PV system with space vector PWM inverter and MPPT

Because of the increasing demand for non-conventional energy sources, photovoltaic system integration into the electrical grid is becoming more crucial. It is advised to employ a double-stage grid-connected PV system. This can be employed with the main parts boost converter, which helps to boost the DC output from the PV channels. And next one is the space vector pulse width modulation (SVPWM) inverter which can provide better harmonic performance and higher efficiency compared to traditional PWM methods. The SVPWM technique is employed to modulate the inverter output, generating a sinusoidal AC waveform that matches the grid frequency and voltage. By adjusting the pulse width to achieve effective and trustworthy grid integration. To maximize power extraction takes place by using maximum power point tracking (MPPT). The SVPWM inverter is crucial in converting DC power to AC power and enabling grid connection. Utilizing SVPWM allows exact control of voltage magnitude, frequency, and phase angle to provide high-quality sinusoidal AC output voltage. The power quality of the electricity pumped into the grid is improved by this precise management, which also ensures adherence to grid standards and reduces harmonic interference.

A New Method for DFIG Control under ‎Unbalanced Grid Voltage Conditions

A New Method for DFIG Control under ‎Unbalanced Grid Voltage Conditions

Phase-locked loop based synchronization schemes for three-phase unbalanced and distorted grid: a review

The rapidly growing dispersion of distributed generation systems into the utility grid needs appropriate control techniques to stay interconnected even under abnormal and distorted grid conditions to ensure the overall grid stability. To avoid the loss of renewable energy sources (RES) based power generation, the disintegration of RES with respect to synchronization issues must be prohibited for efficient operation. RES control highly relies on the synchronization technique as it is faster and accurate enough to detect the utility grid variables in terms of amplitude, phase, and frequency. Mostly, the phase-locked loop (PLL) synchronization schemes are utilized for control of RES and monitoring of grid voltage. The dynamics of the grid side converter (GSC) is directly influenced by the performance and design criteria of the PLLs. This paper proposes an overall review of the performances of three phase PLL based grid synchronization methods under diverse weak grid conditions.

Enhancing grid voltage stability and reliability by harnessing off-grid power sources with multi-objective fuzzy spark firefly optimization algorithm

ABSTRACT In traditional power systems, distribution networks (DNs) often suffer from significant power losses. However, integrating decentralized sources into these networks not only mitigates these losses but also eases the burden on central power sources. As centralized power plants are frequently located at a distance from consumption centers, incorporating off-grid power sources (OPSs) closer to demand hubs enhances overall system efficiency. This paper focuses on optimizing OPS allocation using the fuzzy spark firefly optimization algorithm (FSFOA). By strategically placing various types of OPS units, the aim is to minimize both real and reactive power losses in the distribution system. The study evaluates system performance metrics, showcasing how different types of OPS optimization affect the network in a range of (11 kV to 13 kV) DN base voltages. The FSFOA offers distinct advantages in efficiently navigating the complex optimization landscape, allowing for the precise placement of OPS to achieve significant improvements in system efficiency and performance. For instance, OPS Type-IV at bus number 6 demonstrates substantial reductions in real power loss by 68.92% to 91.464 kW and in reactive power loss by 62.99% to 73.8374 kVAr, highlighting its effectiveness in managing reactive power and improving overall power factor.

Power Quality Enhancement in Grid-Connected Solar PV Systems Using Adaptive Control and Multilevel Inverter Topologies Under Dynamic Grid Conditions

This paper introduces a control strategy that uses an integrator-based positive sequence estimator to improve the power quality of a grid-connected double-stage solar PV system. The control extracts positive sequence components from distorted and unbalanced grid voltages to calculate unit templates and grid reference currents during grid anomalies like distortion, unbalance, sag/swell, and DC offset. A feedforward term is introduced to the photovoltaic array to ensure rapid transient response, and the DC-link voltage is adaptively regulated to reduce the voltage source converter (VSC) losses during weak grid conditions. The paper compares the performance of two-level and three-level inverters in this system configuration, highlighting the differences in power quality improvement, harmonic reduction, and system efficiency under various grid disturbances and intermittent solar conditions. Simulation results, performed in MATLAB, validate the superior performance of the three-level inverter in terms of lower total harmonic distortion (THD) in grid currents, in compliance with IEEE standard 519, while demonstrating the satisfactory response of both inverter types during challenging grid conditions like intermittent solar irradiation, DC offset, voltage distortions, unbalance, and voltage sag/swell.

Multi-level consensus based load frequency controller with multi-battery energy storage systems

This study introduces a primary and secondary level multi-consensus load frequency controller (LFC) with distributed multi-battery energy storage system (MBESS) to regulate the frequency and voltage of the islanded grid. The suggested control approach uses battery storage devices’ ability to deliver or absorb active power during power shortages or surpluses in order to regulate the system frequency and voltage. The controller uses consensus-based distributed coordination among agents in order to achieve stabilise frequency and voltage. In primary mode, each node exchanges local information with its neighbour, such as battery energy, power, and state of charge (SoC), to reach an agreement value in finite time. In secondary mode, the controller achieves its stability by sharing active and reactive power to regulate the frequency and the voltage. The conventional PI controller with a state feedback loop controller is used as a local controller for LFC in the multi-agent control platform. Numerical examples are considered throughout the simulations to highlight the controller’s functionality and are compared with the past literature. As simulation results suggested, the proposed model with the MBESS will have a efficient system performances compare to traditional LFC mode. In this case, each single battery model has the ability to work as a generator and as an active load to the grid to balance frequency and voltage fluctuations. Furthermore, the results are obtained through the OP5700 real-time simulator to compare the values with the simulation. The results are further validated on the IEEE 14-bus power system. Analysis of the results indicates that the proposed system exhibits better characteristics with the multi-level consensus approach, compared to the traditional LFC.

Modeling and Control of Dual Active Bridge‐Modular Multilevel Converter‐Based Solid State Transformer for Grid Integration of SPV and Battery Energy Storage

ABSTRACTThis article deals with the modeling and control of a solid‐state transformer (SST) based on a dual active bridge (DAB) and modular multilevel converter (MMC) for integrating solar photovoltaic (SPV) and battery energy storage (BES) systems into the grid. SST uses DABs for bidirectional DC‐DC conversion and an MMC for DC‐AC conversion. A hybrid control method is developed in this study, which combines proportional‐integral (PI) controllers and model predictive control (MPC) to achieve the multiple objectives of the SST. The DABs' control system uses PI controllers for power extraction from the SPV system and to regulate the charging and discharging of the BES according to power generation and demand fluctuations. MPC is applied to control the active power injection, regulate the DC‐link and sub‐module capacitor voltages of the MMC. Moreover, the developed hybrid control method ensures reliable SST performance even under adverse conditions like grid voltage distortion, unbalance, and frequency variations. An energy management strategy is developed based on total power generation, reference active power injection, and the state of charge of the BES. This strategy ensures accurate reference power injection to the grid despite dynamic changes in operating conditions. The article also presents a detailed mathematical model of the DAB and MMC components, and the stability of the control algorithm is analyzed theoretically. The effectiveness of the SST and the proposed hybrid control scheme is demonstrated through MATLAB/Simulink simulations and hardware‐in‐the‐loop experimental results under various operating conditions.