Stable DC-link Voltage Research Articles

Design, modeling, and validation of a 0.5 kWh flywheel energy storage system using magnetic levitation system

The flywheel energy storage system (FESS) has excellent power capacity and high conversion efficiency. It could be used as a mechanical battery in the uninterruptible power supply (UPS). The magnetic suspension technology is used in the FESS to reduce the standby loss and improve the power capacity. First, the whole system of the FESS with the magnetic levitation system is introduced, and the control diagrams of the charging/discharging processes are developed. Moreover, the force modeling of the magnetic levitation system, including the axial thrust-force permanent magnet bearing (PMB) and the active magnetic bearing (AMB), is conducted, and results indicate that the magnetic forces could stably levitate the flywheel (FW) rotor. The stator part and the FW rotor are analyzed using the FEM model, and the results could satisfy the requirements on stress and strength of the FESS at the rated speed. Then, the control models are established to accomplish the rapid charging/discharging functions of the FESS. Finally, experiments are performed to test the charging/discharging ability, and the results show that an excellent control current could enhance the charging/discharging efficiency so the stable DC link voltage could be outputted at the discharge process. Therefore, the test results prove that the designed FESS could be used as an auxiliary power supply for the UPS when the grid power fails.

Enhanced energy storage system efficiency for remote area-based DC microgrid

This article suggests a hybrid storage system-based DC microgrid to supply the needs of remote areas with variable loads demands. This would help solve problems like limited energy storage systems, complicated consumption, and unstable power production from renewable sources. Energy storage is an attractive option for isolated zone; however, a single storage unit may not be sufficient owing to constraints in capacity, power, energy density, and life cycle. consequence, this study is concerned with hybrid energy storage systems battery/supercapacitor, which combine the most advantageous characteristics of various energy storage technologies to attain relevant performance. Furthermore, the supervision energy management technique based decoupling frequency is designed with low pass filter to separate the current to tow elements, low frequency current absorbed by the battery and high frequency current that absorbed by the supercapacitor. Furthermore, PI controllers are employed to control the DC link voltage, and the current of battery and supercapacitor. Energy management control plays an important role to improve the system performance, ensure power allocation among source, storage devices, and load consumption, and to maintain the battery and supercapacitor at their limitation states of charge (SOC), the system must be able to match the load requirements during a shortage and absorb any surplus power provided by wind energy. To confirm the achievement of the objectives of this study, the comparative simulation between battery storage alone and hybrid storage system combined of battery and Supercapacitor. The simulation results show that the hybrid storage battery and supercapacitor allow to increases the stability of DC link voltage with an overshoot less than 1.5% compared to 7.5% when battery alone and fast dynamic response. in addition, reduces the battery stress and increases its lifetime in the case of hybrid storage.

Performance evaluation of bridgeless isolated SEPIC-Luo converter for EV battery charging using PI and ANN controller

Electric vehicle (EV) rechargeable battery packs that employ traditional power factor correction (PFC) circuit design have performance limitations due to their substantial conductivity loss that ensures at the input of a diode bridge rectifier (DBR). This study suggests a bridgeless (BL) isolated single ended primary inductance converter (SEPIC) - Luo converter to address the problem. As a result, the input current exhibits a power factor operation of unity throughout the charging process. DBR elimination and current conduction through a remarkably small number of circuits both significantly reduce conduction losses. The use of an artificial neural network (ANN) and proportional integral (PI) controller enhances the converter's performance with a stable DC link voltage. The suggested converter overall operation is thoroughly described in terms of variety of operating modes and simulation-based effectiveness. Here, with the assistance of the hysteresis current controller (HCC), the input current disruptions are reduced. Constant current and voltage management is used to successfully charge the EV battery, resulting in improved efficacy and inherent PFC. By utilizing simulation outcomes achieved from MATLAB, the performance of proposed BL isolated SEPIC-Luo in boosting the power quality of EV charger system is examined.

A non-isolated PFC bridgeless SEPIC-Cuk converter with adaptive PI controller for induction motor

In general, the induction motor (IM) is extremely nonlinear in nature and frequency dependent. In most cases, the power generated by the IM has a low power factor (PF), which exhibits detrimental effect on the extent to which the whole transmission and distribution system functions. Since there exists more current harmonics as an outcome of minimized PF, the efficiency of the power system suffers due to transmission line heating and voltage distortion characteristics. Therefore, this paper proposes a power factor correction (PFC) method to overcome the aforementioned issues. Here, by the utilization of AC-DC bridgeless SEPIC-Cuk converter, the power quality is improved by reducing reactive power consumption and enabling better control of voltage and current outputs. To maintain the stable DC link voltage with reduced ripples, the adaptive proportional-integral (PI) controller is used in this work. The three-phase voltage source inverter (VSI) transitioning function is controlled by cascaded fuzzy logic (CFL) controller, which is also utilized for regulating the speed of the three-phase IM. Implementing the proposed control strategy improves power quality significantly by reducing total harmonic distortion (THD). The proposed system is simulated in the MATLAB platform and the attained outcomes, it is clear that the proposed system is highly effective.

Small Signal Modelling and Stability Analysis of a Grid Connected Inverted Based Microgrid

Objectives: This work focuses on the stability analysis of grid connected microgrids. It considers the impact of load disturbance and grid voltage change on voltage and current levels, as well as reactive and active power responses, is analysed. Methods: A comprehensive small-signal state-space model is developed for an inverter-based microgrid, incorporating submodules of inverters, phase-locked loops (PLLs), and LCL filters. The model is linearized around a stable operating point, and eigenvalue analysis is performed and validated through MATLAB/Simulink simulations. A current controller operating in the d-q frame is proposed to enhance stable power conversion and maintain microgrid stability. Findings: The proposed model and control strategy demonstrate the microgrid's ability to maintain transient voltage stability under severe dynamic conditions. During a 10% grid voltage fluctuation, the microgrid exhibits stable active and reactive power responses, with currents and voltages at the point of common coupling stabilizing within 0.2 seconds. Furthermore, when a 25 kVA active load is disconnected, the microgrid effectively manages the power transition, maintaining stable operation with minimal deviations in key parameters. The current controller simplifies AC current control, integrating active power management from solar input, DC-link voltage stability, and reactive power control. Novelty: The novelty lies in the comprehensive analysis of transient voltage stability in grid-connected microgrids under grid voltage fluctuations and load disturbances, areas that have received limited attention in previous research. By developing a detailed small-signal state-space model incorporating PLL and LCL filter dynamics and proposing a robust control strategy with the current controller, this study offers new insights into enhancing the resilience and reliability of grid-connected microgrids during transient events. Keywords: Microgrid, Small Signal Stability, Voltage Source Inverter, State Space model, Eigen Values

A Switched Z-Source and Switched Capacitor Multi-Level Inverter Integrated Low Voltage Renewable Source for Grid Connected Application

Most of the renewable sources generate power at lower voltage levels in the range of 20-50V which cannot be utilized by the loads. Therefore, stacking multiple modules in series increases the voltage level or using conventional boost converter or QZSis helpful. However, due to series stacking and boost converter or QZS there is a great power loss and also have reliability issues.The QZS inverter has very less boosting gain in the range of 2times. Theconventional boost converter or QZSis replaced with SZSC for voltage boosting and inverter operation. The SZSC boosts the voltage 4-5 times to the input voltage level. For further mitigation of harmonics, the conventional 6-switch inverter is replaced with switched capacitor MLI. Multiple renewable sources are at the input which include PV array, battery unit and PMSG wind module. The battery unit is a support to the renewable sources PV array and wind module. The DC link voltage stability is achieved by the battery unit placed in parallel to the renewable sources. The renewable sources share power to the grid through the SZSC and switched capacitor MLI. For DC voltage stability a CV control is integrated to SZSC. And for synchronized power sharing to the grid, a grid voltage feedback synchronization control is included for the control of MLI. A low rating renewable system is modelled and integrated to grid using Simulink MATLAB software. A comparative analysis is carried out operating the system with QZS and SZSC. The performances of the SZSC and MLI are evaluated by the graphs generated by the simulation of the modelled system.

Performance Enhancement of Droop Controlled DC Microgrid Using Solar Fed Hybrid BIFRED Converter with RBFNN

Electric power system’s structure is shifting from a generator to a converter-based, posing the risk of reduced system inertia. This transition is due to the increased penetration of power electronics-based renewable energy sources (RESs) and Energy Storage Systems (ESS). The microgrid concept supports their accommodation into electric networks; however, it requires appropriate control to solve the voltage stability issues created by reduced inertia. The proposed DC microgrid aims to maintain voltage stability in DC-link comprising wind, solar, and ESS, irrespective of changes in operating conditions. An improved Z source- Boost Integrated Fly Back Rectifier/Energy Storage DC–DC (BIFRED) converter is proposed to increase the output voltage of photovoltaic (PV) system to achieve better DC-link voltage stability. Radial basis function neural network (RBFNN) approach is used to harvest the maximum power possible from the PV panel and to improve the conversion efficiency. The proposed DC microgrid also includes Wind Energy Conversion System (WECS) powered by a Doubly Fed Induction Generator (DFIG). It integrates droop control with virtual inertia and damping control and effectively handles the voltage stability issues brought out by RESs and loads. Artificial neural network (ANN) optimized droop-controlled bidirectional converter (BDC) is implemented to integrate ESS and resolve the imbalance created by ESS. The work is validated by MATLAB simulation model and a laboratory prototype.

DC-Link Voltage Stabilization Based on Complex-Coefficient Current Controller for IPMSM Drives Without Electrolytic Capacitors

DC-Link Voltage Stabilization Based on Complex-Coefficient Current Controller for IPMSM Drives Without Electrolytic Capacitors

ANFIS Controlled MMC-UPQC to Mitigate Power Quality Problems in Solar PV Integrated Power System

This paper focuses on the implementation of a Modular Multilevel Converter (MMC) based Unified Power Quality Conditioner (UPQC) in a grid-integrated Photovoltaic (PV) system. The integration of photovoltaic (PV) systems into the grid brings numerous benefits in terms of renewable energy utilization like sustainable energy generation, energy security, grid resilience, and economic growth. However, the voltage source converters (VSCs) employed in PV systems can introduce power quality (PQ) issues, including voltage fluctuations, harmonics, and reactive power imbalances and grid instability. The objective of this work is to enhance power quality by mitigating voltage and current fluctuations and harmonics generated due to VSC, compensating reactive power requirements by the load and PV system, and regulating the DC link voltage. For DC voltage regulation, an Adaptive Neuro-Fuzzy Inference System (ANFIS) controller is employed to control for MMC-UPQC. The proposed control strategy is simulated using MATLAB/SIMULINK software and the results are compared with conventional Proportional Integral (PI) and fuzzy controllers. Various dynamic conditions such as voltage sag and swell at the point of common coupling (PCC), changes in irradiance for the PV system, and load variations are considered. The simulation results demonstrate that the ANFIS-controlled MMC-based UPQC outperforms the PI and fuzzy controllers in terms of power quality improvement. It effectively suppresses harmonics, maintains a stable DC link voltage, and compensates for reactive power fluctuations. The proposed control strategy provides superior performance and achieves better power quality compared to conventional controllers. The findings of this work highlight the potential of using an ANFIS controller in MMC-based UPQC systems for grid-integrated PV systems.

High Gain Zeta Converter with ANFIS Based MPPT for Standalone Application with Galvanic Isolation

The installation of Photovoltaic (PV) systems is steadily increasing globally, as they stand as the primary means of accessing the electrical grid. A considerable amount of effort is dedicated to ensuring the optimal functioning of these PV systems. As a result, the goal of this proposed work is to achieve stable DC-link voltage of the ZETA Converter using the ANFIS MPPT strategy. In this proposed approach, a ZETA converter is used, which results in improved voltage gain and reduced ripple content of the output voltage and current. An isolation transformer is integrated into the system to provide galvanic isolation. This transformer enhances safety by isolating the output from the high-frequency converter from the PV system and other components. Galvanic isolation prevents the transmission of electrical faults and protects connected loads. The output from the isolation transformer is supplied to a DC load through a rectifier. The diode bridge rectifier converts the alternating current (AC) output from the transformer into direct current (DC), making it suitable for powering DC loads. To stabilise the converter’s output voltage and mitigate the intermittent nature of PV, an intelligent MPPT is used, which also aids in maintaining DC-link voltage without distortions and ripples from the converter. The entire paper is validated through a MATLAB simulation 2021a.

Zero-Voltage Ride-Through Scheme of PMSG Wind Power System Based on NLESO and GFTSMC

In this paper, a scheme for zero-voltage ride through of a permanent magnet synchronous generator wind power system is proposed. Maintaining the stability of DC-link voltage is the key to realizing zero-voltage ride through. A braking chopper is used to dissipate the active power to restrain the rise of DC-link voltage during a grid fault. However, the braking chopper-caused disturbance to the double closed-loop control of the grid side converter makes the control effect on DC-link voltage worse. Therefore, a robust current feedforward control, based on a nonlinear extended state observer and global fast terminal sliding mode control is proposed. A nonlinear extended state observer estimates the total disturbance in the system and compensates for the control law. Global fast terminal sliding mode control enables the system to reach the sliding mode surface in a finite time, and its control law is continuous without switching terms, thereby eliminating the chattering phenomenon. A nonlinear extended state observer and global fast terminal sliding mode control change the current feedforward control into a nonlinear robust current feedforward control. The control effect is improved, and the use of current transformers is reduced in practical applications, thereby reducing costs. The validity of this scheme has been verified by simulation.

Efficiency Optimization and Resilience Improvement in Wireless Motor System With Flexible DC-Link Voltage Regulation

This paper proposes a novel dc-link voltage regulation (DCVR) strategy for the series-series compensated wireless motor (SSWM) system. The steady-state voltage control is presented to optimize the system efficiency and the feedforward voltage boost control is proposed to improve system resilience. The rated capacity identification (RCI) scheme is proposed to design proper parameters for the SSWM system. To achieve steady-state voltage control, the system efficiency characteristic is analyzed in detail and the efficiency optimization can be achieved without an auxiliary dc/dc converter. The influence of impedance matching, the power capacity of the system, and overmodulation of the motor drive are all investigated. Then, the dynamic model of the system is established to analyze the stability of dc-link voltage. In the proposed feedforward voltage boost control, the dc-link voltage is boosted according to the motor operation state to increase the instantaneous power capacity. The dc-link voltage stability is improved and the system resilience is enhanced against power disturbance. Besides, at the end of the acceleration process, the dc-link voltage is smoothly adjusted to the optimal dc-link voltage. The effectiveness of the proposed RCI scheme and DCVR strategy is verified by experiments on a three-phase wireless permanent magnet synchronous motor platform.

A novel proposal for harmonic compensation in the grid-connected photovoltaic system under electric anomalies

The accurate estimation and online calibration of the fundamental weight components (FWC) from harmonically contaminated load current is crucial to evaluate the performance of grid-integrated photovoltaic (PV) units especially when exposed to grid anomalies. Driven by this motivation, an adaptive regularized least logarithmic absolute difference (RLLAD) filter is proposed for FWC estimation during nonlinear loading. The proposed filter pertinently captures the FWC of the harmonically distorted load currents. The resulting FWC guarantees balanced and sinusoidal grid currents even under disturbances in the grid voltage and load current thereby achieving different power quality (PQ) improvement targets i.e., grid current balancing and harmonic suppression, active and reactive power management, neutral current compensation, and power factor correction. The proposed RLLAD filter ensures comparable convergence performance and minimum steady-state oscillations in the grid reference currents. Proceeding further, to counter the nonlinearity introduced by the PV array, a feed-forward compensator is judiciously equipped. From a practical standpoint, it ensures superior DC-link voltage stabilization especially under abrupt transition in solar insolation level. The performance of the RLLAD filter is comprehensively assessed through numerical simulations in MATLAB/Simulink software. Furthermore, the practical viability of devised RLLAD filter is confirmed under rigorous experimental scenarios through OPAL-RT control suite. The experimental results demonstrate practicability of the proposed adaptive RLLAD filter and thus, considered to be a promising solution as compared to existing benchmarks and state-of-the-art approaches for online FWC estimation and PQ improvement. Most importantly, in terms of nonlinear load tracking capability, the proposed RLLAD filter is shown to outperform the classical LLAD filter with a response speed of less than 400 μs.

Fault Ride-Through for PMVG-Based Wind Turbine System Using Coordinated Active and Reactive Power Control Strategy

This study investigates a fault ride-through capability for grid-connected permanent magnet vernier generator (PMVG)-based wind turbine system (WTS) using coordinated active and reactive power control strategy. To do this, the generator peak current and speed limitation schemes are proposed for the machine-side converter to satisfy grid code requirements during grid fault conditions. At the same time, the reactive power control is implemented on the grid-side converter to meet the reactive current requirement of the grid code. And then, to suppress the DC-link power unbalance during grid fault conditions, an efficient variable exponential reaching law-based sliding mode control is designed. Further, the coordinated control schemes are employed to ensure the stable DC-link voltage and maintain the converter's maximum peak current during grid faults. Finally, the proposed control methods demonstrate their superiority through simulations on 5-kW PMVG, 1.5 MW PMSG-based WTS, and its application potential is shown through the experimental prototype of a 5-kW PMVG-based WTS.

Adaptive qXE-LMF Filter for Improving Power Quality Using Grid-Supporting Photovoltaic System

In practice, nonlinear electrical loads pose various power quality (PQ) challenges. Driven by these challenges, a parallel combination of a nonlinear load and a photovoltaic (PV) inverter with adaptive quantum normalized-least mean fourth ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> XE-LMF) filter is proposed and experimentally validated to detect and compensate for the harmonics in harmonically contaminated currents. A scheme with an adaptive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> XE-LMF using fundamental weight components is used to generate the harmonics in the inverter output current thereby improving the PQ of the grid supply. The resulting grid current is pure and balanced; the PV inverter connected in parallel with the nonlinear load provides reactive and harmonic current support. Practically, the adaptive feature enables the online learning of filter weights of the load current harmonics to guarantee unconditionally balanced sinusoidal grid current. The proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> XE-LMF filter ensures fast convergence and minimum steady-state oscillations in the grid reference currents. An improved anti-windup PI compensator is used to ensure dc-link voltage stabilization. The practicality of the proposed adaptive <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> XE-LMF filter is experimentally demonstrated using a three-phase four-wire uncontrolled rectifier-based nonlinear load. The experimental results also demonstrate the robustness of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> XE-LMF filter against changes in solar insolation level and nonlinear loads.

A Non-neutral alternate arc suppression method for single phase grounding fault in active distribution network

To fully compensate reactive and active components of the single line-to-ground (SLG) fault current, additional DC power supply devices are usually used for arc suppression devices. Therefore, the alternate arc suppression method is proposed for the non-neutral multi-function arc suppression device (MF-ASD) in this paper, which can achieve energy self-balance in the MF-ASD during the SLG fault without additional DC power supply devices. Firstly, the DC-link charge–discharge characteristic of the MF-ASD is analyzed under different SLG fault conditions. Then, the alternate arc suppression principle and energy flow law between two non-faulty phases of the MF-ASD are described in detail. Further, the relationship between the alternate period, switching time, and the DC-link voltage are deduced as well. Then, the control parameters are reasonably designed for the DC-link voltage stability of two non-faulty phases of the MF-ASD. Finally, the correctness and feasibility of the proposed method are verified by simulation and experiment results.

Harmonic Mitigation in a Hybrid Power System Integrated Shunt Active Power Filter Employing FLC and an Adaptive Current Control Technique

The main objective of this study is to mitigate current harmonic issues in hybrid renewable energy systems based on solar photovoltaic (SPV) and wind energy distribution. This is achieved with the help of a suitable controller-based shunt active power filter (SAPF). The SAPF is designed using a modified synchronous reference frame (MSRF) to reference current generation, an adaptive hysteresis current controller (AHCC) for switching pulse generation, and a fuzzy logic controller (FLC) for DC-link voltage regulation. The results of the proposed SAPF model developed in MATLAB/Simulink, show that the filter performs remarkably well in suppressing harmonics under different loading conditions. It is capable of fast corrective action under dynamic conditions and outperforms previous methods in terms of harmonic mitigation and dc-link voltage stabilization. The control techniques are compared on the basis of parameters such as harmonic compensation and dc-link voltage ripple reduction capability under changing load conditions. The results obtained through simulation represent the validity of the filter performance.

Stable Maximum Power Extraction and DC Link Voltage Regulation for PMVG-Based WECS

This study discusses the power maximization and dc-link voltage regulation problems of a permanent magnet vernier generator (PMVG)-based wind energy conversion system. To do this, first, the dynamical model of PMVG-based wind turbine is developed and presented. Then, the overall control structure is configured utilizing a back-to-back converter with a machine-side converter (MSC) and a grid-side converter (GSC). At this time, the sliding-mode control scheme with the modified enhanced exponential reaching law is proposed for both MSC and GSC control to achieve maximum power extraction and stable dc link voltage, respectively. Furthermore, the sliding manifold’s stability condition is derived using the Lyapunov function, which guarantees a better transient performance and tracking accuracy. Finally, the proposed control scheme’s superiority and efficiency are demonstrated using theoretical simulations on 5 kW PMVG-based and 1.5 MW permanent magnet synchronous generator-based wind turbine systems and empirical findings derived from a grid-connected 5 kW PMVG-based wind turbine in the experimental setup.

Single Phase Grid Connected PV-Wind-Diesel-Battery System Operated Three Phase Induction Motor for Aqua-Farms

Sustainable Aqua Farms requires continuous power supply to drive three phase induction motors for maintaining good oxygen levels. Unfortunately many places are suffering from frequent power cuts as well as availability of only single phase supply. Hence, 1-Φ to 3-Φ conversion is essential to operate 3-Φ motors as well as required operation of diesel generators during no supply from grid. However, consumption of heavy diesel causes many problems in aqua culture which is not sustainable. Hence, in order to reduce diesel consumption, and increase eco-friendly environment, photovoltaic (PV) and wind generator system can be integrated to system. A proper energy management system is required among all these sources to achieve cost effective system with best performance. The battery is used for responding in transient time periods. The proposed energy management system can reduce consumption of diesel by operating it at maximum efficiency. In case of any excess power available from wind and PV, the surplus power can be transmitted to single phase grid to reduce electricity bill. In order to maintain stable dc-link voltage, Sliding Mode Controller (SMC) based DC to DC converters are incorporated. The proposed controller reduces the ripples in motor torque to improve the life time of components used in system as well as can reduce power consumption with the addition these renewable energy resources. For reduction of ripples in torque, a TS-Fuzzy based speed sensor less direct torque controller is implemented to run induction motor through three phase inverter.

A Robust Voltage Control of DAB Converter With Super-Twisting Sliding Mode Approach

This article presents a supertwisting sliding mode control (ST-SMC) for the isolated dc-dc bi-directional dual active bridge (DAB) power converter for enhanced output voltage regulation. The sliding mode control (SMC) is well-known for its robustness and improved dynamic performance for a nonlinear system. However, it includes the drawback of chattering and degradation of tracking performance. Here, the suggested ST-SMC scheme incorporates the advantages of a sliding mode controller and subsequently eliminates the problem of chattering. The average model of DAB under single phase-shift modulation is considered for controller design, which simplifies the design process. Thus, improved dc-link voltage stability and high robustness for accurate reference voltage tracking are obtained. Further, the proposed scheme provides a robust control for parameter uncertainties as well as the steady-state output voltage contains less ripple when compared to the classical SMC and proportional-integral controller. The experimental results for a 2 kW DAB converter are provided to validate the effectiveness and the robustness of the proposed strategy.