Voltage Ride-Through Research Articles

Enhancing Low Voltage Ride-Through Resilience using Empowering Solar Energy Strategies

The rapid advancement of Low Voltage Ride-Through (LVRT) technology has been highlighted by the exponential rise of photovoltaic (PV) generation systems. An extensive analysis of LVRT methods specifically designed for PV generating systems is presented in this research. Important topics like main causes, current control schemes, power balance and overall solutions are the main focus of the review. Moreover, it provides comprehensive insights and elaborates on integrated solutions intended for large-scale PV systems. The objective of this research is to improve the resilience and reliability of renewable energy sources, especially solar photovoltaic systems, against grid disruptions and voltage changes by investigating LVRT approaches in solar power systems. Enhancing the integration of solar power systems into current electrical grids, reducing downtime, and optimizing system performance are the objectives in order to accelerate the shift to a more resilient and sustainable energy infrastructure.

Dynamic Coupling and Cooperative Control for Multi-Paralleled Doubly Fed Induction Generator Wind Farms During Symmetrical Low Voltage Ride-Through in a Weak Grid

Dynamic Coupling and Cooperative Control for Multi-Paralleled Doubly Fed Induction Generator Wind Farms During Symmetrical Low Voltage Ride-Through in a Weak Grid

Neural network predictive control for fault detection and identification in DFIG with SMES for low voltage ride-through requirements

The increasing reliance on renewable energy sources brings to light the operational challenges of doubly fed induction generators (DFIGs), particularly under grid disturbances. This study introduces an innovative approach employing Neural Network Predictive Control (NNPC) for fault detection and identification (FDI) in DFIG systems, integrated with Superconducting Magnetic Energy Storage (SMES) to meet Low Voltage Ride-Through (LVRT) requirements. Our method uniquely combines NNPC for dynamic wind speed prediction and precise control of rotor-side and grid-side converters with the stability enhancement offered by SMES. Simulation results demonstrate a notable improvement in DFIG performance under variable wind conditions and grid failures. The system-maintained voltage stability at the Point of Common Coupling (PCC) with less than 5% deviation during transients and ensured consistent power output, marking a significant advancement in LVRT compliance. However, the model assumes steady-state grid conditions and does not account for extreme weather scenarios, indicating areas for future research. This study's findings contribute valuable insights into the robust operation of DFIGs within modern renewable energy grids.

Identification of High and Low Voltage Ride-Through Control Parameters for Electromechanical Transient Modeling of Photovoltaic Inverter

The electromechanical transient model of a photovoltaic (PV) inverter’s high and low voltage ride-through has complex operating circumstances and a large number of control parameters, which makes parameter adjustment difficult. Furthermore, it is frequently challenging to identify a single set of control parameters that can successfully handle a variety of operating conditions. The Improved Differential Evolution Particle Swarm Optimization (IDEPSO) algorithm is proposed in this paper to provide a control parameter identification technique for high and low voltage ride-through that addresses these problems. Taking a 320kW PV inverter of a certain company as the research object, based on the specified current control strategy of high and low voltage ride-though, the parameters to be identified were determined by analyzing the influence of model parameters. Secondly, To enhance the algorithm’s capability to solve multidimensional optimization problems, convergence speed, and global search ability, the Differential Evolution (DE) algorithm’s search mechanism is incorporated into the Particle Swarm Optimization (PSO) algorithm, along with a non-fixed gradient inertia weight strategy for the algorithm’s inertia weight and the elite retention idea for the cross factor. Then, the objective function of the IDEPSO algorithm was built based on the concept of minimum deviation between simulation data and various groups of test data, and the significance of various working conditions was distinguished by weight division to improve the robustness of identification parameters. Finally, the identification parameters are imported into the PSASP program type 2 photovoltaic power station model, and the interval division and deviation calculation of the test data and simulation data are carried out. It is confirmed that the identification parameters meet the standards of the maximum variation permitted in GB/T 32892-2016 and are appropriate for a variety of working scenarios.

Over-current low voltage ride-through operation of grid-connected converters based on thermal analysis

The grid-connected converters are becoming an important role in modern power grid. The grid codes have been proposed for the operation of grid-connected converters. The low voltage ride-through, namely one of the grid codes, is the operation of grid-connected converters under grid fault. The reactive power is generated by gird-connected converters to support grid under low voltage ride-through operation. However, the maximum reactive power is restricted by the capacity of converter, which is designed for long-term operation. Since the low voltage ride-through is a short-term operation, the maximum output reactive power can be enhanced. An over-current low voltage ride-through operation is proposed, and it is designed based on the maximum short-term capacity. The maximum short-term capacity is designed to ensure the junction temperature of semiconductor devices in the converter under the reliable operation, which is calculated based on thermal analysis. Furthermore, the different approaches to enhancing the maximum short-term capacity is analyzed.

Transient synchronous stability analysis and enhancement control strategy of a PLL-based VSC system during asymmetric grid faults

The stability of a voltage source converters (VSC) system based on phase-locked loop (PLL) is very important issue during asymmetric grid faults. This paper establishes a transient synchronous stability model of a dual-sequence PLL-based VSC system during low voltage ride-through by referring to the equivalent rotor swing equation of synchronous generators. Based on the model, the synchronization characteristics of the VSC system under asymmetric grid faults are described, and the interaction mechanisms, as well as the transient instability phenomena of positive and negative sequence PLL during asymmetric faults are explained. Using the equal area criterion, the influences of sequence control switching action, detection delay, and interaction between the positive and negative sequence PLL on the transient synchronous stability of the VSC system are analyzed, respectively. In addition, a transient stability assessment criterion based on the critical fault clearance angle and time and an enhancement control strategy based on the improved positive and negative sequence PLL are proposed. Finally, the analytical results are validated through simulation and experiments.

Designing a Smart Inverter for Compensating the Voltage Sag Caused by Motor Start-up

Starting a large induction motor will always follow up with an inrush current as the nature of an induction motor. On a less stiff power system, that inrush current will be causing a Voltage Sag (VS). A big VS can lead to significant disruptions in power quality and reliability. To address this, a Smart Inverter with an Artificial Intelligence (AI) -driven controller installed in a Photovoltaic (PV) farm is proposed for voltage sag recovery. During normal conditions, the PV farm acts as a power source supporting the main grid, but when large induction motors are started, the smart inverter connected to the PV is responsible for power conversion to recover sags caused by the Induction motor inrush current. The controller inside the Inverter ensures optimal operation. The use of AI also compares the effectiveness of using the Fuzzy Logic Controller (FLC) with the Proportional Integral (PI) Controller to assess their performance in reducing current spikes. Based on simulations, the FLC outperformed PI Controller in mitigating the voltage sag and avoiding the Low Voltage Ride-Through (LVRT). Simulation results show that voltage sag can be recovered for up to 97% of the nominal voltage, a significant improvement over the 80% sag recovery without the smart Inverter. At a nominal grid voltage of 6,600 volts, the VS Magnitude was successfully increased from 5,210 volts to 6,368 volts and the VS Duration also decreased from 6.96 s to 4.97 s. The results achieved validate the effectiveness of the approach in improving the power quality.

Single-phase PV generator model for distribution feeders considering voltage ride through conditions

This paper presents a model for photovoltaic (PV) distributed generators that operates in abnormal electrical voltage scenarios — Voltage Ride Through (VRT), following the Brazilian standard NBR 16149 of 2013. The model includes various modes of operation, such as interruption of energy supply, disconnection, and reconnection of the PV system to the grid. Two types of simulations were performed to test the model’s performance: the first involved using a ramp function to test the activation of different operating modes, while the second connected the PV model to a distribution feeder and tested its response to a short circuit. The results showed that the model met the requirements established by the standard and was efficient in representing the behavior of the PV system in real-world scenarios.

An adaptive fuzzy logic control technique for LVRT enhancement of a grid-integrated DFIG-based wind energy conversion system

The fast improvement of wind energy conversion technology with optimization algorithms has recently received a lot of attention. However, their slow convergence speed, huge computational load, and low efficiency are the main drawbacks and to improve these disadvantages, a new adaptive fuzzy logic controller strategy is proposed to enhance the low voltage ride-through of the grid-connected doubly fed induction generator during severe grid faults. The rotor side converter and the grid side converter are controlled using an adaptive fuzzy logic controller topology under cascaded structure to improve the performance. The novel application of the ‘generalized variable step-size diffusion continuous mixed p-norm’ adaptive filtering algorithm is proposed to modify the calibrating factors of the fuzzy logic controllers at a rapid convergence speed with low normalized misalignment error. The proposed adaptive algorithm-based fuzzy logic controller has a better low voltage ride-through improvement capability than that of using the particle swarm optimization-based proportional-integral controller during severe grid disturbances. The convergence speed of the proposed adaptive filtering algorithm is compared to that of existing algorithms such as least mean fourth, least mean square, and continue mixed p-norm algorithms. In addition, a comparison is also made with different common optimization methods. The field-programmable gate array-based real-time experimental results are presented to validate the proposed adaptive control topology.

An aggregated dynamic model of Photovoltaic units for large voltage disturbances

Many Photovoltaic (PV) units connected to the low-voltage level greatly impact the distribution network’s dynamic characteristics. However, the dynamic characteristics of PV units under large disturbances are widely different, which leads to the model being unable to effectively describe the dynamic performance of aggregated PV units in the low-voltage transient stability analysis. To overcome this issue, an aggregated dynamic model of PV units is proposed in this paper. First, a general dynamic model of a PV unit is proposed, focusing on the control triggered by voltage disturbances, and multiple PV units is established based on ADPSS. The simulation results show that the major factor which influences the transient characteristics of multiple distributed PV units is its Low Voltage Ride-Through (LVRT) control. Then, an aggregated dynamic model that can describe the multiple transient characteristics is proposed. The simulation verifies that the proposed model can effectively represent aggregated transient characteristics.

Improving Voltage Ride-Through Capability of Grid-Tied Microgrid With Harmonics Mitigation

When the microgrid operates in grid-tied mode, the voltage ride-through (VRT) capability presents a challenge in its inverter controller design. This letter proposes an effective method to support the VRT capability of an inverter-based grid-tied microgrid during grid fault. In addition, the inverter control is implemented by a combined method to mitigate its output current harmonics under normal or faulty grid conditions, even if the grid voltage is distorted. Simulations are performed using Matlab/Simulink and implemented in a real-time simulator with a hardware setup to validate the usefulness of the proposed method.

Fault Ride-Through Operation Analysis of Doubly Fed Induction Generator-Based Wind Energy Conversion Systems: A Comparative Review

In present electrical power systems, wind energy conversion systems based on doubly fed induction generators represent one of the most commonly accepted systems in the global market due to their excellent performance under different power system operations. The high wind energy penetration rate makes it challenging for these wind turbines to follow grid code requirements. All operations of a wind energy system during a dip in voltage require special attention; these operations are critically known as fault ride-through and low voltage ride-through. In this paper, various fault ride-through techniques of doubly fed induction generator-based wind energy conversion systems, such as protective circuitry, reactive power injection, and control methods for transient and steady state operations, have been presented to improve the performance. During system disturbances, protective circuitry or control mechanisms are typically used to limit the over-current of the rotor and the generated inappropriate DC link over-voltage. Simultaneously, the reactive power injection system overcomes the reactive power scarcity and enhances the transient response, further limiting the DC bus voltage and rotor current. This review paper compares and suggests appropriate FRT methods that are driven by external modifications and internal system improvements. Furthermore, typical case studies are discussed to illustrate and support the FRT system. The impact of each case study was evaluated and analyzed using the results obtained from the MATLAB/Simulink application and the OPAL-RT (OP4500) real time simulator (RTS).

Review on Stability and Power Quality Problem and Mitigation on Renewable Energy Penetration in Grid System

Abstract: An increase in the production and integration of renewable energy sources to the power grid system have begun to have an impact on the stability and security of the power grid. As renewable energy sources (RESs) like solar PV array plant and wind plant begin to displace traditional power plants, grid integration requirements have become an important issue. To ensure grid stability, additional criteria and technological constraints have been implemented. An updated assessment of current integration criteria and compliance control techniques for renewable power plant integration into the electric grid is being conducted as part of this study to close the knowledge gap. There is a comparison of the most important criterion for grid stability, including frequency stability and voltage stability, quality of power, voltage ride-through (VRT), reactive and active power controls. To meet these standards, a variety of control techniques have recently been proposed. As a result, cutting-edge options for compliance technologies and control techniques are analysed and evaluated in this paper. Additionally, a thorough examination of the benefits, challenges, and drawbacks of global harmonisation of integration requirements is included. Even though current incorporation necessities may enhance grid security, stability, operation, and dependability, a thorough assessment concludes that further improvements to shielding legislation, optimization of control system and international harmonisation are still required. There are a number of recommendations for further research into the integration and technical limitations of RESs that follow this. This study's findings could help to create a seamless and stable grid integration of RESs, as well as aid researchers in the development of new design methods and control systems based on current requirements. Educate and support operators in power system for creating or cultivating their individual standards that differ from the international norms that remain in place. Keywords: fault ride-through, Current limitation, grid forming control, grid connection, voltage-source converter

Enhanced Deadbeat Control Approach for Grid-Tied Multilevel Flying Capacitors Inverter

This paper proposes an enhanced Deadbeat Controller (DBC) for a grid-tied Flying Capacitors Inverter (FCI). The proposed DBC guarantees the balancing of the capacitors’ voltages while injecting current to the grid with lower Total Harmonics Distortion (THD). The proposed controller has the following advantages: 1) Improved current tracking quality even at zero crossing instants by using a weighted state-space model, 2) Superior steady-state performance (lower current THD) compared to other prediction-based control techniques such as Finite-Control-Set Model Predictive Control, 3) The generated duty cycles are normalized to the common base when the desired state is out of reach within the sampling time, 4) Voltage Ride-Through (VRT) capability, and 5) Robustness to parameters variation. Theoretical analysis, simulation, and experimental results are presented to show the effectiveness of the proposed control technique in ensuring uninterruptible and smooth transfer of energy to the grid during normal/abnormal operating conditions (severe voltage sags, parameters variation, etc.).

Formulation of Low Voltage Ride-Through (Lvrt) Curve Using Discrete Optimization Strategy with Reliability Constraints for High Penetration of Wind Power - a Case Study in Taipower System

Formulation of Low Voltage Ride-Through (Lvrt) Curve Using Discrete Optimization Strategy with Reliability Constraints for High Penetration of Wind Power - a Case Study in Taipower System

A Cooperative Approach of Frequency Regulation Through Virtual Inertia Control and Enhancement of Low Voltage Ride-through in DFIG-based Wind Farm

Doubly-fed induction generator (DFIG)-based wind farms (WFs) are interfaced with power electronic converters. Such interfaces are attributed to the low inertia generated in the WFs under high penetration and that becomes prevalent in a fault scenario. Therefore, transient stability enhancement along with frequency stability in DFIG-based WFs is a major concern in the present scenario. In this paper, a cooperative approach consisting of virtual inertia control (VIC) and a modified grid-side converter (GSC) approach for low voltage ride-through (LVRT) is proposed to achieve fault ride-through (FRT) capabilities as per the grid code requirements (GCRs) while providing frequency support to the grid through a synthetic inertia. The proposed approach provides LVRT and reactive power compensation in the system. The participation of the VIC in a rotor-side converter (RSC) provides frequency support to the DFIG-based WFs. The combined approach supports active power compensation and provides sufficient kinetic energy support to the system in a contingency scenario. Simulation studies are carried out in MATLAB/Simulink environment for symmetrical and unsymmetrical faults. The superiority of the proposed scheme is demonstrated through analysis of the performance of the scheme and that of a series resonance bridge-type fault current limiter (SR-BFCL).

Multi-Functional PV Inverter With Low Voltage Ride-Through and Constant Power Output

Renewable photovoltaic (PV) energy is a primary contributor to sustainable power generation in microgrids. However, PV grid-tied generators remain functional as long as the grid voltage and the input PV source remain normal. Abnormal conditions like transient grid sags or solar irradiation flickering can make the grid-tied inverter go offline. Simultaneous shut down of PV generators residing in the distribution grid may lead to an overall grid instability or outage. Therefore, PV generators must be equipped with fault-ride-through mechanisms in order to remain connected and operational during faults. This paper presents a PV-inverter with low-voltage-ride-through (LVRT) and low-irradiation (LR) compensation to avoid grid flickers. The single-phase inverter rides through the voltage sags while injecting reactive power into the grid. The proposed control strategy ensures a steady DC-link voltage and remains connected to the grid during AC-side low voltage and DC-side low-irradiation faults. Unlike other PV inverters, the controller maintains the maximum-power-point-tracking (MPPT) in all conditions. LVRT, constant power output, and robust MPPT are the noticeable features of the proposed system. Frequency analysis, simulations, and a laboratory prototype validate the proposed control strategy.

High voltage ride-through of doubly-fed induction generator based on grid side and rotor side converters cooperative control

In order to further improve the doubly-fed wind turbine high voltage ride-through ability, this article is different from the traditional control research only considering the rotor side converter in the power grid failure in stator flux dynamic changes of active and reactive power decoupling, the influence of the coupling current and the additional quantity of the stator flux changes as the feedforward compensation component in the current reference value. On this basis, an improved control strategy is also proposed for the grid-side converter, which takes into account the power imbalance between the two ends of the DC bus and the voltage mutation of the grid. Simulation in power grid voltage surge, coordinated control based on the grid-side converter and rotor-side converter control strategy of doubly-fed wind power generator of high voltage ride-through the active power and reactive power of wind power unit, the rotor over current, DC bus voltage fluctuations, etc all have better inhibition, effectively improve the doubly-fed wind turbine high voltage crossing ability.

Coordinated Low Voltage Ride-Through of MMC-HVDC Transmission System and Wind Farm With Distributed Braking Resistors

Modular multilevel converter-based high-voltage direct current (MMC-HVDC) transmission is becoming a trend in offshore wind-farm integration. However, the large DC-side energy dissipation equipment, which is utilized to dissipate surplus wind power under grid fault conditions, will largely increase the cost of MMC-HVDC systems. To reduce the cost, a novel low voltage ride-through (LVRT) strategy is proposed in this paper. When a grid fault occurs and the DC voltage exceeds the limit, the sending end converter is controlled to reduce the AC voltage of the wind farm. The LVRT of the wind generators will be activated, and the output active power of the wind farm is reduced. With this coordination, the DC-side energy dissipation equipment only needs to dissipate surplus power in the early stage of the grid fault before the output active power of the wind farm drops. Therefore, the heat generated by braking resistors can be significantly reduced. On this basis, the braking resistors can be distributed into the submodules of the receiving end converter (REC) station. The LVRT problem can be solved without building an individual energy dissipation station. Using the proposed coordination strategy, the construction cost of the MMC-HVDC system with offshore wind farm integration can be significantly reduced.

Inverter Protection and Ride-Through: Today's Photovoltaic and Energy Storage Inverters

Modern grid-tied photovoltaic (PV) and energy storage inverters are designed with control capabilities that can support and/or enhance the existing global grid infrastructure. Inverter-based generation is growing today in the residential, commercial, and utility segments. This article will explore how modern inverter controls can have a positive effect on today's evolving electrical grids in the utility sector. I will examine the inverter protection mechanisms used to keep dc-side and ac-side faults from causing damage to the inverter. Inverter grid supporting functions, along with voltage and frequency ride-through, provide key behaviors that both support and enhance grid reliability. Today's PV and energy storage inverters can be deployed individually and in a mixed design, affording plant designers options for energy capture and grid support. The following topics are as general as possible with some unavoidable linkage to SMA inverters.