Control Strategy Of Converter Research Articles

Transient Synchronous Stability Analysis of Grid-Following Converter Considering Outer-Loop Control with Current Limiting

With the evolution of modern power systems, inverter-based resources have become increasingly prevalent. As critical energy conversion interfaces, grid-following converters exhibit dynamic performances, presenting challenges for system security and stability. This paper focuses on the transient synchronization stability of converters after disturbances, highlighting differences in mechanisms compared to synchronous generators. Although previous studies on the transient synchronization stability of converters have been conducted, they primarily concentrate on the dynamics of the phase-locked loop, with limited consideration of the effects of outer-loop control. This has created a cognitive bottleneck in understanding the transient synchronization mechanisms of converters. To address these challenges, this paper models a grid-following voltage source converter system, incorporating detailed converter control strategies and current-limiting control. The stability regions of the stable equilibrium point under various fault severities are first analyzed. Then, the impacts of outer-loop control, including PI control and current-limiting control, on transient synchronization are examined. The study systematically elucidates the influence of outer-loop control on the transient synchronization stability of converters. Finally, the validity of the proposed theory is confirmed through simulations conducted in PSCAD/EMTDC.

Sliding mode control strategy of grid-forming energy storage converter with fast active support of frequency and voltage

The random fluctuation of renewable power generation output makes the frequency and voltage of distribution network fluctuate frequently. And the stable operation performance of the system is decreased. Therefore, the sliding mode control (SMC) strategy of grid-forming (GFM) energy storage converter with fast active support of frequency and voltage is proposed in this paper. Firstly, the virtual synchronous generator (VSG) control possessing the superior GFM performance is applied to single-stage neutral point clamped (NPC) converter of energy storage system. Meantime, the improved comprehensive equivalent circuit model of lithium iron phosphate battery and equivalent model of converter are constructed by means of ampere-hour method and Kirchhoff’s law. Then, the SMC with fast response and strong robustness is utilized into the current inner-loop controller. Combined with VSG control, the SMC strategy of GFM energy storage converter is proposed, so that the converter could play an active supporting role by quickly adjusting the output power while the frequency and voltage are reduced. Finally, the simulation model of GFM energy storage converter SMC system is established. Through the simulation analyses, it can be seen that the response time of the proposed strategy to complete the active support is about 0.65 s.

Enhanced voltage source converter control strategy for improved grid resilience: A 2DOF-PI approach

This paper presents a control strategy for voltage source converters connected to weak grids. The proposed approach is based on slight modifications to the conventional vector current control strategy, including the use of two degrees of freedom proportional-integral controllers, with reference weighting factors, in the inner current loop and a proportional controller in the outer loop, resulting in the introduction of only three additional parameters. The paper analyses the effect of these additional design parameters on the robustness improvement and studies the limitations of the proposal, providing design steps to achieve given performance prescriptions such as speed response, noise amplification, delays and phase-locked loop bandwidth, and the ability to face weak grids. Simulations are conducted to evaluate the effectiveness of the proposed approach, which demonstrates that it is possible to achieve a more robust behaviour compared with the conventional vector current control strategy when facing weak grids.

A unified approach to modeling and stability equivalence analysis for grid-forming and grid-following converters

With the increasing penetration of renewable energy generation, the large-scale integration of grid-connected converters, serving as interfaces, has led to the characteristics of a weak grid with low strength and low inertia, resulting in insufficient stability of existing grid-following (GFL) converters. Grid-forming (GFM) converters, by emulating the characteristics of traditional synchronous machines, can operate stably in weak grids, but their introduction creates a complex operational state with mixed modes, presenting unprecedented challenges to the system. To address this, this paper first analyzes the structure and GFM/GFL control strategies of grid-connected converters; based on this, a comprehensive model framework for GFM/GFL converters is established, and the control of the converters is divided into three parts: LCL with the grid, output control, and power control, each modeled with a small-signal approach; using the established small-signal models, the stability of GFM/GFL converters under different grid short circuit ratios (SCR) is analyzed. Finally, a 20 kW test platform was constructed, and the correctness of the modeling and analysis was jointly verified using simulation frequency sweep methods and experimental time-domain stability analysis techniques.

A Sea-State-Dependent Control Strategy for Wave Energy Converters: Power Limiting in Large Wave Conditions and Energy Maximising in Moderate Wave Conditions

A Sea-State-Dependent Control Strategy for Wave Energy Converters: Power Limiting in Large Wave Conditions and Energy Maximising in Moderate Wave Conditions

Impact of current limiters and fast voltage boosters in grid-forming VSC-based generators on transient stability

Transient stability is a complex phenomenon presented in multi-machine and multi-converter systems, and it is still considered a key limiting factor for stressed power systems. The increasing integration of non-synchronous generation further emphasises the need to address the challenges of improving the transient stability faced by these power systems. Several studies have focused on developing control strategies for Grid-forming voltage source converter (GFM-VSC) to improve transient stability. These strategies include the use of current limiting algorithms and/or control of active/reactive power injections. This paper investigates the impact of fast voltage boosters (FVBs) and hybrid current limiters (HCLs) on transient stability of power systems with 100% grid-forming VSC-based generators. Short-circuit simulations and critical clearing time analysis are performed to evaluate the effectiveness of HCLs and FVBs in improving transient stability. The simulation results demonstrate the effectiveness of these approaches in avoiding the loss of synchronism. This research contributes to the current studies on transient stability in power systems and provides valuable insights into the potential of HCLs and FVBs as effective approaches to improve system stability.

IMC based robust and innovative control strategies for higher-order DC-DC converter in DC microgrid applications

The extensive practice of DC-DC converter interfacing circuits to maintain DC link voltage in DC microgrid applications introduces unavoidable voltage regulation problems due to its nonlinearity. These unregulated voltages demean the performance and result in an unstable system. This brief proposes an internal model control (IMC) non-linear approach based robust proportional-integral-lead (PI-Lead) controller design for regulating a practical fifth-order DC-DC boost converter. The main innovation of this paper is the developed procedure for designing controller. The prominent feature of IMC filter coefficient is to fulfil the desired level of gain margin and phase margin to show the trade-off between performance and robustness. The proposed controller's performance is evaluated in the presence of uncertain disruptions and its effectiveness is verified by comparing it with the some conventional proportional-integral (PI) as well as with recently published IMC-proportional-integral-derivative (IMC-PID) and IMC-proportional integral derivative double derivative (IMC-PIDD2) controllers. The applicability of the proposed control methodology has been validated under varying supply and load current levels in presence of parametric uncertainty using a MATLAB/Simulink tool along with a low-cost microcontroller DSP F280379D based laboratory prototype.

Emergency coordinated control of multiple VSC‐HVDC for improving power system transient frequency and steady‐state frequency

AbstractWith the penetration of the high proportion of power electronics interfaced energy resources, the frequency stability issue in power systems is becoming increasingly prominent. This paper proposes a coordinated control strategy of multiple voltage source converter based high voltage direct current transmission (VSC‐HVDC) to simultaneously improve the transient frequency and steady‐state frequency after a severe disturbance. Firstly, a modified average system frequency response (MASFR) model is constructed with reserve power limitation, which takes into account the frequency responses of different types of generators (thermal, hydro and new energy resources). Secondly, according to the frequency stability requirements, the corresponding constraints, which consider the overload capacity of VSC‐HVDC, the AC transmission capacity and the frequency of AC grids on both sides of VSC‐HVDC, are formulated. Thirdly, for the transient frequency control, the coordinated optimization control model of multiple VSC‐HVDC is established, which aims to minimize the control energy considering the transient frequency threshold. For the steady‐state frequency control, the coordinated optimization control model is fomulated, which aims to minimize the control cost while considering the steady‐state frequency threshold. The two control schemes achieve seamless and smooth switching. Finally, the correctness and effectiveness of the proposed control strategy are verified in the improved IEEE 39 bus system.

Adaptive control strategy for grid-based energy storage converter under frequency disturbance

Abstract The grid-based energy storage converter is regarded as vital equipment for constructing a new power system because of its ability to sort out new energy consumption and improve the system’s moment of inertia. Currently, most of the adaptive control strategies of Grid-configured energy storage are optimized for the dynamic virtual synchronous generator technology (VSG) process. More research is needed on the steady-state deviation of VSG under grid frequency disturbance. To solve this problem, this paper proposes an adaptive control strategy for grid-based energy storage converters. First, this essay examines the control approach used by VSG. Subsequently, the damping and inertia of VSG with fixed parameters are replaced by the inertia, and damping is calculated using the adaptive algorithm to optimize the dynamic and steady-state performance. Finally, Simulations utilizing MATLAB/Simulink are employed to confirm the efficacy of the adaptive VSG network-building control approach.

Experimental validation of data-driven reactive control strategy for wave energy converters: A Gaussian process regression approach

Wave energy is a renewable energy source that can generate electricity without emitting carbon dioxide using wave energy converters (WECs). WECs face several challenges, such as effectively harnessing wave energy, ensuring operational safety, and implementing cost-saving measures. In this study, a data-driven reactive control strategy for WECs using Gaussian process regression is experimentally validated. The control strategy aimed to maximize energy absorption while satisfying physical constraints without a WEC dynamic model. In this study, the Gaussian process regression model represents a WEC dynamic model using an approximation function based on the input/output data. Experimental validation results confirmed that the proposed data-driven reactive control strategy effectively controlled the WEC and improved its performance using the Gaussian model. Moreover, performance was improved under different wave conditions compared to those used during training. The control strategy can be useful in situations where conventional methods cannot realize ideal control parameters, such as when substantial model errors exist or the WEC dynamic model changes over time. The data-driven approach that uses Gaussian process regression reduces learning costs compared to other machine-learning methods. It also has stable control performance because it is independent of the training dataset. The potential of data-driven approaches for optimizing WEC control strategies was highlighted.

Guest Editorial: Identification, stability analysis, control, and situation awareness of power systems with high penetrations of renewable energy resources

AbstractIt is with great pleasure that the authors introduce this special issue, commemorating the 8th Asia Conference on Power and Electrical Engineering held in Tianjin in 2023. This conference served as a nexus for researchers, practitioners, and industry experts from around the globe to convene and exchange cutting‐edge insights, innovative ideas, and transformative advancements in the field of power and electrical engineering. The contributions featured in this special issue represent a diverse array of research endeavours, spanning from fundamental theories to practical applications, all aimed at addressing the myriad challenges and opportunities facing the power and electrical engineering domain. From novel methodologies in renewable energy integration to advancements in smart grid technologies, each article encapsulates the spirit of innovation and collaboration that characterised the conference. This special issue includes scientific investigations on topology modelling and virtual stability analysis methods for distribution networks with high penetration of renewable energy resources, monitoring and situation awareness on grid inertia and power‐frequency evolution, novel voltage source converter control schemes, and reviews of low‐carbon planning and operation of electricity, hydrogen fuel, and transportation networks.

Real-time Assessment of Ride-through Capability of Grid-tied Converter in Renewable Power Applications

This paper presents a comprehensive strategy for controlling grid-tied converters, with the primary goal of seamlessly integrating renewable power sources into the grid while ensuring stability and reliability. The control strategy is designed to achieve unity power factor operation under normal grid conditions, while also adhering to ride-through requirements to withstand voltage dips. Using the Typhoon HIL604 real-time simulation platform, extensive testing of the grid-tied converter is conducted to validate its performance. The results of the performance assessment are thoroughly analyzed and presented to exemplify the efficacy of the proposed control strategy. Notably, the paper emphasizes the converter's operation at unity power factor during normal grid conditions, indicating maximized active power delivery to the grid. Furthermore, the grid-tied converter demonstrates impressive ride-through capability during symmetrical voltage dip, achieved through the dynamic adjustment of grid current references to maintain grid stability. This research contributes to the advancement of grid-tied converter control strategies, offering insights into enhancing the integration of renewable power sources into the power grid while upholding system reliability and stability. Overall, this research offers valuable insights into the practical implementation of grid-tied converters for renewable power integration. It presents a comprehensive control strategy that not only enhances the integration of renewable power sources into the power grid but also prioritizes system reliability and stability.

Modern control strategy of bidirectional DAB converter with consideration of control nonlinearity

Modern control strategy of bidirectional DAB converter with consideration of control nonlinearity

Evolving Power Factor Correction in Solar Water Pumping Systems through Zeta Converter-Based BLDC Motor Drives

The aim of this paper is to present the design and implementation of a new power conditioning system for a stand-alone solar-powered water pumping system. The system integrates a Brushless DC (BLDC) motor drive with a Power Factor Correction (PFC) Zeta converter to improve energy efficiency and reliability. In order to power BLDC motors for water pumping applications—which are essential for irrigation in isolated locations without access to the grid—the suggested solution attempts to overcome the difficulties related to the direct use of variable solar power. The PFC Zeta converter, which is the system's central component, is made to maximize power extraction from photovoltaic (PV) panels under fluctuating solar irradiation, guarantee high power factor, and reduce harmonic distortion in the electrical grid. A BLDC motor that powers a water pump is efficiently operated by this converter, which also optimizes the DC link voltage. A BLDC motor is especially well-suited for solar-powered applications due to its increased efficiency, dependability, and longer lifespan when compared to traditional induction motors. In order to continuously modify the PV panels' operating point to the maximum power point and maximize the amount of energy they capture, a Maximum Power Point Tracking (MPPT) algorithm is incorporated into the PFC Zeta converter's control strategy. The BLDC motor drive control strategy is carefully designed to guarantee seamless operation and flexibility in response to the fluctuating output from the solar panels, upholding the best possible pumping action in any solar situation. The system's capacity to sustain high efficiency and power factor under a variety of operating circumstances is demonstrated by the experimental findings. When the PFC Zeta converter is used, the solar-powered water pumping system performs much better overall. It shows a notable increase in energy conversion efficiency and lowers total harmonic distortion, which prolongs the pumping system's lifespan. By offering a solid method for raising the effectiveness and dependability of solar-powered water pumping devices, this study advances the sector and holds the possibility of a long-term water supply option for agricultural irrigation in isolated locations. In addition to utilizing renewable solar energy's environmental advantages, the suggested solution tackles the real-world difficulties associated with putting dependable and effective water pumping equipment into off-grid applications.

High-performance finite-time adaptive control strategy for three-level T-type converters

Three-level T-type converters are necessary interfaces for distributed energy resources to interact with the public grid. Naturally, designing a control strategy, featuring superior dynamics and strong robustness, is a promising solution to guarantee the efficient operation of converters. This article presents an improved finite-time control (IFTC) strategy for three-level T-type converters to enhance the dynamic performance and anti-disturbance capacity. The IFTC strategy integrates a dual-loop structure to regulate the dc-link voltage and grid currents. Specifically, the voltage regulation loop employs a finite-time adaptive controller that can counteract load disturbances without relying on current sensors. In the current tracking loop, finite-time controllers combined with a command filter are constructed to obtain fast and accurate current tracking. In this loop, the command filter is utilized to avoid calculating the derivative of current references. Theoretical analysis and experimental results demonstrate the IFTC strategy’s effectiveness.

Enhancing FRT capability of DFIG based on RC-crowbar considering the resonance and matching control strategies for different fault degrees

This paper compares the problems existing in the current fault ride-through (FRT) schemes of the doubly-fed induction generator (DFIG), and deeply analyzes the transient characteristics of DFIG during FRT. A comprehensive FRT scheme is proposed to improve the FRT capability by using an RC-crowbar and matching control strategy switching. The main innovation of this scheme lies in the consideration of resonance and other factors in the capacitance design of the RC-crowbar. To ensure that the DFIG still has good FRT capability after the RC-crowbar is cut off in advance in the later stage of FRT, an improved rotor side converter (RSC) control strategy is proposed for this situation. At the same time, to balance the reactive power on the stator side and accelerate the recovery of stator voltage throughout the entire FRT period, the control strategy of the grid side converter (GSC) is also improved. The comprehensive FRT scheme proposed in this paper can dynamically switch based on the degree of fault so that it still has good FRT ability when applied to different degrees of faults. Finally, the correctness and effectiveness of the proposed comprehensive FRT scheme were verified through simulation experiments.

Combined Control Strategy of Wind Storage Based on Power Electronic Transformer

Because of the inherent randomness and instability of the wind power generation system, the energy storage device and power electronic transformer are introduced into the wind power generation system to restrain the fluctuation of DC bus voltage and power junction, and improve the stability of the wind power generation system. This paper first introduces the basic characteristics of wind turbines and the basic idea of maximum wind energy capture and puts forward the control strategy of wind turbine side converter and grid side converter. Then the topological structure, mathematical model, and working principle of the power electronic transformer are described, and the control strategy of the power electronic transformer is proposed. Finally, the power electronic transformer is applied to the grid-connected wind storage system, and the grid-connected wind storage system model is built in MATLAB/Simulink platform, and the grid-connected control strategy under wind power fluctuation is simulated and verified. The simulation results show that the topology structure of the grid-connected wind storage system and the effectiveness of the grid-connected control strategy are proposed.

Multi‐mode converter control for linear generator‐based wave energy system

AbstractThe electrification of remote islands has long been a subject of research interest, primarily because of their historical reliance on fossil fuels, leading to a significant carbon footprint. Recent advancements in wave energy converters offer a promising avenue to make these islands more self‐sustainable while considerably reducing carbon emissions. However, the persistent issue of voltage dips due to weaker grids continues to pose a challenge. This study introduces a multi‐mode converter control strategy with the goal of electrifying remote islands, employing a linear generator‐based wave energy converter in a unified electrical model. Various scenarios, including voltage dips and mainland grid disconnection, are simulated using MATLAB/Simulink. The study demonstrates the converter's ability to transition swiftly and smoothly in response to these scenarios, ensuring an uninterrupted power supply. Furthermore, the analysis indicates that the power quality at the point of common coupling remains well within acceptable standards.

Composite control strategy for wide-gain LLC resonant converters with photovoltaic energy storage inputs

Composite control strategy for wide-gain LLC resonant converters with photovoltaic energy storage inputs

New analysis of VSC-based modular multilevel DC-DC converter with low interfacing inductor for hybrid LCC/VSC HVDC network interconnections

The integration of multiterminal hybrid HVDC grids connecting LCC- and VSC-based networks faces several technical challenges such as DC fault isolation, ensuring multi-vendor interoperability, managing high DC voltage levels, and facilitating high-speed power reversal without interruptions. The two-stage DC-DC converter emerges as a key solution to address these challenges. By implementing the modular multilevel converter (MMC) structure, the converter's basic topology includes half-bridge sub-modules on the VSC side and full-bridge sub-modules on the LCC side. However, while this topology has been discussed in the literature, its connection to an LCC-based network with controlled current magnitude lacks detailed analysis regarding operational challenges, control strategies under various scenarios, and design considerations. This paper fills this gap by providing comprehensive mathematical analysis, design insights, and control strategies for the modular DC-DC converter to regulate DC voltage on the LCC-HVDC side. Additionally, the proposed control scheme minimizes the interfacing inductor between the two bridges, ensuring uninterrupted power flow during reversal and effective handling of DC faults. Validation through Control-Hardware-in-the-Loop testing across diverse operational and fault scenarios, along with a comparative analysis of different converters, further strengthens the findings.© 2017 Elsevier Inc. All rights reserved.