Control Strategy Of Converter Research Articles

A Hardware-Simplified Soft-Start Scheme for Current-Fed Full-Bridge DC-DC Converter

At present, the current-fed full-bridge DC-DC converter still faces two inherent defects, namely, the soft-start issue during the start-up process and the voltage spike issue in normal working conditions. In existing research, a large number of attempts have been reported to overcome these two inherent issues. However, the existing solutions are all based on both redundant soft-start circuits and snubber circuits, and two different circuits are required. As a result, the cost of the current-fed full-bridge DC-DC converter is high, especially because the soft-start circuits are only used during the start-up process. So, to reduce device redundancy, a hardware-simplified soft-start scheme is proposed in this paper. In the proposed scheme, the snubber circuit is reused for the soft-start process based on topology reconfiguration, avoiding additional soft-start circuits to reduce the cost of this DC-DC converter. In this proposed method, the current-fed full-bridge DC-DC converter is operated as the voltage-fed full-bridge DC-DC converter by always turning on the snubber switch during the start-up process. Then, the output capacitor can be charged by slowly increasing the output voltage of the H bridge. Then, when the output voltage is high enough, the current-fed full-bridge DC-DC converter is again operated in the current-fed mode to boost the voltage. Subsequently, the converter characters and control strategy were examined and analyzed. The experimental results verify the feasibility of the proposed hardware-simplified soft-start scheme for the current-fed full-bridge DC-DC converter.

Design and control of modular multilevel matrix converter with symmetrically integrated energy storage for low frequency AC system

AbstractIntegrating energy storage units (ESUs) into part of sub‐modules (SMs) enables the decoupling active power control for the modular multilevel matrix converter (M3C). The low frequency AC (LFAC) system based on M3C with symmetrically integrated energy storage (SI‐AM3C) can provide functions such as renewable power fluctuation smoothing and other power grid auxiliary services, which is attractive in engineering practices. This paper focuses on the design and control of SI‐AM3C. For the converter design, an evaluation method for the number of required active SMs (ASMs) is presented. On this basis, the influences of different system operating conditions on the ASM requirement are analyzed in case studies, and the effects of specific circulating injection strategies are also investigated. The control system targeted at decoupled AC side active power for SI‐AM3C is introduced. A modified inner‐arm capacitor voltage balance strategy is introduced to reduce the capacitor voltage deviation between ASMs and passive SMs (PSMs). The conclusions related to the presented estimation method and converter control strategy are verified by time‐domain simulations in PSCAD/EMTDC.

Research on control strategy of dual active full bridge converter based on deep deterministic strategy gradient

In order to cope with the need for fast and adaptive voltage regulation in the face of large-scale disturbance in future smart grid EV grid-connected converters, a control strategy based on deep reinforcement learning is proposed in this paper. For electric vehicle grid-connected dual active bridge (DAB) DC–DC converter, a deep deterministic strategy gradient (DDPG) reinforcement learning intelligent controller based on an actor-critic architecture is designed. Through real-time online learning and training by collecting a large amount of system data, the intelligent controller can automatically adjust the power parameters of the DAB converter to ensure that the DC converter has strict stability in the face of various system disturbances. Simulation results show that the control strategy is effective. This research provides an innovative and feasible solution, which has important practical application value to the voltage regulation of electric vehicle grid-connected converters.

Reinforcement Learning-Based Event-Triggered FCS-MPC for Power Converters

This article aims to first focus on an improvement of finite control-set model predictive control strategy for power converters that is based on reinforcement learning event-triggered predictive control architecture with the help of adaptive dynamic programming technique and event-triggered mechanism subject to system uncertainties. Our development, endowed with the merits of reinforcement learning and event-triggered control as well as predictive control solution, is able to alleviate the issues of parametric uncertainties and high switching frequency inherent in the existing scheme, while retaining the merits of the finite control-set model predictive control. Finally, this proposal is experimentally evaluated, where robust performance tests confirm the interest and applicability of the proposed control methodology.

Model Predictive Control for Matrix Converters in Grid-Interactive Applications

Model Predictive Control (MPC) is a promising control strategy for matrix converters in grid-interactive applications. MPC optimizes a cost function over a finite time horizon, considering system constraints like voltage and current limits, grid codes, and power factor requirements. This enables effective grid synchronization, power quality regulation, and efficient power conversion. Advancements in MPC include predictive modelling techniques, adaptive algorithms, optimization algorithm integration, hybrid control strategies, and multi-objective optimization formulations. Benefits include fast response to changes in grid conditions, robustness in handling uncertainties, and extended time-horizon optimization. This study provides insights into MPC techniques and highlights the potential for further research.

Enhancing Performance of Andronov-Hopf Oscillator-Based Grid-Forming Converters in Microgrids With Non-Invasive Online Impedance Estimation

The Andronov-Hopf based Virtual Oscillator Control (AHO) is an emerging control strategy for grid-forming converters (GFC) to ensure the stability of the future power system with high level of penetration of renewable energies. AHO allows converters to operate in either grid-connected and islanded operating modes. However, the application of this control strategy is limited due to the inherent problem in simultaneous controlling active and reactive power output of GFCs. This paper presents a modification in AHO control structure, and adopts a wide-band grid impedance estimation to improve the dispatchability of AHO in grid-connected mode. The impedance estimation algorithm is embedded into the control loop of AHO, and requires only the measurement of the voltages and currents at the point of common coupling. Thus it is cost-effective and practical. The performance of the proposed method is validated in both simplestructure, and large low-voltage benchmark distribution systems, using MATLAB/Simulink software and the real-time Opal-RT platform. The simulation results confirm the high-accuracy of the estimation and the capability of AHO in simultaneously controlling active and reactive power with zero steady-state errors. Additionally, this paper discusses the small-signal stability and Lyapunov large signal stability of the proposed AHO and compares it to existing methods.

Adaptive droop control strategy of parallel LLC converters

AbstractWhen the resonant converters are connected in parallel, the output current is unbalanced without additional current‐sharing measures due to differences in resonant component. In the input‐parallel output‐parallel resonant converter system, the output voltage accuracy of the converter under the traditional droop control is analyzed when the load changes. In this paper, an adaptive droop control is proposed, in which the droop coefficient is adaptively adjusted as the load changes. The control method proposed in this paper realizes the current sharing between the converters and solves the shortcomings of the output voltage changing under different loads in the conventional droop control. Taking two parallel LLC converters as an example, the control block diagram of the parallel control method for adaptive adjustment of the droop coefficient proposed in this paper is given, and the stability of the control loop is analyzed. Finally, two parallel prototypes of LLC converters with input 200 V/output 24 V input are built by digital control, and the experiment shows that the proposed control method improves the shortcomings of excessive output voltage droop caused by traditional droop control during dynamic load switching, which verifies the effectiveness of the method.

Proposed Adaptive Control Strategy of Modular Multilevel Converter Based on Virtual Synchronous Generator

In the context of weak grids, vector-controlled modular multilevel converters (MMC) suffer from issues such as low inertia, low damping, and poor system stability. To address these challenges, this paper proposes a control strategy for virtual synchronous generators (VSGs) based on a fuzzy logic control algorithm. The conFtrol strategy leverages the capability of fuzzy algorithms to handle the fuzziness and uncertainty of input signals, enabling adaptive control of the virtual inertia and damping coefficient of the VSG, thus empowering the system with autonomous frequency and voltage regulation capabilities. When the system deviates from or approaches the stable operating point, increasing or decreasing the virtual inertia allows for dynamic adjustment of the virtual inertia and damping coefficient in response to load fluctuations during MMC operation. Through simulation verification, it is demonstrated that the proposed control method provides inertia support to the system during sudden changes in active load during MMC grid-connected operation. This control method achieves adaptive adjustment of the virtual inertia and damping coefficient, effectively enhancing system stability. The simulation results validate the effectiveness and correctness of the proposed control strategy.

Three Phase PFC Converter With Multilevel Inductive Switching Network

The rising power requirement of the on-board charger (OBC) demands high efficiency and high power density in the 3-phase power factor correction (PFC) converters. However, due to the large volume of boost inductors and filters of the conventional 2-level converters, their power density is limited. In this paper, multilevel inductive switching network (MISN) modules based on low-voltage switches are arranged in series at the ac-side to reduce the large size of inductors and filters. Besides, the operating principle and control strategy of the 3-phase MISN-PFC converter are analyzed. In addition, to determine the multiple variables of the MISN module, the design methodology is proposed based on the loss model and volume model for the multilevel converter. Finally, a 10kW prototype has been established to verify the analysis, where 99% efficiency at full load and 430W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> power density are achieved.

Design and analysis of multiple input single output converter for hybrid renewable energy system with energy storage capability

This paper proposes the design and analysis of a multiple-input-single-output (MISO) DC-DC converter suitable for a hybrid renewable energy system with energy storage capability. The converter design and control strategy validated in this research can be used to regulate the output dc voltage obtained from multiple-source renewable energy systems. The design is realized using a non-isolated double boost converter as it can handle bidirectional power flow at the storage port and has other advantages like compact structure, reduced number of components, and double boosting capability. The converter can also work without transformers, enabling the input renewable energy sources to operate individually. An inverted decoupler control strategy is adopted in the design of this novel converter. Mathematical models were developed to obtain the decoupler matrix, and the proposed control strategy is utilized to analyze the output. Simulations were performed on MISO converters with load and reference variations and is validated with the prototype. The current ripple percentage at the dual source side is found to be reduced by 2.6%. Also, the rise time, settling time, and percent overshoot of the output voltage were reduced by 0.03 s, 45 ms, and 3.6%, respectively. The performance of the proposed MISO converter is validated on a 50 W hardware prototype. The results validate the MISO converter's superior dynamic performance, output voltage regulation and reduced dual source ripple current, all of which are in agreement to the results of the simulation. A comprehensive comparison with the traditional controller is also conducted to further illustrate the advantages of the proposed inverted decoupler. The inverted decoupler validated in this work can be effectively used in hybrid renewable energy systems with energy storage capability, as it is found to be immune to the disturbances from the source end.

Nonsingular fast terminal sliding mode control for two-stage converters of AC island photovoltaic microgrid

Taking into account almost all kinds of variations and uncertainties to which AC island photovoltaic (PV) microgrid is often subjected, this paper proposes a new nonsingular fast terminal sliding mode control (NFTSMC) strategy for two-stage converters to enhance robustness against those disturbances and improve system dynamic performance. Firstly, to effectively decrease the adverse effect on the system from intermittent solar irradiation and uncertain environmental temperature, a NFTSMC cascaded with perturb and observe (P&O) scheme is put forward for fore-stage DC/DC converter, and PV output voltage is controlled to track its reference and thus maximum power point tracking (MPPT) performance is improved. Then, to significantly decrease the adverse effect on the system from variations of load and LC filter parameters, by incorporating an extended state observer (ESO) into NFTSMC, an ESO-based NFTSMC scheme is proposed for post-stage DC/AC converter, and the load voltage is regulated to track its reference and thus system robustness is strengthened, in which ESO is designed to replace load current sensor and thus reduce hardware cost. By using global terminal attractor without discontinuous switching function, the proposed NFTSMC strategy can not only strengthen system robustness but also improve system dynamic performance. Lastly, on account of the variations of PV generation and load demand, a conventional double-loop PI scheme is put into use for bidirectional DC/DC converter and thus system power balance is ensured. Comprehensive MATLAB simulation and StarSim/Hardware experiment results show that the proposed NFTSMC strategy for two-stage converters can overcome negative effects caused by various internal and external disturbances, and thus enable island PV microgrid to operate reliably and supply high-quality AC power.

Reliability Evaluation of DC/DC Converter in Direct Current Collection System of Wind Farm Considering the Influence of Control Strategy

The DC collection system of wind farms can effectively solve the problems of harmonic resonance and reactive power transmission in large-scale wind power AC collection systems, and has broad development prospects. The DC/DC converter is critical equipment in the wind farm DC collection system, and its reliability is related to the entire collection system’s safe and stable operation. The reliability of DC/DC converters is affected by factors such as system operating conditions and control strategies. Based on this, a reliability evaluation model for boost full-bridge isolated (BFBIC) DC/DC converters is proposed from the device level to the submodule level and then to the equipment level, incorporating operating conditions and control strategies into reliability analysis. Firstly, in device-level reliability modeling, the impact of DC/DC converter operating conditions and control strategies on insulated gate bipolar transistor (IGBT) module losses and junction temperature fluctuations are considered. Secondly, fault tree analysis (FTA) is used to establish the reliability model of the BFBIC submodule and DC/DC converter. In the end, we verify the effectiveness of the proposed model through a numerical example, and provide solid data support for analyzing the reliability of the wind farm DC collection system.

Power control strategy of wave energy converter with a hybrid double-machine hydraulic energy storage and generating system

Wave energy converters (WEC) with the increasing capacity, which has reached a level of hundreds of kilowatts, would play a role in the connected microgrid. Due to the inherent fluctuation and randomness of wave energy, the unstable output power of WEC is a threat to the power balance of the microgrid. Machines start and stop periodically and the output power changes continuously and significantly. The previous study focused little on the power control of grid-connected WECs. In this paper, a power control strategy is proposed for WECs to achieve stable power output and regulation in various wave conditions. The power control strategy is based on a hybrid double-machine hydraulic energy storage and generating system composed of a controlled unit and an uncontrolled unit. The control strategy enables the stability control and the controllable regulation of power of WEC in various wave conditions. Simulation results of several wave conditions have validated the effect of the power control strategy. The power control strategy would contribute to the extensive deployment of WECs.

Dynamic Performance Improvement of Continuous Control Set Model Predictive Control for High-Frequency Link Matrix Converter

In this paper, a comprehensive control strategy of a high frequency link matrix converter (HFLMC) based on the interaction technology between electric vehicle and power grid is proposed to improve the dynamic performance of the system. The continuous control set model predictive control (CCS-MPC) is applied to the current loop to solve the problems of difficult selection of PI control parameters and slow dynamic response speed. In order to ensure that the grid-connected current can achieve better command tracking, a deviation suppression term is introduced into the cost function of CCS-MPC, and the online auto tuning method of weight factors of fast-tracking term and deviation suppression term is designed. On this basis, the PWM signals are generated by the coordinated modulation strategy of the HFLMC to obtain a constant switching frequency, which makes the harmonic of the grid connected current easier to be filtered out. Experimental results show the correctness and feasibility of the proposed control strategy.

An Improved Arc Fault Location Method of DC Distribution System Based on EMD-SVD Decomposition

The influence of the control strategy of the power electronic converter obscures the fault characteristics of DC distribution networks. The existence of arc faults over an extended period of time poses a grave threat to the security of power grids and may result in electric shock, fire, and other catastrophes. In recent years, the method of fault localization based on the traveling wave method has been a popular topic of research in the field of DC distribution system protection. In this paper, the fault localization principle of the traveling wave method is described in depth, and the propagation characteristics of the traveling wave of fault current in the online mode network are deduced. We present a method for wave head calibration that combines empirical mode decomposition (EMD) and singular value decomposition (VMD). After the fault-traveling current signal has been subjected to EMD, the first eigenmode function is extracted and subjected to singular value decomposition (SVD). After SVD, the detail component can reflect the singularity of the signal. The point of the maximum value of the detail component signal corresponds to the moment when the faulty traveling wave head reaches the monitoring point. Finally, the DC distribution system is modeled based on the PSCAD/EMTDC simulation environment, and the fault location method is verified. The simulation results show that the method can effectively realize fault localization.

A virtual inertial control strategy for bidirectional interface converters in hybrid microgrid

Insufficient inertia is one of the urgent problems to be solved in the stability of AC-DC hybrid microgrid. In order to improve AC bus frequency and DC bus voltage inertia in hybrid microgrid, a virtual inertia control strategy for bidirectional interface converter (BIC) based on virtual synchronous generator (VSG) is proposed. The virtual inertia equations on both sides of the AC and DC are used to slow down the variation of the DC voltage and the AC frequency. When the load fluctuates, the dynamic response of the DC voltage, the AC frequency and the power transmission between the AC and DC subnets is improved, thus improving the stability of the system. This control strategy enables BICs to share active power equally under stable conditions, prevents circulating power, and achieves accurate power sharing among parallel BICs. The small signal model of BIC under virtual inertia control is established, the dynamic characteristics of the system under different control parameters are analyzed, and the influence of the control parameters on the system is discussed. The simulation model is established in PSCAD/EMTDC software to verify the correctness of the proposed control strategy.

Design of Novel Modified Double-Ended Forward Converter for Stepper Motor Drive

This paper presents the design and analysis of a modified double-ended forward converter (DEFC) for stepper motor-based robotic applications. The proposed converter topology provides galvanic isolation between the input and output while also higher efficiency with a smooth operative system, making it suitable for use in robotic systems that require both power and control signals to be transmitted. The paper also discusses the control strategy for the converter, which uses Proportional Integral (PI) to regulate the output voltage and current. The control strategy is implemented using a microcontroller-based system, which provides precise control of the output parameters. The converter is tested using a stepper motor-based load, and the results demonstrate the effectiveness of the proposed topology and control strategy. In addition to the experimental results, the paper also presents a detailed analysis of the converter’s performance. The analysis includes the input voltage and current, capacitor voltage, MOSFET parameters, output voltage and current, and calculation of efficiency. The analysis results show that the proposed converter topology and control strategy offer high efficiency comparing to existing converting approaches. Overall, the proposed double-ended forward converter offers a suitable solution for stepper motor-based robotic applications, providing efficient and reliable power and control signals. The results demonstrate the effectiveness of the proposed converter topology and control strategy, making it a promising option for use in future robotic systems.

VSC control strategy for HVDC compensating harmonic components

This paper proposes a voltage source converter (VSC) control strategy for the high voltage direct current (HVDC) transmission systems compensating the harmonic components. For VSC-HVDC AC system accounted for a relatively large share of the 5th, 7th, 11th, 13th and other low harmonics. A selective harmonic current control strategy based on vector proportional integral (VPI) regulator in dq coordinate system is proposed on the basis of PI control. In which, PI is used to control the DC component of the current error, while VPI is used to suppress the multiplicative fluctuations of the current error. Unlike the proportional-integral resonant (PIR) regulator, the VPI contains a second-order numerator that achieves the ideal 0° phase delay of the closed-loop transfer function of the control system at the set resonant frequency point, so its control accuracy for harmonic currents is better than that of the PIR. A two-terminal VSC-HVDC system is built using Simulink software, and current compensation simulations are performed for three control methods: conventional PI, PIR and PI parallel VPI schemes. The superior harmonic suppression performance of VPI is verified by comparing the harmonic content.

A Lifetime Improvement Active Thermal Control Strategy for Wind Turbine Parallel Converters Based on Reactive Circulating Current

When the wind turbine operates under frequently fluctuating mission profiles, the power semiconductors of its converter will generate low-frequency junction temperature fluctuations, resulting in accumulation of damage to the devices and affecting the converter’s lifetime. To address the above issues, an active thermal control (ATC) strategy based on reactive circulating current for the parallel converter of permanent magnet synchronous generator wind power system was proposed in this paper, by introducing reactive circulating current during sudden wind speed drops, the thermal cycle of the power semiconductor can be effectively smoothed. On the other hand, considering the impact of the proposed strategy on the voltage vector and modulation index of the converter, both the machine-side converter (MSC) and the grid-side converter (GSC) during the control process will be analyzed in detail, then the reactive current of GSC will be limited to prevent excessive modulation index and maintain system stability without reducing the filter size. Finally, a 2 MW wind power system is utilized as a benchmark, and both short-term simulation analysis and long-term numerical results reveal the effectiveness of the control strategy proposed in this paper.

Grid-Forming Controller Based on Virtual Admittance for Power Converters Working in Weak Grids

The high penetration of distributed energy resources, based on power electronics, is giving rise to stability issues in the electrical network, as initially those plants were not required to provide either voltage or frequency support. Due to this, TSOs and DSOs have set new requirements for them to provide grid support functionalities. This paper presents a grid forming control strategy for power converters which is based on a virtual admittance loop. By means of this strategy it is possible to use a conventional current control based inverter, just adding this outer loop. By doing so, the converter is not only able to perform current control, but also frequency and voltage support functionalities. In this work, the proposed control is described and analyzed, checking as well its stability boundaries. After this analysis, the results obtained in a hardware-in-the-loop platform, where faulty scenarios, islanding or black start conditions, will be shown. Finally, the results obtained in an experimental true scale workbench will show its effectiveness for providing such services.