Showing papers in "IEEE Journal of Emerging and Selected Topics in Power Electronics in 2021"

Review on Advanced Control Technologies for Bidirectional DC/DC Converters in DC Microgrids

Abstract: DC microgrids encounter the challenges of constant power loads (CPLs) and pulsed power loads (PPLs), which impose the requirements of fast dynamics, large stability margin, high robustness that cannot be easily addressed by conventional linear control methods. This necessitates the implementation of advanced control technologies in order to significantly improve the robustness, dynamic performance, stability and flexibility of the system. This article presents an overview of advanced control technologies for bidirectional dc/dc converters in dc microgrids. First, the stability issue caused by CPLs and the power balance issue caused by PPLs are discussed, which motivate the utilization of advanced control technologies for addressing these issues. Next, typical advanced control technologies including model predictive control, backstepping control, sliding-mode control, passivity-based control, disturbance estimation techniques, intelligent control, and nonlinear modeling approaches are reviewed. Then the applications of advanced control technologies in bidirectional dc/dc converters are presented for the stabilization of CPLs and accommodation of PPLs. Finally, advanced control techniques are explored in other high-gain nonisolated (e.g., interleaved, multilevel, cascaded) and isolated converters (e.g., dual active bridge) for high-power applications.

Detection of False Data Injection Cyber-Attacks in DC Microgrids Based on Recurrent Neural Networks

Abstract: Cyber-physical systems (CPSs) are vulnerable to cyber-attacks. Nowadays, the detection of cyber-attacks in microgrids as examples of CPS has become an important topic due to their wide use in various practical applications from renewable energy plants to power distribution and electric transportation. In this article, we propose a new artificial intelligence (AI)-based method for the detection of cyber-attacks in direct current (dc) microgrids and also the identification of the attacked distributed energy resource (DER) unit. The proposed method works based on the time-series analysis and a nonlinear auto-regressive exogenous model (NARX) neural network, which is a special type of recurrent neural network for estimating dc voltages and currents. In the proposed method, we consider the effect of cyber-attacks named false data injection attacks (FDIAs), which try to affect the accurate voltage regulation and current sharing by affecting voltage and current sensors. In the presented strategy, first, a dc microgrid is operated and controlled without any FDIAs to gather enough data during the normal operation required for the training of NARX neural networks. It is worth mentioning that in the data generation process, load changing is also considered to have distinguishing data sets for load changing and cyber-attack scenarios. Trained and fine-tuned NARX neural networks are exploited in an online manner to estimate the output dc voltages and currents of DER units in dc microgrid. Then, based on the error of estimation, the cyber-attack is detected. To show the effectiveness of the proposed method, offline digital time-domain simulation studies are performed on a test dc microgrid system in the MATLAB/Simulink environment, and the results are verified using real-time simulations using the OPAL-RT real-time digital simulator (RTDS).

Cyber Security in Control of Grid-Tied Power Electronic Converters—Challenges and Vulnerabilities

Abstract: Grid-tied power electronic converters are key enabling technologies for interfacing renewable energy sources, energy storage, electrical vehicles, microgrids, and high-voltage dc transmission lines with the electrical power grid. As the number of power converters in modern grids continually increases, their monitoring and coordinated control in a way to support the grid have become topics of increased practical and research interest. In connection with this, latest standards have also defined a mandatory set of control parameters for grid-tied converters, which should be adjustable by a remote entity that sends commands through a communication network. While such a remote control capability allows many new control functions in grid-tied converters, it also renders them vulnerable to cyber-attacks. The aim of this article is first to shed light on the portions of the power converter control systems that are vulnerable to cyber-attacks. Next, typical cyber-attacks are overviewed by considering different applications of the grid-tied converters. Further, the impact of different types of cyber-attacks on grid support functions is studied. Finally, this article is concluded with summary and recommendation for further research.

Bipolar DC Power Conversion: State-of-the-Art and Emerging Technologies

Abstract: This article provides a detailed analysis of the power electronics solutions enabling bipolar dc grids. The bipolar dc grid concept has proven to be more efficient, flexible, and higher in quality than the conventional unipolar one. However, despite its many features, these systems still have to overcome their issues with asymmetrical loading to avoid voltage imbalances, besides meeting regulatory and safety requirements that are still under development. Advances in power electronics and the large-scale deployment of dc consumer appliances have put this growing architecture in the spotlight, as it has drawn the attention of different research groups recently. The following provides an insightful discussion regarding the topologies that enable these architectures and their regulatory requirements, besides their features and level of development. In addition, some future trends and challenges in the further development of this technology are discussed to motivate future contributions that address open problems and explore new possibilities.

A Review of Switching Slew Rate Control for Silicon Carbide Devices Using Active Gate Drivers

Abstract: Driving solutions for power semiconductor devices are experiencing new challenges since the emerging wide bandgap power devices, such as silicon carbide (SiC), with superior performance become commercially available. Generally, high switching speed is desired due to the lower switching loss, yet high $dv/dt$ and $di/dt$ can result in elevated electromagnetic interference (EMI) emission, false-triggering, and other detrimental effects during switching transients. Active gate drivers (AGDs) have been proposed to balance the switching losses and the switching speed of each switching transient. The review of the in-existence AGD methodologies for SiC devices has not been reported yet. This review starts with the essence of the slew rate control and its significance. Then, a comprehensive review categorizing the state-of-the-art AGD methodologies is presented. It is followed by a summary of the AGDs control and timing strategies. In this work, using AGD to reduce the EMI noise of a 10-kV SiC MOSFET system is reported. This work also highlights other capabilities of AGDs, including reliability enhancement of power devices and rebalancing the mismatched electrical parameters of parallel- and series-connected devices. These application scenarios of AGDs are validated via simulation and experimental results.

Incorporating Power Electronic Converters Reliability Into Modern Power System Reliability Analysis

Abstract: This article aims to incorporate the reliability model of power electronic converters into power system reliability analysis. The converter reliability has widely been explored in device- and converter-levels according to physics of failure analysis. However, optimal decision-making for design, planning, operation, and maintenance of power electronic converters require system-level reliability modeling of power electronic-based power systems. Therefore, this article proposes a procedure to evaluate the reliability of power electronic-based power systems from the device-level up to the system-level. Furthermore, the impact of converter failure rates including random chance and wear-out failures on power system performance in different applications such as wind turbine and electronic transmission lines is illustrated. Moreover, because of a high calculation burden raised by the physics of failure analysis for large-scale power electronic systems, this article explores the required accuracy for reliability modeling of converters in different applications. Numerical case studies are provided employing modified versions of the Roy Billinton Test System (RBTS). The analysis shows that the converter failures may affect the overall system performance depending on its application. Therefore, an accurate converter reliability model is, in some cases, required for reliability assessment and management in modern power systems.

Direct Torque Control Based on a Fast Modeling Method for a Segmented-Rotor Switched Reluctance Motor in HEV Application

Abstract: This article proposes a fast-nonlinear modeling method for the direct torque control (DTC) of a segmented-rotor switched reluctance motor (SSRM), excluding the rotor clamping device. First, the torque-balanced method is used to measure the flux-linkage values at five crucial positions. The flux-linkage profile of the SSRM is represented by the fourth-order Fourier series based on the measured values. Then, the Kriging model is employed to further describe flux linkage and torque characteristics based on the Fourier series. A combination of Fourier series and Kriging model can greatly incorporate their merits and improve the accuracy of the models. Compared with the conventional methods, the finite-element analysis data are not required for the modeling process in the proposed method. Finally, the simulations and experiments of the DTC and the current chopping control (CCC) methods based on the modeling method are carried out. The amplitude of flux linkage under DTC can be well controlled, while that under CCC is increased with the enlargement of load torque. Compared with the CCC mode, DTC greatly reduces the torque ripple and exhibits the better speed response, while the torque per ampere with CCC mode is higher.

A Unified Modeling Method of Virtual Synchronous Generator for Multi-Operation-Mode Analyses

Abstract: To provide inertia support for the grid, virtual synchronous generator (VSG) control of inverter-interfaced distributed generators (IIDGs) becomes a focus of worldwide attention. However, a VSG-based IIDG behaves differently in the grid-connected (GC) mode, the islanded-single-DG mode, and the islanded-multi-DG mode, whereas the mathematical and physical interpretations of this phenomenon are not well studied. In this article, we propose a unified modeling method of VSG-based IIDG to analyze its different dynamic performance in each operation mode. The proposed unified formulas can obtain the state-space models of the islanded-single-DG and islanded-multi-DG modes from that of GC mode for any VSG control method. With the obtained models, for several different types of VSG control in different operation modes, we analyze the distribution and sensitivity of the closed-loop poles and investigate the step responses both analytically and experimentally. These analyses reveal the intrinsic differences and correlations of the dynamics of VSG-based IIDG between each operation mode. These intrinsic features are valid independent of the applied VSG control scheme; thus, a test method to evaluate the parameters and performance of an unknown IIDG is derived. The findings of this article provide important instructions for engineers to model and design and test multi-operation-mode distributed generators.

Isolated and Non-Isolated DC-to-DC Converters for Medium Voltage DC Networks: A Review

Abstract: MVDC technology is a promising solution to avoid installation of new AC networks. MVDC can provide optimum integration of large-scale renewable energy sources, the interconnection of different voltage levels of DC and AC grids with the ancillary services. The development in MVDC depends significantly on the DC-DC converters. Such converters support the modern trends of utilising medium-frequency transformers in power networks. Research on isolated converters technology is in its infancy and limited by the conversion ratio and component ratings. Besides, there is no standards exist covering specific aspects of isolated converter product. Thus, a review of such converters is needed. This work presents, for the first time, a review of the DC-DC power converter families in MVDC grids including the leading families which are isolated and non-isolated converters, as well as other subfamilies comparing the specifications and characteristics. Also, the applications of these converters are provided by focusing on the essential requirements for each application.

Two-Stage 48-V VRM With Intermediate Bus Voltage Optimization for Data Centers

Abstract: In this article, a high-efficiency and power-density unregulated inductor-inductor-capacitor (LLC) converter (DCX) is proposed for a first-stage converter in a two-stage 48-V voltage regulator module (VRM) for data center applications. The intermediate bus voltage in the two-stage architecture is evaluated by designing two LLC-DCX converters with fixed transformation ratios of (4:1) and (8:1). The overall efficiency of the two-stage architecture is evaluated, and the optimal bus voltage is selected. The LLC-DCX is designed using gallium nitride (GaN) devices and an optimized integrated magnetic structure. An enhanced primary and secondary termination method, as well as a printed circuit board (PCB) winding structure for equal current sharing among all transformer layers, is proposed, A significant reduction in the total conduction loss for the high-frequency transformer is achieved. The designed LLC-DCX can provide a continuous output power of 900 W with maximum efficiencies of 98.4% for the (4:1) conversion, and 98.0% for the (8:1) conversion, with high-power densities of 1600 and 1200 W/in3, respectively. The overall efficiency of the two-stage VRM was evaluated, and the results show a superior performance when using a lower bus voltage of 6 V.

High Frequency Resonant Converters: An Overview on the Magnetic Design and Control Methods

Abstract: Resonant converters, especiallyLLC converters, are deployed in many applications thanks to their reliability and high efficiency. With the introduction of wide band gap (WBG) devices and the soft switching feature of the LLC converter, the switching frequency of the LLC can be pushed to the order of megahertz, to shrink the converter size and increase the power density. However, magnetic design and control challenges stand in the way of doing so. This article addresses the challenges of high-frequency magnetic design for the LLC converter, and presents an overview for the latest solutions on the magnetic design of the LLC transformer. The matrix transformer is suitable for an LLC converter where high output current at high frequency is required. Different integration methods for the matrix transformer are discussed and demonstrations of hardware prototypes are provided. The dynamic behavior of the LLC converter presents another significant challenge against deploying an LLC converter in applications where fast transient response is needed. This article discusses such challenges as well and provides an overview on the latest control techniques, including average current-mode control, charge control, and simplified optimal trajectory control, to improve the dynamic performance of an LLC converter. A 1 megahertz LLC converter with digital control is presented, using simplified optimal trajectory control with improved transient performance over a wide frequency range.

An Extended-State-Observer-Based Sliding-Mode Speed Control for Permanent-Magnet Synchronous Motors

Abstract: To improve the tracking performance of the speed controllers of permanent-magnet synchronous motor (PMSM) drive systems with different disturbances, such as internal parameter variations and external load changes, a novel extended-state-observer-based sliding-mode speed control (ESO-SMSC) scheme for PMSM drives is proposed in this article. First, a fast-response SMSC is designed based on the upper bound of the total disturbance. Then, an ESO is designed to estimate the total disturbance in real time. The parameters of the ESO can be easily designed based on the desired bandwidth of the ESO. The estimated total disturbance is then used to update the control law of the SMSC in real time. The resulting ESO-SMSC has improved speed tracking performance and strong robustness to disturbances while maintaining the fast dynamic response. The stability of the closed-loop PMSM drive system with the proposed ESO-SMSC is proven through the Lyapunov theory. The proposed ESO-SMSC is validated by experimental results for a 200-W salient-pole PMSM drive system.

Transient Analysis and Verification of a Magnetic Gear Integrated Permanent Magnet Brushless Machine with Halbach Arrays

Abstract: The magnetic gear integrated permanent magnet brushless machine (MG-IPMBM) is a kind of compact structure with high torque density and complex electromagnetic energy transfer In order to analyze the transient characteristics of the machine, an analysis method of field circuit coupling is proposed Both magnetic gear and permanent magnet motor are magnetized by Halbach array Combining the analytical model of the magnetic gear magnetic field with MATLAB motor simulation module, a joint simulation model of field circuit coupling double closed-loop control system based on the Simulink-analytical method is established The electromechanical transient response characteristics of machine under load starting, load mutation and overload self-protection are analyzed The simulation results show that the output speed and torque of machine can accurately follow the given value, and its unique overload self-protection ability greatly improves the safety of machine operation In addition, a prototype is made and an experimental platform is built The experimental results show that the output torque follows quickly, the torque ripple is small, and transient performance of the machine is good

Hybrid Nine-Level Boost Inverter With Simplified Control and Reduced Active Devices

Abstract: The single-phase hybrid nine-level boost inverter (H9LBI) with single input is presented to simplify the control and reduce the active devices. The proposed H9LBI includes only four complementary power transistor pairs to realize twofold voltage gain, requiring only four independent control signals from the controller. The voltages of the capacitors in the proposed topology can get inherent balance without auxiliary sensors or methods. The switched capacitors $C_{1}$ and $C_{2}$ of the proposed topology can naturally maintain at $V_{\mathrm {in}}$ ; the floating capacitor $C_{3}$ inherently balances at $0.5~V_{\mathrm {in}}$ . Therefore, the simplified control of the proposed topology is reflected in the greatly few independent control signals and the capacitors’ inherent voltage balance without sensor or complex balancing algorithm. The mentioned features show its suitability for distributed generation applications. The operation principles are fully illustrated in this article. The inherent balance of the proposed topology has been deduced in detail. Moreover, the comparative assessment containing multiple nine-level inverters indicates the merits of the proposed H9LBI on fewer devices, simplified control, reduced total voltage stress, and lower power loss. The cost function (CF) is also used to evaluate different multilevel inverters in a comprehensive way. The result of CF shows that the proposed H9LBI has the advantage of reduced overall cost for design. Finally, the simulation and experimental prototype are implemented to verify the steady and transient performance of the proposed topology.

Direct Power Control of Shunt Active Power Filter Using Space Vector Modulation Based on Supertwisting Sliding Mode Control

Abstract: This article proposes direct power control (DPC) associated with space vector modulation (SVM) for a shunt active power filter (SAPF). This control is suggested in order to overcome the drawbacks of the conventional DPC, where the SVM is able to decrease the high active and reactive power ripples maintaining a fixed switching frequency. In addition, the performance of the proposed scheme is improved by replacing PI controllers with supertwisting second-order sliding mode controllers (ST-SMCs) in the active and reactive power control loops. This technique provides high robustness and dynamics for external perturbations. The proposed control DPC-SVM based on ST-SMC is investigated by simulation and practical implementation using MATLAB/Simulink with a real-time interface based on a dSPACE 1104 board.

A 13-level Switched-Capacitor Multilevel Inverter with single DC source

Abstract: In this article, a novel 13-level inverter Single source, Switched-Capacitor Multi-Level Inverter (SSC-MLI), is proposed. This topology is suitable for renewable energy applications using less input voltage source magnitude. This structure is capable of boosting the input voltage six times with the help of switched capacitors. The capacitors are automatically balanced without any control algorithms, complex circuits, or closed-loop controllers. The advantages of the proposed structure are high power density and high efficiency by use of only switches. Since, there is no diodes there is no forward conduction loss, and no reverse recovery delay. The maximum blocking voltage across individual switch is three times the input voltage. The functionality of the SSC-MLI is described in detail. The capacitance calculation and optimum value of capacitors are discussed. A suitable comparison is presented for the proposed structure with the existing literature to check the inverter performance. The power loss for exiting a 13-level inverter is presented. The simulation is carried out for both pure resistive and inductive load. Later, the experimental results are presented for variation in frequency, dynamic change in load, variation in modulation index, and step-change in input voltage to validate the proposed topology performance and feasibility.

Symmetrical and Asymmetrical Reduced Device Multilevel Inverter Topology

Abstract: This article presents a single-phase symmetrical and asymmetrical multilevel inverter (MLI) topology. The presented topology can generate 9-level output voltage in a symmetrical configuration and 13- and 17-level output voltage in asymmetrical configuration with a single cell. The number of output levels can be improved further by increasing either the number of cells or switches in a single cell. The presented topology contains the least number of dc sources, semiconductor switches, capacitors, and diodes compared with classical and recently proposed topologies. Reduction in component count decreases the size, complexity, and cost of the overall converter. A detailed comparison has been done of the presented topology with the recently proposed topologies in terms of dc sources, semiconductor switches, capacitor, and total blocking voltage. Finally, to validate the presented concept, the prototype of the presented 9-, 13-, and 17-level MLI topologies has been tested in the laboratory for different switching frequencies, different modulation indexes, sudden load changes, and nonlinear load.

A Nonisolated Buck–Boost DC–DC Converter With Continuous Input Current for Photovoltaic Applications

Abstract: In this article, a novel nonisolated buck–boost dc–dc converter is introduced with a wide range of conversion ratios. The proposed buck–boost converter, unlike the traditional one, draws continuous current from its input port. Moreover, the proposed converter has high step-up voltage gain, which makes it suitable for industrial and renewable energy applications. Operation principles and small-signal modeling of the proposed converter are addressed in detail. Furthermore, the proposed converter is compared with other buck–boost topologies regarding different criteria, such as the number of elements, voltage gain, switch stress, and the type of input current (continuous or discontinuous). By considering the features of the proposed converter, it can be used in renewable applications, specifically in photovoltaic systems. A prototype is developed to experimentally evaluate the validation of theoretical analysis.

Recent Advancements in Submodule Topologies and Applications of MMC

Abstract: Modular multilevel converter (MMC) is a promising topology for medium- and high-power conversion systems. In recent years, it has been prominent over other power converters because of its exceptional features, including modularity and flexibility to adapt any voltage level, remarkable harmonic performance, no dc-link capacitors, transformerless operation, absence of ac-side filters, and capacitive nature of phase legs. However, there are some challenges, for instance, submodule (SM) capacitor voltage balancing, output current control, circulating current control, minimization of SM capacitor voltage ripple, dc-side faults, and efficient SM topologies that have been addressed by the research studies over time. In this article, we focus on the recent advancements in SM structures and their capability to overcome the faults, reduction in switching losses, decrease in voltage sensor count, and minimization of SM capacitor voltage ripple and provide the quick restoration of SM capacitor voltages after the removal of faults. Finally, the applications and development prospects of MMC are discussed in detail.

Rapid Power Compensation-Based Frequency Response Strategy for Low-Inertia Power Systems

Abstract: To reduce the frequency deviation and the rate of change of frequency (RoCoF) in a low-inertia power system, some converters are required to provide the frequency response (FR) power normally associated with the frequency deviation and/or the RoCoF, by droop/inertia/PD control. In this article, a rapid power compensation (RPC)-based FR strategy is developed to optimize the ability to compensate grid imbalance power, by fully exploiting the converter idle capacity. To this end, first, mathematical proof demonstrated the improved performance of the RPC strategy in terms of frequency deviation suppression versus droop control, and in terms of RoCoF suppression versus inertia control, with identical converter capacity limit. Moreover, it is proven that the RPC strategy can achieve consistent FR performance with respect to the optimal PD control, i.e., it can maximize the suppression of frequency deviation and RoCoF simultaneously, yet avoiding the limitations due to unknown grid parameters. Finally, by analyzing the operation modes and identifying the pertinent switching logic, the detailed implementation of the proposed RPC strategy is developed. Its superb FR performance is verified by the experiment results in a two-converter low-inertia system, and simulation results in an IEEE four-machine two-area system.

Design, Challenges, and Trends of Inductive Power Transfer Couplers for Electric Vehicles: A Review

Abstract: The magnetic coupler is the heart of an inductive power transfer (IPT) system, which facilitates wireless power transfer through its air gap. The couplers are designed to maximize efficiency, power density, power transfer distance, and misalignment tolerance while minimizing leakage flux, weight, cost, and volume. The coupler design process becomes complex due to the nonlinear behavior of magnetics, sophisticated geometrical structures, and mandatory design limitations imposed by standards, such as SAE J2954/1, IEC 61980-1:2015, and ISO 19363:2020. Initially, this article reviews the advancements in coil design methodologies and their structures over the last few decades to identify the ongoing challenges and trends. The impacts of the power electronics system, industrial standards, material selection, numerical and analytical modeling methods, and thermal modeling on the coil design process are identified to formalize the design procedure. A coil design example based on finite element analysis (FEA) tools is presented to identify the drawbacks of the existing design and optimization process. A sensitivity analysis, 3-D-Pareto plots, and optimal design selection by considering misalignment variations are proposed to improve the multiobjective optimization process. A generalized guideline for coil design is proposed, which highlights the essential design stages of an IPT coupler. Current trends are identified, and future directions are proposed.

Fault Detection and Protection Strategy for Islanded Inverter-Based Microgrids

Abstract: This article proposes a fault detection and protection strategy for islanded inverter-based microgrids (IBMGs). Reliable and accurate protection is one of the main challenges in the proliferation of modern microgrids (MGs). Considering the limited fault current of the voltage–frequency-controlled inverter-based distributed energy resources (VF-IBDERs), the protection is more challenging in islanded IBMGs. In this regard, the control scheme of VF-IBDER with a current limiting strategy plays an important role. Due to the limited fault currents close to the converter nominal current, the conventional fault detection methods do not work properly. In addition, bidirectional fault currents worsen protection coordination. In this article, first, an analytical sequence network modeling for VF-IBDERs is derived to specify their behavior under fault conditions. Then, a voltage-restrained negative-sequence resistance-based fault detection approach is proposed, which is based on the derived sequence networks. This quantity inherently detects the fault and its direction and is independent of the fault current magnitude. The proposed feature can be employed in both the conventional and communication-assisted coordination strategies. In addition, a protection coordination strategy based on a definite-time grading approach is employed. Finally, the performance of the proposed scheme is demonstrated by applying different faults in a test MG in PSCAD/EMTDC environment.

State of Health Estimation of Lithium-ion Battery Based on Constant-Voltage Charging Reconstruction

Abstract: State of health (SOH) estimation is essential for life evaluation and health management of lithium-ion battery (LIB). This paper proposes a novel SOH estimator by using the partial constant-voltage (CV) charging data. First, a thorough analysis is performed over different CV health indicators (HIs) in terms of the HI-SOH correlation as well as the robustness to CV partialness and disturbances, and the CV capacity is proved to be more informative and robust for SOH estimation. Second, to tackle the practical challenge arising from CV charging partialness, a novel CV phase reconstruction method combining Q-V modeling and open-circuit voltage (OCV) estimation iteratively is proposed to predict the CV capacity authentically based on the available partial CV data. The extracted CV capacity is further used to estimate the battery SOH precisely. The proposed method is validated with long-term degradation experiments performed on NCA cells. Results suggest that the proposed method manifests itself with a high estimation accuracy, a low requirement on the charging completeness, and a high robustness to cell inconsistency.

Supervised Learning Model Predictive Control Trained by ABC Algorithm for Common-Mode Voltage Suppression in NPC Inverter

Abstract: Training the weighting factors of model predictive control in multiobjective problems is a time consuming and sophisticated process. In this article, conventional model predictive control (CMPC) has been developed as supervised learning model predictive control (SLMPC) to cancel common-mode voltage (CMV) in a three-phase neutral-point-clamped (NPC) inverter, while other control objectives are desirably tracked. SLMPC is accurately and quickly trained through the artificial bee colony (ABC) algorithm to optimize the controller weighting factors. Using the optimized weighting factors, transient response is minimized and CMV is surpassed. After training the weighting factors, SLMPC containing the optimized waiting factors is applied to the three-phase NPC inverter without considering the ABC algorithm in the control loop. By applying the optimized weighting factors to the cost function, SLMPC has been evaluated under several experimental and simulation tests to show that desired control objectives, particularly CMV suppression, have been attained. The proposed training process can be generalized and used for MPC cost functions with more control objectives to obtain the best possible performance.

Analysis and Design of an LCCC/S-Compensated WPT System With Constant Output Characteristics for Battery Charging Applications

Abstract: The wireless power transfer (WPT) system has been extensively studied for its safety, convenience, and esthetics and has gradually been introduced into our life applications. In order to maintain battery performance, constant-current (CC) and constant-voltage (CV) charging outputs are generally regarded as the dominant charging modes. However, battery equivalent resistance changes significantly during the charging, so it is difficult to simultaneously achieve load-independent CC and CV charging outputs and zero phase angle (ZPA) condition. This article proposes a new LCCC/S topology and its corresponding parameter tuning method to obtain CC and CV charging modes at two different ZPA operating frequency points, respectively. In addition, it is worth mentioning that the receiver has only one compensation capacitor, which follows the principle that the receiver of the WPT system should remain compact and portable. Furthermore, a simple frequency modulation controller is designed to solve the problem of inaccuracies of the charging outputs due to parasitic losses of components and fluctuations of dc input voltage. Finally, a verification setup with 3-A output current in the CC mode and 48-V output voltage in the CV mode was built to validate the feasibility and rationality of the proposed LCCC/S-compensated WPT system and the corresponding control method.

Decentralized Model Predictive Control of DC Microgrids With Constant Power Load

Abstract: This article introduces a decentralized model predictive controller (DMPC) to ensure power sharing and regulate dc bus voltage in dc microgrids (MGs) with a constant power load (CPL). The proposed method replaces the conventional primary layer of dc MGs, i.e., inner loops and droop control, with a single optimal controller. A predictive automatic model of the system is realized for prediction purposes and to be used in the cost function. The control objectives are then incorporated in the cost function to attain an optimal state switching in each sampling time, hence regulating the dc bus voltage and accurate sharing of current among the MG. The proposed solution provides the system with a fast dynamic response and a zero steady-state error. The effectiveness of the proposed control is verified by hardware-in-the-loop (HIL) real-time experiments, and the results are compared with the conventional primary control.

Disturbance-Observer-Based Complementary Sliding-Mode Speed Control for PMSM Drives: A Super-Twisting Sliding-Mode Observer-Based Approach

Abstract: This article proposes a novel disturbance-observer-based complementary sliding-mode (DO-CSM) speed controller for the field-oriented controlled permanent-magnet synchronous motor (FOC-PMSM) drive system. At first, the rotor speed dynamics of the PMSM drive system considering the lumped disturbance, which consists of external disturbances, parametric uncertainties, and unmodeled dynamics, is presented. Then, the classic CSM speed controller and a typical artificial neural network (ANN)-based CSM speed controller, i.e., the Elman NN (ENN)-based intelligent CSM (ENN-ICSM) speed controller for the FOC-PMSM drive system, are reviewed. Afterward, the design of the proposed DO-CSM speed controller, which combines the signum-function-based CSM controller with the super-twisting sliding-mode observer (STSMO), is presented. In such a speed controller, the rotor speed tracking control is accomplished by the adopted CSM controller, whereas the STSMO is employed to estimate and compensate for the lumped disturbance in the rotor speed dynamics. Finally, experimental comparisons among the proposed DO-CSM speed controller, the classic CSM speed controller, and three selected ENN-ICSM speed controllers are carried out. Experimental results verify the effectiveness and superiority of the proposed DO-CSM speed controller.

Nonlinear Transient Stability Analysis of Phased-Locked Loop Based Grid-Following Voltage Source Converters Using Lyapunov’s Direct Method

Abstract: In this paper, using Lyapunov’s stability theorem, the transient stability conditions for a grid-following Voltage Source Converter (VSC) are found These conditions take into account both the grid specifications and the VSC’s dynamics The derived conditions are based on a well-known nonlinear model of the VSC’s Phase-Locked Loop To evaluate the stability of the nonlinear system, Lyapunov’s direct method is employed To this end, a new Lyapunov function is proposed, and its characteristics are analysed Using this Lyapunov function, the domain of attraction of the system’s equilibrium point is calculated Additionally, a novel system strength index based on the domain of attraction of the system is proposed The privilege of this index over the conventional indices are absoluteness, VSC’s dynamics consideration, and comparability of different VSCs with each other from a stability point of view In the end, the correctness of the proposed stability analysis is validated via simulation in Matlab/PLECS and experiment

Fault Current Control and Protection in a Standalone DC Microgrid Using Adaptive Droop and Current Derivative

Abstract: This article presents a novel fault detection, characterization, and fault current control algorithm for a standalone solar-photovoltaic (PV) based dc microgrids. The protection scheme is based on the current derivative algorithm. The overcurrent and current directional/differential comparison based protection schemes are incorporated for the dc microgrid fault characterization. For a low impedance fault, the fault current is controlled based on the current/voltage thresholds and current direction. Generally, the droop method is used to control the power-sharing between the converters by controlling the reference voltage. In this article, an adaptive droop scheme is also proposed to control the fault current by calculating a virtual resistance $R_{\mathrm{ droop}}$ , and to control the converter output reference voltage. For a high impedance fault, differential comparison method is used to characterize the fault. These algorithms effectively control the converter pulsewidth and reduce the flow of source current from a particular converter, which helps to increase the fault clearing time. Additionally, a trip signal is sent to the corresponding dc circuit breaker (DCCB), to isolate the faulted converter, feeder or a dc bus. The dc microgrid protection design procedure is detailed, and the performance of the proposed method is verified by simulation analysis.

Transient Control and Soft Start-Up for 1-MHz LLC Converter With Wide Input Voltage Range Using Simplified Optimal Trajectory Control

Abstract: The 48-V bus converters are widely used in telecommunications and network power architectures. A single-stage regulated $LLC$ bus converter can achieve high efficiency and high power density. This article addresses the control challenges of a regulated $LLC$ converter for 48-V bus converter applications. Simplified optimal trajectory control (SOTC) is used to control a 1-MHz $LLC$ converter with an input voltage range of 40–60 V and a frequency range of 0.8–1.8 MHz. A digital implementation of two-step SOTC is proposed for the high-frequency $LLC$ using a low-speed microcontroller (MCU). The proposed implementation can achieve the optimum transient performance and minimize settling time. SOTC can achieve the optimum transient response for an $LLC$ operating at resonant frequency but has a limited impact at a wide gain range. As a result, a feedforward compensation is proposed, in conjunction with SOTC, to achieve optimum transient response at a wide input voltage range or wide gain range. Moreover, a soft start-up with adaptive switching frequency is proposed to achieve start-up under limited current stress over the whole input voltage range. The experimental results are demonstrated on a 1-MHz $LLC$ 48-V bus converter using a 90-MHz TMS320F28069 Piccolo MCU.