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Under fault conditions, virtual synchronous generators (VSGs) are prone to lose transient stability, similar to synchronous generators. However, the existing studies on VSG transient stability are not comprehensive. The transient characteristics of VSGs are highly affected by control parameters, but the transient models of VSGs in existing studies are overly simplified. In addition, the critical clearing angle (CCA) and critical clearing time (CCT) are two indices used to measure the transient stability of a system, but there are few studies that consider both CCA and CCT. In this article, we analyze the CCA and CCT quantitatively to describe the transient stability boundary of a VSG under different control parameters and fault conditions. Then, an equal proportional area criterion is proposed to provide guidance for the control of virtual inertia in the VSG. Based on a theoretical analysis, a transient control method for a VSG is proposed, which can improve the transient stability of the VSG in terms of both CCA and CCT. Finally, simulation and experimental tests are performed to validate the correctness of the theoretical analysis and the proposed method. [ABSTRACT FROM AUTHOR]

Hybrid energy storage systems (HESSs) can simultaneouslyharness the advantages of batteries and supercapacitors (SCs) in various loading situations. Coupled with communication links, cyber-physical HESSs would be threatened by unexpected cyber attacks that may cause damage to electrical devices and even collapse the entire system. To overcome the adverse impacts of attacks, a resilience control scheme is proposed in this article. The proposed scheme provides a unified form integrated with adaptive laws to guarantee multifunctional HESS operations, i.e., dc bus voltage restoration, transient current allocation between batteries and SCs, proportional battery current sharing, and battery state-of-charge balancing, under cyber attacks. The proposed resilience control allows us to establish communication links only among batteries, whereas SCs are free of the data exchange process, which can save system capital costs. The stability of the proposed control is proved by the Lyapunov stability theory. The effectiveness and feasibility of the proposed approach are validated on a hardware-in-the-loop testing platform. [ABSTRACT FROM AUTHOR]

Slow load transient performance, potential cross-regulation, and low efficiency are the major drawbacks for pseudocontinuous conduction mode single-inductor dual-output (SIDO) dc–dc converters. To overcome these drawbacks, this article proposes a voltage-ripple (VR)-based dynamic freewheeling (DF) control technique for hybrid conduction mode (HCM) SIDO buck converter. With the employment of VR controller, the proposed control technique improves the load transient performance significantly. As the fast recovery during load transition, the cross-regulation is minimized. Additionally, due to the DF controller, the freewheel current value automatically updates in each switching period, which can improve the efficiency of the HCM SIDO buck converter, especially under the light load conditions. Finally, the proposed converter has been verified through experimental results. The transient response time on 0.5 A load change takes only 1–2 switching periods. No observable cross- regulation is found and maximum efficiency of 92.03% is achieved. Finally, the experimental waveforms are presented to verify the theoretical research. [ABSTRACT FROM AUTHOR]

Nowadays, due to many limitations in reality, the optimization of tracking precision and convergence time has attracted the attention of researchers in robotics community. In this article, a fixed-time adaptive neural network (NN) controller is proposed for unknown robot manipulators. A switching mechanism is integrated into the control design such that the semiglobal stability of the conventional NN control systems can be extended to global stability. The time-varying barrier Lyapunov function and the fixed-time control technique are incorporated into the controller design to guarantee the prescribed motion constraints and the fixed-time convergence simultaneously. Compared with some existing fixed-time NN control algorithms, the assumption that NN weight should be upper bounded can be relaxed in our work. Finally, the simulation and experiment studies are respectively carried out based on an unknown 2-degree of freedom robot and a Baxter robot to demonstrate the effectiveness and superiority of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Aluminum electrolytic capacitors (Al-Caps) are widely used in the dc link of ac/dc applications; however, they are one of the weakest components in power electronic converters. With the degradation of Al-Cap, its capacitance (C) decreases, and the equivalent series resistance increases. Based on this, many efforts have been made to realize condition monitoring (CM) of Al-Caps. Unfortunately, additional hardware (including current sensors and sampling circuits) and/or powerful data processing tools are usually required, which increases the cost and would bring new reliability risks. Considering this issue, this article presents a transient-based CM scheme for dc-link capacitors in digital-controlled boost power factor correction (PFC) converters, which does not need additional sampling devices. By analyzing the relationship between large-signal transient voltage profile and dc-link capacitance, a calculation model is established. Based on the sampled voltage and current signals used for digital control, the dc-link capacitance can be online estimated. Its feasibility is validated in simulation with a boost PFC operating in continuous conduction mode (CCM) and discontinuous conduction mode. Furthermore, taking a 1-kW boost PFC operating in CCM as a case study, experimental results illustrate that the estimation errors of the dc-link capacitance are less than 3.5% (error of a single test) and 1.5% (average error of multiple tests). [ABSTRACT FROM AUTHOR]

One of the main limitations of the classic control of the syncronverter is that there are not enough degrees of freedom to allow the designer to set the desired dynamics of the injected active and reactive powers ($p$ and $q$ , respectively). Moreover, the classic control also results in great coupling between $p$ and $q$. To solve these issues, a controller based on the feedback linearization technique is presented in this article. The proposed strategy allows the designer to set the dynamics of $p$ and $q$ , and also reduces the coupling between them to negligible levels. This controller also reproduces the behavior of the classic controller in steady state, modifying both $p$ and $q$ to changes in the grid frequency and point of common coupling voltage, respectively. [ABSTRACT FROM AUTHOR]

Two-mode low-voltage dc–dc converter (LDC) has been proposed for high and wide input voltage range in order to overcome the drawbacks of the conventional converters. With two operational modes, the two-mode LDC reduce the voltage stresses on the switches and dc offset current. However, it has large differences of capacitor voltage resulting in voltage spike on the switch at the mode transient. Moreover, the dc offset current has large variation between two modes. In this article, a variable control for two-mode LDC is proposed for changing the operational mode softly. The two mode LDC employing the proposed control is shown to minimize the difference of capacitor voltage and dc offset current over the entire input voltage range. The proposed control is verified by a 350–800 V input and 13.9 V/600 W output laboratory prototype. [ABSTRACT FROM AUTHOR]

In this article, we present the exact transient solution to the unbalanced and balanced faults in the doubly fed induction machine (DFIM). Stator currents, rotor currents, and stator fluxes have been validated using simulation and experiment. The work is meant to strengthen and fasten the predictability of large DFIMs in the design stage to comply with mechanical constraints or grid fault issues. Moreover, the analytical approach reduces the computational costs of large-scale stability studies and is especially suited to the initial phase, where plethora design computations must be carried out for the DFIM before it is checked for its transient interaction with the power system. The possibility to dynamically estimate the DFIM performance is simplified by original equations derived from first principles. First, case studies of two large $265 \,{\rm MVA}$ DFIMs are used to verify the analytical approach, and to justify the proposed “large machine approximation” using simulation with an exact match. Finally, laboratory measurements were conducted on a 10.96 and a $1.94 \,{\rm kVA}$ DFIM to validate the transient current peaks predicted in the proposed analytic expressions for two-phase and three-phase faults, respectively. [ABSTRACT FROM AUTHOR]

Output voltage deviation is a key performance index of voltage regulator modules (VRMs) with consecutive load transients. Usually, a large-capacity filter capacitor bank is used in VRMs to reduce the voltage deviation and stabilize the output voltage during transients. However, capacitors are one of the most vulnerable links in power electronic converters. For reliability reasons, it is essential to reduce the capacitance requirement while guaranteeing the transient performances of VRMs. Focusing on this, many efforts have been made to optimize the design of VRMs, where the transient auxiliary circuit-based scheme is a popular one. Unfortunately, there exists a large number of additional components in the existing auxiliary circuits. Considering this issue, in this article, we present a virtual series voltage source (VSVS) based auxiliary circuit scheme, which has minimum component counts. By using a controlled coupled inductor as the VSVS, the proposed scheme enables VRMs to have a relatively small transient voltage overshoot and without needing large bulk capacitance. Moreover, considering different control schemes with the same designing aim, the number and the electrothermal stress of critical components (e.g., capacitors) of VRMs are different; it is difficult to compare directly their advantages and disadvantages. Regarding this issue, this article investigates the converter-level reliability of VRMs with different control schemes. Taking a 12–3.3 V VRM as a case study, the reliability benchmarking results illustrate that the proposed scheme can significantly improve the reliability of VRMs. [ABSTRACT FROM AUTHOR]

This article presents an analytical derivation of transient performance deterioration for high-speed surface-mounted permanent magnet synchronous machine (SPMSM) drives under parameter mismatches, with an advanced deadbeat predictive current control (DBPCC), which exhibits fast dynamics and strong robustness with disturbances rejection. All the influential factors, including permanent magnet flux linkage and inductance mismatches, inverter nonlinearity, and speeds are taken into account in the analysis. It is shown that the transient performance with the advanced DBPCC is only dependent on inductance accuracy. Large transient overshoot and cross-coupling in the dq-axis currents at high speeds arise due to inductance mismatch. Based on the understanding gained through the analysis, a novel inductance identification method is also proposed in this article, which significantly improves the transient performance of high-speed SPMSM drives. The proposed online inductance identification method does not require signal injection, is nonintrusive, and can be easily implemented. By integrating the proposed method with the advanced DBPCC, the close-to-ideal deadbeat control can be achieved for high-speed SPMSM drives even in the presence of parameter mismatch and inverter nonlinearity. Both the analysis and proposed method have been validated experimentally on a prototype high-speed (30 000 r/min) SPMSM drive under various conditions. [ABSTRACT FROM AUTHOR]

This article proposes a discrete-time dynamic-decoupled current controller for an LCL-equipped high-speed permanent magnet synchronous machine with only the motor currents measured. The controller is designed in the synchronous coordinate based on a complex $\boldsymbol{z}$ -domain transfer function. The main contribution of the proposed current controller is the robust dynamic decoupling performance to achieve better transient behavior. Moreover, an effective coefficient selection method is developed to acquire sufficient phase margin and gain margin, even with the system parameters varying $\boldsymbol{\pm 50\%}$. Additionally, the stable region of the LCL resonance with the proposed method is discussed. Finally, the effectiveness of the proposed method is verified by driving the tested motor to 100 kr/min. [ABSTRACT FROM AUTHOR]

This article proposes a novel and easily implementable overcurrent suppression control for voltage-controlled virtual synchronous generators (VSGs). The VSG is vulnerable to grid voltage disturbances, such as voltage dip/recovery, because it consists of voltage source inverters (VSIs). In the worst case, the overcurrent caused by the voltage disturbance damages the VSI. The proposed VSG control can suppress the overcurrent caused by not only symmetrical but also asymmetrical voltage dip/recovery. The key idea is to use novel virtual grid voltages for the VSG reference output voltage. The proposed VSG control requires no complicated analysis/tuning for the implementation and no additional equipment, such as a fault-current limiter. Because of these advantages, the overcurrent in the VSG can be suppressed without increasing the cost and the tuning effort. The effectiveness of the proposed method is verified through simulations and experiments. [ABSTRACT FROM AUTHOR]

Due to a short-time gap breakdown in electrical discharge machining (EDM), a high dynamic response and flexible discharge current control ability are required for a pulse power generator. Therefore, a one-cycle control(OCC) of output current for a buck-type EDM pulse power generator is proposed. Considering the inductor current operating state, a full-range OCC current control is presented, and the Taylor expansion method is used for the duty cycle calculation. A duty cycle optimization strategy is proposed for transient states. Based on the small signal modeling, the dynamic response ability of the system is analyzed. The discharge current can switch from many transient states to a steady state in a few switching cycles without a current overshoot, and follow the average current reference well in the steady state. [ABSTRACT FROM AUTHOR]

The article presents the analytical derivation of the minimum dc link capacitance in single-phase front ends with active power factor correction (PFC) without hold-up time requirements. Such systems typically employ boost-type rectifiers; operate under restricted total harmonic distortion (THD) of the grid-side current. Moreover, PFC rectifiers must be capable of tolerating step-like zero-to-rated load power variations. It is well known that these two constraints contradict each other, posing nontrivial design challenges. The revealed value of minimum capacitance is expressed by an explicit function of grid voltage and frequency, converter rated power, dc link voltage reference, and grid current THD and voltage loop phase margin set points. Experimental results validate the proposed methodology, closely matching corresponding analytical predictions. [ABSTRACT FROM AUTHOR]

Three-phase pulsewidth modulated converters are usually controlled to achieve sinusoidal currents in the grid side and tight voltage regulation in the dc-link capacitor. The implementation of linear controllers based on small-signal models is a well-established solution for these converters. However, the dynamic performance can be improved only to a limited extent and it deteriorates under different operating conditions which may result in the uncontrollability of the dc-bus voltage during transients. In this work, a state-plane model and control strategy are introduced to improve the dc-link dynamics for three-phase converters. The proposed method provides fast, reliable, and consistent transient responses under the entire operating range, including rectifier and inverter modes. First, a normalized model that describes the natural dynamic behavior of the converter is derived and represented in the state-plane. In this way, the dynamic evolution of the operating point is described in a graphical domain as circular trajectories with well-defined characteristics. The insight provided by these natural trajectories is used to develop a control strategy to improve the dc-link dynamics by selecting a unique combination of circular paths to solve the transients. As a result, the operating point follows well-defined trajectories to achieve fast and consistent dc-link voltage responses under a wide operating range. The effectiveness and feasibility of the proposed control strategy are validated by several simulation and experimental results. [ABSTRACT FROM AUTHOR]

This article proposes a two-stage power converter with novel control methods for pulsed load applications. The first stage is an isolated converter that transfers only average power to the second stage, which dramatically reduces the input filter size and components’ current rating. The second stage is a buck converter designed for a fast response during pulsed load transients. A flexible intermediate voltage is implemented to reduce the size of the midpoint energy storage capacitor that is responsible for compensating the instantaneous power difference between the two stages. A novel digital input feed-forward controller is proposed for the second stage to eliminate the poor line regulation issue caused by the flexible intermediate voltage. To verify the effectiveness of the two-stage power supply and the control methods, a full-scale 800 W (average)/4 kW (peak) converter prototype is built and tested. The results prove the feasibility of the proposed topology as well as control methods and demonstrate the advantages over traditional concepts. [ABSTRACT FROM AUTHOR]

Inverter nonlinearity and nonsinusoidal back electromagnetic forces (EMFs) can cause large current harmonics in permanent magnet synchronous machine (PMSM) drives, especially for those with low inductance, resulting in increased torque ripples and losses. With deadbeat predictive current control (DBPCC), the feature of high control bandwidth can reduce, to some extent, the unwanted low-order current harmonics but not remarkably. Therefore, this article presents a novel method, named adaptive harmonic reference correcting current injection, to compensate the effects of inverter nonlinearity and back EMF harmonics for DBPCC of PMSM drives. It can effectively eliminate all the resultant current harmonics caused by nonideal factors and maintain the high dynamic responses of DBPCC, even under the conditions where the sampling-to-harmonic frequency ratios are quite low. Furthermore, the proposed method requires no information about both the machine and inverter. It can be easily implemented and is parameter insensitive. Extensive simulation and experimental results of a prototype low-inductance PMSM drive have been presented to verify the proposed method. [ABSTRACT FROM AUTHOR]

Traditional time–frequency analysis (TFA) methods can effectively obtain instantaneous frequency (IF) features of nonstationary signals by constructing the signal model in the time domain. However, they fail to deal with the transient signal because the IF of the transient signal is discontinuous in the time domain and is a multivalued function with respect to time. Thus, in this article, we introduce a new TFA method, termed generalized transient-extracting transform (GTET), to obtain sharper time–frequency representation (TFR) of the transient signal by constructing frequency-domain model. First, we propose a new computational framework for group delay (GD). By deriving the general explicit formula for the Nth-order GD, the programming implementation of any order GD can be achieved. Next, the concentrated TFR of GTET can be generated by extracting the energy from the generalized GD estimation. Finally, the signal reconstruction of GTET is derived from a new perspective. It overcomes the difficulty that the reconstruction method of transient-extracting transform cannot be generalized to high-order algorithms. The analysis result of the simulated signal with high-order GD shows that GTET has better performance than other TFA methods. Experimental results demonstrate that GTET can be used to analyze practical transient signals. [ABSTRACT FROM AUTHOR]

This article addresses the synchronization control problem for dual-linear-motors-driven systems with model uncertainties and disturbances. An approximation-free robust synchronization control scheme based on cross-coupled control (CCC) frame is proposed to achieve high-precision tracking and synchronization performance, along with excellent uncertainties and disturbances rejection ability. More specifically, the CCC frame is designed to handle the asynchronous motion of two parallel motors. The main advantage is that the proposed method does not require the explicit system model, and any approximations utilized to handle the model uncertainties, such as estimation, identification, and online learning, are not required. Therefore, the computational burden and complexity of the controller are significantly reduced. Considering the importance of the transient and steady-state response, the concept and technology of prescribed performance are adopted to guarantee the control effect and state constraints. In addition, none of the high-order derivatives of desired trajectory, difficult to obtain directly in many applications, are used in the proposed controller. Furthermore, the stability and convergence performance of the closed-loop system are rigorously demonstrated. Finally, comparative experiments show the effectiveness of this study via a dual-driven H-type gantry. [ABSTRACT FROM AUTHOR]

High voltage dc grids are raised high-speed operation and high reliability requirement for relay protection. This article aims at proposing a protection scheme with high operation speed, high sensitivity, and high reliability. First, the symbolic expressions of the line-mode fault component traveling wave in case of the internal and external faults are derived, which consist of the traveling wave propagation term and the dc line boundary term. It is theoretically demonstrated that the index of the traveling wave propagation term in case of internal faults is greater than that for the external faults, and the index is independent of fault impedance. Second, the Levenberg–Marquardt algorithm is introduced to extract the index and an index-based nonunit protection method as well as the protection scheme is proposed. The proposed method is theoretically robust and independent of fault impedance and fault type. In the validation, the fitting results are indicated that the symbolic expressions are correct and the extracted indices are effective to characterize the location of the faults. Numerous fault cases of different fault distances, fault impedances, and fault types have demonstrated that the proposed protection scheme is of high sensitivity, high operation speed, and high reliability. [ABSTRACT FROM AUTHOR]

This article proposes a novel objective function formulation based on gradient descent (GD) for finite control set predictive current control (FCS-PCC) with extended horizon. FCS-PCC has become increasingly attractive for electrical drive applications owing to its short settling time, lower switching frequency, capability to handle multiple conflicting targets, and feasible inclusion of constraints. However, it still suffers from high-torque ripple and poor current quality at the steady state. To tackle the aforementioned issue, a GD-based objective function reformulation is employed in the FCS-PCC with extended horizon. First, the optimization problem underlying FCS-PCC is formulated as a constrained quadratic programming problem with proved convexity from a geometric perspective. Based on the above, the tracking error of the control objective is minimized more efficiently by searching along the direction of GD. Consequently, the objective function is reconstructed as the deviation between the normalized GD and derivative, combined with the extension of feasible set. The abovementioned procedures are iteratively learned in every prediction horizon. The effectiveness of the proposed algorithm is verified on a 2.2-kW induction machine platform with a prediction horizon of $N$ = 3. It is confirmed that the proposed algorithm outperforms the conventional and multistep FCS-PCC in steady state and transient state. [ABSTRACT FROM AUTHOR]

Attributed to the ability of inertia provision and good regulation performance, the virtual synchronous generator (VSG) has been proven as a promising solution to the problems introduced by using converter interfaced generation. Although the small-signal stability control of the VSG has been widely analyzed, the transient characteristics still needs more study, which belongs to a large-signal problem. In this article, the transient angle stability control of the VSG is investigated. Two possible VSG emulation methods, i.e., the power-emulation and the torque-emulation, are compared from the perspective of transient characteristics. Then, the transient of the VSG internal voltage and its impact on the transient angle stability are quantitatively studied in details. Thereafter, an enhanced VSG controller is proposed, where a large-signal analysis is also presented to evaluate its influence on the acceleration and deceleration areas. Finally, the analysis and effectiveness of the enhanced VSG method are validated by the experimental results. [ABSTRACT FROM AUTHOR]

Wide-bandgap (WBG) power devices have better dynamic characteristics and higher working temperatures compared to traditional Si devices and are more suitable for high-frequency and high-voltage applications because of fast turn-on and turn-off speeds. The main obstacle for the use of WBG devices is the high-frequency oscillation (HF-Osc) in voltage and current during the switching process. In this article, a new method of predicting the SiC mosfet switching behavior (including HF-Osc and slow switching) is proposed. First, the models of nonlinear capacitances are improved and parasitic elements are taken into account for improving the RLC equivalent circuit of the mosfet switching transient. On this basis, the LC equivalent frequency is obtained. Then, a new method is proposed to obtain the SiC mosfet instantaneous frequency. The comparison between them in the time domain makes it possible to analyze the SiC mosfet switching behavior. The prediction method is verified using a CREE SiC mosfet via a double pulse test. Experimental and simulation results show that the prediction method is effective in describing the HF-Osc characteristics. The proposed method can be used to effectively improve the mosfet HF-Osc, which provides guidance for the application of SiC mosfets. [ABSTRACT FROM AUTHOR]

The nonlinearity of the voltage source inverter (VSI) leads to the error between output voltage and reference voltage, and causes the phase current harmonics. It is necessary to compensate its influence in the fields such as parameter identification, sensorless control, and servo drives. In this article, an industrial solution for VSI nonlinear compensation method based on lookup table (LUT) is introduced. The characteristics of semiconductor devices, equivalent dead-time and influence of parasitic capacitance effects are calculated quantitatively though injecting increase and decrease current during self-commissioning process. The critical current value for parasitic capacitor and the variation of equivalent dead time are verified through different distorted voltage curves. Considering dc-link voltage variation is irresistible for industrial products, 3-D linear interpolation is adopted to compensate the variation of VSI nonlinearity under different voltage conditions. Proposed LUT method does not require VSI datasheet and complicated calculation formula during implementation. Experiments are carried out on a commercial permanent magnet synchronous motor drive system to verify the proposed LUT method. [ABSTRACT FROM AUTHOR]

Differential protection, as the key protection element in the power transformers, has always been threatened with sending false trips subjected to external transient disturbances. As a result, differential protection needs an additional block to distinguish between internal faults and external transient disturbances. The protection system should, first, be able to perform based on raw data, second, be able to learn fully temporal features and sudden changes in the transient signals, and, third, impose no assumption on noise. To address these challenges, a fast RNN, namely fast gated recurrent neural network (FGRNN). By removing reset gate in the gated recurrent unit (GRU), the proposed network is capable of learning abrupt changes in addition to significantly reducing the computational time. Furthermore, a loss function based on an information theory concept is formulated in this article to enhance the learning ability as well as robustness against non-Gaussian/Gaussian noises. A generalized form of mutual information is also adopted to form a noise model-free loss function, then incorporated with the designed deep network. Simulated and experimental examinations engaging various external factors, in addition to comparison between the proposed FGRNN, GRU, and seven firmly established methods indicates the faster and more reliable performance of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Wound rotor induction motors (WRIM) are widely used in a vast number of high output power industrial applications due to their capability of reaching high start torques while maintaining low inrush currents. Nonetheless, these machines are very prone to require early maintenance, and the possibility of presenting rotor winding asymmetry failures is high due to their more complex rotor circuit. Although some recent works have proposed techniques that overcome the drawbacks of conventional methods, an additional research effort for the development of alternative approaches able to enhance their performance and reliability is desirable. In this work, a new method for the diagnosis of rotor asymmetries in WRIM is presented. The proposed methodology is based on a feed-forward neural network fed by suitable fault severity indicators, which rely on the maximum energy density of higher order harmonics (amplified by the failure) at strategic regions of the time-frequency maps obtained from stray flux signals under startup transient. Experimental results for three different levels of rotor asymmetries in a 11-KW WRIM prove the reliability of the enhanced proposed system in comparison to conventional approaches that only rely on the main sideband fault-harmonic amplitudes. [ABSTRACT FROM AUTHOR]

DC short-circuit current calculation is necessary to design and protect modular multilevel converter-based (MMC-based) multiterminal dc (MTDC) grids. In this article, a general and analytical short-circuit current calculation method is proposed for bipolar MTDC grids. For pole-to-pole (P2P) faults, the superposed fault equivalent network of the MTDC grid is first developed in the frequency-domain. Then, a decoupling method based on the network inductance ratio is proposed, which simplifies the high-order network into the superposition of several independent two-order RLC circuits. As a result, the short-circuit current can be expressed as the sum of the currents of these RLC circuits. For pole-to-ground (P2G) faults, the phase-domain dc line impedance considering the coupling effects is determined based on its modal-domain parameters, so that the P2G fault current can be calculated using the method of the P2P fault. The proposed method’s effectiveness is verified through simulations and experiments, and the calculation error is classified and analyzed. Compared with the existing methods, the proposed method is more accessible, more accurate, and available for hand-solution. [ABSTRACT FROM AUTHOR]

This article proposes a non-smooth funnel control (NSFC) strategy based on the extended state observer (ESO) for motor-drive servo systems with unknown dynamics. These unknown dynamics, including the modeling error, the external disturbances, and the non-linear friction, are considered as a lumped disturbance. For estimating the unknown states and the lumped disturbance, a non-linear bandwidth extended state observer (NLB-ESO) is developed. The NLB designed using the Gaussian function and the position observation error can deal with the “peaking value problem” caused by the high observer gains. Furthermore, a funnel error surface is proposed based on the non-smooth error transformation (NSET) and incorporated into the dynamic surface control design procedure, where the NSFC can prescribe the position tracking error in a funnel region with small steady-state error and overshoot and short adjustment time. The non-smooth funnel error surface also avoids the singular problem in controller design by selecting the non-smooth parameter. Moreover, the stability of the closed-loop control system with the NLB-ESO is guaranteed by the Lyapunov theory. Comparative simulations and experiments show that the proposed NSFC can prescribe the tracking error in a funnel and ensure better tracking performance. [ABSTRACT FROM AUTHOR]

In this article, a basic capacitive power transfer topology with series-parallel compensation is developed for load-independent step-up voltage output. There are three main contributions. First, the step-up constant-voltage (CV) output and zero-phase angle property are designed by using an h-parameter modeling method. Second, a current-source rectifier is proposed at the secondary side and the working transient is analyzed. Third, the impact of parasitic resistances is investigated, and the output voltage attenuation and system efficiency are analyzed at different loads, coupling coefficients, and quality factors. A 130-W prototype is implemented with 150 × 300-mm metal plates. Experiments validate the CV output property with a step-up voltage gain of 2. The peak efficiency is 86.6% at a coupling coefficient of 0.16 and a transfer distance of 4 mm. [ABSTRACT FROM AUTHOR]

This article proposes a zero-current-prediction based digital control scheme to achieve the seamless dynamic transition of dual-active-bridge (DAB) converters. Compared with existing methods, only an extra variable between the master pulsewidth modulation and the sawtooth carrier is introduced. This extra variable is only determined by the voltage conversion ratio and the change of the existing phase shifts between master and slave legs. It accurately predicts the zero crossings of the inductor current and tunes it with the end of the carrier period. When the output power varies, the controller updates the digital registers at the beginning of the new carrier period, when the inductor current is zero. Thus, a seamless dynamic transition is achieved with zero dc bias current. This proposed digital control scheme is universally valid for the mainstream modulation methods of a single DAB converter. Moreover, it is adaptive to any load conditions, regardless of the zero-voltage-switching conditions and power flow directions. A hardware prototype is designed, tested, and compared with the conventional control method. The experimental results well validate the advantages of the proposed concept. [ABSTRACT FROM AUTHOR]

With an increasing number of inverter-interfaced generators (IIGs), the power system is undergoing massive shifts toward the power electronic dominated power system. Such paradigm change poses significant challenges to existing fault analysis theory and the protection system, as a result of the disparate short-circuit response. Given this, the fault analysis theory needs to be further investigated and expanded to address issues arising from the new grid paradigm. Under this context, this article proposes an analytic model for short-circuit analysis of IIGs with decoupled sequence control (DSC) based on the Laplace transform. With the proposed model, the analytic fault current expression can be obtained and the fault characteristic can be analyzed. Compared with existing studies, the proposed model distinguishes itself by three key merits. First, the proposed model takes into account the delay feature of the controller, which enables transient analysis. Second, the model covers the impact of controller parameters and low voltage ride through strategy in detail which is missing in the most existing literature. Third, the proposed model provides a theoretical foundation of IIGs with DSC in the fault analysis, which makes it more applicable for the protection setup issues in reality. In the end, the correctness and feasibility of the proposed model is validated by the simulation and experimental result. [ABSTRACT FROM AUTHOR]

The virtual synchronous generator (VSG) control of a grid-connected converter is an attractive interfacing solution for high-penetration renewable generation systems. Unfortunately, the synchronous resonance can appear due to the power control loops, which are usually damped by adopting a virtual resistance (VR). However, the effects of VR on the transient stability of the VSG are rarely studied. In this article, a virtual point of common coupling and a virtual power angle concept are proposed to represent the mathematical model of the VSG with VR damping. Based on the model, the transient stability is further analyzed using the phase portrait and the attraction regions of the nonlinear system. It reveals that the VR has negative and different impacts on the transient stability compared with the real grid resistor. In order to keep the VSG with VR to work normally during the grid voltage sag, an enhanced transient stability method, by reducing the active power commands when the grid fault is detected, is introduced. A design-oriented analysis and the parameter design with different VRs are also presented. Finally, the theoretical analysis is verified by the experimental results. [ABSTRACT FROM AUTHOR]

Most dc power distribution architectures are organized as a typical cascaded converter system that is composed of source and load converters, and may experience a system oscillation due to the negative impedance effect of constant power loads. The load-side virtual impedance method is a possible solution to such stability problem, which however makes the dynamic response of the load converter slow, and thus increases the requirement of the filter capacitance. In this article, an auxiliary circuit that is connected to the output port of the load converter is proposed to enhance the transient performance of the power converter system, while the system can be stabilized by the virtual impedance method. The control and parameter design of the proposed auxiliary circuit is introduced. The capacitance requirement of the system for an expected transient deviation of the output voltage is significantly reduced by using the proposed auxiliary circuit. An example design is given to verify the feasibility of the proposed method with simulation analysis and experimental results. [ABSTRACT FROM AUTHOR]

Input parallel output parallel (IPOP) modular power converters have been used to supply high power and high current in various applications. In general, the IPOP modular power converter uses an output power balancing method to equally distribute the amount of output power to each converter. In this article, a hybrid input power balancing method is proposed to obtain high power conversion efficiency, high reliability, and enhanced dynamic performance of the IPOP modular power converters. In the steady state, the proposed method controls input power to be balanced in each converter. A power loss distribution capability of the input power balancing method can improve the entire power conversion efficiency and can reduce the overall operating temperature of the IPOP converters, which can increase lifetime and can improve reliability. During the transient operation, the proposed method makes the IPOP converters under an interleaving mode to tightly regulate the output voltage and to obtain fast dynamic performance. Experimental results with 200-W prototype modular synchronous buck converters verify the performance improvements of the proposed method such as high power conversion efficiency, the power loss distribution capability in the steady-state operation, and the enhanced dynamic performance in the transient operation. [ABSTRACT FROM AUTHOR]

The rapid discharge of the dc-link capacitors during the short-circuit fault would cause the transient current with fast propagation speed in the voltage-source-converter-based dc system. Therefore, it is necessary to limit the dc fault current and lower the requirement of fault-detection speed. However, the traditional fault current limitation method with directly installed inductors in the dc line will prolong the fault-isolation time and result in the system instability during the power flow shifting. In this article, an adaptive solid-state circuit breaker (SSCB) is proposed for the low- and the medium-voltage dc system, which can bypass the installed inductors during the normal state and connect them into the dc line when the fault occurs. Besides, the energy dissipation circuit and the snubber circuit are applied to release the energy stored in the installed inductors and the dc line inductance after tripping. Hence, the fault-isolation speed can be accelerated, and it is not necessary to use the metal-oxide varistors in the proposed SSCB. By comparing with other SSCB schemes with the fault current limitation function, the effective fault current limitation, the instantaneous fault isolation, and the valid fault ride-through of the health part of the proposed SSCB are verified in the OPAL-RT-based simulation and the hardware test. [ABSTRACT FROM AUTHOR]

In this article, a quantized control capable of appointed-time performances for quadrotor attitude tracking is investigated. A continuous and piecewise behavior boundary, rather than an exponential decaying function employed in traditional prescribed performance control, is devised using error transformation to enforce attitude convergence to preassigned transient and steady zones in an appointed time. To circumvent the inertia moment uncertainties and external perturbations, an extended state observer with only one parameter to be tuned is introduced to precisely estimate the total disturbances acting on the angular rate subsystem. Additionally, a hysteretic quantizer capable of converting continuous control behaviors to finite discrete scalars is established in a controller to actuator channel to reduce the transmission burden and amount of sampling data. With a novel quantization decomposition, an attitude quantized controller is integrated in terms of guaranteed tracking. The prominent feature is that a prescribed appointed-time attitude response can be preserved with a decreased demand of communication bandwidth, despite uncertainties. Theoretical analysis shows that all error signals are ultimately uniformly bounded. Eventually, the superiority of explored control strategy is demonstrated through experimental results. [ABSTRACT FROM AUTHOR]

This article develops a novel decentralized controller for multi-area secondary load frequency control (LFC) of power systems. The proposed robust-adaptive approach estimates the external disturbance input and uncertainties, which are assumed to be matched with the control input. In this regard, a disturbance-observer state-feedback controller is designed. To offer a systematic approach, controller design conditions are derived in terms of linear matrix inequality constraints. Thereby, for any given representation of the LFC area, the controller gains can be straightforwardly obtained by using numerical solvers. Moreover, in order to enhance the steady-state performance, the controller is modified through the heuristic genetic algorithm. The controller design procedure is wholly offline and can be simply implemented. The developed decentralized approach does not need the information of the other areas, which reduces the cost and the number of measuring units. It is also robust against the power fluctuations of the load and renewable energy sources. To show the superiorities of the developed controller, four scenarios are considered. These scenarios comprise the aggregation of the photovoltaic, wind turbines, and electric vehicle to the power system. OPAL-RT experiments are given to verify the transient and steady-state performance and robustness of the proposed controller. [ABSTRACT FROM AUTHOR]

The L/C-based fixed-admittance model (L/C model) is usually used in the real-time simulation for power electronic converters. However, the L/C switch model suffers from the problems of virtual power loss and complicated optimal parameter settings. This article proposes a small-step synthesis real-time simulation method suitable for power electronic converters. By modeling the power electronic converter with a small (nanosecond) time-step and simulating with a normal (microsecond) time-step, the issue of virtual power loss of the L/C model caused by the transient process after the switching action is solved. The real-time simulation experiments with different type converters based on one set of simulation parameters are carried out on field-programmable gate array separately to verify the insensitivity to converter topologies. Furthermore, the real-time simulation results of the small-step synthesis method using the L/C model are compared with those of the traditional electromagnetic transient program (EMTP) method using the L/C model and the Ron/Roff model. The simulation results provide verification of the effectiveness of the small-step synthesis method as well as the insensitivity to carrier frequencies, and L/C model parameters. [ABSTRACT FROM AUTHOR]

In wireless power transfer (WPT) systems, the relative position between the transmitting and receiving coils could change suddenly, which is one of the most significant distinctions between wireless and wired power transfer systems. To the best of the authors’ knowledge, no theoretical analysis has been reported on the dynamic behavior of the WPT systems under the relative position transient (RPT). This article proposes the concept of “coupling-coefficient susceptibility” to describe this dynamic behavior. The extended describing function method is applied to extract the mathematical model of the coupling-coefficient susceptibility. Finally, an RPT testing platform, composed of a series-series compensated WPT system and a coil motion mechanism is designed and fabricated to verify the theoretical analysis. The experimental results exhibit a good agreement with the proposed model. [ABSTRACT FROM AUTHOR]

The design and analysis of megawatt power electronics systems calls for an accurate and efficient simulation approach that can consider the switching transients. However, the state-of-the-art simulation methods and tools exhibit low efficiency in megawatt power electronics systems, even with ideal switch model. It is hardly possible to perform physical-switch-model-based simulation due to the time cost and the convergence issue. This article proposes a switching transient simulation approach based on the discrete state event-driven approach. The proposed method is composed of a switch-pair-based modeling method and a timescale-decoupling simulation method. In the example of a 2-MW power electronics transformer composed of 576 semiconductor switches, the proposed method enables the switching transient simulation of a 0.2-s dynamic within 10 min and is free of convergence problems. The speed is 20-fold faster than commercial software adopting ideal switch model. The accuracy is attested to by comparisons with both experimental and commercial software results. Meanwhile, this article demonstrates the application in system efficiency evaluation. Due to the speed gain and the ability of capturing switching transients, the proposed method enables simulation of the efficiency curve, and hence, the locating of the maximum efficiency point and the optimized design of the conversion system. [ABSTRACT FROM AUTHOR]

For antiswing control of underactuated cranes, how to guarantee the converging speed of cranes through control design is essential but still remains unsolved. In this article, the adaptive antiswing control for underactuated gantry cranes with guaranteed transient performance under unmodeled dynamics and external disturbances is investigated. To sovle this problem, a set of filters are proposed to make the backstepping technique applicable for the control of crane systems. Then through variable transformation the position error and swing angel could be guaranteed converging to the origin with a given exponential speed. Hardware experiments are conducted to show that the proposed scheme achieves better control performance over existing methods, and it is illustrated that the proposed control scheme possesses strong robustness to unmodeled uncertainties and external disturbances. [ABSTRACT FROM AUTHOR]

This article presents a novel high temperature heat flux (HTHF) sensor based on micromachined thermocouple (MTC) to meet the needs of transient high heat flux detection in ultrahigh temperature environments, such as fire research, high-power pulsed lasers testing, and aerospace engineering. The targeted design, fabrication, and package of an MTC-based HTHF sensor with excellent heat dissipation capacity are proposed, and relevant experiments were conducted in two aspects. First, powerful laser tube-based tests at ambient temperature show that such a sensor can detect a heat flux high to 10.8 MW/m2 with an extremely fast response; its response time, in this case, is 1.9 ms. And then, turbine engine test pipe based tests at high temperature reveal that the sensor with water cooling could survive at 1200 °C for at least 100 s. Compared to conventional heat flux sensors, it is more sensitive to transient heat flux changes and has a faster response speed. Such satisfactory performance makes the sensor extremely competitive in ultrahigh heat flux detection in extremely harsh environments. [ABSTRACT FROM AUTHOR]

This article identifies the parameters of an induction machine using limited and nonintrusive observations of available input voltages, stator currents, and the rotor speed. Parameter extraction is formulated as a nonconvex estimation problem, which is then relaxed to a convex conic optimization problem. While the resulting relaxation could exhibit a satisfactory performance, there might be cases where the solution of convex relaxation fails to satisfy the dynamic equations of the machine. This is remedied through a local search approach initiated using the solution obtained from the relaxed problem. The proposed method is experimentally verified on a squirrel-cage induction machine with missing measured data. Using the measured signals as the benchmark, time-domain transients produced by the parameters estimated using the proposed method show almost 20% better match compared to time-domain transients produced by the parameters obtained via conventional testing. [ABSTRACT FROM AUTHOR]

In this article, we propose a new improved fast-transient-response and low-noise high-efficiency buck converter with second-order continuous-time delta-sigma-modulation (CT-DSM) techniques. First, by utilizing the oversampling theorem and noise-shaping technique with the second-order delta-sigma modulation, the output noise within the bandwidth can be reduced effectively. Second, the adding of the transient acceleration loop not only can improve the transient recovery time when the load current changed but also lowers the undershoot and overshoot voltage. Third, a rail-to-rail operational transconductance amplifier without voltage dividers is employed in the proposed converter, which helps sensing the inductor current, moving the inductor pole to a high frequency, speeding up the transient response, and stabilizing the proposed converter modules. Finally, the proposed converter has been implemented with TSMC 0.18 μm 1P6M process and occupies an area of 1.19 × 1.19 mm2. When the load current changed from 50 to 500 mA and 500 to 50 mA, the transient recovery time was both 4 μs, which improved 8 and 16 μs than the traditional CT-DSM converter. The output voltage ripples are kept under 13 mV and the overshoot and undershoot voltage is 20 and 14 mV, respectively. The measured output-to-noise ratio is 80.7 dB, with the sampling frequency of 10 MHz. The peak efficiency is 92.1%, at the output voltage of 2.5 V and load current of 150 mA. [ABSTRACT FROM AUTHOR]

A seven-level hybrid-clamped (7L-HC) converter is a promising option for medium-voltage drives due to its low number of devices and the ability to well balance all the capacitors. However, like other hybrid-clamped multilevel converters, the freewheeling paths during deadtime can produce unexpected output voltage levels. The unexpected output voltage can cross a few consecutive output levels, introducing a large dv/dt to the system. To address this problem, in this article, we conduct a detailed study of the mechanism that produces such undesirable voltages and propose a commutation scheme to coordinate the turn-on/off sequence of switches in the 7L-HC converters. The proposed method is based on an easy-to-implement bitwise operation of switching vectors, where the number of switching actions is not increased. The proposed method is validated by both simulation and experimental results. [ABSTRACT FROM AUTHOR]

Accurate and reliable machine performance degradation tracking and remaining useful life (RUL) prognosis establish the foundation for predictive maintenance scheduling toward improved safety and productivity of machine operations. In general, machine performance degradation exhibits a nonlinear and nonhomogeneous pattern that arises from time-varying degradation rate and abrupt performance changes. To address this challenge and improve the generalizability of degradation modeling, in this article, we present a stochastic modeling technique based on the Lévy process, which generalizes system variations as the accumulations of successive and jump increments. The developed Lévy process model consists of two terms: a linear Brownian motion term for capturing the gradual degradation with time-varying rates and a nonhomogenous compound Poisson process term for capturing transient performance changes. By calculating the moments of the characteristic function of the Lévy model, explicit expressions for the probability distributions of predicted performance degradation and RUL are derived. To obtain the time-varying parameters in the Lévy model, Markov chain Monte Carlo is investigated. The developed technique is evaluated through simulation and run-to-failure tests of roller and ball bearings, and the good performance of the developed Lévy model is confirmed. [ABSTRACT FROM AUTHOR]

This article proposes a controller for dc–dc converters to achieve fast load-transient responses. The controller is developed for both continuous conduction mode (CCM) and discontinuous conduction mode (DCM) of operation. The main idea is developed for buck converters, but it is shown that the proposed controller can be applied to other topologies, such as the noninverting buck–boost converter. The controller derivation, analysis, and experimental verifications are provided in both CCM and DCM, and its performance is compared with other methods. The main advantage of the proposed controller is that it minimizes the recovery times associated with load-transient responses in dc–dc converters while maintaining component sizes and other system parameters within the acceptable range. The proposed controller can be used to minimize load transients in electronic portable devices and electric vehicle charging. [ABSTRACT FROM AUTHOR]

Due to the rapid discharging of the dc-link capacitors, the short-circuit fault normally results in a fast-growing transient current in the voltage source converter (VSC) based dc power system. Therefore, a fast and sensitive fault detection method is required. In this article, the feasibility of Hilbert-Huang transform (HHT) for fault detection in VSC-based high-voltage direct current systems is analyzed. The instantaneous energy density level is used as the fault detection criterion, which emphasizes the fault characteristics in a predefined frequency range and suppresses the effect of steady-state ripple components. The theory of the proposed HHT-based fault detection method is presented in detail. Its effectiveness is tested on an OPAL-RT based multiterminal dc system and a point-to-point experimental dc system. A response delay within 2 ms after the fault inception is achieved. The comparison with other popular frequency-domain based fault detection methods including the wavelet transform, the short-time Fourier transform, the S transform, and the existing HHT-based analysis, using amplitude frequency coefficient as detection criterion, underlines the performance of the proposed method. [ABSTRACT FROM AUTHOR]

Accurate set-point tracking across a broad operating region with minimum transients is a crucial requirement during the start-up and shutdown phases of a process plant operation. The emotional learning based controller, with its model-independent and nonlinear features, is extremely suitable for plant-based operations. However, the design of most of the existing emotional-learning strategies is based on narrow operating regions, and, hence, they may not yield satisfactory tracking performance when operated on a broader region. In this correspondence, a new design approach is adopted, which takes into consideration the specific requirements of multiple set-point tracking. This approach fuses a regression model with a constrained optimization problem to generate stimuli weights as well as the learning and inhibition parameters. Experimental validation of the proposed method on a quadruple tank system and comparison of its performance with an optimized second-order sliding mode controller illustrates its effectiveness. [ABSTRACT FROM AUTHOR]

The bidirectional buck–boost current-fed isolated dc–dc converter is an emerging topology and has the advantages of low current stress, high efficiency, and wide power/voltage conversion range. However, it suffers from the inductor current mutation and transient voltage spike when the converter is directly switched between the buck and boost modes in the actual operation. By analyzing in detail the process of directly switching the two operation modes, it reals the reason of causing these transient problems is the duty ratio, and shoot-through duty ratio is not correctly set when the operation mode is switched. In order to solve this problem, a smooth switching scheme between the buck/boost operation modes is proposed by setting a special relationship between the closed-loop controller output of the inductor current and the two control variables based on the system model. The detailed simulation and experimental results verify the theoretical analysis and the proposed solutions. [ABSTRACT FROM AUTHOR]