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The remaining useful life (RUL) of transformer insulation paper is largely determined by the winding hot-spot temperature (HST). Frequently the HST is not directly monitored and it is inferred from other measurements. However, measurement errors affect prediction models and if uncertain variables are not taken into account this can lead to incorrect maintenance decisions. Additionally, existing analytic models for HST calculation are not always accurate because they cannot generalize the properties of transformers operating in different contexts. In this context, this paper presents a novel transformer condition assessment approach integrating uncertainty modeling, data-driven forecasting models, and model-based experimental models to increase the prediction accuracy and handle uncertainty. The proposed approach quantifies the effect of measurement errors on transformer RUL predictions and confirms that temperature and load measurement errors affect the RUL estimation. Forecasting results show that the extreme gradient boosting (XGB) algorithm best captures the nonlinearities of the thermal model and improves the prediction accuracy among a number of forecasting approaches. Accordingly, the XGB model is integrated with experimental models in a particle filtering framework to improve thermal modeling and RUL prediction tasks. Models are tested and validated using a real dataset from a power transformer operating in a nuclear power plant. [ABSTRACT FROM AUTHOR]

The rising cost of production testing for a system-on-a-chip (SoC) is one of the crucial matters to chip makers, due to long test time and costly automated-test-equipment. This paper proposes a spectral leakage-driven built-in self-test (BIST) scheme to precisely predict the nonlinearity of mixed-signal circuits in the loopback mode, thereby accomplishing cost-effectiveness (compared to previous BIST-based works). A digitally synthesized single-tone sinusoidal stimulus used for conventional harmonic testing is incoherently sampled by a device under test (DUT). The DUT output signal exhibits the correlation between the DUT harmonics and the spectral leakage introduced by the incoherent sampling. The DUT output signal is then fed to another DUT through a loopback path, so that the harmonics of a pair of DUTs are correlated with the spectral leakage on the loopback response; the magnitude of the spectral leakage is considered as a weighting factor on the harmonic magnitude of those DUTs. The correlation is quantitatively modeled as characteristic equations in , and postprocessing predicts the harmonics of the two individual DUTs, by simultaneously solving the characteristic equations using on-chip DSP core available in an SoC. Simulation and hardware measurements validated that this paper can be practically used for production testing by showing less than 0.3 and 0.6 dB of the prediction errors, respectively. [ABSTRACT FROM AUTHOR]

The reliable operation of battery management systems depends critically on the accurate estimation of the state of charge (SOC) and characterizing parameters of a battery system. SOC estimation employs models that must be robust against variations in battery cell electrochemical features, aging, and operating conditions. This paper reveals that commonly used SOC estimation schemes are fundamentally flawed in providing the robustness of SOC estimation against model uncertainties. Parameter estimation methodologies and adaptive SOC estimation design are introduced in this paper to enhance SOC estimation accuracy and robustness. By a scrutiny of the impact of parameter variations on SOC estimation accuracy, the SOC–open-circuit-voltage mapping is identified to be the most critical function that must be accurately established. Identification algorithms are introduced, and their convergence properties are established. The integration of the identification algorithms and SOC estimation schemes lead to an adaptive SOC estimation framework that is superior over the existing methods in providing much improved accuracy and robustness. Experimental studies are conducted to validate the algorithms. [ABSTRACT FROM PUBLISHER]

Finite set model predictive torque control (FCSMPTC) of induction machines has received widespread attention in recent years due to its fast dynamic response, intuitive concept, and ability to handle nonlinear constraints. However, FCSMPTC essentially belongs to the open-loop control paradigm, and unmatched parameters inevitably cause electromagnetic torque tracking error. In addition, the outer loop (i.e., the speed loop) based on a proportional-integral (PI) regulator cannot achieve optimal control between speed dynamic response and torque tracking error compensation. The traditional control paradigm is abbreviated as PI-MPTC. In order to solve the aforementioned problem, this paper proposes active disturbance-rejection-based model predictive torque control (ADR-MPTC). First, the influence mechanism of mismatched parameters on torque prediction error in PI-MPTC is studied, and then the performance of a traditional PI regulator used to compensate for torque prediction error is analyzed. Second, this paper introduces several parts of the proposed ADR-MPTC, including the design of the torque prediction error observer, nonlinear prediction error compensation strategies, an enhanced predictive torque control, and a simplified full-order flux observer. Finally, PI-MPTC and ADR-MPTC are studied experimentally. The experimental results show that compared with PI-MPTC, ADR-MPTC performs better in dynamic and steady states, and has stronger robustness. [ABSTRACT FROM AUTHOR]

This paper proposes a bioinspired reference model based fuzzy adaptive tracking control for active suspension systems. A general bioinspired nonlinear structure, which can present ideal nonlinear quasi-zero stiffness for vibration isolation, is adopted as tracking reference model. Fuzzy logic systems are used to approximate unknown nonlinear terms in nonlinear suspension systems. Particularly, a nonlinear damping is designed to improve damping characteristics of the bioinspired reference model. With beneficial nonlinear stiffness and improved nonlinear damping of the bioinspired reference model, the proposed fuzzy adaptive controller can effectively suppress vibration of suspension systems with less actuator force and much improved ride comfort, thus energy saving performance can be achieved. Finally, a quarter-vehicle active suspension system with considering payload uncertainties, general disturbance, and actuator saturation is provided for evaluating the validity and superiority of the bioinspired nonlinear dynamics based fuzzy adaptive control approach proposed in this paper. [ABSTRACT FROM AUTHOR]

Lithium-ion (Li-ion) batteries have been used in a wide variety of applications, ranging from portable electronics to electric vehicles. During repetitive charging and discharging, a battery's capacity fades due to electrochemical reactions such as solid electrolyte interphase growth. Li-ion batteries reach an end-of-life (EOL) point, after which using them is not recommended. However, some unhealthy batteries reach their EOL sooner than expected. A qualification test is usually conducted to evaluate the reliability of Li-ion batteries and classify unhealthy batteries, but this test requires several months. This paper develops a data-driven method to reduce the qualification time by detecting anomalies before EOL. This method detects an anomaly in the capacity fade curve of unhealthy batteries based on their capacity fade trend. Since the developed method detects anomalies of unhealthy batteries before EOL, the method is effective in reducing the time for the qualification test of Li-ion batteries. [ABSTRACT FROM AUTHOR]

This paper presents the accurate modeling of HVdc links for the dynamic studies of automatic generation control/load frequency control (AGC/LFC) of the multiarea interconnected power system. In earlier AGC studies, HVdc links were simply modeled by using the first-order transfer function with system time constant ${T_{{\rm{dc}}}}$. It was argued that ${T_{{\rm{dc}}}}$ is the time required by HVdc links to establish dc current after following a load disturbance in the power system. However, no mathematical or analytical justification was provided in support to the existing transfer function model of HVdc links. This paper presents the accurate modeling of HVdc links for AGC studies. The comparative analysis has also been performed to demonstrate error being accrued due to the use of the conventional model of HVdc links. Furthermore, this paper also implements the inertia emulation based control strategy in AGC, which allows us to harness the stored energy from the capacitance of HVdc links for AGC operations. [ABSTRACT FROM AUTHOR]

The predictive control method deals with the prediction of the motor behavior based on a mathematical model of the motor. This model is dependent on the motor parameters. However, these parameters may not match with their actual values due to the measurement error or they may change during the operation of the motor. All these uncertainties and model inexactitude lead to inaccurate prediction of the motor behavior and deteriorate the performance of the predictive algorithm. This paper presents an extension of the predictive current control (PCC) method to improve the prediction accuracy for a permanent-magnet synchronous motor (PMSM). The proposed strategy not only reduces the current ripple but also improves the robustness of the system against parameter uncertainties. Simulation and experimental results that confirm the good performance of the proposed method are presented. [ABSTRACT FROM PUBLISHER]

In the paper by Jin et al. (IEEE Trans. Ind. Electron., vol. 62, no. 3, pp. 1363–1371, Mar. 2015), the authors present an expansion of Ohm's law in the nonsinusoidal ac circuit, based on which a distinct instruction for analyzing and designing nonsinusoidal circuit including ac/dc link circuit is provided. This paper is very interesting and a good work. However, some equations and expressions may be improved. In this paper, they are discussed and modified. [ABSTRACT FROM AUTHOR]

This paper presents a practical robust controller that solves the problem of accurate motion control of ultrasonic motors (USMs) over prolonged durations, where temperature increases pose a significant challenge. This paper focuses on USMs with driver circuits that have a single user-controllable input. Prior to developing the robust controller, a nonlinear model of the system was identified by experimentally measuring the temporal relationship between motor speed and temperature to the applied input control signal. A linear approximation of this model was used to design two robust inverse dynamic controllers: one used temperature feedback and the other did not. Both control methods were implemented on a custom designed embedded control system and achieved highly consistent and accurate performance while under load over a range of working frequencies. Step-response experiments (1 rad) demonstrated a rise time of 0.1 s without any overshoot or steady-state error. A normalized RMSE below 3% with a delay of 25 ms was achieved for reference inputs with frequencies up to 1 Hz. This performance was maintained during prolonged continuous dynamic operation of several minutes, despite the great variation in the motor’s dynamics due to the temperature effects (over a range of 25 °C–45 °C) and modeling uncertainties. [ABSTRACT FROM AUTHOR]

In this paper, the use of the Dual Kalman Filter for the identification of photovoltaic system parameters is presented. The system includes the photovoltaic source, the dc/dc converter and the battery/dc bus and both its states and parameters in the actual operating conditions are identified. In particular, the proposed approach gives the confidence interval for the system settling time, which is used for the real-time optimization of the perturbative maximum power point tracking algorithm. The proposed technique is implemented by using a Field-Programmable Gate Array and it is validated by means of both simulation and experimental results. [ABSTRACT FROM PUBLISHER]

The aim of this paper is to study the dynamics of a permanent magnet direct current (PMDC) brushed motor while two crucial space-domain effects, namely, slotting effect and commutation phenomenon are taken into account. Semi-analytical dynamic time-domain PMDC brushed motor model inclusive of these space-domain effects is used to analyze and investigate the dynamics. Pulse width modulation operated discontinuous current PMDC brushed motor drive with steady duty cycle is employed to acquire the bifurcation patterns. The chaotic nature due to slotting effect and commutation is identified from the bifurcation patterns and reported. It also has to be admired that such nonlinear dynamical behavior with the same set of parameters at similar operating condition has not been observed when a conventional PMDC brushed motor dynamic model is considered. These space-domain effects, namely, slotting effect and commutation also have a prominent impact to make some time-domain states of a PMDC brushed motor drive chaotic. The role of slotting effect and commutation phenomenon to analyze the chaos over time-domain state variables of the PMDC brushed motor drive is investigated and validated experimentally in this paper. [ABSTRACT FROM PUBLISHER]

In order to suppress the torque ripple of an open-end winding permanent-magnet synchronous machine (OEW-PMSM), a q-axis current injection method is typically employed but the disturbances caused by the third flux linkage parameter mismatch can augment the torque ripple. To solve this problem, in this paper, first, a zero-sequence current (ZSC) and zero-sequence back-EMF observer (ZCBO) are proposed based on an adaptive sliding mode control, which is able to simultaneously estimate ZSC and zero-sequence back EMF under varying conditions. Based on this ZCBO, the estimated ZSC and zero-sequence back EMF could compensate for the one-step control delay and suppress the aforementioned disturbances. Second, although central hexagon modulation is employed in the predictive current control (PCC) scheme, zero-sequence voltage (ZSV) still exists in the zero-sequence path due to the dead time of the inverter, affecting the predictive accuracy of the ZCBO. To accurately establish the ZCBO, the ZSV caused by the dead time of the inverter is considered in the ZCBO. Finally, a comparative study of two types of methods is presented, and simulations established by MATLAB software and experimental confirmations are carried out to verify the effectiveness of the proposed PCC scheme in this paper. [ABSTRACT FROM AUTHOR]

This paper presents an optimization method for selective harmonic elimination in a cascaded multilevel inverter using teaching–learning-based optimization (TLBO). The main objective in selective harmonic elimination (SHE) strategy is to eliminate low-order harmonics by solving nonlinear equations and reaching optimal solution, while the fundamental component is satisfied. In this paper, in one side, the influence of optimal dc sources is investigated to reach the SHE goal, and in another side, comparing optimization methods is considered. In this paper, the TLBO as a recently emerged nature-inspired algorithm is presented to provide better results for the SHE in comparison with genetic algorithm, artificial bee colony, imperialistic competitive algorithm, harmony search, ant colony optimization, particle swarm optimization, and differential evolution. For better comparison of those methods and influence of optimal dc sources, 5-, 9-, and 15-level inverters are chosen and MATLAB software is used for optimization. Simulation results show the superiority of TLBO, higher precision and probability of convergence than other mentioned algorithms. Finally, to validate the influence of optimal dc sources and the accuracy of TLBO results, the experimental setup is conducted for a 5-level cascaded H-bridge inverter with optimal dc sources. [ABSTRACT FROM AUTHOR]

Selective catalytic reduction (SCR) systems have been widely used to meet the emission regulations and two-cell SCR systems have shown the advantages of high NO $_{x}$ conversion efficiency and low NH $_{3}$ slip simultaneously. However, it is noteworthy that the catalyst performance of SCR device would degrade over the service time gradually. If the performance degrading is not well-compensated, the NO $_{x}$ conversion efficiency would reduce significantly. Different from detecting the aging issue in the laboratory, a practical method is to design an observer to estimate the aging factor online such that the urea injection can be modified accordingly. In this paper, we aim to construct an aging-factor observer for two-cell SCR systems. In order to reduce the algorithm computational load and guarantee the implementation performance, we propose a dual time-scale algorithm based on two-cell SCR model and unscented Kalman filter. There is a fast time scale and a slow time scale in the algorithm. Two simulation studies of constant aging factor and time-varying aging factor are investigated in the simulation environment of MATLAB/SIMULINK. The simulation results indicate that the proposed dual time-scale observer works well under different conditions and the calculational load is reduced significantly. [ABSTRACT FROM AUTHOR]

Thanks to the advantages of high power density and the capacity of bidirectional power transfer, the CLLC resonant converter is widely used in the hybrid ac–dc microgrid as a dc transformer to interlink the ac and dc bus. Since the voltages of ac and dc bus are controlled by the energy management system, the CLLC resonant converter operates under open-loop condition, which means the switching frequency and duty cycle are fixed. As a result, in the hybrid ac–dc microgrid applications, for the CLLC converter, the main concern is not the voltage regulation but the conversion efficiency. This paper focuses on the total power loss optimization and the magnetic design of the CLLC resonant converter based on artificial intelligence (AI) algorithm. In order to optimize the total power loss, an AI algorithm-based two-stage optimal design method is proposed. In the first stage, the total power loss, including the driving loss, turn-off loss, conduction loss of the switches, the power loss of the resonant capacitances, and copper and core loss of the transformer are optimized by the proposed AI algorithm, GA+PSO, and the optimal parameters, including the leakage inductances (Lr1 and Lr2), magnetizing inductance (Lm), and resonant capacitances (Cr1 and Cr2) are derived. In the second stage, the optimal leakage inductances and magnetizing inductance are realized by setting proper distance between the primary winding and the secondary winding (dw), and the thickness of the air gap (da). As for the magnetic design, in this paper, the leakage inductances of a planar transformer are used as the resonant inductances. The equations of dw and da to achieve the optimal leakage inductances and magnetizing inductance are derived. Both the proposed optimal design method and the equations of dw and da are validated by simulations and experiments. [ABSTRACT FROM AUTHOR]

Solid state transformer (SST) integrated hybrid dc–ac microgrid (HMG) has wide operating capabilities in presence of dc–ac loads, renewable energy resources, and energy storage. This paper proposes control strategies for localized control of zonal hybrid microgrid, enabled by the SST and centralized energy storage devices (ESD) integrated using dual active bridge (DAB) converter. The control of DAB dc–dc converter is modified for zero circulating power flow (ZCPF) operation in both SST and ESD. Power management and coordination control used in this paper ensures the power supply reliability of the zonal HMG integrated through the SST. Microgrid system, along with its proposed controllers, provides a stabilized low-voltage dc and ac network ports, in both grid feeding and forming modes. The performance of the configured HMG system is evaluated under various power management scenarios using the MATLAB software platform. Further, the SST architecture, with its proposed controller, is tested on FPGA-based hardware platform. [ABSTRACT FROM AUTHOR]

Induction motor fault identification is essential to improve efficiency in industrial processes improving costs, production line, and maintenance time. This paper presents a novel motor fault detection methodology based on quaternion signal analysis. The proposed method establishes the quaternion coefficients as the value of motor current measurement, and the variables x, y, and z are the measurements from a triaxial accelerometer mounted on the induction motor chassis. The method obtains the rotation of quaternions and applies quaternion rotation statistics such as mean, cluster shades, and cluster prominence in order to get their features, and these are used to classify the motor state using the proposed tree classification algorithm. This methodology is validated experimentally and compared to other methods to determine the efficiency of this method for feature detection and motor fault identification and classification. [ABSTRACT FROM AUTHOR]

In this paper, a cost-effective and highly accurate resolver-to-digital conversion method is presented. The core of the idea is to apply a third-order rational fraction polynomial approximation for the conversion of sinusoidal signals into the pseudo linear signals, which are extended to the range 0°–360° in four quadrants. Then, the polynomial least squares method is used to achieve compensation to acquire the final angles. The presented method shows better performance in terms of accuracy and rapidity compared with the commercial available techniques in simulation results. This paper describes the implementation details of the proposed method and the way to incorporate it in digital signal processor-based permanent magnet synchronous motor drive system. Experimental tests under different conditions are carried out to verify the effectiveness for the proposed method. The obtained maximum error is about 0.0014° over 0°–360°, which can usually be ignored in most industrial applications. [ABSTRACT FROM AUTHOR]

In this paper, a new hybrid model is proposed for the prediction of air gap magnetic field distribution (MFD) in interior permanent magnet machines with any rotor configuration. The slotless magnetic field is first predicted by finite-element method (FEM) with automatic scripting in MATLAB to consider saturation in the rotor iron. Afterward, the conformal mapping viz., Schwarz–Christoffel mapping is introduced to take the slotting effect into account. Consequently, the MFD could be calculated. The back electromagnetic forces, cogging torque, and output torque are obtained accordingly. Then a subdomain model is developed to consider the armature reaction. The results show that the proposed hybrid approach agrees well with the FEM. The model is further verified by experiments. The main contribution of this paper is to reduce the computation time remarkably while maintaining the calculation accuracy. [ABSTRACT FROM AUTHOR]

In this paper, a method to determine load conditions under which the armature current of a salient pole synchronous machine is on the q-axis is described. The proposed method allows the determination of a locus in the $P-Q$ space in which the armature current is completely on the q-axis. The derivation of these conditions simplifies the determination of the machine q-axis parameters during load rejection tests, since it eliminates the necessity for trial and error procedures or power angle estimation. The method was tested in a 100 MVA, 13.8 kV, 60 Hz, 40 poles salient pole synchronous machine installed in a hydro power plant. Tests results show that loads calculated with the proposed method are in fact points where the armature current is on the q-axis. [ABSTRACT FROM AUTHOR]

Modern electric-powered vehicles include several sources and loads. This paper extends the idea of introducing multiple sources and loads into an onboard vehicular integrated power system. The proposed power conditioning system is formed around a multiwinding integrated transformer. Both inductive and capacitive elements of this magnetic component affect the power conditioning stages of the system. This paper proposes an experimental transformer modeling procedure that includes the inductive and capacitive parameters. A mathematical procedure is developed, simplifying this more detailed experimental model of the multiwinding transformer into a $\Pi\ RLC$ circuit that can be utilized in the system transient analysis. The modeling method is applied to a three-winding transformer and is verified through simulations and experiments. [ABSTRACT FROM PUBLISHER]

The phasor-PWM-based current source inverter (CSI) is a boost inverter. The difference between conventional CSIs and the boost inverter is that the boost ratio (VLLrms/Vdc ) in the boost inverter can easily be above 3.0, whereas this ratio is around 1 in conventional CSIs. In order to realize the potential capabilities of the boost inverter and to assist its penetration into renewable energy systems, the boost inverter dynamic behaviors are studied in this paper. First, the large- and small-signal models as well as the dq-equivalent circuits of the boost inverter are presented. Then, the developed models are verified using circuit simulations and experiments on a laboratory-scale 2-kW 208/240- V_{\rm LLrms} V_{\rm dc}=65\ \hbox{V} $ boost inverter made of reverse-blocking IGBTs. Finally, the developed small-signal model is used to study the stability of the boost inverter through root locus of small signal poles (eigenvalues) as control inputs, and load parameters vary within the boost inverter's operating limits. [ABSTRACT FROM PUBLISHER]

This paper addresses the problem of thermal energy control in shopping centers through the application of model predictive control (MPC) strategies. In particular, this paper uses an existing shopping center as pilot case, which is characterized by a large common multifloor space, which, in turn, gives rise to a significant vertical thermal stratification. This paper explores the importance of MPC parameters to energy efficiency and comfort levels. In addition, it addresses some notable extensions, from economic optimization, which paves the way to real-time pricing techniques, to integration with renewables, to robustness enforcement through Kalman filters, to hybrid control with switching signals mixed with continuous signals. [ABSTRACT FROM PUBLISHER]

In this paper, impedance control for rotatory test beds is presented and discussed. Its goal is highly realistic testing of rotating machinery such as combustion engines through hardware-in-the-loop simulation. As rotatory test beds are typical examples of elastic drive systems, modeling and control of the oscillations arising on the test bed are of great importance. Additionally, a so-called impedance model emulates real-world operating conditions and delivers the load for the unit under test, which is then imposed using an appropriate controller. Specifically, in this paper, model predictive control (MPC) was chosen as it allows for high dynamic control including a priori consideration of constraints. In addition to the MPC, a control Lyapunov function based controller is proposed, resulting in guaranteed closed-loop stability even when active constraints prevent the use of classic MPC stability criteria. Finally, simulations and experimental results achieved on a laboratory setup as well as on an industrial test bed illustrate the efficiency of the proposed control scheme. [ABSTRACT FROM PUBLISHER]

Recently, to ensure the reliability and safety of modern large-scale industrial processes, data-driven methods have been receiving considerably increasing attention, particularly for the purpose of process monitoring. However, great challenges are also met under different real operating conditions by using the basic data-driven methods. In this paper, widely applied data-driven methodologies suggested in the literature for process monitoring and fault diagnosis are surveyed from the application point of view. The major task of this paper is to sketch a basic data-driven design framework with necessary modifications under various industrial operating conditions, aiming to offer a reference for industrial process monitoring on large-scale industrial processes. [ABSTRACT FROM PUBLISHER]

This paper presents a rotor speed observer for induction-machine drives based on a sliding-mode approach and magnetizing current estimation. The back electromotive force (EMF) is calculated from the stator current and the stator voltage signals. The magnetizing currents are obtained from the back EMF. A theorem which gives the rotor speed estimate in the continuous-time domain is formulated using the magnetizing current estimation. The stability analysis is achieved based on the Lyapunov approach. Moreover, the discrete-time approach of the method is discussed, and a theorem for the discrete-time implementation is proposed. The limits that ensure the system stability for the switching gains and for the observer gain are discussed. This paper shows that the limits for the gains of the discrete-time algorithm are different from the limits for the gains of the continuous-time algorithm. Simulation results are presented to validate the theoretical analysis. In addition, experimental results based on a fixed-point digital signal processor (DSP) platform (DSP TMS320F2812) demonstrate the performance of the proposed scheme. [ABSTRACT FROM PUBLISHER]

The shunt regulator is a key part of the power conditioning unit, which is becoming more and more important in the spacecrafts. Due to the nonlinear link, the switch operating with hysteresis control, the shunt regulator is a nonlinear system; however, the stability analysis method for the system is still grounded on the approximate linearization method, which neglects some of the ac and dc characteristics. In this paper, a novel stability analysis method for the nonlinear systems is proposed based on the describing function, which can be used to model the nonlinear link in the shunt regulator system. Further, the different conclusion of the shunt regulator system stability are drawn, by the approximate linearization method and the stability analysis method proposed in this paper, respectively. Finally, the simulation and experimental results prove the correctness of the stability analysis method with describing function and discover the incompletion of the approximate linearization methods on the stability analysis. Therefore, this paper provides a new way to analyze the stability of the nonlinear systems. [ABSTRACT FROM PUBLISHER]

This paper deals with a specific explicit design of Generalized Predictive Control (GPC) for speed and position of three-phase Permanent Magnet Synchronous Motors (PMSM). Predictive algorithms are designed with single and double integrations with respect to step and ramp reference signals. Needful field weakening and current limitation are solved by specific procedures based on a local indirect tuning/amplification of the relevant GPC parameters. The proposed solution due to low computational demands is suitable for real applications. Designed algorithms and procedures are demonstrated by figures and oscillogram screenshots of representative variables measured on the 10.7 kW PMSM drive. [ABSTRACT FROM PUBLISHER]

Microgrids (MGs) are often unbalanced due to the integration of single-phase generators, unbalanced loads, and asymmetrical faults. To better analyze such MGs, this paper presents an approach to analyze the transient response for an inverter-based MG under the unbalanced condition. The dynamic phasor (DP) concept is used for the MG modeling under the stationaryabcreference frame. First, the DP model of the inverter-based distributed generation (DG) is developed. The influence of unbalanced conditions on the inverter including oscillations on the dc side is considered in this paper. Then, the model of the network and loads is developed. Finally, all the submodules are combined on a time-variable system frequency to obtain the complete DP model of the unbalanced MG. To validate the proposed approach, the DP method is applied to an MG test system with three-phase and single-phase DGs. Small-signal analysis is carried out to derive the dominant modes and their influence on the system response. Simulation results from the DP model are compared against the detailed model built in MATLAB/SimPowerSystem. The results from load disturbances and asymmetrical faults are used to verify the DP model. [ABSTRACT FROM AUTHOR]

This paper proposes a novel causality analysis approach called the causal Markov Elman network (CMEN) to characterize the interdependence among heterogeneous time series in multinetwork systems. The CMEN performance, which comprises inputs filtered by Markov property, successfully characterizes various multivariate dependencies in an urban environment. This paper also proposes a novel hypothesis of characterizing joint information between interconnected systems such as electricity and transportation networks. The proposed methodology and the hypotheses are then validated by information theory distance-based metrics. For cross validation, the CMEN is applied to the electricity load forecasting problem using actual data from Tallahassee, Florida. [ABSTRACT FROM AUTHOR]

An interacting multiple model (IMM) filter is a recognized method for adaptive estimation of states that is often necessary to characterize the behavior of dynamic systems with a multiple-mode operation. The traditional IMM filter adopts the measurement set to update the information about the active models. However, when this approach is used for fault-prognostic applications, it can lead to misleading state estimation. To overcome this problem, this paper proposes a novel fault-prognostic technique based on a modified IMM filter with fuzzy systems. The main methodological contribution of this paper is to build an approach based on an IMM filter able to make long-term fault predictions without measurements. This is done by incorporating a fuzzy system into the proposed IMM filter with the objective of modeling the system's dynamics and updating the probabilities of the observed modes. Furthermore, the proposed method and the standard IMM filter are compared in a numerical example and a real experimental platform PRONOSTIA for validation. The results analysis indicates a better prediction performance than the conventional IMM filter considering the failure time predictions and a measurement model not properly adjusted. [ABSTRACT FROM AUTHOR]

In this paper, the quadruple active bridge (QAB) dc–dc converter is proposed to be used as a building block to implement the dc–dc stage of a smart transformer (ST). Different configurations (symmetrical, asymmetrical, and rated for voltage/power) for this converter are considered for investigation. Four different architectures of ST, including one based on the dual active bridge converter as a benchmark and three based on the QAB converter, are presented and compared in terms of cost, efficiency, reliability, and implementation complexity. As an additional contribution, different semiconductor technologies (silicon IGBT and silicon-carbide MOSFETs) are evaluated in order to verify their impact on ST application. The design for each architecture is described and the results are compared. In order to validate the theoretical analysis developed in this paper, a 20-kW prototype is built and experimented. [ABSTRACT FROM AUTHOR]

The paper deals with some new results on the averaging theory approach for the analysis of feedback controlled pulsewidth modulation power electronic converters. It develops some considerations regarding the averaging approximation of time-variant differential systems proving an analytical relationship between the accuracy with which the solution of the averaged model converges to the solution of the original time-variant model (i.e., the switched model) and the switching frequency of the converters. This relation is valid both for stable and unstable systems. Moreover, this paper confirms, as corollary, that under suitable conditions (verified during the standard operations of the power electronic converters) the averaged model uniformly converges to the switched model. [ABSTRACT FROM AUTHOR]

This paper investigates the use of large-scale wayside energy storage to reduce operational costs of ac electric traction power networks. This paper also introduces a method of estimating the battery capacity, based on manufacturer's charging and discharging specifications. The battery model is simple and easy to incorporate into load flow simulation algorithms. The concept and the battery model are validated through a feasibility study within Aurizon's heavy haul electric railway network. [ABSTRACT FROM AUTHOR]

Inclusion of power electronics allows increased controllability and stability in power systems. The simulation of such systems on a large-scale is challenging due to the presence of a large number of switches and nonlinear devices. This paper presents an advanced simulation algorithm to solve the aforementioned problem. The algorithm considers separation of differential algebraic equations (DAEs) on the basis of numerical stiffness and applies hybrid discretization algorithms to simulate the DAEs. The DAEs, in this paper, represent the nonlinear nonautonomous switched system dynamics of power systems. Stability analysis is performed on a general class of nonlinear nonautonomous switched systems to show the constraints under which the proposed algorithm is stable. To show the validity of the proposed algorithm, two case studies are considered: 1) single high-voltage direct current (HVdc) substation based on the modular multilevel converter (MMC); and 2) an example three-terminal MMC-HVdc system. Relaxation techniques are introduced to create a stable interface for the separated DAEs. The developed algorithms are also validated with PSCAD/EMTDC-detailed reference models. [ABSTRACT FROM AUTHOR]

A grid-tied microgrid (MG) with a battery energy storage system (BESS) is studied in this paper. The energy storage efficiencies of the BESS are considered to optimize the operational cost of the MG. Two quadratic functions are verified and utilized to formulate the efficiencies of BESS in both charge and discharge process. Afterward, constraints of MG power scheme are investigated based on aforementioned equations. Furthermore, the 24-h ahead forecasting data of photovoltaic (PV) generation and loads demand are also utilized during MG modeling. To minimize the operational electricity cost of the MG in the next 24 h, a nonlinear programming with discontinuous derivatives solver is applied based on the proposed constraints. Additionally, to balance the power flow of MG and reduce the effects of the forecasting error of PV generation, a two steps MG management strategy is therefore developed based on the scheduled power. Experiments are conducted to verify the relationship between battery energy storage efficiency and charging/discharging current of the lithium-ion battery. Moreover, the proposed energy management strategy is validated by the hardware-in-the-loop experiments for real-time MG operation. [ABSTRACT FROM AUTHOR]

This paper describes a control algorithm for a battery energy storage system (BESS) to deliver a charge/discharge power output in response to changes in the grid frequency constrained by the National Grid Electricity Transmission (NGET)—the primary electricity transmission network operator in the U.K.—while managing the state of charge of the BESS to optimize the availability of the system. Furthermore, this paper investigates using the BESS in order to maximize triad avoidance benefit revenues while layering other services. Simulation using a 2 MW/1 MWh lithium–titanate BESS validated model is carried out to explore possible scenarios using the proposed algorithms. Finally, experimental results of the 2 MW/1 MWh Willenhall Energy Storage System verify the performance of the proposed algorithms. [ABSTRACT FROM AUTHOR]

This paper presents a novel two-dimensional real-time modeling approach for a proton exchange membrane fuel cell (PEMFC) based on a tridiagonal matrix algorithm (Thomas algorithm). The Thomas algorithm consists of a forward elimination and a backward substitution, its arithmetic complexity of computations being much lower than the Gaussian elimination. In order to use this advanced numerical solver, the differential equations of reactant gas convection and diffusion phenomena in serpentine channels are transformed into a tridiagonal equations system. In addition, a three-level bisection algorithm has been developed to solve spatial physical quantities distribution for electrochemical domain. The real-time computing methods developed in this paper are then implemented in C language for a fast execution time in a real-time processor. The proposed real-time model is experimentally validated using a 1.2 kW Ballard NEXA fuel cell system, and its practical feasibilities in advanced real-time control for PEMFC systems have been experimentally demonstrated in an RT-LAB real-time simulator. [ABSTRACT FROM PUBLISHER]

In this paper, the model predictive current control is introduced in the semicontrolled open-winding permanent magnet synchronous motor (OW-PMSM) generation system with a common dc bus to suppress the zero-sequence current for the first time. Particularly, the basic voltage vectors of the semicontrolled OW-PMSM, which are synthesized by the three-phase full-controlled converter and the three-phase uncontrollable diode bridge, is analyzed and their influences on the zero-sequence current are investigated for the first time in this paper. Then the current-error-based cost function that includes dq-axis current error and zero-sequence current error is designed to evaluate all the voltage vectors. Moreover, to further improve the steady-state control performance of the whole generation system, a zero-sequence current suppression method based on the uncontrollable side voltage vector adjustment, which has the advantage of low computation burden, is developed. In this method, two voltage vectors of the controllable converter are applied during one control period. Based on the distribution character of the basic voltage vector in the semicontrollable OW-PMSM generation system, the first voltage vector is selected according to the three-phase current direction to adjust equivalent vector of the uncontrollable diode bridge, whereas for the second voltage vector, the selection method based deadbeat voltage vector sector is designed to reduce the range of the candidate voltage vector. In addition, the vector durations are also computed. Finally, simulation and experiment are carried out to validate the proposed control approaches. [ABSTRACT FROM PUBLISHER]

This paper presents the implementation of a novel vibration amplitude control and resonant frequency tracking for piezoelectric transducers (PTs) and ultrasonic motors (USMs). It is based on a generalization of the vector control method to the PT and the USM, which is explained in the first part. We show that two independent controllers with a similar structure are required: one tracks the resonant frequency and the second controls the amplitude. We then present the implementation into a low-cost digital signal processing controller with a sampling period of 200  $\mu$s. Experimental results on a Langevin transducer achieved a time response of 20 ms approximately, and the generality of the method is further demonstrated on a 2-D tactile stimulator at the end of this paper. [ABSTRACT FROM PUBLISHER]

In order to effectively suppress surplus torque, realizing high precision loading, this paper applies proportional resonant (PR) control to the load torque control of electric load simulator (ELS), and analyzes and optimizes the stability and dynamic performance of ELS. The mathematical model of ELS is built in z-domain first in this paper, to establish foundation for designing and analyzing PR controller. The stability of the ELS with PR controller is analyzed through Nyquist diagrams, and optimized by reasonably designing the phase compensation angle of PR controller. The dynamic performance is analyzed through pole–zero plots, and the resonant gain of PR controller is designed based on the pole–zero plots to optimize the dynamic performance. Experimental results on ELS are provided, and the proposed method is compared with other typical methods, validating the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

Simulating photovoltaic (PV) power systems becomes important when studying integration issues of the intermittent solar energy into electric grids. The accuracy of the maximum power point (MPP) in PV output model is a concern since it represents the capacity of power generation. This paper proposes a comprehensive approach to identify PV cell parameters and avoid model errors of the MPP based on standard and simplified equivalent circuits. The estimation accuracy has been improved while maintaining the computational simplicity. This paper begins with the definition of the performance index used to quantify the model accuracy at the MPP. Based on the availability of information from the manufacturer’s datasheets, the accuracy and complexity of different equivalent circuits are discussed and investigated. The proposed approach has been successfully tested for solar cells made of mono and multi crystalline material. [ABSTRACT FROM PUBLISHER]

This paper deals with embedded real-time (RT) simulators applied in power electronic applications and implemented in low-cost field-programmable gate arrays. Indeed, such simulators' intellectual properties (IPs) are not only intended for hardware-in-the-loop (HIL) testing but also can be advantageously embedded within digital controllers to ensure functions such as observation, estimation, diagnostic, or health monitoring. Conversely, to the HIL case, the main challenge when designing such simulators' IPs is to cope with their complexity having in mind that, in the case of embedded systems, the available hardware resources are limited due to the cost. Furthermore, this challenge is strengthened by the need of very short simulation time steps that is typically the case when simulating power converters. By this way, this paper presents the design of an embedded RT simulator of a three-phase grid-connected voltage-source rectifier, based on the associated discrete circuit modeling approach. This IP is associated with the one of a three-phase $RL$ filter, and both are implemented within the rectifier controller to estimate the grid currents. The latter is injected in the controller when a fault is detected in the current sensors. The ability of this estimator to guarantee the service continuity in case of faults has been validated through HIL tests and experiments. [ABSTRACT FROM PUBLISHER]

Slotted axial-flux machines have excellent power and torque densities. However, it is difficult to reduce their cogging torque due to the complexity associated with implementing classical techniques. In this paper, slot-opening widths and tooth profiles will be shown to be significant in mitigating cogging torque in these machines. In particular, varying the slot opening reduced it by 52%, whereas a parallel-tooth (rectangular) profile lowered it by 24%, when compared with a conventional trapezoidal-tooth profile. An analytical quasi-3-D analysis was formulated and used to analyze and determine cogging torque. It was validated numerically and experimentally. Its versatility is in its ability to analyze different shapes of poles and slot openings, which can be extended to model air-gap nonuniformity. This paper also presents cogging torque minimization techniques that maintain the ease of manufacture of the parallel-tooth stator. Experimental results showed 73% and 48% reduction in cogging torque, which are achieved by the use of alternating pole arcs and skewed poles. [ABSTRACT FROM PUBLISHER]

A merit of the interleaving reducing the switching harmonics allows for the reduction of the filter inductance. However, in the case of direct parallel voltage source inverters (VSIs), a severe circulating current occurs. To suppress the high frequency circulating current, coupled inductors (CIs) for the high impedance is inserted. However, the employed CIs induce a positive- or negative-sequence circulating current (i.e., a cross current) besides the zero-sequence circulating current already mentioned in the other papers. Due to different impedances developed by the current characteristics and the cross current in the CIs, VSIs becomes unstable when the resonant controllers are applied for the harmonic compensation such as 5, and 7th harmonics. In this paper, the cross currents and the impedances of CIs varying with the current characteristics are mathematically analyzed, and a novel current controller is proposed to solve this stability problem. The experimental results validate the proposed control scheme. [ABSTRACT FROM PUBLISHER]

This paper is dedicated to the design of unknown input (UI) observers for linear parameter-varying (LPV) systems using algebraic matrix manipulation. First, a discussion is provided concerning the classical design approach, which requires the matching condition. This condition is satisfied for a class of systems having relative degree 1. Second, for the same class of systems, a new generalized approach is proposed for simultaneous state and UI estimation. It is demonstrated that the proposed approach is more general than the classical approach. Finally, an extension of the approach is provided for LPV systems with arbitrary relative degree. Simulation examples are provided to illustrate the main results of the paper. [ABSTRACT FROM PUBLISHER]

This paper presents a robust input–output linearization controller as maximum power point tracking (MPPT) technique in a photovoltaic (PV) buck dc–dc converter with applications to dc microgrids, solar vehicles, or stand-alone systems. Due to the control structure proposed in this paper, the MPPT control system is able to track very fast irradiance changes. Meanwhile, the internal stability of the overall closed-loop system is guaranteed for different load scenarios. A sector condition is only required for the load current, which is satisfied for most of the current PV applications. In turn, this condition implies the robustness against oscillations in the dc bus voltage. Finally, the MPPT control system is validated through experimental results, where the closed-loop performance is evaluated under abrupt irradiance and set-point changes, parametric uncertainty, and dc bus load variations. [ABSTRACT FROM PUBLISHER]

The realm of hardware-in-the-loop simulation resorts to field-programmable gate arrays to achieve time steps below 1 \mu\s . Such low time steps are of importance for the aerospace and automotive industries, where power converters have their switching frequencies in the 10- to 200-kHz range. This paper proposes a network tearing technique that allows subsets of switches to be treated independently, alleviates embedded memory requirements, and reduces the computational burden. An iterative algorithm is used to determine the state of naturally commutated switches, thus offering a realistic model of the power converter, independently of its operation mode or topology. A Gauss-Jordan processing unit is implemented to solve interface voltages/currents from the torn circuit. Custom floating-point operators are used to ensure good accuracy, high-frequency operation, and low computational latency. A neutral-point-clamped converter case study is presented to demonstrate the effectiveness of the method. Simulation results are validated against a reference model at a 750-ns time step and a 30-kHz sine pulsewidth modulation switching frequency. [ABSTRACT FROM PUBLISHER]

In this paper, new half-bridge and full-bridge topologies for a switched-boost inverter are proposed. These topologies have a high boost factor in comparison with conventional types. In addition, the proposed topologies have continuous input current and can generate zero-voltage level in output. In this paper, the operation of the proposed inverters in different operating modes is analyzed. Then, the values of inductors and capacitors are designed. Moreover, the used switching pattern and its logical diagram are introduced. A comprehensive comparison between the proposed and conventional topologies in terms of the boost factor, the number of elements, and the efficiency shows the good features of the proposed inverters. Finally, to verify correct operation of the proposed topologies and derived equations, simulation and experimental results are presented. [ABSTRACT FROM AUTHOR]