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Energy harvesting has attracted increased attention recently. Energy sources are present all around us, such as, mechanical vibrations, stress, strain, waste heat, sunlight or room light, electromagnetic rays, and chemical or biological sources. Vibration generators based on piezoelectric elements have been highlighted as low-power sources; however, their output power is very low, around the milliwatt or microwatt level, and thus, improving their performance is necessary to make the generated power usable. This paper investigates the use of passive devices to improve output characteristics of the vibration generators. The proposed circuits are a resonator and a passive rectifier. The proposed resonator consists of a parallel inductor and capacitor for $LC$ resonance. The $LC$ resonance equivalently reduces the internal capacitor of the piezoelectric elements. As a result, the output voltage and power are increased compared with that of conventional circuits. In addition, a boost-type current-improving passive rectifier is applied as the passive rectifier. The validity of the proposed circuit is numerically and experimentally verified. [ABSTRACT FROM AUTHOR]

The increased power and voltage ratings of semiconductors fosters the use in medium voltage components, such as ac–dc converters. With a bipolar medium frequent rectangular (MF RECT) voltage, the converter size can be reduced and the efficiency increased. Possible insulating materials for medium voltage transformers are oil and insulation paper. The breakdown voltage of insulation materials is depending on the frequency and the shape of the voltage curve. Until today, only a few investigations of the breakdown voltage of insulating materials at sinusoidal and RECT voltages up to a few tens of kilohertz have been published. To design and optimize MF transformers at RECT voltages, further investigations are necessary. Therefore, a test bench for measuring the breakdown voltage at RECT voltages in the frequency range between one and ten kilohertz up to several tens of kilovolts is developed. The test bench is inspired by a Marx generator, which is a high voltage source for impulse voltages. By substituting resistances and spark gaps by IGBTs and adding galvanically insulated power sources, a medium frequent bipolar voltage can be generated. The test bench is characterized with respect to slew rate, input power, frequency, and voltage amplitude. Its usability is shown in first breakdown voltage measurements of insulation papers, used for transformer insulation. [ABSTRACT FROM AUTHOR]

This paper proposes a novel direct power control (DPC) method for the doubly fed induction generators (DFIGs) power control system. The proposed DPC method is based on extended power theory rather than conventional instantaneous power theory. The proposed method calculates the rotor reference voltage based on the principle of deadbeat power control. Then, it synthesizes the rotor reference voltage using space vector modulation (SVM). As a result, the switching frequency is constant, and satisfactory control performance is achieved under both balanced and unbalanced network conditions. This technique achieves the control target of ensuring a constant stator-side active power, constant extended reactive power, and sinusoidal stator currents without power compensation terms or other measures under unbalanced network conditions. Different from other DPC-SVM methods, the phase-locked loop block is eliminated and the whole structure of the control system is simple and easy to use. No parameter needs to be tuned in the proposed method. The effectiveness of the proposed method is validated by the presented simulation and experimental results on a 1.5-kW laboratory DFIG control system. [ABSTRACT FROM AUTHOR]

This paper focuses on the zero-voltage ride-through (ZVRT) capability of a transformerless back-to-back (BTB) system intended for installation on a power distribution system with many distributed power generators. The BTB system consists of two modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC) and their ac sides are connected to a common ac mains via ac-link inductors. This paper provides an experimental discussion on the DSCC-based BTB system under voltage sags by using a three-phase 200-V 10-kW downscaled system. Experimental results show that the BTB system is equipped with ZVRT capability without causing any overvoltage and/or overcurrent even under the most severe voltage sags. [ABSTRACT FROM PUBLISHER]

Small grid-tied wind turbines based on permanent magnet generators often use a cost-effective power converter topology consisting of a passive rectifier, a boost converter, and an H-bridge inverter. Speed or position sensors are rarely used due to cost issues. Model-based estimators relying on electrical magnitudes are used instead. However, such estimators are parameter sensitive, which limit their accuracy. Further concerns arise if these parameters change with the operating condition of the machine, mainly due to temperature. Speed sensorless control using the rectifier voltage ripple is analyzed in this paper. This technique provides good dynamic response and does not depend on machine parameters. Simulations are provided for speed and power tracking comparison with an accurate model-based speed estimation method operating at non-rated parameters. They show the speed accuracy and power tracking capability of the proposed method are similar to that provided by a speed sensor. This is translated into a 0.9% power increase when the model-based speed estimator shows 9% of error. Experimental results are carried out to test the effect of current and temperature in the estimation, showing temperature insensitivity and some distortion due to fast current transients. A speed estimation accuracy of zero mean error and 1.7% standard error is experimentally obtained in the regular operation of the wind turbine. [ABSTRACT FROM AUTHOR]

This paper presents a model predictive current control (MPCC) for three-phase four-switch converters (TPFSC) connected to surface permanent magnet synchronous generators (SPMSGs) in oscillating water column (OWC) wave energy plants, that brings some benefits over the existing control methods used in this type of plants. The proposed MPCC for TPFSC follows the current references with great accuracy, whereas the switching frequency of the insulated-gate bipolar transistor (IGBTs) is fixed and low. This method minimizes the current reference tracking error, and its fast response makes it suitable for the power take-off systems present in wave energy converters. Furthermore, the system features a fast capacitor voltage offset suppression control. The dynamic performance and the voltage offset control of the proposed strategy for TPFSC feeding a SPMSG is evaluated in the Simulink environment. Later, experimental studies are carried out on an 8.7 kW laboratory SPMSG prototype. Finally, the capability of the proposed method to harvest the maximum energy from irregular waves is assessed using an OWC power plant emulator. [ABSTRACT FROM AUTHOR]

Nowadays, active-front-end rectifiers are increasingly used as grid connected devices. Their efficiency and performances have become relevant for reducing the overall grid losses. This paper thus introduces a predictive hybrid pulse-width-modulation (PH-PWM) technique, adaptable to any space-vector PWM (SVPWM) controller. As opposed to hybrid PWM techniques based on sector partitioning, the PH-PWM technique selects the appropriate PWM sequence online with the help of a predictive algorithm. This selection is based on a cost-function where users can define a tradeoff between various criteria, such as the reduction of current distortion and switching losses, as presented in this paper. The use of the PH-PWM technique increases performances in comparison with the conventional PWM techniques. The simulation and experimental results are presented to confirm the effectiveness of the proposed PH-PWM technique. Aside from the tradeoff capacity of the proposed PH-PWM technique, the simulation results validate a reduction of the switching losses for the converter up to 23$\%$ as compared with the conventional SVPWM technique. [ABSTRACT FROM AUTHOR]

The large-scale spread of hybrid electric vehicles (HEVs) in the automotive industry is dominated today by continuous variable transmission parallel powertrain as far as medium size car are concerned. As a matter of fact, the tendency in this sector is to design parallel architectures in that they have provided until now a higher overall powertrain efficiency. However, technological improvements in many electric components and their increased efficiency can reshape this vision and give new outlines on HEV structure design. This paper aims to show the potentials of the series architecture, thanks to the latest electrical improvements especially in storage systems and power electronics. In particular, simulation models and fuel consumption data over different road missions are presented for the series architecture proposed in this study. In addition, a comparison between these results and data available in the scientific literature for state-of-the-art HEVs is reported. [ABSTRACT FROM AUTHOR]

In order to obtain the benefits of both passive and active methods, a well-designed hybrid islanding detection method for grid-connected microgrids with multiple inverter-based distributed generators (IBDGs) is presented in this paper. Considering that IBDGs located at different positions can detect the same frequency variation (FV) characteristics, linear reactive power disturbance (RPD) is utilized, which can guarantee the synchronization of RPDs added on different IBDGs in the microgrid without the need for communication. In addition, the disturbance slope can change adaptively to reduce the disturbance in grid-connected mode and enlarge the reactive power mismatch during islanding for effective and rapid detection. Setting principles of slope values for IBDGs operating at the unity power factor and those generating active and reactive power simultaneously are analyzed in detail. Considering different conditions that may occur after islanding, three passive criteria, including voltage variation, voltage unbalance, and rate of change of frequency, are sufficiently utilized to activate disturbance slope adjustment, further shortening the detection time. Moreover, the correlation factor between the RPD and FV is also designed as another frequency-related criterion, and the slope adjustment logic is provided. This method is simple and easy to implement with excellent performance regardless of the IBDG power factor, parallel number, and connection mode. According to the anti-islanding test system recommended by IEEE Std.929-2000 and IEEE Std.1547-2003, the method effectiveness has been validated with several test cases in the power systems computer-aided design (PSCAD)/electromagnetic transients including DC (EMTDC) environment. [ABSTRACT FROM AUTHOR]

The more electric aircraft concept aims at increasing the amount and the power of the electrical subsystems on the next generation of aircraft. One of the major challenges in this framework is that the electric power is generated by means of electrical generators connected to the jet turbine shaft. In order to satisfy the peak power demand and overload conditions, the generators are oversized, increasing weight and total cost of operation. Possible solutions to this problem is to decrease the size of the generator and to provide the peak power with storage systems. As an alternative, load disconnection during peak demand (load-shedding) can be enforced with solid-state switches. This paper presents a different approach, i.e., by modifying the dc voltage of the distribution, the load can be controlled. In order to achieve this objective, a precise on-line identification algorithm is proposed. Theoretical analysis is performed, and simulation results on a study-case distribution system are reported, highlighting how the proposed load identification and control method effectively manages a power curtailment condition without load-shedding or storage systems. Power hardware in the loop simulations on a dc microgrid with a multiport power converter confirm the simulation analysis. [ABSTRACT FROM AUTHOR]

This paper proposes a simple and practical duty cycle modulated direct torque control (DDTC) for permanent magnet synchronous motors. The duty cycle of active vector is obtained using a duty cycle generator according to the torque error and motor speed, which can avoid the complex calculation process associated with conventional DDTC. The design details about the duty cycle generator are illustrated, and the stability of the proposed DDTC is analyzed, which ensures the reliable operation of the motor system. Experimental results are presented to validate the effectiveness of the proposed DDTC. Furthermore, the comparative evaluation of the proposed DDTC and conventional DDTC is conducted to verify the superiority of the proposed DDTC. [ABSTRACT FROM AUTHOR]

This paper investigates the diode reverse recovery process and reduction of a half-wave (HW) series Cockcroft–Walton (CW) voltage multiplier based on the steady-state analysis for high-frequency high-voltage (HV) generator applications. The diode reverse recovery process for a multistage voltage multiplier is analyzed after the introduction of steady-state operation. The diode reverse recovery problem is the bottleneck to further increase the circuit operation switching frequency for achieving high power density and short HV pulse rise and decay times. The diode reverse recovery problem is mainly caused by the diodes in the first-stage voltage multiplier. It is suggested that the most effective and economic way to alleviate the diode reverse recovery problem is by employing diodes without reverse recovery such as silicon carbide Schottky diodes in the first stage only. The silicon carbide Schottky diode without reverse recovery needs to be used only in the first stage of the voltage multiplier to effectively mitigate the reverse recovery problems at high frequency. The 300 kHz switching frequency three-stage voltage multiplier circuit hardware prototype experimental results finally validate the analysis. A technology demonstrator of a 300 kHz 8 kW 160 kV HV generator based on the proposed hybrid silicon carbide and silicon diode solution for the HW series CW voltage multiplier is provided finally. [ABSTRACT FROM AUTHOR]

Rising power demands in more electrical aircraft (MEA) put power converters for commercial airplanes under increasing pressure to fulfill current harmonic distortion regulations as specified, for example, in DO-160G. Today, the implementation of filters is seen as an effective tool for dealing with harmonics; however, their increased weight and volume are not welcomed in the aerospace industry. This paper proposes a circuit, named forced commutation controlled series capacitor (FCSC-rectifier), which is able to maintain low individual harmonic current levels without the need for filter components. The FCSC-rectifier includes a variable capacitive line reactance that interacts in a controlled manner with the inductive line impedance. The result is that the converter input current is nearly purely sinusoidal with a power factor of almost unity. The FCSC-rectifier is to be used for stand-alone variable-voltage, variable-frequency generation systems and can, therefore, power the full authority digital electronic control system (FADEC) in an MEA. This paper shows that the FCSC-rectifier can maintain a high power factor and acceptable current harmonic levels without the use of filters, despite large voltage and frequency variations. A full description of the circuit modes of operation is presented in this paper together with simulation results showing circuit performance characteristics over a range of voltages and frequencies. Results are experimentally verified using a 1-kW test circuit. [ABSTRACT FROM AUTHOR]

A transmission line emulator has been developed to flexibly represent interconnected ac lines under normal operating conditions in a voltage-source-converter-based power system emulation platform. As the most serious short-circuit fault condition, the three-phase short-circuit fault emulation is essential for power system studies. This paper proposes a model to realize a three-phase short-circuit fault emulation at different locations along a single transmission line or one of several parallel-connected transmission lines. At the same time, a combination method is proposed to eliminate the undesired transients caused by the current reference step changes while switching between the fault state and the normal state. Experiment results verify the developed transmission line three-phase short-circuit fault emulation capability. [ABSTRACT FROM AUTHOR]

This paper proposes a new soft-stalling control strategy for grid-connected small wind turbines operating in the high and very high wind speed conditions. The proposed method is driven by the rated current/torque limits of the electrical machine and/or the power converter, instead of the rated power of the connected load, which is the limiting factor in other methods. The developed strategy additionally deals with the problem of system startup preventing the generator from accelerating to an uncontrollable operating point under a high wind speed situation. This is accomplished using only voltage and current sensors, not being required direct measurements of the wind speed nor the generator speed. The proposed method is applied to a small wind turbine system consisting of a permanent magnet synchronous generator (PMSG) and a simple power converter topology. Simulation and experimental results are included to demonstrate the performance of the proposed method. The paper also shows the limitations of using the stator back electromotive force to estimate the rotor speed in PMSG connected to a rectifier, due to significant $d$-axis current at high load. [ABSTRACT FROM AUTHOR]

In this paper, a high-performance grid simulator based on a parallel structure fractional repetitive control scheme is employed to emulate various operation scenarios of power grids for testing power products. In this paper, a simple fractional repetitive control scheme is proposed for grid simulators to achieve high-accuracy tracking performance. Using parallel branches, the proposed repetitive controller can flexibly select the interested harmonics for compensation, and independently, tune the convergency rate at selective harmonic frequencies. Compared with the conventional repetitive control, the proposed control scheme achieves faster transient response. Moreover, the number of delay units required in the proposed repetitive controller is reduced to at least half of that in a conventional repetitive controller. Design process and stability criteria are presented in details. A set of experimental results is provided to verify the effectiveness of the proposed approach. [ABSTRACT FROM PUBLISHER]

This paper presents an intensive discussion on a transformerless back-to-back (BTB) system using modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC). It is expected to be applied to a power distribution system with many distributed power generators. This paper designs, constructs, and tests a three-phase 200-V, 10-kW DSCC-based BTB system installed on a 200-V, 40-kW power distribution simulator consisting of two radial feeders. Experimental results show that the BTB system can mitigate power-flow imbalance between the two feeders. Moreover, the zero-sequence current circulating between the two feeders can be suppressed to be as small as 10 mA (0.02%) in rms by connecting a common-mode choke to the common dc link of the BTB system. [ABSTRACT FROM AUTHOR]

Recent years have witnessed a continuing increase in the wind turbine (WT) size and penetration level into the grid, revealing critical challenges to sustainable market development and urgent demands of low voltage ride-through, load reduction, and optimal operation. This paper presents an overview on grid-friendly WTs and relevant technologies for control and monitoring. The development trends are discussed as well to explore potential approaches for optimizing WT systems. The main body contains three parts: the “grid-friendly” criterion and a prototype, the overview and suggestions for WT controller design concerning load reduction and power optimization, and suggested solutions for wind power monitoring systems. This paper is expected to be a reference for extending the knowledge of grid-friendly WTs and optimizing the performance of future large-scale wind power systems. [ABSTRACT FROM AUTHOR]

Multifunctional grid-tied inverters (MFGTIs) have been paid much attention to handle the commonly concerned power quality issues of the microgrids. An MFGTI can not only interface the renewable energy resource into the utility grid, but also can compensate the harmonic and reactive current in the microgrid as an auxiliary service. However, the apparent capacity of an MFGTI for power quality compensation is limited. Therefore, how to enhance the power quality of the microgrid by optimal utilization of the limited and valuable capacity becomes a technical challenge. In this paper, two optimal control objectives of MFGTIs are presented based on a comprehensive power quality evaluation algorithm by means of analytic hierarchy process theory. One objective aims to obtain the expected power quality using minimal apparent capacity of the MFGTI. Another objective focuses on enhancing the power quality as well as possible in the given available apparent capacity condition. The two proposed strategies are compared in performance, and the paper also discusses how to use them in practice for the best performance. Experimental results performed on a microgrid in the laboratory confirm the validation and feasibility of the proposed optimal control strategies. [ABSTRACT FROM AUTHOR]

The contribution of decentralized generators in the provision of ancillary services, such as voltage and frequency regulations, is currently growing in many power systems. The impact of these new regulations on islanding detection is generally investigated by calculating the nondetection zone (NDZ) of the protective relay located at generator level. This subject has already been studied in the literature, but has been generally treated by means of steady-state calculations only. As demonstrated in the present paper, the analysis yields very different results when the entire time-evolution of the system is taken into account. It is shown that the impact of the studied regulations, i.e., the P(f) and Q(U) controls, on a standard test system is to reduce the NDZ which goes against the conclusion of several previous works based on steady-state calculations. Then the generalization of this result to other loads and generators is investigated. At last, the impact of the dynamics of the grid and the dynamics of the regulations is further investigated through a parametric study which shows that, if the power regulations dynamics are slow enough compared to the voltage and frequency dynamics, then the NDZ is necessarily reduced by the addition of the new regulations. [ABSTRACT FROM AUTHOR]

This paper presents a novel three-phase DC-link multilevel inverter topology with reduced number of input DC power supplies. The proposed inverter consists of series-connected half-bridge modules to generate the multilevel waveform and a simple H-bridge module, acting as a polarity generator. The inverter output voltage is transferred to the load through a three-phase transformer, which facilitates a galvanic isolation between the inverter and the load. The proposed topology features many advantages when compared with the conventional multilevel inverters proposed in the literatures. These features include scalability, simple control, reduced number of DC voltage sources, and less devices count. A simple sinusoidal pulse-width modulation technique is employed to control the proposed inverter. The performance of the inverter is evaluated under different loading conditions and a comparison with some existing topologies is also presented. The feasibility and effectiveness of the proposed inverter are confirmed through simulation and experimental studies using a scaled down low-voltage laboratory prototype. [ABSTRACT FROM AUTHOR]

The More Electric Aircraft concepts aims at increasing the penetration of electric systems on aircrafts. In this framework, the electrical power distribution system (EPDS) is of high importance. In order to improve the utilization of the generators and face the peak power demand without disconnecting the loads, different technologies of storage are employed. This paper proposes the use of a quadruple active bridge converter, already employed in other fields, to interface a fuel cell, a battery, and a supercapacitor bank to the dc bus of the EPDS. This objective can be achieved by employing multiple dc/dc converters, which allow an individual control of the energy sources and a good efficiency. Obtaining the same power control and efficiency with a multiport power converter constitutes a challenge that is worth taking to reduce cost, volume, and weight and increase the system reliability. A novel control based on proportional integral (PI) controllers in conjunction with a decoupling system and current feedforward allow shaping the power request to each port. This, however, leads to an asymmetrical loading of each port, which could decrease the efficiency. A laboratory prototype is used to confirm that this asymmetrical kind of operation, where each port processes a different amount of power, does not imply a marked reduction of efficiency. [ABSTRACT FROM AUTHOR]

In this paper, a unified equivalent circuit model which can simplify the design and analysis of a family of high-voltage (HV) generation architectures based on the series–parallel (LCC) resonant converter is proposed. First, four HV generation architectures are reviewed in terms of the modularization level of HV transformers and rectifiers. Next, the steady-state, unified equivalent resistor and capacitor (RC) model that can be easily embedded into the resonant tank to replace the complex HV transformers and rectifiers is derived. The generic model can be applied to the HV generators with different architectures, different voltage multiplier topologies, stage, and polarities number. Further analysis of the power factor of the resonant tank, the voltage gain of HV generators, and electrical stresses of power components is achieved with the derived equivalent circuit model. The analysis reveals the inherent circuit properties among HV generators with different configurations. Subsequently, a comprehensive design methodology considering the power factor, conduction angle, and quality factor is presented, which leads to low electrical stresses on the components and high efficiency. Furthermore, the parameter selection constraint based on the power factor, conduction angle, and quality factor is derived, which can ensure the effective design outputs. Finally, the proposed unified equivalent model and comprehensive design methodology are validated by the experimental results of a 250 V input, 20 kV output 500 W HV generator hardware prototype with distributed transformers and voltage multipliers. [ABSTRACT FROM AUTHOR]

Grid faults are one of the most severe perturbations in power systems. During these extreme disturbances, the reliability of the grid is compromised and the risk of a power outage is increased. To prevent this issue, distributed generation inverters can help the grid by supporting the grid voltages. Voltage support mainly depends on two constraints: the amount of injected current and the grid impedance. This paper proposes a voltage support control scheme that joins these two features. Hence, the control strategy injects the maximum rated current of the inverter. Thus, the inverter takes advantage of the distributed capacities and operates safely during voltage sags. Also, the controller selects the appropriate power references depending on the resistive–inductive grid impedance. Therefore, the grid can be better supported since the voltage at the point of common coupling is improved. Several voltage objectives, which cannot be achieved together, are developed and discussed in detail. These objectives are threefold: to maximize the positive sequence voltage; to minimize the negative sequence voltage; and to maximize the difference between positive and negative sequence voltages. A mathematical optimal solution is obtained for each objective function. This solution is characterized by a safe peak current injection, and by the optimization of the voltage profile in any type of grid connection. Therefore, the proposed control scheme includes advanced features for voltage support during voltage sags, which are applicable to different power facilities in different types of networks. Due to system limitations, a suboptimal solution is also considered, analyzed, and discussed for each of the optimization problems. Experimental results are presented to validate the theoretical solutions. [ABSTRACT FROM AUTHOR]

Plug-in hybrid electrical trucks (PHETs) are a kind of emerging transport solution to reduce greenhouse gas emissions. Switched reluctance motors (SRMs) are one of the popular choices for PHETs applications due to characteristics of rear-earth free, high starting torque, wide-speed range, and good fault tolerance. Usually, more than two converters are needed to achieve flexible energy conversion among multiple electrical energy components on board, i.e., generator, battery bank, and motor. High-power converters should be used to drive the trucks that occupy the limited on-board space. Furthermore, an extra converter is also needed to achieve ac grid connecting charging. All these converters make the on-board power electronics converter complicated. In this paper, a modular tri-port high-power converter for SRM based PHETs is proposed to combine the multiple electrical energy components into one converter. The modular tri-port high-power converter can not only support flexible energy flow, but also support parallel and series winding connections according to different conditions. Furthermore, ac grid connecting nodes are also developed in the drive, which allows the proposed converter to work as a grid connecting charger without extra facilities. The simulation and experiments are employed to verify the feasibility of the proposed converter and corresponding control strategies. [ABSTRACT FROM PUBLISHER]

In this paper, an overall power control strategy is proposed for control of a fixed-pitch small-scale wind energy conversion system operating at both underrated and overrated wind speeds. At underrated wind speeds, the dynamical behavior of the rotor is considered, and the optimal reference torque is generated without the need of wind speed sensors through a robust variable structure observer with the aim of maximum power point tracking. At overrated wind speed, the flux-weakening strategy is invoked to let the machine exploit maximum electrical torque under given current and voltage constraints. As a new approach, the optimal reference flux magnitude together with a reference torque angle is provided by online numerically solving an optimization problem in the whole wind speed range. Moreover, a space-vector-modulation -based direct torque control (SVM-DTC) is used to track the provided references for flux magnitude and torque angle. In particular, the SVM-DTC is composed of a reference voltage vector calculator providing a desired voltage vector. The effectiveness of the proposed overall power control strategy is verified not only by applying the strategy to a commercial 10-kW wind turbine simulated in MATLAB/Simulink, but also by experimental results derived from a developed laboratory setup. [ABSTRACT FROM PUBLISHER]

Frequency control in autonomous microgrids (MG) with high penetration of renewable energy sources represents a great concern to ensure the system stability. In this regard, this paper presents an enhanced control method for battery energy storage systems (BESS) to support the frequency of MG and with the ability of disconnecting from the MG to supplying in the island mode a local consumer. A frequency controller, combining a conventional droop control with an inertia emulation function, governs the BESS active power transfer during the primary frequency control level. The BESS may also provide voltage support in the point of common coupling with the MG. Moreover, the proposed BESS may compensate, partially or totally, the power absorbed by the local loads in order to improve the MG frequency response. When the MG power quality worsens below a certain level, in terms of voltage and frequency, the BESS detaches from the MG and continues to operate islanded. The reconnection is accomplished following a smoothly resynchronization of the local voltage with the MG, without disturbing the local loads supply. Additionally, this paper also discusses about the aspects related to the BESS management and its integration within the proposed system. The simulation and experimental results assess the feasibility of the proposed control solutions. [ABSTRACT FROM AUTHOR]

Recent advances in solid-state semiconductors have led to the development of medium-voltage power converters (e.g., 6-36 kV) which could obviate the need for the step-up transformers of renewable power generation systems. The modular multilevel cascaded converters have been deemed as strong contenders for the development of medium-voltage converters, but the converters require multiple isolated and balanced dc supplies. In this paper, a high-frequency link multilevel cascaded medium-voltage converter is proposed. The common high-frequency link generates multiple isolated and balanced dc supplies for the converter, which inherently minimizes the voltage imbalance and common mode issues. An 11-kV system is designed and analyzed taking into account the specified system performance, control complexity, cost, and market availability of the power semiconductors. To verify the feasibility of the proposed system, a scaled down 1.73-kVA laboratory prototype test platform with a modular five-level cascaded converter is developed and explored in this paper, which converts a 210 V dc (rectified generator voltage) into three-phase 1 kV rms 50 Hz ac. The experimental results are analyzed and discussed. It is expected that the proposed new technology will have great potential for future renewable generation systems and smart grid applications. [ABSTRACT FROM AUTHOR]

The digital implementations of Sinusoidal Pulse Width Modulation (SPWM) generators have dominated over their counterparts based on analog circuits. In this paper, an FPGA-based SPWM generator is presented, which is capable to operate at switching frequencies up to 1 MHz (requiring FPGA operation at 100-160 MHz), thus it is capable to support the high switching frequency requirements of modern single-phase dc/ac power converters. The proposed design occupies a small fraction of a medium-sized FPGA and, thus, can be incorporated in larger designs. Additionally, it has a flexible architecture that can be tuned to a variety of single-phase dc/ac inverter applications. The post-layout simulation and experimental results confirm that compared to the past-proposed SPWM generation designs, the SPWM generator presented in this paper exhibits much faster switching frequency, lower power consumption, and higher accuracy of generating the desired SPWM waveform. [ABSTRACT FROM AUTHOR]

High-voltage direct-current (HVDC) based power distribution networks have become an attractive alternative to classical ac distribution networks in more electric aircrafts (MEAs). This paper proposes a power flow management system for an isolated multiport power converter (MPC), which includes a high-frequency transformer, that controls the power flow between three HVDC electric networks in MEAs. The operation of the MPC system and the control stability analysis are presented. The proposed power flow management is tested under normal operation mode and different fault conditions of the power generators. The experimental results demonstrate that the isolated MPC reduces the effect of a power generator failure to the other networks, thus enhancing the fault tolerance of the entire power distribution network of the aircraft. [ABSTRACT FROM AUTHOR]

Offshore wind farms with series-interconnected structures are promising configurations because bulky and costly offshore substations can be eliminated. In this paper, a medium-frequency transformer (MFT)-based wind energy conversion system is proposed for such wind farms based on current source converters. The presented configuration consists of a medium-voltage permanent magnet synchronous generator that is connected to a low-cost passive rectifier, an MFT-based cascaded converter, and an onshore current source inverter. Apart from fulfilling traditional control objectives (maximum power point tracking, dc-link current control, and reactive power regulation), this study endeavors to ensure evenly distributed power and voltage sharing among the constituent modules given the cascaded structure of the MFT-based converter. In addition, this paper thoroughly discusses the characteristic of decoupling between the voltage/power balancing of the modular converter and the other control objectives. Finally, both simulation and experimental results are provided to reflect the performance of the proposed system. [ABSTRACT FROM AUTHOR]

A photovoltaic (PV) generator is internally a power-limited nonlinear current source having both constant-current- and constant-voltage-like properties depending on the operating point. This paper investigates the dynamic properties of a PV generator and demonstrates that it has a profound effect on the operation of the interfacing converter. The most important properties an input source should have in order to emulate a real PV generator are defined. These properties are important, since a power electronic substitute is often used in the validation process instead of a real PV generator. This paper also qualifies two commercial solar array simulators as an example in terms of the defined properties. Investigations are based on extensive practical measurements of real PV generators and the two commercial solar array simulators interfaced with dc–dc as well as three- and single-phase dc–ac converters. [ABSTRACT FROM AUTHOR]

In this paper, a new energy management strategy (EMS) for a dc distribution system in buildings is being proposed. The dc distribution system is considered as a prospective system according to the increase of dc loads and dc output type distribution energy resources (DERs) such as photovoltaic (PV) systems and fuel cells. Since the dc distribution system has many advantages such as feasible connection of DERs and electric vehicles (EVs), reduction of conversion losses between dc output sources and loads, no reactive power issues, it is very suitable for industrial and commercial buildings interfaced with DERs and EVs. The establishment of an appropriate EMS based on the economic point of view can reduce energy costs of buildings and provide benefits to participants in energy management. Applicable elements for the dc distribution system are identified and the real-time decision-making-based algorithm for minimizing operating costs is proposed in this paper. The EV service model for the EMS to offer incentive to EV owners who participate in battery discharging is described. To verify the performances of the proposed algorithm, computer simulation and economic analysis are being performed where the results show that the proposed EMS reduces energy costs, motivates EV owners, and can be applied to the dc distribution buildings. [ABSTRACT FROM AUTHOR]

In this paper, the concept of a modulated-ramp pulse-width modulation (PWM) generator is presented. The specific nonlinear behavior of this generator enables an exact linear control-to-output static conversion characteristic of DC-DC switching converters, such as the boost (step-up), buck/boost, Ćuk, or SEPIC, operating in continuous conduction mode. The resulting linearization leads to a significant improvement of the control accuracy and simplification of the converters, operating mainly in the open-loop architecture. In this paper, the concept of the modulated-ramp PWM generator is described, followed by a detailed steady-state and small-signal AC analysis. The key aspects for practical implementation are also highlighted. All results and benefits of the modulated-ramp PWM generator are demonstrated here on the boost converter power stage. [ABSTRACT FROM AUTHOR]

This paper presents an online procedure for the automatic search of the maximum-torque-per-ampere operating region for a synchronous reluctance motor. The algorithm is based on a signal-injection method with a random-based perturbation pattern applied to a common direct-torque-controlled drive. Among motor parameters, only the stator resistance is required to perform the automatic procedure. Simulations and experimental results are presented in the paper, demonstrating the benefits of the proposed algorithm. The solution is easily extended to any ac drive. [ABSTRACT FROM PUBLISHER]

A key feature of microgrid concept is the ability to operate in islanding mode. Under such operating scenario, the distributed generators within microgrid should form a high-quality voltage supply for the load to sustain its normal operation. Power converters, the interface of renewable sources and energy storage systems, are important components of microgrids. The size and the number of the power converters required will depend on the fluctuating power flow within the microgrid. In this paper, we propose a hybrid control architecture to balance the power shared among the multiple interfacing inverters and optimize the system-operating efficiency. Simulation and real-time test results are provided to validate the proposed hybrid control scheme. [ABSTRACT FROM PUBLISHER]

In order to overcome the limitations of the existing classical and solid-state Marx pulse generators, this paper proposes a new modular multilevel voltage-boosting Marx pulse generator (BMPG). The proposed BMPG has hardware features that allow modularity, redundancy, and scalability as well as operational features that alleviate the need of series-connected switches and allows generation of a wide range of pulse waveforms. In the BMPG, a controllable, low-voltage input boost converter supplies, via directing/blocking (D/B) diodes, two arms of a series modular multilevel converter half-bridge sub-modules (HB-SMs). At start up, all the arm's SM capacitors are resonantly charged in parallel from 0 V, simultaneously via directing diodes, to a voltage in excess of the source voltage. After the first pulse delivery, the energy of the SM capacitors decreases due to the generated pulse. Then, for continuous operation without fully discharging the SM capacitors or having a large voltage droop as in the available Marx generators, the SM capacitors are continuously recharged in parallel, to the desired boosted voltage level. Because all SMs are parallelly connected, the boost converter duty ratio is controlled by a single voltage measurement at the output terminals of the boost converter. Due to the proposed SMs structure and the utilization of D/B diodes, each SM capacitor is effectively controlled individually without requiring a voltage sensor across each SM capacitor. Generation of the commonly used pulse waveforms in electroporation applications is possible, while assuring balanced capacitors, hence SM voltages. The proposed BMPG has several topological variations such as utilizing a buck–boost converter at the input stage and replacing the HB-SM with full-bridge SMs. The proposed BMPG topology is assessed by simulation and scaled-down proof-of-concept experimentation to explore its viability for electroporation applications. [ABSTRACT FROM AUTHOR]

This paper proposes an improved voltage regulation method in a multisource-based dc electrical power system in the more electric aircraft. The proposed approach, which can be used in terrestrial dc microgrids as well, effectively improves the load sharing accuracy under high droop gain circumstance with consideration of cable impedance. Since no extra communication line and controllers are required, it is easily implemented and also increases the system modularity and reliability. By using the proposed approach, the dc transmission losses can be reduced and the system stability is not deteriorated for normal and fault scenarios. In this paper, optimal droop gain settings are investigated and the selection of individual droop gains as well as the proportional power sharing ratio has been described. Simulation and experimental results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Unprecedented expansion of native dc powered equipment (LEDs, computers, and consumer electronics) has increased commercial and residential dc electricity usage over the past decade. Thus, it is foreseeable that hybrid ac/dc buildings featuring both ac and dc infrastructures will coexist. A hybrid ac/dc building will involve an efficient centralized rectifier that supplies all the dc loads, while legacy ac loads will remain connected to the existing ac infrastructure. This paper explores the opportunity of harmonic mitigation at distribution level in small hybrid ac/dc building by using a centralized power factor corrector (PFC) with large bandwidth. The current reference generator for the harmonic mitigation function (HMF) is explained along with power considerations. The PFC uses a proportional resonant controller, instead of a PI controller, without requiring additional sensors in the rectifier. A computationally inexpensive implementation of the phase-locked loop is also proposed along with considerations on parameter selection. The proposals provide all the steps for the straightforward control design of the PFC+HMF with fast calculations. The HMF requires only software modifications in the PFC and one sensor to measure the nonlinear load. Simulation and experiments validate the proposed procedures. [ABSTRACT FROM AUTHOR]

The structure and control strategy of a novel two-phase brushless main exciter (ME) are proposed in this paper to solve the excitation problem of the main generator (MG) when the aircraft brushless wound-rotor synchronous starter/generator start up as a motor. Two-phase symmetrical winding is adopted as the field winding of the ME and is supplied with two-phase ac by a two-phase inverter in the starting mode and dc by the traditional generator control unit in the generation mode. In order to make the field current of the MG remain constant during the start-up process, the excitation control method for the two-phase ME in the starting mode is proposed, which contains the feedback control for the two-phase field currents and speed reference control for the excitation frequency. The proposed two-phase ME and excitation control method have the advantages of capability for higher and constant field current for the MG in the starting mode and unchanged structure and control methods in the generation mode. A two-phase ME prototype, based on an original single-phase ME, is designed, manufactured, and tested. Finite-element analysis (FEA)-based simulation and experimental results verify the feasibility and advantages of the novel two-phase brushless ME and excitation control method. [ABSTRACT FROM AUTHOR]

Conventional three-phase rectifiers are controlled to achieve good power factor and low total harmonic distortion in the input. In the case of pulsating power loads, the fast dynamic response implies that the load pulses are reflected in the generator. These pulsating loads affect the lifetime operation of the generator, especially when it is not oversized (as in the case of aircraft applications). In order to smooth the power demanded from the generator, it is preferable to reduce the bandwidth of the output voltage controller for the rectifier but it affects its stability due to the fact that the right-half-plane (RHP) pole given by the negative impedance of a constant power load requires high-bandwidth control loop to compensate it. In this paper, an energy control method is proposed that utilizes the energy stored in the output capacitor of the rectifier to control the output voltage of the rectifier. In such a way, the minimum bandwidth restriction imposed by the RHP pole of the power load is eliminated and the bandwidth of the voltage loop can be defined low enough to demand smooth power from the generator. [ABSTRACT FROM PUBLISHER]

This paper proposes a high efficiency class-D amplifier (CDA) with embedded single-inductor bipolar output (SIBO) power module. The characteristics of SIBO converter's bipolar outputs not only suppress equivalent common-mode noise but also remove several large external bulky components in conventional boost supply CDA systems. Since bipolar outputs in the SIBO provide independent driving capability, CDA is capable of operating in both single-ended and bridge-tide load configurations. Furthermore, the proposed dynamic voltage boosting technique adjusts the SIBO output voltage level according to the CDA's output level with 5% power efficiency improvement. Peak total harmonic distortion plus noise performance is 0.012%. Peak power efficiency of SIBO and CDA is 89% and 93.2%, respectively. [ABSTRACT FROM PUBLISHER]

Flapping electromagnetic-reed generators are investigated to harvest wind energy, even at low cutoff wind speeds. Power electronic interfaces are intended to address ac–dc conversion and power conditioning for single- or multiple-channel systems. However, the generated voltage of each generator reed at low wind speed is usually below the threshold voltage of power electronic semiconductor devices, increasing the difficulty and inefficiency of rectification, particularly at relatively low output powers. This paper proposes a multiinput bridgeless resonant ac–dc converter to achieve ac–dc conversion, step-up voltage and match optimal impedance for a multichannel electromagnetic energy harvesting system. Alternating voltage of each generator is stepped up through the switching LC network and then rectified by a freewheeling diode. Its resonant operation enhances efficiency and enables miniaturization through high frequency switching. The optimal electrical impedance can be adjusted through resonance impedance matching and pulse-frequency-modulation control. A 5 cm × 3 cm, six-input standalone prototype is fabricated to address power conditioning for a six-channel wind panel. [ABSTRACT FROM PUBLISHER]

In this paper, a simple method of tracking the maximum power (MP) available in the wind energy conversion system (WECS) for dc microgrid application is proposed. A three-phase diode bridge rectifier along with a dc–dc converter has been employed between the terminals of a wind-driven induction generator and dc microgrid. Induction generator is being operated in self-excited mode with excitation capacitor at stator. The output current of the dc–dc converter, i.e., dc-grid current is considered as a control variable to track the MP in the proposed WECS. Thus, the proposed algorithm for maximum power point tracking (MPPT) is independent of the machine and wind-turbine parameters. This algorithm has been implemented using dsPIC30F4011 controller. Furthermore, a method has been developed for determining the duty ratio of the dc–dc converter for operating the proposed system in MPPT condition using wind-turbine characteristics, steady-state equivalent circuit of a induction generator, and power balance in power converters. Circuit simplicity and simple control algorithm are the major advantages of the proposed configuration for supplying power to the dc microgrid from the proposed small-scale WECS. The successful working of the proposed algorithm for MPPT has been demonstrated with extensive experimental results along with the simulated values. [ABSTRACT FROM PUBLISHER]

A digital predictive peak current control (PPCC) employing the adaptive slope compensation is proposed in this paper. The PPCC precisely predicts the peak current reference with the adaptive slope compensation according to operation regions and load conditions. Thereby, the PPCC can control the peak inductor current, and it significantly reduces the total harmonic distortion compared to that of the conventional digital average current control with duty ratio feed-forward which is widely used. In addition, parts of the PPCC are implemented by utilizing the internal high-resolution ramp generator and comparator of a digital signal processor without external components. The principle and analysis of the PPCC are presented, and the performance and feasibility are verified by experimental results with universal input (90\; Vrms \sim 260\; Vrms ) and 750\; W-400\; V output laboratory prototype. [ABSTRACT FROM AUTHOR]

Series hybrid electric vehicles improvements in fuel consumption and emissions directly depend on the operating point of the auxiliary power unit (APU). A new APU operating point optimization approach based on dynamic combined cost map (DCM) and particle swarm optimization (PSO) is presented in this paper. The influence of coolant temperature, catalyst temperature, and air/fuel (A/F) ratio on fuel consumption characteristics and HC, CO, NOx emission characteristics are quantitatively analyzed first. Then, the DCM is derived by combining the individual cost maps with predefined weighting factors, so as to balance the potentially conflicting goals of fuel consumption and emissions reduction in the choice of operating point. The PSO is utilized to search the optimum APU operating point in the DCM. Finally, bench experiments under three typical driving cycles show that, compared with the results of the traditional static steady-state fuel consumption map-based APU operating point optimization approach, the proposed DCM and PSO-based approach shows significant improvements in emission performance, at the expense of a slight drop in fuel efficiency. [ABSTRACT FROM AUTHOR]

For the LCL-Filtered single-stage photovoltaic (PV) generators, the low-frequency power oscillation (<50 Hz) occurs frequently when they are connected to the weak grid, whose oscillation mechanism has been a hot topic recently. However, the existing stability analysis methods rarely take the complete model of the PV generators into consideration, thus the accuracy and completeness of the corresponding conclusions are influenced. In this paper, a novel stability analysis method is proposed to obtain the more accurate and complete results for the LCL-Filtered single-stage PV generators. First, the complete model of the PV generators is established including the perturbation and observation (P&O) based PV power loop and dc voltage loop, which are rarely considered by the existing stability analysis methods. Especially, the P&O based PV power loop is nonlinear and discontinuous, and the conventional small-signal modeling is inapplicable. Hence, its influence is completely ignored in the existing stability analysis methods. Second, considering the nonlinear discontinuous link, the describing function method is adopted to analyze the whole system stability based on the established complete model. In this way, the accuracy and completeness of the stability analysis are enhanced. Furthermore, for the critically stable state, both the oscillation amplitude and frequency can be calculated accurately. At the same time, different influence factors are analyzed quantitatively including the operation points, grid strength, and the interaction of multiple control loops. It is first revealed that the grid impedance has different influence on the system high-frequency and low-frequency stability. Also, the proposed analysis method and the conventional method are compared, which presents the advantages of the proposed analysis method. Finally, all the theoretical analyses are verified by the real-time hardware-in-loop tests. [ABSTRACT FROM AUTHOR]

The interest in distributed generators (DGs), especially those associated with renewable energies, has increased in recent years. The number of functionalities that their commonly associated voltage source inverters (VSIs) can deal with is rising, harmonic currents compensation being one of them. VSI control is in charge of accomplishing the different capabilities, and it must be done without exceeding the limited and variable dc voltage margin, if undesirable effects want to be avoided. If limitations are reached, capabilities will be reduced in order to remain within the limitations. At the same time, as the number of DGs is also increasing, when capabilities are not able to be coped with exclusively one VSI, the cooperation among VSIs appears as a solution. A key point is to establish a strategy in this kind of topology when one of the VSI is brought to its limits. In this paper, a new strategy is proposed, where even under limited situation VSIs always try to inject the maximum power extracted from the DG and achieve the harmonic compensation (multifrequency) by cooperation among the different parallel VSIs. Newest multifrequency saturation strategies are studied, modified, and applied to cooperative applications. Simulations, hardware in the loop (HiL), and experimental results are included and compared. [ABSTRACT FROM AUTHOR]

In this paper, a coupled-inductor-based LCC resonant converter with the primary-parallel–secondary-series (PPSS) configuration is proposed to achieve output-voltage sharing ability for HV generator applications. The PPSS configuration of the LCC resonant converter with the voltage multipliers is introduced to achieve high output-voltage and increase the output-power level. However, the variations of the magnetizing inductance, leakage inductance, and winding capacitance of the HV transformer and voltage multiplier impact on the output-voltage sharing performance. Subsequently, the resonant inductors in the primary side of the conventional LCC resonant converters with the PPSS configuration are coupled to achieve the output-voltage sharing without any additional circuits and control efforts. Furthermore, an analytical equivalent circuit model considering the magnetizing inductor of the HV transformer is derived to analyze the output-voltage sharing ability. Moreover, the design method for the coupled inductors considering the output-voltage sharing performance affected by the leakage inductance of the coupled inductors is presented. Finally, the output-voltage sharing performance of the proposed coupled-inductor-based LCC resonant converter with the PPSS configuration is validated by the experimental results of a 50-V input, 5-kV output 100-W prototype. The prototype experimental results show that the unbalance voltage degree decreases from 67.7% to 8.5% with the utilization of the coupled inductor. [ABSTRACT FROM AUTHOR]

This paper introduces a maximum power point tracking (MPPT) method based on a power (P) versus static conductance (G) curve of a photovoltaic (PV) array. The maximum power point (MPP) is tracked by comparing the PV array instantaneous power to a varying power reference generated by the MPPT algorithm. The comparison error is used to reduce or increase the conductance at which the PV array is forced to operate until the MPP is reached. Simultaneously, the error is used to change the power reference until the trajectory of this reference in the P–G curve enters a limit cycle around the MPP. The P–G curve is derived from a piecewise linear approximation of the current versus voltage (I–V) curve, which facilitates the analytical description of the tracking operation. The technique reported can also be implemented by means of simple analog or digital circuitry and requires two sensors to measure the instantaneous PV array current and voltage. It uses only four tuning parameters, which are selected depending on the maximum value of the derivative of the power with respect to the conductance. The theoretical predictions are verified with simulations and experimental results. The latter shows that the procedure performs well enough to be favorably compared with the most efficient MPPT methods. [ABSTRACT FROM AUTHOR]