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SiC-based diodes and mosfets switch extremely quickly with low conduction losses. Thus, from the perspective of efficiency, such devices are ideal for a continuous conduction mode (CCM) boost power factor correction (PFC) converter. However, the circuit parasitic becomes alive while switching with high $dv/dt$ and $di/dt$ values, which necessitates the need for electromagnetic compatibility (EMC) compliance measurements. Employing the best available low-loss SiC mosfet and SiC diode, in this paper, a 1-kW PFC boost converter prototype was designed, developed, and evaluated with the objective of quantifying the efficiency and EMC signature. The efficiency is evaluated through two approaches, namely, a circuit simulation and a laboratory measurement. With the first approach, the switching losses are obtained using a widely accepted double-pulse test methodology, and the conduction losses are taken from the data sheet, whereas with the second approach, the current and voltage are recorded at the input and output of the PFC converter using power analyzer. The electromagnetic interference (EMI) is monitored using line impedance stabilizing network and EMC analyzer. To maximize the efficiency, a fast, clean switching of the silicon carbide (SiC) is necessary. Utilizing a low-parasitic printed circuit board design approach and switching the selected low-loss SiC devices with a 0  $\Omega$ external gate drive resistance, this PFC boost yields a peak efficiency of 97.2% at full-rated power when switched at 250 kHz. Furthermore, the EMI noise was measured at 66 and 250 kHz. It was found that the same EMI filter size satisfies the CISPR 11 Class B conducted EMI limit at both switching frequencies with a noise of approximately 10 dB higher at 250 kHz. As the main contribution of this paper, the best case efficiency and worst case EMI are evaluated in this paper. [ABSTRACT FROM AUTHOR]

The series bridge converter (SBC) is a modular multilevel converter (MMC) recently developed to enhance power density in high-voltage high-power applications. The MMC is a well-established solution, widely researched, and exploited in practical HVdc connections, thanks to its high power quality and high efficiency. However, the main limitation of the MMC is the relatively large energy storage, also due to the fact that power ripples in the submodule capacitors include a component at the fundamental ac frequency. As a result, volume becomes critical in applications such as offshore or city center in-feeds, where space is restricted and expensive. The SBC offers a more compact footprint by exploiting a series connection on the dc side and by operating the submodules with rectified waveforms, thus moving the minimum component of the instantaneous power to twice the ac fundamental and reducing capacitors size. The drawback of the converter is a more complex energy control compared to the MMC. This paper proposes the first experimental validation of the SBC, using a 2-kW laboratory-scale prototype. Since the basic converter design has been discussed in previous papers, the focus of this paper is on converter control design and experimental validation. [ABSTRACT FROM AUTHOR]

This paper proposes a novel technique using fuzzy logic controller (FLC) in circulating mode to improve the performance of the International Thermonuclear Experimental Reactor (ITER) poloidal field (PF) converter systems. The accurate mathematical modeling of the complex system is challenging using conventional proportional integral and derivative (PID) controller. The novel approach using FLC overcomes the complexity of the modeling by human expert’s knowledge and experience. The FLC is considered for ITER PF converter system and compared with a conventional PI controller. The dynamic behavior and transient response of the PF converter system in the circulating mode are verified by analysis and simulation. The analysis results determine that the FLC can achieve better operation performance. [ABSTRACT FROM AUTHOR]

The term Virtual Synchronous Machine (VSM) commonly refers to the emulation of synchronous machines operation by using power electronics converters. However, a wider application of this control technique is still pending on further refinement of its design aspects and digital implementation. In this paper, a systematic approach to design the VSM parameters is introduced. First, a simplified third-order small-signal model of a VSM based on the conventional model of synchronous generators is developed. Unlike the existing works published in literature, the proposed model takes into account the effects of inductive and resistive weak grids. The model is then used to design the controller parameters by appropriately placing the poles of the closed-loop system. VSM robustness is studied for weak grids dominated by either inductance or resistance, and the aspects of digital control implementation are addressed. All the control system features and improvements were tested on a 15 kW prototype of a battery-supported VSM connected to a weak grid. [ABSTRACT FROM AUTHOR]

In this paper, the active differential-mode (DM) electromagnetic interference (EMI) filter topology for ac/dc converters is first briefly investigated. The active DM EMI filter model was developed based on the models of filter components including a current transformer, a high-pass filter, an operational amplifier, and a class AB amplifier. The system model including the active filter, ac/dc converter, and line impedance stabilization networks (LISNs) are explored. With the developed system model, the loop gain and insertion gain of the active filter are derived. Based on the loop gain, the stability of the active filter is investigated and the compensation is applied to achieve stability and good EMI reduction. Both simulations and experiments are conducted to validate the developed technique. [ABSTRACT FROM AUTHOR]

This paper proposes a single-stage three-phase-to-single-phase current-fed high step-up ac–dc matrix converter. The proposed converter inserts a boost-type matrix converter, which is formed by three boost inductors and six bidirectional switches, between a three-phase ac source and a Cockcroft–Walton voltage multiplier (CWVM). By using this topology associated with power factor correction technique, the proposed converter not only achieves almost unity power factor and sinusoidal input currents with low distortion but also obtains high voltage gain at the output end. Moreover, the matrix converter generates an adjustable-frequency and adjustable-amplitude current, which injects into the CWVM to regulate the dc output voltage and smooth its ripple. With this flexible injection current, the performance of the proposed converter is superior to the conventional CWVM, which is usually energized by a single-phase ac source. The operation principle, control strategy, and design considerations of the proposed converter are detailed in this paper. Finally, simulation and experimental results demonstrate the claims and validity of the proposed converter. [ABSTRACT FROM PUBLISHER]

The introduction of communication systems to power system controllers has brought in another layer of complexity in their design and operation. In this paper, a plug-in hybrid electric vehicle charging facility is studied. A linearized model of the facility is built, including both the dc/dc and dc/ac converters of the distributed energy resources. In addition, a control strategy that includes both local and networked loops is proposed to monitor and control the dc bus voltage of a local energy storage unit. This dc bus voltage is crucial to the self-sustaining capabilities of the system. A review of challenges and opportunities in networked control systems is presented, and the impacts of communication factors to the charging facility stability are analyzed. Finally, a real-time simulation platform which combines both electrical and communication networks is presented to validate the small-signal model, control strategy, and stability analysis including the communication effects. [ABSTRACT FROM PUBLISHER]

This paper proposes a single-stage single-switch light-emitting diode (LED) driver that integrates a buck–boost circuit with a Class-E resonant converter by sharing single-switch device. The buck–boost circuit, working as a power-factor correction (PFC) stage, operates in the discontinuous conduction mode (DCM) to shape the input current. The Class-E converter steps down the voltage to drive the LED. For specific component parameters, the Class-E converter can achieve soft-switching on the power switch and two rectifier diodes, and reduce switch losses at high frequencies. Electrolytic capacitors are used in the proposed converter to achieve a lower cost, but the system reliability decreases. To overcome this disadvantage, film capacitors can be used, but the current ripple increases. Neglecting the cost, multilayered film capacitors are the best option, if higher reliability and lower current ripple are required. The proposed driver features high efficiency (90.8%), and a high power factor (PF) (0.995). In this paper, analytical results and design considerations at 100 kHz are presented, and a 100-W prototype with 110 \textV\text{AC} input was built to validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

Multilevel power electronic topologies are being proposed in the recent technical literature for use in power generating units, especially when the reduction in the power filter overall dimensions and the lowering of current and voltage waveform ripple and total harmonic distortion are considered of primary importance. This is the case of high-speed gen-set units, where recent design techniques on high rotational speed permanent-magnet synchronous generators (PMSGs) have significantly reduced the inductance even for industrial voltage rated applications. This paper deals with a five-level unidirectional T-rectifier (5L T-RECT); the proposed topology is theoretically investigated, and simulation results and losses analysis are achieved with reference to an insulated-gate bipolar transistor (IGBT) phase-leg module which has been manufactured on purpose and tested. [ABSTRACT FROM AUTHOR]

The International Thermonuclear Experimental Reactor (ITER) poloidal field (PF) ac/dc converter operates in four quadrants to provide the control of current necessary to PF coils for plasma initialization and the plasma shape control. The technical details for thyristor triggering of high-power ac/dc converter lay the foundation for the regular operation of ITER PF ac/dc converter. With the characteristics such as high power, complex operating modes of ac/dc converter, the synchronization, reliability, and high security have to be critically concerned in the pulse distributor design. In this paper, a pulse distributor is designed to convert the optical signal to high current electrical trigger pulse with less than 1- $\mu \text{s}$ rising time, thereby triggering the paralleled thyristors reliably and isolating 20-kV voltage from the converter unit to controller. Furthermore, the signals of crucial status are online acquired and encoded, then transmitted to controller by optical fiber, thus implementing the online status diagnosis to guarantee the safety operation of ITER PF ac/dc converter. The pulse distributor has been experimented in ITER PF ac/dc converter and all functions have been effectively verified. [ABSTRACT FROM AUTHOR]

JT-60SA is a superconducting tokamak in the framework of the broader approach agreement between Europe and Japan. For this international project among its various procurements, the Italian National Agency for new technology energy and sustainable economic development (ENEA) is providing four ac/dc converters for the central solenoid (CS) superconducting magnets, two ac/dc converters for the equilibrium field (EF) superconducting magnets, and two ac/dc converters for the fast plasma position control coils (FPPCC). Furthermore, ENEA is also providing six converter transformers of which four are of the dry type for FPPCC power supplies (PSs) and two of oil type for CS PSs. CS/EF PSs feed poloidal superconducting magnets of JT-60SA, whose purpose is the generation of strong magnetic fields able to induce and confine the plasma current in a prefixed geometrical configuration. The control system of CS/EF PSs has to be able to reproduce in real-time a reference current or voltage profile, known as “scenario” and these are particularly critical in these systems for the high currents required and for the high magnetic energy stored in the superconducting magnets. All performed type tests, carried out in accordance to the IEC60146 Standards, pointed toward a good dynamic behavior of the control system both for forward and for reverse rectifier bridges, assuring the smooth transitions between different operating modes: single mode, circulating current mode and dual mode. This is the focus of this paper. [ABSTRACT FROM AUTHOR]

Conventionally, a proportional-integral (PI)-based dual-loop control strategy, in which both the dc-bus voltage and the inductor current are regulated, is utilized to control ac/dc converters with power factor correction (PFC). Due to the characteristics of the PI controller, converters experience poor control performance such as current distortion and slow dynamic response. This paper proposes a novel cascaded proportional control in conjunction with algebraic estimation method for PFC ac/dc converters. Different from the conventional control system, the average dc-bus energy and the instantaneous input power of the converter are regulated. Moreover, system nonlinearity, load power and uncertainties are estimated by incorporating algebraic estimators. A holistic design of controller parameters and stability analysis are presented based on the z-domain transfer functions. A 1 kW PFC ac/dc prototype is designed and experimental results demonstrate the effectiveness of the proposed control scheme. [ABSTRACT FROM AUTHOR]

Power factor correction (PFC) converter suffers from serious double-line-frequency output voltage ripple due to the difference between instantaneous ac input power and dc output power. To suppress such double-line-frequency output voltage ripple, a ripple cancellation circuit (RCC) is utilized to generate the same magnitude but 180° phase shifted double-line- frequency voltage ripple. This paper provides an insight into the relationship between control scheme and double-line-frequency ripple suppression from the perspective of audio susceptibility model. For the purpose of reducing the double line frequency ripple, the closed-loop audio susceptibility of series RCC should be designed relatively low at double line frequency. According to such requirement, a ripple controller with improved voltage feed-forward (FF) scheme and quasi-proportional-resonant (QPR) compensator is designed. As QPR compensator can increase the denominator of the closed-loop audio susceptibility, while voltage FF scheme can reduce its numerator, its magnitude at double line frequency is thus greatly reduced and double-line-frequency ripple is also significantly suppressed. Moreover, due to the flexibility of QPR compensator, the proposed ripple controller presents good ripple suppression in a different line frequency application. Finally, experimental results of a flyback PFC with buck-type RCC quasi-single-stage ac–dc converter are provided to verify the validity of the proposed ripple controller. [ABSTRACT FROM AUTHOR]

LED lamps are both potential victims and sources of electromagnetic disturbances in the frequency range between 2 and 150 kHz (“supraharmonics”). Immunity tests for this frequency range are important due to possible performance degradation of light intensity with LED lamps. In this paper, the impact of supraharmonics (SHs) on light intensity from LED lamps has been analyzed. LED lamps have been exposed to SH test profiles based on IEC 61000-4-19. Three phenomena that impact light intensity metrics have been observed and explained by models: 1) earlier conduction/later blocking caused by SH voltage, 2) intermittent conduction depending on the SH impedance of the LED driver, and 3) reverse-recovery current of the diodes at higher frequency. It is observed that impact on the light intensity metrics shows up around the beginning and end of the conduction period. The results reveal that the profile of the SH voltage could cause deviations in the modulation depth and the average light intensity. The immunity of LED lamps against SHs shall be further studied and discussed by research groups and standard committees. [ABSTRACT FROM AUTHOR]

This paper presents a reduced-stage three-phase isolated AC/DC converter topology used for auxiliary power units (APUs) in avionics and electric vehicle (EV) applications. Traditional two-stage cascaded AC/DC converters are widely used for these applications due to their ease of implementation and simple control schemes. With the objective of improving the power density of the APUs, the proposed converter achieves reduction in the number of active power devices along with a smaller DC link capacitance by implementing an unconventional structure with a bandpass filter, to allow only the required frequency components to transfer the rated power. To accurately characterize the proposed converter, a detailed formulation of the filter design for the circuit along with mathematical derivation of the control scheme is presented. In terms of achieving enhancement in the overall efficiency, a comparative study is presented that focusses on the conduction and switching losses incurred in the proposed topology as compared to the state of the art (SOA) two-stage AC/DC conversion topologies. The analyses portray efficiency improvement of 0.8% for a 6 kW rated load, with significant reduction in active device losses. Additionally, to support the formulations and derivations, simulation studies and experimental verifications are also presented. The results show an input power factor of 0.9918 (lagging) with a conversion efficiency of 97.6%, a tightly regulated output voltage with less than 1% peak-peak ripple and the input current total harmonic distortion (THD) of as low as 1.57%. [ABSTRACT FROM AUTHOR]

The load-commutated inverter (LCI)-based synchronous motor (SM) drive that is fed by a 12-pulse ac–dc converter results in harmonics mitigation. These drives have a further improved power quality at the ac mains if an appropriate passive filter is used at the ac mains for power factor (PF) correction and harmonics reduction. This paper deals with a simplified optimization algorithm based on a particle swarm optimization method for the selection of passive filter components. This algorithm is used to design passive filters for three types of loads on an LCI–SM drive, i.e., constant-torque–variable-speed loads, constant-speed–variable-torque loads, and variable-speed–variable-torque loads, to meet the requirements of a wide range of applications. The obtained results show reduction in the total harmonic distortion in the current and voltage at ac mains, reduced supply current, and improved PF. [ABSTRACT FROM AUTHOR]

This paper discusses a new circuit configuration and a new control method for a single-phase ac–dc converter with power factor (P.F.) correction and a power pulsation decoupling function. The proposed converter can achieve low total harmonic distortion (THD) on the input current and the power pulsation decoupling function between the input and output sides, which allows low output voltage ripple even on a small output energy buffer at the same time using an active buffer. Therefore, the proposed converter does not require large smoothing capacitors or large smoothing inductors. The buffering energy is stored by a small capacitor, which controls the variation of the capacitor voltage through the active buffer. In this paper, the fundamental operations of the proposed converter are investigated experimentally. The experimental results reveal that the input current THD is 1.44%, the rate of the output voltage ripple is 6.33%, and the input P.F. is over 99%. In addition, a maximum efficiency of over 96% is obtained for a 750-W prototype converter. [ABSTRACT FROM PUBLISHER]

This paper demonstrates the stabilization of large power systems using voltage-source-converter-based high voltage direct current (HVDC) links. Based on global power system measurements, a model predictive control (MPC) scheme manipulates the power injections of the HVDC links to damp oscillations in the ac system. The grid controller explicitly accounts for constraints and the expected future behavior of the system. Different scenarios like the loss of production, the loss of consumption and changes to the grid topology are studied in the continental European Network of Transmission System Operators for Electricity (ENTSO-E) system. The simulations illustrate the performance enhancement obtained with a global MPC-based grid controller, compared to a local damping controller and HVDC links with constant reference values. [ABSTRACT FROM PUBLISHER]

Microgrids are unique in that they can combine unbalanced three-phase systems with other AC and DC network sections, which may include a range of renewable energy sources, energy storage elements, and controllable AC-DC converters. Existing unbalanced power flow techniques such as the Ladder Iterative Technique and the three-phase Newton-Raphson (NR) method can analyze microgrids in sections but lack a complete system representation. Hence, there is a need for a power flow algorithm that considers the complete system model and solves it. A novel \pi-model of a controllable AC-DC converter and a single set of power balance equations for modeling a grid comprising multiple three-phase AC and DC sections is proposed. The \pi-model of a controllable AC-DC converter enables its inclusion into the network bus admittance matrix (YBUS) along with three-phase AC and DC network sections. Verification of the \pi-model is also described in the paper. The results of power flow studies with three-phase balanced and unbalanced AC and DC network sections are presented. The outcome of the \pi-model verification study and power flow study show that the proposed \pi-model is consistent and accurate. While the proposed model was developed for microgrids, it is applicable for all power system analysis applications. [ABSTRACT FROM PUBLISHER]

Single-phase inverters and rectifiers require the use of an energy buffer to absorb twice-line-frequency power ripple. Historically, this challenge has been addressed by the use of large electrolytic capacitors. Lifetime constraints and the need for improved system performance have motivated designers to seek other capacitor technologies, such as ceramic and film, which are frequently used in conjunction with active filtering converters to reduce the capacitance required. Active filtering converters cycle the capacitor voltage over a wide voltage range while maintaining a constant dc bus voltage. This large-swing operation demands different capacitor qualities than most other filtering applications, and the data sheet parameters available for commercial capacitors may be ineffective or require special care for calculating characteristics, such as efficiency and energy storage capability. This work presents an experimental setup for evaluating capacitor performance under a large voltage swing along with detailed experimental results. Energy storage data for a number of capacitors in the 50–630 V range from several manufacturers are included. The approach and findings of this paper can serve as an aid to power electronics designers for the selection and evaluation of capacitors in energy buffering applications. [ABSTRACT FROM AUTHOR]

In this paper, the models of active differential mode electromagnetic interference input filters for ac–dc converters are first investigated. The models are developed for active filters with single feedback (FB) and single feedforward (FF) configurations, which include an active filter, passive filters, and the noise model for a converter. To increase the gain of the single active filter, the models for FB–FF, FF–FB, parallel FB, and series feedback (SFB) configurations are developed and investigated. Loop gains and insertion gains for all of these configurations are derived and compared. Stability has been analyzed based on the loop gains and a compensation technique is introduced to ensure stability. Based on the comparison among all these control configurations, it has been found that the SFB configuration can achieve the highest noise reduction. The loop gains and insertion gains of an active filter prototype with the SFB configuration are measured using a network analyzer to validate the developed model and compensation technique. Finally, spectrum measurements with a commercial boost power factor correction ac–dc converter have been conducted to verify the developed modeling and control techniques as well as the predicted performance for the SFB configuration. [ABSTRACT FROM AUTHOR]

The forced commutated controlled series capacitor (FCSC) rectifier has been recently proposed to power stand-alone variable-voltage variable-frequency generation systems, such as the full authority digital electronic control (FADEC) system, in more electric aircraft. The employment of this rectifier helps to meet increasing power demand requirements while maintaining low current harmonic levels without the need for bulky filters. The FCSC rectifier is controlled to maintain resonance with line frequency variation by inserting variable capacitive reactance in series with the variable-frequency generator's inductive reactance. Unity power factor operation with nearly pure sinusoidal converter input currents is thus achieved, for better utilization of the generator. The FCSC rectifier operation with a variable dc on-board load is analyzed in this paper, including a description of the principle modes of operation of the circuit. The enhancement in circuit's output voltage and output power achieved by replacing the conventional diode bridge rectifier with the FCSC rectifier is also demonstrated. Both rectifiers are analyzed numerically using Saber/Synopsys over a wide range of operating voltages and frequencies. Results are experimentally verified using 1-kW laboratory test rig. [ABSTRACT FROM AUTHOR]

When fast voltage control is used in a power factor control, the ripple of the dc link causes current harmonics. This paper proposes a method to reduce the harmonic content of a fast voltage loop in a power factor correction, which can both produce low distortion during steady-state operation and fast recovery from a load transient. The performance is achieved by using a Takagi–Sugeno-type nonlinear controller for dc-link voltage control. The proposed nonlinear control is compared with linear proportional–integral (PI) control, which is tuned to meet the standardized regulations for the harmonic content in a 3-kW single phase power supply. The results show that the presented nonlinear voltage controller can maintain the dynamic performance of the linear control with reduced current harmonics. It is also shown that the used nonlinear control method requires only marginally more complex control algorithm compared to commonly used linear PI control. [ABSTRACT FROM AUTHOR]

Novel single-phase ac–dc converters based on dual-voltage-rectifier (DV-rectifier) and voltage-sigma architecture is proposed in this paper. Dual dc-buses, i.e., a constant dc voltage bus and an adjustable dc voltage bus, are provided by the DV-rectifier. Voltages of the two dc-buses are stacked together on the output port through down-stream dc–dc transformers (DCXs). The dc output voltage is controlled by regulating the voltage of the adjustable dc-bus of the DV-rectifier. Therefore, voltage regulation is not required for the DCXs, which can always operate at their optimized operation point to ensure high efficiency. Since the voltage of the adjustable dc-bus is lower than the constant dc-bus, multi voltage-level characteristics can be obtained with the DV-rectifier, which is benefit for reduction of switching losses and improvement of conversion efficiency. In order to achieve current regulation of ac input port and voltage regulation of the two dc-buses simultaneously, multimode operation, and smooth mode transition strategies are proposed for the DV-rectifier. Operation principles, control strategies, and characteristics of the DV-rectifier and DCX-based ac–dc converter are analyzed in detail. Feasibility and effectiveness of the proposed solutions are verified with experimental results. [ABSTRACT FROM AUTHOR]

With the development of distributed power generation sources and the widely used dc characterized loads, the dc nanogrid becomes more and more attractive and the converters with three terminal outputs are increasingly studied. Considering the costs, the efficiency, and also the safety, the grounding configuration needs to be addressed when designing the ac–dc converter for a dc nanogrid system. An ac–dc converter with three terminal outputs has been presented for the united grounding configuration based dc nanogrid. Nevertheless, for this type of converters, the output voltages are unbalanced in case of unequal dc loads. This paper proposes a novel buck–boost ac–dc converter with the capacity of output voltages self-balancing by using a coupled inductor. The operation of this converter will be presented in details through analyzing its equivalent circuits. The small signal model of the system in different working modes is given, and the whole system control diagram shows how to balance the dc output voltages. A 220 V/50 Hz/1.5 kW prototype has been developed. Experiments are carried out to verify the effectiveness of the coupled-inductor-based converter. [ABSTRACT FROM AUTHOR]

A two-stage electric vehicle (EV) battery charger typically consists of an ac–dc converter cascaded with a dc–dc converter. In such a cascaded system, maintaining stability at the intermediate dc link is imperative for reliable operation of the battery charger under different operating modes. This paper addresses the intermediate dc-link stability challenges that exist in a bidirectional two-stage grid connected single-phase battery charger. It is delineated that the small-signal load-dependent resistance of the ac–dc converter plays a crucial role in determining the stability of the bidirectional battery charger. A virtual-resistor-based active damping control strategy that does not require any additional sensors is explored for the ac–dc converter to stabilize the cascaded system under all operating modes irrespective of the power flow direction. Experimental results on a grid-connected single-phase battery charger hardware prototype are presented to validate the proposed models and showcase the improvement in the dc-link stability due to the virtual-resistance-based active damping approach. [ABSTRACT FROM AUTHOR]

DC microgrid systems with hybrid energy resources are of significant interest in shipboard and spacecraft applications. In such a system, coordinated operation of circuit breakers (CBs) and disconnecting switches (DSs) can rapidly isolate short-circuit faults and restore the system very fast. In this paper, we investigate a new protection scheme for a Multi-Bus dc systems based on an event classification approach. The proposed protection scheme transfers less data when compared with commonly used data-based protection methods and does not require high-speed communication and synchronization. The results show that the developed protection scheme is able to identify the type of fault accurately, isolate the faulted area, and restore the system very quickly while maintaining continuous power to the loads. [ABSTRACT FROM PUBLISHER]

Since noise degrades the control precision of International Thermonuclear Experimental Reactor (ITER) poloidal field (PF) ac/dc converter control system, a real-time wavelet filter algorithm for feedback signal denoising is studied. According to the requirements of ITER PF ac/dc converter controller, a real-time digital filter based on a wavelet transform is designed in this paper. The Daubechies wavelet is used as the wavelet basis and the mandatory denoising method is taken to remove the noise. In order to improve the boundary effects of wavelet transform when the width of sliding window and decomposition scale is quite small, the left and right symmetric boundary extension method is proposed. Three different boundary extension methods are compared, and the effectiveness of the proposed boundary extension method for denoising are described. The experiments are carried out on ITER PF ac/dc converter sequential control test platform to prove that the designed real-time wavelet filter eliminates the noise effectively and guarantees the real-time processing of feedback signal. [ABSTRACT FROM AUTHOR]

Parallel ac-link universal power converters are a relatively new class of power converters that can be configured as dc–dc, dc–ac, ac–dc, and ac–ac. These converters are extensions of a buck–boost converter in which the current of the inductor is alternating and the input and output can have any number of phases with any forms, voltage amplitude, or frequency. By placing a small capacitor in parallel with the link inductor, all the switches can benefit from soft switching. The main limitation of the parallel ac-link universal power converter is its large number of switches. A three-phase ac–ac configuration requires 24 unidirectional switches. This paper proposes two topologies based on the parallel ac-link universal power converters that significantly reduce the number of switches. One of the proposed topologies reduces the number of switches in a three-phase ac–ac configuration to 16. The other topology reduces the number of switches to 10. The latter can offer galvanic isolation with only a single-phase high-frequency transformer. This paper presents the principles of the operation of the proposed topologies and evaluates them through simulation and experiments. [ABSTRACT FROM AUTHOR]

This paper presents a unified power flow algorithm for large and complex mixed ac/dc power systems based on the partitioning of power grids, a version of the two-level Newton method, and the modified nodal analysis formulation. Partitioning significantly increases numerical efficiency without altering the accuracy of the power flow solution. This approach can be applied to any combination of multiple dc and possibly non-synchronized ac systems. It considers the steady-state interaction of ac and dc systems for a wide range of converter representations and control functions. Simplification of elements within the converter stations is not required. Both dc and ac-side converter losses are adequately accounted for by using a generalized converter loss model. The steady-state converter equations are derived in their most general form, with the ac and/or dc-side power exchange or voltages defined as controlled quantities. [ABSTRACT FROM AUTHOR]

A single-phase bridgeless Cuk ac/dc power factor correction (PFC) rectifier with positive output voltage is proposed in this paper. For low output voltage product applications, the rectifier is designed to convert high input voltage to low output voltage. Due to no bridge diodes required and thus decreased input conduction losses, the proposed rectifier efficiency can be improved. The proposed rectifier operates in discontinuous conduction mode, and the current-loop circuit is hence not needed. In addition, only a single switch is used in the rectifier to simplify the control circuit design. A simple translation method to have the positive output voltage in the Cuk converter is presented in the rectifier to reduce the component counts and the cost. The operational principles, steady-state analysis, and design procedure of the proposed rectifier are addressed in detail in this paper. Simulation and experimental results obtained from a 150-W rated prototype circuit with input of 90–130 Vrms, 60 Hz, and output of 48 Vdc have verified the validity of the proposed rectifier. [ABSTRACT FROM PUBLISHER]

In this paper, a straightforward plug-and-play voltage ripple mitigator (RM) is proposed. Unlike existing voltage ripple reduction methods, the proposed device can be attached to the dc link of a hybrid ac–dc power system without modifying the host system itself. In particular, a local bus-voltage control scheme is employed to achieve the plug-and-play operation. With the requirement of the dc-link voltage measurement only, this device can be operated as a standalone module. Theoretical analysis and experimental work on a boost-type power factor correction rectification system have been successfully performed to validate the effectiveness of the ripple-mitigating function, the hot-swap operation and the nonintrusive property of the RM. Practical results obtained from a 110-W miniature hybrid ac–dc power system comprising an ac/dc converter and two resistive loads are included to demonstrate some of the functions of the RM. [ABSTRACT FROM PUBLISHER]

The switching pulses of the wavelet modulation technique are generated as sets of dilated and shifted scale-based linearly combined synthesis wavelet functions. The duration and location of each switching pulse are set by the scale (resolution level) at which its associated synthesis wavelet function is generated. In this paper, a novel controller is developed and tested for three phase (3\phi) voltage source (VS) six-pulse wavelet-modulated ac–dc converters. The proposed controller is structured to adjust the maximum value reached by the scale. This maximum value, J, is adjusted based on two angles. The first angle, \thetaI, maps changes in the 3\phi supply voltages to adjustments in J, while the second angle, \thetaO, maps changes in the dc output voltage to adjustments in J. The net adjustment in J is optimized based on the mapped changes by \thetaI and \thetaO. The optimal resolution-level controller is implemented in order to evaluate its performances for operating 3\phi VS six-pulse ac–dc converters. The performances of the proposed controller are tested when the converter is supplied with balanced, unbalanced, and distorted 3\phi voltages for feeding static and dynamic loads. Test results demonstrate fast and accurate responses, stable functioning, and good dynamics to ensure that the output dc voltage follows its command value for different supply and loading conditions. [ABSTRACT FROM PUBLISHER]

This paper explains the working principles, supported by simulation results, of a new converter topology intended for HVDC applications, called the alternate arm converter (AAC). It is a hybrid between the modular multilevel converter, because of the presence of H-bridge cells, and the two-level converter, in the form of director switches in each arm. This converter is able to generate a multilevel ac voltage and since its stacks of cells consist of H-bridge cells instead of half-bridge cells, they are able to generate higher ac voltage than the dc terminal voltage. This allows the AAC to operate at an optimal point, called the “sweet spot,” where the ac and dc energy flows equal. The director switches in the AAC are responsible for alternating the conduction period of each arm, leading to a significant reduction in the number of cells in the stacks. Furthermore, the AAC can keep control of the current in the phase reactor even in case of a dc-side fault and support the ac grid, through a STATCOM mode. Simulation results and loss calculations are presented in this paper in order to support the claimed features of the AAC. [ABSTRACT FROM PUBLISHER]

A new interleaved single-stage ac–dc converter is proposed in this paper to reduce line current harmonics while achieving power factor correction (PFC). The proposed rectifier can produce input currents that do not have deadband regions with high PFC, operate with a continuous output current, and minimize the input electromagnetic interference filter size. In this paper, the operation of the new converter is explained, its features and design are discussed in results, and its operation is confirmed with experimental results obtained from a prototype. [ABSTRACT FROM AUTHOR]

In this paper, the electrical safety of dc urban traction systems is analyzed, with particular focus on fault current detection and on dangerous voltages which could arise in case of fault. For the discussion, the tram network of Turin, Italy, is used as a case study. First, the structure of the dc traction power supply is described, analyzing in detail the different components; then, the safety of the system is analyzed, examining possible types of fault. In particular, ground faults inside the substation and ground faults along the line are analyzed in detail. Fault currents and dangerous voltages are calculated, thanks to a simplified steady-state circuital model of the traction system. Finally, the consequent risks for the people are examined and some conclusions and possible solutions are presented. [ABSTRACT FROM AUTHOR]

Due to the widely used dc characterized loads and more distributed power generation sources, the dc nanogrid becomes more and more popular, and it is seen as an alternative to the ac grid. For safety considerations, the dc nanogrid should provide reliable grounding for the residential loads such as the low-voltage ac power system. There are three typical grounding configurations for a dc nanogrid: the united grounding, the unidirectional grounding, and the virtual isolated grounding. Each grounding configuration has its own specifications to ac/dc converters. In this paper, a dual-buck–boost ac/dc converter for use in the united-grounding-configuration-based dc nanogrid with three terminal outputs is proposed. The working principle of this converter is presented in detail through analyzing the equivalent circuits. Experiments are carried out to verify the theoretical analysis. [ABSTRACT FROM PUBLISHER]

This paper presents new look-up table methods for a three-level ac/dc converter supplied from the grid. The nonlinear direct power control (DPC) method, by reason of its drawbacks resulting from the omission of grid inductance voltage drop, has been improved in the DPC-\updelta $5\times2$ method by rotating the orientation of coordinates by angle \updelta, i.e., the angle between grid voltage vector and set converter voltage vector. The other proposed development involves further improvement of the DPC-\updelta $5\times2$, into which a new optimal division of the current error plane is introduced. The new optimal voltage vector assignment allows us to choose a converter voltage vector using the modified error current vector. The proposed look-up table methods have been tested and compared applying the following criteria: current error, total harmonic distortion (THD) of input current, average transistor switching frequency, and response time on step changes of set current. The experimental results validate the proposed control schemes and show good system performances that were verified according to above criteria. [ABSTRACT FROM AUTHOR]

The ITER pulsed power electrical network (PPEN) supplies the superconducting magnets and the heating and current drive systems. During the experimental pulses, about several hundreds of seconds long, active power consumption of 500 MW and reactive one of 950 Mvar are expected. The ITER power supply system is very large and complex, and a careful design is required to assure a safe operation. Stability of ITER PPEN has been already investigated in recent studies by numerical simulation and analytical methods. Now, a new dynamic analytical model of the ITER power supply system is being developed, based on the state-space theoretical approach, which allows the application of the linear control theory to study the stability of the whole system. For each subsystem of the ITER power supply, a state-space model was developed, and in this paper, the ac/dc converter model is presented and validated for six and twelve pulse operation, and circulating current mode. [ABSTRACT FROM AUTHOR]

Zero-sequence blocking transformers (ZSBTs), used to block the zero-sequence components that are present in a three-phase system, are commonly built winding the three phases around the same core limb. They are difficult to construct, especially in high-power applications that use large cross-sectional cables, as they require a symmetrical winding distribution for not to produce any flux for positive- and negative-sequence components. This paper presents a novel ZSBT configuration using three single-phase transformers. Although slightly greater in size, they can be easily wound, even when thick cables are used. Moreover, the proposed topology can be used as a simulation model of any ZSBT configuration, where core losses and magnetic saturation of the core are included by connecting a single inductor to the secondary windings of the transformers. This paper provides full details of the circuit and is supported by simulation and experimental results of the proposed ZSBT. [ABSTRACT FROM AUTHOR]

An onboard charger is responsible for charging the battery pack in a plug-in hybrid electric vehicle (PHEV). In this paper, a 3.3-kW two-stage battery charger design is presented for a PHEV application. The objective of the design is to achieve high efficiency, which is critical to minimize the charger size, charging time, and the amount and cost of electricity drawn from the utility. The operation of the charger power converter configuration is provided in addition to a detailed design procedure. The mechanical packaging design and key experimental results are provided to verify the suitability of the proposed charger power architecture. [ABSTRACT FROM PUBLISHER]

This paper presents a current control scheme for a voltage-source converter connected to the grid through an LCL filter. The proposed current control is based on the linear quadratic (LQ) Gaussian (LQG) servo controller technique, which combines the LQ regulator and the Kalman filter (KF). The use of the KF instead of a Luenberger estimator improves the quality of the estimation of state variables in noisy environments, increasing the noise immunity of the control loop. This paper focuses on giving some criteria and practical hints to choose both the KF and LQ design parameters to achieve null steady-state tracking error, channel decoupling, and noise immunity. Furthermore, this paper analyzes the steady-state KF approximation that allows a significant decrement in the computational complexity of the algorithm at nearly no cost in accuracy. Simulation and experimental results prove the correct operation of the proposed LQG current control and the possible advantages of using KF to estimate the state vector. [ABSTRACT FROM PUBLISHER]

This paper deals with the design solution adopted for a high-speed axial-flux permanent-magnet generator devoted to supplementing power in automotive 42 V electrical systems through a low-voltage multilevel neutral-point-clamped converter. The axial-flux permanent-magnet generator is suitably designed to be directly coupled with a radial turbo-expander which provides recovery of kinetic energy available from the exhaust gases of an internal-combustion engine. The multilevel converter is properly sized for systems having low voltage and high first-order harmonic frequency. The paper describes the proposed 4-kW power rating generating system and discusses various issues resulting from electromagnetic, thermal, and mechanical design of the high-speed axial-flux permanent-magnet generator. As well, investigations on modulation strategy, total harmonic distortion, and power losses are presented for the low-voltage neutral-point-clamped power electronic converter. [ABSTRACT FROM PUBLISHER]

Renewable energy sources, such as offshore wind farms, require high voltage gains in order to interface with power transmission networks. These conversions are normally made using bulky, complex, and costly transformers and high-voltage ac–dc converters with unnecessary bidirectional power flow capability. Multiple modules of single-switch single-inductor dc–dc converters can reach high gains without transformers in these applications due to low semiconductor conduction loss in high-power devices. This paper describes a new approach for high-gain high-voltage dc–dc converters using multiple modules of single-switch single-inductor transformerless converters. Results for low-voltage experimental prototypes show gains of up to 29 p.u. and demonstrate the potential of the approach as high-gain dc–dc converters for offshore wind farms. This paper then demonstrates the viability of multiple-module converters compared to a conventional high-voltage dc converter and a theoretical full-bridge converter due to fewer devices and valves, comparable isolation levels, and ease of interleaving for increased reliability. [ABSTRACT FROM AUTHOR]

The dual active bridge (DAB) topology is frequently preferred in industry as a dc–dc converter with various current modulation methods, such as phase shift modulation (PSM), trapezoidal modulation (TZM), triangular modulation (TRM), and hybrid methods. The TZM and TZM–TRM hybrid methods can solve the current circulation problem of PSM, extend the zero voltage switching region to the full operating range, and thereby improve the light load efficiency. However, all these methods have been developed for a dc–dc converter, and cannot be directly applied to a single-stage DAB-based ac–dc converter due to the low input voltage close to the zero crossing points of the grid, otherwise significant distortion is created. This paper analyzes the line current distortion related with the modulation for a single-stage DAB-based ac–dc converter, and a novel hybrid current modulation (HCM) method that solves the distortion problem is proposed. However, since the HCM method increases the rms current as side effect, the improved version of the iHCM method is developed and the distortion-free current without increasing the rms current is obtained. The results obtained from the theoretical analysis are verified by an experimental prototype of 250 W. [ABSTRACT FROM AUTHOR]

Multilevel-cascaded H-bridge converters are promising candidates for next generation photovoltaic power converters. They feature reduced switching losses and higher conversion efficiency with modular structure; characteristics vital for large-scale photovoltaic power plants. However, the stochastically-variable nature of irradiance levels and ambient temperatures affects the normal operation of this topology, because power levels in the three phases can be unequal. The existing zero sequence injection method can deal with the power imbalance problem, but it is limited in its application. The paper proposes a zero sequence injection method to optimize the converter power balance, extending the converter operation with severe power imbalance. Based on the proposed optimal method, a simplified optimal zero sequence injection method requiring less calculation effort is derived and compared with the optimal method. Simulation and experimental results validate the effectiveness and feasibility of the proposed methods. [ABSTRACT FROM AUTHOR]

Multilevel cascaded H-bridge converters are promising candidates for large-scale photovoltaic power plants. They allow direct connection to medium-voltage distribution networks without the presence of bulky line frequency power transformers. Owing to the stochastically variable nature of irradiance level, ambient temperature, and other factors, power levels in the three phases are expected to be unequal. The power imbalance condition creates unexpected problems with this topology, which was initially designed to operate under balanced power conditions. To deal with this issue, the paper proposes three novel zero-sequence injection methods as an expansion to the conventional zero-sequence injection method. Results obtained from simulations and a 430-V 8-kW three-phase seven-level cascaded H-bridge prototype are presented to verify the effectiveness and feasibility of the proposed methods. [ABSTRACT FROM AUTHOR]

A cascaded H-bridge (CHB) converter is one of the viable options for next-generation large-scale photovoltaic (PV) power conversion. Owing to the increased number of components involved, converter reliability and fault-tolerant control are important issues. A CHB converter must also manage unequal power generation among bridges, which is inherent in PV applications because of unequal solar irradiance and/or module temperatures. This paper proposes a fault-tolerant strategy, which maintains balanced three-phase grid currents during faults with unequal power generation in healthy H-bridges. The effectiveness of the presented fault-tolerant control is verified using the results obtained from a 430-V 10-kW laboratory prototype. [ABSTRACT FROM PUBLISHER]