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The commutation failure (CF) is the most common fault in line-commutated high voltage direct current (LCC-HVDC) systems that may lead to the transient overvoltage in the sending-side system. In the worst condition, the CF may lead to large-scale wind turbine tripping. To resolve this problem, the mathematical relationship between the reactive power consumed by the rectifier and DC voltage, DC current is derived. Then, a transient overvoltage calculation method is proposed in this paper. Furthermore, the mechanism of transient overvoltage caused by the CF is analyzed; it is revealed that the reason for three times transient overvoltage is the rapid decrease of the reactive power consumed by the rectifier during the CF and the recovery period from the CF. This paper proposes a constant reactive power control (CRPC) to inhibit transient overvoltage of the sending-side AC system. The proposed CRPC can increase the reactive power consumed by the rectifier, reduce the exchange reactive power between AC and DC systems, and suppress the transient overvoltage. A simulation model in PSCAD serves to verify the proposed CRPC on the transient overvoltage suppression in the situation of different fault types, fault duration, fault severity and short circuit ratio (SCR). [ABSTRACT FROM AUTHOR]

This paper proposes a resonant switching cell model to analyze and design the single-ended resonant dc–dc converters. The single-ended zero-voltage switching (ZVS) converters such as the Class E converter are efficient for megahertz switching because they feature low turn-on and turn-off switching losses. Also, they use only a ground-referenced switch, allowing a simple gate drive circuit. In this paper, we investigate the single-ended resonant converter with the small input inductance, whereas the conventional Class E converter has a large input inductance. The main contribution of this paper is to propose the resonant switching cell as an analytic model that simplifies the analysis and the design of the resonant dc–dc converters. Furthermore, this paper presents the design method of the resonant switching cell model for minimizing the resonant current magnitude and conduction loss while the converter maintains ZVS property. The experimental results from a 10-MHz GaN-based prototype demonstrate the feasibility and effectiveness of the analysis and design based on the proposed resonant switching cell model. [ABSTRACT FROM AUTHOR]

The hybrid LCC/VSC cascaded HVDC (HC-HVDC) scheme, in which the LCC is adopted as rectifier, and one LCC in series with multiple paralleled VSC based MMCs is adopted as inverter, combines the advantages of both LCC and VSC-MMC technologies. Presently, a HC-HVDC project is planned to deliver the hydro power from Baihetan to Jiangsu in China. One of the major challenges is to suppress the DC overcurrent issue of VSC-MMCs especially under commutation failure condition of LCC at inverter side. Based on Baihetan-Jiangsu project under construction, the model of HC-HVDC system is developed in PSCAD/EMTDC. In the system, the rectifier employs a dual 12-pulse LCC, while the inverter adopts a hybrid scheme, i.e., one LCC converter in series with three paralleled VSC-MMC converters. This paper addresses the main cause and feature of the DC overcurrent, then proposes an overcurrent suppression control method for HC-HVDC system based on fuzzy clustering and identification approach. And the system transient performances with the proposed control approach are evaluated under AC fault conditions. The results show that the proposed approach can not only suppress the DC overcurrent following the commutation failure to a certain extent, but also improve the post-fault recovery performance of the overall system. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are widely used in street lighting, landscape lighting, liquid crystal display (LCD) backlighting, healthcare, etc. As an important part of LED lighting products, LED driver plays a vital role in maintenance costs reduction, energy saving and lifetime prolongation. In this paper, a single-stage LED driver is proposed, which is integrated by a totem-pole bridgeless power factor correction (PFC) unit and several modular LCL-T resonant rectifiers. The totem-pole bridgeless PFC unit and the LCL-T resonant rectifiers are integrated by sharing switches, which can simplify the circuit and reduce the system cost. The output current can be regulated by applying the variable inductor control. Constant duty cycle and fixed switching frequency operation can be achieved as well. The operating principle and the performance of the proposed converter are analyzed in this paper. In addition, a precise parameter design method is proposed by considering the high-order harmonics. At last, an experimental prototype is established to validate the proposed parameter design and variable inductor control method. [ABSTRACT FROM AUTHOR]

The main standard for avionic equipment DO-160G defines a set of tests that require compliance before the employment of a device in aircraft. An important test involves the generator voltage and consequential current distortion of the three-phase load in the variable 360–800 Hz frequency grid. The main purpose of this paper is to present and analyze a systematic design methodology for three-phase boost and buck rectifiers in order to meet with the voltage distortion test requirement. For a given voltage harmonic profile, the current harmonic limits that have to be satisfied are translated into equivalent per-harmonic admittances and a profile of maximum rectifier input admittance versus frequency is obtained. The defined profile, due to normalization, is applicable to arbitrary power level with simple shifting by the base admittance governed by the converter nominal power. It is shown that for boost-type rectifiers there is a tradeoff between current controller bandwidth and input inductor size, while for the buck-type rectifiers main limitation lies in the input LC filter design used for differential electromagnetic interference filtering. The experimental results conducted on an SiC three-phase 10 kW VIENNA rectifier are tightly backing up the proposed theoretical analysis. This paper is accompanied by three videos demonstrating experimental measurement of d-axis open-loop duty cycle to inductor current transfer function, loop-gain of d-axis current controller with 3.8 kHz bandwidth and variable grid frequency 360–800 Hz operation of the converter under 0% and 10% input three-phase voltage total harmonic distortion. [ABSTRACT FROM AUTHOR]

This paper deals with a multilevel ac–ac double conversion system that uses the intercell transformer (ICT) for applications which include generating systems and the interfacing of renewable energy sources with the utility grids. Each phase of the proposed configuration is formed through the ICT interleaving operation of two multilevel 5-level E-type legs to achieve the 3-phase 5-level back-to-back E-type converter (3Φ5L BTB E-type converter). The analytical procedure to select the inductance and capacitance values of both the input and output filters is described in the paper. Furthermore, the design and implementation of the input/output ICTs and inductors is discussed. The simulation and the experimental results on the 20-kVA interleaved 3Φ5L BTB E-type converter prototype are presented to validate the proposed analysis. [ABSTRACT FROM AUTHOR]

Hybrid high voltage direct current systems utilized for bulk-power transmission have recently attracted more attention. The overhead lines (OHLs) are mainly used for the implementation of such systems due to their outstanding economic advantages. However, OHLs are vulnerable to temporary faults, jeopardizing the safe and reliable operation of the network. The resiliency to the line faults is of considerable significance to the power transmission. This paper proposes a fault property identification strategy based on the Pearson correlation coefficient for the LCC-MMC hybrid HVDC system which can differentiate temporary and permanent faults. To achieve this, a voltage signal is injected into the faulty line by decreasing the firing angles of the LCC-based rectifier. Based on the established OHLs model and the injected signal, an estimated backward travelling wave can be accurately calculated. The fault property is identified by comparing the wave difference of the real backward travelling wave and the estimated backward travelling wave. The proposed strategy has a high accuracy since all influencing factors including the fault resistance, fault distance, and line parameters have been taken into account. Finally, to verify the efficacy of the proposed algorithm, several simulations have been performed using PSCAD/EMTDC. The simulation results show that the proposed algorithm can effectively distinguish the fault property. [ABSTRACT FROM AUTHOR]

The existing research on voltage-source converter HVDC (VSC-HVDC) system stability mostly focuses on small-signal stability analysis methods. However, when large-signal disturbances occur, the intrinsic nonlinearity of the VSC-HVDC system becomes inevitable so that the small-signal studies are no longer valid. In this paper, a large-signal stability analysis method of the VSC-HVDC system is proposed based on the estimation of domain of attraction (DOA). This method can not only analyze the asymptotic stability of the operating point, but also answer the question of how large deviations from the operating point can be tolerated by the system. By using Takagi-Sugeno (T-S) fuzzy model and Lyapunov stability theorem, the DOA of the VSC-HVDC System at the operating point is estimated, and the large-signal stability of VSC-HVDC System is analyzed. On this foundation, the influence of system parameters on the large-signal stability is studied. The results can be used to guide the adjustment of system parameters to solve the problem of system instability. The time-domain simulations conducted in Matlab/Simulink are used to test the stability of the system under large-signal disturbance in the range of DOA. The simulation results verify the feasibility and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Line-commutated converters are extensively used as the interface between ac grids and classic HVDC systems. At the inverter side, commutation failure of switches is one of the most common faults that can pose threats to the system operation. Practical and reliable study of such phenomena relies on accurate and efficient converter models for simulations. Recently, a parametric average-value model (PAVM) has been presented for ac–dc rectifiers, which considers the internal faults of the converter. In this paper, the PAVM methodology is extended to the dc–ac inverter systems, including the commutation failure of switches. The proposed PAVM also augments an automatic fault detection technique to determine the faulty switches. Using comprehensive simulation studies, the developed model is verified to accurately predict the commutation failure of switches and reconstruct the waveforms consistent with the detailed switching models of inverters while being computationally more efficient. The proposed PAVM is envisioned to be an efficient and accurate asset for simulation of HVDC systems and inevitable when faults of switches need to be considered. [ABSTRACT FROM AUTHOR]

Miniaturization and low cost contribute to the development and popularization of wireless power transfer (WPT). Reducing the number of power conversion stages can reduce the volume and cost of the WPT converter, and even make it possible to improve the efficiency. A single-stage WPT converter with constant current (CC) and constant voltage (CV) output and its asymmetric modulation method are proposed in this paper. A direct AC-AC converter is applied to the primary side of the WPT converter to directly convert line-frequency AC to high-frequency AC. The applied direct AC-AC converter that can replace the commonly used multi-stage primary converter reduces the number of circuit devices, thereby reducing the volume and cost of primary converter. The proposed WPT converter can realize zero voltage switching (ZVS) and power factor correction (PFC). In order to achieve CC and CV output, a switchable hybrid compensation topology is applied to the proposed WPT converter. A 720-W experimental prototype was manufactured to verify the rationality of the proposed WPT converter and the correctness of the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper describes the design strategy for a new Marx generator, based on SiC metal–oxide–semiconductor field-effect transistors (MOSFETs), proposed for Kicker magnet applications. As a starting point, the possible replacement of a thyratron tube associated with an existing kicker system, at CERN, is considered. The specifications of the output pulse are: 40-kV, 3.2-kA, 3- $\mu \text{s}$ flat top duration, 30-ns rise- and fall-time, and 1-Hz repetition rate. A theoretical study for a Marx generator topology, using 50 stages, each 800-V stage comprising 24 SiC MOSFETs in parallel, each MOSFET conducting approximately 140-A pulses is considered. In addition, a four-stage prototype has been evaluated, with almost full current and 3 kV, based on the proposed design, in order to assess the technological advantages of such a system and limitations for the scale up. First tests using parallel SiC MOSFETs are described and results discussed in light of the proposed topology and the physical structure of the assembly. [ABSTRACT FROM AUTHOR]

This paper proposes a novel comprehensive model of a rectifier-controlled induction motor drive for use in positive-sequence transient stability simulation (PSTSS) programs. The model is implemented to approximately capture the behavior of the point-on-wave drive model, and applied to investigate the dynamic performance of the advanced drive loads in system-level simulations. This positive-sequence drive model is systematically developed by reducing the detailed three-phase electrical and control representations into $dq$ axes positive-sequence formulations. For the positive-sequence model, the line-side rectifier is interfaced to the grid through a voltage source with separate $dq$ axes controls to regulate the active and reactive power of the drive. The machine-side inverter control system is represented based on rotor flux oriented control. The dc-link of the drive converter is implemented by employing the average model of the pulse width modulated converter, and is utilized to integrate the line-side rectifier and machine-side inverter. The proposed motor drive model is validated by comparing the performance with the electromagnetic transient point-on-wave drive model. The VAr support capability of the drive load model is investigated by incorporating the developed model into a composite load structure in PSTSS programs. Multiple units of the developed drive models are represented in large-scale transmission systems to examine the system-level responses of drive loads. [ABSTRACT FROM AUTHOR]

A compact and efficient design for the electromagnetic interference (EMI) filter stage has become one of the most critical challenges in designing a high-density power converter, particularly for avionic applications. To maintain the regulatory standard requirements, EMI filter design needs to be precisely implemented. However, the attenuation characteristics of common-mode (CM) and differential-mode (DM) EMI filters may vary in practice from their respective theoretical calculations due to difficulty and inaccuracy in the noise modeling. This is particularly true for a three-phase active boost rectifier, which inherently has a CM high-frequency component in the rectifier output. This paper puts forward a detailed mathematical modeling of CM noise, originated from different sources, and discusses a concept to significantly reduce the CM noise effects. Furthermore, minimizing the weight and size of DM filter stage has been a design concern as the DM stage consumes a significant part of the weight of the whole system. This paper proposes a compact EMI filter topology with enhanced power density, which aims at satisfying the conducted EMI requirements according to DO-160F in avionics applications. The experimental verifications of the designed EMI filter are performed from the conducted emission results, obtained from a 6-kW laboratory prototype of an integrated stage of EMI and three-phase boost PFC converter. [ABSTRACT FROM AUTHOR]

This paper proposes an input voltage sensorless control algorithm for three-phase active boost rectifiers. Using this approach, the input ac-phase voltages can be accurately estimated from the fluctuations of other measured state variables and preceding switching state information from converter dynamics. Furthermore, the proposed control strategy reduces the input current harmonics of an ac–dc three-phase boost power factor correction (PFC) converter by injecting an additional common-mode duty ratio term to the feedback controllers’ outputs. This additional duty compensation term cancels the unwanted input harmonics, caused by the floating potential between ac source neutral and dc link negative, without requiring any access to the neutral point. A 6-kW (continuous power)/10-kW (peak power) three-phase boost PFC prototype using SiC-based semiconductor switching devices is designed and developed to validate the proposed control algorithm. The experimental results show that an input power factor of 0.999 with a conversion efficiency of 98.3%, total harmonic distortion as low as 4%, and a tightly regulated dc-link voltage with 1% ripple can be achieved. [ABSTRACT FROM PUBLISHER]

In this paper, a dynamic model based on the sampled-data method is presented for a wireless power transfer (WPT) system. The orders of the derived model are equal to the orders of a system. The modeling is different from the existing dynamic modeling for WPT systems, which almost double the model's order. Furthermore, the systematic analysis process is suitable for any WPT topologies and without the higher harmonics neglected and low-frequency approximation. Meanwhile, the state variables are allowed to vary up to twice the switching frequency, since the half-period symmetry property is exploited. In this paper, the series–series (SS) compensated WPT system is chosen as an example and the large-signal model and the steady-state operation point are determined. The small-signal responses perturbed by the phase-shift angle, switching frequency, and input voltage are obtained. The derived model is more adequate with simulation and experimental validation. [ABSTRACT FROM AUTHOR]

The analysis of wind turbine output power measurements from the offshore wind farm Horns Rev 1 demonstrates a significant likelihood of wind turbine output powers to be very similar at a given time within offshore wind farms. This paper exploits this observation by proposing a new offshore wind farm configuration with DC collection system and series-connected wind turbines based on partial power processing converters (PPPCs) and diode-bridge rectifiers. In the proposed wind farm configuration, PPPCs are only required to process output power differences among wind turbines in a wind farm to achieve maximum power point (MPP) operation, yielding a potential for efficiency and sizing improvements. This paper addresses major design considerations at wind farm, wind turbine, and PPPC levels. System operation of the wind turbine design is derived, alongside with a matching control system and HVDC-link current scheduling algorithm. The proposed wind farm is successfully tested for low voltage ride through, power curtailment, inertia response, and communication system outage scenarios. Time-transient simulations of a 30-turbine series string using measured and artificial wind speed profiles demonstrate that wind turbines can achieve MPP operation while only a fraction of power needs to be processed by the PPPCs. [ABSTRACT FROM AUTHOR]

The dc cables of the voltage-sourced converter-based HVDC link, including the modular multilevel converter (MMC) configuration, must be protected by surge arresters against transient overvoltages. The selection of the appropriate surge arresters requires a comprehensive understanding of the phenomena that cause the overvoltages and accurate calculation of energy discharged in the arresters. This paper investigates the mechanism that causes transient overvoltages, due to dc-side line-to-ground faults, in a cable-connected MMC–HVDC link. This paper also evaluates the impacts of various system parameters, for example, the prefault power transfer level, the MMC arm inductance, the transformer leakage inductance, the fault location, the ac system short-circuit capacity, the cable inductance, and the MMC blocking delay, on the peak transient overvoltages and the amount of energy discharge in the cable surge arresters. The transient overvoltage studies are also conducted when the dc cable is replaced by an overhead line. The studies are performed in the PSCAD platform. The studies conclude that the prefault power transfer level and the MMC blocking delay have the most significant impacts on the surge arrester energy discharge under dc-side line-to-ground faults in the MMC–HVDC link. The study results also provide essential information for the design of the MMC–HVDC link components. [ABSTRACT FROM AUTHOR]

This paper presents real-time diagnosis for open-circuited (O-C) and unbalance faults in power electronic converters (PECs) connected to residential small wind systems grid-tied. The spectrum analysis along with the dc components of the voltage and current measurements available in the converter is utilized for the O-C fault detection, classification and localization of the power switching devices in the PEC, as well as the identification of the unbalance input voltage to the converter. The proposed methodologies in this paper require much fewer inputs compared to the previous researches; therefore, they avoid any additional sensors or hardware which include further costs and expenses on such systems. The experimental evaluations for the proposed algorithms are provided and demonstrate the effectiveness and the robustness of the proposed diagnostic algorithms in this paper. The PEC under study consists of three main subsystems: uncontrolled three-phase rectifier, boost chopper, and single-phase inverter. [ABSTRACT FROM PUBLISHER]

The operational availability of mining shovels is the focus of this paper. The hypothesis is that energy quality is responsible for the frequent shutdowns of the shovels. Previous engineering studies have highlighted a large presence of harmonics and reactive power in the mine loop electric system. A common solution proposed was to use a combination of active filters, larger mobile substations, shorter mining cables, and equipment location constraints. The aim of this paper is to produce a precise diagnosis of the source and nature of the energy quality issues. Mine loop electric quality monitoring, system modeling, equipment technologies, and shovel's histograms are considered. Results are measured against IEEE standards and shovel's voltage regulation susceptibility. With the diagnosis, the goal was to produce a reliable cost-effective solution. Different alternatives are crosschecked with this paper proposal. The solution presented provides energy quality well within the shovel's susceptibility and improves energy efficiency. The lower energy consumption pays the investment required and is currently under construction. [ABSTRACT FROM AUTHOR]

This paper presents an DC/DC topology achieving high efficiency of over 97-% for electric vehicle (EV) fast chargers requiring a very wide output voltage range. The proposed topology consists of an unregulated resonant converter and a non-isolated buck converter. The unregulated resonant converter is responsible for the galvanic isolation for overall system, and the buck converter carries out the charging of the battery inside EV by constant-current or constant-voltage mode control. This structure provides a number of advantages such as easy realization of a very wide voltage range, no circulating-current, zero-voltage-switching operation on all the switches of the unregulated resonant converter running at high frequency and high voltage, and the achievement of high efficiency at every time over the entire battery charging profile. The availability of small passive components is a benefit because it enables the design of high power-density. In this paper, the feasibility of the proposed topology in EV fast charger applications has been verified by a prototype converter developed with the specification of 120-kHz or 50-kHz switching frequencies, maximum power rating of 20-kW, maximum charging current of 30-A, and battery voltage range of 50-650-Vdc. [ABSTRACT FROM AUTHOR]

This paper presents a new design of round-shaped transformers applied in diode and controllable rectifiers. Despite conventional three-phase transformers, in round-shaped transformers, voltage is induced on the secondary winding by rotating magnetic field. As a result, in the secondary of this transformer, there can be more than three phases with desired shifts. On the other hand, some rectifier systems may use more bridges supplying from the secondary to improve output dc voltage. However, the rectifier systems produce undesirable current harmonics, especially in controllable systems. This paper discusses how the new design of round-shaped transformers can significantly reduce the harmonic contents of the input current by sinusoidal skewing of the secondary core. The new design is investigated in this paper and its analysis confirms that the harmonics of the input currents can be effectively reduced. Experimental results are also provided to validate the analysis carried out in this paper. [ABSTRACT FROM AUTHOR]

This paper investigates a Vienna rectifier as a charger for series-connected battery packs. Focusing on carrier-based pulsewidth modulation (CBPWM), the ripple current flowing through the neutral point (NP) results in the voltage oscillation if the loads are resistive. To reduce the ripple of average NP current with mitigated distortion under balanced and unbalanced dc-link voltages conditions, a novel CBPWM with segmented component injection scheme (SCIS) is proposed in this paper. After dc component injection, continuous intervals for optimized component injection and clamping intervals for compensation component injection are identified. Optimized components are calculated originally based on unbalanced factor to make the average NP current zero-size in one switching period. Moreover, unique compensation components generate suitable NP current to shape the sinusoidal input currents according to the circuit analysis. In consequence, the SCIS not only keeps the input current with low-harmonic distortion, but also minimizes the oscillation of dc-link voltage under balanced and unbalanced conditions. In addition, the value of the NP current during the clamping intervals is analyzed under various operating conditions. The effectiveness and the performance of the proposed SCIS are verified by simulation and experiments. [ABSTRACT FROM AUTHOR]

Electrically excited synchronous machines have shown potential to be an alternative to permanent magnet synchronous machines in electromobility and wind power applications. High-frequency wireless power transferring technology enables a compact design of brushless exciters for the machine. In this paper, a dynamic model of high-frequency brushless exciters is proposed for the purposes of operating condition monitoring and excitation control. The modeling is done by using arithmetic and differential equations as well as considering different operation modes of the system. The operation modes are defined based on the physical behaviors of the excitation circuit. Experiments are performed to verify the model with variations of different circuit parameters. Furthermore, parameter sensitivity study, component parameter selection, and loss analysis are conducted to demonstrate the effectiveness of the model. The model is therefore proposed as an effective tool to assist the design and optimization of the brushless excitation system. [ABSTRACT FROM AUTHOR]

SiC mosfet based converters are capable of high switching frequency operation. In this paper, the converter is operated with 50-kHz switching frequency for an active front-end rectifier application. Due to high switching frequency, the grid-side filter size is reduced, and the possibility of a high bandwidth current control loop is utilized in this paper. A current control loop with bandwidth of 5 kHz is designed using a proportional–integral controller in synchronously rotating dq-reference frame. In addition, the performance of the controller is tested under unbalanced input supply conditions. During this condition, new feed-forward signals, which are added to the controller output, are proposed. The gain of the feed-forward signal can be modified to achieve balanced sinusoidal grid currents, constant dc-link voltage, or a controlled negative-sequence input current, which are typical application-depending requirements. A closed-form formula to calculate the gain of the feed-forward signal to achieve the above-mentioned requirements is also proposed in this paper. To verify the proposed method, the simulation and experimental results are presented in this paper. [ABSTRACT FROM PUBLISHER]

This paper investigates the stability of diode rectifier based HVDC (DR-HVDC) connected offshore wind farms. The impedance model of the DR-HVDC connected offshore wind farms in dq frame is analytically developed and is validated by comparing its impedances to those obtained from frequency scanning of time domain EMT model in PSCAD/EMTDC. Based on the impedance model, the impacts of the sizes of DR-HVDC DC smoothing reactors and AC filters on offshore system stability are analyzed. It shows reduced DC smoothing reactance degrades the d-axis stability margin and can potentially lead to system instability. Higher bandwidth of offshore AC voltage control of wind turbine line side converter is proposed to minimize such instability potential. The analysis also shows that reduced AC filters size helps to increase q-axis stability margin and leads to a more stable system. Moreover, stability analysis considering the interaction between WTs is conducted and it reveals that the WT P-V control has a significant impact on the stability of the DR-HVDC connected WTs. [ABSTRACT FROM AUTHOR]

In this paper, the holomorphic embedding power flow method (HELM) is designed to solve the AC/DC hybrid power flow equations. According to the power flow model of the high voltage direct current systems (HVDC), an appropriate embedding technique with three recursive algorithms is developed for three different control modes, which is compatible with existing achievements of HELM for AC systems. In this method, the advantages of HELM, such as non-iterative, deterministic and non-ambiguous, are fully retained. In addition, a new calculation strategy based on Bauer's Eta algorithm is designed for the implementation of Padé approximations and the recursive process to avoid redundant calculations without reducing accuracy. In order to verify the reliability and effectiveness of the proposed extended HELM, several power flow cases with different scale are studied by HELM and traditional iterative method. [ABSTRACT FROM AUTHOR]

This paper proposes a novel active-clamp forward converter (ACFC) with a lossless-snubber on the secondary-side, which combines a resonant capacitor and a clamping diode with an output inductor in parallel. The conventional ACFC achieves zero-voltage-switching on switches of the primary-side during dead time for reducing the switching loss and voltage spike. Unfortunately, on the secondary-side of transformer, the voltage spike damages the free-wheeling diode and rectifier diode due to the reverse recovery current and junction-capacitor of the diode and leakage inductance of the transformer. This paper proposes a lossless-snubber on the secondary-side operation for reducing the voltage spike on the free-wheeling diode and forward-rectifier diode. Therefore, the converter proposed in this paper is suitable for high-output-current applications. Experimental results are shown to verify the analysis and design procedure of the proposed forward converter. [ABSTRACT FROM AUTHOR]

This paper introduces modeling and control of a cascaded flying capacitor bridge (CFCB) multilevel converter for a solid-state transformer. The finite control set-model predictive control (FCS-MPC) is easy and simple to implement for many applications. However, the computational complexity increases with the increase in the number of switches. Furthermore, as the number of control variables increases, the weighting factors also increase. Thus, it is difficult to apply to a system with a large number of switches and variables to be controlled similar to a CFCB multilevel converter. In this paper, the proposed method divides variables such as current, dc-link voltage, and flying capacitor voltage into layers. The proposed method reduces the number of states to be considered in the control, which shortens the computational time and simplifies expansion of the flying capacitor bridge. In addition, since weighting factors are not used, there is no tradeoff between current quality and voltage quality, and there is no difficulty in selecting weighting factors. Algorithms that include a method for compensating for the distortion caused by the delay of the digital control system are also described. The effectiveness of the proposed method is verified via experiments using a two-cell CFCB multilevel converter. [ABSTRACT FROM AUTHOR]

This paper proposes a predictive zero-voltage-switching (ZVS) control with improved ZVS time margin and limited variable switching frequency range for a 99% efficient megahertz (MHz) GaN totem-pole power-factor-correction (PFC) rectifier. The conventional ZVS control methods for totem-pole PFC may lead to zero ZVS time margin and ultra-wide switching frequency range. This paper proposes that the synchronous rectifier (SR) turn-off current is a new degree of freedom for the ZVS control. Thus, the proposed cycle-by-cycle predictive ZVS control method controls the SR turn-off currents to extend the ZVS time margin and to reduce the maximum switching frequency. With the proposed ZVS control, the minimum ZVS time margin and a limited maximum switching frequency can be realized in a MHz GaN-based totem-pole PFC. With the improved ZVS time margin, the reliability for realizing ZVS is significantly improved. With the limited maximum frequency and the limited frequency range, the difficulty in high-speed current sensing and digital control is reduced, and the frequency-related loss is also reduced, which is important for improving the light-load efficiency. To accurately extract the current and timing parameters for the proposed ZVS control, an analytical model for the ZVS totem-pole PFC is proposed. The proposed ZVS control and analytical model are applicable over the full input and output voltage range, and over the full load range. In addition, a hybrid current control is proposed and implemented based on the proposed ZVS control. Finally, a 3.2-kW MHz GaN totem-pole PFC prototype is developed and tested with full-range ZVS, minimum ZVS time margin, limited switching frequency range, 99% peak efficiency, and 130-W/in3 power density based on the proposed ZVS control and system control strategy. The realized efficiency, power level, and power density are among the best ever reported for the GaN-based totem-pole PFC. [ABSTRACT FROM AUTHOR]

The utilization of wide bandgap devices such as silicon carbide (SiC) diode and mosfet can significantly increase the power density and the efficiency of rectifier circuits. However, SiC-based circuits always suffer from the high cost of their power stage. In this paper, a highly efficient low-cost hybrid three-phase three-level rectifier is proposed. Instead of using SiC diode and Si IGBT, it consists of SiC mosfet and Si diode. It presents extremely low switching losses because the reverse recovery losses of all the Si diodes are eliminated. At the same time, the total device cost of this rectifier is much lower than the all-SiC-based rectifiers. Furthermore, half-bridge modules can be used to comprise the rectifier circuit, which makes it suitable for high-power applications. In this paper, the circuit operational analysis, simulation, and experimental results are given. A comparison is given to show the advantages of the proposed rectifier. [ABSTRACT FROM AUTHOR]

This paper introduces a compensation strategy to deal with both current and voltage measurement errors in the three-phase pulsewidth modulated rectifier system. The dc offset and scaling errors in the voltage and current measurements cause the injection of undesired dc and unbalanced currents into the three-phase input current and subsequently lead to voltage ripple at the dc output voltage. This paper proposes a compensation scheme for current measurement error where the dc offset and scaling errors in the current measurement are estimated from the characteristic of the dc output voltage ripple combining with simple band-pass and low-pass filters. Meanwhile, an advanced current controller designed with a proportional integral plus two resonant controllers tuned at the fundamental grid frequency $({{\omega _s}})$ and $2{\omega _s}$ in the synchronous (d–q) reference frame is suggested to reject the impact of the dc offset and scaling errors in the voltage measurement. The proposed compensation method is developed without the need of extra hardware circuit, sensor, or precise information of system parameters so that it can be considered as more cost-effective and robust solution. The effectiveness of the proposed solution is verified by experimental results. [ABSTRACT FROM AUTHOR]

In this paper, the application of SMES system in the electrical multiple unit (EMU) was studied. With a new type of SMES rectifier and its novel control strategy, the EMU could immune through the over-phase region from the power off. The overvoltage impact on the related equipment due to the frequent power switch could also be reduced. With the combination of the DQ current decoupling control and transient direct control, the output power quality of the motor train grid side was obviously improved and the voltage adjustment time was significantly improved. The grid side harmonic was also suppressed, and the harmonic content was obviously reduced. All advantages on the dynamic response abilities presented above had been verified by the simulation and test results in this paper. [ABSTRACT FROM AUTHOR]

This paper analyzes a cost-effective modification of the power topology commonly found in small wind turbine systems based on a passive rectifier and a boost converter. The boost-converter inductor and the input filter capacitor often placed at the rectifier output can be replaced by the generator-phase inductance. Different controller structures have been proposed for this low-cost inverter, but they have been focused on the converter itself rather than the overall turbine control. Moreover, only steady-state behavior has been demonstrated. This paper proposes a control structure only requiring retuning of the boost-current controller found in systems equipped with boost inductance, with other control loops remaining unchanged. The inductorless converter dynamic performance is studied and compared with the conventional topology in terms of current- and torque-control capability. The system efficiency, including the losses’ distribution in the generator, is analyzed. Simulation and experimental results are presented to demonstrate the technical viability of this proposal. [ABSTRACT FROM AUTHOR]

DC ice melting is an effective technical method against ice disaster on transmission lines. To satisfy the demand for simultaneous de-icing and reactive power compensation for substations, this paper proposed a large-capacity low-cost DC deicer with reactive power compensation, which is mainly composed of rectifier transformer, Static Var Generator (SVG) and diode rectifier. In the proposed topology, SVG and diode rectifier share the rectifier transformer, but rectifier transformer capacity is not increased compared with a single deicer. This paper firstly presents the proposed topology and analyzes its advantages. Then, the rectifier transformer design is introduced, and the SVG control strategy is presented. Simulation results for the proposed device are presented, and an engineering devices with a capacity of 21.8 MVA developed for the 220 kV Fuchong substation is described. The simulation and application results indicate that the proposed devices work well. [ABSTRACT FROM AUTHOR]

Magnetically coupled resonant (MCR) wireless power transfer (WPT) is one of the most promising WPT technologies for its remarkable capability of simultaneous noncontact power transfer for multiple independent loads. Nevertheless, diverse energy requirements of different loads and efficiency quota make it difficult to design and optimize the multiload system. In this paper, a novel driver configuration for the MCR WPT system with multiple loads is proposed, in which the transmitting resonant tank is driven synchronously by multiple inverters operating at multiple switching frequency and sharing a common dc voltage source, then a multifrequency superposition methodology is presented to achieve high efficiency and targeted power distribution. The dominant features of the methodology are listed as follows: 1) the multifrequency power components from multiple inverters can be simultaneously delivered to multiple loads through a single transmitter; 2) the receiving coils are elaborately designed at different resonant frequencies that correspond to the operating frequencies of multiple inverters to achieve targeted power transfer and high efficiency; 3) the resonant frequency of the transmitter can be modulated within the adjacent area of multiple operating frequencies, and the power distribution to meet the requirements of selective loads will be realized; and 4) the resonant frequencies of receivers can also be adjusted to effectively realize the power distribution. In this paper, a double-frequency MCR WPT system with two loads is comprehensively investigated as a representative example, and the studied methodology has been experimentally verified by two prototypes of the proposed circuit configurations. [ABSTRACT FROM AUTHOR]

It is known that, when tightly regulated, actively controlled power converters behave as constant power loads (CPLs). These loads can significantly degrade the stability of their feeder system. The loop-cancelation technique has been established as an appropriate methodology to mitigate this issue within dc–dc converters that feed CPLs. However, this has not yet been applied to uncontrolled rectifier based ac–dc converters. This paper therefore details a new methodology that allows the loop-cancelation technique to be applied to uncontrolled rectifier based ac–dc converters in order to mitigate instability when supplying CPLs. This technique could be used in both new applications and easily retrofitted into existing applications. Furthermore, the key contribution of this paper is a novel adaptive stabilization technique, which eliminates the destabilizing effect of CPLs for the studied ac–dc power system. An equation, derived from the average system model, is introduced and utilized to calculate the adaptable gain required by the loop-cancelation technique. As a result, the uncontrolled rectifier based ac–dc feeder system is always stable for any level of CPL. The effectiveness of the proposed adaptive mitigation has been verified by small-signal and large-signal stability analysis, simulation, and experimental results. [ABSTRACT FROM AUTHOR]

Future U.S. Navy shipboard power architectures will integrate new ac and dc rep-rate pulsed loads that must be reliably energized. Delivering power to these loads typically requires charging large capacitor banks in a highly transient manner that causes a lot of stress on the ship’s prime power sources. Controlled multipulse rectifiers have been proposed as a direct solution to charging these capacitor banks and may eliminate the need for large passive filter components. Though multipulse rectifiers are well documented in the literature, there is little to no published work that studies the impact of multipulse rectifiers have on power quality when loaded by large capacitive loads in high rep-rate profiles. It is desired that MATLAB/Simulink models be developed for deployment on the OPAL-RT real-time simulator for predicting power quality in existing ship power system models. This paper discusses the development of 6-, 12-, and 24-pulse models based on equivalent hardware at a low voltage and power rating for study. Experiments are performed on the hardware equivalent systems, and data are collected. The data are then compared with the simulation results in the time and frequency domain for model validation. Issues encountered when modeling the phase-shifting transformers are discussed, and recommendations and cautions are proposed for future work. [ABSTRACT FROM AUTHOR]

This paper proposes a medium-frequency (MF) solid-state transformer (SST) based grid interface for high-power multipulse rectifiers. In the proposed approach, the low-frequency ac (grid) voltage is transformed to MF voltage via front-end converters. The three single-phase MF outputs from these converters are fed to the primary side of a three-phase, five-limb multiwinding isolation transformer (or alternately three one-phase transformers). The secondary side windings from the transformer are configured in a certain “zig-zag” arrangement, which are connected to the inputs of three-phase diode rectifier modules as in a typical multipulse system. The proposed topology can better than double the power density by reducing volume (or weight) of the required front-end isolation transformer while maintaining the same input current quality as a conventional low-frequency transformer based approach. Usage of an open-loop square wave pulse width modulation for the front-end converters makes this approach simple to implement. This paper explains the proposed concept taking an adjustable speed drive application's perspective using modeling, simulation, and experimental results from a scaled down laboratory prototype. [ABSTRACT FROM AUTHOR]

Commutation failures (CFs) including repetitive CFs (RCFs) are frequently occurring faults in line commutated converter based high voltage direct current (LCC-HVDC) systems. Consequently, sending end system will suffer transient voltage disturbances (TVD) with a characteristic of “first reduce then rise and may repeat”. Due to the complex interaction process of TVD, the electromagnetic process behind this phenomenon cannot be easily explained, which imposes great challenges on the development of mitigation strategies. Given this, this paper provides a deep insight into the mechanism and the impact factors of the TVD caused by CFs and RCFs. The numerical relationship between the transmitting power and the TVD is derived. Research results revealed that the transient process after fault can be segmented into five stages. In each stage, the control interactions among HVDC controllers and power interactions at the PCC are analyzed. Besides, we discussed the TVD under RCFs in detail. Several indices are further proposed to facilitate the characterization of the TVD, and main control loops of HVDC that have impacts on the characteristics of TVD are thereby studied. Finally, the mathematical relationship between wind farm power and the TVD is derived to quantify the impact of wind farms on the TVD. [ABSTRACT FROM AUTHOR]

This paper proposes an algorithm to control the suspension dynamics with an energy regeneration capability and high conversion efficiency. Central to the concept is the development of a switched-mode rectifier (SMR) that is capable of providing either an equivalent positive or negative damping and alternating between regenerative and motoring modes. Simulation results are presented to demonstrate power flow in regeneration and motoring modes and verify the equivalent damping characteristic and vibration energy harvesting. The studies are conducted on a small-scale proof-of-concept electromagnetic suspension system excited by emulated International Standard Organization (ISO) 8608 road profiles. An autonomous start/stop algorithm is proposed such that autonomously turns on or off the converter. This mechanism mitigates quiescent power consumption of auxiliary integrated circuits (ICs) such as gate drivers and current transducers, therefore increasing the conversion efficiency of the power electronics throughout an ISO standardized variable-speed driving cycle. The autonomous start/stop algorithm is implemented experimentally to demonstrate its feasibility under typical standardized driving cycles. [ABSTRACT FROM PUBLISHER]

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]

This paper presents a Scott-transformer-based power factor correction (PFC) rectifier for a three-level neutral-point-clamped (NPC) inverter-fed induction motor drive (IMD) for enhanced power quality at ac mains. Here, the Scott-transformer-based PFC rectifier is digitally controlled by a current feedforward control. The torque component of the stator current is added to the output of the dc-bus voltage proportional plus integral (PI) controller as a feedforward term, which enhances the dynamic performance of the dc-bus voltage regulation. The three-level NPC inverter is controlled by a space vector-modulated (SVM) indirect vector control scheme. The performance of the proposed dc-bus voltage loop with feedforward control is compared with the conventional one and found to offer faster response with less overshoot and undershoot. The proposed IMD system is simulated using MATLAB/Simulink and the same is validated experimentally. The proposed drive system is analyzed for a wide variation in reference speed and load torques demonstrating significant improvement in the performance indices. [ABSTRACT FROM AUTHOR]

Simulation is a valuable way to develop cleaner transportation systems. Nevertheless, the complexity of this kind of system leads to complex models, particularly when taking into account nonlinear aspects of traction power substations (TPSs). Thus, this paper proposes different TPS models based on energetic macroscopic representation. An appropriate model is deduced from comparisons between the different models to realize energetic studies. It is finally applied to the simulation of a simple subway line, which is experimentally validated. [ABSTRACT FROM AUTHOR]

Back-to-back converters have been typically used to interconnect microgrids. For a back-to-back current-source converter, the dc-link current ripple is one of the important parameters. A large ripple will cause electromagnetic interference, undesirable high-frequency losses, and system instability. Conventionally, with a given switching frequency and rated voltage, the current ripple can be reduced by increasing the dc-link inductor, but it leads to bulky size, high cost, and slow dynamic response. To solve this problem, this paper reveals that the current ripple can be significantly reduced by adjusting the gate patterns of space vector modulation between the rectifier and the inverter in a back-to-back converter. The experimental results verify the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

High-voltage direct-current (HVDC) systems for constant or intermittent power delivery have recently been developed further to support grid frequency regulation (GFR). This paper proposes a new control strategy for a line-commutated converter-based (LCC) HVDC system, wherein the dc-link voltage and current are optimally regulated to improve real-time GFR in both rectifier- and inverter-side grids. A dynamic model of an LCC HVDC system is developed using the dc voltage and current as input variables, and is integrated with feedback loops for inertia emulation and droop control. A linear quadratic Gaussian (LQG) controller is also designed for optimal secondary frequency control, while mitigating conflict between the droop controllers of HVDC converters. An eigenvalue analysis is then conducted, focusing on the effects of model parameters and controller gains on the proposed strategy. Simulation case studies are performed using the models of a real HVDC system and a CIGRE benchmark system. The case study results confirm that the proposed strategy enables the HVDC system to improve GFR, in coordination with generators in both-side grids, by exploiting the fast dynamics of HVDC converters. The proposed strategy is also effective under various conditions for the LQG parameters, inertia emulation, and droop control. [ABSTRACT FROM AUTHOR]

Under the unbalanced condition of grid voltages, the second-order harmonic voltage ripple will appear on the DC bus of the three-phase PWM rectifier due to the existence of the negative sequence voltages. In addition, the total harmonic distortion (THD) of the grid currents will increase correspondingly. In this paper, the coupling mechanism between the DC bus voltage ripple and the grid harmonic currents is revealed. Based on the situation above, a grid harmonic current suppression method is proposed. Compared with existing methods, the proposed method has the advantages in the following three aspects. Firstly, the proposed method does not require either the extraction of positive/negative sequence or the positive/negative sequence current control, which can highly reduce the complexity of the system. Secondly, the grid current harmonics can be reduced by an improved proportional quasi resonant (IPQR) controller. Thirdly, the IPQR controller has little effect on the parameter design of the control system, which facilitates the control design. Finally, the experiments show the accuracy of the theoretical analysis and the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper presents a new modular ac/dc step-up soft-switched converter with unity turns ratio high-frequency transformers for medium-voltage (MV) dc grid in wind energy systems. In the proposed converter, the three-phase boost rectifier is combined with step-up resonant circuits and high-gain output rectifier modules (called voltage quadrupler modules) to form a modular step-up power conversion unit. As a result, the proposed converter is able to achieve very high voltage gain without using any medium-to-high frequency transformers with very large turns ratio, which greatly simplifies the insulation requirement and design of the high-frequency transformer. In addition, soft-switching operations are achieved in all the semiconductor devices to maintain high efficiency. The techniques to ensure voltage balancing across the dc-link capacitors and to achieve output short-circuit protection will be discussed in this paper. To realize high-frequency MV operation, silicon carbide (SiC) devices are utilized in the converter implementation on a 1.5 MW, 690 VAC/40 kV converter system to validate the performance of the proposed circuit. Experimental results on a 3.5 kW, 145 VAC/6.2 kV, 95.4% efficiency SiC-based laboratory-scale proof-of-concept prototype are then provided to highlight the merits of this work. [ABSTRACT FROM AUTHOR]