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This paper presents a study of the losses in the integrated buck–flyback converter (IBFC) used as high-power-factor LED driver. The aim of the study is to investigate the possibilities of increasing the efficiency of the IBFC converter. The procedure of the improvement is done by obtaining the equations of the current through each component in terms of converter parameters. The current is found in an average value or rms value, depending on the type of the parasitic component, whether it is modeled by a parasitic forward voltage source or by a parasitic resistance, respectively. Using these equations and the parasitic model, the losses of each element of the converter are estimated. This paper proposes a technique to increase the efficiency of the IBFC by redesigning the converter parameters. Furthermore, this paper presents a case of study with a step-by-step efficiency enhancement process of an existing driver. The driver is operating under universal input conditions, and 38 V output, supplying an LED luminary of 26.5 W. The new design shows an improvement of the efficiency from 82% in the old design to 89% in the proposed one. Moreover, the new design shows an improvement in the power factor and the THD and a 50% reduction in the output current ripple. Furthermore, a reduction in the number of components has been achieved, as it is found by the analysis that by adjusting the converter parameters, one diode can be removed. Finally, the presented methodology is explained in detail so that it can easily be applied to other dc–dc converters. [ABSTRACT FROM AUTHOR]

This paper proposes a new modulated model predictive control method for the control of modular multilevel converters (MMCs) in voltage source converter-high voltage dc systems. The proposed method retains the advantages of the conventional finite control set-model predictive control methods by programing the nonlinear properties of the MMC into the design calculations while minimizing the ac line and circulating current ripples and steady-state error by generating modulated switching signals with a fixed switching frequency. In this paper, first, the predictive modeling of the MMC is provided. Next, the proposed control method is described. Then, the application of the proposed method to an MMC system is detailed. Finally, experimental results from an MMC system connected to a three-phase grid are provided to validate the theoretical outcomes. [ABSTRACT FROM AUTHOR]

This paper extends the dynamic coherency determination (DCD) method by including Type-3 wind power plants (WPPs) models in the coherency evaluation process and quantifies impacts of the high depth of wind power penetration on the coherency phenomena of interconnected power systems. The method is based on frequency-deviation signals, measured at nongenerator buses and terminal buses of WPPs and synchronous generators. Salient features of the presented method are its ability to account for the hybrid nature of enhanced generic models of Type-3 WPPs and expanding notion of the power system coherency beyond the classical definition by including models of Type-3 WPPs. This paper also investigates impacts of the high depth of wind power penetration; i.e., up to 30%, on the coherency structure of the 16-machine/68-bus NPCC equivalent system. The studies are based on time-domain simulations in PSS/E software. The investigations reveal that Type-3 WPPs can introduce new coherent areas, significantly change areas’ boundaries and number of areas, and alter frequencies/dampings of interarea modes. [ABSTRACT FROM AUTHOR]

This paper provides an intensive discussion on analysis, simulation, and experiment of a back-to-back (BTB) systemunifying two modular multilevel cascade converters based on double-star chopper cells (MMCCs-DSCCs). Each of the twoDSCCs connected back-to-back consists of multiple cascaded chopper cells and a center-tapped inductor per leg. Lowvoltage steps bring significant reductions in harmonic voltage and current to the BTB system. Neither dc-link capacitornor voltage sensor is required for regulating the dc-link voltage and controlling the dc-link current. A three-phase200-V, 10-kW, 50-Hz downscaled BTB system with phase-shifted PWM is designed, constructed, and tested to verify itsoperating principles and performance. Analytical, simulated, and experimental results agree well with each other insteady and transient states. Experimental waveforms confirm the effectiveness of a self-starting/restartingprocedure. [ABSTRACT FROM AUTHOR]

The harmful effects of harmonics are an important issue in wind power plants (WPPs), especially in offshore applications. In offshore WPPs, the wind turbines are linked to the network through high-power converters that produce harmonics at relative low frequencies. Moreover, in the network of a WPP, the propagation of noncharacteristic harmonics and the effect of resonance contribute as well in boosting the harmonic distortion. In this paper, a solution for compensating the harmonics in a WPP by means of using hybrid filters is proposed. In this paper, not only the filtering solution is tested, but also a method for finding the best place where to connect the filter, based on a modal analysis or a harmonic modal resonance analysis, is implemented. The proposed solution has been tested by considering the model of a real 400-MW offshore WPP as the study case. As it will be shown, the hybrid filter is capable of damping the resonances in the plant, while the analysis conducted permits us to optimize its location in the plant. [ABSTRACT FROM PUBLISHER]

Using VSC-MTDC to provide frequency support for interconnected power systems is an attractive solution. Considering the disadvantages of traditional methods in power shortage or surplus absorption into the VSC-MTDC from AC systems requiring active power support (RAPS system) as well as flexible and effective power balance in AC systems providing active power support (PAPS system), this paper proposes a novel frequency support control method for interconnected power systems using VSC-MTDC. The main principle of the proposed frequency support control method is firstly to make the active power shortage or surplus of the RAPS system be fully and naturally absorbed into the DC grid with the AC slack bus mode control proposed for RAPS converters; in addition, the smooth switching control and the power limiting control are further proposed to realize smooth and safe power shortage or surplus absorption. Secondly, according to the proposed flexible PAPS systems matching strategy, one or more appropriate PAPS systems with adequate capacity are selected to effectively and accurately balance the unbalanced power via the corresponding PAPS converters using the active balancing power control. The theoretical analysis and simulation results using PSCAD/EMTDC have verified the validity, flexibility and universality of the proposed frequency support control method. [ABSTRACT FROM AUTHOR]

In this paper, a cascaded H-Bridge (CHB)-multilevel converter (MC)-based photovoltaic (PV) system with no voltage or current sensors at the dc-side is proposed. Eliminating the dc-side sensors simplifies the hardware, leading to lower cost and higher reliability of the PV system. A novel scheme estimating the capacitors’ voltages from the ac output voltage of the inverter is developed. The scheme allows replacing all dc-side voltage sensors by a single-voltage sensor at the ac-side of the converter. Furthermore, the dc current sensors, conventionally required for the maximum power point tracking (MPPT), are also eliminated. Instead, the outputs from the capacitors’ voltage control systems are utilized for the MPPT. The effectiveness of the proposed dc-side sensorless system is experimentally demonstrated on a 2-kW single-phase seven-level CHB converter-based PV system. [ABSTRACT FROM PUBLISHER]

Steep-slope heterojunction tunnel field-effect transistor (HTFET) devices promise new opportunities beyond CMOS in low-power high-performance communication applications. In this paper, the circuit design optimization of a low-power 14-bit 1-GS/s current-steering digital-to-analog converter (DAC) using 0.4/0.3 V mixed-supply HTFETs is explored. Based on the device characteristics comparison and circuit analysis, it is shown in this paper that HTFET endorses significant differences in both $I$ – $V$ and $C$ – $V$ due to the steep-slope tunneling mechanism and a nature of vertically fabricated structure. While such differences significantly affect the circuit design corners, this paper gives the device-circuit co-optimization for the HTFET DAC, reaching at higher current source output impedance, less nonlinear switching glitch distortions, and thus superior spectral performance over the Si-CMOS DAC. HTFET device variation is also discussed, and calibration techniques are adopted for the static matching accuracy. [ABSTRACT FROM AUTHOR]

This paper describes a phase-locked loop (PLL) converter with improved dynamic response for the determination of mechanical angle from sinusoidal encoders and resolvers. PLL converters are tracking-type converters that use the sine and cosine signals of the transducer in a closed-loop arrangement aiming to match an estimated output angle to the true angle encoded in the sine and cosine input signals. Such a scheme requires means to determine the sine and cosine of the estimated output angle; conventional converters achieve this by using voltage-controlled oscillators, digital-to-analog converter (DAC), counter, and lookup tables. The proposed converter simplifies implementation by making use of the estimated output angle signal to approximate its sine and cosine using analog triangle-sine conversion technique. A new method is also proposed to enhance the dynamic performance of the converter enabling near instantaneous response. This paper describes the proposed method, full details of its analog implementation, and experimental results. Results demonstrate agreement with theory and computer simulation. [ABSTRACT FROM AUTHOR]

This paper provides a theoretical discussion and comparison in energy balancing between a modular multilevel cascade inverter based on single-star bridge cells (SSBC) and that on single-delta bridge cells (SDBC). Attention is paid to applications involving asymmetric active-power generation in utility-scale grid-tied photovoltaic systems. Both qualitative and quantitative evaluation metrics to assess the energy-balancing capability are introduced and applied to both SSBC and SDBC inverters. As for the SSBC inverter, six zero-sequence voltage waveforms with different harmonic content enabling enhanced energy-balancing capability are analyzed and compared regarding their effectiveness. This paper also emphasizes on the SDBC as an alternative to the SSBC and highlights its superior operating characteristics under asymmetric active-power generation. [ABSTRACT FROM PUBLISHER]

For interleaved boost-type converters, both functions of voltage regulation and current balance are important. In this paper, the decoupled current-balancing control (DCBC) with two parallel loops is proposed. At first, the small-signal transfer functions of the voltage-regulation loop and the current balancing loop to the controller output are derived. The results show that the voltage-regulation loop and the proposed current-balancing loop are nominally decoupled. That is, two PI-type controllers can be designed independently and included to implement the proposed DCBC. Additionally, the single-sensor sampling-current strategy is proposed to obtain two average inductor currents by sensing only the sum of diode currents. All the controllers are implemented in field-programmable gate array (FPGA). The provided simulation and experimental results demonstrate the proposed DCBC. [ABSTRACT FROM PUBLISHER]

Modular multilevel converters (MMCs) have become one of the most promising topologies for high-voltage dc–ac conversion. DC-side fault blocking capability of the MMC has prompted significant research in recent years. In this paper, a new switched capacitor submodule (SCSM) for MMCs is proposed which provides operation with DC fault blocking capability. In addition, successful voltage balancing is achieved with half the number of voltage sensors used with existing MMC cells. Generally, conventional sensor-based balancing techniques require a significant amount of measurements, 2m(N-1) voltage sensors, and 2m current sensors for an N-level m-phase MMC. The proposed cell will thus aid in reducing the complexity of the control system. A detailed illustration of the operational concept of the proposed architecture is presented in this paper. A comparison between the proposed SCSM and other existing MMC cells has been included to highlight the benefits of the proposed SCSM. A simulation model for an MMC-based HVDC system along with the proposed cell has been built to test its performance during normal as well as abnormal operating conditions. The simulation results show the effectiveness of the proposed architecture. [ABSTRACT FROM PUBLISHER]

This paper presents the design, modeling, and characterization of 3-D-printed air-core inductors for high-frequency power electronics circuits. The use of 3-D modeling techniques to make passive components extends the design flexibility and addresses some of the fabrication limitations of traditional processes. Recent work [1]– [9] has demonstrated the feasibility of incorporating air-core inductors in high-frequency ( $>$10 MHz) switching power converters. These implementations have used discrete wire wound solenoids and toroids, and planar components that use printed circuit board traces or microfabrication techniques to make air-core inductors. However, realizations of such components have limitations in performance and applicability including open paths conducive to the flow of leakage fields, and difficulties in achieving optimal cross section to minimize loss. Along with the current effort of involving 3-D printing technology to make inductors [10], [11], we propose the use of 3-D printing and casting/plating techniques as a simple and accessible alternative that adds flexibility and functionality to the air-core inductor design for high-frequency power conversion at moderate to high-power (e.g., tens to thousands of watts) and high-voltage (greater than 100 V) levels. In this paper, we present several examples of air-core inductors realized using 3-D printing and casting/plating techniques to give an idea of the geometries that are possible to design. Moreover, we show that some of these designs can lead to improved electrical performance. This paper also describes the tools used by the authors to design, fabricate, and characterize the electromagnetic performance of the air-core inductors. The software used to generate the 3-D scaffolds for the inductors are freely available and easily accessible. Readers are encouraged to explore more possibilities of geometries that can lead to better performance with the ease of manufacturing. As progress in additive manufacturing continues, we envision 3-D printing of a complete scaffold structure that after plating (or casting) will contain all resonant passive components of an RF switching converter. Toward this goal, we present a 70-W prototype 27.12-MHz resonant inverter that incorporates some of the 3-D-printed components developed for this paper. [ABSTRACT FROM AUTHOR]

A fully digital, nonlinear, wide-bandwidth current controller for dc–ac and dc–dc voltage source converters is presented in this paper. Exploiting oversampling, the controller mimics an analog hysteresis current controller, but it does not employ analog comparators, digital-to-analog converters, or any other analog signal pre- or postprocessing circuitry. Indeed, it fully virtualizes the hysteresis controller's operation and, based only on a nonlinear, efficient current error processing algorithm, drives the power converter at almost constant switching frequency. Overall, it offers the same excellent dynamic performance of the analog hysteresis controller and, at the same time, solves most of the related problems. Because the current error sample processing algorithm is inherently parallel in structure, the controller is suited for VHDL synthesis and field-programmable gate-array implementation, which guarantees flexibility and low cost, together with minimum computation and signal conversion delays. Its intended application areas include active filters, uninterruptible power supplies, microgrid distributed energy resource controllers, laboratory battery testers, and welding machines. [ABSTRACT FROM PUBLISHER]

This paper studies the effect of common-mode voltage elimination (CMVE) on the iron loss of electrical machine core laminations under multilevel converter supply. Three identical magnetic ring cores are excited by either a three-level converter or a five-level voltage source converter to study the behavior of CMVE on a three-phase system. Both multilevel converters are controlled by using a space vector pulsewidth modulation as it is one of the most often used techniques for CMVE. These experimental results are confirmed numerically with a dynamic iron loss model. In addition, the effect of CMVE, at different switching frequencies, on the core loss of a synchronous machine is numerically studied. The results presented in this paper show that the core loss is considerably increased when the CMVE is implemented. However, this iron loss increase in the five-level drive systems is lower compared with the three-level ones. Therefore, it is important that the designers of drive systems take such effects into consideration. [ABSTRACT FROM AUTHOR]

This paper provides experimental verification of a modular multilevel cascade converter based on triple-star bridge cells (MMCC-TSBC) for a low-speed, high-torque motor drive. The TSBC is one of direct ac-to-ac power converters capable of achieving bidirectional power flow and drawing/feeding three-phase sinusoidal input (supply-side) and output (motor-side) currents with any power factor at both sides. This paper designs, constructs, and tests a downscaled drive system combining a 400-V, 15-kW, phase-shifted-carrier PWM TSBC equipped with four bridge cells per cluster and a 320-V, 38-Hz, 6-pole, 15-kW induction motor loaded at the rated torque. Experimental waveforms obtained from the downscaled drive system verify stable operation across a broad range from a standstill to the rated speed, showing satisfactory start-up performance. [ABSTRACT FROM PUBLISHER]

The ac/dc front-end converter in low-power applications such as household appliances usually contains diode rectifiers equipped with smoothing dc capacitors, which generate a large amount of harmonic current. As a solution for reducing the harmonic current, distributed generation (DG) units with a harmonic compensation function have become an attractive topic. In three-phase three-wire systems, the effect of the third-harmonic current is not serious, because most of the current is zero-sequence current. However, if many single-phase DG units are unevenly installed in three-phase grids, the third-harmonic currents may be serious. This paper shows that conventional harmonic suppression can increase third-harmonic currents in three-phase three-wire grids. To prevent an increase in the harmonic current, a third-harmonic suppression method called the balancing third-harmonic function is proposed. To validate the proposed control strategy, experimental results using a laboratory system are presented. [ABSTRACT FROM PUBLISHER]

This paper presents the modular multilevel cascade converter based on double-star chopper-cells, which is intended for grid connection to medium-voltage power systems without using line-frequency transformers. The converter is characterized by a modular arm structure consisting of cascade connection of multiple bidirectional pulsewidth modulation chopper-cells with floating dc capacitors. This arm structure requires voltage-balancing control of all the dc capacitors. However, the voltage control combining an averaging control with an individual-balancing control imposes certain limitations on operating conditions. This paper proposes an arm-balancing control to achieve voltage balancing under all the operating conditions. The validity of the arm-balancing control as well as the theory developed in this paper is confirmed by computer simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper presents a novel dc–dc converter incorporating a distributed impedance-source network ( Z-source network, or Z-network) to achieve the buck (step-down) and boost (step-up) function of a transformer-isolated dc–dc converter. In this paper, the distributed impedance source network composed of an array of inductors and capacitors is coupled between power source and main switching devices. The great and unique feature about the distributed impedance source network dc–dc converter is that unlike the traditional V-source or I-source converters, it can be open- and short-circuited without damaging switching devices. Therefore, the desired buck and boost function can be achieved. Moreover, converter reliability can be greatly improved. A dc–dc converter using this proposed concept is built and tested. Its performances are verified with experimental results. [ABSTRACT FROM PUBLISHER]

Reliability evaluation of multiterminal HVDC systems has received very little attention in the past. This paper presents reliability modeling and analysis of an HVDC transmission system incorporating a voltage-sourced converter (VSC) tapping station. The use of VSC tapping stations enables the supply of power along the route to areas with comparatively little consumption. In this paper, a comprehensive detailed reliability model is developed and then converted to a manageable and computationally efficient model. Using this equivalent reliability model, various reliability indices are calculated at the load point of the system and the impacts of the VSC tapping station on these indices are illustrated. Sensitivity analyses are conducted to investigate the impacts of the load level and the location of the tapping station on the reliability indices. The conducted studies are numerically applied on a typical HVDC system and thorough discussions are presented. [ABSTRACT FROM AUTHOR]

In this paper, a new control system to regulate the reactive power supplied by a variable-speed wind energy conversion system (WECS), based on an induction generator fed by a matrix converter (MC), is presented. The control system discussed in this paper is based on an input current observer, implemented using an estimation of the modulation matrix, and a nonlinear control loop that regulates the displacement angle at the MC input. The reactive power capability of the proposed system is also investigated. The work presented in this paper demonstrates that, for the proposed WECS, the maximum reactive power supplied to the grid is about 40% of the nominal value. Experimental results obtained from an experimental prototype are presented in this paper. The performance of the system using a wind turbine emulator and typical wind profiles is discussed in this paper. [ABSTRACT FROM AUTHOR]

This "Special Section on New Technique Trends for Power Converters in Distributed Power Generation Systems" of the IEEE Transactions on Industrial Electronics (TIE) 35 papers selected among 89 submitted papers. Therefore, this Special Section will be published in two parts. In Part I, all the papers are related to dc/ac grid-tied inverters. [ABSTRACT FROM PUBLISHER]

In this paper, a composite prescribed performance control strategy is developed for stabilizing dc/dc boost converter feeding constant power loads. First, by employing the exact feedback linearization technique, the nonlinear uncertain dc converter system is first transformed into the Brunovsky’s canonical form. Then, a nonlinear disturbance observer is utilized to evaluate the dynamic change of load power and the accuracy of output voltage regulated by feedforward compensation. Next, the prescribed performance controller is elaborately designed to ensure that the tracking error of output voltage is always within the margin of predefined error bounds. Based on the backstepping design approach, the composite nonlinear controller with prescribed performance is determined. Finally, the numerical simulation results are presented to demonstrate the tracking performance of the proposed controller. [ABSTRACT FROM AUTHOR]

Constant on-time V^2 control for point-of-load buck converters has instability issues in the cases that the output capacitors' RC time constants are small. This paper intensively studies the proposed solution using capacitor current ramp compensation, which is a superior solution featuring fast response and universality. A frequency-domain small-signal model based on describing function method is proposed in this paper. The time-domain large-signal response to the load step change is analyzed. The analysis illustrates the unique transient response behaviors of the capacitor current ramp compensated V^2 control. The design optimization methodology based on frequency-domain and time-domain analysis is presented. The proposed model and the design guidelines are verified by the experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a generalized power-decoupling control scheme using a multiport isolated bidirectional converter for a multilevel inverter, which has multiple dc links inside. In the proposed method, a single power-decoupling capacitor is needed for all the dc links in the multilevel inverter cell. First, a prototype of the power-decoupling concept of individual H-bridge cells in the multilevel inverter is proposed, using a separate power-decoupling circuit. Then, a more advanced one-step power-decoupling method is proposed. The lifetime and reliability of the multilevel inverter is improved as film capacitors replace the large capacitance electrolyte capacitors. A multi-input ports/single output voltage-fed dual half-bridge converter (MDHB) is used for the power-decoupling circuit. A steady-state analysis for the peak and root mean square of the MDHB current is carried out for the loss breakdown. The currents are functions of the switching frequency, phase shift, leakage inductance, turn ratio, and output voltage, which make the multiport transformer design complex. A design methodology is proposed, which takes into account the design of the copper and core losses as functions of the switching frequency and number of turns. Furthermore, a special winding method for the input port is illustrated to obtain identical leakage inductances for the uniform current distribution in the multiport transformer. The proposed MDHB employs a current-sensorless power-decoupling control that contributes to the spontaneous ripple rejection of all the dc links without individual link current information, as well as to the cost and size reduction. Hence, the ripple-rejection controller is independent of the control configuration of the multilevel inverter, and also available for universal applications of various inverter topologies. Since the primary-input ports of MDHB share a single magnetic core for interfacing the ripple power to the unified secondary ripple capacitor, the controller design becomes difficult in considering the dynamic interaction among the ports, along with the average-voltage control loop design. In this paper, the dynamic analysis and controller design procedure of the circuit is also presented. The power decoupling is achieved even when the ripple frequency is other than the double frequency of the inverter output, since the single-pole transfer function of the small-signal model of the MDHB allows sufficient phase margin, along with high bandwidth. The proposed power-decoupling method for the multilevel inverter is validated with the help of simulation and 1.2-kW hardware prototype experimental results. [ABSTRACT FROM AUTHOR]

Class $E^2$ DC–DC converter composed of Class $E$ power amplifier (PA) and rectifier is a promising candidate for MHz wireless power transfer. It is soft-switching based and able to achieve high efficiency at MHz frequency. However, the converter implemented through traditional static design is sensitive to the variations of operation condition. Its performance gets deteriorated when DC load and coil coupling deviate from their respective optimum values. This paper demonstrates that the degradation of system efficiency is mostly due to the mismatch of PA load, and the efficiency drop can be efficiently improved by adding an L-type impedance matching network (IMN) after PA. A fixed IMN is sufficient to maintain a high efficiency, while a tunable IMN is required to ensure stable output power when operation condition dramatically changes. Key techniques, particularly system-level optimization, are discussed in this paper that ensure high efficiency over a wide range of variation in operation condition and also with reduced capacitor/inductor tuning ranges in the IMN. The 6.78-MHz Class $E^2$ DC–DC converters with and without the fixed/tunable IMN are fabricated and measured for validation purposes. The experimental results show that both high efficiency ( $>$66%) and stable output power (around 9 W) are maintained for the tunable converter when there are variations in the DC load and coil coupling. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate how latency insertion method (LIM) can be used for real-time simulation of high switching frequency power electronics systems and how this approach can be implemented for scalable Field Programmable Gate Array (FPGA) execution. We first present a summary of the LIM and how this method can be developed into a solver for high-performance FPGA execution. We then present how common power electronics topologies—buck and boost—can be modeled using the LIM approach, followed by how the LIM model of a three-phase dc/ac converter is created. Afterward, we demonstrate the accuracy of the developed FPGA solver through a set of power electronic system examples, with each example compared with near ideal results of same example provided by a traditional electromagnetic transient type solver. We complete the paper analyzing the scalability of the proposed approach on FPGA devices, both in terms of achievable time step as well as of resource usage. [ABSTRACT FROM AUTHOR]

Medium to long-distance underground ac lines and both short- and long-distance HVdc are frequently integrated into network expansion plans. In conjunction with growing numbers of power-electronic converters in the grid, there is a rising risk related to the effects of harmonic currents. Resonance analysis should therefore be part of power system expansion planning. In this paper, network harmonic modeling and analysis are discussed, in particular, power transformer and power converter frequency models are proposed. Frequency scanning and resonance mode analysis are compared and discussed. The changes in resonance response due to transmission network expansion are drawn. The methods are applied to the investigation of the impact of one link reinforcement, both ac and ac solutions, as well as the impact of the power transformer disconnection. The performed analysis enables finding the resonance location at each studied case. The frequency analysis methods presented in this paper enable forseeing network frequency behavior that is valuable for both network analysis and network expansion planning. [ABSTRACT FROM AUTHOR]

This paper proposes a new bidirectional resonant dc–dc converter suitable for wide voltage gain range applications (e.g., energy storage systems). The proposed converter overcomes the narrow voltage gain range of conventional resonant dc–dc converters, and meanwhile achieves high efficiency throughout the wide range of operation voltage. It is achieved by configuring a full-bridge mode and a half-bridge mode operation during each switching cycle. A fixed-frequency phase-shift control scheme is proposed and the normalized voltage gain can be always from 0.5 to 1, regardless of the load. The transformer root-mean-square (rms) currents in both the forward and reverse power flow directions have a small variation with respect to the voltage gain, which is beneficial to the conduction losses reduction throughout a wide voltage range. Moreover, the power devices are soft-switched for minimum switching losses. The operation principles and characteristics of the proposed converter are firstly analyzed in this paper. Then the analytical solutions for the voltage gain, soft-switching, and rms currents are derived, which facilitates the parameters design and optimization. Finally, the proposed topology and analysis are verified with experimental results obtained from a 1-kW converter prototype. [ABSTRACT FROM PUBLISHER]

The modeling and control of a buck–boost and stacked dual half-bridge (DHB) integrated bidirectional dc–dc converter have been studied in this paper. This converter features high-voltage transfer ratio, high efficiency, and the minimum number of switches. In this paper, an extended, continuous, full-order, state-space averaging modeling method is proposed. Compared with existing methods, the proposed method exhibits higher coincidence with the switching circuit simulation, in steady and especially dynamic states. Due to its high dynamic accuracy and low complexity, the proposed modeling method provides a better theoretical analysis and a fast simulation tool for transient process and control design of converters with dual-active-bridge units, especially with DHB units. By using this method, the high-frequency transformer series inductance current is directly divided into a sampled dc component and a fluctuant component. Only the sampled dc one is included into state variables, but both components are considered into state equations. Besides, this method regards the entire converter as a linear superposition of its subsections, which provides a stepwise modeling based on linearization of subsections. Moreover, a decoupled proportional-integral control method is proposed to enhance the stability and dynamic response of the converter. This control method is analyzed by the proposed models, which can be regarded as an application of the proposed modeling method. Simulation and experiments have validated both the proposed modeling and the decoupled control strategy. [ABSTRACT FROM PUBLISHER]

This paper presents a new feed-forward strategy for suppressing low-order harmonic circulating currents in pulsewidth-modulated (PWM) based modular multilevel converters (MMCs). The approach is based on the new average model approach established in this paper, which identifies cross-coupling interactions between the system-level and submodule elements using decomposed dependent sources. As well as improving the damping of the system, the major advantage of this approach is that it maintains the natural DC bus balance property of a PWM modulated MMC by considering the upper and lower arms together (unlike existing feed-forward schemes which treat each MMC arm independently). Moreover, unlike existing direct control resonant strategies, which require careful gain tuning and are highly dependent on the ac system frequency, the proposed approach achieves wideband circulating current ripple suppression without requiring knowledge of the circulating current harmonic frequencies and needs only a simple proportional–integral (PI) controller to regulate the circulating current dc component for power balance. This makes it particularly suitable for use in multifrequency or variable-frequency ac systems. Extensive simulation and matching experimental results, including steady-state and transient responses compared against existing circulating current suppression approaches, validate the effectiveness and benefits of this new feed-forward compensation technique. [ABSTRACT FROM PUBLISHER]

This paper presents a hybrid seven-level converter based on T-type converter and H-bridge cascaded suitable for low-voltage and high-power-density applications. The operation principles and conduction paths are analyzed comprehensively. Voltage balance control of the floating capacitors is the key point of this paper. Mathematical expressions of capacitor voltage balance conditions are deduced based on sinusoidal pulse width modulation (SPWM). The results show that floating capacitor voltages are only balanced when the modulation index is below 0.82 under SPWM. In order to enlarge the modulation index ensuring the capacitor voltage balance, space vector modulation (SVM) is also applied to regulate floating capacitor voltages taking advantage of redundant switching vectors. Meanwhile, in SVM, there are no additional control requirements for the capacitor voltage. Taken both SPWM and SVM into consideration, the limit to the range of operation for this seven-level converter is presented, which is a function of the modulation index and the power factor. The merit of dc voltage utilization improvement in this topology is also analyzed based on simulation results. Simulations and experimental results under different modulation index and RL load are presented to verify the modulation strategies illustrated in this paper. [ABSTRACT FROM PUBLISHER]

A time-based (TB) receiver (RX) with a 2-tap TB decision feedback equalizer (DFE) is proposed for mobile DRAM interface. The TB RX consists of a voltage-to-time converter (VTC), a TB DFE, and a time comparator. The VTC converts the RX input voltage to a time difference between two VTC outputs by using the difference in clock-to-Q delays between two latches with different input offset voltages. The TB DFE inserts an additional delay to one of the two VTC outputs and bypasses the other VTC output to increase the time opening. The time comparator makes a decision with the first arriving edge of the two outputs of the TB DFE. While the feedback loop delay must be less than 1 UI for proper operation in the conventional voltage-based DFE, the TB DFE allows the feedback loop delay up to 1.43 UI in this paper. A transmitter (TX) transmits a single-ended signal of 200-mV swing by using an n-over-n voltage-mode driver. The transceiver in a 65-nm CMOS process achieves a 12.5 Gb/s with a 0.8-V supply through a 15-inch FR-4 channel of 14-dB loss. The TX and RX chip consume 4.3 and 3.4 mA, respectively. The energy efficiency is 0.49 pJ/b. [ABSTRACT FROM AUTHOR]

An extended-duty-ratio (EDR) boost converter is studied extensively in this paper for high voltage gain applications with a wide input (and/or output) voltage range. The EDR is a unique combination of an interleaved, multiphase boost converter and switched capacitor configuration that achieves high voltage gain with significantly lower switch voltage stress and switching losses compared to conventional high-gain solutions. Most of the switches in the multiphase EDR experience only a fixed fraction of the output voltage ($1/M, 2/M$ , etc., where $M$ is the number of phases). Through extensive analysis over a wide operating range, it is shown here that the EDR boost converter has inherent current sharing among the phases only in a limited range of duty ratio— $(M-1)/M \leq D \leq 1$. As the duty ratio reduces beyond this range as required in wide input voltage applications, inherent current sharing property is lost. In this paper, techniques to ensure current sharing under all operating zones without requiring current sensors are presented. Instead of having equal duty ratio for each phase, it is adjusted for each phase according to the operating region of the converter. Extensive analysis is presented to derive the required duty ratio changes for the different phases. The proposed concept is validated with experimental results from a 250 W, 3-phase EDR boost, and GaN-based hardware prototype. [ABSTRACT FROM AUTHOR]

This paper proposes a family of soft-switching bidirectional converters. In many applications, the bidirectional converters operate over a wide range of duty cycle and load variations. In the proposed converters, in order to extend the zero-voltage switching operation range, two supplemental voltage sources utilizing passive components are implemented in the auxiliary circuit. By using this method, the soft-switching features are ensured for an extensive range of the converter duty cycles. This is achieved independent of the output power value or the converter operation mode, and so, soft switching is ensured within the entire converter operating region. In these converters, all semiconductors components are soft switched, and the auxiliary circuit does not contribute to the complexity of the control circuit. Also, no extra voltage stress exists on the main switches and the voltage stress on the auxiliary switches is lower than the main switches voltage stress. In this paper, the proposed bidirectional buck/boost converter is analyzed and to confirm the feasibility of the proposed method, experimental results of a 150-W prototype converter are presented. [ABSTRACT FROM PUBLISHER]

In the presence of multiple power converters in a power system the total current may exhibit zero-crossing distortion in the form of recurrent damped oscillations with high magnitude. These oscillations are synchronized with the power system frequency. This paper presents a comprehensive analysis of the input current of single-phase ac-dc converters fitted with power factor correction (PFC) controllers. Emphasis is given on the impacts of the source impedance, and on how the number of converters connected to a common coupling point (PCC) impacts the PFC controller’s performance. A system model is developed followed by simulation and measurements in a real installation with electronic ballasts used to drive fluorescent lighting tubes. Results show that the recurrent damped oscillations originating from PFC controllers are close to the harmonic range and with a very low level of cancellation between devices. The magnitude therefore increases proportionally with the number of devices. As the source impedance increases, instability may occur. Possible explanations for these observations are discussed. [ABSTRACT FROM AUTHOR]

The single-phase-to-ground (SPG) fault at the valve side of the converter transformer is one of the most critical faults threatening the operation of bipolar half-bridge modular-multilevel-converter-based multi-terminal direct-current (HB-MMC MTDC) systems. Following a valve-side SPG fault, the upper-arm submodule (SM) capacitors in the faulty converter may suffer a serious overvoltage, and the grid-side fault currents may experience no zero-crossings. The existing protection methods generally rely on tripping the grid-side alternate-current circuit-breaker (ACCB), which cannot fully isolate the fault. The healthy poles and stations may encounter severe disturbance and be all blocked, which will lead to a power outage of the entire MTDC system. This paper proposes an ACCB-independent scheme based on thyristor-pairs and damping SMs to address these problems. Antiparallel thyristor-pairs are connected in series within the upper and lower arms in each phase. Serial damping SMs are connected within the lower arms to help the lower-arm thyristor pairs cut off the fault currents. Although the proposed additional devices inevitably cause conduction losses, they can effectively protect the faulty converter and healthy circuit in the MTDC system. Simulations in PSCAD/EMTDC have been conducted to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

Differing from a two-level voltage source converter (TL-VSC), the internal dynamics of a modular multilevel converter (MMC) are much more complicated. Since the fluctuation of submodule capacitor voltage is unavoidable when transmitting power, the MMCs output voltages cannot track the references perfectly. The interaction between the time-varying capacitor dynamics and controllers may lead to self-instability of the MMCs. In order to address this self-instability issue, this paper first establishes the small-signal closed loop transfer function matrices (TFMs) of the external and internal control loop by the harmonic linearization method. Further, a novel design principle of MMC controllers is proposed. Then, the critical impact factors on the stability of circulating current controller and AC voltage controller are investigated based on the generalized Nyquist criterion(GNC). The proposed models and analysis methods are validated by time-domain simulations in PSCAD/EMTDC. [ABSTRACT FROM AUTHOR]

A rapid deployment of renewable generation has led to significant reduction in the rotational system inertia and damping, thus making frequency control in power systems more challenging. This paper proposes a novel control scheme based on Model Predictive Control (MPC) for converter-interfaced generators operating in a grid-forming mode, with the goal of exploiting their fast response capabilities to provide fast frequency control service to the system. The controller manipulates converter power injections to limit the frequency nadir and rate-of-change-of-frequency after a disturbance. Both centralized and decentralized MPC approaches are considered and compared in terms of performance and practical implementation. Special attention is given to the decentralized controller by generating an explicit MPC solution to enhance computational efficiency and reduce hardware requirements. Simulation results obtained from a detailed dynamic model of the IEEE 39-bus system demonstrate the effectiveness of the proposed control schemes. [ABSTRACT FROM AUTHOR]

This paper proposes an interleaved buck converter (IBC) with continuous input current, extremely low output current ripple, low switching losses, and improved step-down conversion ratio. Unlike the conventional IBC, the proposed converter has a continuous input current, and its output current ripple is extremely low. The proposed converter has a lower voltage stress in comparison to the conventional IBC and can also provide a high step-down ratio, which makes it a proper choice for high-power applications where a nonisolated step-down converter with low output current ripple and continuous input current is required. Also, the proposed converter can provide current sharing between two interleaved modules without using additional current-sharing control method. All of these benefits are obtained without any additional stress on the circuit components. A prototype converter with 200-V input and 24-V–10-A output is implemented to verify the theoretical analysis. Operational principles and experimental results are presented in this paper. [ABSTRACT FROM PUBLISHER]

Direct ac/ac topologies for ac-to-ac power conversion benefit from the absence of dc-link capacitors, and therefore, are highly reliable and have low cost as compared to the traditional voltage-source inverter (VSI)-based topologies. This paper deals with one of the more important tradeoffs considered in designing highly efficient converters: Losses. It is shown in this paper that the direct ac/ac converters have an inherently higher efficiency than their VSI-based back-to-back counterparts due to a dramatic reduction in switching losses (nearly 60%). Further, this paper compares the performance of three different device types (SiC MOSFETs, hybrid Si IGBT/SiC diode, and Si IGBTs) using wide-range device characterization that help to create detailed loss models. It is conjectured that traditional datasheets lack the level of detail needed for computing losses in direct ac/ac converters, and the availability of a multivalue voltage, current, and temperature-based loss profile is advocated. Using the obtained loss models, a comparison is drawn between the considered devices through simulations when operated in a 13-kV/1-MW direct ac/ac power flow controller, the controllable network transformer (CNT). The same loss-models are also used to compute losses in an experimental prototype of a 720-V, 10-kVA CNT and the results are compared with direct efficiency measurements. A similar computation is carried out for another experimental prototype at a 6.7-kV, 400-kVA, three-level, paralleled CNT. These experimental tests are used to confirm the validity of the analytical results presented in this paper. [ABSTRACT FROM AUTHOR]

In recent years, many advanced control strategies have been proposed for wave energy converters (WECs), which significantly increase the energy conversion rate of the devices. So far, most of these control schemes have only been investigated theoretically using simulations, which, to a great extent, are based on idealized assumptions. On the contrast, far less information regarding the testing of these control schemes in experimental setups can be found. Under such circumstances, the control performance might be compromised by many factors such as model uncertainties, measurement noise, or delay. This paper compares the performance of a spring damper control and an advanced control strategy for a point absorber WEC in wave tank experiments. For two different irregular sea states, the energy conversion of the advanced control, which uses an observer to estimate the wave excitation force, is compared to the performance of a spring damper control. The results show that, with the advanced controller around 13%–14%, more energy could be converted when compared to the spring damper control. Additionally, the observing process was found to be critical in the advanced control. The conducted experiments show that an increase in the observer accuracy holds a theoretical potential to further improve the energy conversion rate by 15%–25%. [ABSTRACT FROM PUBLISHER]

Permanent magnet brushless dc (BLDC) machines are widely used due to various advantages such as high efficiency and high torque density, and therefore compactness as well as long expected lifetime. All of these benefits are of major interest when designing a drive for a small fan application of a few watts. This paper presents the design investigations of a small single-phase BLDC motor for such an application. Notably, it discusses different constraints which arise during the design process and which may be of special relevance due to the particular given power level and application. [ABSTRACT FROM PUBLISHER]

This paper presents the performance analysis and comparison of two types of bidirectional dc–dc converters—cascaded buck–boost capacitor in the middle and cascaded buck–boost inductor in the middle for use in plug-in electric and hybrid electric vehicles. The comparison of the two converters is based on device requirements, rating of switches and components, control strategy, and performance. Each of the converter topologies has some advantages over the other in certain aspects. Efficiency analysis has been carried out for specific scenarios in vehicle applications. The simulation and experimental results are provided for both converter types. [ABSTRACT FROM PUBLISHER]

The growing interest in clean and sustainable electric energy pushes toward increasing the interconnection of wind energy conversion systems (WECSs) to utility grids. The designs of the majority of WECSs employ power electronic converters (PECs), which generally have nonlinear and switched characteristics. The characteristics, operation, and control of PECs in WECSs can result in nonconventional voltage–current behaviors during faults. This paper investigates the voltage–current behaviors during faults that occur in grid-connected WECSs. Two types of WECSs are considered in this paper, which are the doubly fed induction generators and permanent magnet generator based WECSs. The voltage–current behaviors are investigated in experimentations for different faults occurring in different parts of the test grid-connected WECSs. [ABSTRACT FROM PUBLISHER]

This paper presents a modified Dickson converter to achieve wide input range capacitive DC-DC converters. Several implementations are carefully studied and compared, which shows that the folding Dickson converter is the best choice, not only for its reduced dynamic losses, but also for its very regular structure and operation. Folding is achieved by merging the terminals of two or more flying capacitors, creating one equivalent flying capacitor. In this design, a four stage folding Dickson converter is implemented to achieve four different voltage conversion ratios. A Bootstrapped Gate Boost Converter (BGBC) is proposed which uses a bootstrapping technique to generate a floating rail for the flying switches, whose terminal voltages vary by large amounts depending on input voltage and VCR. The inherent operation of the Dickson topology is used by copying the voltage of the flying capacitors on a grounded capacitor in one phase, which can then be used to generate a floating 1.2 V in the second phase. The converter has been implemented in a 90 nm technology, achieving a maximum output power of 50 mW, peak efficiency of 76.6% in the 2:1 conversion mode, and an average efficiency above 60% over the entire Vin and Pout range. [ABSTRACT FROM AUTHOR]

Resonances can have a negative impact on a voltage-source converter–high voltage dc (VSC–HVDC) system. This paper develops dc impedance models for the rectifier and inverter stations for a VSC-HVDC system when they are viewed from a dc terminal. The impedance models take converter controllers into account. The derived impedance models are validated by comparing frequency responses of the analytical model and the impedance measured at the dc terminal from a detailed VSC–HVDC model simulated in a real-time digital simulator. Resonances are examined in the frequency domain (e.g., Bode plots and Nyquist plots) using the derived analytical impedance models. The analysis is verified by time-domain simulations. Real-time digital simulation in RT-Lab demonstrates that the dc capacitor has a significant impact on resonances while the power transfer level has an insignificant impact on resonances. [ABSTRACT FROM AUTHOR]

This paper presents the results of an investigation of the steady-state safe operating conditions for large-signal silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) circuits. By calculating capacitive currents within the intrinsic transistor, avalanche inducing currents through the transistor junctions are isolated and then compared with dc instability points established through simulation and measurement. In addition, calibrated technology computer-aided design simulations are used to provide further insight into the differences between RF and dc operation and stress conditions. The ability to swing the terminals of a SiGe HBT beyond the static $I$ – $V$ conditions coincident with catastrophic breakdown is explained. Furthermore, hot-carrier effects are also compared from multiple perspectives, with supporting data taken from fully realized $X$ -band and $C$ -band cascode driver amplifiers. This analysis provides microwave circuit designers with the framework necessary to better understand the full-voltage-swing potential of a given SiGe HBT technology and the resultant hot carrier damage under RF operation. [ABSTRACT FROM AUTHOR]

A new, simple and high-accuracy impedance-to-digital converter (IDC) is proposed in this paper. Conventionally, the parameters of sensors that can be modeled using a parallel combination of a capacitor ( C ) and a resistor ( R ) are measured using ac bridges, excited from a sinusoidal source. Recently, with the widespread use of digital systems in instrumentation, capacitance-to-digital converters and resistance-to-digital converters gained a lot of importance. An IDC that accepts sensors having C and R in parallel and provides digital outputs directly proportional to the C and R values is presented in this paper. This can be used not only for sensors whose C and R values vary with the measurand but also when C or R of a sensor needs to be measured keeping the output not affected by parasitic R or C present in parallel with the sensing element. Another application of the IDC is in the measurement of the dissipation factor of dielectric materials. The proposed IDC is based on a dual-slope technique, and hence provides high accuracy and immunity to noise and interference. A prototype of the proposed IDC has been developed and tested in the laboratory. Accuracy of the prototype IDC developed was 0.15% for the measurement of C and 0.04% for the measurement of R . The total conversion time of the prototype converter developed is 3 s, and its total power dissipation is 175.8 mW. The IDC was also interfaced with a polymer-based impedance humidity sensor, measured its C and R values for a range of humidity, computed the humidity, and compared its performance with another instrument, showing the practicality of the proposed IDC. [ABSTRACT FROM PUBLISHER]