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A multi-level boost topology based on a flying capacitor is compared in this work with the hybrid, multi-level, partial power processing topology already presented in the literature for use as a highly efficient and compact dc/dc stage in 1500-V, two-stage, grid-connected PV systems. Different variations of the resonant stage of the hybrid topology are analyzed and compared in terms of losses, volume and complexity. Full multivariable optimization is conducted for the multi-level boost topology with different number of levels and for all the analyzed variations of the resonant stage of the hybrid topology. Appropriately rated new classes of 650-V and 900-V WBG devices are included in the optimization algorithm. It is concluded that due to the dominant conduction losses and gap in the voltage rating of the commercially available WBG devices between 650V and 200V, increase of the number of levels over 4 leads to the deteriorated loss and volume performances. All the analysis related to the resonant stage of the hybrid topology is confirmed by detailed and comprehensive measurements of two prototypes of 4kW of nominal and 7kW of maximal power. Additionally, all the loss models applied in the optimization algorithms presented in this paper are confirmed by detailed measurements, thermal calibration and finite element thermal simulations of the wide bandgap devices and inductor designs employed in this work. [ABSTRACT FROM AUTHOR]

Multilevel inverters (MLIs) are playing a pivotal role in the power sector with potential applications, such as interfacing renewable energy sources with the grid and several industrial drive applications. MLIs with a smaller number of switching devices are more promising due to their compact size, reduced cost, and higher efficiency compared with their traditional counterparts. This paper, therefore, presents a new three-phase seven-level inverter. This topology is a combination of two cascade-connected two-level voltage-source inverters (VSIs) and H-bridge cells with flying capacitors (FCs). This paper presents the operating principle and the balancing technique for the dc-link capacitors and FCs. The generation of various output voltage levels and the limitation of the sinusoidal pulsewidth modulation control for FC voltage balancing is also presented. The number of components in the proposed circuit configuration and their voltage ratings are considerably lower compared with the recently proposed topologies. The behavior of the proposed circuit configuration is first assessed with simulation studies and is then tested with a laboratory prototype. The simulation and experimental results validate the effectiveness of the proposed topology and the voltage balancing technique. [ABSTRACT FROM AUTHOR]

With the rapid development of photovoltaic and fuel cell stacks, high voltage gain converters are urgently demanded. Conventional boost is limited by the exaggerated duty cycle, it is impossible to obtain a high voltage gain while ensuring efficiency. Therefore, a zero-voltage switching (ZVS)-modified SEPIC converter that combines a voltage multiplier cell with traditional SEPIC is proposed in this paper. With detailed parameters design process, this presented converter works at zero voltage switching (ZVS), while obtaining high voltage gain without extremely high duty cycle. Besides, voltage stress is also reduced and low-voltage component with lower parasitic parameters can be used, thus efficiency is maintained. In order to further improve the power density, an integrated inductor scheme is adopted in this paper without changing intrinsic working states of the two inductors. A 36-W prototype is built, and experiments are conducted to verify the advantages of the proposed converter. The efficiency is up to 91.5% at full load. [ABSTRACT FROM AUTHOR]

This paper presents a dc–dc input-parallel output-parallel (IPOP) converter configuration for renewable energy integration with medium-voltage dc grids. A full-bridge zero-current-switching (FB-ZCS) converter with voltage-doubler output is proposed as the fundamental module. To achieve smooth current commutation and ZCS, the leakage inductance of transformer and a resonant capacitor across its secondary are utilized. This resonant capacitor is always charged to its full-rated capacity irrespective of converter loading and requires a dedicated charging interval resulting in duty-cycle loss. For a given leakage inductance, a large resonant capacitor is required for higher current ratings. With a single-centralized converter, these operational and design constraints result in significant duty-cycle loss, restricting the operation range. This paper proposes an IPOP configuration for high-power applications. Phase shedding at reduced loading ensures that individual modules are operated optimally. Input inductance requirement in modules is reduced due to interleaving of the input current. Additionally, voltage stress across converter components and input current ripple are reduced by 50% in the proposed converter modules. Steady-state operation, modeling, current-sharing control, start-up, and shutdown of modules in the IPOP configuration are demonstrated using simulations. Experimental results on a scaled-down prototype are presented to validate its operation. [ABSTRACT FROM AUTHOR]

This paper presents a neutral-point deviation and ripple compensating control method applied to a three-level neutral-point-clamped (NPC) converter. The neutral-point deviation and its harmonic components are analyzed with a focus on the average current flowing through the neutral-point of the dc link. This paper also proposes a control scheme compensating for the neutral-point deviation and dominant harmonic components under generalized unbalanced grid operating conditions. The positive and negative sequence components of the switching functions and ac input currents are employed to accurately explain the behavior of three-level NPC converter. Simulation and experimental results are presented to verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]

A high-frequency high voltage gain discontinuous conduction mode coupled-inductor boost LED driver based on planar component is presented in this paper. GaN switch is adopted with lower conducting resistance and higher switching speed. Zero voltage switching (ZVS) is achieved at the same time to reduce high switching loss caused by high switching frequency. Compared with the previous work, the voltage gain is higher and efficiency is higher because of ZVS. This paper focuses on high efficiency; therefore, resonant gate driver is adopted and efficiency is increased by 0.6%. In terms of the coupled-inductor, planar component is used and parameter optimization is also proposed to realize lower loss, including wingding loss and fringing loss caused by the air gap. A 500 kHz 36 W prototype has been designed to demonstrate theoretical analysis. In addition, comparison of drive loss between the resonant gate driver used in this paper and conventional driver implemented by Si8271 is made, revealing advantages of the resonant driver. Obtained efficiency was up to 92.1% at full load. [ABSTRACT FROM AUTHOR]

Power converters are one of the failure sources in modern power systems, and hence driver of maintenance and downtime costs, which should be reduced by reliable design, control, and operation of converters. This paper proposes a power sharing control strategy for evenly distributing the thermal stresses among dc converters in dc microgrids, and consequently enhancing the overall system reliability. The aim of this paper is to extend the aging process of failure prone converters by adjusting their loadings. The proposed approach employs the prior experienced thermal damages on the converter's fragile components in order to adjust its contribution on demand supply. According to the proposed strategy, the higher the thermal stress on a converter is, the lower the power it will supply. As a result, the overall system reliability will be improved. A numerical case study on a dc microgrid is presented to illustrate the effectiveness of the proposed power sharing strategy. Moreover, experimental tests are provided to demonstrate the applicability of the reliability-oriented power sharing method. [ABSTRACT FROM AUTHOR]

This paper presents a high power factor (PF), low total harmonic distortion (THD) light-emitting diode (LED) driver with dimming capability. In addition, the proposed technique ensures a high PF and low THD at any dimming level. The driver is implemented by using an interleaved capacitor, which is placed between the rectifier and the integrated buck flyback converter (IBFC). In this way, the line current conduction angle is increased, which in return increases the PF and decreases the THD. The operation of the proposed converter ensures that one diode of the conventional IBFC will not conduct, so that it can be removed. Moreover, owing to the continuous power flow, the proposed technique makes a significant reduction of the converter output ripple. The paper presents a prototype of the proposed converter supplying an LED luminaire of 37 V/ 0.67 A. The prototype shows a high PF of 0.997, small THD of 2.5%, output current ripple of 6%, and an efficiency of 80%. [ABSTRACT FROM AUTHOR]

The switching speeds of next-generation power semiconductor devices, such as those made of silicon carbide and gallium nitride are roughly ten times those of conventional devices (e.g., silicon insulated-gate bipolar transistors). This increases the frequency range of the electromagnetic noise accompanying the switching operations of pulsewidth modulated (PWM) converters and worsens the influence of radiated noise. The authors have previously proposed an active common-mode filter (ACF) that reduces the radiated noise from the power cables connected to a PWM converter and evaluated its effect in reducing radiated noise by using a function generator as a common-mode (CM) noise source. In this paper, the ACF is applied to a motor drive system fed by a three-phase PWM inverter, and the attenuation characteristics of the CM voltage are evaluated. To avoid saturating the ACF, the combination of an active common-noise canceller and the ACF is discussed. The experimental results show that the system constructed in this paper can suppress the CM voltage produced by the PWM inverter over a wide frequency range from 100 to 100 MHz. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) has been a promising candidate in high voltage direct current (HVdc) transmission systems. Due to the features of simple structure, low cost, and low power losses, half-bridge (HB) is usually adopted as the submodule circuit in the traditional MMC. However, an HB submodule circuit-based MMC does not have the capability of blocking dc short-circuit fault, which obstructs the development of low-cost HVdc systems with overhead lines. In order to solve this problem, an MMC with active clamped T-type submodule (ACTSM) to own dc fault blocking capability is proposed in this paper. Compared with other submodule circuits, the proposed ACTSM has many features, such as symmetrical blocking capability, low power losses, low voltage stress, and low amount of independent drive signals. The topology, operation principle, dc fault blocking capability, and distribution of power losses of the ACTSM are presented in this paper. The effectiveness of the ACTSM-based MMC is validated by both simulations and experiments. [ABSTRACT FROM AUTHOR]

Achieving high efficiency and high power density features of intermediate bus converter (IBC) in data center application is very critical. This paper proposes a nonisolated switched-tank dc–dc converter (STC) to meet the high requirement of IBC. The proposed STC has fixed voltage conversion ratio. Theoretical analysis provides the guideline for designing resonant tank and nonresonant tank as well as selecting proper deadtime for the proposed circuit. With resonant operation feature of the proposed circuit, zero current switching is realized on all switching devices to help the high-efficiency operation of the proposed converter. Through the proposed design methodology in this paper, power loss on switching devices and planar inductors can be minimized. In addition, detailed power loss analysis and breakdown provide hints for further efficiency improvement. Simulation has been performed to validate the operating principle of the proposed STC. A designed 6x STC (450 W nominal/600 W maximum) based on eGaNFETs is demonstrated. With 54 V typical input voltage, the output of the 6x STC is 9 V. The GaN-based prototype achieves a peak efficiency of 98.55%. Also, it achieves 97.18% efficiency and 750 W/in3 power density at 450 W. [ABSTRACT FROM AUTHOR]

This paper presents theoretical and experimental discussions on low-voltage-ride-through operation of a modular multilevel single-delta bridge-cell (SDBC) inverter intended for utility-scale photovoltaic (PV) systems. Modern grid codes require grid-tied inverters to provide dynamic grid support during grid-fault events by injecting reactive current. This paper discusses decoupled positive- and negative-sequence reactive-current control, focusing on asymmetric voltage sags with imbalanced magnitude and phase relationships. The main objective is to present a feedforward control method based on calculation of the zero-sequence current required for achieving power balance during normal and grid-fault conditions. Moreover, this paper demonstrates a practical method that minimizes overcurrent stress in the three inverter clusters by adjusting active power drawn from PV arrays. Experimental results on a three-phase 12.6-kVA system prove that the SDBC inverter is capable of seamlessly operating through asymmetric voltage sags. [ABSTRACT FROM AUTHOR]

This paper proposes an online condition monitoring system for aluminum electrolytic capacitors used as dc-link capacitors in industrial power converters. Electrolytic capacitors are one of the most fragile components of a power converter system because of their wear-out failures and short lifespan. Therefore, the use of condition monitoring systems for aluminum electrolytic capacitors allow preventive maintenance to be performed, thereby avoiding unexpected shutdown and downtime. The dominant wear-out mechanisms in aluminum electrolytic capacitors are characterized by the increase in equivalent series resistance. Hence, the condition monitoring system proposed in this paper is based on the online estimation of the capacitor's equivalent series resistance using the switching frequency components of the dc-link capacitor voltage and current. The equivalent series resistance estimation method is tested using the PSpice circuit simulator and is validated experimentally using a custom-made inverter. Finally, the equivalent series resistance estimation method is adapted for the condition monitoring of capacitors in industrial power converters and the proposed condition monitoring system is implemented in a commercial ac drive system to prove the applicability of the proposed method to industrial power converters. [ABSTRACT FROM AUTHOR]

Harmonic distortion and harmonic resonance problems have been widely concerned and reported in railway electrification systems (RESs) due to the harmonic injection from the nonlinear electric train, especially high-speed/high-capacity/large-power trains. This paper presents an overview of the harmonic and resonance problems in the RES, including harmonic problem composition, harmonic modeling, available influential factors assessment, harmonic resonance, and associated suppression methods. The harmonic problem mainly consists of the background harmonics brought from the utility system, resonance-region harmonics interacted by capacitive and inductive network elements, and characteristic harmonics generated from the switching process of the onboard power conversion system. The mathematical modeling and analysis methods are introduced, including frequency scanning analysis, S-domain analysis, resonance mode analysis, and modal sensitivity analysis. Available influential factors/parameters have been fully investigated against above-mentioned harmonic problems. Finally, different harmonic suppression methods have been compared and summarized in this paper. [ABSTRACT FROM AUTHOR]

A breaker-less shipboard medium-voltage dc (MVDC) system is gaining more attention recently due to its advantage in dealing with a dc fault by using switched-mode power modules and disconnectors. The specific power module investigated in this paper is the power conversion module (PCM) that transforms power from a MVDC to a low-voltage dc (LVDC) bus. The PCM plays an important role in a system-level fault management. The recently emerging isolated modular multilevel dc/dc converter and the widely used dual active bridge converter are promising solutions for PCM applications. The control algorithms including fault protection strategy for both topologies have been developed and presented in this paper. The MVDC side fault and LVDC side fault of each topology has been analyzed and evaluated. The simulation and experimental results are provided to demonstrate the fault protection features of two topologies in a breaker-less dc system. [ABSTRACT FROM AUTHOR]

In this paper, a dc–ac buck converter is proposed as a grid-side converter in high voltage dc (HVdc) transmission systems for high-power renewable energy source grid integration. The proposed architecture consists of multimodules of half-bridge voltage source converters (HB-VSCs). The dc terminals of the HB-VSCs are connected in series across the entire dc link (i.e., capacitor tapped), whereas their ac outputs are connected to multiwinding transformers to provide the three-phase terminals for ac grid integration. The proposed grid-connected capacitor-tapped multimodule converter (CT-MC) architecture, inspired from the HVdc shunt tap proposed by ABB, provides a dc–ac conversion with a relatively moderate voltage rating of semiconductor devices. It also provides operation with a lower number of semiconductor devices, gate driver circuits, voltage sensors, and lower total MVA rating of semiconductor devices (67%) compared with the conventional three-phase HB modular multilevel converter, which positively affects the system cost and reduces the computational burden of the employed controller. In this paper, the operational concept and control of the CT-MC are presented along with a capacitor voltage balancing approach. Simulation results are presented during normal and abnormal conditions to show the viability of the proposed architecture. Finally, a scaled down prototype for the CT-MC is employed to validate the converter operation. [ABSTRACT FROM AUTHOR]

A large number of distributed energy resources (DERs) integrate into the distribution network, which changes the power flow, increases the power fluctuations, and complicates the scheduling of the distribution network. To cope with that, a multitimescale scheduling method, which considers the demand response as well as user satisfaction, is proposed in this paper. First, in the day-ahead stage, both the generation-side and demand-side are combined to minimize the operating costs and reduce the impact of DERs. Second, in the real-time stage, the model predictive control method is introduced, smoothing the power fluctuations and maximizing the consumed renewable energy. Finally, the user comprehensive satisfaction is considered, ensuring the users’ benefit and improving the flexibility of users to participate in scheduling while shifting electricity demands. By optimizing the generation-side and demand-side on both day-ahead and real-time timescales, the proposed method can improve the operation status for the distribution network effectively while ensuring the interests of users. Simulation on an improved IEEE-33 bus distribution system verifies 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]

Multilevel converters with floating capacitors (FCs) are widely applied in recent years in a wide range of industrial applications from high-voltage direct current systems to high power drives. However, some FC topologies lack complete FC voltage balancing capability due to the inherent topology limitation or the insufficient switching state for capacitor balancing. This will result in large ripples on capacitors at low frequency (such as fundamental frequency), limiting their performance and application, particularly, when the fundamental frequency is very low in low-speed drive operations. Typical examples of those multilevel converters are modular multilevel converters (MMC), nested neutral-point-clamped (NNPC) converter, etc. In order to improve the FC balancing for this kind of multilevel converters, this paper proposes a carrier-based pulse-width modulation (PWM) method, named stair edge PWM method. This method can obtain sufficient redundant switching states for FC voltage balancing by producing multiple levels in one PWM period. The FC voltage balancing is thus achieved at switching frequency, which can greatly reduce the capacitor voltage ripple and therefore enable the use of much smaller FCs. Meanwhile, the voltage stress on each device and low $dv/dt$ feature are still the same as the normal multilevel operation, reserving two of the most salient features of multilevel converters. The proposed method also features much simpler and easier implementation compared with space-vector-based approaches, particularly when high-level converters are considered. An application example using a four-level NNPC converter is provided in this paper. The effectiveness and performance of the proposed method are verified by both simulation and experiment. [ABSTRACT FROM AUTHOR]

This paper presents a single-stage nonisolated switched capacitor ac–dc converter for power-factor correction (PFC). This converter features reduced passive components, single switch, transformerless high voltage gain, and improves the power factor, reduces total harmonic distortion, and voltage stress across the switch. The peak current mode with a dynamic resonant perturbation scheme compensates the subharmonics that exist at zero crossing of the source current is implemented for PFC. In this paper, the principle of operation, large signal modeling of the circuit, and control method for the proposed PFC converter are provided. [ABSTRACT FROM PUBLISHER]

With offline single-phase power supplies moving toward the megahertz switching frequency range, the converter's bus capacitor becomes the bottleneck of further improvement of power density. Partial constant power operation is effective in reducing the bus capacitance and capacitor current stress for low-power applications. However, its impact on circuit design and operation design has not been studied thoroughly. With the developed circuit operation and loss model, this paper presents design considerations and power loss analysis of megahertz ac/dc converters in partial constant power operation. An adaptive constant power control is also proposed, based on the developed models, to improve the light-load efficiency and power factor. A 65 W, megahertz critical conduction mode GaN-based ac/dc converter prototype has been developed to validate the analysis and circuit operation method. Compared with power factor correction (PFC) operation, partial constant power control exhibits an efficiency drop of less than 1%. However, a 50% reduction of bus capacitance can be realized. With the proposed adaptive constant power control, the light-load efficiency and power factor can be improved to be a level similar to the PFC operation. This paper ends with a discussion of the possibility of extending the proposed operation method to higher power applications. [ABSTRACT FROM PUBLISHER]

The safe operation of grid-connected power converters during abnormal condition is a key issue in order to guarantee operation and to avoid undesired trips. In this paper, different control strategies for the operation of a D-STATCOM are introduced, where the reference currents are determined in such a way that not only will none of the phase currents go over the limits, but also the dc voltage fluctuations remain in safe operation limits. Fluctuating active power interchange during unbalanced condition leads to dc voltage oscillation. Severe unbalanced condition and small dc capacitor selection (to meet the size and cost constraints) intensify the dc voltage oscillation. Therefore, the contribution of this paper relies on the combination of the dc voltage oscillations and the current limit control. The effectiveness of three proposed control strategies is verified by simulating a D-STATCOM tied to an industrial distribution network. Moreover, a scaled scenario has been reproduced experimentally which shows that the results cope well with the analytical equations and the simulation results. [ABSTRACT FROM AUTHOR]

This paper proposes a method to suppress the resonant current circulating between integrated half-bridge modules with phase-leg capacitors in two legs. This circuit configuration has the advantage of low stray inductance between power semiconductor devices and dc-link capacitors (phase-leg capacitors). This paper presents an analysis of the equivalent circuit for the circuit configuration that suggests that the dc-link capacitor current will increase depending on the relationship between resonant and switching frequencies. The capacitor current was experimentally evaluated under pulse-width modulation operation at switching frequencies up to 100 kHz using SiC-mosfet s. As a result, the resonant current may occur in the dc side when the resonant frequency between phase legs was close to either the fundamental or the third harmonic of the switching frequency. In order to suppress the circulating resonant current, a graphite bus bar is applied to the phase-connecting bus bar. Using the graphite bus bar, the capacitor current can be reduced by 35% without any influence from the ac-side output current. [ABSTRACT FROM AUTHOR]

This paper presents a novel single source fed isolated gate driver circuit based on the dual-forward converter topology. The two forward converters are paralleled at the secondary side to achieve 0%–100 $\%$ duty cycle range together with galvanic isolation. The gate driver switching frequency is independent of the main pulse-width modulation frequency (PWM). As a result, the gate driver switching devices and magnetics are designed for high frequencies independent of the main PWM frequency. At high frequencies, problems of resonance due to parasitics become significant. This paper discusses this problem and proposes a novel solution to mitigate it. In addition, this paper also presents a novel solution and circuit to produce negative gate pulse for miller clamp. The proposed circuit can be used for any application, irrespective of switching frequency, thus making it a wide band generalized gate driver. The circuit is analyzed and verified experimentally. [ABSTRACT FROM PUBLISHER]

Low-voltage dc (LVdc) distribution networks have the potential to release larger capacity without having to upgrade the existing cables. One of the main challenges of LVdc networks is the extra customer-end dc–ac conversion stage. This paper proposes and evaluates a five-level Si mosfet-based modular multilevel converter (MMC) as a promising alternative to the conventional two-level insulated gate bipolar transistor-based converter. This is due to the comparatively higher efficiency, power quality and reliability, and reduced electromagnetic (EM) emissions. A comprehensive analysis of a Si mosfet five-level MMC converter design is performed to investigate the suitability of the topology for LVdc applications. Detailed theoretical analysis of the five-level MMC is presented, with simulated and experimental results to demonstrate circuit performance. To suppress the ac circulating current, especially the dominant second harmonics, this paper presents a double line-frequency proportional integral (PI) with orthogonal imaginary axis control method. Comparison of simulation and experimental results with those for double line-frequency proportional resonant control shows that the proposed PI controller has a better performance. In addition, it is simpler to implement and more immune to sampling/discretization errors. [ABSTRACT FROM PUBLISHER]

In this paper, a generalization for three-phase four-wire inverters is proposed. In this generalization, an arbitrary number of three-phase four-wire dc–ac converters are cascaded by means of injection transformers, in order to compose a resultant inverter with a single dc link. Its converters may have four or three legs composed by a pair of the complementary insulated-gate bipolar transistor. The injection transformers have different turns ratios calculated in order to maximize the number of levels produced in the output voltage. In this way, the converter cells within the inverter are asymmetrical in terms of power rating. In this paper, the proposed generalization is applied to a specific case, where two four-wire converters are cascaded, which generates four different proposed configurations. These configurations are analyzed in detail and compared with the conventional four-leg inverter by means of data acquired from simulation and experimental results. In these results, the proposed and conventional inverters feed an unbalanced three-phase load accordingly to the same reference voltage, and the load current total harmonic distortion, voltage weighted total harmonic distortion, transformers and semiconductors losses, switching frequency, and power rating are analyzed in order to conclude that proposed configurations present better performance, even though they have more semiconductors and demand injection transformers. [ABSTRACT FROM PUBLISHER]

This paper discusses and compares phase-shifted pulse-width modulation (PS-PWM) and level-shifted PWM (LS-PWM) in a modular multilevel single-delta bridge-cell (SDBC) inverter for utility-scale grid-tied photovoltaic applications. This three-phase SDBC inverter provides the capability of operating even under power-distribution imbalances not only among three clusters, but also among cascaded bridge cells in each cluster. The main focus of this research lies in analyzing the capability of operation under severe power-distribution imbalances and presenting power-balancing methods based on zero-sequence current injection, which result in an extended power-balancing capability. This paper highlights that LS-PWM is superior to PS-PWM in both power-balancing capability and harmonic performance at the ac side of the SDBC inverter when operating under power-distribution imbalances. Experimental results obtained from a three-phase 10-kW downscaled system show good agreement with those from the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper proposes an LC-compensated electric field repeater to extend the transfer distance of a capacitive power transfer (CPT) system. The repeater contains two metal plates connected with an external capacitor and an external inductor. The plates are used to generate electric fields to transfer power. The external inductor and capacitor are used to resonate with the plates in order to increase the voltage levels. The repeater is placed between a transmitter and a receiver, which also contains metal plates compensated by an LC network. The repeater can increase the transfer distance of the CPT system without significantly influencing the system power and efficiency. In this paper, the capacitive coupler structure and dimensions are designed and simulated using Maxwell software. Considering all the capacitive coupling between plates, an equivalent circuit model is derived. The fundamental harmonics approximation method is used to analyze the working principle of the circuit. A 150 W input power CPT system is designed as an example to validate the proposed repeater structure and compensation circuit topology. The system can achieve an efficiency of 66.9% from dc source to dc load, when the transfer distance is 360 mm and the repeater is placed between the transmitter and the receiver. [ABSTRACT FROM AUTHOR]

In this paper, an electric vehicle (EV) battery charger with interleaved Landsman converter (ILC) followed by a flyback converter, is designed and evaluated for improved power quality (PQ) charging of battery. A built-in wave-shaping is obtained at the charger front-end due to improved PQ characteristics of ILC. This PFC converter consists of two Landsman converter cells, which are designed in discontinuous conduction mode (DCM) to share the input and output currents. The current sharing at input results into lower input current ripple as well as peak current stress through the switch, is reduced. This, further improves the input current harmonics profile. Moreover, the reduced output voltage ripple gives reduced rms current in the output capacitor. A phase shift PWM scheme (PSPWM) is used for ILC and the duty cycle for the switches is selected below 50%. This allows the ripple cancellation at line and load sides. The interleaving at PFC stage as well as DCM based design ensures a low cost charging solution as compared to the conventional Landsman converter (CLC) based chargers in this power range. However, the flyback converter provides the current control during the charging of the battery in constant current (CC) and constant voltage (CV) regions. The harmonics spectrum of mains current follows the recommended PQ regulations over a range of varying line voltages and loadings. [ABSTRACT FROM AUTHOR]

High penetration of renewable energy sources, such as photovoltaic (PV), promotes the clean and sustainable energy spread. Subject to the environmental conditions, intermittency in irradiation change poses the challenge in terms of variable power input to the electrical system. Conventional interfacing power converters such as a boost converter integrating photovoltaic source to the dc utility microgrid in order to push the requisite power to the microgrid suffer from increased stress, resulting in a drop of the system efficiency and possible shutdown of the system. This paper proposes a continuous input current, modular T-impedance boost converter for photovoltaic applications. The boosting capabilities of the converter during both normal boost and shoot-through conditions ensure efficient operation over wide input voltages with reduced stress on the switches. The proposed half-bridge floating ground structure restricts the flow of the common-mode current through the converter. The converter response under intermittent irradiation changes and partial shading conditions are simulated under MATLAB Simulink environment and also are experimentally validated to affirm the capability of the converter. [ABSTRACT FROM AUTHOR]

This paper proposes a modular multilevel converter (MMC) with a filter capacitor for medium-voltage long-cable-fed drive applications. Arm inductors that are inherent components in each phase of MMC are tuned with a filter capacitor to behave like a low-pass LC filter at the MMC output terminal. As a result, the output voltage of the converter is highly sinusoidal with negligible switching frequency harmonics. The overvoltage phenomenon that occurs at motor terminal due to cable resonance and voltage reflection is almost eliminated, and hence, with the proposed concept, the motor can be installed at very long distances from the converter. The voltage amplification at the motor terminal is negligible for different cable lengths with the proposed filter. Additionally, the output voltage quality of the converter is not degraded due to internal fault and subsequent bypass in power cells. The validity of the proposed concept is supported by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a new configuration of high gain (HG) single ended primary inductor converter (SEPIC) with a ripple-free input current to maximize the efficiency of the PV panel for standalone water pumping system (WPS). The ripple eliminating circuit combined with the HG SEPIC converter to achieve reduced ripples in photovoltaic (PV) current is independent to the duty cycle control and hence, it can be easily integrated to the main power circuit of configuration. This circuit does not need any active switches, control, or drive circuit for its execution. The ripple eliminating circuit yields a complete removal of the electrolytic capacitor connected across the PV array and significantly reduces the inductance of the HG SEPIC converter. It also improves the response and power density of the dc–dc converter. The large gain of dc–dc converter enables the use of low-voltage PV panel and minimizes the partial shading and parasitic capacitance effects on PV array source. Due to the substantial compatibility between natural characteristics of switched reluctance motor (SRM) drive and WPS, a four-phase SRM drive is utilized in the proposed scheme. In addition, a single current sensor based maximum power point tracking technique is utilized in the proposed system, which helps to reduce the cost and improve the accuracy of the overall system. Analytical, simulated, and experimental results of the developed system are presented to demonstrate the performance of the system. [ABSTRACT FROM AUTHOR]

This paper proposes two hybrid asymmetric cascaded multilevel inverters for driving medium-voltage open-end winding motors. Each phase of the proposed systems consist of a three-level (3L) H-bridge cell and a nine-level (9L) H-bridge cell connected in series. An unequal dc-voltage ratio of 1:8 between cells is used, providing 19 phase voltage levels. The topologies of the 9L H-bridge cell are based on modular multilevel cascade converter (MMCC) with double-star chopper cells, while the 3L H-bridge cell is fed by a floating capacitor. Compared to conventional MMCC for open-end stator winding motor drives, the proposed inverters can produce more phase voltage levels. In addition, they require a smaller number of power semiconductor switches, drivers and capacitors. Simulations and experimental results are presented in order to demonstrate the performance and feasibility of the proposed topologies. [ABSTRACT FROM AUTHOR]

The operating principle of the clamp circuits like clamping diodes and flying capacitor in three-level LLC converter is different from other three-level converters, because the mean value of the resonant tank current is always zero and pulse-frequency modulation control is generally used instead of pulsewidth modulation control. And the converter with only the clamping diodes or flying capacitor is difficult to realize voltage balance. In this paper, the characteristics of the three-level LLC converter with single clamp circuit are first analyzed. Then, the operation principle of the hybrid-clamped circuit under the unbalanced voltages on input capacitors is described with the mode analysis, based on which the mechanism for voltage autobalance is elaborated and the effects of two clamp circuits are derived. Then, the design of the clamping diodes and the flying capacitor is also involved. Finally, a three-level LLC converter prototype is built and the experimental results verify the validity of the theoretical analysis and design. [ABSTRACT FROM AUTHOR]

A modular quasi-resonant bidirectional dc–dc converter composed of half-bridge gallium nitride modules (HBGM) with reduced switch voltage stress is proposed in this paper. By using an auxiliary capacitor, a resonant circuit is formed to shape the current and voltage so that zero-voltage switching at turn-on instant is achieved. Since the switching loss dominates the power losses in a high-frequency dc–dc converter, the soft-switching performance leads to a noticeable reduction in the total loss; so, the operating temperature will decrease, and consequently, size of the heatsink will be reduced. The proposed circuit takes advantage of enhancement-mode gallium nitride (eGaN) switches regarding their small on-resistance RDS(on), low gate charge, and fast switching speed to improve both efficiency and power density. The main performance issue of adopting GaN switches in a bidirectional dc–dc converter is the high voltage stress of GaN devices, which is handled by connecting the HBGM in the active-clamped stacked configuration, as well as optimizing printed circuit board layout design. Finally, a 1 kW, 600 V laboratory prototype operating at 100 kHz is implemented to validate the proposed concept. [ABSTRACT FROM AUTHOR]

DC microgrid is gaining attraction and a recent trend in distribution power generation system due to penetration of renewables (especially photovoltaic or fuel cell). In this paper, a new triple-switch-triple-mode high step-up converter (TSTM-HS converter) is presented for dc microgrid applications. In the proposed converter, voltage lift technique is employed and range of duty cycle is extended by incorporating an additional switch in converter circuitry. By doing this, high voltage conversion ratio is achieved without using a transformer, coupled inductor, and multiple stages of switched capacitors. Moreover, the TSTM-HS converter operated in three modes with two types of the duty cycles to achieve low to high voltage conversion without using high duty cycle for each switch. The effects of difference in the inductance values on the regulation and operating behavior of the TSTM-HS converter are discussed. The continuous conduction mode and discontinuous conduction mode characteristics of the TSTM-HS converter are discussed in detail with steady-state analysis and boundary condition. The comparison is provided to highlight the benefits of the TSTM-HS converter. The selection of semiconductor devices and the design of reactive components are discussed for the TSTM-HS converter. The experimental results of the proposed converter are provided which validate the theoretical approach, performance, and feasibility of converter. [ABSTRACT FROM AUTHOR]

This paper introduces a new zero current switching topology for parallel balancing of serially connected batteries string. The main advantage of the balancing concept in this study is that energy is transferred only when the cells are unbalanced. As a result, the power losses are significantly reduced since no current circulates through the system when balanced. This has been enabled by a modification of an isolated series-resonant converter operating in a discontinuous conduction mode. A single transformer for two cells is used, as opposed to conventional isolated topologies that require a transformer per cell. The realization is simple and sensorless. Experimental results have been obtained by a prototype of two modules balancing four series-connected batteries. [ABSTRACT FROM AUTHOR]

Matrix-based high-frequency linked (MBHFL) bidirectional dc–ac converters are getting much interest in grid-tied applications due to their high efficiency and the compacted footprint. This paper proposes a new PWM switching technique of the MBHFL dc–ac converters based on phase shift angle considering compensation of the LC filter current at the grid side in order to realize accurate unity power factor and to reduce the total harmonic distortion (THD) of the grid current waveform. The proposed technique estimates the phase shift angle error between the grid voltage and current waveforms due to the capacitor injected current that reduces the power factor at the grid side. It considers two operational modes based on the patterns of three-phase grid voltage and current waveforms. Therefore, it provides the matrix converter switches with different duties according to the pattern of the detected grid voltage and the reference grid current to compensate the phase shift angle error. Also, grid LC filter design and the system controllable limit of the matrix converter output voltage are presented. In addition, the PWM switching technique of the H-bridge circuit is modified to realize safe operation of the converter during step changes at the grid voltage. The effectiveness of the proposed PWM switching technique and its related mathematical model have been investigated experimentally using laboratory prototype based 200 V, 2 kW. [ABSTRACT FROM AUTHOR]

This paper introduces a generalized control method based on the finite control set-model predictive control for a single-phase N-level flying capacitor multilevel rectifier used for solid state transformers. Unlike the conventional finite control set-model predictive control, the proposed method does not use the switching function to calculate the predicted value of the grid current. The proposed method also predicts the dc-link voltage without switching function so that it enables each leg voltages to be controlled stably and independently. Therefore, the number of states to be considered is significantly reduced, in addition to the computational time; and the level expansion of the flying capacitor multilevel rectifier is facilitated. In addition, since the cost function for controlling the grid current and that for controlling the voltage of the flying capacitor is separated, weighting factors are not required. The validity of the proposed method was verified by a simulation of a single-phase 11-level flying capacitor multilevel rectifier using Powersim software, and an experiment on a single-phase 5-level flying capacitor multilevel rectifier prototype. [ABSTRACT FROM AUTHOR]

The integration of switched-capacitor techniques into multilevel inverters (MLIs) with a dc source string contributes to the boosting of voltage gain, renders it particularly attractive in reducing the number of input dc sources in the series string. However, the recent two-stage MLI topologies suffer from high voltage stress across the backend H-bridge. Addressing this concern, an improved topology, namely the one-switched-capacitor integrated MLI (1SCI-MLI) is proposed in this paper. An extended topology of 1SC-MLI is also established by appropriate incorporation of another switched-capacitor circuit. The two proposed topologies are endowed with voltage boosting capability. They also feature low switch count and low number of dc sources. More importantly, they resolve the high voltage stress problem in the existing counterparts. Their corresponding operational analysis and comparisons with recent MLI topologies are discussed. Simulation and experimental results from a laboratory prototype are presented to validate the effectiveness of the proposed topologies. [ABSTRACT FROM AUTHOR]

Recently multilevel inverters (MLIs) have received wide attention from industry and academia, as they are changing into a viable technology for diverse applications. To produce high-quality output using less switch count, development of novel reduced switch MLI (RS MLI) topologies has been a focus of current research theme. This paper presents design and control of a switched-diode dual source single switch MLI (SDDS MLI). The generalized SDDS MLI is first designed using an asymmetric basic unit. Proposed SDDS MLI requires less switch count and driver circuit count compared with the few recently developed RS MLI topologies. To improve the voltage quality by eliminating targeted low-order harmonics, a modified version of fish swarm optimization algorithm is examined for computing optimum switching angles required to control the SDDS MLI. Moreover, suitability and superiority of the derived algorithm are established by comparing with traditional selective harmonic elimination techniques. The developed topology is investigated through several MATLAB simulations as well as experimental tests in the laboratory applying the modified control approach. [ABSTRACT FROM AUTHOR]

The main objective of a photovoltaic (PV) inverter is to inject the PV power into the ac grid. Generally, due to variations in solar irradiance, inverters operate below their rated current. Therefore, this current margin can be used to perform ancillary services, such as reactive power control and harmonic current compensation. However, it is necessary to evaluate the effects of these ancillary services on the converter. The harmonic current compensation, for example, affects the efficiency of the maximum power point tracking (MPPT) algorithms. Therefore, this paper presents a mathematical modeling that relates the harmonic current compensation with the oscillation in the dc-link capacitor voltage, validated through simulation and experimental results. Simulation results show the instantaneous and dynamic efficiency of MPPT algorithms during rapidly irradiance variations and harmonic current compensation. The results lead to the conclusion that all MPPT strategies tested have faced degradation in efficiency due to harmonic current compensation. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMCs) are a realistic alternative to the conventional voltage source converters for medium-voltage (MV) and high-voltage direct current (HVdc) applications. The number of submodules (SMs) per arm of the MMC can be as high as 512 to achieve desired high dc voltage levels required for HVdc with a very low total harmonic distortion (THD) (e.g., <0.1%) of the MMC ac-side interface voltage. Although the low THD of the MMC output voltage with a high number of SMs is desirable, the MMC control implementation and complexity is also important to be considered for the high number of SMs. The MMC control complexity significantly increases as the number of SMs increases. Redesigning the number of SMs in MMCs also becomes quite difficult and may require significant control upgrade, which in turn also needs additional tests and validations. This paper presents an MMC scale-up control methodology applicable for MV and HVdc applications. The number of SMs can be conveniently increased or reduced without any significant control modifications. The proposed control method and capacitor voltage balancing algorithm are implemented in the real-time digital simulator and MMC support units based on field-programmable gate array boards. The performance of the proposed MMC control method is investigated for a point-to-point MMC-based HVdc system under various operating conditions. [ABSTRACT FROM AUTHOR]

This paper presents a novel grid synchronization method with bumpless start that requires minimal computational load and can selectively track the positive sequence of the grid voltage in an unbalanced and distorted three-phase weak grid. Only 12 floating-point operations are required to obtain the in-phase and quadrature components that define a synchronous frame which tracks the positive sequence of the grid voltage. Contrary to a phase-locked loop (PLL), the presented scheme does not require to measure any ac voltages. Therefore, this sensorless method is particularly suited for weak-grid conditions, in which the voltage at the point of common coupling may contain significant noise and can experience larger deviations from the grid voltage (compared to a strong grid) due to the voltage drop in the weak grid impedance. The error in the estimated phase depends on the accuracy of the plant model. If the LCL filter parameters are known, then both the proposal and a PLL-based scheme result in the same steady-state error. Experimental results show the advantages of the proposal compared to a moving average filter PLL. [ABSTRACT FROM AUTHOR]

Mission profiles such as environmental and operational conditions together with the system structure including energy resources, grid and converter topologies induce stress on different converters and thereby play a significant role on power electronic systems reliability. Temperature swing and maximum temperature are two of the critical stressors on the most failure-prone components of converters, i.e., capacitors and power semiconductors. Temperature-related stressors generate electrothermal stress on these components ultimately triggering high potential failure mechanisms. Failure of any component may cause converter outage and system shutdown. This paper explores the reliability performance of different converters operating in a power system and indicates the failure-prone converters from wear out perspective. It provides a system-level reliability insight for design, control, and operation of multiconverter system by extending the mission-profile-based reliability estimation approach. The analysis is provided for a dc microgrid due to the increasing interest that dc systems have been gaining in recent years; however, it can be applied for reliability studies in any multiconverter system. The outcomes can be worthwhile for maintenance and risk management as well as security assessment in modern power systems. [ABSTRACT FROM AUTHOR]

A dv/dt filter is useful to mitigate the deleterious effects of voltage pulses with high edge rates, such as voltage overshoot and ringing in motor drive systems, which can cause premature motor failure. With the introduction of wide-bandgap semiconductor drives, these issues will become more pronounced. This paper introduces a new type of dv/dt filter where the inductor, capacitor, and damping resistor are integrated into the output bus bar or cable of a silicon carbide (SiC) inverter. This integrated filter may be smaller, lighter, and cheaper to construct than filters built from discrete components. An analytical model of the integrated dv/dt filter is developed, and this model is used to design output filters for a 460 V AC, three-phase SiC motor drive. Prototype filters are constructed and tested with a SiC inverter connected to a 460 Vrms, 30-HP induction motor, and experimental results demonstrate output waveforms that match the analytical model and meet the National Electrical Manufacturers Association (NEMA) MG 1 Part 31 requirements for inverter-rated motors. Finally, the voltage waveforms and losses of the prototype-integrated filter are compared with several other mitigation options, demonstrating that the integrated filters meet the NEMA specification at a fraction of the mass and volume of the discrete component solution without sacrificing efficiency. [ABSTRACT FROM AUTHOR]

An improved bridgeless (BL) Cuk converter-based electric vehicle (EV) battery charger with high power factor and increased efficiency is designed and developed in this paper. It provides low cost and high-power-density-based charging solution for the EV. This charger incorporates less number of devices operating over one switching cycle, which reduces the additional conduction loss incurred by a diode bridge rectifier of the conventional charger. Hence, it improves the charger's efficiency. The added advantage of the proposed topology is that the unwanted capacitive coupling loop is removed, as well as the unwanted conduction through the body diode of the inactive switch in the previously developed BL Cuk converter is avoided. This significantly improves the charger's efficiency. For the constant current and constant voltage charging, the commands are synchronized by a flyback converter. The proposed charger draws a sinusoidal current from ac mains and the total harmonic distortion in the supply current is reduced to the limits specified by the IEC 61000-3-2 guidelines. The improved efficiency and power quality indices of the proposed charger are investigated to demonstrate its satisfactory charging operation at all operating conditions. [ABSTRACT FROM AUTHOR]

This paper provides a theoretical and experimental discussion on a modular multilevel triple-star bridge-cell converter with focus on mitigating the capacitor-voltage fluctuation contained in each bridge cell. A new control method proposed in this paper is characterized by properly superimposing both common-mode voltage and circulating currents in the whole speed range. Moreover, this paper optimizes the amplitude and frequency of the superimposed common-mode voltage on the basis of theoretical analysis, thus resulting in minimizing the voltage fluctuation. The optimized control method makes both voltage fluctuation and cluster-current amplitude smaller than do the existing methods. Experimental waveforms obtained from a three-phase downscaled system using a 370-V, 15-kW, 75-Hz, six-pole, permanent-magnet synchronous motor verify good start-up performance from a standstill to the rated speed, keeping both capacitor-voltage and cluster current within acceptable levels. [ABSTRACT FROM AUTHOR]

The hybrid modular multilevel converter with cascaded full bridges (HMMC-CFB) is a recently proposed dc fault tolerant converter topology for high-power applications. It has a director part (DP) consisting of a series of connected half-bridge submodules, and a wave-shaping part (WSP) composed of a series of connected full-bridge submodules (FBSMs). The submodules in DP avoid high voltage stresses and improve synchronization between DP and WSP by slowing down the change rate of DP output voltage. This slowdown is achieved by using a trapezoidal reference signal for DP. The WSP attenuates the voltage harmonics produced by DP. However, the energy exchanged by WSP changes with modulation index, which may cause improper voltage regulation of the submodule capacitors. This paper proposes a new control technique to regulate the energy exchanged by WSP, which uses a variable slope trapezoidal reference signal of DP. To obtain this slope, the feedforward and feedback controllers are used. The feedforward controller gives the value of slope depending on the modulation index (mv) to keep the energy exchanged by WSP nearly equal to zero, whereas the losses and nonideality of the converter are taken care of by the feedback controller. This technique guarantees proper voltage regulation of the submodule capacitors for all modulation indices. The efficacy of the proposed technique is confirmed using simulations and experimentations. This paper also presents a circulating current suppressing controller for HMMC-CFB. The proposed control schemes and dc fault tolerant capability of HMMC-CFB are tested on a grid-connected model built in PSCAD. [ABSTRACT FROM AUTHOR]

Modular multilevel converter (MMC) is believed the most competitive solution for high-voltage direct current (HVDC) transmission using voltage source converters. Circulating current suppressing strategies based on proportional resonant (PR) controllers are widely used in MMC. This kind of strategies can effectively eliminate all the circulating current components in MMC-HVDC. Unfortunately, it can result in dc-line voltage ripples under unbalanced grid conditions, and thus, deteriorates system performance and stability. Moreover, its existing control model may not exactly reveal the inherent characteristic of MMC, and consequently blocks the further understanding and application. To solve these two problems, first, this paper builds a new and effective control model for this strategy. Second, based on the new model, this paper studies the relationship between circulating current reference value and submodule capacitor voltage, modulation index, and arm current to correct and improve the current understanding of this control strategy. Finally, three improved strategies based on PR controllers are proposed. These improved control strategies can eliminate both circulating current and dc-line voltage ripples, which greatly enhance the fault ride-through capability of MMC-HVDC without adding extra control cost or the number of controllers. [ABSTRACT FROM AUTHOR]