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This work studies a multilevel inverter topology composed of two MPUC7s cascaded connected fed by only one dc power source by using a high-frequency link (HFL). This topology can provide up to 49 voltage levels by using four asymmetrical dc links, 12 power switches, and an HFL system. The dc link with higher voltage is fed by a dc source. The other dc links, with lower voltage, are supplied from the main one via high-frequency transformer with unidirectional power flow that processes up to 33% of the load power. A nearest-level control, analysis of power distribution among each dc link, and the HFL system design are presented in detail. Besides, comparisons with other multilevel topologies using HFL are carried out. Experimental results are presented to validate the theoretical studies. [ABSTRACT FROM AUTHOR]

This article provides a distinctive unipolar/bipolar high voltage pulse power generator (PPG) architecture that produces exponential waveform with a rise time in the range of nanosecond. The setup is fit for dielectric barrier discharge applications, in practice. In this work, a push-pull circuit with a three-winding transformer is utilized on the charging side, as well as a quasi-resonant between the transformer leakage inductance and the capacitor on the discharging side to boost the voltage gain. As a result of the two windings on the primary side, and the bidirectional switches on the high voltage side, the tool offers either unipolar or bipolar high voltage pulses from a relatively low dc source. In addition to accomplishing the high gain objective, the effort focuses on lowering the number of circuit elements in contrast to previously studied topologies. The generator functions in discontinuous conduction mode, which enhances system efficiency by allowing complete positive and/or negative waves to be generated while lessening conduction losses. The pulse generator operation intervals are described in depth. The simulation results will demonstrate how this topology outperforms the prior models. Moreover, a 1000-V experimental prototype is also implemented to validate the projected PPG-enhanced properties in real-time. [ABSTRACT FROM AUTHOR]

Modular multilevel converters (MMC) are increasingly gaining its importance in HVDC, drive applications due to several attributes such as modularity, scalability, low device stress, excellent output voltage waveform. For MMC operations, it is important to accurately measure the voltages across the individual capacitors of submodules (SMs). These voltage sensors, while upgrading for high voltage applications, may cause a few concerns in terms of cost, complexity, and data acquisition system. To avoid all these, a discrete time adaptive observer (DTAO) is proposed in this article to observe the voltages across the capacitors of the SMs and use the observed values for closed-loop operation of the MMC. The proposed observer is designed by considering the parametric uncertainty in the MMC and its convergence is proved mathematically. Moreover, the DTAO is compared with existing observation techniques for MMC SM capacitor voltages. The efficacy of the proposed observer is shown through simulation and validated using an experimental setup. [ABSTRACT FROM AUTHOR]

The cascaded H-bridge (CHB) multilevel converter is an attractive solution for integrating photovoltaic (PV) generators with the ac grid. However, the power generated in the PV panels may be unequal due to partial shading, temperature change, and dust layer accumulation leading to unequal and unbalanced power between the phases and possible violation of power quality constraints. Fundamental frequency zero-sequence voltage (FFZSV) injection can be applied, but this method can produce overmodulation in conditions with high PV power mismatch. A new FFZSV is proposed in this article assuming a CHB with a battery energy support (BES) to compensate for the effects of unbalanced PV power generation. A barycentric coordinate representation helps to determine the capacity of the BES required. A coordinated control between the PV system and BES is also proposed in the article. Additionally, a novel approach to deliberate FFZSV injection is discussed in this article by which the maximum charge and discharge rate for the BES can be obtained along with balanced current injection into the grid. The effectiveness of the proposed technique is verified in numerical simulations and with experimental results. [ABSTRACT FROM AUTHOR]

This article investigates the functional link neural network assisted deadbeat predictive current control for an onboard charger (OBC) of an e-rickshaw with multistep charging capability. This control algorithm is presented for wide load operation of OBC since a multistep charging scheme is introduced to reduce the electricity consumption by OBC in the course of the peak load hours. The presented grid-connected OBC topology has two stages interconnected with the dc link capacitor. The first stage is a front-end converter to regulate the voltage at the dc link capacitor. Moreover, it regulates the power quality within the IEEE-519 standard. Furthermore, a dc–dc converter to regulate the charging current is the second stage of the OBC. Keeping this in view, a bidirectional interleaved isolated single ended primary inductor converter (SEPIC) converter topology is utilized. To analyze the performance of the OBC under distinct operating conditions such as grid voltage variations, an experimental prototype of the bidirectional OBC, is developed. Furthermore, the efficacy of the bidirectional operation of the designed system is analyzed through the vehicle to grid operation. [ABSTRACT FROM AUTHOR]

Unlike VSIs, the single-stage inverters (SSIs) from the family of Z-converters are capable of boosting input dc to a desired ac voltage. The Z-network of these converters consists of a symmetric X-shaped network or a combination of inductors and capacitors. The basic Z-source converter (ZSC), connected in X-shaped fashion is modeled as a fourth-order system. This can be further modeled as a second-order system to reduce the sensor count but this may lead to an unstable system if there is an asymmetry in network parameters. Also, the source current of SSIs contains second-order ripple current (SRC) component, which oscillates at twice the supply frequency and has detrimental effects on sources. To alleviate the above problems, a parametric uncertainty compensation and ripple mitigation (PUCRM) control methodology is proposed. PUCRM control can be used to maintain stability and achieve desired performance during parametric uncertainties in the dc–dc stage and to reduce SRC propagating to the sources while feeding ac loads. PUCRM consists of a nominal dual-loop PI controller, which regulates the SSIs to achieve desired performance and a nonlinear integral sliding mode component that mitigates the uncertainties and ripple component. The proposed method is verified using simulation and experimentation. [ABSTRACT FROM AUTHOR]

Battery energy storage systems (BESS) based on modular multilevel converters (MMCs) allow battery packs to be integrated into the electrical grid in a modular fashion. Inherent to the operation of the MMC, the module's dc-link capacitor voltage experiences oscillations at grid frequency and its harmonics. This article investigates the close relation between this voltage oscillation and the battery current ripple. The precise capacitor energy requirements for various operations of BESS-MMC, which include arm/phase power balancing and state-of-charge balancing are analyzed in this article. Furthermore, this article also explores the relation between the controller design and the submodule's (SMs) capacitor sizing in terms of its energy requirements. Design guidelines for the SM level voltage control to attenuate battery ripple and detailed analysis for the capacitor energy requirement in each operating mode are presented. The control and capacitor sizing design are validated in real-time using embedded microprocessors in a Typhoon-based controller hardware-in-the-loop environment. [ABSTRACT FROM AUTHOR]

A 1 MHz active-clamp flyback converter for solar street-lighting applications, featuring a partial power processing, is proposed in this article. The secondary-side resonance between the output capacitor and transformer leakage inductor is utilized to reduce rms current and conduction losses. In comparison with the traditional light-emitting diode drivers based on full power converters (FPCs), the proposed approach that uses partial power converters (PPCs) can significantly improve the overall system efficiency by eliminating the redundant power handling process. The universal schemes are discussed and the optimal solution is eventually determined by the partial power ratio. The advantages of PPC compared with FPC in device stress, losses, and regulation capability are demonstrated by simulation. With GaN devices, a 100 W/1 MHz prototype was built to verify the analysis. The experimental results show that the proposed topology can reduce the power rating of the converter by up to about 80% while increasing the system efficiency by up to 95.8%. [ABSTRACT FROM AUTHOR]

In this article, a multioutput-based transformerless hybrid solar inverter (TLHSI) with no right half-plane zero (RHPZ) and reduced common-mode leakage/ground current is presented for photovoltaic (PV) based microgrid applications. In the proposed multioutput TLHSI, two magnetically coupled inductor coils are placed between the input and dc output sides along with a dc-link capacitor to continuously provide the stored energy to the dc load so that the RHPZ is eliminated and, thus, makes it a minimum phase system. Furthermore, a hybrid unipolar sinusoidal pulsewidth modulation technique is established to nullify the high-frequency components of common-mode voltage across the PV to ground stray capacitor. Also, it normalizes both dc and ac loads at the same instant from a single dc input during each operating state of the proposed TLHSI. The shoot-through issue is resolved in the proposed TLHSI, which increases the system reliability. Furthermore, as the deadtime is not required in between the switching pulses, the quality of the inverter output voltage improves. The performance analysis of the proposed TLHSI is compared with the existing topologies. To validate the performance of TLHSI, a scaled down 340 W laboratory prototype is developed. [ABSTRACT FROM AUTHOR]

In this article, a hybrid wireless power transfer system, which combines induction heating (IH) and inductive power transfer functionalities, is proposed to improve the performance of a domestic IH application with small loads weakly coupled to distant inductors. Considering the basic single-inductor domestic IH application, the proposed system adds a secondary inductor with a series compensation capacitor directly attached to the small ferromagnetic cookware. The extended distance can be used to implement the glassless induction concept, where the ceramic glass of typical cooktops is substituted by the kitchen surface itself. The design of the secondary coil is carried out by means of a combination of finite-element and electrical simulations. A design process, including the housing of the resonant capacitors and the selection of the secondary winding number of turns and cabling, is presented. As a result, a prototype is implemented and tested under working conditions up to 1500 W at several distances. Experimental results validate the electrical modeling and simulation. Moreover, thermal results confirm the feasibility of the proposal and validate the adopted strategies for the capacitor housing. [ABSTRACT FROM AUTHOR]

Global electricity generation by renewable energy sources and the electrification of the transportation system are gaining more importance to mitigate climate change. The dc system plays a significant role in these developments. To protect dc systems, dc circuit breakers with advanced technology are required that are fast and reliable. Various solid-state dc circuit breakers, such as $Z$ -source and $T$ -source circuit breakers, have been presented in the literature to meet the dc system demand; however, these topologies suffer from limitations such as high conduction loss, complexity in design, no physical isolation, and presence of negative current flow in load during reclosing. To overcome the aforementioned limitations, a bidirectional solid-state dc circuit breaker (BD-SSCB) that detects the overload or short-circuit faults and responds instantaneously to mitigate the fault current has been proposed in this article. The controllable shutoff function is much needed in applications where sudden load change occurs continuously during the normal operation, such as varying acceleration of an electric vehicle. The proposed BD-SSCB is validated using spice simulations and hardware experiments with varying system parameters for a system rating of 400 V/10 A. [ABSTRACT FROM AUTHOR]

In this article, a 13-level switched capacitor multilevel inverters (SC-MLI) based single-phase inverter is proposed in which desired levels of output ac voltage are realized with reduced number of switch counts. The proposed inverter requires 12 switches, three diodes, one input dc source, and three capacitors. The requirement of less number of switches reduces the requirement of gate drivers, which enhances power density of converter. The second challenge in SC-MLI is to maintain self-voltage balancing across the capacitors. The self-voltage balancing capability becomes poor at low values of modulation index. The capacitors connected in proposed SC-MLI are capable to maintain the self-voltage balancing without requiring auxiliary circuits or complex control strategies. The operation of capacitors is self-balanced at all regions of modulation index values. The comparison of the proposed SC-MLI is carried out with state-of-art SC-MLIs discussed in the literature using the parameters like peak inverse voltage and total standing voltage. The switches connected in the proposed 13-level SC-MLI undergoes less voltage stress as compared to the SC-MLI configurations discussed in the literature. The proposed SC-MLI is highly competent to achieve good power quality and is capable to ensure voltage balancing of capacitors even at low values of modulation index. The validation of the proposed inverter topology is carried out using a laboratory prototype. The efficiency of the converter claimed using the simulation results is observed to be 96.2% while the efficiency evaluated using the experimental results is 94.1% at 500 W. [ABSTRACT FROM AUTHOR]

This article develops a solid-state transformer (SST), which integrates PV panels and EV chargers together through the open-dc modular multilevel converter (MMC). Different from the well-known MMC, which has a common dc link, the discussed MMC is open-circuited at the dc link so that it should be analyzed from the three-phase viewpoint. The developed SST performs like two parallel-connected cascaded converters, and they are operated with opposite power flow directions. Compared with the conventional SST solution using two separate cascaded H-bridge (CHB) converters, the developed SST has relatively low component count so that it is expected to be of superiority in cost, footprint, and even power density. In addition, the usage of zero sequence voltage in the CHB converter can be replaced by circulating currents in the open-dc MMC so as to greatly reduce the risk of overmodulation. After the thorough power flow analysis on the open-dc MMC and the corresponding controller design, the developed SST is capable of freely working at any operating points with PV panels and EV chargers. Moreover, the developed SST takes the unbalanced grid conditions into account, which is another key contribution of this article. Finally, the balanced and unbalanced operations of the developed SST are both confirmed by the laboratory test results, and furthermore, the dynamic performance of the developed SST considering the time-variant characteristics of PV panels and EV chargers is also demonstrated through the PLECS simulation platform. [ABSTRACT FROM AUTHOR]

Three-phase (3-φ) induction motor drives operated with switched capacitor (SC) inverter circuits offer superior harmonic performance and voltage boosting. The SC network, however, generally requires additional circuitry to precharge the capacitor(s) to prevent inrush current. To obviate the requirement of the extra circuit, an innovative SC precharging scheme is presented, which utilizes the winding inductance of the motor. The inverter circuit is so operated that the motor winding inductance first stores electrical energy from the input dc source and then releases it to the SC. These two actions are continued till the SC is precharged to a voltage equal to the magnitude of the input dc source. The circuit operation during the precharging is similar to the operation of a conventional buck-boost type dc–dc converter. The precharging action is so designed that the voltage of the SC cannot increase further. Therefore, the proposed scheme does not need any voltage sensor. The operation of the circuit during precharging is analyzed extensively to develop a mathematical background for the given method. It is shown that by manipulating the switching frequency during the precharging the precharging time can be controlled as per the user requirements. Various claims are validated using computer simulations and experiments. All the results are presented. [ABSTRACT FROM AUTHOR]

A triple-coil pulsed magnet aiming at 100 T (Tesla) was designed and tested at the Wuhan National High Magnetic Field Center. The magnet was powered by a 100 MJ pulse generator, a battery bank, and 25 kV capacitor banks in combination. The magnet failed at 83 T, while the whole structure remained intact. The failure process was analyzed by using the recorded waveforms of the voltage and the current, as well as disassembling and dismantling the failed magnet. It shows that the inner coil broke down first, and then the electrical breakdown occurred between the middle and outer coils. The possible reasons were also discussed. The buckling analysis results show that the inner and middle coils would buckle at 71 T and 83 T, respectively, which were consistent with the experimental results. The cross-ply reinforcement method is proposed to enhance the structural stability of high field magnets. [ABSTRACT FROM AUTHOR]

Especially in the mining industry, pulsewidth modulation voltage source converters driving induction motors located far away are often present. In this case, due to the long cable used for the converter-to-motor connection, several unwanted high-frequency phenomena are generated. In this context, a new configuration for motor drive systems was proposed, in which the rectifier is kept in its original position and the inverter bridge is installed close to the motor terminals, being the long cable used as a dc transmission line. Since this environment is always more hostile and can compromise the inverter lifetime, new concerns regarding the system reliability arise, despite the various technical-economic advantages of this new configuration. In this way, this article presents a comprehensive comparison of commercially widely accepted multilevel inverter topologies, searching for the best technical features for the aforementioned dc transmission applicability/feasibility. Simulations were performed assessing several essential quantities/indexes, with a major focus on reliability. Then, a discussion was made seeking those sets that could minimize the implementation costs and improve the system reliability, concerning the insulated gate bipolar transistor (IGBTs) and the metalized film and aluminum electrolytic capacitors of the dc link. [ABSTRACT FROM AUTHOR]

Doubly fed induction machines, wound field synchronous machines and dc homopolar machines all require a brushed slip ring connection to the rotor conductors. This connection inherently limits the performance and/or lifespan of these machines. Noncontact methods, such as brushless exciters and wireless power transfer, have been used to support some of these machine types, but they can be physically large and/or overly reliant on power electronics. Additionally, these methods do not support the cooling of the rotor conductors since their function is purely electrical. This article introduces a rotating electric double layer capacitor concept, or supercapacitor, to form a noncontact, slip-ring-like, ac electrical connection between a stator and rotor that simultaneously provides a cooling platform. An experimental proof-of-concept consists of concentric stainless-steel sleeves separated by a ceramic bearing to facilitate relative rotary motion but maintain constant facing area and gap distance. Electrolyte floods the space between the sleeves to form double layer capacitances and can also serve as a heat transfer mechanism. The sleeves were tested as bare metal and with an activated carbon coating to enhance capacitance further. Measurements demonstrate coupling capacitances up to Farad levels with three to six orders of magnitude improvement in A/Hz over rotary air capacitors, enabling low frequency operation. [ABSTRACT FROM AUTHOR]

Modularity, scalability, and efficiency of modular multilevel converters (MMCs) have shown clear advantages among the multilevel topologies, being ideal for medium and high voltage applications. However, they require several control loops in order to achieve multivariable control, where the main challenge is the voltage balancing of the submodules capacitors, usually requiring large capacitances. To extend the MMC application to the low-voltage range, the arm link enhanced MMC solves this issues by adding dual active bridges (DABs) between the upper and lower submodules (SMs) in order to transfer the power ripple between each other. This allows the use of small capacitances in the SMs and greatly reduces the control and measurement complexity, while maintaining a low voltage ripple in an extended output frequency range. In this scenario, this work studies how the circulating current suppression control (CCSC) affects the DABs power transfer, as well as the overall effects in the converter and its performance. Considering the variable frequency operation of the converter, the effects at low and high frequencies are analyzed, as well as the consequences in the DABs high-frequency transformers. The main objective is to determine whether it is convenient or not to enable the circulating current suppression depending on the operation conditions of the converter. [ABSTRACT FROM AUTHOR]

Maximum power point tracking (MPPT) plays a significant role in a photovoltaic (PV) system's optimal performance. Bypass diodes create multiple peaks on the power–voltage curve during partial shading conditions (PSCs), reducing the PVs overall power extraction capability. This article proposed a new hybridized architecture for switched inductor and switched capacitor circuit based voltage equalizer (VE) topology with reduced switch count to prevent the multiple peaks and increase the energy yield during PSCs. The proposed VE operates with a fixed duty cycle and frequency. The MPPT controller with PSC detection is also proposed to operate VE only when the PSC is detected to avoid unwanted switching and conduction losses. The proposed system's effectiveness for ten modules connected in series has been determined compared with other modular state-of-the-art VEs. The proposed topology can be extended with a smaller number of control switches. On average, the experimental results showed a 30.42% improvement in energy yield in comparison with the conventional systems. Furthermore, the proposed controller offers the MPPT efficiency of 99.28% with a tracking time of 0.10 s for uniform shaded conditions and 0.692 s for PSCs on average. [ABSTRACT FROM AUTHOR]

For variable frequency induction motor drive application, conventional modular multilevel converter (MMC) faces some issues, like high capacitor voltage ripple at low frequency, high circulating current, and high component count. This article proposes a novel configuration to address these issues, where a six-pulse thyristor-based controlled rectifier is combined with a waveshaper-based MMC (WS–MMC). Each phase of the converter consists of a WS and director valve, and then the phases are connected in series to create a common dc-link. The use of a thyristor-based controlled rectifier as a front-end converter increases reliability and reduces component count to a large extent. Unlike conventional MMC, circulating current does not exist in this converter, and the capacitor voltage ripple does not depend on the operating frequency. As a consequence, the current rating of the switching devices is reduced for the same power output, and capacitor voltage ripple at low frequency stays within the specified limit. Besides this, the component count of the proposed configuration is far less than the MMC-based topologies available so far. The operation principle, relevant control techniques, and analysis of the converter are discussed in detail in this article. The complete system is simulated in MATLAB/SIMULINK, and the performance of the control methods has been validated at different operating frequencies with various load torques. The results show satisfactory performance. [ABSTRACT FROM AUTHOR]

The five-level active neutral-point-clamped (5L-ANPC) inverter has been applied to increase the power capacity of photovoltaic (PV) systems. However, this type of configuration requires to balance neutral point (NP) voltage and flying capacitor (FC) voltage properly. For the operation of the transformerless five-level inverter, another requirement is to suppress the leakage current associated with the common-mode voltage (CMV) vectors. Due to the mutually coupled issues, the conventional model predictive control (MPC) methods reported so far cannot deal with them properly at the same time. To address these problems, a novel double-vector MPC (DV-MPC) strategy with zero CMV vector is proposed in this article. First, 19 voltage vectors with zero CMV are implemented as candidate vectors. Then, for the purpose to reduce output current ripples, two voltage vectors are penalized by the cost function without weighting factors to track the reference voltage. In addition, the dwell times are optimized to further mitigate current ripples. Finally, to avoid the sharply increasing computational burden of the online iteration caused by the introduction of the second vector and its corresponding redundant switching states, a voltage-balance strategy is presented for the DV-MPC method, which can determine the suitable switching combinations directly and adapt them to the selected vectors to balance the voltages of the NP and FCs together. The effectiveness of the proposed method is verified by the simulation and experiment at the end of this article. [ABSTRACT FROM AUTHOR]

The ac transmission network of modular multilevel converters (MMCs) usually adapts the overhead line, so the single-phase grounding faults of the ac side are rather general. At this time, the protection system will cut off the fault line for the first time, so two unbalanced grid conditions (UGCs) are possible, i.e., single-phase grounding (SGUGC) and disconnection (SDUGC). However, the comparative analysis of small-signal stability under two UGCs has never been involved. Therefore, when ignoring the transient process of faults and protection actions and considering the inherent properties of the MMC system, two small-signal models based on linear time-periodic theory are built under SGUGC and SDUGC. Then, the influence of the control parameters on the system stability under the two UGCs is compared in detail. The analysis results show that the control parameters should be optimized to avoid small-signal instability under different UGCs. Finally, the original nonlinear MMC grid-tied system verifies the analysis results. [ABSTRACT FROM AUTHOR]

This article introduces a novel electrical variable capacitor (EVC) circuit for use in the impedance matching circuits employed by 13.56 MHz RF plasma systems. The proposed design employs a turn-on/off using bias current and voltage condition technology, reducing the number of active components necessary for the EVC to operate. Experiments comparing the proposed EVC to state-of-the-art alternatives confirmed that the proposed design successfully operated with the reduced number of active components. Proposed EVC of automatic bias action by the power semiconductor switch may improve the impedance matching circuits used in high-power and high-frequency RF plasma system. [ABSTRACT FROM AUTHOR]

An analytical approach to size a dc-link capacitor for a three-phase current-controlled voltage-source inverter used for a permanent magnet synchronous motor is presented in this article considering the dc-link ripple voltage and capacitor ripple current. The analytical method derived in this article shows the variation of the dc-link voltage ripple with the change of the power factor and the modulation index. This analysis can be applied to determine the maximum possible ripple voltage for a given capacitor or the minimum capacitance needed to keep the voltage ripple under a limit. Then, current ripple analysis is used to determine the root-mean-square capacitor ripple current taking account of the thermal duty cycles of the application. Finally, capacitor life estimation analysis is used using the operating condition, thermal duty cycle, and ripple current to determine the capacitor end life for a given application. The research presents a sequential process to select a dc-link capacitor accounting for the electrical and thermal requirement of the system. The analysis is verified by simulation and experimental results, where the effect of components’ parasitic on the voltage and current ripple is presented. [ABSTRACT FROM AUTHOR]

This article presents a new topology for a single-stage nine-level (9L) switched-capacitor inverter. The structure of the proposed topology is not only simple but also compact. The proposed topology is developed with self-voltage balancing and a low number of power components. The output voltage (vo) gain is four times higher than the input voltage (vin). Each mode of operation is discussed with a detailed current path. The conventional sinusoidal pulsewidth modulation technique is used to generate the gate pulses. Next, the experimental results are obtained from a 1 kW prototype setup. The proposed topology is tested under different scenarios such as load change, input voltage changes, and modulation variations. Both simulation and experimental results have good agreement in terms of efficiency. Finally, a detailed comparative study is performed with other recent 9L inverters to prove the merits of the proposed topology. [ABSTRACT FROM AUTHOR]

This article proposes a single dc source-based hybrid three-phase thirteen-level inverter suitable for medium voltage applications. The multilevel structure is composed of a three-level T-type neutral point clamped (NPC), half-bridge, and three-level Flying capacitor converter with optimal switch count and high dc bus voltage utilization as high as 0.63 times the dc-link voltage. This requires a special attention to a novel capacitor balancing method using redundant switching states in order to operate at any power factor under grid-connected mode. A unified common-mode voltage is injected in the carrier based pulse width modulation (PWM) technique to maintain the voltage balance in dc-link capacitors as well as floating capacitors. Simulation results are presented under different operating conditions that include unity power factor operation with passive load as well as grid-connected inverter mode. The performance of the proposed multilevel inverter in the grid-connected mode is also validated with experimental results using a lab prototype. [ABSTRACT FROM AUTHOR]

A switching capacitor-based boost converter topological evolution is proposed in this article. Switching capacitor with dual-switch configuration is the basis for the topological evolution with common ground feature. The topologies evolved are capable of yielding high-voltage transformation ratio at smaller duty ratios like in Z-source dc–dc converter topologies. The front-end structure provides a voltage gain of 1/(1 − 2D) while the upstream circuit structure is compatible for embedding the voltage multiplier cells and thus gain enhancement becomes an easier task. On this basis, four different enhanced gain boost topologies with common ground feature [dual-switch-based switching-capacitor converter (DSSCC) Type-1 and -2, and dual-switch-based switching-capacitor fourth-order converter (DSSCFO) Type-1 and -2] are introduced in this article. In all these topologies, a small adjustment in the duty cycle is sufficient enough to ensure load voltage regulation even if the input supply voltage varies over wide ranges. Among these four proposed topologies, DSSCC Type-1 and DSSCFO Type-2 exhibit low source current ripple content due to the presence of inductance at the source side. Of these two, DSSCFO Type-2 exhibits low source current ripples as well as high voltage gain at moderate duty ratios. In view of this, detailed analysis and experimental investigations are established for DSSCFO Type-2. A comprehensive comparison of the proposed topologies with other reported topologies is given, wherein they exhibit identical as well as closely following voltage gain. A 220 V, 120 W, 50 kHz prototype is constructed for performance verification. Measurement results are provided to demonstrate the enhanced gain boosting along with low source current ripple features. [ABSTRACT FROM AUTHOR]

To balance dc voltage, a two-module structure based on a dc–dc three-level boost converter is utilized. In this article, the possible operating modes for a two-module converter in the steady state are introduced. These modes are performed according to different states of opening or closing of the switches. Total 16 possible operating modes and the operation of different switches in the circuit are shown. The circuits for each operating mode are drawn according to the switch command signals. The relationships governing the system are given in different modes. These equations include the currents through three output capacitors and the inductor voltages of each module. The system is simulated by MATLAB/Simulink. The waveforms of the system are presented in two cases for different operating points. The operating mode of this structure is validated using simulations and experimental results. [ABSTRACT FROM AUTHOR]

This article proposes the high-frequency link three-phase integrated-optimized power electronic transformer (PET) for electric vehicle (EV) charging infrastructure in the distribution network. The structural elements and configuration of PET significantly affect its design and performance. However, the different topologies of PET available in the literature did not consider the influence of the circuit’s structural elements with their parasitic components. Consequently, it violates the value of control variables which fails to accomplish essential control characteristics required for EV charging infrastructure in the smart distribution network. Therefore, in this article, detailed modeling and analysis of the proposed PET are carried out at each stage by incorporating its structural effect to analyze the circuit behavior during different operating conditions. As a result, it provides the design and operating constraints for the proposed PET, employed in the design procedure and control algorithm. Furthermore, the dual-degree control (DDC) method is proposed to utilize the structural framework and dual control variables of the proposed PET to meet out significant aspects of EV charging infrastructure in the distribution network such as wide range of voltage regulation, active control over the power flow, and soft-switching operation. Finally, a 4-kW prototype of the proposed PET is built up, which has a bidirectional power flow feature and isolated dc dual-port output terminals. Hardware testing and experimental results verify the effectiveness of the proposed PET based on the DDC method. [ABSTRACT FROM AUTHOR]

This article proposes three-phase cascaded multilevel rectifiers for wind energy conversion system applications. These configurations operate as machine-side converters and play an essential role in the integration of wind power generation units. The proposed rectifiers are connected to a permanent magnet synchronous machine by an open-end winding arrangement, making the ac–dc conversion of the power delivered with high-power factor operation. Their structures are composed of a combination of a converter based on Vienna rectifiers and one H-bridge per phase with a floating capacitor. Compared with the conventional configurations, the proposed ones provide sinusoidal currents with lower harmonic distortion using, proportionally, a fewer number of controlled switches. Furthermore, they can operate with a lower switch blocking voltage. These features make them attractive options for industrial applications due to their good performance, providing an interesting cost–benefit. The system model, pulsewidth modulation technique, capacitor voltage balancing, and control strategy are detailed. Computer simulations and experimental tests are provided in order to validate their feasibility. [ABSTRACT FROM AUTHOR]

DC-link-based variable speed constant frequency (VSCF) ac power generating system is being considered as one of the popular power architectures in the new generation aircraft to provide backup power to the 115 V, 400 Hz aircraft loads. These systems directly convert the variable frequency output of the generator to the fixed frequency of 400 Hz using a voltage source inverter. These inverters use dc-link capacitors that are heavy and space consuming. In aircraft, the weight requirement is very critical; hence, minimizing the dc-link capacitance is one of the major research challenges to achieve high power density in the VSCF power converter. In this article, novel control strategies to minimize the dc-link capacitance of the ac–dc–ac VSCF power converter are presented. The proposed control strategies enable to achieve 95% reduction in dc-link capacitance value when compared with the conventional control strategy, while the control is robust enough to meet MIL-STD-704F transient specification at the inverter output. The proposed strategies are validated through controller hardware-in-loop testing of the VSCF system based on an 80 kVA brushless synchronous generator and a four-leg inverter. The transient and steady-state operation of the VSCF system with a 95% reduction in dc-link capacitance has been verified for rated power operation. [ABSTRACT FROM AUTHOR]

A transformerless electric vehicle (EV) onboard charger is designed for robust grid fault ride-through/trip capabilities and the attenuation of leakage current ($< $ 20 mA) with high efficiency. A zero sequence voltage control method is developed with a modified grid-connected $LCL$ inverter to stabilize the zero-sequence voltage and bypass the leakage current. The topological modification is configured by connecting the common points of three-phase output capacitors and the positive/negative dc bus terminals. The control strategies include 1) ac grid side: $dq$ sequence grid side current control, $q$ sequence reactive power control, and zero-sequence grid voltage/switch side inductor current control; and 2) dc battery side: constant current and constant voltage control. An optimal control parameter design procedure is developed based on active damping method to improve the dynamic performance and attenuate the $LCL$ filter resonance for a better grid disturbance response. The developed onboard charger is capable of dealing with abnormal grid voltage/frequency conditions to properly ride through and trip based on the standard requirements of IEEE Std. 1547. Also, the onboard charger can be applied to the integrated drivetrain. An ac current mode variable-frequency critical-soft-switching technique is developed for the onboard charger to achieve high efficiency ($>$ 99%). The performance under abnormal grid conditions are tested experimentally to verify the ride-through and trip capabilities of the developed onboard charger in compliance with IEEE Std. 1547. Also, the experiments have validated the low leakage current, stable zero sequence voltage, and full range of variable-frequency soft-switching for high efficiency. [ABSTRACT FROM AUTHOR]

Conventional full-bridge and half-bridge (HB) converters are quite popular for front-end power factor preregulation (PFP) in electric vehicle (EV) battery chargers. Discontinuous conduction mode (DCM) operation at high power causes increased oscillation in the circuit. These oscillations increase with parasitic components of circuit. During deep DCM operation, these oscillations are seen to be significant and contribute to harmonic content in the input current. Therefore, a PFP bridgeless isolated HB converter based EV charger with reduced LC oscillation in DCM is presented in this article. To reduce LC oscillation, two diodes are used in series with minimum number of magnetic components. The design of proposed charger in DCM is illustrated to facilitate uniform battery current during constant current/constant voltage charging. The inherent advantage of reduced conduction loss with bridgeless topology is achieved. The performance of this isolated HB converter based charger is shown for improved oscillation characteristics and power quality operation at steady state and over a range of varying input voltages. [ABSTRACT FROM AUTHOR]

This article focuses on the coupled inductor single input dual output (CI-SIDO) boost converter topology. The CI-SIDO boost converter can be used in many practical applications, such as electric vehicles, renewable energy systems, and portable electronic devices. Several applications, such as battery charging, fuel cells, photovoltaic systems, and ultracapacitors, require ripple-free currents, as the lifetime of sources in these applications gets reduced by higher current ripples. However, there is no method in the existing literature to obtain a zero-ripple input current in the CI-SIDO boost converter. This article proposes an approach to design a CI-SIDO boost converter such that the ripple in input current is either zero or less than the maximum specified ripple limit. The analytical proofs of the design method are presented, and the usability analysis is evaluated by taking practical design examples. The effect of variations in the input voltage, CI parameters, and closed-loop control on the proposed design method is analyzed. The proposed design method is verified in experiments by laboratory prototype and in LTspice simulations. [ABSTRACT FROM AUTHOR]

This article discussesthe control method for an ac/dc rectifier system consisting of a three-phase diode rectifier, a buck converter, and an instantaneous reactive power compensator (IRPC). The IRPC makes the grid current sinusoidal by controlling only the instantaneous reactive power. Thus, it is possible to reduce the size of the dc capacitors and ac inductors. This article analyzes the overlap in the rectifier, derives the suitable gain in the damping control, and proposes a modified control method for the IRPC to reduce the current ripple. A 4.5-kW laboratory setup was assembled and examined to verify the theory developed in this article. As a result, the modified control method effectively suppresses the spike current around the overlap duration and damps the overshoot/ringing caused by the resonance. The proposed ac/dc rectifier exhibits an improved power conversion efficiency of 98.2%. [ABSTRACT FROM AUTHOR]

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]

IEEE recently introduced new revisions to the medium- and high-voltage circuit breaker standards. The revised standards provide for new ratings and capabilities; expand choices for users by making it easier to certify and accept under IEEE/ANSI standards equipment originally destined for the IEC market; and clarify the scope and limitations of various ratings of importance to the industrial user. This article presents some of the more pertinent changes and how these changes affect the application of circuit breakers in the petroleum and chemical industries. [ABSTRACT FROM AUTHOR]

Modulation ratio is an important index for power converters, which is related to the circuit parameter selection, converter transformer taps changing, control scheme design, etc. Nevertheless, the modulation ratio in modular multilevel converters (MMC) has not been well studied yet, and in most cases, it is used by referring to the modulation ratio of two-level converters. However, considering the particular features of MMCs, whether the modulation ratio can likewise be applied for MMCs is required to be studied. This article found that there are three problems lying in the modulation ratio of MMCs; as a result, the modulation ratio cannot always accurately reflect the modulation characteristics of MMCs. The study concluded that, in evaluating the overmodulation risk of MMCs, the modulation ratio is only accurate in the situation where the circulating current suppression controller is adopted in the control scheme. Using modulation ratio as the substitution of the amplitude of fundamental modulation signal can introduce large errors (from −15.63% to 12.74% in case studies), except when the MMC mainly outputs/consumes the active power. Finally, the analyses and conclusions are verified by the Zhangbei HVDC project based on the RT-Lab platform and by the 5 kVA/400 V downscaled MMC prototype. [ABSTRACT FROM AUTHOR]

Impedance-source inverters (ZSIs) are getting more attention in renewable energy generation over conventional inverters due to their inherent boosting ability and shoot-through immunity. However, most of the ZSI expansion abilities are somehow limited by the component stresses and poor performance, particularly at a low modulation index. In this article, a new coupled inductor-based switched quasi-ZSI is proposed to accomplish enhanced boost inversion at a high modulation index. It offers a robust boosting feature even with a very low turns ratio, which significantly reduces the passive circuit element's size. The working principle, steady-state analysis, and the design guidelines for selecting circuit parameters are addressed. The proposed inverter significantly improves the input current ripple with enhanced boosting with appropriate control of the impedance-network active switch. A comprehensive comparative analysis with allied topologies is presented to show the proposed inverter's effectiveness. The superior features offered are more suitable for renewable energy generation from low- and variable-voltage renewable sources, such as solar PV and fuel cells. A laboratory prototype is made for experimental verification. Analytical, MATLAB simulation and experimental results are presented to validate the proposed theory. [ABSTRACT FROM AUTHOR]

Nonisolated dc–dc converterswith multi-inputfeatures are very popular in the area of hybrid energy integration since they are compact and cost efficient compared to the isolated topologies. A dual-input hybrid step-up dc–dc converter (DIHDC) with a compact structure is introduced in this article. DIHDC operates based on the switched inductor technique. DIHDC has two inductors with equal values that are parallelly energized in the initial working modes (i.e., switch on condition) and dissipates the stored energy in series in the final working mode (switch off condition). Also, the proposed converter can be extended up to multiple inputs with slight modifications in the structure. Simple and compact structure, relatively higher efficiency, and good voltage conversion ratio are the potential merits of the new converter. Analysis of DIHDC in steady-state condition is explained elaborately and the simulation results are presented. Detailed dynamic analysis of the converter has been performed based on the small signal model of the converter and the necessary transfer functions are derived. A laboratory scale converter model is developed to confirm the efficient operation of DIHDC in realistic environments. [ABSTRACT FROM AUTHOR]

This article presents a new state-space model (SSM) to represent the four types of currents flowing through a modular multilevel converter (MMC). In line with the converter topology, the model itself is modular and scalable. In other words, its configuration adapts itself to the number of ac phases, to the active or passive nature of the ac-side grid, to the connection between the ac and dc neutral points, and to the number of SMs. The model describes the influence of the MMC arm voltages on the currents using an average behavior of the SMs. An analysis of the operating space for the currents flowing in the MMC is proposed. Simulations performed covering the region of operation and using a software dedicated to electrical engineering systems demonstrate the value and the accuracy of the proposed model with negligible differences observed for all test conditions. A computational time comparison between the proposed model and the commercial software shows that the model runs about 2 times faster. Hardware-in-the-loop (HIL) testing demonstrates the capability of the scalable model to be used in order to derive a current-control law on a five-phase ac-system. [ABSTRACT FROM AUTHOR]

This article presents a model predictive control (MPC) algorithm for a three-level neutral point clamped converter connected to the grid via an LCL filter. The proposed long-horizon MPC method, formulated as a multicriterion quadratic program (QP), simultaneously controls the grid and converter current as well as the filter capacitor voltage, while meeting the relevant grid standards. To achieve the latter, a carrier-based pulsewidth modulation stage is employed. Finally, soft constraints are included to ensure operation of the system within its safe operating limits, particularly with regards to a potential overcurrent or overvoltage trip during transient operation. The presented simulation results based on a medium-voltage system as well as experimental studies based on a scaled-down prototype verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, the open-circuit fault-tolerant operation of a multimode stacked switch rectifier leg is presented and investigated. A fault-tolerant control technique is proposed through the built-in circuit redundancy operation of the presented multimode stacked switch rectifier leg. A bidirectional CLLC resonant dc–dc converter that employs the presented leg is used to demonstrate the features of the presented control scheme. The proposed control can allow post fault operation of the converter to continue to deliver the demanded load power with soft-switching operation in case any switch experiences an open-circuit fault. In addition, the built-in circuit redundancy of the leg allows the resonant converter to operate in different operating modes, resulting in an enhanced control in regulating the output voltage while avoiding the switching frequency to diverge far from the resonant frequency, leading to better performance and improved efficiency with the complete soft-switching operation before and after the fault. To highlight the merits of the proposed fault-tolerant control in the multimode stacked switch rectifier leg, experimental results are provided on a 300-W resonant converter prototype with an input of 250 V and an output voltage of 400 V. [ABSTRACT FROM AUTHOR]

This article presents a new hybrid three-phase cascaded modular multilevel inverter developed with a reduced switch count concept for harvesting renewable energy. The basic module of the proposed inverter consists of six switches, three asymmetric dc links, and two blocking diodes. The inverter can generate six positive voltage states, which are negatively polarized by the end-side H-bridge unit. As a result, a higher number of voltage levels are obtained with a minimum number of switches that ensure reduced total harmonic distortion in the grid current. Additionally, the proposed inverter can operate at a comparatively lower switching frequency, which decreases the switching losses. Most of the switches in each individual module conduct for a small period resulting in low conduction losses. The reduced switch count with the low switching and conduction losses increases the compactness and the efficiency of the proposed inverter. Multiple high-frequency magnetic links are utilized for the dc sources required for the proposed inverter to achieve inherent dc-link voltage balancing ability and galvanic isolation. The performance of the proposed inverter is validated by simulation and experimental investigations. [ABSTRACT FROM AUTHOR]

This article presents a new modular dc–dc converter topology. As a modular topology, the converter can be used for several energy sources. Each converter module is based on a three-level dc–dc converter, which contains two output capacitors. The first module shares the second capacitor in common with the first capacitor of the next module. In this way, the N-module can be utilized for an N-energy source. The output capacitor voltages are balanced due to the proposed topology and the controller. The controller is based on the indirect sliding mode controller, where the input current of each energy source and the capacitor voltage balancing are taken into account. One of the aims of this article was to obtain the general system relationships for the N-module system. The process of obtaining recurrence equations for the duty cycles of the system is provided for the desired number of modules. Simulation and experimental results are provided to validate the topology. [ABSTRACT FROM AUTHOR]

In the energy storage field, supercapacitors (SCs) are gaining more and more attention thanks to features, such as high-power density, high life cycles, and lack of maintenance. In this article, an improved SC three-branch model, which considers the residual charge phenomenon, is presented. The procedure to estimate the model parameters and the related experimental setup are presented. The parameter estimation procedure is repeated for several SCs of the same type. The average parameters are, then, obtained and used as initial guesses for a recursive least squares optimization algorithm to increase the accuracy of the model. The model of a single SC is, then, extended to SC banks, testing different configurations and operating conditions. The simulation results, obtained in the MATLAB/Simulink environment for both the single SC and the different SC bank configurations, are validated with experimental tests to assess the model accuracy. [ABSTRACT FROM AUTHOR]

Damping of low-frequency oscillations (LFOs) has become a critical challenge in modern power system. Since interarea LFO modes are associated with power oscillation, therefore, proper modulation of power through energy capacitor system (ECS) can be a competent way to conserve system stability. In this article, modeling of grid-connected ECS unit is explained thoroughly. Further to provide adequate damping to critical LFO modes, a linear quadratic Gaussian (LQG) based optimal $ H_{2}$ wide-area damping controller (WADC) is proposed for ECS integrated power grid. The parameters of the proposed WADC are tuned by accelerated particle swarm optimization (APSO) technique. Furthermore, to select the proper wide-area signals for controller design, geometric approach is adopted. The efficacy of proposed methodology has been tested on large power systems containing multiple interarea modes viz. 10-machine, 39-bus system and 16-machine, 68-bus system. Simulation studies demonstrated the capability of proposed WADC to adequately damp the multiple interarea modes simultaneously. Moreover, it also provides robust performance for operating point uncertainties (load variation, permanent outage of transmission lines, etc.) and variable time delays in feedback signals. [ABSTRACT FROM AUTHOR]

This articleproposes a new control scheme for extension of speed range of dual inverter fed induction motor drives with open-end stator windings. One of the inverters connected to one end of the stator windings is fed by a dc power source whereas the inverter connected to the other end of the windings is fed by a capacitor. The control scheme ensures that only active power required by the drive is supplied by the inverter fed by dc power source and the reactive power alone is provided by the capacitor fed inverter. The modulation index of the capacitor fed inverter is varied to provide higher voltage to the motor at higher speeds keeping the capacitor voltage constant, thereby facilitating operation above base speed without field weakening. An alternative scheme in which the capacitor voltage is allowed to vary while keeping the modulation index of the capacitor fed inverter at its maximum value is also presented in this article. The proposed schemes, based on constant v/f ratio control, are simple compared to the existing schemes. Validation of the proposed schemes is carried out under transient and steady state operating conditions by extensive simulation using PLECS software. Experimental verification is also carried out on a laboratory prototype using a digital signal controller for implementation of the control scheme. [ABSTRACT FROM AUTHOR]

Multilevel inverters (MLI) are gaining wider popularity owing to their increasing power handling capability and improving power quality output. With an inclining trend towards renewable energy utilization, they find a vital application in wind and solar power generation systems. This article proposes a new multilevel dc–ac inverter. The proposed MLI produces a twenty five level output and offers an inherent capacitor self-balancing capability. The inherent self-balancing eliminates the requirement of auxiliary sensor circuit or capacitors voltage balancing algorithms. Dual asymmetric voltage sources and switched capacitors along with their proper charging/discharging pattern are utilized for the generation of output levels. A voltage gain of 2 and a total standing voltage (TSV) of 10 is achieved though the proposed inverter. In order to realize the merit of the proposed MLI over recently developed topologies, a comparative analysis in terms of system components such as numbers of power electronic switches, gate driver circuits, diodes, and capacitors as well as system parameters such as voltage gain, TSV and power loss is presented. The proposed MLI is developed in the laboratory and is controlled through the digital signal processor TMS320F28379D using nearest level control technique. The experimental results are acquired for different loads and under varying modulation index to validate the feasibility of the proposed inverter. [ABSTRACT FROM AUTHOR]

This article proposes a harmonic compensation method using an open-end winding interior permanent magnet synchronous motor driven by an electrolytic capacitorless dual inverter under grid disturbances. In a conventional electrolytic capacitorless single inverter, harmonic currents are superimposed on the output current of the inverter owing to the increase in the dc-link voltage ripple caused by grid disturbances. Consequently, the reliability of the motor drive system is reduced, and the torque ripple causes mechanical vibrations. The proposed harmonic compensation method estimates the harmonic voltage and outputs it using a compensating inverter. The experimental results show that peak-to-peak of the motor current and the 150 Hz component of the shaft torque are reduced by 10.3 and 92.4%, respectively, compared to the conventional system under unbalanced input voltage. Therefore, the improvement of reliability of a motor drive system and reduction of the torque ripple are achieved without an energy buffer under grid disturbances. [ABSTRACT FROM AUTHOR]