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Modular Multilevel Converters (MMCs) are promising candidates for high‐voltage high‐power applications. The main challenge of the MMCs is the zero‐frequency operation. To achieve a successful DC–DC conversion process with balanced capacitors' voltages with limited voltage ripple, this paper suggests the employment of the conventional two‐leg half‐bridge submodule‐based MMC structure in conjunction with a single bidirectional high‐voltage (HV) valve across the low‐voltage side. In the suggested structure, the HV valve is controlled on and off to ensure energy equalization for the MMC arms. In addition, soft‐switching for the HV valve is proposed to reduce the switching losses. Detailed illustration and design of the proposed concept are presented. Simulation and experimentation results are elucidated to show the effectiveness of the proposed DC–DC hybrid MMC. The results showed efficient performance of the suggested converter. [ABSTRACT FROM AUTHOR]

The modular multilevel converter (MMC) is a promising candidate for high-/medium-voltage high-power applications such as medium voltage ac drives due to its modularity, reliability, and scalability. The main challenge of a conventional MMC is low-frequency operation. Capacitor voltage ripple is inversely proportional to the operating frequency. Hence, operating at low frequency necessitates employing large submodule capacitances to limit voltage ripple or the utilization of energy equalization modules (EEMs). The first option negatively affects converter lifetime, and the second option requires a large number of semiconductor devices and isolating transformers. In this article, a modified MMC topology with self-energy equalization is proposed to ensure converter operation with balanced capacitor voltages with low ripple during zero-/low-frequency conditions. Operating with balanced capacitor voltages with low ripple is achieved by maintaining the same energy level in the involved upper and lower arms. A low device count alternative to the EEMs approach is proposed in this work. Detailed illustration of the operational concept and design of the associated passive components is presented. The performance of the proposed medium voltage ac drive is elucidated through simulation and experimental results. [ABSTRACT FROM AUTHOR]

Conventional modular multilevel converters (MMCs) are promising converters for high-voltage high-power applications. Unlike DC-AC conversion, DC-DC conversion of MMCs suffers from unbalanced capacitor voltages due to the energy drift problem. In this study, a new modular DC-DC converter is proposed, which consists of front-end half-bridge MMC with half-bridge submodules followed by full-bridge MMC with full-bridge submodules. The proposed modular multilevel DC-DC converter can be used effectively for connecting two different DC voltage levels in high-/medium-voltage DC grids. The proposed architecture provides successful DC-DC conversion with balanced capacitor voltages throughout the arm interchange concept. It also provides a high conversion ratio, bidirectional power flow, low losses, low current stresses, reduced number of submodules, and DC fault blocking capability. Detailed illustration, operational concept, and design of the proposed architecture with the arm interchange concept are presented. Simulation results for a high-voltage high-power DC-DC converter with the suggested approach are presented to demonstrate the system performance during different normal as well as abnormal operating conditions. Finally, a scaled-down prototype has been implemented for validation. The extracted simulation and experimental results elucidate the presented claims. [ABSTRACT FROM AUTHOR]

Conventional modular multilevel converters (MMCs) are promising converters for high‐voltage high‐power applications. Unlike DC–AC conversion, DC–DC conversion of MMCs suffers from unbalanced capacitor voltages due to the energy drift problem. In this study, a new modular DC–DC converter is proposed, which consists of front‐end half‐bridge MMC with half‐bridge submodules followed by full‐bridge MMC with full‐bridge submodules. The proposed modular multilevel DC–DC converter can be used effectively for connecting two different DC voltage levels in high‐/medium‐voltage DC grids. The proposed architecture provides successful DC–DC conversion with balanced capacitor voltages throughout the arm interchange concept. It also provides a high conversion ratio, bidirectional power flow, low losses, low current stresses, reduced number of submodules, and DC fault blocking capability. Detailed illustration, operational concept, and design of the proposed architecture with the arm interchange concept are presented. Simulation results for a high‐voltage high‐power DC–DC converter with the suggested approach are presented to demonstrate the system performance during different normal as well as abnormal operating conditions. Finally, a scaled‐down prototype has been implemented for validation. The extracted simulation and experimental results elucidate the presented claims. [ABSTRACT FROM AUTHOR]

High-voltage (HV) pulse generators (PGs) are the core of pulsed electric field applications. Applying HV pulses produces electrical pores in a biological cell membrane, in which if the size of the pores increases beyond a critical size, the cell will not survive. This paper proposes a new HV-PG based on the modular multilevel converter with full-bridge submodules (FB-SMs). In order to alleviate the need of complicated sensorless or sensor-based voltage balancing techniques for the FB-SM capacitors, a dedicated self-regulating charging circuit is connected across each FB-SM capacitor. The individual capacitor charging voltage level is obtained from three successive stages, namely, convert the low-voltage dc input voltage to a high-frequency square ac voltage, increase the ac voltage level via a nanocrystalline step-up transformer, and rectify the secondary transformer ac voltage via a diode FB rectifier. The HV bipolar pulses are formed across the load in a fourth stage through series connected FB-SMs. The flexibility of inserting and bypassing the FB-SM capacitors allows the proposed topology to generate different pulse-waveform shapes, including rectangular waveforms with specifically reduced dv/dt and ramp pulses. The practical results, from a scaled-down experimental rig with five FB-SMs and a 1-kV peak-to-peak pulse output, validate the proposed topology. [ABSTRACT FROM PUBLISHER]

In high-voltage applications, the magnitude of total semiconductor losses (on-state and switching) determines the viability of modular-type multilevel converters. Therefore, this paper presents a new cell arrangement that aims to lower total semiconductor loss of the modular multilevel converter (MMC) to less than that of the half-bridge modular multilevel converter (HB-MMC). Additional attributes of the proposed cell are: it eliminates the protective thyristors used in conventional half-bridge cells that deviate part of the dc-fault current away from the antiparallel diode of the main switch when the converter is blocked during a dc short-circuit fault, and it can facilitate continued operation of the MMC during cell failures without the need for a mechanical bypass switch. Thus, the MMC that uses the proposed cell retains all advantages of the HB-MMC such as full modularity of the power circuit and internal fault management. The claimed attributes of the proposed cell are verified using illustrative simulations and reduced scale experimentations. Additionally, this paper provides brief and critical discussions that highlight the attributes and limitations of popular MMC control methods and different MMC cells structures proposed in the literature, considering the power electronic system perspective. [ABSTRACT FROM AUTHOR]

Repetitive high pulsed electric field (PEF) is an effective method to kill microorganisms and bacteria in water treatment applications. The PEF can be generated by applying high-power electromagnetic pulse across the sample to be treated. There are two main types of high-voltage pulse generators, namely, unipolar and bipolar. In this paper, a full-bridge submodule-based modular high-voltage pulse generator, having the ability to generate unipolar and bipolar high-voltage pulses with different shapes from a relatively low-voltage input dc supply, is proposed. In the proposed configuration, relatively low-voltage insulated gate bipolar transistors (IGBTs) are required to generate the high-voltage bipolar pulses. A thyristor rated at the level of the pulsed output voltage is required in the proposed configuration to bypass the load during the charging process of capacitors. In the proposed approach, a thyristor is used instead of the self-commutated high-voltage switch (e.g., series-connected IGBTs), as thyristors are available with high-voltage ratings and possess inherent reverse voltage blocking capability. A detailed illustration of the proposed configuration and its operational concept are introduced in this paper. Simulation and experimental results are presented to validate the proposed approach. [ABSTRACT FROM AUTHOR]

Hybrid multilevel converters are contemplated in an attempt to optimize the performance of voltage source converters in terms of magnitude of semiconductor losses and converter footprint, and to achieve additional features such as dc short circuit proof, which is essential for a high integrity multiterminal HVDC grid. Therefore, this paper considers an emerging hybrid cascaded converter that offers the dc side short circuit proof feature at reduced loss and footprint compared to the existing multilevel and other hybrid converters. Its operating principle, modulation, and capacitor voltage balancing strategies are described in detail. Furthermore, hybrid converter scalability to high voltage applications is investigated. The validity of the modulation and capacitor voltage strategy presented are confirmed using simulation and experimentation. The hybrid cascaded converter is extendable to a large number of cells, making it applicable to high voltage applications, and operation is independent of modulation index and power factor. On these ground, the converter is expected to be applicable for both real and reactive power applications. [ABSTRACT FROM AUTHOR]

This article presents an isolated high-frequency (HF) multiport dc–dc converter for photovoltaics (PV) interfacing systems. In the proposed multiport converter, an HF transformer with multiple input windings and single output winding is utilized. Each input port is based on a proposed two-quadrant inverter topology, which connects a PV module to the HF transformer. The output port is tied to a dc bus using a rectifier. The proposed two-quadrant inverter topology prevents current flow from the ac side to the dc side. This action prevents circulating currents between different ports. Each two-quadrant inverter is controlled to harvest maximum power from its associated PV module. The analysis and operation scenarios of the proposed multiport converter are discussed. PSCAD/EMTDC software package is used to simulate the proposed PV interfacing system to investigate the operation of the proposed multiport converter topology and to examine the dynamic system behavior. In addition, an experimental prototype is developed to validate the operation scenarios of the proposed multiport dc–dc converter and to examine the performance of the presented PV interfacing system. [ABSTRACT FROM AUTHOR]

This paper proposes a medium-/high-voltage high-power hybrid modular dc–dc converter to interconnect two different dc-voltage levels in medium-/high-voltage dc grids. The converter consists of half-bridge submodules (SMs) rated at a moderate voltage level, i.e., series connection of semiconductor devices is avoided while connecting two high dc-voltage levels. The proposed architecture provides self-balancing operation, i.e., unlike conventional modular converters, no need for capacitor voltage measurement, which enhances the system reliability and simplicity. Sequential charging/discharging of SMs capacitors is adopted in the proposed approach to ensure a self-balanced operation. The proposed architecture can provide a high conversion ratio as well as power transfer in both directions, i.e., bidirectional dc–dc converter. Detailed illustration of the proposed approach operational concept, design, and overall control system is presented. Simulation and experimental results are presented to show the viability of the proposed configuration and validate the claims. [ABSTRACT FROM AUTHOR]

This paper employs an amplitude modulation with sinusoidal plus third harmonic injection instead of trapezoidal modulation to operate a controlled transition bridge (CTB) converter as ac/dc and dc/ac converter terminals. With such an operation, the CTB converter may require small ac filters; thus attractive for high-voltage direct current (HVDC) transmission systems. To facilitate ac voltage control over a wide range and black-start capability, the injected 3rd harmonic allows the cell capacitor voltages of the CTB converter to be regulated independent of the modulation index and power factor. The insertion of 3rd harmonic into modulating signals achieves two objectives: extends the regions around voltage zeros so that the total voltage unbalanced can be distributed between the cell capacitors, thereby exploiting the bipolar capability of the full-bridge cells in each limb; and to ensure that each limb can be clamped to the positive and negative dc rails every half fundamental period independent of the modulation index to allow recharge of the cell capacitors from the active dc link. The suitability of the CTB converter for HVDC type applications is demonstrated using a two-terminal HVDC link that employs a 21-cell CTB converter, considering normal operation and ac faults. [ABSTRACT FROM AUTHOR]