Search

In order to overcome the limitations of the existing classical and solid-state Marx pulse generators, this paper proposes a new modular multilevel voltage-boosting Marx pulse generator (BMPG). The proposed BMPG has hardware features that allow modularity, redundancy, and scalability as well as operational features that alleviate the need of series-connected switches and allows generation of a wide range of pulse waveforms. In the BMPG, a controllable, low-voltage input boost converter supplies, via directing/blocking (D/B) diodes, two arms of a series modular multilevel converter half-bridge sub-modules (HB-SMs). At start up, all the arm's SM capacitors are resonantly charged in parallel from 0 V, simultaneously via directing diodes, to a voltage in excess of the source voltage. After the first pulse delivery, the energy of the SM capacitors decreases due to the generated pulse. Then, for continuous operation without fully discharging the SM capacitors or having a large voltage droop as in the available Marx generators, the SM capacitors are continuously recharged in parallel, to the desired boosted voltage level. Because all SMs are parallelly connected, the boost converter duty ratio is controlled by a single voltage measurement at the output terminals of the boost converter. Due to the proposed SMs structure and the utilization of D/B diodes, each SM capacitor is effectively controlled individually without requiring a voltage sensor across each SM capacitor. Generation of the commonly used pulse waveforms in electroporation applications is possible, while assuring balanced capacitors, hence SM voltages. The proposed BMPG has several topological variations such as utilizing a buck–boost converter at the input stage and replacing the HB-SM with full-bridge SMs. The proposed BMPG topology is assessed by simulation and scaled-down proof-of-concept experimentation to explore its viability for electroporation applications. [ABSTRACT FROM AUTHOR]

This paper presents a drive system based on a modular multilevel converter (MMC) with high-frequency magnetic channels between adjacent-arm submodules (SMs), suitable for medium-voltage, high-power three-phase variable-speed machines. The configuration employs chains of dual half-bridge (DHB) modules linking adjacent SMs of three-phase symmetrical arms. The DHB modules are operating as power channels enabling energy exchange to restore the power imbalance among the SM capacitors. This allows arms’ ripple-powers to be entirely decoupled through bidirectional power transfer between adjacent-arm SMs, resulting in a near ripple-free SM capacitor voltage profile. Therefore, the MMC common problem of wide voltage fluctuation across SM capacitors is comprehensively solved, independent of the operating frequency. Additionally, a significant reduction in the sizing requirement of SM capacitance is achieved. The configuration is able to drive multimegawatt machines from standstill to the rated speed at the rated torque operating condition. The operating principle of the proposed MMC configuration is explained and necessary mathematical analysis is derived. Features and viability of the proposed drive system are verified through simulation and experimentation. [ABSTRACT FROM AUTHOR]

This paper presents a dual modular multilevel converter (MMC) topology that utilizes energy exchange between adjacent-arm submodules (SMs), operating with out-of-phase modulation. The proposed configuration is applicable to medium-voltage high-power variable-speed drives incorporating open-end stator winding machines. A novel concept of power decoupling between adjacent-arm SMs in the dual MMC topology is realized through high-frequency transformer-based dc–dc converter modules. This concept offers a significant reduction in the sizing requirement of the SM capacitance and the stored energy in the MMC system, while avoiding the problem of wide voltage fluctuations of SM capacitors, especially at low operating frequencies. The proposed configuration can produce dc voltage; therefore, a machine speed range from zero speed to the rated speed is possible under the rated torque operating condition. The operating principles of the proposed dual MMC configuration are elaborated and necessary mathematical analysis is derived. Simulation and experimental results verify the concept of the proposed drive configuration. [ABSTRACT FROM AUTHOR]

High-voltage (HV) pulses are used in electroporation to subject pulsed electric field (PEF) onto a sample under treatment. Pulse-waveform shape, voltage magnitude, pulse duration, and pulse repetition rate are the basic controllable variables required for particular PEF application. In practice, a custom-made pulse generator is dedicated for each PEF application with limited flexibility in changing these variables. In this paper, a universal pulse-waveform generator (UPG) is proposed, where the controller software algorithm can manipulate a basic generated multilevel pulse waveform to emulate many different PEF pulse waveforms. The commonly used PEF HV pulse waveforms can be generated as bipolar or monopolar with controllable pulse durations, repetition times, and voltage magnitudes. The UPG has the ability to generate multilevel pulses that have controllable $dv/dt$, which allows reduction of the electromagnetic interference generated by the converter. The UPG topology is based on half-bridge modular multilevel converter (HB-MMC) cells forming two transition arms in conjunction with two bistate arms, together creating an H-bridge. The HB-MMC cell capacitors provide a controllable energy source which charge from the dc input supply and discharge across the load, while the two bistate arms allow charging the HB-MMC cell capacitors. Hence, the UPG topology offers modularity, redundancy, and scalability. The HB-MMC individual cell capacitance is low and the cell voltages are balanced by employing the sorting and rotating algorithm used in conventional HB-MMC topologies for HV dc transmission applications. The viability of the proposed UPG converter is validated by MATLAB/Simulink simulation and scaled-down experimentation. [ABSTRACT FROM PUBLISHER]

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]

High-voltage (HV) pulses are used in pulsed electric field (PEF) applications to provide an effective electroporation process, a process in which harmful microorganisms are disinfected when subjected to a PEF. Depending on the PEF application, different HV pulse specifications are required such as the pulse-waveform shape, the voltage magnitude, the pulse duration, and the pulse repetition rate. In this paper, a generic pulse-waveform generator (GPG) is proposed, and the GPG topology is based on half-bridge modular multilevel converter (HB-MMC) cells. The GPG topology is formed of four identical arms of series-connected HB-MMC cells forming an H-bridge. Unlike the conventional HB-MMC-based converters in HVdc transmission, the GPG load power flow is not continuous which leads to smaller size cell capacitors utilization; hence, smaller footprint of the GPG is achieved. The GPG topology flexibility allows the controller software to generate a basic multilevel waveform which can be manipulated to generate the commonly used PEF pulse waveforms. Therefore, the proposed topology offers modularity, redundancy, and scalability. The viability of the proposed GPG converter is validated by MATLAB/Simulink simulation and experimentation. [ABSTRACT FROM PUBLISHER]

The role of irreversible electroporation using pulsed electric field is to generate high-voltage (HV) pulses with a predefined magnitude and duration. These HV pulses are applied to the treatment chamber until decontamination of the sample is completed. In this paper, a new topology for HV rectangular pulse generation for water disinfection applications is introduced. The proposed topology has four arms comprised of series-connected half bridge modular multilevel converter cells. The rectangular pulse characteristics can be controlled via the software controller without any physical changes in power topology. The converter is capable of generating both bipolar and monopolar HV pulses with microsecond pulse durations at high a frequency rate with different characteristics. Hence, the proposed topology provides flexibility by software control, along with hardware modularity, scalability, and redundancy. Moreover, a cell’s capacitance is relatively small, which drastically reduces the converter footprint. The adopted charging and discharging process of the cell capacitors in this topology eliminate the need of any voltage measurements or complex control for cell-capacitors voltage balance. Consequently, continuity of converter operation is assured under cell malfunction. In this paper, analysis and cell-capacitor sizing of the proposed topology are detailed. Converter operation is verified using MATLAB/Simulink simulation and scaled experimentation. [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]

The nine-arm modular multilevel converter (9A-MMC) has been recently proposed as a reduced MMC topology variation for six-phase drive applications, with 25% reduction in the number of employed arms and associated components, compared to a standard dual three-phase MMC, however with a limited output voltage amplitude. This paper proposes a hybrid 9A-MMC comprised of half-bridge submodules (SMs) in both the upper and lower arms, and full-bridge SMs in the middle arms. By employing the negative-voltage state of the full-bridge SMs, the hybrid 9A-MMC avoids the limitations imposed on the dc-link voltage utilization, while achieving further reduction in the component count, compared to a standard 9A-MMC with identical half-bridge SMs. The operating principles of the proposed hybrid 9A-MMC are illustrated with mathematical analysis, whereas its characteristics are verified through both simulation and experimentation. An assessment of the proposed topology quantifying its employed components is also provided, in comparison to other MMC-based six-phase machine drives. [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]

The conventional unipolar Marx generator can be employed for bipolar pulsed electric field by adding a high-voltage H-bridge at the load side which necessitates stacked switches. Alternatively, bipolar Marx generator with low-voltage switches can be employed. The existing bipolar Marx generators are typically fed from dc supplies, where polarized capacitors are employed. The capacitance of involved capacitors is selected such that the total energy stored in the generator's capacitors is higher than the bipolar pulse energy. As a result, polarized capacitors with relatively high capacitances are required. In addition, a high number of controlled switches per stage are required (at least four switches per stage). In this paper, a new solid-state bipolar Marx pulse generator with only three controlled switches per stage is proposed. The proposed generator is fed from sinusoidal/square ac voltage and non-polarized capacitors with low capacitance are employed. The proposed bipolar Marx-generator can be used effectively with resistive loads for exponential pulse generation. A detailed illustration of the proposed approach is presented and a discussion, to elucidate the differences between the proposed pulse generator and the other existing ones, are presented. Simulation results for the proposed pulse generator are presented to validate the concept. Finally, experimental results have been obtained from a low-voltage model of the proposed generator. [ABSTRACT FROM AUTHOR]

Differential-mode buck-boost inverters have merits such as reduced switch number, ability to provide voltages higher or lower than the input voltage magnitude, improved efficiency, reduced cost and size, and increased power density, especially in low-power applications. There are five buck-boost inverters that can provide flexible output voltage without the need of a large electrolytic input side capacitor, which degrades the reliability of inverters. The continuous input current of these inverters is appropriate for maximum power point tracking operation in photovoltaic and fuel cells applications. Three of the five inverters can be isolated with high-frequency-link transformers where the common-mode leakage current can be mitigated. However, the performance and control of such converters have not been discussed in detail. In this paper, the five possible single-stage three-phase differential-mode buck-boost inverters with continuous input current are investigated and compared in terms of total losses, maximum ripple current, total harmonic distortion, and device and passive element ratings. In addition, the possible methods are presented for eliminating the input third-order harmonic current, resulting from the stored energy in the passive elements, as well as the output second-order harmonic currents. The ability for isolating the input and output sides of the inverters with a small–high frequency transformers is discussed. A changeable-terminal 2.5-kW bidirectional inverter is used to validate the design flexibility of the inverter topologies, when digital signal processor-controlled. [ABSTRACT FROM AUTHOR]

The four-switch three-phase (FSTP) inverter has been proposed as an innovative inverter design to reduce the cost, complexity, size, and switching losses of the dc–ac conversion system. Traditional FSTP inverter usually operates at half the dc input voltage; hence, the output line voltage cannot exceed this value. This paper proposes a novel design for the FSTP inverter based on the topology of the single-ended primary-inductance converter (SEPIC). The proposed topology provides pure sinusoidal output voltages with no need for output filter. Compared to traditional FSTP inverter, the proposed FSTP SEPIC inverter improves the voltage utilization factor of the input dc supply, where the proposed topology provides higher output line voltage which can be extended up to the full value of the dc input voltage. The integral sliding-mode control is used with the proposed topology to optimize its dynamics and to ensure robustness of the system during different operating conditions. Derivation of the equations describing the parameters design, components ratings, and the operation of the proposed SEPIC inverter is presented in this paper. Simulation model and experimental setup are used to validate the proposed concept. Simulations and experimental results show the effectiveness of the proposed inverter. [ABSTRACT FROM AUTHOR]