High-voltage pulse generators incorporating modular multilevel converter sub-modules

Recent research established the effectiveness of applying a pulsed electric field to deactivate harmful microorganisms (such as bacteria and E. coli). Successful deactivation is achieved by lethal electroporation; a process that produces electric pores in the biological cell membrane of the harmful microorganisms when subjected to high-voltage (HV) pulses. The HV pulses are designed to create pores beyond a critical size at which the biological cell can reseal.;In contrast when applying non-lethal electroporation, the cell-membrane survives after the electroporation process. This is required, for example, when inserting protein cells in the cell-membrane. In both lethal and non-lethal electroporation, HV pulses in the kilo-Volt range (1-100 kV) with durations ranging between nanoseconds and milliseconds are required.;This thesis proposes nine pulse generator (PG) topologies based on power electronic devices and modular multilevel converter sub-modules. The proposed topologies are divided into two main groups namely: PGs fed from a HV DC supply and PGs fed from an LV DC supply. The first group presents a new family of HV DC fed topologies that improve the performance of existing HV DC fed PGs, such as flexible pulse-waveform generation and full utilisation of the DC link voltage.;The second group is dedicated to a new family of LV DC fed PG topologies which have flexible pulse-waveform generation, controlled operation efficiency, and high voltage gain.;All the proposed PG topologies share the important aspect in the newly developed HV PGs, that is modularity, which offers redundancy and robust pulse generation operation.;The presented PG topologies are supported by theoretical analysis, simulations, and experimentation.Recent research established the effectiveness of applying a pulsed electric field to deactivate harmful microorganisms (such as bacteria and E. coli). Successful deactivation is achieved by lethal electroporation; a process that produces electric pores in the biological cell membrane of the harmful microorganisms when subjected to high-voltage (HV) pulses. The HV pulses are designed to create pores beyond a critical size at which the biological cell can reseal.;In contrast when applying non-lethal electroporation, the cell-membrane survives after the electroporation process. This is required, for example, when inserting protein cells in the cell-membrane. In both lethal and non-lethal electroporation, HV pulses in the kilo-Volt range (1-100 kV) with durations ranging between nanoseconds and milliseconds are required.;This thesis proposes nine pulse generator (PG) topologies based on power electronic devices and modular multilevel converter sub-modules. The proposed topologies are divided into two main groups namely: PGs fed from a HV DC supply and PGs fed from an LV DC supply. The first group presents a new family of HV DC fed topologies that improve the performance of existing HV DC fed PGs, such as flexible pulse-waveform generation and full utilisation of the DC link voltage.;The second group is dedicated to a new family of LV DC fed PG topologies which have flexible pulse-waveform generation, controlled operation efficiency, and high voltage gain.;All the proposed PG topologies share the important aspect in the newly developed HV PGs, that is modularity, which offers redundancy and robust pulse generation operation.;The presented PG topologies are supported by theoretical analysis, simulations, and experimentation

A comparative review of three different power inverters for DC–AC applications

This paper presents a comparative review of three different widely used power inverters, namely the conventional six-switch inverter; the reduced switch count four-switch inverter; and the eight-switch inverter. The later inverter can be reconfigured as a neutral-point diode-clamped inverter at the failure of one inverter leg. The three power inverters are compared and discussed with respect to cost, complexity, losses, common mode voltage, and control techniques. The paper is intended to serve as a guide regarding selecting the appropriate inverter for each specific application. Simulation results are presented to demonstrate the performance of the three power inverters, followed by a comprehensive comparison between the three power inverters

Electroporation for water disinfection: a proof of concept experimentation

This paper is a proof of concept showing the effectiveness of using irreversible electroporation (IRE) as a stage of water disinfection in the water treatment process. The IRE process essentially requires relatively high voltage pulses to pose a pulsed electric field across harmful microorganisms. In this paper, a laboratory-based solid-state Marx generator was built for this purpose and untreated water samples have been used to test the effectiveness of applying variable pulse width, magnitude and rate. All the pulses are unipolar rectangular. The tested samples are all from the same water source with the same coliform count. After performing the electroporation disinfection process the coliform count reached zero proving the effectiveness of IRE

Current-source single-phase module integrated inverters for PV grid-connected applications

This paper presents a modular grid-connected single-phase system based on series-connected current-source module integrated converters (MICs). The modular configuration improves the reliability, redundancy and scalability of photovoltaic (PV) distributed generators. In this system, each PV panel is connected to a dc/ac inverter to permit individual Maximum Power Point Tracking (MPPT) operation for each panel. Thus, the harvested power from the PV system will increase significantly. There are four different inverter topologies suitable to be used as MICs with different performances in terms of filtering elements size, power losses, efficiency, output voltage range, and high frequency transformers’ size. For the MPPT control, the oscillating even order harmonic components should be eliminated from the inverter’s input side otherwise the maximum power cannot be extracted. The proposed modulation scheme in this paper will ease the control of inverter’s input and output sides. Therefore, the 2nd order harmonic in the input current can be eliminated without adding new active semiconductor switches. A repetitive controller coupled with proportional-resonant controllers are employed to achieve accurate tracking for grid side as well as input side currents. Comparisons and performance evaluations for the proposed MICs are presented and validated with 1 kVA prototype controlled by TMS320F29335 DSP

A modular multilevel based high-voltage pulse generator for water disinfection applications

The role of irreversible electroporation using pulsed electric field (PEF) 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 H-bridge modular multilevel converter cells. The rectangular pulse characteristics can be controlled via a software controller without any physical changes in power topology. The converter is capable of generating both bipolar and monopolar HV pulses with micro-second pulse durations at a high 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

A new DC-DC converter linking LCC-HVDC transmission networks

Transferring bulk power via high voltage direct current (HVDC) transmission is dominated by line commutated converters (LCC). This is due to the robustness and higher ratings of the thyristors as well as the higher converter efficiency. Nevertheless, most of these transmission networks are point to point. This is due to the challenges of allowing multi-terminal LCC based networks and power reversal. This paper introduces a new dc-dc converter topology that allows connecting two independent LCC networks. The proposed converter is based on insulated gate commutated thyristors (IGCTs). Utilizing IGCTs allow mimicking similar control and performance as in insulated gate bipolar transistor (IGBT) based voltage source dc-dc converters. However, IGCTs have more superior features over IGBTs such as higher efficiency, higher short circuit current and higher power ratings. Detailed analysis and simulations are provided to validate the proposed converter topology, which confirms its potential in connecting HVDC-LCC networks

Unlocking the UK continental shelf electrification potential for offshore oil and gas installations: a power grid architecture perspective

Most of the UK Continental Shelf (UKCS) oil and gas (OG) installations have traditionally adopted in situ power generation, which is not only inefficient but also generating about 70% of the offshore CO2 emissions. The offshore wind and energy storage technologies for deep water are developing at a fast pace, enabling great opportunities for the OG installations located in the North Sea. In this paper, a pathway for the UKCS offshore OG installations electrification is introduced. The aim is to provide different power architectures that facilitate the OG installations' electrification, while benefiting from the existing and planned UK offshore wind power. Four hypothetical case studies (based on real data) were created, along the UKCS, where the corresponding power architectures were proposed. The selection of each architecture power component (e.g., transformers, converters and cables), as well as the transmission and distribution technology (e.g., AC or DC), is also provided and justified. Further, an overview cost estimation is carried out to predict the architecture capital cost. It is concluded that the four architectures can be mimicked not only along the UKCS but also worldwide, promoting the UKCS potential for a world-leading offshore energy hub and fostering the UK offshore wind-energy resources

Cancer treatment: an overview of pulsed electric field utilization and generation

Patients diagnosed with cancer receive different types of treatments based on the type and the level of the tumour. An emerging treatment that differs from well-developed systematic therapies (i.e., Chemotherapy, Radiotherapy, and Immunotherapy) is Tumour Treating Field (TTF) treatment. Tumour behaviour under TTF treatment varies based on the electric field intensity; the process of exposing the tumour cells to an electric field is called electroporation. From the electrical perspective, the most efficient method for electroporation is to use a voltage pulse generator. Several pulse generator topologies have been introduced to overcome existing limitations, mitigate the drawbacks of classical generators, and provide more controllable, flexible, and portable solid-state voltage pulse generators. This paper provides a review of cancer treatment using TTF and highlights the key specifications required for efficient treatment. Additionally, potential voltage pulse generators are reviewed and compared in terms of their treatment efficacy and efficient use of electrical power

Modified variable step-size incremental conductance MPPT technique for photovoltaic systems

A highly efficient photovoltaic (PV) system requires a maximum power point tracker to extract peak power from PV modules. The conventional variable step-size incremental conductance (INC) maximum power point tracking (MPPT) technique has two main drawbacks. First, it uses a pre-set scaling factor, which requires manual tuning under different irradiance levels. Second, it adapts the slope of the PV characteristics curve to vary the step-size, which means any small changes in PV module voltage will significantly increase the overall step-size. Subsequently, it deviates the operating point away from the actual reference. In this paper, a new modified variable step-size INC algorithm is proposed to address the aforementioned problems. The proposed algorithm consists of two parts, namely autonomous scaling factor and slope angle variation algorithm. The autonomous scaling factor continuously adjusts the step-size without using a pre-set constant to control the trade-off between convergence speed and tracking precision. The slope angle variation algorithm mitigates the impact of PV voltage change, especially during variable irradiance conditions to improve the MPPT efficiency. The theoretical investigations of the new technique are carried out while its practicability is confirmed by simulation and experimental results