Ahmed Darwish

A Single-Stage Three-Phase Inverter Based on Cuk Converters for PV Applications

This paper presents a new three-phase inverter based on the Cuk converter. The main feature of the proposed topology is that the energy storage elements, such as inductors and capacitors, can be reduced in order to improve the reliability, and reduce size and total cost. The buck-boost inherent characteristic of the Cuk converter, depending on the time-varying duty ratio, provides flexibility for standalone and grid connected applications when the required output ac voltage is lower or greater than the dc side voltage. This property is not found in the conventional current source inverter when the dc input current is always greater than the ac output or in the conventional voltage source inverter as the output ac voltage is always lower than the dc input. The proposed system allows much smaller, more reliable nonelectrolytic capacitors to be used for energy source filtering. The new three-phase inverter is convenient for photovoltaic applications where continuous input currents are required for maximum power point tracking operation. Average large and small signal models are used to study the Cuk converters nonlinear operation. The basic structure, control design, and MATLAB/SIMULINK results are presented. Practical results substantiate the design flexibility of the Cuk-based topology controlled by a TMSF280335 DSP.

Single-Stage Three-Phase Differential-Mode Buck-Boost Inverters With Continuous Input Current for PV Applications

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.

A Modular Multilevel-Based High-Voltage Pulse Generator for Water Disinfection Applications

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 cells 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 Transition Arm Modular Multilevel Universal Pulse-Waveform Generator for Electroporation Applications

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

A single-stage three-phase DC/AC inverter based on Cuk converter for PV application

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Plug-In Repetitive Control Strategy for High-Order Wide-Output Range Impedance-Source Converters

, 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.

A Modular Multilevel Generic Pulse-Waveform Generator for Pulsed Electric Field Applications

This paper presents a new three-phase dc-ac inverter based on the basic Cuk converter. The main feature of the proposed topology is the fact that the energy storage elements as inductors and capacitors values can be reduced in order to improve the reliability, reduce the size, and the total cost. Moreover, the bucking-boosting inherent nature of the Cuk converter, depending on the time-varying duty ratios, provides more flexibility for stand-alone and grid connected applications when the required output AC voltage is lower or greater than the DC side voltage. This property is not found in the conventional current source inverter (CSI) when the DC input current is always greater than the ac output one or in the conventional voltage source inverter (VSI) as the output ac voltage is always lower than the dc input one. Averaged large and small signal models are used to study the Cuk nonlinear operation. Basic structure, control design, and MATLAB/SIMULINK results are presented in this paper. The new three-phase DC-AC inverter is very convenient for PV applications where continuous average input currents are required for appropriate Maximum power Point Tracking (MPPT) operations.

Operation and control design of new Three-Phase inverters with reduced number of switches

High-order wide-output (HOWO) impedance-source converters (ISCs) have been presented for ac inverter applications that require voltage step-up ability. With intrinsic passive impedance networks as energy sources, these converters are able to achieve voltage boosting with either polarity, leading to improved dc-link voltage utilization compared with the conventional two-level converter. However, HOWO-ISCs suffer from transfer functions giving low bandwidth, a penalty of increased passive devices and right-half-plane zeros, which result in lower order distortion of the ac output power. In this paper, a modified plug-in repetitive control scheme is presented for HOWO-ISCs with accurate reference tracking (hence low distortion), fast dynamic response, and enhanced robustness. By using zero-phase-shift finite impulse response filters in both the internal model of the repetitive controller and its compensation network, the proposed method achieves zero steady-state error and an extended closed-loop bandwidth. For HOWO-ISC cases, this method outperforms conventional proportional-integral (PI) control, which has considerable steady-state error. It also eliminates the need of parallel loops for several frequencies when proportional resonant control or orthogonal transformation-based PI schemes are used to remove lower order distortion. The design process and performance analysis of the proposed repetitive control strategy are based on a novel three-phase HOWO-ISC configuration with a reduced number of switches. Simulation and experimental results confirm the feasibility and effectiveness of the proposed control approach.

A step-up modular high-voltage pulse generator based on isolated input-parallel/output-series voltage-boosting modules and modular multilevel sub-modules

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.

Simplified generic on-line PWM technique for single phase grid connected current source inverters

DC/AC inverter topologies having reduced numbers of switches to reduce costs, total inverter size and switching losses have previously been proposed. In addition, these topologies reduce the likelihood of semiconductor switch damage, and have lower common-mode currents. This paper proposes new designs for inverters with reduced switch numbers. For three-phase systems, the proposed inverters use four switches instead of the six used in the traditional three-phase Voltage Source Inverter (VSI). Compared to the traditional Four-Switch Three-Phase (FSTP) inverter, the proposed FSTP inverters improve the voltage utilisation factor of the input dc supply, without the need for triplen injection. Sliding-mode control is used to demonstrate the dynamic response and robustness of the inverters. Also the paper presents new single-phase inverters with two switches instead of the four used in the traditional VSI. The capability of suppressing the 2nd order current harmonic from the input dc side is discussed. The basic structures of the proposed inverters and their operation, switch ratings, controller design with supporting mathematical equations, and MATLAB/SIMULINK results are presented. Practical results, based on laboratory prototype circuitry controlled using a Texas Instruments TMSF280335 DSP, are presented to demonstrate the design flexibility and operation of the proposed topologies.