Five-level Converter Topology Research Articles

A Five-Level Nested Diode-Clamped Converter for Medium-Voltage Applications

This article presents a new three-phase five-level converter topology with a single dc source. The proposed topology combines the features of the conventional flying capacitor multicell and diode-clamped multilevel topologies. An important advantage of the proposed topology is the reduced volt-ampere, and hence, the volume, of the flying capacitors in its structure while keeping the same voltage blocking capability for semiconductor switches. The appropriate modulation strategy along with the flying capacitor voltage balancing technique is presented. To show the advantages of the proposed converter, different performance criteria such as switch count and rating, volt-ampere of flying capacitors, component cost, losses, and switching frequency are compared with some existing five-level topologies with a single dc source and the same voltage rating of switches. The results indicate that the proposed structure is superior to other five-level converters from different standpoints of the performance criteria. Simulation results are shown to verify the converter operation and its performance. The validity of the theoretical analysis is verified by experimentation on a scaled-down prototype system.

Modified SPWM technique for improved harmonic performance of single PV array fed grid‐tied five‐level converter

This study presents a performance assessment of a single photovoltaic (PV) array fed transformer-based five-level converter topology with optimal shift factor-based modified sinusoidal pulse width modulation (OSF-MSPWM) technique under a dynamic solar PV environment. The five-level converter output is generated using H bridge cells and single-phase transformers. A single PV array is fed to all cascaded H bridge cells and isolation is provided by cascading secondary windings of the transformers in the AC side. The separate DC sources requirement is eliminated and galvanic isolation is provided by single-phase transformers. The decoupled controller with modified in-phase disposition PWM technique is used for active power injection into the grid at unity power factor. This work uses a new carrier shape at the same input carrier frequency and modulation index m f for improving the harmonics performance of the five-level converter. Hence, shift the dominant harmonics to the higher side for developed topology and performing optimal shift factor-based modulation is compared with the conventional SPWM technique. The steady-state and dynamic responses of the PV multilevel converter are observed in MATLAB simulation and tested in a real-time platform.

Control of Multi-cell AC/DC and Cascaded H-bridge DC/AC-basedAC/DC/AC Converter

A single-phase two-stage AC/DC/AC converter topology is investigated in this paper, which involves multi-winding transformer-fed multi-cell AC/DC and cascaded H-bridge multi-level (CHBMLI) DC/AC converter stages. Both the converter stages utilize current control using the fixed and uniform switching methods, which simultaneously achieve the regulation of the DC link voltages of all the cells. The proposed control loop for the AC/DC converter stage uses a single-voltage sensor to control the DC link voltages of all the cells using self-voltage regulating property of the multi-winding transformer. This single-control loop uses the feedback of the instantaneous AC current at the primary of the transformer and any one of the DC link voltage to achieve the input AC current control and multiple DC link voltage control. The fixed frequency ramp comparison current control in AC/DC stage of the converter provides a uniform switching cycle among all the units. A phase-shifted multi-carrier PWM (PS-MCPWM)-based fixed frequency current control of the DC/AC converter comprising CHBMLI provides equal loading across all DC links of the AC/DC converter. The results are verified through PSCAD simulations and experimental results are obtained through the LabVIEW FPGA controller implemented for two-cell, five-level converter topology.

A Two-Phase Five-Level Converter With Least Number of Power Switches Requiring Only a Single DC Source

A novel single dc source fed five-level converter topology for medium-voltage high-power isolated grid-tied systems requiring only 12 power switches is proposed. The present configuration has two stages namely, five-level converter and the Scott-T transformer. The five-level converter stage generates only two phase voltages. Latter, these voltages are converted into three phases by using the Scott-T transformer connection. This topology requires less number of power devices and its associated gate drivers in comparison to any existing topology. In addition, the dc-link capacitors used in the topology have an ability to self-balance by themselves which eliminates the requirement of capacitor balance circuitry and complex control algorithms. The overall component count in the present configuration is very less in comparison to other topologies. Further, each device in the converter is stressed to only half of the dc-link voltage. A level-shifted carrier pulsewidth modulation scheme is adopted to control the converter, and proportional integral controllers are used to inject current into the grid at unity power factor. Theoretical analysis and simulation of the proposed converter are performed and a prototype with 1 kVA rating is validated by connecting it to a three-phase grid.

A New Two-Phase Five-Level Converter for Three-Phase Isolated Grid-Tied Systems With Inherent Capacitor Balancing and Reduced Component Count

This paper presents a single dc source fed five-level converter topology for medium-voltage high-power isolated grid-tied systems with reduced power switch count. The proposed converter generates two-phase systems of voltages that are further converted to three phases by using Scott-T transformer connection. Compared to existing topologies, the proposed converter requires fewer power switches, gate drivers, and power diodes. An added advantage is that only a single dc source is required. An important feature of this topology is that the dc-link capacitor voltages have an inherent ability to self-balance by themselves without the need for extra balance circuitry and special control algorithms. The voltage stress across the power devices of the proposed converter is equal to half of dc-link voltage. A level-shifted carrier-based pulsewidth modulation scheme is used to inject current into the grid at unity power factor. Analysis and simulation and experimental results are presented to validate the performance of the proposed converter under grid-tied operation.

English

3 ABSTRACT:In low power renewable systems, a single phase grid-connected converter is usually adopted. This paper deals with a novel five-level converter topology that follows this trend. A review of the state of the art of the five-level topologies and a theoretical power loss comparison with the proposed solution is realized. The proposed converter architecture is based on a full-bridge topology with two additional power switches and two diodes connected to the midpoint of the dc link. Since the two added levels are obtained by the discharge of the two capacitors of the dc link, the balancing of the midpoint voltage is obtained with a specific pulse width modulation (PWM) strategy. Simulation results carried on MATLAB/SIMULINK model design show the effectiveness of the proposed solution.

English

A single-phase grid-connected converter is usually adopted in low-power renewable systems. This paper deals with a novel five-level converter topology that follows this development.. The proposed converter architecture is based on a full-bridge topology with two additional power switches and two diodes connected to the midpoint of the dc link. Since the two added levels are attained by the discharge of the two capacitors of the dc link, the midpoint voltage is balanced and obtained with a specific pulse width modulation (PWM) strategy. This solution is designed for renewable energy systems, where unity power factor operations are generally required. Never the less, a variation of the proposed topology which allows four-quadrant operations

Space Vector Modulation Controlled Single Phase Five Level Inverter for Fuel Cell Applications

In low power system a single phase converter is usually adopted. This paper deals with five-level Converter topology with SPWM technique. A review of the state of the art of five-level topologies and theoretical power loss comparison with proposed solution is realized. The main characteristics of these modulations are reduced, switching losses, balanced power loss dissipation among the devices with in a cell and among the series connected cells. A Neutral point Clamped type of Multilevel Inverter is more efficient .The proposed converter architecture is based on Single-Phase five-level system for Fuel cell with Polymer Exchange type. In this system, Space Vector Modulation (SVM) technique is used. Simulation and Experimental results show the effectiveness of the proposed solution.

A Five-Level Single-Phase Grid-Connected Converter for Renewable Distributed Systems

In low-power renewable systems, a single-phase grid-connected converter is usually adopted. This paper deals with a novel five-level converter topology that follows this trend. A review of the state of the art of the five-level topologies and a theoretical power loss comparison with the proposed solution is realized. The proposed converter architecture is based on a full-bridge topology with two additional power switches and two diodes connected to the midpoint of the dc link. Since the two added levels are obtained by the discharge of the two capacitors of the dc link, the balancing of the midpoint voltage is obtained with a specific pulse width modulation (PWM) strategy. Simulation and experimental results show the effectiveness of the proposed solution.