A NEW REDUCED SWITCH ZVS-PWM THREE-PHASE INVERTER

Dc-ac inverters convert a dc input voltage into a desired ac output voltage and are widely used in many industrial applications, including utility grid interfaces, motor drives, and wind energy systems. Because of their widespread use, there has been considerable interest to try to make them more efficient to conserve energy. One way of doing so is to reduce the losses that are generated by the switching of the inverter devices as they help convert the dc input voltage into an ac output. As a result, there has been considerable research into implementing inverters with so-called soft-switching - zero-voltage and zero-current switching techniques that make either the voltage across a switch or the current through it zero at the time of a switching transition (from on to off or off to on). Since the power dissipated in a switch is related to the amount of overlap of voltage and current during a switching transition, making either the switch voltage or switch current zero at this time can result in a significant reduction in switching losses. A new, reduced switch, zero-voltage switching (ZVS), three-phase dc-ac inverter is proposed in this thesis. The proposed inverter does not have the drawbacks that other previously proposed ZVS-PWM inverters have such as cost, increased conduction losses, the appearance of distortion in the output waveforms, and the lack of bidirectional operation capability. In the thesis, an extensive literature review of previously proposed soft-switched inverters is performed. The new inverter is then presented and its operation is explained in detail. The steady-state operation of the new inverter is analyzed and the results of the analysis are used to determine the converter\u27s steady-state characteristics. Based on these characteristics, a procedure for the design of the inverter is developed and then demonstrated with an example. Finally, the feasibility of the proposed converter and the validity of the analysis are confirmed with simulation results obtained from PSIM, a widely used, commercially available software simulation package for power electronic

Soft switching modulation strategy based on bipolar (PSM) with improved efficiency in high-frequency link inverters

High Frequency-Link (HFL) Inverters have been employed to integrate renewable energy sources into utility grids and electric vehicles. The soft-switching range of High-Frequency Link Inverters (HFLI) is increased using auxiliary inductors and capacitors. The application of auxiliary components increases the conduction loss and the complexity of the circuit. The literature indicates that the existing soft-switching methods suffer from higher duty cycle loss, voltage spikes, and lower efficiency owing to the resonance between the parasitic capacitance of switches and the leakage inductance of the transformer. Therefore, it is imperative to develop a modulation strategy that can improve the efficiency of HFLI. In this context, the proposed study develops a cycloconverter-type High-Frequency Link Inverter (CHFLI) based on a Bipolar Phase Shift Modulation (BPSM) strategy without the use of auxiliary components. The proposed modulation strategy enables the semiconductor switches to operate under zero voltage switching. The full-bridge inverter and Full Bridge Active Clamper Circuit (FBAC) switches operate at the same gating signals with a constant duty cycle of 50%. The proposed topology uses built-in magnetizing inductance to achieve zero voltage switching and reduce the duty cycle loss. The leakage energy is recycled from the output filter inductor to the load side using the FBAC. The results indicate that the proposed modulation strategy achieves ZVS and simultaneously achieves an efficiency of 95%. The proposed modulation strategy is easy to implement and does not require complex circuitry

Power Converters in Power Electronics

In recent years, power converters have played an important role in power electronics technology for different applications, such as renewable energy systems, electric vehicles, pulsed power generation, and biomedical sciences. Power converters, in the realm of power electronics, are becoming essential for generating electrical power energy in various ways. This Special Issue focuses on the development of novel power converter topologies in power electronics. The topics of interest include, but are not limited to: Z-source converters; multilevel power converter topologies; switched-capacitor-based power converters; power converters for battery management systems; power converters in wireless power transfer techniques; the reliability of power conversion systems; and modulation techniques for advanced power converters

Modular Medium-Voltage Grid-Connected Converter with Improved Switching Techniques for Solar Photovoltaic Systems

© 1982-2012 IEEE. The high-frequency common magnetic-link made of amorphous material, as a replacement for common dc-link, has been gaining considerable interest for the development of solar photovoltaic medium-voltage converters. Even though the common magnetic-link can almost maintain identical voltages at the secondary terminals, the power conversion system loses its modularity. Moreover, the development of high-capacity high-frequency inverter and power limit of the common magnetic-link due to leakage inductance are the main challenging issues. In this regard, a new concept of identical modular magnetic-links is proposed for high-power transmission and isolation between the low and the high voltage sides. Third harmonic injected sixty degree bus clamping pulse width modulation and third harmonic injected thirty degree bus clamping pulse width modulation techniques are proposed which show better frequency spectra as well as reduced switching loss. In this paper, precise loss estimation method is used to calculate switching and conduction losses of a modular multilevel cascaded converter. To ensure the feasibility of the new concepts, a reduced size of 5 kVA rating, three-phase, five-level, 1.2 kV converter is designed with two 2.5 kVA identical high-frequency magnetic-links using Metglas magnetic alloy-based cores

A Review on Multilevel Inverter Topologies

In this paper, a brief review of the multilevel inverter (MLI) topologies is presented. The two-level Voltage Source Inverter (VSI) requires a suitable filter to produce sinusoidal output waveforms. The high-frequency switching and the PWM method are used to create output waveforms with the least amount of ripples. Due to the switching losses, the traditional two-level inverter has some restrictions when running at high frequencies. For addressing this problem, multilevel inverters (MLI) with lower switching frequencies and reduced total harmonic distortion (THD) are employed, eliminating the requirement for filters and bulky transformers. Furthermore, improved performance at the high switching frequency, higher power quality (near to pure sinusoidal), and fewer switching losses are just a few of the benefits of MLI inverters. However, each switch has to have its own gate driver for implementing MLI, which adds to the system's complexity. Therefore, reducing the number of switches of MLI is necessary. This paper presents a review of some of the different current topologies using a lower number of switches. Doi: 10.28991/ESJ-2022-06-01-014 Full Text: PD

Transformerless Inverter Topologies for Single-Phase Photovoltaic Systems:A Comparative Review

In photovoltaic (PV) applications, a transformer is often used to provide galvanic isolation and voltage ratio transformations between input and output. However, these conventional iron-and copper-based transformers increase the weight/size and cost of the inverter while reducing the efficiency and power density. It is therefore desirable to avoid using transformers in the inverter. However, additional care must be taken to avoid safety hazards such as ground fault currents and leakage currents, e.g., via the parasitic capacitor between the PV panel and ground. Consequently, the grid connected transformerless PV inverters must comply with strict safety standards such as IEEE 1547.1, VDE0126-1-1, EN 50106, IEC61727, and AS/N ZS 5033. Various transformerless inverters have been proposed recently to eliminate the leakage current using different techniques such as decoupling the dc from the ac side and/or clamping the common mode (CM) voltage (CMV) during the freewheeling period, or using common ground configurations. The permutations and combinations of various decoupling techniques with integrated voltage buck-boost for maximum power point tracking (MPPT) allow numerous new topologies and configurations which are often confusing and difficult to follow when seeking to select the right topology. Therefore, to present a clear picture on the development of transformerless inverters for the next-generation grid-connected PV systems, this paper aims to comprehensively review and classify various transformerless inverters with detailed analytical comparisons. To reinforce the findings and comparisons as well as to give more insight on the CM characteristics and leakage current, computer simulations of major transformerless inverter topologies have been performed in PLECS software. Moreover, the cost and size are analyzed properly and summarized in a table. Finally, efficiency and thermal analysis are provided with a general summary as well as a technology roadmap.</p

Health Condition Monitoring and Fault-Tolerant Operation of Adjustable Speed Drives

Adjustable speed drives (ASDs) have been extensively used in industrial applications over the past few decades because of their benefits of energy saving and control flexibilities. However, the wider penetration of ASD systems into industrial applications is hindered by the lack of health monitoring and fault-tolerant operation techniques, especially in safety-critical applications. In this dissertation, a comprehensive portfolio of health condition monitoring and fault-tolerant operation strategies is developed and implemented for multilevel neutral-point-clamped (NPC) power converters in ASDs. Simulations and experiments show that these techniques can improve power cycling lifetime of power transistors, on-line diagnosis of switch faults, and fault-tolerant capabilities.The first contribution of this dissertation is the development of a lifetime improvement Pulse Width Modulation (PWM) method which can significantly extend the power cycling lifetime of Insulated Gate Bipolar Transistors (IGBTs) in NPC inverters operating at low frequencies. This PWM method is achieved by injecting a zero-sequence signal with a frequency higher than that of the IGBT junction-to-case thermal time constants. This, in turn, lowers IGBT junction temperatures at low output frequencies. Thermal models, simulation and experimental verifications are carried out to confirm the effectiveness of this PWM method. As a second contribution of this dissertation, a novel on-line diagnostic method is developed for electronic switch faults in power converters. Targeted at three-level NPC converters, this diagnostic method can diagnose any IGBT faults by utilizing the information on the dc-bus neutral-point current and switching states. This diagnostic method only requires one additional current sensor for sensing the neutral-point current. Simulation and experimental results verified the efficacy of this diagnostic method.The third contribution consists of the development and implementation of a fault-tolerant topology for T-Type NPC power converters. In this fault-tolerant topology, one additional phase leg is added to the original T-Type NPC converter. In addition to providing a fault-tolerant solution to certain switch faults in the converter, this fault-tolerant topology can share the overload current with the original phase legs, thus increasing the overload capabilities of the power converters. A lab-scale 30-kVA ASD based on this proposed topology is implemented and the experimental results verified its benefits

Comparative Study of Power Semiconductor Devices in a Multilevel Cascaded H-Bridge Inverter

This thesis compares the performance of a nine-level transformerless cascaded H-bridge (CHB) inverter with integrated battery energy storage system (BESS) using SiC power MOSFETs and Si IGBTs. Two crucial performance drivers for inverter applications are power loss and efficiency. Both of these are investigated in this thesis. Power devices with similar voltage and current ratings are used in the same inverter topology, and the performance of each device is analyzed with respect to switching frequency and operating temperature. The loss measurements and characteristics within the inverter are discussed. The Saber® simulation software was used for the comparisons. The power MOSFET and IGBT modeling tools in Saber® were extensively utilized to create the models of the power devices used in the simulations. The inverter system is also analyzed using Saber-Simulink cosimulation method to feed control signals from Simulink into Saber. The results in this investigation show better performances using a SiC MOSFET-based grid-connected BESS inverter with a better return of investment

An Advanced Three-Level Active Neutral-Point-Clamped Converter With Improved Fault-Tolerant Capabilities

A resilient fault-tolerant silicon carbide (SiC) three-level power converter topology is introduced based on the traditional active neutral-point-clamped converter. This novel converter topology incorporates a redundant leg to provide fault tolerance during switch open-circuit faults and short-circuit faults. Additionally, the topology is capable of maintaining full output voltage and maximum modulation index in the presence of switch open and short-circuit faults. Moreover, the redundant leg can be employed to share load current with other phase legs to balance thermal stress among semiconductor switches during normal operation. A 25-kW prototype of the novel topology was designed and constructed utilizing 1.2-kV SiC metal-oxide-semiconductor field-effect transistors. Experimental results confirm the anticipated theoretical capabilities of this new three-level converter topology