Common-mode voltage cancellation in single- and three-phase transformer-less PV power converters

Electrical Energy generation is an issue that is continuously cause of concern around the world. Many efforts have been done in this sense to cover the requirements of the constantly growing in the electrical energy demand. But not only the electrical energy demand is growing but also clean electrical energy demand. In this sense, many countries are taking advantage from the renewable energy generation systems, considering mainly wind and solar energy. Solar energy systems provide a high percentage of the total energy production, according with the latest report of the International Energy Agency (IEA) regarding Photovoltaic Power System Program (PVPS), the cumulative installed PV power at the end of 2009 it was around 20.3 GW out of which 6.188 GW were installed in 2009. From the total PV power installed in 2009, 6.113 are grid connected systems. The growing of the PV systems is due to the new technologies and developments that have permitted to reduce costs in the total design and installation of a PV source. As the major percentage of the total PV energy installed is from grid connected systems, this thesis work deals with the analysis and proposals in the transformerless grid-connected PV systems which can provide higher efficiencies regarding PV system with transformer. In this sense, when there is not transformer between the electrical grid and the power converter, a problem regarding leakage ground currents appears, this is the main issue in this thesis work. The main research task in this thesis work is to analyze and evaluate the operation of the different transformerless topologies presented in the bibliography and then to provide some solutions to minimize the leakage ground current phenomenon in order to comply with the standard requirements

Development Of Multistage Cuk Converter For Pv Voltage Regulation.

Tesis ini mengemukakan reka bentuk pengubah SPMS untuk aplikasi berkuasa rendah.Litar penukar adalah berdasarkan topologi CUK yang secara asasnya ialah kombinasi topologi penukar “buck” dan “boost”. This thesis presents the design of a transformerless SMPS for low power applications. The converter circuit is based on CUK topology which is basically a combination of buck and boost converter topologies

A High Step-Up Transformerless DC-DC Converter with New Voltage Multiplier Cell Topology and Coupled Inductor

In this paper, a new high step-up transformerless DC-DC converter based on voltage multiplier and coupled inductor topology is presented. The proposed converter has two stages. In the first stage, a modified boost converter is designed by the coupled inductor and in the second stage, a new voltage multiplier by using a coupled inductor was illustrated. In this converter, high voltage gain can be achieved by adjusting the turn ratio of two coupled inductors and duty cycle which result in three degrees of design freedom. Using a single power switch with low on-resistance in the converter structure leads to simple control and low conduction loss. Also, total voltage stresses of active elements are decreased which cause to increase efficiency. Steady-state performance and theoretical achievements are confirmed by experimental test results on a test setup with one 200 W DC-DC prototype.©2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.fi=vertaisarvioitu|en=peerReviewed

Performance evaluation of a 3-level ANPC photovoltaic grid-connected inverter with 650V SiC devices and optimized PWM

Photovoltaic (PV) energy conversion has been on the spotlight of scientific research on renewable energy for several years. In recent years the bulk of the research on PV has focused on transformerless grid-connected inverters, more efficient than traditional line transformer-based ones, but more critical from a power quality point of view, especially in terms of ground leakage current. Neutral point clamped (NPC) inverters have recently gained interest due to their intrinsically low ground leakage current and high efficiency, especially for MOSFET-based topologies. This paper presents an active NPC (ANPC) topology equipped with 650 V SiC MOSFETs, with a new modulation strategy that allows to reap the benefits of the wide-bandgap devices. An efficiency improvement is obtained due to the parallel operation of two devices during the freewheeling intervals. Simulations and experimental results confirm the effectiveness of the proposed converter

Modeling and Control of Single Phase Grid-Tie Converters

The penetration of renewable energy into the electric utility grid is growing worldwide. At the heart of these renewable sources is the power electronic systems used to convert the renewable source to an output that can be connected to the grid. In recent years, there has been a great deal of work in designing converters for grid-tie applications and is continuing to grow. With recent smart grid activities, it is not likely that this work will cease in the short term. Most of the recent research is in ancillary services that the converter can offer in addition to the normal energy transfer. With more advanced converters, the ability to provide reactive power and harmonic compensation has triggered many researchers to look at more advanced control schemes. The work in this thesis focuses on modeling and control of single phase grid connected converters with an emphasis on grid interactions and ancillary services. While there has been a great deal of work in the modeling and control area for general converter operation, there has been little analysis in the converter’s response to grid disturbances. There are very few resources that discuss the controller design as it relates to power quality. However, these are issues that must be considered in a real design and what separates the research and commercial level converters. In addition to control and modeling work, the author suggests two new transformerless converter topologies for photovoltaic applications. In general, these converters can be viewed as a hybrid converter topology comprised of a two level and multi-level structure. Both converters show conducted emissions improvements over the standard commercial transformerless converters while also meeting leakage current requirements

Beijing converters: bridge converters with a capacitor added to reduce leakage currents, DC-bus voltage ripples, and total capacitance required

Abstract: Isolation transformers and bulky electrolytic capacitors are often used in power electronic converters to reduce leakage currents and voltage ripples but this leads to low power density and reduced reliability. In this paper, an auxiliary capacitor is added to the widely used conventional full-bridge converter to provide a path for, and hence significantly reduce, the leakage current. The operation of the full-bridge converter is split into the operation of a half-bridge converter and a dc-dc converter so that the ripple energy can be diverted from the dc-bus capacitor to the auxiliary capacitor. Hence, the dc-bus capacitor can be significantly reduced while maintaining very low voltage ripples on the dc bus because it is only required to filter out switching ripples. The auxiliary capacitor is designed to allow high voltage ripples because its voltage is not supplied to any load. Accordingly, the auxiliary capacitor can also be very small as well. As a result, the total required capacitance becomes very small. The reduction ratio of the total capacitance is significant, which makes it cost-effective to use film capacitors instead of electrolytic capacitors. The proposed converters can be also operated as an inverter without any restriction on power factor because the adopted four switches are all bidirectional in terms of power flow. Experimental results for both rectification and inversion modes are presented to demonstrate the performance of the proposed converter in reducing the ripples, the leakage currents, and the total capacitance needed, with comparison to the conventional bridge converter without the auxiliary capacitor

Design and Evaluation of High Efficiency Power Converters Using Wide-Bandgap Devices for PV Systems

The shortage of fossil resources and the need for power generation options that produce little or no environmental pollution drives and motivates the research on renewable energy resources. Power electronics play an important role in maximizing the utilization of energy generation from renewable energy resources. One major renewable energy source is photovoltaics (PV), which comprises half of all recently installed renewable power generation in the world. For a grid-connected system, two power stages are needed to utilize the power generated from the PV source. In the first stage, a DCDC converter is used to extract the maximum power from the PV panel and to boost the low output voltage generated to satisfy the inverter side requirements. In the second stage, a DC-AC inverter is used to convert and deliver power loads for grid-tied applications. In general, PV panels have low efficiency so high-performance power converters are required to ensure highly efficient PV systems. The development of wide-bandgap (WBG) power switching devices, especially in the range of 650 V and 1200 V blocking class voltage, opens up the possibility of achieving a reliable and highly efficient grid-tied PV system. This work will study the benefits of utilizing WBG semiconductor switching devices in low power residential scale PV systems in terms of efficiency, power density, and thermal analysis. The first part of this dissertation will examine the design of a high gain DC-DC converter. Also, a performance comparison will be conducted between the SiC and Si MOSFET switching devices at 650 V blocking voltage regarding switching waveform behavior, switching and conduction losses, and high switching frequency operation. A major challenge in designing a transformerless inverter is the circulating of common mode leakage current in the absence of galvanic isolation. The value of the leakage current must be less than 300mA, per the DIN VDE 0126-1-1 standard. The second part of this work investigates a proposed high-efficiency transformerless inverter with low leakage current. Subsequently, the benefits of using SiC MOSFET are evaluated and compared to Si IGBT at 1200 V blocking voltage in terms of efficiency improvement, filter size reduction, and increasing power rating. Moreover, a comprehensive thermal model design is presented using COMSOL software to compare the heat sink requirements of both of the selected switching devices, SiC MOSFET and Si IGBT. The benchmarking of switching devices shows that SiC MOSFET has superior switching and conduction characteristics that lead to small power losses. Also, increasing switching frequency has a small effect on switching losses with SiC MOSFET due to its excellent switching characteristics. Therefore, system performance is found to be enhanced with SiC MOSFET compared to that of Si MOSFET and Si IGBET under wide output loads and switching frequency situations. Due to the high penetration of PV inverters, it is necessary to provide advanced functions, such as reactive power generation to enable connectivity to the utility grid. Therefore, this research proposes a modified modulation method to support the generation of reactive power. Additionally, a modified topology is proposed to eliminate leakage current

Dual Output and High Voltage Gain DC-DC Converter for PV and Fuel Cell Generators Connected to DC Bipolar Microgrids

This paper introduces a new topology for a DC-DC converter with bipolar output and high voltage gain. The topology was designed with the aim to use only one active power switch. Besides the bipolar multiport output and high voltage gain this converter has another important feature, namely, it has a continuous input current. Due to the self-balancing bipolar outputs, the proposed topology is suitable for bipolar DC microgrids. Indeed, the topology balancing capability can achieve the two symmetrical voltage poles of bipolar DC microgrids. Furthermore, it is possible to create a midpoint in the output of the converter that can be directly connected to the ground of the DC power supply, avoiding common-mode leakage currents in critical applications such as transformerless grid-connect PV systems. The operating principle of the proposed topology will be supported by mathematical analysis. To validate and verify the characteristics of the presented topology, several experimental results are shown.info:eu-repo/semantics/publishedVersio