Multistage Power Conversion Research Articles

Reduced stage three phase multisource hybrid converter for integration of PV and grid power

A three-phase-based Modified Dual Source Inverter has been proposed in this manuscript. The existing three-phase system is plagued with multistage power conversion, reducing its efficiency. The proposed converter can integrate two sources (AC and DC) simultaneously and supplies power to the three-phase load. It can switch its operation from the grid to grid-solar, solar to grid, as per the availability of the source. The inverter can operate as a three-phase DC to AC inverter, AC to AC inverter, and it can use grid and PV power directly with the help of a sino-squo-sino waveform. The system has been studied when switching from one mode to another. The system behavior has been analyzed on MATLAB SIMULINK and experimental setup. The proposed approach has been experimentally validated and operated using a TEXAS-based microcontroller (TMS320F28739d). The proposed method has reduced the THD to 4.32% when operated on solar and grid. The THD is 0.25% when operated on the grid power. The proposed system has also been compared based on components. It uses six IGBTs, One Mosfet and three Bidirectional switches.The reduced number of components reduces switching losses, which increases the system's efficacy and performance.

Three-Port Converters for Energy Conversion of PV-BES Integrated Systems—A Review

The integration of battery energy storage (BES) with photovoltaic (PV) systems is becoming economically attractive for residential customers. The conventional approach for the interconnection of PV and battery systems requires at least two separate power converters that results in multistage power conversion for some power flows. The dc-dc three port converters (TPCs) are an alternative solution. These converters have many topological variants and possess different operating principles, topological benefits and limitations, and complexities. This paper concentrates on the topological study of TPCs for integrated PV and BES systems applications in the power range from a few hundred watts to 350 kW. These are classified into three different categories based on their isolation features between the ports to establish a topological mapping of the reported TPCs. This provides a framework that systematically explores the full range of technical benefits and limitations of each TPC topology. This paper also examines the possible extension of the TPC topologies for grid-interactive PV-BES systems where bidirectional power flow capability is required between grid and BES systems. This extensive review will provide a useful framework and a strong point of reference for researchers for the selection of TPC topologies to meet the system requirements for PV and energy storage applications.

A transformerless three‐level three‐phase boost PWM inverter for PV applications

Multilevel converters have seen rising demands in the past decades, due to their increased power ratings, enhanced power quality, low switching losses and reduced electromagnetic interference. Prominent among them are the three-level (3L) neutral point clamped and the flying capacitor inverter topologies along with their derivatives. Nevertheless, the main drawback of these topologies is the requirement of a front-end boost DC–DC converter to compensate the high dc-link voltage demand, which is usually twice the grid peak voltage. This multi-stage power conversion further pulls down the overall system efficiency. A single-stage dc–ac power converter with boost capability offer an interesting alternative compared to the two stage approach. Considering this aspect, a novel three-level three-phase boost type inverter is introduced in this paper for general-purpose applications (prominently grid-connected renewable energy). The proposed inverter would reduce the DC-link voltage requirement to half using the same or even less number of active and passive components, compared to the conventional three-level neutral point clamped and flying capacitor family. The principle of operation and theoretical analysis are discussed in detail. The design methodology along with simulation and experimental waveforms for a 5 kVA inverter are presented to prove the concept of the proposed inverter topology for practical applications.

Design of novel universal converter for integration of solar and wind energy for AC and DC load

AbstractPower generation through renewable sources using a multistage power conversion process was plagued with efficiency and reliability issues. It led to the evolvement of a novel universal converter for the simultaneous interfacing of solar and wind energy. Solar energy is extracted using a multiphase boost converter, while a 2n converter with a switch reluctance generator has been used for wind energy extraction. In this paper, a novel universal converter is used to integrate both solar and wind energies, which will reduce multiple stages of the power conversion process. This converter generates an output voltage of the sino‐square waveform, which is a combination of a sinusoidal and square waveform. Enhanced efficiency and competency of this sino‐square waveform in domestic and industrial applications have been validated with a systematic comparison with conventional square waveform. These two waveforms have been compared based on various harmonics generation, total harmonic distortion (THD), and switching losses. The proposed topology has been validated with an experimental setup using a PV emulator for solar energy. Wind energy has been implemented using an induction motor with switch reluctance generator.

A New Generalized Step-Down Single-Stage AC/AC Power Converter

Most traditional AC/AC power converters suffer from power quality problems and multi-stage power conversion losses. The rectifier and inverter-based AC/AC converter topology not only increases multi-stage power conversion losses, but also increases the volume, weight, and cost, and decreases the longevity of the converter due to the DC-link capacitor, line filter and electromagnetic interference (EMI) filter. High-frequency (about 10 kHz) switching advanced pulse width modulation techniques are generally used in order to compensate the power quality problems, which increase the switching losses and introduce the EMI problems. In this paper, a new generalized step-down single-stage line-frequency switching AC/AC power converter topology is proposed. The proposed converter uses line-frequency switching, and does not require any pulse width modulation techniques. The proposed topology offers promising performances in terms of lower order harmonics, total harmonic distortion, the elimination of DC-link capacitors and EMI filters, and switching losses. The circuit was designed and simulated in a MATLAB/Simulink environment. A scaled-down laboratory prototype of the proposed topology was developed in order to validate the feasibility. The experimental and simulation results reveal the feasibility of the proposed generalized step-down single-stage converter topology, and its excellent features.

A Transformerless Three-Port Nonagonal MMC for the Grid Connection and Local Consumption of Distributed Generation

While large-scale distributed generation (DG) grid connection requires its grid-connected converter to be able to boost the output voltage and connect it to the host grid, its priority is still to consume the power locally so as to increase the energy utilization rate. Using a common ac bus to transmit the distributed power to local load requires two separate converters, resulting in large size and multistage power conversion. Therefore, to lose the transformer and increase the compactness, a three-port nonagonal modular multilevel converter (MMC) is proposed in this paper, which consists of nine bridge arms connected from end to end. From the vertexes, three 3-phase ac ports protrude, connecting DG, ac grid, and local load together. By reusing power modules, with only nine bridge arms, the proposed nonagonal MMC realized three-port direct ac/ac power conversion in a single converter. Furthermore, the topology can operate without a transformer or high-voltage dc link, and under low frequency. It is then compared with other topologies to demonstrate its advantage in applications that require high compactness and flexibility. Finally, the proposed topology and its corresponding control are verified in RTlab to be effective for DG grid connection and local consumption.

Cross-Regulation Assessment of DIDO Buck-Boost Converter for Renewable Energy Application

When medium- or high-voltage power conversion is preferred for renewable energy sources, multilevel power converters have received much of the interest in this area as methods for enhancing the conversion efficiency and cost effectiveness. In such cases, multilevel, multi-input multi-output (MIMO) configurations of DC-DC converters come to the scenario for integrating several sources together, especially considering the stringent regulatory needs and the requirement of multistage power conversion systems. Considering the above facts, a three-level dual input dual output (DIDO) buck-boost converter, as the simplest form of MIMO converter, is proposed in this paper for DC-link voltage regulation. The capability of this converter for cross regulating the DC-link voltage is analyzed in detail to support a three-level neutral point clamped inverter-based grid connection in the future. The cross-regulation capability is examined under a new type of pulse delay control (PDC) strategy and later compared with a three-level boost converter (TLBC). Compared to conventional boost converters, the high-voltage three-level buck boost converter (TLBBC) with PDC exhibits a wide controllability range and cross regulation capability. These enhanced features are extremely important for better regulating variable output renewable energy sources such as solar, wind, wave, marine current, etc. The simulation and experimental results are provided to validate the claim.