Power electronic transformer based on cascaded H-bridge converter
01 Oct 2017-Bulletin of The Polish Academy of Sciences-technical Sciences (Sciendo)-Vol. 65, Iss: 5, pp 675-683
TL;DR: In this article, the authors proposed a control strategy of power electronic transformer (PET) using two seven-level cascaded H-bridge rectifiers, which allowed for controlling the active and reactive power with a low level of harmonic distortions.
Abstract: In this paper the control strategy of power electronic transformer (PET) is proposed. The analyzed structure of PET uses two seven-level
cascaded H-bridge (CHB) rectifiers. The electrical power of PET is transferred between DC-links of CHB converters using dual-active-bridges
(DABs) and low voltage high frequency transformers. The roposed solution allows for controlling the active and reactive power with a low
level of harmonic distortions. The DC-link voltages and the load of the utilized H-bridges are controlled using appropriate modulation strategy.
The theoretical issues are confirmed by simulation and experimental results.
Citations
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TL;DR: In this paper, an overview of the DC link development and evolution dedicated to HVDC structure for connecting offshore wind power plants to onshore power systems is presented, where the advantages of DC-DC conversion over HVAC technology in relation to transmission distance are given.
Abstract: This paper presents an overview of the DC link development and evolution dedicated to HVDC structure for connecting offshore wind power plants to onshore power systems. The growing demand for the green energy has forced investors in power industry to look for resources further out at sea. Hence, the development of power electronics and industrial engineering has enabled offshore wind farms to be situated further from the shore and in deeper waters. However, their development will require, among other technologies, DC-DC conversion systems. The advantages of HVDC over HVAC technology in relation to transmission distance are given. The different HVDC configurations and topologies of HVDC converters are elucidated. In this context, the HVDC grids are a promising alternative for the expansion of the existing AC grid.
46 citations
TL;DR: This study presents the structure and the space vector pulse-width modulation (SVPWM) for power electronic transformer (PET) based on two seven-level cascade H-bridge (CHB) inverters and proposes the optimal management of the DC-link voltage distribution.
Abstract: This study presents the structure and the space vector pulse-width modulation (SVPWM) for power electronic transformer (PET) based on two seven-level cascade H-bridge (CHB) inverters. The DC links of CHB inverters are coupled with nine dual-active bridge (DAB) converters with medium-frequency transformers. The DC-link voltages are equalised with two methods - through the control of DAB voltages and through the modulation strategy applied to both CHB inverters. In the proposed SVPWM, the influence of vector sequences on predicted DC-link voltages is analysed, and the optimum vector sequence is selected to equalise them. Regardless of this, the proposed SVPWM strategy enables the proper generation of output voltage vector also in the case of DC-link voltage imbalance - the calculation of the space-vector area takes into consideration the inequality of the DC-link voltages and its influence on the lengths and positions of active vectors. To simplify the modulation algorithm, the multilevel CHB inverter is considered as a set of three-level inverters connected in series. Each of them is controlled using the same SVPWM algorithm. The proposed modulation method reuses the H-bridges with zero duty cycles determined in the initial stages of the output voltage generation process. This enables the optimal management of the DC-link voltage distribution. The experimental research was carried out on a 600 kW/3.3 kV PET. The results are presented in this study.
9 citations
TL;DR: A new type of electronic voltage transformer based on the SF_6 coaxial capacitor satisfies the requirements of the 0.2 accuracy class and can promote the use of new high-performance products for data transmission in the era of big data and specific test analyses.
Abstract: A new type of electronic voltage transformer is proposed in this study for big data background. By using the conventional inverted SF_6 transformer insulation structure, a coaxial capacitor sensor was constructed by designing a middle coaxial electrode between the high-voltage electrode and the ground electrode. The measurement of the voltage signal could be obtained by detecting the capacitance current i of the SF_6 coaxial capacitor. To improve the accuracy of the integrator, a high-precision digital integrator based on the Romberg algorithm is proposed in this study. This can not only guarantee the accuracy of computation, but also reduce the consumption time; in addition, the sampling point can be reused. By adopting the double shielding effect of the high-voltage shell and the grounding metal shield, the ability and stability of the coaxial capacitor divide could be effectively improved to resist the interference of stray electric fields. The factors that affect the coaxial capacitor were studied, such as position, temperature, and pressure, which will influence the value of the coaxial capacitor. Tests were carried out to verify the performance. The results showed that the voltage transformer based on the SF_6 coaxial capacitor satisfies the requirements of the 0.2 accuracy class. This study can promote the use of new high-performance products for data transmission in the era of big data and specific test analyses.
8 citations
TL;DR: In this paper, a power electronic transformers (PET) with an improved structure that is applicable for multi-voltage level AC/DC hybrid distribution network is proposed. And the topology of the proposed PET is analyzed, and corresponding control methods are suggested for different parts.
Abstract: Power electronic transformers (PETs), as the core devices of the energy internet, are the key to achieve both effective consumption for renewable energy and the safe and coordinated operation for AC/DC hybrid system. In order to overcome the shortcomings of the existing PETs, a novel PET with an improved structure that applicable for multi-voltage level AC/DC hybrid distribution network is proposed. The topology of the proposed PET is analyzed, and the corresponding control methods are suggested for different parts. The input stage utilizes the modular multilevel converter structure and applies the virtual synchronous machine control strategy to enhance the inertia and damping of the system. The power of the output stage is adjusted flexibly and that enables the PET to provide certain power support to the upper grid and participate in its primary frequency regulation. A combined connection of input-series output-series and input-series output-parallel is applied for the dual-active-bridge modules of the isolation stage to enable network interconnection and electrical isolation of AC/DC grids with significantly different voltage levels. A power coordinated control method is then proposed to meet the power demand of the distribution networks connected to the output stage and ensure stable operations of PET simultaneously. The reliability and efficiency of the proposed PET topology and control strategy for AC/DC hybrid distribution network are finally verified via PSCAD/EMTDC simulation.
4 citations
TL;DR: In this article, a simple three-stage, modular architecture for SST with a minimal switch count, high power density and input power factor correction for low power applications is proposed.
Abstract: Ever since the rise in infiltration of renewable sources into the modern electric grids, the concept of solid-state transformer (SST) has garnered special attention to dynamically control and regulate the power flow while preserving the quality of supply. Though SSTs are capable of catering to a myriad of service demands by customers, their complex multistage architecture, large device count, complexity in control, increased device losses and relatively higher cost remain major bottlenecks for their widespread market penetration. This paper is intended to address the major impediments mentioned above by proposing a simple three-stage, modular architecture for SST with a minimal switch count, high power density and input power factor correction for low power applications. Each stage of SST is equipped with independent, simple and robust controllers contributing to high degree of modularity. A 1 kVA laboratory prototype is built for supplying power to sensitive electric equipment and the results presented in support of the proposed architecture. The developed prototype is shown to have unity power factor at the input, less than 10 percent of the weight and more than thrice the power density relative to the conventional transformer of similar rating.
2 citations
References
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TL;DR: The most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-Clamped (flying capacitor), and cascaded multicell with separate DC sources are presented and the circuit topology options are presented.
Abstract: Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate DC sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed.
6,472 citations
"Power electronic transformer based ..." refers background in this paper
...Multilevel (ML) VSI solutions meet that requirement in MV applications [3, 6, 7, 21]....
[...]
TL;DR: This paper covers the high-power voltage-source inverter and the most used multilevel-inverter topologies, including the neutral-point-clamped, cascaded H-bridge, and flying-capacitor converters.
Abstract: This paper presents a technology review of voltage-source-converter topologies for industrial medium-voltage drives. In this highly active area, different converter topologies and circuits have found their application in the market. This paper covers the high-power voltage-source inverter and the most used multilevel-inverter topologies, including the neutral-point-clamped, cascaded H-bridge, and flying-capacitor converters. This paper presents the operating principle of each topology and a review of the most relevant modulation methods, focused mainly on those used by industry. In addition, the latest advances and future trends of the technology are discussed. It is concluded that the topology and modulation-method selection are closely related to each particular application, leaving a space on the market for all the different solutions, depending on their unique features and limitations like power or voltage level, dynamic performance, reliability, costs, and other technical specifications.
2,254 citations
"Power electronic transformer based ..." refers background in this paper
...The voltage sources connected to the cells have to be independent or isolated [7, 12]....
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TL;DR: A survey of different topologies, control strategies and modulation techniques used by cascaded multilevel inverters in the medium-voltage inverter market is presented.
Abstract: Cascaded multilevel inverters synthesize a medium-voltage output based on a series connection of power cells which use standard low-voltage component configurations. This characteristic allows one to achieve high-quality output voltages and input currents and also outstanding availability due to their intrinsic component redundancy. Due to these features, the cascaded multilevel inverter has been recognized as an important alternative in the medium-voltage inverter market. This paper presents a survey of different topologies, control strategies and modulation techniques used by these inverters. Regenerative and advanced topologies are also discussed. Applications where the mentioned features play a key role are shown. Finally, future developments are addressed.
2,111 citations
"Power electronic transformer based ..." refers background or methods in this paper
...The voltage sources connected to the cells have to be independent or isolated [7, 12]....
[...]
...Among all types of inverters, cascaded H-bridge converters are the most interesting [7]....
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...Multilevel (ML) VSI solutions meet that requirement in MV applications [3, 6, 7, 21]....
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...The galvanic isolation can be realized using grid-connected single-phase or multi-phase transformers [7] or using isolated DC-DC converters in CHB converter topology [13]....
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TL;DR: An energy-balance control strategy for a cascaded single-phase grid-connected H-bridge multilevel inverter linking n independent photovoltaic arrays to the grid, ensuring the stability of the system for the whole range of PV array operating conditions.
Abstract: This paper presents an energy-balance control strategy for a cascaded single-phase grid-connected H-bridge multilevel inverter linking n independent photovoltaic (PV) arrays to the grid. The control scheme is based on an energy-sampled data model of the PV system and enables the design of a voltage loop linear discrete controller for each array, ensuring the stability of the system for the whole range of PV array operating conditions. The control design is adapted to phase-shifted and level-shifted carrier pulsewidth modulations to share the control action among the cascade-connected bridges in order to concurrently synthesize a multilevel waveform and to keep each of the PV arrays at its maximum power operating point. Experimental results carried out on a seven-level inverter are included to validate the proposed approach.
293 citations
"Power electronic transformer based ..." refers background in this paper
...The uniform DC-link voltage distribution can also be maintained using separate controllers for each of the H-bridges of grid-connected CHB inverter [16]....
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...The uniform DC-link voltage distribution can be also maintained using separate control ers for each of the H-Bridges of grid-con ected CHB inverter [16]....
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...The uniform DC-link voltage distribution can be also maintained using separate controllers for each of the H-Bridges of grid-connected CHB inverter [16]....
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TL;DR: In this paper, a high-frequency link multilevel cascaded medium-voltage converter is proposed, which generates multiple isolated and balanced dc supplies for the converter, which inherently minimizes the voltage imbalance and common mode issues.
Abstract: Recent advances in solid-state semiconductors have led to the development of medium-voltage power converters (e.g., 6-36 kV) which could obviate the need for the step-up transformers of renewable power generation systems. The modular multilevel cascaded converters have been deemed as strong contenders for the development of medium-voltage converters, but the converters require multiple isolated and balanced dc supplies. In this paper, a high-frequency link multilevel cascaded medium-voltage converter is proposed. The common high-frequency link generates multiple isolated and balanced dc supplies for the converter, which inherently minimizes the voltage imbalance and common mode issues. An 11-kV system is designed and analyzed taking into account the specified system performance, control complexity, cost, and market availability of the power semiconductors. To verify the feasibility of the proposed system, a scaled down 1.73-kVA laboratory prototype test platform with a modular five-level cascaded converter is developed and explored in this paper, which converts a 210 V dc (rectified generator voltage) into three-phase 1 kV rms 50 Hz ac. The experimental results are analyzed and discussed. It is expected that the proposed new technology will have great potential for future renewable generation systems and smart grid applications.
262 citations
"Power electronic transformer based ..." refers background in this paper
...Increasing the level of inverter output voltage or increasing the amplitude of output voltage can be done easily by adding more cells to the converter structure [8]....
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