Startup Strategy With Constant Peak Transformer Current for Solid-State Transformer in Distribution Network
01 Mar 2019-IEEE Transactions on Industry Applications (Institute of Electrical and Electronics Engineers (IEEE))-Vol. 55, Iss: 2, pp 1740-1751
TL;DR: A new startup strategy is proposed to make the peak transformer current in the charging process a constant value, indicating that the strategy is insensitive to initial values.
Abstract: Solid-state transformer (SST) is widely used in many fields and it plays a key role in the development of energy internet. The startup strategy of SST adopted in distribution network has to be designed elaborately because in this application the requirement of functionality, flexibility, and expandability is very high. A number of researches for the startup process of SST were made and several solutions were proposed. In these solutions, the transformer current in the charging process was unable to be observed or controlled, leading to the lack of analytical basis in a startup strategy design. In order to make the charging process observable and controllable, the authors developed a mathematical model of this process. Based on the model, a new startup strategy is proposed to make the peak transformer current in the charging process a constant value. Cases with different conditions are analyzed, indicating that the strategy is insensitive to initial values. Experimental results are provided to validate the accuracy of the mathematical model and the effectiveness of the presented solution.
Citations
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TL;DR: In this paper , the authors proposed an efficiency-oriented automatic triple phase shift (TPS) modulation approach, which utilizes neural network, particle swarm optimization, and fuzzy inference system, respectively, in its three stages.
Abstract: Currently, triple phase-shift (TPS) modulation has attracted more and more attention of researchers as an advanced modulation strategy for dual active bridge converter (DAB). Since it has three degrees of freedom, it can realize better performance both in soft switching ranges and power efficiency. However, how to choose these three degrees of freedom to realize optimal power efficiency of DAB converter becomes a concern for researchers. Generally, there exist two difficulties to apply efficiency-oriented TPS modulation. The first difficulty lies in the analysis process in which the main task is to figure out the relationships between modulation parameters and power loss. The three modulation parameters in TPS bring difficulties in analysis and deduction process, which suffers from high computational burden and low accuracy. Additionally, the second difficulty lies in the real-time realization of TPS modulation. If a look-up table is applied to store the optimized modulation parameters, it is highly likely that its discrete nature will result in unsatisfactory modulation performance. Therefore, this article proposes an efficiency-oriented automatic TPS (ATPS) modulation approach, which utilizes neural network, particle swarm optimization, and fuzzy inference system, respectively, in its three stages. The proposed ATPS is able to mitigate labor in computational burden with a highly automatic fashion. Finally, this proposed ATPS has been validated with 1-kW hardware experiments.
16 citations
TL;DR: Simulation and experiment on a 510 V/380 V 500 kW cascaded-full-bridge SST reveal that the proposed controls can effectively reduce the inrush currents during the start-up and restart processes of SSTs.
Abstract: The three-stage modular solid-state transformer (SST) is a typical SST with a non-trivial start-up process. Specifically, special controls must be used to reduce the inrush current in the DC/DC stage during the start-up process of these SSTs. For the DC/DC stage based on the widely studied single-phase-shift dual active bridge (DAB), no inner-phase-shift control is required in its normal operations. In this case, using the existing inner-phase-shift control to reduce the inrush current increases the PWM channel requirements of microprocessors and the complexity of the control system. To address this problem, this paper proposes a long-dead-time control with easy implementation to reduce the inrush current without introducing additional PWM channel requirements. Fixed-dead-time and varied-dead-time controls are also proposed to reduce the inrush current when restarting three-stage modular SSTs with small cell capacitors without increasing the PWM channel requirements. The varied-dead-time control is faster than the fixed-dead-time one. The magnitude of the DAB current under these controls is calculated, and the overall time for fulfilling the proposed controls is estimated. The simulation and experiment on a 510 V/380 V 500 kW cascaded-full-bridge SST reveal that the proposed controls can effectively reduce the inrush currents during the start-up and restart processes of SSTs.
10 citations
Cites background from "Startup Strategy With Constant Peak..."
...The major difference of the proposed control and the existing inner-phase-shift control [23] is the absolute value of the reverse voltage on Lt....
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TL;DR: In this paper, the multiscale method is applied in the power electronic modeling which provides a qualitative methodology to combine the scales appropriately, and to obtain the dynamic response under the action of multiphysics accurately.
Abstract: Designing of power electronics converters seldom considers multiscale coupling relationship between components and circuits. Although macroscale is computationally efficient, it barely contains the micro implications about aging, deterioration, transient performance, etc. Conversely, the microscale obtains multiple observation scope, however, with computational disaster. In this paper, the multiscale method is applied in the power electronic modeling which provides a qualitative methodology to combine the scales appropriately, and to obtain the dynamic response under the action of multiphysics accurately. Firstly, the concept of multiscale and the scale division of power electronic system are expounded. Considered the dynamic behavior of components and converters with different complexity, the framework of multiscale converters and modeling method is proposed. Afterwards, a scalable coupling separation method is presented, providing interfaces for the multiphysics and dielectric physics. Additionally, a multiscale conversion algorithm considering both efficiency and accuracy is designed. In the end, a DC/DC converter is taken for the verification. The feasibility and advantages of multiscale method and conversion algorithm have been demonstrated in accuracy, consistency and multiple analysis. By filling in the microscale observation, it is plausible to provide theoretical guidance for reducing margin, accurate analysis and reliability estimation of electronic components.
6 citations
Cites methods from "Startup Strategy With Constant Peak..."
...The transient process of non-linear system has no way but to be simulated by the numerical solution method of conventional differential equation, which leads to long simulation time and poor numerical stability [6]....
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TL;DR: Results show that SSTs can acceptably decrease grid unbalanced voltage by an optimal injection current, and a searching optimization algorithm is presented to estimate the optimal required negative-sequence current vector.
Abstract: Solid-state transformers (SSTs) have a great ability to improve power quality problems. In this article, an effective strategy is proposed to improve voltage unbalance conditions by these transformers. A searching optimization algorithm is presented to estimate the optimal required negative-sequence current vector. Injection of this current vector into a medium-voltage network provides maximum compensation in the voltage unbalance factor. In this method, the amplitude of the negative-sequence current vector is determined based on the current limitation of the SST and its phase angle is optimized to maximum improve the voltage unbalance conditions. Parametric analysis proves that the proposed injection current vector is unique. This negative-sequence current vector is obtained based on a simple process that is presented in the form of a flowchart. Independence from the extraction of positive and negative sequences of the measured currents is one of the main advantages of the proposed control method. Simulation and experimental results by using a laboratory three-stage SST approve the proposed optimization method. These results show that SSTs can acceptably decrease grid unbalanced voltage by an optimal injection current.
5 citations
11 Oct 2020
TL;DR: A generalized DCX modulation scheme is proposed in this paper to maximize the average DCX output current and to enable soft startup transitions in the two configurations considered.
Abstract: In a composite dc-dc converter, regulation and dual active bridge (DAB)-based fixed-ratio (DCX) modules are arranged to minimize stresses and losses over wide ranges of input and output voltages. The system relies on smooth mode transitions in which a DCX must be quickly powered up from zero output to its nominal fixed-ratio operation. In the case a DCX precedes a regulation stage, the DCX is exposed to a high input voltage, leading to a large inrush current during startup. In the case a DCX follows a regulation stage, the DCX needs to charge the output dc capacitor while simultaneously supplying a high load current. To address these challenges, a generalized DCX modulation scheme is proposed in this paper to maximize the average DCX output current and to enable soft startup transitions in the two configurations considered. The approach is verified by simulations and by experimental results on a 350 V, 25 kW SiC-based prototype.
4 citations
Cites background or methods from "Startup Strategy With Constant Peak..."
...DCX soft startup strategies presented in previous works can generally be classified into the following two types: 1) introducing auxiliary charging resistors [3] or charging circuits [4], [5], which complicates the power stage, and may compromise power density, efficiency, or speed of mode transitions; 2) limiting volt-seconds applied to Lr by applying a custom modulation scheme to the existing full-bridge switches [6]– [9]....
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...At some operating points, duty-cycle modulation must be implemented on both sides to sufficiently reduce the inrush current [9]....
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References
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TL;DR: In this paper, the dual-active-bridge (DAB) isolated bidirectional dc-dc converter (IBDC) serves as the core circuit of high frequency-link (HFL) power conversion systems.
Abstract: High-frequency-link (HFL) power conversion systems (PCSs) are attracting more and more attentions in academia and industry for high power density, reduced weight, and low noise without compromising efficiency, cost, and reliability. In HFL PCSs, dual-active-bridge (DAB) isolated bidirectional dc-dc converter (IBDC) serves as the core circuit. This paper gives an overview of DAB-IBDC for HFL PCSs. First, the research necessity and development history are introduced. Second, the research subjects about basic characterization, control strategy, soft-switching solution and variant, as well as hardware design and optimization are reviewed and analyzed. On this basis, several typical application schemes of DAB-IBDC for HPL PCSs are presented in a worldwide scope. Finally, design recommendations and future trends are presented. As the core circuit of HFL PCSs, DAB-IBDC has wide prospects. The large-scale practical application of DAB-IBDC for HFL PCSs is expected with the recent advances in solid-state semiconductors, magnetic and capacitive materials, and microelectronic technologies.
1,306 citations
"Startup Strategy With Constant Peak..." refers background in this paper
...Normally, a full-bridge IBDC (or dual active bridge, DAB) is preferred because it is simple in topology and easy to control [8]....
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01 Jan 2011
TL;DR: The architecture described in this paper is a roadmap for a future automated and flexible electric power distribution system that is suitable for plug-and-play of distributed renewable energy and distributed energy storage devices.
Abstract: This paper presents an architecture for a future electric power distribution system that is suitable for plug-and-play of distributed renewable energy and distributed energy storage devices. Motivated by the success of the (information) Internet, the architecture described in this paper was proposed by the NSF FREEDM Systems Center, Raleigh, NC, as a roadmap for a future automated and flexible electric power distribution system. In the envisioned “Energy Internet,” a system that enables flexible energy sharing is proposed for consumers in a residential distribution system. The key technologies required to achieve such a vision are presented in this paper as a result of the research partnership of the FREEDM Systems Center.
1,237 citations
"Startup Strategy With Constant Peak..." refers background in this paper
...as intelligent energy management, or energy router (ER) [7]....
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TL;DR: In this article, the authors present a systematical technology review essential for the development and application of SST in the distribution system, including high-voltage power devices, high-power and high-frequency transformers, ac/ac converter topologies, and future research directions.
Abstract: The solid-state transformer (SST), which has been regarded as one of the 10 most emerging technologies by Massachusetts Institute of Technology (MIT) Technology Review in 2010, has gained increasing importance in the future power distribution system. This paper presents a systematical technology review essential for the development and application of SST in the distribution system. The state-of-the-art technologies of four critical areas are reviewed, including high-voltage power devices, high-power and high-frequency transformers, ac/ac converter topologies, and applications of SST in the distribution system. In addition, future research directions are presented. It is concluded that the SST is an emerging technology for the future distribution system.
897 citations
"Startup Strategy With Constant Peak..." refers background or methods in this paper
...Because of the voltage potential difference between different ports, an input-series output-parallel pattern is applied to reduce the voltage level of each submodule [1]....
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..., traction system, renewable energy integration, and distribution network [1], [2]....
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TL;DR: In this article, a transformerless intelligent power substation (TIPS) is proposed as a three-phase SST interconnecting a 13.8 kV distribution grid with a 480 V utility grid.
Abstract: Medium-voltage (MV) SiC devices have been developed recently which can be used for three-phase MV grid tie applications. Two such devices, 15 kV SiC insulated-gate bipolar transistor (IGBT) and 10 kV SiC MOSFET, have opened up the possibilities of looking into different converter topologies for the MV distribution grid interface. These can be used in MV drives, active filter applications, or as the active front end converter for solid-state transformers (SSTs). The transformerless intelligent power substation (TIPS) is one such application for these devices. TIPS is proposed as a three-phase SST interconnecting a 13.8 kV distribution grid with a 480 V utility grid. It is an all SiC device-based multistage SST. This paper focuses on the advantages, design considerations, and challenges associated with the operation of converters using these devices keeping TIPS as the topology of reference. The efficiency of the TIPS topology is also calculated using the experimentally measured loss data of the devices and the high-frequency transformer. Experimental results captured on a developed prototype of TIPS along with its measured efficiency are also given.
307 citations
"Startup Strategy With Constant Peak..." refers methods in this paper
...Analyses, modeling, and design of an SST can be found in [3] and [4] and implementations of industry applications are investigated as well [5], [6]....
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TL;DR: A minimum-backflow-power-based extended-phase-shift control strategy is proposed with the determination of optimal phase-shift pairs by using the Karush–Kuhn–Tucker function for various scenarios and shows the proposed control can improve the output power regulation flexibility, minimize the backflow power, and improve the efficiency in wide operating range.
Abstract: As key component for the flexible dc distributed power system, the dual active bridge (DAB)-converter-based solid-state transformer (SST) with high efficiency for a wide operating range is essential. However, with the traditional phase-shift control, high backflow power and current stress will significantly affect the conversion efficiency. In this paper, the backflow power characteristics in both sides of DAB-based SST converters are comprehensively analyzed. On this basis, complete transmission power, backflow power, and peak current mathematical models are established. Then, a minimum-backflow-power-based extended-phase-shift control strategy is proposed with the determination of optimal phase-shift pairs by using the Karush–Kuhn–Tucker function for various scenarios. The backflow power and current stress curves with different algorithms are compared. It shows the proposed control can improve the output power regulation flexibility, minimize the backflow power, and improve the efficiency in wide operating range. Finally, a DAB-based SST prototype was developed and the experimental results verified the effectiveness of the proposed control strategy.
127 citations
"Startup Strategy With Constant Peak..." refers methods in this paper
...Analyses, modeling, and design of an SST can be found in [3] and [4] and implementations of industry applications are investigated as well [5], [6]....
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