Showing papers by "Qin Lei published in 2018"
TL;DR: This paper presents a new voltage source converter topology for medium to high voltage dc application, named modular embedded multilevel converter (MEMC), based on a three-level topology structure and consists of series-connected insulated-gate bipolar transistor (IGBT) bridge stacks.
Abstract: Many of the renewable energy resources, like offshore wind, utility PV farms, are located far away from the load centers, which requires dc power transmission system to efficiently deliver power. Voltage-source converter solution is required in many applications due to the stability and compensation requirement. This paper presents a new voltage source converter topology for medium to high voltage dc application, named modular embedded multilevel converter (MEMC). MEMC is based on a three-level topology structure and consists of series-connected insulated-gate bipolar transistor (IGBT) bridge stacks, like the popular modular multilevel converter (MMC) and series-connected thyristor or press-pack high voltage integrated gate-commutated thyristor or IGBT stacks. The basic operation principle, control solutions, and the methods to commutate the thyristors are explained in detail. Due to the three-level structure, the total number of IGBT stacks are reduced by half compared with MMC, leading to much lower energy storage, weight, volume, and system complexity. Also by replacing part of the IGBT stack in MMC with thyristor stack, both of the system conduction loss and switching loss can be further reduced. There are other topology variations of MEMC with a similar operational principle but different characteristics.
40 citations
18 Apr 2018
TL;DR: The proposed main idea is to use super capacitor to prevent large voltage and frequency fluctuation during the transient and use the battery to maintain the long-term Voltage and frequency stability.
Abstract: The goal of this paper is to solve the voltage and frequency fluctuation problem of microgrid in the standalone operation. The proposed main idea is to use super capacitor to prevent large voltage and frequency fluctuation during the transient and use the battery to maintain the long-term voltage and frequency stability. The control strategies for the renewable energy sources, storage system, load and power quality improvements devices in three different operation modes “grid-connected”, “standalone”, and “transient of islanding and reconnection” have been proposed. A sample microgrid system is used to verify the effectiveness of the control strategies.
9 citations
20 May 2018
TL;DR: A game changing and universally applicable standard block of "series connected SiC MOSFET" with excellent dynamic voltage sharing and high reliability is proposed, including the current source gate driver with device synchronization function.
Abstract: The goal of this paper is to significantly improve the efficiency and power density of medium voltage drive and high-power converters. To achieve the goal, the proposed approach is to replace the high voltage Si IGBT by series connected SiC MOSFETs. Specifically, a game changing and universally applicable standard block of "series connected SiC MOSFET" with excellent dynamic voltage sharing and high reliability is proposed. The core technology in the block is the current source gate driver with device synchronization function. A down-scaled medium voltage drive prototype has been developed to demonstrate the feasibility and advantages of the standard block.
8 citations
03 Dec 2018
TL;DR: In this article, a 1000V/1.5MHz 80kVA pulse power inverter is developed and its design considerations and performance in such voltage and frequency level are discussed.
Abstract: SiC device has supreme switching performance over Si device which helps to shrink the power converter filter size and improve the converter power density. In pulse power supply area, without the tight thermal dissipation limitations, higher voltage and higher frequency can be achieved. In this paper, a 1000V/1.5MHz 80kVA pulse power inverter is developed. Its design considerations and performance in such voltage and frequency level are discussed.
5 citations
03 Dec 2018
TL;DR: An ABC to Alpha-Beta transformation based method has been implemented in order to solve the moving average problem and a PLECS simulation with equation based switching mode has been conducted to test the performance of the control algorithms and to improve the simulation speed.
Abstract: A standard pump-back system consisting of two Modular Multilevel Converters (MMCs) has been proposed. Compared with traditional two-level inverter based pump-back system, the MMC based topology is able to produce a virtual grid with multilevel voltage output. In addition, energy control loops are unique for MMC to ensure the energy balance between its DC and AC side. The associating challenge is to retrieve the moving average of the capacitor energy under variable frequency condition. The basic operation principle and control strategies including all the energy and current loops have been discussed in detail. Moreover, an ABC to Alpha-Beta transformation based method has been implemented in order to solve the moving average problem. A PLECS simulation with equation based switching mode has been conducted to test the performance of the control algorithms and to improve the simulation speed. The simulation results and analysis have been provided and future work has been mentioned.
4 citations
22 Oct 2018
TL;DR: Energy density and system efficiency can be largely improved since the capacitor size is reduced and energy storage devices can be integrated in the proposed topology and thus make it feasible for smart grid and marine applications.
Abstract: This paper proposes a standard module of "Isolated Half Bridge (IHB)" or "Isolated Full Bridge (IFB)" and its application in MVDC/MVAC system by using modular structure. The fundamental and 2nd harmonic current ripple can be eliminated through connecting the DC links of three phase on the same level. Energy density and system efficiency can be largely improved since the capacitor size is reduced. In addition, energy storage devices can be integrated in the proposed topology and thus make it feasible for smart grid and marine applications. Detailed simulation results of comparison between proposed topology and traditional MMC have been presented. Moreover, medium voltage drive starting from zero frequency is also simulated. Modular DC/DC converters with energy storage are discussed as well.
1 citations