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A modular-multilevel (MMC) DC/DC converter is proposed in this paper, which can be deployed to inter-connect DC grid of different voltage levels, especially in the new energy sources such as wind power and solar power grid connection. Its key features include: 1) step-up and step-down operation. 2) bidirectional power flowing. 3) bi-directional fault blocking similar to a DC breaker. The operation...
To reduce the cost and footprint of a Magnetic Resonant Imaging (MRI) scanner setup in a hospital, a modification in the existing power architecture of the MRI system has been proposed. A high frequency alternative for the frontend bulky low frequency transformer has been proposed. The implementation challenges and workaround solutions for the High Frequency Power Distribution Unit (HFPDU) has been...
This paper presents an algorithm for determining fault section on Modular Multilevel Converter (MMC) based hybrid High Voltage DC (HVDC) transmission system. The hybrid transmission system consists of an overhead line followed by a subsea cable for deep-water oil and gas processing. The algorithm is based upon independent analysis of post fault characteristic signals at each terminal. These characteristic...
In this paper, a multi-degree open-circuit faults diagnostic algorithm, for improving condition monitoring ability of spacecraft solar cell system, has been proposed. This algorithm combines the output parameter, output voltage, output current and the impedance of solar cell system under low frequency domain. The algorithm can be used to diagnose the degree of faults quantitively and quickly. The...
This paper presents a protection scheme for a medium voltage dc (MVDC) link, that meshes three different MVAC distribution grids through ac/dc power converters. The proposed scheme includes active current limiters, hybrid circuit breakers and a communication layer for the coordination of these protection devices and power converters (logic selectivity). Active current limiters, installed just after...
Large inrush currents can occur when power transformers are connected to the grid. In the past, a wide range of countermeasures has been developed whereof the application of power electronic converters recently received more attention. With hybrid transformers combining a conventional transformer with a power electronic converter, the elimination of inrush currents can be realized without considerable...
Modular Multilevel Converter (MMC) has served as a promising Voltage Source Converter (VSC) for High Voltage Direct Current (HVDC) applications. In this paper, a new MMC Submodule (SM) topology called Modified Switched Capacitor Sub-Module (MSCSM) is proposed. The MSCSM is able to block the DC fault using the power electronics semiconductor diodes due to its intelligent configuration without the need...
In future high-voltage direct current (HVDC) systems, a large number of HVDC breakers will be required. In this paper, the influence of HVDC breakers on the transient performance of point-to-point HVDC links in both asymmetrical and symmetrical monopolar configuration with half-bridge modular multilevel converters is studied with simulations in PSCAD. As HVDC breakers, the active resonant breaker...
Recently introduced Bi-directional Z-Source breakers [1] are capable of clearing the short circuit fault within a few microseconds. In this paper, various applications and protection requirements for Bidirectional Z-Source breakers are discussed. Detailed comparison between de-rated AC breakers and Z-Source breakers is discussed. Breaker design criteria are explained with the help of simulation results...
DC is regarded as an attractive alternative to conventional AC technology in collection networks for large-scale wind and PV generation systems. Playing the role in the stepping up voltage and exporting the power from the individual generation units, DC/DC converters are one of the most crucial parts of the DC collector. Isolated medium-power DC/DC converters would require a medium voltage medium...
In this paper, two new hCB concepts for DC-grids are presented, which use a pulse current to extinguish the arc in the mechanical switch after opening. Both concepts are capable to adjust the pulse current amplitude/waveform to the fault current amplitude and so generate a slow current slope di/dt directly before the zero current crossing without large passive components for a fast and reliable fault...
Renewable sources like solar photovoltaic (PV) are preferred to be operated at low voltages. This necessitates high voltage boosting when they have to be connected to the high voltage DC bus. Conventional DC-DC converters (eg. boost and buck-boost) offer high voltage gain at the cost of reduced efficiency. This paper proposes a novel method to integrate low voltage PV power to the high voltage DC...
Modular multi-level converters (MMC) are considered a promising topology for HV applications Uke HVDC transmission systems. Such systems must be designed to provide high reliability against different types of faults. MMCs using Half-Bridge (HF) cells are well known for lacking the capability to block short circuits in the DC link. On the contrary, Full-Bridge (FB) cells can block the short circuit...
A DC fault will propagate quickly in a DC grid and results in significant DC voltage drop and large current increase. To protect the DC grid from the DC faults, the concept of hybrid HVDC circuit breaker (DCCB) is widely-accepted due to its low conducting loss and fast operation speed. The unidirectional DCCB recently is considered to fulfil the protection criteria. However, for a well-built DC grid,...
The Z-Source circuit breaker is a type of DC power electronic circuit breaker, which is able to autonomously isolate faults. It uses a circuit of passive components to autonomously commutate the main conducting switch (a thyristor) off during a fault. In order for the ZCB to operate correctly, the thyristor must remain reverse-biased for a defined time period when a fault occurs, i.e., the minimum...
Nitriding in plasma is a power-saving technology that provides thermochemical heat treatment used for metallic workpieces in order to improve their mechanical characteristics like hardness and resistance to wear. This paper describes the new implementation of a microcontroller based platform for pulsed Power Supplies used in Plasma Nitriding Systems (PNS). A programmable hardware was integrated into...
This paper introduces the fault behavior of full bridge modular multilevel converters (MMCs) considering a non-simultaneous blocking of the two half bridges in each sub-module. In order to protect IGBTs in the full bridge sub-module, both sides of a full bridge sub-module are not blocked at same time point. It is assumed that the first blocking of both sides is random in each sub-module, so there...
A four-terminal overhead line demonstration high voltage direct current (HVDC) grid for renewable energy power integration and transmission will be constructed around 2019 in Zhangbei district, northwest of Hebei province of China. As the high failure probability of the overhead and the low damping coefficient of DC grid, the suitable ultra-high speed protection against DC line fault needs to be developed...
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