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Iron core of transformer somehow always have non-linear hysteresis characteristics. Generally, they are symmetry on their three legs of iron core. However, it may also suffer from unsymmetrical flux hysteresis characteristic due to inappropriate or special design. On the other hand, transformer is very sensitive to ferroresonance if it works on saturation area of its flux characteristic. Therefore,...
In this paper a novel and fast open-circuit fault detection and localization method is proposed for Five-level active-neutral-point-clamped (5L-ANPC) converter. The method is based on comparing the measured output voltage with the reference voltage and the voltage obtained from the fault analysis. The implementation scheme of the method is presented; and all the practical aspects including capacitors...
This paper proposes an adaptive democratic current sharing control scheme for interleaved dc-dc converters under faulty condition. The proposed fault tolerant control approach can achieve the desired output voltage generation, and equal current sharing among the remaining healthy modules as more and more modules fail. The main idea is to adaptively change the outer voltage and inner current controller...
In this paper, an asymmetric mixed MMC topology of multilevel converter for bipolar HVDC transmission systems is introduced. Among the existing MMC topologies for the bipolar HVDC systems, the asymmetric mixed MMC topology provides the benefits of: a lower number of submodule cells, fewer switching devices and lower conduction losses. Furthermore, the HVDC based on asymmetric mixed MMC can be flexibly...
This paper puts forth a vision for scalable distribution grid integration of energy resources such as rooftop photovoltaics (PVs) and electric vehicles (EVs). The output of these resources vary temporally in an unpredicted manner. Therefore, they bring substantial challenges to utilities vis-a-vis massive deployment of such resources. By leveraging the fact that most of the distributed energy resources...
To reduce the current loop reference distortion in traditional average current control and total harmonic distortion of line current, this paper employs improved average current control (IACC) of Boost PFC, in which a digital-generated unit sinusoidal half-wave (USHW) is introduced as current loop sinusoidal reference. Aimed at generating USHW with DSP's enhanced capture module correctly and conveniently,...
High Resistance Grounding is preferred in many industrial applications. However, there are some drawbacks for the traditional HRG detection methods to locate a ground fault in Adjustable Speed Drive systems. The existing methods cannot detect or identify which phase faulted once the drive has HRG fault. This paper will present a leakage flux linkage detection based HRG fault identification method...
Hybrid DC circuit breaker, a combination of disconnector and multiple power electronic devices, has gained popularity for its low-loss at normal operation and its quick and effective circuit breaking during fault protection. However, its bulkiness threatens to limit its application in multi-terminal DC system, where the terminal is usually connected to more than one transmission lines and hence the...
A low voltage ride-through solution for an indirect three-level matrix converter based open-end winding drive is demonstrated. The proposed method uses the input filter capacitors to exchange the inertial energy from the motor and thereby maintain the flux in the motor during grid fault conditions. The input filter capacitors act as the voltage source for inverters during the fault. Ride-through is...
This paper proposes a new modular multilevel converter with symmetric bidirectional DC fault blocking capability for high voltage direct current transmission systems. The new modular multilevel converter is composed of novel submodules, which is developed from a three-level T-type converter combined with some clamp circuits. The proposed novel submodule can output three voltage levels with six IGBTs,...
Nowadays, the Modular Multilevel Converter (MMC) based HVDC has been considered as a promising technology to meet the increasing electric power demand. However, constructing new transmission lines becomes more and more difficult because of environmental issues. Consequently, the newly constructed DC lines have to share the right of way with existing AC transmission in close proximity. Meanwhile, as...
This paper proposes a novel input-series output-parallel (ISOP) current-fed modular dual-active-bridge (CF-MDAB) dc-dc converter for medium-voltage dc (MVDC) system application. The proposed converter exhibits favorite features of DAB converter such as galvanic isolation, soft-switching condition and small passive components. Compared to ISOP DAB converter, the proposed topology has direct dc current...
Fault tolerant operation can significantly improve the reliability of a Modular Multilevel Converter (MMC), but the precondition is that a fast and accurate fault detection and localization method has been embedded into the MMC control system. This paper proposes a fault diagnosis method used in a distributed control architecture, which makes the local controllers capable of identifying the switching...
In this paper, a method to diagnose and identify the open-circuit faults of IGBT for a six-level hybrid inverter (6L-HI) is proposed, which is based on the signals of the inner device voltages, the flying capacitor voltages and the phase currents of the inverter. Since the flying capacitor voltage sensors and the output current sensors are already employed for the inverter operation, only one additional...
Three-channel controller of FB-MMC HVDC that enables four-quadrant operation on DC side and fault ride through on AC and DC sides without blocking IGBTs is proposed. Phasor modeling of FB MMC is studied to provide insight into independent AC and DC control. Three modulation indices are used: the conventional d-axis, q-axis AC-side modulation indices Md, Mq and a newly proposed DC modulation index...
This paper presents an optimized active power control method for two-stage photovoltaic (PV) grid-connected inverter under unbalanced grid faults. The purpose of the control method is to reduce the active power deficit of grid by injecting the maximum active power of the PV system under the premise of ensuring the safety of the inverter itself. Safe operation region (SOR), which considers the limitation...
This study proposed a novel protective action for converter side phase-to-ground fault of FB-MMC-based bipolar HVDC. The faulty converter is kept in operation during fault, and its dc-link voltage reference is set to zero in order to avoid serious overvoltage of the sub-module capacitors. This protective action was verified by simulation. The overcurrent and overvoltage of converter arms are moderate...
The hybrid high voltage direct current (Hybrid HVDC) system based on line commutated converter (LCC) and modular multilevel converter (MMC) is a feasible solution for long distance bulk power transmission. In order to handle the dc-side short-circuit fault, two kinds of methods can be adopted. The first one is to replace half-bridge sub-modules (HBSMs) with full-bridge SMs or clamp-double SMs which...
Hybrid modular multi-level converter (Hybrid MMC) topology, consisting of both half-bridge (HB) and full-bridge (FB) submodules, is suitable for HVDC application as it combines the advantages of both HB-MMC and FB-MMC. This paper focuses on the control aspects of hybrid MMC with the objective of limiting DC fault current. It is also controlled to exchange reactive power with the AC grid during DC...
Fast detection and isolation of DC faults is recognized as the main challenge in developing DC transmission grids. Voltage source converter blocking must be prevented which can be very difficult given the large rate-of-rise of fault currents. The concept of multi-converter DC bus is introduced as a grid design approach aimed towards increasing robustness of DC grids to DC faults. Behavior of a multi-converter...
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