A Robust Vector Current Controller with Negative-Sequence Current Capability for Grid-Connected Inverters

This paper presents a vector current controller (in the synchronous reference, or the dq, frame) with negative-sequence current injection capability for three-phase grid-connected converters. This capability is desired for the operation of the converter during unbalanced conditions and also for a certain type of islanding detection. The proposed controller first determines the double-frequency current references and then uses a sixth-order two-input two-output proportional-integral-resonance (PIR) structure, which is optimally designed. Compared with the existing similar approaches, the proposed controller has a simpler structure and more robust performance, e.g., against system parameter uncertainties and weak grid conditions. The proposed controller is developed for converters with both the L-type and LCL-type filters. For the LCL-type converter, a suboptimal partial state feedback control is also proposed to achieve robust stability and active damping of resonance poles without requiring additional sensors. Detailed experimental results are presented to illustrate the properties and performances of the proposed controller.

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Study of Low Voltage Ride through in Photovoltaic Grid-Tied Inverter Based on Unsymmetrical Grid Voltage Fall

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.986-987.1277 ◽

2014 ◽

Vol 986-987 ◽

pp. 1277-1281

Author(s):

Tian Fa Liao ◽

Yang Chun ◽

Wen Si ◽

Chang Wen Dong ◽

Jia Xiang Xue

Keyword(s):

Power Output ◽

Low Voltage ◽

Hardware Platform ◽

Negative Sequence ◽

Grid Voltage ◽

Low Voltage Ride Through ◽

Current Controller ◽

Three Phase ◽

Overall Efficiency ◽

Negative Sequence Current

In this paper, 10KW three-phase three-level photovoltaic grid-tied inverter is applied as hardware platform. Considering the insufficiency of PV arrays power output and low overall efficiency due to grid voltage falls asymmetrically, P-R current controller is used to provide unsymmetrical positive and negative sequence current to the grid so that low voltage ride through (LVPT) in photovoltaic inverter can be achieved. Through the implement of experiments, it is well proved that the requirement of LVPT when the grid voltage falls asymmetrically can be met by applying the solution proposed in this paper.

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A Study on DG Control Strategy and Grid Protection

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.521.204 ◽

2014 ◽

Vol 521 ◽

pp. 204-212

Author(s):

Xin Chao Wang ◽

Chen Xin Yang

Keyword(s):

Load Capacity ◽

Short Circuit ◽

Current Source ◽

Islanding Detection ◽

Test Results ◽

Total Load ◽

Line Voltage ◽

Negative Sequence ◽

Three Phase ◽

Negative Sequence Current

DG integration reduces the selectivity and sensitivity of grid relay protection. A new control algorithm is proposed. It shows that the negative sequence current will not be affected by DG when the DG is designed as a symmetric three-phase current source. In this case, the negative sequence characteristic can be utilized for grid protection during short-circuit faults. If DGs maximum power capacity is restricted to be lower than total load capacity, DG terminal line-voltage and the negative sequence voltage can be used as the criteria for islanding detection. Then it is possible to cutoff DG in order to fulfill the reclosing requirement. A complicated simulation system is designed using PSCAD/EMTDC program. Different short-circuit faults are simulated to verify the proposals. The test results confirm well with the conclusions.

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Study on LVRT Decoupling Dual Synchronous Current Controller

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.668-669.532 ◽

2014 ◽

Vol 668-669 ◽

pp. 532-539

Author(s):

Tian Fa Liao ◽

Chun Yang Yi ◽

Zhao Quan Cai ◽

Chang Wen Dong ◽

Wei Shi ◽

...

Keyword(s):

Pi Controller ◽

Positive Sequence ◽

Negative Sequence ◽

Flexible Control ◽

Current Reference ◽

Current Controller ◽

Totally Positive ◽

Three Phase ◽

Negative Sequence Current ◽

The Impact

Under three-phase grid asymmetric fault conditions, use traditional PI controller of PV inverters to inject symmetric current positive sequence into the grid, ignoring the impact of the negative sequence current on LVRT, thus traditional PI controller does not apply to three-phase grid asymmetric faults. The paper proposes the decoupling dual synchronous current controller to reject positive, negative sequence current into the grid simultaneously and adopt positive and negative sequence flexible control to determine the active current reference and reactive current reference, avoiding the various drawbacks such as power control, totally positive sequence control bringing. Experiment verify the science and feasibility that decoupling dual synchronous current controller applies to asymmetric faults riding-through.

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Turn-to-Turn Fault Diagnosis on Three-Phase Power Transformer Using Hybrid Detection Algorithm

Applied Sciences ◽

10.3390/app11062608 ◽

2021 ◽

Vol 11 (6) ◽

pp. 2608

Author(s):

Chien-Hsun Liu ◽

Willybrordus H. P. Muda ◽

Cheng-Chien Kuo

Keyword(s):

Fuzzy System ◽

Power Transformer ◽

Detection Algorithm ◽

Current Response ◽

Negative Sequence ◽

Three Phase ◽

Hybrid Detection ◽

Incipient Faults ◽

Increase In Accuracy ◽

Negative Sequence Current

A power transformer (PT) in power generation or transmission is critical to maintaining electrical continuity. Fault detection on a PT is needed, especially of incipient faults, which are often caused by a turn-to-turn fault (TTF) before it develops into a more severe fault. We use a hybrid algorithm between conventional and modern techniques to detect a developing fault in a PT. The current response signals from a negative sequence current directional algorithm, extended park vector algorithm (EPVA), differential negative sequence current, and EPVA-fuzzy system are combined to distinguish the possibility of a TTF. The subalgorithms are combined using a hybrid detection algorithm to distinguish the faults. The model is a 10 MVA, three-phase PT with Δ-Y configuration 150/300 kV, simulated using MATLAB Simulink software. The results show that by combining the subalgorithms, several limitations are distinguished within the TTF with a slight increase in accuracy.

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