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Enhanced control of grid forming VSCs in a micro-grid system under unbalanced conditions
, Article 9th Annual International Power Electronics, Drive Systems, and Technologies Conference, PEDSTC 2018, 13 February 2018 through 15 February 2018 ; Volume 2018-January , April , 2018 , Pages 380-385 ; 9781538646977 (ISBN) ; Mokhtari, H ; Ghasemi, M. A ; SHarif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
Due to the technical advances in power electronic industry, employing inverter-based distributed energy resources (IBDERs) are increased in electric power systems. Distributed generators (DGs) with the rating capacity of few megawatts are commonly connected to the distribution level of power systems which are inherently unbalanced. A cluster of IBDERs and loads form a small-scale grid called microgrid (MG) which can operate independent of the main grid. In a MG, grid forming voltage source converters (VSCs) are used to control the voltages and frequency of the MG. However, grid forming VSCs with conventional control schemes cannot do this task properly when the MG is unbalanced. In this...
Improvement of DFIG Under Unbalanced Voltage Condition
, M.Sc. Thesis Sharif University of Technology ; Parniani, Mostafa (Supervisor)
Abstract
In this thesis, performance of doubly fed induction generators in wind turbine, under stator unbalanced voltage condition has been studied. Therefore, beside of presenting related equations and models for DFIG, drawbacks of DFIG performance under unbalanced voltage condition on variables such as electric torque, active and reactive stator power and stator current have been shown. Then, controller have been designed in the way that can eliminate electric torque oscillation, active power oscillation, negative sequences of stator current and rotor current. The controller is designed base on decoupling sequences in synchronous reference and stator voltage orientation method(SVO) that consist of...
Modeling and control of a grid-connected BDFM under unbalanced grid voltage conditions
, Article 2011 IEEE International Electric Machines and Drives Conference, IEMDC 2011, 15 May 2011 through 18 May 2011 ; May , 2011 , Pages 1647-1651 ; 9781457700613 (ISBN) ; Seyed Mahdi Izadkhast ; Khosravi, H ; Oraee, H ; Sharif University of Technology
2011
Abstract
This paper presents a mathematical model for Brushless Doubly-Fed Machine (BDFM) based on Stator Flux Orientation (SFO) in positive and negative reference frames under unbalanced grid voltage conditions. A negative controller is designed to eliminate the effects of unbalanced conditions on electrical torque. The model and controller performance during unbalanced conditions is validated by time domain simulation in MATLAB/Simulink
Robust control of an autonomous four-wire electronically-coupled distributed generation unit
, Article IEEE Transactions on Power Delivery ; Volume 26, Issue 1 , September , 2011 , Pages 455-466 ; 08858977 (ISSN) ; Yazdani, A ; Iravani, R ; Sharif University of Technology
2011
Abstract
This paper proposes a control strategy for the autonomous (islanded) operation of a four-wire, electronically-coupled distributed generation (DG) unit which can feed a highly unbalanced load, e.g., due to the presence of single-phase loads. In the grid-connected mode, the power-electronic interface of the DG unit enables the exchange of real and reactive power with the distribution network, based on the conventional dq-frame current control strategy. The current control scheme is disabled subsequent to the detection of an islanding event, and the proposed controller is activated. The proposed control strategy utilizes: i) an internal oscillator to maintain the island frequency and ii) a...
Stability Improvement and Protection of Grid-following Bidirectional Three-phase Voltage-sourced Converters under Unbalanced Grid Conditions
, M.Sc. Thesis Sharif University of Technology ; Mokhtari, Hossein (Supervisor) ; Karimi, Houshang (Co-Supervisor)
Abstract
With the increasing expansion of modern DC loads and utilizing energy storage systems along with distributed renewable energy resources, grid-following bidirectional voltage-sourced converters (GFBVSCs) with fast dynamic performance are required. Due to the presence of single-phase loads and asymmetrical short circuit faults, unbalanced grid voltage conditions are available in the distribution system. Under unbalanced conditions, an oscillating component with a frequency of twice the grid angular frequency appears on the DC side. Removing double-frequency ripple in the DC link voltage without third harmonic current injection and reactive power injection to the grid based on the grid codes to...
A new approach to determine reference current for shunt active power filters: According to IEEE Std.1459 definitions
, Article 2012 3rd Power Electronics and Drive Systems Technology, PEDSTC 2012, 15 February 2012 through 16 February 2012 ; February , 2012 , Pages 156-159 ; 9781467301114 (ISBN) ; Mokhtari, H ; Sharif University of Technology
2012
Abstract
Increase of nonlinear loads has led to the rise of harmonic currents, voltage distortion and imbalance in power systems. IEEE Std. 1459 proposes new definitions for electric power in sinusoidal, nonsinusoidal, balanced and unbalanced conditions which can be used for compensation of nonsinusoidal and unbalanced systems. Among different definitions, IEEE Std. 1459 proposes the new concept of effective apparent power and power factor which is more related to the real losses in a power system. In this paper, by expansion of definitions of IEEE Std. 1459, instantaneous forms of effective parameters are defined. Then, a new control strategy for a Shunt Active Power Filters (SAPFs) is defined based...
A new control strategy for a multi-bus MV microgrid under unbalanced conditions
, Article IEEE Transactions on Power Systems ; Volume 27, Issue 4 , 2012 , Pages 2225-2232 ; 08858950 (ISSN) ; Karimi, H ; Mokhtari, H ; Sharif University of Technology
2012
Abstract
This paper proposes a new control strategy for the islanded operation of a multi-bus medium voltage (MV) microgrid. The microgrid consists of several dispatchable electronically-coupled distributed generation (DG) units. Each DG unit supplies a local load which can be unbalanced due to the inclusion of single-phase loads. The proposed control strategy of each DG comprises a proportional resonance (PR) controller with an adjustable resonance frequency, a droop control strategy, and a negative-sequence impedance controller (NSIC). The PR and droop controllers are, respectively, used to regulate the load voltage and share the average power components among the DG units. The NSIC is used to...