Toronto, Canada

Time filter

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Mohamed Y.A.-R.I.,University of Alberta | Zeineldin H.H.,Masdar Institute of Science and Technology | Salama M.M.A.,University of Waterloo | Seethapathy R.,Hydro One Networks Inc.
IEEE Transactions on Power Electronics | Year: 2012

Seamless formation and robust control of distributed generation microgrids are essential requirements to facilitate powerful and flexible control infrastructure in future smart power grids. Motivated by this objective, this paper presents a control structure for microgrid converters based on direct-voltage control and optimized dynamic power sharing. The salient features of the proposed scheme are 1) minimum switching actions between grid-connected and isolated microgrids systems to minimize internal microgrid formation disturbances; 2) active damping control performance in the converter control voltage vector to effectively reject both voltage magnitude disturbances and power angle swings associated with mode transition and load disturbances; and 3) high bandwidth direct voltage control loop in both grid-connected and isolated microgrid modes to improve the dynamic response and disturbance rejection performance. Theoretical analysis and comparative experimental results are presented to validate the effectiveness of the proposed control scheme. © 2011 IEEE.


Mohamed Y.A.-R.I.,University of Alberta | Rahman M.A.,National Research Institute | Rahman M.A.,ABB | Seethapathy R.,Hydro One Networks Inc.
IEEE Transactions on Power Electronics | Year: 2012

This paper presents a robust control scheme for high power quality grid connection of inductor-capacitor-inductor (LCL)-filtered distributed generation (DG) inverters. The presence of the LCL filter complicates the dynamics of the inverter control system, particularly when the uncertain nature of the grid background distortion and system parameters is considered. The proposed scheme addresses such practical difficulties by providing: 1) robust and simple active damping control performance under grid and filter parameter variation; 2) suppression of grid-induced distortion without a-priori knowledge of the grid background distortion and unbalance via real-time generation of the frequency modes and disturbances that should be eliminated from the closed-loop current control system; 3) robust deadbeat digital control performance that maximizes the dynamic performance of the converter; and 4) robustness against interaction dynamics between active damping and current tracking controllers. Furthermore, the proposed control scheme facilitates line-voltage sensorless current control and grid-synchronization performance, which enhances the reliability and cost measures of the DG interface. Theoretical analysis and comparative evaluation results are presented to demonstrate the effectiveness of the proposed control scheme. © 2011 IEEE.


Farag H.E.,University of Waterloo | El-Saadany E.F.,University of Waterloo | Seethapathy R.,Hydro One Networks Inc.
IEEE Transactions on Smart Grid | Year: 2012

Smart grid initiative is based on several pillars among which integrating a wide variety of distributed generation (DG) is of particular importance. The connection of a large number of DG units among loads may result in a severe voltage regulation problem and the utility-side voltage regulators might no longer be able to use conventional control techniques. In addition, smart grid should provide new digital technologies such as monitoring, automatic control, and two way communication facilities to improve the overall performance of the network. These technologies have been applied in this paper to construct a distributed control that has the capability to provide proper voltage regulation in smart distribution feeders. The functions of each controller have been defined according to the concept of intelligent agents and the characteristics of the individual DG unit as well as utility regulators. To verify the effectiveness and robustness of the proposed control structure, a real time simulation model has been proposed. The simulation results show that distributed control structure has the capability to mitigate the interference between DG facilities and utility voltage regulators. © 2011 IEEE.


Marti L.,Hydro One Networks Inc. | Rezaei-Zare A.,Hydro One Networks Inc. | Narang A.,Hydro One Networks Inc.
IEEE Transactions on Power Delivery | Year: 2013

This paper proposes a method to estimate transformer hotspot heating due to half-cycle saturation caused by geomagnetically induced currents (GICs). The method is based on fitting a closed-form analytical function to the calculated or measured thermal response of a particular transformer design, typically provided by the manufacturer, at its hotspot locations to a step dc current excitation. This fitted function can then be used to simulate the hotspot temperature profile for transformers of that particular design when subjected to GIC having an arbitrary profile over time. Using this approach, examples are presented of the winding and metallic hotspot thermal responses of the two transformers to recorded GIC time sequences, to illustrate how hotspots may be impacted on during a geomagnetic disturbance event. © 1986-2012 IEEE.


Rezaei-Zare A.,Hydro One Networks Inc.
IEEE Transactions on Power Delivery | Year: 2015

An analytical method is employed to characterize the reactive power loss of a single-phase transformer when subjected to geomagnetically induced current (GIC). A general closed-form formula is proposed to calculate the reactive power loss of the transformer as a function of the applied voltage, air-core inductance, and GIC. The developed equation reveals that the reactive power loss is a nonlinear function of the GIC and the applied voltage, implying that the reactive power loss is not scalable with the voltage or GIC. The presented function can also be used to estimate the GIC from the measured transformer reactive power in the case of lacking direct GIC measurement. Based on high accuracy confirmed by the time-domain simulations, the developed formula can substitute for a large number of lookup tables required in a power system analysis program dealing with GIC studies. © 2015 IEEE.


Rezaei-Zare A.,Hydro One Networks Inc.
IEEE Transactions on Power Delivery | Year: 2015

Based on an enhanced topological representation of the transformer core, flux air paths, and tank, a duality-based transformer model is proposed for low and mid-frequency transients analysis. In the developed transformer model, the core and tank iron are represented based on a frequency-dependent hysteresis model. The winding capacitances and the frequency dependency of the winding resistance are also incorporated in the developed model. Furthermore, a detailed model is developed for the air gap and tank, and the corresponding average equivalent is presented which is more appropriate for extracting the parameters from the measurement. In addition, the nonuniform air gap and the fringing flux effects are taken into account, and an approach is presented to obtain the corresponding parameters. The developed models also include the equivalents of the tank magnetic shield and the structural parts. Part II of this paper provides validations and further simulation results. © 2014 IEEE.


Rezaei-Zare A.,Hydro One Networks Inc.
IEEE Transactions on Power Delivery | Year: 2015

The transformer model developed in Part I is validated based on the zero-sequence test data, a ferroresonance event, and the geomagnetically induced current (GIC) measurements. Various transformer core constructions, including single phase, three limb, five limb, conventional shell type, and seven-limb shell type are represented, based on the proposed transformer model. The simulation results show high accuracy of the proposed transformer model in representing the studied cases. The study reveals that the saturation of the transformers at a given GIC level is more severe than that predicted by the existing transformer models. Furthermore, the proposed transformer model clearly explains the reasons for the previously reported discrepancies between the GIC experimental and simulation results. The study also concludes that for an accurate transformer model, particularly for the three-limb core type, the detailed representation of the zero-sequence characteristic is an essential requirement. Such a characteristic can be obtained based on either the proposed approach of the paper or a zero-sequence dc excitation test in addition to the test data at the power frequency. © 2014 IEEE.


Rezaei-Zare A.,Hydro One Networks Inc.
IEEE Transactions on Power Delivery | Year: 2014

Based on a proposed analytical approach and time- domain simulation, this paper investigates the operating condition of single-phase transformers under steady-state and quasi-dc transient of the geomagnetically induced current (GIC). The analytical approach employs a two-slope piecewise linear magnetization characteristic and facilitates the development of generic characteristics for system studies to reduce the risk of power system instability and blackout during geomagnetic disturbances (GMDs). In addition, such characteristics can be used to estimate the transformer GIC, reactive power, and harmonic currents in the absence of direct measurements. The results obtained from the proposed approach are compared with the laboratory GIC test results of 500-kV and 230-kV transformers. In addition, the estimated dynamic behavior of a 500-kV autotransformer during a GMD event is compared with the measurements obtained from Hydro One SCADA and GIC monitoring systems. The study results reveal that under steady-state conditions, the transformer reactive power increases with GIC with an initial slope equal to the transformer ac peak voltage which is equivalent to 2.0 on a per-unit basis. Depending on the transformer air-core inductance, the slope decreases at higher GIC levels. Unlike the steady-state conditions, the GIC behavior of the transformer during a GMD event is influenced by the core kneepoint and the transformer delta winding. © 1986-2012 IEEE.


Li C.,Hydro One Networks Inc.
IEEE Transactions on Power Delivery | Year: 2015

This paper highlights an immediate need for renewable generation developers, manufacturers, utilities and industry standardization institutes to jointly address a challenge of capacitor switching transient immunity in inverter-based wind or solar farms. The need was identified from wide-area operation records which showed partial or full generation loss in coincidence with routine utility-owned capacitor switching. The lack of a clear industry guideline has caused confusion to all involved parties. This paper recommends all entities to address this challenge collaboratively through enhanced equipment specification, design, and test before a well-defined industry guideline becomes available. © 1986-2012 IEEE.


Li C.,Hydro One Networks Inc.
IEEE Transactions on Power Delivery | Year: 2012

This letter presents field measurements of capacitor switching transients with initial bus voltage changes different from widely used assumptions. Instead of being pulled toward zero in all three phases, initial voltage changes in both directions are seen in grounded capacitor switchings. Electromagnetic Transients Program simulation shows that the reason could be pole spread in breaker closing and mutual coupling between the three phases. The letter suggests that this transient pattern be considered in capacitor switching research. © 2006 IEEE.

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