A Hierarchical Control Strategy With Fault Ride-Through Capability for Variable Frequency Transformer

Ambati, Bharath Babu; Kanjiya, Parag; Khadkikar, Vinod; Moursi, Mohamed Shawky El; Kirtley, James L.

doi:10.1109/tec.2014.2336981

Cited by 25 publications

(15 citation statements)

References 12 publications

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“…A variable frequency transformer (VFT) has been used in the interconnection of systems to control active and reactive power flow for a long time, in addition to being used to compensate for frequency fluctuations through a torque that is furnished by an external machine [40,41]. Nevertheless, this device has not been used to connect variable speed hydro generation synchronously to a system.…”

Section: Variable Frequency Transformermentioning

confidence: 99%

“…Nevertheless, this device has not been used to connect variable speed hydro generation synchronously to a system. Essentially, it is a wound rotor induction motor acting as a transformer, i.e., the stator is the primary transformer and the rotor is the secondary one [41,42]. Figure 3 presents a connection using the VFT.…”

Section: Variable Frequency Transformermentioning

confidence: 99%

“…Thus, in order to have rated frequency in its output, rated frequency must be inserted directly into its input. Hence, it can be concluded that if the frequency of input and output are different, the machine must rotate at a given speed that is proportional to this difference in order to match primary and secondary frequencies [40,41].…”

Section: Variable Frequency Transformermentioning

confidence: 99%

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The Benefits of Variable Speed Operation in Hydropower Plants Driven by Francis Turbines

et al. 2019

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Climate change and environmental degradation has resulted in a reduction in water inflow at hydropower plants, as well as a decrease in reservoir levels. Existing hydropower plants suffer from water head reduction, mainly with decrease in efficiency of energy conversion in hydro turbines. This paper showcases the benefits of operations with variable speed in existing hydropower plants, when working at a lower water head than the rated one. Theoretical analyses and tests were performed in a special constructed laboratorial setup aiming at evaluating the amount of efficiency recovery with variable speed operation. Connection alternatives for a constant frequency grid and applications of the learned concepts in an existent hydropower plant are presented. The investigations were applied to the Furnas hydropower plant. The results point out that economic feasibility of the application can be achieved.

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Section: Variable Frequency Transformermentioning

confidence: 99%

Section: Variable Frequency Transformermentioning

confidence: 99%

Section: Variable Frequency Transformermentioning

confidence: 99%

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The Benefits of Variable Speed Operation in Hydropower Plants Driven by Francis Turbines

et al. 2019

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“…A new concept that facilities the controllable, bi-directional power flow between two asynchronous networks has emerged in the form of the VFT [1]. Traditionally, the transfer of power between two grids with different frequencies has been accomplished through the use of phase shifting transformers and back-to-back high-voltage direct-current (B2B-HVDC) converters, however each of these solutions has its drawbacks [2].…”

Section: Introductionmentioning

confidence: 99%

“…If torque is applied in the opposite direction, power flow will reverse and move from rotor to stator. If the two systems are not in synchronism, the rotor will rotate constantly at a speed proportional to the slip given by (2), where f s , f r are the frequencies of the stator and rotor respectively. Load flow is maintained during this operation despite the drifting frequencies [3].…”

Section: Introductionmentioning

confidence: 99%

Mathematical Modelling of Reduced Order Induction Machines for VFT Applications

Lucas

Campos‐Gaona

Anaya‐Lara

2018

2018 IEEE International Autumn Meeting on Power, Electronics and Computing (ROPEC)

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This paper presents a reduced order approach to the modelling of induction machines for the purposes of power transfer between asynchronous networks. The method of interconnection between the networks under consideration is a variable frequency transformer (VFT) whose technology is rooted in that of an induction machine. Attempts to apply a high-order model to VFT studies have been met with numerical instabilities and unacceptably long computation times. A reduced order approach therefore serves to reduce the complexity of the simulation by neglecting transient behaviour. The classical fifth order method is presented, upon which a third order and first order model are derived. These differ from the traditional reduced order models due to the inclusion of an otherwise neglected frequency differential term. Care has also been taken to avoid algebraic loops during simulation so that additional delays need not be introduced. The performance of the models is then analysed when they are operating as an induction machine and then as a VFT for asynchronous power transfer simulations. The result is a stable, low-order model that performs correctly under a wide range of VFT operative scenarios, including asynchronous and different-frequency networks connected to its terminals.

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