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

A variable frequency transformer (VFT) is being considered as a new alternative to the classical back-to-back high voltage direct current (HVDC) link for interconnection of two asynchronous networks. The VFT is a retrospective form of frequency converter using the wound rotor induction machine (WRIM), which converts the constant frequency input into a variable frequency output. The prime objective of VFT is to achieve controlled bidirectional power transfer between the two asynchronous networks. This paper presents a detailed working principle of VFT technology and proposes a new hierarchical control strategy for establishing the VFT connection with two power systems to achieve bidirectional power transfer between them. Also, to restrict the grid fault propagation from one side of the VFT to the other side, a series dynamic braking resistor based fault ride-through (FRT) scheme is proposed. The performance of the VFT during the synchronization process, steady-state, dynamic, and the grid fault conditions is evaluated using the real-time hardware in-loop (HIL) system. The plant is simulated in real time using OPAL-RT real-time simulator while the control algorithm is implemented in digital signal processor to carry out HIL study. All the important results supporting the effectiveness of the proposed control strategy and FRT scheme are discussed.

[1]  M.P. Bahrman,et al.  OVERVIEW OF HVDC TRANSMISSION , 2006, 2006 IEEE PES Power Systems Conference and Exposition.

[2]  R.J. Piwko,et al.  Variable frequency transformer - a new alternative for asynchronous power transfer , 2005, 2005 IEEE Power Engineering Society Inaugural Conference and Exposition in Africa.

[3]  Li Wang,et al.  Reduction of Power Fluctuations of a Large-Scale Grid-Connected Offshore Wind Farm Using a Variable Frequency Transformer , 2011, IEEE Transactions on Sustainable Energy.

[4]  Xiaoxin Zhou,et al.  Digital Simulation of Variable Frequency Transformers for Asynchronous Interconnection in Power System , 2005, 2005 IEEE/PES Transmission & Distribution Conference & Exposition: Asia and Pacific.

[5]  E. V. Larsen.  A classical approach to constructing a power flow controller , 1999, 1999 IEEE Power Engineering Society Summer Meeting. Conference Proceedings (Cat. No.99CH36364).

[6]  D. Nadeau.  A 100-MW Variable Frequency Transformer (VFT) on the Hydro-Québec TransÉnergie Network - The Behavior during Disturbance , 2007, 2007 IEEE Power Engineering Society General Meeting.

[7]  A. H. El Din,et al.  A MATLAB/SIMULINK model to study the performance of the VFT for the interconnection of weak and strong AC grids , 2011, 2011 IEEE International Electric Machines & Drives Conference (IEMDC).

[8]  N. Garcia,et al.  Accelerated time domain solutions of a VFT using the Poincaré map method with an embedded implicit integration algorithm , 2008, 2008 40th North American Power Symposium.

[9]  N. Garcia,et al.  Fast convergence to the steady-state operating point of a VFT park using the limit cycle method and a reduced order model , 2009, 2009 IEEE Power & Energy Society General Meeting.

[10]  V. T. Ranganathan,et al.  Direct torque and frequency control of double-inverter-fed slip-ring induction motor drive , 2004, IEEE Transactions on Industrial Electronics.

[11]  Ayman S. Abdel-Khalik,et al.  Performance of VFT when connecting two power grids operating under different frequencies , 2010 .

[12]  B. Bagen,et al.  Evaluation of the Performance of Back-to-Back HVDC Converter and Variable Frequency Transformer for Power Flow Control in a Weak Interconnection , 2007, 2007 IEEE Power Engineering Society General Meeting.

[13]  N. Garcia,et al.  Steady-state solution of a VFT park using the limit cycle method and a reduced order model , 2009, 2009 IEEE Bucharest PowerTech.

[14]  D. Wallace,et al.  VFT maintenance and operating performance , 2008, 2008 IEEE Power and Energy Society General Meeting - Conversion and Delivery of Electrical Energy in the 21st Century.

[15]  Ayman S. Abdel-Khalik,et al.  Brushless doubly fed induction machine as a variable frequency transformer , 2012 .

[16]  M.P. Bahrman,et al.  HVDC transmission overview , 2008, 2008 IEEE/PES Transmission and Distribution Conference and Exposition.

[17]  A. Merkhouf,et al.  Variable Frequency Transformer—Concept and Electromagnetic Design Evaluation , 2008, IEEE Transactions on Energy Conversion.