Variable-frequency transformer

About: Variable-frequency transformer is a research topic. Over the lifetime, 112 publications have been published within this topic receiving 872 citations. The topic is also known as: VFT.

Variable frequency transformer - a new alternative for asynchronous power transfer

Abstract: A new power transmission technology has been developed The variable frequency transformer (VFT) is a controllable, bi-directional transmission device that can transfer power between asynchronous networks Functionally, the VFT is similar to a back-to-back HVDC converter The core technology of the VFT is a rotary transformer with three-phase windings on both rotor and stator A motor and drive system are used to adjust the rotational position of the rotor relative to the stator, thereby controlling the magnitude and direction of the power flowing through the VFT The world's first VFT was recently installed in Hydro-Quebec's Langlois substation, where it will be used to exchange up to 100 MW of power between the asynchronous power grids of Quebec (Canada) and New York (USA) This paper describes the VFT technology and provides an overview of the VFT equipment installed at Langlois substation Results of commissioning tests are also included

Reduction of Power Fluctuations of a Large-Scale Grid-Connected Offshore Wind Farm Using a Variable Frequency Transformer

Abstract: This paper presents a novel control scheme using a variable frequency transformer (VFT) of 100 MW to effectively reduce power fluctuations of an equivalent 80-MW aggregated doubly-fed induction generator (DFIG)-based offshore wind farm (OWF) connected to an onshore 120-kV utility grid. The q-d axis equivalent-circuit model is employed to establish the mathematical models for the VFT and the OWF to derive the complete dynamic equations of the studied system under three-phase balanced conditions. A frequency-domain approach based on a linearized system model using eigen techniques and a time-domain scheme based on a nonlinear system model subject to disturbance conditions are both performed to examine the effectiveness of the proposed control scheme. It can be concluded from the simulation results that the proposed VFT is effective to smooth the fluctuating active power of the OWF injected into the power grid while the damping of the studied OWF can also be improved.

Variable Frequency Transformer—Concept and Electromagnetic Design Evaluation

Abstract: Variable frequency transformer (VFT) is a controllable bidirectional transmission device that can transfer power between asynchronous networks. The construction of VFT is similar to conventional asynchronous machines, where the two separate electrical networks are connected to the stator and rotor respectively. Electrical power is exchanged between the two networks by magnetic coupling through the air gap of the VFT. This paper describes the basic concept of the VFT and presents an overview of the mechanical and electromagnetic design of a unit having four poles and rated at 100 MW, 17 kV/17 kV, 60 Hz.

Evaluation of the Performance of Back-to-Back HVDC Converter and Variable Frequency Transformer for Power Flow Control in a Weak Interconnection

Abstract: This paper compares performance of a back-to-back HVDC system with series compensation external to the converter transformers, and a variable frequency transformer for power flow control feeding or supplying a weak AC network. The steady state and dynamic simulations show that both technologies are able to control power flow accurately. The variable frequency transformer consumes less reactive power than a back-to-back HVDC system, provides faster initial transient recovery and better natural damping capability. Back-to-back HVDC converters, however, provide smoother and faster recovery to pre-disturbance level for the same system faults. A back-to-back HVDC system also provides smoother and faster response to a controlled power change.

A classical approach to constructing a power flow controller

Abstract: A new approach is described for realizing continuous control of power flow in AC power lines. The approach is based on "classical" electrical engineering concepts using rotary transformers in place of a tap changer in a conventional phase-shifting transformer design. This approach has several apparent benefits compared to the recently-introduced power flow controller based entirely on power electronics.