Zhenhuan Yuan

Analysis of IGBT Power Cycling Capabilities Used in Doubly Fed Induction Generator Wind Power System

The doubly fed induction generator (DFIG) is one of the most popular topologies applied in wind power systems. Its main advantage is to adjust the speed of a large system with much lower power converters. This is because its rotor-side converter (RSC) operates under slip frequency and it needs only to support slip power to the overall system. However, this slip frequency is much lower than the grid frequency, and insulated-gate bipolar transistors (IGBTs) in the RSC are susceptible to power cycling failures. This paper provides a method to analyze the power cycle capability of a DFIG power converter under wind power applications. Different current control methods, including minimal stator losses, minimal rotor losses, and minimal overall losses, are analyzed and compared. It is verified that the sizes of the IGBT must be selected appropriately to avoid earlier power cycling failures. Designing a wind power converter into the targeted system is critical for cost reduction without sacrificing the reliability of the whole system.

Analysis of IGBT power cycling capabilities used in Doubly Fed Induction Generator wind power system

The Doubly Fed Induction Generator (DFIG) is one of the most popular topologies applied in wind power systems. Its main advantage is to adjust the speed of a large system with much lower power converters. This is because its rotor side converter (RSC) operates under slip frequency and it needs only to support slip power to the overall system. However, this slip frequency is much lower than the grid frequency and IGBTs in the RSC are susceptible to power cycling failures. This paper provides a method to analyze the power cycle capability of a DFIG power converter under wind power applications. Different current control methods, including minimal stator losses, minimal rotor losses and minimal overall losses, are analyzed and compared. It is verified that the sizes of the IGBT must be selected appropriately to avoid earlier power cycling failures. Designing a wind power converter into the targeted system is critical for cost reduction without sacrificing the reliability of the whole system

Parameter Sensitivity Analysis of Flux Observers for Induction Motors

This paper analyzes the effect of the variation of machine parameters on flux observers in the steady-state condition by the frequency-domain method. Both the flux estimation and the torque estimation are evaluated. The frequency response function (FRF) expressed by the ratio of the estimated flux/torque to the corresponding physical one is derived to evaluate the parameter sensitivity. The flux observers investigated in this paper include the open-loop voltage model, the open-loop current model, and three types of closed-loop adaptive flux observers with PI regulator. Computer simulations are conducted to validate the theoretical analysis.

Induced Voltages and Power Losses in Single-Conductor Armored Cables

Single-conductor armored cables are often used to carry high currents in buildings. This paper presents an experimental investigation into both induced voltages and cable resistances associated with the installation of these cables within the buildings. Both induced armor voltages and cable resistances under different installation practices were measured at both power frequency and its harmonic frequencies. The impact of cable formation, bonding arrangement, and cable supporting method on these issues was addressed and illustrated experimentally via 185-mm2 (365-kcmil) single-conductor armored copper stranded cables. The standing voltage is generally small for the armored cables used in the buildings. The power losses increase significantly when the cable armor is bonded at two cable ends, particularly in the case of rich harmonic currents in the cables. Recommendations are finally provided for the installation of single-conductor armored cables in buildings.

LVRT performance limit of DFIG with traditional AC crowbar and DC-link brake approach

Doubly Fed Induction Generator (DFIG) system is subject to high transient voltage at rotor side when there is voltage sag at stator/grid side, which is beyond the capability of rotor side converter to handle. Traditional approach is to apply crowbar circuit to shunt the transient rotor current from the rotor side converter. DC-link brake is also typically applied to suppress the rise in DC bus voltage. This paper discusses the transient process and pointes out the performance limit for low voltage ride through (LVRT) with the traditional AC crowbar + DC-link brake approach. Both balanced and unbalanced grid faults will be addressed.