Roy Nilsen

Active damping of resonance oscillations in LCL-filters based on virtual flux and virtual resistor

This paper presents several methods for active damping of resonance oscillations in LCL-filters. All the methods are implemented using only estimated values of the capacitor voltages and currents. The sensorless control strategy used in this paper is based on the virtual flux concept and all voltages and currents with the exception of the dc bus voltage and the converter output currents are derived from the virtual flux. The presented theory is then verified experimentally in the lab.

New self sensing scheme based on INFORM, heterodyning and Luenberger observer

Self sensing techniques for AC machines has been a research topic for almost two decades. Two promising methods are found in injection of high frequency carrier and the INFORM method. Both schemes are based on utilization of saliency in order to make position estimate. The excitation and signal processing for these methods differs. A new scheme based on the INFORM measurements a tracking observer is presented. The new scheme gives the modified INFORM method a close to zero phase lag in rotor position estimate. The new scheme is implemented and evaluated with a 32 kW IPMSM.

Investigation of magnetic field and radial force harmonics in a hydrogenerator connected to a three-level NPC converter

This paper investigates spatial and time harmonics of flux density and radial force distributions in the airgap of a hydrogenerator with fractional-slot windings. Hydrogenerator is connected to a neutral-point-clamped (NPC) converter, representing a converter-fed synchronous machine (CFSM) in pumped-storage hydropower plant. Magnetic field in the hydrogenerator is computed using time-stepping finite element (FE) analysis, coupled with an external circuit (where PWM converter is modelled). Radial forces are calculated analytically based on Maxwell stress tensor. Three loading conditions are studied (i.e. resistive loading and converter-fed operation with two different carrier frequencies). In the paper, it is investigated how converter-fed operation could change the characteristics of the radial magnetic forces. It is also discussed how vibration of the hydrogenerator is expected to be affected by additional harmonics generated by the PWM converter.

Analysis of magnetic forces and vibration in a converter-fed synchronous hydrogenerator

This paper investigates the influence of converter-fed operation on magnetic forces and radial vibration in a hydrogenerator. Flux density distribution is computed using time-stepping finite element (FE) analysis and used to calculate force density distribution based on Maxwell stress tensor. Both temporal and spatial characteristics of selected flux density and force density waves are studied. Important spatial harmonics of radial forces are investigated and compared for converter-fed and converter-less operations. Vibration analysis is also presented based on the magnetic field data computed by FE analysis.