Vortex motion noise in micrometer-sized thin films of the amorphous Nb0.7Ge0.3 weak-pinning superconductor

The modeling and control of a three-phase threes-witch buck-type rectifier system with integrated boost output stage (Voltage Range Extended 4-Switch Rectifier) is analyzed in this paper. A cascaded multiloop control structure is presented that has the following features: constant output voltage for a wide input voltage range and stepwise changes of load; sinusoidal input currents in phase with the mains voltages that also remain sinusoidal in case of unbalanced mains conditions; and active damping of the input filter resonance. For the control design, an equivalent dc-dc small-signal model of the converter is derived and verified by simulations and measurements. Based on this and on the identification of the critical operating point, the controllers for the inner dc current and outer voltage control loops are selected. The stability of the closed loop system is discussed and the robust operation of the system is verified by measurements on a 5-kW prototype.