Small Signal Dynamic Model of a Self-Synchronising Current Regulated Rectifier for a Permanent Magnet Wind Energy Conversion System (WECS)

Permanent magnet synchronous generators (PMSGs) are attractive for wind energy applications since they can both self-excite and operate at high power densities. Recent work has shown how the rectifiers for these systems can self-synchronise to the stator output voltage using a phase-locked-loop (PLL), and thus control the stator current without requiring rotor position sensors/observers and/or field orientation/direct torque control concepts. This paper now presents a small signal model of this strategy that accounts for the dynamic elements of the current regulator, the PLL, converter modulation delays, and the generator electrical dynamics. The model establishes design principles for this control strategy that confirm its stability when the PLL bandwidth is set to one decade below the current regulator bandwidth. The theoretical findings have been validated using a full-switched model of a PMSG based Wind Energy Conversion System (WECS).