Power System Electromechanical Oscillation Modes as Affected by Dynamic Interactions From Grid-Connected PMSGs for Wind Power Generation

Dynamic interactions between a grid-connected permanent magnet synchronous generator (PMSG) and power system are normally weak. This paper reports a special condition of modal resonance, under which the grid-connected PMSG may dynamically interact with power system strongly to affect power system electromechanical oscillation modes (EOMs). The special condition of modal resonance reported in this paper is that an open-loop converter oscillation mode (COM) of PMSG is close to an open-loop EOM of a power system on the complex plane. Damping torque analysis is carried out to explain why strong dynamic interactions between PMSG and power system may occur under the condition of modal resonance. Results of theoretical analysis in this paper indicate that occurrence of modal resonance may possibly cause the damping of either closed-loop COM or EOM to decrease such that power system small-signal angular stability is affected negatively by grid connection of PMSG. Responsible COMs for modal resonance are found to be related with active/reactive power control systems of a grid-side converter of PMSG. In the paper, an example multimachine power system with PMSGs is presented to demonstrate and validate analysis and conclusions made.