Analysis of SSO Characteristics of D-PMSGs Based Wind Farm Under Weak AC System

Aiming at the problem of subsynchronous oscillation (SSO) of the direct-drive permanent synchronous generators (D-PMSGs) based wind farm under weak AC system, the electromagnetic transient equivalent model of the D-PMSGs based wind farm is established. This model is used to study the influence of AC system strength, the online number of D-PMSGs, the control parameters of the active current inner loop controller and the control methods of static var generator (SVG) on the SSO characteristics. The results show that with increasing of online number of D-PMSGs and decreasing of AC system strength, the SSO frequency decreases. Within a certain range, when the integral parameter of the active current inner loop increases, the frequency of SSO decreases and the increasing of proportional parameter has little effect on SSO, when it reaches certain value, the system operates stably. When the SVG use the grid-connected voltage amplitude control instead of the constant reactive power control, D-PMSGs based wind farm is more likely to oscillate. Finally, the simulation model of the three-machine parallel D-PMSGs based wind farm is built and compared to the single-machine equivalent model in different conditions.