Small Disturbance Stability And Control Of Wind Turbine With Induction Generator Integration Into Weakly Interconnected System

Induction generator abounds in power grid because of its characteristics ofsimple structure,reliable operation,low cost, easy maintenance,etc.It is necessary toresearch the small disturbance stability and stability control methods of wind turbinewith induction generator integration into weakly interconnected system.In this article,the mathematical models are built of wind turbine, transmissionshaft, pitch angle system, induction generator and synchronous generators.On thebasis of above, differential equations are linearized in the vicinity of steady-statevalue and intermediate variables are eliminated, then the linear differential equationsof total system are established.Then the oscillation modes and their mechanisms areanalysed to external small disturbance by analyzing the eigenvalues and theinfluencing factors.On the basis of loop correlation ratio, the low-frequencyelectromechanical oscillations are found. The major generators involved in theseoscillations are discussed according to the right eigenvectors and the influence of thestate variables on the oscillation modes. Then the effects of wind speed, thetransmission distance of wind farm and reactive power compensation on characteristicroots are analyzed.On the one hand, the oscillation modes between wind turbine with inductiongenerator and synchronous generators are inter-area oscillation modes. On the otherhand, the main component gearbox of shaft easily goes wrong under the long-termvibration. Therefore, the power system stabilizer (PSS) is firstly designed accordingto the principle of phase compensation in the pitch angle control system. That is, aleading phase signal is added at the input point to create positive damping torquethrough the pitch system and increase the damping of shaft oscillation modes.Secondly, energy storage system is also designed on the basis of positive power of I G.That is, the electromagnetic power offset of IG is used as the active power outputInstruction ESS so that the power of ESS can be equivalent to an additional positivedamping electromagnetic torque to increase the damping ratio. Finally, the feasibilityof the strategy is verified by characteristic roots and time-domain simulation inMatlab/Simulink, and the results show that both PSS and ESS can improve thedamping of shafting to restrain oscillation and improve dynamic stability of powersystem.