Method for improving small disturbance stability after double-fed unit gets access to the system

A computer implemented method for improving small disturbance stability after a double-fed power generation unit gets access to a power transmission system characterized in that the method comprises the following steps executed on a processor:

• step 1:
• building complete mathematical models for the double-fed power generation unit, the mathematical models mainly include an aerodynamic model, a power generator model, a mechanical model and a control system model;
• listing a system state equation and an output equation and then building a small disturbance mathematical model Δ{dot over (x)}=A′Δx by integrating power flow equation of the system after double-fed power generation unit gets access to the system;
• step 2:
• calculating a left modal matrix ψ and a right modal matrix φ of a matrix A′, determining the sensitivity of unstable modes or weak damping modes to matrix A′ with the formula
• ∂
• λ
• i
• ∂
• a
• k
• ⁢
• ⁢
• j
• =
• ψ
• ik
• ⁢
• ϕ
• ji
• and finding out one to two nonzero elements a′ij with the highest sensitivity in the matrix;
• analysis indicating that at a low and middle frequency band concerned by small disturbance stability of the system, the difference between eigenvalue of the matrix A′ and that of the state matrix A is not very large and as expression of A′ is very complex, element aij in A is used to make sensitivity analysis instead of the element a′ij in A′;
• step 3:
• for controller or system parameters that can be set in aij, changing value of these parameters within a certain interval, observing steady-state value of the variable required while calculating eigenvalue of matrix A′ in simulation results, then putting the steady-state value in A′ to solve the eigenvalues that correspond to each group of parameters and drawing a chart on the change track of eigenvalues;
• if eigenvalues are disperse, a part of the overlapped eigenvalues need to be locally enlarged to observe the trend for eigenvalues of dominant modes of the system;
• step 4:
• if there are other parameters that can be set in aij, then repeating Step 3;
• step 5:
• comprehensively analyzing the chart on modal eigenvalues change with the track of parameters in Step 4, adjusting the parameters in Step 4, then selecting appropriate parameter combination upon comparison, with which both dominant modal damping and small disturbance stability margin of the system can be obviously improved.