## Nomenclature  
\(\beta\)Blade pitch angle  
\(\beta_{ref}\)Reference value of pitch angle  
\(\beta_{max}\), \(\beta_{min}\)Maximum and minimum values of pitch angle  
\(\rho\)Air density (=1.205 kg/m\({}^{2}\))  
\(\lambda\)Tip speed ratio  
\(\lambda_{opt}\)Optimal tip speed ratio  
Figure 14: Comparison of the system frequency response.  
\begin{tabular}{l l} \(B\) & Friction coefficient of generator \\ \(C_{p}\) & Power coefficient of wind turbine \\ \(C_{p,opt}\) & Optimal power coefficient of wind turbine \\ \(S_{w}\) & Wind speed \\ \(J\) & Moment of inertia of wind turbine (kg/m\({}^{2}\)) \\ \(V_{dc}\) & DC link voltage \\ \(V_{dc,ref}\) & Reference value of DC link voltage \\ \(V_{di}\), \(V_{di}\) & Inverter voltages in \(d\)-\(q\) axis \\ \(V_{ds}\), \(V_{sg}\) & Stator voltages in \(d\)-\(q\) axis \\ \(V_{dg}\), \(V_{sg}\) & Grid-side voltages in \(d\)-\(q\) axis \\ \(I_{ds}\), \(I_{qs}\) & Stator currents in \(d\)-\(q\) axis \\ \(I_{ds,ref}\) & Reference value of stator currents in \(d\)-\(q\) axis \\ \(I_{dg}\), \(I_{qs}\) & Grid-side currents in \(d\)-\(q\) axis \\ \(I_{dg,ref}\) & Reference values of grid-side currents in \(d\)-\(q\) axis \\ \(\theta_{r}\) & Electrical angle between \(a\)-axis and \(q\)-axis (rad) \\ \(u\) & Any of the variable (voltage, current, and flux linkage) to be transformed from the _abc_ \\ \(R_{s}\), \(R_{g}\) & Resistances of PMSG winding and grid sides \\ \(T_{e}\) & Electromagnetic torque \\ \(T_{m}\) & Mechanical torque \\ \(\Psi_{f}\) & Magnetic flux \\ \(C\) & Capacitance of DC link capacitor \\ \(L_{d}\), \(L_{q}\) & Machine inductances in \(d\)-\(q\) axis \\ \(L_{s}\), \(L_{g}\) & Inductances of PMSG winding and grid sides \\ \(p_{n}\) & Number of pole pairs \\ \(\omega_{dd}\) & Reference value of rotational speed of de-loaded control \\ \(\omega_{e}\) & Electrical rotational speed \\ \(\omega_{g}\) & Rotational speed of grid side \\ \(\omega_{m}\) & Mechanical rotational speed \\ \(\omega_{m,limit}\) & Maximum limited rotational speed \\ \(\omega_{m,opt}\) & Optimal rotational speed \\ \(\omega_{m,ref}\) & Reference value of mechanical rotational speed \\ \(\omega_{out}\) & Rotational speed output \\ \(\omega_{t}\) & Rotational speed of turbine \\ \(R\) & Rotator radius \\ \(P_{m}\) & Mechanical power \\ \(P_{t}\), \(P_{g}\) & Active powers of wind turbine and grid side \\ \(P_{max}\), \(P_{min}\) & Maximum and minimum possible powers \\ \(P_{margin}\) & Power margin \\ \(P_{out}\) & Active power output \\ \(P_{ref}\) & Reference value of active power \\ \(P_{dd}\) & De-loaded power reference \\ \(P_{ref,KE}\) & Reference value of KE power \\ \(P_{ref,raf}\) & Reference value of active power of wind farm \\ \(N\) & Number of PMSGs in wind farm \\ \(\Delta\)\(P_{KE}\) & KE power increment \\ \(\Delta\)\(P_{loss}\) & Lacking active power under grid fault \\ \(Q_{g}\) & Reactive power of grid side \\ \(Q_{nf}\) & Reference value of reactive power \\ \(K_{dd}\) & Rotational speed coefficient of de-loaded control \\ \(K_{opt}\) & Coefficient of rotational speed for maximum power \\ \(KE_{res}\) & Kinetic energy (KE) reserve \\ \(KE_{res,ref}\) & Total KE reserve of wind farm \\ \(H_{spatten}\) & Equivalent inertia of entire power system \\ \end{tabular}