Online Nonlinear Quadratic Tracking Control Accompanied by Selective Current Harmonic Compensator for MPPT of PMSG Drives

This paper proposes an online nonlinear quadratic tracking (NQT) control scheme accompanied by an active harmonic suppressor (AHS) of wind turbine permanent magnet synchronous generator (PMSG) drives. An online solution to a nonlinear control problem is proposed to address the complex dynamic characteristics of the wind turbine operation and maximize wind speed tracking performance. The new NQT design employs a polynomial-based dynamic model to derive an exact online solution of the state-dependent Riccati equation (SDRE). The control law is formulated by solving the optimal Hamilton-Jacobi-Bellman (HJB) equation for nonlinear systems with state-dependent coefficients, providing online control gains. This approach ensures that nonlinear feedback gains are continuously adjusted online in response to tracking errors. AHS is integrated into the NQT control scheme to overcome the reversed effects of inevitable harmonic currents in switch-mode converters. The selective current harmonic compensators (SCHCs) are directly designed in aabc-frame using virtual oscillators to improve the control performance of PMSG’s currents and rotor speed. Comparative studies on MATLAB/Simulink and power-hardware-in-loop platforms verify the superiority of the NQT-AHS scheme over standard linear quadratic regulator (LQR) and sliding mode control (SMC) schemes. Significant improvements in current stability, precise speed tracking capability, and reduced distortion in stator currents are demonstrated using real wind speed data.