Passivity-Based Control of a Grid-Connected Small-Scale Windmill With Limited Control Authority

The problem of controlling small-scale wind turbines providing energy to the grid is addressed in this paper. The overall system consists of a wind turbine plus a permanent magnet synchronous generator connected to a single-phase ac grid through a passive rectifier, a boost converter, and an inverter. The control problem is challenging for two reasons. First, the dynamics of the plant are described by a highly coupled set of nonlinear differential equations. Since the range of operating points of the system is very wide, classical linear controllers may yield below par performance. Second, due to the use of a simple generator and power electronic interface, the control authority is quite restricted. In this paper we present a high performance, nonlinear, passivity-based controller that ensures asymptotic convergence to the maximum power extraction point together with regulation of the dc link voltage and grid power factor to their desired values. The performance of the proposed controller is compared via computer simulations against the industry standard partial linearizing and decoupling plus PI controllers.