Direct Speed Control of a PMSM Drive Using SDRE and Convex Constrained Optimization

The challenge for control of permanent magnet synchronous motor (PMSM) drives is to achieve high dynamics, accurate steady-state performance, and to respect all constraints on input voltage and stator currents. Many partial results on each of these aspects are available. Recently, it has been shown that the existing techniques can be combined with ideas from predictive control to achieve satisfaction of state constraints such as maximum current amplitude. In this article, we propose to complement the direct-speed-control-based state-dependent Riccati equation (SDRE) approach by explicit constraints on the current amplitude and the field-weakening curve. Since the cost-to-go function for the SDRE is available, the problem is formulated as quadratic programming with a quadratic constraint. The resulting controller achieves an excellent steady-state solution due to SDRE and satisfies constraints on the maximum current amplitude and field-weakening operation. Experimental tests of the proposed cascade-free speed control are performed on a laboratory prototype of a 10.7-kW PMSM drive. The proposed optimization routine can be used to enforce state constraints in other unconstrained control methods.