Robust feedback linearization technique for speed control of PM synchronous motor under parameter variations and speed measurement error

Abstract

A permanent magnet synchronous motor(PMSM) drives are being increasingly used in a wide range of applications due to their high power density, large torque to inertia ratio, and high efficiency. This dissertation deals with the nonlinear speed control of a surface mounted permanent magnet synchronous motor with sinusoidal flux distribution. Since the dynamics of the currents are much faster than that of the mechanical speed, the speed is considered as a constant parameter rather than a state variable and they can be approximately linearized by the field orientation and current control. However, this approximate linearization leads to the lack of torque due to the incomplete current control during the speed transient and reduces the control performance in some applications such as industrial robots and machine tools. A solution to overcome this problem proposed in the previous research is to consider the motor speed as a state variable in electrical equations, which results in a nonlinear model. Then the nonlinear control method, so called a feedback linearization technique, is applied to obtain a linearized and decoupled model and the linear design technique is employed to complete the control design. Since the nonlinear controller is very sensitive to the speed measurement error, even small measurement error results in a significant speed error and its robustness can be improved by carefully selecting the gains in the linear control loops. However, besides the speed measurement error, there are parameter variations such as the stator resistance, flux, and inertia due to the temperature rise and load variations. The stator resistance and flux variations also show a steady state speed error and the inertia and flux variations degrade the transient performance. The steady state speed error may also go to zero by properly choosing the linear controller gains. However, the transient and even steady state performances can still be significantly degraded due to the ...