Two-Degree-of-Freedom Discrete-Time Decoupled Current Control of IPMSM With High Parameter Robustness

Field-oriented synchronous reference frame-based current control is well known to ac machine control. But the speed-dependent cross-coupling terms significantly degrade the control performance, especially in high-speed applications, such as electric vehicles (EVs). Among the control schemes, the internal model control (IMC) is usually regarded as the most promising one due to its parameter insensitivity. However, this method in essence belonging to one-degree-of-freedom (1-DOF) control, has the problem of the limited closed-loop bandwidth and the poor disturbance rejection performance, which is fatal to EV applications. Although the state-of-the-art two-degree-of-freedom (2-DOF) control scheme can release these problems, it is at the cost of parameter robustness especially to dynamic decoupling effectiveness. This phenomenon as well as the root reason is discussed in this article. To dig out of this dilemma, the controller is optimized further through moderately modifying the controlled plant with an extra inner feedback loop. The achieved control system is of 2-DOF. Different from commonly used pure calculation one, the designing process proposed in this article is meaningful. Moreover, the parameter robustness merit of IMC is retained in addition to the increased control bandwidth and enhanced disturbance rejection capability. Its performance is studied through experiments.