System and method of a robust startup and stop scheme for position sensorless control of an electric machine

A system for controlling an electric motor via an inverter, the system comprising:

• an estimator configured to estimate a first mode rotor speed under a first current control model and a second mode rotor speed under a second current control mode of the electric motor in accordance with a first speed estimator for the first mode simultaneously with a second speed estimator for the second mode based on observed voltages and observed currents at the terminals of the electric motor;
• a mode controller configured to determine whether to control the inverter to operate the electric motor in a first mode or a second mode, wherein the first mode comprises a current frequency control mode and wherein the second mode comprises a back electromagnetic force mode;
• a current regulator, the current regulator comprising a first current controller or current-frequency current controller for determining a first current command associated with a first mode of operating the electric motor, if the estimated rotor speed is a less than a speed threshold;
• the current regulator, the current regulator comprising a second current controller determining a second current command associated with a second mode of operating the electric motor if the estimated rotor speed is equal to or greater than the speed threshold;
• and
• a limiter configured to limit an instantaneous change in a commanded voltage or a commanded current applied to the electric motor during a transition between the first mode and the second mode, wherein the limiter further comprises an electronic data processor that is configured to adjust or reset such that an initial commanded direct-axis current and an initial commanded quadrature-axis current, in the second mode, that are aligned to match a final commanded direct-axis current and final commanded quadrature-axis current in the first mode during a start-up, where an increasing rotational speed of the rotor changes to exceed the speed threshold for a transition between the first mode and the second mode.