Optimization of transient operations in sensorless control techniques based on carrier signal injection

Rotor position estimation techniques based on signal injection represent the only way to develop sensorless vector control schemes for permanent magnet synchronous motors able to operate at low and zero speed. Unfortunately an unwanted interaction between transient current components and signal produced by the injection makes necessary to inject a quite strong signal to accomplish a correct estimation. The injection of a strong signal causes extra power losses, while resulting in a poor exploitation of the DC bus voltage. The paper first analyzes the mechanisms that generate such a phenomenon. A new approach is then proposed to overcome any interaction that has been positively evaluated by experimental tests.