Low-amplitude Carrier Signal Injection-based Techniques for Sensorless Control of Permanent Magnet Drives

Several sensorless vector control schemes able to continuously operate at low and zero speed are based on carrier signal injection. Unfortunately, due to unwanted interactions between transient current components and the carrier signals, a strong high-frequency signal must be injected to accomplish correct estimations. Injection of an intense additional signal causes extra power losses and acoustic noise while resulting in a poor exploitation of the DC bus voltage. After a description of the mechanisms that generate such a phenomenon, this article discusses the real and effective levels of signal amplitude needed during transients and presents a new approach to overcome any interaction and reduce the high-frequency injection. The proposed method is confirmed by experimental tests.