No abstract

Methods for sensorless control involving the injection of a high-frequency signal into the low-speed range of an interior permanent-magnet synchronous motor (IPMSM) have been proposed. However, audible noise is a concern for these methods. We propose a method to reduce the audible noise due to a high-frequency current by minimizing the injection-signal amplitude suitable for IPMSM driving states.Keywords: audible noise, high-frequency, IPMSM, position sensorless control IntoroductionIPMSMs are often used in elevators, air conditioners, and HEVs because they are more compact and efficient as compared to induction motors. To drive an IPMSM, the pole position information is necessary. Hence, position sensors such as rotary encoders or hole-effect sensors are used. Because position sensors have disadvantages such as reduced reliability and increased costs, many sensorless control methods have been proposed(1)-(7) . Generally, sensorless control methods of IPMSM utilize the back electromotive force (EMF) that is proportional to the motor speed (2) . These methods become common technologies, and the microcomputer that automatically carries out a computation (current control(ACR), coordinate transformation, etc.) for the vector control by the embedded hardware in it is available (8) . When this microcomputer is used, the software to drive the IPMSM is only the estimation of the rotor position and the current command calculation.Methods based on back EMF presents good performance in middle and high-speed range drive of the IPMSM. However, they are not able to be applied to drive of the IPMSM at lowspeeds or standstill, because the back EMF is proportional to the motor speed. So, methods based on saliency of IPMSM have been proposed too (3)- (7) . These methods present good performance at standstill and low-speed range drive of the IPMSM. The saliency based sensorless methods have to inject high-frequency current (3) , high-frequency voltage (4)-(6) , or pulse voltage (7) . But, audible noise is a concern when a highfrequency signal is injected. In general, the high-frequency signal amplitude is maintained at a required constant value. This general approach makes a large audible noise.To solve the problem, a method to determine the highfrequency signal amplitude from experimental results has been proposed (9) . This method changes the injection signal amplitude within the range of the lower limit and the higher a) Correspondence to: Yuki Tauchi. E-mail: ce31054@meiji.ac.jp * Meiji University 1-1-1, Higashi-mita, Tama-ku, Kawasaki, Kanagawa 214-8571, Japan limit which are determined experimentally. At the transient state, the injection signal amplitude is increased to the higher limit in order that estimation performance does not deteriorate. At the steady state, the injection signal amplitude is decreased to the lower limit which does not depend on conditions such as rotational speed or load torque. In order to minimize the audible noise, the injection signal amplitude should be changed depending on conditions such as ro...