Analysis Of Position Estimation Error In Carrier Signal Injection Based Sensorless Control Of PMSM

Permanent magnet synchronous motors (PMSM) have been widely used in high-performance applications because of their high efficiency and high power density. The operation of a PMSM requires the rotor position information, which is usually provided by a mechanical position sensor. In order to reduce both cost and size, as well as to improve reliability by eliminating the sensor and related cabling connection, sensorless control techniques have been an intensive research subject in the last two decades. The high frequency signal injection are given a growing concern because of the advantages of they can operate over a wide speed range, including zero speed, and can achieve parameter-independent position estimation.Firstly, the theory of rotating high frequency voltage signal injection method and pulsating high frequency voltage signal injection method in rotor position detection is presented in this paper, the mathematical model of the PMSM is constructed, and further derivation and collation of the relevant high frequency current response formulas are presented.The influences of the stator resistance on rotor position errors in high-frequency-signal-injection-based sensorless control of PMSM are analyzed. Expressions of carrier current induced by the carrier voltage are derived for both rotating voltage injection and pulsating voltage injection method when the stator resistance is all taken into account, and the position estimation error expressions are obtained. It is shown that the stator resistance has influence on the position estimation error in steady state condition in rotating injection, but has little influence on the position estimation error in pulsating injection.Position estimation errors resulted from filters in carrier signal injection based sensorless control of permanent magnet synchronous motor (PMSM) are analyzed. Expressions of position estimation error are derived for both rotating and pulsating voltage injection method when the stator resistance and filter’s characteristic are taken into account. It is shown that influences of the filter on above two methods are quite different. In rotating injection, the position estimation error includes two components attributed to the stator resistance and the filter respectively. The latter is determined by the lagging phase angle of the filter at frequency (ωc-2ωr). It is independent of motor parameters and can be compensated easily and perfectly. In pulsating injection, the error is determined by the difference of lagging phase angles of the filter at (ωc+ωr) and (ω-ωr), and strongly depends on motor parameters. In a motor with low Lq/Ld, the pulsating injection method without compensation may fail to track the rotor position at high speed. Compensation methods are proposed.The influences of the speed EMF on rotor position errors in high-frequency-signal-injection-based sensorless control of PMSM are analyzed. Expressions of carrier current induced by the carrier voltage are derived for both rotating voltage injection and pulsating voltage injection method when the stator resistance and speed EMF terms are all taken into account, and the position estimation error expressions are obtained. It is shown that in the rotating voltage injection method, the speed EMF has little influence on the position estimation error in steady state condition and can be neglected as usual. But in the pulsating voltage injection method, the position error may be appreciable for a motor with low Lq/Ld value, thus correction or compensation measures may be needed to improve the performance.Finally, in order to verify the correctness of theory analysis, simulation model of rotor position estimation error of PMSM based on rotating and pulsating high frequency voltage signal injection methods are constructed respectively using MATLAB/Simulink.