Abstract
This paper proposes a new rotor phase estimation method for sensorless drive of permanent-magnet synchronous motors (PMSMs), which uses motor-driving stator voltage and current information for estimation. The proposed estimation method utilizes two high order low-pass filters that can change their bandwidth according to speed estimate. The high order filters have a potential to attenuate sufficiently harmonics contaminating the stator voltage and current and to produce almost-pure-sinusoidal rotor flux estimate consisting of fundamental component only. Such a sinusoidal rotor flux estimate allows high accurate estimation of rotor phase even at very low speed. In order to separate the fundamental component of the rotor flux estimate from its harmonics with no phase lag/lead in variable-speed environments, the proposed low-pass filters have a function to change its bandwidth adaptively to rotor speed. The sensorless drive system using the proposed phase estimation method can show such high performance that 1) it can startup PMSMs from standstill under the rated load; 2) it can drive PMSMs stably even at very low speed such as 1/60 of the rated speed under the rated motoring/regenerating load; 3) it can drive PMSMs accompanied with a load of over 50 times large inertia. The proposed estimation method is simple and easily installed into sensorless drive systems. This paper presents the new estimation method in detail and show how it is installed into the drive systems by using a concrete example. The usefulness of the method and the performance of the drive system are examined and confirmed through extensive experiments.
