Variable voltage variable frequency control of tubular linear permanent magnet synchronous machine for drilling applications

This paper presents variable voltage variable frequency (VVVF) control scheme to tubular linear permanent magnet synchronous machine (TLPMSM) with gas springs. To achieve constant drilling speed in the presence of different magnitudes of hardness of rocks, it is necessary to change the input voltage to the machine. Therefore, with change in input voltage, the natural frequency of the spring system changes. In order to maintain the same displacement of the drill bit, the input voltage frequency should also change. The main contribution of this paper is the modeling of the system and analysis of the variation of the natural frequency and a variable voltage variable frequency control method. Simulation results show that VVVF is capable of achieving the desired performance.