Abstract: Aiming at the problem that the frequency interval of emission current controlled by traditional method was fixed and the frequency domain was not completely controllable, in order to improve the efficiency of frequency domain electromagnetic sounding, we proposed a selective harmonic eliminated pulse width modulation (SHEPWM) control method based on improved particle swarm optimization algorithm. Firstly, the expected spectrum was cal
culated according to the exploration target. Secondly, the half-cycle symmetric SHEPWM nonlinear equations were established according to the time-frequency domain characteristics of the emission current. Finally, the improved particle swarm optimization algorithm was used to solve the nonlinear equations, and the corresponding switching time sequence was obtained. By controlling the inverter of the emission system by the switching time sequence, the emission current required for detection could be output. When the depth target was explored, the launch system could output the optimal launch current, and then improve the vertical resolution.

Key words:  , frequency domain electromagnetic sounding, selective harmonic eliminated pulse width modulation (SHEPWM), improved particle swarm optimization algorithm, nonlinear equations, vertical resolution