Research On Frequency-domain Electromagnetic Emission Current Control Method Based On Improved Particle Swarm Optimization

Frequency-domain electromagnetic sounding method is a geophysical method for surveying underground resources.By emitting different frequency current to excite space electromagnetic field and observing the distribution characteristics and changes of space electromagnetic field,the geological structure and mineral distribution can be detected.In the actual detection process,different emission current corresponds to different detection frequency,thus corresponding to different detection depth.At present,2~n pseudo-random method is widely used in frequency-domain electromagnetic sounding to control the emission current,and the frequency interval of the emission current is fixed.When detecting the target body at a specific depth,multiple emission current is needed to achieve all the frequencies needed for detection,which leads to insufficient detection efficiency and high exploration cost.In view of the above problems,the best way of detection is to face any detection target,the transmission system can output the optimal transmission current,its frequency meets the needs of detection,and then achieves high efficiency and low cost detection.In this paper,the emission current control method of SHEPWM in frequency-domain based on improved particle swarm optimization algorithm is studied.The main contents are as follows:1)Based on the principle of frequency-domain electromagnetic sounding,the detection frequency is calculated for the target body.Then,Fourier series is used to analyze the emission current.According to the information of the emission current in time and frequency domain,a half period mirror symmetric SHEPWM nonlinear equation group which can control the amplitude,phase,distribution and quantity of odd harmonics is derived.The switch angle is obtained by solving it,and the emission current with the best detection efficiency can be output.The vertical single resistance forward model is designed and its apparent resistivity is analyzed.It is proved that the vertical resolution of the SHEPWM control method is higher when detecting the target body at a certain depth.2)Based on the SHEPWM nonlinear equations,neural network algorithm,particle swarm optimization algorithm and improved particle swarm optimization algorithm are used to solve them.According to the performance of the three algorithms,the improved particle swarm optimization algorithm is selected to solve the SHEPWM nonlinear equations.The results show that the improved particle swarm optimization algorithm is the most efficient.3)According to the working principle of frequency-domain electromagnetic sounding transmitting circuit,Simulink is used to simulate the circuit of the launch system,and it is verified that the half cycle mirror symmetric SHEPWM control method can control the frequency-domain information of odd harmonics of the transmission current autonomously.The SHEPWM controller is designed,FPGA is used as the main control chip,which is used for data acquisition and conversion,parameter selection display and SHEPWM control pulse generation,and the controller is tested.4)The SHEPWM control method has been successfully applied to the frequency-domain electromagnetic detection launch system.The results show that the SHEPWM control method can be applied to field experiments.At the same time,in Wanchao Town,Kaili City,Guizhou Province,the distribution of goaf is detected,which proves the feasibility of SHEPWM emission current control method.