Research On Phase-locked Control And Generalized Predictive Control Of Electromagnetic Vibrator

Vibroseis in seismic exploration is an important equipment,which is used to generate seismic wave. Its application area ranges throgout shallow engineering geological exploration, oil exploration, mineral exploration. Relative hydraulic vibrator, Electromagnetic vibrator has better high-frequency response, with a light weight, attracted widespread attention in shallow seismic exploration. But the current phase lag of the vibrator, power amplifiers phase shift, poor coupling of baseplate and ground, mechanical delay, electromagnetic vibrator excitation signal exists distortion. The distortion includes a phase distortion and amplitude distortion aberration. It would not only affect the accuracy and resolution of seismic exploration, but also affect the application of phased array vibroseis and combination vibroseis on electromagnetic vibrator.Based on the electromagnetic vibrator-PHVS500, designed by Jilin University independently, this paper summarized the sinusoidal signal phase meter method, zero-crossing comparator, correlation analysis, DFT transform method, and analyze their characteristics. Analyzed the characteristics and sources of noise in electromagnetic vibrator feedback loop, discuse using zero-phase filter or linear phase FIR filter to suppress noise, then research the Phase-locked control of vibroseis, combining with phase precompensation. In the process of practical seismic exploration, vibroseis would always be influenced by the surface conditions, its model parameters are not fixed. For this problem, generalized predictive control, which not relys on model, can adapt to changes of ground surface conditions in seismic exploration and improve reliability of vibroseis control system. But the generalized predictive control is a time-consuming operation process. All this limited its ability to track high frequency signal. This paper proposes using the generalized predictive algorithm in the PLL to reduce the phase distortion and amplitude distortion of vibrator pilot signal.Based on FPGA, this paper designed electromagnetic vibrator excitation signal quality control system, completed the direct frequency synthesizer with multiple frequency scanning methods, linear phase FIR digital filter, ADS1255 control logic, phase discriminator and other digital circuit design, to provide guarantee for high precision vibroseis seismic prospecting.According to the above methods, we use the vibrator model established by experimental data to simulate the vibrator output signal. In simulation results of conventional phase lock control, the largest phase distortion was lower than 5 °, amplitude distortion was also effectively suppressed. The control precision of vibrator signal will fall, when the model changes. The generalized predictive control algorithm need a long operation time and cannot directly be used to tracking vibroseis high frequency signal. Combining the generalized predictive control algorithm with the phase-locked control can enhance the system adaptability to the change of ground surface conditions. The simulation results show that the phase control precision of it was less than 3 °, under 3000 m/s speed model, the positioning error caused by the vibrator signal distortion was less than 0.2 m and the vibrator would satisfy the requirement of high resolution seismic exploration.