Highly precise acoustic impedance inversion is a key technology for pre-drilling prediction by VSP data. In this paper, based on the facts that VSP data has high resolution, high signal to noise ratio, and the downgoi...Highly precise acoustic impedance inversion is a key technology for pre-drilling prediction by VSP data. In this paper, based on the facts that VSP data has high resolution, high signal to noise ratio, and the downgoing and upgoing waves can be accurately separated, we propose a method of predicting the impedance below the borehole in front of the bit using VSP data. First, the method of nonlinear iterative inversion is adopted to invert for impedance using the VSP corridor stack. Then, by modifying the damping factor in the iteration and using the preconditioned conjugate gradient method to solve the equations, the stability and convergence of the inversion results can be enhanced. The results of theoretical models and actual data demonstrate that the method is effective for pre-drilling prediction using VSP data.展开更多
Power electronic converters under weak grid conditions may trigger new dynamic stability problems.Even though massive internal and external damping methods have been investigated,their system costs and robustness have...Power electronic converters under weak grid conditions may trigger new dynamic stability problems.Even though massive internal and external damping methods have been investigated,their system costs and robustness have not been solved in an effective way.This paper first proposes a sensorless active damping method based on the grid current feedback filter.The mid-frequency non-passive region of converters can be reduced effectively,thus system stability improvement in weak grids can be realized.Then this paper analyzes the feedback filter which may bring about additional non-passive regions in high frequency.What’s more,it has a poor robustness.The residual mid-frequency non-passive region can be enlarged under converter parameter variations.Furthermore,this paper proposes a hybrid active damping method.The grid voltage is fed forward through a low pass filter.The robustness against parameter variation is greatly improved and the non-passive region in high frequency is also totally eliminated.In order to further improve the system robustness in high frequency,a simple passive damping is also added.The damping resistor is designed small to reduce the damping loss.The simulation and experimental results prove that the proposed sensorless method can realize robust damping in an economic way.展开更多
文摘Highly precise acoustic impedance inversion is a key technology for pre-drilling prediction by VSP data. In this paper, based on the facts that VSP data has high resolution, high signal to noise ratio, and the downgoing and upgoing waves can be accurately separated, we propose a method of predicting the impedance below the borehole in front of the bit using VSP data. First, the method of nonlinear iterative inversion is adopted to invert for impedance using the VSP corridor stack. Then, by modifying the damping factor in the iteration and using the preconditioned conjugate gradient method to solve the equations, the stability and convergence of the inversion results can be enhanced. The results of theoretical models and actual data demonstrate that the method is effective for pre-drilling prediction using VSP data.
基金This work was supported in part by the National Natural Science Foundation of China under Grant 51720105008 and Grant 51807033.
文摘Power electronic converters under weak grid conditions may trigger new dynamic stability problems.Even though massive internal and external damping methods have been investigated,their system costs and robustness have not been solved in an effective way.This paper first proposes a sensorless active damping method based on the grid current feedback filter.The mid-frequency non-passive region of converters can be reduced effectively,thus system stability improvement in weak grids can be realized.Then this paper analyzes the feedback filter which may bring about additional non-passive regions in high frequency.What’s more,it has a poor robustness.The residual mid-frequency non-passive region can be enlarged under converter parameter variations.Furthermore,this paper proposes a hybrid active damping method.The grid voltage is fed forward through a low pass filter.The robustness against parameter variation is greatly improved and the non-passive region in high frequency is also totally eliminated.In order to further improve the system robustness in high frequency,a simple passive damping is also added.The damping resistor is designed small to reduce the damping loss.The simulation and experimental results prove that the proposed sensorless method can realize robust damping in an economic way.
