| The gravitational wave detection satellite adopts drag-free control technology,which generates thrust through the micro-propulsion system to offset the non-conservative forces,thus maintaining the ultra-static experimental platform and ensuring the stable operation of the laser interferometry experiment.At the same time,the performance of the micro-propulsion system seriously affects the design process of the drag-free control system and restricts the accuracy of drag-free control,so the performance requirements of the micro-propulsion system are"wide range adjustable,high resolution,fast response,low noise".First,for the traditional open-loop operation of the thruster to meet the problem of high-precision performance,the thrust estimation accuracy,controllability and other key characteristics of micro-newton microwave ion thruster as a research object,the first microwave modulation-based ion thruster thrust feedback control strategy,and through the analog circuit,digital control technology combined with precision feedback control method,to achieve a 0.1μN resolution force,the 23ms fast response,10-3～1Hz frequency band noise less than 0.1μN/Hz1/2 thrust performance to meet the micro-propulsion index of gravitational wave detection.The study shows that,compared with the open-loop regulation,the feedback control can effectively suppress various noises and disturbances brought by the device temperature drift and the complex coupling of the thruster and other operating characteristics,and the anti-aliasing filter scheme adopted in this paper can effectively suppress the folding of high-frequency data in the low and middle frequency bands during the digital control process,thus improving the thrust noise index.Second,for the ultra-high control accuracy and robustness requirements of the drag-free control system,a fractional-order PID is designed as the drag-free system controller under the constraints of frequency domain indexes such as bandwidth,phase margin,and disturbance suppression capability,and the simulation results reflect the effective suppression capability of the drag-free controller for internal and external noise and disturbance of the system.Finally,for drag-free control of the micro-propulsion system needs a wide range of fast adjustment,combined with the actual operating characteristics of microwave ion thrusters,the need for a wide range of adjustment of xenon gas flow to achieve thrust range coverage,but also brings the problem of large changes in propulsion system gain.In this regard,the thrust adaptive adjustment method based on the coordinated control of multiple input parameters is proposed to achieve a wide range of thrust adjustment by slow-adjusting the flow rate,and to compensate for the shortage caused by slow-adjusting the flow rate by using the microwave source to adjust the thrust quickly;at the same time,the adaptive control law is introduced to automatically compensate for the control loop gain,which improves the stability of the thrust system and ensures the achievement of the full working condition thrust index.Through the integration of micro-propulsion and drag-free simulation,the relative displacement index of the satellite and the test mass of 1nm/Hz1/2 and the residual acceleration index of the test mass of 10-15/m/s2/Hz1/2 have been achieved,indicating that the internal feedback loop of the propulsion system and the external loop of the drag-free control can work together to accomplish the drag-free control task of the gravitational wave detection satellite. |
