Research On High-Precision And High-Stability Constant Current Source For Inductive Load

Helmholtz coil is a commonly used device for generating a stable magnetic field,and the magnitude of the generated magnetic field has an approximately linear relationship with the current passing through the coil.When a variable magnetic field with high precision and high stability is required to be generated,it is required to provide an adjustable constant current source with high precisi on and high stability.However,achieving a high-stability constant current source usually requires the design of complex temperature control devices as power increases.At the same time,when the load of the constant current source is inductive,the contradiction between system accuracy and stability and dynamic performance is more protruding.Thus,the high-precision and high-stability constant current source for inductive loads is studied based on these.A low-noise switch-linear series composite constant current source structure is proposed based on the switch-linear composite technology,which utilizes the parallel structure of the pre-stage switch section and the advantages of interleaving control,and the high power supply rejection ratio capability of the linear part of the latter stage,plus the fourth-order low-pass filter structure existing in the topology not only greatly improves the system efficiency,but also eliminates the influence of switching noise on the accuracy of the constant current source.A hierarchical control strategy for MOS voltage drop is proposed on this basis.The pre-stage switch section adjusts the voltage drop of the MOS by controlling the linear part of the rear stage to ensure that it operates in the linear region and adjusts th e MOS voltage drop according to the magnitude of the output current,further reducing the power consumption of the linear portion of the constant current source.Aiming at the contradiction between the accuracy and dynamic performance of the constant current source system,the front-stage switch part reduces the output ripple and improves the dynamic response through the interleaved parallel technology.At the same time,the current mode control is used to further improve the dynamic performance.The linear part of the latter stage adopts single closed-loop PI control to improve the accuracy and ensure the high-bandwidth capability of the linear stage.For the contradiction between the stability and dynamic performance of the inductive load constant current source system,the driver stage is added between the compensator and the linear adjustment tube,and the small-signal theory analysis method is proposed.By performing small-signal modeling and analysis on the switch part and the linear part respectively,the dynamic performance of the system is improved as much as possible under the premise of ensuring the stability of the system.In order to verify the feasibility of the proposed constant current source structure and the practicability of the control strategy,a 50~70V input,0.1~2.5A output,experimental prototype with inductive load was built to test the accuracy,stability,output current rate of change and immunity.The experimental results show that the proposed structural scheme and control strategy not only achieve high precision and high stability of the inductive load constant current source system,but also simplify the design of the system temperature control platform,reduce the cost,and have strong engineering practical value.