Sliding mode controller for RF cavity tuning loop

The authors designed a robust and adaptive controller based on sliding mode techniques for a cavity tuning system on the ISIS synchrotron. A modern control technique for designing a robust feedback controller such as the sliding-mode starting from an experimental Bode diagram of the system is described. The proposed techniques retain all the simplicity of the state feedback controller and add robustness to handle variation in tuning errors due to beam loading or other uncertainties in the system. Although the controller is robust, a nonrobust state estimator may give problems unless the eigenvalues are carefully selected. The feedback loop can be implemented in two ways, using analog or digital circuits. A schematic layout for analog implementation is shown. The controller implementation would require a multiplexer to determine the sign change in the sliding variable. For digital implementation, a DSP chip, TMS320C30, from Texas Instruments, with 32-b floating point multiplication and accumulation time of 60 ns, can compute the control signal in under 5 mu s, in real time.<>