Compensation of the nonlinearities present in the digital control loop

Abstract

This paper highlights the digital control problems and issues during the controller design and suggests the solutions to resolve them. For this purpose, digital controller designed on the basis of digital redesign or emulation technique is applied to a buck converter working in continuous conduction mode. Nonlinearities due to the ADC and DAC quantizers, loop-delay, etc. are introduced into the control loop and their adverse effects on performance are interrogated. The nonlinearities are suppressed by retuning the digital controller. The order of the controller may increase and require more resources for its implementation. The quantizers' nonlinearities add quantization noise into the loop and may cause offsets and limit cycle oscillations (LCOs). The overall phase margin gets reduced due to the delay thus keeping the bandwidth limited and leading the system towards instability. The well-tuned loop remains asymptotically stable if the nonlinearities are neglected. MATLAB/Simulink environment is used to address all the issues.