Abstract-A time-domain design method for the digital controller of pulsewidth modulation dc-dc converters was developed. The proposed approach is based on the fact that the closed-loop response of a digitally controlled system is largely determined by the first few samples of the compensator. This concept is used to fit a digital PID template to the desired response. The proposed controller design method is carried out in the time domain and, thus, bypasses errors related to the transformation from the continuous to discrete domain and to discretization. The method was tested by simulations and experimentally. Digital PID controllers for experimental buck-and boost-type converters were designed according to the proposed method and implemented on a TMS320LF2407 DSP core. The measured closed-loop attributes were found to be in good agreement with the design goals. The study was further expanded to investigate the possible realistic closed-loop performance that can be obtained from a system that is controlled by a PID template controller, as well as the stability boundaries of the proposed time-domain controller design approach. The results of the study delineate a normalized map of deviation from the target closed-loop performance goals possible for PID control of switchmode converters and the areas in which the use of this control law is feasible.
A discrete time domain-based system identification method for PWM DC-DC converters is proposed. Accurate information on the system's open-loop response is essential in the design of the system controller in order to obtain the desired closed-loop response. This is especially true in switch-mode converters where component uncertainty exists. It is conjectured in this study that an identification method that is based on time-domain signals will be relatively simple to realise with a digital processor. The method that is proposed is capable of successfully reconstructing the system model by an arbitrary excitation at the command input. In this study, a step perturbation was employed, which is simple to apply and leads to an intuitive interpretation of the output response. The effects of switching and quantisation noise have been overcome by choosing the sampling interval after the switching oscillations have decayed and by averaging the responses of synchronously perturbed sequences. The proposed method has been evaluated on Buck and Boost converters. The method was verified in two phases: Off-line-data acquisition procedure was implemented on a TMS320F2407-DSP and the identification calculations were carried out on a PC. On-line-The identification procedure (data acquisition plus fitting algorithm) was programmed on a TMS320F2808-DSP.
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