Design and Implementation of Digital Current Mode Control
Type of DegreeDissertation
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Presented in this dissertation are three digital control methods of current mode control for switch-mode power supplies. Both the current and voltage loop are implemented on the digital processor. Digital versions of peak current mode control (predictive current mode control), average current mode control and I2 average current mode control are proposed and investigated in sequence. Issues of noise filtering, high frequency analog-to-digital (ADC) sampling and digital PWM modulations are discussed. Since the peak current mode control (PCM) finds wide application in low-to-medium power DC-DC converters, the digital predictive current mode control is first presented in this dissertation which is the equivalent digital version of PCM. The control law is derived based on the steady state operation of analog PCM control, which only needs one sample per cycle to estimate the current peak signal. The small-signal model is developed and verified by measurements from an AP300 network analyzer. Because of the common configuration for the digital current mode control methods, the small-signal model developed for predictive current mode control can be used as a basis for other digital current mode control. Then, three digital implementations of average current mode control are discussed which are the basis for the digital I2 average current mode control in the later chapter. The advantages and disadvantages of each implementation are compared. The modification of the small-signal model for predictive current mode control is developed to predict the frequency response of digital average current mode control. I2 average current mode control was proposed in 2013, a small-signal modeling for an analog implemented I2 average current mode is presented. This small-signal model successfully predicts the “sub-harmonic” oscillation when the duty cycle is close, or greater than 0.5. By paralleling the current loops of peak current mode and average current mode, the digital I2 average current mode control is designed using predictive current mode control and digital average current mode control. A TMS320F2812 DSP controlled boost converter is built to serve as a prototype to experimentally demonstrate the feasibility of these digital current mode control technique.