Adaptive control methods for DC-DC switching power converters

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Tight regulation of the output voltage is often required in many power supply applications, despite the highly dynamic nature of the loads. This is conventionally obtained by the design of high bandwidth feedback loop or recently by using adaptive control methods. The control loop is designed with specified safe bandwidth and gain and phase margins such that it maintains stable operation under variable conditions and parameters. However, this results in a compromise between achievable dynamic performance and robustness of control loop. The large variations in operating points and load makes the system design challenging. The tight regulation requirements, in addition to size and weight requirements, are getting stricter by time, which makes it necessary to investigate new control concepts in order to meet these requirements. Not meeting the tight regulation requirements may result in either the malfunctioning of the device (load) being powered or the destruction of that device. This work focuses on the development and implementation of adaptive control methods that result in the improvement of the dynamic performance of power converter, by utilizing the flexibility of digital controllers to realize advanced control schemes. Four different methods are proposed that improve the dynamic performance of converter without compromising the steady-state performance. A Sensorless Adaptive Voltage Positioning (SLAVP) control scheme is proposed in Chapter 2, in order to realize Adaptive Voltage Positioning (AVP) control without the need for load or inductor current sensing and high-resolution high-speed Analog-to-Digital Converter (ADC) sampling. The SLAVP control law utilizes the readily available error signal of the conventional voltage-mode closed-loop compensated controller, or in other words the duty cycle of a DC-DC buck converter, in order to realize AVP control. The elimination of the need for high-speed and accurate sensing and sampling of currents using the proposed SLAVP control reduces the size and cost of the digital controller, reduces the power losses associated with current sensing and sampling, and simplifies hardware design, apart from improving dynamic performance. In Chapter 3, an Adaptive Digital PID (AD-PID) controller scheme is proposed. The controller adaptively adjusts the integral constant (K_i) and the proportional constant (K_p) of the compensator following a new control law. The control law is a function of the magnitude change in the error signal and its peak value during dynamic transients. The proposed AD-PID controller adaptively detects the peak value of the error signal which is a function of the transient nature and magnitude and utilize it in the control law such that no ocillations are generated as a result of the adaptive operation. As a result, the dynamic output voltage deviation and the settling time of the output voltage are reduced. A novel Compensator Error Observe and Modulate method (CEO&M) for online closed-loop-compensator auto-tuning of digital power controller is proposed in Chapter 4. The proposed method is relatively simple and does not require the knowledge and/or measurement of the power stage or closed-loop frequency response. Moreover, the proposed method does not depend on conventional design methods and the associated rule of thumb design criteria in order to tune closed-loop feedback controllers of power converter for high, and possibly optimum, dynamic performance. Furthermore, two approaches for dynamic variable switching frequency digital control scheme under dynamic transients are proposed in Chapter 5 in order to improve the dynamic performance of the DC-DC switching power converter. The proposed controller varies the switching frequency of the converter, higher or lower than the steady-state frequency, during the transient as a function of peak and magnitude of error signal depending on the amount and type of the transient. Finally, Chapter 6 summarizes this work and provides conclusions before discussing future related research direction.

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