Abstract
This paper presents the design and application of the modified relay feedback test (MRFT) auto-tuning method to the PID voltage-mode control of dc-dc buck converters. The proposed method, which also includes a set of tuning rules, does not require knowledge of the converter or load parameters, and produces a controller with near-optimal dynamic performance for virtually any dc-dc buck converter. The proposed MRFT auto-tuning also guarantees a specified phase margin. An important feature of the MRFT auto-tuning is that it is non-complex and thus practical, consisting of a simple test stage and a quick tuning stage. In the test stage oscillations are excited using the MRFT algorithm, and the frequency and amplitude of these oscillations are measured. In the tuning stage, these measurements are used with the pre-designed tuning rules to calculate PID controller parameters. The designed MRFT auto-tuning is evaluated experimentally by using it to auto-tune four different dc-dc buck converter designs, where in each case parameters of the converter are unknown to the auto-tuning algorithm. The experimental results show good performance of the MRFT auto-tuned controller in all cases. A mathematical proof that the MRFT auto-tuning guarantees a specified phase margin is also provided.
Highlights
The constant evolution of digital controllers with improved speeds and lower cost-to-performance ratio has led to their increased adoption in switching power converters, where analog controllers used to be prevalent [1]
A TMS320F28335 digital microcontroller is utilized; the pulse-width modulation (PWM) frequency is set to 200 kHz, and the sampling rate is set to 200 KHz and is synchronized with the PWM
This paper presents the design and implementation of the modified relay feedback test (MRFT) auto-tuning method applied to a digitally-controlled dc-dc buck converter
Summary
The constant evolution of digital controllers with improved speeds and lower cost-to-performance ratio has led to their increased adoption in switching power converters, where analog controllers used to be prevalent [1]. With a single set of pre-designed tuning rules (being the major contribution of this work), the presented method may be used for the auto-tuning of a wide range of designs of a digital PID-controlled dc-dc buck converter. Advantages of the MRFT auto-tuning method are: (i) the auto-tuning is simple, fast, and reliable; (ii) it guarantees a certain specified gain or phase margin; (iii) it provides near-optimal dynamic performance; (iv) it does not require knowledge of any of the converter or load parameters; (v) has a minimal impact on the converter’s operation; and (vi) it is a small program, so in most cases it can be added to the existing digital controller.
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