ECEA 5708 Current Mode Control

Duration: 5 hours

In this module, operating principles of peak current mode control are introduced, and a simple model is developed based on the fact that peak current mode control enables direct and fast, cycle-by-cycle control of the switch or the inductor current. Practical advantages of peak current mode control are discussed, including built-in overcurrent protection, simpler and more robust dynamic responses, as well as abilities to ensure current sharing in parallel connected converter modules. A simple averaged model is developed where the average inductor current is directly controlled by the current command in the peak current mode control modulator. Period-doubling stability issues are explained, and the need for slope compensation is introduced. Week 1 includes application examples and practice Quizzes and concludes with a graded Quiz on Introduction to peak current-mode control.

Duration: 4 hours

In this module, a more accurate averaged model is developed, which takes into account the impact of the inductor current ripple, and the slope of the compensation ramp. The large-signal more accurate averaged model is used to develop an averaged simulation model for the peak current mode modulator, which can be combined with averaged-switch circuit models of the power converter. Furthermore, a more accurate small-signal model is developed by linearizat8ion of the more accurate large-signal averaged model. It is shown how the small-signal model of the modulator can be combined with known small-signal models of duty-cycle controlled converters. Examples are included to illustrate the design of the peak current mode control loop and voltage control loops around peak current mode controlled .converters. Week 2 includes practice Quizzes and concludes with a graded Quiz on the design of a voltage regulator using peak current mode control.

Duration: 3 hours

In this module, we discuss sampling and high-frequency effects in switched-mode power converters. It is shown how the pulse-width modulator can be viewed as a sampler in the small-signal sense, and how the converter response to pulse-width modulated control signals can be viewed as responses of an equivalent hold. The sampled-data modeling techniques are applied to peak current mode control to clarify the origins of the period-doubling instability and to enable improved modeling of high-frequency effects as well as the design of high-performance current and voltage control loops. Approximations to the sampled-data model are compared to the more accurate average model. Week 3 includes application examples and practice Quizzes, as well as a graded Quiz on high-frequency effects in peak current-mode controlled converters.

Duration: 3 hours

In this module, we discuss average current mode control, another popular and practical control technique for switched-mode power converters. It is shown how a converter average current can be controlled to follow a reference, leading to some of the same advantages as with peak current mode control, but with additional benefits of improved immunity to noise. Small-signal models are developed for regulators that employ an inner average current-mode control loop, and an outer voltage control loop. Week 4 includes application and design examples, and a graded Quiz on average current-mode control of dc-dc converters.

Duration: 2 hours

Final Exam for this course.