Digital Control Measures In-System Response
by Mark Hagen, Systems Application Engineer, and Dave Freeman, System Engineering Manager, Texas Instruments, Dallas, Power Electronics Technology, Nov 01 2006
Focus:
In power supply designs with digital loop control, the digital power controller can be used to determine the frequency response of the control loop. The controller is used to both inject and measure test signals at various points into the loop, and frequency response is obtained by performing a discrete fourier transform on the result. The article discusses the possible locations in the loop where test signals may be injected, and uses a buck converter example to illustrate how the different options affect the ease of measurement. The article also discusses the use of a pc-based design tool to perform in-circuit loop analysis on a telecom rectifier reference design that uses the TMS320F2808 digital controller. For a given control loop, this tool can be used to obtain the frequency response of the power stage, the digital compensator, the open-loop system, or the closed-loop system. Once the response of the analog power stage has been obtained, a Bode plot function within the tool allows the designer to vary the compensator coefficients and see their impact on system response. The benefits of using a digital controller to perform loop analysis are discussed. These benefits include the ability to optimize control-loop frequency response during power supply production, overcoming the usual effects of component tolerances. And in-system analysis permits frequency response to be optimized for different levels of load capacitance in the application.
What you’ll learn:
- How to measure frequency response of a power supply control loop in digitally controlled power supplies
- How to determine where to inject and measure test signals when using a digital controller to measure frequency response of a power supply control loop
- How to understand the benefits of using a digital power controller to measure the frequency response of power supply control loops in-system
Notes:
Article appeared in PET's November 2006 supplement on Digital Control. In the same supplement, also see "Digital Power Control Enables System Identification."
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