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+--- Thread: Different Control Loops Have More in Common than You Might Think (/showthread.php?tid=6)
Different Control Loops Have More in Common than You Might Think - Tom - 09-30-2020
Having worked around operational amplifiers since the advent of the uA709 integrated amplifier and around all manner of controls for various sorts of instrumentation, I thought that controls to regulate a switched-mode power converter would be an entirely different matter. Only after internalizing the problems encountered, and after 10 years of learning, did I realize that the underlying problem was the same. Whether you are controlling temperature with a loop running at 1 Hertz, or regulating a power supply voltage with a loop running at 100 kHz, the problem with trading off between stability and speed of response is fundamentally linked. The problem reduces to delayed feedback.
The terminology is different for different fields, but whether you are compensating an op amp or tuning a PID loop, you are changing the response of a feedback loop to get around the problem of delayed response causing a tendency toward oscillation. The answers we found for power converters involved prediction, which moved the filter delay to outside of the feedback loop. It was a pleasant surprise to discover that the same concept, applied to PID type loops, was a huge help.
Operational amplifiers have specs for bandwidth. open loop gain, slew rate, small signal response, large signal response, unity gain stability, and capacitive load tolerance, and on and on. These are some of the factors relating to that loop compensation, which is the tradeoff between stability and agility. Switched-mode power converter control loops have to remain stable in the face of an analogous set of varying conditions, made worse by the discontinuous feedback in many power supply topologies. A deterministic prediction enables uncompromised dynamic response by removing the loop delay. We call that breakthrough Predictive Energy Balancing, or PEB.
For power converters, the PEB technology is patented, but that same learning underpins the free data acquisition and control templates that we provide. We make it easy to take advantage of a lifetime's work.
Tom Lawson