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Hit the switch.
A quick demonstration on how a feedback controller works, by maintaining the output voltage level of a buck converter as specified by the 5V source (Set Point) at the top right of the schematic.
In this circuit I've used a PI controller not PID, only because of the space limitation.
Let's see a bit about feedback controllers.
1, P (proportional) controller: control action is directly proportional to the error, the error signal is the difference between the setpoint (desired output, often manually set) and the output (controlled variable),
advantageous because of immediate control action based on the immediate value of the error.
It's disadvantage is steady state error caused when a change occurs in process dynamics this can be overcome by an integral controller, oscillatory behavior at higher gains
2, I (Integral) controller: control action given, is based on the integral of the error, this type of controller gives the control by taking into account the past and the present value of the error
Advantage, steady state error elimination.
Disadvantage, sluggish and oscillatory response during startup and load changes.
3, D (Derivative) controller: also called predictive controller, gives control action based on the derivative of the error, so this type takes in to account the speed at which the error is increasing or decreasing, which gives a better transient performance. Cannot be used by it self.
Advantage: fast and predictive response, greatly improves transient performance
Disadvantage: no steady state error elimination, no control action for constant error, amplification of consistent high frequency noise...
4, PI (Proportional-Integral) controller: combines the advantage of both P and I controller, provides imidiate control action and also steady state elimination but has sluggish response and poor transient performance.
5, PD (Proportional-Derivative) controller: combines the advantages of both P and D controller thus greatly improving transient performance, at the cost of steady state error elimination.
6, PID controller: the most versatile and industrial controller, combines all three controllers for best performance.
What makes feedback controllers very popular is that they can be designed to satisfy requirements with minimal knowledge of the dynamics of the process at hand, just by using tuning methods such as Ziegler Nicolas tuning technique.
As you can see from my circuit the output of the PI controller is fed to a pulse width modulator, this circuit together with the transistor forms the final control element that manuplates the input variable, i.e. the time the inductor is conducting.
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