Loop compensation feedback

Compensating the voltage feedback loop (refer to Appendix B)... 

This completes the design of the feedback loop compensation elements, and the error amplifier curves and the overall plots are also included in Figure 3-66. This also completes the design of the major portions of the switching power supply. The schematic is shown in Figure 3-67. 

Example 8.14. Designing phase-lead and phase-lag compensators. Consider a simple unity feedback loop with characteristic equation 1 + GCGP = 0 and with a first order process... 

There are two ways of handling the ohmic drop effect. One consists of equipping the instrument with a positive feedback loop that subtracts from E a tension, Rei, proportional to the current, thus eliminating, at least partially, the effect of the ohmic drop.14 One may even get the impression that total compensation, or even more, overcompensation, could be achieved. In fact, before total compensation is reached, oscillations appear as a result of the bandpass limitations of the operation amplifiers. The entire instrument can indeed be represented by a self-inductance, La, that is a... 

The basic controller in the feedback loop is designed for load disturbances Ui) A precompensator is used on the setpoint signal. This element is designed so that the response to setpoint changes, with the compensator in service, is the desired one. The precompensator is defined as I>ss(z) ... 

Feedback loop A set of geochemical processes that influence each other. In a negative feedback, an alteration in the rate of one process is at least partially compensated for by changes in the rates of the other interconnected processes. In a positive feedback, an alteration in the rate of one process is amplified by accompanying changes in the rates of the other interconnected processes. 

Autonomic and hormonal control of cardiovascular function. Note that two feedback loops are present the autonomic nervous system loop and the hormonal loop. The sympathetic nervous system directly influences four major variables peripheral vascular resistance, heart rate, force, and venous tone. It also directly modulates renin production (not shown). The parasympathetic nervous system directly influences heart rate. In addition to its role in stimulating aldosterone secretion, angiotensin II directly increases peripheral vascular resistance and facilitates sympathetic effects (not shown). The net feedback effect of each loop is to compensate for changes in arterial blood pressure. Thus, decreased blood pressure due to blood loss would evoke increased sympathetic outflow and renin release. Conversely, elevated pressure due to the administration of a vasoconstrictor drug would cause reduced sympathetic outflow, reduced renin release, and increased parasympathetic (vagal) outflow. 

Consider a simple feedback loop (Fig. 7.3a) in which the feedback path consists of elements which approximate to a steady-state gain K (Fig. 7.37). In this instance, the equivalent unity feedback loop is determined by placing 1 IK in the set point input to the main loop and compensating for this by adding an additional factor K in the forward part of the loop prior to the entry of the load disturbance, as in Fig. 7.38. It is easy to confirm that the standard closed loop transfer functions and are the same for the block diagrams in Figs 7.37 and 7.38. 

The signal X can be introduced by means of an internal feedback loop within the controller (Fig. 7.60) which constitutes the dead time compensator GDTC(s) such that ... 

The relevant block diagram is composed of two loops (Fig. 7.97)—a normal feedback loop and a loop which contains the parameter adjustment mechanism (comparable to feed-forward compensation—Section 7.14.1). 

In order to avoid the distortion caused by these two effects, the usual approach is to compensate the resistance Ru by a positive feedback loop (this is imperative in systems like plasticized membranes for which the uncompensated resistance can be of the order of megaohms [32-34]). Another possibility is to use microelectrodes, for which a decrease in the measured current is obtained which minimizes the ohmic drop and charging current distortion (see Sects. 2.7 and 5.4.1). 

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