Digital feedback signal

Consider the block diagram of a direct digital feedback control loop shown in Figure 29.9. Such loops contain both continuous- and discrete-time signals and dynamic elements. Three samplers are present to indicate the discrete-time nature of the set point j/Sp( ), control command c(z), and sampled process output y(z). The continuous signals are denoted by their Laplace transforms [i.e., y(s), Jn(s), and d(s)]. Furthermore, the continuous dynamic elements (e.g., hold, process, disturbance element) are denoted by their continuous transfer functions, H(s), Gp(s), and GAs), respectively. For the control algorithm, which is the only discrete element, we have used its discrete transfer function, D(z). 

A DC motor is feedback-controlled by a current sub-control loop and a primary speed control loop. In order to close the control loop, the actual current value is fed back to the current control loop and a speed signal to the speed control loop. While current is measured in the power converter, a shaft encoder on the motor is required for speed signal feedback. Either a tacho-generator or a digital encoder is used as a speed transmitter. If speed measurement accuracy is not very important, the speed feedback can be measured via armature voltage. In this case, this measurement can also be done within the power converter. Static control accuracy reaches... 

Self-adaptive control, 436-38, 662-67 Self-regulating systems, 7, 34, 180 Self-tuning regulator, 437-38, 662-67 references, 447, 673 Serial transmission, digital signals, 561 Servo problem (see Feedback control)... 

DSP Digital signal processor. Computer processor used to control SPM feedback loop... 

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