Q. Show Block diagram of proportional and integral controller?

The block diagram of Figure illustrates a typical microprocessor system used to implement the digital PI controller. It would be simple to include the derivative operation to implement the PID controller. While an analog timer is shown in Figure to determine the start of the next sampling period, a software timing loop can be used to keep track of when T seconds have elapsed. The output pulse, once every T seconds, is applied to the interrupt line of the microprocessor. This will cause the processor to execute the interrupt routine to output the next value of the control, u[(k + 1)T ], which is sent to the D/A converter, whose output in turn controls the power amplifier. The timing pulse from the timer is also sent to the "sample" command line, thereby triggering the sample-and-hold circuitry; the motor velocity ω(t) is sampled and held constant for one sampling period. The value of ω(kT) is then converted to an N-bit binary number by the A/D circuitry. The microprocessor is signaled via "data ready" line (which may be attached to the interrupt line of the microprocessor) that the sampled data have been converted. The second interrupt will cause the processor to read in the value of ω(kT) and then compute the next value of control, u[(k + 1)T]. After calculation of the control, the microprocessor waits for another interrupt from the timer before it outputs the control at t = (k + 1)T .An assembly-language program can be developed for the implementation of the PI controller.

The control of a dc motor can be achieved with a PI controller discretized for microprocessor programming. The starting point is that the PI controller is described by a differential equation.

The latter is discretized at the sampling instants by one of the numerical approximation methods, and then is programmed in the microprocessor machine language.