An introduction to the implementation of digital control — Leading to the control of electrical power systems

The control of modern electrical power systems is, in some respects, limited by traditional analogue control methods. It is recognised that digital control can offer significant advantages in enhancing a power system's closed-loop performance and improve control implementation over traditional analogue methods. In particular, an electrical power system can exhibit optimum performance throughout its operating range and even enhance its operating range through the use of dynamic digital control-coefficients. This paper seeks to describe the process by which a system under continuous-time control can be converted into one which operates with digital control. The aim is to provide an introduction to digital control, based on a design process using the open-loop frequency response of a system. Several problems encountered when designing a digital controller are highlighted; in particular, the effect of the sampling time on the performance of the system. The system performance under digital control is compared to its analogue equivalent, and suggestions are made to minimise the difference between the performances of the two types of implementations.