Comprehensive, yet computationally simple, direct digital control-system design technique

As a result of the enormous impact of microprocessors, electronic engineers, with sometimes only a cursory background in control theory, are being involved in direct-digital-control (d.d.c.) system design. There appears to be a real need for an easily understood and simply implemented comprehensive design technique for single-input d.d.c. systems. This is the objective of this largely tutorial paper, which assembles for the first time information that is widely scattered in the control-engineering literature. The proposed design technique provides, first of all, a simple calculation that ensures that the data sampling rate is consistent with the control system´s accuracy specification or the fatigue life of its actuators. Pulsed transfer-function design for a plant controller is based on two simple rules and a few standard frequency-response curves, which are easily computed once and for all time. Structural resonances are eliminated by digital notch filters, the pole-zero locations of which are directly related to the frequency and bandwidth of an oscillatory mode; this is exactly as with analogue networks. In addition a computationally simple formula gives an upper bound on the amplitude of the control error (deviation) component due to multiplicative rounding effects in the digital computer; this thereby enables the selection of a suitable machine wordlength or machine. A distinct advantage of the proposed design technique is that its implementation does not necessarily involve a complex computer-aided-design facility. This aspect is confirmed by a class-2 design example in the text. Furthermore, the frequency-domain design curves are a versatile design tool in that they can also be used to design conventional 3-term digital controllers, or to translate a working analogue controller into its digital counterpart.