Digital implementations of linear feedback controllers: qualitative properties and limitations

Once the design of a linear feedback control system has been completed (using any one of the well-known classical or modern techniques), the designer is faced with issues relating to the digital implementation of the controller, should such an implementation be required. Specifically, the designer needs to select a topology for the controller (e.g. direct form), type of architectures (fixed point or floating point), type of quantizer, size of quantizer steps, type of overflow nonlinearities (e.g. saturation), and type of processor. These choices affect the qualitative and quantitative dynamic properties of the resulting nonlinear discontinuous feedback control system. In particular, the resulting feedback control system may have several kinds of limitations (involving accuracy and properties of the system) and may not meet the desired specifications of the original linear prototype. The authors address these issues.<>