Process control schemes involving fluid-flow machinery with traditional adjustable speed drives (ASDs) or modules encounter limitations such as control flexibility and accuracy. In this context, the traditional approach implies that proportional integral derivative (PID) methods can be used and that these methods can directly control frequency. However, applying PID and directly controlling frequency on centrifugal pump drives restricts flowrates and pressures along a nonlinear pump-performance curve. The widely known pump-performance curve shapes are determined by a particular machines impeller design or fabrication details. With respect to controlling flowrate and/or pump discharge pressure, ASD modules using traditional PID methods suffer from trying to apply a linear equation to solve a nonlinear problem.