Feed-Forward Dynamometer Controller for High Speed Inertia Simulation

In general, control systems may be divided into two categories, feed-back and feed-forward systems. The output of a feed-back system is controlled by first comparing it to a desired value and then generating an error function proportional to the difference. The error function is then added to the system input through a regulator and a feed-back path. Thus, the output is forced to converge toward its correct value. Although this system achieves accurate results, it does so at the expense of response time. A feed-forward system does not employ a feed-back path nor does it generate an error signal. The elimination of these two functions can result in a substantial decrease in response time, particularly, when dealing with inherently slow systems and large errors functions. A feed-forward system controls its output by precisely computing the input function from all state variables that affect the system. In practice, results obtained with feed-forward control alone are not as accurate as those obtained with feed-back. For this reason, a certain amount of feed-back should be used with feed-forward when the system control accuracy must be high. This paper describes a feed-forward control system used in the simulation of road load and inertia in an electric chassis dynamometer. This system is implemented with a digital microcomputer and a high-speed arithmetic logic unit (ALU) to produce high-speed inertia simulation comparable to simulation done with flywheel.