Abstract: In order to annul the steady state error of the system, the additional integral term has been introduced into the control loop. The term could be introduced either before or after a variable structure regulator (VSR). The first case increases the system order, while the second case simplifies the design procedure. However, the speed response, until system reaches sliding surface, is decreased in both cases. This problem has been solved by using the PI action. In this paper, the detailed analysis of VSS with proportional--plus--integral control will be elaborated. The efficiency of such a type of regulation has been shown in the example of DC motor speed control.
Key words: Automatic control, variable strucyure regulator, sliding surface, proportional plus integral control, speed control, DC motor speed control.