Analysis of Initial Undershoot in Step Response of Type-1 Nonminimum Phase Systems

Abstract

In this paper, the analysis of initial undershoot for the step response of Type -1 nonminimum phase systems is carried out. In view of this, a theorem is proposed which enables the identification of various system parameters on the magnitude of undershoot. This involves the use of Markov parameters of the system. The theorem is accompanied by the mathematical proof and validated using two practical situations. First, a DC motor is operated in the open-loop configuration, where the input signal is delayed by a certain amount of time. The presence of delay element incites nonminimum phase behaviour, and thus can lead to the presence of initial undershoot in the system's step response. The analysis showed how the motor's parameters and the delay time affects the undershoot in the angular displacement curve of the motor. Following this, the concept of initial undershoot is used to analyze the effect on the system frequency deviation. The problem adopted is a single area power system consisting of a hydro turbine (a nonminimum phase plant), where system frequency is perturbed by sudden load disturbances. The effect of this system's characteristic on the maximum initial frequency deviation of the electric power is analyzed. It aims at providing means to identify how a controller's parameters affect the change in frequency due to sudden load disturbances. © 2019 IEEE.