“…However, setting up a direct self-tuning PID control system requires time-consuming tuning [11], [12], exact plant models [11], a highly specialized mathematical background [13], [14], [15], substantial computing power [11], [12], and very often the presence of expensive experts and one or more microcomputers and computers [14], [16]. Besides the limited availability of reductions of online computation load in other adaptive control [17], the studies reported in [2], [7], [8], [9], [18], [19], [20], [21], [22], [23], [24], [25] used a class of simple nonlinear self-tuning PID controllers (NPID, for short) that helps to make a conventional linear fixed-gain PID controller an adaptive controller, where nonlinear control encountered in various practical systems, which is frequently one of the main causes of poor performance, oscillation, or even instability [26], is envisioned for linear systems with the aim to improve performance [27]. For example, on the occasion where the error generated is high, the self-tuned nonlinear function will automatically amplify the gain in order to correct the error until the desired output has been achieved.…”