“…The barrier Lyapunov function (BLF) and its variants have been widely applied to state constraint and output constraint problems (Niu & Zhao, 2013;Ren et al, 2010;Tee et al, 2009Tee et al, , 2011 for nonlinear systems in Brunovsky form (Ngo, Mahony, & Jiang, 2005) using the backstepping technique (Krstic, Kanellakopoulos, & Kokotovic, 1995). With these approaches, good tracking performance without violation of any constraints has been achieved.…”