“…Surprisingly, unlike the planar systems, where the number of limit cycles is finite [23], a simple three-dimensional system may have an infinite number of small amplitude limit cycles [24]. At present Huang, Gu and Wang [25] introduced some results on the bifurcation of limit cycles for three-dimensional smooth systems, such as Lotka-Volterra systems, Chen systems, Lorenz systems, Lü systems, and three-dimensional piecewise smooth systems. Sanchez and Torregrosa [26] studied several classes of three-dimensional polynomial differential systems by using the parallel computing method, and determined that there are at most 11, 31, 54, and 92 limit cycles at the origin for three-dimensional quadratic, cubic, quartic, and quintic systems, respectively.…”