ZG control for 2-output tracking of 3-input nonlinear system with GD used additionally twice more

In this paper, the Zhang-gradient (ZG) method, which is a combination of Zhang dynamics (ZD) and gradient dynamics (GD) methods, is proposed for solving the tracking control problem of the multiple-input multiple-output (MIMO) system. Different from the traditional ZG method, GD is used additionally twice more in this paper to get through the derivation procedure. Moreover, each GD parameter is tunable for each GD design formula instead of being traditionally assigned the same value, which is the key point in this research for making simulations successful. Besides, simulation verifications further illustrate that the proposed controller group based on the ZG method achieves not only satisfactory tracking accuracy but also rapid tracking rate.