Cascade control is a frequently used control strategy in industrial processes. It can reduce the maximum deviation and the integral error compared with the single loop. Currently, the minimum variance method of parallel cascade control system are developed based on the assumption that all the disturbance are subject to Gaussian distribution. However, in the practical condition, some disturbances do not obey the Gaussian distribution. The minimum entropy index of performance assessment of the parallel cascade control system subjected to non-Gaussian disturbances is proposed. In the stochastic process, the information entropy has more general significance than mean or variance for any random variable. The estimated ARMA model for the parallel cascade control loop based on the minimum entropy instead of the minimum mean squares error has better performance for non-Gaussian disturbances. The result of proposed methods are demonstrated through a simulation example. 

The formation control for underactuated surface ships with 3 degree － of － freedom is investigated，and the shape tracking
controllers based on Leader /Follower method are developed． The ship is controlled respective，when the system received the shape-command．
The Leader tracked the shape-command directly，and the Followers tracked the designed trajectory，which is designed by the
shape-command and the state of the Leader． For the design of tracking control，firstly，reference tracking path and reference forward
speed are designed based on desired formation shape． Secondly，path tracking controller and speed tracking controller are constructed by
nonlinear control theory and Lyapunov theory． Finally，the shape tracking error of the follower is uniformly ultimately bounded． Numerical
simulations show the system can tracking any curves． The results validate the effectiveness of proposed controller．

By using the decoupled double synchronous coordinate system software phase locked loop ( DDSRF-SPLL) ，it can detect the
unbalanced grid voltage of positive sequence component and negative sequence component，and put forward the coordinate transformation
of the mathematical to establish the grid side of directly-driven permanent wind generator's mathematical model，which includes
network side PWM inverter control and Voltage phase locked loop． A kind of current decoupling control strategy is proposed． It uses the
space vector pulse width modulation ( SVPWM) on AC output current control． This method can independently control the output current
of the active and reactive component，and can make the output current waveform of sine and grid voltage in phase with the same frequency．
Thus it can greatly reduce the harmonic pollution． It can eliminate the influence of unbalance voltage，and to achieve a precise
phase-locked output current and gird voltage three-phase grid voltage amplitude imbalance． In this paper，using Matlab /Simulink software
platform，the simulation proves the validity and feasibility of the control system when the grid stays in balance and unbalance． This
system improves reliability of wind power grid connection．