Erik Kostson
Ansys Employee

See our help manual for more information. 
(MPC is based on constraint equations, while penalty is based on contact stiffness approach which is updated for frictional nonlinear type of contact, but not for bonded linear type of contact (so whatever initial contact stiffness Ansys calculates or the user provides (normal stiffness set to Absolute value), then that is used for the penalty stiffness of the bonded contact throughout the analysis, and is not updated/changed like a frictional contact which requires iterations and update of the initial contact stiffness). We also have courses on contact which can be helpful.