How do you design decoupling controllers for interacting multivariable processes?

Decoupling reduces interaction so each loop can be tuned independently. Methods: static decoupling (compensates steady-state interaction using inverse of gain matrix), dynamic decoupling (accounts for dynamic interactions using transfer function compensation), and simplified decoupling (partial compensation for practical implementation). RGA (Relative Gain Array) analysis identifies pairing and quantifies interaction. For 2x2 system: decoupler elements = -G12/G11 and -G21/G22. Limitations: model uncertainty affects effectiveness, may amplify noise, and dynamics complicate design. MPC is often preferred for complex interactions.