## Help in studying of Preview Control Theory and Riccati equations

I am very new to the topic of optimal control. I am trying to learn the Preview Control Theory to understand the methodology in [1].

My background is in Mechanical Engineering. I took a couple of courses in Control Theory in my Undergrad, but they only touched the basic concepts.

From what I found so far (for example [2]), while using preview control, one first builds the augmented state space equation that includes the future reference values. Then uses some of optimal control methods to find the optimal controller gains. In the example I am trying to recreate to learn the topic [2], authors use the Hinf optimal control, which boils down to solving a Riccati equation.

Here goes my question. Can anyone recommend me any source of easy to understand materials concerning the following topics:
- preview control (there is very few materials on the net)
- Hinf and other optimal control theory (there is quite a number of books, but since they are usually quite thick and pricey I would highly appreciate any advice before I buy one)
- Riccati equation (I guess it should be discussed in the books about optimal control)

Przemo

References:
[1] Kajita, S., Kanehiro, F., Kaneko, K., Fujiwara, K., Harada, K., Yokoi, K., & Hirukawa, H. (2003). Biped walking pattern generation by using preview control of zero-moment point. Proc. IEEE Int. Conf. Robotics and Automation ICRA ’03 (Vol. 2, pp. 1620-1626). doi:10.1109/ROBOT.2003.1241826

[2] Takaba, K. (2003). A tutorial on preview control systems. SICE 2003 Annual Conference, 1561-1566.
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 Tags optimal control, preview control, robotics