Recent Advances on Off-Policy Reinforcement Learning for Optimization Control

Reinforcement learning (RL), a key artificial intelligence technique, has been widely studied and applied over the past two decades to solve various optimization control problems. Generally speaking, there are two basic frameworks for RL-based control design, i.e., on-policy and off-policy RL (OffP-RL). The essential distinction between the two frameworks lies in whether the policy used to generate training data is the behavior policy or the target policy. In on-policy RL-based control methods, the data used for evaluating the target control policy at each iteration must be collected from the system under the target policy itself. In contrast, in OffP-RL methods, the system data is generated by other behavior control policies. It addresses the inadequate exploration problem in on-policy RL methods, making OffP-RL methods more practical and easier to implement. In this article, the recent advances in OffP-RL-based control methods are classified into three categories based on the number of controllers/players involved, i.e., single-/two-/multiplayer. For the single-player case, it is an optimal control problem, which aims to use OffP-RL to learn the optimal control policy, which minimizes the performance index. In the two-player case, most works focus on the H_∞ control problem and the two-player zero-sum game, using learning to find the Nash equilibrium. In the multiplayer case, a multiplayer game involves a single system with multiple control inputs, while a multiagent system consists of multiple systems with independent control inputs. Finally, related applications of OffP-RL-based control and future work are analyzed.