Joshua Ott, Mykel J. Kochenderfer, Stephen Boyd
Stanford University
Efficiently estimating system dynamics from data is essential for minimizing data collection costs and improving model performance. This work addresses the challenge of designing future control inputs to maximize information gain, thereby improving the efficiency of the system identification process. We propose an approach that integrates informative input design into the Dynamic Mode Decomposition with control (DMDc) framework, which is well-suited for high-dimensional systems. By formulating an approximate convex optimization problem that minimizes the trace of the estimation error covariance matrix, we are able to efficiently reduce uncertainty in the model parameters while respecting constraints on the system states and control inputs. This method outperforms traditional techniques like Pseudo-Random Binary Sequences (PRBS) and orthogonal multisines, which do not adapt to the current system model. We validate our approach using aircraft and fluid dynamics simulations to demonstrate the practical applicability and effectiveness of our method. Our results show that strategically planning control inputs based on the current model enhances the accuracy of system identification while requiring less data. Furthermore, we provide our implementation and simulation interfaces as an open-source software package, facilitating further research development and use by industry practitioners.
Efficient System Identification: Our proposed approach designs control inputs to target uncertainty in the current system model reducing the data required for model improvement.
Scales to Large State Spaces: Dynamic Mode Decomposition with control (DMDc) reduces the dimension of the state and control space to plan informative inputs in the reduced order model space.
Real-time Applications: By using the Convex-Concave Proecdure (CCP) we are able to approximately optimize future inputs. The speed of our solution method allows us to rapidly replan as new data is collected online.
Targeted Data Collection: Our method outperforms traditional input design methods in accuracy and runtime efficiency, with an open-source implementation available for broader use.
Convex-Concave SDP + LP: our proposed methods.
Orthogonal Multisines: optimizes combination of sinusoids to be orthogonal in the time and frequency domain.
Random: randomly moves between input constraints.
Takeaway: Planning future control inputs to target uncertainty in the current model parameters results in more accurate future models given the same amount of data.
Takeaway: We can efficiently plan informative inputs for systems with large state spaces by first decomposing the prominent modes of the dynamics.
Takeaway: Using convex approximations allows us to approximately optimize control inputs rapidly allowing for real-time applications where the control inputs and model estimates are updated as new data is acquired.
As data continues to become more abundant, the question becomes not only what information is contained in your data, but often, and more importantly – what is not!