Robust Subspace System Identification via Weighted Nuclear Norm Optimization

Subspace identification is a classical and very well studied problem in system identification. The problem was recently posed as a convex optimization problem via the nuclear norm relaxation. Inspired by robust PCA, we extend this framework to handle outliers. The proposed framework takes the form of a convex optimization problem with an objective that trades off fit, rank and sparsity. As in robust PCA, it can be problematic to find a suitable regularization parameter. We show how the space in which a suitable parameter should be sought can be limited to a bounded open set of the two dimensional parameter space. In practice, this is very useful since it restricts the parameter space that is needed to be surveyed.Comment: Submitted to the IFAC World Congress 201

A Learning Based Approach to Control Synthesis of Markov Decision Processes for Linear Temporal Logic Specifications

We propose to synthesize a control policy for a Markov decision process (MDP) such that the resulting traces of the MDP satisfy a linear temporal logic (LTL) property. We construct a product MDP that incorporates a deterministic Rabin automaton generated from the desired LTL property. The reward function of the product MDP is defined from the acceptance condition of the Rabin automaton. This construction allows us to apply techniques from learning theory to the problem of synthesis for LTL specifications even when the transition probabilities are not known a priori. We prove that our method is guaranteed to find a controller that satisfies the LTL property with probability one if such a policy exists, and we suggest empirically with a case study in traffic control that our method produces reasonable control strategies even when the LTL property cannot be satisfied with probability one

Piezoelectric vibration energy harvesting: A connection configuration scheme to increase operational range and output power

For a conventional monolithic piezoelectric transducer (PT) using a full-bridge rectifier, there is a threshold voltage that the open-circuit voltage measured across the PT must attain prior to any transfer of energy to the storage capacitor at the output of the rectifier. This threshold voltage usually depends on the voltage of the storage capacitor and the forward voltage drop of diodes. This article presents a scheme of splitting the electrode of a monolithic piezoelectric vibration energy harvester into multiple ( n) equal regions connected in series in order to provide a wider operating voltage range and higher output power while using a full-bridge rectifier as the interface circuit. The performance of different series stage numbers has been theoretically studied and experimentally validated. The number of series stages ([Formula: see text]) can be predefined for a particular implementation, which depends on the specified operating conditions, to achieve optimal performance. This enables the system to attain comparable performance compared to active interface circuits under an increased input range while no additional active circuits are required and the system is comparatively less affected by synchronized switching damping effect. </jats:p

Distribution-Aware Sampling and Weighted Model Counting for SAT

Given a CNF formula and a weight for each assignment of values to variables, two natural problems are weighted model counting and distribution-aware sampling of satisfying assignments. Both problems have a wide variety of important applications. Due to the inherent complexity of the exact versions of the problems, interest has focused on solving them approximately. Prior work in this area scaled only to small problems in practice, or failed to provide strong theoretical guarantees, or employed a computationally-expensive maximum a posteriori probability (MAP) oracle that assumes prior knowledge of a factored representation of the weight distribution. We present a novel approach that works with a black-box oracle for weights of assignments and requires only an {\NP}-oracle (in practice, a SAT-solver) to solve both the counting and sampling problems. Our approach works under mild assumptions on the distribution of weights of satisfying assignments, provides strong theoretical guarantees, and scales to problems involving several thousand variables. We also show that the assumptions can be significantly relaxed while improving computational efficiency if a factored representation of the weights is known.Comment: This is a full version of AAAI 2014 pape

A Cold-Startup SSHI Rectifier for Piezoelectric Energy Harvesters with Increased Open-Circuit Voltage

Piezoelectric vibration energy harvesting has drawn much research interest over the last decade towards the goal of enabling self-sustained wireless sensor nodes. In order to make use of the harvested energy, interface circuits are needed to rectify and manage the energy. Among all active interface circuits, SSHI (synchronized switch harvesting on inductor) and SECE (synchronous electric charge extraction) are widely employed due to their high energy efficiencies. However, the cold-startup issue still remains since an interface circuit needs a stable DC supply and the whole system is completely out of charge at the beginning of implementations or after a certain period of time without input vibration excitation. In this paper, a new cold-startup SSHI interface circuit is presented, which dynamically increases the open-circuit voltage generated from the piezoelectric transducer (PT) in cold-state to start the system under much lower excitation levels. The proposed circuit is designed and fabricated in a 0.18 um CMOS process and experimentally validated together with a custom MEMS (microelectromechanical systems) harvester, which is designed with split electrodes to work with the proposed power extraction circuit. The experiments were performed to start the system from the cold state under variable excitation levels. The results show that the proposed system lowers the required excitation level by at least 50% in order to perform a cold-startup. This aids restarting of the energy harvesting system under low excitation levels each time it enters the cold state

Eight parametric resonances in a multi-frequency wideband MEMS piezoelectric vibration energy harvester

This paper presents a multi-order parametric resonant MEMS piezoelectric disk membrane, for the purpose of broadening the operational frequency bandwidth of a vibration energy harvester by employing the nonlinearity-induced bandwidth broadening associated with this phenomenon as well as the multi-frequency response associated with the higher orders. The fundamental mode -3dB bandwidth at 2.0 g recorded 55 Hz, while the first parametric resonant peak exhibited 365 Hz and the -3dB of the first 8 orders accumulated to 604 Hz. The membrane parametric resonator also experimentally demonstrated over 3-folds improvement in power density compared to a conventional direct resonator (cantilever), when subjected to band-limited white noise.This work was supported by Innovate UK (Project reference: 131183).This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/MEMSYS.2016.742186

Rectified Output Power Analysis of Piezoelectric Energy Harvester Arrays under Noisy Excitation

In the past decade, vibration energy harvesting has emerged as a potential alternative solution to power wireless sensor nodes. In real-world implementations, external excitation can be very noisy and includes noise signals in a wide frequency band. In order to accommodate operation under noisy excitation, arrays of energy harvesters with different resonance frequencies are often employed to improve responsibility. Due to the nature of noisy excitation and the difference in resonance frequencies, the response voltage signals from each harvester can be very different in amplitude, frequency and phase. In this paper, an array with two cantilevered energy harvesters is studied to analyze the rectified output power with different configurations using full-bridge rectifiers (FBR). The experiments show that connecting the two harvesters in parallel or in series before connecting with a FBR results in significant voltage cancellation due to phase mismatch. The most efficient way to extract energy is to use two FBRs for the two cantilevered energy harvesters, individually, and charge to one single storage capacitor connected at the outputs of the two FBRs