Showing papers by "Jonathan W. Kimball published in 2013"

Solid-State Transformer Architecture Using AC–AC Dual-Active-Bridge Converter

Abstract: Modern development of semiconductor power-switching devices has promoted the use of power electronic converters as power transformers at the distribution level. This paper presents an ac–ac dual-active-bridge (DAB) converter for a solid-state transformer. The proposed converter topology consists of two active H-bridges and one high-frequency transformer. Four-quadrant switch cells are used to allow bidirectional power flow. Because power is controlled by the phase shift between two bridges, output voltage can be regulated when input voltage changes. This paper analyzes the steady-state operation and the range of zero-voltage switching. It develops a switch commutation scheme for the ac–ac DAB converters. Experimental results from a scaled-down prototype are provided to verify the theoretical analysis.

Stability of a cyber-physical smart grid system using cooperating invariants

Abstract: Summary form only given. Cyber-Physical Systems (CPS) consist of computational components interconnected by computer networks that monitor and control switched physical entities interconnected by physical infrastructures. Ensuring stability and correctness (both logical and temporal) of a Cyber-Physical System (CPS) as a whole is a major challenge in CPS design. Any incorrectness or instability in one component can impact the same features of other components. The fundamental challenge in developing a design framework that unifies the various components is the heterogeneity of the component types, resulting in semantic gaps that must be bridged. For example, while the physical entities in a smart grid are electric devices whose stability and correctness may be expressed in terms of Lyapunov and Lyapunov-like functions, the notion of correctness in the context of the cyber devices are best expressed in the form of a conjunction of logical operators on system parameters. In our work, we employ a fundamentally different approach than much existing work; our work composes correctness instead of functionality. The basic idea, is to express the stability and correctness constraints of all components in the form of logical invariants and ensure that system actions are performed only if and when they are guaranteed not to violate the conjunction of these invariants. In recent work, we developed invariants that must be satisfied by the physical system to ensure its stability. However, the state of the physical system and, hence, its stability, is dependent on power transfers (migrations) initiated by the cyber algorithm within each node in the system and by the state of the communication network that carries messages between the cyber nodes to signal initiation and acknowledgement of physical power migrations. The state and stability of the communication network is in turn affected by the number of migration messages in transit at any given time. In this poster, we present a distributed, adaptive algorithm for scheduling power migrations between nodes in a smart grid in such a way that the overall stability of the system, including physical and network stability, is maintained. The results show that preserving the system invariant preserves system stability.

Input voltage control of SEPIC for maximum power point tracking

Abstract: The SEPIC (Single Ended Primary Inductor Converter) topology is an excellent choice for a maximum power point tracking (MPPT) converter in small solar energy systems. To achieve MPPT, the input voltage of the SEPIC, corresponding to the photovoltaic (PV) module's output voltage, must be regulated. In this paper, a model is derived with the voltage on the input capacitor as the plant output. The model is used to design a closed-loop controller to regulate the PV module voltage to match the output of an MPPT algorithm. Simulation and experimental validation are given.

Selective source power converter for improved photovoltaic power utilization

Abstract: This work proposes a new power conversion system suitable for supplying power to both ac and dc loads simultaneously from both ac sources, such as the power grid, and dc sources, such as a photovoltaic (PV) panel. First, an introduction of the motivation for proposing the new system and the objectives of the new system is given. Next, the new system and its building blocks are introduced. Then, the technical details about a built prototype conversion system are presented. Finally, a number of experimental results are provided to demonstrate the performance of the proposed system.

High-gain DC-DC conversion for parallel photovoltaic arrays

Abstract: A new approach to photovoltaic (PV) arrays is proposed based on a parallel connection scheme In a series-connected array, differing insolation due to shading or obstructions causes disproportionate reduction in power output Because operating voltage is governed more by temperature than by insolation, a parallel-connected array is much more robust to the shading effect Direct paralleling is inappropriate due to the low voltage of a conventional PV module Therefore, high-gain dc-dc converters are introduced in the proposed system Three converter types are discussed Two use transformers to increase gain and one uses a tapped inductor Experimental results validate the concept and demonstrate tracking accuracy up to 9987% despite a 39% difference in insolation, and weighted efficiency of up to 929%

Performance analysis of generalized algebraic switched capacitor converters

Abstract: Recently, several new families of switched capacitor converters (SCCs) have been proposed using algebraic methods to generate switching states. Because of their regular structure, the switching states may be translated directly into matrices that may be used to compute performance via statespace analysis. This paper provides an algorithm for creating the matrices. Simulated results are given for three different types of generalized algebraic SCCs. The computed equivalent resistance matches simulation results within numerical precision.