Publications

Microgrids with significant renewable penetration will likely require storage devices to maintain a stable bus voltage due to the stochastic behavior of renewable sources and grid loads. The distribution and frequency response characteristics of the storage are two important variables when designing these types of microgrids. For example, storage can be distributed at renewable sources located centrally on a common bus, or a combination thereof. Storage devices will need to compensate for both long and short period disturbances such as the changing output of a photovoltaic (PV) array and the switching of large loads. Simulation results indicate that a cost function based on bus voltage stability is suitable for computing optimal converter capacitances when the load contains cyclic transients. © 2012 IEEE.

This paper explores the effect of a distributed control system for the charging of plug-in hybrid electric vehicles utilizing an agent-based approach in a smart grid. The vehicles are regarded as additional loads in addition to a primary forecasted load and use information transfer with the grid to make their charging decisions. MATLAB was used as the simulation tool to design the control strategy and simulate its effect on a power grid. The findings of this study are that the charging behavior and peak loads on the grid can be reduced by use of this distributed control strategy. © 2012 IEEE.

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This paper will present the design of collective feedback controllers for the integration of renewable energy into networked DC bus microgrids. These feedback controllers are based on a single DC bus microgrid because the networked DC bus microgrids are self-similar. As a result, these feedback controllers are divided into two types. Type 1 is based on a feedback guidance command to determine the boost converter duty cycle. Type 2 is based on Hamiltonian Surface Shaping and Power Flow Control (HSSPFC) [1], [2], [3], [4], [5], [6] to determine the required distributed energy storage systems to ensure stability and performance. Two DC bus microgrids coupled with a transmission line is used as an example. This model architecture can vary from 0% energy storage with transient renewable energy supplies to 100% energy storage with fossil fuel energy supplies which will be useful in the future to demonstrate the benefits and costs of networked microgrids. © 2012 IEEE.

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The swing equations for renewable generators connected to the grid are developed and a wind turbine is used as an example. The swing equations for the renewable generators are formulated as a natural Hamiltonian system with externally applied non-conservative forces. A two-step process referred to as Hamiltonian Surface Shaping and Power Flow Control (HSSPFC) is used to analyze and design feedback controllers for the renewable generators system. This formulation extends previous results on the analytical verification of the Potential Energy Boundary Surface (PEBS) method to nonlinear control analysis and design and justifies the decomposition of the system into conservative and non-conservative systems to enable a two-step, serial analysis and design procedure. The first step is to analyze the system as a conservative natural Hamiltonian system with no externally applied non-conservative forces. The Hamiltonian surface of the swing equations is related to the Equal-Area Criterion and the PEBS method to formulate the nonlinear transient stability problem. This formulation demonstrates the effectiveness of proportional feedback control to expand the stability region. The second step is to analyze the system as natural Hamiltonian system with externally applied non-conservative forces. The time derivative of the Hamiltonian produces the work/rate (power flow) equation which is used to ensure balanced power flows from the renewable generators to the loads. The Second Law of Thermodynamics is applied to the power flow equations to determine the stability boundaries (limit cycles) of the renewable generators system and enable design of feedback controllers that meet stability requirements while maximizing the power generation and flow to the load. Necessary and sufficient conditions for stability of renewable generators systems are determined based on the concepts of Hamiltonian systems, power flow, exergy (the maximum work that can be extracted from an energy flow) rate, and entropy rate. This paper will present the analysis and numerical simulation results for two nonlinear control design examples that include: (1) the One-Machine Infinite Bus (OMIB) system with a Unified Power Flow Controller (UPFC) and (2) the swing equation for a wind turbine connected to an infinite bus through a UPFC to determine the required performance of the UPFC to enable the maximum power output of a wind turbine subject to stochastic inputs while meeting the power system constraints on frequency and phase. The energy storage requirements will also be identified from the UPFC and/or FACTS devices while working in combination with the wind turbine.

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In this paper1, the swing equations for renewable generators are formulated as a natural Hamiltonian system with externally applied non-conservative forces. A two-step process referred to as Hamiltonian Surface Shaping and Power Flow Control (HSSPFC) is used to analyze and design feedback controllers for the renewable generator system. This formulation extends previous results on the analytical verification of the Potential Energy Boundary Surface (PEBS) method to nonlinear control analysis and design and justifies the decomposition of the system into conservative and non-conservative systems to enable a two-step, serial analysis and design procedure. In particular, this approach extends the work done by [1] by developing a formulation which applies to a larger set of Hamiltonian Systems that has Nearly Hamiltonian Systems as a subset. The results of this research include the determination of the required performance of a proposed Flexible AC Transmission System (FACTS)/storage device to enable the maximum power output of a wind turbine while meeting the power system constraints on frequency and phase. The FACTS/storage device is required to operate as both a generator and load (energy storage) on the power system in this design. The Second Law of Thermodynamics is applied to the power flow equations to determine the stability boundaries (limit cycles) of the renewable generator system and enable design of feedback controllers that meet stability requirements while maximizing the power generation and flow to the load. Necessary and sufficient conditions for stability of renewable generators systems are determined based on the concepts of Hamiltonian systems, power flow, exergy (the maximum work that can be extracted from an energy flow) rate, and entropy rate. © 2010 IEEE.

This paper1 discusses the modeling, analysis, and testing in a real-time simulation environment of the Lanai power grid system for the integration and control of PhotoVoltaic (PV) distributed generation. The Lanai Island in Hawaii is part of the Hawaii Clean Energy Initiative (HCEI) to transition to 30% renewable green energy penetration by 2030. In Lanai the primary loads come from two Castle and Cook Resorts, in addition to residential needs. The total peak load profile is 12470V, 5.5 MW. Currently there are several diesel generators that meet these loading requirements. As part of the HCEI, Lanai has initially installed 1.2MW of PV generation. The goal of this study has been to evaluate the impact of the PV with respect to the conventional carbon-based diesel generation in real time simulation. For intermittent PV distributed generation, the overall stability and transient responses are investigated. A simple Lanai "like" model has been developed in the Matlab/Simulink environment [1] (see Fig. 1) and to accommodate real-time simulation of the hybrid power grid system the Opal-RT Technologies RT-Lab environment [2] is used. The diesel generators have been modelled using the SimPowerSystems toolbox [3] swing equations and a custom Simulink module has been developed for the High level PV generation. All of the loads have been characterized primarily as distribution lines with series resistive load banks with one VAR load bank. Three-phase faults are implemented for each bus. Both conventional and advanced control architectures will be used to evaluate the integration of the PV onto the current power grid system. The baselne numerical results include the stable performance of the power grid during varying cloud cover (PV generation ramping up/down) scenarios. The importance of assessing the real-time scenario is included. © 2010 IEEE.

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