Active Power Control of Photovoltaic Systems and  Electric Vehicle Charge Optimization Including the Costs of Battery Degradation

Hoke, Anderson Foster

Graduate Thesis Or Dissertation

Active Power Control of Photovoltaic Systems and Electric Vehicle Charge Optimization Including the Costs of Battery Degradation Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/8623hx837

Abstract

This thesis consists of two parts. The first describes new methods for use in the active power control of photovoltaic (PV) inverters without the need for energy storage. As increasing numbers of PV power systems are interconnected with the electric power system, those PV systems displace some of the conventional generators that currently balance generation and load and stabilize the grid frequency by modulating their active power output. At very high levels of PV penetration, it may be desired or required that PV generators contribute to the stabilization and regulation of grid frequency by modulating their output power. This work proposes a novel method of estimating the maximum power available from a PV array, allowing an inverter to minimize the opportunity cost of providing any required reserve power for up-regulation. It also proposes a novel method of increasing the speed at which a PV inverter can reach a new power set point in response to a frequency event, which increases the effectiveness of the inverter’s active power response. Both of these methods are validated experimentally using a prototype inverter. The second component of this thesis describes a method for optimizing the charging of electric vehicles taking into account both a time-varying cost of electricity and the impact of the charge profile on Lithium-ion battery lifetime using a simplified Lithium-ion battery lifetime model. The simple battery lifetime model, also developed and presented here, estimates both energy capacity fade and power fade and includes effects due to temperature, state of charge profile, and daily depth of discharge. Resulting vehicle charge profiles show a compromise among four trends: charging during low-electricity cost intervals, charging slowly, charging towards the end of the available charge time, and suppression of vehicle-to-grid power exportation. Simulations based on experimental Prius PHEV usage data predict that batteries charged using optimized charging last significantly longer than those charged using typical charging methods, potentially allowing smaller batteries to meet vehicle lifetime requirements. These trends are shown to hold across a wide range of battery sizes and hence are applicable to both pure electric vehicles and plug-in hybrid electric vehicles.

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