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Advanced monitoring and control of distributed DC systems : an embedded impedance detection approach

University of British Columbia

Direct Current (DC) systems, made possible by power electronics technology, are becoming more prevalent due to their advantages when integrating renewable energy sources, energy storage, and DC loads. Microgrids and local area energy systems are instrumental to DC systems, and much progress has been made around them. However, DC microgrids face numerous challenges due to their decentralized nature, such as resource optimization, control, and protection. This thesis focuses on developing a core technology, an embedded impedance detection (EZD) method for DC systems, and its application to five critical challenges in DC systems. The proposed method uses a reference signal of minimal amplitude and high frequency, injected in the control loop of the power electronic converter, and a digital Lock-In Amplifier to extract the incremental behavior of the voltage and current around the DC operating point. These are used to calculate the incremental impedance, which is representative of the reactive part of the system as well as the nonlinear characteristics of the system. The proposed EZD method is applied to address five critical problems in today's DC systems: 1) adaptive control in the presence of active loads - to expand stability and improve transient response; 2) islanding detection - to detect the connection and disconnection of the utility grid and change controllers for autonomous operation; 3) fault location - to detect the distance to a fault and simplify the system restoration; 4) high-impedance fault detection - to accurately distinguish a fault condition from a load increase; and 5) maximum power point tracking of photovoltaic panels - to ensure efficient energy harvesting. For all these applications, the proposed EZD-based solution offers critical benefits and advantages, such as high sensitivity and accuracy at a low system disturbance and fast detection. The work presents a detailed analysis of the proposed EZD technique as well as considerations for its implementation in commercial microcontrollers, followed by simulations to illustrate its capabilities. The thesis also presents a detailed analysis of each DC system application and its particular considerations. The outlined benefits are supported by simulations and validated through experimental results using a real power electronics platform.

Text

2020-02-06

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/73491

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/