Electro-Thermal Analysis of Power Converter Components in Low-Voltage DC Microgrids for Optimal Protection System Design

Abstract

Bidirectional power converters are considered to be key elements in interfacing the low voltage dc microgrid with an ac grid. However to date there has been no clear procedure to determine the maximum permissible fault isolation periods of the power converter components against the dc faults. To tackle this problem, this paper presents an electro-thermal analysis of the main elements of a converter: ac inductors, dc capacitors and semiconductors. In doing this, the paper provides a methodology for quantifying fault protection requirements for power converter components in future dc microgrids. The analysis is performed through simulations during normal and fault conditions of a low voltage dc microgrid. The paper develops dynamic electrothermal models of components based on the design and detailed specification from manufacturer datasheets. The simulations show the impact of different protection system operating speeds on the required converter rating for the studied conditions. This is then translated into actual cost of converter equipment. In this manner, the results can be used to determine the required fault protection operating requirements, coordinated with cost penalties for uprating the converter components. Index Terms--Microgrid, DC fault current, AC-DC power conversion, thermal design, power semiconductor diode switches, thermal stress, fault protection requirements. Graeme M. Burt (M'95) received the B.Eng. degree in electrical and electronic engineering from the University of Strathclyde, Glasgow, UK, in 1988, and the Ph.D. degree from the University of Strathclyde in 1992, following research into fault diagnostic techniques for power networks. He is currently a Director of the Institute for Energy and Environment at the University of Strathclyde, where he also directs the University Technology Centre in Electrical Power Systems sponsored by Rolls-Royce. He is a professor of electrical power engineering, and has research interests in the areas of: integration of distributed generation; power system modelling, real-time simulation, protection and control; microgrids and more-electric systems.

A Protection System for Improved Ring-Bus DC Microgrids

“…During a serious fault, the controllable electric electronic components can be turned off by its self-protection immediately after fault, while the uncontrollable component would continue bearing the overcurrent and they are also easily damaged [18]. Those vulnerable devices should be the main protection objects, because only if they can avoid being damaged by faults, the converters can restart soon after fault is cleared.…”

Thermal Analysis and Junction Temperature Estimation under Different Ambient Temperatures Considering Convection Thermal Coupling between Power Devices

“…The existing thermal analysis models [1,2] are often based on fixed ambient temperature values, such as 25 • C or 30 • C [3,4]. However, the ambient temperature is widely variable [5,6]. Different ambient temperatures have different effects on the convection thermal coupling between power devices [7,8].…”

“…The short-term and long-term electro-thermal models are analyzed in [6], and the long-term one is considered to be affected by the ambient temperature. Moreover, the junction and case temperatures of power devices can be estimated by these models.…”

Bi‐level multi‐agent system (MAS) to protect DC microgrids (DCMGs) in free renewable sources and uncertainties penetration

“…Besides, the fault current in an AC grid has a zero-crossing point due to its alternating nature. But in a DC grid, the fault current will never have a zero point due to the direct nature of the fault current, and breaking the fault current is not simply an AC fault current [23][24][25]. Also, a phase to ground high impedance fault is difficult to detect because the fault current is small and might not variate the current path at fault beginning [22].…”

“…Also, a phase to ground high impedance fault is difficult to detect because the fault current is small and might not variate the current path at fault beginning [22]. Researchers in [23] implemented an electrothermal simulation to detect the fault according to changing thermal conditions through the fault. In this approach, the proposed protection plan speed is directly related to the plan's cost.…”