Solid-state power controllers for protection of DC grids

• Main Author: Loh, Wen Jie
• Other Authors: Josep Pou
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering
• Online Access: https://hdl.handle.net/10356/181716
• Institution: Nanyang Technological University

In recent years, studies have indicated that the adoption of dc grids has emerged as a more effective option for integration into the electrical system, enhancing overall performance. However, a significant challenge faced by dc grids is the lack of current zero-crossing, which complicates fault isolation. In ac grids, mechanical circuit breakers are the most used protection devices to safeguard the system network. However, MeCBs cannot be adopted into dc grids due to their limitations such as the absence of current zero-crossing, slow response time, and the capability of breaking dc fault current. To mitigate these challenges, solid-state power controllers appear to be the rising technology for protecting dc networks. This report focused on SSPC technologies. In SSPCs, the power semiconductors are used as the main switching element, this could result in high on-state losses. Therefore, to mitigate these challenges, this report will mainly focus on silicon-controlled rectifier (SCR) based SSPCs. In the system, the capacitive loads associated with power electronic converters often have no stored charge. Directly connecting a dc supply to an SSPC can result in high peak current and voltage, placing significant stress on the main power semiconductor devices and other components in the network. One of the main challenges of SSPCs is smoothing out the peak current. Therefore, this report covers the type of pre-charging methods to smoothen the inrush current. Another challenge encountered is the excessive voltage that occurs during a fault. To address this, an SSPC must include overvoltage protection devices to clamp the voltage. The types of clamping devices have also been discussed in the report. Z-source SCR-based SSPC topologies have been discussed along with their advantages and disadvantages. A selection of SCR-based bidirectional SSPCs with soft reclosing has been simulated using LTspice software, and its significance has been explained as well.