Short-circuit protection for DC microgrids and power converters (MS)

Abstract

A DC Microgrid is an interconnection of distributed energy generation sources, energy storage banks, and loads. Usually, interconnection is carried out by DC busses through various power converters. Whereas distributed energy sources are regarded as renewable energy sources such as wind turbines, photovoltaic. In some applications, DC power grids are interconnected to utility or AC grid also. The power electronics interface at each node provides a robust response and additional controllability among the sources and loads. A significant advantage of these converters can be referred at the time of load shedding. The DC Microgrid fault protection is one of the critical challenges for its widespread adaptation. The short-circuit (SC) faults are frequent faults in the industries and other DC microgrid applications. The SC leads to a current overshoot that damages the circuit components connected through the network. Usually, overshoot fault currents are SC detection parameters whereas, it is observed that variable SC fault current level is one of the critical challenges for its detection. The different conditions and modes (grid-connected or islanded mode) of operation lead to different SC peak fault current levels. Therefore, SC's current limitation and protection are challenging. In DC systems, there are two basic types of faults reported in the literature. These are__(i) Lineto-Line fault, and (ii) Line-to-Ground Fault. These faults can occur at various nodes and points, therefore, fault at distinct points have a different impact on the system. Thus, while developing the fault protection scheme, it is very important to identify and consider all the fault possibilities and incorporate them into the protection algorithm. Apart from the DC bus faults, literature also reports the faults due to power converter/component failure during mission. The semiconductor components and capacitors are the most fault-prone components. Out of all the circuit components, semiconductor switches are the most fragile in the power converters contributing 30-35% of converter faults. Its failure is random in nature. The converter component fault (open-circuit and short-circuit) interrupts DC bus voltage level. To address this issue, several fault-tolerant converter schemes are proposed in the literature to increase the reliability. In this research work, SC fault protection and fault-tolerant schemes are reviewed, and new SC fault protection and fault-tolerant approaches are addressed based on the converter output voltage (bus) characteristics. The proposed approaches are implemented on boost converter. The SC fault protection approach isolates the power source from the voltage source converter connected to the DC bus if SC fault is identified at the DC bus or within the converter. On the other hand, the fault-tolerant approach provides the continuous output power if the switching action (power switch) fails while operating. The proposed SC fault protection and fault-tolerant approaches can find their application at low to medium scale DC microgrids.