Smart Microgrid Protection System (SMPS)

At the end of the 19th century, AC power systems started to be widely used in the power dis tribution system by replacing the DC. The main reason behind these changes was that the AC could be more easily transmitted over a long distance and easily transformed into different voltage levels. However, increasing global warming, ageing of current power system infrastruc tures, increased awareness of limited energy generation resources, higher energy consumption standards, persuaded the scientific community to modernize the conventional power system. In addition to these, advancements in the field of semiconductor and power electronics con verter technology also motivates to modernize the distribution system. To manage our future energy demands, a more configurable, flexible, informative energy system is needed. Due to this point of view, microgrids are emerging and becoming more attractive structures with the integration of renewable-based distributed generation (DG) units and energy storage systems (ESSs). In India, still, more than 50 percent of total energy generation comes from coal-based energy resources. Therefore, more penetration of renewable energy is required to reduce the climate change impacts of power generation.

The energy resources such as photovoltaic panels and fuel cells produce DC power and they can be easily connected to a DC distribution system directly or through a DC-DC converter. Us ing a DC distribution system, it is easier to incorporate more local energy storage and sources. To connect anenergy source to aDCsystemonlythevoltagehastobecontrolled, as compared to the AC system where voltage magnitude, frequency, and phase must be matched.

The practical implementation of the LVDC microgrid distribution system is quite challenging. The major challenges are the lack of effective protection solutions that keep the AC-DC sys tems safe and reliable. DC faults are more difficult to detect and clear; their associated arcs lack zero crossing points and are more dangerous than in AC, and thus require a longer time to be cleared. Additionally, it is challenging to implement protection selectivity due to the compar atively low resistance and inductance in cables. Thus, the protection of an LVDC distribution system differs from the conventional AC distribution system. In addition, LVDC distribution sys tem has more fault situations compared to the conventional distribution system. Therefore, a protection system designed for the conventional system may not protect the LVDC distribution system fully. Researchers have addressed several problems like design of solid state circuit breakers for the interruption of DC faults, converter based fault protection, fault current limiter circuits for protection of converter switches, etc. But still there is a lack of effective protection solutions. Therefore, in depth research is required for the practical implementation of LVDC distribution system.

The researchers have analysed the fault characteristics of asymmetrical faults on the AC side of the converter. They have also analysed the characteristics of the single pole to the ground as well as pole-to-pole faults. But the effects of AC side faults on the DC side has not been discussed much. Similarly, the effect of DC side faults on the AC side converters has very few analysis. Without considering these effects, protection systems may fail to operate appro priately in a hybrid grid system created by meshed DC and AC systems. For exploring these aspects, smart electricity systems and technologies laboratory under center for energy, AIT provided the facility of HIL environments for real-time simulation under Erigrid 2.0 project. By using typhoon HIL 604 setup, the short-circuit behaviours of AC and DC sides of the converters has been explored. Moreover, the effects of short circuit fault on the AC side of the converter to the DC side of the converter has also been explored. Grid connected converters are simulated under a real-time environment to achieve the following goals:

1. To extract real-time data for different AC and DC faults in the hybrid microgrid.
2. To design better protection system that consider the effect of AC side faults on the DC side of the converter and vice-versa in the hybrid microgrid system.
3. To develop an advanced protection algorithm for fast and selective protection of faults for an LVDC distribution system

Preliminary findings

1. Faults occurred in AC side of the converter affects the DC side converter’s voltage and current. The simulations result show that if an asymmetrical fault occurs in AC side of the converter, negative sequence components will appear in AC side voltages and currents. The negative sequence components will not only change the ac side voltages, but also cause the second harmonics components of voltage and current in DC side.
2. The effect of DC side short circuit faults on the AC side of converter are considered. The simulation results show that DC faults have similar characteristics as symmetrical ac short circuit faults.
3. The DC side faults cannot be detected by AC side protection system unless it is a low impedance fault.

Open threads

1. Test performed to emulate hybrid distribution system does not contain several renewable based distributed generation units, energy storing elements, and different natures of loads due to low processing power of HIL 604