A Stable Operation Strategy in Micro-grid Systems without Diesel Generators

Abstract

Recently, as one of the countermeasures to reduce carbon dioxide($CO_2$) for global warming problems, operation methods in micro-grid systems replacing diesel generator with renewable energy sources including wind power(WP) and photovoltaic(PV) system have been studied and presented in energetic manners. However, it is reported that some operation problems in micro-grid systems without diesel generator for carbon-free island are being occurred when large scaled WP systems are at start-up. To overcome these problems, this paper proposes an operation strategy in micro-grid systems by adapting control devices such as CVCF(constant voltage constant frequency) ESS(energy storage system) for constant frequency and voltage regulation, load control ESS for balancing demand and supply and SVC(static-var compensator) for reactive power compensation. From the simulation results based on the various operation scenarios, it is confirmed that the proposed operation strategy in micro-grid systems without diesel generators is a useful tool to perform a stable operation in micro-grid systems without diesel generator and also make a contribution to reduce carbon dioxide in micro-grid systems.

Fig. 1. Concept of micro-grid system in Gapa-island

Fig. 2. Operation case in micro-grid system without dieselgenerators

Fig. 3. Concept of novel micro-grid system without dieselgenerator

Fig. 4. Operation strategy for carbon-free island micro-gridsystem

Fig. 5. DFIG WP system modelling

Fig. 6. Modeling of wind power energy

Fig. 7. Modeling of current control in PV system

Fig. 8. Modeling of ESS for load control

Fig. 9. Modeling of CVCF ESS

Fig. 10. Exciter modeling of diesel generator

Fig. 11. Governor modeling of diesel generator

Fig. 12. Modeling of SVC

Fig. 13. Modeling of total system

Fig. 14. Characteristic of active and reactive powers duringstart-up in WP system

Fig. 15. Frequency characteristic during startup in WPsystem

Fig. 16. Voltage and frequency characteristics in micro-grid system with CVCF ESS

Fig. 17. Voltage and frequency characteristics in existingmicro-grid system

Fig. 18. Voltage and frequency characteristic in existingmicro-grid based on CVCF ESS

Fig. 19. Voltage and frequency characteristic by proposedmethod

Table 1. Operation characteristics at start-up of WP system

Table 2. Capacity of each component in micro-grid system

Table 3. Operation strategies of micro-grid system