The Power Quality and Stability Improvement of Wind Power Plant Connected with Medium Voltage Distribution Network

Abstract

Thailand has continuously increased its installation of wind power plants, as the country has the potential for good wind energy, especially in the southern and north-eastern regions. Additionally, the support from the Ministry of Energy has led to an increase in the installation of wind power generation systems in accordance with the Alternative Energy Development Plan. However, the wind power generation system has limitations in terms of installation space, particularly for large-scale wind power plants that are connected to the distribution system. In Thailand, wind power plants are installed in remote areas such as mountains or coastal regions because of the potential for good wind energy and the relatively low demand for electricity. Consequently, when wind power plants operate, there will be a significant amount of electricity injected into the distribution system, causing problems with power quality such as overvoltage, voltage fluctuations, and voltage dips, resulting in feeder trips and plant shutdowns. These power quality issues have a significant impact on electricity consumers in the affected feeders, particularly if there are factories, shops, or important government facilities in the area. Frequent power outages can cause public dissatisfaction, damage to electrical equipment, and other problems. According to the literature review, integration of energy storage systems (ESS) with high-variability wind power plants can significantly improve system stability, maintain power quality, and enable the management and scheduling of power output. because ESS can perform several functions, such as power quality and UPS, bridging power, and energy management.

In this study, an operational 8 MW wind farm (Nakhon Ratchasima province) faces severe annual feeder trips of 146 times, which is not permissible according to the manufacturers. The feeder trips are mostly attributed to the high grid voltage caused by the low load demand. The Battery Energy Storage System (BESS) is developed to minimize the feeder trip using DigSILENT. The simulation results conclude that the optimal value for a 5 MWh BESS and the State of Charge (SOC) value were set to be between 20% and 100%. The energy storage system could charge and discharge to adjust the voltage in the Provincial Electricity Authority distribution system throughout the day, demonstrating zero feeder trips. To ensure stable wind farm operation, the BESS is capable of supplying voltage to the grid without any feeder trips. The energy storage system can maintain and improve the power quality in the distribution system. It can manage the electricity generated by the wind turbines and keep the voltage in the distribution system within the standard specified by the Provincial Electricity Authority. When the data is analyzed, it is found that the wind power plant can generate 2.41% more electricity without the energy storage system.

We conducted an economic analysis of a 5 MWh energy storage system in conjunction with an 8 MW wind power plant. The results showed that the payback period would be shorter and the return on investment would be higher if the cost of the energy storage system was lower. The installation of the energy storage system increased the wind power plant's revenue by 2,825,000 THB per year, bringing the Internal Rate of Return (IRR) to 7.76% for the original wind power plant and 9.03% for the wind power plant with the energy storage system. We found that the wind power plant with the energy storage system had a shorter payback period (PB) due to its increased revenue, which helped the plant operate at full efficiency and significantly reduced plant trips. However, we conducted a sensitivity analysis to determine the appropriate price for the integration of the energy storage system into the system. The findings indicated that the optimal investment cost ratio for energy storage systems is about 67%, equivalent to 10,000 THB/kWh. Implementing this strategy would lead to a payback time of under 10 years and raise the internal rate of return (IRR) to 14.54%, resulting in a benefit-cost ratio (BCR) of 1.45.

The study found that the BESS alone did not provide the economic benefits. Integrating with a wind farm boosts energy generation and reduces the feeder trip period, thereby improving the BESS's return on investment. Installation of an energy storage system can solve tripping problems, improve power quality, increase wind power plant efficiency, and enhance power stability. It can also act as a backup system, providing backup power during power outages and adjusting voltage and reactive power. This reduces maintenance and management costs, reduces wind turbine damage risk, and increases electricity generation efficiency.

-