# Development of Energy Storage Systems for High Penetration of Renewable Energy Grids
## 1 Introduction  
As the penetration of renewable energy generation systems in power systems gradually increases, it has both positive and negative impacts on power systems. The positive impacts of renewable energy generation systems on power systems include reducing carbon emissions, reducing dependence on imported energy price volatility, and so on. The global focus on decarbonization has elevated it to a crucial policy objective, stimulating the growth of renewable energy in various countries [1]. In addition, renewable energy generation systems can be integrated into power systems in each region and use their generation in that region, which can reduce energy loss during long-distance transmission. However, high penetration of renewable energy also brings new challenges, becoming a new issue facing power systems. If the converter equipment does not provide a virtual inertia function, the renewable energy generation system cannot provide inertia to the power system [2]. Reference [3] discusses various inertia emulation and frequency control techniques for grid-connected wind energy conversion systems. Reference [4] discusses wind and solar generation plants and their contributions to inertia in terms of frequency control strategies. In the future, power systems need to be planned and operated in different ways to maintain a certain level of reliability. In the past, power systems were composed of thermal generators, hydropower generators, diesel generators, and a small number of solarand wind power generation systems, many of which are based on large rotating machines that are of high inertia. In the future, power systems will be composed of a majority of solar and wind power generation systems, a small number of traditional generators, and battery energy storage systems which are mainly inverter-based resources and which have low inertia. Currently, renewable energy in Taiwan is dominated by solar and wind energy which are both affected by factors such as the time and season. Solar and wind power generation is intermittent, uncontrollable, and gives large short-term output fluctuations, which have a negative impact on the power system [5; 6]. According to the above, future power systems with a large number of inverter-based resources have the following problems compared to traditional power systems: reduced system inertia, weakened frequency regulation capability, weakened regional reactive power regulation capability [7], and increased requirements for the rise/fall active power speed of traditional units. Renewable energy can also be applied in the islanding operation and fault recovery strategy of a distribution network [8]. Battery energy storage systems can be derived from many auxiliary services according to different control strategies, such as frequency regulation reserve, peak shaving and valley filling, smoothing of solar output power, load dispatch, islanding operation, reactive power compensation, and virtual inertia provision. In [9], by operating the battery energy storage system and implementing an adaptive primary frequency control strategy, the system frequency is adjusted by flexibly and rapidly controlling the charge and discharge capabilities of the battery energy storage system. An integrated control approach combines decentralized and cluster-based load control in [PERSON] et al. [10], which uses a battery energy storage system to determine the activation and deactivation of flexible load clusters based on frequency measurements. Reference [11] studies the smoothing quality of the solar output power with the help of battery energy storage system, using a couple of approaches, such as low pass filtering (LPF), moving average (MA) filtering, the Gaussian filter (GF) and the Saviztky-Golay (S-G) filter. Reference [12] introduces a technical approach for employing the battery energy storage system to achieve load balancing and reactive power compensation within distribution grids.