The paper discusses the main challenges in the grid integration of Battery Energy Storage Systems together with renewable power plants when Hybrid Control at the plant level and the Grid Forming Control at PCS level are utilized. The combination of the BESS with existing or newly built Wind Plants shows that top challenges are related to Grid Code compliance of Hybrid plants at connection point and controllers’ interoperability. This is mainly due to split of control functionalities between Master Plant Control, Slave Control loops and Power Electronic converters with variety of control approaches. In order to control a renewable plant optimally the special approach needs to be applied allowing that Grid forming capabilities are fully present at the Point of connection, especially, in the case of the fast grid events when Frequency Converters (PCS) are acting individually without coordination form Master (hybrid) controller. Beside of the Grid Forming response, the modern Hybrid Plants are expected to be able to operate in island mode and to provide system restoration support. When performing the hybrid plant related studies, the challenge is in realistic representation of the all-hybrid plant components in order to cover a different detailed phenomenon such as latency and the control loops stability. This is typically investigated by Hardware in the Loop that is shown in the paper. The situation gets more complex, when the simulation models and control hardware are provided by several different OEMs. The paper presents an approach where the grid code compliance of the plant components are validated by real time simulation to achieve entire plant control verification. Beside of grid code evaluation, paper presents also another hybrid application where BESS provides an emergency supply to a Wind Park. That means that BESS during the loss of the network supply is providing energy from batteries to perform emergency stop by safe positioning of the wind turbines by yawing and pitching.