This paper presents a four terminal bipolar DC grid demonstrator, composed of two VSCs and two DC/DC converters in a loop topological structure. The wind and photovoltaic power generations together with battery energy storage are connected with the DC grid through three converters respectively, in order to demonstrate the control flexibility of the grid-connected fluctuated renewables and its shaving using energy storage. The DC grid demonstration system is built in the laboratory environment with homothetic design in terms of the actual HVDC project data, and the corresponding coordinated control strategies on system voltage and power are studied. A SCADA system to monitor and control the DC grid is designed and developed. A series of operational and control scenarios of the DC grid are studied and verified, such as the start-up and shutdown of the DC grid, multi-sources hybrid-operation, shaving power fluctuations, wind generation shutdown and single-polar failure, etc. Those scenarios are also compared with the results obtained from the MATLAB/Simulink software simulations.