Generating abundant, renewable energy from Earth's oceans is an attractive option for meeting increasing energy demand. Marine renewable energy, like wind and solar, is variable, which impacts the power quality of the electrical grid with phenomena such as flicker. Flicker refers to the visual change in brightness of an electrical lighting source observed by the human eye due to fluctuations in voltage. Standards such as IEC 61000-45-15 and IEEE 1547 outline methods to measure and quantify flicker. In addition, the IEC 62000-30 standard gives specific guidelines for measuring the flicker output of marine renewable energy.
Analysis of flicker from marine energy sources such as wave energy converters (WECs) is often based on models of both WECs and the electrical grid. Harsh ocean conditions combined with wave resonance effects that require full-scale prototypes make grid-connected WEC prototypes complex and expensive. Both simulated and scaled physical models present limitations for applying findings to full-scale grid-connected testing. Real-time hybrid simulation looks to ease these issues by splitting testing into a computer-based numerical model and a connected physical system, using appropriate testing techniques for each portion.
The hybrid simulation idea originates in the field of seismic-resistant civil engineering but has been applied to marine renewable energy already. Previous research has shown hybrid simulation to work with WEC testing of complex wave fluid dynamics and power takeoff (PTO) as well as numerical modeling of a WEC with a physical directly grid connected generator. This work looks to expand the hybrid modeling of WEC interconnection by including simple control of the generator representing the physical PTO and measuring the flicker output of the hybrid simulated WEC.
The real-time hybrid simulation testbed is housed in Oregon State University’s Wallace Energy Systems and Renewables Facility (WESRF) and consists of two mechanically coupled electrical machines each with electrical drives, a low-voltage grid connection, and a Speedgoat real-time target machine for simulation of WEC models. A simulation, implemented in Simulink, models the effect of waves on the PTO device. An induction motor acts as the physical PTO generator, with the simulation controlling the torque output of a second mechanically connected motor. A motor drive controls the PTO generator and allows for various control schemes which are implemented through Simulink logic on the real-time target machine. This setup allows flexibility for researchers to test multiple types of WECs as well as multiple control schemes. Since the PTO of the hybrid simulated WEC is connected to an electrical grid, researchers can measure the electrical output of the PTO generator.
This work presents an application of a WEC hybrid simulation to measuring the flicker based on current standards. It looks to verify the application of flicker standards to WECs as well as present flicker results from select WEC topologies.