Modeling and Implementation of a Wave Energy Converter Emulator for Testing Multiport Power Electronic Converters in Marine DC Microgrid Applications

Wave energy converters (WECs) hold tremendous promise for ocean wave energy integration into marine DC microgrids. However, practical experimentation poses challenges due to limited accessibility to actual WECs. Developing WEC emulators becomes imperative to overcome this obstacle, providing a reliable testbed for comprehensive investigations into WEC characteristics within the context of DC microgrid system design and optimization. This research focuses on modeling, control, and experimental validation of motor-generator coupling WEC emulators, emphasizing their integration in marine DC microgrids by means of a power electronic multi-port converter (MPC).

The WEC emulator is designed to accurately replicate the torque-speed behavior of real WECs when driven by ocean waves. The generator is effectively rotated through a shaft coupling by replacing the traditional paddles and shaft with an electronic drive and an Induction Motor. The dynamic behavior of the WEC system is evaluated using a digital signal processor (DSP) that enables the computation of the driving torque exerted on the generator by the WEC. A practical sea wave input is utilized to simulate real-world ocean waves, thereby exciting the WEC model during computation. The motor transforms the computed reference torque into physical torque, propelling the generator and generating three-phase AC power with variable voltage and frequency.

To ensure efficient power processing and integration into marine DC microgrids, the three-phase AC output of the generator is subjected to processing using a power scaled-down 5-kW multi-port converter (MPC) prototype developed in our laboratory. This MPC manages the power and facilitates its injection into the marine DC microgrid. The integration of the marine DC microgrid is particularly crucial as it addresses the energy needs of coastal communities that can significantly benefit from using wave energy. Therefore, proper testing and prototyping of these MPCs is important before wide deployment in DC microgrids. This is facilitated by the proposed WEC emulator testbed. Furthermore, multiple MPCs can be paralleled to boost power processing capabilities, allowing for the harnessing of larger amounts of ocean wave energy. This paralleled MPC configuration collectively converts the generated power and feeds it into the DC microgrid and can also be tested and validated through the proposed WEC emulator testbed.

In this paper, we present the modeling, design, and implementation of the WEC emulator. After verifying the WEC emulator output, it is used to test a modular 5-kW power electronic MPC that can harness the WEC output. With this WEC emulator, wave energy capacity model will also be incorporated. The paper will then highlight the industrial applications of the proposed WEC emulator testbed in controlling and testing power electronic units before deployment in marine DC microgrids.