RT22 | Investigation of Ripple Currents in DC Ship Systems with Power Hardware-in-the-Loop

The design of a sustainable energy systems for ships is becoming increasingly important and politically relevant as the climate crisis intensifies. An electrical power system based on direct current (DC) is seen as having great potential for increasing energy efficiency and promoting the decentralized integration of alternative energy supply concepts such as fuel cells, photovoltaic systems or battery storage systems. These DC components can be integrated into DC grids without the conversion to alternating current (AC), which reduces the losses and increases the system efficiency. When loYesing into DC grid technologies, converters with high-speed switching are used to perform voltage transformation and three-phase sine wave generation. This fast-switching behavior not only results in imperfect DC voltages, but also introduces the so-called ripple currents to the system. Due to the large amount of DC/DC converters for grid segment coupling and DC/AC converters for the connection of conventional loads on ships, a huge amount of ripple will be found on DC ships. These ripples in voltage and current might lead to a violation of the safe operation range for consumers, or in the worst case, to oscillations in power flow and control logic and therefore result in partial or total system failure. By using Power Hardware-in-the-Loop (PHiL), the impact of these ripple currents on DC systems should be investigated in a safe environment with as much flexibility as possible. For this, a stable interface between the hardware-under-test (HUT) and the real-time system is a basic requirement, which must be re-evaluated continuously due to occurring delay times between the components as well as varying HUT parameters. Additionally, the system must be stable within the whole bandwidth of the amplifier which requires special considerations when selecting an interface algorithm. This presentation gives a brief overview of the current state of research regarding an interface algorithm which uses online impedance measurement of the HUT as well as the simulated grid. The information of the impedance measurement is taken to identify unstable regions and perform a frequency filtering algorithm to overcome these instabilities for the whole PHiL System bandwidth. Additionally, a short insight in the project ‘Sustainable DC Systems’ (SuSy) is provided and future applications for the stable PHiL simulations are shown.