Abstract
Medium voltage DC (MVDC) networks are attracting more attention amid increased renewables penetration. The reliability of these DC systems is critical, especially following grid contingencies to maintain critical loads supply and provide ancillary services, such as black-start. This paper proposes an innovative energy management system (EMS) to maintain reliable MVDC network operation under prolonged AC grid contingencies. Similar EMS designs in literature tend to focus on limited operating modes and fall short of covering comprehensive elongated blackout considerations. The proposed EMS in this paper aims to preserve the distribution network functionality of the impacted MVDC system through maintaining a constant DC bus voltage, maximizing critical load supply duration, and maintaining the MVDC system black-start readiness. These objectives are achieved through controlling generation units between Maximum Power Point Tracking (MPPT) and Voltage Regulation (VR) modes, and implementing a smart load shedding and restoration algorithm based on network parameters feedback, such as storage State of Change (SoC) and available resources. Practical design considerations for MVDC network participation in AC network black start, and the following grid synchronization steps are presented and tested as part of the EMS. The proposed system is validated through simulations and scaled lab setup experimental scenarios.
Highlights
The share of electricity generation from renewable energy sources (RES) is soaring on a global scale due to their maturing technology and rapidly falling costs
An increasingly attractive trend is emerging to establish intermediate collecting medium voltage DC (MVDC) distribution networks that integrate the output from various renewables, such as PV and offshore wind farms [3,4,5]
Key industrial manufacturers are proposing the use of MVDC solutions in distribution networks, such as the MVDC Plus technology from Siemens [6]
Summary
The share of electricity generation from renewable energy sources (RES) is soaring on a global scale due to their maturing technology and rapidly falling costs. A recent example of such implementation in 2018 is for MVDC converters connecting distributed generation and load centers in the UK [7] Another example for MVDC applications is the Angle-DC project, which aims to convert distribution MVAC lines operation to MVDC to increase power transfer limit and improve controllability [8,9]. (a) Connecting dump loads at the DC bus to absorb the excess power [12]: this approach requires installing expensive variable controllable loads that track the power output from the RES to attain voltage stability, making it a complex and expensive option. This partial load shedding should be proportional to the power shortage to maintain a constant DC voltage
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