Modeling and control of HVDC grids: A key challenge for the future power system

Abstract

HVDC technology is developing fast and HVDC grids are increasingly seen as a possible and feasible solution to manage the future power system with large amounts of renewables in a secure and cost-effective manner. However, systems with significant amounts of DC transmission behave in a fundamentally different manner when compared to the traditional AC power system. The integration of HVDC systems introduces new fast dynamics on different time frames and adds controllability to the combined system. As a result, the modeling and control of the entire interconnected system needs to be reevaluated in order to accurately compute the system behavior, both from the AC and DC system. This survey paper gives an overview of the current research in the field of HVDC grids focusing on the interaction of the AC and DC system. The converters and their behavior are discussed in greater detail. A second component which is discussed is the DC breaker. Both devices operate fundamentally different than their AC counterparts. The fast interaction between AC and DC systems requires changes in the manner in which the modeling and computation of the system is done, both at the DC and the AC side. Although these considerations are needed within all relevant time frames, two relevant cases are specifically addressed in this paper: the connection of offshore wind power through a HVDC system and the optimal operation of the power system with a strong presence of HVDC.

Improved Accuracy Average Value Models of Modular Multilevel Converters

“…For the SAVM, the internal AC converter voltages are scaled by instantaneous DC voltage measurement as described by (3). However, the instantaneous DC voltage does not impact on the internal AC converter voltages for a HB-MMC providing that the following two conditions are met: 1) the arm voltages for the MMC change instantaneously with variations in the DC voltage and 2) the internal converter voltage reference is between the positive and negative pole to ground voltages, V pg and V ng , since the arm voltages are normally limited to the DC link voltage.…”

“…Today, the main HVDC manufacturers offer a VSC-HVDC solution which is based on MMC technology. Accurate and computational efficient models are therefore necessary for the development and understanding of these transmission systems [1][2][3].…”

The Effect of FRT Behavior of VSC-HVDC-Connected Offshore Wind Power Plants on AC/DC System Dynamics

“…All submarine cables are modeled according to their π-equivalent. All simulations are carried out with PSS R E using the VSC-MTDC model developed in [12], [22], complemented with multi-rate improvements for the MTDC model in order to achieve workable simulation speeds [25], [26].…”

Modular modelling of combined AC and DC systems in dynamic simulations

“…The latter can be modeled in detail or replaced by a single, isolated AC bus if the generators are lumped into one equivalent. In the future, the need for dynamic simulation of combined AC and DC systems will keep increasing [5]. For instance, HVDC systems are expected to take a greater part in frequency and voltage control [6].…”