Maximum-Receiving-Capability Assessment of a Receiving-End Urban Power Grid Incorporating MMC-MTEDC

Against the backdrop of the transition toward power systems with high shares of renewable energy and power electronics and the rapid growth of urban load, large receiving-end urban grids are fed by multiple line-commutated-converter HVDC (LCC-HVDC) links, so that their maximum receiving capability is frequently limited by the static-voltage-stability margin. To assess the receiving capability of such large urban grids, this paper proposes a method for evaluating the maximum receiving capability of a receiving-end urban grid that incorporates a Modular-Multilevel-Converter-based multi-terminal embedded DC (MMC-MTEDC) system. First, a quasi-steady-state model of the receiving-end urban grid with LCC infeed and an embedded MMC-MTEDC system, in which the DC-network equations characterize the mutual coupling among the AC active-power injections of the receiving-end converter stations, is established. Second, an augmented extended Jacobian that incorporates the MMC control equations and the DC power-flow equations is constructed; its minimum singular value is adopted as the static-voltage-stability index, and the corresponding sensitivities are derived to reveal the mechanism by which the receiving capability is formed. On this basis, a unit-commitment optimization model that centers on the stability-margin constraint and accounts for the converter-capability curve, the bus-voltage limits, and the line-loading limits is built; the model is solved iteratively by a column-and-constraint-generation (CCG) method, and the feasibility of the unit commitment is used to estimate the maximum receiving capability. A modified IEEE 39-bus system is used as a case study, which quantitatively verifies the effectiveness of the MMC-MTEDC in enhancing the receiving capability of the receiving-end urban grid.