ABSTRACT High renewable penetration and stringent decarbonisation targets are reshaping power system planning. Although carbon pricing and emission constraints are widely adopted, most existing planning models represent carbon incentives in a mechanism‐specific or reduced‐form manner, making policy comparisons inconsistent and obscuring how cooperation and controllable transfers respond under different carbon designs. This paper develops a mechanism‐switchable carbon policy representation under unified emission accounting, enabling consistent comparisons across major carbon policies. An integrated planning–operation co‐optimisation model is formulated to capture generation and network expansion, controllable interarea transfers, storage and demand‐side flexibility and chronological operational constraints. Interarea cooperation is modelled explicitly through reserve procurement, mutual‐aid costs and coordination frictions, allowing the marginal value of cooperation to be quantified in a policy‐consistent way. A multi‐cut L‐shaped Benders decomposition ensures computational tractability. Case studies on an IEEE 118‐bus three‐area system show that a moderate carbon tax reduces emissions by 45.7% mainly via photovoltaic expansion, whereas deep decarbonisation requires a diversified portfolio and stronger interarea deliverability, revealing a policy‐dependent role of controllable flows.
Cui et al. (2026) studied this question.