The Chinese government has set long-term carbon neutrality and renewable energy (RE) development goals for the power sector. Despite a precipitous decline in the costs of RE technologies, the external costs of renewable intermittency and the massive investments in new RE capacities would increase electricity costs. Here, we develop a power system expansion model to comprehensively evaluate changes in the electricity supply costs over a 30-year transition to carbon neutrality. RE supply curves, operating security constraints, and the characteristics of various generation units are modelled in detail to assess the cost variations accurately. According to our results, approximately 5.8 TW of wind and solar photovoltaic capacity would be required to achieve carbon neutrality in the power system by 2050. The electricity supply costs would increase by 9.6 CNY¢/kWh. The major cost shift would result from the substantial investments in RE capacities, flexible generation resources, and network expansion.

The interdependence of different energy forms in multiple energy systems (MESs) could leverage their synergies to reduce carbon emissions. However, such synergies cannot be exploited without the right incentives. This paper studies the low-carbon operation of MESs by coordinating the transmission-level and distribution-level via the energy-carbon integrated prices. Energy prices are decided by locational marginal pricing principles in transmission-level MES. At the same time, the carbon emissions of different energy systems are uniformly priced using a carbon emission flow (CEF) model based on the consumers’ actual emission contributions by tracing the embedded flow of CO2. Various distribution-level MESs modeled by energy hubs (EHs) are independently operated in response to the variation in the integrated prices. The whole bi-level model formulates an equilibrium problem and is solved iteratively. Case studies based on two MESs at different scales illustrate the effectiveness and benefit of the proposed carbon pricing method in reducing carbon emissions more efficiently than current methods.

Linearized power flow models are of great interest in power system studies such as contingency analyses and reliability assessments, especially for large-scale systems. One of the most popular models-the classical DC power flow model-is widely used and praised for its state independence, robustness, and computational efficiency. Despite its advantages, however, the DC power flow model fails to consider reactive power or bus voltage magnitude. This paper closes this gap by proposing a decoupled linearized power flow (DLPF) model with respect to voltage magnitude and phase angle. The model is state independent but is distinguished by its high accuracy in voltage magnitude. Moreover, this paper presents an in-depth analysis of the DLPF model with the purpose of accelerating its computation speed, leading to the fast DLPF (FDLPF) model. The approximation that is applied to obtain the FDLPF model from the DLPF model is justified by a theoretical derivation and numerical tests. The proposed methods are provably accurate and robust for several cases, including radial distribution systems, meshed large-scale transmission systems and ill-conditioned systems. Finally, expressions for sensitivity with regard to MW flow and bus voltage are provided as a potential application.

Multiple energy systems (MES) bring different types of energy together and are able to improve the energy utilization efficiency and promote the integration of renewable energy. The embedded carbon emission in MES is coupled among the energy flow across different energy systems. The understanding of how the embedded carbon emission should be allocated along with the energy delivery and conversion is significant in the policy making and market design to facilitate the carbon emission reduction. A novel analytical model for carbon emission flow (CEF) in MES is proposed in this paper to quantify the carbon emission associated with the energy delivery and conversion process. First, key indicators and basic principles of CEF are defined. Then, the explicit CEF models for different energy networks, including the power network, gas network and heating network, are established. On the basis of the CEF models of energy converters, the CEF model for an energy hub (EH) is further formulated to analyze the flow of carbon emission across different energy systems during the conversion process. Finally, the procedure of CEF calculation in MES is provided. The case study results based on two systems are presented to verify the effectiveness of the proposed method.

The power system inertia is gradually decreasing with the growing share of variable renewable energy (VRE). This may jeopardize the frequency dynamics and challenges the secure operation of power systems. In this paper, the concept of frequency security margin is proposed to quantify the system frequency regulation ability under contingency. It is defined as the maximum power imbalance that the system can tolerate while keeping frequency within the tolerable frequency range. A frequency constrained unit commitment (FCUC) model considering frequency security margin is proposed. Firstly, the analytical formulation of system frequency nadir is derived while considering both the frequency regulation characteristics of the thermal generators and the frequency support from VRE plants. Then, the frequency security margin is analytically formulated and piecewise linearized. A novel FCUC model is proposed by incorporating linear frequency security constraints into the traditional unit commitment model. Case studies on a modified IEEE RTS-79 system and HRP-38 system are provided to verify the effectiveness of the proposed FCUC model. The impacts of VRE penetration on system frequency security are analyzed using frequency security margin.