Static Security Risk Assessment for Islanded Hybrid AC/DC Microgrid

Abstract

Due to the lack of the support from the main grid, the islanded hybrid ac/dc microgrid will more likely cause the power flow severe fluctuation and even the microgrid to be split once a serious contingency occurs. To maintain the security and stability of the system under such a condition, this paper proposes a new static security risk assessment of the islanded hybrid ac/dc microgrid considering that the hybrid ac/dc microgrid was split. First, this paper presents a static security analysis criterion to determine the post-contingencies splitting scheme and a new load-shedding strategy to achieve power balance of subsystems. On this basis, a probabilistic power flow calculation method based on Levenberg-Marquardt with a nonmonotone line search (LMNL) algorithm is applied to calculate the probabilistic power flow of the islanded subsystems. Finally, the probability distribution of static security risk assessment indexes, including the dc loss load risk, ac loss load risk, and interlinking converter (ILC) active power limit violation risk, are obtained. The simulation results on the test system demonstrate the necessity of considering the hybrid ac/dc microgrid was split, and prove the feasibility and effectiveness of the proposed method. INDEX TERMS Islanded hybrid ac/dc microgrid, interlinking converter, static security risk assessment, subarea load-shedding strategy, LMNL algorithm.

Static security assessment of power systems: A review

“…From the implementation point of view, the security analysis in a power system can be conducted in online and offline studies. The former module is used in the operation phase of the power system and its results determine the preventive and corrective control policies while the latter is employed in the planning phase of the power system and the results are used for expansion planning studies of the power system 9 …”

“…Security assessment of power systems can be divided into deterministic and probabilistic categories. While the former studies deterministic security criteria, for example, operational limitations of buses, lines, and transformers after an equipment outage such as a line, a generating unit or a transformer, the probabilistic security assessment considers the probability of occurring each contingency and analyses the power system security with a preset level of confidence 9 …”

An Incremental-Variable-Based State Enumeration Method for Power System Operational Risk Assessment Considering Safety Margin

“…k s = {j|j ⊂ s, Card(j) = k} (8) where Card(j) represents the cardinality of the jth contingency state; k s is the k-order contingency state sets and if k = 0, k s = φ; P j is the occurrence probability of the jth contingency state; X i,j is the state variable of the ith component for the jth contingency state, which is calculated according to the following formula:…”

“…In [7], an online branch thermal overload risk assessment method is proposed and the Bayesian time series model is used to simulate the weather conditions of the transmission line. Reference [8] proposed a probabilistic power flow Monte Carlo simulation based on Levenberg-Marquardt with a nonmonotone line search (LMNL) algorithm to calculate risk indices for islanded hybrid AC/DC microgrid. Reference [9] proposed a risk assessment method for large-scale distributed photovoltaic feeding into distribution networks.…”

Multi-Time Scale Optimal Dispatch for AC/DC Distribution Networks Based on a Markov Chain Dynamic Scenario Method and MPC

“…e DC network has better energy quality and longer transmission distance than the AC network. e energy storage system (ESS) and some distributed generation (DG) must be connected to the AC distribution network by a voltage source converter (VSC); if the dc distribution network is used for power supply, a large number of converters will be saved and energy loss will be reduced [9][10][11].…”