Modular Power Flow Analysis

The widespread deployment of distributed energy resources, including volatile renewable generation, necessitates detailed distribution network analysis. However, in many cases, the vast system size renders the joint analysis of multiple voltage levels computationally impracticable. Due to the scalability limitations of conventional power flow analysis, most studies focus on individual or selected voltage levels, representing subordinate system portions through static load models.

The parameters of these load models are typically identified using simplified aggregation methods that do not account for intermediate network effects, such as losses and spatial voltage variations. This approach involves inaccuracies and does not allow for validating compliance with the voltage and current limits inside subordinate system parts that are not explicitly represented in the model.

Challenges in Conventional Power Flow Methods

The conventional approach to power flow analysis of extensive distribution grids has several critical limitations:

• The validation of limit compliance: Conventional static load models do not facilitate the verification of voltage and current limit compliance within the system parts they represent. For example, in a medium-voltage-level study, compliance within the low-voltage level cannot be validated if low-voltage subsystems are not explicitly modeled but merely represented by static load models.

• Inaccuracy in load model parametrization: The parameters of conventional static load models are usually identified through simplified aggregation methods that neglect effects such as losses and spatial voltage variations. Depending on system characteristics, this can lead to significant inaccuracies, particularly when voltage-dependent elements, such as Volt/var-controlled photovoltaic inverters, are present.

• Redundant computational effort in repeated simulations: Many studies require multiple simulations of the same distribution system while varying only a limited set of parameters. This applies to n-1 security analysis (where a single element is taken out of service), static voltage stability analysis (where active or reactive power injections at specific nodes are incremented), and control parameterization studies (where controller parameters are varied). The conventional approach recalculates the entire studied system part for each simulation run, even when certain subsystems remain unchanged, leading to unnecessary computational overhead.

The Modular Power Flow Analysis method facilitates the separate investigation of different system portions without introducing significant inaccuracies.

Dr. Daniel-Leon Schultis

How the Modular Approach Power Flow Analysis Works

The Modular Power Flow Analysis splits the distribution system into hierarchical levels (e.g. high, medium, and low-voltage) and further subdivides each level into discrete modules that are separately analysed. It starts with the lowest level and aggregates each corresponding module by a series of power flow simulations. These simulations identify the voltage limits to be respected by the superordinate module to ensure limit compliance within the aggregated system part, as well as the voltage-dependent power exchanges between the modules.

The results of the lowest level are used to parametrise an Extended Static Load Model – which includes voltage limits to be respected at its connection node – allowing for the aggregation of the next-level modules. This procedure can be repeated multiple times, enabling the systematic aggregation of large system portions as needed.

Solutions Offered by the Modular Approach

The Modular Power Flow Analysis method facilitates the separate investigation of different system portions without introducing significant inaccuracies. This enables precise, systematic, and computationally efficient power flow analysis while ensuring voltage and current limit compliance across extensive distribution networks.

• Accurate Computation of Power Flows: The modular approach allows for the separate simulation of different system parts, maintaining accuracy even if voltage-dependent elements such as Volt/var controlled PV inverters are present.

• Validation of Compliance with Actual Limits: Unlike conventional methods, which often assume conservative voltage limits at the medium-voltage level to account for low-voltage uncertainty, the modular approach enables systematic validation of compliance with actual voltage and current limits across the entire distribution network.

• Systematisation of Power Flow Studies: The modular approach significantly reduces computational overhead in studies requiring repeated power flow simulations under varying conditions, such as n-1 security analysis, static voltage stability assessment, network reinforcement planning, and control parameterization studies. By aggregating system parts that remain unchanged, the approach isolates the sections subject to parameter variations, allowing for multiple simulations without redundant recalculations.

• Enhanced Computational Performance: The modular method enables the separate analysis of distinct system modules and comprehensive parallelization of computations, ensuring scalability. Additionally, users can tailor module sizes according to specific memory constraints, optimising computational efficiency.

Working with this Modular Approach?

At Magnus Energy, we have successfully integrated the Modular Power Flow Approach into our Python-based toolbox for power system simulation, optimization, and analysis. This allows us to conduct precise analyses of extensive distribution grids, also in the presence of voltage-dependent controls.

Please get in touch with Daniel-Leon Schultis to talk about your needs and our solutions.