Simulation Of Distribution Grids Research Articles

Continuous Time Simulation and System-Level Model of a MVDC Distribution Grid Including SST and MMC-Based AFE

Medium-voltage DC (MVDC) technology has gained increasing attention in recent years. Power electronics devices dominate these grids. Accurate simulation of such a grid, with detailed models of switching semiconductors, can quickly became very time-consuming, according to the number of connected devices to be simulated. A simulation approach based on interactions on a continuous time model can be very interesting, especially for developing a system-level control model of such a modern MVDC distribution grid. The aim of this paper is to present all the steps required for obtaining a continuous time modelling of a +/−10 kV MVDC grid case study, including a solid-state transformer (SST)- and modular multilevel converter (MMC)-based active front end (AFE). An additional aim of this paper is to supply educational content about the use of the continuous time simulation approach, thanks to a detailed description of the various devices modelled into the presented MVDC grid. The results of a certain number of simulation scenarios are eventually presented.

Validation framework for integration of hydrogen-based technologies in electric distribution grid

This paper describes the development of a framework for testing the integration of heat pumps and hydrogen-based components (HBC) for instance combined heat and power (CHP) systems in a low voltage distribution grid. The proposed power hardware-in-the-loop framework is viable for demonstration of grid and subsequently component response. The structure for such a cyber physical system is presented along with the preliminary distribution grid simulation results. The study emphasizes the contribution of power hardware-in-the-loop application for validation, inclusion and characterization of HBC in addition to other active grid participants in the energy system.

Mitigating the impact of fast charging on distribution grids using vehicle‐to‐vehicle power transfer: A Paris city case study

AbstractThe deployment of DC fast charging stations (DCFCSs) in cities requires costly reinforcement of low‐voltage (LV) distribution grids, due to the high power required. It results in high investments for the station operator as well as for the distribution system operator and limits the profitability of such projects. In this study, a novel concept of fast charging station which reduces the connection to the grid is presented. This station uses Vehicle‐to‐vehicle (V2V) power transfer from a fleet of carsharing electric vehicles to provide a high charging power while mitigating the power demand on the grid. Based on data from a carsharing operator in the city of Paris, a simulation model of a combined carsharing/V2V fast charging system is proposed, allowing to simulate carsharing trips and V2V transfers. The reduction of the grid connections required to provide fast charging is evaluated and the impact of the repeated discharges on the level of service of the carsharing system is discussed. Moreover, simulation of LV distribution grids allows to compare the grid losses of the V2V system with conventional DCFCSs.

Coordinated scheme for expansion planning of transmission system with active distribution system flexibility provision

The extensive access of distributed renewable energy at the level of distribution network makes the distribution grid have the ability of active regulation similar to the transmission grid, and the power exchange between transmission and distribution systems becomes more flexible bidirectional. In order to make full use of the complementary collaboration ability between the distribution and transmission systems, this paper proposes a flexible planning method of transmission system coordinated with distribution system for the future scene of high proportion renewable energy. This collaborative optimization framework is a double-layer structure: The upper layer goes on the expansion planning of transmission system, and the lower layer goes on the operation simulation of distribution grid. The upper-level model transfers the marginal price of nodes to the lower-level model, and the lower-level model feeds back the purchase and sale agreement to the upper model. The linear transformation of the model is deployed using piecewise linearization and big-M method. We use the strong duality theory to transform the original double problem into an equivalent single-layer form, and then the effective solution of the commercial application is realized. Aiming at the high proportion renewable energy in transmission and distribution systems, the performance of the formulated problem is validated by comparative analyses of examples.

Experimental verification of smart grid control functions on international grids using a real‐time simulator

The drastic increase in distributed energy resources (DERs) leads to challenges in the operation of distribution systems worldwide. While several solutions for grid monitoring and control are available on the market and in literature, this research is the first of its kind aiming to supervise the grid by providing a modular configurable unified hardware and software architecture. The control algorithms are configured using data models according to IEC 61850-7-3 and IEC 61850-7-4. The novel system architecture is a portable, modular and flexible architecture that aggregates smart grid control functions onto a standardised hardware platform, emphasising the need for hardware independence. The central controller contains several smart grid control functions and the various field devices are distributed across the distribution grid. This paper deals with the simulation of different real-world distribution grids on the Real-Time Simulator (RTS) and experimental verification of the control algorithms. Smart grid control functions such as Coordinated Voltage Control (CVC) and Optimal Power Flow (OPF) are experimentally verified on a German grid. The grid dynamics are compared when the central controller executes the CVC against the OPF implementations. The experimental results, advantages and challenges of each control are presented here. The results also showed the variation in grid behaviour when the control parameters were varied. The paper also shows that the algorithm and the choice of the control parameters depend upon the distribution grid's complexity and the system operator's individual needs. The results illustrate the potential of such a universal distribution automation solution for system operators worldwide.

Реконфигурация распределительных электрических сетей

Optimizing the grid structure becomes necessary in case of post-emergency power restoration or when overloaded. In normal operation, distribution grid parameters are adjusted to reduce the overload and the electricity losses; reconfiguration is not considered. The grid topology is reconfigurable by solving the optimization problem by the branch-and-bound algorithm subject to keeping the parameters within their acceptable limits in the context of line resistance, electricity losses, and power flows for all possible grid layouts. Simulation of a 10-kV distribution grid with four power centers shows that reconfiguring reduces power consumption by 2.9% and the inline active power losses by 256 kW. In this case study, reconfiguring has helped keep the voltage within the acceptable range while not overloading the lines. This study shows the proposed approach is suitable for dynamic grid reconfiguration as a way to reduce the overload and the electricity losses; at the same time, the approach does not require calculating nonlinear steady-state equations for each possible grid topology.

A Transformerless DSTATCOM Based on Cross-Switched Multilevel Inverter for Grid Voltage Regulation

In this paper, a transformerless distribution static synchronous compensator (DSTATCOM) based on the cross-switched (CS) multilevel inverter (CSMLI) is introduced. In comparison with the well-known cascaded h-bridge (CHB) topology, CS inverter produces higher number of voltage levels using fewer number of power components. Since CS inverter produces ac side voltage with high quality and has the ability to work at high voltage and power levels, the proposed CS-DSTATCOM is directly connected to the distribution grid without the need for a transformer. In the proposed CS-DSTATCOM, all the dc sources are replaced with dc capacitors. In this paper, an effective voltage balancing control scheme is proposed to keep the capacitors voltages balanced in the CS structure. The control scheme balances the capacitors voltages in two levels, i.e., inter-cell and within-cell level. On the other hand, the over-voltage and under-voltage phenomena are of the most common power quality (PQ) issues in distribution grids. The proposed DSTATCOM is able to cope with these issues by exchanging reactive power with the grid. Applying the CSMLI in the DSTATCOM structure as well as the capacitors voltage balancing methods are the main novelties of the paper. Also, the capacitors values are considered to be different (which is unavoidable in practice) while their voltages are balanced using the proposed voltage balancing methods. In this paper, a CS-DSTATCOM has been designed for 11 kV distribution grid and several simulation results are provided in the MATLAB/Simulink environment which validate the feasibility and performance of the proposed CS-DSTATCOM.

Steady-State Simulation for Combined Transmission and Distribution Systems

The future electric grid will consist of significant penetration of renewable and distributed generation that is likely to create a homogenous transmission and distribution (T&D) system, requiring tools that can model and robustly simulate the combined T&D networks. Existing tools use disparate models and formulations for simulation of transmission versus distribution grids and solving for the steady-state solution of the combined T&D networks often lacks convergence robustness and scalability to large systems. In this paper, we show that modeling both the T&D grid elements in terms of currents and voltages using an equivalent circuit framework enables simulation of combined positive sequence networks of the transmission grids with three-phase networks of the distribution grids without loss of generality. We further demonstrate that we can ensure robust convergence for these resulting large-scale complex T&D systems when the circuit simulation methods are applied to them. Our results illustrate robust convergence of combined T&D networks using a direct Newton-Raphson solver on a single machine for smaller sized systems and using a parallel Gauss-Seidel-Newton solver on multiple machines for larger sized systems with greater than million nodes.

Market-Based Multi-Agent Coordination to Manage Energy Balance in Smart Grids

Widespread adoption of sustainable energy sources is driving electricity grid operators to supplement hierarchical control regimes with market-based control that better motivates stakeholder involvement. However, to prevent market failures, such controls require testing before real-world implementation. The Power Trading Agent Competition is a competitive simulation of distribution grids that mirrors real-world scenarios and tests alternative policy and business scenarios. In Power TAC, broker agents acquire energy through bidding in a forward wholesale market to satisfy their customers’ overall demand on an hourly basis. In addition, a balancing market is intended to resolve real-time energy imbalances caused by broker prediction errors using demand response resources. As part of the annual alignment process, we discovered that brokers in the 2015 competition were persistently buying insufficient energy on the wholesale market to satisfy their customer demand. Instead, the balancing market made up the deficit, charging brokers a premium over the wholesale price. Also, demand response resources were heavily underused. We studied the economic impact of this systematic imbalance on brokers and discovered that they were behaving rationally, given the prices they faced in the two markets. We present the process and results of this analysis, and show how the balancing market’s pricing mechanism can be adjusted for the 2016 competition to make it rational for brokers to achieve an overall neutral imbalance.

Control model for distributed generation and network automation for microgrids operation

This paper describes a model for power distribution grid simulation with distributed generation, designed to be a simulation environment of two proposed elements: (1) an algorithm to reconfigure the circuit topology to enable a microgrid during an outage of power supply, and (2) a specific limiter to allow safe operation of distributed generation in the network. Moreover, an interface of the simulation model with a SCADA was designed to suggest possible operational screens for both: the generator and the utility. The simulation model was designed with a synchronous generator with all cogeneration typical controls: speed, active power, voltage, reactive power and power factor. Thus, it is possible to simulate critical situations with all control modes available in a typical cogeneration plant in addition to the proposed limiter. Due to the immense number of possible combinations of circuit breakers in the grid, the proposed algorithm is based on genetic algorithms to enable a fast enough autonomous reconfiguration to avoid the outage perception by the customer.