Chengdi Ding

Krylov subspace based model reduction method for transient simulation of active distribution grid

With the increasing integration of distributed generation, distribution grids are evolving from passive networks to active grids. The existence of DGs and energy storage devices makes the transient simulation of active distribution grids more meaningful compared with that of traditional distribution grids, but at the same time limits the simulation speed and system scale. This paper presents a passivity-guaranteed model order reduction method based on Krylov subspace theory for active distribution grids. Then simulations are performed using the IEEE 123-node test feeder, proving that the proposed method is feasible as a powerful tool in typical applications of the transient simulation of active distribution grids.

State-space model generation of distribution networks for model order reduction application

Model order reduction has been the research focus for a long time in large system modeling and simulation field and is also of great significance in distribution grid simulations. However the model formulation requirements of many typical MOR (Model Order Reduction) methods restrict their applications in distribution grids. This paper presents an automated state-space model generation method of large-scale distribution networks for MOR application. The formulation requirements of general MOR methods can be well satisfied with this proposed model. It also shows great advantages over the commonly used MNA (Modified Nodal Analysis) formulation in many aspects. Simulations are performed using the benchmark low voltage test case, proving that the proposed method is feasible as a powerful tool in the modeling and simulation of large-scale distribution grids.

Matrix exponential based electromagnetic transients simulation algorithm with Krylov subspace approximation and accurate dense output

The ever-increasing scale of system interconnection and diverse dynamic time constants of power equipment pose challenges to power system electromagnetic transients simulation algorithm. In this paper, an advanced numerical integration method based on matrix exponential operator is proposed. Krylov subspace approximation is utilized to effectively reduce the problem dimension, and an accurate dense output formula is established to enable the method adopting larger simulation step size and revealing higher frequency dynamic details simultaneously. Accuracy, numerical stability and computation efficiency is demonstrated through numerical case studies.

A design of grid-connected PV system for real-time transient simulation based on FPGA

A photovoltaic (PV) system based on FPGA is designed in real-time in this paper. It is partial work of hardware-in-loop simulation of high penetration PV systems. The real-time simulation methods of power electronic devices and control system are introduced. The interaction method of electrical and control system under different time steps is proposed. With the highly parallelism, distributed memory and deep pipelined structure of FPGA, typical control element modules are designed, which leads to the modeling of PV array and its controller. A single-stage PV generation system is simulated in real-time under different time steps. The minimum time step for electrical and control system can reach 1μs and 2μs. The simulation results are compared with PSCAD/EMTDC and RTDS to validate the correctness and effectiveness of the design.

EMTP-type realization of model reduction algorithms for transient simulation of distribution networks

Model reduction is a popular trend in large-scale system simulations. It is also an effective way to improve the efficiency of distribution system simulations. In this paper, the realization of state-space-based model reduction methods in EMTP-type programs is presented. The state-space model of linear time-invariant distribution network is reduced and simulated with the detailed nodal model in EMTP-type programs. The combined state-space nodal analysis algorithm is adopted as the interface between the state-space models and the nodal models. Simulations are performed to show the feasibility and validity of the proposed method, and the improvement in efficiency with the application of model reduction.

A real-time transient simulator of grid-connected photovoltaic/battery system based on FPGA

A grid-connected photovoltaic (PV)/battery simulation system based on FPGA (Field Programmable Gate Array) is designed in real-time in this paper. It provides a simulation platform for hardware-in-loop test of physical devices. The simulation framework is designed and functional modules are introduced. The modeling of PV and battery is realized in a single FPGA chip. A typical PV/battery system is simulated in real time. The time step for electrical and control system is 1.096μs and 1.696μs. The simulation results are compared with PSCAD to validate the correctness and effectiveness of the design.

Adaptive DAE solving algorithm for power system transient simulation via matrix exponential operator

The ever-increasing scale of system interconnection and diverse dynamic time constants of power equipment pose challenges to power system transient simulation algorithms. In this paper, an adaptive numerical integration method for DAE systems based on matrix exponential operator is presented. Krylov subspace technique is utilized to effectively reduce the problem dimension. A novel step adaption scheme is established to enable the method adjusting the computation step size according to error budget while maintaining the output step size unchanged. Acceleration is accomplished without perceived degradation in the simulation results. Numerical performance and computation efficiency is demonstrated through numerical case studies.

An equivalent A-Stable dynamic simulation algorithm of active distribution networks based on the implicit projective method

The dynamic characteristics of active distribution networks (ADNs) need to be concerned if a large number of distributed generators are connected. A highly efficient and reliable simulation algorithm with good numerical stability is therefore essential for the stability analysis of ADNs. This paper proposes a novel dynamic simulation algorithm of ADNs based on the implicit projective method, which is a second order integration algorithm. The proposed method is an equivalent A-Stable method and the calculation efficiency is increased significantly compared with the traditional integration algorithms. It is especially suitable for the dynamic simulation and stability analysis of the ADNs with a large number of DGs. Case studies based on the IEEE 123-node test feeder show the feasibility and effectiveness of the proposed method, which is verified through the comparison with the commercial simulation tool DIgSI-LENT/PowerFactory and the traditional trapezoidal method.

Dynamic time-domain simulation and analysis of medium-low voltage microgrid

Considering different application scenarios and questions to be solved, electromagnetic transient simulation and transient stability simulation are rarely performed simultaneously for the calculation of traditional bulk power system, which are quite different from element modeling to simulation algorithm. But its not true for the analysis and calculation of microgrid and active distribution system. Its a common question for the user to choose a proper simulation tool. Meanwhile, the two simulation results should be consistent with each other intrinsically due to the same physical system. In this paper, the difference and consistency of the two type simulations is set forth in detail. They are applied to a typical microgrid test case respectively using DIgSILENT and Matlab/SimPowerSystems, and detailed comparisons are provided to verify their consistency and difference. Its helpful to understand the various transient processes and make a more reasonable choice for the related research. At the same time, the application guidance for the two type simulations is drawn.