An improved Newton-Raphson based linear power flow method for DC grids with dispatchable DGs and ZIP loads

Author(s):  
Hongwei Li ◽  
Xiao Wang ◽  
Junmu Lin ◽  
Lei Wu ◽  
Tong Liu

Purpose This study aims to provide a solution of the power flow calculation for the low-voltage ditrect current power grid. The direct current (DC) power grid is becoming a reliable and economic alternative to millions of residential loads. The power flow (PF) in the DC network has some similarities with the alternative current case, but there are important differences that deserve to be further concerned. Moreover, the dispatchable distributed generators (DGs) in DC network can realize the flexible voltage control based on droop-control or virtual impedance-based methods. Thus, DC PF problems are still required to further study, such as hosting all load types and different DGs. Design/methodology/approach The DC power analysis was explored in this paper, and an improved Newton–Raphson based linear PF method has been proposed. Considering that constant impedance (CR), constant current (CI) and constant power (CP) (ZIP) loads can get close to the practical load level, ZIP load has been merged into the linear PF method. Moreover, DGs are much common and can be easily connected to the DC grid, so V nodes and the dispatchable DG units with droop control have been further taken into account in the proposed method. Findings The performance and advantages of the proposed method are investigated based on the results of the various test systems. The two existing linear models were used to compare with the proposed linear method. The numerical results demonstrate enough accuracy, strong robustness and high computational efficiency of the proposed linear method even in the heavily-loaded conditions and with 10 times the line resistances. Originality/value The conductance corresponding to each constant resistance load and the equivalent conductance for the dispatchable unit can be directly merged into the self-conductance (diagonal component) of the conductance matrix. The constant current loads and the injection powers from dispatchable DG units can be treated as the current sources in the proposed method. All of those make the PF model much clear and simple. It is capable of offering enough accuracy level, and it is suitable for applications in DC networks that require a large number of repeated PF calculations to optimize the energy flows under different scenarios.

2017 ◽  
Vol 8 (6) ◽  
pp. 2754-2764 ◽  
Author(s):  
Chendan Li ◽  
Sanjay K. Chaudhary ◽  
Mehdi Savaghebi ◽  
Juan C. Vasquez ◽  
Josep M. Guerrero

2019 ◽  
Vol 1213 ◽  
pp. 032027
Author(s):  
Jiawei Li ◽  
Xueshan Han ◽  
Wenbo Li ◽  
Zhe Jiang

Author(s):  
Jiazhi Lei ◽  
Qingwu Gong ◽  
Jun Ye

Purpose This paper aims to propose a simplified model of vanadium redox flow batteries (VRBs) for VRB energy storage system (ESS) design considering the operational characteristics of VRB, and a VRB ESS, considering the low terminal voltage of VRB, was presented. Design/methodology/approach According to the designed topology of VRB ESS and the simplified model of VRB, a small perturbation analysis method was used to establish the transfer function of VRB ESS, and the controller parameters of VRB ESS under constant charging and discharging current were designed. Findings Test results have demonstrated that this designed VRB ESS has fast response, small overshoot, strong adaptation and high steady precision, which strongly verified the reasonable design. Practical implications This simplified model of VRB can be suitably used for VRB ESS design. This designed VRB ESS realized the bidirectional power flow of VRB and AC grid. In this designed VRB ESS, phase-shifted full-bridge converter and a single-phase inverter were used and VRB was charged and discharged under constant current. Originality/value The paper presents a topology of VRB ESS which can realize the bidirectional power flow of VRB and AC grid. Considering the complexity of VRB model, a simplified model of VRB was proposed for the controller parameters design of VRB ESS, and this method can be used in application.


Author(s):  
João Alberto Passos Filho ◽  
Othon Ferreira Avila ◽  
Paula Oliveira La Gatta

AbstractThe main objective of this paper is to review and compare two methodologies to solve the power flow problem considering active power generation droop control. The first methodology is based on a DC power flow model, and the second one is based on a conventional full Newton power flow formulation. The study of two test systems is used to validate the proposed analysis; the first one is the 11-bus system with two distinct areas, and the second one is the 39-bus New England power system. The results presented validate and indicate the effectiveness of the DC power flow approach in order to estimate the steady-state system frequency deviations.


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