Power Flow Analysis of AC/DC Distribution System with Multiple Voltage Levels

doi:10.12204/j.issn.1000-7229.2020.10.005

Abstract

Abstract:

With the development of distributed generation and DC loads, a safe, reliable, and efficient AC-DC hybrid distribution network will become an important form for future development of distribution network. The DC distribution network based on the voltage source converter has the advantages of strong controllability, few power quality problems, and good economy. At the same time, it also introduces a problem of power flow calculation that is different from the AC distribution network. This paper firstly establishes a model for power flow calculation that takes into account inverter losses and DC converter losses, and gives calculation method for loss parameters. Secondly, the method for solving the DC power flow model is introduced. When analyzing the power flow of the DC system, the influence of control method of the voltage source converter and the DC / DC converter on the power flow calculation is mainly considered. Different power flow solving methods are given for different control strategies. Several effective solutions are given when the flow exceeds the limit. Finally, an IEEE 33-node DC distribution network example is used to verify the correctness of the loss model proposed in this paper and the effectiveness of the power flow solution method.

Key words: AC/DC system, voltage source converter, DC/DC converter, power flow calculation

CLC Number:

TM744

WANG Xiaoxiao, HAN Minxiao, CAO Wenyuan, XIE Wenqiang, XIAO Feng, LI Rui, QIN Jianhua. Power Flow Analysis of AC/DC Distribution System with Multiple Voltage Levels[J]. ELECTRIC POWER CONSTRUCTION, 2020, 41(10): 38-46.

Figures/Tables 16

Fig.1 Model of VSC converter station

Fig.2 Equivalent circuit of VSC

Table 1 VSC control modes and equivalent methods in load flow calculation

Fig.3 Unified steady-state model of DC converter

Fig.4 ISOP model and IPOS model

Fig.5 π-type equivalent model for DC converter

Table 2 DC converter control modes and equivalent methods in power flow

Fig.6 Characteristic curve of droop control

Fig.7 IEEE 33-node AC / DC network

Table 3 Duty cycle of DC converter and modulation ratio of inverter under scenario 1

Table 4 Duty cycle of DC converter and modulation ratio of inverter under scenario 2

Table 5 Converter power without control mode switching

Table 6 Converter power after control mode switching

Table A1 VSC loss parameters

Table A2 DC / DC converter control methods and submodule types under scenario 1

Table A3 DC converter control methods and submodule types under scenario 2

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