Adaptive Segmented Droop Control for Flexible Output of Photovoltaic Converter in DC Distribution Network

doi:10.12204/j.issn.1000-7229.2021.10.007

Abstract

Abstract:

In a DC distribution system with photovoltaic power, according to traditional droop control, when photovoltaic power output changes, there will be problems such as unbalanced power distribution and large deviation of bus voltage. Photovoltaic power output is seriously affected by environmental factors, which causes the effect of traditional droop control to deteriorate. In response to this problem, the droop characteristic curve can be adaptively adjusted according to the changes in the photovoltaic output, so that it can achieve accurate power distribution under heavy load conditions. At the same time, this solution can also achieve stable control of the bus voltage under light load conditions. Through the establishment of the output impedance model of droop control, the influence of the adaptive change of droop coefficient on the system's circulation suppression and current sharing is analyzed. In addition, a DC distribution network with photovoltaic power is built in MATLAB/Simulink for simulation verification. A combination of theoretical analysis and simulation verification shows that the proposed adaptive segmented droop control for flexible output of photovoltaic converter can dynamically adjust the power distribution task according to the photovoltaic power output. Specifically, the system power distribution accuracy can be improved when the load is heavy, and the DC bus voltage deviation can be reduced when the load is light.

Key words: DC distribution network, droop control, PV output, power distribution

CLC Number:

TM402

LIU Qing, ZHANG Tongyu, TIAN Yanjun. Adaptive Segmented Droop Control for Flexible Output of Photovoltaic Converter in DC Distribution Network[J]. ELECTRIC POWER CONSTRUCTION, 2021, 42(10): 60-70.

Figures/Tables 18

Fig.1 Topology of photovoltaic power's parallel connection to DC distribution network

Fig.2 Coordinated operation control of DC distribution network

Fig.3 Characteristic curve of segmented droop

Fig.4 Simplified circuit model of DC distribution network

Fig.5 Characteristic curve of adaptive segmented droop control based on flexible output of PV converter before optimization δichanges

Fig.6 Adaptive segmented droop control curve for flexible output of photovoltaic converter before optimization for photovoltaic power supply with different output

Fig.7 Optimized adaptive segmented droop control curve for flexible output of photovoltaic converter

Fig.8 Control block diagram of adaptive segmented droop control for flexible output of photovoltaic converter

Fig.9 Control block diagram of energy storage device

Fig.10 G-VSC control block diagram in PQ control mode

Table 1 Main parameters of the system

Table 2 Value of each droop control method

Fig.11 Bode diagram of the output impedance characteristics with k ' d r o o p i

Fig.12 Radiation variation diagram of photovoltaic power supply

Fig.13 Radiation variation diagram of photovoltaic power supply

Fig.14 Voltage comparison chart of different droop control method

Fig.15 Output power diagram of each converter under four droop control methods

Fig.16 Comparison of output power of each PV-side converter

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