Security Control Strategy of Micro-grid Between Grid-connected and Off-grid Based on Virtual Synchronous Generator

doi:10.12096/j.2096-4528.pgt.19151

Abstract

Abstract:

As a major branch of integrated energy system, micro-grid is widely used in the local consumption of distributed generation. With the introduction of cold, heat and gas, the requirement of micro-grid security control is becoming higher and higher. The grid-connected and off-grid mode of micro-grid and the transition process between two operating states were analyzed, furthermore, a control strategy based on improved virtual synchronous generator (VSG) model was proposed. By using appropriate virtual impedance, the characteristics of synchronous reactance were effectively simulated, which ensured the stability of off-grid operation and makes the transition from grid-connected mode to off-grid mode smooth without adding additional control. An improved pre-synchronization control model was proposed for the switching from off-grid mode to grid-connected mode, which could accurately and quickly track the voltage amplitude, frequency and phase. Finally, the model was simulated in Matlab/Simulink environment with a practical example to verify the correctness and advantages of the proposed model.

Key words: micro-grid, seamless switch, virtual synchronous generator (VSG), virtual impedance, improved pre-synchronization control

CLC Number:

TK01
TM727

Yizong GUO, Chuangxin GUO. Security Control Strategy of Micro-grid Between Grid-connected and Off-grid Based on Virtual Synchronous Generator[J]. Power Generation Technology, 2020, 41(6): 650-658.

Figures/Tables 15

Fig.1 Comparison of grid-connected between VSG and SG

Fig.2 Phase diagram of PCC voltage tracing grid voltage

Tab. 1 Simulation parameters of system

参数	数值
直流电压/V	800
电网线电压/V	$220 \sqrt{3}$
开关频率/Hz	1 350
滤波电容/μF	30
滤波电感/mH	3.5
滤波电阻/Ω	0.01
等效线路电阻/Ω	0.892 9
等效线路电感/mH	16.58
转动惯量/(kg?m²)	0.5
阻尼系数	20
有功频率调节系数	10 000
无功电压调节系数	0.000 1

Tab. 1 Simulation parameters of system

参数	数值
直流电压/V	800
电网线电压/V	$220 \sqrt{3}$
开关频率/Hz	1 350
滤波电容/μF	30
滤波电感/mH	3.5
滤波电阻/Ω	0.01
等效线路电阻/Ω	0.892 9
等效线路电感/mH	16.58
转动惯量/(kg?m²)	0.5
阻尼系数	20
有功频率调节系数	10 000
无功电压调节系数	0.000 1

Fig.3 Simulation model of load-shedding in off-grid state

Fig.4 Frequency curve of load-shedding in off-grid state

Fig.5 Voltage curve of load-shedding in off-grid state

Fig.6 Current curve of load-shedding in off-grid state

Fig.7 Simulation model of grid-connected to off-grid state

Fig.8 Frequency curve of grid-connected to off-grid state

Fig.9 PCC voltage and current curves of grid-connected to off-grid state

Fig.10 Simulation model of improved pre-synchronization control

Fig.11 Simulation model of switching switch subsystem

Fig.12 Frequency curve of off-grid to grid-connected

Fig.13 PCC voltage and current curves of off-grid to grid-connected state

Fig.14 Uq curve of off-grid to grid-connected state

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