Inside-Plant and Plant-Grid Sub-synchronous Oscillation Characteristics Analysis of Multiple PV Generation Units Connected to a Weak AC Power Grid

doi:10.12204/j.issn.1000-7229.2021.12.006

Abstract

Abstract:

Aiming at the problem of sub-synchronous oscillation (SSO) when multiple PV generation units are merged into the weak AC power grid, three small signal models of PV generation units merged into the weak AC power grid system is established in this paper. Through the analysis of eigenvalue method, the SSO mode existing in the system is obtained, and the participation factor of each SSO mode is calculated. The result shows that there are two inside-plant SSO mode and one plant-grid SSO modes in the system. The inside-plant SSO mode is generated by the interaction among the three power generation units inside the PV plant. The dominant factors are the DC-side capacitance and the parameters of the inverter current inner loop controller; the plant-grid SSO mode is generated by the interaction between the three PV generation units and the AC power grid. The dominant factors are the DC-side capacitance, the inverter current inner loop controller parameters and the AC power grid. Meanwile, by analyzing the damping coupling characteristics of the dominant factors in inside-plant and plant-grid SSO mode, it is concluded that the influence of the PV unit’s generating capacity, DC-side capacitance, and current inner loop controller parameter changes on the damping of the two SSO modes is convergent. Finally, a time-domain simulation model was built in PSCAD/EMTDC to verify the correctness of the theoretical analysis results.

Key words: PV generation unit, weak AC power grid, sub-synchronous oscillation (SSO), eigenvalue analysis, damping coupling

CLC Number:

TM615

ZHAO Shuqiang, GAO Ruixin, SHAO Bingbing, LONG Xin, SUN Mengxue, LI Siyan. Inside-Plant and Plant-Grid Sub-synchronous Oscillation Characteristics Analysis of Multiple PV Generation Units Connected to a Weak AC Power Grid[J]. ELECTRIC POWER CONSTRUCTION, 2021, 42(12): 49-58.

Figures/Tables 17

Fig.1 Structure of grid-connection system of three PV generation units

Table 1 State variables of main circuit of PV plant

Table 2 State variables of PV plant controller

Table 3 State variables of PV plant grid-connection lines

Table 4 SSO mode of PV grid-connection system with three PV generation units (kp2=0.025)

Fig.2 Normalized participation factor of SSO mode of PV grid-connection system with three PV generation units

Fig.3 The active power of each PV generation unit

Fig.4 Active power of grid-connected PV plant

Fig.5 The variation curve of the real part of the eigenvalue of the system SSO mode with the CDC

Fig.6 The variation curve of system active power with CDC

Fig.7 The variation curve of the real part of the eigenvalue of the system SSO mode with the kp2、ki2

Fig.8 The variation curve of system active power with kp2、ki2 and the FFT analysis results

Fig.9 The variation curve of the real part of the eigenvalue of the system SSO mode with S

Fig.10 The variation curve of system active power with S

Fig.A1 Block diagram of inverter control

Fig.A2 Block diagram of system PLL control

Table A1 Parameters of single PV generation unit and grid-connection line parameters

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