Abstract
The proliferation of Photovoltaic (PV) generation has brought several changes in the transient stability analysis of power systems. The rotor angle dynamics based stability analysis used for synchronous generators may not be applicable for PV generators. In the existing literature, the transient stability of a grid connected PV generator with dc link voltage and reactive power control ( $V_{dc}$ and $Q$ control) is analyzed from the coupled nonlinear functions corresponding to PV control loops, Phase Locked Loop (PLL) and network dynamics. The existing method may not be suitable for online transient stability assessment because it is computationally heavy. This paper proposes an online transient stability criterion for a PV generator (with $V_{dc}$ and $Q$ control) connected to grid modelled as infinite bus. The PV generator is considered to have Low Voltage Ride Through (LVRT) capability, but does not provide voltage support. In this study, the relation between the ac and dc side dynamics is explored. A stability criterion is proposed to assess the transient stability by monitoring the swing in the energy of the dc link capacitor. The proposed criterion requires the dc link voltage trajectory only till the first swing of the dc link voltage. As a result, the proposed assessment criterion is computationally less demanding and less prone to measurement errors in comparison to existing methods. Thus, the proposed criterion is suitable for online transient stability assessment. The effectiveness of the proposed criterion is verified for single-stage as well as two-stage converter configurations of PV generator. The proposed criterion is also verified on a modified IEEE 39 bus system. Time-domain simulations are carried out to validate the proposed criterion. The proposed approach is compared with an existing transient stability criterion for $V_{dc}$ and $Q$ control based grid connected PV generator. The advantages of the proposed method as compared to the existing method are discussed.
Highlights
I N transition towards green energy, the penetration of Photo Voltaic (PV) generators is increasing in power system
The PV generator in the study is equipped with Low Voltage Ride Through (LVRT) capability
The stability of grid connected PV generator is assessed based on the net energy of the dc link capacitor after the first swing of the capacitor voltage
Summary
I N transition towards green energy, the penetration of Photo Voltaic (PV) generators is increasing in power system. A method to assess transient stability of SPIB system is proposed by exploring the relation between converter control loops, PLL stability and dc link capacitor dynamics. COUPLING BETWEEN AC-SIDE CONVERTER CONTROL, PLL DYNAMICS AND DC LINK CAPACITOR DYNAMICS In case of a disturbance, the PLL tries to trace the voltage phase angle at the PV generator terminals This helps the PV generator to remain in synchronism with rest of the grid. It can be concluded that the ac-side converter control loops and PLL stability can be analyzed from the dc-link capacitor voltage dynamics.
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