Photovoltaic power generation relies on power electronics and therefore does not have natural inertia and damping characteristics. In order to make the capacitance of the medium time scale participate in the grid frequency response without adding additional equipment, this paper takes the grid-connected photovoltaic power generation system based on DC voltage droop control as the research object, and establishes the static synchronous generator (SSG) model of the system. The model is used to analyze the main parameters affecting the inertia, damping and synchronization characteristics of the system and their influence laws. The research results show that the energy storage effect of the capacitor on the medium time scale can also make the system exhibit certain inertia characteristics. From the point of view of control parameters, as the droop coefficient Dp decreases, the inertia characteristic exhibited by the system is stronger. The larger the DC voltage outer loop proportional coefficient Kp is, the stronger the damping effect of the system is. The larger the DC voltage outer loop integral coefficient Ki, the stronger the synchronization capability of the system. In addition, the MATLAB/Simulink simulation platform is used to verify the correctness of the theoretical analysis results.
- Grid-connected photovoltaic power generation system
- DC voltage droop control
- Inertia characteristic
- Damping effect
- Synchronization ability
Figure 1. Grid-Connected Photovoltaic Power Generation System Based On Dc Voltage Droop Control.
EXPECTED SIMULATION RESULTS
Figure 2. Influence Of Different Parameter Changes On System Inertia.
Figure 3. Influence Of Different Parameter Changes On System Inertia.
Figure 4. Influence Of Droop Coefficient Dp On Dc Voltage.
Figure 5. Influence Of Droop Coefficient Dp On System Power.
Figure 6. The Influence Of P Controller On Dc Voltage.
Figure 7. The Influence Of P Controller On System Power.
Figure 8. The Influence Of I Controller On Dc Voltage.
Figure 9. The Influence Of I Controller On System Power.
This paper introduces a new GFC scheme for PV systems that do not employ real-time estimation of the MPP and make optimal use of the limited power reserves. By operating in full or limited grid-forming mode, the PV plant preserves its voltage source nature and manages to assist the grid during disturbances similarly or even better than synchronous machines. The modified current saturation scheme performs smoothly, without any need for fault detection or control switching. Replacing SMs with PV GFC results in improved frequency profile during load disturbances due to faster response from the PV plant, and comparable terminal voltage profiles during faults despite the strict inverter over current limits. However, the PV GFC introduces another source of disturbances to the power system resulting from irradiance transients during cloud movement.
Inverters in GFL mode with ancillary services can support the grid during disturbances, but the contribution becomes limited as the system strength decreases. The GFC mode of inverter operation is the way forward for the renewables-rich and inverter-dominated power systems of the future. Future work involves a complete investigation of the dynamic interactions between GFC and GFL inverters and the rest of the power system at various sizes and generation mixtures. Similarly, a methodology to determine the appropriate ratio of GFC and GFL resources would be very useful in converter-dominated power systems. Furthermore, the proposed method is designed for uniform illumination, which is the common assumption for utility-scale PV systems; an extension of the method to partial shading would improve its credibility and reliability at all possible conditions.
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