Frequency support from photovoltaic power plants using offline maximum power point tracking and variable droop control

Abstract

With higher penetration of converter-connected renewable energy sources (RES) into power systems, the successful operation of the system is challenged by significant reductions in system inertia. Presently, given the dominant share of conventional synchronous power plant, RES power plants are not demanded to provide ancillary services. However, as RES connections increase, RES power plants will play a major role in power system operation contributing to frequency control. This paper demonstrates that Photovoltaic Power Plants (PVPP) can provide effectively different types of frequency support based on a power reserve and an Offline Maximum Power Point Tracking (MPPT) technique. An innovative method to de-load the PVPP without significantly increasing the MPPT complexity is proposed. Results from different PVPP frequency support methods, under varying levels of photovoltaic penetration, are presented which demonstrate their capability to provide inertia support comparable to that of synchronous generators. A new variable droop control method, which releases maximum power during the inertial response and returns to fixed droop gain value after a specified time is also presented. The results from using the variable droop show that the frequency nadir and the rate-of-change-of-frequency (ROCOF) can be significantly reduced and some power reserve still maintained after a frequency event.

Future-oriented generic grid code regarding wind power plants in Europe

“…unconverted solar irradiance to electric energy). To overcome these drawbacks, some studies proposed offline control method, which is simply a 2D lookup table receiving the solar irradiation and module temperature as inputs and provides the optimum operating voltage and current, which are used to adjust the setpoints of the buck-boost converter and hence the grid-side inverter [39]. To enable frequency support simple droop controller (similar to this in a synchronous generator) could manipulate the produced increment power during frequency deviations.…”

Effects of Inertia, Load Damping and Dead-Bands on Frequency Histograms and Frequency Control of Power Systems

“…Another aspect is that D L adds to 2Hα and it is thus deemed to play a significant role in limiting frequency variations. In the light of this, D L could be increased by exploiting thermostatically controlled loads that link frequency variations to the absorbed power [11]- [15], as well as load damping and synthetic inertia, which require a suitable implementation of RES generation and storage systems [16]- [18].…”

Frequency support strategy for single-Stage grid-Connected photovoltaic generation with active power reserves

“…Large-scale PV generation grid connection weakens the system inertia, reduces the system ability of frequency regulation, and seriously endangers system frequency security and stability (Pedro et al, 2016;Jesus et al, 2017;Fang et al, 2019). Some countries and regions have issued requirements and technical guidelines, which require PV plants to have the ability to respond to system frequency changes (Datta et al, 2011;Liu et al, 2014;Jibji-bukar and Anaya-lara, 2019). Field test on PV generation participating in primary frequency control was conducted by the State Grid Corporation of China (Xiaoqiang et al, 2017;Xiaoqiang et al, 2018).…”