The share of electrical power generation from renewable energy sources is increasing and is expected to keep on increasing as various countries intensify their efforts to reduce CO2 emissions. Differences in the nature and characteristics of some renewable generation affect the ability of power systems to maintain frequency stability. This is because some renewable generation sources do not have inertia or are converter connected and decoupled from grid frequency. Solar Photovoltaic system do not have any stored inertia and usually operate at maximum power. There is need for control method for solar PV systems to contribute to frequency stability. This thesis proposes operation methodologies for photovoltaic (PV) systems to carry out active power control functions - including frequency control and proposes a framework for comparing frequency support ability of different generation sources. First, a modification to the conventional Perturb and Observe (P&O) maximum power point tracking (MPPT) algorithm is proposed to avoid leftward and rightward from maximum power. Results presented show that PV systems employing P&O with the proposed modification avoid both leftward and rightward drift when subjected to rapidly increasing irradiance, sinusoidal irradiance, and real irradiance. This drift-free P&O enables the PV system to participate in active power control function at rapidly increasing irradiance. An offline MPPT that uses the characteristics of PV modules to determine the maximum power point offline and reduce online computation is proposed for frequency support. Two methods for achieving de-loaded operation of a PV system using the offline MPPT are presented and compared for accuracy. The ability of offline MPPT and the P&O with proposed modification to maintain a power reserve under different irradiance conditions are compared. Second, this thesis examines the ability of a PV system to contribute to frequency support. Different methods for frequency support from a PV power plant under different penetration levels are examined. Results show with the appropriate amount of reserve and support parameters, PV systems can contribute to frequency support. The results also show that PV power plants with the proper support parameters can adequately compensate for the loss of inertia with regards to its effect on the nadir of frequency response. A variable droop control method for frequency support is proposed to reduce the amount of reserve required for frequency support. The effect of MPPT choice on frequency support is evaluated by comparing responses from PV systems with the offline MPPT, P&O with proposed modification, and the constant voltage MPPT. Lastly, this thesis proposes a framework for comparing the frequency support ability of different generating units based on their response speed and support parameters. Different response speeds are emulated by changing one the time constant of a Second-order system. The effect of response speed, support method, and support parameters on the nadir of frequency response and maximum power increase are evaluated for different response speeds. A method for comparing support ability by considering the economic cost and benefit for support is also presented.
|Date of Award
|11 Aug 2020
- University Of Strathclyde
|Olimpo Anaya-Lara (Supervisor) & Alasdair McDonald (Supervisor)