Ricardo Vasques de Oliveira

The high penetration of photovoltaic (PV) generation has introduced critical control challenges for modern power systems, such as reduction of the system power reserve and degradation of the inertial response, frequency control, and voltage control. In response to these challenges, grid codes increasingly require PV power plants (PVPPs) to provide ancillary services through power reserve control (PRC) to mitigate the detrimental impact of PV generation and increase the reliability and dynamic performance of modern power systems. The development of practical approaches for PRC in PVPPs operating under dynamic irradiance conditions is challenging due to the fast variations in the maximum available power. To address this issue, this work presents a low-cost and straightforward PRC approach for PVPPs operating under cloud or clear-sky scenarios without incorporating additional devices in the power plant. A practical approach to estimate the maximum available power typically required to implement most PRC approaches is proposed based on multiple reference inverters (i.e., PV generation units, PVUs). An analytical expression is derived to determine the number of PVUs that must be operated in de-loaded control mode using a classical flexible power point tracking (FPPT) algorithm. A PVPP with 49 PVUs is employed to validate the overall formulated control approach using time-domain simulations, incorporating realistic technical and meteorological parameters alongside an accurate dynamic model. A comprehensive assessment is also conducted to investigate the impact of intrinsic and extrinsic factors on the performance of the PRC, showing the key challenges inherent to the PRC.

Inertial response support from wind turbine generators has become a priority requirement in most grid codes to improve the frequency response and frequency stability margins of power systems. However, the interaction between MPPT and inertial controllers may significantly degrade the power system dynamics. Therefore, there is a need to comprehensively understand the electromechanical dynamics of power systems with high penetration of wind generation. In this context, this work proposes a simplified dynamic model to assess the electromechanical dynamics of modern power systems with inertial response support from wind generation. The proposed simplified model allows simple analyses of the intrinsic and extrinsic aspects of wind generation that directly affect the system frequency dynamics and the dynamics of wind turbine generators. As a secondary contribution, this work also provides a comprehensive assessment of intrinsic and extrinsic aspects of wind generation that significantly affect the electromechanical dynamics of power systems with inertial response support from wind generation.

Microgrids and modern bulk power systems usually have multiple time scale dynamics, such as slow and fast dynamics. In this study, the stability of a wind–diesel hybrid microgrid is investigated to show a mechanism of system collapse caused by the interaction between fast dynamics of interface converters and slow electromechanical dynamics. This mechanism leads to a Hopf bifurcation of the fast subsystem due to slow changes in the variables of the slow subsystem and is completely understood by decomposing the stability analysis of the microgrid into the stability assessment of two simpler subsystems: the slow and the fast subsystems. The time‐scale method proposed in this study for stability analysis of the microgrid extends the existing proposals in the literature and is able to detect this kind of instability scenario, where the interaction between fast and slow subsystems is the cause of collapse, while the existing approaches, such as quasi‐steady‐state analysis, fail in detecting instability.

The de‐loaded operation of wind turbine generators (WTGs) with inertial and frequency control considerably affects the dynamics and stability of variable speed wind turbines. In this context, this work proposes a comprehensive assessment of the simultaneous impact of virtual synchronous generator and frequency controllers on the electromechanical dynamics of type 4 WTGs. The proposed power balance formulation and the performed analysis, which are the main contributions of this work, provide insight into the simultaneous impact of the inertial and frequency control on the dynamics of the wind generation unit and system frequency. The assessment has been performed by means of an analytical formulation for the power balance in the WTG, characteristic curves of the wind turbine, and non‐linear time‐domain simulations of two test systems. The analyses have shown that the speed and torque deviation magnitudes of the wind turbine, as well as the amount of kinetic energy released by the wind turbine, depend on the wind turbine operating point. The study has also shown that the de‐loaded operation considerably increases the inertial response capability of WTGs. The integrated inertial and frequency control approach has resulted in well‐behaved electromechanical dynamics for the WTG.

This work proposes an operational and control approach to provide frequency regulation service by means of wind generation units based on fully rated converter. The proposed control approach simultaneously provides inertial response, primary frequency control, and secondary frequency control to the wind generation. The operational approach automatically enables the secondary frequency control in the wind generation or in the conventional generation, depending on the system loading and the wind speed conditions. The proposition of an approach to control the wind turbine speed is the main contribution of this work. The speed control strategy provides a power margin to the wind generation based on the control of the turbine pitch angle. The electromechanical dynamics of the wind generation unit operating in the frequency control mode are also evaluated. The results have shown that the proposed control approach was effective in providing frequency regulation service to the considered power system. The action of the proposed control was not detrimental to the electromechanical dynamics inherent to the wind generation unit.

The penetration of wind generation has grown significantly in many countries. As a result, the frequency response and stability has become a concern for power system operators. Thus, this work proposes an operational and control approach for wind generation units based on fully rated converter in order to simultaneously provide virtual inertia, primary frequency control, and secondary frequency control for power systems. The proposed control approach, based on virtual synchronous generator, also enables the wind generation to operate as a grid former (frequency control mode). The main contribution of this work is the proposition of an optimization formulation which optimizes the operating point of the wind generation, in order to reduce the deviation magnitude of the wind turbine speed after load variations. As a result, the optimization reduces the magnitude and settling time of mechanical dynamics and mechanical stress of the wind turbine, gearbox, and generator. The results have shown that the proposed control approach is effective in the provision of virtual inertia and frequency regulation. The proposed optimization approach has significantly reduced the deviation magnitude and settling time of the wind turbine speed after load variations.