Active power control of power systems with high renewable penetration

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Konstantinopoulos, Stavros
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Electronic thesis
Electrical engineering
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The future power grid will be subject to a rapid transformation as more inverter-based generation is introduced. The dynamics are expected to be very different as less rotating inertia is available. This implies that instabilities will start ensuing in faster time scales than up until today. However, issues of this nature can be effectively alleviated with the intelligent utilization of the highly controllable converters that are available on renewable generation units. This dissertation introduces concepts that demonstrate how the active power controllability of converter-enabled renewable generation, can enhance the stability of the grid and allow more efficient utilization of the transmission infrastructure. This work initially investigates the problem of transient stability in systems with high renewable penetration. The objective is to allow renewable energy to be transferred through already congested transmission corridors, by exploiting the highly controllable active power output of the plants. The incentive in such a scenario, is to accommodate more active power transfers without the need for additional expensive transmission infrastructure. For illustration, Type-3 Wind Turbine Generators (WTG) are used, but the concepts are readily extendable to Type-4 WTGs, batteries and PhotoVoltaics (PV). The control scheme has 3 distinct components. If transient instability is predicted, the active power is drastically curtailed so the WTG acts as a dynamic brake. In succession, the power is adaptively ramped, by monitoring the Rate of Change of Frequency (ROCOF) of the terminal bus. This offers damping to the system and allows for faster active power recovery for the WTG. The third stage implements a reactive power damping control, in order to accommodate the faster ramping of the plant without risking second-swing instabilities. The control is tested extensively in simple systems with one generator, the two area Kundur system and finally the NPCC 16-Machine system. In succession, in order to provide means to effectively tune and assess the performance of the controller, we propose the use of Lyapunov functions, as they allow for efficient screening of various controller configurations and parameterizations, without requiring excessive simulation effort. As a second step, we expand on the justification for our control, by quantifying the impact of the WTG's actions in the transient period in transient energy terms. The second topic of investigation of this dissertation concerns the impact of renewable penetration on electromechanical disturbance propagation across power systems. As more renewable generation will be introduced in power systems, such disturbances are expected to propagate faster and with more severe frequency excursions. We proposes an active power flow control that allows the WTGs to halt the propagation of such disturbances while utilizing only local signal feedback. It is shown that if WTGs are installed along the critical paths disturbances propagate through, local feedback controls can attenuate or even stop them. The third topic of this work concerns the monitoring of the reactive power control performance of Wind Turbine Generator (WTG) units, as measured from Phasor Measurement Units (PMU) data. This is achieved by estimation of low-order models that can be identified by measurements at the terminals of the wind farm. For this purpose, linearized models of each mode of operation are developed. The purpose can be twofold, as the models are used as a guide to assess the regulation performance of the plants and in cases that no agreement is found, they can be used for model calibration. The proposed linearized models are validated by system identification on two PMU datasets containing measurement of a WTG complex during disturbances.
August 2021
School of Engineering
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Rensselaer Polytechnic Institute, Troy, NY
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