A Probabilistic Framework for the Robust Stability and Performance Analysis of Grid-Tied Voltage Source Converters

Abstract

This paper proposed a probabilistic framework that could be used for the sensitivity assessment of grid-connected voltage source converters (VSCs), where uncertainties in the grid short circuit ratio (SCR) and operating point conditions, as well as control-loop interactions, were considered. The proposed method tried to broaden the available knowledge on the small-signal stability analysis of VSCs and provide a probabilistic point of view of this subject. It considered the probability of different operational conditions in order to obtain less conservatism and more accurate results. Based on uncertain inputs and the employed stability model, the proposed model produced statistical distributions of the critical mode and its damping factor and ratio, which were not accessible by existing deterministic methods. Crucial statistical information measures how much system stability and performance are maintained or changed over the system uncertainties and disturbances, as well as provides a clear insight into the system stability problem. For instance, as concluded in this paper, for the conventional control system design, fast dynamic parts of a VSC, such as the current controller and control delay, significantly impact the minimum damping ratio. Furthermore, slow dynamic parts, such as outer voltage control loops and the synchronization block, influence the maximum damping factor. For strong grids, the AC voltage magnitude controller (AVC) significantly impacts the maximum damping factor due to its lower bandwidth among all control loops. For weak grids, the damping factor of the critical mode is highly affected by interactions between the VSC, the power grid, and different control loops due to the synchronization mechanism. The other contributions of this paper were the introduction of robust stability and performance definitions and indices; explanations of the pros and cons of probabilistic assessment methods and their applicability; interpretation of the obtained results; and, finally, a link was provided between system stability and reliability, which will be crucial for future power system design.

Special Issue on Power Converters: Modelling, Control, and Applications

“…Beshir et al [10] presented the interesting problem of the choice of PWM modulation in the switching mode power converters that minimizes conducted emissions and reduces the influence on the power line communication. Gholami-Khesht et al [11] proposed a probabilistic framework that could be used for the sensitivity assessment of grid-connected voltage source converters, where uncertainties in the grid short circuit ratio and operating point conditions, as well as control-loop interactions, were considered. The on-grid connection is a very important topic for many renewable power sources.…”

“…Finally, all five papers from the second edition of the Special Issue covered the expected range of topics. Paper [11] concerned on-grid inverters, papers [12,13] showed the problems of power converter's component modelling, paper [14] presented control in DC/DC converters, and paper [10] presented an interesting PWM idea for the reduction in conducted emissions.…”

Stability Impacts of an Alternate Voltage Controller (AVC) on Wind Turbines with Different Grid Strengths

“…In addition, the impact of AVC is included in [18], where the state-space model is obtained after the transfer function of the VSC output voltage is derived. The AVC controller is included in the models designed in [19][20][21].…”

Modeling and Stability Analysis of Converter-Based Wind Turbine Systems

“…Moreover, the AVC's effect is included in the state-space model derived from the VSC output voltage transfer function in [66]. Models in [67][68][69] also incorporate the AVC controller. However, the stability impact of the AVC controller's design has not been studied in depth, indicating an area that demands further investigation.…”