Decoupled voltage sensitivity analysis for cluster-oriented smart grid operations

The power systems of today use “smart grids” to improve grid operations and energy efficiency. State-of-the-art technologies and advanced control mechanisms have meant the renewable energy sources (RESs) can now be increasingly integrated into power grids. The grid integration of the RESs makes power generation more sustainable but concurrently causes bidirectional energy flow. This can lead to imbalances between phases. Instability during grid operations is consequently concerned, such as overcurrent in power lines and over/under bus voltages. In the power systems, distribution grids are especially affected, since they were not originally designed to handle power generation. The traditional grid operation, which is a centralised architecture, is therefore impractical for smart grids. Accordingly, an active distribution network is required. In this thesis, an impedance network model and a method for decoupled voltage sensitivity analysis are proposed. Their key contribution to the academic community in the field of smart grids is to enable distributed steady-state analysis based on a clustering power systems approach (CPSA), resulting in decentralised active operations in distributed areas of the smart grids. The voltage sensitivity analysis proposed in this thesis examines the response of voltage magnitude and angle in relation to bus current in sequence systems, active power, and reactive power. The results from the analysis therefore indicate that there are impacts between buses in term of the voltage magnitudes, which can be further used for power management and voltage regulation. The proposed analysis method is derived from a mathematical description of complex bus voltage, based on the proposed impedance model. It requires only measurement data gathered from the phasor measurement unit, without the information from grid topology. The required measurement data consist of bus voltages, bus currents, and the line currents of the connecting line between the distributed areas. As the foundation of the proposed method, first, the impedance model for each distributed area is determined from the measurement data. Only bus impedances between buses of concern are produced in this step. The impedance model is further used together with the measured voltage of the concerned bus in the sensitivity analysis. The proposed analysis method is devised to deal with both balanced and unbalanced grid conditions. The accuracy of the proposed analysis method was verified by simulations in three case studies. The results from the first two case studies demonstrated the accurate voltage sensitivity analysis in all selected grid cases under the balanced and unbalanced grid conditions, including the case of the measurement errors up to the maximum of 1% total vector error. Use of the outcome from voltage sensitivity analysis for regulating voltage profile was then examined in the third case study. Once verification was achieved, the proposed analysis method enabled decoupled voltage sensitivity analysis by using only the measurement data. This makes the proposed method suitable for further use in smart grids. Further research is recommended, which should give consideration to possible additional measurement errors, dynamic characteristics of the power grid, and the implementation of the proposed method