On the State Estimation of Three Phase Micro-Grids with Distributed PV Generators
Rubbrecht, Tom (2016)
Rubbrecht, Tom
2016
Master's Degree Programme in Electrical Engineering
Tieto- ja sähkötekniikan tiedekunta - Faculty of Computing and Electrical Engineering
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Hyväksymispäivämäärä
2016-08-17
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201608034365
https://urn.fi/URN:NBN:fi:tty-201608034365
Tiivistelmä
This thesis investigates the application of three-phase State Estimation in Micro-Grids with distributed PV generators. In particular, it explores the use of three-phase Power Flows and State Estimation together with VSC modeling. The VSC may be used to provide voltage regulation at selected nodes of the micro-grid in which case it acts as a STATCOM or it may be used to provide the interface between the DC PV generator and the AC side of the micro-grid.
Small renewable energy plants are increasing their share of the overall energy resource. They are installed at the low-voltage end of the grid and this is blurring the otherwise classical concept of producers and consumers of electrical energy. More and more, consumers are able to produce electrical energy by installing PV cells at their premises and so they are becoming prosumers. This has resulted in the appearance of energy plants distributed all over the power grid. Hence, power flows might not be as straightforward to determine as previously, when producers and consumers were very clearly separated.
In order to ensure an effective control of the operation of the grid it is of paramount importance to have an effective knowledge of the actual state of the power network. Single-phase state estimators for power grids represent a classical concept in electric power systems theory but this is limited to positive-sequence representations of the power grid, i.e., three-phase power networks which exhibit a perfect balance. Needless to say that a major limitation of the positive-sequence network representation is its inapplicability to cases when the network unbalances are significant and cannot be ignored. In real life the load is not always equally spread between the three phases; no matter how hard engineers try to achieve a reasonable balance, there is always a degree of unbalance which ought to be studied because it may impair the operation of the grid and increase its power losses. This can only be assessed by representing the three-phase power grid on its natural coordinate system, which is the abc frame-of-reference.
This thesis presents a three-phase modeling approach to power flows and state estimation of balanced and unbalanced power networks. A second contribution is the modeling of a three-phase VSC that has been derived from an existing single-phase VSC. The model is then extended to incorporate the model of PV generator. Because of the flexibility with which the code has been developed, the incorporation of multiple STATCOMs and PV generators may be simulated to be a realistic part of the power grid, enabling the distributed concept and the micro-grid concept to be brought together.
Small renewable energy plants are increasing their share of the overall energy resource. They are installed at the low-voltage end of the grid and this is blurring the otherwise classical concept of producers and consumers of electrical energy. More and more, consumers are able to produce electrical energy by installing PV cells at their premises and so they are becoming prosumers. This has resulted in the appearance of energy plants distributed all over the power grid. Hence, power flows might not be as straightforward to determine as previously, when producers and consumers were very clearly separated.
In order to ensure an effective control of the operation of the grid it is of paramount importance to have an effective knowledge of the actual state of the power network. Single-phase state estimators for power grids represent a classical concept in electric power systems theory but this is limited to positive-sequence representations of the power grid, i.e., three-phase power networks which exhibit a perfect balance. Needless to say that a major limitation of the positive-sequence network representation is its inapplicability to cases when the network unbalances are significant and cannot be ignored. In real life the load is not always equally spread between the three phases; no matter how hard engineers try to achieve a reasonable balance, there is always a degree of unbalance which ought to be studied because it may impair the operation of the grid and increase its power losses. This can only be assessed by representing the three-phase power grid on its natural coordinate system, which is the abc frame-of-reference.
This thesis presents a three-phase modeling approach to power flows and state estimation of balanced and unbalanced power networks. A second contribution is the modeling of a three-phase VSC that has been derived from an existing single-phase VSC. The model is then extended to incorporate the model of PV generator. Because of the flexibility with which the code has been developed, the incorporation of multiple STATCOMs and PV generators may be simulated to be a realistic part of the power grid, enabling the distributed concept and the micro-grid concept to be brought together.