Voltage quality enhancement by coordinated operation of cascaded tap changer transformers in bidirectional power flow environment
Azimzadeh Moghaddam, Farzad (2015)
Azimzadeh Moghaddam, Farzad
2015
Master's Degree Programme in Electrical Engineering
Tieto- ja sähkötekniikan tiedekunta - Faculty of Computing and Electrical Engineering
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Hyväksymispäivämäärä
2015-12-09
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tty-201511251799
https://urn.fi/URN:NBN:fi:tty-201511251799
Tiivistelmä
Existing voltage control methods have been developed considering unidirectional power flow, and the power flow direction has been assumed to be from substation toward consumption points. In unidirectional power flow environment, undervoltage is considered to be the main voltage quality problem. However, increasing trend of integration of distributed generation (DG) such as solar and wind power to the grid has created possibility for bidirectional power flow and also emerging voltage rise as another voltage quality problem. Therefore, the previous control methods are not capable of efficient handling of the voltage problems and there is a need for development of new control methods.
Since transformers are the main voltage control resources and are owned by the system operator, the main focus in this thesis is on the voltage control using on-load tap changer (OLTC) transformers and especially on the coordinated operation of cascaded transformers. A centralized unit (algorithm) called Block OLTCs of Transformers (BOT) is defined for this purpose. The system operator can use the BOT in two different control schemes. In the first scheme, the BOT acts as a standalone unit that enhances the voltage quality by coordinating the cascaded transformers. In the second control scheme, the BOT unit acts as a supplementary algorithm for other voltage control algorithms (integrated operation) which again aims to improve the voltage quality by coordinating the cascaded OLTCs. The standalone operation of the BOT is the integral part of this thesis. However, integrated operation is also explained.
Performance of the BOT in standalone operation is widely tested and compared with the local control methods of cascaded OLTCs. The obtained results indicate that the BOT is able to prevent unnecessary tap actions of the cascaded OLTCs. This leads to a reduction in total number of tap operations and as a result an improvement in the supply quality regardless of power flow direction is achieved.
Since transformers are the main voltage control resources and are owned by the system operator, the main focus in this thesis is on the voltage control using on-load tap changer (OLTC) transformers and especially on the coordinated operation of cascaded transformers. A centralized unit (algorithm) called Block OLTCs of Transformers (BOT) is defined for this purpose. The system operator can use the BOT in two different control schemes. In the first scheme, the BOT acts as a standalone unit that enhances the voltage quality by coordinating the cascaded transformers. In the second control scheme, the BOT unit acts as a supplementary algorithm for other voltage control algorithms (integrated operation) which again aims to improve the voltage quality by coordinating the cascaded OLTCs. The standalone operation of the BOT is the integral part of this thesis. However, integrated operation is also explained.
Performance of the BOT in standalone operation is widely tested and compared with the local control methods of cascaded OLTCs. The obtained results indicate that the BOT is able to prevent unnecessary tap actions of the cascaded OLTCs. This leads to a reduction in total number of tap operations and as a result an improvement in the supply quality regardless of power flow direction is achieved.