Interactions analysis between VSC converters and an onshore AC network
This thesis starts by addressing two modelling techniques for power systems in qd0-domain. The first technique is the state-space representation, which describes the behaviour of a physical system by means of its state variables in the time domain. The second modelling technique is the admittance ma...
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| Tipo de recurso: | tesis de maestría |
| Fecha de publicación: | 2019 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/174903 |
| Acceso en línea: | https://hdl.handle.net/2117/174903 |
| Access Level: | acceso abierto |
| Palabra clave: | Electric current converters Electric networks Convertidors de corrent elèctric Xarxes elèctriques Àrees temàtiques de la UPC::Enginyeria elèctrica |
| Sumario: | This thesis starts by addressing two modelling techniques for power systems in qd0-domain. The first technique is the state-space representation, which describes the behaviour of a physical system by means of its state variables in the time domain. The second modelling technique is the admittance matrix, which expresses the voltage-current relationship of the system as a transfer function in the frequency s-domain. The main reason for using these two techniques is because both are equivalent, allows to model the same system in two different ways providing different insights. This is an important point because every modelling technique has its own drawbacks and benefits in terms of derivation and information that they can provide. Deriving properly the model is crucial for studying the behaviour of the system under any condition of operation. The power network studied in this thesis is comprised by seven overhead power lines interconnecting five buses, this power network is addressed by the name of " Five Bus Network". The state-space model and admittance matrix model of the five Bus network is derived and compared on the basis of eigenvalues and singular values. Later, a voltage source converter (VSC) is connected to the power system. The power system in this thesis is comprised by a grid-connected VSC converter, an equivalent network and the five bus network. The control system of the VSC converter is described and properly validated to ensure its correct operation. The two main studied interactions between the VSC converter and the power network are related to the strength of the equivalent network and the disconnection of a power transmission line. The strength of an AC grid is normally defined by the short circuit ratio (SCR), which has negative effects on the stability of the control system of the converter. Also, the loss of a power line imposes newconstraints on the system and changes drastically the topology of the network. The simulations are performed inMATLAB-SIMULINK. Two models are created to capture the dynamics of the system. The first is a non-linear model created in SIMULINK (VSC converter and the AC grid) and the second is a linear model (VSC converter and the AC grid) based on the state space representation. The linear model is validated to assure that matches the nonlinear model whenever a small perturbation in the system occurs. Results are expressed in time-domain and in the frequency s-domain. Finally, the obtained results shows the impact of low SCRs on the stability of the system. The lower the SCR, the more prone the system is to become unstable. On the other hand, the loss of a power line limits the power transfer capabilities between the converter and the network. And if proper power adjustments are not made the system could become unstable. |
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