| Voltage source converters (VSCs) are widely used today. At the generation level, VSCs serve as interfaces for distributed energy sources. At the transmission level, VSCs are employed to improve system stability and control power flow. At the distribution level, VSCs are used to improve power quality. Therefore, accurate models of the VSC are essential for system planning. The focus of this dissertation is on steady state models of the VSC for harmonic study. In order to interface a VSC model with existing harmonic power flow programs, the VSC is modeled either as a voltage-dependent harmonic current source or a Norton equivalent harmonic current source. However, due to the nonlinear and time-varying nature of the VSC, iterative techniques need to be employed in the models in order to fully characterize the steady state behavior of the converter. This dissertation presents two types of iteration techniques. The first one is based on the time domain shooting method and Broyden's iterative algorithm to greatly improve the iteration time required for the VSC. The second method is based on a hybrid method in which the VSC is modeled in the time domain while the controller is modeled in the frequency domain. The hybrid method offers an advantage of not enlarging the number of unknown variables as the switching frequency increases.;Unlike the existing current injection models, both proposed VSC models can account for (i) the interaction between the power system and the VSC, (ii) the interaction between the ac side and dc side of the converter, (iii) the controllers' impact on the harmonics, (iv) the harmonic interaction between multiple VSCs. |
