To analyze the influence of our power plant on the grid, we built a Simulink model based on the IEEE 5-Bus System.

The generator on bus 1 represents the power plants that already exist, and the generator on bus 2 represents our hydro plants.

There are 3 types of buses in the system, PV, PQ, and slack or swing. A PV bus is a bus that the real power consumed or provided by this bus and the voltage magnitude on the bus are specified, while the reactive power is to be solved. Similarly, a PQ bus is a bus that the real power and the reactive power consumed or provided by this bus are specified while the voltage on the bus is to be solved. There is one and only one swing bus in the system, which is assumed to be bus 1. The swing bus is a bus that has a fixed voltage magnitude and voltage angle, with an undermined real power and reactive power.

In our 5-bus system, there are npv PV buses, npq PQ buses, and 1 slack bus. We have (npv + npq) equations where P are specified and npq equations where Q are specified. Therefore there are a total of (npv + 2npq) equations. Similarly, we have npq unknown voltage magnitudes, and (npv+npq) unknown voltage angles. Thus, there are a total of (nov + 2npq) unknown variables, which are as many as equations.

The generator used in our hydro plants can work either as an asynchronized generator or a variable-speed generator. We build two models to analyze them respectively. In the model of the asynchronized generator, the generator is directly connected to the grid and has no voltage control devices, so it is set to be a PQ generator. In the model of the variable speed generator, the generator is connected to the grid through a back-to-back converter, the terminal voltage is regulated by that back-to-back converter, so it is set to be a PV generator.