Induction Motor Initialization with Loadflow

Open Model

This example shows how to initialize a three-phase induction motor as part of a load flow analysis. When initializing an induction machine that is directly connected to an AC network, in steady state there is one degree of freedom which can be set by any one of shaft torque, shaft power, motor speed or electrical power.

Here the model is configured to initialize delivering 8kW of mechanical power to a load. Hence the mechanical power consumed variable on the induction motor variables tab is set to -8kW with high priority. The slip and real power generated variables are left at priority none. Similarly, because the inertia initial speed is equivalent to slip, the rotational velocity is set to priority none. To help the intialisation converge, the beginning value is set to synchronous speed rather than left at zero.

The shaft torque is set to -8kW divided by the synchronous mechanical speed. This is an approximation as some negative slip is expected when generating. The error will result in an initial acceleration of the inertia. If increased accuracy is required, the measured slip from the first simulation can be used to correct the shaft torque applied, and the simulation run a second time. However, it is important to note that this error in the shaft torque will not change load flow results for the rest of the electrical network.

Model

Simulation Results from Simscape Logging

The plot below shows the simulation results following the steady state initialization to meet load flow targets. It can be seen that there is no transient, indicating that the induction motor has been correctly initialized.