SimPowerSystems

Discretizing the PWM Motor Drive

You probably have noticed that the simulation using a variable-step integration algorithm is relatively long. Depending on your computer, it might take some minutes to simulate one second. In order to shorten the simulation time, you can discretize your circuit and simulate at fixed simulation time steps.

Copy the Discrete System block of the powerlib library into your circuit5 system. Open it and set the sample time to 10e-6 s. When you restart the simulation, the power system, including the asynchronous machine, will be discretized at a 10 µs sample time.

As there are no more continuous states in the electrical system, you do not need a variable-step integration method to solve this system. In the Simulation --> Simulation parameters --> Solver dialog pane, you could select the Fixed-step and discrete (no continuous states) options. However, as your system contains two blocks that contain continuous states (Fourier blocks), you still need continuous integration. In the Simulation--> Simulation Parameters --> Solver dialog pane, select the Fixed-step and ode1 (Euler) options and specify a fixed step of 10 µs.

Start the simulation. Observe that the simulation is now approximately three times faster than with the continuous system. Results compare well with the continuous system.

Using the Multimeter Block

Session 6: Introducing the Phasor Simulation Method