SimPowerSystems

The Nonlinear Model Library

The building blocks used to assemble the Simulink model of the nonlinear circuit are stored in a library named powerlib_models. You do not normally need to work with the powerlib_models library. However, you might have to look inside the models or modify them for particular applications. You can access that library by entering powerlib_models in the MATLAB Command Window.

Figure 4-7: The powerlib_models Library

The Continuous Library

The Continuous library contains two types of blocks:

• Current sources simulating continuous machine models, surge arrester, saturable transformer, and distributed parameter lines
• Switching logics used for purely resistive power electronic devices: breaker, diode, three-level bridge, thyristor, universal bridge, and individual forced-commutated devices

  

Nonlinear Blocks Simulated by Current Sources

These blocks use a voltage input (output of the state-space model of the linear circuit) and their current output is fed into the state-space model. For complex models, such as electrical machines requiring several inputs and outputs, vectorized signals are used. Useful internal signals are also returned by most of the models in a measurement output vector m.

For example, the Asynchronous Machine model is stored in the block named asynchronous_machine. The model uses as inputs a vector of four voltages, two rotor voltages and two stator voltages, respectively: (VabR, VbcR, VabS, VbcS). It returns a vector of four currents, two rotor currents and two stator currents, respectively: (IaR, IbR, IaS, IbS). The model also returns a measurement output vector of 20 signals. When the Asynchronous Machine block is used from powerlib this measurement output vector is accessible through the m output of the machine icon. You can get details on the model inputs and outputs from the documentation of powerlib and powerlib_models block icons.

Logics for Switches and Power Electronic Devices

For switches and power electronic devices, the blocks contain only the logic returning the status (open or closed) of the switch. The switch status is passed to an S-function, which recomputes the state-space model of the linear circuit each time that a switch status is changed. The m output is a vector returning the switch current and voltage. The i output returns the tail current of forced-commutated devices such as IGBTs and GTOs. All the switch logics are vectorized. This means that a single model is used by power_analyze to simulate all the devices having the same type.

The Discrete Library

The Discrete library contains the discrete versions of the continuous models described above.

The Phasors Library

The Phasors library contains the phasor versions of some of the continuous models described above. See the Modeling Simple Systems chapter for more details on the phasor simulation.

The Switch Current Source Library

This library contains models of power electronic devices, which are simulated by a current source external to the linear circuit.

These devices are the diode and the thyristor with Lon > 0, and the three forced-commutated devices: gate-turn-off thyristor (GTO), metal-oxide-semiconductor field-effect transistor (MOSFET), and the insulated-gate-bipolar transistor (IGBT). All these models are continuous and contain an internal inductance, allowing you to handle fast transitions of forced-commutated converters. As for electrical machines, these models use a voltage input (output of the state-space model of the linear circuit) and their current output is fed into the state-space model. All these models are vectorized.

Increasing Simulation Speed

Limitations of the Nonlinear Models