Learn more about SimPowerSystems

How SimPowerSystems Software Works

Every time you start the simulation, a special initialization mechanism is called. This initialization process computes the state-space model of your electric circuit and builds the equivalent system that can be simulated by Simulink software. This process performs the following steps:

1. Sorts all SimPowerSystems blocks, gets the block parameters and evaluates the network topology. The blocks are separated into linear and nonlinear blocks, and each electrical node is automatically given a node number.

2. Once the network topology has been obtained, the state-space model (A, B, C, D matrices) of the linear part of the circuit is computed. All steady-state calculations and initializations are performed at this stage.

   If you have chosen to discretize your circuit, the discrete state-space model is computed from the continuous state-space model, using the Tustin method.

   If you are using the phasor solution method, the state-space model is replaced with the complex transfer matrix H(jω) relating inputs and outputs (voltage and current phasors) at the specified frequency. This matrix defines the network algebraic equations.

3. Builds the Simulink model of your circuit and stores it inside the Powergui block located at the top level of your model.

The Simulink model uses an S-Function block to model the linear part of the circuit. Predefined Simulink models are used to simulate nonlinear elements. These models can be found in the SimPowerSystems powerlib_models library. Simulink Source blocks connected at the input of the State-Space block are used to simulate the electrical source blocks.

The next figure represents the interconnections between the different parts of the complete Simulink model. The nonlinear models are connected in feedback between voltage outputs and current inputs of the linear model.

Interconnection of Linear Circuit and Nonlinear Models

Once SimPowerSystems software has completed the initialization process, the simulation starts. You can observe waveforms on scopes connected at the outputs of your measurement blocks. Through the Powergui, you can access the LTI viewer and obtain transfer functions of your system between any pair of input and output. The Powergui also allows you to perform a FFT analysis of recorded signals to obtain their frequency spectrum.

If you stop the simulation and double-click the Powergui block, you have access to the steady-state values of inputs, outputs, and state variables displayed as phasors. You can also use the Powergui to modify the initial conditions. The Powergui block interface allows you to perform a load flow with circuits involving three-phase machinery and initialize the machine models so that the simulation starts in steady state. This feature avoids long transients due to mechanical time constants of machines. The Powergui block allows you to specify the desired frequency range, visualize impedance curves, and store results in your workspace for Impedance Measurement blocks connected in your circuit.

Improving Simulation Performance

Choosing an Integration Method

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