Environment block for Simscape Electrical Specialized Power Systems models

Simscape / Electrical / Specialized Power Systems / Fundamental Blocks

The powergui block allows you to choose one of these methods to solve your circuit:

Continuous, which uses a variable-step solver from Simulink

^{®}Discretization of the electrical system for a solution at fixed time steps

Continuous or discrete phasor solution

The powergui block also opens tools for steady-state and simulation results analysis and for advanced parameter design.

You need the powergui block to simulate any Simulink model containing Simscape™ Electrical™ Specialized Power Systems blocks. It stores the equivalent Simulink circuit that represents the state-space equations of the model.

When using one powergui block in a model:

Place the powergui block in the top-level diagram for optimal performance.

Make sure that the block uses the name

`powergui`

.

The powergui block becomes disabled during model update. To ensure proper model execution, do not restore the library link for the powergui block.

You can use multiple powergui blocks in a system that contains two or more independent electrical circuits that you want to simulate with different powergui solvers. For example, this system simulates the upper electrical circuit in discrete mode and the bottom circuit in continuous mode. The purpose is to compare simulation performance of the two methods.

To do so, put each circuit in a different subsystem, and then add a powergui block inside each subsystem.

When you use more than one powergui block in a model:

Do not place a powergui block in the top-level diagram.

Place every independent model in a different subsystem.

Place a single powergui block in the top level diagram of every subsystem.

Do not include commented-out powergui blocks in your model. Doing so will prevent the model from simulating.

The configuration of the **Solver** tab depends
on the option that you select from the **Simulation type** list.

**Simulation type**Select

`Continuous`

( default) to perform a continuous solution of the model.Select

`Discrete`

to perform a discretization of the model. You specify the sample time in the**Sample time**parameter.Select

`Phasor`

to perform continuous phasor simulation of the model, at the frequency specified by the**Frequency (Hz)**parameter.If

**Simulation type**is set to`Discrete phasor`

, you can perform a phasor simulation at fixed time steps specified by the**Sample time (s)**parameter, at the frequency specified by the**Frequency (Hz)**parameter. The`Discrete phasor`

solver uses simplified machine models that produce simulation results similar to transient stability software.**Sample time (s)**Specify the sample time used to discretize the electrical circuit. This parameter is visible only when the

**Simulation type**parameter is set to`Discrete`

or to`Discrete phasor`

.Set the

**Sample time**parameter to a value greater than`0`

. The powergui block displays the value of the sample time. The default value is`50e-6`

s.**Frequency (Hz)**Specify the frequency for performing the phasor simulation of the model. This parameter is enabled only when you set

**Simulation type**to`Phasor`

or to`Discrete phasor`

. The powergui block displays the value of the phasor frequency. The default value is`60`

Hz.

**Steady-State**Open the Steady-State Voltages and Currents Tool dialog box to display the steady-state voltages and currents of the model. For more information, see

`power_steadystate`

.**Initial State**Open the Initial States Setting Tool dialog box to display and modify initial capacitor voltages and inductor currents of the model. For more information, see

`power_initstates`

.**Machine Initialization**Open the Machine Initialization Tool dialog box to initialize three-phase networks containing three-phase machines so that the simulation starts in steady state. The Machine Initialization tool offers simplified load flow features but can still initialize machine initial currents of your models. For more information, see

`power_loadflow`

.**Impedance Measurement**Open the Impedance vs Frequency Measurement Tool dialog box to display the impedance versus frequency defined by the Impedance Measurement blocks. For more information, see

`power_zmeter`

.**FFT Analysis**Open the FFT Analysis Tool dialog box to perform Fourier analysis of signals stored in a structure with time format. For more information, see

`power_fftscope`

.See Performing Harmonic Analysis Using the FFT Tool for an example that uses the FFT Analysis tool .

**Use Linear System Analyzer**Open a window to generate the state-space model of your system (if you have Control System Toolbox™ software installed) and open the Linear System Analyzer interface for time and frequency domain responses. For more information, see

`power_ltiview`

.**Hysteresis Design**Open a window to design a hysteresis characteristic for the saturable core of the Saturable Transformer block and the Three-Phase Transformer blocks (two- and three-windings). For more information, see

`power_hysteresis`

.**RLC Line Parameters**Open a window to compute RLC parameters of an overhead transmission line from conductor characteristics and tower geometry. For more information, see

`power_lineparam`

.**Generate Report**Open the Generate Report Tool dialog box to generate a report of steady-state variables, initial states, and machine load flow for a model. For more information, see

`power_report`

.**Customize SPS blocks**Open

`power_customize`

to create custom Simscape Electrical Specialized Power Systems blocks.**Load Flow**Open the Load Flow Tool dialog box to perform load flow and initialize three-phase networks and machines so that the simulation starts in steady state.

The Load Flow tool uses the Newton-Raphson method to provide robust and faster convergence solution compared to the Machine Initialization tool.

The Load Flow tool offers most of the functionality of other tools available in the power utility industry. For more information, see

`power_loadflow`

.**Max iterations**Defines the maximum number of iterations the Load flow tool iterates until the P and Q powers mismatch at each bus is lower than the

**PQ tolerance**parameter value (in pu/Pbase). The power mismatch is defined as the difference between the net power injected into the bus by generators and loads and the power transmitted on all links leaving that bus. For example, if the base power is 100 MVA and**PQ tolerance**is set to`1e-4`

, the maximum power mismatch at all buses does not exceed 0.1 MW or 0.1 Mvar. The default value is`50`

.**Frequency (Hz)**Specify the frequency used by the Load Flow tool to compute the normalized Ybus network admittance matrix of the model and to perform the load flow calculations. The default value is

`60`

Hz.**Base power (VA)**Specify the base power used by the Load Flow tool to compute the normalized Ybus network admittance matrix in pu/Pbase and bus base voltages of the model, at the frequency specified by the

**Load flow frequency**parameter.To avoid a badly conditioned Ybus matrix, select the base power value in the range of nominal powers and loads of the model. For a transmission network with voltages ranging from 120 kV to 765 kV, a 100 MVA base is usually selected. For a distribution network or for a small plant consisting of generators, motors, and loads having a nominal power in the range of hundreds of kilowatts, a 1 MVA base power is better adapted. The default value is

`100e6`

VA.**PQ tolerance (pu)**Defines the tolerance between P and Q when the Load flow tool stops to iterate. The default value is

`0.0001`

.**Voltage units**Determine the voltage units (V, kV) used by the Load Flow tool to display voltages. The default is

`kV`

.**Power units**Determine the power units (W, kW, MW) used by the Load Flow tool to display powers. The default is

`MW`

.

The load flow parameters are for model initialization only. They do not have an impact on simulation performance.

**Disable Specialized Power Systems warnings**When this check box is selected, the Simscape Electrical Specialized Power Systems warnings do not display during model analysis and simulation. By default, this option is not selected.

**Display Specialized Power Systems compilation messages**Select to enable the command-line echo messages during model analysis. By default, this option is not selected.

**Use TLC file when in Accelerator Simulation Mode and for code generation**Select to use TLC state-space S-functions (

`sfun_spssw_contc.tlc`

and`sfun_spssw_discc.tlc`

) in Accelerator mode and for code generation.Clear this box if you notice a slowdown in performance when using Accelerator mode, compared to previous releases. This slowdown occurs if you have the LCC compiler installed as the default compiler for building external interface (

`mex`

). By default, this option is not selected.**Disable ideal switching**Select this option to model switching devices as current sources. By default, this option is not selected, which corresponds to the recommended setting for most of your applications.

Modeling switches, such as circuit breakers or power electronic devices, as current sources implies that the on-state switch resistance Ron cannot be zero. In this modeling method, the switches cannot be connected in a series with an inductive circuit or with another switch or current source.

This parameter is available only when the

**Simulation type**parameter is set to`Continuous`

.When this option is enabled, you must add a circuit (R or RC snubber) in parallel with the switches in your model so that their off-state impedance has a finite value. If your real circuit does not use snubbers, or if you want to simulate ideal switches with no snubber, you must at least use resistive snubbers with a high resistance value to introduce a negligible leakage current. The drawback of introducing such high-impedance snubbers is that the large difference between the on-state and the off-state switch impedance produces a stiff state-space model.

**Disable snubbers in switching devices**Select to disable the snubber devices of the power electronic and breaker blocks in your model. This parameter is enabled only when the

**Simulation type**parameter is set to`Continuous`

and the**Disable ideal switching**option is cleared. By default, this option is cleared.**Disable Ron resistance in switching devices**Select to disable the internal resistance of switches and power electronic devices and to force the value to zero ohms. This parameter is enabled only when the

**Simulation type**parameter is set to`Continuous`

and the**Disable ideal switching**option is cleared. By default, this option is cleared.**Disable forward voltage in switching devices (Vf=0)**Select to disable the internal forward voltage of power electronic devices and to force the value to zero volts. This parameter is enabled only if the

**Simulation type**parameter is set to`Continuous`

and if the**Disable ideal switching**option is cleared. By default, this option is cleared.**Display circuit differential equations**Select to display the differential equations of the model in the Diagnostic Viewer when the simulation starts. This parameter is enabled only when the

**Simulation type**parameter is set to`Continuous`

and the**Disable ideal switching**option is cleared. By default, this option is cleared.**Automatically handle Discrete solver and Advanced tab solver settings of blocks**Select this parameter to automatically set the discretization method to

`Trapezoidal robust`

in models that contain at least one of the following blocks:Asynchronous Machine

Permanent Magnet Synchronous Machine

Simplified Synchronous Machine

Synchronous Machine

Surge Arrester

Variable Resistor

Variable Inductor

Variable Capacitor

Nonlinear Resistor

Nonlinear Inductor

Variable-Ratio Transformer

Any transformer blocks that are modeling saturation

If your model contains none of these blocks, the discretization method is automatically set to

`Tustin/Backward Euler (TBE)`

. This parameter is available only when the**Simulation type**parameter is set to`Discrete`

.**Discrete solver**Set this parameter to

`Tustin/Backward Euler (TBE)`

to simulate the model using a combination of the Tustin and Backward Euler methods.Set this parameter to

`Tustin`

to discretize the electrical model using the Tustin method. If you use this solver, you need to specify the*Rs*and*Cs*snubber values to avoid numerical oscillations when the firing pulses are blocked (when the bridge is operating as a rectifier). You can use the following formulas to compute the values of*Rs*and*Cs*:*Rs*> 2**Ts*/*Cs***(1)***Cs*<*Pn*/(1000*2*pi**f***Vn*^2**(2)**where:

*Pn*is the nominal power of the single-phase or three-phase converter, in VA.*Vn*is the nominal line-to-line AC voltage, in Vrms.*f*is the fundamental frequency, in Hz.*Ts*is the sample time, in s.

These values are derived from these criteria:

The snubber leakage current at fundamental frequency is less than 0.1% of nominal current when power electronic devices are not conducting.

The RC time constant of the snubbers is larger than two times the sample time,

*Ts*.

### Note

The

*Rs*and*Cs*values that guarantee the numerical stability of the discretized bridge can be different from the actual values used in the physical circuit.Set this parameter to

`Backward Euler`

to discretize the electrical model using the Backward Euler method.The default is

`Tustin/Backward Euler (TBE)`

. This parameter is enabled only if you set the**Simulation Type**parameter to`Discrete`

and the**Automatically handle Discrete solver and Advanced tab solver settings of blocks**parameter is cleared.**Interpolate switching events**This parameter is enabled only when

**Discrete solver**is set to`Tustin`

. Select to increase simulation speed by enabling the solver to interpolate in discrete models using power electronics. When this option is selected, the solver captures gate transitions of power electronic devices occurring between two sample times, allowing larger sample times (typically 20×) than you use with the standard solvers. For example, simulating a 5 kHz PWM converter with Tustin (no interpolation) or Tustin/Backward Euler normally requires a 1.0 µs sample time (sampling frequency = 200 × PWM frequency) to obtain a good resolution on pulse generation and guarantee accurate results. With interpolation enabled, using a sample time as large as 20 µs executes faster while preserving model accuracy.When you select this option:

Use a continuous pulse generator to guarantee the best accuracy on pulse generation (specify sample time = 0 in pulse-generation blocks).

In

**Simulink Model Configuration Parameters**, select a continuous, variable-step solver (`ode45`

or`ode23tb`

with default settings). The continuous solver is required by the interpolation solver to compute the gate signals time delays with respect to discrete sample times. The solver uses these pulse delays to interpolate between sample times and produce accurate results.

See the power_buck example model to see how interpolation increases accuracy and simulation speed.

**Use time-stamped gate signals**This option is enabled when the

**Interpolate switching events**option is selected. The interpolation method computes model outputs at fixed sample times while taking into account switching events that occur between two sample times. The method receives pulses at fixed time steps and computes the time delays of gate signals arriving within each time step. Computing the time delays enables the method to capture the evolution of states at different switching times.When

**Use time-stamped gate signals**is cleared, the interpolation method computes the time delays of gate signal.When

**Use time-stamped gate signals**is selected, the block does not compute the time delays of gate signals. You then need to directly provide time-stamped gate signals to the switching devices in your model. See the power_buck example for more information on the concept of time-stamped gate signals in Simscape Electrical Specialized Power Systems switching devices.The

**Use time-stamped gate signals**parameter is enabled only when you set**Simulation type**to`Discrete`

, set**Solver type**to`Tustin`

, and select the**Interpolate**option. By default, this option is cleared.**Store switching topologies**Select to increase simulation speed by enabling the solver to store and reuse matrix computation results. This parameter is enabled only when you set

**Simulation type**to`Continuous`

or`Discrete`

. By default, this option is not selected.**Buffer Size (MBytes)**Specify the buffer size for saving state-space matrix computations. This parameter is enabled only when you set

**Simulation type**to`Discrete`

, set**Solver type**to`Tustin`

, and select the**Store switching topologies**options. The default value is`100`

MB.**Start simulation with initial electrical states from**If you select

`blocks`

, initial state values defined in blocks are used for the simulation.If you select

`steady`

, force all initial electrical state values to steady-state values.If you select

`zero`

, force all initial electrical state values to zero.The default is

`blocks`

.**Solver details for nonlinear elements**When selected, the

**Solver tolerance**,**Maximum number of iterations**, and**Continue simulation if maximum number of iterations is reached**parameters define the discrete solver used for nonlinear iterative elements such as the nonlinear resistor in the Surge Arrester block and nonlinear inductors modelling saturation in the Saturable Transformer block.This parameter is enabled only when the

**Simulation type**parameter is set to`Discrete`

.**Solver tolerance**Specify the largest acceptable solver error. Default is

`1e-4`

.**Maximum number of iterations**Specify the maximum number of iterations. Iterations stop when the

**Solver tolerance**is achieved. A solution is usually found within 1 to 3 iterations. An error message is returned and simulation stops if a solution is not found when the maximum number of iterations is exceeded. Default is`100`

.**Continue Simulation if maximum number of iterations is reached**Select to limit the maximum number of iterations. This parameter is used for real-time applications. Usually, limiting the number of iterations to 2 produces acceptable results.

`power_customize`

, `power_fftscope`

, `power_hysteresis`

, `power_initstates`

, `power_lineparam`

, `power_ltiview`

, `power_loadflow`

, `power_report`

, `power_steadystate`

, `power_zmeter`