Skip to main content

PSCAD™ smiby

PSCAD™ smiby

Last updated: 4 November 2024

Software required:

PSCAD™

Background​

smiby is a PSCAD™ Definition provided with the gridmo software platform which enables gridmo to easily interface with your PSCAD™ Workspace. smiby is a Thévenin equivalent source, used for SMIB studies, which can be controlled using the Grid controls. A simplified representation of smiby is shown below.

smiby-simplified

Adding smiby into a model​

danger

The video below states that smiby can be found in your gridmo Engine's Inputs folder - this is no longer the case.

Instead - please download the latest version of smiby using the DOWNLOAD MODEL button above.

Step 1: Disable/remove existing external grid representation​

Disable or remove the existing external grid representation (if any) at the connection point.

Step 2: Add smiby​

Add the smiby block into your PSCAD™ Workspace. Add a single smiby block in the same PSCAD™ Case file (.pscx) where your existing external grid representation was disabled/removed. The three phase electrical grid connection is on the left hand side of smiby. In your PSCAD™ Case file, connect this to your connection point using the PSCAD™ wire tool. An example of a correctly configured PSCAD™ Case file is shown below.

screenshot from the PSCAD software package showing a simplified single line diagram of how smiby works

caution

gridmo requires that the PSCAD™ Case file (.pscx) which contains the smiby block is first in the list of Case files. If required, right click the relevant Case file and select 'Move Up', as shown below, to move the Case file to the top of the list of Case files.

smiby-configure-case-files

Step 3: Configure control channels​

In addition to providing a controllable Thévenin equivalent source, smiby also contains 12 independent multi-purpose control channels which can be controlled using the CONTROL Command. Control channels should normally be used for values which you may want to vary during a PSCAD™ simulation. Examples of common control channels:

  • Active power setpoint
  • Reactive power setpoint
  • Voltage control mode
  • Voltage setpoint
  • Source energy (e.g. wind speed, solar irradiance)

In your PSCAD™ Case file, connect these control channels to your generating system using the PSCAD™ wire tool and Data Signal Array Tap.

In the smiby parameter window, configure the following settings for each control channel:

  • Enable/disable: This defines whether the control channel is enabled or disabled.
  • Scale: This defines the scaling applied to any CONTROL Commands (i.e. control channel output = CONTROL Command value x scale). This scale is not applied to the default value.
  • Defaults: This is the control channel output value used if there are no CONTROL Commands for this channel.
note

Depending on the definition of an externally defined or black-boxed PSCAD™ models, you can use the control channels as parameters by defining the channel with a name and adding the value into the parameters box.

Step 4: Configure smiby parameters​

Right click on the smiby block and navigate to 'Edit Parameters'. In the 'Base values' section, set the following values considering the requirements of your generating system:

  • Base voltage (float): Connection point base voltage [kV].
  • Base apparent power (float): Connection point base apparent power [MVA].
  • Base frequency (float): Base frequency [Hz].
  • Project rated active power (float): The combined maximum amount of active power that the generating system can deliver at the connection point [MW]. This value is used in combination with plant SCR Commands.

Updating smiby to a new version​


caution

Updating smiby may overwrite any of your custom modifications to smiby. In general, we recommend not making any changes to the smiby block or OEM libraries so that newer versions may be accommodated easily.

Over-voltage snubber circuit​

note

In versions of smiby earlier than v18, the following optional mode was called 'pre-insertion resistors' and worked in a similar way, however the resistance target was not dependent on the SCR and X/R ratio.

The VDISTURBANCE command controls the smiby block to apply a disturbance to the connection point. Under-voltages are applied via a fault block in PSCAD™, whereas over-voltages are applied by switching in/out an ideal capacitor. A capacitive load block in PSCAD™ is not suitable as it cannot be changed at runtime, meaning it limits to a single over-voltage event per simulation.

As PSCAD™ is an EMT tool, switching in an ideal capacitor can cause substantial oscillation of the RMS voltage at the connection point, especially under low SCR conditions.

To mitigate this, a non-linear snubber circuit can be activated in the smiby block to dampen the oscillations caused by the ideal capacitor. The snubber circuit is a resistor connected in series with the capacitor. The resistor's resistance starts at the critical damping value (given the SCR and X/R) and decays rapidly after switched in. The snubber circuit is only active when a capacitor is switched in for an over-voltage disturbance.

However, due to the non-linear nature of the snubber circuit, there may be a damped initial rise time which is longer than the result from RMS tools. The rise time may be up to 75 ms at very high SCR values or for severe overvoltages.

tip

To activate the snubber circuit, set the Use snubber circuit to dampen oscillations? to Yes in the VDISTURBANCE section of smiby, or alternatively use the following gridmo command in your PSCAD™ node.

SET, CNAME=smiby, PARAM=cap_capcharge2_enabled, VAL=1 // turn on snubber circuit

Revision history​

  • v19 (4 November 2024)
    • Fixed incorrect base value applied to positive/negative reactive current (IQ) and positive/negative active reactive current (ID), output channel unit is now consistent with total IQ and ID.
  • v18 (31 October 2024)
    • Changed to integer version number (rather than linking smiby version to the version of the engine when it was updated).
    • Added positive, negative and zero sequence voltage and current output channels.
    • Fixed incorrect unit conversion on positive/negative reactive current (IQ) and positive/negative active reactive current (ID) output channels (was radians, should have been degrees).
    • Low SCR initialisation mode now on by default for new smiby blocks added to a workspace.
    • Added large resistances to prevent rare singularity error on SIMPLEFAULT and VDISTURBANCE Commands.
    • Pre-insertion resistance setting (for VDISTURBANCE) and distance factor setting (for all faults) was greyed out unless faults were enabled - now always available.
    • Replaced non-linear pre-insertion resistance mode (for VDISTURBANCE) with automatic snubber circuit which auto-calculates impedances required to achieve critical damping (based on the SCR), with a non-linear resistance ramp-out to prevent benchmarking mismatch during the disturbance.
    • Fixed inductive kickback experienced on some models with transmission line blocks (caused by VDISTURBANCE CB opening at any current incorrectly set to true, rather than a zero crossing).
  • v1.4.13.2 (13 May 2024)
    • smiby's automatic infinite bus voltage not used to bias relative voltage steps.
    • smiby's automatic infinite bus voltage mode incorrectly applies a fixed ramp rate to all subsequent voltage changes in a simulation.
  • v1.4.13 (7 May 2024)
    • Added automatic infinite bus voltage calculation capability.
  • v1.4.12 (15 April 2024)
    • Expanded low-SCR initialisation mode options. New modes include infinite bus voltage ramps, and infinite bus voltage and SCR ramps.
  • v1.4.11 (20 March 2024)
    • Updated power factor calculation logic to improve handling for indeterminate cases (0/0).
note

To see the changelog for older changes to this model, please see the main gridmo change log here.