Impedance Scan (Three-Phase)

Detect oscillatory instabilities in power networks with inverter-based renewable resources

Since R2026a

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  • Impedance Scan (Three-Phase) block

Libraries:
Simscape / Electrical / Control / Renewables Control

Description

The Impedance Scan (Three-Phase) block injects voltage or current disturbances into a balanced three-phase electrical system and measures the perturbed currents or voltages. Use this block to:

  • Detect oscillatory instabilities in power networks with inverter-based renewable resources, like solar plants, wind generators, and battery energy storage systems (BESS).

  • Detect sub-synchronous and super-synchronous oscillations in the power grid.

  • Obtain the D-axis and Q-axis impedance or admittance Bode plots to assist you in tuning controllers and designing inverters.

To inject disturbances into single-phase, unbalanced, or DC networks, use the Frequency Response Estimator (Simulink Control Design) block instead.

To use the Impedance Scan (Three-Phase) block, you need a Simulink® Control Design™ license.

The Impedance Scan (Three-Phase) block is a discrete-time block that runs at a fixed sample time. Specify the sampling frequency by using the Sampling frequency (Hz) parameter.

You can choose whether to inject voltage or current disturbances by using the Type of injection parameter. Use series voltage injection when the resource impedance is lower than the impedance of the rest of the system. Use shunt current injection when the resource impedance is higher than the impedance of the rest of the system.

You can also choose whether to inject disturbances in the form of a pseudorandom binary sequence (PRBS) or a sinestream with variable frequency by using the Disturbance parameter. A PRBS is faster to simulate. A sinestream gives more accurate results.

This figure shows the control structure. The physical system comprises the energy source, the disturbance injection point, the point of interconnection, and the grid. The control algorithm comprises a sinestream or PRBS generator, an inverse Park transform, a phase-locked loop (PLL), and Park transforms. The control algorithm measures the three-phase voltages at the point of interconnection and outputs the three-phase current or voltage disturbance at the disturbance injection point. The block uses the PLL to track the steady-state grid frequency F and phase angle θ. Park transforms then convert the voltages measured at the point of interconnection (POI) into their respective D and Q components for data processing. The block also uses θ to convert the reference D- and Q-axis voltage perturbations into their corresponding phases before injection.

The mabc port outputs the three-phase per-unit current or voltage disturbance injection. To inject the disturbance into your electrical network, use this signal as a pulse-width modulation (PWM) reference for an inverter.

Specify the magnitude of the signal that you inject into the D- and Q-axis by setting the Disturbance amplitude along D-axis (pu) and Disturbance amplitude along Q-axis (pu) parameters, respectively. A typical voltage injection is 1-10% of the rated voltage of the device you want to scan. To identify the D- and Q-axis impedance spectrums sequentially, first run a simulation where you inject the disturbance along the D-axis only. Then, run a second simulation where you inject a disturbance along the Q-axis only.

Specify the duration of the disturbance injection by setting values for the Disturbance injection start time (s) and Disturbance injection end time (s) parameters. To limit the overall simulation time, start the injection soon after the simulation has reached a periodic steady state. Longer durations capture impedance spectra more accurately but also slow down the simulation. The minimum duration of the disturbance depends on the values of the Disturbance, Disturbance frequency vector (Hz), and Sampling frequency (Hz) parameters. If you set the Disturbance parameter to Sinestream, then the minimum duration also depends on the value of the Number of cycles at each frequency parameter. You can check the minimum duration in the Disturbance Injection Parameters tab of the block dialog box, underneath the parameters. If you change any parameter values, click the Apply button in the block dialog box to update the duration that the block dialog box displays.

Perturbed Measurement Data

The signal at the data port is a structure containing the perturbed measurements. To create Bode plots of the admittance or impedance, store this signal in a variable and use the impedanceScanBodePlot function. The data structure contains these ten fields:

  • DD — Voltage and current measurements along the D-axis for a disturbance injection along the D-axis, in volts and amps respectively, specified as a structure.

  • DQ — Voltage and current measurements along the Q-axis for a disturbance injection along the D-axis, in volts and amps respectively, specified as a structure.

  • QD — Voltage and current measurements along the D-axis for a disturbance injection along the Q-axis, in volts and amps respectively, specified as a structure.

  • QQ — Voltage and current measurements along the Q-axis for a disturbance injection along the Q-axis, in volts and amps respectively, specified as a structure.

  • Dd — Per-unit amplitude of the disturbance along the D-axis, specified as a time series. The value of the Data property of this time series is equal to the value of the Disturbance amplitude along D-axis (pu) parameter.

  • Dq — Per-unit amplitude of the disturbance along the Q-axis, specified as a time series. The value of the Data property of this time series is equal to the value of the Disturbance amplitude along Q-axis (pu) parameter.

  • Tstart — Time at which the disturbance injection starts in seconds, specified as a time series. The value of the Data property of this time series is equal to the value of the Disturbance injection start time (s) parameter.

  • Tend — Time at which the disturbance injection ends in seconds, specified as a time series. The value of the Data property of this time series is equal to the value of the Disturbance injection end time (s) parameter.

  • f — Frequencies at which the block calculates the frequency response in hertz, specified as a time series. The value of the Data property of this time series is equal to the value of the Disturbance frequency vector (Hz) parameter.

  • scan — Type of disturbance injected, specified as a time series. The value of the Data property of this time series is 0 for a sinestream injection and 1 for a PRBS injection. This value corresponds to the Disturbance parameter.

Visualization

The visualization port outputs a bus containing these five signals for visualization:

  • Per-unit D-axis current iD

  • Per-unit Q-axis current iQ

  • Frequency F of the voltage measured at the POI, in hertz

  • Per-unit D-axis voltage VD

  • Per-unit Q-axis voltage VQ

Ports

Input

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Three-phase per-unit voltage measured at the point of interconnection.

Data Types: single | double

Three-phase per-unit current measured at the point of interconnection.

Data Types: single | double

Output

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Structure containing the perturbed measurement data. For more information about this structure, see Perturbed Measurement Data.

Data Types: single | double

Bus containing internal signals for visualization. For a list of signals, see Visualization.

Data Types: single | double

Three-phase per-unit shunt current or series voltage disturbance injection.

Specify whether to inject shunt current or series voltage disturbances by using the Type of injection parameter.

To inject the disturbances into your electrical network, use this signal as a pulse-width modulation (PWM) reference for an inverter.

Data Types: single | double

Parameters

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To edit block parameters interactively, use the Property Inspector. From the Simulink Toolstrip, on the Simulation tab, in the Prepare gallery, select Property Inspector.

Type of disturbance, specified as one of these options:

  • PRBS — Inject disturbances as a pseudorandom binary sequence. Choose this option to prioritize faster simulation over accuracy.

  • Sinestream — Inject disturbances as a sinestream with variable frequency. Choose this option to prioritize accuracy over faster simulation.

Type of injection, specified as one of these options:

  • Series voltage injection — Use this option when the resource impedance is lower than the impedance of the rest of the system.

  • Shunt current injection — Use this option when the resource impedance is higher than the impedance of the rest of the system.

Disturbance Injection Parameters

Per-unit amplitude of the disturbance along the D-axis.

A typical voltage injection is 1-10% of the rated voltage of the device you want to scan.

Per-unit amplitude of the disturbance along the Q-axis.

A typical voltage injection is 1-10% of the rated voltage of the device you want to scan.

Disturbance frequency vector, in hertz.

Number of cycles at each frequency.

Dependencies

To enable this parameter, set the Disturbance parameter to Sinestream.

Disturbance injection start time, in seconds.

To limit the overall simulation time, start the injection soon after the simulation has reached a periodic steady state.

Disturbance injection end time, in seconds.

This parameter and the Disturbance injection start time (s) parameter determine the duration of the disturbance injection. Longer durations capture impedance spectra more accurately but also slow down the simulation. The minimum duration depends on the values of other parameters. You can check the minimum duration in the Disturbance Injection Parameters tab of the block dialog box, underneath the parameters. If you change any parameter values, click the Apply button in the block dialog box to update the duration that the block dialog box displays.

AC base voltage, in volts.

Sampling frequency, in hertz.

PLL Parameters

Proportional gain of the phase-locked loop.

Integral gain of the phase-locked loop.

Initial frequency for the phase-locked loop, in hertz.

Initial angle for the phase-locked loop, in degrees.

References

[1] Riccobono, Antonino, Markus Mirz, and Antonello Monti. “Noninvasive Online Parametric Identification of Three-Phase AC Power Impedances to Assess the Stability of Grid-Tied Power Electronic Inverters in LV Networks.” IEEE Journal of Emerging and Selected Topics in Power Electronics 6, no. 2 (2018): 629–47. https://doi.org/10.1109/JESTPE.2017.2783042.

[2] Jiang, Ying, and A. Ekstrom. “General Analysis of Harmonic Transfer through Converters.” IEEE Transactions on Power Electronics 12, no. 2 (1997): 287–93. https://doi.org/10.1109/63.558741.

[3] Zhu, Yue. Impedance Model Analysis and Measurement for Power System Stability. August 2022. https://doi.org/10.25560/100373.

Extended Capabilities

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C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2026a

See Also

Functions

Blocks

Teaching Resources