The rapid proliferation of high-penetration renewable energy and inverter-based resources (IBR) within power grids has brought the issue of small-signal instability—triggered by wideband oscillations in the IBR-dominated power system—into sharp focus. This instability significantly compromises the reliable integration of renewable energy and threatens the secure and stable operation of the IBR-dominated power system. The national standard "GB38755-2019 Guide for Power System Security and Stability" mandates analysis of sub-synchronous and super-synchronous oscillations. Among the wideband oscillation analysis methods for the IBR-dominated power system, the impedance-based analysis method is favored for its simplicity, clear physical interpretation, and strong engineering practicality. When device parameters are difficult to obtain, the equipment under test can be treated as a black box, with its impedance characteristics assessed via simulation and measurement techniques.

Building upon years of theoretical research and practical engineering validation of impedance-based analysis, KeLiang has successfully developed the Impedance Injection Tester, capable of wide-frequency-band sweep excitation and high-precision impedance characterization. Utilizing adaptive frequency-point injection technology, the instrument covers a frequency range from 1 Hz to 10 kHz. It synchronously generates impedance results, such as Bode plots and Nyquist plots, within the accompanying QuiKIS Impedance Scanning and Stability Analysis software. Featuring a modular design, the Impedance Injection Tester is adaptable for testing various power electronic converter controllers. It provides measured data and scan results to support stability analysis for renewable energy equipment and the development of oscillation mitigation strategies.

KL2900阻抗注入测试仪: KL2900 Impedance Injection Tester

The impedance scanning system comprises the QuiKIS Impedance Scanning and Stability Analysis software, the KL2900 Impedance Injection Tester, a real-time simulation platform, and the actual controller under test. Following standard impedance testing protocols, disturbance signal parameters are configured in the QuiKIS software. The KL2900 tester injects this disturbance signal via analog outputs or high-speed fiber-optic communication. Simultaneously, it acquires the voltage and current signals at the equipment's grid-connection point. The KL2900 performs real-time impedance calculation and analysis, with the resulting impedance/admittance characteristics of the power electronic converter displayed synchronously in the QuiKIS software.

• Analog Input Channels: 4 channels/card; 2 cards per unit (8 channels total).

• Analog Output Channels: 4 channels/card; 1 card per unit (4 channels total).

• Sampling Rate per Channel: Up to 2 MS/s.

• Input/Output Signal Range: ±10 VDC.

• Analog Input Type: Differential voltage.

• Analog Output Type: Single-ended voltage.

• Sampling Resistor: ≥10 kΩ.

• Output Accuracy per Channel: ≤0.1% FS + 0.02% RD.

• Data Storage: 4 TB SSD.

• Ethernet Interfaces: 2 Gigabit Ethernet ports.

• Display Interface: 1 mini DisplayPort.

• USB Interfaces: 2 ports.

• Multi-unit Synchronization Port: 1 port.

• SFP Fiber Optic Interfaces: 2 ports.

• Unit Weight: 10 kg.

• Unit Dimensions: 360 mm × 253 mm × 148 mm (W × H × D).

QuiKIS Impedance Scanning and Stability Analysis Software

The QuiKIS Impedance Scanning and Stability Analysis software facilitates automated impedance scanning for power electronic converters and enables impedance-based stability analysis at the port level for the IBR-dominated power system. It offers a comprehensive suite of user-friendly features, including graphical editing, general analysis, scripting, impedance scanning, impedance identification, and impedance analysis. The software interface is available in either Simplified Chinese or English.

Disturbance Injection Settings

Once the QuiKIS software is connected to the KL2900 Impedance Injection Tester, users can configure all relevant test parameters, including disturbance signal settings, impedance selection, injection frequencies, data recording, and file download management.

QuiKIS 下位机配置界面: QuiKIS Lower-Computer Configuration Interface

Impedance/Admittance Graphical Presentation

During an impedance scan, the results calculated in real-time by the tester are presented graphically within the QuiKIS software. Available plot types include Magnitude and Phase Bode plots, Real and Imaginary Part vs. Frequency plots, and Nyquist plots. 

QuiKIS Magnitude and Phase Bode Plot

QuiKIS Real and Imaginary Part vs. Frequency Plot

QuiKIS Nyquist Plot

Impedance/Admittance Data Verification

This feature verifies the accuracy of test data by calculating its deviation from a set of benchmark impedance/admittance data. Users can select up to two datasets for simultaneous comparison against the benchmark. The verification results display the maximum magnitude and phase differences. The software also plots separate Bode diagrams for the benchmark data, the comparison data, and the difference data.

Impedance/Admittance Data Verification

Stability Analysis

The QuiKIS software performs both qualitative and quantitative stability analysis on source and load impedance data using either the Nyquist criterion or the Maximum Peak Criterion. Quantitative analysis includes calculations for stability margin and risk frequency. The Maximum Peak Criterion allows users to define forbidden region radii for specific frequency bands and generates the Nyquist plot for the source-to-load impedance ratio.

Maximum Peak Criterion