Grid-Connected Inverter Insulation Impedance Detection
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Solution Overview
Problem
Conventional methods for detecting insulation impedance of an inverter cannot accurately measure impedance to ground when the inverter is connected to a power grid, limiting the detection to only pre-connection scenarios.
Innovation Solution
A method involving a power supply that outputs different test signals to disturb the voltage or current of the power grid during grid-connected operation, allowing for the calculation of insulation impedance using a test resistor and voltage or current changes, enabling direct-current and alternating-current insulation impedance detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional impedance detection methods are used with known voltage sources arranged between power grid and ground, then impedance to ground before inverter connection can be detected, but impedance to ground when inverter is connected to power grid cannot be detected
Solution Approach 1:
The patent applies dynamics by making the test voltage source switchable and controllable during grid-connected operation. The voltage source can be dynamically adjusted to output different test voltages (first and second test voltages) while the inverter is connected to the power grid, enabling real-time insulation impedance detection during operation rather than only before connection.
Solution Approach 2:
The patent changes the voltage parameter by using two different test voltages with opposite polarities (first test voltage and second test voltage). By applying different voltage levels and measuring the corresponding current changes, the system can calculate insulation impedance dynamically during grid-connected operation, resolving the limitation of conventional single-voltage methods.
2Measurement precision
If test circuits are connected to detect insulation impedance during grid-connected operation, then detection accuracy improves, but mechanical stress and wear on switching components increases
Solution Approach 1:
The patent implements periodic action by detecting insulation impedance at specific intervals (before grid connection and after grid connection) rather than continuously. The test voltage source is activated only when needed for detection, reducing the operating time of switching components while still providing accurate impedance measurements at critical moments.
Solution Approach 2:
The patent ensures continuity of useful action by maintaining the test voltage source readiness without requiring frequent mechanical switching. The controller can smoothly activate and deactivate the test voltage source based on operational conditions, minimizing mechanical stress on switches while ensuring detection capability is always available when needed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate and real-time detection of insulation impedance during grid-connected operation, improving detection accuracy and response speed while reducing mechanical stress on components.
Implementation Method 1
impedance of the power grid to ground is calculated based on a impedance voltage-division principle
Implementation Method 2
measures the insulation resistance with respect to ground of a DC power supply circuit
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3
AI summary
An inverter and a method for detecting insulation impedance of the inverter are provided. During grid-connected operation of the inverter, the method includes: controlling a power supply to output two different test signals, and recording voltages of a power grid to ground corresponding to the two test signals; and calculating the insulation impedance to ground of the inverter during the grid-connected operation of the inverter according to the two test signals and the voltages of the power grid to ground corresponding to the two test signals. According to the present disclosure, the power supply outputs different test signals to disturb the voltage of the power grid to ground, so as to detect insulation impedance of the inverter during grid-connected operation of the inverter.