Transformerless Inverter Insulation Resistance Measurement
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Solution Overview
Problem
Existing methods cannot measure the insulation resistance of a DC voltage input of a running transformerless inverter with respect to ground, especially when the AC voltage output has a specified ground reference, as they rely on a ground reference that is not available during operation.
Innovation Solution
A method that generates a periodic test voltage signal with a lower frequency than the AC voltage output, modulating it onto the DC voltage input, and records the resulting ground current to continuously measure insulation resistance, even with a specified earth reference of the AC voltage output, using either an additional voltage source or a potential shifting device to affect the DC voltage input.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ground reference is used for the AC voltage output to establish a stable reference, then the ground reference for DC voltage input is also established, but insulation resistance measurement becomes impossible during operation
Solution Approach 1:
The patent applies periodic action by modulating a test voltage signal with a specific frequency onto the DC voltage input through the inverter's switching elements. This periodic modulation allows the measurement system to distinguish the test signal from other electrical noise and operate continuously during inverter operation, resolving the contradiction between maintaining ground reference stability and enabling insulation resistance measurement.
Solution Approach 2:
The patent introduces an intermediary approach by using the inverter's switching elements as mediators to couple the test voltage signal onto the DC voltage input. This allows the measurement to be performed through the existing inverter structure without requiring direct access to the DC input terminals, enabling measurement while maintaining the ground reference.
2Productivity
If transformerless inverter operation is continuous to improve productivity, then galvanic isolation is absent, but insulation monitoring cannot be performed
Solution Approach 1:
The patent applies universality by designing a measurement system that functions during both operation and standby states. The same measurement circuitry and test voltage signal approach can be used regardless of whether the inverter is actively converting power or in idle state, allowing continuous monitoring without interrupting productivity while maintaining safety.
Solution Approach 2:
The periodic modulation of the test voltage signal enables the measurement system to operate continuously during inverter operation by distinguishing the test signal from other electrical noise through frequency discrimination, allowing uninterrupted insulation monitoring that maintains productivity.
3Measurement precision
If standard insulation measurement methods are used to achieve accurate measurement, then ground reference is required, but these methods cannot be applied during inverter operation
Solution Approach 1:
The patent applies parameter changes by modifying the measurement approach to use frequency-domain separation. The test voltage signal is modulated at a specific frequency, and the measurement system extracts the response at this frequency to calculate insulation resistance. This allows accurate measurement during operation by changing from DC-based methods to AC-based frequency-selective methods that are compatible with operating conditions.
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 continuous measurement of insulation resistance with a running transformerless inverter, providing a sensitive and accurate assessment of insulation resistance and leakage capacitance, even with varying ground references, and is less affected by fluctuating leakage capacitances.
Implementation Method 1
a periodic test voltage signal with a lower frequency than that of the alternating current is generated with respect to the specified ground reference of the alternating voltage output so that it is modulated onto the voltage at the direct voltage input
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
In order to measure the insulation resistance (Riso) of a DC voltage input (2) of a running transformer-less inverter (1) which emits an alternating current at an AC voltage output (3) with predetermined earthing, and of DC voltage sources (6) connected to the DC voltage input (2) relative to earth, a periodic test voltage signal is generated with a frequency lower than that of the AC voltage with respect to the predetermined earthing of the AC voltage output (3) such that it is modulated upwards when the inverter (1) is running to the voltage at the DC voltage input (2), and an earth current caused by the test voltage signal is detected.