PV Ground Insulation Impedance Detection Using Dual Harmonics
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Solution Overview
Problem
Existing photovoltaic energy systems face challenges in accurately detecting ground insulation impedance due to the impact of parasitic capacitance, leading to low detection accuracy and potential safety risks.
Innovation Solution
A photovoltaic energy system with a detection circuit that includes a signal source excitation branch, sampling circuit, and control circuit, which uses harmonic signals of different frequencies to measure ground insulation impedance without considering parasitic capacitance, thereby improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional detection methods are used to measure ground insulation impedance, then the measurement includes parasitic capacitance, but the detection accuracy deteriorates
Solution Approach 1:
The patent segments the impedance measurement into two separate measurements at different frequencies. By injecting harmonic signals at fundamental frequency and third harmonic frequency, the system separates the capacitive reactance component (which varies with frequency) from the resistive insulation component, enabling accurate extraction of ground insulation impedance while eliminating parasitic capacitance interference.
Solution Approach 2:
The patent changes the frequency parameter of the detection signal to resolve the measurement problem. By measuring impedance at two different frequencies (fundamental and third harmonic), the system creates a solvable system of equations that separates the frequency-dependent capacitive component from the frequency-independent resistive insulation component, thereby achieving accurate measurement despite parasitic capacitance.
2Power
If multiple conversion circuits are connected in parallel to increase system capacity, then the system power increases, but the ground insulation impedance detection becomes more difficult due to cumulative parasitic capacitance
Solution Approach 1:
The patent applies segmentation by dividing the impedance measurement into frequency-based components. This approach works regardless of the number of parallel conversion circuits, as it separates the measurement into solvable equations that account for cumulative parasitic capacitance without increasing measurement complexity.
Solution Approach 2:
The control circuit uses feedback by comparing the measured voltages at different frequencies and iteratively solving the impedance equations. This feedback mechanism automatically compensates for the cumulative effect of parasitic capacitance in parallel configurations, maintaining detection accuracy as system capacity scales.
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
The solution enhances the accuracy of ground insulation impedance detection, ensuring the safety and reliability of the photovoltaic energy system by excluding parasitic capacitance from the measurement, thus preventing false readings and improving fault detection.
Implementation Method 1
the control circuit is configured to control the alternating current signal source to output harmonic signals of a first frequency and a second frequency
Implementation Method 2
the first sampling circuit is configured to: when the alternating current signal source outputs the harmonic signal of the first frequency, collect a voltage at both terminals of the sampling resistor to obtain a first voltage
Implementation Method 3
the control circuit is further configured to detect, based on the harmonic signals of the first frequency and the second frequency, the first voltage, and the second voltage, a ground insulation impedance
Data Source
AI summary
A photovoltaic energy system and a method for detecting a ground insulation impedance, improve accuracy of detecting a ground insulation impedance after one or more conversion circuits are connected in parallel. The photovoltaic energy system includes one or more conversion circuits and a detection circuit. The detection circuit includes an alternating current signal source and a sampling resistor that are connected in series, a first sampling circuit, and a control circuit. The control circuit is configured to control the alternating current signal source to output harmonic signals of a first frequency and a second frequency. The first sampling circuit is configured to: when the alternating current signal source outputs the harmonic signal of the first frequency, collect a voltage at both terminals of the sampling resistor to obtain a first voltage.