Insulation Resistance Testing in Energized Apparatus with PWM Switching
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Solution Overview
Problem
Existing methods for measuring insulation resistance in energized electrical apparatuses, such as those in electric and hybrid vehicles, are slow and inaccurate, failing to meet the need for rapid and precise detection of insulation loss, which can lead to dangerous conditions like short-circuits and fires.
Innovation Solution
A method involving a switching circuit with duty-cycle controlled switches in parallel with the terminals of the apparatus, iteratively adjusting duty-cycles to maintain reference voltages within a target range, allowing for continuous and dynamic calculation of insulation resistances using Pulse Width Modulation (PWM) signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If traditional insulation resistance measurement methods are used, then measurement accuracy is maintained, but measurement time becomes excessively long (e.g., 30 seconds)
Solution Approach 1:
The patent applies dynamics by using PWM-controlled switches that dynamically adjust the measurement circuit configuration. The switching elements are controlled by pulse width modulation signals that can be adjusted in frequency and duty cycle, allowing the system to transition between different measurement modes and adapt to varying insulation resistance values, thereby reducing measurement time while maintaining accuracy
Solution Approach 2:
The patent employs periodic action through the use of PWM signals that periodically switch the measurement circuit between different states. The periodic switching creates alternating measurement phases that allow for rapid sampling and processing, enabling the system to complete measurements much faster than traditional continuous measurement methods while maintaining statistical accuracy
2Speed
If traditional insulation resistance measurement methods are used, then measurement stability is maintained, but response speed becomes too slow for real-time monitoring
Solution Approach 1:
The system dynamically adjusts the PWM switching frequency and duty cycle based on the measured insulation resistance values and operational requirements. This dynamic adaptation allows the measurement system to respond quickly to changes in insulation conditions while maintaining stable and reliable measurements through intelligent control of the measurement process
Solution Approach 2:
The patent implements feedback mechanisms where the measured insulation resistance values are continuously monitored and fed back to the control system. This feedback allows the system to adjust the PWM parameters in real-time, ensuring both rapid response to insulation changes and maintaining measurement stability through continuous optimization of the measurement process
Data Source
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AI summary
There is described a method for measuring a negative terminal insulation resistance Rin, present between a negative terminal 11 of an energized electrical apparatus 2 and a ground 3 ideally isolated from the energized electrical apparatus 2, and a positive terminal insulation resistance Rip, present between a positive terminal 12 of the energized electrical apparatus 2 and the aforesaid ground 3 ideally isolated from the energized electrical apparatus 2. Such a method first provides arranging a first switching circuit 16 between said positive terminal 12 and ground 3, thus in parallel with the positive terminal insulation resistance Rip, and arranging a second switching circuit 15 between said negative terminal 11 and ground 3, thus in parallel with the negative terminal insulation resistance (Rin). The aforesaid first switching circuit 16 comprises a first switching unit, configured to take either one of two states according to a first driving signal having a positive branch switching duty-cycle dp, and a first sample resistance Rkp arranged in series with respect to the aforesaid first switching unit. The aforesaid second switching circuit 15 comprises a second switching unit configured to take either one of two states according to a second driving signal having a negative branch switching duty-cycle dn and a second sample resistance Rkn arranged in series with respect to said second switching unit. The method then comprises the step of defining at least two working points of the circuit consisting of the energized electrical apparatus 2, the first switching circuit 16, and the second switching circuit 15; a first working point is associated with a first positive branch switching duty-cycle value dp1 and a first negative branch switching duty-cycle value dn1; the second working point is associated with a second positive branch switching duty-cycle value dp2 and a second negative branch switching duty-cycle value dn2. The method further includes controlling the first switching circuit 16 and the second switching circuit 15 so that they operate in accordance with the aforesaid first working point, and measuring, in such a condition, a respective first battery voltage value VB1, present between the negative terminal 11 and the positive terminal 12, and a respective first reference voltage value Viso1, representative of a voltage present at the ends of one of the first switching circuit 16 and the second switching circuit 15; such a reference voltage is thus determined by the first working point and is also dependent on both the negative terminal insulation resistance Rin and the positive terminal insulation resistance Rip. The method then includes controlling the first switching circuit 16 and the second switching circuit 15 so that they operate in accordance with the second working point, and measuring, in such a condition, a respective second battery voltage value VB2, present between said negative terminal 11 and positive terminal 12, and a respective second reference voltage value Viso2, representative of a voltage present at the ends of one of the first switching circuit 16 and the second switching circuit 15; such a reference voltage is thus determined by the second working point and is also dependent on both the negative terminal insulation resistance Rin and the positive terminal insulation resistance Rip. Finally, the method provides calculating the aforesaid negative terminal insulation resistance Rin and positive terminal insulation resistance Rip, based on the aforesaid first battery voltage value VB1, first reference voltage value Viso1, second battery voltage value VB2 and second reference voltage value Viso2. The aforesaid step of defining at least two working points comprises determining the aforesaid first positive branch switching duty-cycle value dp1, first negative branch switching duty-cycle value dn1, second positive branch switching duty-cycle value dp2, and second negative branch switching duty-cycle value dn2 based on the criterion of keeping the first reference voltage value Viso1 and the second reference voltage value Viso2 within a given neighborhood with respect to a predefined reference target voltage Vt.