Comparative Analysis of Superimposed AC Voltage (Ripple Voltage) Test Differences

1. Purpose

The design of the "Reference Test (Pre-scan UR value)" aims to determine the accurate power supply terminal voltage setting value through pre-testing, addressing the issue of "DUT terminal voltage attenuation" caused by factors such as equivalent internal resistance (power supply internal resistance, wiring harness impedance, device under test input impedance) in actual testing, ensuring the actual ripple voltage (Upp) at the DUT terminal complies with standard requirements.

2. Why Add Reference Test

With the popularization of new energy vehicles, the switching frequency (increased from traditional tens of kHz to hundreds of kHz or even higher) and ripple noise (generated by high-frequency switching of power devices) of vehicle power supply systems (such as DC/DC converters, battery management systems) have increased significantly. The traditional "open-loop injection" test (such as ISO 16750-2:2012 edition) cannot monitor the DUT terminal voltage in real time, easily leading to the problem of "power supply terminal voltage meeting standard but DUT terminal voltage insufficient" due to factors like equivalent internal resistance, failing to accurately assess equipment performance under actual operating conditions.

To address this issue, the "Superimposed AC Voltage Test" has been upgraded from "open-loop" to "closed-loop," requiring a reference test (pre-scan UR value) first, which can more accurately calibrate the Vpp injected into the DUT terminal.

3. How the Test Operates

Under the minimum load condition of the DUT, through closed-loop monitoring (using an oscilloscope to measure the ripple voltage Upp and current Ipp at the DUT terminal in real time), gradually increase the ripple voltage UR at the power supply terminal (frequency step is 2% logarithmic step, dwell time ≥2 seconds per frequency point), until the DUT terminal reaches the target ripple voltage Upp or the maximum current limit Ipp. The purpose of this step is to record the correspondence between the "power supply terminal UR value" and the "DUT terminal Upp value" at each frequency point (factors such as equivalent internal resistance may cause UR > Upp, e.g., UR = Upp + Ipp × Ri).

Based on the "UR-Upp" template generated by the reference test, directly use the power supply terminal's UR value for injection (without further adjusting UR), ensuring the Upp at the DUT terminal meets the standard requirements.

4. Why It Can Avoid Power Supply Internal Resistance Impact?

Equivalent internal resistance (Ri) is an inherent characteristic of the vehicle power supply system (such as battery internal resistance, cable resistance), causing a difference (ΔU = Ipp × Ri) between the "UR value output by the power supply terminal" and the "Upp value actually received by the DUT terminal." Traditional open-loop testing, unable to monitor the DUT terminal voltage, can only compensate for the internal resistance impact by "increasing the power supply terminal UR value," easily leading to "over-injection" (Upp exceeding standard limits) and damaging the DUT.

The reference test (pre-scan UR value) establishes the correspondence between the "power supply terminal UR value" and the "DUT terminal Upp value" through real-time monitoring of the DUT terminal voltage, ensuring the injected UR value can meet the Upp requirement at the DUT terminal. This "closed-loop control" method uses the same power supply setting value for the injection test as the reference test, meaning the UR value is considered the same, ensuring the required ripple level (e.g., 6Vpp) has been achieved.