Abstract This study investigates how the power output states of off-board chargers for electric vehicles (EVs) affect the results of vehicle interface disconnection tests. Using comparative experiments that alter current and voltage outputs, the research measures the time delay between “CC1 disconnection” and the opening of contactors K1/K2, based on national standard testing protocols. Results indicate that under normal charging conditions, variations in power output (both current and voltage) do not significantly impact the disconnection test results. This finding validates the reliability of the test method specified in GB/T 34657.1-2017 and provides a technical basis for interoperability testing of EV charging equipment.
Keywords: electric vehicle (EV); off-board charger; power output state; vehicle interface disconnection test; interoperability; contactor disconnection time
1. Introduction
The rapid proliferation of electric vehicles (EVs) has heightened the focus on the safety and stability of supporting charging infrastructure. Off-board chargers, which deliver direct current (DC) to EV batteries through conductive connections, are widely adopted due to their high power output and short charging times . As a critical component of EV charging systems, ensuring their interoperability is essential to safeguard user safety and property .
Vehicle interface disconnection testing is a key part of evaluating charger performance under abnormal conditions. This test simulates the scenario of a charging interface disconnection (e.g., CC1 line breakage) during normal charging and measures whether the charger can promptly stop power output . A core metric of this test is the disconnection time of contactors K1 and K2, which must occur within 100 ms to meet safety standards .
While GB/T 34657.1-2017 specifies the test methodology for interoperability, it does not address how different power output states (e.g., varying current and voltage levels) might influence results . This study aims to fill this gap by systematically analyzing the impact of power output variations on disconnection test outcomes, providing practical guidance for charger testing and safety assurance .
2. Vehicle Interface Disconnection Test Basics
2.1 Test Standards and Objectives
The test adheres to GB/T 34657.1-2017, which outlines procedures for evaluating charger interoperability . The primary objective is to verify that when a vehicle interface disconnects (simulated by CC1 line breakage), the charger promptly de-energizes the output terminals by opening contactors K1 and K2 within the specified time limit .
2.2 Key Test Parameters
- CC1 Disconnection Detection: Monitored via the voltage between CC1 and PE (voltage value 1).
- Contactor State: Determined by the voltage between DC+ and DC- (voltage value 2).
- Critical Time Delay: The interval from CC1 disconnection (voltage value 1 rise) to contactor disconnection (voltage value 2 fall), denoted as ΔX .
3. Experimental Methodology
3.1 Test Setup and Equipment
- Charger Models: Three off-board chargers (A, B, C) from different manufacturers, covering varied specifications.
- Instrumentation:
- Oscilloscope: Two channels for monitoring voltage value 1 (普通探头) and voltage value 2 (high-voltage differential probe, 1/500 range), with a time measurement accuracy of ±0.1% .
- Calibration Device: Includes a CC1 on/off switch (to simulate disconnection) and signal acquisition terminals for CC1, PE, DC+, and DC- .
3.2 Test Protocols
- Current Variation Test:
- Fixed voltage: 450 V.
- Tested currents: 0 A, 9 A, 60 A, 90 A.
- Each condition tested 10 times for statistical analysis.
- Voltage Variation Test:
- Fixed current: 60 A.
- Tested voltages: 225 V, 300 V, 375 V, 450 V.
- Each condition tested 10 times for statistical analysis .
3.3 Data Acquisition
The oscilloscope records the timing of voltage value 1 rise (CC1 disconnection) and voltage value 2 fall (contactor disconnection). The time delay ΔX is calculated as the difference between these two events .
4. Experimental Results
4.1 Current Variation Test Results
Table 1. Disconnection Time (ΔX) at Different Output Currents (Voltage = 450 V)
| Charger | Current (A) | Test Trials (ms) | Average (ms) | Variance (ms²) |
|---|---|---|---|---|
| A | 0 | 43.7, 41.9, … | 40.77 | 2.05 |
| B | 0 | 72.7, 74.5, … | 72.92 | 3.31 |
| C | 0 | 57.2, 57.5, … | 55.89 | 2.52 |
| A | 9 | 44.3, 38.8, … | 45.71 | 8.25 |
| B | 9 | 75.7, 73.0, … | 75.32 | 1.70 |
| C | 9 | 58.7, 59.6, … | 59.07 | 1.81 |
| A | 60 | 46.4, 47.8, … | 45.73 | 2.21 |
| B | 60 | 73.6, 76.4, … | 75.01 | 4.65 |
| C | 60 | 59.7, 60.3, … | 59.20 | 1.34 |
| A | 90 | 44.7, 43.6, … | 45.45 | 1.99 |
| B | 90 | 77.8, 75.8, … | 75.84 | 1.14 |
| C | 90 | 58.3, 59.6, … | 59.11 | 1.42 |
Note: Data for charger A at 60 A includes values like 46.4, 47.8, etc., as detailed in .
4.2 Voltage Variation Test Results
Table 2. Disconnection Time (ΔX) at Different Output Voltages (Current = 60 A)
| Charger | Voltage (V) | Test Trials (ms) | Average (ms) | Variance (ms²) |
|---|---|---|---|---|
| A | 225 | 44.2, 44.5, … | 44.33 | 5.63 |
| B | 225 | 73.6, 74.4, … | 74.92 | 3.85 |
| C | 225 | 59.7, 58.4, … | 59.67 | 1.01 |
| A | 300 | 45.4, 47.5, … | 46.06 | 1.62 |
| B | 300 | 75.4, 77.3, … | 75.51 | 1.95 |
| C | 300 | 60.1, 59.2, … | 59.26 | 1.56 |
| A | 375 | 45.1, 45.2, … | 46.03 | 1.53 |
| B | 375 | 78.2, 78.5, … | 75.76 | 2.87 |
| C | 375 | 58.5, 58.1, … | 59.07 | 1.05 |
| A | 450 | 46.4, 47.8, … | 45.73 | 2.21 |
| B | 450 | 73.6, 76.4, … | 75.01 | 4.65 |
| C | 450 | 59.7, 60.3, … | 59.20 | 1.34 |
Note: Data for charger B at 300 V includes values like 75.4, 77.3, etc., as detailed in .
5. Statistical Analysis of Results
5.1 Hypothesis Testing with Independent Sample t-Test
To determine if power output states significantly affect disconnection time, we use the independent sample t-test. The test statistic is calculated as:
\(t = \frac{|\overline{x}_1 – \overline{x}_2|}{\sqrt{\frac{s_1^2}{n_1} + \frac{s_2^2}{n_2}}}\)
where:
- \(\overline{x}_1, \overline{x}_2\) = sample means of two power states,
- \(s_1^2, s_2^2\) = sample variances,
- \(n_1, n_2\) = sample sizes (n = 10 for all tests) .
The null hypothesis (H₀) assumes no significant difference between groups, with a significance level of α = 0.05 and degrees of freedom (df) = n₁ + n₂ – 2 = 18. The critical t-value for a two-tailed test at α = 0.05 is ±2.101 .
5.2 Current Variation Test Analysis
Table 3. t-Test Results for Different Output Currents
| Power Combinations (450 V) | Charger A | Charger B | Charger C |
|---|---|---|---|
| 9 A vs. 60 A | 0.020 | 0.389 | 0.231 |
| 9 A vs. 90 A | 0.257 | 0.975 | 0.070 |
| 60 A vs. 90 A | 0.432 | 1.091 | 0.171 |
All calculated t-values are less than the critical value (2.101), indicating no significant difference in disconnection time across different current levels .
5.3 Voltage Variation Test Analysis
Table 4. t-Test Results for Different Output Voltages (60 A)
| Power Combinations | Charger A | Charger B | Charger C |
|---|---|---|---|
| 225 V vs. 300 V | 2.032 | 0.811 | 0.808 |
| 225 V vs. 375 V | 2.009 | 1.065 | 1.320 |
| 225 V vs. 450 V | 1.581 | 0.101 | 0.968 |
| 300 V vs. 375 V | 0.053 | 0.360 | 0.371 |
| 300 V vs. 450 V | 0.533 | 0.616 | 0.111 |
| 375 V vs. 450 V | 0.491 | 0.865 | 0.265 |
All t-values remain below the critical threshold, confirming no significant impact of voltage variations on disconnection time .
6. Discussion
6.1 Implications of Findings
The results demonstrate that under normal charging conditions (power output > 0 kW), changes in current or voltage do not significantly affect the disconnection time of contactors K1/K2. This validates the GB/T 34657.1-2017 standard’s approach, which allows testing under any power output state during normal charging .
6.2 Practical Applications
- Test Efficiency: Chargers can be tested at any practical power level, eliminating the need for strict power control during interface disconnection tests.
- Safety Assurance: The consistency of results across power states ensures reliable safety evaluations, regardless of real-world charging scenarios (e.g., varying battery states of charge) .
6.3 Limitations and Future Work
This study focuses on normal charging conditions and does not address extreme fault scenarios (e.g., overcurrent or voltage surges). Future research could explore power output impacts under abnormal conditions to further enhance charger safety protocols.
7. Conclusion
Through systematic experimentation and statistical analysis, this study confirms that the power output state of off-board chargers for electric vehicles (EVs) does not significantly influence the results of vehicle interface disconnection tests under normal charging conditions. The consistent disconnection times across varying current and voltage levels validate the robustness of the GB/T 34657.1-2017 test method. These findings provide a solid technical foundation for interoperability testing, ensuring the safety and reliability of EV charging infrastructure.