With the rapid growth of the electric car industry, the safety and reliability of charging infrastructure have become critical concerns. In China, the adoption of electric vehicles, often referred to as China EV, has surged, driving demand for efficient and safe charging solutions. Off-board chargers, which provide direct current to electric car batteries, are widely used due to their high power output and fast charging capabilities. Ensuring their interoperability and safety is essential, particularly under abnormal conditions such as sudden disconnections. This study investigates how different power output states of off-board chargers affect the results of vehicle interface disconnection tests, a key aspect of charging safety for electric cars.
Vehicle interface disconnection tests are mandated by national standards, such as GB/T 34657.1-2017, to verify that chargers can promptly stop power delivery when the connection is interrupted. During normal charging, if the vehicle interface is disconnected, the charger must open its contactors (K1 and K2) within 100 milliseconds to prevent hazards. The time delay between CC1 disconnection and contactor opening is a crucial parameter, as it indicates the charger’s responsiveness. However, the standard does not specify the power output level for testing, raising questions about whether variations in current or voltage affect the disconnection time. In this analysis, I explore this issue through experimental data, focusing on electric car chargers commonly used in China EV applications.
The test method involves simulating a vehicle interface disconnection during charging by breaking the CC1 connection and monitoring the response. I used an oscilloscope to capture voltage changes: one channel tracked the voltage between CC1 and PE (voltage value 1), which rises upon disconnection, and another channel monitored the voltage between DC+ and DC- (voltage value 2), which drops when contactors open. The time difference between these events, denoted as ΔX, represents the disconnection response time. This setup ensures accurate measurements with a time resolution of ±0.1%. For safety, a high-voltage differential probe was used for voltage value 2, while a standard probe sufficed for voltage value 1. The charging system included a resistive load and a calibration device with a CC1 disconnect switch to replicate real-world electric car charging scenarios in China EV environments.
To assess the impact of power output state, I conducted experiments on three off-board chargers from different manufacturers, labeled A, B, and C. These chargers are typical of those used in electric car infrastructure across China. The tests varied two parameters: output current at a constant voltage and output voltage at a constant current. For each condition, I performed 10 repeated measurements of the disconnection time and calculated averages and variances to ensure statistical reliability. This approach aligns with standards for electric car charger testing and helps evaluate consistency in China EV applications.
First, I examined the effect of output current by setting the voltage to 450 V and testing currents of 0 A, 9 A, 60 A, and 90 A. A current of 0 A represents a no-load condition, which, although not typical of normal charging, serves as a baseline. The results, summarized in Table 1, show the disconnection times in milliseconds for each charger under different current outputs. The data indicate that the average times remain relatively stable across current levels, suggesting that output current may not significantly influence the disconnection response for electric car chargers.
| Output Current (A) | Charger | Disconnection Time (ms) – Measurements 1-10 | Average (ms) | Variance (ms²) |
|---|---|---|---|---|
| 0 | A | 43.7, 41.9, 40.6, 41.4, 40.3, 41.3, 38.7, 39.8, 40.8, 39.2 | 40.77 | 2.05 |
| B | 72.7, 74.5, 72.5, 71.7, 70.5, 73.8, 70.3, 75.1, 72.5, 75.6 | 72.92 | 3.31 | |
| C | 57.2, 57.5, 55.9, 56.2, 54.4, 56.5, 57.4, 54.5, 52.6, 56.7 | 55.89 | 2.52 | |
| 9 | A | 44.3, 38.8, 48.4, 47.6, 45.4, 46.5, 48.3, 45.9, 47.7, 44.2 | 45.71 | 8.25 |
| B | 75.7, 73.0, 74.8, 76.4, 74.4, 75.6, 75.2, 77.6, 76.3, 74.2 | 75.32 | 1.70 | |
| C | 58.7, 59.6, 59.4, 60.7, 59.2, 56.5, 58.7, 57.3, 60.0, 60.6 | 59.07 | 1.81 | |
| 60 | A | 46.4, 47.8, 44.0, 45.3, 46.7, 43.3, 47.2, 45.9, 44.2, 46.5 | 45.73 | 2.21 |
| B | 73.6, 76.4, 75.5, 75.9, 73.2, 75.7, 78.2, 76.3, 70.4, 74.9 | 75.01 | 4.65 | |
| C | 59.7, 60.3, 60.6, 59.2, 58.6, 58.2, 59.9, 57.1, 60.3, 58.1 | 59.20 | 1.34 | |
| 90 | A | 44.7, 43.6, 45.7, 46.2, 44.9, 48.5, 45.4, 46.2, 43.7, 45.6 | 45.45 | 1.99 |
| B | 77.8, 75.8, 76.2, 75.6, 75.7, 74.1, 76.5, 76.8, 75.3, 74.6 | 75.84 | 1.14 | |
| C | 58.3, 59.6, 57.7, 57.2, 59.9, 59.4, 60.5, 58.3, 60.8, 59.4 | 59.11 | 1.42 |
Next, I evaluated the effect of output voltage by maintaining a constant current of 60 A and testing voltages of 225 V, 300 V, 375 V, and 450 V. This range covers typical operating conditions for electric car chargers in China EV systems. The disconnection times, presented in Table 2, demonstrate consistent averages across voltage levels, further supporting the idea that power output state does not alter the test outcomes. The variances are relatively small, indicating high repeatability in the measurements for electric car applications.
| Output Voltage (V) | Charger | Disconnection Time (ms) – Measurements 1-10 | Average (ms) | Variance (ms²) |
|---|---|---|---|---|
| 225 | A | 44.2, 44.5, 46.4, 44.9, 38.0, 45.8, 43.7, 44.6, 45.8, 45.4 | 44.33 | 5.63 |
| B | 73.6, 74.4, 73.7, 76.8, 76.6, 77.5, 74.8, 72.5, 72.7, 76.6 | 74.92 | 3.85 | |
| C | 59.7, 58.4, 61.2, 59.4, 59.7, 59.5, 61.3, 58.8, 58.5, 60.2 | 59.67 | 1.01 | |
| 300 | A | 45.4, 47.5, 46.2, 43.9, 47.8, 46.2, 46.4, 45.8, 44.3, 47.1 | 46.06 | 1.62 |
| B | 75.4, 77.3, 77.7, 74.0, 76.3, 75.7, 75.0, 75.9, 73.2, 74.6 | 75.51 | 1.95 | |
| C | 60.1, 59.2, 59.3, 61.6, 59.1, 57.3, 59.5, 60.3, 57.8, 58.4 | 59.26 | 1.56 | |
| 375 | A | 45.1, 45.2, 44.6, 48.1, 46.9, 45.2, 47.4, 44.7, 46.9, 46.2 | 46.03 | 1.53 |
| B | 78.2, 78.5, 77.3, 75.0, 75.5, 73.2, 75.3, 74.6, 74.8, 75.2 | 75.76 | 2.87 | |
| C | 58.5, 58.1, 59.8, 59.4, 57.0, 60.4, 59.4, 59.9, 58.5, 59.7 | 59.07 | 1.05 | |
| 450 | A | 46.4, 47.8, 44.0, 45.3, 46.7, 43.3, 47.2, 45.9, 44.2, 46.5 | 45.73 | 2.21 |
| B | 73.6, 76.4, 75.5, 75.9, 73.2, 75.7, 78.2, 76.3, 70.4, 74.9 | 75.01 | 4.65 | |
| C | 59.7, 60.3, 60.6, 59.2, 58.6, 58.2, 59.9, 57.1, 60.3, 58.1 | 59.20 | 1.34 |
To statistically analyze the impact of power output state, I employed an independent samples t-test to compare the disconnection times under different conditions. The t-value is calculated using the formula:
$$ t = \frac{\bar{x}_1 – \bar{x}_2}{\sqrt{\frac{s_1^2}{n_1} + \frac{s_2^2}{n_2}}} $$
where \(\bar{x}_1\) and \(\bar{x}_2\) are the sample means, \(s_1^2\) and \(s_2^2\) are the sample variances, and \(n_1\) and \(n_2\) are the sample sizes (each n=10). The null hypothesis assumes no significant difference between groups, and a p-value threshold of 0.05 is used, with a critical t-value of 2.101 for 18 degrees of freedom.
For output current variations at 450 V, the t-values between pairs of current levels (e.g., 9 A vs. 60 A, 9 A vs. 90 A, 60 A vs. 90 A) are all below 2.101, as shown in Table 3. This indicates that changes in output current do not produce statistically significant differences in disconnection times for electric car chargers. Similarly, for output voltage variations at 60 A, the t-values between voltage pairs (e.g., 225 V vs. 300 V, 225 V vs. 375 V, 225 V vs. 450 V) are also below the critical value, confirming that voltage changes do not affect the results. These findings are consistent across all three chargers, reinforcing the reliability of vehicle interface disconnection tests for China EV applications regardless of power output state.
| Comparison | Charger A t-value | Charger B t-value | Charger C t-value |
|---|---|---|---|
| Current: 9 A vs. 60 A | 0.020 | 0.389 | 0.231 |
| Current: 9 A vs. 90 A | 0.257 | 0.975 | 0.070 |
| Current: 60 A vs. 90 A | 0.432 | 1.091 | 0.171 |
| Voltage: 225 V vs. 300 V | 2.032 | 0.811 | 0.808 |
| Voltage: 225 V vs. 375 V | 2.009 | 1.065 | 1.320 |
| Voltage: 225 V vs. 450 V | 1.581 | 0.101 | 0.968 |
| Voltage: 300 V vs. 375 V | 0.053 | 0.360 | 0.371 |
| Voltage: 300 V vs. 450 V | 0.533 | 0.616 | 0.111 |
| Voltage: 375 V vs. 450 V | 0.491 | 0.865 | 0.265 |
The analysis demonstrates that the power output state—whether varying current or voltage—does not influence the vehicle interface disconnection test results for electric car chargers. This conclusion holds under normal charging conditions, where the output power is greater than 0 kW, as required by standards. The consistency in disconnection times across different power levels suggests that chargers can be tested at any feasible output state without compromising result accuracy. This is particularly relevant for China EV ecosystems, where diverse charging scenarios are common. The implications extend to safety protocols and interoperability testing, ensuring that electric car charging infrastructure remains reliable. Future work could explore other abnormal conditions or environmental factors to further enhance electric car charger safety in the rapidly evolving China EV market.
In summary, this study validates that off-board chargers for electric cars maintain consistent disconnection responses regardless of power output variations. By adhering to national standards and employing rigorous testing methods, we can ensure the safety and interoperability of charging systems, supporting the sustainable growth of the electric car industry. As China continues to lead in EV adoption, such insights contribute to robust infrastructure development, ultimately benefiting consumers and manufacturers alike in the electric car domain.