During a high-temperature, full-load durability test, the EPS system of a new OEM model experienced occasional undervoltage alarms and loss of power steering in the controller. Investigation revealed the problem stemmed from the performance degradation of the DC-Link bus capacitor under high temperature and high ripple current conditions. This not only affected the overall vehicle reliability testing but also posed risks to mass production schedules. In automotive EPS controllers, liquid aluminum electrolytic capacitors at the VBAT input or DC-Link location are core components ensuring system reliability and facilitating mass production. This article will explore liquid aluminum electrolytic capacitor solutions adapted for EPS power steering controllers in the context of high-temperature, heavy-load operation and domestic substitution.

I. Core Requirements for Capacitors in EPS Controllers

During low-speed parking and stationary turning operations, EPS experiences significant current pulsation on the motor side. The VBAT input and DC-Link terminals must withstand strong transient impacts. If the capacitor's ESR is too high or its ripple current handling capacity is insufficient, it will lead to increased bus ripple and aggravated transient voltage drops. Furthermore, a key challenge in EPS applications is that the capacitor must operate stably for extended periods in high-temperature environments. High temperatures accelerate the degradation of the dielectric oxide film and electrolyte system, causing a rapid increase in leakage current, which can lead to difficulties in voltage boosting and abnormal system function. Therefore, capacitor selection requires comprehensive consideration of ESR, ripple current handling capacity, high-temperature lifespan, and project feasibility, rather than solely focusing on capacitance value and voltage rating.

II. What Parameters Should Be Considered for Capacitors in EPS Systems?

When selecting liquid aluminum electrolytic capacitors for automotive EPS power steering controllers, five core indicators should be prioritized:
* **Voltage and Capacitance:** Do they match the design requirements of the VBAT input or DC-Link bus position?
* **ESR (Equivalent Series Resistance):** Do they help reduce ripple and transient voltage drop?
* **Ripple Current Capacity:** Can they withstand pulse currents during stationary steering and rapid return to center?
* **High-Temperature Lifespan:** Can they withstand long-term high-temperature (135℃) operation?
* **Size and Installation Method:** Are they suitable for existing board space and replacement implementation timelines?

It is important to note that EPS is a high-temperature, heavy-load controller application scenario, different from general filtering scenarios involving low stress, low temperature, and low pulsation. Therefore, the selection criteria for general liquid aluminum electrolytic capacitors cannot be applied.

III. Why are YMIN LKL(R) series capacitors better suited for EPS applications? YMIN LKL(R) series liquid aluminum electrolytic capacitors are specifically designed for EPS applications. They are primarily used at the VBAT input and DC-Link/bulk positions of the main power path on EPS controller power boards. They provide input buffering, absorb pulse current, suppress bus ripple and transient voltage drop, and stabilize the power supply environment.

The core reason this series is well-suited for EPS applications is that its design logic precisely addresses the root causes of capacitor failure in EPS scenarios: by using anhydrous high-conductivity electrolyte, high-voltage high-density positive electrode foil, and low-density protective paper, coupled with higher-specification process control, it effectively suppresses leakage current growth while achieving lower ESR performance. This allows for bus stability under high-temperature, heavy-load conditions, reducing temperature rise risks and improving the long-term reliability of the controller.

IV. From a project implementation perspective, why is domestic substitution not just about parameter replacement?

The core value of domestic substitution lies in realizing the transformation from parameter benchmarking to actual project implementation. Yongming's LKL(R) series has successfully replaced the NCC GPD series in an EPS project. After customer replacement, testing was passed and mass production began, verifying its ability to switch from verification to mass production in real-world projects.

Experimental Data Verification: Using 135℃ as the uniform test temperature, 3000 hours of tests were conducted on Yongming's LKL(R) series, NCC GPD series, and a domestic brand of capacitors to measure loss values, capacitance decay changes, and leakage current. The results are as follows: Loss Tangent (DF): Yongming average 6.584, NCC average 6.647, domestic brand average 8.012. A lower DF value results in less heat generation from the capacitor under AC ripple, which helps reduce the temperature rise of the EPS controller and extend its service life.

Capacitance Change Rate: Both Yongming and NCC capacitors maintain capacitance changes within -1%, showing similar performance. A certain domestic brand experienced a capacitance decay of -2.814%. A smaller capacitance change rate indicates stronger capacitance retention under high-temperature conditions, better maintaining circuit design stability.

Leakage Current (LC): Both Yongming and NCC capacitors maintain leakage current values ​​at a low level of approximately 6μA. A certain domestic brand's leakage current rose to 743.032μA. Lower leakage current helps reduce system static power consumption and lowers the risk of circuit failures caused by insulation degradation.

VI. Customer FAQs

Question: In high-temperature aging tests for EPS projects, capacitors are often a weak point. Are there any recommended alternatives to NCC automotive-grade aluminum electrolytic capacitors with a temperature resistance of over 135℃ and a longer lifespan? Answer: Yongming LKL(R) series liquid aluminum electrolytic capacitors are designed for high-temperature, high-ripple, and high-reliability applications. They are optimized to address the performance degradation issue of DC-link bus capacitors in EPS systems under high temperature and high ripple conditions, and have become a domestic alternative to the NCC GPD series.

Question: To suppress high-frequency noise from EPS motor drives, is a lower ESR for DC-link capacitors always better? How should low-ESR capacitors be selected based on switching frequency? Answer: For EPS operating conditions with high ripple and high vibration, lower ESR helps reduce voltage drop, improve ripple, and control heat generation. However, engineering selection cannot solely rely on ESR; it must also consider ripple current capability, capacitance, withstand voltage, temperature rise, and actual installation space.

Question: Currently, EPS designs use Japanese GPD/UPW/UPY capacitors. Are there any domestic models that can directly replace them with comparable or even better performance? Answer: YMIN LKL(R) series capacitors have been successfully implemented as a replacement for NCC GPD series capacitors, passing customer testing and entering mass production. Specific project selection requires a one-on-one confirmation based on voltage withstand capability, capacitance, size, ripple, and lifespan requirements.

VII. Conclusion
In automotive EPS power steering controllers, the core value of liquid aluminum electrolytic capacitors lies not only in energy storage but also in their support for DC-Link bus stability, control continuity, and long-term reliability under high-temperature, heavy-load conditions, as well as their ability to promote domestic substitution. YMIN LKL(R) series liquid aluminum electrolytic capacitors are designed based on EPS application requirements, providing a suitable capacitor solution for automotive EPS projects.

For further evaluation of specific models, please contact us to obtain datasheets, selection tables, sample support, or test data for targeted confirmation based on project requirements such as voltage withstand capability, capacitance, size, and lifespan limits.

Abstract
Applicable Scenarios: VBAT input terminal and DC-Link/bulk position of automotive EPS power steering controller
Core Advantages: Low ESR, high ripple, long lifespan at 135℃, domestic alternative
Recommended Models: YMIN LKL(R) 25V 4700μF, 50V 3600μF, 63V 2700μF