I. Technical Challenges to Capacitor Reliability in EPS Systems

With the increasing prevalence of Electric Power Steering (EPS) systems in passenger vehicles, the requirements for system safety, comfort, and electrification compatibility are continuously rising. EPS control modules are typically located in the engine compartment or near the steering column, operating under high temperature and high vibration environments for extended periods. Simultaneously, low-speed parking and stationary turning frequently generate high ripple current surges. Traditional liquid electrolytic capacitors are prone to performance degradation under these harsh conditions, becoming a key bottleneck restricting system reliability.

II. Typical Failure Phenomena and Root Cause Analysis

In vehicle durability testing, some EPS modules exhibited a slight decrease in steering assist torque after tens of thousands of kilometers of complex road conditions and high/low temperature cycling tests, affecting project acceptance and overall vehicle quality assessment.

The original solution used conventional low-impedance liquid electrolytic capacitors. The failure mode was electrolyte drying at high temperatures, leading to an increase in ESR, a decrease in filtering and transient discharge capabilities, and consequently, affecting motor response speed.

There are two main reasons for this: First, liquid capacitors rely on ionic conductivity, and their ESR is approximately 10 times that of hybrid solid-liquid capacitors, leading to increased internal resistance and output voltage ripple. Second, liquid capacitors typically have a lifespan of only 4000 hours at 125℃, which cannot meet the automotive industry's requirement of a 10-year or 150,000-kilometer lifespan.

III. Yongming Solution: VHT Series Hybrid Solid-Liquid Capacitors

Addressing the pain points of EPS systems, Yongming launched the VHT series hybrid solid-liquid capacitors, specifically designed for EPS motor drive modules.

Representative model: VHT_35V_330μF_10*10.5.

Key performance parameters (typical values ​​at 20℃/100kHz): Rated voltage 35VDC, nominal capacitance 330μF, ESR 20mΩ, rated ripple current 2800mA, operating temperature range -55℃ to +125℃, high-temperature lifespan up to 4000 hours at 125℃.

Core technologies support this performance in three aspects: First, solid-liquid hybrid technology combines the advantages of solid conductive polymers and liquid electrolytes to achieve ultra-low ESR and low leakage current, fundamentally preventing electrolyte drying and ensuring ESR stability during high-temperature and long-term use; second, a shock-resistant structural design, through optimized internal structure and terminal design, meets stringent mechanical vibration testing requirements; and finally, strong overload capacity, possessing high ripple current withstand capability to cope with extreme conditions such as motor stall.

IV. Application Verification: Comparison of Customer Test Data

This series of products has been mass-produced and applied in the new generation EPS motor drive modules of several mainstream vehicle platforms and Tier 1 suppliers, primarily for DC bus support and filtering.

The actual test results of the original liquid capacitor solution and the Yongming VHT solution are clear. In the durability test, the original solution showed a slight decrease in power steering torque, while the Yongming solution passed all tests smoothly without any power steering attenuation. Regarding the failure mechanism, the original solution suffered from electrolyte drying and increased ESR, while the Yongming solution had no electrolyte drying risk. Under 125℃/4000h conditions, ESR deterioration was significant in the original solution, while the increase in the Yongming solution was less than 5%. In terms of bus voltage ripple, the original solution was higher, while the Yongming solution reduced it by approximately 40%. Regarding high-temperature lifespan, the original solution could not meet the requirement of more than 10 years, while the Yongming solution met automotive-grade standards with a 4000-hour lifespan at 125℃. In terms of reliability certification, the original solution failed the whole vehicle durability test, while the Yongming solution passed all AEC-Q200 tests, including temperature cycling, vibration, and high temperature and humidity tests.

The conclusion shows that after the customer replaced the EPS module with the Yongming VHT series, it successfully passed all durability verifications, and the power steering attenuation problem no longer occurred. V. Certifications and Support Yongming VHT series hybrid capacitors have passed numerous international authoritative tests and compliance certifications, including AEC-Q200 automotive-grade reliability testing, ELV vehicle environmental compliance certification, TSCA toxic substance control compliance, and RoHS and REACH environmental compliance certifications. These tests and certifications fully verify the long-term reliability of the product under harsh conditions such as temperature cycling, vibration, and high temperature and humidity, making it suitable for steering systems with high requirements for response speed and safety throughout their entire life cycle.