As the new energy industry accelerates its upgrade path toward high power, high reliability, and long life, DC-Link capacitors, as core components connecting rectifiers and inverters, have a significant impact on system performance. Yongming's MDP series DC-Link film capacitors, with their excellent adaptability, have become a mainstream choice for applications such as automotive electric drives, photovoltaic inverters, and energy storage systems. To address industry concerns, we have summarized the key issues surrounding this series of products below to provide a reference for industrial applications.

## Q1: What is a DC-Link capacitor? What core role does it play in new energy systems?
DC-Link capacitors, also known as DC link capacitors, are core components connected in series between the DC bus of the rectifier and inverter in new energy systems. During system operation, they perform three key functions: first, stabilizing the DC bus voltage to prevent voltage fluctuations from impacting downstream power devices; second, absorbing high-frequency ripple current generated in the circuit to purify power supply quality; and third, suppressing voltage spikes generated during the switching of power devices such as IGBTs to ensure the safety of key components. As a system's "voltage stabilizer" and "safety buffer," its performance directly determines the operating efficiency and reliability of new energy equipment.

## Q2: Why are film capacitors, rather than electrolytic capacitors, commonly chosen as DC-Link capacitors in new energy systems (such as automotive electric drives and photovoltaic inverters)?
This choice stems from the new energy industry's demand for high reliability, high power density, and long lifespan in core components, which aligns perfectly with the performance advantages of film capacitors. Film capacitors offer a non-polar design, strong ripple current resistance, low equivalent series inductance (ESL) and equivalent series resistance (ESR), and eliminate the electrolyte dry-out issues common with electrolytic capacitors. They offer a service life of over a decade, fully covering the entire lifecycle of new energy equipment. Electrolytic capacitors, on the other hand, experience rapid lifespan degradation in high-temperature environments and have weak ripple current resistance, making them less suitable for long-term use in demanding scenarios such as automotive vibration and outdoor photovoltaic operation.

## Q3: What are the main technical features of Yongming's MDP series DC-Link film capacitors?
Yongming's MDP series capacitors build their core competitiveness through "dielectric innovation + structural optimization." The core dielectric is metallized polypropylene film, which provides the product with low loss and high insulation resistance, as well as excellent self-healing properties. The compact design reduces installation space while enhancing high voltage and ripple current resistance. Optimized internal electrode layout and terminal structure minimize equivalent series inductance (ESL). This design allows them to easily withstand the high voltage and high current conditions of new energy systems, as well as complex environmental stresses such as high-temperature cycling and vibration.

## Q4: What new energy application scenarios are the MDP series film capacitors specifically suitable for?
This series of products is widely applicable to the three core areas of new energy vehicles, new energy power generation, and energy storage. Specifically, it covers: new energy vehicle electric drive inverters, on-board chargers (OBCs), and DC-DC voltage converters; new energy power generation equipment such as photovoltaic inverters and wind turbine converters; and the DC bus voltage stabilization of energy storage systems (ESS). It can effectively adapt to all core new energy scenarios requiring DC bus voltage stability.

## Q5: How do I select the appropriate MDP series capacitor capacity and voltage level for an electric drive inverter?

Selection must adhere to the principle of "parameter matching + safety redundancy." This process involves three key steps: First, accurately determine key system parameters, including the DC bus voltage level, maximum ripple current RMS, and allowable voltage ripple rate, as a basis for calculation. When selecting the voltage level, allow a safety margin of 1.2-1.5 times the rated voltage to avoid overvoltage breakdown. The capacity must meet the system's voltage ripple suppression requirements. Most importantly, the capacitor's rated ripple current must exceed the system's actual maximum ripple current to prevent thermal aging issues.

## Q6: What exactly does the "self-healing property" of a capacitor mean? How does it contribute to system reliability?

The "self-healing property" is a unique reliability-enhancing technology of thin-film capacitors: when a thin-film dielectric breaks down due to a localized, microscopic defect, the instantaneous high temperature generated at the breakdown point causes the surrounding metallized electrode to rapidly evaporate, forming an insulating region and enabling the breakdown point to "self-heal." This feature fundamentally avoids the problem of traditional capacitors where local defects lead to overall failure, significantly reducing the probability of sudden failures and providing critical reliability support for the long-term continuous operation of new energy systems.

## Q7: In design, how should capacitors be used in parallel to increase capacity or current?
Paralleling capacitors requires a focus on "parameter balancing + layout optimization" to avoid the risk of current bias. First, the rated voltage of all parallel capacitors must be consistent to prevent uneven voltage distribution and device damage. Second, products from the same batch with minimal parameter deviation should be selected to ensure even current distribution. Symmetrical low-inductance connection design should be used in the PCB layout to minimize parasitic parameter variations and avoid current concentration in a single capacitor, ensuring safe and efficient operation of the parallel circuit.

## Q8: What is equivalent series inductance (ESL)? Why is low ESL crucial for high-frequency inverter systems?
Equivalent series inductance (ESL) is an inherent parasitic parameter of capacitors. Although the value is small, it has a significant impact in high-frequency scenarios. In new energy high-frequency inverter systems, high ESL can cause two key issues: first, high-frequency oscillation and voltage overshoot, which increase electrical stress on switching devices like IGBTs and shorten their lifespan; second, it exacerbates electromagnetic interference (EMI), causing the system to fail EMC certification. The Yongming MDP series achieves extreme ESL optimization through innovative internal structures, effectively suppressing these issues and meeting the upgrade needs of high-frequency inverter systems.

## Q9: What factors determine the rated ripple current capability of a film capacitor? How is its temperature rise evaluated?
The rated ripple current capability of a film capacitor is primarily determined by its equivalent series resistance (ESR). When current flows through the ESR, Joule heating is generated. The lower the ESR, the less heat generated at the same current, and the higher the rated ripple current carrying capacity. Temperature rise assessment must be conducted based on actual operating conditions. When selecting a capacitor, use a thermal imager to measure the core temperature under maximum ripple current conditions to ensure that the temperature rise is within the rated range. Excessive temperature rise accelerates dielectric aging, directly shortening the capacitor's lifespan.

## Q10: When installing DC-Link capacitors, what considerations should be made regarding the mechanical structure and electrical connections?
The installation process must balance mechanical stability with optimized electrical performance. For mechanical fastening, a high-strength fastening solution must be used, especially in high-vibration environments such as automotive and wind turbines. Ensure that the capacitor and mounting bracket are securely attached to prevent loosening of the terminals or structural damage. Electrical connections should adhere to the "short and wide" principle, using large-cross-sectional busbars or cables and shortening the connection path to reduce parasitic inductance. Furthermore, installation torque must be strictly controlled to prevent overtightening that may cause terminal cracking, or over-loosening that may cause poor contact and heating.

## Q11: What key tests can be used to verify the performance of DC-Link capacitors in a system? To ensure the compatibility and reliability of capacitors, they must pass four core tests: First, a high-voltage insulation test (Hi-Pot) verifies insulation performance and mitigates leakage risks; second, precise capacitance and ESR measurement verifies that core parameters meet design requirements; third, a ripple current temperature rise test simulates actual operating conditions to verify heat dissipation capabilities; and fourth, a system-level surge/switching overvoltage withstand test verifies safety margins under extreme operating conditions. These four tests cover comprehensive verification, from initial performance to operating reliability.

## Q12: What are the common failure modes of film capacitors? How does the MDP series mitigate these risks?

Common failure modes of film capacitors are concentrated in three categories: overvoltage, overheating, and mechanical damage. The Yongming MDP series achieves a closed-loop risk management system through targeted design. To prevent overvoltage breakdown, high-voltage dielectrics and a reinforced packaging structure are used. To prevent overheating and aging, a low-ESR design reduces heat generation and is combined with an efficient heat dissipation structure. To prevent mechanical terminal damage, an integrated, robust terminal design enhances vibration and torque resistance. Combined with self-healing features, this provides a comprehensive failure protection system.

## Q13: How can capacitor connection reliability be ensured in high-vibration environments (such as vehicles)?

Ensuring reliability in high-vibration environments requires a "device hardening + system coordination" approach. On the device side, the MDP series features a vibration-resistant structural design, and the terminal-to-housing connection strength has been rigorously verified. On the system design side, anti-loosening fasteners (such as spring washers and locknuts) are required. Thermal adhesive is applied between the capacitor and the mounting surface for dual fixation (which also improves heat dissipation). Modal analysis is also used to optimize the support structure to avoid system resonant frequencies, thereby mitigating the impact of vibration shock at its source.

## Q14: What causes "capacitance fade" in film capacitors? Does it fail suddenly or gradually age?
Capacitance fade in film capacitors is primarily due to the long-term cumulative effect of their self-healing properties: each self-healing process is accompanied by the evaporation of a small amount of metallized electrode, resulting in a slight decrease in capacity over long-term operation. Unlike the sudden failure of electrolytic capacitors due to electrolyte depletion, this degradation process is characterized by a slow and gradual degradation. The degradation trend can be predicted through test data, facilitating the development of lifespan management plans and providing predictable support for the operation and maintenance of new energy systems.

## Q15: What new challenges do future new energy systems pose to DC-Link capacitors? What is Yongming's approach?
With industry upgrades, DC-Link capacitors face three core challenges: First, increasing power density requires capacitors with "small size and large capacity"; second, the prevalence of wide-bandgap devices such as SiC (silicon carbide) and GaN (gallium nitride) forces capacitors to reduce ESL/ESR to adapt to high-frequency operating conditions; and third, the increasing use in extreme environments places higher demands on temperature and vibration resistance. To address this, Yongming has developed a clear technical strategy: increasing power density through dielectric material innovation and structural miniaturization; optimizing internal electrode layout to reduce parasitic parameters; and developing high-temperature-resistant dielectric systems to adapt to extreme environments, continuously adapting to the needs of industry upgrades.