在新能源领域运用中，DCLink电容作为一个关键器件，不管是在风力发电系统、光伏发电系统还是在新能源汽车系统中都要求高可靠性及长寿命，其选型显得尤为重要。下面介绍薄膜电容与电解电容的特性对比及在DC-Link电容运用中两者的分析对比：
In the application of new energy, dclink capacitor, as a key device, requires high reliability and long life in wind power generation system, photovoltaic power generation system and new energy vehicle system, and its selection is particularly important. The following is the comparison of the characteristics of thin film capacitor and electrolytic capacitor, and the analysis and comparison of the two in the application of DC link capacitor:
特性对比
Characteristic comparison
薄膜电容
Film capacitance
首先介绍薄膜金属化的原理，薄膜金属化技术的原理：在薄膜介质表面蒸镀上足够薄的金属层，在介质存在缺陷的情况下，该镀层能够蒸发并因此隔离该缺陷点起到保护作用，这种现象被称作自愈。
Firstly, the principle of film metallization is introduced. The principle of thin film metallization technology is as follows: a thin enough metal layer is evaporated on the surface of thin film medium. In the case of medium defect, the coating can evaporate and isolate the defect point to protect it. This phenomenon is called self-healing.
图4为金属化镀膜的原理图，蒸镀前薄膜介质先进行前期处理(电晕或其他方式)以便金属分子能够附着在上面。
Figure 4 is the schematic diagram of metallization coating. Before evaporation, the film medium is pretreated (corona or other methods) so that metal molecules can adhere to it.
金属通过在真空状态下高温溶化蒸发(铝的蒸发温度1400摄氏度~1600摄氏度，锌的蒸发温度400摄氏度~600摄氏度)，当金属蒸气遇被冷却的薄膜后凝结在薄膜表面(薄膜冷却温度-25摄氏度~-35摄氏度)，从而形成金属镀层。
Metal is dissolved and evaporated at high temperature in vacuum (the evaporation temperature of aluminum is 1400 ℃ ~ 1600 ℃, and that of zinc is 400 ℃ ~ 600 ℃). When the metal vapor meets the cooled film, it condenses on the surface of the film (film cooling temperature is - 25 ℃ ~ - 35 ℃), thus forming a metal coating.
金属化技术的发展提高了单位厚度的薄膜介质的介电强度，干式技术脉冲或放电运用电容设计可以达到500V/μm,直流滤波运用电容设计可以达到250V/μm.DC-Link电容属于后者，根据IEC61071对于电力电子运用电容的要求可以承受较为苛刻的电压冲击，可以达到2倍的额定电压。
The development of metallization technology improves the dielectric strength of thin film dielectric per unit thickness. The capacitance design of dry technology pulse or discharge can reach 500V / μ M, The design of DC filter capacitor can reach 250V / μ M. DC link capacitor belongs to the latter. According to the requirements of iec61071 for power electronic application capacitor, it can withstand severe voltage impact and can reach twice the rated voltage.
因此使用者只需考虑其设计所需的额定工作电压就可以了。金属化薄膜电容器具有较低的ESR,使其能承受较大的纹波电流;较低的ESL满足逆变器的低电感设计要求，减少了开关频率下的震荡效应。
Therefore, users only need to consider the rated working voltage required by their design. The metallized film capacitor has lower ESR, which makes it able to withstand larger ripple current; the lower ESL can meet the requirements of low inductance design of inverter and reduce the oscillation effect at switching frequency.
薄膜介质的质量、金属化镀层质量、电容器设计及制造过程工艺决定了金属化电容器自愈特性的好坏。Faratronic生产的DC-Link电容用的薄膜介质主要为OPP薄膜。
The quality of thin film dielectric, metallized coating quality, capacitor design and manufacturing process determine the self-healing characteristics of metallized capacitor. The main thin film dielectric used for DC link capacitor produced by faratronic is OPP film.
电解电容
Electrolytic capacitor
电解电容使用的介质为铝经过腐蚀形成的氧化铝，介电常数为8~8.5,工作的介电强度约为0.07V/A(1μm=10000A)，按照计算对于900Vdc的电解电容需要的厚度为12000A.然而要达到这样的厚度是不可能的，因为为了获得好的储能特性所用铝箔要进行腐蚀形成氧化铝膜，表面会形成许多凹凸不平的曲面，铝层厚度会降低电解电容的容量系数(比容)。另一方面，低电压的电解液电阻率为150Ωcm,高电压(500V)的电解液的电阻率则达到5kΩcm.
The dielectric of electrolytic capacitor is aluminum oxide formed by corrosion, and the dielectric constant is 8 ~ 8.5, The working dielectric strength is about 0.07v/a (1 μ M = 10000a). According to the calculation, the thickness required for 900vdc electrolytic capacitor is 12000A. However, it is impossible to achieve such thickness, because in order to obtain good energy storage characteristics, the aluminum foil is corroded to form alumina film, and the surface will form many uneven curved surfaces, and the thickness of aluminum layer will reduce the capacitance coefficient (specific capacitance) of electrolytic capacitor 。 On the other hand, the resistivity of electrolyte with low voltage is 150 Ω cm, and that of electrolyte with high voltage (500V) is 5K Ω cm
电解液较高的电阻率限制了电解电容所能承受的有效值电流，一般为20mA/μF.
The higher resistivity of electrolyte limits the effective value current that electrolytic capacitor can bear, which is generally 20 mA / μ F
基于上述原因电解电容的设计最高电压典型值为450V(有个别厂家设计600V)。
Based on the above reasons, the typical design maximum voltage of electrolytic capacitor is 450V (some manufacturers have designed 600V).
因此，为了获得更高的电压必须用电容器串联实现，然而因各个电解电容的绝缘电阻存在差异，为了平衡各串联电容的电压，各电容必须连接一个电阻。此外，电解电容为有极性器件，当施加反向电压超过1.5倍Un时，会发生电化学反应。
Therefore, in order to obtain higher voltage, capacitors must be connected in series. However, due to the difference of insulation resistance of electrolytic capacitors, in order to balance the voltage of series capacitors, each capacitor must be connected with a resistor. In addition, the electrolytic capacitor is a polar device, when the applied reverse voltage is more than 1.5 times UN, the electrochemical reaction will occur.
当施加的反向电压时间足够长，电容将发生爆炸，或冒顶电解液将外溢。为了避免该现象发生，使用的时候要在每个电容旁并上一个二极管。除此之外，电解电容的耐电压冲击特性，一般为1.15倍Un,好的可以达到1.2倍Un.这样设计师在使用时就不但要考虑稳态工作电压大小，而且还要考虑其冲击电压大小。
When the reverse voltage is applied for a long enough time, the capacitor will explode or the top will fall, and the electrolyte will overflow. In order to avoid this phenomenon, a diode should be placed next to each capacitor. In addition, the withstand voltage impulse characteristic of electrolytic capacitor is generally 1.15 times UN, and the good one can reach 1.2 times UN. In this way, designers should not only consider the steady-state working voltage, but also the impulse voltage.
综上所述，可以得出薄膜电容与电解电容如下特性对比表，见表1.
To sum up, the following characteristic comparison table of film capacitor and electrolytic capacitor can be obtained, as shown in Table 1
运用分析
Application analysis
DC-Link电容作为滤波器要求大电流和大容量设计。新能源汽车主电机驱动系统就是一个例子。在该运用中电容起到退耦作用，电路特点工作电流大。薄膜DC-Link电容具有较大优势，能承受较大的工作电流(Irms)。以50~60kW新能源汽车参数为例，参数如下：工作电压330Vdc,纹波电压10Vrms,纹波电流150Arms@10KHz.
DC link capacitor as a filter requires high current and large capacity design. The main motor drive system of new energy vehicles is an example. In this application, the capacitor plays the role of decoupling, and the circuit features high working current. Thin film DC link capacitors have great advantages and can withstand large operating current (IRMS). Taking the parameters of 50 ~ 60kW new energy vehicle as an example, the parameters are as follows: working voltage 330VDC, ripple voltage 10vrms, ripple current 150Arms@10KHz.
那么最小电容量计算为：
Then the minimum capacitance is calculated as:
这样对于薄膜电容设计很容易实现。假设采用电解电容，如果考虑20mA/μF,那么为了满足上述参数， 计算电解电容最小的容值为：
This is easy to implement for thin film capacitor design. Assuming that electrolytic capacitor is used, if 20mA / μ f is considered, then in order to meet the above parameters, the minimum capacitance value of electrolytic capacitor is calculated as follows:
这样需要多个电解电容并联获得该容值。
This requires multiple electrolytic capacitors in parallel to obtain the capacitance value.
在过电压运用场合，如轻轨、电动巴士、地铁等，考虑这些动力通过受电弓连接到机车集电弓，在运输行进过程中受电弓与集电弓的接触是间续的。当两者不接触时通过DC-Link电容进行支撑供电，当两者接触恢复时过电压就会产生。
In the case of over-voltage application, such as light rail, electric bus, subway, etc., considering that these power is connected to the locomotive pantograph through pantograph, the contact between pantograph and pantograph is intermittent during transportation. When the two are not in contact, the DC link capacitor is used to support the power supply, and when the contact is restored, the overvoltage will be generated.
最坏的情况是断开时由DC-Link电容完全放电，此时放电电压等于受电弓电压，当恢复接触时，其产生的过电压几乎就是额定工作时的2倍Un.对于薄膜电容DC-Link电容可以处理不需额外考虑。
The worst case is that when the DC link capacitor is disconnected, the discharge voltage is equal to the pantograph voltage. When the contact is restored, the over-voltage generated by the DC link capacitor is almost twice the UN of the rated operation. The DC link capacitor can be treated without additional consideration.
如果采用电解电容，过电压为1.2Un .以上海地铁为例，Un=1500Vdc,对于电解电容要考虑电压为：那么要用6个450V的电容进行串联连接。若采用薄膜电容设计在600Vdc到2000Vdc,甚至3000Vdc都容易实现。
If the electrolytic capacitor is used, the over-voltage is 1.2un. Take Shanghai Metro as an example, UN = 1500vdc. For the electrolytic capacitor, the voltage should be considered: then six 450V capacitors should be connected in series. If the thin film capacitor is designed, it can be easily realized from 600vdc to 2000vdc, even 3000vdc.
此外，在电容完全放电情况下能量在两电极间形成短路放电，产生很大冲击电流通过DC-Link电容，通常电解电容很难满足要求。
In addition, when the capacitor is fully discharged, the energy forms a short-circuit discharge between the two electrodes, which generates a large impact current through the DC link capacitor, which is difficult to meet the requirements of the electrolytic capacitor.
另外，相对于电解电容DC-Link薄膜电容器通过设计可以达到很低的ESR(通常低于10mΩ，更低的<1mΩ)和自感LS(通常低于100nH,有的可以低于10或20nH)。
In addition, compared with electrolytic capacitors, DC link thin film capacitors can achieve very low ESR (usually less than 10 m Ω, lower than 1 m Ω) and self inductance LS (usually less than 100 NH, some can be lower than 10 or 20 NH).
这样在运用时DC-Link薄膜电容器可直接安装到IGBT模块，可以把母线整合到DC-Link薄膜电容器中，因此采用薄膜电容器则不再需要专门的IGBT吸收电容，为设计者节约了一笔不小的费用。表2和表3为Faratronic C3A和C3B部分产品的技术参数。
In this way, the DC link film capacitor can be directly installed into the IGBT module, and the bus can be integrated into the DC link thin film capacitor. Therefore, the use of the film capacitor will no longer require a special IGBT absorption capacitor, which saves a lot of cost for the designer. Table 2 and table 3 show the technical parameters of some products of faratronic C3a and C3b.
作为直流支撑滤波用电容，DC-Link 电容早期考虑到成本及尺寸因素大部分选择电解电容。然而电解电容受到耐压、电流承受能力(相对薄膜电容ESR高很多)等因素的影响，为了获得大容量和满足高压使用要求，则必须要用多个电解电容进行串、并联。
As a DC support filter capacitor, DC link capacitor mostly chooses electrolytic capacitor considering the cost and size factors in the early stage. However, the electrolytic capacitor is affected by the withstand voltage and current carrying capacity (much higher than the ESR of thin film capacitor). In order to obtain large capacity and meet the requirements of high voltage application, it is necessary to use multiple electrolytic capacitors in series or in parallel.
另外考虑到电解液材料的挥发，所以要定期进行更换，新能源运用一般要求产品寿命要达15年，那么在这段时间内必须更换两到三次，因而在整机售后服务方面存在不小的费用和不方便性。
In addition, considering the volatilization of electrolyte materials, it is necessary to replace them regularly. Generally, the service life of new energy products should reach 15 years. Therefore, it is necessary to replace them two or three times during this period of time. Therefore, there is no small cost and inconvenience in the after-sales service of the whole machine.
随着金属化镀膜技术及薄膜电容器技术的发展，采用安全膜蒸镀技术已经可以用超薄OPP膜(最薄2.7μm,甚至2.4μm)生产出电压450V到1200V甚至更高电压的大容量直流滤波电容。另一方面通过DC-Link电容与母排整合，使得逆变器模块设计更加紧凑，大大降低了电路的杂散电感使电路更加优化。
With the development of ultra-thin film (452.0 μ m) and the technology of thin film capacitor (1200 μ m), the most safe capacitor can be produced by using the technology of thin film evaporation with the voltage of 450 μ M. On the other hand, through the DC link capacitor and bus integration, the inverter module design is more compact, greatly reducing the stray inductance of the circuit, making the circuit more optimized.
以此同时，薄膜电容制作成本在不断下降，相比电解电容更凸显其经济性，在要求工作电压高、承受高纹波电流(Irms)、有过电压要求、有电压反向现象、处理高冲击电流(dV/dt)以及长寿命要求的电路设计中，选择DC-Link薄膜电容替代电解电容将成为设计者今后设计选择的一种趋势。
At the same time, the production cost of thin-film capacitor is declining, and its economy is more prominent than electrolytic capacitor. In the circuit design that requires high working voltage, high ripple current (IRMS), over-voltage requirement, voltage reversal phenomenon, handling high impulse current (DV / DT) and long life, DC link thin film capacitor will be the designer's choice in the future A trend of choice.