隨著汽車配備越來越多的電子系統，出現電磁干擾問題的可能性越來越大。這尤其適用于帶有用于電機逆變器的附加電力電子設備的電動汽車 (xEV)。EMC 濾波器的使用提供了一種可靠且重量輕的方法來消除密集源的相互干擾。

混合動力和全電動汽車（xEV）都裝有電子設備，在數量和技術要求上都遠遠超過內燃機汽車。因為，除了日益復雜的安全、舒適和通信系統之外，真正為電子系統增加賭注的是電力驅動系統——高壓電池、逆變器和至少一個電動機。因此，開發此類車輛的首要任務是確保擠在非常有限的空間中的各個系統不會造成相互干擾。同樣重要的是，沒有干擾會影響車輛外部的系統。這些 EMC 要求受 CISPR 25 或歐盟指令 ECE-R10 等國際標準的監管。

屏蔽電纜引起的 EMC 問題

逆變器通過電機的脈寬調制控制運行。脈沖的陡峭邊緣會在逆變器的輸入和輸出端引起相當大的 EMC 問題，表現為輻射和傳導發射。為了將這些保持在最低限度，迄今為止的大多數傳統設計都基于完整的封裝或屏蔽。

為了節省空間并改善重量分布，各個驅動部件分布在整個車輛中。電池通常位于后部，逆變器位于前部。一個或多個電機安裝在車軸上，有時直接安裝在車輪上。逆變器與電池的連接需要一根長的屏蔽電纜，這會給 EMC 帶來很大的潛在風險，因為一方面會產生高屏蔽電流，從而導致高頻范圍內的輻射。另一方面，足夠大的電壓尖峰甚至會損壞逆變器或電池。此外，不能排除干擾耦合到車輛低壓系統的可能性。

The electrical and mechanical connection of the cable shielding to the shielding of the battery and inverter poses a further problem. The impedance of this connection must be extremely low in order to guarantee adequate shielding. But the vibrations and impacts inherent in vehicles create forces that weaken the shielding connection, causing a gradual long-term rise in impedance. Aging processes caused by oxidation, or even corrosion, are not insignificant either.

The radiated and conducted emissions of a system with shielded cable between the battery and inverter are depicted in Figure 2.

Fig. 2: The use of a shielded cable between battery and inverter reduces the radiated emissions (above), it does not reduce the conducted emissions (below).

Clear improvement in EMC through use of filters

A superior approach to coping with the growing demands made on EMC design involves the use of high-voltage DC filters. To be suitable for electric vehicles they need to be designed for a maximum voltage of 600 V DC, corresponding to the typical voltages of high-voltage batteries. To enable the filtering of drive systems with power ratings considerably in excess of 100 kW, their current capabilities should cover the range of up to around 150 A DC or 350 A DC. The EMC filters must offer a very low DC resistance to avoid significant losses.

As shown in Figure 3, it was possible to confirm the improved EMC performance when an EMC filter was used in the test setup.?

Fig. 3: An EMC filter between battery and inverter results in a dramatic reduction in the conducted interference, in particular.

盡管使用了非屏蔽電纜，但傳導干擾尤其可以降低多達 70 dB，或 3,000 倍。此外，使用 EMC 濾波器可以顯著減少單個系統組件中常規 EMC 措施的數量。例如，消除對屏蔽電纜的需求有助于節省重量和空間。?

用于 EMC 的兩線高壓直流濾波器可從許多制造商處獲得。查看http://en.tdk.eu/tdk-en/530186/products/product-catalog/emc-components了解 TDK 和 Epcos 的 EMC 組件。




審核編輯：劉清