用于电动汽车的创新EMC滤波器解决方案

随着汽车配备越来越多的电子系统，出现电磁干扰问题的可能性越来越大。这尤其适用于带有用于电机逆变器的附加电力电子设备的电动汽车 (xEV)。EMC 滤波器的使用提供了一种可靠且重量轻的方法来消除密集源的相互干扰。

混合动力和全电动汽车（xEV）都装有电子设备，在数量和技术要求上都远远超过内燃机汽车。因为，除了日益复杂的安全、舒适和通信系统之外，真正为电子系统增加赌注的是电力驱动系统——高压电池、逆变器和至少一个电动机。因此，开发此类车辆的首要任务是确保挤在非常有限的空间中的各个系统不会造成相互干扰。同样重要的是，没有干扰会影响车辆外部的系统。这些 EMC 要求受 CISPR 25 或欧盟指令 ECE-R10 等国际标准的监管。

屏蔽电缆引起的 EMC 问题

逆变器通过电机的脉宽调制控制运行。脉冲的陡峭边缘会在逆变器的输入和输出端引起相当大的 EMC 问题，表现为辐射和传导发射。为了将这些保持在最低限度，迄今为止的大多数传统设计都基于完整的封装或屏蔽。

为了节省空间并改善重量分布，各个驱动部件分布在整个车辆中。电池通常位于后部，逆变器位于前部。一个或多个电机安装在车轴上，有时直接安装在车轮上。逆变器与电池的连接需要一根长的屏蔽电缆，这会给 EMC 带来很大的潜在风险，因为一方面会产生高屏蔽电流，从而导致高频范围内的辐射。另一方面，足够大的电压尖峰甚至会损坏逆变器或电池。此外，不能排除干扰耦合到车辆低压系统的可能性。

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.

尽管使用了非屏蔽电缆，但传导干扰尤其可以降低多达 70 dB，或 3,000 倍。此外，使用 EMC 滤波器可以显着减少单个系统组件中常规 EMC 措施的数量。例如，消除对屏蔽电缆的需求有助于节省重量和空间。 

用于 EMC 的两线高压直流滤波器可从许多制造商处获得。查看http://en.tdk.eu/tdk-en/530186/products/product-catalog/emc-components了解 TDK 和 Epcos 的 EMC 组件。




审核编辑：刘清