August 03, 2021

Innovative filter solutions for electric vehicles

As automotive systems are equipped with more and more electronic systems, the requirements for EMC have also increased. For electric vehicles (xEV), EMC is more demanding due to the addition of power electronics to the motor inverter. TDK Group's new filter solutions are available to provide an elegant and lightweight solution for solving EMC problems.

Whether it's a hybrid or a pure electric car, these models (xEV) are loaded with a variety of electronic devices. The electronic equipment loaded on the electric vehicle is far superior to the electronic equipment used in the internal combustion engine vehicle in terms of quality and technical requirements. In order to meet the safety, comfort and communication requirements, the complexity of electronic systems on electric vehicles is increasing. In addition, electric drive systems (including high-voltage batteries, inverters and at least one motor) also require the use of electronic systems.

Therefore, when developing such a vehicle, it is first necessary to ensure that a single system can be perfectly installed in a small space without causing interference with each other or interference with the outside system. These EMC requirements must be in strict compliance with international standards such as CISPR25 or EUDirecTIveECE-R10.

The EMC problem caused by the shielded cable is the power and speed required to effectively control the motor. The inverter uses a pulse width modulation (PWM) mode of operation. The rising or falling edge of the pulse can cause significant EMC problems on the input and output sides of the inverter, such as the initiation of radiated emissions and conducted emissions. In order to minimize the impact of these EMC problems, most designs use the concept of completely electromagnetically sealing or shielding the entire system.

In order to save space and improve weight distribution, various drive components are installed separately throughout the vehicle. For example, the battery is usually placed at the rear of the car and the inverter is placed at the front of the car. The motor is mounted on the axle and mounted directly on the wheel for the hub motor. Therefore, connecting the inverter to the battery requires a long shielded cable. However, this brings great potential risks, mainly for three reasons: 1. It is easy to generate high shielding current, which causes strong radiation in the high frequency region; 2. It causes a large voltage spike and may even damage the inverter. Or battery; 3, may couple through, thus interfering with the vehicle's low-voltage system.

Electrical and mechanical connections between shielded cables, shielded batteries, and inverters can also create additional problems. Therefore, the impedance of the connection must be extremely low to ensure the effectiveness of the shield. However, the internal vibration and shock of the vehicle will gradually weaken the shield connection, causing a long-term increase in impedance. In addition, the aging process caused by oxidation or even corrosion can not be ignored. Figure 1 shows the setup requirements for measuring the electromagnetic emissions of power electronics (in accordance with CISPR 25).

Figure 1: Measurements based on CISPR25 settings

The radiated and conducted emission properties of the system (connected by a shielded cable between the battery and the inverter) are shown in Figure 2.

Figure 2: Emission performance with shielded wires

Although the use of a shielded cable between the battery and the inverter reduces the radiation emission (top), it does not reduce the conducted emissions (bottom).

Significantly improved EMC with new filters

In order to meet the increasingly stringent EMC requirements in the market, TDK Group has developed EPCOS P100316* series 2-wire high-voltage DC filters specifically for the application of electric vehicle drive systems. Designed for 600VDC high voltage applications, this series is suitable for typical voltages supplied by high voltage batteries. Its current capability is approximately 150ADC or 350ADC. Even if the rated power of the drive system exceeds 100kW, the filter can still be effective. This series of filters is available in a variety of models, and all models have a DC resistance of only 0.05m?, which means there is no significant loss even at high currents.

As shown in Figure 3, the excellent filter performance of the new filter can be confirmed according to the test setup requirements.

Figure 3: System emission characteristics after using EPCOS high voltage DC filter

It is clear that the use of the new EPCOS EMC filter between the battery and the inverter significantly reduces conducted interference even with unshielded cables.

It can be seen that with the new filter, even with unshielded cables, conducted interference can be significantly reduced by up to 70 dB (or a power factor of 3000) and the number of conventional EMC components in individual systems can be significantly reduced.

In addition to its excellent electrical performance, the filter is compact and lightweight, making it ideal for automotive applications. The size of the product is between 121mmx52mmx52mm and 186mmx65mmx65mm, depending on the model.

The new series includes 12 models with not only 2 different current capabilities (150 ADC and 350 ADC) but also different filtering characteristics. In other words, customers can get a more targeted solution to their own EMC problems and choose the filter model that suits the application requirements. In addition, in addition to the regular performance models, we offer other models with superior filtering performance between 150kHz and 300kHz in the long-wave spectrum.

Extend motor life

High-frequency shielding currents represent only part of the challenge of ensuring electromagnetic compatibility. For example, at the output of the inverter, the rising edge of the pulse causes a voltage spike, which increases as the inductance of the cable increases. These environmental spikes can cause arcing and damage the motor windings once environmental conditions are unfavorable. At the same time, ground leakage currents also occur, which flow through the motor bearings, causing spikes. In turn, the bearing balls or rollers are damaged, causing them to fail prematurely.

One remedy is to use a ferrite toroidal core that allows motor cables to pass through these cores. This significantly reduces common mode interference and ground leakage current, ensuring that it does not exceed the critical value. Here, the TDK Group also offers a variety of solutions, such as toroidal cores with different geometries and ferrites of different materials, and these products can be optimized for specific frequency regions, tailored to each drive system.

Table: Technical data for EPCOS 2-wire HVDC filters

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