EMC Management in HEV/EV Applications

Shielding of the high voltage cabling is a cost effective method for reducing unwanted EMI in hybrid and electric vehicles. Ensuring the shielding effectiveness (SE) of the high voltage (HV) cabling and connectors is critical at the component and subsystem level. The effectiveness of the shielding must also be proven for the useful life of the vehicle. This paper will examine some of the critical aspects of ensuring good SE of HV cabling and connectors in hybrid and electric vehicles. This paper will also review some of the test methods utilized to make these measurements. CITATION: Boyer, R., "EMC Management in HEV/EV Applications," SAE Int. J. Passeng. Cars – Electron. Electr. Syst. 7(1):2014, doi:10.4271/2014-01-0219. 2014-01-0219 Published 04/01/2014 Copyright © 2014 SAE International doi:10.4271/2014-01-0219 saepcelec.saejournals.org The HV connector must be shielded and designed to continue the shield of cable into the next shielded structure. Therefore the connection of shielded cable to the shielded connector becomes one of the critical aspects of ensuring the effectiveness of the shielding. The design of the connector shield must maintain good coverage by minimizing openings, gaps, and seams. This connector shield then becomes the next critical piece in maintaining the effectiveness of assembly. The connection of shielded connector to either the header connector or connector in an in-line connection becomes the third interface of importance. And finally the connection from either header connector shield or the connector shield to shielded cable in an in-line connection is the final critical link of the shielded assembly. Figure 2 is a simplified block diagram outlining the HV shielded assembly. Figure 2. Simplified block diagram of assembly. Blue outlines indicate shielded and the orange blocks are critical shielded connection paths. As can be seen in figure 2, the interfaces are important to the overall SE performance because of their need to continue the shielding performance of components and connectors. These interfaces can represent some of the greatest challenges in maintaining good SE because of the automotive OEM temperature, humidity, and vibration requirements. These connectors and interfaces must maintain their SE performance throughout their life cycle and therefore the SE must be measured as the product is goes through accelerated life cycle testing. These interfaces have to seamlessly continue the shield of components to the next shielded component. These components and interfaces must remain a cost effective solution for reducing unwanted EMI. In order to optimize the design of connectors and interfaces a test method that predicts performance in vehicle must be utilized. This will allow the designer to try out concepts for the intended frequency range and then modify these concepts to ensure best performance at reasonable cost. AVAILABLE TEST METHODS TO MEASURE SE Having shown the block diagram of the cable assembly it is obvious that a test method needs to be able to measure the shield interfaces into and out of connector. There are a number of industry standards for measuring SE Most of these were developed for RF cabling and connectors. The test method must give results that predict vehicle performance reliably. Also when choosing an appropriate method one must account for the ability to perform measurements on the samples throughout their exposure to accelerated environmental testing without disturbing the interfaces that must be measured. This becomes a challenge due to the various sizes of connectors in use. Although the author has researched and tried many different test methods, this paper will only address a few of them. One of the industry standard test methods that will accommodate all of the sizes is IEC 61726 Reverberation Chamber Method. According to IEC 61726 the smallest dimension of reverb chamber must exceed 3 wavelengths at the lowest test frequency. The lowest test frequency we are interested in is 100 kHz. This would make the smallest dimension of reverb chamber approximately 9 km! Another industry standard test is IEC 62153-4-7 Tube in Tube Method. The physical length of tubes is dictated by frequency range. The commercially available systems can test in the frequency range of 30 kHz 3 GHz. The limiting factor in using this method is that it allows for only devices less than the diameter of tubes or use of test boxes attached to the tubes as long as test box resonance does not affect the measurements in selected frequency range. This is a feasible test but requires time consuming construction of needed test boxes and varying tube diameters for the various sizes of connectors. This method usually requires additional preparation of the samples used in the accelerated environmental testing that can disrupt the interfaces. Another test method is IEC 61196-1 Absorbing Clamp Method, measurement with extension lines. This method utilizes measuring the RF currents on the shield outside of the connector and does not require placing the sample inside of the absorber clamp. This will ensure that the interfaces are not disrupted. This method also allows for all of the various sizes of connectors to be measured. Figures 3 and 4 show the setup diagram and the picture of setup. Figure 3. Absorbing Clamp Method, measurement with extension lines diagram. Boyer / SAE Int. J. Passeng. Cars – Electron. Electr. Syst. / Volume 7, Issue 1 (May 2014)