You will find the figures mentioned in this article in the German issue ofATZelektronik 03I2007 beginning on page 72.

Passive Komponenten für die Hochvolt-Energieverteilung

in Hybridfahrzeugen

The Importance of High

Power Components in Hybrid

Concepts

Author:Uwe Hauck

High power connectors, high voltage main relays and circuit protection devices can be used across many hybrid systems and car lines. Most hybrid car topologies, however, are based on similar requirements for system components. This Tyco Elec-tronics feature provides information on some common hybrid vehicle components.

1 Introduction

The desire to attain mobility has been driv-vving engineers to develop ever more effec-tive and safe vehicle components for dec-ades. Ferdinand Porsche, for instance, wasway ahead of his time when he investigatedhow a combustion engine could be com-bined with the advantages of an electricalengine. Some worthy vehicle conceptscould not be implemented due to the com-plexity of managing component interac-tion in the vehicular system as a whole.Another reason why ideas may have failedwas the cost of new components requiredby alternative systems as compared to com-ponents in established systems.

In the following article, the author dis-cusses factors in the successful specifica-tion of passive components in vehicles with alternative propulsion systems. The articlediscusses components such as power distri-bution units, high power connectors, mainrelays and their pre-charge circuits.

2 The Importance of Passive Components for HV Power Nets

The electrical power net of hybrid and fuel cell cars is quite complex. Due to the higher voltage level, additional components andsafety features are needed, Figure 1.

2.1 Electrical High Voltage ConnectorsHybrid drives call for electrical connectionsbetween energy storage devices and theelectrical drive. Besides non-detachableconnections, such as laser or resistancewelding connections, which are generally used within components only, screw andplug-in solutions are available for energy distribution. Plug-in connectors have thelargest future potential in hybrid systems

2.1.1 Plug-in ConnectorsA key advantage of plug-in connectors isfast, secure connection in the vehicle as-sembly process. Multi-pole plug-in connec-tors can be safely connected with a single

ATZelektronik 03I2007 33

hand manoeuver. There is no requirementfor a post-process installation of covers toprovide touch and humidity protection, as both functions are already incorporated in the component. Plug-in connectors will al-low hybrid vehicles to be assembled with the speed and reliability of conventional vehicles. Plug-in connectors are highly reli-able thanks to the reproducibility of plug-in processes and the utilization of multiplecontact fuses [1, 2]. Exchange of compo-nents during servicing is facilitated as well. All of these benefits lower the overall sys-tem costs.

High voltage plug-in connectors devel-oped by Tyco Electronics for shielded single or multiple wire lines feature common de-sign characteristics. The design provides EN60529 IP2xB compliant finger protec-tion against the touching of voltage carry-ing components prior to plug-in, a defini-tive benefit for later servicing, but also dur-rring factory installation. The transfer of the voltage shield is ensured by these plug-inconnectors. The air and creepage distances are designed for utilization with 750 VDC.The various solutions available comply with protection classes IP6k9k and IPx7. The plug-in connector has an added safety feature built in. It cannot be opened with-out a special tool, and is also available with a HVIL (high voltage interlock) safety cir-cuit. The HVIL circuit has two signal cir-rrcuits that are designed to be opened first, before the main contacts can be interrupt-tted, Figure 2.

2.1.2 Bolted ConnectionsIt is, however, safe to assume that initial technical and economic restrictions will limit the use of high voltage connectors. In ranges of 300 A and more, temperatures ex-xxceeding 125 °C or under extreme shock and vibration requirements, bolted solu-tions are the preferred approach. Nonethe-less, their use in factory assembly and inafter-sales services is more complex and re-quires more intense inspection. If the bolt-tting process is only controlled with torquemonitoring, deficient or loose connectionscannot be ruled out. Consequently, to guar-rranty gastight connections and to avoid arc-ing, torque angle monitoring is recom-mended for the production of the bolt con-nection. One area that is challenging in terms of environmental impact is the inter-rrface between the cover insulator and shieldand to the metal housing. Humidity canpenetrate this area and may cause corro-sion in the long run. Bolted connection so-lutions by Tyco Electronics address this very problem thanks to a special feature as

shown in Figure 3. A cable lug is processed in the standard manner and the shield is crimped with a shielding spring. In assem-bly, this shielding spring is electrically con-nected to the metal surface of the housing.This contact is maintained due to the press-ing force generated by the bolt-on assembly of the housing and retained compression seal to the metal housing. The key advan-tage of this solution is that the functional components are pre-assembled. In vehicle assembly, the cable lug is installed and the two housing components are screwed to-gether. The result is a sealed shielded boltconnection that meets the most exacting requirements.

2.2 Safety in the High Voltage Vehicle Electrical System

2.2.1 Safe Separation of LoadsSeparating the electrical energy storage from the vehicle electrical system is abso-lutely necessary under various condi-tions, such as service work being per-formed, in the event of a crash or line in-terruption. Given that power semicon-ductors are unable to achieve a galvanic separation, they cannot be successfully used in this case. Power relays, on the other end, provide a technically excellent and highly cost-effective solution. Given the high voltages and currents that occur during cut-offs from full load, a high lev-el of arc energy has to be anticipated. Therefore only HV relays make the grade for use as main relays. Relay principles that apply to applications up to 1000 VDC have been commonly known for a long time. The real challenge is the transfer of electrical industry technology to the au-tomotive environment. Material selectionand miniaturization are key targets in this context. Nowadays, special epoxy res-ins are available to take the place of ex-pensive ceramics. This enables designs with significant weight and cost reduc-tions.

2.2.2 Voltage Separation with the Main RelayThe gas filled HV main relays possesses ex-cellent separation properties. Voltages of up to 1000 VDC can be switched off. The utilization of extinguishing chambers and magnets allows the safe control of even ex-treme arc energies. To warrant the reliable performance of HV relays, certain ancillary conditions must be met. This pertains, for example, to activation power peaks and shut-down times. Both can have a signifi-cant impact on behavior patterns and lon-

gevity. This results in dynamic effects, suchas bouncing. If, for instance, as shown in Figure 4, the main relay is closed, high ca-pacitive load currents will be carried through the contacts.

If bouncing occurs in the first momentsof switching, arcs are ignited as a result of the brief opening of the contacts, which heat up the contact point severely. Arcs can reach temperatures of up to 12,000 K [3]. The contact zones which have heated up earlier start to cool down and begin to stick. The relay would show a malfunc-tion. To prevent this effect the peak cur-rrrent during the switch on period must be limited. This is achieved through the pre-charge of the sub-circuit capacities up to a load level of 80-90 %. The relay coil driver may be yet another critical design. Diodes are frequently used to protect the relay driver. As a consequence, magnetic energy dissipates only slowly and therefore slows down the dynamics of the opening mo-tion of the relay armature. When opening the relay under full load, this can trans-late into significantly longer arc burning times. The contact erosion causes wear and tear, and can shorten the contacts’ lifetime. In this case too, the timely align-ment of the demanded relapse times is critical for the entire system.

2.2.3 Arc SensingAt the voltages common in hybrid cars, each abrupt interruption of power results in the development of arcs. Differentiationbetween parallel and serial arcs is absolute-ly essential. A parallel arc can develop if a line was for example short-circuited. This would be non-critical insofar as the insula-tion monitor as well as the fuses can con-trol this error if the system design is cor-rrrect. Serial arcs, which can be caused by faulty bolt connections or interrupted wires, are more critical. The interruption occurs between the energy source and the load. The arc burns above this interruption and allows the current to continue to flow through the load. Current sensors that are commonly being used are therefore unable to identify this serial arc. Consequently, a lot of care has to be invested into the pre-vention of arc development. The solution concept introduced by Tyco Electronics makes it possible to identify hazardous steady arcs in high voltage vehicle electri-cal systems [4]. The sensor utilizes the high frequency noise spectrum of the arc, which spreads through the vehicle electrical sys-tem as a line-bound interference. This con-cept is shown in Figure 5. This noise signal is coupled into a resonance circuit, rectified,

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ATZelektronik 03I2007 34

Energy Distribution

integrated and triggered. The output signal of the sensor can then be integrated into the safety topology. The main relays can forinstance be opened to interrupt the flow of electrical current. A thermal destruction of vehicle components by extreme arc energy can thus be averted.

2.2.4 Overheat ProtectionThe monitoring of temperatures in the electrical areas of hybrid vehicles requires special attention. Excess temperatures in the vicinity of the energy storage system reduce its lifetime considerably or can evenbecome a source of danger. Consequently, it is expedient to implement multi-level safety mechanisms. Redundant tempera-ture monitors that act with high priority independently from the μC to manipulatethe safety logic, provide an additional safe-ty level. Cost-effective polymer PTC resistors(Positive Temperature Coefficient) of thePolySwitch device type have proven to beperfect for this application. For monitoring a maximum temperature level, they aremuch less expensive than measuring sen-sors. Below the threshold temperature, the semi-conductor material remains low inresistance.

If the contact with its environmentheats up the PTC to a level above the transi-tion temperature, it responds with a sharpincrease in resistance. As shown in Figure 6, this temperature-dependent switch ele-ment allows the creation of a very simple protection circuit.

3 Applications

The list of components used in HEV couldbe continued. One fact is evident from thereview of the various hybrid systems: most concepts utilize the same component fami-lies, frequently multiple times per vehicle.Therefore specifying them in such a way that they aim at becoming standard com-ponents is an important success factor fortheir use in hybrid systems. On the onehand, this approach helps cut down devel-opment capacities tied up and time re-quired. During the design process, inter-rrfaces and systems components that havebeen previously specified and tested can beconfidently used. In addition, this ap-proach delivers the desired volume effectsin the procurement of these components, thus reducing the overall system costs. Thecomponent industry needs to know the ba-sic specifications if it is to manufacture components in economic numbers.

4 Conclusion and Outlook

The portfolios of components introducedabove, including HV plug-in and boltedconnectors, HV relays, arc sensors and over-rrheat protection devices, can be used invarious applications of a hybrid system. To this end, application work becomes a key factor. Tyco Electronics has had very posi-tive experiences in tackling this global challenge. Thanks to a strong focus on localcustomer service which is being supportedby pivotal technical competence centers, awide spectrum of know-how is at the cus-tomer’s disposal although this develop-ment trend is still relatively new.

In conclusion, it is safe to say that the successful market launch of hybrid cars will depend on the component industry tocome up with products that can be utilizedin a wide spectrum of applications and that are competitive. They will be expectedto promote the rapid and mass utilizationof these components.

References[1] Stabroth, W.: Strom- und Spannungsgipfel – Steck-

verbindersysteme für Automobilanwendungen neu-

ester Generation. In: Fachbuch Markenmanagement

in der Automobilzulieferindustrie, 2006

[2] Krause, N.: Hochstrom- und Hochspannungskontak-

tierungen im Automobil. Sonderausgabe von ATZ und

MTZ, September 2005, Seite 62-65

[3] Kroeker, M.: Extinguishing Steady Arcs. AutoTechnolo-

gy, Vol 4, August 2005

[4] Hauck, U.: Bedeutung der High Power Komponenten

für den Erfolg von Hybridkonzepten. 15. Aachener

Kolloquium Fahrzeug- und Motorentechnik, 2006

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