Delphi Weighs in on Hybrids
By Randy Sumner, Delphi Packard Electrical/Electronic Architecture

The common goal of every hybrid vehicle is to produce fuel economy benefits to the consumer through the addition of an electrical system that reduces or eliminates the dependence on the internal combustion engine. Today’s hybrid vehicles range from the simple Belt Alternator Starter (BAS), 14-volt, stop/start system to fully electric systems capable of driving the vehicle with an energy storage battery pack and electric motor alone. Unique electrical requirements of connection systems and wiring must be taken into account when designing and developing a hybrid electric vehicle.

Delphi is an expert in hybrid vehicle systems, including electrical/electronic (E/E) architecture, and has developed application-specific components such as high-power electrical wiring harnesses, connectors, and hybrid electrical centers. A vehicle’s E/E architecture is a natural integrator. It touches all vehicle systems, and has to account for harsh environments and densely packaged real estate. Hybrid vehicles present unique challenges when it comes to E/E architecture. Hybrid vehicles have rigorous power requirements, and demand robust component performance and additional safety features, due to the challenging environment in which they operate. DC/DC converters, drive motors, battery packs, and E/E systems capable of managing high-voltage and currents are increasingly sophisticated.

Delphi’s hybrid development center in Champion, Ohio, is an accredited, full-service test facility dedicated to developing hybrid-specific technologies, including harness protection systems, battery monitoring devices, and Delphi’s new series of connection systems. These new connection systems incorporate the shielding, sealing, and high-voltage safety interconnects required for high-voltage/high-power applications.

EMI Shielding
Hybrid vehicles may be best known for generating greater fuel economy, but they can also generate something much less desirable to automakers—electromagnetic interference (EMI). At least they would generate EMI if it weren’t for electromagnetic compatibility (EMC) engineers like those at Delphi Packard Electrical/Electronic Architecture. These engineers are responsible for testing and overcoming the challenge of EMI in hybrid electric vehicles (HEV).

EMI has always needed to be managed with electronics and wiring, even in 12-volt systems. This unwanted noise can interfere with radio reception and other vehicle signals, such as AM/FM radio frequency, cell phone usage, and Bluetooth capability.

In order to operate, hybrid vehicles make use of high-current, high-voltage power inverters. The power inverters typically generate unwanted EMI in the frequency range of 100.0 kHz to 200.0 MHz. The high power switching between AC (alternating current) and DC (direct current) in these inverters makes this an even greater issue in HEVs.

Electronics are preferable to transformers to invert AC to DC to charge the battery pack, because they are much lighter. In fact, electronics are the only feasible technology applicable at this time for inverting the DC to AC, in order to have the battery pack propel the vehicle. However, these electronics generate more EMI. High-voltage wires act as antennas for EMI, carrying the EMI out of the electronic box through the cable across the vehicle.

In traditional vehicles, the most cost-effective method of suppressing EMI noise is through the use of components such as capacitors, inductors, diodes, etc. But shielding electronics and wiring becomes a more cost-effective solution in HEVs, because the traditional suppression components required would be too large and heavy to be practical.

So, what is shielded cable exactly? It is essentially standard cable with a metal wrapping around it to contain the interference. The material could be a metal foil or a braided wire mesh. In order to develop shielded cable, Delphi first set out to establish shielding effectiveness test specifications specific to HEV applications. The existing standards did not encompass the conditions experienced in an HEV application. So, Delphi engineers spent a year in a state-of-the-art EMC lab developing the test specifications and the resulting shielded cable technology. These specifications are among the best in the industry for HEV EMC, and are under consideration by USCAR as the global standard. The lab enabled the EMC team to administer very thorough tests in an environment that most closely resembles that of the HEV. By incorporating measurement techniques that more closely resemble the complete vehicle, our products not only exceed the expectations of our customers, but also the expectations of vehicle drivers and occupants.

Hybrid vehicle technology will continually change, and as this happens, the need for shielded cable will become increasingly important. Automakers will continue to need to use electronics for weight and cost savings, and, as a result, they will continue to need to reduce the noise generated by those electronics. We are well equipped to keep ahead of the pace as the technology of hybrid electric vehicles evolves. Delphi is an active member of the global EMC community, providing direction to the bodies that govern the present and future standards for EMC.

Safety First
To keep drivers and service technicians safe in high-voltage environments, a number of complex factors in the electrical system must be addressed and engineered for reliability and peak performance. A key component in the high-voltage electrical wiring harness is the connection system, with special attention paid to the design of the high-power connections. Two areas are paramount to safety in high-voltage connection systems design. They are the Hazardous Voltage Interlock Loop, or HVIL, and the environmental sealing of connectors to protect against short-circuiting between high-voltage terminals when the vehicle is in use.

Sealing high-voltage connections is critical, due to the failure modes, which may result when connections are left unsealed, such as short circuits. As we all know, water and electricity don’t mix. Using silicone cable and connector peripheral seals, the connections are sealed to make sure moisture cannot enter and create a thermal incident or fire. High-voltage systems require more robust sealing than traditional 12-volt systems, because the higher the voltage, the higher the potential for arcing.

The HVIL is a necessary feature of high-power connection systems that protects against arcing that could occur if the connectors used in the power electronics are pulled apart too quickly. Special consideration must be taken to ensure the connection system cannot be disconnected while powered. In the event of a disconnection, the HVIL communicates a signal to safely shut down power. This is necessary in an accident situation, or during repair, when a technician needs to disconnect power to service the vehicle.

It’s not too often that you get to witness an entire industry shift before your eyes, but that is exactly what is happening today with the introduction of hybrid electric vehicles to the automotive industry. It is an exciting time for automotive suppliers, especially those of us who supply electrical/electronic systems and components, as we rely on the vast experience we’ve honed over more than 100 years of supplying traditional automobiles to design, develop, and manufacture the high-voltage systems that will power us into the future.