Power Electronics

OPD Update: Reducing Inductance In Power Distribution Systems

Laminated bus bars provide better electric performance, an ability to handle higher currents with less voltage drop, lower noise and inductance.

Find a downloadable version of this story in pdf format at the end of the story.

Electrical and electronic systems are now being asked to deliver higher performance, higher quality, and more capabilities, with better reliability, lower cost, and smaller size, than previously thought possible. This puts increased pressure on system designers to find better technologies that will provide more efficient power distribution to meet current and future needs.

For example, high frequency switching applications (IGBT technology) require that “Litz” magnet wire be used to reduce inductance. However, these bundles can be large and difficult to assemble due to the varnishing of individual strands. Instead, laminated bus construction is ideal for this high power distribution. The interleaved conductors are thin and flat making excellent low magnetic flux emitting conduits. The dielectric materials used provide high voltage isolation with minimal distance between conductive materials. This combination of thin flat conductors with thin high dielectric insulation creates a low inductance power distribution system ideal for high frequency switching applications utilizing IGBT technology.

Fig. 1 shows an inverter application for a motor drive. Utilizing the low inductance of a busbar, the customer was able to eliminate the snubber capacitors from the assembly. This resulted in a direct cost savings through both the reduction of components and the labor to install them. The laminated conductor assembly resulted in a component reduction of 40% by eliminating the cabling required and mechanical hardware used originally to locate the individual cables.

The section view in Fig. 2, illustrates the construction of the busbar. The ability of the insulation to have a high dielectric breakdown resistance enables the conductor plates to be interleaved with a minimal spacing between plates, resulting in low inductance. This is very advantageous in systems using IGBT's. The laminated conductors are fused together with NomexR insulation coated with a flame retardant epoxy adhesive. The composite system is UL flame rated at 94-0 and meets all the requirements of UL 508c. The insulation material was selected to enable the customer to wave solder discreet radial lead components to the assembly, further compacting the motor drive.

COST SAVINGS, ELECTRICAL BENEFITS

The drawn conductor (embossed) area eliminates the use of bushings to have coplanar contact surfaces for the component attachment. This is both a cost savings in the manufacture of the busbar and an electrical benefit. The bushing is attached using a filler metal that does not have the electrical conductivity of copper, resulting in a voltage loss at the joint.

The customer was able to reduce cost and space by edge sealing the conductor layers. This method optimizes the processing of the assembly, as it is created during the lamination sequence and not as a secondary process. The space is reduced by having the edges sealed electrically. The customer is able to place components in closer proximity and reduce the size of the enclosure.

As evidenced by Methode's experience with high power system applications, the utilization of laminated busbars have many benefits, including better electric performance, an ability to handle higher currents with less voltage drop, lower noise and inductance. The electrical performance of the system is optimized resulting in fewer components. This directly correlates to cost reductions in both component and assembly time for the customer. The insulation material and conductor isolation reduces the footprint of the motor drive.

AEROSPACE APPLICATION

An aerospace company tasked Methode with creating a reliable-but-compact power distribution system that would efficiently distribute power for a helicopter application. Our team developed a laminated bus bar configuration as a pentagram to rotate about its center during operation. The low profile of the assembly enabled the power to distribute from the center to the PCBs at each edge. The PowerFlex™ cables come from a circular connector passing through the center hole to supply power to the pads on the bus bar which then distributes the power to circuit boards.

These performance enhancements to busbars combine to produce a system design that allows the customer to market the drive more competitively with a higher profit margin.

Download the story in pdf format here.

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