Power Electronics

Appliances Drive Power Module Packaging, But Where?

Today, intelligent power modules have become the preferred power semiconductor solution for motor drives in consumer applications. Their functionality incorporates the power silicon for the inverter section, consisting of IGBTs, free-wheel diodes (FWDs) and a driver circuit that includes different protection features. Some module concepts also offer integration of passive components. These integrated solutions are becoming the preferred choice over discrete components, mainly due to their more compact size, greater ease-of-use, shorter design cycles and better reliability.

However, one question remains: How will the module concept continue to evolve in light of conflicting customer interests? Although system cost remains the dominant factor in the white goods market, other considerations, such as intellectual property (IP) protection, are becoming increasingly important to the OEMs. The IP referred to is mainly for the motor control software for dc motors. The use of these motors is increasing in applications, such as room air conditioners, where improved efficiency is desired.

To a certain degree, IP is also in the hardware design of the power stage. Inherently, this goes along with the question of how OEMs differentiate themselves. Do they still consider the motor-control electronics to be an element of the design that sets them apart from the competition? Or, do they view the control software as the piece of the design where they gain an edge? Alternatively, do the OEMs view the power stage simply as a commodity that is provided by a Tier-2 supplier and only customized for specific applications?

There are two ways of addressing these questions with new module concepts. One way is to further and continuously increase the functionality of the intelligent power modules to the point where full-inverter functionality is achieved in a single package. The first step in this direction, which requires designing the module from a system perspective, could be the integration of additional logic functions such as a microcontroller or PWM controller.

This approach would enable the most compact designs and shift the design effort towards the semiconductor supplier, resulting in a lower cost of ownership on the customer side. With this kind of solution one tradeoff is the module's fixed-form factor, which will be dictated by the number of variants that arise from different application and customer requirements. The need for different form factors may increase the piece-price because of lower volume production (as compared to the cost of a discrete solution). Ultimately, the end customers/OEMs will determine whether this move to full-scale integration takes place.

If motor-control electronics stay on the list of differentiation factors for OEMs and their intention will be to keep buying discrete components, which are then assembled into a subsystem, the “game” will be different. Cost for power silicon will be the main driving factor leading to commoditization of the power modules with a tendency towards higher power densities, which are enabled through shrunken silicon and smaller packages. In this case, the value chain would not change at all. It would, however, be much more difficult to achieve cost reductions, as the discrete approach will not take into account the full set of system requirements of the OEMs.

Currently we can find both tendencies in the marketplace. We do find module suppliers who follow the strategy of high-volume production, trying to push the limit for the best cost-performance ratio on the limited functionality offered (typically an inverter structure including IGBT driver ICs).

Meanwhile, others approach the module design from a system perspective including the motor to find the optimum partitioning of the system. This typically results in a more highly integrated module in which passive components are included and where the power-module system is tuned to fit the overall drive performance. The option of having the motor-control logic integrated in the module is currently under discussion, and even the software for motor control could be part of the system module offering.

The ultimate power module would have a rugged package that incorporates a whole system with the highest power densities at benchmark cost. Power-module examples today achieve only two out of three of these goals. Meeting all three would change the value chain for motor drives in home appliance applications, shifting the power-system design to the module supplier.

Wolfgang Ademmer was vice president of sales and marketing at Eupec, which previously was a wholly owned subsidiary of Infineon.

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