Collaborative Approach to Overhaul Motor Inverters

With the exhibition and conference season in full swing, Silicon Carbide topics continue to dominate discussions but real business now being done. We have reached a transition phase cementing market sentiment and commitment.

PCIM 2016 offered all those who visited the chance to see an exciting array of core SiC-based solutions from SMPS, to Automotive, Transportation and wider Industrial applications. The conference papers highlight the massive investments that continue to be made globally, even if some come with prize money, such as the Google Little Box Challenge. ETH Zurich, Switzerland, for me touched upon a key message that will no doubt be music to the Semiconductor manufacturers alike: “The Ideal Switch Is Not Enough”[1].

Herein lays the next challenge for the Power Electronics industry. Huge investments from the semiconductor manufacturers have realised working WBG nuclei, even in high voltage classes, introduced new ultra-low inductance packaging technologies to exploit the base technology, such as nHPD2, introduced novel new cooling methods to attain high-temperature operation and innovative bonding processes for improved reliability[2]. It is definitely not enough to rely upon the switch alone.

Inductance is a formidable foe for the successful deployment of WBG devices for motor inverters. By reducing only semiconductor package inductance, the system-level value remains too high. Over-voltage and EMI may nullify the performance benefits. More action is required to reach nirvana.

High power density switches must have higher junction temperature capability. It is no longer a nice to have feature. Seeking to break through the 200°C barrier, WBG can exploit its high thermal conductivity; substantially lower switching losses and benefit from inherently lower leakage-current. However, materials such as the isolation gel within larger power modules, or the interface with system component parts becomes a critical bottleneck high temperature.

The single largest challenge facing converter designers to maximise the full WBG potential is sub-system parts. Many have yet to catch-up with the rapid development pace set by the semiconductor industry.

For those engaged in busbar development, for example, the challenges to overcome include the skin effect in high-frequency domains, or the durability of insulation films at high temperature. Capacitor development hurdles include optimum mechanical outlines, connections, voltage versus temperature, and so on.

Bulk wafer suppliers continue to optimise crystal growth methods and the semiconductor process engineers maintain efforts to improve SiC on-state performance.
The International Energy Agency (IEA) estimated almost half of global electricity production is consumed by electric motor-driven systems, drawing more than 7,000TWh a year (2011) and 13,000TWh by 2030.

The automotive sector forges ahead embracing PMSM technology, medium & high-frequency DC-DC, to realize smaller, lightweight, high-efficiency systems to achieve their CO2 obligations. Meanwhile, the majority of market sectors mull over the technology shift based on cost-performance benefit.

As a procurement professional reading this, you might consider your influence. Without relying on specific legislation as a catalyst to embrace WBG, cost-performance benefits have to be neutral worst case. It is feasible, even if your suppliers’ switching device appears to be higher at first glance today. Using a crude example, the opportunity to operate a WBG switch at much higher frequencies should lead to a transformer weight reduction inversely proportional to the frequency. The smaller transformer means a lower cost and lower weight, which itself leads to lower cost, and so on. A price cascade effect begins when a traditional paper component price comparison is exchanged for a detailed system-level re-calculation.

We all have much more to do to achieve our social responsibility to make a brighter, more sustainable future for the next generation.

In this Olympic year I would pass the “relay baton” to fellow industry colleagues in the key fields of capacitors, busbars, magnetics and materials development, to boost product characteristics further, notably even lower inductance and higher operational temperatures, such as Rogers’ “Rolinx®” and Mersen’s “highT°”, system architects to embrace PMSM just as Singapore’s SMRT Trains have done, and for purchasers to think “system-level savings”.

With deeper collaborations between all product groups in the Power Electronics sector, let us accelerate and unlock the full benefits of WBG devices and their adoption beyond the “Google Little Box Challenge” to include the “Bigger Industrial Boxes” too.

 

References

1. The Ideal Switch Is Not Enough. J. W. Kolar, D. Bortis and D. Neumayr. ISPSD 2016.
2. Highly Reliable and Lead-Free High Power IGBT Modules Using Novel Copper Sintering Die Attachment. Yasuke Yasuda and Akitoyo Konno. PCIM 2016.

 

This article originally appeared in the Bodo’s Power Systems magazine.