Enabling the Future of Electrically Powered Systems

The world’s consumption of electrical energy is rapidly expanding, driven by growing mobile media, cloud computing infrastructure, the expansion of industrial power demand, and an emerging electric vehicle market.

Worldwide consumption of electricity has grown by more than 47% from 2000 to 2012 (Figure 1), and is expected to expand even faster in the future.

This expanded pressure on demand is fueling the need for more renewable energy generation, smarter utility grids, and more energy efficient power conversion systems, each of which use power conversion electronics – the devices responsible for converting energy from solar panels or windmills to utility grid standards or converting utility power to useful DC and AC power.

To maintain the proliferation of new applications and new power conversion systems, the industry needs more efficient, more reliable, and lower cost power system electronics.

In the process of converting electricity, power systems both consume and waste electricity. Energy inefficiency produces heat that needs to be dissipated and contributes to higher electric bills, more complex systems, and higher system and operating costs.

The worldwide consumption of electricity (in terawatt hours) spanning the years 2000 to 2012.graph image www.energy-options.info

Although these losses seem relatively low (between five and 15 percent) they require large and expensive heatsinks, or more complex water cooling or air conditioning systems, to dissipate the energy losses, which increases system size and weight and adds complexity that translates into poor reliability and short system lifetimes. As such, the best way to limit future new energy needs and power conversion systems costs is to avoid wasting energy in the first place.

The primary contributors to poor efficiency in power systems are the silicon semiconductor devices. Power semiconductor devices have been used in power converters since the 1960s, but silicon based power transistors and diodes that carry, switch, and convert the system power can be inefficient and slow to switch due to their intrinsic material properties.

Device inefficiency in power systems is realized as heat that needs to be dissipated. Also, slow, inefficient switching speeds require large, bulky, and costly passive components to filter the power, step voltages up or down, and provide electrical isolation within the system. Despite generations of silicon device improvements, they have reached their practical limit.

Silicon carbide (SiC) is a superior material for making power semiconductor devices; however, the technology to produce reliable, cost effective SiC devices only emerged within the past fifteen years. SiC is capable of blocking higher voltages, carrying more current, and suffering fewer losses per unit area, making it a truly disruptive technology in two ways.

First, SiC reduces the conduction losses inherent to Si, which enables higher efficiency, lower thermal management costs and improved system reliability. For applications in which efficiency is key, this advantage can be extremely impactful.

Second, due to its smaller die size, SiC also reduces switching losses, enabling higher speed circuits, smaller form factors, and higher efficiency, and allowing SiC to switch faster than similar silicon switches, which enables systems with smaller, lighter, and less costly inductive and capacitive elements. Fast switching speeds also enable the use of simpler, more straightforward system design techniques.

For power system users, these benefits translate into lower system and operating costs, smaller physical footprints, lower cooling costs, and longer lasting, more reliable systems.

Silicon carbide devices have been commercially available since 2002, starting with SiC Schottky diodes. Silicon diodes in blocking voltages above a few hundred volts are limited to junction devices that consume energy to create and dissipate the junction needed to block and conduct electricity.

SiC’s superior material characteristics allow use of field-effect (Schottky) device topologies that can block high voltages (as high as 15 KV) without the need to establish a junction barrier. The result is a quantum reduction in energy losses during switching.

SiC Schottky diodes are instrumental in enabling computer and digital data storage power supplies to reduce energy losses to less than half that of their silicon predecessors. They also enable more delivered power in the same physical power supply size, which helps reduce the cost of high performing data centers. Applied similarly, SiC diodes helped enable the high efficiency that fueled the initial wave of solar inverter system growth.

As impressive as those savings are, however, SiC diodes alone are not enough to impact more than a few power applications. SiC transistors were needed to broaden the applications and enable more significant system impact. The first commercial SiC power transistors were introduced in 2011.

Today, both SiC diodes and transistors are available from more than ten suppliers. As portfolios of various blocking voltage and current rated devices are now proliferating, SiC-based power systems are expanding from watts to megawatts of system power.

Beyond power supplies and solar inverters, SiC devices are being used in battery chargers, welding and cutting tools in factory automation, and for the rugged electronics required by the oil and gas industry. A combination of both lower and higher voltage SiC prototype devices are even being used in the new solid-state transformers and power switches that will enable DC microgrids, distributed power generation systems, changing grid architectures, and the future smart grid.

Additionally, SiC power devices will play a major role in the drive train electronics and charging systems of electric vehicles, enabling lighter, cheaper, and faster charging, and extending the range between charges.

As one can imagine, the transportation and installation costs of the SiC solution are also much lower than the silicon solution, adding even more value to the SiC cost advantage.

For example, an electric bus charger system now running the streets of China features an impressive 60 percent weight reduction (see Figure 2), which was driven by the faster, more efficient switching of the SiC devices.

Size and performance comparison of a Si- vs. SiC-based charger system. china bus system image www.energy-options.info

In addition, the SiC solution runs efficiently enough to eliminate the need for fans, improving overall system cost and reliability. Moreover, in a design by Toyota on a full SiC drive train, a prototype electric vehicle achieved a 40% reduction of the electronics size and weight and provided an additional 10 percent improvement of the vehicle’s mileage from a charge.

Beyond these examples, SiC customers have developed smaller, lower cost SiC based solutions ranging from LED lighting power supplies to auxiliary power supplies for trains and industrial power systems, such as laser and metal cutting solutions.

In the future, the medium voltage SiC devices now being sampled will bring similar advantages to the smart utility grids of the future, enabling smaller, lighter transformers and switching gear — which can bring medium voltage power deeper into factories and data centers, closer to the point of load, enabling additional savings — as well as more flexible and decentralized grid topologies, all at a lower total system cost. However, despite the impressive array of SiC solutions available today, we are only at the beginning of the SiC power device revolution.

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Henry Sapiecha

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