Semiconductors hold key to electric and hybrid vehicles

The concept of the electric car is older than the internal combustion engine, and over the years there have been numerous attempts to develop electric vehicle technology. However, it is only in recent years – thanks in no small part to consumer environmental concerns and legislation on vehicle emissions – that we are seeing signs of a commercially viable electric vehicle market.

For the same reasons, the market for hybrid automobiles is also set to see significant growth. However, estimates for such growth vary widely, partly due to the fact that this is an emerging market and partly because of the various definitions that can be applied to the hybrid concept. It may, for example, include vehicles that feature a “start-stop” function that switches off the combustion engine when a vehicle is stationary (for instance at traffic lights). Then there are “micro-hybrids”, which add an energy recovery braking system to start-stop capabilities, or so-called “mild hybrids” that incorporate a medium-power electric motor to assist the combustion engine and improve efficiency. Finally we have the full hybrids that can drive small distances using only electric motors.

The good news for the electronics industry is that electric vehicles (EVs) and hybrid electric vehicles (HEVs) of all types require much higher levels of silicon content than the majority of vehicles based on the combustion engine. In fact, semiconductors and complementary electronic technologies – and in particular those technologies that can deliver cost-effective and efficient power management systems - are critical to the successful commercialization of EV and HEV designs.

START-STOP EXAMPLE

Take, for example, the start-stop capability mentioned above. This has an attractive cost advantage in that it runs on a standard 12V powernet, eliminating the need for both higher voltage schemes and batteries for energy storage. The challenge, however, comes from the fact that a powerful starter-alternator motor typically operating at up to 6kW is required for the frequent engine cranking cycles. Such an application requires very rugged MOSFETs that combine the ability to withstand junction temperatures as high as 200°C with very high avalanche capabilities.

In addition, providing the power for re-starting the engine without any perceptible disruption to other vehicle functions requires very efficient DC/DC converters that can buffer the power demand during engine start. These, in turn, create a demand for fast semiconductor switching components that feature very low EMI ratings.

EVs and HEVs that combine batteries, regenerative braking systems and combustion energy technologies and that work with high voltage powernets have even more requirements for advanced power management silicon. These include high-power switch, driver and control ICs capable of handling voltages anywhere between 600V and 1,200V.

Indeed, the biggest challenge for automotive designers who are used to living in a “12V world” is how to implement systems that address the very high voltages required for EVs and HEVs.

Fortunately, semiconductor companies are rising to the challenge and there is a growing range of automotive-certified silicon devices and integrated ASSPs available to designers of EV and HEV applications. International Rectifier, for instance, expects to release over 200 new products for the automotive sector within the coming 12 months. These include highly efficient power devices such as IGBTs and MOSFETs, and novel, rugged driver ICs with enhanced safety features. Indeed, there is a particularly strong focus on protection functionality – the latest motor driver ICs now incorporate functionality that protects both the device and the associated electronics without the need for microcontroller intervention in the case of catastrophic failure or conditions such as short-circuit of the HEV traction motors. It is also worth noting that International Rectifier’s power semiconductors were the “first” to offer guaranteed safe operating areas for negative voltage spike immunity – a common problem when switching high currents with the high voltage IGBTs employed in HEV inverters.

Semiconductor packaging developments are also important in helping automotive engineers to meet key design criteria when developing EVs and HEVs. AEC-qualified versions of technologies such as DirectFET, for example, with its double-sided cooling capabilities allow automotive engineers to realise drastic space reductions in power-hungry and high-speed switching applications such HEV DC/DC converters, while techniques that eliminate bond wires between package and die significantly increase overall reliability.

SILICON ADVANCES SAVES SPACE, IMPROVES RELIABILITY

At the same time, ongoing advances in silicon current densities reduce the number of devices that need to be connected in parallel in order to handle the high currents required by EV and HEV designs. This, again, saves space and improves reliability, while offering additional benefits to engineers tasked with developing their own control units and power modules using bare die components.

Finally, while high power motor drives are the most obvious opportunities for new and emerging silicon devices, other opportunities for semiconductor content in EVs and HEVs should not be underestimated. In line with their more environmentally friendly credentials, EVs and HEVs also demand ever greater efficiency in a wide variety of peripheral systems. From battery management to the brushless AC motors deployed in air conditioning compressors, electric power steering, fuel and oil pumps and engine cooling fans, more and more semiconductors are needed to optimize the efficiency and reliability of EVs and HEVs and, thus, realize their true potential for commercial success.