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Automotive Power Electronics: New Applications Drive the Need for Advanced Components

Thu, 01/27/2011 - 11:07am
Henning Hauenstein, International Rectifier Corp., www.irf.com

Not too long ago, car makers competed with each other mainly with the performance of a car. Highest horsepower, fastest acceleration and top speed have been typical benchmark parameters to establish a superior brand. Those benchmark cars in the fleet helped car manufacturers sell the actual mainstream of smaller and midsized cars just by establishing a brand leadership in the market. This has changed a lot in recent years. Customers are no longer attracted by pure performance values. Instead,fuel economy and low emission replaced many purchasing decisions. And, every brand needs to have benchmark cars with lowest emission and fuel consumption in the fleet to prove their technical leadership position. Another important category in the fleet is a hybrid electric vehicle (HEV), at least visible in the OEM’s roadmap and shown as prototypes in corresponding motor shows.

Clearly the consumer behavior has changed a lot, and our society is undergoing a paradigm change with regard to our transportation concepts and mobility behavior. Also, the “quality of transportation” becomes a more important factor for the car buyer.

Therefore we see a tremendous growth of electronic systems entering the car, and this starts from convenience and safety systems such as lane departure warning, electric power steering, rear view and infrared nigh vision cameras, head up displays, LCD-monitors for the dashboard, infotainment, and extensive cruise control, which all add up to the extreme case of the electrification of the entire power train. From a leading power management company’s point of view, this is excellent news since even all these systems have in common that they need power management devices. These are complex chipsets with advanced Si content that a semiconductor supplier like International Rectifier can provide in order to make the power management as efficient as possible to supply all these consumers.

Today we see two big trends: One is electrification of (so far) hydraulic or purely mechanically driven systems, such as water pumps, oil pumps, fans, the steering, braking, and air conditioning in order to make those systems much more efficient. To save fuel, these systems switch to electric motor drives with variable speed. The second big trend is the introduction of many new applications and systems into the car that we haven’t seen before. Some of them are already mentioned above, and this also includes the electrification of the power train for hybrid, plug-in hybrid and electric vehicles.

Looking 10 years ahead, power management efficiency will play an even more important role. What is done today to make the fuel consumption more efficient by minimizing the energy loss of power management and energy distributing systems in the car will become even more essential when our society starts using a significant number of electrical vehicles. Then the range of the vehicle is determined by the stored energy, and the consumption on board will be a major contributor to the available miles of an electric or plug-in hybrid vehicle. Still, customers will not sacrifice any of the acquired convenience and safety features that our state-of-the-art cars provide. Nobody wants to have an electric vehicle with no air conditioning, infotainment or driver assistance systems. Instead the efficiency of those power consumers needs to be maximized. And this will drive the trend of power management devices to become even much more efficient than today.

Energy-efficient, Environmentally Friendly Automotive Applications
Here is a quick overview of the new applications that those energy efficient and environmentally friendly cars require and which will drive the roadmap of power components. From a semiconductor supplier point of view, the some of the most interesting applications are the systems that consume a lot of valuable Silicon. Here, the electrification of the power train is definitely one of the important focus areas since this will utilize a huge amount of Silicon for the high voltage inverters or the DC/DC converters and the battery chargers or the battery and energy management itself. The second biggest Silicon utilization will come from peripheral systems with larger motor drives in the Kilowatt-power range such as air-conditioning compressors or the electric power steering.

Do not forget about those applications that drive the more incremental evolution of cars and which might even have a bigger impact on the short term requirements of power management devices to the improvements of the fuel efficiency of standard combustion engine cars. Influenced by the marketing messages of the hybrid vehicle manufacturers, many people think that the fuel efficiency can only be improved significantly through revolutionary systems like a hybrid or electric vehicle power train. Actually, the evolution of the standard combustion engine still has a huge potential to improve worldwide fuel consumption and the reduction of pollution and emission on a much broader scale -- and much faster than the relatively slow penetration of hybrid vehicles seems to promise. Like the history of the diesel engine in Europe, there is already a huge difference between the fuel efficiency of a modern direct injected and turbo charged diesel engine and a standard gasoline engine with equal horsepower. The Diesel engine offers nearly the same fuel efficiency as a much more expensive hybrid-gasoline car. On highway drive cycles where the hybrid is not adding too much value to the consumption, the diesel is a superior performance engine. But in order to achieve such good fuel consumption, the former purely mechanical combustion engine receives quite some electric aids and system support. The direct fuel injection for example uses high voltage power switches and driver ICs to control the sensitive and highly precise injectors. Power management devices play a key role in the fuel injection systems, and they also enter the turbocharger -- a former purely mechanically driven belt system that in the near future will also become electrically inverterized and therefore more efficient and better controlled with variable speeds. Overall, expect a big evolutionary development of the combustion engine utilizing more electronics and power management devices to contribute significantly to solve our environmental problems.

With those upcoming new applications in the background of OEM’s car evolution it is imminent to improve the efficiency of power management devices. Silicon power switches, after decades of big improvements, are slowly approaching an area where every additional efficiency improvement is paid by very expensive R&D work and also much more expensive manufacturing processes. This all defeats the trend and mission of many car manufacturers to make cars safer, more efficient, and also affordable. International Rectifier’s mission is to support energy efficient power management not only with very advanced Silicon, but also with major improvements in the packaging of those devices. There are many examples where the Silicon capabilities are tremendously advanced so the state-of-the-art wirebonded plastic packages cannot even take advantage of ultra low on-state resistances of our most advanced FETs. Often, the parasitic inductance of standard packages eliminates the advantages of fast switching devices, too, which could make DC/DC converters and switched mode power supplies much more efficient.

The automotive division has a very strong focus to develop advanced power management technology that addresses especially those package problems. A proprietary automotive capable front metallization can be applied, for instance, to advanced power switches like MOSFETs and IGBTs. This metallization eliminates all wirebonds in the packages to enable complete bondwire-free package solutions. Devices can be soldered on both sides and therefore can also include cooling and heat sinks on both sides of the products (see Figure 1). This increases tremendously the electrical, thermal and mechanical performance at the same time, since without wirebonds, the well-known bondwire lift is eliminated as the primary mechanical stress failure mechanism after power cycling. In addition, minimal parasitic inductance and basically negligible package resistance is achieved, taking full advantage of modern Silicon capabilities.

Figure 1. Comparison of cooling routes for a D2Pak and Large Can DirectFET package using IR’s proprietary automotive bondwireless package technology

In power steering applications, DirectFET technology enables high power motor drives for power hungry electric steering motors, which used to have thermal and size problems. A dual-side cooled DirectFET offers 60 to over 80 percent smaller footprint at >90 percent less volume, which enables for the first time new designs of power steering motor drives for all categories of cars. Bondwireless IGBTs in proprietary Direct-Packages should also have a big impact for HEVs where motor inverters and DC/DC converters will see a revolutionary improvement in size, performance and even in cost reduction, which is beneficial for the end user and the market penetration success of the environmentally friendly cars.

Overall, the needs for advanced power management components can be summarized with four key requirements: 

• High Efficiency in the applications: To avoid sacrificing the valuable onboard energy through power losses and heat, which would also defeat the purpose of an energy efficient vehicle concept; 

• High Current carrying capabilities, which can be in the range of several 100 A up to 300 A and more while handling high voltages of typically 600 V to 1200 V; 

• Increased mechanical and electrical performance, since the automotive applications will require the electronics to withstand the harsh environment of a car while safety and protection requirements will demand a fail proof and safe high power system designs. 

• Low EMI and low parasitic Inductance, since switching high currents and high voltages will cause very high electromagnetic fields and introduce conducted or transmitted noise/EMI, overvoltage spikes and other disturbance to the sensitive electronics (like microprocessors, sensors, safety critical monitoring devices, etc..) that typically operates at low voltages.

International Rectifier’s Automotive division addresses those requirements with chipsets that comprise of corresponding components that include fully protected and optimized driver ICs, advanced power switches and bondwireless packages (Figure 2). In the near future our GaN power management solution will enter the automotive world, giving car manufacturers and system suppliers a huge degree of freedom to provide innovative and very advanced cars which are fun to drive, energy efficient and still very affordable for the broad consumer base. 

Figure 2. Advanced Power Management Components

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