Think City electric car.
Think has incorporated HE power converter technology in its City electric car.

Efficient EV Charging

Efficient charging is as important as the ability to quickly charge an EV's battery.

By Morten Schoyen

With a renewed sense of urgency to reduce carbon footprint and an overwhelming consumer desire to cut costs in the face of wildly fluctuating gas prices, the movement toward electric vehicles is alive and well. In fact, the US Federal government has set a target of 1 million electric cars on the road by 2012.

Companies like Tesla are pushing the envelope on electric car performance, while other firms, like Th!nk, are bringing advanced style and comfort to these vehicles. The goals for many electric car consumers are to reach zero emissions and to save money.

One aspect of the design of these cars that impacts these goals is the power loss inefficiency during the battery charging process, specifically in converting the AC power from the utility into DC for the battery. Consumers want to see the efficiency as high as possible because it affects their pocket book. Car companies want to make improvements because their goals is to make sure that as much of the energy that is taken from the utility as possible, ends up in the shaft (or wheels) of the car.

Historically, between 10%-12% of the power drawn from an outlet is simply lost in this conversion process, damping the impact electric vehicles can have on carbon footprint and raising the cost to the consumer who will pay higher than necessary electricity bills. However, high efficiency technology is now catching up with the zero-emissions lifestyle in the form of high-efficiency battery chargers.

According to recent statistics from the “Advanced Vehicle Testing Activity” report produced by Idaho National Laboratory, production and conversion electric cars typically use between 10 kWh to 23 kWh per 60 miles traveled. Assuming the average person drives 20,000 miles/year, these electric cars require between 3,200 and 7,360 kWh per year.

With industry standards for power conversion efficiency hovering near 88%, at the low end of power requirements, these cars require a draw of 3,584 kWh and 8,243 kWh to power that battery. Alternately stated, this conversion process can waste more than 880 kWh per year.

Rectifiers are the part of the battery charging system that sits inside the engine cavity and converts AC power from an outlet to DC power for the battery. This is the key element inside of the charging system that impacts efficiency and power loss during charging.

Rectifiers have evolved over the last 15-20 years, dramatically improving their efficiency. First came the switch from Ferroresonant conversion technology, with efficiency in the 70% range to switch mode technology, which brought efficiency to the mid 80% range. Now, that technology has been improved as well with zero-voltage switch techniques and high efficiency design that has elevated the efficiency to its highest point ever – 96%.

These high-efficiency (HE) switch-mode rectifiers provide AC-DC conversion that offers faster charging of batteries and increased distance per kWh by drastically reducing power lost in the process. Additionally, this decreased power loss significantly reduces heat generated in the rectifier, simplifying cooling and enabling a higher maximum operating ambient temperature.

With this new 96% efficiency attached to the numbers previously discussed, the necessary power draw drops to between 3,328 kWh and 7,654 kWh. Therefore, the amount of power wasted on conversion from AC to DC is a maximum of 294.4 kWh per year – saving roughly two-thirds of the power in this application.

One company that has converted to the HE power converter is Th!nk, a Norwegian firm whose cars are produced in a low-carbon factory— billed as the most efficient small assembly plant in Europe. With this level of green-consciousness, Th!nk has made efficient battery systems a tenet its electric vehicles, which can run on either Lithium-based or on Sodium-based batteries.

All Th!nk cars, though, are available with the company’s “mobility pack” option, which allows consumers to pay a monthly fee to have Th!nk take full responsibility for the performance of the battery including a full maintenance service agreement, insurance, carbon offset payments and, in some countries, even all electricity used.

With these innovative service offerings, the company implemented an HE rectifier in its charging system to further its commitment to efficiency, and also to deliver these services cost effectively.

Making electric cars better is a continual job, but the technology exists today to take a big step forward in increasing their battery charging efficiency through the use of high efficiency rectifier technology.

Times Article Viewed: 15399
Published: 21-Jul-2009


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