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Original Date: 11/03/1996
Revision Date: 01/18/2007
Information : Power Converter/Inverter
Oak Ridge National Laboratory (ORNL) has developed a new, advanced electric power converter/inverter. This power inverter provides a much higher power density, produces less electromagnetic interference, and works more efficiently than a conventional inverter. In addition, ORNL's inverter is two to three-fold smaller and lighter than its counterpart.
In an electric vehicle, the power available to the vehicle's electric drive motor must be varied to allow the motor to adjust to the varying speeds and loads encountered during normal operations. Inverters convert DC power into AC power. An electric vehicle's DC power, stored in batteries, needs to be converted into AC power which is more efficient at running the electric drive motor.
To be practical for commercial electric vehicles, an inverter must meet critical factors such as power efficiency, reliability, size, weight, and electromagnetic interference. Conventional inverters use six power switches to achieve the desired voltage output. ORNL’s inverter uses three small auxiliary switches which temporarily and briefly deliver current and then reroute it back to one of the six main switches. This diversion, which lasts a few microseconds, produces a zero voltage across the switch and helps reduce power spikes from occurring. The result is an increase in reliability and a decrease in electromagnetic interference problems. The soft switching also decreases power consumption of the inverter. Lower power consumption reduces the need for heavy heat sinks, which in turn reduces the weight of the inverter.
Because it can smoothly change the voltage and current of a motor, ORNL's inverter reduces the possibility of electric motor failures caused by insulation breakdown and bearing overheating. At 11 kilowatts per kilogram, the inverter's power density exceeds the Partnership for New Generation of Vehicles’ goal of 5 kilowatts per kilogram. In addition, the inverter operates at 98% efficiency at high speeds and 80% efficiency at low speeds. Conventional inverters supply 94% efficiency at high speeds and 60% to 70% at low speeds.
ORNL's power converter/inverter offers many benefits for hybrid and electric vehicles. Other potential applications include improving the operating efficiency of air conditioners and heat pumps.
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