Tokai University achieves more than 96% efficiency through a DC motor with a power of about 100W


A research team LED by Professor Kimura Hideki, a professor of engineering at the University of Tokai University in Japan, developed a DC (DC) brushless motor that can convert power to motor power with an efficiency of over 96%. The public release was made on the "56th Joint Symposium on Applied Physics" (the University of Tsukuba) held from March 30th to April 2nd, 2009. "The high-efficiency method used in it can also be applied to high-output motors for electric vehicles" (Kimura).

The motor developed this time is a DC motor with a rated power of about 100 W. The core of the motor is made of iron-based amorphous metal (see this report). The conversion efficiency is as high as 96.5% around 100W power. "It can reach more than 96% when it contains error factors" (Kimura). In addition to such high efficiency, the conversion rate of 93 to 96% can be maintained when the power is changed between 50 and 200 W, which is also a major feature.

In 2003, Tokai University developed a DC motor with an efficiency of 93%. And with the special electric equipment, Japan, the company and other companies to achieve productization.

The high efficiency of the motor is achieved by identifying the cause of the energy loss and improving several of them. The energy loss of the motor is caused by: (1) power consumption of the control circuit (controller loss), (2) loss due to coil winding (copper loss), and (3) loss due to eddy current in the core (iron loss) (4) Loss (mechanical damage, wind damage) caused by friction of the rotating shaft and air resistance.

The high efficiency of more than 96% of this time is mainly achieved by improving (1) and (2). To reduce (1) controller losses, the microcontroller uses a 156mW low-power product. In addition, the inverter also uses a product consisting only of nMOSFETs. The reason is that "the on-resistance of nMOSFET is smaller than that of pMOSFET" (Kimura).

(2) The copper loss is reduced by optimizing the thickness and number of turns of the winding. The copper loss generally increases as the current flowing through the motor increases, so the benefits of improvement are significant.

(3) Iron loss is controlled to a low level by the use of iron-based amorphous metal in the motor core material. The reason is that "amorphous metal has a small electron mobility and a small eddy current" (Kimura). This improvement is the same as the 2003 motor.

In addition, Kimura also said that in (4) wind damage, "it has been confirmed that it is only necessary to add a cover to the motor to block air ingress, which can reduce the loss."

The difficulty is that the manufacturing cost is higher

The difficulty of this motor is that the manufacturing cost is also high while the efficiency is very high. Therefore, it is currently limited to applications such as energy-saving vehicles for competitions that do not consider price and emphasize high efficiency. Energy-efficient cars developed in 2003 also achieved outstanding results in the competition. However, "the cost is nearly 20 times higher than the ordinary motor with an efficiency of about 80%" (Kimura).

The reason for the high cost is that the magnetic core uses an iron-based amorphous metal. "A magnetic core composed of an iron-based amorphous metal is formed by spraying a metal to a low-temperature cylinder to rapidly cool it. The primary processing can only form a thickness of 25 μm. To ensure the required thickness, it is necessary to repeat the same multiple times. Processing, which leads to increased costs" (Kimura).

However, the cost of the iron material itself is not high, so mass production can be carried out by automating the manufacturing process, so that "it is expected to be manufactured at a cost of only 1/4 to 1/5" (Kimura).

If the cost of removal is high, the motor can be used in a wide range of fields such as refrigerators, automobiles and electric motorcycles by virtue of power and speed. The high output power "can basically be achieved by increasing the motor. After the power is increased, the efficiency is also easy to increase" (Kimura).

High-efficiency DC motor developed this time

Conversion efficiency to drive current. The operating voltage is 24V, and the power consumption is 96W when the current is 4A. The three curves represent the difference in PWM duty cycle.

Toka University's energy-saving car "Faradays Magic 2" with high-efficiency DC motor

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