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Variable-frequency motor control circuit for DC cooling fans

Category:

Industry Trends

Release time:

2020-01-06

DC cooling fans are widely used in our daily lives. So, what exactly is a variable-frequency motor? And does it have a close relationship with cooling fans?
A variable-frequency motor exhibits characteristics of a DC motor yet employs an AC motor structure. In other words, although the external power supply is DC, the motor itself is equipped with DC-to-AC variable-frequency control technology and operates entirely according to AC principles. For this reason, the variable-frequency motor is also referred to as a “self-controlled variable-frequency synchronous motor.” The motor’s rotational speed, n, depends on the frequency, f, set by the controller.
The drive circuit of a variable-frequency motor consists of two main parts: the power circuit and the control circuit. Today, these two parts have been integrated into a single chip, enabling all control functions of the variable-frequency motor to be implemented using just one device, thereby simplifying the circuit architecture. As industries increasingly emphasize energy efficiency and noise reduction, many industrial products are shifting toward brushless motors, which places higher demands on motor microcontrollers. As a next-generation digital signal processor chip for motor control, the cost-effective TMS320C240 is ideally suited to meet these challenges.
The three-phase star-connected DC cooling fan features a variable-frequency motor control circuit. The DC power supply is sequentially applied to the motor’s three windings via a three-phase inverter circuit composed of metal-oxide-semiconductor field-effect transistors (MOSFETs). At any given moment, only one pair of the three winding pairs carries current, generating a magnetic field. Once the current supply to that pair of windings is stopped, the supply is switched to the adjacent pair of windings instead. As a result, the magnetic field axis in the stator rotates by 120 degrees in space, and the rotor, under the influence of magnetic forces, follows the stator’s magnetic field and rotates by 120 degrees as well. When the voltage is applied in sequence to A, A, C, B, C, B, A, C, A, C, B—this creates a rotating magnetic field in the stator, thereby causing the motor to rotate continuously.
As cooling-fan experts all know, as soon as we disassemble the motor of a DC cooling fan, we can see that it uses a variable-frequency motor—this can be identified by the position of the coil. The control circuit board for the variable-frequency motor integrates digital signal processing functions and drive circuits into the control chip, simplifying the overall circuit design. The motor’s speed can be adjusted by programming the control chip. Shenzhen Jiangshanlai Electronic Technology Co., Ltd. is a large-scale enterprise specializing in the R&D, manufacturing, sales, and service of brushless DC motors, DC cooling fans, DC brushless fans, DC stand fans, boosted cooling fans, micro cooling fans, DC cooling fans, DC blowers, and non-standard custom fans. We are a direct manufacturer and wholesale supplier of DC fans. Our products are best-selling in Guangdong, Shenzhen, Guangzhou, Dongguan, Fujian, Zhejiang, Jiangsu, and other regions.

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Next: Basic Knowledge of DC Brushless Fans

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