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Posted on 02 September 2019

A System Approach, Comprehensive Motor Solution

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Re-Build Your PMSM/BLDC Designs and Provides Faster Design Time

The irreversible trend of moving to high efficiency energy design for motor has been well known and recognized. From high power fan in industry to middle power fan in major home appliance such as range hood fan, or further down to small power fan such as ceiling fan and pedestal fan in your living room, inverter motors using PMSM/BLDC controller are easily accessible today. Although all of them are using PMSM/BLDC controller and motor, there are still several discrepancies in terms of control technologies that will cause safety and acoustic noise issues.

By Wen Hsi Chien, Fairchild

In this article, we will share with you 2 real design examples in which a comprehensive motor solution with digital and analog hybrid sensorless motor controller is used to help them easily and quickly get rid of aforementioned design challenges.

The first story is about a pedestal fan manufacturer who has encountered design challenge in reducing acoustic noises and had been struggling for a while. This hybrid solution helped them to solve the issue in 3 weeks, move to mass production in only 2 months, and in the same time helped them reduce system BOM cost.

The second story is about a range hood manufacturer who had been designing a very low speed range hood fan with DSP solutions for over a year. The hybrid motor controller not only provided easy to use development tool and powerful motor control libraries that deliver sensorless sinusoidal control with constant torque to meet their motor design needs, but also provided PFC solution and the capability to develop simple LED control and touch control.

Details of FCM8531

Pedestal Fan

Pedestal fans (or so called circulation fans) are quite popular in both Asia and North America. Usually the fan is controlled by 3 or 4 buttons on a panel or a pedestal to regulate the fan speeds. In addition to the benefit of energy saving when converting from induction motor to PMSM/BLDC motor, a so called linear speed control can deliver step-less nature breeze instead of the 3-step speed control of conventional AC fan. Step-less means users can get any desired speed by changing the speed rotary knob accordingly. Certainly the air flow is more natural and pleasant. Particularly when the PMSM/BLDC fan is running in an air conditioner room, the air flow from fan is circulating in the room and makes better efficiency and cozy for the whole room collaboratively with air conditioner system.

Because the fan stands on the floor, any tiny acoustic noise is easy to be heard If PMSM/BLDC motor is driven by trapezoidal electric current, the torque ripple will occur at every 60 degrees of electric angle and thus consequently generate acoustic noise. The noise is particularly noticeable at late night when you are sleeping. One of our customers, a pedestal fan manufacturer in Asia, used a general purpose micro controller that generate trapezoidal electric current to drive PMSM/BLDC fan mainly because they were lack of PMSM/BLDC control knowledge and engineers in that background. At the beginning of their production the quantity was small and almost no one noticed the annoying acoustic problem, but more and more complaints about the noise were collected from the market. This field return almost forced the manufacturer to stop developing and producing PMSM/BLDC fan. Fairchild team, was aware of this problem, quickly introduced Fairchild’s true sinusoidal electric current solution with Field Oriented Control (FOC) and implemented the control functions for pedestal fan with an easy-to-use development tool - FCM8531 MCDS IDE. The customer was impressed with the first demonstration, and their engineers accelerated board design to adopt the motor controller (FCM8531, Figure 1). In 3 weeks, 10 pieces of working samples had been proved to run silently with almost no noise. In just 2 months, the manufacturer had finished pilot production and moved to mass production, therefore just in time to reverse and rescue the PMSM/BLDC fan business. In the meantime, Fairchild was aware that the customer’s design used low voltage topology, which means it needs an external switching mode power supply costing more than $3. In collaboration with Fairchild power team, we proposed high voltage technology directly deriving from AC line, and a Fairchild aux power ( FSL206 ) was selected to supply small power to PMSM/BLDC controller and inverter gate driver ( FAN7388 ). The entire system (Figure 2) cost, therefore, had dramatically reduced. The pedestal fan customer now has become one of the world’s leading supplier of PMSM/BLDC pedestal fans.

System solution from Fairchild

Range hood Fan

Range hood is one of the most important appliances in your kitchen. Similar to pedestal fan, there are usually 3 buttons at front panel to select the fan’s rotation speed. Rang hood fan needs relatively higher power to resist air flow in the duct, thus you would never see a range hood fan powered by AC induction motor (ACIM) can run at low speed because ACIM has almost zero torgue at low speed. When you are busy at kitchen, many of us should have the experience that phone ring is not being heard while range hood fan is running. Thanks to PMSM/BLDC technology, we are able to run range hood fan at very low speed when the smoke from oven is not much; consequently the noise is much more reduced. PMSM/BLDC motor can quickly speed up if smoke is getting strong. The full-range speed control is another benefit in addition to the energy saving when converting to PMSM/BLDC motor from ACIM. Because the lifespan of the hall sensor is relatively shorter in this working environment, generally sensorless controller is definitely required in the application. Moreover, acoustic noise is annoying issue, thus sinusoidal electric current control is a must.

One of our customers, a rang hood fan manufacturer in Italy, selected a DSP for sensored design and the project had run over 1 year before we approached. The manufacturer was struggle because they do not have the capability of developing sinusoidal electric current control over sensorless design. A DSP might be powerful, but the difficulty is always on how to implement the motor control algorithm into the DSP controller. Moreover, constant torque design is required because range hood fan is running based on the feedback of air pressure instead of speed. This requirement further increased the complexity of design. Fairchild’s solution introduced a whole new design concept to them: modularized hardware libraries of motor control algorithms.

When we had shown the concept of our motor control libraries of Speed Integral and Sliding Mode, they were thinking this might just be the best solution for them and realized that there were some easier way to develop a motor control based system. Particularly sliding mode is focusing on supporting pump application, which has the same constant torque loop that they were pursuing to meet one of their design needs.

Additionally, a modern rang hood is equipped with LED lighting indicators and even touch control. Thanks to the two cores architecture in FCM8531, the 8051 MCU core gives a great freedom for the customer to develop any user interfaces they want, such as simple LED lighting control and touch control (Figure 3 ) while the AMC(Advanced Motor Controller) core provides the powerful motor control libraries.

Application diagram of FCM8531

Power factor is naturally worsened in PMSM/BLDC control because of its PWM driving current. Fairchild is also strong in PFC control in the industry for many years, Fairchild power team is requested to support this rang hood fan design for PFC. FAN6982 was selected because its CCM mode is able to cover the power range of range hood elegantly, and FSL206 was selected to serve the aux power.

The entire project took only 2 months to come out a prototype and 6 months to finalize all required user interfaces. Now the customer product is ready for launch.

Conclusion

Energy saving is a global trend and PMSM/BLDC motor is recognized as the best solution to substitute conventional AC induction motor to increase energy efficiency. However, the complex of electronic control and software algorithm for PMSM/BLDC motor quite often trouble engineers with little electronic motor control background. The two examples mentioned in this article can be quite representative of the general design pains they are suffering. Fairchild’s FCM8531 PMSM/BLDC controller solves their pains with the unique features of AMC libraries and a versatile MCU to increase the flexibility. Moreover, Fairchild’s other devices such as the SPM@ Smart Power Modules, FPSTM power switch for aux power, and PFC controllers... etc constitute a complete solution and quicken customer’s time to market.

 

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