Precision Variable Frequency Drive
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Precision Variable Frequency Drive. May07-13. Abstract. Proposed Approach and Considerations.

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Precision Variable Frequency Drive



Proposed Approach and Considerations

AC synchronous motors are used in a variety of applications. They are used for anything that needs a constant speed. The speed of the motor sometimes varies from the desired speed. The precision variable frequency drive will allow a user to turn a dial and change the speed of the motor to the correct speed. Currently a variable frequency drive retails for around $350 or more. We plan to develop our precision variable frequency drive for under $100.

  • Proposed Approach

    • Research technologies

    • Simulate entire system

    • Purchase and build components

    • Test components

    • Build entire system

  • Technologies Considered

    • Pulse width modulator

    • Crystal oscillator

    • Function generator chip

  • Testing Considerations

    • Function generator chip with oscilloscope

    • Entire system with an AC synchronous motor

    • Entire system with a record player

    • Strobe system with a record player


  • Problem Statement

    • The general problem is the control of speed of an AC synchronous motor. Synchronous motors are designed to run at a certain speed depending on the frequency of the supply power. Synchronous motors and the subsequent drive mechanisms do not always keep the correct speed due to a variety of reasons (gear deterioration, motor age, etc.).

  • Solution Statement

    • We are creating a precision variable frequency drive (VFD), which will allow the user to manually change the frequency using a dial, which will in turn change the speed of the motor.

  • Assumptions

    • The belt connecting the motor to the turntable is constant over a short time period. Basically, an increase in motor speed by a certain factor will result in an increase in the speed of the turntable by the same factor.

    • The plug from the AC synchronous motor can plug into a standard three pronged outlet.

  • Limitations

    • The total end product cost must be less than $350.

    • Power output must be a minimum of 75 W.

    • The input voltage will be a household outlet of 120 V AC, 60 Hz, single phase.

  • Expected End Product

    • Precision variable frequency drive for use with a small power AC synchronous motor.

    • Portable strobe light system for checking the RPM of a record player

    • Users manual, schematics, and parts list

  • The end product will be designed so a user will be able to plug the precision variable frequency drive into a standard wall outlet. They will then be able to plug a small power AC synchronous motor into the VFD using a standard wall plug. They will be able to adjust the motors speed by adjusting the frequency on the VFD.

  • Intended Users and Uses

    • Intended Users

    • -Avid music listener

    • -Lay person

    • Intended Uses

    • -Adjust the frequency of a turn-table

    • -Usable with other synchronous motors

  • Design Objectives

    • Adjustable from 58-62 Hz by 0.1 step

    • Includes a strobe light system that measures the frequency accurately to 0.1Hz

    • Operate at a power output of minimum 75 W

    • Must be have short-term stability of 0.01%

  • Functional Requirements

    • Synchronous motor frequency controller

    • Knob controller to adjust frequency

    • Digital read-out of frequency

    • Portable strobe system

  • Design Constraints

    • Maximum weight and size

    • Minimum power output

    • Minimum operating frequency

Figure 2:Project Design

Estimated Resources and Schedule

Figure 1:End Product

  • Operating Environment

    • Indoors

    • No extreme conditions

    • Milestones

    • Define problem statement

    • Select technology

    • Simulate end product design

    • Build and test prototype

    • Demonstrate end product

Figure 3:Estimated Timeline

Figures 4 and 5 below show the estimated resources required for the development of the Precision Variable Frequency Drive.

Project Requirements

Figure 4:Estimated Budget

Figure 5:Estimated Effort, Hours


Variable frequency drives are something that are not new to the market. The majority of the small motor variable frequency drives are used on devices such as turn-tables. Currently variable frequency drives are very expensive, in excess of $350. This seems quite excessive for personal use with a record player, since sound quality is much better with newer technologies. With our precision variable frequency drive, users will be able to enjoy their older records not sounding out of pitch, but more importantly, they will not have to worry about the price. This precision variable frequency drive will be available for a variety of uses for a fraction of current VFD prices.

Project TeamInformation

Team Members:

Jason Kilzer EE

Dave Rienhardt EE

Matt Shriver EE

Nick Nation EE


Jim Walker


Professor Ajjarapu

Project Web Site: