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What Is An AC or DC Drive?

Posted April 21, 2019 12:01 AM by ahorner_22

AC and DC are different types of voltage or current used for the conduction and transmission of electrical energy.

AC stands for alternating current. AC drives are frequency converters designed to control the speed and torque of an electric motor. The speed is controlled by changing the frequency of the electrical supply to the motor.

AC Drives Benefits

The types of motors that AC drives control normally operate at constant speed. Enabling the user to control the speed of a motor potentially gives the user benefits in terms of process control and energy savings.

DC stands for direct current. DC motor drives are a type of amplifier or power modulator that integrate between the controller and a DC motor. It takes the low current and then converts it into a high current which is appropriate for the motor.

DC Drives Benefits

Despite the popularity of AC drives, DC drives have favorable characteristics that prove to be appropriate for many applications. The characteristics of a DC drive include speed changes that are made by increasing or decreasing the amount of DC voltage fed to the motor from the drive; low cost for medium and high-HP applications; wide speed range; and good speed regulation. DC drives can also be very compact in size.

Advantage of AC Electricity over DC Electricity

The major advantage that AC electricity has over DC electricity is that AC voltages can be readily transformed to higher or lower voltage levels, while it is difficult to do that with DC voltages. Since high voltages are more efficient for sending electricity great distances, AC electricity has an advantage over DC.

AC and DC drives are used in many industrial applications including:

  • Hoisting and lowering
  • Crane travel
  • Trolley travel
  • Paper Industry (pulp and paper making)
  • Textile Industry (weaving and spinning)
  • Conveyors
  • Compressors
  • Pumps

This is a sponsored blog post by Radwell International.

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#1

Re: What Is An AC or DC Drive?

04/21/2019 11:24 PM

You seem to be giving conflicting information here...on one hand you say that it is difficult to alter DC voltage to higher or lower levels, then you say it can be done with a very compact drive....

..."AC voltages can be readily transformed to higher or lower voltage levels, while it is difficult to do that with DC voltages."...

...". It takes the low current and then converts it into a high current which is appropriate for the motor."...

..."DC drives have favorable characteristics that prove to be appropriate for many applications. The characteristics of a DC drive include speed changes that are made by increasing or decreasing the amount of DC voltage fed to the motor from the drive; low cost for medium and high-HP applications; wide speed range; and good speed regulation. DC drives can also be very compact in size."...

This is not clear at all....so I'm including these video primers....

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#2

Re: What Is An AC or DC Drive?

04/21/2019 11:54 PM

The term "Drive" seems to be overused. It seems to me that you really mean "(motor) controller". There are controllers for AC, DC, stepper, Universal, Variable voltage, variable frequency, variable current, etc. When I hear "DC drive", i'm thinking of the motor and not the controller (same for AC). Using this term this way, is like me using "Hey You" as a nick-name.

Reminds me of when somebody shouted, "Hey you in the blue shirt!" on a Navy base. Except, I can't tell if you're trying to be funny or not.

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#3
In reply to #2

Re: What Is An AC or DC Drive?

04/22/2019 5:28 AM

The term"Drive" is used a lot because that is what they are called industry wide. Their "function" is speed control of motor(s) either AC or DC. Each type has it's particular purposes,so yes,they are motor speed controllers,but the term "Drive" has much more far reaching implications,such as synchronization of multiple motors. "Driver" or "Drive" has many meanings,such as a taxi driver,a golf club,a psychological motivation,a hammer,a hard charging boss,cowboys herding cattle,etc,but when used in the electrical trade,it is normally used to indicate a multiple motor control "System". In electronics,it is used to designate the final output stage,or an intermediate output to another stage. People well versed in the electrical trade know this meaning as it applies to their trade,same with golf,cowboys,managers,psychologists,etc.

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#4
In reply to #2

Re: What Is An AC or DC Drive?

04/22/2019 5:45 AM

From my experience is Aust the term Drive is used for the device which changes the state of the supply to the motor which is either AC or DC.

The motors are generally named for the mechanical device they drive in the real world like conveyor #1 motor, Swing motor, Synchronous motor #1.

I did commissioning back in the mid 70s on an Irrigation pump station where the slip frequency voltage was recovered from the motor. This was then rectified and chopped back into AC and fed back into the supply. The purpose was to boost the overall efficiency of the motors on the pumps to greater than 97%.

A controller takes in the various inputs for protection, stop/start and feedback signals and controls the drive that supplies power to the field device. The drive can be a Motor Control Center, Variable Frequency Drive, Ward Leonard DC drive system.

Also DC voltage is used for very high voltage high power transmission and is converted back to AC by Thyristors so it can be transformed for final distribution.

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#5

Re: What Is An AC or DC Drive?

04/22/2019 9:27 AM

It looks to me like this article was not written by somebody with an electrical engineering background. This is sad for an IEEE organization.

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#6
In reply to #5

Re: What Is An AC or DC Drive?

04/23/2019 6:25 PM

I believe this is just an advertiser...

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#7
In reply to #5

Re: What Is An AC or DC Drive?

03/11/2020 7:27 AM

So sad.

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