Reverse Current PMDC Motor Braking Using Power Electronics

In summary, the conversation discusses determining the armature current during the braking time for a simple permanent magnet DC motor with known resistance and inductance. It is mentioned that applying maximum reverse voltage is the quickest way to stop the motor, but the current does not reverse immediately due to motor inductance. Available parametric information includes inductance, resistance, generated back emf, current to torque relationship, and inertia of motor and load. State variables that can be measured in real time include RPM, current, and applied voltage.
  • #1
dvscrobe
51
11
Summary: How do you determine the armature current during the braking time?

For a simple permanent magnet DC motor with a known resistance and inductance in series with the armature, I would like to know how to determine the armature current if there was an electronic motor drive controlling the terminal voltage. During steady state conditions with the motor handling a particular load, terminal voltage needs to be a little higher than the back emf. If I needed the motor to stop as soon as possible, could I make my terminal voltage lower than the back emf? This would cause a reverse current. This instantaneous moment I can calculate but I can’t figure what my current does after, whether it is constant or gradually declines.
 
Physics news on Phys.org
  • #2
The quickest way to stop a motor is to generate a maximum reverse torque.
Torque is proportional to motor current.
So applying a maximum reverse voltage is the quickest way to stop.
But the current does not reverse immediately because of motor inductance.

The difference between generated emf and applied voltage will appear across the series resistance and inductance of the motor. The voltage across the inductance will decide the rate of change of current since; V = L * di/dt; so di/dt = V/L.

As the reversed torque decelerates the motor, it will stop, but the braking current will still be flowing. Again, that braking current cannot be reduced to zero instantly because of motor inductance, so you must anticipate zero, or overshoot and reverse the motor.

What parametric information is available about the motor?
Inductance, resistance.
Generated back emf in volts/rpm.
Current to torque relationship.
Inertia of motor and load.

What state variables can be measured in real time?
RPM, current, applied voltage.
 
  • #3
Baluncore,

I probably should have posted in homework section. Would you please take a look at the second problem? Is my thinking off? The supply voltage is being controlled by an electronic drive. My thinking is that if I lowered the terminal voltage, KVL dictates a reverse current. But that just seems odd. Thanks.
 

Attachments

  • rYT6mPU1eN1g_doc.pdf
    1.1 MB · Views: 359
  • #4
dvscrobe said:
I probably should have posted in homework section.
Thread moved to the Homework Help section.
 

FAQ: Reverse Current PMDC Motor Braking Using Power Electronics

1. What is Reverse Current PMDC Motor Braking?

Reverse Current PMDC Motor Braking is a method of slowing down or stopping a permanent magnet DC (PMDC) motor by reversing the flow of current through the motor. This is achieved through the use of power electronics, such as diodes or transistors, to control the direction of current flow.

2. Why is Reverse Current PMDC Motor Braking important?

Reverse Current PMDC Motor Braking is important because it provides a more efficient and controlled way to slow down or stop a PMDC motor compared to traditional braking methods, such as mechanical braking. It also helps to reduce wear and tear on the motor and can extend its lifespan.

3. How does Reverse Current PMDC Motor Braking work?

Reverse Current PMDC Motor Braking works by using power electronics to switch the direction of current flow in the motor. When the motor is running, the current flows in one direction, causing the motor to rotate. To slow down or stop the motor, the power electronics will switch the current flow in the opposite direction, creating a braking effect.

4. What are the advantages of using Reverse Current PMDC Motor Braking?

Some of the advantages of using Reverse Current PMDC Motor Braking include: improved efficiency, precise speed control, reduced wear and tear on the motor, and the ability to quickly stop the motor in emergency situations. It also allows for regenerative braking, where the energy generated during braking can be fed back into the power supply.

5. Are there any limitations to Reverse Current PMDC Motor Braking?

One limitation of Reverse Current PMDC Motor Braking is that it requires the use of power electronics, which can add complexity and cost to the motor system. Additionally, the effectiveness of the braking may be limited by the motor's size and design. It is also important to ensure that the motor is properly sized for the braking application to avoid overheating or other issues.

Similar threads

Engineering Calculating EMF and Motor Speed for a Compound Wound D.C. Motor
Replies
3
Views
3K
Engineering Electrical Machine - Shunt DC Motor Problem
2
Replies
41
Views
6K
Engineering Solve Motor Coil Current at Startup & Full Speed
Replies
4
Views
1K
Calculating Motor Load Capacity for a 4kg Vehicle
Replies
2
Views
2K
Engineering Electrical Machines DC Shunt Motor
Replies
16
Views
3K
Engineering DC Shunt Motor Starting Current
Replies
1
Views
4K
Engineering Synchronous motor coupled to a DC Compound Motor Problem
Replies
2
Views
2K
Engineering Calculating Power Loss and Input for a Permanent Magnet DC Motor
Replies
3
Views
2K
Engineering Solve DC Motor Problem: 250W 24V 1800rpm
Replies
1
Views
2K
Engineering How Does Armature Voltage Affect the Speed of a Separately Excited DC Motor?
Replies
3
Views
2K

Hot Threads

Recent Insights

Back
Top