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Question
How to control the speed of the electric motor
How to control the speed of the electric motor
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Solution
AC motors work using the interaction of the induced magnetic fields in their two main components.
The inner part that moves, called the rotor has no electrical connection to the surrounding stator which does not move. When the motor is energized by an AC energy source, there is a magnetic field which moves axially around the stator.
This magnetic field is not consistent and yet it is in a way. This analogy is far from perfect, but think of a boat in the water. There may be small waves around the boat, but there is an overall elevation at which it is suspended.
When an AC motor is fed irregular but steady electrical energy, the motor turns at a steadyspeed.
If you change the properties of the waves of the water, it will affect how steady the position of the boat is. If you change the properties of the waves of electrical energy applied to the motor, you will change how steady the motor's speed will be.
A variable frequency drive or VFD is a device that changes the electrical energy from its typical steady sine wave pattern to waves of any shape.
If you look at the sine wave of electrical energy with respect to time, you can add up the moments of how much energy over a given period. The speed of the motor will be a function of how much of the time in that period, that energy was actually applied.
Think of pedaling a bike up a slight incline. If you pushed the pedals with a steady alternating vertical force, say with either pedal reaching top dead center once per second, the bike would move along a a certain speed.
Now suppose you pedaled with a back-and-forth ratcheting motion instead. Once every revolution (still once per second) your feet only exerted a brief instant of pedaling force.
Even though the frequency of your effort was the same, the duration of each pedaling event would be partial and sometimes you would just be coasting. The bike wouldn't move as quickly. If you did little bursts of pedaling more frequently, you could make up for the loss. There are lots of ways to pedal a bike, and they all affect how quickly the bike will move.
VFDs do more than change the frequency of electrical energy. They can change the actual wave shape of AC energy, from a full sine wave to any portion thereof, and this affects how quickly the motor turns.
The inner part that moves, called the rotor has no electrical connection to the surrounding stator which does not move. When the motor is energized by an AC energy source, there is a magnetic field which moves axially around the stator.
This magnetic field is not consistent and yet it is in a way. This analogy is far from perfect, but think of a boat in the water. There may be small waves around the boat, but there is an overall elevation at which it is suspended.
When an AC motor is fed irregular but steady electrical energy, the motor turns at a steadyspeed.
If you change the properties of the waves of the water, it will affect how steady the position of the boat is. If you change the properties of the waves of electrical energy applied to the motor, you will change how steady the motor's speed will be.
A variable frequency drive or VFD is a device that changes the electrical energy from its typical steady sine wave pattern to waves of any shape.
If you look at the sine wave of electrical energy with respect to time, you can add up the moments of how much energy over a given period. The speed of the motor will be a function of how much of the time in that period, that energy was actually applied.
Think of pedaling a bike up a slight incline. If you pushed the pedals with a steady alternating vertical force, say with either pedal reaching top dead center once per second, the bike would move along a a certain speed.
Now suppose you pedaled with a back-and-forth ratcheting motion instead. Once every revolution (still once per second) your feet only exerted a brief instant of pedaling force.
Even though the frequency of your effort was the same, the duration of each pedaling event would be partial and sometimes you would just be coasting. The bike wouldn't move as quickly. If you did little bursts of pedaling more frequently, you could make up for the loss. There are lots of ways to pedal a bike, and they all affect how quickly the bike will move.
VFDs do more than change the frequency of electrical energy. They can change the actual wave shape of AC energy, from a full sine wave to any portion thereof, and this affects how quickly the motor turns.
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