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This way, the rectified AC current can be set to any desired frequency, which changes the effective motor speed. As previously stated, AC controllers convert an input AC frequency into a DC current that simulates an AC frequency, which can then be set by the user, thus controlling the speed of the motor.
This is accomplished using three main components: a rectifier, an inverter, and a DC circuit that connects the two. The connecting DC circuit then stores this energy usually via high power capacitors for the inverter component to use. The inverter is powered by the connecting DC circuit and modulates the rectified frequency to the motor, effectively changing the speed of the motor.
Figure 1 visualizes this explanation via a basic circuit diagram, and shows the transfer of frequencies between components:. There are also methods for increasing the slip of an AC motor, which will change the speed of rotation in relation to the AC frequency, thus controlling speed.
Increasing the slip can be done by either varying the resistance through the motor coils variable series resistance, see our article wound rotor motorsor varying the voltage to the coils variable voltage transformers ; however, AC drives are more commonplace, as they are more modular and have been engineered to give the user precise digital control over their motor without using integrated components such as resistors or rheostats in the motor windings.
There are some common ways in which AC drives take incoming AC current and transform it into a simulated, controllable frequency. In each method, the goal is to allow operators to input frequency commands to the stator RMF, and as such change the rotation speed of the rotor.
There are three main methods for doing this: variable voltage inversion VVIpulse-width-modulation PWMand flux vector drives. In this method, the AC frequency of the power source is rectified to a DC current, which is then increased and decreased in discrete steps to imitate a sine wave or how a true AC current oscillates. This way, operators can vieeo these steps to effectively change down,oad motor speed, and these are commonly referred to as six-step inverters though different steps exist.
Figure 2 below shows an example of how a VVI controller sends stepwise power to a motor, simulating a true sine wave:.
Motor Controller and Drive Types
Pulse doanload modulator circuitsor PWMs, are a popular method to simulate AC oscillations, as they often provide more precise control than variable voltage inverters. Recall from calculus that the integrals of any two continuous graphs are equal if their areas priniple their curves are equal; the goal of PWM is to more accurately approximate the area of a sine wave using many pulses of voltage, and the density of these pulses will dictate the size of the simulated sine wave and thus change the motor speed.
Figure 3 visualizes these spikes on a voltage over time graph:. The remaining current is the portion that generates torque, and flux vector drives hold the coupling current to a minimum while allowing operators to adjust this downloadd current.An even simpler motor (one that is also much simpler to understand!) is the homopolar motor.. AC motors With AC currents, we can reverse field directions without having to use brushes. This is good news, because we can avoid the arcing, the ozone production . Electromagnetic or magnetic induction is the production of an electromotive force across an electrical conductor in a changing magnetic field.. Michael Faraday is generally credited with the discovery of induction in , and James Clerk Maxwell mathematically described it as Faraday's law of induction. Lenz's law describes the direction of the induced field. Induction Motor. Induction motors are the most commonly used motors. Induction motors are also known as asynchronous motors because they always run slower than synchronous speed. Based on the type of rotor construction, they are divided into two types as follows: Squirrel Cage Motor; Slip Ring Motor; Working Principle of Induction Motors.
This is easier said than done, as controlling both torque and flux current is analytically intensive, and prlnciple continuous transformations between coordinate systems. Flux vector drives, therefore, require microprocessor-based controllerssoftware, and oftentimes encoded sensors to precisely tune the independent currents.
These drives typically provide speed accuracy of up to prinviple. AC motor controllers have upgraded traditional AC motors, and have allowed them to serve functions in even more areas of industry. One of the most common areas where AC drives are implemented is in HVAC systemsspecifically in fanspumpsand blowers.Types of Motor Controllers and Drives
They are used in many applications including machine tools, micro-positioning, and robotics, among many other types of machinery, such as conveyors or OEM equipment. Stepper drives are also known as pulse drives and step amplifiers. Stepper controllers are also known as motor indexers. AC motor drives are used when speed control of an AC motor is desirable because controlling speed in an AC induction motor is not normally done—once a motor has been specified by the number of poles the operating speed is stated on the nameplate.2 days ago · Figure 1: Basic circuit diagram for most AC motor controllers. Notice how AC current is still used to power the motor but is conditioned for speed control using the AC drive. There are also methods for increasing the slip of an AC motor, which will change the speed of rotation in relation to the AC frequency, thus controlling speed. An even simpler motor (one that is also much simpler to understand!) is the homopolar motor.. AC motors With AC currents, we can reverse field directions without having to use brushes. This is good news, because we can avoid the arcing, the ozone production . China Motor manufacturers - Select high quality Motor products in best price from certified Chinese Mini Motor, Electric Motor suppliers, wholesalers and factory on scratchhouse.co
Brushed DC motors, on the other hand, fundamentally speed-controllable by merely varying the voltage going to the motor rotor and field. This can be accomplished with a simple rheostat; no controller or drive is necessary. Newer brushless DC motors are not mechanically commutated and hence require controllers and drives to commutate the magnetic field electronically.
All About AC Motor Controllers - What They Are and How They Work
Servomotors and steppers, because they are positioning devices downnload opposed to rotary motion machines, also require controllers and drivers for their operation. AC motors drives are used to control the speeds of motors that drive pumps, fans, etc. AC motor drives are used to increase efficiency by setting pump, fan, etc.
DC motors have very good low-speed torque, making them especially suited to winches, cranes, etc.
Electric motors and generators
Servomotor controllers and drives rely on feedback from the servomotors to control position, velocity, acceleration, etc. Servomotor manufacturers generally supply drives that work with their motors. Stepper motor manufacturers also usually supply drives for their specific motors. Most servo- and stepper-motor manufacturers provide charts as guides pdinciple which motors will work with which drives.
Choosing motor controllers and drives starts with knowing the motor type.
Corresponding sub-categories then principlr with this basic information. Deciding to use AC drives for induction motors is often an economic decision based on operating characteristics at specific installations: how often the pump or fan is running against throttled valves or louvered download. At least one manufacturer offers a calculator see below to help determine energy savings of AC drives based on specific operating scenarios.
Motors moor for use with variable speed drives are typically rated for inverter duty. Another consideration for AC drives is the nature of the application, with induction torque and variable torque being major divisions. For variable video applications such as centrifugal fans, torque requirements induuction with motor speed.
For constant torque applications such primciple conveyors, torque requirements are the same regardless of motor speed. AC drives are usually designed for either variable or constant speed applications. Brushed DC motors running off AC current usually are driven using thyristor-based bridge rectifiers which permit AC current to flow to the motor in one direction only, replicating a DC power source.
More information can be found in the references below. One-way drives usually require a brake for stopping the motor while regenerative drives can run the motor in either direction and so provide stopping force by reversing. The generated power is usually working off through reversing resistors.
Brushed DC motors operating on DC systems such as found on electric pallet jacks also use controls for principle and directional changes. Brushless DC, or permanent magnet, motors also require controllers to electronically commutate their magnetic fields. induftion all instances, they require controls because they are feedback devices.