As far as I know, since the advent of active induction motors, there has been a variable frequency operation in the way of communicating generators. Change the rotational speed of the generator, and change its output frequency. Prior to the advent of high-speed transistors, this was one of the main ways to change the speed of a motor, but the frequency change was limited because the generator speed dropped the output frequency instead of the voltage.
So, let's take a look at the components of the drive and see how they actually work together to change the frequency and motor speed.
1. Inverter element - rectifier
Since it is difficult to change the frequency of the communication sine wave in the form of communication, the first operation of the inverter is to convert the waveform to DC. To make it look like an AC, it is relatively easy to operate the DC. The first component of all AC converters is a device known as a rectifier or converter, which converts AC into DC power in much the same way as a battery charger or arc welder. It uses a diode bridge to restrict the communication sine wave from moving in only one direction. The result is a thoroughly rectified communication waveform that is interpreted by the DC circuit as a local DC waveform. The three-phase inverter accepts three independent communicating input phases and converts them into a single DC output.
Most three-phase drives are also capable of accepting single-phase (230V or 460V) power, but since only two input branches are required, the converter output (HP) must be derated and the DC current incurred decreases proportionally. On the other hand, a true single-phase inverter (a single-phase inverter that controls a single-phase motor) uses a single-phase input and generates a DC output that is proportional to the input.
When it comes to variable speed operation, there are two reasons why three-phase motors are more ubiquitous than single-phase counter components. First and foremost, they have a wider power scale. Single-phase motors, on the other hand, usually require some external intervention to start the end rotation.
2. Inverter components - DC bus
The second component of the DC bus (shown in the DC bus diagram) is not visible in all inverters, as it does not directly affect the inverter operation. However, it is always present in high-quality universal frequency converters. The DC bus uses capacitors and inductors to filter out the communicating "ripple" voltage from the converted DC current, which then goes to the inverter section. It also includes a filter that thwarts harmonic distortion and is able to feed back to the inverter power. Older frequency converters and the need for their own line filters to complete this process.
3. Inverter components - inverters
On the right side of the illustration is the "guts" of the drive (shown by the inverter in the diagram). The inverter uses three sets of high-speed switching transistors (shown in the IGBT pictured) to create DC "pulses" that mimic all three phases that communicate a sine wave. These pulses determine not only the voltage of the wave, but also its frequency. The term inverter or inverter means "reversal", which simply means the up-and-down movement of the waveform that takes place. Modern frequency converter inverters use a technique called "pulse width modulation" (PWM) to regulate voltage and frequency.
Then let's talk about IGBT, IGBT refers to "insulated gate bipolar transistor", which is the switching (or pulsing) element of the inverter. Transistors (instead of vacuum tubes) serve two effects in our electronic world. It has the ability to act as an amplifier and add a signal, as an amplifier would, or it can act as a switch and simply turn the signal on and off. IGBTs are a modern version that offers higher switching speeds (3000 - 16000 Hz) and reduced heat generation. The higher switching speed can improve the degree of communication radio wave simulation and reduce the noise of the motor. The resulting heat reduction means that the heat sink is smaller, and therefore the drive has a smaller footprint.
Fourth, the PWM waveform of the inverter
The waveform of the inverter of the PWM inverter is shown compared to the real AC sine wave. The inverter output consists of a series of rectangular pulses with a fixed height and adjustable width. In this particular case, there are three sets of pulses - a wide set in the center and a narrow set at the beginning and end of the positive and negative parts of the AC cycle.
The sum of the areas of the pulses is equal to the effective voltage of the real AC wave. If you were to cut out the pulses above (or below) the real communication waveform and fill in the empty space below the curve with them, they would almost match. It is in this way that the inverter controls the voltage of the motor. The sum of the pulse widths and the blank widths between them determines the frequency of the waveform seen by the motor (hence PWM or pulse width modulation). If the pulses are continuous (i.e. there are no gaps), the frequency is still correct, but the voltage will be much larger than the real AC sine wave.
Depending on the required voltage and frequency, the inverter will vary the height and width of the pulses and the width of the gap between the two. Some of you may wonder how this "fake" AC (which is actually DC) operates a communicative induction motor. Is there a need for a communication current to "induce" the current in the motor's rotor and its corresponding magnetic field? Well, AC will naturally cause induction, since it is constantly changing the direction and on the other hand, DC will not behave normally due to the fact that once the circuit is activated.
However, if the DC is open and closed, the DC can sense current. Regarding those who are very old, the sedan ignition system (before solid-state ignition) used to have a set of points in the distributor. These key intentions are to "pulse" from the battery to the coil (transformer). This induces a charge in the coil and then raises the voltage to a level that is acceptable for the spark plug to ignite. The wide DC pulses seen in the diagram above are actually made up of hundreds of individual pulses, and this open and closed motion of the inverter output promises to occur via DC induction.
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