What do inverters do and do they work?
The most common form of inverters that you can buy on the automation market is the frequency inverter. The most common phrase on the lips of buyers is usually ‘what do inverters do?’ – this post should help to answer that question, and make the subject of frequency converters more easy to understand.
What do inverters do?
A frequency inverters main job is to change output voltage frequency and magnitude to vary the speed and power of a connected motor. They do this by taking an alternating current mains and changing it to direct current – this is because it is very difficult to alter the frequency of an alternating current. The component that performs this task within the inverter is called a rectifier or converter. This is the first step in carrying out the inverters overall function. Next, the DC bus uses capacitors and an inductor to filter the AC ‘ripple’ voltage from the converted DC. Then, the inverter, the main component, uses three sets of high speed switching transistors to make DC pulses which simulate the AC current.
These pulses are what will determine both the voltage of the wave and it’s frequency. Modern frequency inverters will include an IGBT (insulated gate, bipolar transistor) which effectively reduces heat generation and audible motor noise – the reduce in heat produces a smaller frequency inverter footprint. The last component of a frequency inverter is the inverter output – this consists of a series of rectangular pulses with a fixed height but an adjustable width, which help to control the voltage which enters the motor. Depending on the desired voltage and frequency, the frequency inverter will vary the width of the pulse and the width of the black spaces in between to alter the current to the motors requirements. So, this is what inverters do – the way in which they do it are rather complex, but the result is quite simple.
What are the advantages?
Now that the question of what inverters do is answered, let’s move on to the advantages of using one in a circuit. Frequency inverters provide over-current protection, which is especially useful and important when the motor it is providing voltage for has a particularly high inertia. The inverter also provide a wider range of speed control which enable a higher energy efficiency. They also act as a barrier between the motor and any input voltage disturbances like harmonics, ripples, sags and surges, which could overpower and render the motor unusable.
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