What is a Voltage Source Inverter? A Comprehensive Guide

You all must have heard about inverters and might have a sound knowledge of what they are. But are you aware of a voltage source inverter? Let us learn more about it. A voltage source inverter, often known as a VSI, is a converter that changes a voltage’s waveform from unidirectional to bidirectional, or from DC to AC. The optimum voltage source inverter maintains a consistent voltage throughout the operation. 

Source: Luminous 

A VSI typically consists of one sizable DC link capacitor, a transistor for switching, a DC voltage source, and a DC voltage source. A transistor utilized might be an IGBT, BJT, MOSFET, or GTO. A DC voltage source might also be a battery, dynamo, or solar cell. The two topologies of VSI are three-phase and single-phase inverters, with each phase, further subdivided into half-bridge and full-bridge inverters. 

• Single Phase Half Bridge VSI: One DC voltage source, four transistors (S1, S2, S3, S4), four antiparallel diodes (D1, D2, D3, D4) for switching, and one sizable DC link capacitor (C) make up this device. 
• 3 Phase Full Bridge VSI: It comprises one DC source, six anti-parallel diodes (D1, D2, D3, D4, D5, D6), three load terminals, six transistors (T1, T2, T3, T4, T5, T6), one big DC linked capacitor, a thyristor, and a commutation circuit. The three outputs are labeled “ABC,” with “A” linked to T1 and T4, “B” to T3 and T6, and “C” to T5 and T2. A three-phase balanced load is then attached to these ABCs. 

There are two primary parts that make up a balanced load: a source and a load. A balanced source implies that phase and magnitude are equal and that they are phase-shifted by 120 degrees.  

The balanced load implies that all load impedances in all three phases are equal in magnitude and phase, in accordance with the KCL principle. Thyristors T1, T3, and T5 give current to the load or serve as forwarding paths, whilst thyristors T6, T4, and T2 serve as return paths and transport the current back to the source. 

How Single Phase Voltage Source Inverter Operates?

There are two conduction moods in which a voltage source inverter can operate: 

• Conduction moods of 180 degrees 
• Conduction moods of 120 degrees 

Let us take a look at the case of a three-phase inverter operating in a 180-degree conduction mode. Because both switches S1 and S2 conduct at 180 degrees, the three-phase inverter is depicted in 180-degree conduction mode. In contrast, all four switches (S1, S2, S3, S4) in a full-bridge voltage source inverter conduct at 180 degrees. The switches T1 and T4 are coupled to a phase, which T1 and T4 conduct at 180 degrees each, according to the circuit diagram below, where the total length is indicated as 1800 + 1800 = 3600. A short circuit could result if both switches operate at the same time. 

The graph, which has wt as the X-axis and amplitude as the Y-axis, shows that 

• T1 operates between 0 and 1800. 
• T4 operates between 1800 and 3600. 
• A phase shift of 1200 must exist between B phase and A phase for a balanced output. Angle B should be 1200, angle C should be -2400, and angle A should be 00 at that time. 
• T3 will therefore begin operating between 1200 and 3000. Following this phase, T6 begins to conduct between 3000 and 3600. T6 is also operating between 00 and 1200. 
• T5 begins running from 2400 to 3600 and from 00 to 600. 

• T2 transmits between 600 and 2400. 
• We can infer from the graph above that 3SCR switches conduct periodically. 

Advantages Of a Voltage Source Inverter

• Takes up less space 
• The load employed has no bearing on the output voltage. 
• Uses common sense 
• With a single voltage source inverter, multiple motors can be driven. 
• Range of design up to 500 Hz 

Drawbacks Of a Voltage Source Inverter

• When a short circuit happens, it is unsafe 
• Lower speed 
• There is a lower i.e., 1s input power factor 

Which One Is Better: The Voltage Source Inverter or The Current Source Inverter?

The table below illustrates the difference 

Voltage Source Inverter	Current Source Inverter
The inverter is often provided with a rigid voltage source.	The inverter is already equipped with a powerful current source.
A DC source’s low internal impedance necessitates the use of feedback diodes	A DC source’s high internal impedance not having feedback diodes
The capacitor causes a minor variation in output voltage	A change in load causes a change in output voltage.
Complicated structuring	Simple structuring
Decreased output impedance	Increased output impedance

Implementations

These are some uses for voltage source inverter. 

• AC speed drivers with uninterruptible power supply 
• Filters 
• Circuits for electronic frequency changers 

So, an inverter is a piece of equipment that changes dc into ac. Current source inverter and voltage source inverters are two categories of self-commutated inverters. A device that changes a voltage’s shape from DC to AC is known as a voltage source inverter. 

Either one phase or three phases might be used to represent it. The function of the 3-phase VSI is explained in the following article. Where each phase has a conduction mood of 180 degrees and 120 degrees. The key benefit is that the output voltage is unaffected by the applied load.  

We hope this blog provided you with in depth knowledge about Voltage Source Inverter. If you are keen to know more about current source inverter or single phase voltage source inverter, check our website and explore a whole new world inverters and batteries! 

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