Equivalent circuit for Step-III & IV for three phase bridge inverter is shown below.
During Step-I, SCRs 5, 6 & 1 are conducting. These are shown as closed switches and the non-conducting SCRs are shown as open switches. The load terminals a & c are connected to the positive bus of DC source whereas terminal b is connected to the negative bus of DC source. The load voltage vab = vbc = Vs in magnitude. The magnitude of neutral voltage can be calculated as shown below:
During Step - I, 0 < wt < π/3 SCRs 5,6 & 1 are only conducting
Current i =
The line to neutral voltages are given as
The above line to neutral voltage may be written as Vao = Vco= (Vs/3) and Vbo = -(2Vs/3).
During Step - II, π/3 < wt < 2π/3 SCRs 6,2 & 1 are only conducting
The line to neutral voltages are given as
The above line to neutral voltage may be written as Vbo = Voc= -(Vs/3) and Vao = (2Vs/3). The output voltages as calculated for step-I & II are plotted to get the output voltage waveform of the three phase bridge inverter. The variation in phase voltages for remaining steps are calculated in the same manner and plotted. The output voltage waveform is shown below.\
From the above waveform, it is clear that for each cycle of output voltage of each phase, six steps are required and each step has a duration of 60°.
The line voltage Vab = Vao + Vbo or Vab = Vao – Vbo is obtained by reversing Vbo and adding it to Vao. This is shown in the output waveform (b). Similarly, line voltages Vbc & Vca are plotted.
The purpose of diode D1 to D6 is to allow the flow of current through them when the load is inductive in nature.
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1. What is a three-phase bridge inverter in electrical engineering? |
2. How does a three-phase bridge inverter work? |
3. What are the advantages of using a three-phase bridge inverter? |
4. What are the applications of three-phase bridge inverters in electrical engineering? |
5. How does a three-phase bridge inverter differ from a single-phase inverter? |
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