difference between 120 degree conduction and 180 degree conduction

[Guest]

Help... Difference between 180 degree and, 120 degree mode of conduction needed...

[jaseela123d]

The 180 degree mode and the 120 mode of operation 120 are two different strategies for changing the electronic power switches to obtain the desired AC output waveform. In the 180 degree operating mode, if you divide a 360 degree cycle into 6 intervals of 60 degrees each, you will have 3 devices in each interval

If I name the upper leg switches as 1,3,5 and the lower leg switches as 4, 6, 2, the switchboard would be- (180 degree mode)

0-60 degrees - Switches 1,6 and 5 are on

60-120 degrees - Switches 1, 6 and 2 are on

120-180 degrees - Switches 1, 3 and 2 are on

180-240 degrees - Switches 4, 3 and 2 are on

240-300 degrees - Switches 3, 4 and 5 are on

300-360 degrees: Switches 4, 5 and 6 are on

Inference: each switch will perform a 180 degree interval and for each 60 degree interval, three switches are on and three switches are off.

For 120 degree operation mode-

Each switch is on by a 120 degree interval on each cycle and two switches are on simultaneously.

0-60 degrees - Switches 1 and 6 are on

60-120 degrees - Switches 1 and 2 are on

120-180 degrees - Switches 3 and 2 are on

180-240 degrees - Switches 3 and 4 are on

240-300 degrees - Switches 5 and 4 are on

300-360 degrees - switches 5 and 6 are in

Inference: each switch will perform an interval of 120 degrees and for each interval of 60 degrees, two switches are on and four switches are off.

Efficiency and loss analysis (neglecting switching losses as it would depend on the type of electronic power device used) MOSFET, IGBT, BJT ETC.

Loss of power in electronic power switches can be classified as loss of state of shutdown, loss of conduction and loss of switching. The out-of-state loss (the switch is in deactivated state) the current flow is very low and, therefore, the loss of state off is very small. The conduction loss will be Von (voltage drop in the state) * Ic (current carrying capacity) which in high current applications is considerably higher than out of state losses.

Inference (High current application)

Loss of driving> Loss of commutation .................. (1)

180 degree mode (each 60 degree range) - 3 switches on, 3 switches

loss (180) = 3 * 3 * Loss of driving + loss ...... out of state. (2)

120 degree mode (each 60 degree interval) - 2 switches on, 4 switches off

loss (120) = 2 * Loss of driving + 4 * loss out of state ...... (3)

Therefore, from (1), (2) and (3) if it is a high current application

The 120 degree mode would have lower losses than the 180 degree mode.

For low current and high voltage applications, the difference between conduction loss and loss of state is not significant and therefore can be neglected.

Based on THD (Total Harmonic Distortion and Load Power Factor)

For delay and main loads if the p.f is more than 0.9- Select the 180 degree mode

For ohmic loads: select the 180 degree mode

For inductive and capacitive loads: pure It does not matter, since the resistive damping effect is negligibly small in the harmonics and therefore can be triggered in 120 degree mode or 180 degree mode.