Electronics > Power/Renewable Energy/EV's
Asymetric half bridge
nix85:
I im trying to understand how AHB inverter works, seems very simple, but direction of diodes doesnt make sense. Can you please elaborate exactly what happens when transistors are ON and what exactly happens when they are OFF and cap is supposed to discharge producing another halfphase of the sinewave.
This circuit is apparently most used to run stepper motors.
Another illustration of the same circle.
https://postimg.cc/nsssS6tB
Is the circle above even correct?
This is where i heard about it, comment below the first answer.
https://www.quora.com/How-suitable-is-a-half-bridge-converter-for-DC-AC-power-conversion-within-a-certain-kW-range
Quoting the guy:
"I have used a Asymetric halfe bridge (see picture) or motor control of an SRM
I think the motor was rated to about 40kW. We used a DC voltge of 540 V and an RMS current of approcimately 270 A. Nominal speed and torque was 14300 RPM and 30 Nm. A full bridge would have caused excessive switching losses and an increased risk of switching failure effectively resulting in short circuitting
asymmetric half bridge is also capable of supplying an alternating waveform. Both transistors on results in positive voltage where as both transistor off results in negative voltage and either transistor on results in free wheeling.
http://www.mdpi.com/sensors/sensors-17-01146/article_deploy/html/images/sensors-17-01146-g002.png
"
This last link is obviously different with additional diodes in parallel with transistors. Can someone clear this up?
Another illustration of similar circle without cap in parallel.
bob91343:
Turning on both transistors causes current to flow in the inductor. Turning off both transistors causes the inductor current to divert through the diodes and charge the capacitor. When the current drops sufficiently the diodes stop conducting and the circuit is ready for the next pulse.
Current always flows in the same direction through the inductor. When the transistors are on, the magnetic field of the inductor causes the motor to move.
So you pulse the transistors to get one jump of the motor. Wait for discharge, then pulse again. Motor jumps again, same direction as before.
nix85:
I just want to know can this circle be used to produce AC from DC, i don't need it to run a stepper motor of course.
Are you saying winding of the motor (what you call "inductor") comprises the integral part of the oscillating circuit? Hmm, hope to clear this up.
nix85:
When i look at this diagram that seems to be the same only missing cap in parallel it makes more sense, im not sure why, but if we add a cap in parallel, i can see convetional current flowing
through Q1, load, Q2 to the ground, then transistors turn off, and cap discharges in reverse direction through D2, load, D1 and into itself, cycle repeats, but this is not sinewave but pulsed dc on the load. But if we just reverse how D1 and D2 are connected to the load, we do get sinewave on the load.
bob91343:
As drawn, it doesn't oscillate. You need a circuit to drive it. You can't leave the transistor bases open in a practical circuit.
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