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I am running an induction motor and a stepper motor simultaneously through a driver board I designed. The board has a dual H-bridge for driving a bipolar stepper motor, and an inverter for driving the induction motor. The DC voltage supplied to the dual H-bridge and the inverter comes from a bench supply, which is 25 Vdc. The bench supply supplies another 11 Vdc tothe gate driving ICs (IR 2112S).

The gate driving signals come from a micro-controller board, which also has the run-profile for the two motors including other logic.

Both motors run almost perfectly individually, and when running simultaneously, they work fine during acceleration and steady state phases of the program/recipe.

However there comes a time during the program/recipe when the stepper motor is running at full speed (max rated) and the induction motor starts to decelerate/brake. At a very specific point during the deceleration (almost precisely) the stepper motor (which was running fine at full speed stalls.

I can't find anything wrong with the program logic, so I am thinking of an electrical problem. I initially thought it could be crosstalk in the two sets of motor driving signals. But the stall comes at too specific a time to be just crosstalk.

My current theory is the current generated due to braking by the induction motor, becomes too large and interferes with the stepper motor. But I am not sure how to test and rectify this.

Any ideas would be welcome.

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  • \$\begingroup\$ Do some measurements \$\endgroup\$ – PlasmaHH Oct 8 '16 at 19:20
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    \$\begingroup\$ Especially, what happens to the supply voltage at that point ? \$\endgroup\$ – Brian Drummond Oct 8 '16 at 19:25
  • \$\begingroup\$ @PlasmaHH What do I measure? I don't even know where to start. Can you please elaborate? \$\endgroup\$ – Safiullah Hussaini Oct 8 '16 at 19:25
  • \$\begingroup\$ @BrianDrummond My bad, should have mentioned this in the details, the supply voltage seems steady, though the current fluctuates significantly. \$\endgroup\$ – Safiullah Hussaini Oct 8 '16 at 19:27
  • \$\begingroup\$ You say you do not see anything wrong in logic. What is about implementation of logic? The first obvious idea: connect LEDs to digital signals driving motors to see their activity. If motor stalls and digital driving signal is still active, you have problem in further circuit, but if LED changes its state when it stalls, you have issue in logic or its implementation. \$\endgroup\$ – Anonymous Oct 8 '16 at 19:28
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The theory about current generated by braking seems like a valid point to investigate thoroughly. The problem would likely be the energy that he motor is returning to the supply. The motor current might not change much, but the average DC current supplying the inverter would reverse. If the supply is not designed to absorb the reverse current, any available capacitors across the supply will be charged to a higher voltage. You need to look at the power circuit and determine where reverse current can go. You also need to determine the reaction to reverse current of any protection circuits.

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