Inverter to control hydraulic pump

rguimond

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Jul 2009
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Escuminac
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Has anyone successfully used an inverter to limit speed of a motor driving a hydraulic pump?

My plans are to crank up the pressure relief valve (currently set at 800 PSI) to about 1000 PSI and use a pressure transducer tied to a PID loop to control the motor to keep the pressure at 800 PSI.

The pump is driven by a 40 Hp inverter-duty 3-phase electric motor.

The hydraulic system is closed-center (only flow is over the top of the relief valve if nothing is calling for hydraulic power).

There are a couple very small motors driven all the time, but 90%+ of the loads are cylinders that run intermittently.

I have a surplus inverter already and there is a 4-20mA transducer feeding the a PLC, so the only expense will be re-routing the power supply wiring from the motor started to the inverter and an analog output cable from the PLC to the inverter.

Suggestions & advise are welcome!
 
I use inverters on fixed displacement hydraulic pumps all the time. But not to control pressure. An inverter can be used to control pump volume on a fixed displacement pump by controlling motor speed within some limits. However most pumps have a minimum speed, for example I don't recommend running an axial piston pump that you want to have a very long life continuously much below 800 RPM as the pump needs a certain amount of internal lubrication. A gear or vane pump might could be run slower.

Its doubtful that you will achieve any kind of decent pressure control using the method you proposed.

What kind of a problem are you experiencing that makes you want to take this approach? A little more information about your system will be helpful. Are you using a gear pump or an axial piston pump? If the latter, is it pressure compensated?
 
I have a customer that makes small presses and uses small servos to control pressure directly. They have been doing it for years. When applying pressure the motor must turn very slowly to make up for leakage.

Controlling pressure is a problem if the flow demands are always changing.

but 90%+ of the loads are cylinders that run intermittently.
Use an accumulator. The accumulator can store energy for peak demands. This way the motor only needs to supply the average flow per cycle. The accumulator also makes the pressure control MUCH easier.
 

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