Problem with GD20-EU and PID control at low speeds

[sprig]

I am testing the PID control on INVT inverter and my system consists of GD20-EU 2.2kW, 0.4kW asynchronous motor, incremental encoder connected to the motor shaft. I have done rotary autotuning and no load is applied to the engine.

The reference signal is sent through the analog port AI2 and is a simple linear ramp until the desired value is reached. The PID feedback signal is the pulse train sent by the encoder via the HDI fast input. Here are the oscillograms detected by the program INVT studio.

• (Figure 1) Everything works perfectly but in the first part of the ramp (indicatively from 0 to 5 Hz) the system starts very slowly and then accelerates and reaches the reference signal. I have tried to literally change every parameter of the inverter including those of group P03 and the speed control method (P00.00) but the first part of the ramp never changes even using parameters that subsequently make the PID system unstable.
• (Figure 2) If instead I deactivate the PID control the ramp is perfect.
• (Figure 3) With PID control active, but with parameters that lead to motor instability, the first part of the ramp is always identical.

Thanks for any suggestion.

[Sergio Bertana]

It seems that the feedback suddenly increases a lot ...

Try to set up P00.00=2 SVPWM control.

Try acting on the feedback sampling by decreasing it:

P05.54 HDI frequency input filter time
P09.07 Sampling cycle

[Author]

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