Tuning The Closed-Loop Controller; Manual Pid Adjustment; General Aspects Of Emc; General Aspects Of Emc Emissions - Danfoss VLT HVAC Drive FC 102 Design Manual

Introduction

2.8.11 Tuning the Closed-loop Controller

Once the closed-loop controller has been set up, the performance of the controller should be tested. In many cases, its
performance may be acceptable using the default values of 20-93 PID Proportional Gain and 20-94 PID Integral Time.
However, in some cases it may be helpful to optimize these parameter values to provide faster system response while still
controlling speed overshoot.

2.8.12 Manual PID Adjustment

1. Start the motor.
2. Set 20-93 PID Proportional Gain to 0.3 and increase it until the feedback signal begins to oscillate. If necessary, start
and stop the adjustable frequency drive or make step changes in the setpoint reference to attempt to cause
oscillation.
3. Reduce the PID proportional gain until the feedback signal stabilizes. Reduce the proportional gain by 40–60%.
4. Set 20-94 PID Integral Time to 20 sec. and reduce it until the feedback signal begins to oscillate. If necessary, start
and stop the adjustable frequency drive or make step changes in the setpoint reference to attempt to cause
oscillation.
5. Increase the PID integral time until the feedback signal stabilizes. Increase the integral time by 15–50%.
6. 20-95 PID Differentiation Time should only be used for fast-acting systems. The typical value is 25% of 20-94 PID
Integral Time. The differential function should only be used when the setting of the proportional gain and the
integral time has been fully optimized. Make sure that oscillations of the feedback signal are sufficiently dampened
by the low-pass filter for the feedback signal (parameters 6-16, 6-26, 5-54 or 5-59 as required).

2.9 General aspects of EMC

2.9.1 General Aspects of EMC Emissions

Electrical interference is usually conducted at frequencies in the range 150 kHz to 30 MHz. Airborne interference from the
adjustable frequency drive system in the range 30 MHz to 1 GHz is generated from the inverter, motor cable, and motor.
Capacitive currents in the motor cable coupled with a high dU/dt from the motor voltage generate leakage currents.
The use of a shielded motor cable increases the leakage current (see Figure 2.26) because shielded cables have higher
capacitance to ground than non-shielded cables. If the leakage current is not filtered, it will cause greater interference on
the line power in the radio frequency range below approximately 5 MHz. Since the leakage current (I
unit through the shield (I ), there is only a small electromagnetic field (I
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The shield reduces the radiated interference, but increases the low-frequency interference in the line power supply. The
motor cable shield must be connected to the adjustable frequency drive enclosure as well as the motor enclosure. This is
best done by using integrated shield clamps so as to avoid twisted shield ends (pigtails) These increase the shield
impedance at higher frequencies, which reduces the shield effect and increases the leakage current (I
If a shielded cable is used for serial communication bus, relay, control cable, signal interface and brake, the shield must be
mounted on the enclosure at both ends. In some situations, however, it will be necessary to break the shield to avoid
current loops.
MG16C122
Design Guide
) from the shielded motor cable.
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) is carried back to the
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).
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