Setting the parameters of a frequency converter is crucial during commissioning. Improper parameter settings can fail to meet production needs, leading to starting and braking failures, frequent tripping during operation, and in severe cases, burning out components such as the power module IGBT or rectifier bridge. Different types of frequency converters have different parameter values.
A typical single-function frequency converter has about 50-60 parameter values, while a multi-function frequency converter has more than 200 parameters. But regardless of the number of parameters, is it necessary to readjust all of them during commissioning? No, most can remain unchanged; the factory default values are sufficient. Only resetting the factory default values that are unsuitable for current use is necessary. For example, external terminal operations, analog operations, base frequency, maximum frequency, upper limit frequency, lower limit frequency, start time, braking time (and method), thermal electronic protection, overcurrent protection, carrier frequency, stall protection, and overvoltage protection must be adjusted. If the operation is unsatisfactory, then other parameters should be adjusted.
Troubleshooting several common problems during on-site commissioning
The principle for setting the start-up time is that it should be short rather than long, and the specific values are as follows.
If the overcurrent setting OC is too low, increase it appropriately, up to a maximum of 150%. An empirical value of 1.5–2 seconds/kW is recommended; use a larger value for lower power ratings; for power ratings greater than 30kW, use >2 seconds/kW. If the motor stalls when the start button *RUN is pressed, it indicates that the load torque is too high and the starting torque is too low (try to increase it). Immediately press STOP to stop the motor; otherwise, it will burn out if left running for too long.
Since the motor is stalled (not rotating), the back electrothermal energy E=0. At this time, the AC impedance Z=0, and only the DC resistance is very small. Therefore, a large current is very dangerous, necessitating a trip (OC) action. The braking time should be set longer rather than shorter, as this can easily lead to overvoltage tripping (OE).
For water pumps and fans, free braking is preferable; rapid and forceful braking can easily cause severe water hammer effects. Setting the starting frequency is beneficial for accelerated starting, especially under light loads. For heavy loads, a high starting frequency results in increased starting current, making it easier to overshoot the overcurrent (OC) at low frequencies. Generally, starting the starting frequency from 0 is appropriate. Setting the starting torque is also beneficial for accelerated starting, especially under light loads. For heavy loads, a high starting torque results in increased starting current, making it easier to overshoot the OC at low frequencies. Generally, starting the starting torque from 0 is appropriate.
The standard base frequency setting is 380V at 50Hz, i.e., V/F = 380/50 = 7.6. However, heavy loads (such as extruders, washing machines, spin dryers, mixers, blenders, dewatering machines, etc.) often fail to start, and adjusting other parameters is often ineffective. Therefore, adjusting the base frequency is an effective method. This involves lowering the 50Hz setting to 30Hz or below. At this point, V/F > 7.6, meaning that the output voltage increases, especially at lower frequencies (i.e., torque ∝ U²). Therefore, heavy loads can generally start better. Overvoltage during braking is caused by a short braking time and an excessively low braking resistance value. This can be avoided by appropriately increasing the braking time and the resistance value.
Selection of braking method
(1) Energy-consuming braking. When using conventional braking, energy is consumed in the resistor and lost as heat. At lower frequencies, the braking torque is too small, resulting in a creeping phenomenon.
(2) DC braking. Suitable for precise parking or positioning, with no crawling phenomenon. It can be used in conjunction with energy-saving braking. Generally, DC braking is used when the frequency is ≤20Hz, and energy-saving braking is used when the frequency is >20Hz.
(3) Regenerative braking. Applicable to motors ≥100kW with a speed ratio D≥10, alternating high and low speeds or forward and reverse rotation, and short cycle time. In this case, regenerative braking is suitable, and the regenerative energy can reach 20% of the motor power. More detailed analysis and parameter selection are available. No-load (or light-load) tripping of OC: In theory, the current is not large under no-load (or light-load) conditions, and OC should not trip. However, this phenomenon has occurred in practice. The reason is often that the compensation voltage is too high, the starting torque is too large, causing severe excitation saturation, resulting in severe distortion of the excitation current, causing excessive peak current and tripping of OC. Appropriately reduce or restore the factory value or set it to 0.
The reason for tripping the OC (overcurrent protection) at low frequencies ≤20Hz during startup is due to overcompensation, high starting torque, short starting time, and excessively low protection values (including overcurrent and stall overcurrent values). Reducing the base frequency will solve the problem. Difficulty starting, inability to start general equipment, excessive moment of inertia GD2, excessive resistance torque, and heavy load starting are common issues, especially with large fans and pumps. The solution is as follows:
① Reduce the base frequency;
② Appropriately increase the starting frequency;
③ Appropriately increase the starting torque;
④ Decrease the carrier frequency by 2.5–4 kHz to increase the effective torque value;
⑤ Reduce startup time;
⑥ Increase the protection value;
⑦ To change the load from starting under load to starting under no-load or light load, the inlet valve of the fan can be closed slightly. After using a frequency converter, the motor temperature rises, vibrations increase, and noise increases. Our company's carrier frequency setting is 2.5kHz, which is lower than usual, with the aim of ensuring safety. However, the above three problems are commonly reported. These problems are solved by increasing the carrier frequency value.
After powering on, pressing the RUN button has no effect.
(1) The panel frequency is not set;
(2) If the motor does not move, press "STOP" immediately and check the following:
① Double-check the correctness of the route;
② Double-check the identified code (especially the parts related to startup);
③Is the operating mode setting correct?
④ Measure the input voltage, and the three-phase voltages R, S, and T;
⑤ Measure the DC PN voltage value;
⑥ Measure the voltage values of each group of the switching power supply;
⑦ Check the contact of the drive circuit plug-in;
⑧ Check the contact of the panel circuit components;
9. Power should only be turned on after a thorough inspection.
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