Frequency converter debugging step analysis - Database & Sql Blog Articles

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When the inverter is being debugged, the basic steps to be taken include no-load inspection, no-load operation with motor, load-bearing test operation, and on-line adjustment with the host computer; problems to be noted when completing these steps.

First of all, before the inverter is powered on, it is necessary to check whether its input and output meet the requirements of the manual. In particular, it is necessary to see if there is any new content, and read the precautions carefully.

First, the inverter's no-load power-on inspection

1. Ground the ground terminal of the inverter.

2. Connect the power input terminal of the inverter to the power supply through the leakage protection switch.

3. Check if the factory display of the inverter display window is normal. If it is not correct, it should be reset. Otherwise, it is required to be returned.

4. Familiar with the operation keys of the inverter.

The general inverter has 6 keys, such as RUN, STOP, PROG, DATA/ENTER, UP (UP), DOWN, DOWN, and The definition of the operation keys is basically the same. In addition, some inverters also have function keys such as monitor (MONTTOR/DISPLAY), reset (RESET), JOG, and shift (SHIFT).

Second, the inverter with motor running at no load

1. Set the power and number of poles of the motor, and consider the operating current of the inverter.

2. Set the maximum output frequency, fundamental frequency and set torque characteristics of the inverter. The V/f type selection includes items such as the highest frequency, basic frequency, and torque type. The highest frequency is the highest frequency that the inverter-motor system can operate. Since the maximum frequency of the inverter itself may be high, when the maximum frequency allowed by the motor is lower than the highest frequency of the inverter, it should be set according to the requirements of the motor and its load. set. The basic frequency is the dividing line between the inverter for constant power control and constant torque control of the motor, which should be set according to the rated voltage of the motor. The torque type refers to whether the load is a constant torque load or a variable torque load. The user selects one of the types according to the V/f type map and load characteristics in the inverter's instruction manual. The general-purpose inverters are equipped with multiple V/f curves for the user to select. The user should select the appropriate V/f curve according to the nature of the load. In the case of fan and pump loads, set the torque running code of the frequency converter to variable torque and torque reduction operating characteristics. In order to improve the low-speed performance of the inverter when starting, the torque output from the motor can meet the requirements of the production load start-up, and the starting torque should be adjusted. In the asynchronous motor variable frequency speed control system, the torque control is more complicated. In the low frequency band, the influence of resistance and leakage reactance cannot be ignored. If V/f is kept constant, the magnetic flux will decrease, which will reduce the output torque of the motor. For this reason, the voltage is appropriately compensated at the low frequency band to increase the torque. Generally, the inverter is manually compensated by the user. The Hitachi J300 inverter offers users two options: self-setting and automatic torque boost.

3. Set the inverter to its own keyboard operation mode, press the run key and stop key to observe whether the motor can start and stop normally.

4. Familiar with the protection code when the inverter runs fault, observe the factory value of the thermal protection relay, observe the setting value of the overload protection, and modify it if necessary. The user of the inverter can set the electronic thermal relay function of the inverter according to the instruction manual of the inverter. The threshold of an electronic thermal relay is defined as the ratio of the rated current of both the motor and the frequency converter, usually expressed as a percentage. When the output current of the inverter exceeds its allowable current, the overcurrent protection of the inverter will cut off the output of the inverter. Therefore, the maximum threshold of the inverter electronic thermal relay does not exceed the maximum allowable output current of the inverter.

Third, with load test run

1. Manually operate the running stop button of the inverter panel, observe the motor running stop process and the display window of the inverter to see if there is any abnormality.

2. If the inverter has an overcurrent protection action during the start and stop of the motor, the acceleration and deceleration time should be reset. The acceleration of the motor during acceleration and deceleration depends on the acceleration torque, and the frequency change rate of the inverter during start and brake is set by the user. If the motor's moment of inertia or motor load changes, when the speed is increased or decelerated according to the preset frequency change rate, there may be insufficient acceleration torque, which may cause the motor to stall, that is, the motor speed is not in harmony with the inverter output frequency, resulting in Current or over voltage. Therefore, it is necessary to set the acceleration and deceleration time according to the motor inertia and load, so that the frequency change rate of the inverter can be coordinated with the motor speed change rate. The reason for checking whether this setting is reasonable is to first select the acceleration and deceleration time according to experience, and if there is overcurrent during the starting process, the acceleration time can be extended appropriately; if overcurrent occurs during braking, Prolong the deceleration time appropriately. On the other hand, the acceleration and deceleration time should not be set too long. If the time is too long, it will affect the production efficiency, especially when it is frequently started and braked.

3. If the inverter is still protected for a limited time, change the start/stop running curve from straight to S-shaped, U-shaped or anti-S-shaped, anti-U-shaped. When the motor load inertia is large, a longer start-stop time should be used and the run curve type should be set according to its load characteristics.

4. If the inverter still has an operational fault, try to increase the maximum current protection value, but you cannot cancel the protection. Leave at least 10%-20% of the protection margin.

5. If the inverter operation failure still occurs, replace the inverter with a larger power.

6. If the inverter drives the motor to reach the preset speed during the startup process, there may be two cases:

(1) Electromechanical resonance occurs in the system and can be judged from the sound of the motor running. By setting the frequency jump value, you can avoid the resonance point. Generally, the inverter can set three-level jump point. When the V/f controlled inverter drives the asynchronous motor, the current and speed of the motor will oscillate in some frequency segments. In severe cases, the system cannot run, and even the overcurrent protection occurs during the acceleration process, so that the motor cannot start normally. It is more serious when the light load or the moment of inertia is small. The common inverters are equipped with a frequency jump function. The user can set the jump point and the jump width on the V/f curve according to the frequency point at which the system oscillates. These frequency segments can be automatically skipped when the motor accelerates to ensure that the system can operate normally.

(2) The torque output capability of the motor is not enough. The factory parameters of different brands of inverters are different. Under the same conditions, the load capacity is different, and the load capacity of the motor may be different due to different control methods of the inverter; or Due to the different output efficiencies of the system, the load capacity will vary. In this case, the value of the torque boost amount can be increased. If it is not available, the manual torque boost function can be used. Do not set too large, and the temperature rise of the motor will increase. If it still does not work, the new control method should be used. For example, the Hitachi inverter adopts a constant V/f ratio method. When the startup fails to meet the requirements, it uses the speed sensorless space vector control method, which has a larger torque output. ability. For fan and pump loads, the curve for the torque reduction should be reduced.

Fourth, the inverter is connected with the host computer for system debugging

After the manual basic setting is completed, if there is a host computer in the system, connect the control line of the inverter directly to the control line of the host computer, and change the operation mode of the inverter to terminal control. According to the needs of the host computer system, set the range of the inverter receiving frequency signal terminal 0-5V or 0-10V, and the response speed of the inverter to the sampling of the analog frequency signal. If an additional monitoring head is required, select the monitoring amount of the analog output and adjust the range of the inverter output monitoring terminal.

One frequency setting signal gain

This function is only effective when the frequency is set with an external analog signal. It is used to compensate for the inconsistency between the external set signal voltage and the internal voltage of the inverter (+10v); at the same time, it is convenient to select the analog set signal voltage. When setting, when the analog input signal is maximum (such as 10v, 5v or 20mA), find the frequency percentage of the f/V pattern that can be output and set it as a parameter; if the external setting signal is 0~5v, if the output frequency of the inverter is 0~50Hz, the gain signal will be Set to 200%.

Two frequency limit

That is, the upper and lower limits of the inverter output frequency. The frequency limit is a protection function that prevents the device from malfunctioning or the external frequency setting signal source is faulty, causing the output frequency to be too high or too low to prevent damage to the device. In the application, it can be set according to the actual situation. This function can also be used for speed limit. If there are some belt conveyors, because there is not much material to be transported, in order to reduce the wear of machinery and belts, the inverter can be driven and the upper limit frequency of the inverter can be set to a certain frequency value. This allows the belt conveyor to operate at a fixed, low working speed.

Three acceleration and deceleration time

The acceleration time is the time required for the output frequency to rise from 0 to the maximum frequency, and the deceleration time is the time required to fall from the maximum frequency to 0. The acceleration and deceleration time is usually determined by the frequency setting signal rising and falling. When the motor is accelerating, the rate of increase of the frequency setting must be limited to prevent overcurrent, and when decelerating, the rate of decrease is limited to prevent overvoltage.

Acceleration time setting requirement: Limit the acceleration current below the overcurrent capacity of the inverter, and do not cause the inverter to trip due to the over-speed. The deceleration time setting point is: prevent the smoothing circuit voltage from being too large, and do not make the regenerative overvoltage stall. Let the frequency converter trip. Acceleration and deceleration time can be calculated according to the load, but in the debugging, it is often set to set the long acceleration/deceleration time according to the load and experience. Observe the overcurrent and overvoltage alarm by starting and stopping the motor; then gradually set the acceleration/deceleration time. Shorten, the principle of no alarm occurs during operation, and repeat the operation several times to determine the optimal acceleration and deceleration time.

Four-electron thermal overload protection

This function is set to protect the motor from overheating. It is the CPU inside the inverter calculates the temperature rise of the motor according to the running current value and frequency, thus performing overheat protection. This function is only applicable to the “one-for-one” occasion, and in the case of “one-to-one”, a thermal relay should be added to each motor. Electronic thermal protection set value (%) = [motor rated current (A) / inverter rated output current (A) > × 100%.

Five torque boost

Also called torque compensation, it is a method to increase the low frequency range f/V to compensate for the torque reduction at low speed caused by the resistance of the stator winding of the motor. When set to automatic, the voltage during acceleration can be automatically increased to compensate for the starting torque, so that the motor accelerates smoothly. If manual compensation is used, a better curve can be selected by experiment depending on the load characteristics, especially the starting characteristics of the load. For variable torque loads, if the selection is improper, the output voltage will be too high at low speed, and the phenomenon of wasting electric energy may even occur when the motor is loaded with load and the current is large, and the speed is not going up.

Six offset frequency

Some are also called deviation frequency or frequency deviation setting. Its purpose is to adjust the output frequency of the lowest frequency setting signal when the frequency is set by external analog signal (voltage or current), as shown in Figure 1. In some inverters, when the frequency setting signal is 0%, the deviation value can be applied in the range of 0 to fmax. Some inverters (such as Mingdianshe and Sanhao) can also set the offset polarity. For example, when the frequency setting signal is 0% during debugging, the inverter output frequency is not 0Hz, but is xHz. At this time, the offset frequency is set to negative xHz to make the inverter output frequency 0Hz.