company news

The frequency converter can be successfully applied to various loads and get long-term stable operation. On-site debugging is very important and must be carried out according to the corresponding steps.

1.1 Inspection before no-load power-on of the frequency converter

(1) Connect the power input terminal of the inverter to the power supply through the leakage protection switch;
(2) Ground the grounding terminal of the inverter;
(3) Confirm that the voltage and frequency level on the label of the inverter is consistent with that of the power grid, and then send power after it is correct;
(4) The main contactor is closed, the fan is running, and the ac range of the multimeter is used to test whether the input power voltage is within the standard specification;
(5) Familiar with the operation keyboard keys of the inverter;
Take Powtran as an example: fwd (forward running key: make the drive run forward), rev (reverse running key: make the drive run reversely), esc/displ (exit/display key: exit the data change of the function item, Exit in fault state, exit submenu or enter status display menu from function item menu), stop/reset (stop reset key: stop the drive, reset abnormality, confirm fault), prg (parameter setting/shift key), set (Parameter setting key: save the value after modification, change the monitoring object in the monitoring state), ▲ (parameter change/addition and subtraction key: use for setting value and parameter change, change the given frequency in the monitoring state), jog (jog operation key: press it to run inching, release it to stop running), and the definitions of the operation keys of different inverters are basically the same.
(6) Run the inverter to 50hz, and test the three-phase output voltage balance of the inverter u, v, w;
(7) After the power is off and there is no display at all, connect the motor line.

1.2 No-load operation of inverter with motor

(1) To set the basic rated parameters of the motor, the operating current of the frequency converter should be considered comprehensively.
(2) Set the output frequency, base frequency and torque characteristics of the inverter. The selection of v/f type includes items such as frequency, basic frequency and torque type. The frequency is the frequency at which the inverter-motor system can operate. Since the frequency of the inverter itself may be higher, when the allowable frequency of the motor is lower than the frequency of the inverter, it should be set according to the requirements of the motor and its load. The basic frequency is the dividing line between the constant power control and constant torque control of the motor by the frequency converter, and 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 diagram and load characteristics in the instruction manual of the inverter. There are multiple v/f curves for users to choose from for general-purpose inverters, and users should choose the appropriate v/f curve according to the nature of the load when using it.
In order to improve the low-speed performance of the inverter when it starts, so that the torque output by the motor can meet the requirements of starting the production load, the starting torque should be adjusted. In the frequency conversion speed regulation system of the asynchronous motor, the control of the torque is more complicated. In the low frequency band, since the influence of resistance and leakage reactance cannot be ignored, if the v/f is kept constant, the magnetic flux will decrease, thereby reducing the output torque of the motor. For this reason, the voltage should be properly compensated in the low frequency band to increase the torque. Generally, the inverter is manually set and compensated by the user. Powtran inverters provide users with two choices: 42 kinds of v/f boosting methods and automatic torque boosting.
(3) The frequency setting and operation control of the inverter are all keyboard mode, press the run key and stop key to observe whether the motor can start and stop normally.
(4) Familiarize yourself with the protection code when the inverter fails, observe the factory value of the thermal protection relay, observe the set value of the overload protection, and modify it if necessary. The user of the frequency converter can set the electronic thermal relay function of the frequency converter according to the instruction manual of the frequency converter. The threshold value of the electronic thermal relay is defined as the ratio of the rated current of 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 value of the threshold current of the inverter electronic thermal relay does not exceed the allowable output current of the inverter.
(5) Run the inverter to full frequency, test the output voltage and current, and see if they match the values monitored by the keyboard.

1.3 Test run with load

(1) Manually operate the running stop key on the inverter panel, observe the motor running and stopping process and monitor the inverter to see if there is any abnormality.
(2) If the inverter has an overcurrent protection action during the process of starting and stopping the motor, the acceleration and deceleration time should be reset. The acceleration of the motor during acceleration and deceleration depends on the acceleration torque, while the frequency change rate of the frequency converter during startup and braking is set by the user. If the moment of inertia of the motor or the load of the motor changes, when the speed is increased or decelerated according to the preset frequency change rate, the acceleration torque may be insufficient, which may cause the motor to stall, that is, the motor speed is not coordinated with the output frequency of the inverter, resulting in excessive current or overvoltage. Therefore, it is necessary to set the acceleration and deceleration time reasonably according to the moment of inertia of the motor and the load, so that the frequency change rate of the inverter can be coordinated with the motor speed change rate. The way to check whether this setting is reasonable is to first select the acceleration and deceleration time according to experience. If overcurrent occurs during startup, the acceleration time can be extended appropriately; if overcurrent occurs during braking, then Appropriately extend the deceleration time. On the other hand, the acceleration and deceleration time should not be set too long, which will affect the production efficiency, especially in the operating conditions of frequent starting and braking.
(3) If the inverter still has running faults, try to increase the protection value of the current, but the protection cannot be cancelled, and at least 10% to 20% of the protection margin should be left.
(4) If the inverter fails to operate, it should be replaced with a higher power inverter.
(5) If the motor driven by the frequency converter cannot reach the preset speed during startup, there may be two situations:
● The system has mechanical resonance, which can be judged from the sound of the motor running. The resonance point can be avoided by setting the frequency jump value. Generally, the frequency converter can set three jump points. When the v/f controlled frequency converter drives the asynchronous motor, in some frequency bands, the current and speed of the motor will oscillate, and in serious cases, the system cannot operate, and even the overcurrent protection occurs during the acceleration process, so that the motor cannot start normally. It is more serious when the load is light or the moment of inertia is small. Ordinary inverters are equipped with a frequency jump function, and the user can set the jump point and the jump width on the v/f curve according to the frequency point where the system oscillates. When the motor accelerates, it can automatically skip these frequency bands to ensure the normal operation of the system.
● The torque output capacity of the motor is not enough. Different brands of inverters have different factory parameter settings. Under the same conditions, the load capacity of the motor is different. The output efficiency is different, resulting in a difference in load capacity. For this case, increase the value of Torque Boost. If it cannot be achieved, use the manual torque boost function, do not set it too high, the temperature rise of the motor will increase at this time. For fan and pump loads, the curve value of derating torque should be reduced.

1.4 System debugging of inverter connected with host computer

After the setting is completed, if there is an upper computer in the system, connect the control line of the inverter directly to the control line of the upper computer, and change the operation mode of the inverter to terminal control. According to the needs of the upper 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 analog frequency signal sampling. If additional monitor headers are needed, select the monitor value of the analog output and adjust the range of the inverter output monitor value terminal.

2 Commonly used function parameters of the frequency converter

Because the functions of various types of inverters are different, and the names of the same function parameters are also inconsistent, for the convenience of description, this article takes the basic parameter names of Powtran inverters as an example. Since the basic parameters are almost common to all types of frequency converters, bypassing by analogy is completely possible.

2.1 Acceleration and deceleration time

The acceleration time is the time required for the output frequency to rise from 0 to the frequency, and the deceleration time is the time required for the frequency to drop to 0. Usually, the acceleration and deceleration time is determined by the rise and fall of the frequency setting signal. When the motor is accelerating, the rate of increase of the frequency setting must be limited to prevent overcurrent, and when the motor is decelerating, the rate of decrease must be limited to prevent overvoltage.
Acceleration time setting requirements: limit the acceleration current below the overcurrent capacity of the inverter, so as not to cause the inverter to trip due to overcurrent stall; the main points of the deceleration time setting are: to prevent the voltage of the smoothing filter circuit from being too high, and not to make the regeneration overvoltage This causes the inverter to trip. The acceleration and deceleration time can be calculated according to the load, but in the debugging, it is often used to set a longer acceleration and deceleration time according to the load and experience, and observe whether there is an over-current or over-voltage alarm by starting and stopping the motor; then gradually increase the acceleration and deceleration setting time. The acceleration and deceleration time can be determined by repeating the operation several times based on the principle that no alarm occurs during operation.