I. No-load power-on test of Mitsubishi frequency converter
1. Ground the grounding terminal of the Mitsubishi inverter.
2. Connect the power input terminal of the Mitsubishi inverter to the power supply via a leakage protection switch.
3. Check if the Mitsubishi inverter display window is normal at the factory. If it is incorrect, it should be reset; otherwise, request a return or replacement.
4. Familiarize yourself with the inverter's operation keys. Most inverters have six keys: RUN, STOP, PROG, DATAPENTER, UP, ▲, and DOWN. The definitions of these keys are generally the same across different inverters. In addition, some inverters may have function keys such as MONITOR PISPLAY, RESET, JOG, and SHIFT.
II. Mitsubishi inverter running with motor under no-load
1. When setting the motor's power and number of poles, the inverter's operating current must be taken into account.
2. Set the maximum output frequency, base frequency, and torque characteristics of the Mitsubishi inverter. General-purpose inverters offer multiple VPf curves for users to choose from; users should select the appropriate VPf curve based on the nature of the load. For fan and pump loads, the inverter's torque operation code should be set to variable torque and reduced torque operation characteristics. To improve the inverter's low-speed performance during startup and ensure the motor's output torque meets the startup requirements of the production load, the starting torque needs to be adjusted. Torque control is more complex in asynchronous motor variable frequency speed control systems. In the low-frequency range, the effects of resistance and leakage reactance are not negligible; if VPf is kept constant, the magnetic flux will decrease, thus reducing the motor's output torque. Therefore, appropriate voltage compensation is needed in the low-frequency range to increase torque. Generally, inverter compensation is manually set by the user.
3. Set the Mitsubishi inverter to its built-in keyboard operation mode, press the run button and stop button, and observe whether the motor can start and stop normally.
4. Familiarize yourself with the protection codes when a Mitsubishi inverter malfunctions. Observe the factory default values of the thermal protection relay and the overload protection settings, and modify them as needed. Users of Mitsubishi inverters can set the electronic thermal relay function according to the inverter's instruction manual. When the output current of the Mitsubishi inverter exceeds its allowable current, the overcurrent protection will cut off the inverter's output. Therefore, the maximum threshold value of the Mitsubishi inverter's electronic thermal relay should not exceed the inverter's maximum allowable output current.
III. Load-bearing test operation of Mitsubishi inverters
1. Manually operate the run/stop button on the Mitsubishi inverter panel, observe the motor running and stopping process and the inverter's display window, and check for any abnormal phenomena.
2. If the Mitsubishi inverter trips its overcurrent protection during the start-stop process of the motor, the acceleration/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 Mitsubishi inverter during start-up and braking is set by the user. If the motor's moment of inertia or load changes, insufficient acceleration torque may occur when accelerating or decelerating according to the preset frequency change rate, leading to motor stall. This means the motor speed and the inverter's output frequency are not synchronized, resulting in overcurrent or overvoltage. Therefore, the acceleration and deceleration times need to be set appropriately based on the motor's moment of inertia and load to ensure that the frequency change rate of the Mitsubishi inverter matches the motor speed change rate.
To check if this setting is reasonable, first select and set the acceleration and deceleration times based on experience. If overcurrent occurs during startup, the acceleration time can be appropriately extended; if overcurrent occurs during braking, the deceleration time can be appropriately extended. On the other hand, the acceleration and deceleration times should not be set too long, as this will affect production efficiency, especially during frequent starts and stops.
3. If the Mitsubishi inverter continues to trip within the specified time, the start-stop operating curve should be changed from a straight line to an S-shaped, U-shaped, or S-shaped/reverse U-shaped curve. When the motor load inertia is large, a longer start-stop time should be used, and the operating curve type should be set according to its load characteristics.
4. If the Mitsubishi inverter still malfunctions, try increasing the maximum current protection value, but do not disable the protection; maintain a protection margin of at least 10% to 20%. (Imported pumps and valves)
5. If the Mitsubishi inverter malfunctions, it should be replaced with an inverter of a higher power rating.
6. If the Mitsubishi inverter fails to reach the preset speed during startup, there may be two possibilities:
(1) The system is experiencing electromechanical resonance, which can be determined by the sound of the motor running.
By setting frequency jump values, resonance points can be avoided. Most frequency inverters can be set with three jump points. When a Mitsubishi frequency inverter controlled by VPf drives an asynchronous motor, the motor's current and speed may oscillate in certain frequency ranges. In severe cases, the system may fail to operate, or even trigger overcurrent protection during acceleration, preventing the motor from starting normally. This is more pronounced when the motor is lightly loaded or has low rotational inertia. Ordinary frequency inverters are equipped with a frequency skipping function. Users can set the skipping point and skipping width on the VPf curve according to the frequency points where the system oscillates. When the motor accelerates, it can automatically skip these frequency ranges, ensuring normal system operation.
(2) Insufficient torque output capability of the motor. Different brands of frequency converters have different factory parameter settings, resulting in different load capacities under the same conditions. This may also be due to different frequency converter control methods, causing differences in motor load capacity; or differences in system output efficiency, leading to variations in load capacity. In this case, the torque boost value can be increased. If this is insufficient, the manual torque boost function can be used, but it should not be set too high, as this will increase the motor temperature rise. If this still does not work, a new control method should be used. For example, Hitachi frequency converters use a constant VPf ratio method. If the starting requirement is not met, a sensorless space vector control method should be used, which has a greater torque output capability. For fan and pump loads, the torque reduction curve value should be reduced.
IV. System Debugging by Connecting the Mitsubishi Inverter to the Host Computer: After completing the basic manual settings, if the system includes a host computer, connect the Mitsubishi inverter's control lines directly to the host computer's control lines, and change the Mitsubishi inverter's operating mode to terminal control. Adjust the range of the Mitsubishi inverter's receiving frequency signal terminal (0-5V or 0-10V) and the inverter's response speed to analog frequency signal sampling according to the needs of the host computer system. If additional monitoring meters are required, select the analog output monitoring quantity and adjust the range of the Mitsubishi inverter's output monitoring quantity terminal.
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