1. Selection of V/f type
The V/f type selection includes the maximum frequency, basic frequency, and torque type. The maximum frequency is the highest frequency at which the inverter-motor system can operate. Since the inverter's own maximum frequency may be higher, if the motor's permissible maximum frequency is lower than the inverter's maximum frequency, it should be set according to the requirements of the motor and its load. The basic frequency is the dividing line between constant power control and constant torque control of the motor by the inverter , and should be set according to the motor's rated voltage. The torque type refers to whether the load is a constant torque load or a variable torque load. Users should select one type based on the V/f type diagram and load characteristics in the inverter's instruction manual. Based on the actual situation of the motor and actual requirements, the maximum frequency is set to 83.4Hz , and the basic frequency is set to the industrial frequency of 50Hz. Load type: below 50Hz is a constant torque load, and 50～ 83.4Hz is a constant power load.
2. How to adjust the starting torque
Adjusting the starting torque is to improve the low-speed performance of the frequency converter during startup, ensuring that the motor output torque meets production startup requirements. In asynchronous motor frequency conversion speed control systems, torque control is complex. In the low-frequency range, the effects of resistance and leakage reactance are not negligible. If V/f 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. However, the influence of leakage impedance is not only related to frequency but also to the magnitude of the motor current, making accurate compensation very difficult. In recent years, some frequency converters with self-compensation capabilities have been developed abroad, but the required calculations are extensive, and both the hardware and software are complex. Therefore, most frequency converters require manual compensation settings by the user.
3. How to set acceleration and deceleration times?
The frequency change rate of the inverter during start-up and braking is set by the user. If the motor's moment of inertia J and load change according to the preset frequency change rate for acceleration or deceleration, insufficient acceleration torque may occur, leading to motor stall. This means the motor speed and the inverter's output frequency are not coordinated, resulting in overcurrent or overvoltage. Therefore, the acceleration and deceleration times need to be set reasonably based on the motor's moment of inertia and load to ensure the inverter's frequency change rate matches the motor's speed change rate. The method to check the reasonableness of this setting is to select the acceleration and deceleration times empirically. If overcurrent occurs during startup, the acceleration time can be appropriately extended; if overcurrent occurs during braking, the deceleration time should be appropriately extended. On the other hand, the acceleration and deceleration times should not be set too long, otherwise it will affect production efficiency, especially in cases of frequent start-up and braking.
4. Frequency jump
When a V/f controlled frequency converter drives an asynchronous motor, the motor's current and speed may oscillate in certain frequency ranges. In severe cases, this can prevent the system from operating, or even trigger overcurrent protection during acceleration, preventing the motor from starting normally. This is especially problematic when the motor is lightly loaded or its rotational speed is low. Most frequency converters are equipped with a frequency skipping function. Users can set the skipping point and its width on the V/f curve based on the frequency points where the system oscillates. When the motor accelerates, it can automatically skip these frequency ranges, ensuring normal system operation.
5. Overload rate setting
This setting is used for overload protection of the frequency converter and motor. When the output current of the frequency converter exceeds the overload rate setting value and the OL setting value determined by the rated current of the motor, the frequency converter will perform overload protection (OL) with inverse time characteristic. When the overload protection is activated, the frequency converter stops outputting.
6. Inputting motor parameters
Some of the parameter input items for a frequency converter are basic motor parameters, such as motor power, rated voltage, rated current, rated speed, and number of poles. These parameters are crucial as they directly affect the proper functioning of some of the frequency converter's protection functions. It is essential to input the correct parameters based on the actual motor specifications to ensure the normal operation of the frequency converter.
