Can the torque of the variable frequency drive motor be adjusted?

When the frequency converter is used for speed regulation, the output parameters of the marine motor will change, such as the common constant torque output below the fundamental frequency and the constant power output above the fundamental frequency.

Is the constant torque low-frequency adjustable? The answer is affirmative. All frequency converters basically have the function of adjusting the torque of marine motors, that is, adjusting the output torque of marine motors based on the setting of the power supply voltage and frequency ratio. This is a very practical problem in the application of variable frequency motors.

The selection of starting voltage is very important in the process of variable frequency speed regulation. The selection of starting voltage is directly related to the load nature of the marine motor, that is, it is directly related to the torque magnitude of the marine motor. If the starting voltage is too high, the direct consequence is severe heating of the marine motor, which is caused by the iron core of the marine motor being in an oversaturated state, resulting in severe heating of the winding; But if the starting voltage is set low, the torque corresponding to the marine motor at low frequencies will be too small, and the load capacity of the marine motor will be poor. From this perspective, the reasonable selection of starting voltage is the key to variable frequency speed regulation, which directly determines the torque of marine motors at low frequencies.

For the low-frequency and low-voltage heating problem of marine motors, we can understand it through the characteristics of 60Hz motors and 50Hz no-load operation. Many marine motor manufacturers in our country do not have a 60Hz power supply. When ordering 60Hz products, they can only use a 50Hz power supply for testing. In order to ensure the safety of the performance of marine motors, it is necessary to reduce and adjust the voltage input to the marine motors. The rated voltage corresponding to 60Hz divided by 1.2 is used as the input voltage for 50Hz power supply testing. If the voltage is not reduced, the current of the marine motor will be particularly high due to the power frequency, causing the marine motor to heat up or even burn out.

In order to limit the overload of marine motors, the frequency converter has a torque limiting function. The limitation of torque for marine motors is actually to limit the overcurrent of the frequency converter, usually set at 1.2 to 1.8 times the rated current of the frequency converter. In order to ensure that the torque does not exceed the set value, the method of reducing the frequency in electric state and increasing the frequency in braking state is adopted, but the relative variation range is controlled within 5Hz.