Low voltage inverter

How to choose the capacity of the frequency inverter?

The allowable current of the inverter has an inverse time relationship with the process time. For example, 1.2 (1.5)times the rated current can last for 1 minute, and 1.8 (2.0) times the rated current can last for 0.5 minutes. This means that the duration of the allowable overload current provided to the motor at any time must be within a limited

range. For the motor, the index of overload capacity is meaningful only during the start (acceleration) process. During operation, it is actually equivalent to not allowing overload.

The selection of the inverter capacity is an important and complicated issue. It is necessary to consider the matching of the inverter capacity and the motor capacity. A small capacity will affect the effective torque output of the motor, affect the normal operation of the system, and even damage the device. If the capacity is too large, the harmonic

component of the current will increase, which also increases the equipment investment.

Three steps of inverter capacity selection:

1.        Understand the nature of the load and the law of change, calculate the size of the load current or make a load current diagram I=f(t)

2.        Pre-select inverter capacity

3.        Check the pre-selected inverter, and check the overload capacity and starting capacity if necessary.

If all pass, the pre-selected inverter capacity is selected, otherwise, start from the second step until it passes.

To meet the requirements of production machinery, the smaller the capacity of the selected inverter, the more economical Selection basis for inverter capacity:

1.        Select the inverter capacity according to the motor current

The inverter is used to drive the asynchronous motor for speed regulation. After the asynchronous motor is determined, the inverter should usually be selected according to the rated current of the asynchronous motor, or according to the current value (maximum value) of the asynchronous motor in actual operation.

2.        Select the inverter according to the output voltage

The output voltage of the inverter can be selected according to the rated voltage of the motor. According to my country's standards, it can be divided into 220V and 400V. For a 3KV high-voltage motor, a 400V inverter can be used. An input transformer can be installed at the input of the inverter. Install an output transformer, reduce 3KV to 400V, and then increase the output of the inverter to 3KV.

3.        Select the inverter according to the output frequency

The maximum output frequency of the inverter varies greatly depending on the model, 50/60HZ, 120HZ, 240Hz, or higher. The 50/60HZ frequency inverter aims at speed regulation operation below the rated speed, and large-capacity general frequency inverters basically fall into this category.

The inverters with the highest output frequency exceeding the power frequency are mostly small-capacity inverters. In the area above 50/60Hz, the output voltage is unchanged and is a constant power characteristic. Attention should be paid to the torque reduction in the high-speed area.

However, lathes and other machine tools change the speed according to the diameter and material of the workpiece, and use them within the range of constant power. Using high speed at light load can improve productivity, but care should be taken not to exceed the maximum allowable speed of the motor and load.