Inverter introduction

First, the choice of motor

First, according to the average power and maximum power required when the load is moving, the motor power should be converted to the motor shaft side (reducing device such as reducer, pulley, etc.), and the motor's overload capacity should also be considered. Motor manufacturers can provide motor torque characteristics, and the motor characteristics will change at different temperatures.

By the way, the order of selection is, of course, the selection of the motor and the selection of the frequency converter according to the motor, since the ultimate purpose of the control is not the frequency converter nor the motor but the mechanical load.

Second, the choice of frequency converter

The first point that should be emphasized is that current selection should be based on current. For the general load, the inverter can be selected according to the rated current of the motor, that is, the rated current of the inverter (that is, the maximum continuous operating current in the conventional environment) is greater than the rated current of the motor. However, we must consider the emergence of extreme conditions. Therefore, the inverter needs to be able to provide short-time overload current. (Note: The motor current is determined by the mechanical load.) The inverter has an overload current curve which is an inverse time curve and describes the relationship between overload current and time. This is the inverter manufacturers often say that the overload capacity can reach 150% of the rated current for 2 seconds and 180% of the rated current for 2 seconds. This is actually a curve. Therefore, as long as the current curve of the motor is within the overload current curve of the inverter, it is the correct selection. This is why sometimes the inverter power is greater than the motor power 1st or 2nd gear (such as lifting applications), and sometimes the low-power inverter can still drive high-power motors (such as conveyor belts).

Another must pay attention to: In abnormal circumstances, such as high altitude, high ambient temperature (for example, greater than 50 degrees less than 60 degrees environment), side-by-side installation (some inverters installed side by side without derating, some to derating, according to the frequency conversion In case of design decision) etc., consider the derating of the frequency converter. This information is available from inverter manufacturers.

The result is: The rated power of the frequency converter may be greater than the power of the electrical machinery, also may be smaller than the electrical machinery power, in fact the electrical frequency converter is chosen according to the mechanical load to decide.

Conclusion: The final basis for the selection of the inverter is that the current curve of the inverter covers the current curve of the mechanical load.

Third, Y-type motor and variable frequency motor

Y-type motor, it should be ordinary asynchronous motor (in the impression, is not very sure).

The fundamental function of the frequency converter is to change the frequency of the power supply, thereby changing the speed of the motor. Therefore, in theory, no matter what the motor, as long as you can change the frequency of speed control, you can use the inverter.

Variable frequency motors have a special design and are more suitable for frequency conversion. Therefore, there is not an independent fan that is the so-called variable frequency motor.

When an ordinary asynchronous motor is controlled by a frequency converter, it should be noted that:

1. When the frequency is low (usually less than 25hz), since the motor uses a coaxial fan, the heat dissipation effect at low speeds will be very poor. After the motor heats up, the torque characteristics become soft, causing problems such as unstable speed and large current.

2, high frequency (usually greater than 50hz), depends on whether the motor can withstand high speed brought about such as bearing heat, poor balance and other issues.

3, there are many problems that I can not think of it. So it seems that inverter control ordinary asynchronous motor, depends on the working requirements of the motor. Of course, if the motor does not operate in low frequency or high frequency for a long time, it is no problem to use the inverter control. This kind of application can be seen everywhere.