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The frequency converter is mainly composed of rectifier (AC DC converter), filter, re rectification (DC AC converter), brake unit, drive unit, detection unit, micro processing unit and so on.

1. 电机的旋转速度为什么能够自由地改变？

Why is the rotational speed of the 1. motor freely changed?

Motor rotational speed unit: r/min rotation per minute, also can be expressed as rpm.

For example: 2 pole motor 50Hz 3000 [r/min]

4极电机 50Hz 1500 [r/min]

4 pole motor 50Hz 1500 [r/min]

Conclusion: the rotation speed of the motor is proportional to the frequency The rotational speed of induction type AC motor (hereafter referred to as motor) approximately determines the pole number and frequency of the motor. The working principle of the motor determines that the number of poles of the motor is fixed. Since the pole value is not a continuous value (multiples of 2, such as the number of poles 2, 4, 6), it is generally uncomfortable and adjusts the speed of the motor by changing the value.

In addition, the frequency can be adjusted outside the motor and then supplied to the motor, so that the rotation speed of the motor can be controlled freely.

Therefore, the frequency converter with the purpose of controlling the frequency is the preferred equipment for the motor speed control equipment.

n = 60f/p

N = 60f/p

n: 同步速度

N: sync speed

f: 电源频率

F: power frequency

p: 电机极对数

Pole count of p: motor

Conclusion: changing frequency and voltage is the best method of motor control

If the frequency is changed without changing the voltage, the motor will be burned out due to over voltage (Guo Lici) when the frequency is reduced. Therefore, the converter must change the voltage while changing the frequency. When the output frequency is above the rated frequency, the voltage can not continue to increase, and the maximum is only equal to the rated voltage of the motor.

For example: in order to rotate the motor speed by half, the inverter output frequency from 50Hz to 25Hz, then the inverter output voltage needs to change from 400V to about 200V

2. 当电机的旋转速度（频率）改变时，其输出转矩会怎样？

2. what is the output torque when the rotation speed (frequency) of the motor is changed?

The starting torque and the maximum torque of the inverter are less than that of the direct power supply

When the motor is powered by the power frequency, the starting and accelerating impact is great, and when the inverter is used, the impact will be weaker. The direct starting of the power frequency will produce a large starting starting current. When the inverter is used, the output voltage and frequency of the inverter are gradually added to the motor, so the starting current and impact of the motor are smaller.

Generally, the torque generated by the motor decreases with the decrease of the frequency (the speed decreases). The reduced actual data will be explained in some frequency converter manuals.

By using the flux vector control inverter, the torque of the motor is improved at low speed, and even in the low-speed region, the motor can also output enough torque.

3. 当变频器调速到大于50Hz频率时，电机的输出转矩将降低

3. when the inverter speed is greater than 50Hz frequency, the motor output torque will be reduced

The normal motor is designed and manufactured according to the 50Hz voltage, and its rated torque is also given in this voltage range. Therefore, the speed regulation under rated frequency is called constant torque speed regulation (T=Te, P<=Pe)

When the inverter output frequency is greater than 50Hz frequency, the torque generated by the motor will decline linearly with the frequency.

When the motor is running at a frequency greater than 50Hz, the magnitude of the motor load must be taken into account to prevent the motor output torque from being insufficient.

For example, the torque generated by the motor at 100Hz will be reduced to about 1/2 when the torque is 50Hz.

Therefore, the speed regulation above the rated frequency is called constant power speed regulation (P=Ue*Ie)

4. 变频器50Hz以上的应用情况

Application of 4. inverter over 50Hz

As you know, for a specific motor, its rated voltage and rated current are constant.

Such as inverter and motor ratings are: 15kW/380V/30A, the motor can work more than 50Hz.

When the speed is 50Hz, the output voltage of the inverter is 380V, the current is 30A. when the output frequency increased to 60Hz, the maximum output voltage and current of inverter is only for 380V/30A. obviously the same output power. So we called the constant power speed.

How about the torque at this moment?

Because the P=wT (w: angular speed, T: torque). Because the P does not change, w increases, so the torque will be reduced accordingly.

We can look at it another way:

The stator voltage of the motor is U = E + I*R (I is current, R is electronic resistance, and E is inductive potential)

It can be seen that E is invariant when U and I are invariant

And E = k*f*X, (k: constant, f: frequency, X: flux), so when f is 50-->60Hz, X will decrease accordingly

For the motor, T=K*I*X, (K: constant, I: current, X: flux), the torque T decreases with the decrease of the flux X

At the same time, less than 50Hz, because I*R is very small, so the U/f=E/f at constant flux (X) is a constant torque and current is proportional to T. This is why usually used to describe the flow capacity of the inverter (torque) and overload ability. Called constant torque speed (rated current maximum torque constant -- > unchanged)

Conclusion: when the output frequency of the inverter increases from 50Hz, the output torque of the motor will decrease

5. 其他和输出转矩有关的因素

5. other factors related to output torque

Heating and cooling capacity determine the output current capacity of the inverter, thus affecting the output torque capacity of the inverter.

Carrier frequency: the rated current of the general frequency converter is the highest carrier frequency, the maximum environmental temperature can guarantee the value of continuous output. Reduce the carrier frequency, the motor current will not be affected. But the heating of components will decrease.

Ambient temperature: just like, it doesn't increase the protection current value of the transducer because of the low temperature around it

Altitude: elevation increases, has an impact on the heat dissipation and insulation performance. General 1000m below can not be considered. The above 1000 meters drop capacity 5% can be.