1. What is a frequency converter?
The frequency converter is a power control device that uses the on-off effect of power semiconductor devices to convert the power frequency power supply into another frequency.
2. What is the difference between PWM and PAM?
PWM is the abbreviation of English Pulse Width Modulation, which changes the pulse width of the pulse train according to a certain law to adjust the output and waveform.
PAM is the abbreviation of Pulse Amplitude Modulation, which is a modulation method that changes the pulse amplitude of the pulse train according to a certain law to adjust the output value and waveform.
3. What is the difference between voltage type and current type?
The main circuit of the inverter can be roughly divided into two categories: the voltage type is the frequency converter that converts the DC of the voltage source into AC, and the filter of the DC circuit is the capacitor; The current type is a frequency converter that converts the DC of the current source into AC, and its DC loop filtering is inductor.
4. Why does the voltage and current of the inverter change proportionally?
The torque of the asynchronous motor is generated by the interaction between the magnetic flux of the motor and the current flowing in the rotor, at the rated frequency, if the voltage is certain and only reduces the frequency, then the magnetic flux is too large, the magnetic circuit is saturated, and the motor will be burned in severe cases. Therefore, the frequency and voltage should be changed proportionally, that is, the output voltage of the inverter should be controlled while changing the frequency, so that the magnetic flux of the motor can be maintained to avoid the occurrence of weak magnetic and magnetic saturation. This control method is mostly used in energy-saving inverters such as fans and pumps.
5. When the motor is driven by power frequency power supply, the current increases when the voltage drops; For inverter drives, if the voltage also drops when the frequency drops, does the current increase?
When the frequency drops (low speed), if the same power is output, the current increases, but under the condition of a certain torque, the current is almost unchanged.
6. When the frequency converter is used, how is the starting current and starting torque of the motor?
Using the inverter operation, the frequency and voltage are increased accordingly as the motor accelerates, and the starting current is limited to less than 150% of the rated current (125%~200% depending on the model). When starting directly with power frequency power supply, the starting current is 6~7 times, therefore, mechanical and electrical impact will occur. The use of frequency converter transmission can start smoothly (starting time becomes longer). The starting current is 1.2~1.5 times of the rated current, and the starting torque is 70%~120% of the rated torque; For frequency converters with automatic torque enhancement, the starting torque is more than 100%, and it can be started with full load.
7. What does V/f mode mean?
The voltage V also decreases proportionally when the frequency drops, a question explained in Answer 4. The ratio of V to f is predetermined taking into account the motor characteristics, and usually several characteristics are stored in the controller's memory device (ROM), which can be selected with a switch or dial
8. When V and f are changed proportionally, how does the torque of the motor change?
When the frequency drops, the voltage is completely proportionalized, so because the AC impedance becomes smaller but the DC resistance does not change, the ground torque generated at low speed tends to decrease. Therefore, given V/f at low frequencies, the output voltage should be increased a little in order to obtain a certain starting torque, and this compensation is called enhanced starting. It can be achieved in a variety of ways, such as automating methods, selecting V/f mode, or adjusting potentiometers
9. It is written in the manual that the variable speed range is 60~6Hz, that is, 10:1, so there is no output power below 6Hz?
Below 6Hz, the power can still be output, but according to the temperature rise of the motor and the size of the starting torque, the minimum use frequency is about 6Hz, at this time the motor can output the rated torque without causing serious heating problems. The actual output frequency (starting frequency) of the inverter is 0.5~3Hz according to the model.
10. For the general motor combination is above 60Hz, it also requires a certain torque, is it possible?
Normally not. Above 60Hz (there are also modes above 50Hz) the voltage remains unchanged, generally constant power characteristics, in high speed requirements for the same torque, must pay attention to the choice of motor and inverter capacity.