1.What is a frequency converter?
A frequency converter is an electrical energy control device that uses the on-off action of an electrical power semiconductor device to convert a power frequency power supply into another frequency, it can realize the functions of soft start, variable frequency speed regulation, improving running precision, changing power factor, over-current/over-voltage/over-load protection, etc. .
2.The difference between PWM and Pam
PWM (Pulse Width Modulation) is an abbreviation of Pulse Width Modulation in English. It is a Modulation method to adjust the output and waveform by changing the Pulse Width of Pulse train according to certain rules. Pam (Pulse Amplitude Modulation) is an abbreviation of Pulse Amplitude Modulation, which is a Modulation method to adjust the output value and waveform by changing the Pulse Amplitude of the Pulse train according to certain rules.
3.Why does the voltage of the converter change in proportion to the frequency?
The electromagnetic torque of any motor is the result of the interaction of current and magnetic flux, current is not allowed to exceed the rated value, otherwise it will cause motor heating. Therefore, if the magnetic flux decreases, the electromagnetic torque will also be reduced, resulting in a reduction in carrying capacity.
From the formula E = 4.44 * k * f * N * φ, it can be seen that the magnetic circuit of the motor changes in a considerable range with the operating frequency FX when the speed is regulated by frequency conversion, the waveform of excitation current is seriously distorted, and the peak current is very high.
Therefore, frequency and voltage to be proportional to change, that is, change the frequency while controlling the inverter output voltage, so that the motor flux to maintain a certain degree, to avoid weak magnetic and magnetic saturation phenomenon. This kind of control method is mostly used in the fan, pump type energy-saving inverter.
4.How does the torque of the motor change when V and F are changed proportionally?
If the voltage is reduced in proportion to the decrease in frequency, then the DC resistance will not change as the AC impedance will decrease, and the ground torque will tend to decrease at low speeds. Therefore, given v/F at low frequencies, the output voltage must be increased to obtain a certain starting torque, this compensation is called enhanced starting. Various methods can be used to achieve, there are automatic methods, select the V/F mode or adjust the potentiometer and other methods.
5.It says on the manual that the speed range is 60-6Hz, or 10:1. Is there no power output below 6Hz?
It can output power below 6HZ, but the lowest frequency is about 6HZ according to the temperature rise and the starting torque of the motor. The actual output frequency (starting frequency) of the inverter is 0.5-3Hz according to the type of machine.
6.What do you mean by Open Loop?
To use the motor device speed detector (PG) , the actual speed feedback to the control device for control, called“Closed Loop”, not PG operation is called“Open Loop”. Most of the general-purpose inverters are open-loop, and some of them can be used for PG feedback. The speed sensorless closed-loop control is based on the established mathematical model to calculate the actual speed of the motor according to the flux, which is equivalent to a virtual speed sensor to form a closed-loop control.
7.What happens when the actual speed deviates from the given speed?
Open-loop, even if the inverter output a given frequency, the motor with a load when running, motor speed in the range of rated slip rate (1% -5%) change. The frequency converter (optional) with PG feedback function can be used for the situation that the speed regulation precision is high, even the load variation also needs to operate under the given speed.
8.If you use a motor with a PG, can you improve speed accuracy with feedback?
The frequency converter with PG feedback function can improve the precision. But the value of the speed precision depends on the precision of PG itself and the resolution of the inverter output frequency.
9.What does stall prevention mean?
If the given acceleration time is too short, the frequency of the inverter output changes much more than the speed (angular frequency) of the change, the inverter will flow over the current trip, stop operation, this is called stall. In order to prevent the stall to keep the motor running, it is necessary to check the size of the current frequency control. When the acceleration current is too large, slow down the acceleration rate. The same is true when decelerating. The combination of the two is the stall function.
10.What's the point of having an acceleration time and deceleration time that can be given separately, and an acceleration and deceleration time that can be given together?
Acceleration and deceleration can be given separately, which is suitable for the situation of short-time acceleration and slow deceleration, or for the situation of small machine tools that need to be strictly given production time, but for the situation of fan drive, etc. , the acceleration and deceleration time are both longer, and the acceleration time and deceleration time can be given together.
11.What are the protection functions of the inverter?
The protective functions can be divided into the following two categories:
(1) after detecting the abnormal state, it automatically carries on the correction action, such as the over-current stall prevention and the regenerated over-voltage stall prevention.
(2) the semiconductor device PWM control signal is blocked after the abnormality is detected to make the motor stop automatically. Such as over-current cut-off, regenerative over-voltage cut-off, semiconductor cooling fan overheating and transient power outage protection.
12.Why does the protection function of the inverter operate when the load is connected with a clutch?
When the load is connected by the clutch, the motor changes rapidly from no-load state to large slip rate area at the moment of connection.
13.Why is it that when a large motor starts up in the same factory, the converter stops?
When the motor starts, the starting current corresponding to the capacity will flow through. The transformer on the stator side of the motor produces a voltage drop, which has a great influence when the motor capacity is large, the inverter connected to the same transformer will make the judgment of undervoltage or instantaneous stop, so sometimes the protection function (IPE) action, causing the shutdown.
14.Do not use soft start, will the motor directly into a fixed frequency inverter can?
At very low frequencies it is possible, but at a given high frequency the conditions are similar to those of a direct-start power supply. Will flow too large starting current (6 -7 times the rated current) , due to the inverter cut off the over-current, the motor can not start.
15.Can the inverter be used to drive a single-phase motor? Can I use a single-phase power supply?
Basically unusable. For the single-phase motor with speed regulator switch start, the auxiliary windings will be burned in the speed regulation range below the operating point; for the capacitor start or capacitor operation mode, the capacitor explosion will be induced. Inverter power supply is usually 3-phase, but for small capacity, but also with single-phase power operation of the machine.
16.You want to use a frequency converter to drive a motor with a capacitor to improve the power factor, but the motor is not moving. Please explain why
The current of the inverter flows into the capacitor used to improve the power factor, because its charging current causes the inverter to overcurrent (Oct) , so it can not start, as a countermeasure, please remove the capacitor and run, as for improving the power factor, it is effective to connect AC reactor at the input side of inverter.
17.There is a cooling fan in the inverter. What is the direction of the wind? What happens if the fan breaks?
For small capacity also have no cooling fan type. There are fans of the machine, the direction of the wind is from the bottom up, so the installation of the inverter place, the upper and lower do not place hindrance suction, exhaust mechanical equipment. Also, do not place above the frequency converter parts such as fear of heat. When the fan fails, it is protected by the fan stop detection or the overheat detection on the cooling fan.
18.Frequency converter accessories sinusoidal filter what role?
The sinusoidal filter allows the inverter to operate with a longer motor cable and is also suitable for circuits with an intermediate transformer between the inverter and the motor.
19.Why Can't inverters be used as inverter power?
The whole circuit of frequency conversion power supply is composed of AC, DC, AC and filter, so its output voltage and current waveform is pure sine wave, very close to the ideal AC power supply. It can output the grid voltage and frequency of any country in the world. The frequency converter is composed of AC-DC-AC (modulation wave) and other circuits, the standard name for the frequency converter governor. Its output voltage waveform for pulse square wave, and harmonic components, voltage and frequency at the same time proportional changes, can not be adjusted separately, does not meet the requirements of AC power supply. In principle can not do the use of power supply, generally only used for three-phase induction motor speed.
20.What is the frequency converter interference and how to deal with the general?
Mode of transmission:
(1) radiation interference
(2) conduction interference
Anti-interference measures: for interference signals transmitted by radiation, mainly through wiring and to the radioactive sources and the lines to be jammed by the way of shielding to weaken. For the interference signal propagated through the line, it is mainly processed by adding filters, reactors or magnetic rings on the input and output sides of the inverter. The specific methods and points for attention are as follows:
(1) the signal line and the power line should be crossed vertically or grooved wiring.
(2) do not use wires of different metals to connect each other.
(3) the shielding tube (layer) shall be reliably grounded and shall be continuously and reliably grounded throughout its length.
(4) the twisted pair shielded cable should be used in the signal circuit.
(5) shield layer ground point as far as possible away from the inverter, and with the inverter ground point separate.
(6) the magnetic ring can be used on the input power line and the output line of the inverter. The method is that the input line is wound 4 times in the same direction, and the output line is wound 3 times in the same direction. Take care when winding, try to put the magnetic loop close to the inverter.
(7) generally, shielding and other anti-jamming measures can be adopted for the equipment to be interfered with.
Source: internet (for study only, intrusion and deletion)
