Inverter is the use of power semiconductor devices on and off the role of the power frequency power supply will be converted to another frequency of electrical energy control devices.
2, what is the difference between PWM and PAM?
PWM is the English Pulse Width Modulation (Pulse Width Modulation) abbreviation, according to a certain law to change the pulse width of the pulse train, in order to regulate the amount of output and the waveform of a value-adjusting method.
PAM is the English Pulse Amplitude Modulation (Pulse Amplitude Modulation) abbreviation, is to change the pulse amplitude of the pulse train according to a certain law, in order to regulate the value of the output and the waveform of a modulation mode.
3. What is the difference between voltage type and current type?
The main circuit of inverter can be divided into two categories: voltage-type is the voltage source of DC converted to AC inverter, DC circuit filtering is capacitive; current-type is the current source of DC converted to AC inverter, the DC circuit filter stone inductor.
4, why the inverter voltage and current change proportionally?
The torque of the asynchronous motor is the interaction between the motor flux and the current flowing in the rotor and produce, at the rated frequency, if the voltage is certain and only reduce the frequency, then the flux will be too large, the magnetic circuit is saturated, and in severe cases, the motor will be burned. Therefore, the frequency and voltage should be changed proportionally, that is, to change the frequency while controlling the output voltage of the inverter, so that the magnetic flux of the motor to maintain a certain amount to avoid weak magnetism and magnetic saturation phenomenon. This control method is mostly used for fans, pumps, energy-saving inverter.
5, the motor using industrial frequency power supply drive, the voltage decreases the current increases; for inverter drive, if the frequency decreases when the voltage also decreases, then the current increases?
When the frequency drops (low speed), the current increases if the same power is output, but under the condition of certain torque, the current is almost unchanged.
6, the use of inverter operation, the motor starting current, starting torque how?
With inverter operation, as the motor accelerates, the frequency and voltage are increased accordingly, and the starting current is limited to below 150% of the rated current (125%~200% depending on the type of machine). When starting directly with industrial frequency power supply, the starting current is 6~7 times, therefore, it will produce mechanical and electrical shock. The use of inverter drive can be started 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 the frequency converter with automatic torque enhancement function, the starting torque is more than 100%, and it can be used to start with full load.
7. What is the meaning of V/f mode?
When the frequency decreases, the voltage V also decreases proportionally, which has been explained in answer 4. The proportionality between V and f is pre-determined by considering the characteristics of the motor, and several characteristics are usually stored in the controller's ROM, which can be selected by using switches or dials
8. How does the motor's torque change when V and f are changed proportionally?
When the frequency decreases, the voltage decreases proportionally, and the AC impedance decreases while the DC resistance remains the same, resulting in a tendency to reduce the torque at low speeds. Therefore, in the low-frequency given V / f, to make the output voltage to improve some in order to obtain a certain starting torque, this compensation is called enhanced starting. This compensation is called enhanced starting. It can be realized by various methods, such as automatic method, selecting V/f mode or adjusting potentiometer etc.
9. In the manual, it is written that the speed range is 60~6Hz, i.e., 10:1, so there is no output power below 6Hz?
Below 6Hz can still output power, but according to the motor temperature rise and the size of the starting torque and other conditions, the minimum frequency of about 6Hz, when the motor can output the rated torque without causing serious heating problems. The actual output frequency of frequency converter (starting frequency) is 0.5~3Hz according to the machine type.
10, for the general motor combination is above 60Hz and also requires a certain torque, is it possible?
Not normally. In 60Hz or more (there are also 50Hz or more mode) voltage is unchanged, generally constant power characteristics, in the high-speed requirements of the same torque, we must pay attention to the motor and inverter capacity selection.
11, the so-called open loop is what?
To the use of the motor device set speed detector (PG), the actual speed feedback to the control device for control, known as "closed-loop", do not use PG operation is called "open-loop". General-purpose frequency converter is mostly open-loop mode, but there are also some models can be PG feedback using options.
12, the actual speed for the given speed deviation how to do?
Open loop, even if the frequency converter outputs a given frequency, the motor is running with a load, the speed of the motor in the range of the rated rate of rotation (1%~5%) change. For the requirement of high accuracy of speed regulation, even if the load change is also required to run at a speed close to the given occasion, can be used with PG feedback function of the frequency converter (optional).
13, if the motor with PG, can the speed accuracy be improved after feedback?
Frequency inverter with PG feedback function can improve the accuracy. But the accuracy of speed depends on the accuracy of PG itself and the resolution of inverter output frequency.
14. What is the meaning of stall prevention function?
If the given acceleration time is too short, the output frequency change of inverter is much more than the change of rotational speed (electric angle frequency), the inverter will be tripped due to the flow of over-current, and the operation will stop, which is called stall. In order to prevent stalling the motor to continue to run, it is necessary to detect the size of the current for frequency control. When the acceleration current is too large, the acceleration rate is slowed down appropriately. The same is true for deceleration. The combination of the two is the stall function.
15, there are acceleration time and deceleration time can be given separately, and acceleration and deceleration time *** with the given models, what is the significance of this?
Acceleration and deceleration can be given separately for the type of machine, for a short period of time to accelerate, slow deceleration occasions, or for small machine tools need to be strictly given to the production of beat time occasions is appropriate, but for the fan drive occasions such as acceleration and deceleration time is longer, acceleration time and deceleration time can be given **** the same.
16, what is regenerative braking?
If the command frequency is lowered during the operation of the motor, the motor becomes an asynchronous generator and operates as a brake, which is called regenerative (electrical) braking.
17. Is it possible to get more braking power?
The regenerated energy from the motor is stored in the filter capacitor of the inverter, due to the capacity of the capacitor and the relationship between the voltage, the regenerative braking force of the general-purpose inverter is about 10% to 20% of the rated torque. Such as the use of optional parts of the braking unit, can reach 50% to 100%.
18, please explain the inverter protection function?
The protection function can be divided into the following two categories:
(1) Detecting the abnormal state and then automatically correct the action, such as overcurrent stall prevention, regenerative overvoltage stall prevention.
(2) After detecting anomalies, blocking the power semiconductor device PWM control signal, so that the motor automatically stop. Such as over-current cut-off, regenerative over-voltage cut-off, semiconductor cooling fan overheating and instantaneous blackout protection.
19, why use the clutch continuous load, the inverter protection function on the action?
When connecting loads with clutches, at the moment of connection, the motor changes drastically from no-load state to the area of large turnover rate, and the large current flowing through causes the inverter to trip on overcurrent and fail to operate.
20, in the same plant, large motors together, running inverter stop, this is why?
When the motor starts, the starting current will flow and the capacity corresponds to the starting current, the transformer on the stator side of the motor generates a voltage drop, and when the motor has a large capacity, this voltage drop also has a large impact, and the inverter connected to the same transformer will make a judgment of under-voltage or instantaneous stopping, and thus sometimes the protection function (IPE) operates, resulting in the stopping of the operation.
21, what is frequency resolution? What is the significance?
For digital control of the frequency converter, even if the frequency command is analog signal, the output frequency is also a level given. The smallest unit of this level difference is called the frequency resolution.
Frequency resolution is usually taken as 0.015 ~ 0.5Hz. For example, the resolution is 0.5Hz, then 23Hz above can be changed to 23.5, 24.0 Hz, so the motor action is also a level of follow. This poses a problem for applications such as continuous winding control. In this case, if the resolution is about 0.015 Hz, it is possible to adapt to a 4-stage motor with a step difference of 1r/min or less. In addition, some models have a different resolution between the given resolution and the output resolution.
22. Is there any restriction on the installation direction when installing the inverter?
The internal and back structure of the inverter takes into account the cooling effect, the relationship between the top and bottom of the ventilation is also important, therefore, for the unit type in the disk, hanging on the wall are taken to the longitudinal position, as far as possible, vertical installation.
23, do not use soft start, the motor directly into a fixed frequency inverter can?
In a very low frequency is possible, but if the given frequency is high with the industrial frequency power supply direct start conditions are similar. A large starting current (6-7 times the rated current) will flow, and the motor will not start because the inverter cuts off the overcurrent.
24, the motor over 60Hz operation should pay attention to what problems?
Over 60Hz operation should pay attention to the following matters
(1) machinery and devices running at that speed to be fully possible (mechanical strength, noise, vibration, etc.).
(2) The motor enters the constant power output range, and its output torque should be able to maintain the work (fans, pumps, etc., the shaft output power increases proportionally to the cube of the speed, so it should be paid attention to when the speed rises a little).
(3) Produce bearing life, to be fully considered.
(4) For motors of medium capacity and above, especially 2-pole motors, when running at 60Hz or above, please discuss carefully with the manufacturer.
25, inverter can drive gear motor?
Depending on the structure of the gearbox and lubrication, a number of issues need to be noted. In the structure of the gear can usually be considered 70 ~ 80Hz as the maximum limit, the use of oil lubrication, continuous operation at low speeds is related to gear damage.
26, inverter can be used to drive single-phase motor? Can I use single-phase power supply?
Machines basically can not be used. For governor switch start type single-phase motor, in the working point below the speed range will burn
Auxiliary winding; for capacitor start or capacitor operation mode, will induce capacitor explosion. Inverter power supply is usually 3-phase, but for small capacity, there are also single-phase power operation of the machine.
27, inverter itself consumes how much power?
It is related to the type of inverter, operating conditions, frequency of use, etc., but it is difficult to answer. However, the efficiency of the inverter below 60Hz is about 94%~96%, and the loss can be calculated accordingly. However, if the loss during braking is also taken into account in the built-in regenerative braking type (FR-K) inverter, the power consumption will be larger, and it is necessary to pay attention to the design of the operation panel.
28Why can't it be used in 6~60Hz all-area continuous operation?
General motor using the shaft mounted on the external fan or rotor end ring on the blade for cooling, if the speed is reduced, the cooling effect decreases, and therefore can not withstand the same high speed operation of the heat, you must reduce the load torque at low speeds, or the use of large-capacity frequency converter and the motor combination, or the use of special motors.
29, the use of motors with brakes should pay attention to what?
Brake excitation circuit power should be taken from the input side of the inverter. If the inverter is outputting power when the brake action, will cause over-current cut-off. Therefore, the brake should be operated after the inverter stops outputting.
30、I want to use inverter to drive the motor with capacitor for power factor improvement, but the motor does not move, explain the reason
The current of inverter flows into the capacitor for power factor improvement, and it can't be started because its charging current causes overcurrent (OCT) of inverter, as a countermeasure, please remove the capacitor and then run it to improve the power factor even. It is effective to connect an AC reactor to the input side of the inverter.
31、How long is the life of inverter?
The inverter is a static device, but there are like filter capacitors, cooling fans, such as the consumption of devices, if they carry out regular maintenance, can be expected to have a life of more than 10 years.
32, inverter hidden cooling fan, wind direction? What happens if the fan breaks down?
There are also models without cooling fan for small capacity. Also, do not place parts that are afraid of heat on top of the inverter. Fan failure, by the fan stop detection or cooling fan on the overheating detection for protection
33, filter capacitors for consumables, so how to determine its life?
The electrostatic capacity of capacitors used as filter capacitors decreases slowly over time, so the life span is judged by measuring the electrostatic capacity at 85% of the rated capacity of the product on a regular basis.
34, the installation of inverters installed in the direction of whether there are restrictions.
Should be basically collected in the disk, the problem is that the use of fully enclosed structure of the disk form factor is large, occupy a lot of space, the cost is relatively high. The measures are:
(1) the disk design should be aimed at the actual device required for heat dissipation;
(2) the use of aluminum heat sinks, winged coolant, etc. to increase the cooling area;
(3) the use of heat pipes.
In addition, a type has been developed in which the back of the inverter can be exposed.
35、Want to increase the speed of the original conveyor belt, running at 80Hz, how to choose the capacity of the inverter?
Set the base speed at 50Hz, and above 50Hz is the constant power output characteristic. When the load with constant torque characteristic like conveyor belt increases, the capacity needs to be increased to 80/50≈1.6 times. The motor capacity is also increased like inverter
.