1. What is a frequency converter?
The frequency converter is generally a power control device that utilizes the on-off function of a power semiconductor device to convert an industrial frequency power supply to another frequency.
The frequency converter is generally a power control device that utilizes the on-off function of a power semiconductor device to convert an industrial frequency power supply to another frequency.
What are the differences between PWM and PAM?
PWM is English Pulse Width Modulation (Pulse Width Modulation) (abbreviation of pulse width modulation), according to a certain rule to change the pulse width of the pulse train to adjust the amount of output and waveform adjustment method.
PAM is the abbreviation of English Pulse Amplitude Modulation (Pulse Amplitude Modulation). It is a modulation method that changes the pulse amplitude of a pulse train according to a certain rule to adjust the output value and the waveform.
3. What is the difference between voltage type and current type?
The main circuit of the frequency converter can be roughly divided into two kinds: The voltage type is the frequency converter that converts the direct current of the voltage source into alternating current, the filter of the direct current loop is the electric capacity; The electric current type is the frequency converter that the direct current of the current source transforms into alternating current, Its DC loop filter is inductance.
4. Why does the inverter's voltage and current 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 constant and only the frequency is reduced, the magnetic flux is too large and the magnetic circuit is saturated. The motor will be burned. Therefore, the frequency and voltage must be changed proportionally, that is, changing the frequency while controlling the output voltage of the inverter so that the magnetic flux of the motor can be kept constant to avoid the generation of weak magnetic and magnetic saturation phenomena. This kind of control method is mostly used in fans, pumps and energy-saving inverters.
5. When the motor is driven by the power frequency, the current increases when the voltage drops. For the drive of the inverter, if the voltage drops when the frequency decreases, does the current increase?
When the frequency drops (low speed), the current increases if the same power is output, but the current does not change substantially under the condition of constant torque.
6. What is the starting current and starting torque of the motor when using the inverter?
With the inverter running, the starting current is limited to 150% or less of the rated current (125% to 200% depending on the model) as the motor speeds up the frequency and voltage accordingly. When starting with the power frequency power supply directly, the starting current is 6~7 times. Therefore, mechanical and electrical impact will occur. The inverter drive can be started smoothly (the starting time becomes longer). The starting current is 1.2~1.5 times the rated current and the starting torque is 70%~120% of the rated torque. For the inverter with the torque automatic enhancement function, the starting torque is more than 100%, and it can be started with full load.
7. What does the V/f mode mean?
When the frequency drops, the voltage V also decreases proportionally. This problem has been explained in the answer 4. The proportional relationship between V and f is predetermined in consideration of the characteristics of the motor. Usually, there are several characteristics in the controller's storage device (ROM) that can be selected with a switch or a dial.
8. How does the motor torque change when proportionally changing V and f?
When the frequency is decreased, the voltage is completely proportionally reduced. Therefore, since the AC resistance becomes small and the DC resistance does not change, the torque generated at a low speed tends to decrease. Therefore, given V/f at low frequencies, the output voltage is raised somewhat in order to obtain a certain starting torque. This compensation is referred to as boost starting. Can use various methods to achieve, there are automatic methods, select V / f mode or adjust the potentiometer and other methods.
9, in the description of the shift range of 60 ~ 6Hz, that is 10:1, then there is no output power below 6Hz?
Below 6Hz can still output power, but according to the motor temperature rise and starting torque size and other conditions, the minimum frequency of use to take about 6Hz, then the motor can output the rated torque without causing serious heating problems. The actual output frequency of the inverter (starting frequency) is 0.5~3Hz depending on the model.
10, for the general motor combination is above 60Hz also requires a certain torque, is it possible?
Normally it is not possible. In the above 60Hz (also has the mode above 50Hz) the voltage does not change, basically is the constant power characteristic, when requests the identical torque in the high speed, must pay attention to the choice of the electrical machinery and the frequency changer capacity.
11, what is the meaning of the so-called open-loop?
A speed detector (PG) is provided for the motor device to be used, and the actual speed is fed back to the control device for control. This is called "closed loop", and the operation without PG is called "open loop." General-purpose inverters are mostly open-loop, and some models use options for PG feedback.
12. How to do when the actual speed has a deviation for a given speed?
In the open loop, even if the inverter outputs a given frequency and the motor is running with a load, the motor speed changes within the range of the rated slip (1% to 5%). For the requirement of higher speed control accuracy, even if the load change requires operation near a given speed, an inverter (option) with PG feedback function can be used.
13. If using a motor with PG, can the speed accuracy be improved after feedback?
The inverter with PG feedback function has improved accuracy. However, the speed accuracy value depends on the accuracy of the PG itself and the resolution of the inverter output frequency.
14. What does the stall prevention function mean?
If the given acceleration time is too short, the output frequency of the inverter will change far beyond the change of the speed (electrical angle frequency). The inverter will trip due to the overcurrent and the operation will stop. This is called stalling. In order to prevent the stall from continuing to operate the motor, it is necessary to check the magnitude of the current for frequency control. When the acceleration current is too large, the acceleration rate is appropriately slowed down. This is also true during deceleration. The combination of the two is the stall prevention function.
15. What is the meaning of models with acceleration time and deceleration time given separately, and the type of acceleration/deceleration time given together?
Acceleration and deceleration can be given for each type of machine, for short-time acceleration, slow deceleration occasions, or for small machine tools need to strictly specify the production of the tact time is appropriate, but for fan drive and other occasions, acceleration and deceleration time is longer, Acceleration time and deceleration time can be given together.
16. What is regenerative braking?
If the motor decreases the command frequency during operation, the motor changes to the asynchronous generator state and operates as a brake. This is called regenerative (electrical) braking.
17. Is greater braking power available?
The energy regenerated from the motor is stored in the filter capacitor of the inverter. Due to the relationship between the capacity of the capacitor and the withstand voltage, the regenerative braking force of the general inverter is about 10% to 20% of the rated torque. If using optional brake unit, it can reach 50%~100%.
18, please explain the protection function of the inverter?
Protection features can be divided into the following two categories:
(1) Corrective actions are automatically performed after detection of abnormal conditions, such as overcurrent stall prevention and regenerative overvoltage stall prevention.
(2) Block the power semiconductor device PWM control signal after detecting the abnormality, and make the motor stop automatically. Such as over-current cut-off, regenerative over-voltage cut-off, semiconductor cooling fan overheating and instantaneous power failure protection.
19, why use the clutch continuous load, the inverter's protection function to action?
When the clutch is used to connect the load, the motor rapidly changes from an idle state to a region where the slip rate is large at the moment of connection. A large current flows to cause the inverter to trip due to overcurrent and fail to operate.
20. In the same factory, large-scale motors move together and the inverter stops during operation. Why?
When the motor starts, the starting current corresponding to the flow rate and capacity will cause a voltage drop in the transformer on the stator side of the motor. When the motor capacity is large, the pressure drop will also have a large impact. The inverter connected to the same transformer will make an undervoltage or instantaneous stop. As a result, the protection function (IPE) may be operated to stop the operation.
21, what is the frequency conversion resolution? has no meaning?
For digitally controlled inverters, even if the frequency command is an analog signal, the output frequency is given a step. The smallest unit of this differential is called the frequency resolution.
The resolution of the frequency conversion is usually 0.015~0.5Hz. For example, if the resolution is 0.5Hz, then the upper side of 23Hz can be changed to 23.5, 24.0Hz, so the action of the motor is also followed step by step. This causes problems for the use of a continuous coil control. In this case, if the resolution is about 0.015 Hz, one step for a 4-stage motor is 1 r/min or less, and it can be sufficiently adapted. In addition, some models have different resolutions and output resolutions.
22. Is there any limit to the mounting direction when installing the inverter?
The structure of the internal and the back of the inverter considers the cooling effect. The relationship between the upper and the lower is also important for ventilation. Therefore, take the longitudinal position of the unit type in the tray and hung on the wall, and install it as vertically as possible.
23. Is it possible to use a soft start without inputting the motor directly to a fixed frequency inverter?
It is possible to operate at very low frequencies, but if the given frequency is high then the conditions for direct start with the commercial frequency power supply are similar. A large starting current (6 to 7 times rated current) will flow. The motor cannot start because the inverter cuts off the overcurrent.
24, when the motor exceeds 60Hz operation should pay attention to what the problem?
When operating over 60Hz, please note the following:
(1) Machines and devices must be fully operational at this speed (mechanical strength, noise, vibration, etc.).
(2) The motor enters the constant power output range, and its output torque must be able to maintain the work (shaft, pump, etc. shaft output power in proportion to the cube of the speed increase, so a little increase in speed should also pay attention).
(3) Bearing life issues should be fully considered.
(4) For motors of medium-capacity and above, especially 2-pole motors, it is necessary to carefully discuss with the manufacturer when operating above 60Hz.
25, inverter can drive gear motor?
According to the structure of the reducer and the lubrication method, there are a number of issues that need attention. The maximum limit of 70~80Hz can be considered in the structure of gears. When oil lubrication is used, the continuous operation at low speed is related to the damage of the gears.
26, inverter can be used to drive a single-phase motor? Can I use single-phase power?
Single-phase motors basically do not work. For single-phase motors with governor switch start-up type, the auxiliary winding will be burned when the speed range is below the operating point; for capacitive start-up or capacitor operation, capacitor explosion will be induced. The frequency converter usually has a 3-phase power supply, but for a small capacity, it also has a single-phase power-running type.
27. How much power is consumed by the inverter itself?
It is related to the model, operating status, frequency of use of the inverter, but it is difficult to answer. However, the efficiency of inverters below 60Hz is approximately 94% to 96%. Based on this, the losses can be inferred. However, in the case of built-in regenerative braking (FR-K) inverters, if the loss during braking is also taken into consideration, the power consumption Will become larger, must pay attention to the operating panel design.
28. Why can't I use it continuously in the 6~60Hz region?
General motors use blades mounted on the outer fan or rotor end ring of the shaft for cooling. If the speed is reduced, the cooling effect is reduced. Therefore, the same heat generation as the high speed operation cannot be endured, the load torque at low speed must be reduced, or Large capacity inverter and motor combination, or use a dedicated motor.
29. What should you watch out for when using a motor with brakes?
Brake excitation circuit power should be taken from the input side of the inverter. If the brake is activated when the inverter is outputting power, the overcurrent will be cut off. Therefore, the brake must be operated after the inverter stops outputting.
30. I want to use a frequency converter to drive a motor with an improved capacitor for power factor. However, the motor does not move. Please explain why the inverter's current flows into the capacitor for improving the power factor, and the overcurrent (OCT) of the inverter is caused by the charging current. Can not start, as a measure, please remove the capacitor to run, or even improve the power factor, access to AC reactor on the input side of the inverter is effective.
31. How long is the life of the inverter?
Although inverters are stationary devices, they also have consumer devices such as filter capacitors and cooling fans. If these inverters are regularly maintained, they are expected to have a lifetime of more than 10 years.
32. The inverter contains a cooling fan. What is the direction of the wind? What if the fan is broken?
There is also no cooling fan for small capacity. With a fan type, the direction of the wind is from the bottom up. Therefore, in the place where the inverter is installed, do not place mechanical devices that impede suction and discharge on the upper and lower parts. Also, do not place heat-sensitive parts above the inverter. When the fan fails, it is protected by fan stop detection or overheat detection on the cooling fan
33, filter capacitors for consumables, then how to determine its life?
Capacitors used as filter capacitors gradually decrease in electrostatic capacity over time, and periodically measure the electrostatic capacity. Life is judged on the basis of 85% of the rated capacity of the product.
34. Is there a limit to the mounting direction when installing the inverter?
Should be basically stored in the disk, the problem is that the use of fully enclosed structure of the disk size, space, cost is relatively high. The measures are:
(1) The design of the disk should be based on the heat dissipation required by the actual device;
(2) Increase the cooling area with aluminum heat sinks, airfoil coolants, etc.;
(3) Use a heat pipe.
In addition, a type in which the reverse side of the inverter can be exposed has been developed.
35. Want to increase the speed of the original conveyor belt and operate at 80Hz. How to choose the capacity of the inverter?
Let the reference speed be 50Hz, and 50Hz or more constant power output characteristics. When a constant torque characteristic such as a conveyor belt increases the load, the capacity needs to be increased to 80/50≈1.6 times. The motor capacity also increases like a frequency converter.
PWM is English Pulse Width Modulation (Pulse Width Modulation) (abbreviation of pulse width modulation), according to a certain rule to change the pulse width of the pulse train to adjust the amount of output and waveform adjustment method.
PAM is the abbreviation of English Pulse Amplitude Modulation (Pulse Amplitude Modulation). It is a modulation method that changes the pulse amplitude of a pulse train according to a certain rule to adjust the output value and the waveform.
3. What is the difference between voltage type and current type?
The main circuit of the frequency converter can be roughly divided into two kinds: The voltage type is the frequency converter that converts the direct current of the voltage source into alternating current, the filter of the direct current loop is the electric capacity; The electric current type is the frequency converter that the direct current of the current source transforms into alternating current, Its DC loop filter is inductance.
4. Why does the inverter's voltage and current 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 constant and only the frequency is reduced, the magnetic flux is too large and the magnetic circuit is saturated. The motor will be burned. Therefore, the frequency and voltage must be changed proportionally, that is, changing the frequency while controlling the output voltage of the inverter so that the magnetic flux of the motor can be kept constant to avoid the generation of weak magnetic and magnetic saturation phenomena. This kind of control method is mostly used in fans, pumps and energy-saving inverters.
5. When the motor is driven by the power frequency, the current increases when the voltage drops. For the drive of the inverter, if the voltage drops when the frequency decreases, does the current increase?
When the frequency drops (low speed), the current increases if the same power is output, but the current does not change substantially under the condition of constant torque.
6. What is the starting current and starting torque of the motor when using the inverter?
With the inverter running, the starting current is limited to 150% or less of the rated current (125% to 200% depending on the model) as the motor speeds up the frequency and voltage accordingly. When starting with the power frequency power supply directly, the starting current is 6~7 times. Therefore, mechanical and electrical impact will occur. The inverter drive can be started smoothly (the starting time becomes longer). The starting current is 1.2~1.5 times the rated current and the starting torque is 70%~120% of the rated torque. For the inverter with the torque automatic enhancement function, the starting torque is more than 100%, and it can be started with full load.
7. What does the V/f mode mean?
When the frequency drops, the voltage V also decreases proportionally. This problem has been explained in the answer 4. The proportional relationship between V and f is predetermined in consideration of the characteristics of the motor. Usually, there are several characteristics in the controller's storage device (ROM) that can be selected with a switch or a dial.
8. How does the motor torque change when proportionally changing V and f?
When the frequency is decreased, the voltage is completely proportionally reduced. Therefore, since the AC resistance becomes small and the DC resistance does not change, the torque generated at a low speed tends to decrease. Therefore, given V/f at low frequencies, the output voltage is raised somewhat in order to obtain a certain starting torque. This compensation is referred to as boost starting. Can use various methods to achieve, there are automatic methods, select V / f mode or adjust the potentiometer and other methods.
9, in the description of the shift range of 60 ~ 6Hz, that is 10:1, then there is no output power below 6Hz?
Below 6Hz can still output power, but according to the motor temperature rise and starting torque size and other conditions, the minimum frequency of use to take about 6Hz, then the motor can output the rated torque without causing serious heating problems. The actual output frequency of the inverter (starting frequency) is 0.5~3Hz depending on the model.
10, for the general motor combination is above 60Hz also requires a certain torque, is it possible?
Normally it is not possible. In the above 60Hz (also has the mode above 50Hz) the voltage does not change, basically is the constant power characteristic, when requests the identical torque in the high speed, must pay attention to the choice of the electrical machinery and the frequency changer capacity.
11, what is the meaning of the so-called open-loop?
A speed detector (PG) is provided for the motor device to be used, and the actual speed is fed back to the control device for control. This is called "closed loop", and the operation without PG is called "open loop." General-purpose inverters are mostly open-loop, and some models use options for PG feedback.
12. How to do when the actual speed has a deviation for a given speed?
In the open loop, even if the inverter outputs a given frequency and the motor is running with a load, the motor speed changes within the range of the rated slip (1% to 5%). For the requirement of higher speed control accuracy, even if the load change requires operation near a given speed, an inverter (option) with PG feedback function can be used.
13. If using a motor with PG, can the speed accuracy be improved after feedback?
The inverter with PG feedback function has improved accuracy. However, the speed accuracy value depends on the accuracy of the PG itself and the resolution of the inverter output frequency.
14. What does the stall prevention function mean?
If the given acceleration time is too short, the output frequency of the inverter will change far beyond the change of the speed (electrical angle frequency). The inverter will trip due to the overcurrent and the operation will stop. This is called stalling. In order to prevent the stall from continuing to operate the motor, it is necessary to check the magnitude of the current for frequency control. When the acceleration current is too large, the acceleration rate is appropriately slowed down. This is also true during deceleration. The combination of the two is the stall prevention function.
15. What is the meaning of models with acceleration time and deceleration time given separately, and the type of acceleration/deceleration time given together?
Acceleration and deceleration can be given for each type of machine, for short-time acceleration, slow deceleration occasions, or for small machine tools need to strictly specify the production of the tact time is appropriate, but for fan drive and other occasions, acceleration and deceleration time is longer, Acceleration time and deceleration time can be given together.
16. What is regenerative braking?
If the motor decreases the command frequency during operation, the motor changes to the asynchronous generator state and operates as a brake. This is called regenerative (electrical) braking.
17. Is greater braking power available?
The energy regenerated from the motor is stored in the filter capacitor of the inverter. Due to the relationship between the capacity of the capacitor and the withstand voltage, the regenerative braking force of the general inverter is about 10% to 20% of the rated torque. If using optional brake unit, it can reach 50%~100%.
18, please explain the protection function of the inverter?
Protection features can be divided into the following two categories:
(1) Corrective actions are automatically performed after detection of abnormal conditions, such as overcurrent stall prevention and regenerative overvoltage stall prevention.
(2) Block the power semiconductor device PWM control signal after detecting the abnormality, and make the motor stop automatically. Such as over-current cut-off, regenerative over-voltage cut-off, semiconductor cooling fan overheating and instantaneous power failure protection.
19, why use the clutch continuous load, the inverter's protection function to action?
When the clutch is used to connect the load, the motor rapidly changes from an idle state to a region where the slip rate is large at the moment of connection. A large current flows to cause the inverter to trip due to overcurrent and fail to operate.
20. In the same factory, large-scale motors move together and the inverter stops during operation. Why?
When the motor starts, the starting current corresponding to the flow rate and capacity will cause a voltage drop in the transformer on the stator side of the motor. When the motor capacity is large, the pressure drop will also have a large impact. The inverter connected to the same transformer will make an undervoltage or instantaneous stop. As a result, the protection function (IPE) may be operated to stop the operation.
21, what is the frequency conversion resolution? has no meaning?
For digitally controlled inverters, even if the frequency command is an analog signal, the output frequency is given a step. The smallest unit of this differential is called the frequency resolution.
The resolution of the frequency conversion is usually 0.015~0.5Hz. For example, if the resolution is 0.5Hz, then the upper side of 23Hz can be changed to 23.5, 24.0Hz, so the action of the motor is also followed step by step. This causes problems for the use of a continuous coil control. In this case, if the resolution is about 0.015 Hz, one step for a 4-stage motor is 1 r/min or less, and it can be sufficiently adapted. In addition, some models have different resolutions and output resolutions.
22. Is there any limit to the mounting direction when installing the inverter?
The structure of the internal and the back of the inverter considers the cooling effect. The relationship between the upper and the lower is also important for ventilation. Therefore, take the longitudinal position of the unit type in the tray and hung on the wall, and install it as vertically as possible.
23. Is it possible to use a soft start without inputting the motor directly to a fixed frequency inverter?
It is possible to operate at very low frequencies, but if the given frequency is high then the conditions for direct start with the commercial frequency power supply are similar. A large starting current (6 to 7 times rated current) will flow. The motor cannot start because the inverter cuts off the overcurrent.
24, when the motor exceeds 60Hz operation should pay attention to what the problem?
When operating over 60Hz, please note the following:
(1) Machines and devices must be fully operational at this speed (mechanical strength, noise, vibration, etc.).
(2) The motor enters the constant power output range, and its output torque must be able to maintain the work (shaft, pump, etc. shaft output power in proportion to the cube of the speed increase, so a little increase in speed should also pay attention).
(3) Bearing life issues should be fully considered.
(4) For motors of medium-capacity and above, especially 2-pole motors, it is necessary to carefully discuss with the manufacturer when operating above 60Hz.
25, inverter can drive gear motor?
According to the structure of the reducer and the lubrication method, there are a number of issues that need attention. The maximum limit of 70~80Hz can be considered in the structure of gears. When oil lubrication is used, the continuous operation at low speed is related to the damage of the gears.
26, inverter can be used to drive a single-phase motor? Can I use single-phase power?
Single-phase motors basically do not work. For single-phase motors with governor switch start-up type, the auxiliary winding will be burned when the speed range is below the operating point; for capacitive start-up or capacitor operation, capacitor explosion will be induced. The frequency converter usually has a 3-phase power supply, but for a small capacity, it also has a single-phase power-running type.
27. How much power is consumed by the inverter itself?
It is related to the model, operating status, frequency of use of the inverter, but it is difficult to answer. However, the efficiency of inverters below 60Hz is approximately 94% to 96%. Based on this, the losses can be inferred. However, in the case of built-in regenerative braking (FR-K) inverters, if the loss during braking is also taken into consideration, the power consumption Will become larger, must pay attention to the operating panel design.
28. Why can't I use it continuously in the 6~60Hz region?
General motors use blades mounted on the outer fan or rotor end ring of the shaft for cooling. If the speed is reduced, the cooling effect is reduced. Therefore, the same heat generation as the high speed operation cannot be endured, the load torque at low speed must be reduced, or Large capacity inverter and motor combination, or use a dedicated motor.
29. What should you watch out for when using a motor with brakes?
Brake excitation circuit power should be taken from the input side of the inverter. If the brake is activated when the inverter is outputting power, the overcurrent will be cut off. Therefore, the brake must be operated after the inverter stops outputting.
30. I want to use a frequency converter to drive a motor with an improved capacitor for power factor. However, the motor does not move. Please explain why the inverter's current flows into the capacitor for improving the power factor, and the overcurrent (OCT) of the inverter is caused by the charging current. Can not start, as a measure, please remove the capacitor to run, or even improve the power factor, access to AC reactor on the input side of the inverter is effective.
31. How long is the life of the inverter?
Although inverters are stationary devices, they also have consumer devices such as filter capacitors and cooling fans. If these inverters are regularly maintained, they are expected to have a lifetime of more than 10 years.
32. The inverter contains a cooling fan. What is the direction of the wind? What if the fan is broken?
There is also no cooling fan for small capacity. With a fan type, the direction of the wind is from the bottom up. Therefore, in the place where the inverter is installed, do not place mechanical devices that impede suction and discharge on the upper and lower parts. Also, do not place heat-sensitive parts above the inverter. When the fan fails, it is protected by fan stop detection or overheat detection on the cooling fan
33, filter capacitors for consumables, then how to determine its life?
Capacitors used as filter capacitors gradually decrease in electrostatic capacity over time, and periodically measure the electrostatic capacity. Life is judged on the basis of 85% of the rated capacity of the product.
34. Is there a limit to the mounting direction when installing the inverter?
Should be basically stored in the disk, the problem is that the use of fully enclosed structure of the disk size, space, cost is relatively high. The measures are:
(1) The design of the disk should be based on the heat dissipation required by the actual device;
(2) Increase the cooling area with aluminum heat sinks, airfoil coolants, etc.;
(3) Use a heat pipe.
In addition, a type in which the reverse side of the inverter can be exposed has been developed.
35. Want to increase the speed of the original conveyor belt and operate at 80Hz. How to choose the capacity of the inverter?
Let the reference speed be 50Hz, and 50Hz or more constant power output characteristics. When a constant torque characteristic such as a conveyor belt increases the load, the capacity needs to be increased to 80/50≈1.6 times. The motor capacity also increases like a frequency converter.
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Inverter Structure and Fault Diagnosis Introduction Inverter is a device that converts industrial frequency power supply (50Hz or 60Hz) into AC power of various frequencies to realize the variable speed operation of the motor. The control circuit completes the control of the main circuit, and the rectifier circuit converts the alternating current into direct current. The intermediate circuit of the direct current smoothes the output of the rectifier circuit, and the inverter circuit converts the direct current into the alternating current. For inverters such as vector control inverters that require large amounts of computation, sometimes a CPU for torque calculations and some corresponding circuits are needed.
1. A rectifier, which is connected to a single-phase or three-phase AC power supply, generating a pulsating DC voltage.
2. The intermediate circuit has the following three functions:
a. Make the pulsating DC voltage stable or smooth for use by the inverter.
b. Power each control line through the switching power supply.
c. Filtering or braking devices can be configured to improve drive performance.
3. The inverter converts the fixed DC voltage into an alternating voltage with variable voltage and frequency.
4. The control circuit, which transmits the signal to the rectifier, the intermediate circuit and the inverter, and it also receives signals from these parts. Its main components are: output drive circuit, operation control circuit. The main function is:
a. Use the signal to switch the semiconductor device of the inverter.
b. Provides various control signals for operating the inverter.
c. Monitor the inverter's operating status and provide protection.
The personnel who operate the frequency converter and peripheral control devices at the site can judge and deal with some common fault conditions, which can greatly increase work efficiency and avoid unnecessary losses. For this purpose, we have summarized the basic faults of some inverters for your reference. The following inspection process does not require opening the inverter chassis, but only detects and judges some common phenomena externally.
1, spark on power-on trip or main power terminal of inverter.
Test method and judgment: Disconnect the power cable and check whether the input terminal of the inverter is short-circuited. Check whether the DC-side terminals P and N of the inverter's intermediate circuit are short-circuited. This may be due to a defective rectifier or a short circuit in the intermediate circuit.
2. No display detection method and judgment on power-on: Disconnect the power cable and check whether the power supply has a phase loss or open circuit condition. If the power supply is normal, check whether the DC-side terminals P and N of the intermediate circuit of the inverter are checked after power-on. Voltage, if the above check is normal, judge the internal switching power supply of the inverter is damaged.
3, no output at startup (motor does not start)
Detection method and judgment: disconnect the output motor wire, observe the input frequency displayed on the inverter panel after powering on again, and measure the AC output terminal at the same time. This may be caused by the inverter startup parameter setting or running terminal wiring error, or the inverter may be damaged or the motor may not be linked to the inverter correctly.
4. "Overvoltage" protection during operation, inverter stop output detection method and judgment: Check whether the grid voltage is too high, or the brake problem caused by too much motor load inertia and too short acceleration/deceleration time. Please refer to Article 8 .
5, "over-current" protection during operation, inverter stop output detection method and judgment: motor stall or load is too large. You can check the load condition or adjust the inverter parameters appropriately. If this does not work, it indicates that the inverter part is deteriorated or damaged.
6, "overheating" protection during operation, inverter stop output detection method and judgment: depending on the brand model of the inverter configuration is different, may be the ambient temperature is too high than the inverter allowable limit, check the cooling fan is running or the motor overheating Causes the protection to close.
7, "grounding" protection during operation, inverter stop output detection method and judgment: refer to the operation manual, check whether the inverter and motor are grounded reliably, or measure whether the motor insulation is normal.
8, brake problem (overvoltage protection)
Test methods and judgments: If the motor load is really excessive and needs to be stopped within a short time, it is necessary to purchase an inverter with a braking unit and configure a braking resistor of comparable power. If the brake function is already configured, the brake resistor may be damaged or the brake unit detection may be invalid.
9. The odor-like odor detection method and judgement inside the inverter: Do not turn on the power, it is likely that the internal main filter capacitor of the inverter is damaged and leaked.
10. If it is determined that the inverter components are damaged, contact the supplier or send it to a professional service center for disposal.
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Inverter failure analysis At present, people speak of AC speed control system, mainly refers to the electronic power inverter to AC motor speed control system. The frequency conversion speed control system is superior to the DC drive in that it is used as the preferred transmission scheme in many occasions. The modern frequency conversion speed control basically uses 16-bit or 32-bit microcontroller as the control core, so as to achieve full digital control and speed regulation. The performance is similar to that of DC speed control. However, when the inverter is used, the maintenance work is more complicated than that of DC. Once the fault occurs, the general electrician of the company is difficult to deal with. Here, the common faults of the inverter are analyzed and the cause of the fault is analyzed. Approach.
First, the parameter setting type breakdown Commonly used frequency converter in use, whether can meet the transmission system request, the frequency changer parameter hypothesis is very important, if the parameter setting is not correct, will cause the frequency changer not to work normally.
1. Parameter setting Common frequency converters. Generally, the factory has a default value for each parameter. These parameters are called factory values. In the case of these parameter values, the user can operate normally with the panel operation, but the panel operation does not meet the requirements of most drive systems. Therefore, before the user correctly uses the inverter, it is necessary to perform the following aspects when the inverter parameters:
(1) To confirm the motor parameters, the inverter sets the motor power, current, voltage, rotation speed, and maximum frequency in the parameters. These parameters can be obtained directly from the motor nameplate.
(2) The control method adopted by the inverter, ie speed control, torque control, PID control or other methods. After the control method is adopted, it is generally required to perform static or dynamic identification according to the control accuracy.
(3) Set the start mode of the inverter. Normally, the inverter is set to start from the panel at the factory. The user can select the start mode according to the actual situation, and can use the panel, external terminals, and communication methods.
(4) For the selection of the given signal, the frequency setting of the general frequency converter can also have multiple modes. The panel given, the external setting, the external voltage or current given, the communication method given, of course, for the frequency of the frequency converter It can also be the sum of one or more of these methods. After correctly setting the above parameters, the inverter can basically work normally. If you want to get better control effect, you can only modify the relevant parameters according to the actual situation.
2. Handling of parameter setting faults Once a parameter setting fault occurs, the inverter cannot operate normally. Generally, the parameters can be modified according to the instructions. If the above fails, it is best to restore all parameters to their factory values ​​and then reset them according to the above steps. For each company's inverter, the parameter recovery method is not the same.
Second, overvoltage fault The overvoltage of the inverter is concentrated on the DC bus's tributary voltage. Under normal circumstances, the inverter DC is the average value after three-phase full-wave rectification. If calculated by 380V line voltage, the average DC voltage Ud = 1.35 U line = 513V. When the over-voltage occurs, the storage capacitor of the DC bus will be charged. When the voltage reaches about 760V, the inverter overvoltage protection action. Therefore, the inverter has a normal operating voltage range. When the voltage exceeds this range, the inverter may be damaged. There are two types of common overvoltages.
1, the input AC power overvoltage This situation refers to the input voltage exceeds the normal range, generally occurs in the holiday load is lighter, the voltage is increased or decreased and the line fails, at this point it is best to disconnect the power, check, handle.
2. The probability of occurrence of overvoltage in the power generation category is higher. The main reason is that the synchronous speed of the motor is higher than the actual speed, so that the motor is in the power generation state, and the inverter has no brake unit installed. There are two situations that can cause this. A failure.
(1) When the frequency converter drags a large inertial load, the deceleration time is set to be relatively small. In the deceleration process, the output speed of the frequency converter is relatively fast, and the load decelerates more slowly by its own resistance, so that the load drags the motor's rotation speed. The inverter output frequency is even higher than the corresponding frequency, the motor is in the state of power generation, and the inverter has no energy feedback unit, so the inverter DC DC link voltage rises, exceeds the protection value, failure occurs, and the paper machine often occurs In the dry section, to deal with such faults can increase the regenerative braking unit, or modify the inverter parameters, set the inverter deceleration time longer. The functions of regenerative braking unit include energy consumption type, parallel DC bus absorption type and energy feedback type. The energy consumption type parallels a braking resistor in the DC link of the frequency converter and controls the DC bus voltage to control the on/off of the power tube. The parallel DC bus absorption type is used in a multi-motor transmission system. This type of system often has one or several motors that are often operated in a power generation state to generate regenerative energy that is absorbed by a motor that is in an electric state through the parallel bus. The energy feedback type inverter-side converter is reversible, and the reversible converter feeds the regenerative energy back to the grid when the regenerative energy is generated.
(2) This failure may also occur when multiple electric actuators act on the same load, mainly due to no load distribution. Take two motors to drive one load. For example, when the actual speed of one motor is greater than the synchronous speed of another motor, the motor with a high speed corresponds to the prime mover, and the motor with a low speed is in the power generation state, causing a failure. The paper machine often occurs in the press section and the net section, and the load distribution control must be added during processing. It is possible to soften the characteristics of the frequency converter in the branch of the drive speed chain of the paper machine.
Third, overcurrent fault overcurrent fault can be divided into acceleration, deceleration, constant overcurrent. This may be due to the fact that the inverter's acceleration/deceleration time is too short, the load is suddenly changed, the load distribution is not uniform, and the output is short-circuited. At this time, it is generally possible to extend the acceleration/deceleration time, reduce the sudden change in load, apply dynamic braking elements, design the load distribution, and inspect the line. If you disconnect the load inverter or overcurrent fault, it means that the inverter inverter circuit has been looped and you need to replace the inverter.
IV. Overload Fault Overload fault includes inverter overload and motor overload. This may be caused by short acceleration times, excessive DC braking, low grid voltage, and heavy loads. Generally, it can increase the acceleration time, extend the braking time, check the grid voltage, and so on. The load is too heavy, the selected motor and frequency converter cannot drag the load, or it may be due to poor mechanical lubrication. For example, the former must replace the high-powered motors and inverters; if the latter, the production machines should be overhauled.
V. Other faults
1. Undervoltage indicates that there is something wrong with the input part of the inverter power supply. It must be checked before it can operate.
2, the temperature is too high If the motor has a temperature detection device, check the motor cooling; inverter temperature is too high, check the ventilation of the inverter.
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