Q&A of the SU100 frequency inverter
2024-05-16
Q1: What are the differences between PWM and PAM?
A： PWM is the abbreviation of Pulse Width Modulation in English. It is a modulation method that changes the pulse width of the pulse train according to certain rules to adjust the output volume and waveform. PAM is the abbreviation of Pulse Amplitude Modulation in English. It is a modulation method that changes the pulse amplitude of the pulse train according to certain rules to adjust the output value and waveform.
Q2： What is the difference between voltage type and current type?
A： The main circuit of the frequency converter can be roughly divided into two categories: the voltage type is a frequency converter that converts the DC of the voltage source into AC, and the filter of the DC circuit is a capacitor; the current type is a frequency converter that converts the DC of the current source into AC. The DC link filter is an inductor.
Q3：Why does the voltage of the inverter change in proportion to the frequency?
A： The electromagnetic torque of any motor is the result of the interaction between current and magnetic flux. The current is not allowed to exceed the rated value, otherwise it will cause the motor to heat up. Therefore, if the magnetic flux decreases, the electromagnetic torque must also decrease, resulting in a decrease in load capacity.
It can be seen from the formula E=4.44*K*F*N*Φ that during variable frequency speed regulation, the magnetic circuit of the motor changes within a considerable range with the operating frequency fX, which can easily cause serious damage to the magnetic circuit of the motor. Saturation causes serious distortion of the excitation current waveform, resulting in a peak current with a very high peak value.
Therefore, the frequency and voltage should be changed in proportion, that is, while changing the frequency, the output voltage of the inverter should be controlled to keep the magnetic flux of the motor constant and avoid the occurrence of field weakening and magnetic saturation. This control method is mostly used in energy-saving frequency converters for fans and pumps.
Q4： When the motor is driven by industrial frequency power supply, the current increases when the voltage drops. For inverter drive, if the voltage also drops when the frequency drops, does the current increase?
A： When the frequency decreases (low speed), if the same power is output (constant power), the current will increase, but under the condition of constant torque (constant torque), the current will almost remain unchanged.
Q5： When running with a frequency converter, what are the starting current and starting torque of the motor?
A：Using a frequency converter to operate, the frequency and voltage increase as the motor accelerates, and the starting current is limited to less than 150% of the rated current (125% to 200% depending on the model). When starting directly with a commercial power supply, the starting current is 6 to 7 times the rated current, so mechanical and electrical shocks will occur. Using frequency converter drive 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 inverters with automatic torque enhancement function, the starting torque is more than 100% and can be started with full load.
Q6： What does V/f mode mean?
A: When the frequency decreases, the voltage V also decreases proportionally. This question has been explained in answer 4. The proportional relationship between V and f is predetermined taking into account the characteristics of the motor. There are usually several characteristics stored in the memory device (ROM) of the controller, which can be selected with a switch or dial.
Q7: What does open loop mean?
A: If a speed detector (PG) is provided for the motor device used and the actual speed is fed back to the control device for control, it is called "closed loop". If it does not operate with a PG, it is called "open loop". Most general-purpose inverters are open-loop, and some machines can use options to provide PG feedback. The speed sensorless closed-loop control method is to calculate the actual speed of the motor based on the magnetic flux based on the established mathematical model, which is equivalent to using a virtual speed sensor. Closed-loop control.
Q8: What to do when the actual speed deviates from the given speed?
A: In open loop, even if the frequency converter outputs a given frequency, when the motor is running with load, the motor's speed will fluctuate within the rated slip range (1%~5%). For occasions that require relatively high speed regulation accuracy and require operation close to a given speed even if the load changes, an inverter with PG feedback function (optional) can be used.
Q9: Please explain the protection function of the frequency converter?
A" Protection functions can be divided into the following two categories:
(1) Automatically perform corrective actions after detecting abnormal conditions, such as overcurrent stall prevention and regenerative overvoltage stall prevention.
(2) After detecting the abnormality, block the PWM control signal of the power semiconductor device to cause the motor to automatically stop. Such as over-current cut-off, regenerative over-voltage cut-off, semiconductor cooling fan overheating and instantaneous power outage protection, etc.
A" Protection functions can be divided into the following two categories:
(1) Automatically perform corrective actions after detecting abnormal conditions, such as overcurrent stall prevention and regenerative overvoltage stall prevention.
(2) After detecting the abnormality, block the PWM control signal of the power semiconductor device to cause the motor to automatically stop. Such as over-current cut-off, regenerative over-voltage cut-off, semiconductor cooling fan overheating and instantaneous power outage protection, etc.
Q10: Is it possible to directly put the motor into a fixed frequency inverter without using soft start?
A: It is possible at a very low frequency, but if the given frequency is high, it will be similar to the conditions for direct starting of the power frequency power supply. A large starting current (6~7 times the rated current) will flow, and the motor cannot start because the inverter cuts off the overcurrent.
A: It is possible at a very low frequency, but if the given frequency is high, it will be similar to the conditions for direct starting of the power frequency power supply. A large starting current (6~7 times the rated current) will flow, and the motor cannot start because the inverter cuts off the overcurrent.
Q11: There is a cooling fan built into the inverter. What is the direction of the wind? What will happen if the fan is broken?
A: For small capacities, there are also models without cooling fans. For models with fans, the direction of the wind is from bottom to top, so where the inverter is installed, do not place any mechanical equipment above or below that hinders suction and exhaust. Also, do not place parts that are sensitive to heat above the inverter. In case of fan failure, protection is provided by fan stop detection or overheating detection on the cooling fan.
A: For small capacities, there are also models without cooling fans. For models with fans, the direction of the wind is from bottom to top, so where the inverter is installed, do not place any mechanical equipment above or below that hinders suction and exhaust. Also, do not place parts that are sensitive to heat above the inverter. In case of fan failure, protection is provided by fan stop detection or overheating detection on the cooling fan.
Q12: What is the function of the inverter DC reactor?
A: Reduce the high-order harmonic interference of the input current and improve the power factor of the input power supply.
A: Reduce the high-order harmonic interference of the input current and improve the power factor of the input power supply.
Q13: What are the interference methods of frequency converters and how to generally deal with them?
A: 1. Dissemination method:
(1) Radiation interference;
(2) Conducted interference
(1) Radiation interference;
(2) Conducted interference
2. Anti-interference measures:
Interference signals propagated by radiation are mainly weakened through wiring and shielding of the radiation source and the interfered lines. Interference signals propagated through lines are mainly dealt with by installing filters, reactors or magnetic rings on the input and output sides of the frequency converter.
Interference signals propagated by radiation are mainly weakened through wiring and shielding of the radiation source and the interfered lines. Interference signals propagated through lines are mainly dealt with by installing filters, reactors or magnetic rings on the input and output sides of the frequency converter.
The specific methods and precautions are as follows:
(1) Signal lines and power lines must cross vertically or be routed in separate slots.
(2) Do not use wires of different metals to connect each other.
(3) The shielding tube (layer) should be reliably grounded and ensure continuous and reliable grounding throughout the entire length.
(4) Use twisted pair shielded cables in signal circuits.
(5) The grounding point of the shielding layer should be as far away from the inverter as possible and separated from the grounding point of the inverter.
(6) The magnetic ring can be used on the input power line and output line of the frequency converter. The specific method is: the input lines are wound together 4 times in the same direction, and the output lines are wound 3 times in the same direction. When winding, be careful to keep the magnetic ring as close to the inverter as possible.
(7) Generally, shielding and other anti-interference measures can be taken for the interfered equipment and instruments.
(1) Signal lines and power lines must cross vertically or be routed in separate slots.
(2) Do not use wires of different metals to connect each other.
(3) The shielding tube (layer) should be reliably grounded and ensure continuous and reliable grounding throughout the entire length.
(4) Use twisted pair shielded cables in signal circuits.
(5) The grounding point of the shielding layer should be as far away from the inverter as possible and separated from the grounding point of the inverter.
(6) The magnetic ring can be used on the input power line and output line of the frequency converter. The specific method is: the input lines are wound together 4 times in the same direction, and the output lines are wound 3 times in the same direction. When winding, be careful to keep the magnetic ring as close to the inverter as possible.
(7) Generally, shielding and other anti-interference measures can be taken for the interfered equipment and instruments.
Q14: Why can't the frequency converter be used as a variable frequency power supply?
A: The entire circuit of the variable frequency power supply is composed of AC, DC, AC, and filtering. Therefore, the voltage and current waveforms it outputs are pure sine waves, which are very close to the ideal AC power supply. Can output the grid voltage and frequency of any country in the world. The frequency converter is composed of AC, DC and AC (modulated wave) circuits. The standard name of the frequency converter should be variable frequency speed regulator. The waveform of its output voltage is a pulse square wave with many harmonic components. The voltage and frequency change proportionally at the same time and cannot be adjusted separately, which does not meet the requirements of AC power supply. In principle, it cannot be used as a power supply and is generally only used for speed regulation of three-phase asynchronous motors.
A: The entire circuit of the variable frequency power supply is composed of AC, DC, AC, and filtering. Therefore, the voltage and current waveforms it outputs are pure sine waves, which are very close to the ideal AC power supply. Can output the grid voltage and frequency of any country in the world. The frequency converter is composed of AC, DC and AC (modulated wave) circuits. The standard name of the frequency converter should be variable frequency speed regulator. The waveform of its output voltage is a pulse square wave with many harmonic components. The voltage and frequency change proportionally at the same time and cannot be adjusted separately, which does not meet the requirements of AC power supply. In principle, it cannot be used as a power supply and is generally only used for speed regulation of three-phase asynchronous motors.
Review of the development of the global photovoltaic industry in 2023
Team Building for ZK Variable Frequency Drive Sales Team
Related Article
A brief introduction to the photovoltaic market in 2023
Review of the development of the global photovoltaic industry in 2023
In the competitive world of variable frequency drive sales, having a strong and cohesive team is essential for success. Team building activities can help improve communication, build trust, and foster a positive work environment. In this article, we will explore the importance of team building for variable frequency drive sales teams and discuss some effective strategies for building a strong and successful team.
Team Building for ZK Variable Frequency Drive Sales Team
