JUUL VAPE PEN, Wholesale Juul , Juul manufacture Shenzhen Xcool Vapor Technology Co.,Ltd , http://www.xcoolvapor.com
Since the 1980s, general-purpose inverters have been widely used in just a few decades. At present, general-purpose inverters are increasingly favored by people for their advantages of intelligence, digitization and networking. With the expansion of the application range of general-purpose inverters, the problems exposed are also increasing, mainly in the following aspects:
(1) Harmonic problems (2) Inverter load matching problems (3) Heating problems These problems have caused the attention of relevant management departments and factories and mines and formulated relevant technical standards. In the case of harmonics, China passed the Interim Provisions on Harmonic Management of Power Systems in 1984 to limit the harmonic pollution of power supply systems and electrical equipment.
In response to the above problems, this paper analyzes and proposes solutions and countermeasures.
2 harmonic problems and countermeasures
The main circuit form of a general-purpose inverter generally consists of three parts: a rectification part, an inverter part, and a filtering part. The rectification part is a three-phase bridge type uncontrolled rectifier, the inverter part is an IGBT three-phase bridge inverter, and the output is a PWM waveform. The output voltage of the inverter does contain harmonics other than the fundamental. Lower harmonics usually have a greater impact on the motor load, causing torque ripple, while higher harmonics increase the leakage current of the inverter output cable, resulting in insufficient motor output. Therefore, the high and low harmonics of the inverter output must be suppressed.
As mentioned above, the rectification part of the general-purpose inverter adopts a diode uncontrollable bridge rectification circuit, and the intermediate filter part uses a large capacitance as a filter. Therefore, the input current of the rectifier is actually the charging current of the capacitor, which is a relatively steep pulse wave, and its harmonic component is large. In order to eliminate harmonics, the following countermeasures can be taken:
(1) Increase the internal impedance of the inverter power supply
Normally, the internal impedance of the power supply device can act to buffer the reactive power of the DC filter capacitor of the inverter. This internal impedance is the short-circuit impedance of the transformer. When the power supply capacity is smaller than the inverter capacity, the internal impedance value is relatively larger, and the harmonic content is smaller. When the power supply capacity is larger than the inverter capacity, the internal impedance value is relatively larger, and the harmonic content is larger. For Mitsubishi FR-F540 series inverters, when the internal resistance of the power supply is 4%, it can play a very good harmonic suppression effect. Therefore, when selecting the inverter power supply transformer, it is best to choose a transformer with a short circuit impedance.
(2) Install reactor
The installation of the reactor actually increases the internal impedance of the inverter's power supply from the outside. Install an AC reactor on the AC side of the inverter or install a DC reactor on the DC side of the inverter or install it at the same time to suppress harmonic current.
(3) Transformer multi-phase operation
The rectification part of the general-purpose inverter is a six-pulse rectifier, so the harmonics generated are large. If the multiphase operation of the transformer is applied, the phase angles are different from each other by 30! For example, the combination of two transformers of Y-, - is equivalent to 12 pulses, which can reduce the low-order harmonic current by 28%, and has a good harmonic suppression effect.
(4) Adjust the carrier ratio of the inverter
As long as the carrier ratio is large enough, the lower harmonics can be effectively suppressed. Especially when the reference amplitude and the carrier amplitude are less than 1, the odd harmonics below 13 are no longer present.
(5) Dedicated filter
The dedicated filter is used to detect the amplitude and phase of the harmonic current of the inverter, and generate a current with the same amplitude and opposite phase as the harmonic current, which is passed to the inverter, so that the harmonic current can be absorbed very effectively.
3 load matching problem and its countermeasures
There are many types of production machinery, performance and process requirements are different, and the torque characteristics are complex. There are three general types: constant torque load, fan pump type load and constant power load. Different types of frequency converters should be selected for different load types.
(1) Constant torque load
Constant torque load means that the load torque is independent of the speed. At any speed, the torque remains constant. The constant torque load is further divided into a friction type load and a potential energy type load.
The starting torque of the friction type load generally requires about 150% of the rated torque, and the braking torque generally requires about 100% of the rated torque, so the inverter should select those with constant torque characteristics, and the starting and braking torque. The inverters are relatively large, with long overload time and large overload capacity. Such as Mitsubishi inverter FR-A540 series.
The position energy type load generally requires a large starting torque and energy feedback function, which can realize the forward and reverse rotation quickly. The frequency converter should select the frequency converter with four quadrant operation capability. Such as Mitsubishi inverter FR-A241 series.
(2) Fan pump load
Fan pump load is the most widely used equipment in industrial field. Although the characteristics of pumps and fans are various, it is mainly used in centrifugal pumps and centrifugal fans. General-purpose inverters are the most widely used in such loads. The fan pump type load is a square torque load. The speed n and the flow rate Q, the torque T and the shaft power N of the pump have the following relationship:
T=KLn 2 N=PKn 3 n=n0Q/Q
This type of load does not require high performance of the inverter, only economical and reliable, so choose a frequency converter with U/f=const control mode. Such as Mitsubishi inverter FR-F540 (L) series.
During the actual operation of the fan load, the acceleration time and deceleration time of the inverter are a very important problem because the moment of inertia is relatively large. When the inverter starts, there is no overcurrent trip and the inverter decelerates without overvoltage trip. In the case, choose the shortest time.
In the actual operation process, the pump load is prone to surge, pressure and water hammer. Therefore, when selecting the inverter, select the inverter suitable for the pump load and the inverter should address the above problems when the function is set. Make separate settings:
Surge: Measure the frequency point at which surge is likely to occur. By setting the jump frequency point and width, avoid resonance in the system.
Rolling pressure: When the pump load is running at low speed, the flow is zero due to system pressure, which causes the pump to burn out. When the inverter function is set, the minimum system speed at the critical point of the pump flow is limited by limiting the lowest frequency of the inverter, which avoids such phenomena.
Hammer effect: The pump load reverses due to the gravity of the liquid in the pump pipe during a sudden power failure. If the check valve is not strict or there is no check valve, the motor will be reversed, and the inverter will be burned out due to motor power generation. When designing the inverter system, the inverter should be stopped according to the deceleration curve, and then the main circuit power is disconnected after the motor is completely stopped, or the power-off deceleration stop function is set, thus avoiding this phenomenon.
(3) Constant power load
A constant power load is a load that is generally inversely proportional to the rotational speed, such as a coiler, an unwinder, and the like. When using a frequency converter to drive a constant power load, it should be in terms of a certain speed variation range. Usually, a constant torque speed regulation method is adopted below a certain speed point, and a constant power adjustment is adopted when the speed point is higher than the speed point. Speed ​​mode. We usually refer to this speed point as the fundamental frequency, and the corresponding voltage is the rated output voltage of the inverter. In theory, in order to achieve true constant power control, the output frequency f and output voltage U of the inverter must follow the U/f=const coordinated control, but this is not allowed during the actual inverter operation. Because the output voltage of the inverter can't increase with the output frequency above the fundamental frequency, it can only maintain the rated voltage, so it can only be a constant power control in the approximate sense.
4 fever problems and countermeasures
The above methods have proved to be feasible. They have been widely installed in the installation of the Wuxi Xianyuqiao Water Conservancy Pumping Station and the overhaul of the Zhenjiang Dianbi Pumping Station. The method is simple, the effect is good, the processing time is short, the installation and maintenance time of the unit is greatly shortened, and the work efficiency is improved.
What needs to be explained here is that I did not deny the intention of the textbook, but summarized the new method in practice. The purpose of writing this article is to work together to improve the technical level of the pumping station. Due to the limited level, it is inevitable that there are deficiencies, please experts criticize.
The main parts of the loss are mainly dominated by the main circuit, accounting for 98%, and the control circuit accounts for 2%. In order to ensure the normal and reliable operation of the inverter, the inverter must be dissipated. The following methods are usually used: (1) Fan cooling : The built-in fan of the inverter can take away the heat dissipation inside the cabinet of the inverter. If the fan does not work normally, stop the inverter immediately.
(2) Reduce the installation environment temperature: Since the inverter is an electronic device, which contains electronic components, electrolytic capacitors, etc., the temperature has a great influence on its life. The ambient operating temperature of general-purpose inverters generally requires -10~50#. If measures can be taken to reduce the operating temperature of the inverter as much as possible, the service life of the inverter will be extended and the performance will be stable.
We take two methods: one is to build a separate low-voltage room for the inverter, and the air conditioner is installed inside to keep the low-temperature temperature between +15~+20#. Another method is to install the inverter in accordance with the requirements of the inverter manual.
The above mentioned inverter heating refers to the loss of the inverter operating normally within the rated range. When the inverter is abnormally operated (such as overcurrent, overvoltage, overload, etc.), the loss must be avoided by normal selection.
For the fan pump type load, when we select the Mitsubishi inverter FR-F540, the overload energy is 120%/60s, and the overload period is 300s, that is, when the inverter is overloaded with 120% of its rated load, Its duration is 60s and a second overload is not allowed within 300s. When the inverter is overloaded, the power unit heats up due to the overload current flowing through it, causing the inverter to overheat. At this time, it must be cooled as soon as possible to eliminate the overheat protection action of the inverter. This cooling process is the overload period of the inverter. . Different frequency converters have different overload ratios, overload times and overload periods, and the larger the overload factor, the shorter the overload time.
For the motors driven by the inverter, they can be divided into two categories according to their working conditions: long-term working system and repeated short-time working system. Long-term working motors can be operated for long periods of time according to the data specified by their brand name. For this type of load, the inverter can be selected according to the motor nameplate data, such as the oil pump that runs continuously. If the motor power is 22kW, the FR-F540-22k inverter can be selected. Repeated short-time work-making motor, which is characterized by repeatability and short-term performance, that is, the working time and stop time of the motor are alternately performed, and they are all relatively short. The sum of the two cannot exceed 60s according to national regulations. Repeat short-time work The motor allows it to be overloaded and has a certain temperature rise. At this time, if the inverter is selected according to the motor nameplate data, it will inevitably cause damage to the inverter. For this type of load, the inverter should be selected according to the motor load map and the overload ratio of the inverter, overload time and overload period in the case of referring to the motor nameplate data. For example, the elevator with short-time operation has a motor power of 18.5 kW and can be selected from FR-A540-22k inverter.
5 Conclusion
In this paper, through the analysis of the problems existing in the operation of general-purpose inverters, the practical countermeasures to solve these problems are put forward. With the application of new technologies and new theories on the inverters, these problems in the inverters are expected to pass through the inverter itself. Function and compensation to solve.
As the requirements for inverters in industrial and social environments continue to increase, real green inverters that meet actual needs will soon be available.
Analysis of inverter faults and countermeasures
1 Overview