Variable-frequency drive (VFD) is a power control device that controls the AC motor by changing the working frequency of the motor by applying variable frequency technology and microelectronic technology. The frequency converter is mainly composed of rectification (AC to DC), filtering, inverter (DC to AC), braking unit, drive unit, and detection unit micro processing unit.
The inverter adjusts the voltage and frequency of the output power supply by the internal IGBT breaking, and supplies the required power supply voltage according to the actual needs of the motor, thereby achieving the purpose of energy saving and speed regulation. In addition, the frequency converter has many protection functions. Such as overcurrent, overvoltage, overload protection and so on. With the continuous improvement of industrial automation, inverters have also been widely used.
The main indicators to measure the performance of a general-purpose inverter are: starting torque, control mode, torque control accuracy, speed control accuracy, speed control mode, control signal type, frequency hopping function, carrier frequency, multi-speed setting, communication Interface, etc. The correct selection of the frequency converter plays a vital role in the normal operation of the electronic control system of the mechanical equipment.
Xiao Bian suggested that when you select the inverter, you must first understand the type of mechanical equipment, load torque characteristics, starting torque, speed range, static speed accuracy and requirements of the use environment, and then decide the choice. Which type of control and protection structure is used is the most suitable. The so-called suitable is a statement made under the premise of meeting the requirements of the actual process production and the use of mechanical equipment, and realizes the best cost performance for the application of the frequency converter.
Specifically, the selection of the low-voltage general-purpose inverter includes two aspects: the type selection and the capacity selection of the low-voltage general-purpose inverter. The basic principle of selecting the inverter has two aspects: the special function of the inverter ensures that the process requirements are reliably realized, and the relative requirements can be obtained. Better price/performance ratio.
In order to ensure the functional requirements of the inverter to reliably achieve the process requirements, the following technical parameters should be closely monitored when selecting the inverter:
1. Select the inverter according to the actual working current of the motor.
The actual working current of the motor is the most critical factor for the selection of the inverter. The inverter must meet the actual operating current of the inverter when it is working for a long time. Remember! ! !
In the project, the motor is usually selected first, and then the inverter is selected according to the motor. The actual working current of the motor is not the rated current marked on the nameplate of the motor. The inverter should be familiar with the working conditions before the selection of the inverter. The relationship between the working current of the motor and the change with time is estimated, and then the model of the corresponding inverter is determined.
1.1. Under normal circumstances, the inverter drives the constant torque load motor and selects the inverter based on the rated current of the motor.
1.2 Under normal circumstances, the inverter drives the motor of the fan and pump load, and selects the inverter based on the rated current of the motor.
1.3. For motors that are often overloaded for a short period of time, it is necessary to calculate the overload period and overload current.
The inverter drives the motor of this type of load, and the maximum output current Imax of the inverter is required to be greater than the peak current of the motor, and the parameter I2t of the inverter is within the range allowed by itself. It is possible to enlarge one or several files when the inverter is selected. To meet the needs of the site. Now take 10kW, 20A rated current motor as an example: If the motor works intermittently, the peak current is 40A (2 times rated current) during overload operation within 1 second, then stop running for 20 seconds. At this time, the inverter overload curve is used: firstly, the curve of the motor current changes with time, and secondly, whether the output current curve of the inverter can cover the motor current curve (that is, whether the inverter output current exceeds the actual operation of the motor) Current), only the inverter model whose inverter output current curve covers the motor current curve is applicable to the motor with heavy load. For heavy-duty inverter selection, there are often some empirical data to refer to.
Inverter overload capacity Delixi products are better, generally allow 1.6 times short-term overload. Refer to the inverter selection sample for the overload capability of different brands of inverters.
1, the impact of temperature inverter
When selecting the inverter, the ambient temperature should be taken at -10 to 40 °C. If the temperature of the working environment is higher than 40 °C, the inverter should be derated by 5% for every 1 °C increase; the working environment When the temperature is 10 °C per liter, the life of the inverter will be halved, so the problem of the surrounding environment and the heat dissipation of the inverter must be solved.
2, the impact of humidity on the inverter
When selecting the inverter, if the air humidity is less than 90%, the relative humidity of the air is less than or equal to 90%, and there is no condensation. If the humidity is too high and the humidity changes relatively, the inside of the inverter is prone to condensation, so the insulation performance will be greatly reduced, and even a short circuit will be caused. If necessary, a desiccant or heater must be added to the tank.
3. The influence of altitude on the inverter
The inverter can be installed at rated altitude with an altitude of 1000m or less. When the altitude exceeds 1000m, its output power will decrease.
4, the impact of dust on the inverter
In the case of metal conductive dust, it is not advisable to install the inverter. Because the conductive dust will invade the inside of the inverter, it will easily cause the internal circuit of the inverter to be short-circuited. In severe cases, the inverter will be burnt. Be sure to think about this when selecting the drive.
Commonly used voltages are single-phase AC 220V, three-phase AC 220V, three-phase AC 380V and three-phase AC 690V. The incoming power supply is determined by the voltage level of the existing upstream transformer and should be specified at the beginning of the inverter selection. The voltage level determines the way the motor junction box is wired. The star connection has higher pressure resistance and smaller operating current than the delta connection. The incoming line power frequency is generally 50Hz, the inverter has a relatively high tolerance to the incoming line frequency fluctuation, and the inverter diode rectifier bridge is not sensitive to the frequency.
Fourth, the correct choice of inverter cooling methodCommon low-voltage inverters below 1000VAC are mostly internal air-cooled. In the group drive of high-power inverters, the operating noise of the inverter cooling fan is very large. Water-cooled series inverters can be used if necessary.
V. External configuration requirements for inverter selection1. For inverters that do not have a fast fuse for protecting the silicon device before the internal rectifier circuit, proper fuses and isolating switches should be placed between the inverter and the power supply. (The air circuit breaker cannot be used instead of the fuse and the isolating switch. ) to avoid damage to the inverter rectifier device due to internal short circuit.
2. According to the power of the inverter, select the inverter to introduce and withdraw the cable. If the inverter is to the motor, it is better to use the shielded cable if it is economical, and it should be as short as possible to reduce the capacitive leakage current and electromagnetic radiation. If the actual length of the actual power cable exceeds the allowable output cable length of the inverter, the inverter should be equipped with an output reactor to avoid the stray capacitance of the excessive cable affecting the normal operation of the inverter.
The variable frequency control signal and the inverter feedback signal should be shielded and well grounded to reduce the interference of the frequency converter to other instruments and control systems.
3. If EMC filter or AC reactor is installed at the input end of the inverter, it can effectively suppress the electromagnetic interference caused by the on/off of the inverter power device, and meet the requirements of the grid quality of other equipment in the working condition of the inverter. Note: The neutral point of the transformer in the grid is not grounded, and the EMC filter cannot be used at the input of the inverter.
When selecting the inverter, you can follow the following six steps:
1. Defining the working mode, capacity and load type of the equipment
2. Defining the process, performance indicators and control requirements of the equipment
3. Determine the internal system's formation mode, I/O interface, communication interface, etc. 4. Inductively summarize various performance indicators and requirements.
5. Conduct technical consultation or direct bidding on the results after induction.
6. Comprehensive comparison of inverter performance, inverter service life, inverter price and inverter service
Seven, the frequency converter selection considerations1, pay attention to the voltage
Domestic voltage is divided into three types: low voltage, medium voltage and high voltage. Generally speaking, low voltage includes single phase 220v, three phase 220v (usually applicable to foreign countries, Hong Kong, Macao and Taiwan regions) and three-phase 380v. Generally, three-phase 380v and single phase are used. 220v, the seat must be clear when selecting the voltage, if you choose the wrong, you can not use.
2, pay attention to whether the motor is installed with capacitor
If the motor is a capacitive single-phase motor, the principle of the motor itself is to phase shift the starting winding voltage of the motor by using the phase advance characteristic of the capacitor, thereby generating a rotating magnetic field in the stator of the motor to drive the motor. Once the inverter is directly connected to it, the high-frequency pulse is a path for this capacitor, and it cannot function as a phase shift. It is equivalent to connecting the main winding and the starting winding at the same time, but cannot generate a rotating magnetic field. The motor current will increase sharply due to the blockage, thus burning the inverter IGBT module and motor
3. Is the power consistent?
When selecting the inverter, the power of the inverter must be greater than or equal to the rated power of the motor. If the running load of the motor is relatively large, then the load inverter should be used or the gear position of the inverter should be amplified, so as to ensure the normal operation of the motor of the equipment. When choosing a frequency converter, we must pay attention to the situation of electricity consumption and the motor itself. After all, the main thing we should consider in this line is safety and efficiency. Therefore, when we are uncertain about the motor condition, we should buy a large gear or a better performance. I have to ask the technician some questions about this.
Lcd Tonch Screen For Iphone 8,Lcd Touch Screen For Iphone 8P,Lcd Display For Iphone 8P,Mobile Lcd For Iphone 8P
Shenzhen Xiangying touch photoelectric co., ltd. , https://www.starstp.com