Overview:
Variable-frequency Drive use frequency conversion technology and microelectronic technology, by changing the motor power supply frequency to control power control equipment for AC motor.
VFD is mainly composed of rectifier (ac to dc), filter, inverter (dc to ac), brake unit, drive unit, detection unit and micro processing unit, etc.
VFD can adjust the voltage and frequency for output power supply by internal IGBT cutting off , based on the actual needs of the motor to provide the needed voltage of power supply, and then achieve the goal of energy saving and speed regulating. In addition, VFD also have many functions, such as over-current, over-voltage protection, overload protection, etc.
Along with the continuous improvement of industrial automation, VFD also got very extensive application.
Function:
Frequency conversion and energy saving
The energy-saving of Variable-frequency Drive is mainly showed on the application of fan and water pump. In order to guarantee the reliability of the production, all kinds of production machinery when design with power drive, has the certain amount of surplus. When motors can’t work under full load, In addition to meet the requirements of power driven, superfluous torque increased the consumption of active power and cause the electricity waste. The traditional speed regulation method for equipments such as fan and pump is by adjusting the barrier of entry or exit and valve opening to adjust wind volume and water volume, its input power is large, and a lot of energy consumption in the process of baffle and valve closure. When use the Variable-frequency Drive to speed regulation, If traffic demand decreases, and it can meet the requirements by reducing the pump or fan rotation speed
The motor adopts Variable-frequency Drive is for speed regulation and reduce the starting current. In order to produce variable voltage and frequency, this equipment need to change the power as direct current (DC) instead of alternating current (AC), this process is called rectification.
The device can convert direct current (DC) to alternating current (AC) which scientific terminology is inverter. In general, inverter can change direct current (DC) into inverter power with fixed-frequency and voltage. Inverter with adjustable frequency and adjustable voltage, we call it Variable-frequency Drive (VFD). The waveform output by VFD is modified sine wave, it is mainly used in three-phase asynchronous motor drive for speed regulation, it is also called variable frequency speed controller. Variable-frequency power is the variable frequency inverter which is mainly used in the instrument of testing equipment with higher waveform requirement and it need to arrange waveform and output standard sine wave. The price for variable-frequency power is 15-20 times higher than VDF. Due to the main device in VDF equipment which can produce variable voltage and frequency is called inverter, so the product itself is named for inverter, that is VDF.
VDF can’t save electricity everywhere which contains several occasions. As electronic circuit, inverter itself need power consumption (About 3-5% of the nominal power). A 1.5 air conditioning need 20-30W power consumption, equivalent to an incandescent light. It is the truth that VDF has power saving function when working under power frequency. But the premise conditions are as follows:
1. High power and load for the fan/pump;
2. Device has a power saving function (software support);
This is three conditions reflected power saving function. Besides, no matter save or not save electricity, it has no sense. If advertise VDF has power saving function when working under power frequency without preconditions, it must be exaggerated or commercial hype, if you know it, you can easily let it service for you. It is important to note the usage occasion and service conditions, so that to use right application, or it is follow blindly, readily believe and fraud.
Power factor compensation and energy saving
Reactive power increase the fever of line loss and equipment, what’s more, the decreasing of power factor cause the decreasing of the grid of active power, a large number of reactive power consumption in circuit, equipment efficient is low, and waste is serious, After use frequency conversion device, because the function of filter capacitor which is the inside pats of VDF, reduce the reactive loss and increase the active power of grid.
Soft starting energy saving
1. Hard starting of motors serious impact on power grid and have higher requirement in grid capacity, the big current and vibration which is produced in starting will strong harm the baffle and valve, it is particularly harm the service life of equipment and piping, After use frequency energy saving device, soft starting function of VDF is used to make the starting current start from scratch, the maximum also shall not exceed the rated current, it reduces the impact to the grid and the requirement of power supply capacity, extend the service life of the equipment and valves and save the maintenance charge from equipments.
2. Theoretically, VDF can be used in all mechanical equipment with motor, when start the motor, the current will 5- 6 times higher than rated current, it will affect the service life of the motor and consume more power. The system is design to retain a certain margin in motor selection, the speed of the motor is fixed, but it will working with lower or higher speed in actual use process, so it is essential to do frequency conversion renovation, VDF can realize the motor soft star and power factor compensation.
