Drive (Variable-frequency Drive, VFD) and inverter technology is the application of microelectronic technology, controlling the AC motor by changing the frequency of the motor operating mode power supply control apparatus.
1. Function drive
frequency energy
on the drive energy applied mainly fan and pump. In order to ensure the reliability of production, all kinds of production machinery in the design equipped with power-driven, have left certain amount of surplus. When the motor can not run at full load, in addition to achieve the required drive power, the surplus torque of the active power consumption increases, resulting in waste of energy. Device conventional fans, pumps and the like is adjusted by the governor plate, the valve opening degree of the inlet or outlet of air flow and to adjust the water to which the input power, and a lot of energy consumption in the baffle plate, the valve closure procedure in. When using frequency control, if the required flow rate is reduced, by reducing the speed of the pump or fan to meet the requirements.
using the drive motor speed is to effect, and reduce the starting current. In order to produce a variable voltage and frequency, the apparatus is first necessary powerThe alternating current is converted into direct current (DC), a process called rectification. The direct current (DC) is converted into an alternating current means (AC), which is a scientific terms “inverter” (inverter). Usually the inverter is a DC power supply for the inverter frequency and a certain fixed constant voltage inverter. For frequency inverter is adjustable, adjustable voltage inverter drive we called. Waveform of the inverter output is an analog sine wave is mainly used in a three-phase asynchronous motor with speed control, also called inverter. For instruments mainly used in a waveform detection apparatus requires high variable frequency inverter, to sort waveform may be output standard sine wave, called frequency power. The general frequency inverter power supply is 15 – 20 times the price. Since the main voltage or frequency variation means of the drive device generates called “inverter”, so that the product itself is named “inverter”, namely: the frequency converter.
power frequency can not everywhere, there are many situations not necessarily a power inverter. An electronic circuit, the drive itself, but also power consumption (about 3-5 percentage of rated power). A 1.5 power of the air conditioner itself has 20-30W doing, the equivalent of a long light. In the inverter operation frequency, a power saving function, a fact. But his proviso that:
First, the power and the load for the fan / pump;
Second, the device itself has a power saving function (software support);
This is reflected in the energy-saving effect three conditions. In addition, energy-saving section does not matter, it does not make sense. If without preconditions, said inverter frequency operation of energy-saving, is exaggerated or commercial speculation. Know the whole story, you will be clever use of him for you. We must pay attention to the conditions of use and use the occasion to do correctly, otherwise blind obedience, gullible and “deceived.”
power factor compensation energy-saving
Reactive power only increase the heat losses and equipment lines, the main thing is to reduce the power factor results in a reduction of the active power, a large number of reactive energy consumed in the line which, equipment efficiency low, serious waste, the use of frequency control devices, due to internal filter capacitor of the inverter, thereby reducing the reactive power loss, increase of active power grid.
soft start saving
1: Motor hard start a serious impact on the grid, but also for the high power capacity requirements, resulting in a large current at startupAnd damage to the baffle and a valve when the shock is great, very detrimental to the life of the equipment and pipelines. After the use of energy-conversion means using a soft-start drive current will start from scratch, it does not exceed the maximum rated current, reducing the impact on power requirements and power supply capacity, the extended use of the device and the valve life. Saving equipment maintenance costs.
2: In theory, the inverter can be used in all mechanical devices with electric motor, the motor starting, current will be 5-6 times higher than the nominal, it will not only affect the service life of the motor and consume more and more power. the system was designed in the motor selection will leave a margin, the motor speed is fixed, but in actual use, sometimes you want to run at lower or higher speeds, and therefore be frequency transformation is very necessary. The frequency converter can be soft start the motor, the power factor compensation
2 drive basic composition
Drive generally divided into four parts: a rectifying unit, high-capacity capacitor, the inverter, and a controller .
rectifying unit: the fixed frequency AC power into DC power.
high-capacity capacitor: after storing the converted electrical energy.
Inverter: an array of a high-power switching transistor electronic switch, the DC power is converted into square waves with different frequencies, widths, amplitudes.
Controller: work as programmed to control the amplitude of the pulse width of the output square wave, sine wave so that approximately superimposed alternating current AC motor drive.
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Given the drive mode 3
drive mode for a given common frequency are: given operator keyboard, a given contact signal, the analog signal is given, and a pulse signal of a given communication given the like. These methods have advantages and disadvantages for a given frequency shall be selected in accordance with the desired actual setting
4. The drive control
General low voltage inverter output voltage is 380 ~ 650V, the output power of 0.75 ~ 400kW, operating frequency 0 ~ 400Hz, which are main circuit using AC – DC – AC circuit. Its control through the following four generations.