Frequency inverter brief introduction
Frequency inverter, mainly composed of rectifier (AC to DC), filter, inverter (DC to AC), brake unit, drive unit, detection unit, micro-processing unit, etc., is a kind of electric control equipment, which uses frequency conversion technology and microelectronic technology to control AC motor by changing the working power frequency of the motor. In general, frequency inverter adjusts the voltage and frequency of output power supply by the breaking of internal IGBT, and provides the required power supply and voltage according to the actual needs of the motor, so as to achieve the purpose of energy saving and speed regulation. In addition, the inverter also has many protective functions, such as over-current protection, over-voltage protection, over-load protection and so on. With the continuous improvement of industrial automation, frequency inverter has also been widely used.
The figure above is a circuit that with variable AC frequency. Among them, P and N are converter circuits, which can adjust AC to DC and load it to load Z. When the pulse signal to P is sinusoidal, the tuned DC is sinusoidal, which is the first half of the sinusoidal curve, and the period is the sinusoidal regular period of the pulse signal, which is an integral multiple of the AC period. Through the cooperation of P and N, the periodic sinusoidal current on load Z is formed, and the frequency can be adjusted according to the period of pulse signal, which is the working principle of the frequency inverter.
Frequency inverter benefits
1. Adjustable torque limit
After adjusting the speed by frequency conversion, the corresponding torque limit can be set to protect the machine from damage, so as to ensure the continuity of the process and the reliability of the product. At present, the frequency conversion technology makes not only the torque limit adjustable, but also the control accuracy of the torque reach about 3%-5%. In the power frequency state, the motor can only be controlled by detecting the current value or thermal protection, but can not be operated by setting the precise torque value as in the frequency conversion control.
2. Controllable stopping mode
Like controllable acceleration, the stopping mode can be controlled in the frequency control system and different stopping modes can be selected (decelerated parking, free parking, decelerated parking + DC braking). Similarly, it can reduce the impact on mechanical components and motors, thus making the whole system more reliable and prolonging the service life accordingly.
The energy saving of frequency inverter is mainly manifested in the application of fans and pumps. In order to ensure the reliability of production, all kinds of manufacturing machine have a certain amount of surplus when they are designed and equipped with power drive. When the motor fails to run under full load, it may not meet the requirements of power drive or excess torque increases the consumption of active power, resulting in waste of electrical energy. For traditional equipment such as fans and pumps, the frequency control method is to adjust the air supply and water supply by adjusting the baffle and valve opening at the inlet or outlet, where has a large input power, and a large amount of energy is consumed in the process of closure by the baffle and valve. In the use of frequently control, when the flow requirement is decreased, the frequency control can be achieved by reducing the speed of the pump or fan.
4. Reversible operation control
In the control of frequency inverter, there is no need for additional reversible control devices to realize reversible operation control, just change the phase sequence of output voltage, which can reduce maintenance costs and save installation space.
5. Reduce mechanical transmission components
At present, vector control converter plus synchronous motor can achieve high-efficient torque output, thus saving mechanical transmission components, such as gearboxes, and ultimately constituting a direct frequency conversion drive system. Thus, the cost and space can be reduced and the stability can be improved.
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