Analysis of VFD (Variable-frequency Drive) in centrifuge

The ACS550 used in this article is the latest intelligent VFD (Variable-frequency Drive) launched by ABB Company. This series of VFD (Variable-frequency Drive) is used for low-voltage AC drives of 0.75KW to 355KW. It can precisely control speed and torque, and can match existing standard squirrel cage asynchronous motors. ACS550 has three control methods, namely scalar V/F control, sensorless vector control, and torque control, so this VFD (Variable-frequency Drive) is not only suitable for the simplest motor operation, but also can be applied to complex workplace. Its reliable overload capacity design can also meet the normal load and heavy load work at the same time. The driving motor of separation machinery is generally divided into two types: single motor drive and multi-motor drive. Typical case of driven decanter centrifuge application.

2. Application in VFD (Variable-frequency Drive) three-legged centrifuge

The three-legged centrifuge is a vertical centrifuge with simple structure, strong adaptability to materials and the widest application. It is divided into two categories: sedimentation type and filter type. In this application, VFD (Variable-frequency Drive) drives the drum of the centrifuge, which starts smoothly and the separation factor is adjustable; it completely overcomes the traditional DC carbon brush centrifuge's high noise, high failure rate, short service life, The shortcomings such as unstable speed are the replacement products of gravity sedimentation separation equipment. The AC frequency conversion centrifuge has distinctive features and originality in several important indicators such as shock absorption system and frequency conversion motor. The driving power of a common three-legged centrifuge is between 3KW and 55KW, and the ACS550 is fully capable.

The application principle of ACS550 in three-legged centrifuge The principle of ACS550 VFD (Variable-frequency Drive), in its peripheral circuit, is mainly divided into three parts:

(1) The DC bus UDC, UDC-terminals are connected to the braking unit and -terminal, and then according to different choices (such as the feedback braking is connected to the three-phase power grid, and the energy-consumption braking is connected to the braking resistor), Tk is the braking unit. The internal relay, when the unit fails, the Tk action is defined by the terminal DI4 of the VFD (Variable-frequency Drive), and the U/V/W output is blocked instantly.

(2) In the input and output terminals of the control loop, the definition of macro 9902=5 is adopted

DI1: manual/automatic start/stop (manual): energized start

DI2: Forward/Reverse (Manual): Turning to reverse when energized

DI3: EXT1/EXT2 selection: automatic control when electrified

DI4: Allowed to run: Once the VFD (Variable-frequency Drive) is disconnected, it will stop

DI5: Forward/Reverse (automatic): Turning to reverse when energized

DI6: Start/Stop (Automatic): Electric start

AI1: External speed reference 1: 0...10V (manual control, potentiometer, reference voltage 10VDC)

AI2: External speed reference 2: 0...20mA (automatic control, reference signal: 0...20mA)

AI1: External speed reference 1: 0...10V (manual control, reference voltage 10VDC)

AI2: External speed reference 2: 0...20mA (automatic control, reference signal: 0...20mA)

RO2C/2B: relay output 2, programmable (default action: run)

RO3C/3B: relay output 3, programmable (default action: failure)

AO1: DC digital display (frequency or rotational speed indication)

When the centrifuge uses VFD (Variable-frequency Drive), the braking method should give priority to regenerative braking that feeds energy back to the grid. Electric energy feedback braking is to feed back the braking energy back to the grid for reuse. From the perspective of energy saving, It is the best way, and there is no heat generation, which is very suitable for installation in flammable places (because dynamic braking will generate a lot of heat). In places where this kind of regenerative braking device is not suitable, if there is a requirement for grid harmonics (because the harmonic coefficient of the general energy feedback braking unit is not ideal), a braking resistor with sufficient capacity should be installed and heat dissipation measures should be taken; Of course, in non-flammable situations, energy braking is also mostly used in consideration of saving one-time installation costs.

?General dynamic braking units have the following basic functions:

(1) Parameter setting

Operating voltage setting: The setting value of the operating voltage can be set to 660V or 710V (incoming line is 380V level) through the dial switch.

Braking utilization rate: The working utilization rate of the braking unit can be set through the dial switch. The default value of the general energy consumption braking unit is 10%. However, due to the different braking requirements of the system