First, the industrial centrifuge is one of the main equipments in the chemical industry. It mainly separates solids and liquids through the action of centrifugal force. Generally, it consists of feeding, washing, dewatering, knife cutting, and unloading. It includes feeding, washing, and cutting. The discharge and other parts are controlled by solenoid valves and pneumatic valves. Centrifugal autoclave is the main component for solid-liquid separation and is driven by a three-phase AC motor through a belt. According to the characteristics of the process, the material is mainly a solid-liquid mixture at the initial stage. The load is relatively large when it is started. When a certain rotation speed is reached, the liquid flows out from the outside of the centrifuge under the action of centrifugal force, so that some of the liquid is first separated out and the motor rotates. With further improvement, the load is also reduced accordingly. According to the process requirements, generally divided into several different speeds to achieve the separation effect.
Second, the application of frequency converter in the centrifuge
2.1 The application of frequency converter In recent years, the frequency converter as an industrial control equipment is constantly updated and developed, and all walks of life have a wide range of applications. With the continuous maturation of power electronics, frequency conversion control theory, and microcomputer control technology, the performance of frequency converters has been continuously improved and functions have been continuously enhanced: such as multi-speed, programmable automatic operation, communication functions, etc., which can be used to adapt the inverter. Application scenarios. According to the production process of the centrifuge, the multi-speed control of the frequency converter can be used to realize the function. In addition, the frequency converter generally has a built-in braking unit or an external braking unit, which can solve the difficulty of stopping the centrifuge due to large inertia during parking. The problem.
2.2 Application of the SAIC-J8000 series inverter in the centrifuge The centrifuge load is a constant torque and high inertia load. The SAJ-8000G series general-purpose inverter specially produced by Guangzhou Sanjing is used here. Taking the motor power of 5.5 kW and 6 poles as examples, the SAJ-80007R5G3 frequency converter is used. The external control circuit is shown in Figure 1. The start signal of K1 is connected to the FWD multi-function control terminal of the inverter, and the K2 multi-speed 1 is connected to the MI1 of the frequency inverter, the K3 multi-speed 2 is connected to the MI2 of the frequency inverter, and the K4 multi-speed 3 is connected to the MI3 of the frequency converter, and the three-speed is selected according to the need. That is, low-speed operation, medium-speed operation, and high-speed operation, and the specific operation speed can be set by corresponding parameters.
Figure 1 centrifuge external control diagram of frequency conversion
2.3 Main parameters setting of the three-crystal inverter The main circuit of the universal inverter is shown in the figure below.
According to the load characteristics of the centrifuge, set the following main parameters:
2.4 Application of tri-crystal braking unit
Centrifuge is a large inertial load, the use of the inverter control requires an increase in the brake unit to meet the requirements, but the three crystal drive 15KW and 15KW following the built-in braking unit, this not only saves the user the installation space, but also saves cost. From the operating characteristics of the motor, it is known that when the actual speed of the motor is higher than the synchronous speed, the motor runs in the generator state. When the centrifuge starts to stop, the output frequency of the inverter starts to decrease according to the deceleration time, because the load inertia centrifugal centrifuge does not change at this time. Large, causing the actual speed of the motor to be higher than the synchronous speed, the motor is in the state of generative braking and is known by the main circuit of the inverter. At this time, the energy fed back by the motor side will be fed back to the DC loop through the freewheeling diodes D1-D6 of the inverter circuit. On the filter capacitors C1 and C2, the bus voltage Ud of the inverter will increase (ie pump boost voltage). Excessive pump boost voltage will cause the inverter to have overvoltage protection and even damage the inverter. The brake assembly must be installed. When the control unit of the brake unit detects that the DC bus voltage reaches a certain value, the IGBT of the switch tube is turned on, the braking resistor RB is connected to the circuit, and the braking energy of the feedback of the motor is consumed on the resistor. To maintain the normal bus voltage Ud.
3 Commissioning attention issues According to the centrifuge load characteristics, should pay attention to when debugging:
(1) The load torque requirement of the centrifuge is high, and it may be difficult to start. At this time, the torque compensation value of the inverter can be properly increased. The SAJ-8000-G Series F009 sets the parameter to 3 but the starting torque. Compensation can not be too large, otherwise there may be over-current (fault code OC), overload (fault code OL) and other alarms, if the overcurrent alarm occurs during acceleration should be appropriate to extend the acceleration time;
(2) The inertia of the centrifuge is large. If the inverter is to stop according to the deceleration time, a braking unit must be installed. The selection of the braking resistor is described in the inverter instruction manual. It can be selected according to the operating manual. The braking resistance during normal operation Heat is generated due to energy consumption, and the power of the resistor and the brake operating time can be appropriately enlarged.
(3) Centrifuges are generally installed at the operation site. Multiple inverters are placed in the control room. If the distance between the site and the centrifuge exceeds the allowable range of the inverter, corresponding treatment measures should be taken, such as the rational distribution of the main circuit and control lines. Install an output reactor or filter to prevent the inverter output voltage from decaying, or consider increasing the capacity of the inverter.
4 Conclusion Centrifugal frequency control can be used according to different process requirements for speed control, according to the different materials can be easily selected multi-speed operation, while using frequency control to achieve a soft start of the motor to reduce the impact on the grid, the inverter has over-current , overload, overvoltage and other rich protection functions, when the load or motor abnormality, the inverter stops due to faults and quickly block the output, so that the motor can be protected in time.