Two, the application of frequency converter in centrifuge
2.1 Frequency converter application
In recent years, frequency converter as a kind of industrial control equipment in the continuous updating of the development of all walks of life has a wide range of applications. With the power electronics technology, frequency control theory, microcomputer control technology continues to mature, the performance of the frequency converter continues to improve, the function is also constantly enhanced: such as multi-band speed, programmable automatic operation, communication functions, which use the frequency converter can adapt to a variety of applications. According to the centrifuge's production process, can use the frequency converter's multisection speed function control to realize, in addition to the frequency converter generally with built-in braking unit or external braking unit, which can solve the centrifuge in the stopping due to inertia caused by the parking difficulties.
2.2 Triple crystal SA-J8000 series inverter in the application of centrifuge
Centrifuge load for constant torque and large inertia loads, here the selection of Guangzhou triple crystal company specializing in the production of SAJ-8000G series of general-purpose inverter. The motor power of 5.5kW, 6 pole for example, choose SAJ-80007R5G3 inverter, its external control circuit is shown in Figure 1, where the start signal of K1 connected to the frequency converter FWD multi-function control terminal, K2 multisection speed 1 connected to the frequency converter's MI1, K3 multisection speed 2 connected to the frequency converter's MI2, K4 multisection speed 3 connected to the frequency converter's MI3, according to the needs of the selection of the three-section speed, namely Low-speed operation, medium-speed operation and high-speed operation, the specific running speed can be set by the corresponding parameters.
Figure 1 Centrifuge frequency conversion external control diagram
2.3 Three crystal inverter main parameter setting
General-purpose frequency converter main circuit is shown in the figure below.
According to the centrifuge load characteristics, set the following main parameters:
Function code Parameter setting Remarks Function code Parameter setting Remarks
F000 50.00HZ Main frequency F026 20S Deceleration time for medium-speed operation
F001 200S Acceleration time F027 48HZ High-speed operation frequency
F002 200S Deceleration time F028 20S Acceleration time for high-speed operation
F005 1.0HZ Brake start frequency F029 20S Deceleration time for high-speed operation
F006 5% Brake voltage F030 0 Deceleration braking mode stopping
F007 22S DC action time F031 1 Prohibition of reverse rotation
F008 0.5 DC action delay time F033 2 Starting discharge brake circuit
F021 30.00HZ Low-speed operation frequency F039 2.0 External terminal control
F022 20s Low-speed operation acceleration time F040 0.08 Setting selection of operation frequency
F023 20S Low-speed operation deceleration time F041 4 MI1 Terminal Function Selection
F024 40HZ Medium Speed Running Frequency F042 3 MI2 Terminal Function Selection
F025 20S Medium Speed Running Acceleration Time F043 2 MI3 Terminal Function Selection
2.4 Application of Triple-Crystal Brake Units
The centrifuges are large inertial loads, and the use of frequency converters requires the addition of brake units to meet the requirements. However, the built-in braking unit of 15KW and below inverter not only saves installation space for users, but also saves cost. By the operating characteristics of the motor when the actual speed of the motor is higher than the synchronous speed when the motor is running in the generator state, when the centrifuge began to stop when the output frequency of the inverter began to decline according to the deceleration time, due to the inertia of the load the centrifuge at this time the speed does not change much, resulting in the actual speed of the motor is higher than the synchronous speed, the motor is in the generator braking state, by the inverter's main circuit know that the motor side of the feedback back to the energy will be Through the inverter circuit of the continuous current diode D1-D6 feedback to the DC circuit of the filter capacitor C1, C2, then the frequency converter bus voltage Ud will rise (i.e., pump-up voltage), too high pump-up voltage will make the frequency converter over-voltage protection, or even damage to the frequency converter, for this reason, it must be retrofitted with a braking component, when the control circuit of the braking unit detects the DC bus voltage reaches a certain value to control its switching tube IGBT open, braking resistor RB received in the circuit, the motor feedback braking energy consumption in the resistor, in order to maintain the normal bus voltage Ud.
3 debugging attention to the problem
According to the centrifuge load characteristics, in the debugging should pay attention to:
(1) centrifugal machine load starting torque requirements are higher, there may be a difficult starting situation, then you can appropriate Enhance the torque compensation value of the frequency converter, the setting parameter of SAJ-8000-G series F009 is 3, but the starting torque compensation should not be too big, otherwise there may be alarms of overcurrent (fault code O.C.), overload (fault code O.L.), etc., and if there is an alarm of overcurrent in accelerating the speed, the accelerating time should be prolonged appropriately;
(2) the inertia of the centrifuge is big, and if you want to stop the centrifugal machine according to the decelerating time, you must install a brake to stop the machine. Deceleration time to stop, must be installed with a braking unit, the braking resistor selection of the frequency converter instruction manual have, can be selected according to the operation manual, normal operation of the braking resistor will be due to the consumption of energy and heat, can be appropriately enlarged resistor power and braking action time.
(3) General centrifuges are installed in the operating site, multiple inverters are centrally located in the control room, if the site and the centrifuge distance exceeds the permissible range of the frequency converter should be taken accordingly to deal with measures such as reasonable distribution of the main circuit line and the control line, the addition of output reactors or filters, in order to prevent the attenuation of the output voltage of the frequency converter, or consider increasing the capacity of the frequency converter.
4 Conclusion
The centrifuge adopts the frequency conversion speed control can be according to the different process requirements for speed regulation, according to the different materials can be convenient to choose the multi-stage speed operation, and at the same time using frequency control to realize the soft start of the motor, reduce the impact on the power grid, frequency converter has overcurrent, overload, overvoltage and other rich protection function, when the load or motor abnormal frequency converter due to fault shutdown and fast blocking output, this can protect the timely protection of the motor, and the motor can also be used to protect the motor. Quickly block the output, which can protect the motor in time.