China Aluminum Qinghai Branch First Electrolytic Plant Zhu Youhui Aluminum Qinghai Branch Electrolytic multifunctional cranes are equipped with frequency conversion speed control and the transmission mechanism is SEW triple reducer. The main characteristic of SEW reducer is that the brake is the form of electromagnetic brake, not the mechanical brake axial thruster. During the braking process, the electromagnetic brake does not participate in the deceleration process of the motor and only plays the role of parking and positioning. Before the retrofit, because the original design of the inverter did not use electric brake, the deceleration time set value of the inverter was 10s, and the electromagnetic brake action was delayed after stopping signal. If the electromagnetic brake was operated within 5s, the motor output frequency Has not slowed down to 0Hz, the inertia of the body movement is large, the brake lock will cause great mechanical impact to the vehicle such as electromagnetic brake outside the 5s action, the taxi distance is too long, and no difference between the brake It will cause hidden dangers to the safe operation of the crane. For the electromagnetic brake of SEW reducer, the friction plate should not be adjusted, and the electromagnetic brake plays the role of parking and positioning after the end of the electric brake. In the transformation, the mode of matching the electric brake and the electromagnetic brake is very good. The safety and reliability of parking brakes are achieved.
The braking force state in the drive of the inverter, the latter one belongs to the feedback braking state, and the asynchronous motor itself is in the state of regenerative braking in both braking states. There is also a kind of braking state, that is, the asynchronous motor stator DC-DC motor braking (DC braking).
The choice of electric brake is 2X15 kW for multifunctional overhead cranes, 2X3kW for primary vehicles, and 5.5kW for secondary vehicles. The energy generated during deceleration is not too high. Therefore, the method of regenerative braking is not Economical, and the positioning and parking requirements of overhead cranes are not high, and DC braking is not used. Because of the frequent reverse movement of overhead cranes, dynamic braking is a feasible solution.
Using a braking resistor installed in the DC circuit to absorb the regenerative energy of the motor is used for dynamic braking. The dynamic braking generally includes a braking unit and a braking resistor. The braking unit and the resistance are used to absorb the energy of the regenerative braking of the motor. The freewheeling time for large inertia loads can be shortened as shown in the braking unit.
In the transmission system, when the motor decelerates or the transmitted bit energy is decentralized, the asynchronous motor will be in the regenerative braking state. The mechanical energy stored in the transmission system is converted into electrical energy by the asynchronous motor, and the six feedbacks of the inverter The diode feeds back this energy to the DC side. At this time, the inverter is in a rectified state. If no other measures are taken in the inverter, this part of the energy will increase the voltage of the storage capacitor of the intermediate circuit. If the motor brake is not too fast, the capacitor voltage does not increase significantly. Once the motor returns to the electric state, this part of energy is repeatedly rejected by the load. When the brake is fast, the capacitor voltage will rise very high. The "brake overvoltage protection" in the device will act, so this part of the energy should be handled carefully when the brake is fast.
There are three ways to deal with regenerative energy, and three types of capacitors that are dissipated in the DC loop are set to be connected to the capacitor and the 'brake resistance' is connected to the capacitor. The other 2 ft. working in parallel on the direct current loop absorbs it and returns it to the grid. The main features of the bookmark3 SEW reducer for dynamic and single-acting dynamic braking and SEW triple reducer are: The brake is the electromagnetic brake type, not the mechanical brake (the hydraulic thruster). Electromagnetic brake does not participate in the deceleration process of the motor during braking, and only plays the role of parking and positioning.
In the above, the main circuit diagram should be as the right drawing, which is hereby corrected.
The ± circuit brake unit consists of transistor vB, diode VDB and braking resistor, and the feedback energy of the overhead crane trolley is large, so the external resistor B connected to points H and G is selected. When the motor brakes, the energy After the inverter feeds back to the DC side, the capacitor voltage on the DC side rises. When the value exceeds the set value, a base signal is applied to VB to turn it on, and (B) is connected in parallel with the capacitor and stored in the capacitor. The feedback energy is consumed by (,).
In the control loop, by controlling the software function of the brake unit and properly setting the functions of the control panel, dynamic braking can be conveniently realized.
The brake unit is mounted inside the cabinet and the brake resistor is mounted outside the cabinet.
2. Connection between Braking Unit and Inverter The inverter adopts FRN G9S series from Japan Fuji Electric. The connection with the braking unit is as shown.
The main and sub car inverters have a power of 7.5 kW. Therefore, the inverter is equipped with a braking unit and a braking resistor. However, considering the reliability of the braking, an external braking resistor with a larger capacity of 60D and 1200W and an inverter is selected. External resistor terminals P(+) and DB are connected.
In kW, no resistance is installed inside the inverter. In order to increase the braking capacity, a matching braking unit must be selected. The P(+) and terminals of the braking unit are connected to the main circuit P(+) and N(-) terminals of the inverter respectively. The braking resistor is connected to the P(+) and DB terminals of the braking unit. The overheat protection devices 1 and 2 of the braking unit and braking resistor are connected to the THR and CM terminals of the inverter control circuit. The main circuit of the inverter is Terminals P1 and P(+) are connected to DC reactors to improve the power factor. The distance between the braking unit and the braking resistor is less than 10 m. The braking resistor uses four 60D and 1200W braking resistors.
It is easy to realize electrical braking and reliable, but in order to generate the holding torque at rest, it should be used together with the electromagnetic brake. The use of dynamic braking can generate the braking torque needed to shorten the parking time of overhead cranes. The electromagnetic brake torque produced by SEW reducer electromagnetic brakes provides the braking torque during stationary braking. Two types of braking methods are available. The mutual cooperation satisfies the need for safe stopping, and at the same time, the electromagnetic brake is a remedial measure for safe stopping after the inverter has failed. Two types of braking are essential. The use of the electric brake and the electromagnetic brake of the speed reducer is mainly realized by PLC software programming. When the PLC receives the crane walking instruction, the electromagnetic brake is first activated, and the inverter can be started after the electromagnetic brake is opened. When the inverter is decelerating to zero frequency when it is stopped, the vehicle body will basically reach zero speed by dynamic braking, and then the electromagnetic brake delay action will achieve parking positioning. The cart control PLC program control process as shown in the EA open touch action to open the game