Brief Analysis of the Braking Mode of the Frequency Conversion Drive of the Belt Conveyor
The general-purpose inverters for belt conveyors are all AC-DC-AC voltage inverters, and the uncontrollable rectifier diodes in the rectifier part
Combined, this part is capable of irreversible transmission. When the deceleration of the loading conveyor is too large or the diameters of the two driving conveyor rollers are very different
When it is large, the regenerative energy on the motor side is transmitted to the DC side, and the resistance and capacitance of the DC circuit cannot consume the regenerative energy in time, resulting in
The generated pumping voltage may damage the filter capacitor, so it is difficult for a simple general-purpose inverter to meet the requirements of the double conveyor roller drive.
Applications in belt conveyors. To choose a more suitable inverter, we must first understand the braking of the variable drive.
Mode and main circuit structure.
1. When DC braking, turn off the three-phase AC power of the main motor.
On, any two phases of the stator are connected to the DC power supply to form a fixed magnetic field. Controlling the duration and amplitude of the DC current can control the
The magnitude of the dynamic torque. Braking energy is dissipated in the form of heat on the main motor rotor. General-purpose inverters generally have DC
Braking function, it is mainly used in occasions where the braking is not very frequent and the braking force is not particularly large, such as fans and pumps
Load, generally used in conjunction with frequency reduction and deceleration, and can also be used to eliminate creep before the main motor runs. Due to the acceptor motor
Due to the limitation of rotor heating, DC braking is not suitable for long-distance and large-angle conveyors driven by double conveyor rollers.
2. The general inverter with regenerative braking cannot feed back energy to the power grid. To realize the two-way flow of energy, it must be
A group of active inverter circuits are connected in parallel with the grid-side rectifier. Siemens, Fuji and other companies have made the active inverter part into a
Separate device, so that it can be directly connected to the DC bus. However, the above-mentioned main circuit realizes the quality requirements of the power grid for active inverter
Higher. During inversion, if the power supply voltage is low or the power supply is cut off, the active inverter will be overturned and the fuse will be burned.
In addition, due to the parallel connection of a set of active inverter devices, the cost of the system increases, the volume of the feedback device increases, and the power grid is polluted
. Therefore, this form of regenerative braking is not in line with China's national conditions.
The frequency conversion circuit using dual PWM control is a close
New technologies emerging for several years dealing with energy feedback. It adopts self-shutdown device in both rectifier circuit and inverter circuit for PWM control.
control, without any additional circuit, the four-quadrant operation of the motor can be easily realized, and the power factor of the system is approximately equal to
1. Double PWM frequency conversion main circuit such as. This type of inverter has superior performance, but the price is relatively expensive. Foreign companies have already formed
products, but domestic companies have no mature products. 2. Regenerative braking is generally used in frequent braking and requires precise control of braking
In the case of speed, especially in the case of hoist, elevator and belt conveyor with high inclination angle with potential energy load, it can make
The motor runs in four quadrants, saves energy and reduces consumption, realizes precise braking, and improves the dynamic performance of the motor. 3. Energy consumption braking system
Moving is to consume the feedback energy on the high-power resistance of the DC circuit by means of built-in or external braking resistance, so as to realize the electric motor.
The four-quadrant operation of the machine. This braking method can be applied to general-purpose inverters. The method is simple in principle, low in cost,
High reliability, but waste of energy and low dynamic performance. It is mainly used for less frequent braking and less demanding braking characteristics.
Strict occasions. The energy consumption control control part detects the magnitude of the DC voltage. When it exceeds a certain threshold, the braking unit will chop the wave.
Control the access of the braking resistor. When the internal resistor power of the braking unit is insufficient, an external high-power braking resistor is required. above 3
Brake mode, dynamic braking and regenerative braking are only for the inverter, in fact, the main motor is in the state of dynamic braking
Based on the above analysis, the belt conveyor with large inclination angle is adopted Dynamic braking is a comparison
The easy way. Because the high-inclined belt conveyor does not brake frequently, it is not a potential load, and does not require precise control
Move. If the price factor is put aside, the inverter with dual PWM control is the best choice. If you have finished
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