Construction of multi-motor drive system
In the four independent drive rolls spun after the chemical fiber, in order to maintain a certain draft ratio, usually one draft and two draws are in a power generation state, and three draws and curls are in an electric state.
2.1 Electric and power generation
Usually from the two operating states of the drive speed control system, namely electric and power generation. In the variable frequency speed control system, the speed reduction and stop of the motor are realized by gradually reducing the frequency. At the moment of decreasing the frequency, the synchronous speed of the motor decreases, and the rotor speed of the motor is not due to the mechanical inertia. change. When the synchronous speed w1 is smaller than the rotor speed w, the phase of the rotor current is almost changed by 180 degrees, and the motor changes from the electric state to the power generation state; at the same time, the torque on the motor shaft becomes the braking torque Te, so that the motor The speed of the motor drops rapidly and the motor is in regenerative braking. The electric energy P regenerated by the motor is fully rectified by the freewheeling diode and fed back to the DC circuit. Since the power of the DC circuit cannot be fed back to the grid through the rectifier bridge, it is only absorbed by the capacitance of the inverter itself. Although other parts can consume electric energy, the capacitor still has a short charge accumulation, forming a “pumping voltage”, so that the DC voltage Ud Raise. Excessive DC voltage will damage all parts of the device.
How to deal with regenerative energy? The easiest way is to use energy braking. It uses the method of adding a discharge resistor unit to the DC side of the inverter to dissipate the regenerative energy on the power resistor to achieve braking, but because of one and two The drafting drive is always in the state of power generation, and its power generation is quite considerable. In actual operation, a large braking resistor group is required. Therefore, how to use this electric energy is an urgent problem to be solved.
2.2 Construction of multi-motor drive control
For motors that are frequently started, braked, or operated in four quadrants, how to handle the braking process not only affects the dynamic response of the system, but also has economic benefits. Therefore, feedback braking has become the focus of discussion. However, most of the general-purpose inverters cannot realize the regenerative energy through a single inverter. In order to solve this problem, this paper introduces a regenerative energy feedback system with a shared DC bus method. In this way, it can fully utilize the regenerative energy generated by braking, thereby saving energy and regenerating electric energy. .
The multi-transmission control loop includes a DC input loop, a DC bus supply loop, and a number of inverters (or a general-purpose inverter with input phase loss protection), wherein the energy required by the motor is output through the PWM inverter in a DC mode. In the multi-drive mode, the induced energy during braking is fed back to the DC link. Through the DC loop, this part of the feedback energy can be consumed in other motors in the electric state. When the braking requirements are particularly high, only the common busbar and the common brake unit need to be used.
Figure 2 wiring is a typical shared DC bus braking method. According to the characteristics of the chemical fiber spinning equipment, one drafting M1 and two drafting M2 are in the power generation state during normal operation, and the three drafting M3 and the crimping M4 are in Electric state. Since the M1 and M2 power generation is caused by the three-way drafting electric motor, the feedback energy generated by the two motors is enough to be consumed in the M3 and M4 in the electric state without causing the DC link bus voltage to rise. This completely solves the problem of braking of regenerative energy, so that the system is always in a relatively stable state.
2.3 DC input loop
The DC input circuit is responsible for providing the DC power supply of the multi-motor drive system, the main component of which is the rectifier. However, we know that when the AC/DC power supply is started, it will generate a starting current of up to 50 times the nominal current of the system to charge the input capacitor (this is mainly referred to as the electrolytic capacitor of the VF1-VF4 inverter). This startup current can cause a voltage drop on the main power supply, which can affect the normal operation of other devices connected to the same power network, and even blow the input line fuse. Normally, the front end of the off-line power supply consists of a bridge rectifier and a large-capacity filter capacitor. The charging of the large-capacity filter capacitor at startup generates a surge current called the startup current at the input. If this starting current is not limited, the input fuse may blow or may trigger a circuit protection circuit breaker. Therefore, the core problem of the DC input loop is to control the starting current. One solution to this problem is to connect the impedance in parallel with a silicon via component or electromechanical relay and then in series with the rectifier, which greatly reduces the inrush current to ensure the reliability of the DC input loop.
2.4 characteristics of multiple motor drives
The chemical fiber post-spinning equipment adopts the multi-motor transmission control mode of the shared DC bus, which has the following remarkable features:
a. The shared DC bus and the shared braking unit can greatly reduce the repeated configuration of the rectifier and the braking unit, and the structure is simple and reasonable, and economical and reliable.
b. The intermediate DC voltage of the shared DC bus is constant, and the parallel storage capacity of the capacitor is large;
c. Each motor works in different states, the energy feedback is complementary, and the dynamic characteristics of the system are optimized;
d. Improve system power factor, reduce grid harmonic current, and improve system power efficiency.
Please pay attention to Dc 360 Motor
