Feedback unit suppliers remind you: common DC motherboard technology is a multi-motor AC speed control system, using a separate rectification / feedback device to provide the system with a certain power DC power, speed control inverter directly attached to the DC motherboard. When the system works in the electric state, the inverter obtains electricity from the motherboard; When the system works in the power generation state, the energy is returned directly to the power grid through the motherboard and feedback device to achieve energy savings, improve equipment operating reliability, reduce equipment maintenance and equipment area.
I. Origin of common DC bus system
For motors with frequent start, braking, or four-quadrant operation, how to deal with the braking process affects not only the dynamic response of the system, but also the issue of economic efficiency. So, feedback braking has become the focus of discussion, but how can the easiest way to achieve feedback braking when most common frequency converters are not yet able to achieve renewable energy through a single frequency converter?
In order to solve the above problems, a renewable energy feedback system is introduced here in the form of a shared DC bus line, which can make full use of the renewable energy generated by braking, thus saving electricity and processing renewable electricity.
Composition of common DC bus system
Common DC bus control system usually consists of rectification / feedback unit, public DC bus, inverter unit, etc. Feedback unit can be divided into energy feedback through self-coupled transformer and energy feedback without self-coupled transformer in two ways. The energy feedback not through the self-coupled transformer is actually to keep the system in a feedback state, during the rectification process to be achieved by continuously reducing the voltage of the intermediate circuit with phase control.
Three, the principle of common DC bus system
We know that asynchronous motor multi-transmission in the usual sense includes rectifier bridge, DC bus supply circuit, several inverters, in which the energy required by the motor is output in the DC mode through the PWM inverter. In multi-transmission mode, the energy sensed when braking is fed back to the DC circuit. Through the DC circuit, this part of the feedback energy can be consumed on other electric motors in the electric state, when the braking requirements are particularly high, only need to be on the shared bus and on a shared braking unit.
The wiring shown in Figure 1 is a typical common DC motherboard braking method, M1 is in the electric state, M2 is often in the power generation state, and the three-phase AC power supply 380V is received on the VF1.
Figure 1 Feedback braking method for shared DC bus line
The frequency converter VF1, VF2 on the electric motor M1 in the electric state, is connected to the bus of VF1 by means of a shared DC bus. In this way, VF2 is used only as an inverter, and when M2 is in the electric state, the required energy is obtained by the AC grid through the rectification bridge of VF1; When M2 is in the power generation state, the feedback energy is consumed by the electrical state of M2 through the DC bus line.
The advantages of common DC bus system
1, common DC bus system is the best solution to solve multi-motor transmission technology, well solved the contradiction between the electric state and the power generation state between multiple motors. In the same system, different devices can work in different states at the same time, rectification feedback unit ensures a stable supply of public DC bus voltage, and returns excess energy to the grid, realizing the reasonable use of renewable energy.
2, the common DC bus system equipment structure is compact, stable work. In the multi-motor drive system, a large number of peripheral equipment such as brake units, brake resistors and so on are saved, saving equipment area and equipment maintenance, reducing equipment failure points, and improving the overall control level of equipment.
3, the use of common DC bus technology in multi-motor driven occasions such as roller track is a development direction of roller track speed adjustment, it can achieve high dynamic and static performance, speed adjustment accuracy while rationally using and recycling system renewable energy.
Fifth, a few points of common DC bus system design
1, the inverter needs to share the rectification device, this rectification device is a shared DC bus line special device;
2, inverter try to install together, avoid long-distance wiring, preferably in the same electrical room;
3, each inverter must be separately isolated protection device;
4, can not use a general frequency converter for public DC bus line use, otherwise there will be a danger of the blower;
The capacity power of the motor M1 ~ M4 may not be the same, but it must be considered whether the energy feedback can be used when downtime.
6, the general number of operating stations in 4 ~ 12 units (motor power can be different) a set of public DC bus is good;
7, the inverter can drive the permanent magnet synchronous motor, solve the startup impact problem;