Vector inverter:  The use of vector control in vector inverters requires torque control, low-speed high torque output, wide speed range exceeding rated speed, good control characteristics, etc.

In fact, as long as it is V/F control, vector control is OK. The requirements for debugging of vector control are a little more complicated than those of V/F control, and the determination of motor model is more stringent. That's all.

When driving in parallel, vector control is prohibited, as stipulated in the official documents released by Siemens. And the rationality of using V/F control for multi-machine parallel drive is also sufficient. Although the examples and arguments of using vector control for multiple machines in parallel have been discussed on the website, there have been quite heated exchanges in the industrial control network and the transmission column of this website. But in theory, I think there is no meaning and significance in using vector control for multiple machines in parallel. Especially non-coaxial parallel drive.

The characteristic of multi-machine parallel drive is that the load torque of each motor will not be consistent at the same time. At this time, if it is a large vector control, God knows how the excitation component and torque component of each motor are distributed. From the total power supply of the motor, it is the vector model of the motor, but it is not clear when converted to each motor. Although the equivalent model of the motor is the same, the force is different and the control will also change.

The basic idea of ​​vector control is to imitate the speed regulation characteristics of the DC motor and adjust the speed of the asynchronous motor by controlling two perpendicular DC magnetic fields.

1. Processing of given signals. In the control circuit of the vector inverter, the given signal is decomposed into two rotating DC magnetic field signals, called magnetic field component it *; and torque component im *; thereby simulating the two magnetic fields of the DC motor.

2. Perform equivalent transformation. According to the parameters of the motor, the orthogonal rotating DC magnetic field signal is converted into a control signal.

When the given signal changes, one of the DC magnetic fields (torque component) is adjusted to obtain a speed regulation characteristic similar to that of a DC motor.

The role of speed feedback is to keep the speed of the motor strictly consistent with the given speed. Therefore, the mechanical characteristics of the motor are very hard and have high dynamic response capabilities.

3. Feedback-free vector control. The core of vector control technology is equivalent transformation, and the speed feedback signal is not a necessary condition for equivalent transformation. Therefore, the feedback-free vector control mode appears.

The so-called non-feedback vector control only means that the user does not need to install a speed feedback device outside the vector inverter, and it does not mean that the inverter is also open-loop.

Because speed feedback requires the installation of a speed measuring device outside the vector inverter, it is troublesome. Further research shows that under the premise of known motor parameters, even if only the terminal voltage and current of the motor are detected, the rotor flux and its angular velocity can be calculated, and then the required torque current command iT* and excitation current command iM* can be calculated to achieve vector control.

Non-feedback vector control can also obtain hard mechanical characteristics, but due to the relatively more operating links, the dynamic response capability is slightly inferior to that of feedback vector control.