The inverter uses vector control in the occasions that require torque control, occasions that require low-speed and high-torque output, and occasions that require a wide speed regulation range beyond the rated speed, and require good control characteristics, etc.
In fact, as long as it is V/F control, vector control can be used. The debugging requirements of vector control are a little more complicated than V/F control, and he is more strict in determining the motor model. That’s all.
The biggest feature of multi-machine parallel drive is that the load torque of each motor at the same time will not be the same. If it is a large vector control at this time, the ghost knows how the excitation component and torque component of each motor are distributed. . Judging from the sum of the power supply of the motor, it is a vector model of the motor, but it is not clear when it is converted to each motor. Although the equivalent model of the motor is the same, the control will change due to different forces.
The basic idea of vector control is: imitating the speed regulation characteristics of DC motors, so that the speed of asynchronous motors can also be adjusted by controlling two mutually perpendicular DC magnetic fields.
Block diagram of vector control:
① The processing of a given signal. In the control circuit of the inverter, the given signal is decomposed into two rotating DC magnetic field signals that are perpendicular to each other, respectively called the magnetic field component iT*; and the torque component iM*; to simulate the two magnetic fields of the DC motor .
② Carry out the equivalent transformation. According to the parameters of the motor, a series of equivalent transformations are performed on the rotating DC magnetic field signals perpendicular to each other, and they are transformed into the control signals iU*, iV* and iW* for controlling the three-phase inverter bridge, as shown in the figure below.
When the given signal changes, one of the DC magnetic fields (torque component) is adjusted, so as to obtain the speed regulation characteristic similar to that of the DC motor.
The function 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.
③No feedback 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, a feedback-free vector control method appears.
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