The variable voltage and variable frequency speed regulation algorithm based on the steady-state model of the motor does not take into account the complex electromagnetic dynamic changes in the motor, so the dynamic control performance is not ideal. Until 1971, F.Blaschke of Siemens and others put forward the “control principle of induction motor field orientation”, which is a vector control algorithm based on the dynamic model of the motor, which completely solved the shortcomings of poor dynamic performance in AC induction motor control. The performance of the horizontal vector control inverter has been comparable to that of the DC motor.

Vector control is also called field-oriented control. Its basic idea is to simulate the control method of a DC motor. According to the principle of constant magnetic potential and power, the mathematical model under ABC three-phase coordinates is transformed into α-β through orthogonal transformation. The model of the two-phase stationary coordinate system (Clarke transformation), and then the two-phase stationary coordinate system model is transformed into the model (dq) under the two-phase rotating coordinate system (Park transformation) through the rotation transformation. Under the α-β/dq transformation, the stator current vector is decomposed into two DC components i_{d} and i_{q} (where i_{d} is the excitation current component and i_{q} is the torque current component) oriented according to the rotor magnetic field, and they are respectively controlled and controlled. i_{d }is equivalent to controlling the magnetic flux, and controlling i_{q} is equivalent to controlling the torque, which is similar to the control of a DC motor.

Suppose the axis settings of the three-phase winding (ABC) and the two-phase winding (α-β) of the induction motor are shown in Figure 1. The axis of the A-phase winding coincides with the axis of the α-phase winding, and each axis corresponds to the alternating current i_{A}, i_{B} respectively. , i_{C }and the space vectors of i_{α} and i_{β} are all stationary coordinate systems. Using the absolute transformation of the magnetic potential distribution and the constant power, the magnetic potential F generated by the three-phase alternating current in space is equal to the magnetic potential generated by the two-phase alternating current. It is also called the Clarke transformation. Its transformation matrix is:

The inverse transformation formula is:

The transformation from the two-phase stationary coordinate system (α-β) to the two-phase rotating coordinate system (d-q) is called Park transformation. α-β is a stationary coordinate system, and d-q is a rotating coordinate system that rotates at any angular velocity ω. When the α-β static coordinate system is transformed into the d-q rotating coordinate system, the coordinate axis setting is shown in Figure 2. In Figure 2, θ is the angle between the α axis and the d axis. The dq winding is placed vertically in space, and the current i_{d} and i_{q} are respectively placed on the d and q axes, and the dq coordinate is rotated at the synchronous speed ω, then The generated magnetomotive force is equivalent to the α-β coordinate system. The angle θ between d-q and α-β axis is a variable, which varies with load and speed, and has different values at different times. Park transform is written in matrix form, and its formula is as follows:

The matrix form of Park inverse transformation is:

In the vector control algorithm of magnetic field orientation, if the d-axis of the synchronous rotating coordinate system is placed on the rotor magnetic field, it is called rotor magnetic field orientation; placed on the stator magnetic field, it is called stator magnetic field orientation; placed on the air gap magnetic field, it is called rotor field orientation. Air gap magnetic field orientation. In actual use, the main use is based on the rotor field-oriented coordinate system, because the electromagnetic torque has the simplest form at this time:

It can be seen from the above formula that the electromagnetic torque is proportional to the product of the excitation current i_{d} and the torque current i_{q}. When the rated speed is below the rated speed, keep the excitation current i_{d} at the rated value, and only need to adjust i_{q} to change the torque to achieve constant torque control; when above the rated speed, adjust the excitation current i_{d} setting to automatically adjust with the speed ω_{r} to maintain i_{d}ω_{r} ≈const, while adjusting the torque current i_{q} setting to ensure T_{e}ω_{r}≈const, realizing constant power field weakening control.

Figure 3 is a control block diagram of a vehicle-mounted induction motor drive system based on the rotor flux orientation. The target value of the system torque is set by a given accelerator pedal opening. The control system must achieve both torque closed loop and flux closed loop control. . When the speed is below the rated speed, the rotor flux is kept constant, and the constant power control is realized above the rated speed. The modulation signal of the inverter is realized by space vector PWM (Space Vector PWM, SVPWM).

The field-oriented vector control algorithm has excellent dynamic and static characteristics, but the realization of the control algorithm is very dependent on the parameters R_{r}, R_{s}, L_{m}, L_{sσ} and _{Lrσ} of the motor. During the operation of the motor, these parameters are all changing: The resistances R_{r} and R_{s} change with temperature, and L_{m}, L_{sσ}, and L_{rσ} change with the saturation of the magnetic field. These factors will cause the failure of the rotor flux orientation, so in order to achieve high-performance control effects, it needs to be achieved through parameter identification or adaptive control algorithms.

In 1985, the German scholar Professor M. Depenbrock first proposed the theory of direct torque control based on the dynamic model of induction motors. Subsequently, Japanese scholars also proposed a similar control scheme. Unlike vector technology, direct torque control does not require complex coordinates. Transform and change the estimated rotor flux to the estimated stator flux. Since the stator flux estimation only involves the stator resistance, the dependence on the motor parameters is weakened. The direct torque control method is adopted to detect the motor stator voltage and current, and use the space vector theory (mainly the 3/2 transformation principle) to calculate the motor flux and torque, and use a fast Bang-Bang regulator to The stator flux linkage and electromagnetic torque are controlled to limit the pulsation of the flux linkage and torque value within a predetermined tolerance range. The Bang-Bang regulator is the link for comparison and quantification, and then according to the stator flux linkage The output of the hysteresis Bang-Bang regulator with the amplitude and the motor torque and the space position of the stator flux vector form the information required for the look-up table, and the corresponding voltage vector to be applied can be directly found from the optimal switching signal mode table Switch signal to control the inverter.

The characteristic of the direct torque control algorithm is that the motor model only needs to be transformed by 3/2 in the stator coordinate system, and the stator flux linkage is observed, which is less affected by the motor parameters. Because it is a Bang-Bang control, there is no current closed loop, which is prone to overcurrent. At low speed, the stator flux is circular, and the current is similar to a sine wave, but after entering the high-speed area, the current waveform is very irregular, the harmonics are large, and the electromagnetic noise is large. How to ensure rapid torque response while smoothing the current waveform is an urgent issue to be solved.