Speed ​​regulation characteristics of hybrid excitation motor

As a new type of permanent magnet motor, the hybrid excitation synchronous motor has the advantages of high power density and high efficiency of the permanent magnet synchronous motor, and the characteristic of easy adjustment of the air gap magnetic field of the electric excitation synchronous motor. A hybrid excitation synchronous motor with mixed magnetic poles is proposed, and the mathematical model of the hybrid excitation synchronous motor is derived. The stator current vector trajectory of the hybrid excitation synchronous motor is obtained.

The speed regulation characteristics of a hybrid excitation motor depend on its excitation mode and control method.

For hybrid excitation motors, both their permanent magnets and excitation coils can provide magnetic fields, so their excitation methods can be divided into two types: series excitation and parallel excitation.

For a series-excited hybrid motor, its speed regulation characteristics are similar to those of a traditional series-excited DC motor, that is, as the armature current changes, the motor torque and speed will also change accordingly. However, unlike a traditional series-excited DC motor, the rotor of a hybrid motor is a permanent magnet, so its back electromotive force increases linearly with the increase in speed. This requires adjusting the armature current according to the speed to keep the motor speed stable.

For a parallel-excited hybrid excitation motor, its speed regulation characteristics are similar to those of an asynchronous motor, that is, its speed changes with changes in load, but its efficiency and power factor are higher than those of an asynchronous motor. In terms of control, the speed can be adjusted by controlling the excitation current of the motor.

In general, hybrid excitation motors have good speed regulation characteristics and advantages such as high efficiency and high power factor, but their speed regulation and control methods are more complicated than those of traditional motors.

The hybrid excitation motor is a combination of an electrically excited synchronous motor and a permanent magnet synchronous motor. Therefore, when leakage flux and magnetic saturation are ignored, the flux linkage in the air gap is a combination of the flux linkage generated by the permanent magnet magnetomotive force and the flux linkage generated by the electrically excited magnetomotive force.

The magnetic flux equation is:

In the formula, pm, e are subscripts, representing the permanent magnet section and the electric excitation section respectively;

The subscripts represent the d-axis components of the permanent magnet section and the electromagnetic excitation section, respectively;

The subscripts represent the q-axis components of the permanent magnet section and the electromagnetic excitation section, respectively.

The electromagnetic torque equation is:

Where, Ld is the equivalent d-axis inductance of the stator winding, Ld=Lpm-d+Le-d, H;

Lq——Equivalent q-axis inductance of stator winding, Lq=Lpm-q+Le-q, H.

When the motor is running in steady state, its electromagnetic torque can be expressed as:

In the formula,

The no-load induced electromotive force generated by the permanent magnet, V;

The no-load induced electromotive force generated by the electric excitation winding, V;

xd——equivalent d-axis reactance of stator winding, Q;

xq——Equivalent q-axis inductance of stator winding, Q.

It can be seen from formula (6-10) that the speed regulation characteristics of the hybrid excitation motor combine the speed regulation characteristics of the permanent magnet synchronous motor and the electric excitation motor. The speed can be adjusted by vector control method, and the amplitude of the magnetic field can be adjusted by controlling the current size and direction of the electric excitation winding, thereby increasing the adjustment range of the magnetic field of the hybrid excitation motor and achieving the effect of expanding the constant power speed regulation range of the hybrid excitation motor.