Low voltage DC servo motor speed regulation, often said is brushless DC motor speed regulation, according to the speed equation of DC motor, speed n=(armature voltage U-voltage current Ia* internal resistance Ra)÷(constant Ce* air gap flux Φ), because the armature internal resistance Ra is very small, so voltage current Ia* internal resistance Ra≈0, In this way, the speed n=(armature voltage U)÷(constant Ce* air gap flux Φ), as long as the armature voltage U is adjusted under the air gap flux Φ stable, we can adjust the speed n of DC motor; Or adjust the air gap flux Φ in the armature voltage U stable, the same can adjust the motor speed n, the former is called constant torque speed regulation, the latter is called constant power speed regulation.
In the form of constant torque, it is necessary to adhere to the air gap flux φstable first. The stator and rotor magnetic field of DC motor are orthogonal and have no influence on each other. To adhere to the Φ stable, as long as the excitation coil current stable in a value can be. In theory, it is more perfect to give a constant current source to control the current of the excitation coil, but because the current source is not easy to find, and generally to impose a stable voltage value to the excitation coil, also can approximately make the excitation current stable, so that the air gap flux Φ stable. If it is a permanent magnet DC servo motor, the excitation coil is replaced by a permanent magnet, and the magnetic flux is permanently stable, so there is no need to worry about it.
Simple adjustment voltage, and can not be satisfied with the load shake more fierce occasions, so the introduction of cascade speed regulation system, after the detection of the motor current and speed, separate out the current ring ring and speed ring outside the ring, the use of PID algorithm, useful satisfied with the load shake under the condition of speed regulation, let DC motor speed operation characteristics is very "hard", That is, the maximum torque will not be shaken by the speed change, complete the true constant torque output. This speed regulation method has been the communication of the speed regulation system to copy each other, such as frequency converter vector control, is to copy this method and completed. If only the inner ring of the current ring is used, it can also directly control the motor output certain torque, satisfying different stretching and bending control requirements.
Armature voltage control, before thyristor and IGBT were created, it was not a simple job to control, after all, the power is relatively large, in the early days, it was controlled by a generator DC power generation, after adjusting the magnetic flux of the generator can control the output voltage of the generator, thus adjusting the armature voltage.
In the future, after the thyristor is created, the communication input voltage is applied to the thyristor, and the conduction Angle of the thyristor is controlled by the phase-shift triggering skill, the communication electricity can be rectified into a certain pulsating DC electricity. Because the DC motor is a large inductive load, the pulsating DC electricity will be buffered down by large inductance. This DC voltage can be adjusted, and the thyristor conduction Angle is proportional to a certain relationship. This kind of speed regulation skill is very sophisticated and reliable, in the middle and late last century has been widely used in industry.
Other field effect tubes and IGBT devices appear in the future, low voltage DC servo motor speed regulation can also do more precise, can use PWM chopper skills, so that the output DC voltage is very stable, so that the speed of the DC motor shaking is very small, if the rotor of the motor becomes longer, the moment of inertia becomes smaller, plus the position in the ring, Also can complete accurate positioning control, this is the so-called DC servo system.
Low voltage DC servo motor constant power speed regulation method:
Is the so-called weak magnetic speed regulation, this speed regulation method, the essence is a constant torque speed regulation method to make up for, mainly in some occasions, the demand is relatively wide speed regulation scale, such as some gantry bed, demand motor processing time feed is very slow, torque is very high; And back when the torque is very light is to run very fast, at this time when the feeding time with constant torque speed
regulation form, and back when the weak magnetic speed regulation method, this time the maximum power of the motor is unchanged.
There are also some electric vehicles, at low speed uphill to run very slowly, the need for great torque, and flat resistance and want to run very fast, at this time also need to use constant power speed regulation, similar to mechanical shift or speed ratio reduction method to speed regulation. General weak magnetic speed regulation, is not suitable for permanent magnet motor, so the magnetic flux Φ can not be controlled alone.
To weak magnetic, is to directly reduce the size of the air gap flux Φ, this time can reduce the current of the excitation coil, generally will be used in the excitation coil SCR or field effect tube to do a PI adjustment back output a current source to complete.
Weak magnetic speed regulation, the higher the motor speed, the smaller the maximum torque of the motor output, this is the need to pay attention to, and generally will not be unlimited to reduce, about 90% of the additional excitation current can be controlled.