The structure of the dc motor, frequency conversion motor with dc motor characteristics, adopt the structure of the ac motor.
That is, while the external access is dc, the dc -
Ac variable voltage inverter control technology, motor ontology completely according to the principle of ac motor to work.
Therefore, variable frequency motor is also called 'control variable frequency synchronous motor, the rotating speed of the motor n depends on the frequency set by the controller f.
Three-phase y connection of variable frequency motor control circuit, dc power supply three phase flow of the MOS tube circuit to the motor of the three winding time-sharing power supply.
Every moment, there are only a pair of three pairs of winding winding current through, produce a magnetic field, then stop supply power to the winding, power supply, and adjacent to the other winding the stator magnetic field in the axis of rotation in space 120 °, the role of the rotor by magnetic force with the stator magnetic field to rotate 120 °.
The voltage on A + B - in turn
,A + C -
B + C -
C + B -
, it forms a rotating magnetic field in the stator, so the motor turns continuously.
Motor works: frequency conversion motor drive circuit consists of two parts, the main circuit and control circuit, now will be integrated into a single chip, the two parts such as long as the use of a device can achieve all of variable frequency motor control function, simplify the circuit structure, the commonly used control chip has Japan's sanyo LB1964, America's MAXIM company MAX6625 and stmicroelectronics company ST72141, etc.
As the industry attention to energy saving and noise suppression, many industrial products tend to use brushless motor, micro controller put forward higher requirements on the motor.
As a new generation of motor control DSP chip, cost-effective TMS320C240 TI company is very suitable for to complete the task of speed adjusting methods: dc motor speed control method has two kinds: regulating speed regulation and frequency modulation speed control.
Using a brush motor common cooling fan may change by way of regulating speed, and adopts frequency conversion motor cooling fan, only for speed regulation by frequency modulation.
For a brush motor, change the power supply voltage, to change is a change in the rotor winding current magnetic field and torque, motor speed increased with the increase of torque rise, and decreased with the decrease of the torque.
This kind of motor when the load resistance increases, with the decrease of motor speed.
To maintain speed constant when the load change, must adopt closed loop control, by velocity negative feedback, so the control circuit is more complex.
Figure 13 is a practical motor control scheme, it is to use MIC501 dedicated chip as the core, combined with some peripheral components.
And as shown in figure 10 brushless motor control circuit are compared, and a simple circuit structure can be found two significant differences.