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Permanent magnet synchronous motor control-power level
Release time:2017-02-23 15:42:39| viewed:


1 Background overview:

A motor is an electromagnetic device which can do the conversion of mechanical energy and

electric energy in the magnetic field. There are two methods to establish the necessary air gap magnetic field for the electromechanical energy conversion. One way is to generate a magnetic field by Switching on current in the motor windings, Such as ordinary DC motors, synchronous motors and asynchronous motors, etc,and the other one is to generate a magnetic field by a permanent magnet, for example permanent magnet synchronous motor. According to the principle, the permanent magnet synchronous motor is the same as the traditional electric excitation synchronous motor. The only difference is that the traditional electric excitation synchronous motor generates a magnetic field by Switching on current in the motor windings, and permanent magnet synchronous motor establishs the magnetic field through a permanent magnet.


DC brush motor: mechanical commutation


 

Brushless DC motor: electronic commutation


A DC brush motor completes the function of rectification through the internal mechanical contact or "brush". Because there is no brush in a brushless motor, the brushless motor can only be rectified by the more efficient controller. The controller is usually a micro controller that operates some kind of feedback loop algorithm.In this case, the feedback signal is derived from a position sensor mounted on the motor, and the feedback signal will control the current (25KHz) in the internal control loop and the motor speed (200Hz) in the external control loop.


A permanent magnet synchronous motor has a permanent magnet, and there is no excitation winding, collector ring and motor commutation brush. The stator of permanent magnet motor is similar to that of the traditional three-phase synchronous motor, so it is called permanent magnet synchronous motor (magnet synchronous motor PMSM, Permanent). The synchronization for a permanent magnet synchronous motor is that the current frequency and speed is synchronous.


 

2. Solution implementation

1) System model


 

System control model


 2) Connection diagram


 

Hardware connection diagram


The upper computer which runs the Simulink model and the real-time controller is connected by the cable. The motor is driven by three phase power driver board, and an incremental encoder is installed on the motor shaft. Power devices are available on the market.


 

Hardware detail diagram


Speedgoat real-time target machine can provide 3 PWM output channels, 2 analog input channels for current measurement and 3 dedicated incremental encoder signal channels. All interfaces are provided by the two PCI interface boards.


3) Power device

The power device selects the DRV8312 three phase brushless motor driver of Texas Instruments


 

Power device DRV8312 simple view


4)Realization way

The controller uses PWM technology to change the voltage of the three-phase motor. The real-time target machine provides 3 PWM signals to drive the three half-bridges on driver chip. For the feedback signal, the TI driver board provides a current sensing circuit for the current measurement, and can use optical encoder signals to determine the position and speed of the motor.


5) Clock synchronization

Synchronization is a key technology. For the signal different with PWM, these signals are either high or low. So, at a certain moment, the top or bottom of each bridge is in an open state. For the current measurement point, only when the transistor at the bottom is turned on, the measuring points can flow through the current.


 

The image above shows these signals that need to synchronize. Each PWM signal must be synchronized, which provides the time information for the current measurement.


After XPC target machine of Speedgoat do a simple configuration,you can complete the time synchronization of all waveforms through the Simulink module,and use the external interrupt to synchronize generation of PWM and acquisition of analog channel.


 

Synchronization using external interrupts

 

 
 
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