FOC learning notes - coordinate transformation and simulation verification

Why Clarke Transformation

FOC control technology , Continuous changes of the rotor are required .

• There are three differences around the rotor 120° The coil of , To turn the rotor , A three-phase coil is needed to simulate a rotating magnetic field , Drag this rotor to rotate , And it is a continuous rotating magnetic field .
• How to use a three-phase coil to generate a continuous rotating magnetic field ？ According to electromagnetism , Then there needs to be sinusoidal AC current in the three-phase coil .
• How to generate sinusoidal AC current in the coil ？ It is necessary to connect the three-phase phase difference to the three-phase coil 120° Sinusoidal voltage . A sinusoidal voltage will produce a three-phase sinusoidal current .

Why not use it directly SVPWM Generate three-phase AC voltage and connect it to the coil ？

That is to say , What if there is no coordinate transformation .

Motor control , Generally need to control speed or torque , It's the same thing , Control speed is to control torque and indirectly control speed .
How to control the torque of the motor ？ Suppose you want to increase the torque now , It is necessary to increase the amplitude of stator sinusoidal current , It is necessary to increase the amplitude of sinusoidal voltage . Now we need to dynamically control the amplitude of sinusoidal voltage according to instructions , Generally, closed-loop PID control , use PID To control the AC voltage amplitude and angle information , Because to accurately control the nonlinear signal, it is necessary to use a complex high-order controller , This is important for modeling costs 、 Processor computing power 、 Real time control is unfavorable . In a nutshell , The feedback input variables of our controller are not three current sampling values , It's too troublesome for you to ask me to track three sine waves steadily ！ Can you simply track a straight line （ Constant ） ah ？, That is to convert three-phase alternating current into direct current

therefore , There must be coordinate transformation

Coordinate transformation will exchange signals , Decompose into angle information $\theta$, And amplitude information (Q The shaft controls the torque ,D The axis controls the magnetic field ),

Clarke Transform sum park Transformation is the transformation of current signal , Inverse transformation is the transformation of voltage signal .

Clarke Transformation

clarke Transformation simulink Simulation

The reason why voltage and current can be directly connected is because , Now just to verify this module , The actual is FOC In the algorithm , voltage （Va,Vb,Vc） Connect to the motor , Then current （Ia,Ib,Ic） Is the current collected .

Park Transformation

park Transformation simulink Simulation

\

Transformed curve , And the initial input Vd,Vq Agreement , It indicates that the coordinate transformation verification is successful

back Park Transformation

back park Transformation simulink Simulation

The magnitude is 1, The period is 0.1s, Difference between 90°

back Clarke Transformation

back clarke Transformation simulink Simulation

back clarke The input of the transformation , It's against park The output of the transformation

Phase difference 120°

simulink The whole simulation picture