BLDC motor Ld and Lq

Hi

I have now to deal with the control of a BLDC. This subject is totally new for me. I received from the motor manufacturer the data sheet with a Ld and a Lq inductance in mH. So in order to have the inductive reactance of the stator windings how do I put together Ld and Lq inductance to get a unique value? And probably more important is this the right thing to do? Or should I use only one of the two and if so which one?
Then what do these values mean actually?
 
Hi

I have now to deal with the control of a BLDC. This subject is totally new for me. I received from the motor manufacturer the data sheet with a Ld and a Lq inductance in mH. So in order to have the inductive reactance of the stator windings how do I put together Ld and Lq inductance to get a unique value? And probably more important is this the right thing to do? Or should I use only one of the two and if so which one?
Then what do these values mean actually?
Hi
If they only give you one inductance then you have a nonsalient-pole PMSM or brushless DC motor. (in which case Ld=Lq
. )
 
I guess that one should take account of the line to line reactance

Then you can use then in the transfer function (you can have a search on transfer function of BLDC)
 
Such non salient motor with different Ld and Lq intended for field weakening (mostly used for EV with DC bus from battery) where both inductances are shown efficiency of this method.
 
Some notes regarding sent link:
1. The slotted (aka ironcore) motor has iron core around which are wound stator coils. Therefore such motor has higher power density vs slotless one.
2. The modern power amplifiers for servo applications used motor encoder for commutation as rotor position sensor.
3. One of important application of slotless motors owing absence of cogging is scanning
 
In a Brushless DC (BLDC) motor, the stator windings are typically arranged in a three-phase configuration. The inductance values, Ld and Lq, represent the inductance of the motor windings in the direct (d) and quadrature (q) axes, respectively, of the motor's coordinate system.
To calculate the inductive reactance (X) for each axis, you can use the formula:
X=2πfL
where:
• f is the frequency of the power supply in Hertz (Hz),
• L is the inductance in Henrys (H) (convert mH to H by dividing by 1000), and
• X is the inductive reactance in Ohms (Ω).
However, since BLDC motors are often driven with a sinusoidal voltage or current (using a technique like Field-Oriented Control or FOC), you might use both Ld and Lq to control the motor effectively. The currents in the d and q axes are usually controlled independently to achieve precise torque and speed control.
Here's a simplified explanation of Ld and Lq:
• Ld represents the inductance along the direct axis. This is related to the winding inductance that affects the torque.
• Lq represents the inductance along the quadrature axis. This is related to the back-EMF and affects the motor's speed.
In practical applications, you will use both inductance values for accurate control. Different control algorithms, like FOC, will use these values to control the motor effectively, ensuring a good balance between torque and speed control.
Always consult the motor manufacturer's recommendations and consider consulting with a control systems engineer experienced in BLDC motor control for more specific guidance based on your application requirements.
 
The direction of Ld and lq are correct... But because d-axis is magnetic flux axis thus Ld affects magnetic flux of permanent magnets and therefore affects back-EMF and further the motors speed (field weakening effect with Id<0). And Iq affects the torque as well.
 
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