(2) Lead angle field weakening control and simulink implementation (based on vector control FOC)
Be sure to look at the principle first, and then look at the simulation block diagram
When PMSM runs in a steady state, considering factors such as the structure of the motor and the switching devices of the drive circuit, the motor terminal voltage us and the stator current is are limited to a certain extent, and cannot exceed the limit values ulim and ilim.
For PMSM, the excitation magnetomotive force cannot be changed after leaving the factory; if the motor terminal voltage reaches the limit, if you want to continue to increase the speed, you can only achieve it by adjusting the id, that is, increasing the stator direct axis demagnetization current component to maintain high speed operation The constant voltage balance realizes the field weakening speed expansion. Let the modulus of the current vector be is, the angle between the vector and the q-axis be β, and β = 0 when running below the base speed, and increase the β to increase the d-axis demagnetization current to achieve field weakening. The purpose of speed up. This method is called lead angle field weakening control.
Voltage limit circle and current limit circle:
Voltage limit circle equation:
Current limit circle equation:
Lead angle field weakening control block diagram
The dotted line frame is the lead angle field weakening control part, the speed loop controls the modulus of the output current vector, the voltage outer loop judges whether to enter the field weakening state , the system detects the deviation between the motor terminal voltage us and the DC bus voltage udc, and adjusts it through the voltage regulator The size of the lead angle β. After entering the field weakening stage, appropriately increase the lead angle β, and negatively increase the direct axis current id to achieve the purpose of demagnetization. The control process is mainly divided into three
stages:
(1) When the motor terminal voltage us is less than the DC bus voltage , the voltage outer loop PI controller is in a positive saturation state due to the effect of the limiting link, the output current lead angle β = 0, id =-issinβ = 0, that is, id = 0 control, the motor is in constant rotation below the base speed Torque running state. The turning speed of this stage is the working state of point A, and the expression is
(2) As the motor speed increases, us increases continuously; when us is greater than the DC bus, the input voltage difference of the voltage outer loop PI controller is negative, Exit the saturation state, generate the lead angle β, the motor enters the field weakening control state, and as the speed increases, β gradually increases, the d-axis demagnetization current gradually increases, and the q-axis current gradually decreases.
In this system, the AC-D axis current needs to be limited. On the one hand, it is the maximum demagnetization current idmax = ψf /Ld determined by the motor model, and on the other hand, it is the maximum stator current ilim that the drive circuit and the motor can withstand
. Combining the above two points, limiting the direct axis current id to the maximum speed of the motor at this stage corresponds to: id reaches the maximum value id, β is π/2, and iq is 0. The expression of the motor limit speed is
(3) After the motor reaches the limit speed in the field weakening state, it enters the overmodulation process, and adjusts the action time of the non-zero vector according to the action time of the zero vector to increase the output voltage of the inverter. In this state,
the highest output voltage u*lim = 1.05udc. At this time, the motor speed is
the simulink block diagram: (built according to the above control block diagram)
speed loop:
current loop: magnetic field
weakening control link:
its interior is:
anti-prak (ipark) code
function [ua_out,ub_out] = fcn(theta,uq,ud, id,iq,we,pisa,Ld,Lq)
ud=ud-iq*we*Lq;
uq=uq+id*we*Ld+we*pisa;
ua_out=ud*cos(theta)-uq*sin(theta);
ub_out=ud*sin(theta)+uq*cos(theta);
end
Three-Phase VI Measurement parameters:
Permanent Magnet Synchronous Machine parameters:
Calculate the beita angle:
its interior is:
its ASR parameters are:
speed waveform:
torque waveform:
