Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a method for improving the starting performance of a permanent magnet synchronous motor without a position sensor.
In order to realize the task, the invention adopts the following technical scheme:
A method for improving the starting performance of a permanent magnet synchronous motor without a position sensor comprises the following steps:
Setting a phase current peak value and an open-loop operation frequency of a motor winding, and generating three-phase sine wave current in the motor winding so as to form an active rotating magnetic field and enable the permanent magnet synchronous motor to work in an open-loop operation mode; establishing an equation of stator voltage under an actual rotating coordinate system and an equation of stator voltage under an expected rotating coordinate system when an included angle exists between the equation and the actual rotating coordinate system; calculating a current difference value between the current in the expected rotating coordinate system and the current in the actual rotating coordinate system, calculating the back electromotive force of the motor according to the current difference value, and then estimating the position angle of the motor rotor; calculating the position angle of the active rotating magnetic field in the open-loop operation mode, thereby obtaining the difference value between the position angle and the estimated motor rotor position angle;
Judging whether the value of the phase current peak value of the motor winding is matched with the load size or not according to the size of the difference value, and switching into a position closed-loop operation mode if the value of the phase current peak value of the motor winding is matched with the load size; if not, readjusting the peak value of the phase current of the motor winding until matching; and after the position closed-loop operation mode is switched in, the speed regulation operation of the permanent magnet synchronous motor controlled by the position sensor is carried out.
Further, the determining whether the value of the phase current peak value of the motor winding is matched with the load size includes:
Note thetaerrRepresents said difference, Ip0Representing the peak value of the phase current of the motor winding, then:
if 5 < | θerr< 10 deg., indicating Ip0the values are reasonable and are matched at the moment; if thetaerr| 10 ° or | θerrif | is less than 5 deg., it indicates Ip0The values of (A) are reasonable and unreasonable, and are not matched at the moment.
Further, the re-adjusting the magnitude of the peak value of the phase current of the winding of the motor includes:
If thetaerrI > 10 deg. indicating that the load is currently loaded and Ip0If the value of (A) is smaller, then Ip0The value is increased by 1A; if thetaerrI < 5 deg. indicating that the current starting load is light and Ip0If the value of (1) is too large, then I is addedp0The value is decreased by 1A.
the invention has the following technical characteristics:
The method judges the phase current peak value I of the winding in the open-loop operation mode according to the difference value of the position angle of the active rotating magnetic field in the open-loop operation mode and the estimated rotor position anglep0Whether the value of (A) is matched with the load size or not can avoid I when the load is overweightp0The value is small, and the starting is failed due to small open-loop starting torque; also avoid the load being too light Ip0The value is large, the open-loop starting torque is large, the energy overshoots, and the energy overshoots in the position open-loop switching-in position closed-loop stage cause the non-convergence of the rotor position estimation algorithm, so that the starting failure is caused; through Ip0the start-up characteristics of the permanent magnet synchronous motor can be improved.
Detailed Description
As shown in fig. 1 to 4, the present invention discloses a method for improving the starting performance of a permanent magnet synchronous motor without a position sensor, comprising the following steps:
Step 1, setting a phase current peak value I of a motor windingp0And open loop operating frequency omega0Generating three-phase sine wave current in a motor winding to form an active rotating magnetic field, wherein the permanent magnet synchronous motor works in an open-loop synchronous operation mode;
Wherein, the three-phase sine wave current generated in the permanent magnet synchronous motor winding is expressed as:
in the above formula, IU,IV,IWAre respectively three-phase sine wave current of motor winding Ip0For a set phase current peak value of the motor winding, f0for open loop operating frequency, t is a time parameter.
Step 2, establishing an equation of the stator voltage under an actual rotating coordinate system;
In the scheme, a stator voltage equation under a dp coordinate system is expressed as follows:
in the above formula, ud、uqD-axis voltage and q-axis voltage of the stator winding respectively; i.e. id、iqD-axis current and q-axis current of the stator winding respectively; rsIs a stator resistor; l isd、LqD-axis and q-axis inductors respectively; e is the back electromotive force of the motor; omega is the rotation angular velocity of dq coordinate system; p is a differential operator, and p is d/dt;
Step 3, establishing an equation of the stator voltage under the expected rotation coordinate system when an included angle delta theta exists between the equation and the actual rotation coordinate system;
In this step, the expected rotation coordinate system is a γ δ estimation coordinate system, and a voltage equation of the stator in the coordinate system is:
in the above formula, uγ、uδEstimating the stator voltage components i of the gamma and delta axes in the coordinate system for gamma and delta, respectivelyγ、iδStator current components of gamma and delta axes, omega, respectivelyMEstimating the angular velocity of rotation of the coordinate system for γ δ, p being a differential operator; delta theta is an included angle between the gamma delta estimation coordinate system and the dq coordinate system, namely a position angle estimation error;
step 4, calculating the current difference value between the current in the expected rotation coordinate system and the current in the actual rotation coordinate system;
In the step 4.1, the method comprises the following steps of,Calculating the actual current i of the motor at the sampling point (n +1)γ(n+1)、iδ(n+1):
in the above formula, T is the sampling time of discrete points, iγ(n)、iδ(n) is the actual current of the gamma and delta axis stators of the motor at the sampling point (n), uγ(n)、uδ(n) is the actual voltage of the gamma and delta axis stators of the motor at the sampling point (n); omegaMand (n) is the rotation angular velocity at the sampling point (n) under the expected rotation coordinate system.
Step 4.2, calculating the estimated current i at the sampling point (n +1)Mγ(n+1)、iMδ(n+1):
In the above formula, eMRepresenting the motor back electromotive force;
step 4.3, calculating the gamma and delta axis estimated current error delta i at the sampling point (n +1)γ(n+1)、Δiδ(n+1):
Estimating the current error Δ iγ(n+1)、ΔiδAnd (n +1) is the difference value between the current in the expected rotating coordinate system and the current in the actual rotating coordinate system.
Step 5, calculating the back electromotive force of the motor according to the current difference
eM(n+1)=eM(n)-KδΔiδ(n+1)
In the above formula, eM(n+1)、eM(n) is the back electromotive force of the motor at the sampling point (n +1) and the sampling point (n), respectively, Delta iδ(n +1) is the delta axis current error at sample point (n +1), KδEstimating coefficients for the back emf;
step 6, estimating the motor rotation according to the calculated motor counter electromotive forceSub-position angle thetaM
In the above formula, θM(n+1)、θM(n) is the position angle of the rotor of the motor at the sampling point (n +1) and the sampling point (n), delta iγ(n +1) is the gamma axis current difference at sample point (n +1), T is the time interval of sampling, KEis the motor back electromotive force coefficient, Kθa rotor position angle compensation coefficient;
step 7, calculating the position angle theta of the active rotating magnetic field in the open-loop synchronous operation mode0And calculating theta0And estimating the motor rotor position angle thetaMDifference of (a), i.e. thetaerr=θ0-θM;
Step 8, according to the difference value thetaerrJudging the phase current peak value I of the motor windingp0whether the value of (a) is matched with the load size; if thetaerrthe size of (A) is within a reasonable interval, indicating that Ip0If the value is reasonable, executing the step 9 of switching into a position closed-loop operation mode; if thetaerrIs not in a reasonable interval, indicating that Ip0If the value is larger or smaller, the step 1 is returned to modify Ip0taking the value of (A);
Wherein, according to the difference thetaerrjudging the phase current peak value I of the motor windingp0Whether the value of (a) matches the load size or not, includes:
(1) If 5 < | θerr< 10 deg., indicating Ip0the value of (3) is reasonable, and the cut-in position closed-loop operation mode in the step (9) is executed;
(2) If thetaerrI > 10 deg. indicating that the load is currently loaded and Ip0If the value of (A) is smaller, returning to the step 1 and adding Ip0Increasing the value by 1A, and then re-executing the steps 1 to 8;
(3) If thetaerrI < 5 deg. indicating that the current starting load is light and Ip0If the value of (1) is larger, returning to the step (1) to obtain the value Ip0Reducing the value by 1A, and then re-executing the steps 1 to 8;
and 9, entering a position closed-loop operation mode, and controlling a motor position angle theta to be theta under the control of a non-position sensorM+θerr;
And step 10, carrying out speed regulation operation of the permanent magnet synchronous motor without position sensor control in a position closed loop operation mode.
The principle experiment verifies that the adopted compressor is a scroll compressor for a new energy automobile air conditioner, wherein the parameters of the permanent magnet synchronous motor are as follows: number of pole pairs pn3; stator resistance Rs1.62 Ω; stator straight axis inductance Ld3.5 mH; quadrature axis inductance Lq4.5 mH; back emf coefficient ke=30.8V/krpm。
In the specific embodiment of the present invention, the scroll compressor permanent magnet synchronous motor adopts position-sensorless vector control, and as shown in fig. 1, the system control block diagram includes units such as current sampling, rotor position estimation, Clarke and PARK transformation, maximum torque-to-current ratio control (MTPA), speed loop, dq-axis current loop, PARK inverse transformation, SVPWM calculation, and three-phase PWM inverter.
The invention adopts a motor rotor position estimation method based on an assumed coordinate system, a gamma delta assumed coordinate system is established in a PMSM vector control dq synchronous coordinate system as shown in figure 2, a motor rotates anticlockwise, a three-phase stator winding is U, V, W, theta represents an actual position angle of a rotor, and theta represents an actual position angle of the rotorMRepresenting the estimated position angle of the rotor, theta being the position angle estimation error, and delta theta being theta-thetaM(ii) a e is the actual back-emf, the direction coincides with the q-axis; e.g. of the typeMTo estimate the back emf, the direction coincides with the delta axis.
FIG. 3 is a U-phase current waveform of a motor successfully started, showing a phase current peak value Ip06A, open loop operating frequency f0Starting load torque T of 8HzL1.5Nm, active rotating field position angle theta in open-loop operating mode0And estimating the rotor position angle thetaMThe experimental test result of the difference is thetaerr=8.3°,Ip0The value 6A is matched with the load size, and the closed-loop operation mode is switched in after the open-loop operation is carried out for 3.5 seconds, as shown in figure 3 because of Ip0Cut-in position closed-loop operation die with reasonable valueAnd (4) successfully starting.
FIG. 4 is a U-phase current waveform of a motor with failed start, maintaining the winding phase current peak value and the open-loop operating frequency of the open-loop operating mode unchanged, i.e., Ip0=6A,f0At 8Hz, but the starting load torque is reduced to TL0.5Nm, when the active rotating magnetic field position angle theta is in the open-loop operation mode0And estimating the rotor position angle thetaMExperimental test results for the difference increase to θerrAt 12.7 °, the open loop operation is in the cut-in position closed loop operation mode after 3.5 seconds, as shown in fig. 4, since Ip0The value is large, the open-loop starting torque is large, energy overshoots, the algorithm for estimating the rotor position in the open-loop cut-in position closed-loop stage is not converged, and finally starting failure is caused.