CN111786607A - Reliable and smooth starting method based on permanent magnet synchronous motor without position sensor - Google Patents

Reliable and smooth starting method based on permanent magnet synchronous motor without position sensor Download PDF

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Publication number
CN111786607A
CN111786607A CN202010590948.2A CN202010590948A CN111786607A CN 111786607 A CN111786607 A CN 111786607A CN 202010590948 A CN202010590948 A CN 202010590948A CN 111786607 A CN111786607 A CN 111786607A
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current vector
coordinate system
motor
speed
position sensor
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李光明
李胜
关彦彬
向柏澄
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Qingdao Bantek Invert Technology Co ltd
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Qingdao Bantek Invert Technology Co ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
    • H02P21/34—Arrangements for starting
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P6/00—Arrangements for controlling synchronous motors or other dynamo-electric motors using electronic commutation dependent on the rotor position; Electronic commutators therefor
    • H02P6/20—Arrangements for starting

Abstract

The invention relates to the technical field of permanent magnet synchronous motor control, and discloses a reliable and smooth starting method of a permanent magnet synchronous motor based on a position-free sensor, wherein in a pre-positioning stage, the angular speed of a stator current vector is controlled to be unchanged, and the amplitude is increased to a set amplitude by a first set function; then controlling the amplitude of the stator current vector to be unchanged and the command position angle to be increased by a second set function until the stator current vector is synchronous with the rotor position; in the I/F acceleration stage, the stator current vector and the rotor flux linkage position are kept to synchronously follow through the torque-self-balancing characteristic until the lowest rotating speed of the speed closed-loop operation is reached; in the closed loop cut-in stage, the rotating speed of the motor keeps the lowest rotating speed of the speed closed loop operation unchanged, and the amplitude of the stator current vector is gradually reduced to enable the included angle theta to be includedLGradually decays to be less than threshold value thetaLLmtThe closed loop operating mode is switched. The invention can control the current of the motor before and after the system is started,the current pulsation is small when the closed loop is switched in, and the starting reliability and smoothness are improved.

Description

Reliable and smooth starting method based on permanent magnet synchronous motor without position sensor
Technical Field
The invention relates to the technical field of permanent magnet synchronous motor control, in particular to a reliable and smooth starting method of a permanent magnet synchronous motor based on a position-sensorless motor.
Background
The Permanent Magnet Synchronous Motor (PMSM) has the characteristics of high power density, high efficiency, simple structure, low noise and the like, and a high-performance permanent magnet synchronous motor driving system is widely applied along with the development of a motor control theory and the popularization of a digital microprocessor. In the field of white home appliances, permanent magnet synchronous motors are also increasingly used for driving air conditioning compressors. At present, a PMSM (permanent magnet synchronous motor) driving system applied to an air conditioner compressor and a fan mainly uses a vector control technology, and the vector control needs to acquire real-time position and speed information of a rotor. A position sensor, such as an encoder, a rotary transformer, a hall sensor, etc., is installed in the conventional driving system. However, the position sensor is greatly affected by the working environment, and particularly in an air-conditioning compressor, the motor often runs in a high-temperature and high-pressure closed environment, and the position sensor cannot work normally. Therefore, the position sensorless algorithm of the permanent magnet synchronous motor becomes a research hotspot of related enterprises at home and abroad.
Because the counter electromotive force of the permanent magnet synchronous motor contains the speed information of the rotor, the current speed-free sensor algorithm is mostly based on the observation of the counter electromotive force of the motor. Scholars at home and abroad propose a speed observation algorithm based on advanced control theories such as extended Kalman filtering, model reference self-adaption and sliding-mode observers, and the performance of the control algorithm is verified on a simulation and experiment platform. However, the observation algorithms have large calculated amount and high requirement on the accuracy of the motor parameters, and high-frequency switch buffeting can be introduced by methods such as a sliding mode observer and the like. Although learners apply motor parameter online identification to weaken the disturbance caused by the motor parameters, the calculation amount of the algorithms is large on the whole, the calculation resources of a control chip in an air conditioner compressor controller are limited, the real-time performance of the algorithms is greatly limited, and the dynamic performance is not ideal. The assumed rotating coordinate system method adopted by the method is a closed-loop estimation algorithm based on a motor fundamental wave model, the disturbance of motor parameters can be compensated by the correction of an observer and a regulator, and the method is suitable for surface-mounted and embedded permanent magnet synchronous motors, and is small in calculated amount and good in dynamic response.
When the motor runs at a low speed, phase voltage or counter electromotive force is small, a speed estimation algorithm based on the counter electromotive force fails, and high-frequency signal injection algorithm based on the salient pole effect of the motor is often used for extracting position information of the rotor. The method has limited application range, needs a high-precision current detection circuit to extract a high-frequency current signal and has high cost; and the air conditioner compressor normally runs at a middle-high speed section and cannot run at a low speed section for a long time. Therefore, a control strategy for the zero-low-speed starting of the air conditioner compressor needs to be designed.
Disclosure of Invention
The invention provides a reliable and smooth starting method of a permanent magnet synchronous motor based on a position-sensorless motor, which solves the technical problem of large current pulsation when the permanent magnet synchronous motor is started in the prior art.
The technical scheme of the invention is realized as follows: a reliable and smooth starting method based on a permanent magnet synchronous motor without a position sensor comprises the following steps:
s1, pre-positioning stage: applying a rotating current vector in an armature winding of a stator of the motor to enable the motor to operate in a current closed-loop and speed open-loop mode, and defining a synchronous coordinate system where the open-loop current vector is located
Figure BDA0002555498220000021
A coordinate system, a synchronous coordinate system with the position of the motor rotor as a reference is set as a dq coordinate system, and the phase difference between the two coordinate systems is thetaL：
S11: controlling the angular speed of the stator current vector to keep low-frequency rotation, and increasing the amplitude of the stator current vector to a set amplitude by a first set function so that the current of a rotor winding is gradually increased under the regulation of a current loop PI controller;
s12: controlling the amplitude of the stator current vector to be unchanged and the command position angle to be increased by a second set function, so that the rotor rotates at a low frequency and a constant speed until the stator current vector is synchronous with the rotor position;
s2, I/F acceleration stage: controlling the stator current vector of the motor to rotate at a set angular acceleration to link the stator current vector with the rotor fluxThe synchronous following is kept through the characteristic of torque-self balance, the motor rotor keeps synchronous speed rotation under the traction of the stator current vector until the minimum rotating speed of speed closed-loop operation is reached, and the position estimator of the assumed coordinate system accurately estimates
Figure BDA0002555498220000022
Angle theta between coordinate system and dq coordinate systemL；
S3, closed-loop cut-in stage: the rotating speed of the motor keeps the lowest rotating speed of the speed closed-loop operation unchanged, the current vector amplitude of the stator is gradually reduced, and the included angle theta of the motor is adjusted through the characteristic of torque-self balanceLGradually decays to be less than threshold value thetaLLmtAnd when the motor is switched to the speed closed-loop operation mode.
As a preferred technical solution, in step S11, the first setting function is a ramp function, and the magnitude of the stator current vector is increased to a setting value by the ramp function.
Preferably, in step S12, the second setting function is a linear function, and the command position angle increases as a low-frequency linear function.
Preferably, the included angle θ is set before step S3LObtained by the hypothetical coordinate system position estimator when directly obtained by the hypothetical coordinate system position estimator
Figure BDA0002555498220000031
The range of the angle error tan delta theta of the coordinate system and the dc-qc axis system of the assumed rotating coordinate system method is [ -28.2 degrees, 28.2 degrees °]When tan Δ θ ≈ Δ θ ═ θLStep S3 is executed.
Preferably, in step S3, the stator current vector magnitude is obtained by making the included angle θLAnd adjusting a dynamic function of smooth switching.
As a preferred technical scheme, the dynamic function is Is(n)＝Is(n-1)-Kct(tanΔθ)2·TcWherein: kctFor the current variation coefficient, tan Δ θ is an estimate of the position of the assumed coordinate axisTangent value, T, of error angle of coordinate axis given by calculatorcThe period is controlled by a singlechip.
Preferably, in step S3, the threshold θ is setLLmtIs 5 to 10 DEG
The invention has the beneficial effects that: the invention provides a pre-positioning-open loop starting-cut-in closed loop starting algorithm, which is characterized in that a rotor is reliably pre-positioned when the rotor is static, an I/F (constant current frequency ratio) is used for accelerating to the lowest rotating speed allowed by the closed loop when the rotor is started, and a smooth switching law is designed to be transited to a closed loop algorithm for estimating an assumed coordinate axis error angle. Before and after the system is started, the current of the motor is always controllable, the problem of motor overcurrent in a traditional V/F (constant voltage/frequency ratio) starting algorithm is solved, the current pulsation in the transient process of switching into a closed loop is weakened through a smooth switching law, and the starting reliability and smoothness are improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a block diagram of a position sensorless PMSM starting system according to the present invention;
FIG. 2 shows the I/F startup to closed loop phase | Is |, Tan θLAnd a ω waveform plot;
FIG. 3a is a schematic diagram of a pre-positioning initial stage;
FIG. 3b is a schematic diagram of a pre-positioning end phase;
FIG. 4 is a schematic diagram of the I/F startup acceleration phase coordinate system;
FIG. 5 is a schematic diagram of a hypothetical rotating coordinate system;
FIG. 6 is a block diagram of a hypothetical rotating coordinate system;
FIG. 7 is a diagram of the electromagnetic torque characteristics of a PMSM at different current amplitudes;
FIG. 8 is a diagram of the electromagnetic torque characteristics of a PMSM;
FIG. 9 Is an Is instruction curve θ given with a fixed slopeLA variation graph;
FIG. 10 Is a graph showing the change of tan Δ θ at a given time by dynamically adjusting the Is command;
FIG. 11 is phase current for the press start phase to the closed loop run phase;
FIG. 12 shows the I/F startup to closed loop phase | Is |, Tan θLAnd ω waveform diagrams.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments, and the description of the embodiments is provided to help understanding of the present invention, but not to limit the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the embodiments herein, "/" means "or" unless otherwise specified, for example, a/B may mean a or B; "and/or" herein is merely an association describing an associated object, and means that there may be three relationships, e.g., a and/or B, which may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, in the description of the embodiments of the present application, "a plurality" means two or more than two.
In the following, the terms "first", "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of the present application, "a plurality" means two or more unless otherwise specified.
The structural block diagram of the position sensorless permanent magnet synchronous motor starting system shown in fig. 1 comprises units including current sampling, a position estimator of a hypothetical coordinate system, Clarke and PARK transformation, a speed loop, a dq-axis current loop, Clarke inverse transformation and PARK inverse transformation, a three-phase PWM inverter, an SVPWM computing unit, an I/FStartUp unit and the like. The I/FStartUp unit comprises an I/FStartUp generator, a RAMP function unit RAMP and the like.
The permanent magnet synchronous motor starting method comprises a pre-positioning stage, an I/F acceleration stage, a closed-loop cut-in stage and a closed-loop stage.
At zero low-speed starting, a speed estimation algorithm based on back emf observation cannot obtain accurate and stable position and speed signals, so that only current closed-loop and speed open-loop control can be performed on a system at starting. As shown in fig. 1, the software switches Swt1, Swt2 and Sw3 are all in the 1 position, and the dashed box I/FStartUp generator is used for giving the current vector command value, the command position angle and other operation parameters in the pre-positioning stage and the I/F open loop acceleration stage.
In the I/F open loop acceleration phase, the current vector command value is given by the I/FStartUp generator. The frequency and angle instruction values are respectively given by setting angular acceleration integral and quadratic integral, and the amplitude instruction value is given by a set track. After coordinate transformation, the current of the armature winding is projected to a coordinate system which rotates synchronously with the frequency command value, and the current injected into the armature winding follows a reference value under the control of current loop regulation.
When the speed is accelerated to the lowest speed of the closed loop, the transition stage of the closed loop is entered. Sw3 is in position 2 and the current vector command value is given in terms of switching rate, the speed is kept constant at the closed loop minimum speed. Under the characteristic adjustment of 'torque self-balancing' of the motor, the command assumes that a coordinate system and an actual coordinate system are gradually superposed, and the transition stage of the closed loop is completed.
The closed loop phase, speed loop, current loop open simultaneously, Swt1, Swt2 are both in the 2 position. The velocity and angle are estimated by assuming a rotating coordinate system.
Thus, the system completes a phase from zero low-speed starting to closed-loop stable operation.
The working principle of each stage is described below by combining a block diagram and computational analysis:
s1, pre-positioning stage: applying a rotating current vector in an armature winding of a stator of the motor to enable the motor to operate in a current closed-loop and speed open-loop mode, and defining a synchronous coordinate system where the open-loop current vector is located
Figure BDA0002555498220000051
A coordinate system, a synchronous coordinate system with the position of the motor rotor as a reference is set as a dq coordinate system, and the phase difference between the two coordinate systems is thetaL：
S11: controlling the angular speed of the stator current vector to keep low-frequency rotation, and increasing the amplitude of the stator current vector to a set amplitude by a first set function so that the current of a rotor winding is gradually increased under the regulation of a current loop PI controller;
s12: and controlling the amplitude of the stator current vector to be unchanged and the command position angle to be increased by a second set function, so that the rotor rotates at a low frequency and a uniform speed until the stator current vector is synchronous with the rotor position.
The initial rotor position is random before the motor starts. At open loop I/F start-up, the motor angle is obtained from a given speed integral, since the rotor position is unknown.
As shown in FIG. 2, the synchronous coordinate system where the open-loop current vector is defined is
Figure BDA0002555498220000061
A coordinate system, a synchronous coordinate system with the position of the motor rotor as a reference is set as a dq coordinate system, and the phase difference between the two coordinate systems is thetaL(definition of q-axis lead)
Figure BDA0002555498220000062
Angle of the axis being thetaL) The included angle between the current vector Is and the rotor position Is thetasr，θLAnd thetasrAre complementary angles to each other, and the command position angle is
Figure BDA0002555498220000063
From the mathematical model of the motor, the following torque equation can be derived:
Figure BDA0002555498220000064
wherein T iseIs an electromagnetic torque, PnIs the number of pole pairs, | IsI is the current vector magnitude, psipmIs a permanent magnet flux linkage of a motor rotor, LdIs d-axis inductance, LqIs the q-axis inductance.
As can be seen from the torque equation (1.1), when a certain current vector is applied to the stator of the motor, the generated electromagnetic torque drags the rotor rotation to a fixed position, and then starts acceleration from that position,
the simplest method for pre-positioning is to adopt single positioning, continuously apply current vectors with fixed amplitude and angle on a stator, and if the generated electromagnetic torque can overcome the inherent load torque of the motor, the rotor of the motor rotates to be close to a fixed direction to complete positioning. However, the initial position of the rotor is random, when the included angle between the applied positioning current vector and the position of the rotor is too small or the difference is close to 180 degrees, the electromagnetic torque is not enough to overcome the inherent load torque, and at the moment, the rotor may not rotate and fails to be positioned, so that the success of positioning the rotor every time can not be ensured by single positioning.
Alternatively, a rotating current vector of sufficiently high amplitude and low rotational frequency can be applied to the armature winding. In the invention, in order to avoid the impact on the motor caused by the moment of applying large current, the amplitude of the applied current is set as a ramp function, the current is gradually increased from zero to a certain fixed value, then the amplitude is kept unchanged, and the pre-positioning is completed by rotating 180 degrees at a very low frequency in an electric cycle. The pre-positioning stage coordinate system is shown in fig. 3a and 3 b.
Given a command position angle of initial value of 90 ° (i.e., current vector Is projected onto
Figure BDA0002555498220000065
On axis, initial value is 180 deg.C), then the current vector amplitude instruction is gradually increased to a certain value, under the regulation of current loop PI controller, the winding current tracking instruction is gradually increased, then the instruction position angle is linearly increased at very low frequency, and the rotor is lowThe frequency is rotated at a constant speed. In order to be able to drag the rotor into synchronization. When the commanded position angle reaches 270, the motor position is eventually positioned at the zero position shown in FIG. 3b, where θ isLThe stator current vector is aligned with the d-axis at 90 °.
S2, I/F acceleration stage: controlling the stator current vector of the motor to rotate at a set angular acceleration, enabling the stator current vector and the rotor flux linkage position to keep synchronous following through a torque-self-balancing characteristic, enabling the motor rotor to keep synchronous rotation under the traction of the stator current vector until the minimum rotating speed of speed closed-loop operation is reached, and enabling the position estimator of the assumed coordinate system to accurately estimate
Figure BDA0002555498220000071
Angle theta between coordinate system and dq coordinate systemL。
After the rotor is pre-positioned, the starting acceleration stage is started, and the position angle is commanded
Figure BDA0002555498220000072
And
Figure BDA0002555498220000073
angular velocity of rotation of a coordinate system
Figure BDA0002555498220000074
Angular acceleration
Figure BDA0002555498220000075
The relationship between the two is as follows:
Figure BDA0002555498220000076
angular acceleration
Figure BDA0002555498220000077
Can be designed to be constant or time-varying according to requirements. With following
Figure BDA0002555498220000078
The axis starts at an angular velocity
Figure BDA0002555498220000079
Rotating counterclockwise, stator current vector Is also begins to rotate. The component of stator current vector Is on the q-axis provides electromagnetic torque Te, and when the electromagnetic torque Is balanced with the load torque, stator current vector Is linked with rotor flux ψpmPosition holding fixed angle thetasr(Motor dq coordinate System and commands
Figure BDA00025554982200000710
Maintaining a certain phase difference theta between coordinate systemsL) As shown in fig. 4, so that the motor rotor rotates at a synchronous speed under the traction of Is.
When the electromagnetic torque Te Is smaller than the load torque, the rotor Is decelerated and rotated, so that the stator current vector Is and the rotor flux linkage psipmIncluded angle thetasrIncreasing the electromagnetic torque Te so as to achieve torque balance at a new included angle position; conversely, when Te Is greater than the load torque, the rotor accelerates, so that the stator current vector Is and the rotor flux linkage ψpmIncluded angle thetasrThe electromagnetic torque Te decreases and the torque balance is also achieved at the new angle position. This process is referred to as the "torque-self balancing" characteristic of a permanent magnet synchronous machine: keeping the amplitude of the stator current unchanged, and if the load torque is increased, forming an included angle thetasrIt also gradually increases to produce a greater electromagnetic torque and peaks at 90 deg.. When theta issrWhen the angle exceeds 90 degrees and the angle is continuously increased, the electromagnetic torque is reduced, and the motor loses the torque-self-balancing regulation, thereby causing step loss.
The characteristic of "torque-self balance" makes the system have certain ability of resisting disturbance of load torque in the I/F acceleration stage. Magnitude of starting current vector Is and command angular acceleration
Figure BDA00025554982200000711
These two parameters are adjustable, they follow the following relationship:
Figure BDA00025554982200000712
wherein Kt is an adjustable coefficient of the starting current amplitude, and K alpha is an adjustable angular acceleration coefficient. The larger the amplitude of the given starting current vector Is, the smaller the set angular acceleration Is, the larger the margin of system disturbance resistance Is, and the stronger the anti-step-out capability Is.
The rotating coordinate system method is assumed to be a speed observation algorithm based on a PMSM fundamental wave model. Since the true position of the rotor is unknown, in the estimated synchronous rotating dc-qc axis system, the PMSM stator voltage equation is listed as follows:
Figure BDA0002555498220000081
wherein E0x@E0+p(Lq-Ld)iq+ωr(Ld-Lq)idTo extend the back emf, the Δ θ angle is the error angle between the synchronously rotating dc-qc axis and the true rotor d-q axis, as shown in fig. 5.
And decomposing the expanded back electromotive force on a dc-qc axis, and obtaining an error angle delta theta by utilizing an arc tangent operation:
Figure BDA0002555498220000082
here, an equivalent infinitesimal relationship is applied, and holds true when Δ θ is small. Since the assumed rotational coordinate system dc-qc is equal to the estimated rotational speed
Figure BDA0002555498220000083
When the estimated rotating speed is smaller than the actual rotating speed, the estimated rotating speed error angle delta theta is reduced; when the estimated rotation speed is greater than the actual rotation speed, the estimated rotation speed error angle Δ θ is increased. The estimated speed can thus be obtained from Δ θ via a Phase Locked Loop (PLL). Therefore, the rotation coordinate system method is assumed to be an observation mode of calculating the dc-qc axis component of the extended back electromotive force through a stator voltage equation, then calculating an arctangent value to obtain an error angle, and further estimating the rotation speed. A block diagram of the overall algorithm is shown in fig. 6.
S3 closed loop cut-in phase: the rotating speed of the motor keeps the lowest rotating speed of the speed closed-loop operation unchanged and gradually decreasesThe stator current vector amplitude value enables the motor to make the included angle theta under the regulation of the torque-self-balance characteristicLGradually decays to be less than threshold value thetaLLmtAnd when the motor is switched to the speed closed-loop operation mode.
In the I/F starting stage, when the rotating speed is accelerated to a certain range, the position estimator of the assumed coordinate system can be used for accurately estimating
Figure BDA0002555498220000084
Angle theta to dq coordinate systemLThen, a switch to speed closed loop may be considered. However, if at θLWhen the current is larger, the direct switching can cause the transient fluctuation of the current and the torque, the stable operation of the motor is not facilitated, and the severe vibration of the system can be caused to realize overcurrent protection in serious cases. Therefore, before the closed-loop cut-in, the consideration of theta is neededLGradually decaying below a certain smaller threshold thetaLLmtThen, the operation is switched to the speed closed loop operation stage.
From the formula (1.1), it is easy to applyLThe gradual reduction to a smaller threshold Is achieved by gradually reducing the magnitude of the current Is, such that θ Is adjusted continuously by the "torque-self-balancing" of the motorLIt will gradually shrink.
To enable this process to switch reliably, smoothly and quickly, it Is necessary to align | Is | and θ |LThe relationship was further quantitatively analyzed.
Further transformations are made to equation (1.1):
Figure BDA0002555498220000091
when | Is fixed, the electromagnetic torque Te Is vssrDerivation:
Figure BDA0002555498220000092
from the equation (2.2) and FIG. 7, it can be seen that the following is θsrThe electromagnetic torque reaches an extreme value, in order to make the system work at the electromagnetic torque and thetasrFor monotonically increasing interval, θsrThe following relationship needs to be satisfied:
Figure BDA0002555498220000093
in addition, to avoid following thetasrThe increase of the electromagnetic torque is negative, and the current amplitude value meets the following relation:
Figure BDA0002555498220000094
electromagnetic torque Te and theta of motorsrThe characteristics are shown in fig. 8.
Te90 curve: electromagnetic torque and theta when amplitude of Is 90% of rated currentsrThe remaining curves represent the same meaning.
Under different | Is | amplitudes, outputting the maximum theta corresponding to the maximum point of the electromagnetic torquesrConnected together to form thetasrMaxCurves, as shown by the dashed lines in fig. 8. In the switching process, assuming that the load torque Is constant, the TL curve represents the set load curve in the switching process, and intersects with the torque curves at different | Is | amplitudes at points a, B, C, D, E, respectively, and these points represent steady-state points under the "torque self-balancing" adjustment of the motor at different | Is | amplitudes when the load Is constant.
And (3) drawing tangent lines of torque curves at the points, wherein the included angle is alpha, and the larger the alpha value is, the larger the adjustable force of the motor torque self-balance is, the stronger the load disturbance resistance is, and the more stable the system is. As can be seen from equation (1.3), increasing the adjustable coefficient Kt of the starting current amplitude increases α. Decreasing the angular acceleration factor K α results in a smaller load curve slope and a larger.
As can be seen from fig. 8, the motor torque and torque angle characteristics have the following characteristics:
1: the intersection A 'of the TL' curves and the acceptance theta as the load TL increasessrMaxThe travel between the curve-limiting points of intersection E' is shorter, i.e. thetasrThe range of variation becomes smaller.
2: torque curve as the | Is | magnitude decreasesShift right by theta corresponding to the intersection of the load curves TLsrThe value also increases, thetasrThe range of variation becomes smaller;
3: as the magnitude of Is decreases, the angle α between the torque curve and the load curve becomes smaller.
Switching strategies:
when the motor reaches the minimum operating frequency allowed by the closed loop during the I/F start phase, algorithm switching can begin. In order to make the closed-loop algorithm converge at the time of switching, the closed-loop algorithm and the open-loop algorithm need to be operated simultaneously below the minimum operating frequency. Since the system synchronous rotational speed meets the assumed rotating coordinate system minimum speed requirement before cutting into the speed closed loop, the speed and angle used in the algorithm (angle signal for coordinate transformation of current and voltage) is provided by the I/FStartUp generator.
Assuming that the coordinate system inputs (voltage, current, synchronous speed, and angle of coordinate transformation) all adopt the I/F starting algorithm
Figure BDA0002555498220000101
Variables in a coordinate system. So that the I/F initiates the algorithm before switching into closed loop
Figure BDA0002555498220000102
The coordinate system is overlapped with the dc-qc axis system of the assumed rotating coordinate system method, so the error angle between the synchronous coordinate system with the rotor position as the reference estimated by the assumed rotating coordinate system method can be used as the I/F starting algorithm
Figure BDA0002555498220000103
The error angle between the coordinate system and the synchronous coordinate system with reference to the rotor position can be used as a feedback input for the switching strategy.
When the open loop switches into the closed loop, θ is desiredsrClose to 90 deg., so the angle requirement at the switching can be achieved by lowering Is. However, as the magnitude of Is decreases, θsrApproximately 90 deg. with thetasrA mutual residual thetaLThe angle approaches 0 deg., and the torque angle β also tapers asβ to a certain extent, the system loses the ability to adjust "torque self-balance" and is liable to be out of control and unstableLA margin theta should be leftLmin. If thetaLminIf the value is too large, the impact in the switching process is large, and the system oscillation is easily caused; if thetaLminIf the value is too small, the system may lose stability before switching, and it is necessary to combine with reality, generally setting 5-10 °.
During the switching process, the magnitude | Is | of the current command Is to be reduced. In each self-balancing period, the average acceleration of the rotor can be approximately considered to be 0, so the average value of the electromagnetic torque is equal to the average value of the load torque, and the torque formula is approximated according to
Figure BDA0002555498220000111
TL＝Te＝|Is|*cosθLWhen | Is | decreases with a constant slope, θLThe downward trend of (a) is shown in fig. 9. Theta when Is decreases linearlyLNon-linear decrease, thetaLThe smaller the value, the more severe the drop, which easily causes current oscillation during switching, so the slope of the | Is | drop needs to be dynamically adjusted to slow down θLIs reduced.
In the invention, the | Is | slope Is dynamically adjusted:
in a conventional switching strategy, real-time angles of an open-loop coordinate system and a closed-loop coordinate system need to be calculated respectively, and then an angle difference between the two coordinate systems is obtained by subtraction. Whereas in the algorithm herein, the I/F starts the algorithm when not switching into closed loop
Figure BDA0002555498220000112
The coordinate system is superposed with a dc-qc axis system of an assumed rotating coordinate system method, so that the angle error tan delta theta between the dc-qc axis system and a real d-q axis system is approximately equal to delta thetaLThe tan delta theta value calculated by a closed-loop algorithm can be directly judged, so that the calculation of a real-time angle and the calculation of an angle difference are avoided.
In order to satisfy the approximation condition tan Δ θ ≈ Δ θ to simplify the calculation, Δ θ is limited within the range of variation of [ -28.2 °, 28.2 ° ]. As can be seen from fig. 10, the change of Δ θ in this interval Is near the inflection point, the change rate Is very large, and dynamic adjustment | Is | lag Is easily caused, which results in torque fluctuation and current oscillation during the switching process.
Consider that the cosine quantity has an equivalent infinitesimal cos Δ θ ≈ 1- (Δ θ)2The | Is | variation law designed herein Is as follows (2.6):
Is(n)＝Is(n-1)-Kct(tanΔθ)2·Tc(0.11)
wherein: kctFor the current variation coefficient, tan Δ θ is the tangent of the error angle of the coordinate axis given by the assumed coordinate axis position estimator, TcThe period is controlled by a singlechip.
The change of tan Δ θ Is shown in fig. 10, and it can be seen that when | Is changed according to equation (2.6), the decrease of the angle error Is relatively gentle, and smooth switching can be achieved.
Experimental results and analysis:
in order to verify the practical performance of the method, experiments are carried out on a company intelligent drive hardware platform, wherein the specification parameters of main devices of the hardware platform are described in a table 3-1:
TABLE 3-1 hardware platform Primary device Specification parameters
Figure BDA0002555498220000121
The system carrier frequency is set to 4kHz, the motor has no position sensor, and the phase current waveform in the starting process of the press is shown in figure 11. Wherein Stg1 and Stg2 are predetermined as stages, Stg3 is an I/F accelerated start stage, Stg4 is a switching process, and Stg5 is a closed loop stable operation stage.
As can be seen from the figure 3-1, the whole operation process is smooth and reliable when the press enters a position-sensing-free estimation closed loop stage from the pre-positioning stage, the I/F acceleration starting stage, the switching stage and the position-sensing-free estimation closed loop stage.
The invention has the following advantages:
1: the current in the whole starting process is controllable and is restricted by the instruction value, and compared with V/F starting, the starting failure caused by overcurrent under different loads can be effectively avoided.
2: the pre-positioning is divided into two sections, wherein the angle of a current vector is fixed, the amplitude is gradually increased, and then the amplitude is fixed and the angle is slowly increased. Therefore, the impact on the motor in the pre-positioning stage is avoided, and the pre-positioning reliability is improved
3: the I/F acceleration stage enables the motor to have better load disturbance resistance performance during the starting process through the torque self-balancing characteristic.
4: during the closed-loop switching stage, the current attenuation amplitude is adjusted in real time by monitoring the tangent value of the angle difference between the instruction coordinate system and the actual coordinate system, so that the angle difference of the coordinate system gradually converges to a very small angle, and the smoothness and the rapidity of the switching process are improved.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (7)

1. A reliable and smooth starting method based on a permanent magnet synchronous motor without a position sensor is characterized by comprising the following steps:
s1, pre-positioning stage: applying a rotating current vector in an armature winding of a stator of the motor to enable the motor to operate in a current closed-loop and speed open-loop mode, and defining a synchronous coordinate system where the open-loop current vector is located
Figure FDA0002555498210000011
A coordinate system, a synchronous coordinate system with the position of the motor rotor as a reference is set as a dq coordinate system, and the phase difference between the two coordinate systems is thetaL：
S11: controlling the angular speed of the stator current vector to keep low-frequency rotation, and increasing the amplitude of the stator current vector to a set amplitude by a first set function so that the current of a rotor winding is gradually increased under the regulation of a current loop PI controller;
s12: controlling the amplitude of the stator current vector to be unchanged and the command position angle to be increased by a second set function, so that the rotor rotates at a low frequency and a constant speed until the stator current vector is synchronous with the rotor position;
s2, I/F acceleration stage: controlling the stator current vector of the motor to rotate at a set angular acceleration, enabling the stator current vector and the rotor flux linkage position to keep synchronous following through a torque-self-balancing characteristic, enabling the motor rotor to keep synchronous rotation under the traction of the stator current vector until the minimum rotating speed of speed closed-loop operation is reached, and enabling the position estimator of the assumed coordinate system to accurately estimate
Figure FDA0002555498210000012
Angle theta between coordinate system and dq coordinate systemL；
S3, closed-loop cut-in stage: the rotating speed of the motor keeps the lowest rotating speed of the speed closed-loop operation unchanged, the current vector amplitude of the stator is gradually reduced, and the included angle theta of the motor is adjusted through the characteristic of torque-self balanceLGradually decays to be less than threshold value thetaLLmtAnd when the motor is switched to the speed closed-loop operation mode.
2. The method for starting the permanent magnet synchronous motor based on the position sensor without the position sensor as claimed in claim 1, wherein the method comprises the following steps: in step S11, the first setting function is a ramp function by which the magnitude of the stator current vector is increased to a set value.
3. The method for starting the permanent magnet synchronous motor based on the position sensor without the position sensor as claimed in claim 1, wherein the method comprises the following steps: in step S12, the second setting function is a linear function, and the command position angle increases as a linear function of a low frequency.
4. The method for starting the permanent magnet synchronous motor based on the position sensor without the position sensor as claimed in claim 1, wherein the method comprises the following steps: before step S3, included angle thetaLObtained by the hypothetical coordinate system position estimator when directly obtained by the hypothetical coordinate system position estimator
Figure FDA0002555498210000013
The range of the angle error tan delta theta of the coordinate system and the dc-qc axis system of the assumed rotating coordinate system method is [ -28.2 degrees, 28.2 degrees °]When tan Δ θ ≈ Δ θ ═ θLStep S3 is executed.
5. The method for starting the permanent magnet synchronous motor based on the position sensor as claimed in claim 4, wherein the method comprises the following steps: in step S3, the stator current vector magnitude is determined by making the included angle θLAnd adjusting a dynamic function of smooth switching.
6. The method for starting the permanent magnet synchronous motor based on the position sensor without the position sensor as claimed in claim 5, wherein the method comprises the following steps: the dynamic function is Is(n)＝Is(n-1)-Kct(tanΔθ)2·TcWherein: kctFor the current variation coefficient, tan Δ θ is the tangent of the error angle of the coordinate axis given by the assumed coordinate axis position estimator, TcThe period is controlled by a singlechip.
7. The method for starting the permanent magnet synchronous motor based on the position sensor without the position sensor as claimed in claim 1, wherein the method comprises the following steps: in step S3, the threshold θLLmtIs 5 to 10 degrees.
CN202010590948.2A 2020-06-24 2020-06-24 Reliable and smooth starting method based on permanent magnet synchronous motor without position sensor Pending CN111786607A (en)

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