A method for field weakening of a permanent magnet synchronous motor based on sector offset

Abstract

The application provides a field weakening method of a permanent magnet synchronous motor based on sector offset, and belongs to the technical field of motor control. The field weakening method is suitable for a field weakening method using a control algorithm of a switching table, and achieves the effect of field weakening by changing d-q axis voltage distribution. The field weakening method comprises the following steps: S1, observing a load via a load torque observer; S2, substituting a required maximum motor speed and the observed load into a formula to calculate a sector offset; S3, inputting the calculated sector offset into a switching table to perform sector offset; and S4, inputting an electromagnetic torque signal into the switching table, outputting a switching signal via the offset sector, and further controlling the motor. The application provides a field weakening method of a permanent magnet synchronous motor based on sector offset, the d-q axis voltage distribution is changed by rotating the sector clockwise, the offset can be calculated according to the maximum motor speed, an analytical solution is obtained, the method is suitable for algorithms such as flux linkage closed loop direct torque control, and the field weakening effect is excellent in the whole speed range.

Description

Technical Field

[0001] This invention belongs to the field of motor control technology, and in particular relates to a field weakening method for a permanent magnet synchronous motor based on sector offset. Background Technology

[0002] In the field of permanent magnet synchronous motor (PMSM) control, flux-free closed-loop direct torque control (DTC) is used in some scenarios with stringent dynamic performance requirements due to its advantages of not requiring complex flux observation and fast system response. However, the control logic of this algorithm, which determines the motor sector and selects the voltage vector for the next moment through a switching table, makes it difficult to directly and precisely control the flux. In the switching table, increasing and decreasing torque correspond to the same voltage vector in a specific sector, making it impossible to directly change the voltage vector angle. This makes field weakening control a technical challenge.

[0003] Field weakening control is a key method for extending the high-speed operating range of motors and achieving constant power speed regulation, which is crucial for scenarios such as high-speed cruising in new energy vehicles and high-speed industrial spindles. Addressing the field weakening challenges of flux-free closed-loop direct torque control, designing suitable field weakening methods is urgently needed. This will not only overcome the speed regulation bottleneck of such control algorithms but also further improve the speed regulation flexibility and power density of motors, promoting their application in more high-end speed regulation scenarios, and has significant engineering value and practical significance. Summary of the Invention

[0004] To address the problems existing in the background technology, the present invention provides a field weakening method for permanent magnet synchronous motors based on sector offset, which is applicable to field weakening methods using control algorithms of switching meters, and achieves the field weakening effect by changing the voltage distribution of the dq axis.

[0005] The technical solution adopted by this invention to solve its technical problem is: a field weakening method for a permanent magnet synchronous motor based on sector offset, comprising the following steps:

[0006] S1. The load is observed via the load torque observer;

[0007] S2. Substitute the required maximum motor speed and the observed load into the formula to calculate the sector offset;

[0008] S3. Input the calculated sector offset into the switch table to perform sector offset;

[0009] S4. The switch meter inputs an electromagnetic torque signal, which is then output as a switch signal via the offset sector to control the motor.

[0010] The offset expression in S2 is:

[0011]

[0012] In the formula, Indicates the offset. Indicates the electric angular velocity of the motor. Indicates the motor control cycle. , , For coefficients, This represents the amplitude of the synthesized cosine wave.

[0013] The beneficial effects of the present invention are as follows: The present invention proposes a field weakening method for permanent magnet synchronous motors based on sector offset. By offsetting the sector, the distribution of dq axis voltage of the motor in a specific sector is changed. This method is particularly suitable for algorithms that directly control the motor using a switching meter and have adaptive flux, such as flux-free closed-loop direct torque control.

[0014] This method changes the dq-axis voltage generated when the voltage vector acts in each sector by rotating the sector clockwise. The sector offset can be calculated based on the set maximum motor speed, and an analytical solution can be obtained through precise deduction. It has excellent field weakening effect at different motor speeds. Attached Figure Description

[0015] In the attached diagram:

[0016] Figure 1 This is a control block diagram of the present invention;

[0017] Figure 2 This is a diagram showing the effect of magnetic weakening at an electric angular velocity of 900 rad / s;

[0018] Figure 3 This is a diagram showing the effect of magnetic weakening at an electric angular velocity of 100 rad / s;

[0019] Figure 4 This is a speed-following effect diagram;

[0020] Figure 5 This is a flowchart of the invention;

[0021] Figure 6 This is a schematic diagram showing the relationship between the voltage vector and the three-phase switches of the inverter in this invention. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings. The drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0023] A field weakening method for a permanent magnet synchronous motor based on sector offset includes the following steps:

[0024] S1. The load is observed via the load torque observer;

[0025] S2. Substitute the required maximum motor speed and the observed load into the formula to calculate the sector offset;

[0026] S3. Input the calculated sector offset into the switch table to perform sector offset;

[0027] S4. The switch meter inputs an electromagnetic torque signal, which is then output as a switch signal via the offset sector to control the motor.

[0028] The method for calculating the sector offset in S2 is as follows:

[0029] The rotating sector alters the dq-axis voltage generated when the voltage vector acts within the sector. During field weakening, the rotation is clockwise. At maximum speed, the motor rotor's cycle time is the same within a 60° sector. That is, one rotation of the motor rotor has 6 sector spaces (sector I, sector II, sector III, sector IV, sector V, and sector VI) and 6 sector cycles. The dq-axis voltage vector is symmetrical within the 6 sector cycles, and the stator d-axis flux linkage change is 0 within one cycle.

[0030] For the voltage vectors of the 6 sector spaces, the formula for the dq-axis voltage is:

[0031] (1)

[0032] In the formula, to These represent the relationship between the direct-axis component (d-axis component) of the voltage vector and the electrical angle in the six sector spaces. to These represent the relationship between the cross-axis component (q-axis component) of the voltage vector and the electrical angle in the six sector spaces. Indicates the inverter's DC voltage. This indicates the electrical angle of the motor.

[0033] The magnetic flux linkage formula is:

[0034] (2)

[0035] In the formula, This represents the d-axis voltage of the motor stator. This represents the stator resistance of the motor. This represents the d-axis current of the motor stator. Indicates the electric angular velocity of the motor. This indicates the q-axis flux linkage of the motor stator. Indicates the start time of the control cycle. Indicates the end time of the control cycle.

[0036] Torque for PMSM calculated from flux linkage:

[0037] (3)

[0038] In the formula, Indicates the electromagnetic torque of the motor. Indicates load torque. Indicates the number of pole pairs of the motor. This indicates the magnetic flux linkage of the permanent magnet in the motor. This indicates the magnetic flux linkage along the d-axis of the motor stator. This represents the d-axis inductance of the motor stator. This represents the q-axis inductance of the motor stator.

[0039] For SPMSM (surface-mounted permanent magnet synchronous motor):

[0040] (4)

[0041] Substituting equation (4) into equation (2), we obtain the flux linkage formula for SPMSM:

[0042] (5)

[0043] According to the voltage formula of the motor:

[0044] (6)

[0045] In the formula, This represents the q-axis voltage of the motor stator. This represents the q-axis current of the motor stator.

[0046] The formula for steady-state current is derived as follows:

[0047] (7)

[0048] Substituting the current formula into equation (5), we get:

[0049] .

[0050] By expanding and combining the fractions in the integrand, separating the integral from the constant term, and then multiplying the whole by the denominator and rearranging, we obtain the first transformation of the flux linkage formula:

[0051] (8)

[0052] Since the sector period of each sector space is symmetrical, any sector space satisfies the following equation:

[0053] (9)

[0054] In the formula, Indicates runtime. As an intermediate variable related to torque, This indicates the offset.

[0055] Substituting the constraint condition of equation (9) into equation (8), we obtain the second transformation of the magnetic flux linkage formula:

[0056] (10)

[0057] From the sum-to-product formula:

[0058] (11)

[0059] In the corresponding formula:

[0060] (12)

[0061] The simplified magnetic flux linkage formula is transformed into three forms:

[0062] (13)

[0063] In the formula, For surface-mounted permanent magnet synchronous motors (SPMSMs), the inductor has... ,

[0064] Adding a beat delay yields the following transformation of the flux linkage formula:

[0065] (14)

[0066] In the formula, This indicates the motor control cycle.

[0067] Let the parameters be:

[0068] (15)

[0069] Substituting the parameters shown in equation (15) into equation (14), we obtain the fifth transformation of the magnetic flux linkage formula:

[0070] (16)

[0071] In the formula, These are intermediate variables related to the offset value, motor electric angular velocity, and motor control cycle during the formula derivation process, and have no specific physical meaning.

[0072] Equation (16) can be transformed into a single trigonometric function to obtain the magnetic flux linkage formula transformation six:

[0073] (17)

[0074] In the formula, Indicates the amplitude of the synthesized cosine wave. Let A represent the initial phase angle of the synthesized cosine wave. The value of the initial phase angle is determined by the ratio of coefficients A and B, so that equation (16) can be expressed as a single cosine function.

[0075] That is, transforming equation (17) yields the magnetic flux linkage formula, transformation seven:

[0076] (18)

[0077] according to The physical meaning, ultimately obtained expression:

[0078] (19)

[0079] The load torque in the above equations can be observed by, for example, an extended state observer.

[0080] When this field weakening method is executed (taking the extended state torque observer as an example):

[0081] S1, the extended state torque observer first expands the total system disturbance (including model error and position load torque) into a new state variable, and then designs a linear or nonlinear observer based on the system input (such as voltage and current) and output (such as speed) to estimate the torque disturbance in real time. Finally, the observed torque value is obtained through compensation or direct output.

[0082] S2 executes the calculation process described above.

[0083] S3. Input the sector offset obtained from S2 into the switch table for sector offset. The switch table is as follows (TE in the switch table is the input electromagnetic torque signal):

[0084]

[0085] Subtract the sector offset from the original sector electrical angle. For example, if the sector offset is 30°, the sector switching table will be transformed into the following table:

[0086]

[0087] S4, when the input electromagnetic torque signal TE=1, it increases the motor's electromagnetic torque; when TE=0, it remains unchanged; and when TE=-1, it decreases the motor's electromagnetic torque. The specific output voltage vector is obtained through the offset sector. The relationship between the voltage vector and the inverter's three-phase switches is as follows: Figure 6 As shown, 1 indicates that the phase is on, and 0 indicates that the phase is off. The switching sequence is UVW phase. For example, the inverter three-phase switch corresponding to vector U1 is 100, that is, phase U is on, and phases V and W are both off.

[0088] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A field weakening method for a permanent magnet synchronous motor based on sector offset, characterized in that: Includes the following steps: S1. The load is observed via the load torque observer; S2. Substitute the required maximum motor speed and the observed load into the formula to calculate the sector offset; S3. Input the calculated sector offset into the switch table to perform sector offset; S4. The switch meter inputs an electromagnetic torque signal, which is then output as a switch signal via the offset sector to control the motor.

2. The field weakening method for a permanent magnet synchronous motor based on sector offset according to claim 1, characterized in that: The method for calculating the sector offset in S2 is as follows: For the voltage vectors of the 6 sector spaces, the formula for the dq-axis voltage is: （1） In the formula, to These represent the relationship between the direct-axis component (d-axis component) of the voltage vector and the electrical angle in the six sector spaces. to These represent the relationship between the cross-axis component (q-axis component) of the voltage vector and the electrical angle in the six sector spaces. Indicates the inverter's DC voltage. Indicates the electrical angle of the motor. The magnetic flux linkage formula is: （2） In the formula, This represents the d-axis voltage of the motor stator. This represents the stator resistance of the motor. This represents the d-axis current of the motor stator. Indicates the electric angular velocity of the motor. This indicates the q-axis flux linkage of the motor stator. Indicates the start time of the control cycle. Indicates the end time of the control cycle. Torque for PMSM calculated from flux linkage: （3） In the formula, Indicates the electromagnetic torque of the motor. Indicates load torque. Indicates the number of pole pairs of the motor. This indicates the magnetic flux linkage of the permanent magnet in the motor. This indicates the magnetic flux linkage along the d-axis of the motor stator. This represents the d-axis inductance of the motor stator. This represents the q-axis inductance of the motor stator. For SPMSM: （4） Substituting equation (4) into equation (2), we obtain the flux linkage formula for SPMSM: （5） Substituting the voltage and current formulas of the motor into equation (5), and simplifying and transforming them, we obtain the third transformation of the flux linkage formula: （13） In the formula, This refers to the stator inductor of a surface-mount permanent magnet synchronous motor, specifically an SPMSM stator inductor. For SPMSM, the offset is... For equation (13), we have Adding a beat delay to equation (13) yields the fourth transformation of the flux linkage formula: （14） In the formula, Indicates the motor control cycle. Set parameters: In the formula, To synthesize the amplitude of the cosine wave, The initial phase angle for synthesizing a cosine wave is determined by the ratio of coefficients A and B. Substituting the parameters into equation (15) and simplifying them, we obtain the seventh transformation of the magnetic flux linkage formula: （18） according to The physical meaning, ultimately obtained expression: （19）。

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