CN107979318A - A kind of d axis positive direction determination methods of permanent magnet synchronous motor - Google Patents

Abstract

The invention discloses a kind of d axis positive direction determination methods of permanent magnet synchronous motor, specific steps：1. using pulsating high frequency current injection structure rotor closed-loop system, the response of d shaft voltages is obtained；2. record amplitude of the d shaft voltages response (1) when Injection Current signal phase is pi/2,3 pi/2；3. comparing two amplitude sizes, d axis positive directions are judged, obtain the offset after d axis positive direction judges.Constructed rotor closed-loop system, estimation rotor synchronous rotating frame q shaft currents are given as 0, inject a pulsating high frequency sinusoidal signal to d shaft currents, build rotor closed-loop system, the d shaft voltages response of extraction rotor synchronous rotating frameFor the present invention during d axis positive directions are judged, the electric current of injection is always sinusoidal high-frequency signal, without injecting the signal of the other forms such as positive negative pulse stuffing, simplifies estimation procedure；On motor operation without influence, simple in structure, reliability is high, reduces the complexity of operation, simplifies initial position estimation process.

Description

A method for judging the positive direction of the d-axis of a permanent magnet synchronous motor

technical field

The invention relates to the field of motors, in particular to a method for judging the positive direction of a d-axis of a permanent magnet synchronous motor.

Background technique

For the method of detecting the initial position of the surface-mounted permanent magnet synchronous motor rotor, since the motor rotor is stationary, the initial position of the rotor cannot be estimated by detecting the back EMF of the motor. High-frequency signal injection method.

Liu Ying, Zhou Bo, Li Shuai, et al. Rotor initial position detection of surface-mounted permanent magnet synchronous motor[J]. Proceedings of the Chinese Society for Electrical Engineering, 2011, 31(18): 48-54. Estimation of rotor synchronous rotation coordinates The d-axis of the system injects a high-frequency sinusoidal voltage signal, detects the q-axis high-frequency current response and establishes a position estimation closed loop to obtain the initial estimated value of the rotor position. Then inject positive and negative voltage pulses in the direction of the estimated d-axis, and use the difference in the equivalent time constant of the direct axis under the action of positive and negative currents to judge the positive direction of the d-axis. This method needs to inject two types of signals during the entire process of initial position estimation. , the implementation is more complicated. The process of judging the positive direction of the magnetic pole needs to inject positive and negative voltage pulses and then compare the time it takes for the current response to decay to 0, which also takes a certain amount of time. Liu Ying, Zhou Bo, Zhao Chengliang, et al. Low-speed position sensorless control of SPMSM based on pulsating high-frequency current injection[J]. Chinese Journal of Electrotechnical Society, 2012, 7(27): 139-145. The first use of pulsating high-frequency current injection The SPMSM rotor position estimation method is realized, but there is no mention of how to judge the positive direction of the d-axis.

According to the existing literature review, there is no article dedicated to the judgment of the positive direction of the d-axis in the pulse vibration high-frequency current injection method.

Contents of the invention

The specific technical solution provided by the invention is: a method for judging the positive direction of the d-axis of a permanent magnet synchronous motor.

The technical solution that realizes the object of the present invention is:

1. a d-axis positive direction judging method of a permanent magnet synchronous motor, is characterized in that, concrete steps:

Step 1. Construct a rotor closed-loop system by using the pulse vibration high-frequency current injection method to obtain the d-axis voltage response (1);

Step 2. Record the amplitude of the d-axis voltage response (1) when the phase of the injected current signal is π/2, 3π/2;

Step 3: Comparing the magnitudes of the two amplitudes, judging the positive direction of the d-axis, and obtaining the compensation value after judging the positive direction of the d-axis.

2. In step 1, build a rotor closed-loop system, estimate the q-axis current of the rotor synchronous rotation coordinate system as 0, inject a pulse vibration high-frequency sinusoidal signal into the d-axis current, construct a rotor closed-loop system, and extract d of the rotor synchronous rotation coordinate system Shaft voltage response

3. In step 2, record the d-axis voltage response Voltage amplitudes |U ₁ |, |U ₂ | at ω _h t = π/2 and ω _h t = 3π/2.

4. In step 3, compare the magnitudes of the two amplitudes, and perform a comparison operation on the values of |U ₁ | and |U ₂ | after low-pass filtering (2) to determine the positive direction of the d-axis. Judge the positive direction of the d-axis according to the size comparison of |U ₁ | and |U ₂ |, and obtain the compensation value after judging the positive direction of the d-axis; if |U ₁ |<|U ₂ | In the same direction, the compensation value after judging the positive direction of the d-axis is 0; if |U ₁ |>|U ₂ |, then the positive direction of the d-axis is opposite to the magnetic pole N, and the compensation value after judging the positive direction of the d-axis is π.

Compared with the prior art, the present invention has significant advantages:

(1) In the process of judging the positive direction of the d-axis, the injected current is always a sinusoidal high-frequency signal, and there is no need to inject other forms of signals such as positive and negative pulses, which simplifies the estimation process;

(2) The present invention records the voltage amplitude of the d-axis voltage response when the phase of the injected current signal is π/2 and 3π/2, and judges the positive direction of the d-axis by comparing the amplitude. The process is within a cycle of the injected current signal It can be completed, and the time required for the process of judging the positive direction of the d-axis is shortened.

(3) The d-axis judging method of the present invention is very suitable for the high-frequency current injection method, has no effect on the operation of the motor, has a simple structure, high reliability, reduces the complexity of the operation, and simplifies the initial position estimation process.

Description of drawings

Fig. 1 is a functional block diagram of the signal extraction and modulation process for judging the positive direction of the d-axis;

Fig. 2 is a block diagram of the closed-loop control of the rotor of the surface-mounted permanent magnet synchronous motor based on the high-frequency current injection method;

Fig. 3 is a schematic diagram of the relative relationship between the two-phase stationary coordinate system, the actual two-phase synchronously rotating coordinate system and the estimated two-phase synchronously rotating coordinate system;

In the figure: 1 is the recorded voltage amplitude, 2 is the low-pass filter, 3 is the proportional-integral regulator (PI), 4 is the Park inverse transform, 5 is the space vector pulse width modulation, 6 is the 3-phase inverter, 7 8 is Clarke transformation, and 9 is Park transformation.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

As shown in Figure 1, the present invention provides a new method for judging the positive direction of the d-axis of a permanent magnet synchronous motor, which specifically includes the following steps:

Step 1. Construct a rotor closed-loop system by using the pulse vibration high-frequency current injection method to obtain the d-axis voltage response;

Step 2. Record the amplitude of the d-axis voltage response when the phase of the injected current signal is π/2, 3π/2;

Step 3: Comparing the magnitudes of the two amplitudes, judging the positive direction of the d-axis, and obtaining a complementary value after judging the positive direction of the d-axis.

Further, in step 1, the stator flux linkage of the permanent magnet synchronous motor is generated by the joint action of the three-phase stator current and the rotor permanent magnet, and is related to the rotor position. The flux linkage equation is expressed as:

In the formula, ψ _A , ψ _B , and ψ _C are the flux linkages of the three-phase armature winding turns; for the surface-mounted permanent magnet synchronous motor, because of the uniform air gap, the self-inductance and mutual inductance of the three-phase winding are closely related to the rotor The position is irrelevant, both are constant values, the self-inductance of each phase armature winding L _AA = L _BB = L _CC ; the mutual inductance between two-phase windings M _AB = M _BA = M _BC = M _CB = M _CA = M _AC . Thus, the stator voltage equation is obtained as:

In the formula, u _A , u _B , u _C are the phase voltages of the three-phase stator armature windings, i _A , i _B , i _C are the phase currents of the three-phase stator armature windings, R _A =R _B =R _C = R _s is the resistance of the three-phase stator armature winding, and p is the differential operator.

It can be seen from the above two equations that the mathematical model established by the permanent magnet synchronous motor in the three-phase static coordinate system is a nonlinear and coupled multivariable system, which is not conducive to analysis and control.

In order to simplify the analysis, the stator current space vector i _s is defined as:

In the formula, the operator a=e ^j2π/3 , a ² =e ^j4π/3 .

The real axis of the stator current space vector is the a-axis, which coincides with the A-phase axis as of the stator winding; the imaginary axis is the β-axis, which leads the α-axis by 90° electrical angle. This realizes the transformation from the three-phase stationary coordinate system to the two-phase stationary coordinate system, which is called Clarke transformation. The current relationship and transformation matrix are:

In the formula, i _α and i _β are the α and β axis currents respectively.

The rotor field-oriented control is adopted in the quantity control, and the direction pointed by the N pole of the permanent magnet magnetic field is set as the direct axis (d axis), and the axis that is 90° ahead of the direct axis in the forward rotation direction of the motor is the quadrature axis (q axis). A two-phase rotating coordinate system is formed, and the two-phase static coordinate system is transformed into a two-phase rotating coordinate system, which is called Park change. The current relationship and transformation matrix are:

In the formula, _id and i _q are d and q axis currents respectively.

The above transformation relationship is also applicable to voltage and flux linkage. In order to keep the power constant before and after the transformation, the number of turns of each phase winding in the two-phase coordinate system is equal to the effective number of turns of each phase winding in the original three-phase coordinate system. times. Using the above two coordinate transformation matrices, the mathematical model of the permanent magnet synchronous motor in the two-phase rotating coordinate system can be established.

(1) Flux linkage equation

In the formula, ψ _d , ψ _q and L _d , L _q are the flux linkage and inductance of the d and q axes, respectively.

(2) Voltage equation

In the formula, u _d and u _q are d and q axis voltages respectively, and it is considered that pψ _f =0. In the steady state case, the voltage equation can be written as:

(3) Torque equation

T _e =p _n (ψ _d i _q -ψ _q i _d )=p _n [ψ _f i _q +(L _d -L _q )i _d i _q ] (9)

In the formula, p _n is the number of pole pairs of the permanent magnet synchronous motor. The torque consists of two parts. The first part is the main electromagnetic torque, which is generated by the interaction between the stator rotating magnetic field and the permanent magnetic field, and is proportional to the quadrature axis current; the second part is the reluctance torque, which is due to the The inductance varies and is proportional to the salient pole ratio.

The research object is a surface-mounted permanent magnet synchronous motor. Usually, the AC and D-axis inductances are basically equal, so its torque equation can be simplified as

T _e = p _n ψ _f i _q (10)

It can be seen that there is no reluctance torque in the torque equation, but only the electromagnetic torque proportional to the quadrature axis current, which is very convenient for torque control.

It can be seen from formula (10) that after the vector control is adopted, the torque of the permanent magnet synchronous motor in the two-phase rotating coordinate system is determined by the quadrature axis current and the magnetic field, while the magnetic field of the permanent magnet remains unchanged, and the influence on the motor torque The control can be summed up as controlling the alternating current and the direct axis current of the stator current respectively. The essence of vector control is to decompose the stator current vector into torque current component i _q and excitation current component i _d through coordinate transformation theory to realize decoupling control of torque and magnetic flux.

According to the different control methods of alternating current and direct axis current, the current control strategy in vector control of permanent magnet synchronous motor can be divided into: zero direct axis current control, maximum torque current ratio control, unit power factor control and constant flux linkage control . Among them, unit power factor control and constant flux linkage control are more suitable for high-power permanent magnet synchronous motor control systems. They have the advantages of high power factor and reduced inverter capacity. Direct axis current is zero control, ie _id = 0 control, which is the simplest current control strategy in vector control. The advantage of this control strategy is that the control is the simplest, the amount of calculation is small, and it will not cause the demagnetization effect to cause the demagnetization of the permanent magnet and deteriorate the performance of the motor, so it has been widely used. The disadvantages of this control strategy are: 1) the power factor decreases after the load increases; 2) the reluctance torque cannot be output. The maximum torque-to-current ratio control means that under the condition of the same output torque, the stator current of the motor is the smallest, which can reduce copper loss and inverter loss. The surface-mounted permanent magnet synchronous motor studied in this paper belongs to the small and medium power range, and the motor itself does not have the ability to output reluctance torque. The i _d = 0 control strategy is adopted, which is consistent with the current control with the largest torque-to-current ratio. The reason is that the stator current is all used to generate torque at this time.

Establish the coordinate system relationship diagram, as shown in Figure 3, dq is the actual synchronous rotating coordinate system, In order to estimate the rotor synchronous rotating coordinate system, αβ is the actual two-phase stationary coordinate system, and define the estimation error Among them, θ is the actual rotor initial position, is the final initial position estimate, The initial value of is 0. As shown in Figure 2, the q-axis current of the estimated rotor synchronous rotation coordinate system is given as 0, and the d-axis current is given as a pulse-vibrating high-frequency sinusoidal signal I _mh sin(ω _h t), where I _mh is at d The amplitude of the high-frequency current injected on the d-axis, ω _h is the angular frequency of the high-frequency current injected on the d-axis, and t represents the current moment. A proportional-integral regulator (PI) is used to control the estimated d-axis current and q-axis current to make it consistent with the given; compare the output voltage of the proportional-integral regulator (PI) and Perform Park inverse transformation to obtain the voltages u _α and u _β in the two-phase stationary αβ coordinate system, and then use the space vector pulse width modulation strategy to obtain the six-way switching signals of the three-phase inverter to drive the surface-mounted permanent magnet synchronous motor PMSM; Detect the A-phase and B-phase currents in the three-phase winding A/B/C of the motor, as shown in Figure 2, the current i _α and i _β in the two-phase static αβ coordinate system obtained by the advanced Clarke transformation, and then through the Park transformation Get the d-axis current in the estimated rotor synchronous rotation coordinate system and q-axis current Feed it back to the input of the PI regulator; extract the d-axis voltage response of the rotor synchronously rotating coordinate system

Further, in step 2, as shown in Figure 1, for the surface-mounted permanent magnet synchronous motor, the magnetic field is saturated when the d-axis current acts as a magnetizer, and the inductance decreases; big. Liu Ying, Zhou Bo, Zhao Chengliang, et al. Low-speed position sensorless control of SPMSM based on pulse-vibration high-frequency current injection[J]. After the electric current, the d-axis voltage response of the estimated synchronous rotating coordinate system of the permanent magnet synchronous motor is:

After the initial initial position estimation is completed, the position estimation error Δθ is 0 or π, which can be substituted into formula (11):

In the formula, is the average impedance, is the semi-difference impedance. Substitute into formula (12) to get:

In the formula, Z _d = _rs +iω _h L _d is the d-axis high-frequency impedance, rs _is the stator resistance, L _d is the d-axis inductance. Since the resistance of the winding is much smaller than the high-frequency impedance of the winding, the resistance voltage drop of the stator winding can be ignored. From formula (13):

When ω _h t = π/2, substitute into formula (14) to get record this time Shaft voltage amplitude |U ₁ |; when ω _h t = 3π/2, record this time Shaft voltage amplitude |U ₂ |.

Further, in step 3, when Δθ=0, ω _h t=π/2, the magnetic potential generated by the stator current is consistent with the positive direction of the d-axis, the magnetic circuit is saturated, the inductance of the stator d-axis becomes smaller, and |U ₁ | is smaller ; When ω _h t = 3π/2, the magnetic potential generated by the stator current is opposite to the positive direction of the d-axis, the magnetic circuit desaturates, the inductance of the stator d-axis becomes larger, and |U ₂ | is larger, so |U ₁ |<|U ₂ |.

When Δθ=π, ω _h t = π/2, the magnetic potential generated by the stator current is opposite to the positive direction of the d-axis, the magnetic circuit desaturates, the inductance of the stator d-axis becomes larger, and |U ₁ | is larger; ω _h t = When 3π/2, |U ₂ | is small, so |U ₁ |>|U ₂ |.

In order to avoid interference and misjudgment, the values of |U ₁ | and |U ₂ | must be filtered before they can be used for comparison operations. If |U ₁ |<|U ₂ |, the positive direction of the d-axis is in the same direction as the N pole of the magnetic pole, and the compensation value after judging the positive direction of the d-axis is 0; if |U ₁ |>|U ₂ |, the d-axis is positive The direction is opposite to the N pole of the magnetic pole, and the compensation value after judging the positive direction of the d-axis is π.

Claims (4)

1. a d-axis positive direction judging method of a permanent magnet synchronous motor, is characterized in that, concrete steps: Step 1. Construct a rotor closed-loop system by using the pulse vibration high-frequency current injection method to obtain the d-axis voltage response (1); Step 2. Record the amplitude of the d-axis voltage response (1) when the phase of the injected current signal is π/2, 3π/2; Step 3: Comparing the two amplitudes, judging the positive direction of the d-axis, and obtaining the compensation value after judging the positive direction of the d-axis. 2. The method for judging the positive direction of the d-axis according to claim 1, characterized in that, in the first step, a rotor closed-loop system is constructed, and the q-axis current of the rotor synchronously rotating coordinate system is estimated to be 0, and a current of d-axis is injected into the d-axis current. Pulse high-frequency sinusoidal signal, build a closed-loop rotor system, and extract the d-axis voltage response of the rotor synchronously rotating coordinate system 3. The method for judging the positive direction of the d-axis according to claim 1, characterized in that, in the second step, the d-axis voltage response is recorded Voltage amplitudes |U ₁ |, |U ₂ | at ω _h t = π/2 and ω _h t = 3π/2. 4. The method for judging the positive direction of the d-axis of a permanent magnet synchronous motor according to claim 1 or 3, characterized in that, in the step 3, the two amplitudes are compared, and the values of |U ₁ |, |U ₂ | After low-pass filtering (2), a comparison operation is performed to determine the positive direction of the d-axis. Judge the positive direction of the d-axis according to the size comparison of |U ₁ | and |U ₂ |, and obtain the compensation value after judging the positive direction of the d-axis; if |U ₁ |<|U ₂ | In the same direction, the compensation value after judging the positive direction of the d-axis is 0; if |U ₁ |>|U ₂ |, then the positive direction of the d-axis is opposite to the magnetic pole N, and the compensation value after judging the positive direction of the d-axis is π.