CN108736776A - A kind of control method of internal permanent magnet synchronous motor - Google Patents

Abstract

The invention discloses a control method for a built-in permanent magnet synchronous motor. The specific steps are as follows: 1) A closed-loop rotor system is constructed by using a field-weakening control method to obtain a d-axis voltage response, obtain a corresponding q-axis voltage, and determine a stable operating point Whether the current and voltage conform to the limit circle constraint, if not, select the appropriate voltage according to the rules; 2) Calculate the current drop gradient and constant torque direction through the stable operating point, and then use the vector product to find its angle; 3) Judging by the angle The direction of operating current decreases, and the voltage is changed so that the operating point moves to the direction of decreasing current. The invention considers that the power in the high-speed zone of motor field weakening is large, and the increase of the demagnetization current increases the system loss, and continuously corrects the q-axis voltage to adapt to different loads and speeds; on the basis of analyzing the single current field weakening control, according to the The projection relationship of the constant torque direction of the operating point on the current drop gradient, online optimization and correction of the quadrature axis voltage to make the operating current reach the minimum value.

Description

A control method for a built-in permanent magnet synchronous motor

technical field

The invention relates to the field of motors, in particular to a control method for a built-in permanent magnet synchronous motor.

Background technique

Built-in permanent magnet synchronous motors are widely used in high-performance speed control systems such as electric vehicle drive systems because of their outstanding advantages such as high efficiency, high power density, and easy field-weakening speed expansion. Systems such as electric vehicles require a wide speed range ω to meet the requirements of high-speed driving, so the research on IPMSM high-speed field weakening control is very important. In the traditional field-weakening strategy, there are two current regulators in the system, which regulate the dq axis current respectively. The saturation of the regulator and the mutual coupling of the dq axis current in the high-speed stage will deteriorate the system's regulation performance on the motor speed, current and torque. , and even lead to system instability.

In order to obtain a higher speed ω and solve the cross-coupling of the crankshaft current in the high-speed stage, Xu Longya from Ohio State University in the United States proposed a single-current control strategy. This method uses the coupling of the dq-axis currents instead of trying to eliminate the coupling, and only keeps one The current regulator directly provides the q-axis voltage, thereby simplifying the structure, and has the advantages of fast dynamic response, good robustness to DC bus voltage and load changes, and the like. But because the q-axis voltage is a given constant, the motor efficiency and load capacity cannot be optimized under different working conditions. Considering that the power of the electric vehicle is high in the field-weakening high-speed zone, the increase of the demagnetization current increases the system loss, so how to adjust the q-axis voltage under different loads and speeds, improve the working efficiency of the motor, and increase the mileage of the electric vehicle has become an important issue. research direction.

Contents of the invention

The purpose of the present invention is to provide a control method for an interior permanent magnet synchronous motor.

The technical solution to realize the object of the present invention is: a control method of a built-in permanent magnet synchronous motor, the specific steps are:

Step 1. Use the field weakening control method to build a rotor closed-loop system, obtain the d-axis voltage response, find the corresponding q-axis voltage V _fwc, and judge whether the current and voltage at the stable operating point meet the limit circle constraint. If not, select the appropriate one according to the rules V _fwc ;

Build a closed-loop system for field-weakening control rotor, estimate the d-axis current of the rotor synchronous rotation coordinates through coordinate transformation, and obtain the reference d-axis current through the field-weakening regulator, which includes field-weakening components and torque components; under a fixed q-axis voltage, The d-axis current is automatically adjusted to correspond to the q-axis voltage; specifically:

Assuming that the stator three-phase winding is a three-phase symmetrical sine wave, ignoring the influence of higher harmonics, iron loss, current loss and temperature on the parameters, in the dq coordinate system of the rotor flux orientation, the mathematical model of the permanent magnet synchronous motor is expressed as:

Voltage equation:

u _d ＝ R _s i _d -ω _e L _q i _q

Flux linkage equation:

u _q ＝R _s i _q +ω _e ψ _f +ω _e L _d i _d

Electromagnetic torque equation:

For the interior permanent magnet synchronous motor, L _d <L _q , the electromagnetic torque is composed of excitation torque and reluctance torque; for the reluctance motor, ω _f ＝0; for the surface permanent magnet synchronous motor, L _d = L _q .

Step 2. Calculate the current drop gradient and constant torque direction through the stable operating point, and then use the vector product to find its angle;

Step 3. Determine the direction of reducing the operating current through the angle, change V _fwc so that the operating point moves to the direction of reducing the current, and finally output _id .

In the case of constant speed and load, when the angle between the current drop gradient and the leftward constant torque direction is less than 90 degrees, reduce V _fwc ; when the current drop gradient and the leftward constant torque direction The angle is greater than 90 degrees, Increase V _fwc , the operating point moves to the right along the constant torque curve to reduce the current current; when the angle between the current descending gradient and the rightward constant torque direction is equal to 90 degrees, the current operating point is the pole of the current on the constant torque curve If the operating point is a small value, no correction is required; the minimum operating current is finally output.

Compared with the prior art, the present invention has the following significant advantages: 1) The present invention considers that the power in the high-speed area of weak magnetic field of the electric vehicle is relatively large, and the increase of the demagnetization current increases the system loss. The situation of load and rotating speed; 2) the present invention is first on the basis of analyzing single-current field weakening control thought, according to the projection relationship of the constant torque direction of the motor operating point on the current drop gradient, online optimization corrects the quadrature axis voltage to make it work The current reaches the minimum value; 3) By continuously correcting the q-axis voltage online, the operating current of the motor automatically converges to the minimum value of the current speed and load, thereby reducing the loss of the motor and improving the operating efficiency; 4) the invention proves that the gradient descent The uniqueness and optimality of the results when the method is used to solve the field-weakening optimal control problem of the built-in permanent magnet synchronous motor.

Description of drawings

Figure 1 is a single-current flux-weakening optimization control diagram based on the gradient descent method.

Figure 2 is a single current field weakening control diagram.

Figure 3 is a graph showing the influence of the q-axis voltage on the operating point.

Figure 4 is a single current control trajectory based on the gradient descent method.

In the figure: 1 select the appropriate initial q-axis voltage, 2 calculate the angle between the current drop gradient and the constant torque direction, 3 change the q-axis voltage to output the minimum operating current.

Detailed ways

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

In conjunction with the accompanying drawings, a control method for a built-in permanent magnet synchronous motor of the present invention includes the following steps:

Step 1. Use the field weakening control method to build a rotor closed-loop system, obtain the d-axis voltage response, find the corresponding q-axis voltage V _fwc, and judge whether the current and voltage at the stable operating point meet the limit circle constraint. If not, select the appropriate V _fwc ;

Build a closed-loop system for field-weakening control rotor, estimate the d-axis current of the rotor synchronous rotation coordinates through coordinate transformation, and obtain the reference d-axis current through the field-weakening regulator, which includes field-weakening components and torque components; under a fixed q-axis voltage, The d-axis current is automatically adjusted to correspond to the q-axis voltage; specifically:

Assuming that the stator three-phase winding is a three-phase symmetrical sine wave, ignoring the influence of higher harmonics, iron loss, current loss and temperature on the parameters, in the dq coordinate system of the rotor flux orientation, the mathematical model of the permanent magnet synchronous motor is expressed as:

Voltage equation:

u _d ＝ R _s i _d -ω _e L _q i _q

Flux linkage equation:

u _q ＝R _s i _q +ω _e ψ _f +ω _e L _d i _d

Electromagnetic torque equation:

For the interior permanent magnet synchronous motor, L _d <L _q , the electromagnetic torque is composed of excitation torque and reluctance torque; for the reluctance motor, ω _f ＝0; for the surface permanent magnet synchronous motor, L _d = L _q .

Step 2. Determine the current drop gradient and constant torque direction through the stable operating point, and then use the vector product to obtain its angle;

Step 3. Determine the direction of reducing the operating current through the angle, change V _fwc so that the operating point moves to the direction of reducing the current, and finally output _id to complete the control.

In the case of constant speed and load, when the angle between the current drop gradient and the leftward constant torque direction is less than 90 degrees, reduce V _fwc ; when the current drop gradient and the leftward constant torque direction The angle is greater than 90 degrees, Increase V _fwc , the operating point moves to the right along the constant torque curve to reduce the current current; when the angle between the current descending gradient and the rightward constant torque direction is equal to 90 degrees, the current operating point is the pole of the current on the constant torque curve If the operating point is a small value, no correction is required; the minimum operating current is finally output.

A more detailed description follows.

As shown in Figure 1, it is a single-current field-weakening optimization control diagram based on the gradient descent method. Due to its structural characteristics, the built-in permanent magnet synchronous motor (IPMSM) has many outstanding advantages in performance, such as high power density, high Power factor, compact structure, wide speed range, etc. It is precisely because of these advantages that it is widely used in numerical control systems such as household appliances, transportation, disk drives, machine tools, and robots. Rail transit and electric traction drive systems require the motor to be able to output relatively large torque when the speed is low, which can meet the requirements of starting, acceleration, and low-speed climbing. In addition to some requirements below the base speed, it is also required to The range can be wider, which puts forward requirements for the weak magnetic performance of the motor, and requires a wide range of speed regulation. The embedded permanent magnet synchronous motor is relatively easy to weaken the field due to the structure torque, and the output torque is large, so the research on the embedded permanent magnet synchronous motor is of great significance.

The field weakening control algorithm based on the gradient descent method does not need to look up the table, has high control precision, fast response speed, and good robustness. The specific algorithm is described as follows.

The current and voltage trajectory curves of the built-in permanent magnet synchronous motor during operation are shown in Figure 3. Below the base speed, the motor runs in the constant torque area, and the permanent magnet synchronous motor can obtain the maximum electromagnetic torque by using the linear maximum torque-to-current ratio control. As the speed increases, the motor will run along the constant torque curve between the maximum torque current ratio curve and the maximum torque voltage ratio (MTPV) curve, which is the field weakening area I. In the higher speed range, the motor runs along the maximum torque-to-voltage ratio curve, i.e. field weakening region 2 above. For a given reference torque, as the speed increases, the motor will run along the constant torque curve, if the speed continues to rise, the motor will run along the maximum torque voltage ratio curve, and its output torque will gradually decrease. In the process of field weakening, the most important thing is to determine the magnitude of the set current correction value. First, determine the field weakening area where the motor is located according to the operating curve, and then make corresponding corrections to the current setting value according to the field weakening area where it is located.

Assuming that the stator three-phase winding is a three-phase symmetrical sine wave, ignoring the influence of higher harmonics, iron loss, current loss and temperature on the parameters, in the dq coordinate system of the rotor flux orientation, the mathematical model of the permanent magnet synchronous motor can be expressed as :

Voltage equation:

u _d ＝ R _s i _d -ω _e L _q i _q (1)

Flux linkage equation:

u _q ＝R _s i _q +ω _e ψ _f +ω _e L _d i _d (2)

Electromagnetic torque equation:

It can be seen from formula (3) that for the built-in permanent magnet synchronous motor, L _d < L _q , the electromagnetic torque is composed of the excitation torque and the reluctance torque; for the reluctance motor, ω _f = 0, so only the reluctance Torque; for the surface type permanent magnet synchronous motor, L _d = L _q , the electromagnetic torque is only composed of the excitation torque. It is generally believed that the surface type permanent magnet synchronous motor has limited field weakening capability and is generally not used for field weakening operation. The built-in permanent magnet synchronous motor with a large saliency ratio has a strong field-weakening operation capability.

This method is mainly divided into two parts: determining the field weakening area and correcting the current reference value. The control of the permanent magnet synchronous motor is closely related to the inverter in the system, and the operating performance of the motor is restricted by the inverter. The most obvious one is that the limit value U _lim of the effective value of the phase voltage and the effective value I _lim of the phase current of the motor are limited by the DC side voltage of the inverter and the maximum output current. So there are:

Similarly, the ability of the inverter to output current is also limited by its capacity, and the stator current also has a limit value, namely:

|i _s |≤|i _s | _max (5)

If it is represented by two components of the stator current vector, then:

The voltage limit ellipse and current limit circle are formed by the above formula.

The operating area of the permanent magnet motor is three operating areas (area I, area II and area III). According to the operating conditions of the motor, the three areas are:

1) Area I

Below the base speed, the motor runs in the constant torque area, and the linear maximum torque current ratio control (MTPA) is adopted to make the permanent magnet synchronous motor obtain the maximum electromagnetic torque.

2) Zone II

As the speed increases, the motor will run along the constant torque curve between the maximum torque current ratio curve and the maximum torque voltage ratio (MTPV) curve. This area is called field weakening area II.

3) Zone III

In the higher speed range, the motor runs along the MTPV curve, this area is called field weakening area III.

In the traditional control system, there are two current regulators to adjust the q-axis current respectively. In the low-speed stage, the q-axis voltage does not reach the limit, so two current regulators can be used to independently control the d and q-axis currents. In the high-speed stage, the q-axis voltage is limited below the maximum value, and voltage shortage occurs, resulting in mutual coupling of d-axis and q-axis currents, which deteriorates system performance.

It is assumed that the q-axis voltage is a constant V _fwc and 0<V _fwc <V _max . In the case of a certain speed, the quadrature axis equation is expressed as:

Equation (1) shows that under a given q-axis voltage and a certain speed, the q-axis current and the d-axis current have a linear relationship, that is, the q-axis current can be controlled by controlling the d-axis current. The method actually exploits the inherent cross-coupling relationship of the d and q-axis currents rather than decoupling. Therefore, in the field weakening control stage, only one d-axis current regulator is needed.

Thus, the single current control strategy can be obtained as shown in Figure 1, which includes a speed/field weakening regulator SFWC, and SFWC does not need to use a PI regulator. SFWC input is speed deviation, output is direct axis current given Includes field weakening and torque components. At a fixed q-axis voltage, the d-axis current automatically adjusts to correspond to the q-axis voltage, so only two regulators are needed in the system.

Assuming that the motor load and motor speed are constant, the effect of V _fwc on the operating point is shown in Figure 2: the dotted line is the constant torque curve, the black solid line is the voltage limit circle, and the dotted line is the current limit circle. Under single current control, i _d and i _q are linear relationships shown in formula (1), that is, the relationship between i _d and i _q is a straight line on the plane of i _d and i _q , and the intersection point of the straight line and the horizontal axis is ((V _fwc -ω _e ψ _f )/w _e L _d ,0), when V _fwc increases, the straight line moves to the right.

V _fwc1 < V _fwc2 < V _fwc3 in Figure 2, for V _fwc1 and V _fwc2 , the intersection point of the straight line and the constant torque line is within the voltage limit ellipse, then the motor operating point is the intersection point of the straight line and the constant torque line, respectively for point A and point B. For V _fwc3 , if the output torque is to be maintained, the operating point is point C, but point C is outside the voltage limit ellipse, and the desired torque cannot be achieved under V _fwc3 .

From the above analysis, it can be seen that the stable operating point of the motor is the intersection of the constant torque curve under the voltage constraint and current constraint and the straight line represented by formula (1). If the voltage and current constraints are met, V _fwc increases, and the operating point moves to the right along the constant torque curve. On the contrary, V _fwc decreases, and the operating point moves to the left along the constant torque curve. The basic idea of the single current control based on the gradient descent method is: under the constraints of voltage and current, according to the angle between the current descending gradient and the constant torque direction, judge the moving direction that can reduce the running current, and change V _fwc , so that the operating point moves to the direction of current reduction.

The direction equation of torque rise can be expressed as:

The direction of constant torque is perpendicular to the direction of torque drop, so the direction of constant torque to the left can be expressed as:

Similarly, the direction of the current descending gradient is:

The single current control method based on the gradient descent method is shown in Figure 4. If the speed is ω ₁ , the current operating point is A, and the angle between the current descending gradient and the leftward constant torque direction is less than 90 degrees, it means that the operating point is along the direction of constant rotation Moving the moment curve to the left can reduce the current current, that is, V _fwc should be reduced. Similarly, if the current operating point is C, and the angle between the current drop gradient and the leftward constant torque direction is greater than 90 degrees, V _fwc should be increased. If the current operating point is point B, the angle between the current drop gradient and the rightward constant torque direction is equal to 90 degrees, indicating that the current operating point is the minimum value operating point of the current on the constant torque curve, and no correction is required.

When modifying V _fwc to change the operating point, the operating point should be kept within the voltage limit circle, so V _fwc should be limited according to the maximum output voltage of the inverter. When V _fwc reaches the maximum value, V _fwc should not be corrected. Such as the point D in the figure when the speed is ω ₂ .

In practical applications, the gradient algorithm needs to solve the problem that the optimization result is limited by the initial point, and it is easy to fall into the local minimum. But when the minimum value is unique, the optimization result of the gradient algorithm is not limited by the initial point, and the minimum value is the minimum value.

The extreme point satisfying the constant torque equation can be expressed as:

The vector product of the direction of constant torque to the left and the direction of current drop can be expressed as:

Putting formula (5) into (6) and deriving, the three items in the formula obtained are all positive values, that is, the derivative is monotonous, and the vector product increases during the increase of i _d . The derivative in the closed interval is monotonous, and if the vector product crosses zero, the zero crossing point is unique.

When the vector product at the initial point is less than zero, the operating point is corrected to the right, i _d increases, and there is a unique point where i _d is equal to 0, or the voltage limit is reached, and the correction is stopped. When the vector product is greater than zero at the initial point, the operating point is corrected to the left, i _d decreases, the vector product continues to decrease, and the vector product crosses zero only. In summary, for the single current control based on the gradient descent method proposed in this paper, the current minimum value is unique, and the minimum value is the minimum value.

As can be seen from the above, the present invention aims at the characteristics of the complex structure of the built-in permanent magnet synchronous motor, and on the basis of single current control, proposes a new method of using the current gradient to compare with the constant torque direction to correct the q-axis voltage on-line, so that the motor The operating current automatically converges to the minimum value under the current speed and load, thereby reducing motor loss and improving operating efficiency.

Claims (3)

1. a kind of control method of internal permanent magnet synchronous motor, which is characterized in that include the following steps：

Step 1 builds rotor closed-loop system using weak magnetic control methods, obtains the response of d shaft voltages, finds out corresponding q shaft voltages V_fwc And judge whether stable operating point electric current and voltage meet horicycle constraint, suitable V is selected if not meeting_fwc；

Step 2 determines electric current downward gradient and permanent torque direction by stable operating point, then finds out its angle using vector product Degree；

Step 3, the direction for by angle judging that running current is made to reduce, change V_fwcSo that the direction that operating point reduces to electric current It is mobile, final output i_d, complete control.

2. the control method of internal permanent magnet synchronous motor according to claim 1, which is characterized in that built in step 1 Weak magnetic controls rotor closed-loop system, estimates rotor synchronously rotating reference frame d shaft currents by coordinate transform, is obtained by weak magnetic adjuster Go out to refer to d shaft currents, it includes weak magnetic component and torque component；Under fixed q shaft voltages, d shaft currents are automatically adjusted with right Answer q shaft voltages；Specially：

Assuming that three-phase stator winding is three-phase symmetrical sine wave, ignore higher hamonic wave, iron loss misfortune stream loss and temperature are to parameter It influences, under the dq coordinate systems of rotor flux linkage orientation, permanent magnet synchronous motor mathematical model is expressed as：

Voltage equation：

u_d=R_si_d-ω_eL_qi_q

Flux linkage equations：

u_q=R_si_q+ω_eψ_f+ω_eL_di_d

Electromagnetic torque equation：

For internal permanent magnet synchronous motor, L_d< L_q, electromagnetic torque is made of excitatory torque and reluctance torque；For reluctance type Motor, ω_f=0；For surface permanent magnetic synchronous motor, L_d=L_q。

3. the control method of internal permanent magnet synchronous motor according to claim 1, which is characterized in that turning in step 3 In the case that speed and load are constant, permanent torque angular separation when electric current downward gradient and to the left is less than 90 degree, reduces V_fwc；When Electric current downward gradient is more than 90 degree with permanent torque angular separation to the left, increases V_fwc, operating point moves right along permanent torque curve Reduce current flow；When electric current downward gradient and permanent torque angular separation to the right are equal to 90 degree, current point of operation is permanent torque The minimum operating point of electric current on curve is then not necessarily to correct；The running current of final output minimum.