CN105656379B - A kind of switched reluctance machines position predictor method based on magnetoresistive characteristic coordinate transform - Google Patents

Abstract

The invention discloses a method for estimating the position of a switched reluctance motor based on reluctance characteristic coordinate transformation. Based on the reluctance data at four specific locations, the method estimates the position of the switched reluctance motor according to the phase voltage and phase current values. Firstly, the rotor position is divided into two areas, the square of the rotor position angle in area I and the reluctance value have a linear function relationship, and the 1/2 power of the rotor position angle in area II and the 1/4 power of the reluctance value are quadratic Functional relationship. The fitting coefficients a, b, c, d, e are calculated from the magnetoresistance data at four special positions. Detect the phase voltage and current value, calculate the current magnetic resistance value, and judge the area where the current rotor position is located. If the rotor position is in area I, use a, b to calculate the current position, if the rotor position is in area II, use c, d, e to calculate the current position. This method estimates the position of the switched reluctance motor in an analytical way, and has the advantages of low cost, easy implementation, and good applicability.

Description

A Position Prediction Method for Switched Reluctance Motor Based on Coordinate Transformation of Reluctance Characteristic

technical field

The invention relates to a method for estimating the position of a switched reluctance motor based on reluctance characteristic coordinate transformation, and belongs to the field of motor position sensorless control.

Background technique

In the switched reluctance motor drive system, the rotor position information is crucial to the realization of the control method and the normal operation of the system, and this information is usually obtained by mechanical position sensors such as photoelectric encoders and resolvers. However, the existence of the mechanical position sensor increases the complexity of the system structure, increases the manufacturing cost, and the performance of the sensor is easily affected by the environment. Therefore, it is very necessary to study a low-cost, high-precision, high-reliability position sensorless control method suitable for switched reluctance motors.

In order to realize position sensorless control, researchers have proposed a large number of position estimation methods. These methods are mainly divided into two categories: non-conducting phase position estimation method and conducting phase position estimation method.

The first type of method mainly injects voltage pulses into the non-conducting phase of the switched reluctance motor. Under constant frequency and low duty ratio voltage excitation, the winding will generate a low-amplitude detection current. Since the detection current is small, at this time The back EMF of the motor can be ignored. According to the voltage balance equation, the magnitude of the detected current is inversely proportional to the phase inductance of the current position, so this method can be used for position estimation. Its characteristic is that it can detect the initial position of the rotor, and can detect continuous position information at medium and low speeds, but this method is not suitable for high-speed working conditions.

The second type of method is mainly based on the flux linkage characteristics of the switched reluctance motor. The measured flux linkage characteristic data is stored or expressed in the form of a lookup table, neural network, etc., and then based on the online measured conduction phase current and flux linkage data , to obtain rotor position information. This type of method has high prediction accuracy and wide application range of rotational speed, but requires a large amount of sample data of flux linkage characteristics, and these data are usually obtained through detailed finite element analysis or experimental measurement, which increases the complexity of the method Sex and cost, and at the same time, it often needs to occupy a large physical memory during implementation.

Contents of the invention

The invention divides the relationship curve between the phase reluctance and the rotor position of the switched reluctance motor into two regions, and adopts different reluctance characteristic coordinate transformation methods for different regions, and takes the transformed rotor position as an independent variable, and the transformed magnetic As a dependent variable, resistance is expressed as a linear function and a quadratic function in different regions. On this basis, the rotor position can be solved according to the reluctance. The technical scheme is as follows:

Step 1: In the relationship curve between the phase reluctance and the rotor position of the switched reluctance motor, the interval [θ ₀ ,θ ₁ ] is defined as area I, and [θ ₁ ,θ _a ] is defined as area II. In area I and area II, four special positions θ ₀ , θ ₁ , θ _hr , θ _a are defined. Among them, θ ₀ is the non-aligned position, θ _a is the aligned position, θ ₁ and θ _hr can be obtained by equations (1) and (2).

Among them, β _s and β _r are stator pole arc and rotor pole arc respectively.

Step 2: Detect the flux linkage characteristic data ψ ₀ , ψ ₁ , ψ _hr , ψ _a at the four positions of θ ₀ , θ ₁ , θ _hr , θ _a , and obtain the magnetoresistance characteristics of the four positions through formula (3), where , ψ _x represents the phase flux linkage at four positions of θ ₀ , θ ₁ , θ _hr , θ _a , N is the number of turns of the phase winding, and i is the phase current.

Substitute the calculated R ₀ , R ₁ , R _hr , and R _a into formula (4) to obtain five coefficients a, b, c, d, and e.

Step 3: Detect the conduction phase voltage and current value, and calculate the current phase magnetic resistance value by using formula (5).

Among them, ψ(0) is the initial flux linkage. Since the remanence of silicon steel material is small, ψ(0) is usually taken as 0; u, i and r are the phase voltage, phase current and phase resistance of the switched reluctance motor, respectively.

Step 4: Use linear interpolation to obtain the magnetoresistance value R ₁ (i) at θ ₁ under the current current.

Step 5: If R≥R ₁ (i), it indicates that the rotor position is in area I, and a(i) and b(i) are obtained through linear interpolation calculation. At this time, the relationship between the reluctance and the square of the rotor position angle is a linear function, as shown in formula (6), and the rotor position angle can be obtained through formula (7).

R＝a(i)θ ² +b(i) (6)

Step 6: If R<R ₁ (i), it indicates that the rotor position is in area II, and c(i), d(i) and e(i) are obtained through linear interpolation calculation. At this time, the 1/4 power of the reluctance and the 1/2 power of the rotor position angle have a quadratic function relationship, as shown in formula (8), and the rotor position angle can be obtained by formula (9).

Step 7: If it is necessary to further reduce the systematic error introduced when estimating the rotor position under low current, multi-phase reluctance characteristics can be used instead of single-phase reluctance characteristics for estimation. The principle of phase selection is: according to the magnitude of the current of each phase, select the phase with the largest phase current for position estimation.

Beneficial effects of the present invention: ①The method is simple and easy to realize. After the coordinate transformation of the reluctance characteristics, the rotor position angle can be quickly analyzed and solved; only the flux linkage characteristic data at four rotor positions is required, and only a small amount of physical memory is occupied; ② High precision and strong robustness. The magnitude of magnetoresistance is large and the resolution is high. In addition, the system error is reduced through the multi-phase estimation method; ③ the applicability is good. Angular position control, current chopping control and voltage PWM control all have good accuracy and are also suitable for different switched reluctance motor topologies.

Description of drawings

Figure 1 is a graph showing the relationship between the phase reluctance of a switched reluctance motor and the rotor position angle at a certain current.

Fig. 2 is a curve diagram of the relationship between the square of the rotor position angle and the phase reluctance of the region I switched reluctance motor under a certain current.

Fig. 3 is a graph showing the relationship between the 1/2 power of the rotor position angle of the region II switched reluctance motor and the 1/4 power of the phase reluctance under a certain current.

detailed description

The technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings and specific examples. The motor used in the example is a 1kW three-phase 12/8 pole switched reluctance motor.

Step 1: Figure 1 is a graph showing the relationship between the phase reluctance of the switched reluctance motor and the rotor position angle under a certain current. Define [θ ₀ ,θ ₁ ] as region I, and [θ ₁ ,θ _a ] as region II. For the example given switched reluctance motor, β _s , β _r and θ _a are 15°, 17° and 22.5°, respectively. From formulas (1) and (2), it can be concluded that θ ₁ and θ _hr are 6.5° and 14°, respectively.

Step 2: Using the rotor position fixation method, the flux linkage characteristic data of the switched reluctance motor at 0°, 6.5°, 14° and 22.5° can be obtained, and then the reluctance at these four positions can be obtained by formula (3) Values R ₀ °, R _6.5 °, R ₁₅ °, R _22.5 °. Substitute the calculated R ₀ °, R _6.5 °, R ₁₅ °, R _22.5 ° into formula (4) to obtain 5 coefficients a, b, c, d, e.

Step 3: Detect the conduction phase voltage and current value, and calculate the phase magnetic resistance value R(i) at this time by using formula (5).

Step 4: Using linear interpolation, calculate R _6.5 °(i).

Step 5: If R(i)≥R _6.5 °(i), it means that the rotor position is in area I. At this time, the relationship between the square of the rotor position angle of the switched reluctance motor and the phase reluctance is shown in Figure 2. Calculate a(i) and b(i) by linear interpolation, and then use formula (7) to obtain the rotor position angle.

Step 6: If R(i)<R _6.5 °(i), it indicates that the rotor position is in area II. At this time, the relationship between the 1/2 power of the rotor position angle of the switched reluctance motor and the 1/4 power of the phase reluctance The curve is shown in Figure 3. Calculate c(i), d(i) and e(i) by linear interpolation, and then use formula (9) to obtain the rotor position angle.

Step 7: If it is necessary to further reduce the rotor position estimation error under low current, the three-phase reluctance characteristics are used instead of the single-phase reluctance characteristics for estimation. The estimated phase selection strategy is shown in Table 1.

Table 1. Estimation phase selection strategy

Claims (2)

1. A switched reluctance motor position estimation method based on reluctance characteristic coordinate transformation, is characterized in that: the relationship curve of switched reluctance motor phase reluctance and rotor position is divided into two regions, and adopts respectively for different regions The linear function and the quadratic function represent the relationship between the reluctance characteristics after the coordinate transformation and the rotor position angle after the coordinate transformation, and then are used to solve the rotor position. The implementation steps of the position estimation method are as follows: Step 1: In the relationship curve between the phase reluctance and the rotor position of the switched reluctance motor, define the interval [θ ₀ ,θ ₁ ] as area Ⅰ, [θ ₁ ,θ _a ] as area Ⅱ, and in area Ⅰ and area In II, define four special positions θ ₀ , θ ₁ , θ _hr , θ _a , where θ ₀ is the unaligned position, θ _a is the aligned position, θ ₁ and θ _hr are defined by the formula θ ₁ = θ _a -(β _s +β _r )/2 and θ _hr =θ _a -β _r /2 are calculated, where β _s and β _r are the stator pole arc and rotor pole arc of the motor respectively; Step 2: Measure the flux linkage characteristic data at the above four special positions, and calculate the corresponding magnetic resistance characteristic data R ₀ , R ₁ , R _hr , R _a ; Substitute the magnetic resistance data at the four positions into the coefficients a, b, The analytical expression of c, d, e, calculate the five coefficients of a, b, c, d, e, the analytical expression is Step 3: Detect the conduction phase voltage and current value, and substitute them into the analytical expression of magnetoresistance Obtain the current phase reluctance value R, where ψ(0) is the initial flux linkage, u, i and r are the phase voltage, phase current and phase resistance of the switched reluctance motor, respectively; Step 4: According to the detected phase current i, use linear interpolation to calculate the magnetic resistance value R ₁ (i) at θ ₁ under the current phase current; Step 5: If R≥R ₁ (i), it indicates that the rotor position is located in area Ⅰ. At this time, the square of the rotor position angle and the reluctance have a linear function relationship. Use the linear function expression of the reluctance characteristics after the coordinate transformation to predict the rotor position. Estimation, the linear function expression is R=a(i)θ ² +b(i), at this time the rotor position angle is passed by the formula solve; Step 6: If R<R ₁ (i), it indicates that the rotor position is located in area II. At this time, the 1/2 power of the rotor position angle and the 1/4 power of the reluctance have a quadratic function relationship. After the coordinate transformation, the magnetic The quadratic function expression of the resistance characteristic is used to estimate the rotor position, and the quadratic function expression is At this time, the rotor position angle is passed by the formula solve; Step 7: If it is necessary to further reduce the systematic error introduced when estimating the rotor position under low current, use multi-phase reluctance characteristics instead of single-phase reluctance characteristics for estimation. The principle of phase selection is: according to the magnitude of the current of each phase, select The position of the phase with the largest phase current is estimated. 2. A method for estimating position of a switched reluctance motor based on reluctance characteristic coordinate transformation according to claim 1, characterized in that: the magnetic field at θ ₀ , θ ₁ , θ _hr and θ _a described in step 2 Resistance characteristics R ₀ , R ₁ , R _hr , R _a are obtained by the formula Calculated, where, ψ is the phase flux linkage, N is the number of turns of the phase winding, and i is the phase current.