A calculation method for the stator voltage vector limit of a permanent magnet synchronous motor

Abstract

The present invention discloses a method for calculating the stator voltage vector limit of a permanent magnet synchronous motor, comprising the steps of: S1, determining the action time of the zero vector; S2, determining the voltage vector amplitude; S3, determining the current limit circle and the voltage limit ellipse; and determining the maximum value of the voltage vector according to the voltage vector amplitude, the voltage limit ellipse and the current limit circle. The method for calculating the stator voltage vector limit of a permanent magnet synchronous motor of the present invention achieves the ultimate purpose of weak magnetic speed expansion by increasing the direct axis demagnetization current component and reducing the quadrature axis current component while ensuring that the current vectors are all within the limit range. Compared with the classic SPWM algorithm, the bus voltage utilization rate of the SVPWM algorithm is increased by 15%.

Description

Technical Field

[0001] The invention belongs to the field of permanent magnet synchronous motor control, and in particular relates to a method for calculating a stator voltage vector limit value of a permanent magnet synchronous motor. Background Art

[0002] For high-performance AC drive systems, how to make full use of DC voltage to obtain the maximum output electromagnetic torque is a very important factor. The existing permanent magnet synchronous motor stator voltage vector limit does not take into account that the amplitude of the stator voltage vector is subject to the inverter voltage limit. When the inverter voltage is saturated, the speed can only be further increased by adjusting the direct axis d-axis and quadrature axis q-axis currents. The bus voltage utilization rate of the classic SPWM algorithm has room for further improvement. Summary of the invention

[0003] The purpose of the present invention is to provide a method for calculating the stator voltage vector limit of a permanent magnet synchronous motor, so as to achieve the ultimate goal of magnetic field weakening speed expansion by increasing the direct-axis demagnetization current component and reducing the quadrature-axis current component while ensuring that the current vector is within the limit range.

[0004] The technical solution of the present invention is:

[0005] A method for calculating a stator voltage vector limit of a permanent magnet synchronous motor comprises the steps of:

[0006] S1. Determine the action time T of the zero vector null :

[0007]

[0008] Among them, U s is the voltage vector to be synthesized, T is a PWM cycle; V a 、V b are two adjacent basic voltage vectors, θ is U s With V a The angle of

[0009] S2. Determine the voltage vector amplitude:

[0010]

[0011] Among them U dc is the voltage amplitude on the DC bus side;

[0012] S3. Determine the current limit circle and voltage limit ellipse:

[0013] When the permanent magnet synchronous motor works stably, the current vector amplitude is expressed as:

[0014]

[0015] Among them, I s is the phase current; I d is the d-axis current; I q is the q-axis current; I lim is the amplitude of the phase current;

[0016] When the permanent magnet synchronous motor operates stably, the amplitude of the current vector is expressed as:

[0017]

[0018] Among them, L d is the d-axis inductance; L q is the q-axis inductance; Ψ f is the magnetic flux; ω e is the rotor speed; U lim is the amplitude of the phase voltage;

[0019] Determine the maximum value of the voltage vector according to the voltage vector amplitude, the voltage limit ellipse and the current limit circle.

[0020] Preferably, in step S1, the permanent magnet synchronous motor adopts SVPWM space vector pulse width modulation, and its bus voltage utilization rate = effective value of phase voltage / bus voltage.

[0021] Preferably, in SVPWM space vector pulse width modulation, it is obtained from the sine theorem that:

[0022]

[0023] T a and T b are the action times of V a and V b respectively, and the solution is:

[0024]

[0025]

[0026] When T a + T b < T, a zero vector needs to be applied to keep the control period constant;

[0027] The action time of the zero vector is obtained as:

[0028]

[0029] Preferably, in step S2, in order to simplify the control strategy, the voltage vector amplitude is limited to:

[0030]

[0031] Preferably, in step S3, the voltage equation of the permanent magnet synchronous motor is expressed as:

[0032]

[0033]

[0034] Among them, U d is the d-axis voltage; U q is the q-axis voltage; R is the stator resistance; p is the number of pole pairs;

[0035] When the permanent magnet synchronous motor runs stably and the stator resistance and inductance voltage drop are ignored, the voltage equation is simplified to:

[0036] U d =-ω e L q I q

[0037] U q =ω e (L d I d +Ψ f )

[0038] We can get:

[0039]

[0040] L of interior permanent magnet synchronous motor d ≠L q , so it is an elliptic equation; when the stator voltage reaches U lim When the speed is ω0<ω1<ω2, the voltage limit ellipse decreases as the speed increases, and finally points to (-Ψ f / L d , 0).

[0041] The advantages of the present invention are:

[0042] The calculation method of the permanent magnet synchronous motor stator voltage vector limit of the present invention achieves the ultimate goal of weak magnetic speed expansion by increasing the direct axis demagnetization current component and reducing the quadrature axis current component while ensuring that the current vector is within the limit range. Compared with the classic SPWM algorithm, the bus voltage utilization rate of the SVPWM algorithm is increased by 15%. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0044] Figure 1 It is a schematic diagram of voltage space vector synthesis;

[0045] Figure 2 are the voltage space vector trajectories of SVPWM and sinusoidal PWM;

[0046] Figure 3 is the limit value of the maximum voltage vector. Specific implementation mode

[0047] The calculation method for the limit value of the stator voltage vector of the permanent magnet synchronous motor proposed by the present invention includes the following steps S1 - S3.

[0048] S1. Determine the action time of the zero vector:

[0049] Deduce the bus voltage utilization rate of SVPWM technology.

[0050] In SVPWM control, according to the sine theorem:

[0051]

[0052] In the formula, U s is the voltage vector to be synthesized, T is a PWM period; V a , V b are two adjacent basic voltage vectors, T a , T b are the action times of V a , V b ; θ is the included angle between U s and V a .

[0053] It can be solved from formula (1):

[0054]

[0055]

[0056] When T a +T b <T, it is necessary to apply the zero vector to keep the control period constant. The action time of the zero vector is:

[0057]

[0058] S2. Determine the amplitude of the voltage vector:

[0059] In SVPWM control, the amplitude of the basic voltage vector in the coordinate system is When the amplitude of the reference voltage space vector U s increases, T a , T b also gradually increase, and at the same time, the action time T nullHowever, in order to make the resultant vector in the linear region, T null is a non-negative number, so from formula (4) we can get:

[0060]

[0061] It can be seen from equation (5) that the trajectory of the equivalent voltage space vector is limited to the hexagon formed by the basic voltage vector. In order to simplify the control strategy, this limit is usually reduced to the inscribed circle of the hexagon, that is:

[0062]

[0063] Figure 2 A comparison of the voltage space vector trajectory of SVPWM and sinusoidal PWM is given.

[0064] S3. Determination of current limit circle and voltage limit ellipse:

[0065] Figure 3 Due to the limitation of the maximum output current of the inverter and the rated current of the motor, when the permanent magnet synchronous motor works stably, the current vector amplitude can be expressed as:

[0066]

[0067] I s : Phase current; I d : d-axis current; I q : q-axis current; I lim : The amplitude of the phase current.

[0068] like Figure 1 As shown, the current vector limiting trajectory is drawn in the dq coordinate system with the origin as the center, I s The circle with a radius of is called the current limit circle. When the motor is running stably, the stator current vector cannot exceed the current limit circle.

[0069] For permanent magnet synchronous motors using SVPWM (Space Vector Pulse Width Modulation), U DC is the DC bus side voltage.

[0070] The voltage equation of the permanent magnet synchronous motor can be expressed as:

[0071]

[0072]

[0073] U d : d-axis voltage; U q: q-axis voltage; R: stator resistance; Ψ f : magnetic flux; p: number of pole pairs; L d : d-axis inductance; L q : q-axis inductance; ω e : Rotor speed.

[0074] When the permanent magnet synchronous motor runs stably and the stator resistance and inductance voltage drop are ignored, the voltage equation is simplified to:

[0075] U d =-ω e L q I q (10)

[0076] U q =ω e (L d I d +Ψ f ) (11)

[0077] Substituting equations (10) and (11) into equation (7), we can obtain:

[0078]

[0079] For the interior permanent magnet synchronous motor, L d ≠L q , so it is an elliptic equation. From the voltage limit elliptic equation, we know that when the stator voltage reaches U lim When the stator current is limited by the speed, that is, at a certain speed, the stator current can only be within the corresponding elliptical trajectory. The schematic diagram of the stator current vector limitation range is shown in Figure 1 As shown in the figure, the speed ω0<ω1<ω2, as the speed increases, the voltage limit ellipse decreases and finally points to (-Ψ f / L d , 0).

[0080] The maximum value of the voltage vector is determined based on the voltage vector amplitude, the voltage limit ellipse and the current limit circle.

[0081] Since the constant amplitude principle is adopted (the amplitude of the voltage space vector is equal to the amplitude of the phase voltage), the bus voltage utilization rate of the SVPWM algorithm is:

[0082]

[0083] The bus voltage utilization of the classic SPWM algorithm is:

[0084]

[0085] Compared with the classic SPWM algorithm, the bus voltage utilization of the SVPWM algorithm is increased by 15%.

[0086] In specific implementation, the present invention takes into account that the amplitude of the stator voltage vector is subject to the constraints of the inverter voltage limit, and therefore limits the main output of the current loop, namely the d-axis voltage command MCT_usdPI_sw and the q-axis voltage command MCT_usqPI_sw, according to whether the stator voltage vector exceeds the voltage limit ellipse.

[0087] The specific implementation process is as follows:

[0088] 1. In the program, use the formula To calculate the maximum magnitude of the stator voltage vector, the specific implementation process is: after the bus voltage ISC_UdcLnk is standardized (i.e. divided by 1024), it is sent to the filter module PT1Nrm for filtering to obtain UdcLnkNrmFlt, which is divided by Get UsMaxNrmFlt, multiply it by 1024 to get UsMax, and take the reciprocal to get 1DivUsMax.

[0089] 2. After dividing the d-axis voltage target value UsdPI and the q-axis voltage target value UsqPI by UsMax for standardization, take the maximum value from the standard value and the limit value xLim_C, then take the inverse of the square root value of the maximum value, and then divide it by 8 to obtain UsMax / Us, and take the minimum value from this value and the limit value cMax_P to obtain UsMaxDivUsLim.

[0090] 3. Determine whether (UsMaxDivUsLim*UsdqScalMax_P–1)<0 is true:

[0091] If it is not true, it means that the amplitude of the stator voltage vector does not exceed the voltage limit ellipse, then bUsLimActv is set to False, and then UsdPIScal(UsdPI / UMax) and UsqPIScal(UsqPI / UMax) obtained from the current loop are directly assigned to MCT_UsdScal and MCT_UsqScal; if it is true, it means that the amplitude of the stator voltage vector has exceeded the voltage limit ellipse, then bUsLimActv is set to True, and the d and q axis voltage commands are restricted: first determine the value of bUseUsdqSet_Sw, if it is 1, assign the pre-set parameters UsdScalSet_P and UsqScalSet_P to MCT_UsdScal and MCT_UsqScal, otherwise assign UsdPIScal*cScal and UsqPIScal*cScal to MCT_UsdScal and MCT_UsqScal.

[0092] 4. Take UsResScal, i.e. (UsMaxDivUsLim*UsdqScalMax_P–1), bUsLimActv, MCT_UsdScal and MCT_UsqScal as the output of this module.

[0093] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any modifications made according to the spirit of the main technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for calculating a stator voltage vector limit of a permanent magnet synchronous motor, characterized in that: Includes steps: S1. Determine the action time T of the zero vector null : Among them, U s is the voltage vector to be synthesized, T is a PWM cycle; V a 、V b are two adjacent basic voltage vectors, θ is U s With V a The angle of S2. Determine the voltage vector amplitude: Among them U dc is the voltage amplitude on the DC bus side; S3. Determine the current limit circle and voltage limit ellipse: When the permanent magnet synchronous motor works stably, the current vector amplitude is expressed as: Among them, I s is the phase current; I d is the d-axis current; I q is the q-axis current; I lim is the amplitude of the phase current; When the permanent magnet synchronous motor is running stably, the current vector amplitude is expressed as: Among them, L d is the d-axis inductance; L q is the q-axis inductance; f is the magnetic flux; ω e is the rotor speed; U lim is the amplitude of the phase voltage; The maximum value of the voltage vector is determined based on the voltage vector amplitude, the voltage limit ellipse and the current limit circle.

2. The method for calculating the stator voltage vector limit of a permanent magnet synchronous motor according to claim 1, characterized in that: In step S1, the permanent magnet synchronous motor adopts SVPWM space vector pulse width modulation, and its bus voltage utilization rate = phase voltage effective value / bus voltage.

3. The method for calculating the stator voltage vector limit of a permanent magnet synchronous motor according to claim 2, characterized in that: In SVPWM space vector pulse width modulation, the sine theorem shows that: T a , T b V a 、V b The action time is: When T a + T b < When T, a zero vector needs to be applied to keep the control period constant; The action time of the zero vector is obtained as:

4. The method for calculating the stator voltage vector limit of a permanent magnet synchronous motor according to claim 3, characterized in that: In step S2, in order to simplify the control strategy, the voltage vector amplitude is limited to:

5. The method for calculating the stator voltage vector limit of a permanent magnet synchronous motor according to claim 4, characterized in that: In step S3, The voltage equation of the permanent magnet synchronous motor is expressed as: Among them, U d is the d-axis voltage; U q is the q-axis voltage; R is the stator resistance; p is the number of pole pairs; When the permanent magnet synchronous motor runs stably and the stator resistance and inductance voltage drop are ignored, the voltage equation is simplified to: U d =-ω e L q I q U q =ω e (L d I d +Ψ f ) We can get: L of interior permanent magnet synchronous motor d ≠L q , so it is an elliptic equation; when the stator voltage reaches U lim When the speed is increased, the stator current trajectory is limited by the speed, that is, at a certain speed, the stator current can only be within the corresponding elliptical trajectory; as the speed continues to increase, the voltage limit ellipse continues to decrease, and finally points to (-Ψ f / L d , 0).

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