CN116683810A - Control method of variable-frequency variable-voltage permanent magnet synchronous motor - Google Patents

Abstract

The invention relates to the technical field of motor control, and discloses a permanent magnet synchronous motor control method with variable frequency and variable voltage, comprising the following steps: the first step: establishing a hidden pole permanent magnet synchronous motor model and an IGBT loss model based on an output cycle, And establish the relationship between the two; the second step: take the inverter output current quality as the constraint condition, and the inverter switching frequency and the DC bus voltage as the constraint variables to establish the optimization target; the third step: apply the optimization method to obtain the The IGBT loss of the output cycle is the lowest switching frequency and DC bus voltage. The variable frequency and voltage permanent magnet synchronous motor control method optimizes the DC bus voltage and switching frequency of the motor, which can minimize the IGBT loss, thereby significantly reducing the IGBT junction. temperature, increasing its service life.

Description

A control method for permanent magnet synchronous motor with variable frequency and variable voltage

technical field

The invention relates to the technical field of motor control, in particular to a control method of a permanent magnet synchronous motor with variable frequency and variable voltage.

Background technique

At present, the three-phase voltage source inverter is widely used in the fields of variable speed drive, active power filter and uninterruptible power supply due to the characteristics of easy operation, easy control and easy realization, and has become one of the most commonly used power electronic converters. In view of the voltage vector pulse width modulation (SVPWM) modulation ratio is high and the output waveform is good, the three-phase voltage source inverter usually adopts the SVPWM modulation method. The general SVPWM switching frequency and DC bus voltage are fixed, but simply setting these two parameters to a fixed value reduces the voltage utilization rate, increases the loss of the three-phase voltage source inverter, and makes the inverter work at a higher under the junction temperature environment. Relevant studies have shown that nearly 60% of inverter failures are caused by high junction temperature: for every 10°C increase in inverter temperature, the failure rate doubles; higher junction temperature will also accelerate the aging of IGBTs, reducing Inverter reliability.

In the current technical solution, there is only a method of separately optimizing the switching frequency of the inverter in the motor control system or the DC bus voltage to reduce the junction temperature of the inverter and improve reliability. For example, taking the effective value of the output current ripple of the inverter as the constraint condition and the switching loss as the objective function, a variable switching frequency is obtained to reduce the switching loss. The switching frequency is only related to the switching loss, and only the switching loss is optimized without taking into account The total loss of the IGBT cannot be optimized to a minimum. Another example is to use the DC bus voltage adaptive controller to obtain the optimal DC bus voltage, which only optimizes the quality of the output current, without considering the total loss of the IGBT, which may cause the total loss to increase. In summary, we propose a variable frequency variable voltage control method of permanent magnet synchronous motor.

Contents of the invention

(1) Solved technical problems

Aiming at the deficiencies of the prior art, the present invention provides a permanent magnet synchronous motor control method with variable frequency and variable voltage, which solves the above problems.

(2) Technical solution

In order to achieve the above-mentioned purpose, the present invention provides the following technical solution: a permanent magnet synchronous motor control method with variable frequency and variable voltage, comprising the following steps:

The first step: establish the hidden pole permanent magnet synchronous motor model and the IGBT loss model based on the output cycle, and establish the relationship between the two;

The second step: take the inverter output current quality as the constraint condition, and establish the optimization objective with the inverter switching frequency and DC bus voltage as the constraint variables;

Step 3: Apply the optimization method to obtain the switching frequency and DC bus voltage with the lowest IGBT losses based on the output cycle.

Preferably, the specific content of the first step is:

S1: Establish the voltage equation of the motor on the d-q axis

and

v _qs and v _ds are stator voltages, i _qs and _ids are stator currents, R _q and R _d are stator windings, ω _er is rotor electrical angular velocity, p is a differential operator, λ _qs and λ _ds are stator flux linkages , λ _f is the flux linkage of the rotor magnet;

When the motor is stable, pi _qs and pi _ds can be set to 0, and the stator phase voltage amplitude can be expressed as:

The dq axis current satisfies the Among them, I _max is the magnitude of the stator phase current, i _qs = _max in the case of maximum acceleration, let />

Add _Vcp to the value of stator phase voltage amplitude where, /> is the stator phase current amplitude, and the electromagnetic torque of the motor is />

P _n is the number of pole pairs;

therefore

S2: IGBT loss P _IGBT is divided into conduction loss and switching losses /> The duty cycle of the IGBT in the inverter based on the SVPWM modulation method is:

in, is the power factor angle, the modulation factor /> In the formula, V _dc is the DC side voltage of the inverter;

Conduction loss for a single output cycle and switching losses /> for:

f _sw is the switching frequency, V _ce (t) and I _ce (t) are the on-state voltage drop and on-state current, respectively, E _(+off)nom , V _nom and I _nom are the on-off and off-off conditions of the IGBT under specific test conditions, respectively. The sum of off loss, voltage and current, V _ce (t)=I _ce (t)r _co +V _ce0 , where r _co is the equivalent on-resistance of IGBT, and V _ce0 is the initial on-voltage drop;

The on-state current is:

Among them, θ=ω _er t, The IGBT losses for a single output cycle are:

in, and /> is about the reference angle θ and the power factor angle /> Based on the switching frequency function and the DC bus voltage function, the relationship between the stator phase current of the hidden pole permanent magnet synchronous motor and the IGBT loss is established.

Preferably, the specific content of the second step is:

S1: Optimizing the switching frequency and DC bus voltage of the IGBT loss in a single output cycle can obtain the optimized P _IGBT value in a single output cycle;

S2: Limit the harmonic distortion of the phase current of the motor within a certain range. The harmonic distortion rate of the phase current is marked as H, where H = Δ _ims /I ₁ , the effective value of Δ _ims current ripple, and I ₁ is the output fundamental wave current effective value;

S3: Calculate the current ripple based on Thevenin's equivalent theorem, and calculate the effective value of the current ripple for the entire output cycle as follows

S4: Convert P _IGBT integral form to series form:

in, i=0,...,N, N indicates that [0, 2π] is divided into N small intervals.

S5: The minimum DC bus voltage for the motor to operate normally is meet /> For the switching frequency, set a switching frequency threshold f ₀ to obtain the following optimization objectives:

Among them, Y is determined by the motor rated DC bus voltage and fixed switching frequency The obtained effective value of the output cycle current ripple;

V _s and /> is the stator phase current, phase voltage amplitude and power factor angle under the same conditions;

and /> are the DC bus voltage and switching frequency corresponding to different θ _i .

Preferably, the specific content of the third step is:

S1: Build a hidden pole permanent magnet synchronous motor model, and get the motor's temperature from the Scope module when it runs stably at the rated DC bus voltage and a fixed switching frequency V _s , /> and m, again via /> get Y;

S2: Obtain the IGBT under specific test conditions in the IGBT device manual Obtain V _nom , _Inom , r _co and V _ce0 ;

S3: Convert the integral form of the objective function into a summation form, and then substitute the objective function and constraints into the Matlab optimization toolbox to obtain

S4: Change the voltage of different θ _i The values are summed and averaged to obtain the voltage V _dc-opt .

(3) Beneficial effects

Compared with the prior art, the present invention provides a permanent magnet synchronous motor control method with variable frequency and variable voltage, which has the following

Beneficial effect:

1. The permanent magnet synchronous motor control method with variable frequency and variable voltage optimizes the DC bus voltage and switching frequency of the motor, which can minimize IGBT loss, thereby significantly reducing the junction temperature of IGBT and improving its service life.

2. The frequency-variable-voltage permanent magnet synchronous motor control method improves the utilization rate of the DC bus voltage and increases the drive capacity of the inverter on the basis of ensuring the quality of the output current.

Description of drawings

Fig. 1 is a schematic flow chart of the present invention;

Fig. 2 is a schematic diagram of the technical implementation process of the present invention;

Fig. 3 is a schematic diagram of the current ripple slope under different linear periods;

Fig. 4 is the Thevenin equivalent circuit schematic diagram of linear period 1;

Fig. 5 is a schematic diagram of the current ripple of one switching cycle of SVPWM.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Please refer to Figure 1-5, a permanent magnet synchronous motor control method with variable frequency and variable voltage, including the following steps:

1. Establish the hidden pole permanent magnet synchronous motor model and the IGBT loss model based on the output cycle, and establish the relationship between the two.

1) Establish the voltage equation of the motor on the d-q axis

and

Among them, v _qs and v _ds are the stator voltages, i _qs and _ids are the stator currents, R _q and R _d are the stator windings, ω _er is the rotor electrical angular velocity, p is the differential operator, λ _qs and λ _ds are the stator Flux linkage, _λf is the flux linkage of the rotor magnet.

When the motor is stable, pi _qs and pi _ds can be set to 0, and the stator resistance voltage drop is small and negligible, so the stator phase voltage amplitude can be expressed as

In the formula, the dq axis current must satisfy where I _max is the magnitude of the stator phase current. In the case of maximum acceleration i _qs = _max , let />

Taking into account the stator resistance voltage drop compensation voltage Add _Vcp to the value of stator phase voltage amplitude where, /> is the stator phase current amplitude. The electromagnetic torque of the motor is

Among them, P _n is the pole logarithm. Since the technology of the present invention is based on the hidden pole permanent magnet synchronous motor, so L _q = _d , so

2) Establish the IGBT loss model of the inverter, and the IGBT loss P _IGBT is divided into conduction loss and switching losses The conduction loss is affected by the load current and duty cycle, and the switching loss is affected by the load current, switching frequency and DC link voltage. The modulation mode that the technology of the present invention uses is SVPWM, because the SVPWM modulation method is similar to the third harmonic injection method, so the duty cycle of the IGBT in the inverter is

in, is the power factor angle, the modulation factor /> In the formula, V _dc is the DC side voltage of the inverter. The technology of the present invention takes the A-phase upper bridge arm IGBT of a three-phase voltage source inverter as an example, and the average switching loss and conduction loss of a single output cycle are

Among them, f _sw is the switching frequency, V _ce (t) and I _ce (t) are the on-state voltage drop and on-state current, respectively, V _nom and I _nom are the sum of turn-on and turn-off loss, voltage and current of IGBT under specific test conditions respectively, V _ce (t)=I _ce (t)r _co +V _ce0 , where r _co is the equivalent of IGBT On-resistance, V _ce0 is the initial conduction voltage drop, both of which are related to the IGBT junction temperature. The loss based on the output cycle can be considered as the equivalent on-resistance and the initial conduction voltage drop are test values under specific conditions. r _co , V _ce0 , V _nom and _Inom can all be obtained from the device handbook of the IGBT. It can be known from the on-state current

Among them, θ=ω _er t, Therefore, the IGBT loss of a single output cycle can be obtained

in, and /> is about the reference angle θ and the power factor angle /> The switching frequency function and the DC bus voltage function. Therefore, the relationship between the stator phase current and the IGBT loss of the hidden pole permanent magnet synchronous motor is established.

2. The quality of the inverter output current is used as the constraint condition, and the optimization objective is established with the inverter switching frequency and the DC bus voltage as the constraint variables.

1) Optimizing the switching frequency and DC bus voltage of the IGBT loss in a single output cycle can obtain the optimized P _IGBT value in a single output cycle, but if there are no constraints, the optimized P _IGBT value must be zero, so a certain amount must be added Restrictions.

2) For the inverter, the harmonic quality of the phase current on the AC side is an important performance index. In order to keep the motor running well, it is necessary to limit the harmonic distortion of the motor phase current within a certain range. The phase current harmonic distortion rate H can be expressed as H=Δ _ims /I ₁ , where Δ _ims is the effective value of the current ripple, and I ₁ is the effective value of the output fundamental wave current. Therefore, the effective value of the current ripple can be used to represent the harmonic distortion rate of the phase current.

3) The current on the equivalent inductance in the motor control circuit on the AC side of the inverter is the ripple current of the phase current on the AC side. As shown in Figure 5, under SVPWM modulation, a switching cycle can be divided into eight sub-sections, and the current ripple in each sub-section is regarded as a slanted line, so the current ripple change in one switching cycle has seven linear periods, And output four voltage vectors among the eight basic voltage vectors of SVPWM. The inventive technique uses Thevenin's equivalence theorem to calculate the slope of the slope. For the inverter, the three-phase duty ratios of A, B and C are d _a , d _b , d _c , respectively, and the variation range is from 0 to 1. The corresponding quasi-duty cycle d' _x can be defined as d' _x =2d _x -1(x=a,b,c), and The fundamental wave voltages output by the inverter are Taking the calculation of the slope of the current ripple in the first linear cycle as an example, each linear cycle corresponds to a certain voltage combination, and the output voltages of the B-phase and C-phase branches can be equivalent to the A-phase circuit. The Thevenin equivalent circuit As shown in Figure 4. Since the linear cycle time is very short, the AC load voltage can be regarded as constant, and the voltage drop on the output inductor is also regarded as constant, so the output voltage of phase A /> The slope of the current in the phase A inductor can then be calculated as /> The calculation method of the current ripple slope of other linear periods is similar, and the calculation results are shown in Fig. 3 . Due to the three-phase symmetry, the current ripple of phase B and phase C can be analyzed with the same method. The peak value of the current ripple is then calculated from the slope and the duration of its linear periodic switching state. Take the calculation of the current ripple peak values x, y appearing in the 1st, 2nd, and 3rd linear periods shown in Figure 5 as an example, let the slope of the first oblique line be k ₁ and the slope of the second oblique line be k ₂ available /> Then calculate the average value of the current ripple in the 1st, 2nd, and 3rd linear periods according to the peak value as x ² /3, (x ² +xy+y ² )/3 and (x ² -xy+y ² )/3 , and finally, the effective value of the current ripple of a single switching cycle can be calculated by the average value of the current ripple of the 1st, 2nd, and 3rd linear cycles and the action time of the switch state as follows

On this basis, the effective value of the current ripple of the entire output cycle can be calculated as follows

4) The technology of the present invention optimizes the IGBT loss through an optimization method, so it is necessary to convert the P _IGBT integral form into a series form

in, i=0,...,N, N indicates that [0, 2π] is divided into N small intervals.

Considering that the modulation ratio of the motor is in the linear range in the technology of the present invention, the minimum DC bus voltage at which the motor can operate normally is Therefore, the optimization needs to meet the /> For the switching frequency, taking into account some /> Too low will affect the operation of the motor, and a switching frequency threshold f ₀ should also be set. Taking the effective value of the current ripple to evaluate the quality of the inverter output current as the constraint condition, and taking the switching frequency and the DC bus voltage as the constraint variables, the following optimization objectives can be obtained

Among them, Y is determined by the motor rated DC bus voltage and fixed switching frequency The obtained output cycle current ripple effective value; /> V _s and /> is the stator phase current, phase voltage amplitude and power factor angle under the same conditions; /> and /> are the DC bus voltage and switching frequency corresponding to different θ _i .

3. Apply the optimization method to obtain the switching frequency and DC bus voltage with the lowest IGBT loss based on the output cycle.

1) The technology of the present invention first builds the hidden pole permanent magnet synchronous motor model by Matlab/Simulink, and when running stably with the rated DC bus voltage and fixed switching frequency, the motor's output value is obtained from the Scope module. V _s , /> and m, then pass get Y.

2) Obtain the test conditions under specific test conditions in the IGBT device manual V _nom , _Inom , r _co and V _ce0 are obtained.

3) Convert the integral form of the objective function into a summation form, and then substitute the objective function and constraints into the Matlab optimization toolbox to obtain

4) The optimized DC bus voltage is a value that varies with θ _i . Since the frequently jumping DC bus voltage will cause damage to the motor and inverter, the technology of the present invention converts voltages of different θ _i The values are summed and averaged to obtain the voltage V _dc-opt as follows />

4. The realization process of the technology of the present invention:

First run the motor at rated DC bus voltage and fixed switching frequency, calculate V _s when the motor is stable, Then according to the algorithm proposed above, the corresponding optimal DC bus voltage and switching frequency are listed in the table. When the motor is running, use the look-up table method to obtain the corresponding optimal DC bus and switching frequency. The specific process is shown in Figure 1 and Figure 2.

Although the embodiments of the present invention have been shown and described, those skilled in the art can understand that various changes, modifications and substitutions can be made to these embodiments without departing from the principle and spirit of the present invention. and modifications, the scope of the invention is defined by the appended claims and their equivalents.

Claims (5)

1. The control method of the variable-frequency variable-voltage permanent magnet synchronous motor is characterized by comprising the following steps of:

the first step: establishing a non-salient pole permanent magnet synchronous motor model and an IGBT loss model based on an output period, and establishing a relation between the non-salient pole permanent magnet synchronous motor model and the IGBT loss model;

and a second step of: taking the quality of the output current of the inverter as a constraint condition, and taking the switching frequency of the inverter and the voltage of the direct current bus as constraint variables to establish an optimization target;

and a third step of: and obtaining the switching frequency and the direct current bus voltage with the lowest IGBT loss based on the output period by applying an optimization method.

2. The control method of a variable frequency and variable voltage permanent magnet synchronous motor according to claim 1, wherein: the specific content of the first step is as follows:

s1: establishing a voltage equation of the motor on the d-q axis

and

v _qs and v_ds Is the stator voltage, i _qs and i_ds Is the stator current, R _q and R_d Is a stator winding, ω _er Is the rotor electrical angular velocity, p is the differential operator, lambda _qs and λ_ds Is stator flux linkage lambda _f Is the flux linkage of the rotor magnet;

pi in the case of stable motor _qs and pi_ds Can be set to 0 and the stator phase voltage amplitude can be expressed as:

the d-q axis current satisfies wherein ,I_max Is the amplitude of the stator phase current, i at maximum acceleration _qs ＝I _max Let->

Will V _cp Adding the amplitude of the stator phase voltage wherein ,/>Is the stator phase current amplitude, the electromagnetic torque of the motor is +.>

P _n Is the pole pair number;

thus (2)

S2: loss P of IGBT _IGBT Divided into conduction lossesAnd switching losses->Modulation method inverse based on SVPWM

The duty cycle of the IGBT in the transformer is:

wherein ,for the power factor angle, modulation factor +.> in the formula ,V_dc Is the dc side voltage of the inverter;

conduction loss for a single output cycleAnd switching losses->The method comprises the following steps:

f _sw for switching frequency, V _ce(t) and I_ce (t) on-voltage drop and on-current, E _(on+off)nom 、V _nom and I_nom Respectively the sum of the on-off loss, the voltage and the current under the specific test condition of the IGBT, V _ce (t)＝I _ce (t)r _co +V _ce0, in the formula r_co Is the equivalent on-resistance of IGBT, V _ce0 Is an initial conduction voltage drop;

the on-state current is:

wherein ,θ＝ω_er t，The IGBT loss for a single output cycle is:

wherein , and />Is about the reference angle theta and the power factor angle +.>And the relationship between the stator phase current and the IGBT loss of the non-salient pole permanent magnet synchronous motor is established.

3. The control method of a variable frequency and variable voltage permanent magnet synchronous motor according to claim 2, wherein: the specific content of the second step is as follows:

s1: optimizing the switching frequency of IGBT loss and DC bus voltage in a single output period can obtain optimized P in the single output period _IGBT A value;

s2: limiting harmonic distortion of motor phase currents to a certain range, wherein the harmonic distortion rate of the phase currents is denoted as H, and h=delta _ims /I ₁ ，Δ _ims Current ripple effective value, I ₁ Outputting a fundamental wave current effective value;

s3: calculating current ripple based on Thevenin equivalent theorem, and calculating the effective value of the current ripple of the whole output period as follows

S4: will P _IGBT The integral form is converted into a series form:

wherein ,n represents will be [0,2 pi ]]Divided into N cells.

S5: the lowest DC bus voltage that can normally operate isFor the switching frequency, a switching frequency threshold f is set ₀ The following optimization objectives are obtained:

wherein Y is defined by the rated DC bus voltage of the motor and the fixed switching frequencyThe obtained output period current ripple effective value;

V _s and />Stator phase current, phase voltage amplitude and power factor angle under the same conditions;

and />For different theta _i Corresponding dc bus voltage and switching frequency.

4. A control method of a variable frequency and variable voltage permanent magnet synchronous motor according to claim 3, wherein:

5. a control method of a variable frequency and variable voltage permanent magnet synchronous motor according to claim 3, wherein: the third step comprises the following specific contents:

s1: setting up a hidden pole type permanent magnet synchronous motor model, and obtaining a motor from a Scope module when stably operating under the rated direct current bus voltage and the fixed switching frequencyV _s 、/>And m, pass->Obtaining Y;

s2: obtaining specific test conditions in IGBT device manualObtaining V _nom 、I _nom 、r _co and V_ce0 ；

S3: converting the integral form of the objective function into a sum form, and substituting the objective function and constraint conditions into a Matlab optimization tool box to obtain

S4: will differ by theta _i Voltage of (2)Summing the values and averaging to obtain a voltage V _dc-opt 。