A variable frequency variable voltage permanent magnet synchronous motor control method

Abstract

The application relates to the technical field of motor control, and discloses a variable-frequency variable-voltage permanent magnet synchronous motor control method, which comprises the following steps: first step: establishing a model of a hidden-pole permanent magnet synchronous motor and an IGBT loss model based on an output period, and establishing the relationship between the two; second step: taking the quality of inverter output current as a constraint condition, and taking the switching frequency of the inverter and the DC bus voltage as constraint variables to establish an optimization target; third step: applying an optimization method to obtain the switching frequency and the DC bus voltage with the lowest IGBT loss based on the output period. The variable-frequency variable-voltage permanent magnet synchronous motor control method optimizes the DC bus voltage and the switching frequency of the motor, can reduce the IGBT loss to the maximum extent, thereby obviously reducing the junction temperature of the IGBT and prolonging the service life of the IGBT.

Description

A control method for a variable frequency and variable voltage permanent magnet synchronous motor Technical Field

[0001] This invention relates to the field of motor control technology, specifically to a control method for a variable frequency and variable voltage permanent magnet synchronous motor. Background Technology

[0002] Currently, three-phase voltage source inverters are widely used in variable speed drives, active power filters, and uninterruptible power supplies due to their ease of operation, control, and implementation, making them one of the most commonly used power electronic converters. Given the high modulation ratio and good output waveform of Voltage Vector Pulse Width Modulation (SVPWM), three-phase voltage source inverters typically employ the SVPWM modulation method. Generally, the SVPWM switching frequency and DC bus voltage are fixed, but simply setting these two parameters to fixed values ​​reduces voltage utilization, increases losses in the three-phase voltage source inverter, and causes the inverter to operate at a higher junction temperature. Related research indicates that nearly 60% of inverter failures are caused by high junction temperatures: for every 10°C increase in inverter temperature, the failure rate doubles; higher junction temperatures also accelerate IGBT aging and reduce inverter reliability.

[0003] Current technical solutions only optimize the inverter's switching frequency or DC bus voltage individually in the motor control system to reduce junction temperature and improve reliability. For example, using the inverter output current ripple RMS value as a constraint and switching losses as the objective function to obtain a variable switching frequency to reduce switching losses only optimizes the switching losses without considering the total IGBT losses, thus failing to minimize them. Another approach, using a DC bus voltage adaptive controller to obtain the optimal DC bus voltage, only optimizes the output current quality without considering the total IGBT losses, potentially leading to increased total losses. Therefore, we propose a variable frequency and variable voltage permanent magnet synchronous motor control method. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a variable frequency and variable voltage permanent magnet synchronous motor control method, which solves the aforementioned problems.

[0006] (II) Technical Solution

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: a variable frequency and variable voltage permanent magnet synchronous motor control method, comprising the following steps:

[0008] Step 1: Establish a salient-pole permanent magnet synchronous motor model and an IGBT loss model based on the output cycle, and establish the relationship between the two;

[0009] Step 2: Establish optimization objectives with inverter output current quality as a constraint and inverter switching frequency and DC bus voltage as constraint variables;

[0010] Step 3: Apply optimization methods to determine the switching frequency and DC bus voltage that minimize IGBT losses based on the output cycle.

[0011] Preferably, the first step includes the following:

[0012] S1: Establish the voltage equation of the motor along the dq axis.

[0013]

[0014] and

[0015] v qs and v ds It is the stator voltage, i qs and i ds It is the stator current, R q and R d It is the stator winding, ω er λ is the rotor electric angular velocity, p is the differential operator, and λ is the rotor electric angular velocity. qs and λ ds It is the stator flux linkage, λ f It is the magnetic flux linkage of the rotor magnet;

[0016] pi under stable motor conditions qs and pi ds The value can be set to 0, and the stator phase voltage amplitude can be expressed as:

[0017] dq axis currents satisfy Among them, I max It is the amplitude of the stator phase current, i under maximum acceleration. qs = max ,make

[0018] V cp Adding the stator phase voltage amplitude in, This is the stator phase current amplitude, and the motor electromagnetic torque is...

[0019] P n It is the extreme logarithm;

[0020] therefore

[0021] S2: IGBT loss P IGBTDivided into conduction loss and switching losses The duty cycle of the IGBT in the inverter based on the SVPWM modulation method is:

[0022]

[0023] in, Power factor angle, modulation factor In the formula, V dc This is the DC-side voltage of the inverter;

[0024] Conduction loss per output cycle and switching losses for:

[0025]

[0026]

[0027] f sw V is the switching frequency. ce (t) and I ce (t) represent the on-state voltage drop and on-state current, respectively, E (+off)nom V nom and I nom These represent the sum of turn-on and turn-off losses, voltage, and current under specific test conditions for the IGBT, respectively, V. ce (t)=I ce (t)r co +V ce0 In the formula r co V is the equivalent on-resistance of the IGBT. ce0 This is the initial on-state voltage drop;

[0028] The on-state current is:

[0029]

[0030] Where θ=ω er t, The IGBT loss for a single output cycle is:

[0031]

[0032] in, and It concerns the reference angle θ and the power factor angle. The switching frequency function and DC bus voltage function were used to establish the relationship between the stator phase current and IGBT losses of the salient-pole permanent magnet synchronous motor.

[0033] Preferably, the second step is as follows:

[0034] S1: Optimizing the switching frequency and DC bus voltage of the IGBT losses in a single output cycle can yield the optimized P within that single output cycle. IGBT value;

[0035] S2: The harmonic distortion of the motor phase current is limited to a certain range. The phase current harmonic distortion rate is denoted as H, where H = Δ ims / I1,Δ ims The effective value of the current ripple, where I1 is the effective value of the output fundamental current;

[0036] S3: Based on Thevenin's equivalent theorem, the current ripple is calculated, and the effective value of the current ripple for the entire output cycle is as follows:

[0037] S4: P IGBT Convert the integral form to a series form:

[0038]

[0039] in, i = 0, ..., N, where N represents dividing [0, 2π] into N smaller intervals.

[0040] S5: The minimum DC bus voltage at which the motor can operate normally is satisfy Regarding the switching frequency, by setting a switching frequency threshold f0, the following optimization objective is obtained:

[0041]

[0042]

[0043]

[0044]

[0045] Wherein, Y is determined by the rated DC bus voltage of the motor and the fixed switching frequency. The obtained RMS value of the output periodic current ripple;

[0046] V s and For the stator phase current, phase voltage amplitude, and power factor angle under the same conditions;

[0047] and For different θ i The corresponding DC bus voltage and switching frequency.

[0048] Preferably, the third step is as follows:

[0049] S1: Build a salient-pole permanent magnet synchronous motor model. Run the motor stably at its rated DC bus voltage and fixed switching frequency, and obtain the motor's specifications from the Scope module. V s , and m, then through We obtain Y;

[0050] S2: Obtain specific test conditions from the IGBT device datasheet. Get V nom I nom r co and V ce0 ;

[0051] S3: Transform 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 the result.

[0052] S4: Different θ i voltage The voltage V is obtained by summing the values ​​and taking the average. dc-opt .

[0053] (III) Beneficial Effects

[0054] Compared with the prior art, the present invention provides a variable frequency and variable voltage permanent magnet synchronous motor control method, which has the following characteristics:

[0055] Beneficial effects:

[0056] 1. This variable frequency and variable voltage permanent magnet synchronous motor control method optimizes the DC bus voltage and switching frequency of the motor, which can minimize IGBT losses, thereby significantly reducing the junction temperature of the IGBT and improving its service life.

[0057] 2. This variable frequency and variable voltage permanent magnet synchronous motor control method improves the utilization rate of DC bus voltage and increases the driving capability of the inverter while ensuring the quality of output current. Attached Figure Description

[0058] Figure 1 is a schematic diagram of the process of this invention;

[0059] Figure 2 is a schematic diagram of the technical implementation process of the present invention;

[0060] Figure 3 shows the current ripple slope under different linear periods.

[0061] Figure 4 is a schematic diagram of the Thevenin equivalent circuit with a linear period of 1.

[0062] Figure 5 is a schematic diagram of the current ripple during one switching cycle of SVPWM. Detailed Implementation

[0063] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0064] Please refer to Figures 1-5. A method for controlling a variable frequency and variable voltage permanent magnet synchronous motor includes the following steps:

[0065] 1. Establish a model of a salient-pole permanent magnet synchronous motor and an IGBT loss model based on the output cycle, and establish the relationship between the two.

[0066] 1) Establish the voltage equation of the motor on the dq axis.

[0067]

[0068] and

[0069]

[0070] Among them, v qs and v ds It is the stator voltage, i qs and i ds It is the stator current, R q and R d It is the stator winding, ω er λ is the rotor electric angular velocity, p is the differential operator, and λ is the rotor electric angular velocity. qs and λ ds It is the stator flux linkage, λ f It is the magnetic flux linkage of the rotor magnet.

[0071] pi under stable motor conditions qs and pi ds The stator resistance voltage drop can be set to 0, and since it is small, it can be ignored. Therefore, the stator phase voltage amplitude can be expressed as:

[0072]

[0073] In the formula, the dq-axis current must satisfy... Among them, I max This is the amplitude of the stator phase current. Under maximum acceleration, i qs = max ,make

[0074] Considering the stator resistance voltage drop compensation voltage V cp Adding the stator phase voltage amplitude in, This is the stator phase current amplitude. The motor electromagnetic torque is...

[0075]

[0076] Among them, P n The number of pole pairs is L. Since this invention is based on a salient-pole permanent magnet synchronous motor, L... q = d ,therefore

[0077] 2) Establish the IGBT loss model of the inverter, where the IGBT loss P... IGBT Divided into conduction loss and switching losses Conduction losses are affected by load current and duty cycle, while switching losses are affected by load current, switching frequency, and DC-side voltage. The modulation method used in this invention is SVPWM. Since SVPWM modulation is similar to third harmonic injection, the duty cycle of the IGBT in the inverter is...

[0078]

[0079] in, Power factor angle, modulation factor In the formula, V dc This refers to the DC-side voltage of the inverter. Taking the upper IGBT of phase A in a three-phase voltage source inverter as an example, the average switching loss and conduction loss per output cycle are...

[0080]

[0081]

[0082] Among them, f sw V is the switching frequency. ce (t) and Ice (t) represent the on-state voltage drop and on-state current, respectively. V nom and I nom These represent the sum of turn-on and turn-off losses, voltage, and current under specific test conditions for the IGBT, respectively, V. ce (t)=I ce (t)r co +V ce0 In the formula r co V is the equivalent on-resistance of the IGBT. ce0 The initial on-state voltage drop is related to the IGBT junction temperature. Based on the output cycle loss, the equivalent on-resistance and initial on-state voltage drop can be considered as test values ​​under specific conditions. r co V ce0 V nom and I nom All of this information can be obtained from the IGBT's datasheet. It can be determined from the on-state current.

[0083]

[0084] Where θ=ω er t, Therefore, the IGBT loss for a single output cycle can be obtained.

[0085]

[0086] in, and It concerns the reference angle θ and the power factor angle. The switching frequency function and DC bus voltage function were used to establish the relationship between the stator phase current and IGBT losses of the salient-pole permanent magnet synchronous motor.

[0087] 2. An optimization objective is established with the inverter output current quality as a constraint, and the inverter switching frequency and DC bus voltage as constraint variables.

[0088] 1) Optimizing the switching frequency and DC bus voltage of the IGBT losses in a single output cycle can yield the optimized P within that single output cycle. IGBT Value, but if there are no constraints, the optimized P IGBT The value must be zero, so certain constraints must be added.

[0089] 2) For inverters, the harmonic quality of the AC phase current is an important performance indicator. To maintain proper motor operation, the harmonic distortion of the motor phase current needs to be limited within a certain range. The phase current harmonic distortion rate H can be expressed as H = Δ ims / I1, where Δ ims The effective value of the current ripple is given by I1, which is the effective value of the output fundamental current. Therefore, the effective value of the current ripple can be used to represent the harmonic distortion rate of the phase current.

[0090] 3) The current in the equivalent inductor of the AC side motor control circuit of the inverter is the ripple current of the AC side phase current. As shown in Figure 5, under SVPWM modulation, one switching cycle can be divided into eight segments. The current ripple of each segment can be considered as a diagonal line. Therefore, the current ripple change within one switching cycle has seven linear periods, and four of the eight basic voltage vectors of the output SVPWM are represented. This invention uses Thevenin's equivalent theorem to calculate the slope of the diagonal line. For the inverter, the duty cycles of phases A, B, and C are d... a d b d c Its range is from 0 to 1. The corresponding quasi-duty cycle d′ x It can be defined as d′ x =2d x -1(x=a,b,c), and The fundamental voltages output by the inverter are respectively 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. The output voltages of phase B and phase C can be equivalently applied to the phase A circuit, and its Thevenin equivalent circuit is shown in Figure 4. Since the linear cycle time is very short, the AC load voltage can be considered constant, and the voltage drop across the output inductor can also be considered constant. Therefore, the output voltage of phase A is... Then the slope of the current in the A-phase inductor can be calculated. The calculation method for the current ripple slope of other linear cycles is similar, and the calculation results are shown in Figure 3. Since the three phases are symmetrical, the current ripple of phases B and C can be analyzed using the same method. Then, the peak current ripple is calculated based on the slope and the duration of the linear cycle switching state. Taking the calculation of the peak current ripple x and y appearing in the 1st, 2nd, and 3rd linear cycles as shown in Figure 5 as an example, assuming the slope of the first slope is k1 and the slope of the second slope is k2, we can obtain... Then, based on the peak value, the average current ripple value under the 1st, 2nd, and 3rd linear periods is calculated as x. 2 / 3、(x 2 +xy+y 2 ) / 3 and (x 2 -xy+y 2 Finally, by using the average current ripple values ​​of the 1st, 2nd, and 3rd linear cycles and the duration of the switching state, the effective value of the current ripple for a single switching cycle can be calculated as follows:

[0091]

[0092] Based on this, the effective value of the current ripple throughout the entire output cycle can be calculated as follows:

[0093] 4) This invention optimizes IGBT losses through an optimization method, therefore it is necessary to reduce P IGBT Converting integral form to series form

[0094]

[0095] in, i = 0, ..., N, where N represents dividing [0, 2π] into N smaller intervals.

[0096] In this invention, considering that the modulation ratio of the motor is within the linear range, the minimum DC bus voltage at which the motor can operate normally is: Therefore, optimization needs to satisfy the following conditions. Regarding the switching frequency, considering certain Too low a frequency will negatively impact motor operation, so a switching frequency threshold f0 should also be set. Using the effective value of the current ripple, which evaluates the quality of the inverter output current, as a constraint, and the switching frequency and DC bus voltage as constraint variables, the following optimization objectives can be obtained.

[0097]

[0098]

[0099]

[0100]

[0101] Wherein, Y is determined by the rated DC bus voltage of the motor and the fixed switching frequency. The obtained RMS value of the output periodic current ripple; V s and For the stator phase current, phase voltage amplitude, and power factor angle under the same conditions; and For different θ i The corresponding DC bus voltage and switching frequency.

[0102] 3. The optimal switching frequency and DC bus voltage with the lowest IGBT loss based on the output cycle are obtained by applying the optimization method.

[0103] 1) This invention first uses Matlab / Simulink to build a salient-pole permanent magnet synchronous motor model. Under stable operation at rated DC bus voltage and fixed switching frequency, the motor's [data / mechanics] are obtained from the Scope module. V s , and m, then through We get Y.

[0104] 2) Obtain specific test conditions from the IGBT device datasheet. Get V nom I nom r co and V ce0 .

[0105] 3) Transform 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 the result.

[0106] 4) The optimized DC bus voltage is a variable that varies with θ i The changing value of θ is problematic because frequent fluctuations in the DC bus voltage can damage the motor and inverter. This invention addresses this by using different θ values. i voltage The voltage V is obtained by summing the values ​​and taking the average. dc-opt as follows

[0107] 4. Implementation process of the present invention:

[0108] First, operate the motor at its rated DC bus voltage and fixed switching frequency. Calculate V when the motor stabilizes. s , Then, the optimal DC bus voltage and switching frequency are obtained according to the algorithm proposed above and listed in the table. When the motor is running, the optimal DC bus voltage and switching frequency are obtained by looking up the table. The specific process is shown in Figure 1 and Figure 2.

[0109] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A control method for a variable frequency and variable voltage permanent magnet synchronous motor, characterized in that, Includes the following steps: Step 1: Establish a salient-pole permanent magnet synchronous motor model and an IGBT loss model based on the output cycle, and establish the relationship between the two; Step 2: Establish optimization objectives with inverter output current quality as a constraint, and inverter switching frequency and DC bus voltage as constraint variables; Step 3: Apply optimization methods to obtain the switching frequency and DC bus voltage with the lowest IGBT loss based on the output cycle; Specifically, Step 2 includes: S1: Optimizing the switching frequency and DC bus voltage of the IGBT loss in a single output cycle yields the optimized values ​​within that single output cycle. Value; S2: Limits the harmonic distortion of the motor phase current within a certain range, the phase current harmonic distortion rate is denoted as H, where ， RMS value of current ripple S3: Based on Thevenin's equivalent theorem, the current ripple is calculated, and the effective value of the current ripple for the entire output cycle is calculated as follows: S4: will Convert the integral form to the series form: ;in, ， ， Indicates will Divided into Interval; S5: The minimum DC bus voltage at which the motor can operate normally is For the switching frequency, set a switching frequency threshold. The following optimization objectives are obtained: ； ； ； ;in, Under the conditions of rated DC bus voltage and fixed switching frequency of the motor, The obtained RMS value of the output periodic current ripple; 、 and For the stator phase current, phase voltage amplitude, and power factor angle under the same conditions; and For different The corresponding DC bus voltage and switching frequency.

2. The method for controlling a variable frequency and variable voltage permanent magnet synchronous motor according to claim 1, characterized in that: The specific steps of the first step are: S1: Establish the motor in Voltage equation of the shaft ;and ； and It is the stator voltage. and It is the stator current. and It is the stator winding. It is the rotor's electrical angular velocity. It is a differential operator. and It is the stator flux linkage. It is the magnetic flux linkage of the rotor magnet; Under stable motor conditions and The value can be set to 0, and the stator phase voltage amplitude can be expressed as: ； shaft current satisfies ,in, It is the amplitude of the stator phase current under maximum acceleration. ,make ;Will Adding the stator phase voltage amplitude ,in, This is the stator phase current amplitude, and the motor electromagnetic torque is... ； It is an extreme logarithm; therefore S2: IGBT losses Divided into conduction loss and switching losses The duty cycle of the IGBT in the inverter based on the SVPWM modulation method is: ;in, Power factor angle, modulation factor In the formula, The DC-side voltage of the inverter; the conduction loss per output cycle. and switching losses for: ； ； For switching frequency, and These are the on-state voltage drop and on-state current, respectively. 、 and These represent the sum of turn-on and turn-off losses, voltage, and current under specific test conditions for the IGBT. In the formula This is the equivalent on-resistance of the IGBT. The initial on-state voltage drop is: The on-state current is: ;in, ， The IGBT loss for a single output cycle is: in, and It's about the reference angle. and power factor angle The switching frequency function and DC bus voltage function were used to establish the relationship between the stator phase current and IGBT losses of the salient-pole permanent magnet synchronous motor.

3. The method for controlling a variable frequency and variable voltage permanent magnet synchronous motor according to claim 1, characterized in that: 。 4. The method for controlling a variable frequency and variable voltage permanent magnet synchronous motor according to claim 1, characterized in that: The third step involves: S1: Building a salient-pole permanent magnet synchronous motor model, operating it stably at the rated DC bus voltage and fixed switching frequency, and obtaining the motor's specifications from the Scope module. 、 、 and Then through get S2: Obtain specific test conditions from the IGBT device datasheet. ,get 、 、 and S3: Transform 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 the result. ， ； S4: Different voltage The voltage is obtained by summing the values ​​and taking the average. 。

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