CN109379013B - Torque ripple suppression method for permanent magnet synchronous motor - Google Patents
Torque ripple suppression method for permanent magnet synchronous motor Download PDFInfo
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- CN109379013B CN109379013B CN201811453974.XA CN201811453974A CN109379013B CN 109379013 B CN109379013 B CN 109379013B CN 201811453974 A CN201811453974 A CN 201811453974A CN 109379013 B CN109379013 B CN 109379013B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
- H02P21/05—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation specially adapted for damping motor oscillations, e.g. for reducing hunting
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P2207/00—Indexing scheme relating to controlling arrangements characterised by the type of motor
- H02P2207/05—Synchronous machines, e.g. with permanent magnets or DC excitation
Abstract
The invention provides a torque ripple suppression method of a permanent magnet synchronous motor, which predicts direct torque control based on a model, reduces 7 basic voltage vectors used in the existing method to 3 according to the change trend of a stator flux linkage position and electromagnetic torque, and selects an optimal combination from 3 selectable voltage vectors and duty ratio combinations as the input of the motor at the next moment by combining duty ratio modulation aiming at the unicity of the voltage vectors. Compared with the prior art, the method provided by the invention has the advantage that the calculation amount is obviously optimized on the premise of ensuring the torque ripple inhibition effect.
Description
Technical Field
The application relates to the field of direct torque control of permanent magnet synchronous motors of electric automobiles, in particular to a technology for reducing torque pulsation of a permanent magnet synchronous motor based on model prediction direct torque control.
Background
In an electric automobile driving system, the torque pulsation of a permanent magnet synchronous motor can cause the problems of electromagnetic noise and torque vibration, so that the comfort of people is influenced, and the caused vibration can also cause the motor system to resonate, so that the hysteresis and eddy current loss of the motor are increased, the service life of the motor is shortened, the reliability and the stability of the motor are reduced, and the torque pulsation needs to be effectively inhibited. The existing torque ripple suppression method adopts model prediction to perform direct torque control, which is a feasible solution, but the adoption of the method needs to perform traversal optimization-seeking calculation on all voltage vectors in each period, so that the defect of large calculation amount exists, and the increase of sampling frequency and time domain length is also limited, namely the accuracy of voltage vector prediction is limited. In addition, the inverter can only output one voltage vector in the whole sampling period by model prediction direct torque control, the switching action is irregular, and the torque ripple is larger compared with a control strategy with a modulator. Although some methods for improving the unity of the system computation amount and the voltage vector in terms of model prediction direct torque control exist at present, the basic idea is to sacrifice the performance of the torque ripple to reduce the system computation amount or sacrifice the computation amount to improve the accuracy of voltage vector prediction, and a torque ripple suppression means which can start from both the computation amount and the unity of the voltage vector is still lacked.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a method for suppressing torque ripple of a permanent magnet synchronous motor, which is used for predicting direct torque control based on a model and specifically comprises the following steps:
the method comprises the steps that firstly, based on state variables of a control system in a current sampling period, the position of a stator flux linkage and the change direction required by electromagnetic torque are obtained, a voltage vector screening table is established, and two non-zero voltage vectors and a zero voltage vector are obtained through screening;
establishing an evaluation function based on the electromagnetic torque and the stator flux linkage, and establishing a duty ratio relation related to the evaluation function;
substituting the voltage vectors screened in the step one into the duty ratio relation which enables the evaluation function value to be minimum to obtain different voltage vector and duty ratio combinations, and predicting the electromagnetic torque and the stator flux linkage of the next sampling period corresponding to the different combinations based on a permanent magnet synchronous motor discrete mathematical model considering the duty ratio;
and step four, substituting the electromagnetic torque and the stator flux linkage predicted in the step three into the evaluation function to obtain a voltage vector and duty ratio combination which enables the evaluation function value to be minimum, and enabling the combination which enables the evaluation function value to be minimum to be used as the input of the motor in the next sampling period based on duty ratio modulation.
Further, the state variables of the control system include stator current, stator flux linkage and electromagnetic torque, and satisfy the following relationship:
wherein isIs stator current, id、iqD, q-axis currents,. psid、ψqRespectively d and q axis flux linkage, Ld、LqInductance of d and q axes, psi, respectivelys、ψrRespectively stator, rotor flux linkage, pnNumber of pole pairs, T, of the motoreIs an electromagnetic torque.
Further, the establishing of the voltage vector screening table in the first step specifically includes:
in a two-phase static coordinate system, the stator flux α axes are assumed to be included at an angleθsThe coordinate system plane is divided into 6 sectors by:
(2N-3)π/6≤θs(N)≤(2N-1)π/6，N＝1，…，6；
according to the comparison value delta T of the electromagnetic torque and the reference electromagnetic torqueeAnd screening the symbol and the position N of the stator flux linkage sector to obtain the voltage vector.
Further, the evaluation function established in the second step is:
wherein the content of the first and second substances,
reference values, λ, for the electromagnetic torque and stator flux linkage, respectivelypK represents the current sampling instant for the weighting factor in the evaluation function.
The duty ratio relation with respect to the evaluation function is as follows:
wherein D represents the duty cycle, Δ Te、ΔψsRespectively the theoretical increment of the electromagnetic torque and the stator flux linkage in the sampling period.
Further, the discrete mathematical model of the permanent magnet synchronous motor considering the duty ratio in the third step is as follows:
for the surface-mounted permanent magnet synchronous motor, d-axis inductance and q-axis inductance are the same and are uniformly expressed by L, k +1 represents the next sampling time, and omegarRepresenting angular speed, T, of the rotorsRepresenting the system sampling period, RsRepresents the stator resistance usRepresenting the stator voltage.
The method provided by the invention is based on the suppression of torque ripple, 7 basic voltage vectors used in the existing method are reduced to 3 according to the stator flux linkage position and the electromagnetic torque variation trend, and meanwhile, aiming at the unicity of the voltage vectors, the optimal combination is selected from the combination of 3 optional voltage vectors and duty ratios as the input of the motor at the next moment by combining duty ratio modulation. Compared with the prior art, the method provided by the invention has the advantage that the calculation amount is obviously optimized on the premise of ensuring the torque ripple inhibition effect.
Drawings
FIG. 1 is a functional block diagram of a method provided by the present invention
FIG. 2 is a voltage vector distribution diagram of a two-phase stationary coordinate system plane
FIG. 3 is a block diagram of a conventional model-predicted direct torque control
Detailed Description
The method provided by the invention is explained in further detail below with reference to the accompanying drawings.
The method for suppressing the torque ripple of the permanent magnet synchronous motor provided by the invention is used for predicting direct torque control based on a model, and specifically comprises the following steps as shown in figure 1:
the method comprises the steps that firstly, based on state variables of a control system in a current sampling period, the position of a stator flux linkage and the change direction required by electromagnetic torque are obtained, a voltage vector screening table is established, and two non-zero voltage vectors and a zero voltage vector are obtained through screening;
establishing an evaluation function based on the electromagnetic torque and the stator flux linkage, and establishing a duty ratio relation related to the evaluation function;
substituting the voltage vectors screened in the step one into the duty ratio relational expression which enables the evaluation function value to be minimum to obtain different voltage vector and duty ratio combinations, and predicting the electromagnetic torque and the stator flux linkage of the next sampling period corresponding to the different combinations based on a permanent magnet synchronous motor discrete mathematical model considering the duty ratio;
and step four, substituting the electromagnetic torque and the stator flux linkage predicted in the step three into the evaluation function to obtain a voltage vector and duty ratio combination which enables the evaluation function value to be minimum, and enabling the combination which enables the evaluation function value to be minimum to be used as the input of the motor in the next sampling period based on duty ratio modulation.
In a preferred embodiment of the present application, the state variables of the control system include stator current, stator flux linkage, and electromagnetic torque, and satisfy the following relationships:
wherein isIs stator current, id、iqD, q-axis currents,. psid、ψqRespectively d and q axis flux linkage, Ld、LqInductance of d and q axes, psi, respectivelys、ψrRespectively stator, rotor flux linkage, pnNumber of pole pairs, T, of the motoreIs an electromagnetic torque.
Fig. 2 is a voltage vector distribution diagram of a two-phase stationary coordinate system plane. Assuming that the stator flux linkage is at the position shown in the figure and rotates in the counterclockwise direction, the two-phase stationary coordinate system plane is divided into 4 areas, which are (T) respectively, based on the electromagnetic torque and the required changing direction of the stator flux linkagee+，ψs+)、(Te+，ψs-)、(Te-，ψs-)、(Te-，ψsLet the stator flux linkage form an angle theta with the α axissThe coordinate system plane can be divided into 6 sectors, I, II, III, IV, V and VI, respectively, by the following formula.
(2N-3)π/6≤θs(N)≤(2N-1)π/6，N＝1，…，6。
In a preferred embodiment of the present application, the establishing of the voltage vector screening table in the first step specifically includes: since the stator flux linkage rotates counterclockwise, if the torque error is greater than 0, δ T is obtained if the stator flux linkage is assumed to be in sector I of the figureeIf the voltage vector is greater than 0, the torque is increased and the two adjacent voltage vectors are V2、V3. In a similar manner, if Δ TeLess than 0, the torque is reduced and the two adjacent voltage vectors are V5、V6. In combination with the stepsComparison value δ T of electromagnetic torque observed in step one with reference electromagnetic torqueeAnd the stator flux linkage sector position N, the voltage vector screening table is as follows:
wherein, V1，...，6Is a non-zero voltage vector.
Since the present application is directed to suppression of torque ripple of a permanent magnet synchronous motor, a comparison value δ ψ of an observed stator flux linkage and a reference stator flux linkage is not consideredsAnd (4) a corresponding voltage vector screening table.
In a preferred embodiment of the present application, since two zero voltage vectors are included, the selection of the zero voltage vector should be performed for the minimum number of switching times in order to reduce the switching frequency and reduce the switching loss. That is, in the next sampling period after "100", "010", and "001", if the optimum voltage vector is a zero voltage vector, the switch state "000" is selected. Conversely, the other switch states are selected (111) as the optimal voltage vector for the next sampling period.
In a preferred embodiment of the present application, the evaluation function established in the second step is:
wherein the content of the first and second substances,
reference values, λ, for the electromagnetic torque and stator flux linkage, respectivelypK represents the current sampling instant for the weighting factor in the evaluation function.
The duty ratio relation with respect to the evaluation function is as follows:
wherein D represents the duty cycle, Δ Te、ΔψsRespectively being sampledTheoretical increment of electromagnetic torque and stator flux linkage in a cycle.
The theoretical increment of the electromagnetic torque and the stator flux linkage in the sampling period can be respectively calculated by the following formulas:
Δψs＝DTs(us-Rsis)。
wherein, TsDenotes the system sampling period, usRepresenting stator voltage, RsRepresenting the stator resistance.
In a preferred embodiment of the present application, the discrete mathematical model of the permanent magnet synchronous motor considering the duty ratio in step three is as follows:
for the surface-mounted permanent magnet synchronous motor, d-axis inductance and q-axis inductance are the same and are uniformly expressed by L, k +1 represents the next sampling time, and omegarRepresenting the rotor angular velocity.
Combining (V) the voltage vector calculated in step three with a duty cyclei，di) Substituting into the relation in consideration of duty ratio, predicting the stator flux linkage and electromagnetic torque (T) of next sampling period after each selected voltage vector actse(k+1),ψs(k +1)), and substituting the evaluation function into the evaluation function to obtain the optimal combination (V) of the voltage vector and the duty ratioopt，dopt). In a preferred embodiment of the present application, V is modulated based on duty cycleopt，doptAs input to the motor for the next sample period.
Fig. 3 is a block diagram of a conventional model-predictive direct torque control. The technical scheme of the application can be seen to reduce the voltage vector traversal number, and the selection of the duty ratio and the voltage vector is optimized simultaneously when the duty ratio modulation is introduced.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (3)
1. A permanent magnet synchronous motor torque ripple suppression method is based on model prediction direct torque control and is characterized in that: the method specifically comprises the following steps:
the method comprises the steps that firstly, based on state variables of a control system in a current sampling period, the position of a stator flux linkage and the change direction required by electromagnetic torque are obtained, a voltage vector screening table is established, and two non-zero voltage vectors and a zero voltage vector are obtained through screening;
establishing an evaluation function based on the electromagnetic torque and the stator flux linkage, and establishing a duty ratio relation related to the evaluation function;
the merit function is:
wherein the content of the first and second substances,
reference values, λ, for the electromagnetic torque and stator flux linkage, respectivelypK is a weight factor in the evaluation function and represents the current sampling moment;
the duty ratio relation related to the evaluation function is as follows:
wherein D represents the duty cycle, Δ Te、ΔψsRespectively the theoretical increment of the electromagnetic torque and the stator flux linkage in a sampling period;
substituting the voltage vectors screened in the step one into the duty ratio relation which enables the evaluation function value to be minimum to obtain different voltage vector and duty ratio combinations, and predicting the electromagnetic torque and the stator flux linkage of the next sampling period corresponding to the different combinations based on a permanent magnet synchronous motor discrete mathematical model considering the duty ratio; the discrete mathematical model of the permanent magnet synchronous motor considering the duty ratio is as follows:
wherein isFor stator current, D represents duty cycle, ψsFor stator flux linkage, TeIs an electromagnetic torque, pnFor the pole pair number of the motor, for the surface-mounted permanent magnet synchronous motor, the d-axis inductance is the same as the q-axis inductance and is uniformly expressed by L, k +1 represents the next sampling time, omegarRepresenting angular speed, T, of the rotorsRepresenting the system sampling period, RsRepresents the stator resistance usRepresenting a stator voltage;
and step four, substituting the electromagnetic torque and the stator flux linkage predicted in the step three into the evaluation function to obtain a voltage vector and duty ratio combination which enables the evaluation function value to be minimum, and enabling the combination which enables the evaluation function value to be minimum to be used as the input of the motor in the next sampling period based on duty ratio modulation.
2. The method of claim 1, wherein: the state variables of the control system comprise stator current, stator flux linkage and electromagnetic torque, and satisfy the following relations:
wherein isIs stator current, id、iqD, q-axis currents,. psid、ψqRespectively d and q axis flux linkage, Ld、LqInductance of d and q axes, psi, respectivelys、ψrRespectively stator, rotor flux linkage, pnIs the number of pole pairs, T, of the motoreIs an electromagnetic torque.
3. The method of claim 2, wherein: the establishing of the voltage vector screening table in the first step specifically includes:
in a two-phase static coordinate system, the included angle of the α axes of the stator flux linkage is assumed to be thetasThe coordinate system plane is divided into 6 sectors by:
(2N-3)π/6≤θs(N)≤(2N-1)π/6，N＝1，…，6；
according to the comparison value delta T of the electromagnetic torque and the reference electromagnetic torqueeAnd screening the symbol and the position N of the stator flux linkage sector to obtain the voltage vector.
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| CN110336511B (en) * | 2019-07-11 | 2021-10-22 | 台州学院 | Six-phase motor harmonic current suppression method based on model prediction direct torque control |
| CN110943663B (en) * | 2019-12-02 | 2021-07-02 | 长安大学 | Permanent magnet synchronous motor dynamic finite state set model prediction torque control method |
| CN110971168B (en) * | 2019-12-18 | 2021-08-31 | 福州大学 | Control method for predicting direct torque by induction machine model |
| CN111130419A (en) * | 2020-01-03 | 2020-05-08 | 天津大学 | Permanent magnet motor prediction flux linkage control method based on extended step length and variable action time |
| CN111106773B (en) * | 2020-01-05 | 2023-04-07 | 天津大学 | Permanent magnet synchronous motor model prediction control method based on optimized duty ratio |
| CN111371367A (en) * | 2020-03-16 | 2020-07-03 | 上海航天控制技术研究所 | Model prediction-based direct torque control method and system for energy storage flywheel motor |
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