CN113162505A - Permanent magnet motor torque control method and system - Google Patents
Permanent magnet motor torque control method and system Download PDFInfo
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Abstract
The invention relates to a permanent magnet motor torque control method and a system, comprising the following steps: obtaining a stator current vector at the k +1 moment through the stator current of the permanent magnet motor at the current k moment and the voltage of a capacitor filter of the converter, and calculating a stator current reference value at the k +2 moment, a voltage reference value of the capacitor filter and an electromagnetic torque reference value according to the stator current vector at the k +1 moment; according to the state combination of the current transformer, obtaining the output voltage of the capacitor filter at the k +2 moment and the stator current vector of the output at the k +1 moment corresponding to each state; calculating a stator current output value and an electromagnetic torque output value at the moment k +2 according to the output stator current vector at the moment k + 1; and constructing a torque cost function of the all-state variable according to the obtained data, and solving the torque cost function to obtain the optimal torque control quantity. By simultaneously controlling the stator current of the permanent magnet motor and the voltage of the converter capacitor filter, the resonance of the LC network is effectively inhibited, and the output torque ripple is reduced.
Description
Technical Field
The invention relates to a permanent magnet motor torque control method and system, and belongs to the technical field of motor control.
Background
The Current Source Converter (CSC) has the characteristic of low voltage change rate (dV/dt) friendly to the motor side, the output side of the CSC must output electric energy after passing through a capacitive filter, and the high-frequency component of the capacitive voltage after filtering is greatly reduced, so that the CSC is suitable for a long-cable driving system; in addition, the current source type converter also has the advantages of simple structure, short circuit self-protection capability, low cost and the like.
However, the capacitor filter of the current source type converter and the stator inductance of the permanent magnet motor form an LC network, and when the harmonic frequency in the driving system approaches the resonant frequency of the LC network, the harmonic current is further amplified, which leads to high-frequency oscillation of the output torque and even leads to system instability; therefore, resonance in the converter-driven permanent magnet motor system needs to be suppressed.
In order to solve the above problems, the prior art generally includes two methods, namely a passive damping method and an active damping method.
The passive damping method is characterized in that a resistor or a capacitor branch is connected in series on an inductance branch of a motor stator and is connected in parallel with a capacitor filter to inhibit oscillation of output current; the method is simple and effective, but introduces extra loss, and reduces the conversion efficiency of the converter; when the system is driven by medium voltage, the problems of power loss and heating are caused by the introduction of passive damping, and the operation cost of the system is greatly increased; in addition, passive damping passes through the resistance size and sets up the damping size, and the adjustment is inconvenient after the installation is accomplished, and capacitor filter can take place ageing, and system resonant frequency can change along with the capacitance value, and the damping characteristic also can correspondingly change.
The active damping method is characterized in that a control loop simulating damping characteristics is added in a control strategy to suppress oscillation of output current; however, the method needs to set a feedforward loop and carry out harmonic detection, the implementation and debugging process is complex, a cascade structure is adopted, and the dynamic performance is poor; furthermore, for high power application scenarios, the switching frequency needs to be severely limited.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a method and a system for controlling a torque of a permanent magnet motor, which can effectively suppress resonance of an LC network and reduce output torque ripple by controlling a stator current of the permanent magnet motor and a capacitor filter voltage of an inverter at the same time.
In order to achieve the purpose, the invention adopts the following technical scheme: a permanent magnet motor torque control method comprises the following steps: s1, carrying out one-beat delay compensation on the obtained stator current of the permanent magnet synchronous motor at the current k moment and the filter capacitor voltage of the current source converter to obtain a stator current vector of the stator current at the k +1 moment in a d-q coordinate system; s2, calculating a stator current reference value and a filter capacitor voltage reference value at the moment k +2 according to the stator current vector at the moment k +1, and calculating an electromagnetic torque reference value according to a rotating speed controller of a rotating speed outer ring; s3, constructing a current source converter switch state combination, and obtaining a filter capacitor voltage predicted value, a stator current predicted value and an electromagnetic torque predicted value at the k +2 moment according to an output current vector of the current source converter in each switch state; s4, constructing a cost function of the all-state variable according to the stator current reference value at the k +2 moment, the voltage reference value of the capacitor filter, the electromagnetic torque reference value, the stator current predicted value, the voltage predicted value of the capacitor filter and the electromagnetic torque predicted value, and solving the cost function to obtain the optimal torque control quantity.
Further, the formula for obtaining the stator current vector at the time k +1 in step S1 is:
where k, k +1 denote the current time and the next time, isd(k+1)、isq(k +1) are stator current vectors isConversion to d-and q-axis components, v, in a d-q coordinate systemsd、vsqThe d-axis voltage and the q-axis voltage of the capacitive filter, omega the electrical angular velocity of the rotor flux linkage, psifFor rotor permanent magnet flux linkage, Ld、LqRespectively stator d and q axis inductances, R being a single phase stator winding resistance, TsIs the sampling period.
Further, the formula for obtaining the stator current reference value at the time k +2 and the voltage reference value of the capacitive filter in step S1 is as follows:
Wherein,
respectively d-axis and q-axis components of the reference value of the stator current vector in a d-q coordinate system,
reference voltages, ω, for d and q axes of the capacitive filter, respectivelyIs the electrical angular velocity, psi, of the rotor flux linkagefFor rotor permanent magnet flux linkage, Ld、LqAre respectively stator d-axis inductance and q-axis inductance, R is single-phase stator winding resistance,
for the reference value of the electromagnetic torque at time k, p is the pole pair number.
Further, the calculation formula of the electromagnetic torque is as follows:
wherein psifFor rotor permanent magnet flux linkage, Te(k +1) is the electromagnetic torque at the time k +1, p is the number of pole pairs, isq(k +1) is the stator current vector isAnd converting to a q-axis component under a d-q coordinate system.
The converter is a three-phase full-bridge current source type inverter, the inverter comprises a direct current source, the positive pole P of the direct current source is respectively connected with the upper bridge arms of the a phase, the b phase and the c phase, the negative pole N of the direct current source is respectively connected with the lower bridge arms of the a phase, the b phase and the c phase, at least one switch is arranged on each upper bridge arm and each lower bridge arm, and the state combination of the converter is generated by controlling the on-off of each switch.
Further, the capacitor filter is connected in series with the three-phase full-bridge inverter and is arranged between the three-phase full-bridge inverter and the permanent magnet motor.
Further, the method for obtaining the stator current vector output at the time k +1 in step S2 is as follows: firstly, determining the state of each switch on each upper bridge arm and each lower bridge arm at the moment of k +1, representing the state of each switch as 1 when the switch is turned on and 0 when the switch is turned off, and combining the states of the switches and a direct current i according to the state of the switchesdcCalculating the output current vector i of the converteri：
Wherein idcIs a direct current, SaP、SaN、SbP、SbN、ScPAnd ScNThe dynamic equation of the voltage vector on the output capacitor filter is as follows:
wherein isIs the vector of the current flowing through the stator winding of the motor, vsIs the voltage of the capacitive filter.
Further, the equation for obtaining the output voltage of the capacitive filter at the time k +2 corresponding to each state in step S2 is:
wherein v iss(k +1) is the voltage of the capacitive filter at the moment k +1, vs(k) Is the voltage of the capacitive filter at time k, Ts is the sampling period, CfBeing an output capacitive filter of a converter, iiOutputting a current vector for k moment; i.e. isThe vector of current flowing through the stator winding of the motor at time k.
Further, the all-state variable predicted torque control cost function is:
wherein, JfSVA torque control cost function is predicted for the all-state variables,
Te(k +2) are respectively a reference value and a predicted value of the electromagnetic torque at the time k +2, lambdai、λvAnd λuThe weighting coefficients are respectively corresponding to the d-axis current, the voltage of the capacitor filter and the switch action penalty term;
is a d-axis current penalty term for describing the deviation of the d-axis current from 0 at the moment k +2,
describing the output capacitor filter voltage vector v for the output capacitor filter voltage vector penalty terms(k +1) and reference vector
Deviation at time k + 2; |. Δ u (k) |)2And a, b and c are respectively a phase, b phase and c phase of the three-phase full-bridge inverter, which are 2-norm increments of the switching vector.
The invention also discloses a torque control system of the permanent magnet motor, which comprises: the reference value calculating module is used for carrying out one-beat delay compensation on the obtained stator current of the permanent magnet synchronous motor at the current k moment and the filter capacitor voltage of the current source converter to obtain a stator current vector of the stator current at the k +1 moment in a d-q coordinate system; the prediction module is used for calculating a stator current reference value and a filter capacitor voltage reference value at the moment k +2 according to the stator current vector at the moment k +1 and calculating an electromagnetic torque reference value according to a rotating speed controller of a rotating speed outer ring; the output value calculation module is used for constructing a current source converter switch state combination and obtaining a filter capacitor voltage predicted value, a stator current predicted value and an electromagnetic torque predicted value at the k +2 moment according to an output current vector of the current source converter in each switch state; and the control module is used for constructing a cost function of the all-state variable according to the stator current reference value at the k +2 moment, the voltage reference value of the capacitor filter, the electromagnetic torque reference value, the stator current predicted value, the voltage predicted value of the capacitor filter and the electromagnetic torque predicted value, and solving the cost function to obtain the optimal torque control quantity.
Due to the adoption of the technical scheme, the invention has the following advantages:
1. according to the invention, the stator current of the permanent magnet motor and the voltage of the converter capacitor filter are simultaneously controlled, so that the resonance of an LC network is effectively inhibited, the output torque ripple is reduced, and meanwhile, a capacitor voltage control item is added in a cost function, so that the harmonic content of a power supply end is favorably reduced, the influence of wave reflection is weakened, and the control performance is good in the aspects of steady-state output torque ripple inhibition and dynamic torque quick response.
2. The invention provides a torque control strategy considering all-state variable prediction, under the condition of not considering control variables and state variable constraints, an input voltage value for realizing the dead-beat control of electromagnetic torque is solved, the input voltage value is used as a reference value of the voltage of a capacitor filter, the capability of realizing multi-target global optimization control is realized by utilizing model prediction control, a cost function consisting of four punishment items of electromagnetic torque, d-axis current, output capacitor voltage and switching action is constructed, the cascade structure of the traditional controller is simplified, the torque dynamic response is rapid, the energy oscillation between the capacitor filter and a stator inductor is effectively inhibited, and the electromagnetic steady-state torque pulsation is low.
3. According to the invention, by establishing a converter drive permanent magnet motor model and combining the characteristics of model prediction control and a system equivalent circuit, the output torque of the motor and the voltage waveform on a capacitor filter are predicted and controlled, the energy oscillation between the capacitor filter and a stator inductor is inhibited, the system instability caused by resonance is avoided, the system stability is improved, the output torque pulsation is obviously reduced, the service life of a system mechanical component is prolonged, and the EMI noise of the system is effectively reduced.
4. The invention establishes a current transformer drive permanent magnet motor model based on model predictive control for application occasions of medium voltage drive, high power drive, high performance motor drive and the like, realizes resonance suppression of an LC network formed by a current transformer output capacitance filter and a permanent magnet motor stator inductor by an all-state variable prediction method, and improves the reliability of motor drive systems of medium voltage drive, high power drive, high performance motor drive and the like.
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FIG. 1 illustrates a method for controlling the torque of a permanent magnet motor according to an embodiment of the present invention;
fig. 2 is an effective current vector diagram corresponding to a switching state of a current transformer in an embodiment of the present invention, fig. 2(a) is a basic switching current vector diagram of a current source type current transformer, and fig. 2(b) is a current vector coverage area under control of a continuous control set of the current source type current transformer;
FIG. 3 is a circuit diagram of a current transformer in accordance with an embodiment of the present invention;
fig. 4 is a schematic diagram of a dual closed-loop structure of a converter permanent magnet motor control system according to an embodiment of the present invention.
Detailed Description
The present invention is described in detail by way of specific embodiments in order to better understand the technical direction of the present invention for those skilled in the art. It should be understood, however, that the detailed description is provided for a better understanding of the invention only and that they should not be taken as limiting the invention. In describing the present invention, it is to be understood that the terminology used is for the purpose of description only and is not intended to be indicative or implied of relative importance.
Aiming at a converter permanent magnet synchronous motor driving system, the invention provides a torque control strategy considering all-state variable prediction, calculates a reference value of capacitor voltage, utilizes the capability of model prediction control for realizing multi-target control, constructs a cost function consisting of four punishment items of electromagnetic torque, d-axis current, output capacitor voltage and switching action, obtains the effect of global optimization, and simplifies the cascade structure of the traditional controller; in addition, a method of combining theoretical analysis with simulation data is adopted to provide a design rule of a weight coefficient and a sampling frequency corresponding to a switch action penalty term, so that the optimal system performance is ensured. The control strategy in the application has quick torque dynamic response, can effectively inhibit energy oscillation between the capacitor filter and the stator inductor, and has low electromagnetic torque pulsation.
Example one
The embodiment discloses a method for controlling torque of a permanent magnet motor, as shown in fig. 1, comprising the following steps:
s1, carrying out one-beat delay compensation on the obtained stator current of the permanent magnet synchronous motor at the current k moment and the filter capacitor voltage of the current source converter to obtain a stator current vector of the stator current at the k +1 moment in a d-q coordinate system.
In this embodiment, a PMSM electromagnetic model in a continuous time domain is discretized, model prediction control depends on a mathematical model of a controlled object in a discrete time domain to predict a state trajectory at a future time, and when a sampling period is far smaller than a time constant of the controlled object, a first-order Euler method is used to obtain ideal discretization precision, so as to obtain a prediction formula of an output capacitor filter voltage:
wherein v iss(k +1) is the voltage of the capacitive filter at the moment k +1, vs(k) Is the voltage of the capacitive filter at time k, Ts is the sampling period, CfBeing an output capacitive filter of a converter, iiOutputting a current vector for k moment; i.e. isThe vector of current flowing through the stator winding of the motor at time k.
Obtaining a voltage vector v under a d-q coordinate system through coordinate transformations-dq(k+1)＝[vsd(k+1),vsq(k+1)]T(ii) a Then carrying out first-order Euler discretization on the PMSM electromagnetic model to obtain a formula of a stator current vector at the k +1 moment:
in the above formula, k and k +1 represent the current time and the next time, isd(k+1)、isq(k +1) are stator current vectors isConversion to d-and q-axis components, v, in a d-q coordinate systemsd、vsqAre respectively asThe d and q axis voltages of the capacitive filter, omega, are the electrical angular velocity of the rotor flux linkage, psifFor rotor permanent magnet flux linkage, Ld、LqRespectively stator d and q axis inductances, R being a single phase stator winding resistance, TsIs the sampling period.
According to the formula of the stator current vector at the moment k +1, the calculation formula of the electromagnetic torque can be obtained as follows:
wherein psifFor rotor permanent magnet flux linkage, Te(k +1) is the electromagnetic torque at the time k +1, p is the number of pole pairs, isq(k +1) is the stator current vector isAnd (4) converting to a q-axis component in a d-q coordinate system, wherein the d-axis current does not contribute to the electromagnetic torque. According to the permanent magnet synchronous motor model, when the d-axis current isdWhen the torque is zero, the unit current maximum torque control of the permanent magnet synchronous motor can be realized, and the electromagnetic torque T of the motor is realized at the momenteProportional to stator q-axis current isqThus, torque can be directly controlled by controlling the q-axis current. In addition, a voltage reference value of the capacitor filter under a corresponding d-q coordinate system can be obtained through the formula, the multi-objective optimization capacity is controlled by utilizing model prediction, the voltage of the capacitor filter and the current of an output stator are controlled to follow the reference value, the energy oscillation between passive components is restrained, and the stability of the system is improved.
Assuming that the control set is a continuous control set, such as PWM modulation, and neglecting the saturation effect of modulation, an equivalent continuous control set can be obtained, which is mapped to all regions where the effective current vector of the α - β plane is hexagonally covered, as shown in fig. 2. Fig. 2 is an effective current vector diagram corresponding to the switching state of the current transformer in the present embodiment, fig. 2(a) is a basic switching current vector diagram of the current source type current transformer, and fig. 2(b) is a current vector coverage area under the control of the continuous control set of the current source type current transformer. In FIG. 2, α β is a stationary two-phase coordinate system, I1～I6Is an effective current vector of a current source type converter, I0,abcIs zero vectorAmount of the compound (A).
The formula for the stator current vector at time k +1 is converted to a state space form:
x(k+1)＝Ax(k)+Bu(k)+E
wherein x is ═ isd,isq]T，u＝[usd,usq]T，
Since the matrix B is invertible, the input variables must be found within one sampling period:
u＝u*＝B-1(x(k+1)-Ax(k)-E)
the following relationship is satisfied:
Thus, the reference value of the capacitance voltage in d-q coordinates is given by the above equation:
the reference value of the capacitor voltage in the three-phase stationary coordinate system can be obtained by inverse transformation of the acb coordinate system to the dq coordinate system, wherein
The inverse of the transformation matrix for the abc to dq coordinate system:
the reference value of the stator current at the moment k +2 and the reference value of the voltage of the capacitor filter are obtained by the following reference value formulas:
Wherein,
respectively d-axis and q-axis components of the reference value of the stator current vector in a d-q coordinate system,
reference voltages for d and q axes of the capacitive filter, omega the electrical angular velocity of the rotor flux linkage, psifFor rotor permanent magnet flux linkage, Ld、LqAre respectively stator d-axis inductance and q-axis inductance, R is single-phase stator winding resistance,
for the reference value of the electromagnetic torque at time k, p is the pole pair number.
S2, calculating a stator current reference value and a filter capacitor voltage reference value at the moment k +2 according to the stator current vector at the moment k +1, and calculating an electromagnetic torque reference value according to the rotating speed controller of the rotating speed outer ring.
As shown in FIG. 3FIG. 3 is a circuit diagram of the converter in this embodiment, wherein IdcIs a direct side current, iiFor the converter output current, isIs the motor stator current, vsIs a capacitor filter voltage, CfP, N are the positive and negative poles of the direct current side respectively for the filter capacitance value, and PMSM is permanent magnet synchronous motor. The inverter in fig. 3 is a three-phase full-bridge current source type inverter, and includes a dc current source, the positive pole P of the dc current source is connected to the upper bridge arms of the a-phase, the b-phase and the c-phase, the negative pole N of the dc current source is connected to the lower bridge arms of the a-phase, the b-phase and the c-phase, at least one switch is disposed on each of the upper bridge arm and the lower bridge arm, and the state combination of the inverter is generated by controlling the on/off of each switch. The capacitor filter is connected with the three-phase full-bridge inverter in series and is arranged between the three-phase full-bridge inverter and the permanent magnet motor. Wherein the switch is a symmetrical gate commutated thyristor SGCT with reverse voltage blocking capability or is formed by connecting an insulated gate bipolar transistor IGBT and a diode in series, CfThe output capacitor filter of the converter can filter the high-frequency component of the current on the converter side while providing a follow current loop for the load.
In the permanent magnet synchronous motor, a stator winding can be equivalent to an inductive resistor series circuit, and the stator winding and a converter output capacitor filter CfForming an RLC series circuit having a resonant frequency
Wherein L is the stator winding inductance when the harmonic frequency in the drive system approaches the resonant frequency f of the circuit0In time, the harmonic current is further amplified, which leads to high-frequency oscillation of the output torque of the system and even instability of the system.
In this embodiment, the switch state combination for constructing the converter needs to satisfy the condition that, firstly, the dc side of the converter is a current source property, so that the selection of the switch combination state for opening the dc side is avoided, and secondly, the ac side of the converter is a voltage source property due to the existence of the ac side output capacitor of the converter, so that the selection of the switch combination state for short-circuiting the ac side is avoided. Based on the above two constraintsAnd (3) defining a control vector of u ═ S in 9 effective switch combination states which can be formed by the switches on each bridge arm of the converterAP,SAN,SBP,SBN,SCP,SCNE.u, the details of the combination states of the 9 valid switches are shown in table 1.
The switching function of the converter power device is:
wherein x is a, b, c, j is P, N. P is a power switch at the upper side of the bridge arm, and N is a power switch at the lower side.
TABLE 1 converter active switch combination state table
According to the above-mentioned 9 switch state combinations and DC current idcCalculating the output current vector i of the converteri＝[iA,iB,iC]T：
The method for obtaining the stator current vector output at the time k +1 in step S2 includes: firstly, determining the state of each switch on each upper bridge arm and each lower bridge arm at the moment of k +1, representing the state of each switch as 1 when the switch is turned on and 0 when the switch is turned off, and combining the states of the switches and a direct current i according to the state of the switchesdcCalculating the output current vector i of the converteri。
Voltage vector v on output capacitor filters＝[vsA,vsB,vsC]TThe kinetic equation of (a) is:
wherein isIs the vector of the current flowing through the stator winding of the motor, vsIs the voltage of the capacitive filter.
The equation for obtaining the output voltage of the capacitive filter at the time k +2 corresponding to each state in step S2 is:
wherein v iss(k +2) is the voltage of the capacitive filter at time k +2, vs(k) Is the voltage of the capacitive filter at the moment k +1, Ts is the sampling period, CfBeing an output capacitive filter of a converter, iiOutputting a current vector at the k +1 moment; i.e. isThe vector of current flowing through the stator winding of the motor at time k + 1.
S3, current source converter switch state combination is constructed, and a filter capacitor voltage predicted value, a stator current predicted value and an electromagnetic torque predicted value at the k +2 moment are obtained according to output current vectors of the current source converters in the switch states.
S4, constructing a cost function of the all-state variable according to the stator current reference value at the k +2 moment, the voltage reference value of the capacitor filter, the electromagnetic torque reference value, the stator current predicted value, the voltage predicted value of the capacitor filter and the electromagnetic torque predicted value, and solving the cost function to obtain the optimal torque control quantity. And obtaining the state of each switch in the converter corresponding to the optimal torque control quantity, and applying each switch state to the switch of the current source converter so as to control the permanent magnet synchronous motor to output the optimal torque.
Wherein the all-state variable predicted torque control cost function is:
wherein, JFSVA torque control cost function is predicted for the all-state variables,
Te(k +2) are respectively a reference value and a predicted value of the electromagnetic torque at the time k +2, lambdai、λvAnd λuThe weighting coefficients are respectively corresponding to the d-axis current, the voltage of the capacitor filter and the switch action penalty term;
is a d-axis current penalty term for describing the deviation of the d-axis current from 0 at the moment k +2,
describing the output capacitor filter voltage vector v for the output capacitor filter voltage vector penalty terms(k +1) and reference vector
Deviation at time k + 2; |. Δ u (k) |)2And a, b and c are respectively a phase, b phase and c phase of the three-phase full-bridge inverter, which are 2-norm increments of the switching vector.
The cost function achieves the following control objectives: an electromagnetic torque tracking reference value; d-axis current is 0; a capacitor voltage tracking reference value; the switching frequency is reduced. Enumerating all control elements in each sampling period, obtaining the optimal solution of the torque cost function, directly acting the obtained optimal solution on a power switch of the current source converter,
the method has the advantages that the system model can be used for predicting the change of the variable at the future moment, the method has quick transient response capability, the coupling variable is easy to be restrained, the multi-target control is easy to realize, and the steady-state performance and the transient performance of the system can be considered at the same time. As shown in fig. 4, fig. 4 is a double closed loop junction of the control system of the permanent magnet motor of the inverter in this embodimentA schematic diagram of the structure wherein
ωrRespectively a reference value and an actual value of the rotating speed of the motor,
is a reference value of electromagnetic torque of the motor, thetarFor the rotor position angle of the machine, u is the optimal converter switching vector of the output, vs、isRespectively, the capacitor filter voltage and the motor stator current, the CSC is a current source type converter, and the integral factor dt is an integral link. The double closed loop structure comprises a rotating speed outer loop and a predictive control inner loop. The rotating speed outer ring obtains a torque reference value through a torque controller, the torque tracking of the inner ring is realized by directly triggering a power switch through an output rotating speed controller, and meanwhile, the output torque controller reduces the switching frequency as far as possible; the state variable trajectory prediction link can deduce the state variable after n control periods in the future according to the state quantity at the current moment obtained by the measuring device through a state equation obtained by modeling the system, and the cost function minimization link calculates the optimal switching vector of the n control periods in the future by using the state variable after the n control periods in the future corresponding to the minimized cost function.
The embodiment provides an all-State Variable Predictive Torque Control (FSV-PTC) aiming at a permanent magnet synchronous driving system of a current source converter, by controlling the output torque (stator current) and the voltage of the capacitor filter at the same time, the resonance of the LC network is effectively inhibited, the output torque ripple is obviously reduced, the EMI noise of the system is reduced, meanwhile, as the capacitance voltage control item is added in the objective function, the harmonic content of the power supply end is further reduced in the application scene of long cable driving, the influence of wave reflection is further weakened, the natural rapid dynamic response characteristic of predictive control is inherited, meanwhile, the relation among the sampling frequency, the switch penalty term weight coefficient and the switching frequency is analyzed, a theoretical basis is provided for the design of the current source converter, and the FSV-PTC has good control performance in the aspects of steady-state output torque ripple suppression and rapid dynamic torque response.
Example two
Based on the same inventive concept, the embodiment discloses a torque control system of a permanent magnet motor, which comprises:
the reference value calculating module is used for carrying out one-beat delay compensation on the obtained stator current of the permanent magnet synchronous motor at the current k moment and the filter capacitor voltage of the current source converter to obtain a stator current vector of the stator current at the k +1 moment in a d-q coordinate system;
the prediction module is used for calculating a stator current reference value and a filter capacitor voltage reference value at the moment k +2 according to the stator current vector at the moment k +1 and calculating an electromagnetic torque reference value according to a rotating speed controller of a rotating speed outer ring;
the output value calculation module is used for constructing a current source converter switch state combination and obtaining a filter capacitor voltage predicted value, a stator current predicted value and an electromagnetic torque predicted value at the k +2 moment according to an output current vector of the current source converter in each switch state;
and the control module is used for constructing a cost function of the all-state variable according to the stator current reference value at the k +2 moment, the voltage reference value of the capacitor filter, the electromagnetic torque reference value, the stator current predicted value, the voltage predicted value of the capacitor filter and the electromagnetic torque predicted value, and solving the cost function to obtain the optimal torque control quantity.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims. The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application should be defined by the claims.
Claims (10)
1. A torque control method of a permanent magnet motor is characterized by comprising the following steps:
s1, carrying out one-beat delay compensation on the obtained stator current of the permanent magnet synchronous motor at the current k moment and the filter capacitor voltage of the current source converter to obtain a stator current vector of the stator current at the k +1 moment in a d-q coordinate system;
s2, calculating a stator current reference value and a filter capacitor voltage reference value at the moment k +2 according to the stator current vector at the moment k +1, and calculating an electromagnetic torque reference value according to a rotating speed controller of a rotating speed outer ring;
s3, constructing a current source converter switch state combination, and obtaining a filter capacitor voltage predicted value, a stator current predicted value and an electromagnetic torque predicted value at the k +2 moment according to an output current vector of the current source converter in each switch state;
s4, constructing a cost function of the all-state variable according to the stator current reference value at the k +2 moment, the voltage reference value of the capacitor filter, the electromagnetic torque reference value, the stator current predicted value, the voltage predicted value of the capacitor filter and the electromagnetic torque predicted value, and solving the cost function to obtain the optimal torque control quantity.
2. The torque control method of the permanent magnet motor according to claim 1, wherein the formula for obtaining the stator current vector at the time k +1 in the step S1 is as follows:
where k, k +1 denote the current time and the next time, isd(k+1)、isq(k +1) are stator current vectors isConversion to d-and q-axis components, v, in a d-q coordinate systemsd、vsqThe d-axis voltage and the q-axis voltage of the capacitive filter, omega the electrical angular velocity of the rotor flux linkage, psifFor rotor permanent magnet flux linkage, Ld、LqRespectively stator d and q axis inductances, R being a single phase stator winding resistance, TsIs the sampling period.
3. The torque control method of the permanent magnet motor according to claim 2, wherein the formula for obtaining the stator current reference value at the time k +2 and the voltage reference value of the capacitor filter in step S1 is as follows:
Wherein,
respectively d-axis and q-axis components of the reference value of the stator current vector in a d-q coordinate system,
reference voltages for d and q axes of the capacitive filter, omega the electrical angular velocity of the rotor flux linkage, psifFor rotor permanent magnet flux linkage, Ld、LqAre respectively stator d-axis inductance and q-axis inductance, R is single-phase stator winding resistance,
is an electromagnetic rotorThe reference value of moment at time k, p is the pole pair number.
4. The permanent magnet motor torque control method of claim 3, wherein the electromagnetic torque is calculated by the formula:
wherein psifFor rotor permanent magnet flux linkage, Te(k +1) is the electromagnetic torque at the time k +1, p is the number of pole pairs, isq(k +1) is the stator current vector isAnd converting to a q-axis component under a d-q coordinate system.
5. The torque control method for the permanent magnet motor according to any one of claims 1 to 4, wherein the converter is a three-phase full-bridge current source type inverter, the inverter includes a direct current source, the positive pole P of the direct current source is connected to the upper arms of the a-phase, the b-phase and the c-phase, the negative pole N of the direct current source is connected to the lower arms of the a-phase, the b-phase and the c-phase, at least one switch is arranged on each of the upper arms and the lower arms, and the combination of the states of the converter is generated by controlling the on/off of each switch.
6. The permanent magnet motor torque control method of claim 5 wherein the capacitive filter is in series with the three-phase full-bridge inverter and is disposed between the three-phase full-bridge inverter and the permanent magnet motor.
7. The torque control method of the permanent magnet motor according to claim 5, wherein the method for obtaining the stator current vector outputted at the time k +1 in the step S2 is: firstly, determining the state of each switch on each upper bridge arm and each lower bridge arm at the moment of k +1, representing the state of each switch as 1 when the switch is turned on and 0 when the switch is turned off, and combining the states of the switches and a direct current i according to the state of the switchesdcCalculating the output current vector i of the converteri：
Wherein idcIs a direct current, SaP、SaN、SbP、SbN、ScPAnd ScNThe dynamic equation of the voltage vector on the output capacitor filter is as follows:
wherein isIs the vector of the current flowing through the stator winding of the motor, vsIs the voltage of the capacitive filter.
8. The torque control method of the permanent magnet motor according to claim 7, wherein the formula for obtaining the output voltage of the capacitor filter at the time k +2 corresponding to each state in step S2 is as follows:
wherein v iss(k +1) is the voltage of the capacitive filter at the moment k +1, vs(k) Is the voltage of the capacitive filter at time k, Ts is the sampling period, CfBeing an output capacitive filter of a converter, iiOutputting a current vector for k moment; i.e. isThe vector of current flowing through the stator winding of the motor at time k.
9. The permanent magnet motor torque control method of claim 5 wherein said all-state variable predicted torque control cost function is:
the all-state variable predicted torque control cost function is:
wherein, JFSVA torque control cost function is predicted for the all-state variables,
Te(k +2) are respectively a reference value and a predicted value of the electromagnetic torque at the time k +2, lambdai、λvAnd λuThe weighting coefficients are respectively corresponding to the d-axis current, the voltage of the capacitor filter and the switch action penalty term;
is a d-axis current penalty term for describing the deviation of the d-axis current from 0 at the moment k +2,
describing the output capacitor filter voltage vector v for the output capacitor filter voltage vector penalty terms(k +1) and reference vector
Deviation at time k + 2; | Δ u (k) | non-woven phosphor2And a, b and c are respectively a phase, b phase and c phase of the three-phase full-bridge inverter, which are 2-norm increments of the switching vector.
10. A permanent magnet motor torque control system, comprising:
the reference value calculating module is used for carrying out one-beat delay compensation on the obtained stator current of the permanent magnet synchronous motor at the current k moment and the filter capacitor voltage of the current source converter to obtain a stator current vector of the stator current at the k +1 moment in a d-q coordinate system;
the prediction module is used for calculating a stator current reference value and a filter capacitor voltage reference value at the moment k +2 according to the stator current vector at the moment k +1 and calculating an electromagnetic torque reference value according to a rotating speed controller of a rotating speed outer ring;
the output value calculation module is used for constructing a current source converter switch state combination and obtaining a filter capacitor voltage predicted value, a stator current predicted value and an electromagnetic torque predicted value at the k +2 moment according to an output current vector of the current source converter in each switch state;
and the control module is used for constructing a cost function of the all-state variable according to the stator current reference value at the k +2 moment, the voltage reference value of the capacitor filter, the electromagnetic torque reference value, the stator current predicted value, the voltage predicted value of the capacitor filter and the electromagnetic torque predicted value, and solving the cost function to obtain the optimal torque control quantity.
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| CN114039520A (en) * | 2021-10-28 | 2022-02-11 | 中海石油(中国)有限公司 | Current source type converter driving asynchronous motor torque control method and system |
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