Small-inductance axial flux permanent magnet synchronous motor variable duty ratio hysteresis control system and method

Abstract

The invention discloses a variable duty ratio hysteresis control system and method for a small-inductance axial flux permanent magnet synchronous motor, and relates to the technical field of motor control, and the method comprises the steps: S1, obtaining a current pulsation value under the control of a conventional hysteresis control system when the permanent magnet synchronous motor is connected with different inductors in series, and drawing a relation curve; s2, determining a critical inductance value according to the maximum curvature point of the drawn current pulsation value and inductance value change relation curve of the series inductor, and selecting an optimal inductance value of series connection; s3, the permanent magnet synchronous motor is connected to the optimal inductance value in series, and the duty ratio is calculated; s4, performing variable duty ratio control according to the calculated duty ratio; according to the method, the duty ratio is introduced into a hysteresis control strategy, and on the premise that the sampling frequency is kept unchanged, the switching action frequency of the inverter is improved, so that the current increasing or decreasing time is shortened, and the magnitude of current pulsation is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and particularly to a variable duty cycle hysteresis control system and method for a small inductance axial flux permanent magnet synchronous motor. Background Art

[0002] Permanent magnet synchronous motors have been widely developed in recent years. Among them, axial flux permanent magnet synchronous motors have received extensive attention in fields such as aerospace, electric vehicles, and high-end industrial drives due to their advantages of compact structure, high power density, and high efficiency. Compared with traditional radial flux motors, axial flux motors can achieve higher torque density within a shorter axial dimension, giving them obvious advantages in application scenarios with strict requirements for weight and volume.

[0003] In addition, axial flux permanent magnet synchronous motors have a small inductance, which improves the dynamic response speed of the motor and is beneficial to the realization of high-performance control. However, due to the small inductance, the winding current is very sensitive to changes in the terminal voltage, resulting in increased current control difficulty and easy increase in current ripple, thus affecting the control accuracy and operation stability of the motor.

[0004] The traditional hysteresis control strategy is to subtract the actual current i from the reference current i*, and compare it with the hysteresis width H. If i - i* > H, the hysteresis control output is the on signal V on ; if i - i* < -H, the hysteresis control output is the on signal V off . Therefore, hysteresis control has the advantages of simple structure, fast dynamic response, and strong anti-interference ability. However, due to the small winding inductance of axial flux permanent magnet synchronous motors, the winding current changes quickly, and the simple hysteresis control logic cannot make the inverter bridge arms cooperate. A better hysteresis control effect depends on a higher sampling frequency and switching frequency. However, in actual use, considering the on-off loss and the calculation burden of the control system, the sampling frequency of the commonly used A / D sampling module and the inverter switching frequency usually cannot be designed too high, generally 5kHz, 10kHz, 15kHz. Therefore, it is difficult for hysteresis control to effectively suppress the current change rate at the conventional control frequency, resulting in too high current pulsation in the winding, manifested as high-frequency and high-amplitude interference signals. Therefore, in axial flux permanent magnet synchronous motors with small inductance characteristics, the traditional hysteresis control strategy is difficult to be effectively applied. Summary of the Invention

[0005] The purpose of the present invention is to provide a variable duty cycle hysteresis control system and method for a small inductance axial flux permanent magnet synchronous motor, so as to solve the problem that the traditional hysteresis control strategy is difficult to be applied in axial flux permanent magnet synchronous motors with small inductance characteristics.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A variable duty cycle hysteresis control method for a small inductance axial flux permanent magnet synchronous motor, comprising the following steps:

[0008] Step S1: Obtain the current pulsation values of the permanent magnet synchronous motor under the control of a traditional hysteresis control system when different inductances are connected in series to the permanent magnet synchronous motor, and plot the relationship curve between the current pulsation values and the inductance values of the series inductances;

[0009] Step S2: Determine the critical inductance value according to the maximum curvature point of the plotted relationship curve between the current pulsation value and the change of the inductance value of the series inductance, and select the optimal inductance value to be connected in series on the right side of the critical inductance value;

[0010] Step S3: Connect the inductance with the optimal inductance value in series to the permanent magnet synchronous motor, and calculate the duty cycle when the permanent magnet synchronous motor is working;

[0011] Step S4: Perform variable duty cycle control according to the calculated duty cycle to weaken the current pulsation.

[0012] As a further scheme of the present invention: the obtaining of the current pulsation values of the permanent magnet synchronous motor under the control of a traditional hysteresis control system when different inductances are connected in series to the permanent magnet synchronous motor comprises the following steps:

[0013] Step SA1: Obtain the number of pole pairs p of the permanent magnet synchronous motor, the amplitude ψ of the permanent magnet flux linkage f , the switching frequency f of the power device under the control of the traditional hysteresis control system sw , the inductance value L of the series inductance d , the winding inductance value L of the permanent magnet synchronous motor p , the bus voltage U of the inverter dc , the current i of the permanent magnet synchronous motor d and the rotor position signal θ of the permanent magnet synchronous motor;

[0014] Step SA2: Perform coordinate transformation on the current i of the permanent magnet synchronous motor d to obtain the q-axis current value i q , and calculate the rotational speed n according to the rotor position signal θ of the permanent magnet synchronous motor, and calculate the electrical angular velocity ω of the permanent magnet synchronous motor according to the angular velocity formula through the rotational speed n e ;

[0015] Step SA3: Calculate the current pulsation value Δi according to the formula .

[0016] As a further scheme of the present invention: the calculation formula for the rotational speed n in the step SA2 is:

[0017]

[0018] Where Δθ is the difference between the rotor position signal obtained by the position sensor and the rotor position signal obtained in the previous time, and ΔT is the time interval between two acquisitions by the position sensor;

[0019] In the step SA2, the angular velocity formula is: ω e = 2πpn / 60.

[0020] As a further solution of the present invention: the curvature C calculation formula of the relationship curve between the current pulsation value and the inductance value of the series inductor in the step S2 is:

[0021]

[0022] As a further solution of the present invention: calculating the duty cycle includes the following steps:

[0023] Step SB1, obtaining the number of pole pairs p of the permanent magnet synchronous motor, the permanent magnet flux linkage amplitude ψ f , the optimal inductance value L s , the winding inductance value L of the permanent magnet synchronous motor p , the sampling frequency f of the A / D sampling module swp , the current i of the permanent magnet synchronous motor s , the rotor position signal θ of the permanent magnet synchronous motor S , the bus voltage U of the inverter dc ;

[0024] Step SB2, performing coordinate transformation on the obtained current i of the permanent magnet synchronous motor s to obtain the q-axis current value i qs , and calculating the rotational speed n according to the rotor position signal θ of the permanent magnet synchronous motor S , S ,

[0025] Step SB3, performing hysteresis logic judgment on the q-axis current value i qs , and the judgment process is: subtracting the q-axis current value i qs from the set reference current i * , and comparing it with the set hysteresis width H. If i qs - i * > H, the output is the on signal V on ; if i qs - i * < -H, the output is the on signal V off ;

[0026] Step SB4, calculating the duty cycle D s .

[0027] As a further solution of the present invention: the duty cycle D sThe calculation formula is as follows:

[0028]

[0029] When D s is greater than 1 in the calculated value, then the value of D s is taken as 1; when D s is less than 0 in the calculated value, then the value of D s is taken as 0, where x is a proportionality coefficient, and the value range of x is 3 - 8, and V sw is a switching logic signal output after hysteresis logic judgment.

[0030] As a further solution of the present invention: the variable duty cycle control is performed according to the calculated duty cycle, including obtaining the corresponding square wave switching signal according to the duty cycle D s , then performing level conversion on the square wave switching signal to match the voltage level of the power circuit, and outputting the square wave switching signal to the inverter, so as to achieve variable duty cycle control.

[0031] As a further solution of the present invention: a variable duty cycle hysteresis control system for a small inductor axial flux permanent magnet synchronous motor, which executes the above-mentioned variable duty cycle hysteresis control method for a small inductor axial flux permanent magnet synchronous motor, is characterized by including a main power circuit, a control circuit, a driving module and a sensor module; the main power circuit is connected to the permanent magnet synchronous motor, the sensor module is arranged on the permanent magnet synchronous motor, the sensor module is electrically connected to the control circuit, the control circuit is electrically connected to the driving module, and the driving module is electrically connected to the main power circuit.

[0032] As a further solution of the present invention: the main power circuit includes a DC power supply U ab and an inverter. The positive pole of the DC power supply U ab is connected to the positive pole of the DC power input end of the inverter, the negative pole of the DC power supply U ab is connected to the negative pole of the DC power input end of the inverter, and two groups of bus capacitors C ab are connected in parallel between the DC power supply U p and the inverter. The two groups of bus capacitors C p are connected in series with each other, and an inductor L1 is connected to the output end of the inverter. The other end of the inductor L1 is connected to the winding L2 of the permanent magnet synchronous motor, and the control signal input end g of the inverter is connected to the driving module;

[0033] The sensor module includes a current sensor, a voltage sensor and a position sensor.

[0034] As a further solution of the present invention: the control circuit includes an A / D sampling module, a hysteresis control module, a duty cycle calculation module and a PWM generation module:

[0035] The A / D sampling module is used to receive the bus voltage of the inverter, the permanent magnet synchronous motor current, and the permanent magnet synchronous motor rotor position signal collected by the sensor module from the main power circuit, perform coordinate transformation on the collected permanent magnet synchronous motor current to obtain the q-axis current value, calculate the rotational speed according to the rotor position signal of the permanent magnet synchronous motor, output the q-axis current value to the hysteresis control module and the duty cycle calculation module, and output the bus voltage and rotational speed of the inverter to the duty cycle calculation module;

[0036] The hysteresis control module is used to receive the q-axis current value output by the A / D sampling module, perform hysteresis logic judgment, and output the corresponding turn-on signal V on or turn-on signal V off to the duty cycle calculation module;

[0037] The duty cycle calculation module is used to receive the turn-on signal V on or turn-on signal V off , as well as the q-axis current value, the bus voltage of the inverter, and the rotational speed output by the A / D sampling module, and output the duty cycle to the PWM generation module;

[0038] The PWM generation module is used to receive the duty cycle output by the duty cycle calculation module, generate a square wave switching signal with this duty cycle and output it to the drive module for level conversion and isolation protection;

[0039] The drive module is responsible for performing level conversion on the square wave switching signal to match the voltage level of the main power circuit, outputting the square wave switching signal to the inverter control signal terminal, and weakening current pulsation.

[0040] Advantages of the present invention:

[0041] A variable duty cycle hysteresis control system and method for a small inductance permanent magnet synchronous motor proposed by the present invention uses a series inductor to increase the equivalent inductance of the winding circuit, weaken the current change rate, and reduce current ripple. Moreover, by introducing the duty cycle into the hysteresis control strategy, the control process in the traditional hysteresis control system, which is "sample once, calculate once, and output a single-level control signal", is changed to output a control signal with a high and low varying level. This enables the inverter switch tubes, which originally maintain a single on or off state between two samplings, to have an additional switch state transition. Thus, on the premise that the sampling frequency of the A / D sampling module remains unchanged, the switching operation frequency of the inverter is increased, thereby shortening the time for the current to increase or decrease, and further reducing the magnitude of the current ripple. At the same time, the duty cycle introduced into the hysteresis control strategy in the present invention can also be adjusted according to the real-time operating conditions of the motor to ensure the stable operation of the motor under different working conditions. The variable duty cycle hysteresis control system and method for a small inductance permanent magnet synchronous motor proposed by the present invention gives the calculation method of the inductance value of the series inductor and the real-time calculation method of the duty cycle in the variable duty cycle hysteresis control strategy, which has a guiding role in suppressing the current ripple under the hysteresis control of a small inductance axial flux permanent magnet synchronous motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be further described below with reference to the accompanying drawings.

[0043] Figure 1 is a schematic flow chart of the variable duty cycle hysteresis control method of the present invention;

[0044] Figure 2 is a schematic diagram of the principle structure of the variable duty cycle hysteresis control system of the present invention;

[0045] Figure 3 is a schematic diagram of the control logic of the hysteresis control module of the present invention;

[0046] Figure 4 is a schematic diagram of the current waveforms of the dual three-phase YASA axial flux permanent magnet synchronous motor used in the present invention when different inductance values are connected in series;

[0047] Figure 5 is a schematic diagram of the relationship between the inductance value connected in series and the current ripple value of the dual three-phase YASA axial flux permanent magnet synchronous motor used in the present invention;

[0048] Figure 6 is a schematic diagram of the calculation results of the duty cycle calculation module of the dual three-phase YASA axial flux permanent magnet synchronous motor system used in the present invention;

[0049] Figure 7 is a schematic diagram of the comparison of the motor phase current waveforms under the variable duty cycle hysteresis control strategy and the traditional hysteresis control strategy used in the present invention;

[0050] Figure 8 It is a schematic diagram comparing the phase current waveforms between the traditional hysteresis control with only series inductance in the present invention and the hysteresis control with series inductance and variable duty cycle in the present invention;

[0051] Figure 9 It is a schematic diagram of the duty cycle calculation results in the case of sudden increase and decrease of the load at the motor load end in the present invention;

[0052] Figure 10 It is a schematic diagram of the speed waveform in the case of sudden increase and decrease of the load at the motor load end in the present invention;

[0053] Figure 11 It is a schematic diagram of the three-phase current waveforms in the case of sudden increase and decrease of the load at the motor load end in the present invention;

[0054] Figure 12 It is a schematic diagram of the electromagnetic torque waveforms in the case of sudden increase and decrease of the load at the motor load end in the present invention;

[0055] Figure 13 It is a schematic diagram of the duty cycle calculation results in the case of sudden acceleration and deceleration of the motor in the present invention;

[0056] Figure 14 It is a schematic diagram of the speed waveform in the case of sudden acceleration and deceleration of the motor in the present invention;

[0057] Figure 15 It is a schematic diagram of the three-phase current waveforms in the case of sudden acceleration and deceleration of the motor in the present invention;

[0058] Figure 16 It is a schematic diagram of the electromagnetic torque waveforms in the case of sudden acceleration and deceleration of the motor in the present invention. Detailed implementation manners

[0059] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0060] Embodiment 1

[0061] As Figure 1 shown, this embodiment provides a variable duty cycle hysteresis control method for a small inductor axial flux permanent magnet synchronous motor, including the following steps:

[0062] Step S1: Obtain the current ripple values of the permanent magnet synchronous motor under the control of the traditional hysteresis control system when different inductors are connected in series to the permanent magnet synchronous motor, and draw a relationship curve between the current ripple values and the inductance values of the series inductors;

[0063] It should be noted that the difference between the different inductances connected in series to the permanent magnet synchronous motor lies only in the inductance value, and the traditional hysteresis control system is prior art (reference can be made to Chinese Patent CN206564553U), and the specific system structure and control logic will not be elaborated here.

[0064] Preferably, when obtaining the different inductances connected in series to the permanent magnet synchronous motor, the current ripple values of the permanent magnet synchronous motor under the control of the traditional hysteresis control system are obtained through the following steps:

[0065] Step SA1, obtain the number of pole pairs p of the permanent magnet synchronous motor, the amplitude ψ of the permanent magnet flux linkage f , the switching frequency f of the power device under the control of the traditional hysteresis control system sw , the inductance value L of the series inductance d , the winding inductance value L of the permanent magnet synchronous motor p , the bus voltage U of the inverter dc , the current i of the permanent magnet synchronous motor d and the rotor position signal θ of the permanent magnet synchronous motor;

[0066] It should be explained that the number of pole pairs p of the permanent magnet synchronous motor, the amplitude ψ of the permanent magnet flux linkage f , the winding inductance value L of the permanent magnet synchronous motor p are obtained through the nameplate or product manual of the permanent magnet synchronous motor;

[0067] It should be noted that the above-mentioned power device is a power switching device such as IGBT or MOSFET in the inverter.

[0068] The switching frequency f of the power device under the control of the traditional hysteresis control system sw is equal to the sampling frequency of the A / D sampling module in the traditional hysteresis control system, and the sampling frequency is designed by the user, generally 5kHz, 10kHz, 15kHz;

[0069] The bus voltage U of the inverter dc is obtained by the voltage sensor on the permanent magnet synchronous motor.

[0070] Step SA2, perform coordinate transformation on the obtained current i of the permanent magnet synchronous motor d to obtain the q-axis current value i q , and calculate the rotational speed n based on the rotor position signal θ of the permanent magnet synchronous motor, and calculate the electrical angular velocity ω of the permanent magnet synchronous motor according to the angular velocity formula through the rotational speed n e ;

[0071] Among them, the current i d is obtained by the Hall current sensor on the permanent magnet synchronous motor, and the Clark transformation and Park transformation are used to obtain the q-axis current value iq , the specific transformation method is the prior art. For details, please refer to "Small & Special Electrical Machines - Vol. 49, No. 4, 2021 - Sorting out and Discriminating the ABC to dq0 Coordinate Transformation in Motors - Fu Xinghe, Chen Rui".

[0072] Among them, the rotor position signal θ of the permanent magnet synchronous motor is obtained by a position sensor (photoelectric encoder or resolver) on the permanent magnet synchronous motor. The calculation formula for the rotational speed n is:

[0073]

[0074] In the above formula, Δθ is the difference between the rotor position signal obtained by the position sensor and the rotor position signal obtained in the previous acquisition, and ΔT is the time interval between two acquisitions by the position sensor.

[0075] Furthermore, the angular velocity formula is: ω e = 2πpn / 60.

[0076] Step SA3, according to the formula calculate the current ripple value Δi:

[0077] Among them, the current ripple value Δi represents the current regulation amplitude within one switching tube operation cycle.

[0078] Preferably, plotting the relationship curve between the current ripple value and the inductance value of the series inductor includes: obtaining the corresponding current ripple values when different inductors are connected in series to the permanent magnet synchronous motor, and using software with plotting functions such as Python or Matlab or Excel to plot the relationship curve between the current ripple value and the change of the inductance value of the series inductor. The plotting method is the prior art and will not be elaborated here.

[0079] It should be noted that the inductance value L of the series inductor adopted in this embodiment d is selected at intervals of 0.1 mH within the range of 0 mH to 10 mH;

[0080] Step S2: Determine the critical inductance value L according to the maximum curvature point of the relationship curve between the current ripple value and the inductance value of the series inductor plotted in Step S1 c , and select the optimal inductance value L to be connected in series on the right side of the critical inductance value L c . s .

[0081] It should be explained that as the inductance value L of the series inductor d increases, the current ripple suppression effect tends to be "saturated". Moreover, increasing the inductance value L without limit dThis will cause a sharp increase in the mass, volume and economic cost of the motor system. Therefore, in practical applications, considering the volume and mass of the inductor and the suppression effect of increasing the inductor value on the current ripple, the appropriate optimal inductor value L is selected. s , such as Figure 5 shown, select the optimal inductor value L c on the right side of the critical inductor value L s .

[0082] Preferably, the calculation method of the curvature C of the relationship curve between the current ripple value and the inductor value of the series inductor is as follows:

[0083]

[0084] According to the calculated curvature value, use software with plotting functions such as Python or Matlab or Excel to plot the relationship curve between the curvature and the series inductor value, and confirm the maximum curvature point and the corresponding critical inductor value L c .

[0085] Step S3: Connect the inductor with the optimal inductor value L s obtained in step S2 in series with the permanent magnet synchronous motor, and calculate the duty cycle when the permanent magnet synchronous motor is working.

[0086] Preferably, calculating the duty cycle includes the following steps:

[0087] Step SB1, obtain the number of pole pairs p of the permanent magnet synchronous motor, the amplitude of the permanent magnet flux linkage ψ f , the optimal inductor value L s , the winding inductor value L p of the permanent magnet synchronous motor, the sampling frequency f swp of the A / D sampling module, the current i s of the permanent magnet synchronous motor, the rotor position signal θ S of the permanent magnet synchronous motor, and the bus voltage U dc of the inverter;

[0088] Step SB2, perform coordinate transformation on the obtained current i s of the permanent magnet synchronous motor to obtain the q-axis current value i qs , and calculate the rotational speed n S according to the rotor position signal θ S of the permanent magnet synchronous motor,

[0089] where the current i s is obtained by the Hall current sensor on the permanent magnet synchronous motor, and the Clark transformation and Park transformation are used to obtain the q-axis current value i qs , and the specific transformation method is as described in step SA2;

[0090] Among them, the rotor position signal θ of the permanent magnet synchronous motor S is obtained by the position sensor on the permanent magnet synchronous motor, and the rotational speed n is calculated according to the formula S :

[0091]

[0092] In the above formula, Δθ S is the difference between the rotor position signal obtained by the position sensor after connecting the optimal inductance value L s and the rotor position signal obtained in the previous time, and ΔT is the time interval between two acquisitions by the position sensor.

[0093] Step SB3, perform hysteresis logic judgment on the q-axis current value i qs Specifically: subtract the set reference current i qs from the q-axis current value i * , and compare it with the set hysteresis width H. If i qs - i * > H, the hysteresis control output is the on signal V on ; if i qs - i * < -H, the hysteresis control output is the on signal V off .

[0094] Step SB4, calculate the duty cycle D s ,

[0095] According to the current regulation ability K, which is the product of the number of hysteresis logic judgments m within each 1 / 4 electrical cycle and the current amplitude that can be adjusted after each logic judgment, the expression of K is obtained as:

[0096] K = m·[D s Δi s -(1 - D s )Δi s ;

[0097] Among them, the expression of the number of hysteresis logic judgments m is:

[0098]

[0099] Among them, after connecting the optimal inductance value L s , the expression of the current ripple value Δi s is:

[0100]

[0101] And among them, after connecting the optimal inductance value L s , the expression of the electrical angular velocity ω es is:

[0102] ω es = 2πpn s / 60

[0103] Then the complete expression of the current regulation ability K is:

[0104]

[0105] And the current regulation ability K is designed to be x times the q-axis current value i qs From K = x·i qs , the expression of the duty cycle D s is obtained:

[0106]

[0107] When the calculated value of D s is greater than 1, then the value of D s is 1; when the calculated value of D s is less than 0, then the value of D s is 0, and V sw is the switching logic signal output after the hysteresis logic judgment in step SB3.

[0108] In another preferred embodiment, a correction coefficient y can be introduced into the duty cycle to improve the control effect. The expression of the duty cycle D s after introducing the correction coefficient y is:

[0109]

[0110] When the calculated value of D s is greater than 1, then the value of D s is 1; when the calculated value of D s is less than 0, then the value of D s is 0.

[0111] It should be explained that, through a large number of simulations and experimental verifications, in order to ensure the speed regulation range and current ripple suppression effect of the permanent magnet synchronous motor under this embodiment as much as possible, the value range of x should be between 3 and 8, and the value of y is taken as 0.08 - 0.15. If the operating speed or load torque of the permanent magnet synchronous motor to be controlled is relatively low, larger x and y are selected; if the operating speed or load torque of the permanent magnet synchronous motor to be controlled is relatively high, smaller x and y are selected.

[0112] Step S4, perform variable duty cycle control according to the duty cycle D s calculated in step S3 to weaken the current ripple.

[0113] Preferably, the above variable duty cycle control includes, according to the duty cycle D sObtain the corresponding square-wave switching signal, then perform level conversion on the square-wave switching signal to match the voltage level of the power circuit, and output the square-wave switching signal to the inverter, so as to achieve variable duty cycle control and weaken current pulsation.

[0114] Among them, according to the duty cycle D s To obtain the corresponding square-wave switching signal, a PWM generation module can be used. In this embodiment, the PWM generation module is generally a PWM generation module built into a control chip such as a DSP.

[0115] Among them, the level conversion of the square-wave switching signal to match the voltage level of the power circuit is realized through a driving module in the prior art. The driving module is: a driving chip and its peripheral circuit. The driving chip is selected according to the actual control chip and inverter type used. Common models include 6EDL04N06PT, IR2130, IR2136, etc.

[0116] Embodiment 2

[0117] Such as Figure 2 As shown, this embodiment provides a variable duty cycle hysteresis control system for a small inductor axial flux permanent magnet synchronous motor, which executes the variable duty cycle hysteresis control method for the small inductor axial flux permanent magnet synchronous motor in Embodiment 1;

[0118] The system includes a main power circuit, a control circuit, a driving module, and a sensor module; the main power circuit is connected to the permanent magnet synchronous motor, the sensor module is arranged on the permanent magnet synchronous motor, the sensor module is electrically connected to the control circuit, the control circuit is electrically connected to the driving module, and the driving module is electrically connected to the main power circuit.

[0119] Among them, the main power circuit includes a DC power supply U ab and an inverter. The positive pole of the DC power supply U ab is connected to the positive pole of the DC power input terminal of the inverter, the negative pole of the DC power supply U ab is connected to the negative pole of the DC power input terminal of the inverter, and two groups of bus capacitors C ab are connected in parallel between the DC power supply U p and the inverter. The two groups of bus capacitors C p are connected in series with each other, and an inductor L1 is connected to the output terminal of the inverter. The other end of the inductor L1 is connected to the winding L2 of the permanent magnet synchronous motor, and the control signal input terminal g of the inverter is connected to the driving module;

[0120] It should be noted that the inductance value of the inductor L1 is L s , the inductance value of the winding L2 of the permanent magnet synchronous motor is L p , and the voltage of the DC power supply U ab is U dc .

[0121] Preferably, the sensor module includes a current sensor, a voltage sensor, and a position sensor. The current sensor is a Hall current sensor, and the position sensor is an optical encoder or a resolver. The Hall current sensor, the voltage sensor, the optical encoder, or the resolver are all prior arts, and their specific structures and principles will not be elaborated herein.

[0122] Wherein the positive and negative measurement input terminals of the voltage sensor are respectively connected to the positive and negative electrodes of the DC power supply U ab .

[0123] Preferably, the control circuit includes an A / D sampling module, a hysteresis control module, a duty cycle calculation module, and a PWM generation module;

[0124] The A / D sampling module is electrically connected to the sensor module, the hysteresis control module, and the duty cycle calculation module, and is used to receive the bus voltage U of the inverter collected by the sensor module from the main power circuit dc , the permanent magnet synchronous motor current i s , the rotor position signal θ of the permanent magnet synchronous motor S , and perform coordinate transformation on the collected permanent magnet synchronous motor current i s to obtain the q-axis current value i qs , and calculate the rotational speed n S according to the rotor position signal θ of the permanent magnet synchronous motor S . The q-axis current value i qs is output to the hysteresis control module and the duty cycle calculation module, and the bus voltage U of the inverter dc and the rotational speed n S are output to the duty cycle calculation module; and in this embodiment, sampling chips such as AD7609 can be selected in practice.

[0125] The hysteresis control module is electrically connected to the A / D sampling module and the duty cycle calculation module, and is used to receive the q-axis current value i qs output by the A / D sampling module, and perform hysteresis logic judgment, and output the corresponding turn-on signal V on or turn-on signal V off to the duty cycle calculation module; this module is implemented at the software level by writing a control program and using a control chip, such as the control chips of the TMS320F2833x series or TMS320F2837x series of TI Corporation.

[0126] The duty cycle calculation module is electrically connected to the hysteresis control module, the A / D sampling module, and the PWM generation module, and is used to receive the turn-on signal V on or turn-on signal V off output by the hysteresis control module, as well as the q-axis current value i qs output by the A / D sampling module, and the bus voltage U of the inverterdc and rotational speed n S , output duty cycle D s to the PWM generation module; this module is implemented by writing a control program and using a control chip, such as the TMS320F2833x series or TMS320F2837x series control chips of Texas Instruments.

[0127] Among them, the PWM generation module is electrically connected to the duty cycle calculation module and the drive module, and is used to receive the duty cycle D output by the duty cycle calculation module s , generate the square wave switch signal of this duty cycle D s and output it to the drive module for level conversion and isolation protection.

[0128] Among them, the drive module is responsible for performing level conversion on the square wave switch signal to match the voltage level of the main power circuit, and finally outputting the square wave switch signal to the inverter control signal terminal g to weaken the current ripple.

[0129] The following is a specific example:

[0130] The motor used in this example is a dual-three-phase stator yokeless modular axial flux permanent magnet synchronous motor. The main parameters during the operation of this motor are listed in Table 1:

[0131] Table 1 Main parameters of the dual-three-phase stator yokeless modular axial flux permanent magnet synchronous motor

[0132] Parameter Unit Value Stator winding resistance, R Ω 0.1470 <![CDATA[d-axis main self-inductance, L aad > mH 0.0987 <![CDATA[q-axis main self-inductance, L aaq > mH 0.0987 <![CDATA[Stator winding leakage inductance, L aa1 > mH 0.4710 <![CDATA[Controller bus voltage, U dc > V 50 <![CDATA[Fundamental wave amplitude of permanent magnet flux linkage, ψ f > Wb 0.1290 Number of pole pairs, p - 5 Moment of inertia, J <![CDATA[kg·m 2 > 0.0545

[0133] In the dual-three-phase stator yokeless modular axial flux permanent magnet synchronous motor of this example, the DC bus voltage of the armature winding is 50V, the armature winding is powered by two sets of three-phase voltage source full-bridge inverters, the inductance of the armature winding is 0.661mH, and the switching frequency of the armature winding is 5kHz. The rotational speed regulation range is 0 - 200 RPM. The system principle structure of the motor is as Figure 2 shown.

[0134] The current waveforms when different inductors are connected in series in this example are as Figure 4 shown, and it can be seen that the suppression effect of the series inductor on the current ripple during the control of the hysteresis control system in Example 2 is significant. The relationship curve between the current ripple value and the inductance value of the series inductor is as Figure 5 shown. The red solid line is the change curve of the current ripple value with the inductance value of the series inductor. It can be seen that the current ripple decreases with the increase of the inductance. The blue solid line is the curvature curve of the red curve, and the critical inductance value L is determined by the inductance value corresponding to the maximum curvature point c , and the curve curvature shows a trend of first increasing and then decreasing.

[0135] When the inductance value L of the series inductor cThere is a point with the maximum curvature at 2.34 mH, which is the critical inductance value L in this example. c Take 2.34 mH. At the same time, on the right side of the critical inductance value, as the inductance value of the series inductance continues to increase, the improvement in the current ripple suppression effect tends to be "saturated". Moreover, increasing the inductance value without limit will bring additional mass, volume, and economic costs to the motor system. Therefore, the optimal inductance value L s is selected as 5 mH, and the corresponding current ripple value is 14.5%.

[0136] Preferably, in this embodiment, x = 6 and y = 0.1 are taken, and the value of x can be appropriately adjusted according to the operation steps in other examples;

[0137] Among them Figure 6 is a schematic diagram of the calculation result of the duty cycle calculation module of the dual-three-phase stator yokeless modular axial flux permanent magnet synchronous motor system used. It can be seen that as the current or speed increases, the duty cycle required for the motor operation increases.

[0138] Among them Figure 7 is a schematic diagram comparing the motor phase current waveforms under the hysteresis control system used in this embodiment and the traditional hysteresis control system. It can be seen that after adding the hysteresis control with variable duty cycle in this embodiment, the current ripple is reduced.

[0139] Among them Figure 8 is a schematic diagram comparing the phase current waveforms under the traditional hysteresis control system, the hysteresis control system with only series inductance, and the hysteresis control system with series inductance and variable duty cycle used in this embodiment. The green is the current waveform under the control of the traditional hysteresis control system. It can be seen that the current ripple is 11.45 A. The blue curve is the current waveform after series inductance, and the current ripple is only 1.13 A. The red curve is the current of the variable duty cycle hysteresis control system used in this embodiment on the basis of series inductance, and the current ripple is further reduced to only 0.55 A.

[0140] Among them Figures 9 - 12 are the duty cycle calculation results, speed waveforms, electromagnetic torque waveforms, and three-phase current waveforms in this embodiment for the case of sudden increase and decrease of the load at the motor load end. From Figure 12 it can be seen that the load torque suddenly increases from 5 Nm to 15 Nm at 0.5 s and suddenly decreases to 5 Nm at 1 s; from Figure 11 it can be seen that the change in the load causes the current magnitude to change, increasing from about 2.5 A to 7.5 A at 0.5 s and decreasing to 2.5 A at 1 s ( Figure 11 ); from Figure 9 it can be seen that the duty cycle can effectively follow the change of the load torque and adjust in real time. It increases from 80% to 100% at 0.5 s and decreases to 80% at 1 s. From Figure 10It can be seen that the rotational speed remains stable during load adjustment and only has slight fluctuations during switching.

[0141] Among them Figures 13 - 16 are the duty cycle calculation results, rotational speed waveforms, electromagnetic torque waveforms, and three-phase current waveforms in this embodiment for the sudden acceleration and deceleration of the motor. It can be seen from Figure 14 that the rotational speed suddenly increases from 10 revolutions per minute to 150 revolutions per minute at 0.5 s and then suddenly decreases to 50 revolutions per minute at 1 s; it can be seen from Figure 15 that the change in rotational speed causes the current frequency to change, increasing at 0.5 s and decreasing at 1 s; it can be seen from Figure 13 that the duty cycle can effectively follow the change in rotational speed and adjust in real time, increasing from about 60% to 100% at 0.5 s and then decreasing to about 70% at 1 s. It can be seen from Figure 16 that the steady-state value of the torque can remain stable and only has slight fluctuations during switching.

[0142] The above has described a detailed description of an embodiment of the present invention, but the content described is only the preferred embodiment of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the application of the present invention should still fall within the scope covered by the patent of the present invention.

Claims

1. A variable duty cycle hysteresis control method for a small inductor axial flux permanent magnet synchronous motor, characterized in that It includes the following steps: Step S1: Obtain the current ripple values of the permanent magnet synchronous motor under the control of the traditional hysteresis control system when different inductors are connected in series to the permanent magnet synchronous motor, and plot the relationship curve between the current ripple values and the inductance values of the series-connected inductors; Step S2: Determine the critical inductance value according to the maximum curvature point of the plotted relationship curve between the current ripple value and the inductance value of the series-connected inductor, and select the optimal inductance value to be connected in series on the right side of the critical inductance value; Step S3: Connect the inductor with the optimal inductance value in series to the permanent magnet synchronous motor, and calculate the duty cycle when the permanent magnet synchronous motor is operating; Step S4: Perform variable duty cycle control according to the calculated duty cycle to weaken the current ripple.

2. A variable duty cycle hysteresis control method for a small inductor axial flux permanent magnet synchronous motor according to claim 1, characterized in that, The obtaining of the current ripple values of the permanent magnet synchronous motor under the control of the traditional hysteresis control system when different inductors are connected in series to the permanent magnet synchronous motor includes the following steps: Step SA1, obtain the number of pole pairs p of the permanent magnet synchronous motor, the amplitude ψ of the permanent magnet flux linkage f , the switching frequency f of the power device under the control of the traditional hysteresis control system sw , the inductance value L of the series inductor d , the winding inductance value L of the permanent magnet synchronous motor p , the bus voltage U of the inverter dc , the current i of the permanent magnet synchronous motor d and the rotor position signal θ of the permanent magnet synchronous motor; Step SA2, the current i of the permanent magnet synchronous motor d is subjected to coordinate transformation to obtain the q-axis current value i q , and the rotational speed n is calculated based on the rotor position signal θ of the permanent magnet synchronous motor. The electrical angular velocity ω of the permanent magnet synchronous motor is calculated according to the angular velocity formula through the rotational speed n e ; Step SA3, according to the formula calculate the current ripple value Δi.

3. A variable duty cycle hysteresis control method for a small inductor axial flux permanent magnet synchronous motor according to claim 2, characterized in that The calculation formula for the rotational speed n in the step SA2 is: where Δθ is the difference between the rotor position signal obtained by the position sensor and the rotor position signal obtained in the previous time, and ΔT is the time interval between two acquisitions by the position sensor; In the step SA2, the angular velocity formula is: ω e = 2πpn / 60.

4. A variable duty cycle hysteresis control method for a small inductor axial flux permanent magnet synchronous motor according to claim 2, characterized in that, The calculation formula for the curvature C of the relationship curve between the current ripple value and the inductance value of the series-connected inductor in the step S2 is:

5. A variable duty cycle hysteresis control method for a small inductor axial flux permanent magnet synchronous motor according to claim 1, characterized in that The calculation of the duty cycle includes the following steps: Step SB1, obtain the number of pole pairs p of the permanent magnet synchronous motor, the amplitude ψ of the permanent magnet flux linkage f , the optimal inductance value L s , the winding inductance value L of the permanent magnet synchronous motor p , the sampling frequency f of the A / D sampling module swp , the current i of the permanent magnet synchronous motor s , the rotor position signal θ of the permanent magnet synchronous motor S , the bus voltage U of the inverter dc ; Step SB2, the obtained permanent magnet synchronous motor current i s is subjected to coordinate transformation to obtain the q-axis current value i qs , and according to the rotor position signal θ of the permanent magnet synchronous motor S the rotational speed n is calculated S , Step SB3, the q-axis current value i qs is subjected to hysteresis logic judgment. The judgment process is as follows: The q-axis current value i qs is subtracted from the set reference current i * , and the result is compared with the set hysteresis width H. If i qs - i * > H, the output is the turn-on signal V on ; if i qs - i * < -H, the output is the turn-on signal V off ; Step SB4, calculate the duty cycle D according to the hysteresis logic judgment result s .

6. A variable duty cycle hysteresis control method for a small inductor axial flux permanent magnet synchronous motor according to claim 5, characterized in that The duty cycle D s has the following calculation formula: When D s has a calculated value greater than 1, then the value of D s is 1; when D s has a calculated value less than 0, then the value of D s is 0, where x is a proportionality coefficient and the value range of x is 3 - 8, and V sw is the switching logic signal output after hysteresis logic judgment.

7. A variable duty cycle hysteresis control method for a small inductor axial flux permanent magnet synchronous motor according to claim 6, characterized in that, Performing variable duty cycle control according to the calculated duty cycle, including according to the duty cycle D s obtaining a corresponding square wave switching signal, then performing level conversion on the square wave switching signal to match the voltage level of the power circuit, and outputting the square wave switching signal to the inverter, thereby implementing variable duty cycle control.

8. A variable duty cycle hysteresis control system for a small inductance axial flux permanent magnet synchronous motor, which executes a variable duty cycle hysteresis control method for a small inductance axial flux permanent magnet synchronous motor according to any one of claims 1-7, characterized in that, It includes a main power circuit, a control circuit, a drive module, and a sensor module; the main power circuit is connected to the permanent magnet synchronous motor, the sensor module is arranged on the permanent magnet synchronous motor, the sensor module is electrically connected to the control circuit, the control circuit is electrically connected to the drive module, and the drive module is electrically connected to the main power circuit.

9. A variable duty cycle hysteresis control system for a small inductor axial flux permanent magnet synchronous motor according to claim 8, characterized in that, The main power circuit includes a DC power supply U ab and an inverter. The positive pole of the DC power supply U ab is connected to the positive pole of the DC power input end of the inverter, and the negative pole of the DC power supply U ab is connected to the negative pole of the DC power input end of the inverter. Moreover, two groups of bus capacitors C ab are connected in parallel between the DC power supply U p and the inverter. The two groups of bus capacitors C p are connected in series with each other. The output end of the inverter is connected to an inductor L1, the other end of the inductor L1 is connected to the permanent magnet synchronous motor winding L2, and the control signal input end g of the inverter is connected to the drive module; The sensor module includes a current sensor, a voltage sensor, and a position sensor.

10. A variable duty cycle hysteresis control system for a small inductor axial flux permanent magnet synchronous motor according to claim 9, characterized in that, The control circuit includes an A / D sampling module, a hysteresis control module, a duty cycle calculation module, and a PWM generation module: The A / D sampling module is used to receive the bus voltage of the inverter, the current of the permanent magnet synchronous motor, and the rotor position signal of the permanent magnet synchronous motor collected by the sensor module from the main power circuit, perform coordinate transformation on the collected current of the permanent magnet synchronous motor to obtain the q-axis current value, calculate the rotational speed according to the rotor position signal of the permanent magnet synchronous motor, output the q-axis current value to the hysteresis control module and the duty cycle calculation module, and output the bus voltage and rotational speed of the inverter to the duty cycle calculation module; The hysteresis control module is used to receive the q-axis current value output by the A / D sampling module, perform hysteresis logic judgment, and output the corresponding turn-on signal V on or turn-on signal V off to the duty cycle calculation module; The duty cycle calculation module is used to receive the turn-on signal V output by the hysteresis control module on or the turn-on signal V off , as well as the q-axis current value, the bus voltage of the inverter, and the rotational speed output by the A / D sampling module, and output the duty cycle to the PWM generation module; The PWM generation module is used to receive the duty cycle output by the duty cycle calculation module, generate a square wave switching signal with this duty cycle and output it to the drive module for level conversion and isolation protection; The drive module is responsible for performing level conversion on the square wave switching signal to match the voltage level of the main power circuit, outputting the square wave switching signal to the inverter control signal terminal to weaken the current ripple.

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