Inverter dead time compensation method and permanent magnet synchronous motor control system

Abstract

The invention discloses an inverter dead time compensation method and a permanent magnet synchronous motor control system, an inverter is used for driving a permanent magnet synchronous motor, and the inverter dead time compensation method comprises the following steps: determining a Luenberger observer according to a mathematical model of the permanent magnet synchronous motor; according to the q-axis actual voltage of the permanent magnet synchronous motor, the q-axis actual current of the permanent magnet synchronous motor and the angular frequency of the permanent magnet synchronous motor, the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor is calculated through a Luenberger observer; and according to the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor, the dead zone compensation time of the inverter is adjusted through a PI regulator, so that the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor approaches 0. According to the method, the dead zone compensation time of the inverter can be adjusted on line, so that the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor is close to 0, the influence of the q-axis disturbance voltage is eliminated, the distortion of phase voltage is further inhibited, the current fluctuation is finally relieved, and the torque ripple is reduced.

Description

Technical Field

[0001] The present invention relates to the field of control technology, and in particular to an inverter dead time compensation method and a permanent magnet synchronous motor control system. Background Art

[0002] Permanent Magnet Synchronous Machine (PMSM) is an important actuator of the electric power steering (EPS) system of automobiles. Usually, the field oriented control (FOC) strategy is adopted to complete the current control of PMSM and make it output the corresponding electromagnetic torque to provide corresponding assistance for the EPS system.

[0003] However, the dead time of the inverter increases the amplitude of the high-frequency harmonic components in the permanent magnet synchronous motor current and causes corresponding electromagnetic torque fluctuations, resulting in the problem of unstable power assistance in the EPS system. Therefore, in the control process, it is necessary to compensate for the dead time effect caused by the inverter dead time, reduce the amplitude of the high-frequency harmonic components in the permanent magnet synchronous motor current, and thus improve the power assistance performance of the EPS system. Summary of the invention

[0004] The present invention provides an inverter dead time compensation method and a permanent magnet synchronous motor control system, which can adjust the inverter dead time compensation time online so that the estimated value of the permanent magnet synchronous motor q-axis disturbance voltage approaches 0, eliminates the influence of the q-axis disturbance voltage, and further suppresses the distortion of the phase voltage, and finally alleviates the current fluctuation and reduces the torque pulsation.

[0005] In a first aspect, an embodiment of the present invention provides an inverter dead time compensation method, wherein the inverter is used to drive a permanent magnet synchronous motor, and the inverter dead time compensation method comprises: determining a Romberg observer according to a mathematical model of the permanent magnet synchronous motor; calculating an estimated value of a q-axis disturbance voltage of the permanent magnet synchronous motor through the Romberg observer according to an actual q-axis voltage of the permanent magnet synchronous motor, an actual q-axis current of the permanent magnet synchronous motor and an angular frequency of the permanent magnet synchronous motor; adjusting the dead time compensation time of the inverter through a PI regulator according to the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor, so that the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor approaches 0; wherein the PI regulator is used to characterize the relationship between the estimated value of the q-axis disturbance voltage and the dead time compensation time of the inverter.

[0006] Optionally, the step of determining the Romberg observer according to the mathematical model of the permanent magnet synchronous motor includes: establishing a mathematical model of the permanent magnet synchronous motor in a synchronous rotating coordinate system, and converting the q-axis voltage equation of the permanent magnet synchronous motor into the form of a state equation; constructing a state equation and an output equation of the Romberg observer according to the state equation of the q-axis voltage of the permanent magnet synchronous motor; determining the characteristic polynomial of the Romberg observer according to the state equation and the output equation of the Romberg observer; determining the gain of the Romberg observer according to the characteristic polynomial of the Romberg observer, and then determining a discretized expression of the Romberg observer.

[0007] Optionally, the state equation of the q-axis voltage of the permanent magnet synchronous motor is:

[0008]

[0009] Among them, i q Indicates the actual current of the q axis, i d Indicates the actual current of the d-axis, R s Represents the phase resistance of the permanent magnet synchronous motor, L s represents the phase inductance of the permanent magnet synchronous motor, ω r Represents the angular frequency of the permanent magnet synchronous motor, V q Indicates the actual voltage on the q axis, ΔV q represents the actual value of the q-axis disturbance voltage, Represents the permanent magnet flux linkage coefficient.

[0010] Optionally, the state equation and output equation of the Lumberg observer are:

[0011]

[0012] Among them, i q represents the actual current of q axis, represents the estimated value of the q-axis disturbance current, i d Indicates the actual current of the d-axis, R s Represents the phase resistance of the permanent magnet synchronous motor, L s represents the phase inductance of the permanent magnet synchronous motor, ω r Represents the angular frequency of the permanent magnet synchronous motor, V q Indicates the actual voltage on the q axis, ΔV q represents the actual value of the q-axis disturbance voltage, represents the permanent magnet flux linkage coefficient, represents the estimated value of the q-axis disturbance voltage, and H1 and H2 represent the gains of the Romberg observer.

[0013] Optionally, the characteristic polynomial of the Romberg observer is:

[0014]

[0015] Among them, λ is the eigenvalue of the matrix, E is the unit matrix, R s Represents the phase resistance of the permanent magnet synchronous motor, L s represents the phase inductance of the permanent magnet synchronous motor, and H1 and H2 represent the gains of the Romberg observer.

[0016] Optionally, the gain of the Romberg observer is:

[0017]

[0018] Among them, ω c represents the cutoff frequency of the Romberg observer, R s Represents the phase resistance of the permanent magnet synchronous motor, L s Represents the phase inductance of the permanent magnet synchronous motor.

[0019] Optionally, the step of calculating the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor through a Romberg observer based on the actual q-axis voltage of the permanent magnet synchronous motor, the actual q-axis current of the permanent magnet synchronous motor and the angular frequency of the permanent magnet synchronous motor includes: at each sampling moment, calculating the estimated value of the q-axis current at the current moment based on the actual q-axis voltage of the permanent magnet synchronous motor, the actual q-axis current of the permanent magnet synchronous motor and the angular frequency of the permanent magnet synchronous motor, and the estimated value of the q-axis current at the previous moment; calculating the estimated value of the q-axis disturbance voltage at the next moment based on the estimated value of the q-axis current at the current moment, the actual value of the q-axis current at the current moment, the sampling period of the Romberg observer, and the estimated value of the q-axis disturbance voltage at the current moment.

[0020] Optionally, the discretization expression of the PI regulator is:

[0021]

[0022] K p Represents the proportionality coefficient, K i represents the integral coefficient, ΔT represents the sampling period, represents the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor at the current moment, Indicates the cumulative value of the q-axis voltage estimate from the start time to the current time.

[0023] Optionally, the inverter includes an upper bridge arm and a lower bridge arm, and the upper bridge arm and the lower bridge arm both include a switch tube and a diode connected in anti-parallel to the switch tube; the inverter dead time compensation method also includes: obtaining the dead time compensation time required for the control signal of the switch tube of the upper bridge arm according to the direction of the three-phase current of the permanent magnet synchronous motor and the dead time compensation time.

[0024] In a second aspect, an embodiment of the present invention discloses a permanent magnet synchronous motor control system, which includes a controller and an inverter. The controller is used to execute the inverter dead time compensation method provided in any embodiment of the present invention.

[0025] The inverter dead time compensation method provided by the embodiment of the present invention determines the Lumberg observer according to the mathematical model of the permanent magnet synchronous motor; according to the actual q-axis voltage of the permanent magnet synchronous motor, the actual q-axis current of the permanent magnet synchronous motor and the angular frequency of the permanent magnet synchronous motor, the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor is calculated by the Lumberg observer; according to the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor, the dead time compensation time of the inverter can be adjusted online, so that the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor approaches 0, eliminating the influence of the q-axis disturbance voltage. In the time domain, the distortion of the current can be effectively suppressed; in the frequency domain, the high-order harmonic components in the current can be effectively reduced, and the total harmonic distortion (THD) value of the current can be greatly reduced. In other words, the compensation method proposed in the present invention can effectively suppress the high-order harmonic components generated by the phase current of the permanent magnet synchronous motor during operation, which helps to improve the stability of the EPS system during operation.

[0026] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 It is a circuit principle diagram of an inverter provided by the present invention;

[0029] Figure 2 is a control block diagram of a permanent magnet synchronous motor control system provided by an embodiment of the present invention;

[0030] Figure 3 An inverter dead time compensation method provided by an embodiment of the present invention;

[0031] Figure 4 This is the waveform of the PWM control signal and the output voltage from the midpoint of the bridge arm to the ground when the load current of the inverter is positive under ideal conditions;

[0032] Figure 5 It is the waveform diagram of the PWM control signal and the output voltage at the midpoint of the bridge arm when the load current of the inverter is positive under ideal conditions and actual working conditions;

[0033] Figure 6 It is the waveform diagram of the PWM control signal and the output voltage at the midpoint of the bridge arm when the load current of the inverter is negative under ideal conditions and actual working conditions;

[0034] Figure 7 It is the waveform diagram of the dq axis disturbance voltage of the motor under the influence of the inverter dead zone effect;

[0035] Figure 8 is a flow chart of another inverter dead time compensation method provided by an embodiment of the present invention;

[0036] Fig. 9 Flow chart of another inverter dead time compensation method provided by an embodiment of the present invention

[0037] Fig.10 This is the simulation diagram of the motor α-β axis current without adding dead zone compensation;

[0038] Fig.11 This is the simulation diagram of the motor α-β axis current with online dead zone compensation added;

[0039] Fig.12 This is the simulation diagram of the motor α-β axis current phase without adding dead zone compensation;

[0040] Fig.13 This is the simulation diagram of the motor α-β axis current phase with online dead zone compensation added;

[0041] Fig.14 It is a simulation diagram of the motor phase current spectrum and its THD value. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0043] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0044] Figure 1 1 is a circuit diagram of an inverter provided by the present invention. Figure 1 As shown, the inverter includes an upper bridge arm and a lower bridge arm, and both the upper bridge arm and the lower bridge arm include a switch tube and a diode connected in anti-parallel to the switch tube; wherein, the inverter includes a first group of bridge arms, a second group of bridge arms, and a third group of bridge arms constituting three branches; the first group of bridge arms includes a first upper bridge arm and a first lower bridge arm, the first upper bridge arm includes a first switch tube M1, and the first lower bridge arm includes a fourth switch tube M4; the second group of bridge arms includes a second upper bridge arm and a second lower bridge arm, the second upper bridge arm includes a second switch tube M2, and the second lower bridge arm includes a fifth switch tube M5; the third group of bridge arms includes a third upper bridge arm and a third lower bridge arm, the third upper bridge arm includes a third switch tube M3, and the third lower bridge arm includes a sixth switch tube M6. In the figure, points a, b, and c represent the midpoints of the three-phase bridge arms; point g represents the ground terminal of the inverter, and point s represents the center point of the permanent magnet synchronous motor.

[0045] Under ideal conditions, the control signals of the upper bridge arm and the lower bridge arm satisfy the complementary on-off principle, that is, when the upper bridge arm is turned on, the lower bridge arm is turned off, and vice versa.

[0046] like Figure 1As shown, in order to avoid power supply direct connection, the driving signals of the upper and lower switches of each bridge arm are complementary signals. However, the switching of the switch tube is often accompanied by the charging and discharging of the parasitic capacitance. Therefore, the switching is a process, and the time required for the switching is different. In this way, it is easy for one of the switch tubes to be not completely turned off, and the other switch tube in the same bridge arm is already turned on, that is, the risk of power short circuit. In order to solve this problem, the dead time Td of the driving signal is set. In the complementary signal, the turn-on signal will delay the dead time Td to act, and the turn-off signal will act normally. The addition of the dead time will cause errors in the amplitude and phase of the inverter output, which is called the dead time effect. The dead time effect leads to serious inverter nonlinearity. In order to obtain better results in the linear controller system, effective dead time compensation of the inverter is required. Based on the above problems, an embodiment of the present invention provides a method for dynamic compensation of inverter dead zone effect based on the switching characteristics of the switching tube, which can adjust the dead zone compensation time of the inverter online so that the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor approaches 0, eliminating the influence of the q-axis disturbance voltage, thereby suppressing the distortion of the phase voltage, and ultimately alleviating the current fluctuation and reducing the torque pulsation.

[0047] Figure 2 is a control block diagram of a permanent magnet synchronous motor control system provided by an embodiment of the present invention, such as Figure 2 As shown, the permanent magnet synchronous motor control system includes a rotor position sensor 1, a permanent magnet synchronous motor (PMSM) 2, a current sensor 4, a coordinate transformation module 5, a q-axis current loop PI regulator 6, a space vector pulse width modulation (SVPWM) module 7, a d-axis current loop PI regulator 8 and an inverter 10.

[0048] exist Figure 2 middle, is the q-axis current setting value, is the d-axis current setting value, i s is the target current.

[0049] i as 、i bs and i cs They are the sampling currents of phase A, phase B, and phase C, which can be directly obtained by sampling through the current sensor 4. The electrical angle θ r It can be calculated by reading the value of the magnetic encoder in real time.

[0050] After obtaining the three-phase current and electrical angle, the current loop can be executed: the three-phase current i as 、i bs and i csThe actual current i of the α-axis is obtained by Clark transformation α and the actual current i of the β axis β ; Then the actual current i of the q axis is obtained through Park transformation q and the actual d-axis current i d ; and then respectively with their set values as well as Compare and calculate the current error value; then substitute the q-axis current error value into the q-axis current loop PI regulator 6 to calculate the q-axis actual voltage V q , substitute the d-axis current error value into the d-axis current loop PI regulator 8 to calculate the d-axis actual voltage V d ; Then the actual voltage V on the q axis q and the actual voltage V on the d-axis d Perform inverse Park transformation to obtain the actual voltage V of the α axis α and the actual voltage V β Then the conduction time T of the first switch tube M1 of the inverter phase a is obtained through the space vector pulse width modulation module 7 a , the conduction time T of the second switch tube M2 on the inverter b phase b , and the conduction time T of the third switch tube M3 on the inverter c phase c .

[0051] Figure 3 An inverter dead time compensation method is provided in an embodiment of the present invention. The inverter is used to drive a permanent magnet synchronous motor. The compensation method in the embodiment of the present invention can be executed by a controller of the inverter. The controller can be implemented in software and / or hardware and can be integrated in a permanent magnet synchronous motor system. The controller includes a Romberg observer and a PI regulator. Figure 2 and Figure 3 , the inverter dead time compensation method includes:

[0052] S201. Determine a Romberg observer according to a mathematical model of the permanent magnet synchronous motor.

[0053] Specifically, the mathematical model of the permanent magnet synchronous motor includes the relationship between the motor's voltage, current, flux, speed and other variables. To determine the Lumberg observer, it is first necessary to analyze the mathematical model of the permanent magnet synchronous motor in the synchronous rotating coordinate system to clarify the state variables, input variables and output variables. Secondly, the mathematical model is linearized to meet the construction conditions of the Lumberg observer. Then, based on the linearized state equation, the state variables, input variables and output variables of the system are determined, and then the gain matrix of the Lumberg observer is set according to the principle of the Lumberg observer. When determining the gain matrix of the Lumberg observer, it is necessary to comprehensively consider factors such as the parameter characteristics of the motor, the uncertainty in actual operation and possible external interference. By reasonably setting the gain matrix, the observer can accurately, quickly and stably estimate the q-axis disturbance voltage of the permanent magnet synchronous motor, thereby constructing a Lumberg observer suitable for the permanent magnet synchronous motor.

[0054] S202. Calculate an estimated value of a q-axis disturbance voltage of the permanent magnet synchronous motor through a Romberg observer according to the actual q-axis voltage of the permanent magnet synchronous motor, the actual q-axis current of the permanent magnet synchronous motor, and the angular frequency of the permanent magnet synchronous motor.

[0055] like Figure 2 As shown, the permanent magnet synchronous motor control system also includes a controller, which includes a Romberg observer 11 and a PI regulator 12. q , d-axis actual current i d and angular frequency ω r Input the Lumberg observer 4, and after calculation, the estimated value of the q-axis disturbance voltage is obtained.

[0056] In some embodiments, the discretization expression of the PI regulator is:

[0057]

[0058] K p Represents the proportionality coefficient, K i represents the integral coefficient, ΔT represents the sampling period, represents the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor at the current moment, Indicates the cumulative value of the q-axis voltage estimate from the start time to the current time.

[0059] S203 . According to the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor, adjust the dead zone compensation time of the inverter through a PI regulator so that the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor approaches zero.

[0060] The PI regulator is used to characterize the relationship between the estimated value of the q-axis disturbance voltage and the dead zone compensation time of the inverter.

[0061] Continue to refer Figure 1 , C bulk is the DC bus capacitance, V dc is the DC power supply voltage, i as 、i bs and i cs is the three-phase current of the permanent magnet synchronous motor. Figure 1 The A phase of the permanent magnet synchronous motor is studied, and the positive direction of the current flowing from the inverter to the motor is stipulated as the reference direction. Then, when the current flows from the inverter to the permanent magnet synchronous motor, the load current is positive, and when the current flows from the motor to the inverter, the load current is negative. Figure 4 This is the waveform of the PWM control signal and the output voltage from the bridge arm midpoint to the ground when the load current of the inverter is positive under ideal conditions. A1+ and A1- respectively represent the ideal pulse width modulation (PWM) control signals of the first switch tube M1 and the fourth switch tube M4. A1+ and A1- are complementary. The output waveform of the bridge arm midpoint corresponding to the PWM control signals of A1+ and A1- is shown as Vag. Where: T s It is 1 / 2 switching cycle, T1 is the moment when the first switch tube M1 is turned on and the fourth switch tube M4 is turned off, T2 is the moment when the first switch tube M1 is turned off and the fourth switch tube M4 is turned on, the PWM control signal is used to control the state of the switch tube, and the inverter uses SVPWM to generate the PWM control signal.

[0062] according to Figure 4 It can be obtained that the average value of the voltage of permanent magnet synchronous motor A relative to the "ground" in a complete switching cycle is:

[0063]

[0064] Among them, V ag Represents the voltage between point a and point g, V dc is the DC power supply voltage connected to the inverter, T a Indicates the conduction time of the switch tube in the first group of bridge arms, T s is 1 / 2 switching cycle.

[0065] During the control process, in order to prevent the upper bridge arm and the lower bridge arm of the inverter from being directly connected and causing serious faults such as system short circuit, a certain dead time needs to be inserted, that is, the first switch tube M1 can be turned on only after the fourth switch tube M4 is turned off for the dead time Td. Figure 5 It is the waveform diagram of the PWM control signal and the output voltage at the midpoint of the bridge arm when the load current of the inverter is positive under ideal conditions and actual working conditions. Figure 6 It is a waveform diagram of the PWM control signal and the output voltage at the midpoint of the bridge arm when the load current of the inverter is negative under ideal conditions and actual working conditions.

[0066] Combination Figure 5 and Figure 6 , A1+, A1- respectively represent the ideal PWM control signals when the first switch tube M1 and the fourth switch tube M4 are not set with dead zones, A2+, A2- respectively represent the PWM control signals considering the turn-on delay and turn-off delay of the first switch tube M1 and the fourth switch tube M4, V ag (real) represents the actual output voltage waveform from the bridge arm midpoint to ground, V ag (equivalent) represents the equivalent waveform of the output voltage from the midpoint of the bridge arm to the ground. V ag The actual waveform includes the rising and falling process, which increases the difficulty of analysis and calculation. In order to simplify the analysis and calculation process, V ag (real) is simplified to obtain the corresponding V ag (equivalent).

[0067] T s is 1 / 2 of the switching cycle, T1 is the time when the first switch tube M1 is turned on and the fourth switch tube M4 is turned off, T2 is the time when the first switch tube M1 is turned off and the fourth switch tube M4 is turned on, T d Indicates the dead time, T com Indicates the dead zone compensation time, T on Indicates the on-time of the switch tube, T off Indicates the turn-off time of the switch tube.

[0068] When the A phase load current i as When the inverter working state is "10" (i.e., the first switch tube M1 is turned on and the fourth switch tube M4 is turned off), the output voltage V from point a to point g is ag is the DC power supply voltage V dc and the difference between the conduction voltage of the fourth switch tube M4; when the inverter working state is "00" (that is, the first switch tube M1 and the fourth switch tube M4 are both turned off), the inverter enters the dead zone. At this time, the output voltage V from point a to point g ag is the conduction voltage of the anti-parallel diode of the fourth switch tube M4; when the inverter working state is "01" (i.e., the first switch tube M1 is turned off and the fourth switch tube M4 is turned on), the output voltage V from point a to point g ag is the conduction voltage of the fourth switch tube. Therefore, according to the volt-second equivalent principle, Figure 4 It can be seen that the output voltage V from point a to point g of the inverter is ag The average voltage during the entire switching cycle is:

[0069]

[0070] Among them, T a Indicates the conduction time of the switch tube in the first group of bridge arms, Ts is 1 / 2 switching cycle, T d Indicates the dead time of the PWM control signal, T on , T off Respectively represent the on-time and off-time of the switch tube, T com Indicates the dead zone compensation time, i as Represents the A phase output current (i.e., A phase load current), R ds is the on-resistance of the switch tube, R d is the on-resistance of the inverter diode, V do Represents the conduction threshold voltage of the diode.

[0071] When the A phase load current i as When the inverter working state is "10" (i.e., the first switch tube M1 is turned on and the fourth switch tube M4 is turned off), the output voltage V from point a to point g is ag is the DC power supply voltage V dc and the sum of the conduction voltage of the first switch tube M1; when the inverter working state is "00" (that is, the first switch tube M1 and the fourth switch tube M4 are both turned off), the inverter enters the dead zone, and the output voltage V from point a to point g ag is the DC power supply voltage V dc The sum of the conduction voltages of the diodes connected in antiparallel with the fourth switch tube M4; when the inverter working state is "01" (i.e., the first switch tube M1 is turned off and the fourth switch tube M4 is turned on), the output voltage V from point a to point g is ag is the turn-on voltage of the fourth switch tube M4. Therefore, according to the volt-second equivalent principle, Figure 5 It can be seen that the average value of the inverter point a voltage to ground in a complete switching cycle is V ag for:

[0072]

[0073] In summary, the voltage V from point a of the inverter to ground can be obtained. ag The general expression is:

[0074]

[0075] The sign function is defined as:

[0076]

[0077] Therefore, by combining equations (1) and (4), we can obtain the voltage distortion (ΔV ag )for:

[0078]

[0079] In formula (6), since (Rds -R d ) approaches 0, and its influence can be ignored; R ds ●i as After completing Clarke and Park transformations, it is converted into a DC component, so it is not analyzed. Therefore, equation (6) can be further simplified as:

[0080]

[0081] Similarly, we can get:

[0082]

[0083] For permanent magnet synchronous motors, i d =0 control. Therefore, the phase δ of the current vector is consistent with the q-axis direction, that is, δ = θ r +π / 2. Therefore, the motor three-phase current (i as 、i bs 、i cs ) can be expressed as:

[0084]

[0085] Among them, θ r Indicates the motor rotor position, I m represents the motor target current. According to equations (7) to (9), we can obtain: when 0≤θ r When <π / 3,

[0086]

[0087] Where, ΔV q With ΔV d It represents the disturbance voltage on the dq axis of the motor caused by the inverter dead zone effect.

[0088]

[0089] Similarly, when π / 3≤θ r <2π / 3,

[0090]

[0091] When 2π / t3≤θ r <π,

[0092]

[0093] When π≤θ r <4π / t3,

[0094]

[0095] When 4π / t3≤θ r <5π / t3,

[0096]

[0097] When 5π / t3≤θ r <2π,

[0098]

[0099] Therefore, the dq-axis disturbance voltage waveform of the motor under the influence of the inverter dead zone effect can be obtained from equations (10) to (15), as follows: Figure 7 As shown. At the same time, the average value of the dq axis disturbance voltage can be obtained as:

[0100]

[0101] Add dead zone compensation time T in the control process com After that, ΔV can be expressed as:

[0102]

[0103] According to formula (17), when ΔV = 0, the influence of the inverter dead time can be eliminated. Therefore, we can get:

[0104]

[0105] Where: T com Indicates the inverter dead zone compensation time, T on 、T off Indicates the turn-on and turn-off time of the power device, V do is the voltage drop of the inverter diode, V dc is the DC power supply voltage connected to the inverter. That is to say, by adjusting the dead zone compensation time T com It can make ΔV equal to 0, thus making the q-axis disturbance voltage ΔV q is equal to 0.

[0106] It should be noted that the switch-on time T on and the off time T off It can be further expressed as:

[0107]

[0108] T on_delay is the opening delay time, T on_transient is the turn-on rise time, T off_delay is the turn-off delay time, T off_transientis the turn-off fall time. Since the turn-on delay time, turn-on rise time, turn-off delay time and turn-off fall time are closely related to the switching characteristics of the switch tube, and the values ​​of the above parameters will change with the change of the motor load current, different load currents correspond to different turn-on delay times, turn-on rise times, turn-off delay times and turn-off fall times, and different types of switch tubes have different turn-on delay times, turn-on rise times, turn-off delay times and turn-off fall times. Therefore, it is necessary to compensate the dead zone time T of the inverter. com Make online adjustments.

[0109] The inverter dead time compensation method provided by the embodiment of the present invention determines the Lumberg observer according to the mathematical model of the permanent magnet synchronous motor; according to the actual q-axis voltage of the permanent magnet synchronous motor, the actual q-axis current of the permanent magnet synchronous motor and the angular frequency of the permanent magnet synchronous motor, the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor is calculated by the Lumberg observer; according to the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor, the dead time compensation time of the inverter can be adjusted online, so that the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor approaches 0, eliminating the influence of the q-axis disturbance voltage. In the time domain, the distortion of the current can be effectively suppressed; in the frequency domain, the high-order harmonic components in the current can be effectively reduced, and the total harmonic distortion (THD) value of the current can be greatly reduced. In other words, the compensation method proposed in the present invention can effectively suppress the high-order harmonic components generated by the phase current of the permanent magnet synchronous motor during operation, which helps to improve the stability of the EPS system during operation.

[0110] Figure 8 is a flow chart of another inverter dead time compensation method provided by an embodiment of the present invention, such as Figure 8 As shown, the inverter dead time compensation method includes:

[0111] S801. Establish a mathematical model of the permanent magnet synchronous motor in a synchronous rotating coordinate system, and convert the q-axis voltage equation of the permanent magnet synchronous motor into a state equation.

[0112] According to the relevant theories of permanent magnet synchronous motors, the state equation of the q-axis voltage of a permanent magnet synchronous motor is:

[0113]

[0114] Among them, i q Indicates the actual current of the q axis, i d Indicates the actual current of the d-axis, L s Represents the motor phase inductance, R s Represents the motor phase resistance, ω r represents the motor electrical angular frequency, Represents the permanent magnet flux coefficient, V q Indicates the actual voltage of the motor q axis.

[0115] S802. Construct a state equation and an output equation of a Romberg observer according to the state equation of the q-axis voltage of the permanent magnet synchronous motor.

[0116] The state equation and output equation of the Lumberg observer are:

[0117]

[0118] Among them, i q represents the actual current of q axis, represents the estimated value of the q-axis disturbance current, i d Indicates the actual current of the d-axis, R s Represents the phase resistance of the permanent magnet synchronous motor, L s represents the phase inductance of the permanent magnet synchronous motor, ω r Represents the angular frequency of the permanent magnet synchronous motor, V q Indicates the actual voltage on the q axis, ΔV q represents the actual value of the q-axis disturbance voltage, represents the permanent magnet flux linkage coefficient, represents the estimated value of the q-axis disturbance voltage, and H1 and H2 represent the gains of the Romberg observer.

[0119] S803. Determine a characteristic polynomial of the Lumberg observer according to the state equation and output equation of the Lumberg observer.

[0120] The characteristic polynomial of the Romberg observer is:

[0121]

[0122] Among them, λ is the eigenvalue of the matrix, E is the unit matrix, R s Represents the phase resistance of the permanent magnet synchronous motor, L s represents the phase inductance of the permanent magnet synchronous motor, and H1 and H2 represent the gains of the Romberg observer.

[0123] In order to ensure that the Lumberg observer can accurately estimate the q-axis voltage disturbance, the eigenvalues ​​of the system must all fall on the left half of the s-plane. Here, let the cutoff frequency of the Lumberg observer be ω c , then:

[0124]

[0125] S804: Determine the gain of the Lumberg observer according to the characteristic polynomial of the Lumberg observer, and then determine the discretization expression of the Lumberg observer.

[0126] S805. Calculate an estimated value of a q-axis disturbance voltage of the permanent magnet synchronous motor through a Romberg observer according to the actual q-axis voltage of the permanent magnet synchronous motor, the actual q-axis current of the permanent magnet synchronous motor, and the angular frequency of the permanent magnet synchronous motor.

[0127] In some embodiments, at each sampling moment, an estimated value of the q-axis current at the current moment is calculated based on the actual q-axis voltage of the permanent magnet synchronous motor, the actual q-axis current of the permanent magnet synchronous motor, the angular frequency of the permanent magnet synchronous motor, and the estimated value of the q-axis current at the previous moment.

[0128] The estimated value of the q-axis disturbance voltage at the next moment is calculated according to the estimated value of the q-axis current at the current moment, the actual value of the q-axis current at the current moment, the sampling period of the Romberg observer, and the estimated value of the q-axis disturbance voltage at the current moment.

[0129]

[0130] represents the estimated value of the q-axis current at the current moment, L s Represents the motor phase inductance, R s represents the motor phase resistance, ΔT represents the sampling period of the Romberg observer, represents the estimated value of the q-axis current at the previous moment, represents the estimated value of the q-axis disturbance voltage at the previous moment, ω r (k-1) represents the angular frequency of the permanent magnet synchronous motor at the previous moment, V q (k-1) represents the actual voltage of the q axis at the previous moment, represents the permanent magnet flux coefficient, i d (k-1) represents the actual current of the d-axis at the previous moment, i q (k-1) represents the actual current of the q axis at the previous moment.

[0131] represents the estimated value of the q-axis disturbance voltage at the next moment, represents the estimated value of the q-axis disturbance voltage at the current moment, i q (k) represents the actual value of the q-axis current at the current moment, and H1 and H2 represent the gains of the Romberg observer.

[0132] S806. According to the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor, adjust the dead zone compensation time of the inverter through the PI regulator so that the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor approaches zero.

[0133] The discretization expression of the PI regulator is:

[0134]

[0135] Kp Represents the proportionality coefficient, K i represents the integral coefficient, ΔT represents the sampling period, represents the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor at the current moment, Indicates the cumulative value of the q-axis voltage estimate from the start time to the current time.

[0136] Fig. 9 is a flow chart of another inverter dead time compensation method provided by an embodiment of the present invention, such as Fig. 9 As shown, the inverter dead time compensation method includes:

[0137] S901. Determine a Romberg observer according to a mathematical model of the permanent magnet synchronous motor.

[0138] S902. Calculate an estimated value of a q-axis disturbance voltage of the permanent magnet synchronous motor through a Romberg observer according to the actual q-axis voltage of the permanent magnet synchronous motor, the actual q-axis current of the permanent magnet synchronous motor, and the angular frequency of the permanent magnet synchronous motor.

[0139] S903 . According to the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor, adjust the dead zone compensation time of the inverter through the PI regulator so that the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor approaches zero.

[0140] S904: Obtain the dead zone compensation time required for the control signal of the switch tube of the upper bridge arm according to the direction of the three-phase current of the permanent magnet synchronous motor and the dead zone compensation time.

[0141] Assume that the total dead zone compensation time T is given com If the direction of the three-phase current is known, the dead zone compensation time T can be adjusted according to a certain ratio. com The dead zone compensation time of the control signal allocated to the upper bridge arm switch tube of each phase.

[0142] For example,

[0143] Among them, T a_com It represents the dead zone compensation time of the first switch tube M1 of the upper bridge arm of the inverter phase a, T b_com It represents the dead zone compensation time of the second switch tube M2 of the upper bridge arm of the inverter phase b, T c_com It represents the dead zone compensation time of the third switch tube M3 of the upper bridge arm of phase c of the inverter.

[0144] The effectiveness of the present invention is verified by system simulation. The corresponding simulation parameters are shown in Table 1, and the corresponding simulation results are shown in Table 1. Figure 10-14 As shown in the figure, the motor target current is 10A and the motor speed is 500rpm.

[0145] Table 1 System simulation parameters

[0146]

[0147] Obviously, after adding the online compensation of the inverter dead time, the current distortion can be effectively suppressed in the time domain (such as Figure 10-13 In the frequency domain, it can effectively reduce the high-order harmonic components in the current and significantly reduce the THD value of the current (as shown in Fig.14 As shown). In summary, the compensation method proposed in the present invention can effectively suppress the high-order harmonic components generated by the phase current of the motor during operation, which helps to improve the stability of the EPS system during operation. Compared with the existing main methods, the inverter dead zone compensation method provided in the embodiment of the present invention can update the dead zone compensation time of the inverter online in real time. In addition, the method is simple and easy to implement, and is suitable for various types of EPS systems based on permanent magnet synchronous motors.

[0148] Based on the same inventive concept, the present invention also provides a permanent magnet synchronous motor control system, which includes a controller and an inverter. The controller is used to execute the inverter dead time compensation method provided by any embodiment of the present invention, and has the beneficial effects of the inverter dead time compensation method of any of the above-mentioned embodiments of the present invention.

[0149] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for compensating inverter dead time, characterized in that: The inverter is used to drive a permanent magnet synchronous motor, and the inverter dead time compensation method includes: Determining a Romberg observer according to the mathematical model of the permanent magnet synchronous motor; Calculating an estimated value of a q-axis disturbance voltage of the permanent magnet synchronous motor by the Romberg observer according to the actual q-axis voltage of the permanent magnet synchronous motor, the actual q-axis current of the permanent magnet synchronous motor and the angular frequency of the permanent magnet synchronous motor; According to the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor, the dead zone compensation time of the inverter is adjusted through a PI regulator so that the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor approaches 0; wherein the PI regulator is used to characterize the relationship between the estimated value of the q-axis disturbance voltage and the dead zone compensation time of the inverter.

2. The inverter dead time compensation method according to claim 1, characterized in that: The step of determining the Romberg observer according to the mathematical model of the permanent magnet synchronous motor comprises: Establishing a mathematical model of the permanent magnet synchronous motor in a synchronous rotating coordinate system, and converting the q-axis voltage equation of the permanent magnet synchronous motor into a state equation; Constructing the state equation and output equation of the Romberg observer according to the state equation of the q-axis voltage of the permanent magnet synchronous motor; Determine the characteristic polynomial of the Lumberg observer according to the state equation and the output equation of the Lumberg observer; The gain of the Romberg observer is determined according to the characteristic polynomial of the Romberg observer, and then the discretization expression of the Romberg observer is determined.

3. The inverter dead time compensation method according to claim 2, characterized in that: The state equation of the q-axis voltage of the permanent magnet synchronous motor is: Among them, i q Indicates the actual current of the q axis, i d Indicates the actual current of the d-axis, R s Represents the phase resistance of the permanent magnet synchronous motor, L s represents the phase inductance of the permanent magnet synchronous motor, ω r Represents the angular frequency of the permanent magnet synchronous motor, V q Indicates the actual voltage on the q axis, ΔV q represents the actual value of the q-axis disturbance voltage, Represents the permanent magnet flux linkage coefficient.

4. The inverter dead time compensation method according to claim 2, characterized in that: The state equation and output equation of the Lumberg observer are: Among them, i q represents the actual current of q axis, represents the estimated value of the q-axis disturbance current, i d Indicates the actual current of the d-axis, R s Represents the phase resistance of the permanent magnet synchronous motor, L s represents the phase inductance of the permanent magnet synchronous motor, ω r Represents the angular frequency of the permanent magnet synchronous motor, V q Indicates the actual voltage on the q axis, ΔV q represents the actual value of the q-axis disturbance voltage, represents the permanent magnet flux linkage coefficient, represents the estimated value of the q-axis disturbance voltage, and H1 and H2 represent the gains of the Romberg observer.

5. The inverter dead time compensation method according to claim 2, characterized in that: The characteristic polynomial of the Romberg observer is: C＝[1 0]； Among them, λ is the eigenvalue of the matrix, E is the unit matrix, R s Represents the phase resistance of the permanent magnet synchronous motor, L s represents the phase inductance of the permanent magnet synchronous motor, and H1 and H2 represent the gains of the Romberg observer.

6. The inverter dead time compensation method according to claim 2, characterized in that: The gain of the Romberg observer is: Among them, ω c represents the cutoff frequency of the Romberg observer, R s Represents the phase resistance of the permanent magnet synchronous motor, L s Represents the phase inductance of the permanent magnet synchronous motor.

7. The inverter dead time compensation method according to claim 1, characterized in that: The step of calculating the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor by the Romberg observer according to the q-axis actual voltage of the permanent magnet synchronous motor, the q-axis actual current of the permanent magnet synchronous motor and the angular frequency of the permanent magnet synchronous motor comprises: At each sampling moment, according to the actual q-axis voltage of the permanent magnet synchronous motor, the actual q-axis current of the permanent magnet synchronous motor and the angular frequency of the permanent magnet synchronous motor, and the estimated value of the q-axis current at the previous moment, an estimated value of the q-axis current at the current moment is calculated; The estimated value of the q-axis disturbance voltage at the next moment is calculated according to the estimated value of the q-axis current at the current moment, the actual value of the q-axis current at the current moment, the sampling period of the Romberg observer, and the estimated value of the q-axis disturbance voltage at the current moment.

8. The inverter dead time compensation method according to claim 1, characterized in that: The discretization expression of the PI regulator is: K p Represents the proportionality coefficient, K i represents the integral coefficient, ΔT represents the sampling period, represents the estimated value of the q-axis disturbance voltage of the permanent magnet synchronous motor at the current moment, Indicates the cumulative value of the q-axis voltage estimate from the start time to the current time.

9. The inverter dead time compensation method according to claim 1, characterized in that: The inverter comprises an upper bridge arm and a lower bridge arm, wherein the upper bridge arm and the lower bridge arm both comprise a switch tube and a diode connected in anti-parallel to the switch tube; The inverter dead time compensation method further includes: According to the direction of the three-phase current of the permanent magnet synchronous motor and the dead zone compensation time, the dead zone compensation time required for the control signal of the switch tube of the upper bridge arm is obtained.

10. A permanent magnet synchronous motor control system, characterized in that: The permanent magnet synchronous motor control system includes a controller and an inverter, and the controller is used to execute the inverter dead time compensation method described in any one of claims 1-9.

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