CN110441643B

CN110441643B - Inverter power tube open circuit fault diagnosis method in permanent magnet synchronous motor control system

Info

Publication number: CN110441643B
Application number: CN201910725088.6A
Authority: CN
Inventors: 周新秀; 孙军; 韩邦成; 郑世强; 李海涛
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2019-08-07
Filing date: 2019-08-07
Publication date: 2020-11-06
Anticipated expiration: 2039-08-07
Also published as: CN110441643A

Abstract

The invention relates to a method for diagnosing the open circuit fault of an inverter power tube in a permanent magnet synchronous motor control system, which designs a differential current state observer based on a voltage balance equation so as to realize the estimation of ideal differential current of a permanent magnet synchronous motor and estimate the distortion of the differential current of the motor by combining the measured value of the differential current; and then, according to the distortion rule of the motor differential current caused by the fault, designing a corresponding fault detection and positioning algorithm, thereby realizing the rapid and accurate online fault diagnosis of the inverter switching tube open circuit fault. The method has the advantages of strong anti-interference capability, strong robustness, high detection speed, high detection accuracy and the like, and in addition, the method can be also suitable for the stable speed and variable speed stages of the motor and is suitable for two different modulation modes (a space voltage pulse width modulation mode or a carrier-based pulse width modulation mode), so that the method is a universal voltage source type inverter single switch tube open circuit fault diagnosis method.

Description

Inverter power tube open circuit fault diagnosis method in permanent magnet synchronous motor control system

Technical Field

The invention relates to a method for diagnosing the open circuit fault of an inverter power tube in a permanent magnet synchronous motor control system, which is used for detecting the open circuit fault of a switching tube in an inverter on line in real time and positioning a fault source.

Background

The permanent magnet synchronous motor has the advantages of wide speed regulation range, good dynamic response, strong controllability, high power factor and the like, and is widely applied to the fields of industry, military, aerospace and the like. The open circuit fault of the inverter switching tube is one of the most common faults in the permanent magnet synchronous motor control system, which can greatly reduce the control performance of the motor, increase the power loss of the motor and possibly cause catastrophic accidents in extreme cases. In order to avoid the above disadvantages, it is necessary to research a diagnosis method of the open circuit fault of the inverter switching tube to match with a fault tolerance method, so as to ensure that the motor driving system can still safely and reliably operate with high performance after the fault. The existing fault diagnosis methods for the open circuit of the inverter switching tube include a spectrum analysis method, a wavelet transformation method, a switching function method, an average current Park vector method and the like. The spectrum analysis method and the wavelet transformation method need a large amount of signal processing and analysis operation, which causes the low fault detection speed and the low algorithm efficiency, and are not suitable for online fault diagnosis; the switching function method realizes fault diagnosis by detecting the voltage borne by the power tube, which needs to introduce an additional sensor, thereby introducing a new fault source; the mean current Park vector method is used for fault diagnosis on the basis of taking three-phase current as a symmetrical sine wave, but most of the three-phase current has distortion in engineering practice, so that the method has the defects of poor anti-interference capability, high false detection rate and the like. Therefore, the research of the accurate, universal, rapid and anti-interference inverter switching tube open circuit fault diagnosis method is of great significance.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: in a traditional inverter switching tube open-circuit fault diagnosis method, a new fault source is introduced due to the need of adding an additional sensor, or the problems of narrow application range (incapable of being applied to a motor speed change stage), low detection speed, poor anti-interference capability and the like exist.

The technical scheme adopted by the invention for solving the technical problems is as follows: aiming at the problems, the voltage source type inverter switching tube open circuit on-line fault diagnosis method based on the differential current state observer and applied to the three-phase permanent magnet synchronous motor control system is designed. Firstly, a differential current state observer is designed based on a voltage equation of a motor so as to realize the estimation of a differential current distortion value (residual) of the motor, simultaneously eliminate common mode interference and improve the signal-to-noise ratio of the distortion value (residual). And then, a low-pass filter is designed for the current residual error, so that the signal-to-noise ratio of the residual error is further improved. And then, analyzing a change rule of a current residual error when the inverter fails, and designing a fault detection and positioning algorithm based on template matching (minimum distance principle). In order to reduce the false detection rate and the missed detection rate of fault diagnosis, a self-adaptive detection threshold value is designed. The method based on the differential current state observer does not need to add an additional sensor, has the advantages of high detection accuracy, high diagnosis speed, high algorithm efficiency, good anti-interference performance, high robustness and the like, can be applied to the variable speed stage of the motor, and is a high-performance universal fault diagnosis method.

The method comprises the following steps:

step one, data preprocessing. The first step is responsible for processing three-phase current, motor speed, rotor angular position and voltage instruction information to obtain expected line voltage (when the inverter is normal, the expected value (u) of the motor line voltage is equivalently calculated according to the voltage instruction output by the controller_ab ^*、u_ac ^*、u_bc ^*) Differential back emf (difference e between three phase back emf in pairs)_ab、e_ac、e_bc) And differential current (difference between two three-phase currents). Wherein the desired line voltage may be based on a voltage command (u) output by the current controller_d ^*、u_q ^*) Firstly, three-phase voltage instructions (u) are obtained through Park inverse transformation_an ^*、u_bn ^*、u_cn ^*) Then, the amplitude limiting and differential calculation are carried out to obtain the result; differential back-emf e_ab、e_ac、e_bcMotor speed, rotor angular position and motor inverse measured in advance can be usedThe electromotive force waveform function obtains three-phase counter electromotive force, and then the three-phase counter electromotive force is obtained through differential calculation; differential current i₁₂₃(i₁₂₃＝[i₁,i₂,i₃]^T) The differential operation can be directly carried out on the three-phase current to obtain the three-phase current.

And step two, calculating the expected differential current. Step two, substituting the expected line voltage, the differential counter electromotive force and the differential current obtained in the step one into a state equation of a differential current observer of the motor to obtain an ideal differential current

(the differential current value of the motor without considering factors such as interference, parameter perturbation and inverter nonlinearity).

And step three, residual error calculation and filtering. And step three, subtracting the obtained differential current and the expected value thereof to obtain a differential current residual error, and filtering by using a low-pass filter to obtain r.

And step four, extracting residual error characteristics. Calculating the modulus r of the residual vector r and the unit direction vector r thereof_n。

And step five, fault detection and positioning. Comparing the modulus | | r | | | of the residual vector obtained in the fourth step with a set fault detection threshold Th: if | | | r | | non-conducting phosphor>Th, judging system fault and calculating r_nWith each template vector v_i(inverter T without considering parameter perturbation and noise interference_iResidual direction vector at tube break) of the tube_iJudging the position of a fault switch tube in the inverter according to a minimum distance principle; otherwise, the system is judged to be normal.

Through the five steps, the inverter can be quickly and accurately diagnosed on line.

Further, the designed state equation of the differential current state observer is as follows:

wherein R is_sThe phase resistance of the motor, L is the mean value of three-phase inductance, and M is the mean value of mutual inductance among phases; t is the sampling period of the control system, and k represents the sampling point moment; i.e. i₁、i₂And i₃Is a measure of the differential current of the motor, which can be expressed as [ i ]₁,i₂,i₃]^T＝[i_a-i_b,i_a-i_c,i_b-i_c]^T；

And

are respectively i₁、i₂And i₃An estimated value of (d) indicating an ideal differential current of the motor when the inverter is normal; f is the state feedback coefficient (constant) of the observer; u. of₁、u₂And u₃Respectively, are ideal inputs of the motor, from the desired line voltage (u)_ab ^*、u_ac ^*、u_bc ^*) And differential back electromotive force (e)_ab、e_ac、e_bc) Composition, the value of which can be expressed as [ u ]₁,u₂,u₃]^T＝[u_ab ^*-e_ab,u_ac ^*-e_ac,u_bc ^*-e_bc]^T；

Desired phase voltage u in the input term_ab ^*、u_ac ^*And u_bc ^*The following can be determined according to the motor modulation mode and the instruction output by the controller:

for the SVPWM modulation scheme, the desired line voltage can be expressed as:

wherein, U_dcIs the dc bus voltage of the inverter; u. of_xn ^*、u_yn ^*(x, y are phase names, and a, b, c) are voltage reference values in a-b-c coordinate system and can be controlledVoltage reference value u under d-q coordinate system of output of device_d ^*、u_q ^*And (3) obtaining through Park inverse transformation:

wherein, theta_eIs an electrical angle whose value is equal to the product of the number of pole pairs P of the motor and the mechanical angular position theta, i.e. theta_e＝Pθ；

For the PWM modulation mode based on the carrier wave, the voltage reference value u under the d-q coordinate system can be firstly used_d ^*、u_q ^*Obtaining a phase voltage reference value u under an a-b-c coordinate system through Park inverse transformation_an ^*、u_bn ^*And u_cn ^*Then, the reference value u of the terminal voltage of the motor (namely the voltage of the end point of the three-phase winding to the power supply midpoint) is obtained according to the reference value u_as ^*、u_bs ^*And u_cs ^*Then, the corrected terminal voltage reference value u is obtained through amplitude limiting operation_am ^*、u_bm ^*And u_cm ^*Finally, the expected line voltage u is obtained through differential operation_ab ^*、u_ac ^*And u_bc ^*；

The terminal voltage calculation formula is as follows:

in the formula u_abcn ^*＝[u_an ^*,u_bn ^*,u_cn ^*]Max is a function for solving the maximum value, and min is a function for solving the minimum value;

the clipping operation formula is as follows:

wherein z is a phase name, and may be a, b or c, u_z ^*Of z-phase windings of electric machinesA terminal voltage reference value;

differential operation is represented as u_xy ^*＝u_xm ^*-u_ym ^*；

And the differential back electromotive force term e of the motor_xyIs the counter electromotive force e of motor x_xElectromotive force e opposite to y_yThe difference of e_xy＝e_x-e_yAnd the back electromotive force of the motor can bring the real-time measured mechanical angle theta and mechanical angular velocity omega into the back electromotive force waveform function e of the z phase of the motor_zThe back electromotive force waveform function used in (θ, ω) is a function relationship between the back electromotive force, which is determined in advance through experimental measurement, and the motor rotational angle θ and the angular velocity ω.

Further, a set adaptive fault detection threshold is adopted in the fault detection algorithm:

Th＝Th₀+m*||i₁₂₃||

wherein Th₀The part is a fixed threshold value and is used for avoiding false detection caused by random errors; m x i₁₂₃The I is a variable threshold part for avoiding false detection and missing detection caused by regularity errors₁₂₃And | | is a module value of the measured motor differential current, m is a proportionality coefficient (constant) and the value range is between 0 and 1.

Further, the designed fault location is subjected to template matching according to a minimum distance principle to realize fault location, and the method comprises the following steps of:

firstly, a unit direction vector is obtained according to the obtained residual vector r:

wherein r is_nIs a unit direction vector of a residual vector r, and is a module value of r;

second, respectively calculating residual direction vectors r_nAnd six fault template vectors v_iA distance d between_iI ═ 1,2, …, 6; wherein the template vector is:

the distance calculation formula is as follows: d_i＝||r_n-v_i||，i＝1,2,…,6；

Third, find d_iMinimum value of d_jAnd compare it with a fixed threshold d₀And comparing, and judging the mode of the system according to the comparison result: when d is_j<d₀In time, the switching tube T in the inverter is judged_jWhen an open circuit fault occurs, the fault positioning variable Loc is made to be j; otherwise, it continues to wait, i.e. does not change the value of the fault location variable Loc.

The principle of the invention is as follows: the open circuit fault of the inverter switch tube can cause directional distortion of the output voltage of the inverter, and further cause directional distortion of current, and the distortion direction is related to the fault position. Therefore, fault detection and localization can be designed based on current distortion characteristics. The ideal differential current of the motor is estimated by using a current state equation of the motor, and the ideal differential current is subtracted from the measured value of the differential current to obtain the distortion (residual) of the differential current; and extracting the characteristics of the residual error, matching the characteristics with the ideal characteristics of the residual error in fault, and detecting and positioning the fault according to the matching result. The following are the design principle details of the invention:

(1) and analyzing the distortion rule of the inverter output voltage under the open-circuit fault of the switching tube.

The distortion of the output voltage before and after the failure of the corresponding bridge arm of the A-phase winding is taken as an example. When the inverter is normal, the terminal voltage u output by the bridge arm_aCompletely receiving PWM gate signal (S)₁S₂The two gate signals are opposite) and when a certain switch tube in the bridge arm is disconnected, the fault switch tube is in a constant cut-off state and is not influenced by the gate signal, so that the voltage of the output end of the whole bridge arm is not completely influenced by the PWM gate signal S₁S₂And (4) controlling. An upper switch tube T of the bridge arm is arranged below₁Open circuit is taken as an example and two cases (S) are distinguished₁S₂01 and S₁S₂10) analyzing a phase-a terminal voltage u of the inverter output before and after the failure_aThe distortion law of (2).

When S is₁S₂When equal to 01, no matter T₁If the circuit is broken, the a-phase bridge arms are in a state of upper stop and lower conduction (the upper half bridge arm is closed and the lower half bridge arm is conducted), and the current flows as shown in fig. 1. The current flows through a diode or a triode to be connected with the negative end of the power supply, so that the voltage u of the phase A end output by the motor is enabled to be connected_aIs clamped approximately at 0V. This indicates when S is present₁S₂When 01, the output end voltage of the bridge arm is about 0V before and after the fault, and there is no voltage distortion.

When S is₁S₂When the voltage is 10, if no fault exists, the A-phase bridge arm is in a state of being stopped at the bottom and being communicated at the top, and the A-phase end voltage u output by the bridge arm is_aWill be approximately clamped to the DC bus voltage U_dc；

And at T₁At the time of disconnection, T₁Exhibits an off-state due to disconnection, T₂To be connected with S₂Exhibits an off state. At this time, the current i of the A-phase winding_aOnly through diode D₁Or D₂Follow current (as shown in fig. 2). When i is_a<At 0, current i_aFreewheeling via diode D1 at which the terminal voltage u of the a-phase winding_a≈U_dc(ii) a When i is_a>At 0, current i_aFreewheeling is possible only via diode D2, at which point the terminal voltage u of the a-phase winding_a≈0。

Thus: when S is₁S₂10 and i_a<Terminal voltage u of phase A winding at 0_aApproximately equal to U before and after a fault_dcNo voltage distortion; when S is₁S₂10 and i_a>Terminal voltage u of phase A winding at 0_aApproximately equal to U before failure_dcAnd after the fault, the approximate distortion is 0V. Because the current zero-crossing time is short, the subsequent fault detection speed is hardly influenced, and therefore, the voltage distortion condition when the current passes through zero is not analyzed.

In summary, in combination with the state space averaging method, T is obtained in each PWM cycle₁Average terminal voltage of A-phase winding caused by open circuit fault

Amount of distortion generated

Depending on the direction of the a-phase current:

in the formula (I), the compound is shown in the specification,

is the average terminal voltage distortion of the a-phase winding,

the average terminal voltage of the A phase winding of the normal inverter is obtained.

During the operation of the motor, the motor is in operation,

is almost always true, therefore T₁After the tube has an open circuit fault, if and only if i_a>And when the voltage is 0, the average terminal voltage of the output of the bridge arm corresponding to the phase winding A of the inverter is reduced.

Similarly, the direction of terminal voltage distortion caused by open circuit faults of other switch tubes in the inverter can be obtained as follows: when a single upper switching tube (T) of each bridge arm of the inverter₁、T₃Or T₅) After an open circuit fault, if and only if the corresponding phase current is positive (i)_a>0、i_b>0 or i_c>0) The distortion of the terminal voltage output by the failed bridge arm(s) ((

Or

) Is negative; when a single lower switching tube (T) of each bridge arm of the inverter₂、T₄Or T₆) After an open circuit fault occurs, if and only if the corresponding phase current is negative (i)_a<0、i_b<0 or i_c<0) The distortion of the terminal voltage output by the failed bridge arm(s) ((

Or

) Is positive. Under the action of closed-loop control, the three-phase current after the fault still presents periodicity (the period is the electrical angle period of the motor), so that the positive and negative of the current change along with the electrical angle period, which causes the distortion direction of the voltage to also change along with the electrical angle period.

(2) A differential current state observer is designed.

The distortion of the output voltage of the inverter causes the distortion of the phase current of the motor, and in order to realize the estimation of the current distortion, a state observer can be used for realizing the observation of the ideal current and making a difference with the actually measured current of the motor, thereby estimating the distortion amount of the current. The current state observer can be designed by utilizing a three-phase voltage balance equation of the motor:

wherein i_a ^*、i_b ^*And i_c ^*When the inverter is normal, the ideal three-phase current value of the motor is obtained under the condition of neglecting interference and nonlinearity of the inverter; u. of_an ^*、u_bn ^*And u_cn ^*For desired three-phase voltage reference values (output u via current controller)_d ^*、u_q ^*Determined by inverse Park transformation), e_a、e_b、e_cIs the three-phase back electromotive force of the motor. p is the derivation operator (derivation over time), R_sThe method is characterized in that the method is a motor phase resistance, L is a mean value of self inductance of a three-phase winding of a motor, and M is a mean value of mutual inductance between windings.

Then, according to the voltage balance equation of the motor, the neutral point voltage u of the motor is known_nIs the average of the voltages at the three phases. Therefore, any terminal voltage distortion will be conductedResulting in a voltage u_nAnd the distortion is caused, so that the three-phase voltage of the motor is distorted, and finally, the three-phase current is distorted. Therefore, the method based on the three-phase current state observer is difficult to realize positioning. In order to solve the problem, we perform differential processing on the current observer based on the idea of generalized dedicating the observer (in a single fault, only one state is not affected by the fault, and other states are all affected), so as to obtain a differential current state observer:

in the formula i_ab ^*、i_ac ^*And i_bc ^*Is a desired value of the differential current, and [ i_ab ^*,i_ac ^*,i_bc ^*]＝[i_a ^*-i_b ^*,i_a ^*-i_c ^*,i_b ^*-i_c ^*]；u_ab ^*、u_ac ^*And u_bc ^*To a desired line voltage, and [ u ]_ab ^*,u_ac ^*,u_bc ^*]＝[u_a ^*-u_b ^*,u_a ^*-u_c ^*,u_b ^*-u_c ^*]；e_ab,、e_acAnd e_bcIs a differential back electromotive force, and [ e ]_ab,e_ac,e_bc]＝[e_a-e_b,e_a-e_c,e_b-e_c]. Analysis shows that the distortion of one terminal voltage leads to the distortion of two associated line voltages, while the irrelevant line voltages remain unchanged. Therefore, the design is beneficial to simplifying subsequent fault location algorithms.

Discretizing the observer to obtain:

in the formula (I), the compound is shown in the specification,

and

is an ideal differential current of the motor u₁、u₂And u₃Is a differential output of the motor, and₁,u₂,u₃]＝[u_ab ^*-e_ab,u_ac ^*-e_ac,u_bc ^*-e_bc]k denotes the kth sampling instant, and T is the sampling period (typically a PWM period).

In the observer equation of state input, the phase voltage u is expected_ab ^*、u_ac ^*And u_bc ^*Can be determined by park inverse transformation, amplitude limiting and differential calculation according to the motor modulation mode and the instruction output by the controller.

The Park inverse transformation formula is:

wherein u is_an ^*、u_bn ^*And u_cn ^*Is a phase voltage reference value u in an a-b-c coordinate system_d ^*、u_q ^*Is the output of the current controller, i.e. the voltage reference in d-q coordinate system, theta_eIs an electrical angle whose value is equal to the product of the number of pole pairs P of the motor and the angular position theta, theta_e＝Pθ。

Amplitude limiting and differential calculation: the amplitude limiting and differential calculation refers to a process of correcting the three-phase voltage instruction according to the saturation characteristic of the inverter and obtaining the expected line voltage through differential calculation.

For the SVPWM modulation scheme, the desired line voltage can be expressed as:

in the formula of U_dcIs the dc bus voltage of the inverter; x and y are phase names, and a, b, c and u can be selected_xn ^*、u_yn ^*Is a phase voltage reference value under an a-b-c coordinate system.

For the carrier-based PWM (pulse-width modulation) mode, a three-phase terminal voltage reference value u of the motor is obtained according to a three-phase voltage reference value_as ^*、u_bs ^*And u_cs ^*Then, the corrected terminal voltage reference value u is obtained through amplitude limiting operation_am ^*、u_bm ^*And u_cm ^*Finally, the expected line voltage u is obtained through differential operation_ab ^*、u_ac ^*And u_bc ^*。

The terminal voltage calculation formula is as follows:

in the formula u_abcn ^*＝[u_an ^*,u_bn ^*,u_cn ^*]Max is the function for maximum, min is the function for minimum.

The clipping operation formula is as follows:

wherein z is a phase name, and may be a, b or c, u_z ^*Terminal voltage reference values for the z-phase windings of the machine.

Differential operation is represented as u_xy ^*＝u_xm ^*-u_ym ^*。

And the differential back electromotive force term e of the motor_xyIs the counter electromotive force e of motor x_xElectromotive force e opposite to y_yThe difference of e_xy＝e_x-e_y. The back electromotive force of the motor can measure the electrical angle theta in real time_eAnd electrical angular velocity ω_eBack emf waveform function e taken into the z-phase of the motor_z(θ_e,ω_e) The result is obtained in (1). The back electromotive force waveform function is a functional relation between back electromotive force, which is determined in advance through experimental measurement, and a motor rotation angle theta and an angular speed omega.

In addition, in order to improve the robustness and the anti-interference capability of the observer, the observer can be closed-loop:

wherein F is the feedback coefficient. In engineering practice, the position of the closed-loop pole can be determined according to the stability of the observer, the convergence speed of the residual error and the like, and the value of F can be determined according to the pole position.

(3) And residual calculation and filtering.

Defining the measured value i and the estimated value of the differential current

The difference of (d) is the differential current residual r, i.e.

In order to improve the signal-to-noise ratio of the residual, the residual needs to be filtered. It is considered that the residual error is mainly caused by random errors and regular errors. The former is mostly represented by high frequency noise, and the frequency of the former is mostly not lower than the pulse width modulation frequency f_PWM(ii) a The latter is mainly caused by model parameter errors and faults and its frequency is generally not higher than 5 times the electrical angular frequency f_e. Therefore, the residual can be filtered by a low-pass filter, and the cut-off frequency of the filter should be set at 5 ω_e～f_PWMIn the meantime. To simplify the algorithm, a first order analog low-pass filter may be used and discretized using a bilinear transform:

where T is the sampling period (also PWM period) of the control system, τ is the rise time of the first-order low-pass filter, and τ can be set to:

wherein P is the pole pair number of the motor, omega_rIs the rated rotating speed of the motor.

(4) And (5) residual error orientation analysis.

For this observer, the residual is mainly caused by model parameter inaccuracies and inverter faults. For a closed-loop observer, the former brings less residual. Therefore, when the switching tube fails, only the residual error caused by the failure of the inverter can be considered:

the voltage distortion can be obtained by performing z-transform on the above formula

To residual error r_iTransfer function between:

it can be seen that no matter what value i takes, the corresponding transfer functions are the same first-order inertia elements. Therefore, the residual r can quickly reflect the magnitude and direction of the voltage distortion Δ u. By combining the distortion law of the output voltage of the inverter under the open-circuit fault of the switch tube and the state equation of the residual error, the residual error caused by the open-circuit fault of a single switch tube has directionality, and the direction vector of the residual error is shown in the following table:

(5) and (4) fault detection and positioning algorithm.

The fault detection and positioning algorithm only aims at the open-circuit fault of a single switching tube of the inverter, namely, the faults are considered to not occur simultaneously, and other faults except the open-circuit fault of the switching tube do not exist.

By residual analysis, it can be known that: when the inverter is normal, the residual error amplitude is small, and the direction is indefinite; when a single switch of the inverter is disconnected, the residual error amplitude is rapidly increased, and the residual error is oriented. The fault detection and location algorithm can be designed according to the rule.

And (3) a fault detection algorithm: and calculating residual amplitude r, comparing the residual amplitude r with a detection threshold Th by using the residual amplitude r as a detection index, and judging whether the system fails according to a comparison result. If | | | r | > Th, it is determined that the inverter has a fault, that is, the fault flag variable H is 1, otherwise, the system is considered to be healthy (H is 0). When the system is healthy, the residual error amplitude is not zero due to the existence of random errors and regular errors. The residual error caused by the random error is still the random error, and the size of the residual error can be estimated by a statistical method; the regularity error is mainly caused by model parameter error, and analysis shows that the amplitude of residual error caused by the regularity error is approximately proportional to the current amplitude. In summary, the detection threshold may be set to the adaptive threshold:

Th＝Th₀+m*||i₁₂₃||

in the formula, Th₀Is constant, designed primarily for random errors; m is a proportionality coefficient, | | i₁₂₃I is the measured motor differential current vector i₁₂₃M.i.₁₂₃The term | is designed mainly for regularity errors. The parameter Th can be set by₀And m is selected from:

Th₀: under a rated load, the driving motor operates at a rated rotating speed, and the standard deviation sigma of the random residual error is estimated by using a statistical method. Setting Th₀＝(6～12)·σ。

m: and deviating the parameters of the observer from the calibration parameters of the motor (the resistance is reduced by 30%, the inductance is increased by 50%, and the flux linkage is increased by 30%) according to the most extreme condition, and driving the motor to operate at the rated rotating speed under the rated load. Increasing the value of m from 0 until no error detection happens, and recording the value m of m at the moment₀. Setting m to be (1.5-2.5) · m₀。

And (3) fault positioning algorithm: when the system is detected to be in fault, the algorithm respectively calculates residual direction vectors r_nAnd six fault template vectors v_iA distance d between_iGet d_iMinimum value of d_jWith a fixed threshold value d₀(which can be set between 5 and 10 °) were compared. If d is_j<d₀If the open-circuit fault source of the inverter is determined to be T_jI.e. let the fault locator variable Loc equal j, otherwise, continue to wait (without changing the value of the fault locator variable).

Wherein the template vector is:

the distance calculation formula is as follows: d_i＝||r_n-v_i||，i＝1,2,…,6。

Compared with the prior art, the invention has the advantages that:

1. the online fault diagnosis algorithm designed by the invention can run by depending on the information (rotating speed, angular position, three-phase current and voltage instruction) acquired by the permanent magnet synchronous motor control system, and can realize online fault diagnosis of the inverter switching tube without an additional sensor.

2. The invention does not require three-phase current to be sinusoidal current, so the invention is suitable for both the speed regulation stage and the constant speed stage of the motor.

3. The observer designed by the invention is a closed-loop observer, so that the observer has stronger interference resistance and robustness.

4. The fault detection index adopted by the invention is the modulus of the differential current residual error, and the fault detection index can quickly respond to the fault, so the fault detection speed of the detection algorithm is high.

5. The invention designs the self-adaptive fault threshold value for fault detection, greatly reduces the false detection rate of the algorithm and improves the accuracy of the algorithm detection result.

Drawings

FIG. 1 shows T in the inverter₁Open circuit and S₁S₂When equal to 01The A-phase current of (1) flows to a schematic diagram;

FIG. 2 shows T in the inverter₂Open circuit and S₁S₂The a-phase current flow at 10 is schematic;

fig. 3 is a schematic structural diagram of a permanent magnet synchronous motor control system according to the present invention (illustrating the source of input information of a fault diagnosis algorithm);

FIG. 4 is a block diagram of a fault diagnosis algorithm contemplated by the present invention;

fig. 5 is an algorithm flow chart of the whole system.

Detailed Description

The invention is further described with reference to the following figures and detailed description.

Fig. 4 is a structural diagram of the present invention, wherein 1 represents an inverse coordinate transformation module, 2 represents a voltage command correction module, 3 represents a back electromotive force calculation module, 4 represents a differential current observer module, 5 represents a current differential operation module, 6 represents a low-pass filtering module, 7 represents a residual amplitude and direction calculation module, and 8 represents a fault detection and location module. The eight modules are operated in combination with each other,

the algorithm flow diagram of the present invention is shown in fig. 5, where each step corresponds to one or more of the modules in fig. 4:

after the system is started, the whole algorithm starts:

first, an initial value is assigned. This step performs initial assignments for all variables involved in the algorithm (average magnitude is zero). The fault mark variable H is assigned to be zero to represent that the system is healthy, and the fault location variable Loc is assigned to be zero to represent that the location is uncertain.

Collecting motor system data i_abc、u_dq ^*θ and ω. These data may be collected as shown in fig. 3. Wherein i_abc(three-phase Current of the Motor, i_abc＝[i_a,i_b,i_c]^T) Theta and omega are feedback information of the motor control system, and data acquisition can be realized through an original sensor and an AD converter of the control system; and u_dq ^*Is the output (u) of the current controller_dq ^*＝[u_d ^*,u_q ^*]^T) And the voltage command in the d-q coordinate system can be directly called.

And thirdly, preprocessing the data. The step is composed of four modules of a coordinate inverse transformation module 1, a voltage command correction module 2, a back electromotive force calculation module 3 and a current differential operation module 5 in fig. 4. The functions and specific algorithms of the four modules are as follows:

coordinate inverse transformation module 1: the coordinate inverse transformation module is responsible for converting a voltage command u under a d-q coordinate system_dq ^*Converting the voltage command into a voltage command u under an a-b-c coordinate system_abcn ^*The core algorithm is as follows:

voltage command correction module 2: the voltage instruction correction module corrects the three-phase voltage instruction output by the coordinate inverse transformation module 1 according to the saturation characteristic of the inverter to obtain a corrected line voltage expected value u_xym ^*. The core algorithm is different with different modulation modes:

for SVPWM modulation mode, the expected value u of line voltage_xym ^*The calculation formula of (A) is as follows:

wherein, U_dcFor the DC bus voltage of the inverter, x, y are different phase names, and (x, y) can take three groups of values (a, b), (a, c) and (b, c), u_xn ^*、u_yn ^*The voltage reference values in the a-b-c coordinate system output by the coordinate inverse transformation module 1.

For the carrier-based PWM (pulse-width modulation) mode, a three-phase voltage reference value u can be firstly used_abcn ^*Determining a three-phase terminal voltage reference value u of the electric machine_as ^*、u_bs ^*And u_cs ^*Then, the corrected terminal voltage reference value u is obtained through amplitude limiting operation_am ^*、u_bm ^*And u_cm ^*Finally, the expected line voltage u is obtained through differential operation_abm ^*、u_acm ^*And u_bcm ^*。

The terminal voltage calculation formula is as follows:

in the formula u_abcn*＝[u_an ^*,u_bn ^*,u_cn ^*]Max is the function for maximum, min is the function for minimum.

The clipping operation formula is as follows:

The differential operation is: u. of_xym ^*＝u_xm ^*-u_ym ^*。

Counter electromotive force calculation module 3: the counter electromotive force calculation module substitutes the motor rotation speed omega and the rotation angle theta into a pre-measured counter electromotive force waveform function e (omega, theta) to obtain the three-phase counter electromotive force e of the motor_abc。

Current differential operation module 5: the current differential operation module calculates the current according to three phases i_abcCalculating a differential current i₁₂₃The algorithm is as follows:

[i₁,i₂,i₃]^T＝[i₁-i₂,i₁-i₃,i₂-i₃]^T

calculating the expected differential current

This step corresponds to the differential current observer module 4 of fig. 4, whose core algorithm is:

the selection principle of the parameter F has already been explained in the inventive principle, and is not described again.

And fifthly, residual calculation and filtering. This step corresponds mainly to the low-pass filter module 6 in fig. 4, and is responsible for subtracting the differential current and the expected value thereof obtained in the steps (c) and (c) to obtain the residual error r₁₂₃And then, filtering each component of the obtained residual error by using a digital low-pass filter, thereby increasing the anti-interference capability of a subsequent fault diagnosis algorithm. Wherein the pulse transfer function of the low-pass filter is:

where T is the sampling period (also PWM modulation period) of the control system, τ is the rise time of the first-order low-pass filter, and τ can be set to:

Calculating residual module value r and direction r_n. This step corresponds to the residual module value and direction calculation module 7 in fig. 4, and its algorithm is:

and seventhly, calculating an adaptive threshold Th. This step is accomplished in the fault detection and location module 8 in fig. 4. The algorithm of the step is as follows:

Th＝Th₀+m*||i₁₂₃||

in the formula, Th₀And m is a constant coefficient, and the value principle thereof is shown in the summary of the invention.

And eighthly, fault detection. This step is performed in the fault detection and location module 8 in fig. 4, and is responsible for comparing the residual modulus | | | r | | obtained in step c with the adaptive threshold Th obtained in step c, and determining whether the system is faulty according to the comparison result: if | | | r | > Th, judging a system fault (making a fault mark variable H equal to 1), and performing subsequent fault location; otherwise, the system is considered to be fault-free (the fault flag variable H is set to 0), H, Loc is output, and the loop is ended.

And ninthly, calculating the minimum distance and the position. This step is performed in the fault detection and location module 8 in fig. 4, and can be performed in two steps: firstly, respectively calculating residual direction vectors r_nAnd six template vectors v_iThe minimum value of the six distances and the position of the minimum value are obtained. The core algorithm is as follows:

d_i＝||r_n-v_i||，d_j＝min(d_i)，i＝1,2,……,6。

wherein the template vector is:

and (8) locating the fault in the red (R). This step is performed in the fault detection and location module 8 in fig. 4, which is responsible for determining the minimum distance d determined in step ninu_jWith a set threshold value d₀Comparing the sizes of the two parts (generally arranged between 5 and 10 degrees), and positioning a fault source according to a comparison result: if d is_j<d₀Then, the inverter switch tube T is determined_jAn open circuit fault occurs (let Loc j); otherwise, the previous fault location result (Loc ═ Loc) is maintained. This cycle is ended after this step is completed.

Those skilled in the art will appreciate that the details of the present invention not described in detail herein are well within the skill of those in the art.

Claims

1. A method for diagnosing open circuit fault of an inverter power tube in a permanent magnet synchronous motor control system is characterized by comprising the following steps: the method is applied to a three-phase permanent magnet synchronous motor control system, and realizes the rapid and accurate online fault diagnosis of the inverter by utilizing three-phase current, motor speed, rotor angle position and voltage instruction information which can be obtained and detected in the permanent magnet synchronous motor control system on the premise of not increasing a sensor, and the method comprises the following steps:

step one, preprocessing data; the first step is responsible for processing the obtained three-phase current, the motor rotating speed, the rotor angular position and the voltage instruction information to obtain the expected line voltage u_ab ^*、u_ac ^*、u_bc ^*Differential counter-potential e_ab、e_ac、e_bcAnd a differential current i₁₂₃Wherein the line voltage u is desired_ab ^*、u_ac ^*、u_bc ^*Voltage command u that can be output by a current controller_d ^*、u_q ^*Firstly, three-phase voltage instruction u is obtained through Park inverse transformation_an ^*、u_bn ^*、u_cn ^*Then, the amplitude limiting and differential calculation are carried out to obtain the result; differential back-emf e_ab、e_ac、e_bcThe difference between every two three-phase counter electromotive force can be obtained by firstly utilizing the rotating speed of the motor, the angular position of the rotor and a pre-measured waveform function of the counter electromotive force of the motor, and then the three-phase counter electromotive force is obtained by differential calculation; differential current i₁₂₃＝[i₁,i₂,i₃]^TThen the three-phase current i can be directly controlled_abc＝[i_a,i_b,i_c]^TPerforming differential operation to obtain;

step two, calculating expected differential current; step two, substituting the expected line voltage, the differential counter electromotive force and the differential current obtained in the step one into a state equation of a differential current observer of the motor to obtain an ideal differential current

The ideal differential current is the differential current value of the motor under the premise of not considering faults, interference, parameter perturbation and nonlinear factors of the inverter except saturation characteristics;

step three, residual calculation and filtering; the third step is to make a difference between the obtained differential current and the expected value thereof to obtain a differential current residual error, and filtering is carried out by using a low-pass filter to obtain r;

step four, extracting residual error characteristics; calculating the modulus r of the residual vector r and the unit direction vector r thereof_n；

Step five, fault detection and positioning; comparing the modulus | | r | | | of the residual vector obtained in the fourth step with a set adaptive fault detection threshold Th: if | | | r | | non-conducting phosphor>Th, judging system fault and calculating r_nWith each template vector v_iA distance d between_iJudging the position of a fault switch tube in the inverter according to a minimum distance principle; otherwise, judging the system to be normal; wherein each template vector v_iThe inverter power tube T does not consider parameter perturbation and noise interference_iResidual direction vector during open circuit;

through the five steps, the inverter can be quickly and accurately diagnosed on line;

the designed state equation of the differential current state observer is as follows:

And

are respectively i₁、i₂And i₃An estimated value of (d) indicating an ideal differential current of the motor when the inverter is normal; f is a state feedback coefficient of the observer; u. of₁、u₂And u₃Respectively, are ideal inputs of the motor, respectively, from a desired line voltage u_ab ^*、u_ac ^*、u_bc ^*And differential back electromotive force e_ab、e_ac、e_bcComposition, the value of which can be expressed as [ u ]₁,u₂,u₃]^T＝[u_ab ^*-e_ab,u_ac ^*-e_ac,u_bc ^*-e_bc]^T；

Desired line voltage u in observer input_ab ^*、u_ac ^*And u_bc ^*The following can be determined according to the motor modulation mode and the instruction output by the controller:

for the SVPWM modulation scheme, the desired line voltage can be expressed as:

wherein, U_dcIs the dc bus voltage of the inverter; u. of_xn ^*、u_yn ^*Is a voltage reference value u in a-b-c coordinate system and can be output by the controller_d ^*、u_q ^*And (3) obtaining through Park inverse transformation:

For the PWM modulation mode based on the carrier wave, the voltage reference value u under the d-q coordinate system can be firstly used_d ^*、u_q ^*Obtaining a phase voltage reference value u under an a-b-c coordinate system through Park inverse transformation_an ^*、u_bn ^*And u_cn ^*Then, the terminal voltage reference value u of the motor is obtained according to the value_as ^*、u_bs ^*And u_cs ^*Then, the corrected terminal voltage reference value u is obtained through amplitude limiting operation_am ^*、u_bm ^*And u_cm ^*Finally, the expected line voltage u is obtained through differential operation_ab ^*、u_ac ^*And u_bc ^*；

The terminal voltage calculation formula is as follows:

the clipping operation formula is as follows:

wherein z is a phase name, and may be a, b or c, u_z ^*Terminal voltage reference value of the motor z-phase winding;

differential operation is represented as u_xy ^*＝u_xm ^*-u_ym ^*；

And the differential back electromotive force term e of the motor_xyIs the counter electromotive force e of motor x_xElectromotive force e opposite to y_yThe difference of e_xy＝e_x-e_yAnd the counter electromotive force of the motor can bring the real-time measured mechanical angle theta and mechanical angular velocity omega into the waveform function e of the counter electromotive force of the z phase of the motor_zThe back electromotive force waveform function used in (θ, ω) is a function relationship between the back electromotive force, which is determined in advance through experimental measurement, and the motor rotational angle θ and the angular velocity ω.

2. The fault diagnosis method according to claim 1, characterized in that: the fault detection algorithm adopts a set self-adaptive fault detection threshold value:

Th＝Th₀+m*||i₁₂₃||

wherein Th₀The part is a fixed threshold value and is used for avoiding false detection caused by random errors; m x i₁₂₃The I is a variable threshold part for avoiding false detection and missing detection caused by regularity errors₁₂₃And | | is a module value of the measured motor differential current, m is a proportionality coefficient, and the value range is between 0 and 1.

3. The fault diagnosis method according to claim 1, characterized in that: the designed fault location is subjected to template matching according to a minimum distance principle to realize fault location, and the method comprises the following steps:

second, respectively calculating residual direction vectors r_nAnd six fault template vectors v_iA distance d between_i，i＝1,2,…,6；

Wherein the template vector is:

Third, find d_iMinimum value of d_jAnd compare it with a fixed threshold d₀And comparing, and judging the mode of the system according to the comparison result: when d is_j<d₀In time, the switching tube T in the inverter is judged_jIn the event of a disconnection fault, i.e. orderA fault location variable Loc ═ j; otherwise, it continues to wait, i.e. does not change the value of the fault location variable Loc.