Open-circuit fault diagnosis method of power tube in composite energy source based on Romberg observer

Abstract

The present invention proposes a composite energy source power tube open circuit fault diagnosis method based on a Lumberg observer, comprising the following steps: S1, establishing a global mathematical model; S2, constructing a global Lumberg observer, and using the Lumberg observer for observation; S3, comparing the observed value of the Lumberg observer with the actual system measurement value to obtain the residual of the fault signal; judging whether the power tube is open circuited according to whether the residual evaluation function of the DC bus voltage exceeds the threshold; if an open circuit occurs, comparing the observed residual absolute value of the output current on the battery side with the observed residual absolute value of the output current on the supercapacitor side, and an open circuit fault occurs on the power tube on the side with the larger residual absolute value; finally, judging the open circuit object according to the operating state of the permanent magnet synchronous motor. The present invention can efficiently and accurately realize the detection and positioning of bidirectional DC / DC power tube open circuit faults in the composite energy source system.

Description

Technical Field

[0001] The present invention relates to the technical field of fault diagnosis, and in particular to a composite energy source power tube open circuit fault diagnosis method based on a Romberg observer. Background Art

[0002] For electric vehicles, batteries are often used as on-board energy sources, but the power density of batteries is difficult to meet the power requirements of high-performance electric vehicles. At the same time, the braking energy recovery efficiency is low, and the frequent high-current charging and discharging will seriously reduce the service life and safety of the batteries. Supercapacitors have excellent power density and cycle life performance, and have been increasingly widely used in recent years, but their energy density is low and they cannot become the main energy source of electric vehicles. As single energy sources, batteries and supercapacitors have their own obvious advantages and disadvantages. The composite energy source composed of batteries and supercapacitors can give full play to the advantages of high energy density of batteries and high power density of supercapacitors, and significantly improve the power performance and braking energy recovery efficiency of electric vehicles with the best cost-effectiveness. Considering the randomness and volatility of load power during the driving process of electric vehicles, it is proposed to use supercapacitors with high power density, long charge and discharge cycle life and fast response speed, and batteries with high energy density but not easy to charge and discharge frequently to form an efficient and reliable composite energy storage. In order to reduce the volatility of battery charging and discharging power, effectively protect the battery and extend the service life of the entire system, a low-pass filter is used to reasonably distribute the load power between the two energy storage sources, the battery and the supercapacitor. Usually, both the battery and the supercapacitor are connected to a bidirectional DC / DC converter in parallel with the DC bus to achieve independent control of the two energy storage sources.

[0003] For the composite energy source system for electric vehicles, in actual operating conditions, the bidirectional DC / DC converter is the most prone to failure. Its failures mainly include power tube failure, capacitor failure and interface failure. Among them, power tube failure accounts for about 31% of converter failures, mainly power tube open circuit failure and short circuit failure; short circuit failure evolves quickly, and fast fuses are usually added to the converter to convert short circuit failure into open circuit failure. Power tube open circuit failure is bound to affect the control function of the converter and even the realization of the normal function of the composite energy source permanent magnet motor system. Long-term operation under fault conditions will reduce the reliability of the composite energy source permanent magnet motor system, and even induce secondary faults, causing the entire system to paralyze. Therefore, it is of great significance to study the power tube fault diagnosis technology of the composite energy source system for electric vehicles to ensure the safe operation of electric vehicles. However, the current power tube open circuit fault diagnosis method is relatively complex, costly and unreliable, and is not practical. Summary of the invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a composite energy source power tube open circuit fault diagnosis method based on the Romberg observer.

[0005] The composite energy source power tube open circuit fault diagnosis method based on the Romberg observer proposed in the present invention comprises the following steps:

[0006] S1. Establish a global mathematical model based on the state equation of the composite energy source system;

[0007] S2. Construct a global Lumberg observer according to the state equation of the composite energy source system, and use the Lumberg observer to observe the DC bus voltage, the output current of the battery side, and the output current of the supercapacitor side;

[0008] S3. Compare the observed value of the Lumberg observer with the actual system measurement value to obtain the residual of the fault signal; determine whether the power tube is open-circuited based on whether the residual evaluation function of the DC bus voltage exceeds the threshold; if an open circuit occurs, compare the absolute value of the observed residual of the output current on the battery side with the absolute value of the observed residual of the output current on the supercapacitor side, and the power tube on the side with the larger residual absolute value has an open circuit fault; finally, determine the open circuit object based on the operating status of the permanent magnet synchronous motor.

[0009] Preferably, the global mathematical model in step S1 is:

[0010]

[0011] Where: R1 and L1 are the resistance and inductance of the battery side respectively; R2 and L2 are the resistance and inductance of the supercapacitor side respectively; C dc is the DC bus filter capacitor; V bat is the battery voltage; V sc is the supercapacitor voltage; i o is the DC bus output current; i bat is the output current on the battery side; i sc is the output current on the supercapacitor side; V dc is the DC bus voltage; 01 ,υ 23 They are control signals for the bidirectional DC / DC converter on the battery side and the bidirectional DC / DC converter on the supercapacitor side respectively.

[0012] Preferably, the specific steps of step S1 are as follows:

[0013] S11. Definition of binary switch function:

[0014] Define the binary switching function k of the battery energy storage unit according to the battery charging and discharging state:

[0015]

[0016] Where: i bat,refis the reference value of the output current on the battery side;

[0017] The binary switching function m of the supercapacitor energy storage unit is defined according to the charging and discharging state of the supercapacitor:

[0018]

[0019] Where: i sc,ref is the reference value of the output current on the supercapacitor side;

[0020] S12. Establishment of local model:

[0021] According to Kirchhoff's law, the circuit equations are listed and sorted out to obtain the state equations of the battery energy storage unit and the supercapacitor energy storage unit in the discharge mode:

[0022]

[0023]

[0024] Where: υ0 and υ2 are the duty cycles of the switches S0 and S2 respectively; i1 and i2 are the output currents of the battery and supercapacitor to the load respectively;

[0025] According to Kirchhoff's law, the circuit equations are listed and sorted out to obtain the state equations of the battery energy storage unit and the supercapacitor energy storage unit in the charging mode:

[0026]

[0027]

[0028] Where: υ1 and υ3 are the duty cycles of the switches S1 and S3 respectively;

[0029] S13. Establishment of global mathematical model:

[0030] Substituting the binary switch function of the battery energy storage unit into the state equation of the battery energy storage unit in the charging and discharging modes, the global mathematical models of the battery energy storage unit in the charging and discharging modes are obtained:

[0031]

[0032] Substituting the binary switching function of the supercapacitor energy storage unit into the state equation of the supercapacitor energy storage unit in the charging and discharging modes, the global mathematical models of the supercapacitor energy storage unit in the charging and discharging modes are obtained:

[0033]

[0034] The first coefficient term on the right side of the equal sign in equations (8) and (9) is the control signal of the bidirectional DC / DC converter on the battery side and the bidirectional DC / DC converter on the supercapacitor side, namely:

[0035] υ 01 =k(1-υ0)+(1-k)υ1 (10)

[0036] υ 23 =m(1-υ2)+(1-m)υ3 (11)

[0037] The current i passing through the DC bus capacitor dc for:

[0038]

[0039] According to equations (8), (9), (10), (11), and (12), the global mathematical model of the composite energy system is:

[0040]

[0041] Preferably, the global Lumberg observer in step S2 is:

[0042]

[0043] Where: is the observed value of the output current on the battery side; is the observed value of the output current on the supercapacitor side; is the observed value of DC bus voltage; k e1 , k e2 , k e3 is the feedback gain coefficient.

[0044] Preferably, step S3 specifically includes the following steps:

[0045] S31. Define the DC bus voltage residual as the error between the observed value and the actual value of the DC bus voltage of the Romberg observer, that is,

[0046] S32, determine the evaluation function of the residual signal:

[0047]

[0048] Where: w is the size of the sliding window;

[0049] When the system has no faults, the maximum value of the residual evaluation function is selected as the threshold of the corresponding state during the stable speed period and the sudden change period. The selected thresholds are as follows:

[0050] J th =max(Jr ) (15);

[0051] S33, Comparison J r ((t), J th :If J r (t)<J th , no open circuit fault occurs; otherwise, an open circuit fault occurs; when an open circuit occurs, the absolute values ​​of the observed residuals of the output current on the battery side and the output current on the supercapacitor side are compared, and an open circuit fault occurs in the bidirectional DC / DC power tube on the side with the larger absolute value;

[0052] S34. Determine the open circuit object according to the operating state of the permanent magnet synchronous motor.

[0053] Preferably, the specific steps of step S34 are as follows:

[0054] S341, the motor is in stable operation, the power fluctuation is not large, the power is supplied by the battery side, the bidirectional DC / DC on the battery side is in the discharge boost mode, and the discharge power tube is working; if it is detected that the absolute value of the observed residual of the output current on the battery side is greater than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the discharge power tube on the battery side is open circuited;

[0055] S342, when the motor is in a sudden speed increase, the power fluctuation is large, and the power is supplied by the battery and the supercapacitor at the same time. The bidirectional DC / DC on the battery side and the bidirectional DC / DC on the supercapacitor side are in the discharge boost mode at the same time, that is, the discharge power tubes on both sides work at the same time; if it is detected that the absolute value of the observed residual of the output current on the battery side is greater than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the discharge power tube on the battery side is open-circuited; if it is detected that the absolute value of the observed residual of the output current on the battery side is less than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the discharge power tube on the supercapacitor side is open-circuited;

[0056] S343. When the motor is in a sudden deceleration, the power fluctuation is large, and the motor energy is fed back to the battery and the supercapacitor at the same time. The bidirectional DC / DC on the battery side and the bidirectional DC / DC on the supercapacitor side are in the charging and voltage reduction mode at the same time, that is, the charging power tubes on both sides work at the same time; if it is detected that the absolute value of the observed residual of the output current on the battery side is greater than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the charging power tube on the battery side is open-circuited; if it is detected that the absolute value of the observed residual of the output current on the battery side is less than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the charging power tube on the supercapacitor side is open-circuited.

[0057] The composite energy source power tube open-circuit fault diagnosis method based on the Lumberg observer proposed in the present invention constructs a global mathematical model for the composite energy source and its two interface circuit bidirectional DC / DC, and then establishes a global Lumberg observer. Only one observer is needed to simultaneously observe the DC bus voltage, the battery side output current, and the supercapacitor side output current, so that the bidirectional DC / DC power tube open-circuit fault detection and positioning in the composite energy source system can be realized efficiently and accurately, and the complexity of the observer model is reduced. It is simple and practical, low in cost, and high in reliability, making the fault diagnosis scheme more practical and convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is the topological structure diagram of the composite energy source system;

[0059] Figure 2 The block diagram of the Lumberg observer for bidirectional DC / DC converter in a composite energy source system.

[0060] Figure 3 This is a schematic diagram of the fault diagnosis principle based on the Romberg observer of the present invention. DETAILED DESCRIPTION

[0061] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0062] like Figure 1 As shown, the system consists of a composite energy source system composed of batteries and supercapacitors, two bidirectional DC / DCs as its interface circuits and a five-phase permanent magnet synchronous motor drive system.

[0063] The present invention proposes a composite energy source power tube open circuit fault diagnosis method based on a Romberg observer, comprising the following steps:

[0064] S1. According to Figure 1 The state equation of the composite energy source system is used to establish a global mathematical model:

[0065]

[0066] Where: R1 and L1 are the resistance and inductance of the battery side respectively; R2 and L2 are the resistance and inductance of the supercapacitor side respectively; C dc is the DC bus filter capacitor; V bat is the battery voltage; V sc is the supercapacitor voltage; i o is the DC bus output current; i bat is the output current on the battery side; i sc is the output current on the supercapacitor side; V dc is the DC bus voltage; 01 ,υ 23They are the only control signals for the bidirectional DC / DC converter on the battery side and the bidirectional DC / DC converter on the supercapacitor side respectively.

[0067] according to Figure 1 The composite energy source topology can be built based on local modeling to establish a global mathematical model of the hybrid energy source. The specific modeling process can be carried out in the following three steps:

[0068] S11. Definition of binary switch function:

[0069] Define the binary switching function k of the battery energy storage unit according to the battery charging and discharging state:

[0070]

[0071] Where: i bat,ref It is the reference value of the output current on the battery side.

[0072] The binary switching function m of the supercapacitor energy storage unit is defined according to the charging and discharging state of the supercapacitor:

[0073]

[0074] Where: i sc,ref It is the reference value of the output current on the supercapacitor side.

[0075] S12. Establishment of local model:

[0076] a. Discharge mode (k=1, m=1)

[0077] According to Kirchhoff's law, the circuit equations are listed and sorted out to obtain the state equations of the battery energy storage unit and the supercapacitor energy storage unit in the discharge mode:

[0078]

[0079]

[0080] Where: υ0 and υ2 are the duty cycles of the switches S0 and S2 respectively; i1 and i2 are the output currents of the battery and supercapacitor to the load respectively.

[0081] b. Charging mode (k=0,m=0)

[0082] According to Kirchhoff's law, the circuit equations are listed and sorted out to obtain the state equations of the battery energy storage unit and the supercapacitor energy storage unit in the charging mode:

[0083]

[0084]

[0085] Where: υ1, υ3 are the duty cycles of the switches S1, S3 respectively.

[0086] S13. Establishment of global mathematical model:

[0087] Substituting the binary switch function of the battery energy storage unit into the state equation of the battery energy storage unit in the charging and discharging modes, the global mathematical models of the battery energy storage unit in the charging and discharging modes are obtained:

[0088]

[0089] Substituting the binary switching function of the supercapacitor energy storage unit into the state equation of the supercapacitor energy storage unit in the charging and discharging modes, the global mathematical models of the supercapacitor energy storage unit in the charging and discharging modes are obtained:

[0090]

[0091] The first coefficient term on the right side of the equal sign in equations (8) and (9) is the only control signal of the bidirectional DC / DC converter on the battery side and the bidirectional DC / DC converter on the supercapacitor side, namely:

[0092] υ 01 =k(1-υ0)+(1-k)υ1 (10)

[0093] υ 23 =m(1-υ2)+(1-m)υ3 (11)

[0094] The current i passing through the DC bus capacitor dc for:

[0095]

[0096] According to equations (8), (9), (10), (11), and (12), the global mathematical model of the composite energy system is:

[0097]

[0098] S2. Construct a global Lumberg observer according to the state equation of the composite energy source system, and use the Lumberg observer to observe the DC bus voltage, the battery side output current, and the supercapacitor side output current;

[0099] The global Romberg observer is:

[0100]

[0101] Where: is the observed value of the output current on the battery side; is the observed value of the output current on the supercapacitor side; is the observed value of DC bus voltage; k e1 , k e2 , k e3 is the feedback gain coefficient.

[0102] The specific steps to construct the global Lumberg observer are as follows:

[0103] Change equation (1) into the description form of state space equation:

[0104]

[0105] Where: x(t)=[i bat i sc V dc ] T ,u(t)=[V bat V sc i o ] T .

[0106] Before designing the Lumberg observer, the observability analysis of the system is performed. Since the rank of the C matrix is ​​3, the rank of the system observability matrix must be That is, the system is full rank and fully observable, satisfying the requirements of the Lumberg observer. The Lumberg observer is designed as follows:

[0107]

[0108] Where: is the observed value of the state variable x, is the observed value of the output variable y, the gain coefficient matrix K e The expression is

[0109] Just select a suitable gain coefficient matrix K e , the observation error converges, and the convergence speed can be adjusted by adjusting K e The state observer and the actual system control block diagram are as follows: Figure 2 As shown, the designed Lumberg observer is:

[0110]

[0111] S3, such as Figure 3As shown, the observed value of the Lumberg observer is compared with the actual system measurement value to obtain the residual of the fault signal; whether the power tube is open-circuited is determined based on whether the residual evaluation function of the DC bus voltage exceeds the threshold; if an open circuit occurs, the absolute value of the observed residual of the output current on the battery side is compared with the absolute value of the observed residual of the output current on the supercapacitor side, and the power tube on the side with the larger residual absolute value has an open circuit fault; finally, the operating state of the permanent magnet synchronous motor is used to determine which of the charging power tube and the discharging power tube has an open circuit. Specifically, the following steps are included:

[0112] S31. First, define the DC bus voltage residual as the error between the observed value and the actual value of the DC bus voltage of the Romberg observer, that is,

[0113] S32, determine the evaluation function of the residual signal:

[0114]

[0115] Where: w is the size of the sliding window;

[0116] When the system has no faults, the maximum value of the residual evaluation function is selected as the threshold of the corresponding state during the stable speed period and the sudden change period. The selected thresholds are as follows:

[0117] J th =max(J r ) (15);

[0118] S33. Finally, the remaining signal J r ((t) and J th By comparison, the switch open circuit fault detection can be realized based on the following logic:

[0119]

[0120] It can be seen from formula (13) that by selecting a suitable gain coefficient matrix, when the bidirectional DC / DC power tube is normal, the observed value can quickly converge to the actual value; when the bidirectional DC / DC power tube is open, the mathematical model of the system has changed, so the observed residual of the Romberg observer will diverge rapidly in a short time and exceed the set threshold.

[0121] First, observe the residual evaluation function J of the DC bus voltage r ((t) whether it exceeds the threshold J th To determine whether the bidirectional DC / DC power tube is open circuit; if J r (t)<J th, no open circuit fault occurs; otherwise, an open circuit fault occurs. When an open circuit occurs, the absolute values ​​of the observed residuals of the output current on the battery side and the output current on the supercapacitor side are compared, and the bidirectional DC / DC power tube on the side with the larger absolute value has an open circuit fault;

[0122] S34, judging the open circuit object according to the running state of the permanent magnet synchronous motor, the specific judging steps are as follows:

[0123] S341, the motor is in stable operation, the power fluctuation is not large, the power is supplied by the battery side, the bidirectional DC / DC on the battery side is in the discharge boost mode, and the discharge power tube is working; if it is detected that the absolute value of the observed residual of the output current on the battery side is greater than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the discharge power tube on the battery side is open circuited;

[0124] S342, when the motor is in a sudden speed increase, the power fluctuation is large, and the power is supplied by the battery and the supercapacitor at the same time. The bidirectional DC / DC on the battery side and the bidirectional DC / DC on the supercapacitor side are in the discharge boost mode at the same time, that is, the discharge power tubes on both sides work at the same time; if it is detected that the absolute value of the observed residual of the output current on the battery side is greater than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the discharge power tube on the battery side is open-circuited; if it is detected that the absolute value of the observed residual of the output current on the battery side is less than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the discharge power tube on the supercapacitor side is open-circuited;

[0125] S343. When the motor is in a sudden deceleration, the power fluctuation is large, and the motor energy is fed back to the battery and the supercapacitor at the same time. The bidirectional DC / DC on the battery side and the bidirectional DC / DC on the supercapacitor side are in the charging and voltage reduction mode at the same time, that is, the charging power tubes on both sides work at the same time; if it is detected that the absolute value of the observed residual of the output current on the battery side is greater than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the charging power tube on the battery side is open-circuited; if it is detected that the absolute value of the observed residual of the output current on the battery side is less than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the charging power tube on the supercapacitor side is open-circuited.

[0126] The present invention can make the method for diagnosing the open-circuit fault of the power tube of the bidirectional DC / DC converter under the composite energy source simpler, easier to understand, easier to implement, and more accurate. It is a feasible solution that can effectively improve the open-circuit fault diagnosis of the power tube of the bidirectional DC / DC converter under the composite energy source.

[0127] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A composite energy source power tube open circuit fault diagnosis method based on Lumberg observer, characterized in that: The following steps are involved: S1. Establish a global mathematical model based on the state equation of the composite energy source system; S2. Construct a global Lumberg observer according to the state equation of the composite energy source system, and use the Lumberg observer to observe the DC bus voltage, the battery side output current, and the supercapacitor side output current; S3. Compare the observed value of the Lumberg observer with the actual system measurement value to obtain the residual of the fault signal; determine whether the power tube is open-circuited based on whether the residual evaluation function of the DC bus voltage exceeds the threshold; if an open circuit occurs, compare the absolute value of the observed residual of the output current on the battery side with the absolute value of the observed residual of the output current on the supercapacitor side, and the power tube on the side with the larger residual absolute value has an open circuit fault; finally, determine the open circuit object based on the operating state of the permanent magnet synchronous motor; The global mathematical model in step S1 is: Where: R1 and L1 are the resistance and inductance of the battery side respectively; R2 and L2 are the resistance and inductance of the supercapacitor side respectively; C dc is the DC bus filter capacitor; V bat is the battery voltage; V sc is the supercapacitor voltage; i o is the DC bus output current; i bat is the output current on the battery side; i sc is the output current on the supercapacitor side; V dc is the DC bus voltage; 01 ,υ 23 They are control signals of the bidirectional DC / DC converter on the battery side and the bidirectional DC / DC converter on the supercapacitor side respectively; The specific steps of step S1 are as follows: S11. Definition of binary switch function: Define the binary switching function k of the battery energy storage unit according to the battery charging and discharging state: Where: i bat,ref is the reference value of the output current on the battery side; The binary switching function m of the supercapacitor energy storage unit is defined according to the charging and discharging state of the supercapacitor: Where: i sc,ref is the reference value of the output current on the supercapacitor side; S12. Establishment of local model: According to Kirchhoff's law, the circuit equations are listed and sorted out to obtain the state equations of the battery energy storage unit and the supercapacitor energy storage unit in the discharge mode: Where: υ0 and υ2 are the duty cycles of the switches S0 and S2 respectively; i1 and i2 are the output currents of the battery and supercapacitor to the load respectively; According to Kirchhoff's law, the circuit equations are listed and sorted out to obtain the state equations of the battery energy storage unit and the supercapacitor energy storage unit in the charging mode: Where: υ1 and υ3 are the duty cycles of the switches S1 and S3 respectively; S13. Establishment of global mathematical model: Substituting the binary switch function of the battery energy storage unit into the state equation of the battery energy storage unit in the charging and discharging modes, the global mathematical models of the battery energy storage unit in the charging and discharging modes are obtained: Substituting the binary switching function of the supercapacitor energy storage unit into the state equation of the supercapacitor energy storage unit in the charging and discharging modes, the global mathematical models of the supercapacitor energy storage unit in the charging and discharging modes are obtained: The first coefficient term on the right side of the equal sign in equations (8) and (9) is the control signal of the bidirectional DC / DC converter on the battery side and the bidirectional DC / DC converter on the supercapacitor side, namely: u 01 =k(1-υ0)+(1-k)υ1 (10) u 23 =m(1-υ2)+(1-m)υ3 (11) The current i passing through the DC bus capacitor dc for: According to equations (8), (9), (10), (11), and (12), the global mathematical model of the composite energy system is: Step S3 specifically includes the following steps: S31. Define the DC bus voltage residual as the error between the observed value and the actual value of the DC bus voltage of the Romberg observer, that is, S32, determine the evaluation function of the residual signal: Where: w is the size of the sliding window; When the system has no faults, the maximum value of the residual evaluation function is selected as the threshold of the corresponding state during the stable speed period and the sudden change period. The selected thresholds are as follows: I th =max(J r ) (15); S33, Comparison J r ((t), J th :If J r (t)<J th , no open circuit fault occurs; otherwise, an open circuit fault occurs; when an open circuit occurs, the absolute values ​​of the observed residuals of the output current on the battery side and the output current on the supercapacitor side are compared, and an open circuit fault occurs in the bidirectional DC / DC power tube on the side with the larger absolute value; S34. Determine the open circuit object according to the operating state of the permanent magnet synchronous motor.

2. The composite energy source power tube open circuit fault diagnosis method based on the Romberg observer according to claim 1 is characterized in that: The global Lumberg observer in step S2 is: Where: is the observed value of the output current on the battery side; is the observed value of the output current on the supercapacitor side; is the observed value of DC bus voltage; k e1 , k e2 , k e3 is the feedback gain coefficient.

3. The composite energy source power tube open circuit fault diagnosis method based on the Romberg observer according to claim 1 is characterized in that: The specific steps of step S34 are as follows: S341, the motor is in stable operation, the power fluctuation is not large, the power is supplied by the battery side, the bidirectional DC / DC on the battery side is in the discharge boost mode, and the discharge power tube is working; if it is detected that the absolute value of the observed residual of the output current on the battery side is greater than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the discharge power tube on the battery side is open circuited; S342, when the motor is in a sudden speed increase, the power fluctuation is large, and the power is supplied by the battery and the supercapacitor at the same time. The bidirectional DC / DC on the battery side and the bidirectional DC / DC on the supercapacitor side are in the discharge boost mode at the same time, that is, the discharge power tubes on both sides work at the same time; if it is detected that the absolute value of the observed residual of the output current on the battery side is greater than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the discharge power tube on the battery side is open-circuited; if it is detected that the absolute value of the observed residual of the output current on the battery side is less than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the discharge power tube on the supercapacitor side is open-circuited; S343. When the motor is in a sudden deceleration, the power fluctuation is large, and the motor energy is fed back to the battery and the supercapacitor at the same time. The bidirectional DC / DC on the battery side and the bidirectional DC / DC on the supercapacitor side are in the charging and voltage reduction mode at the same time, that is, the charging power tubes on both sides work at the same time; if it is detected that the absolute value of the observed residual of the output current on the battery side is greater than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the charging power tube on the battery side is open-circuited; if it is detected that the absolute value of the observed residual of the output current on the battery side is less than the absolute value of the observed residual of the output current on the supercapacitor side, it is determined that the charging power tube on the supercapacitor side is open-circuited.

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