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To reduce the influence of unknown disturbance on open-circuit fault diagnosis of inverters in the motor drive system, an open-circuit fault diagnosis method, which is based on extended state observer, is proposed for inverters. A mixed logic dynamic model of the inverters is established by analyzing the current flow path when the system works normally and there are open-circuit faults. A voltage extended state observer is designed for the mixed logic dynamic model. The open-circuit faults are detected according to the phase voltage residual between the observed voltage and the actual voltage. The position of the faulty switches is determined by querying the voltage residual information table. Finally, the simulation results show that the method can effectively reduce the influence of the unknown interference on the inverter faults diagnosis, improve the fault diagnosis rate, and verify the effectiveness and feasibility of the method.

With the rapid development of power electronics technology, motors are widely used in industry, military, aviation, and so on, and many motors are driven by inverters. In reality, if the inverter fault cannot be detected in time, it will directly affect the operation of the motor drive system and even the safety of the whole system. Therefore, fast fault diagnosis of the inverter is of great significance to improve the reliability of the system.

Inverter faults are mainly caused by power electronic fault, and 38% of the inverter faults are IGBT (Insulated Gate Bipolar Transistor) fault [

Compared with the current-based inverter fault diagnosis methods, the inverter fault voltage-based methods have many advantages, such as simple use and low cost, and, in order to reduce the influence of unknown disturbance in motor driven system, extended state observer, which is based on the mixed logic dynamic model, is used to improve robustness of fault diagnostic method.

The remainder of this paper is organized as follows. The mixed logic model of the motor and inverter is introduced in Section

The topology diagram of the motor driving system is shown in Figure _{1}∼_{6} and six reverse diodes _{1}∼_{6}. U_{dc} is the voltage of the DC side, (_{a}, _{b}, _{c}) are the three-phase winding current. (_{a}, _{b}, _{c}) are opposite electromotive forces, _{1}∼_{6} are fast fuses that convert short-circuit fault into open-circuit fault [

The topology diagram of the motor driving system.

In the motor drive system, the motor is equivalent to a circuit consisting of a series of resistor

According to the characteristics of the circuit, the formulas are shown as

Based on (

In practice, three or more IGBTs fault of the inverter will not occur at the same time. This paper discusses the diagnosis method of a single IGBT or two IGBTs open-circuit fault. Taking the _{co} when IGBTs work normally or abnormally.

Due to the change of current flow direction and the on/off signals change of IGBTs in the motor driving system, the operating state of _{co} can be affected. The normal current flow path of the _{1}∼_{6} are the on/off signals of the 6 IGBTs of the inverter, _{i}(_{i}(_{a}, _{b}, _{c}) are the current flow direction of the three-phase winding of the motor, _{i}(_{i}(

The current flow path of the

Figure _{co}. The results are shown in Table _{co} is performed in Table _{co} ≠ 0 by logical OR operation.

The truth table of _{co} when IGBTs are working normally.

_{5} | _{6} | _{c} | _{co} |
---|---|---|---|

0 | 0 | 1 | 0 |

0 | 1 | 1 | 0 |

1 | 0 | 1 | _{dc} |

0 | 0 | 0 | _{dc} |

0 | 1 | 0 | 0 |

1 | 0 | 0 | _{dc} |

So, the formula of _{co} is shown as follows:

When the inverter works normally, the formulas of _{ao}, _{bo}, and _{co} are shown as

Based on (

Substituting (

Equation (9) can be written in matrix form as

In reality, there are a lot of disturbances in the inverter system, so the voltage extended observer is designed to estimate the output three-phase voltage in real time, thus eliminating the influence of some other unknown disturbances and uncertainties in the system and improving the accuracy of fault diagnosis.

Treating

In (^{(1)} (^{(n−1)} (^{(n)} (_{1} ⟶ _{n} ⟶ ^{(n−1)}_{n+1} ⟶ ^{(1)},, ^{(n−1)},

Rewrite the hybrid logic dynamic model (_{1}_{an}, _{bn}, _{cn}]^{T}.

When the extended observer is designed according to equation (3.8), its expression is_{0}(z1) = Az_{1}, _{2}, and _{1} =

Take _{5}, the flow channel of the current is shown in Figure

The flow path of the current when IGBT open-circuit fault only occurs in _{5}.

If the open-circuit fault occurs in _{5}, _{co} is different from (

The truth table of _{5}.

_{5} | _{6} | _{c} | |
---|---|---|---|

0 | 0 | 1 | 0 |

0 | 1 | 1 | 0 |

1 | 0 | 1 | 0 |

0 | 0 | 0 | _{dc} |

0 | 1 | 0 | 0 |

1 | 0 | 0 | _{dc} |

Based on Table

When the open-circuit fault occurs in _{5}, the formulas of

Based on (_{5}, the formulas of voltage residual are shown as

Equation (_{5}, we can obtain △_{an} = △_{bn} ≤ 0, △_{cn} ≥ 0, and △_{cn} = 2△_{an} = 2△_{bn}.

Two IGBTs in a phase

When the open-circuit fault occurs in _{5} and _{6} at the same time, the current flow path is as shown in Figure

The current flow path when the open-circuit fault occurs in _{5} and _{6} at the same time.

The truth table of _{5} and _{6} at the same time.

_{5} | _{6} | _{c} | |
---|---|---|---|

0 | 0 | 1 | 0 |

0 | 1 | 1 | 0 |

1 | 0 | 1 | 0 |

0 | 0 | 0 | _{dc} |

0 | 1 | 0 | _{dc} |

1 | 0 | 0 | _{dc} |

The logical operation of

When the open-circuit fault occurs in _{5} and _{6} at the same time, _{cn} are shown as

Based on (_{5} and _{6} at the same time, the voltage residual is shown as

From (

Two IGBTs in two phases

Two IGBTs at the same position in two phases

Take the open-circuit fault of _{3} and _{5} as an example, and use the calculation method of the open-circuit fault of two switches in the same phase; the specific expressions of

When the open-circuit fault occurs in _{3} and _{5}, the phase voltage of each phase is

According to (_{3} and _{5} is

According to (

However, the voltage residual value of the fault phase is still twice as the normal two-phase voltage in a certain cycle. For example, when the IGBTs _{3} and _{6} are normally on, the expression of the three-phase voltage residual is

When the IGBTs _{4} and _{5} are normally on, the three-phase voltage residual is

When T4 and T5 are normal, the relationship between the IGBTs _{3} and _{5} is the same as that in the case of the open-circuit fault of the IGBT _{5}.

Two IGBTs at different position in two phases

Take the open-circuit fault of _{4} and _{5} of phase

and when the open-circuit fault occurs in _{4} and _{5}, the phase voltage of each phase is

According to (_{4} and _{5} is

From (_{4} and _{6} are normally on, the three-phase voltage residual is as follows:

In conclusion, the fault diagnosis method of single switch open-circuit fault and two switches in the same phase are the foundation of the fault diagnosis in the different phase, and the fault location of two switches in the different phase is a special case of single switch open-circuit fault. Therefore, this paper only simulates the open-circuit fault of a single switch and the open-circuit fault of two switches in the same phase.

The above methods are used to deal with the open-circuit fault of phase

The voltage residual information table.

Bridge arm | Fault switch | Relationship between residuals |
---|---|---|

Normally | ||

a | _{1} | |

_{2} | ||

_{1} and _{2} | ||

b | _{3} | |

_{4} | ||

_{3} and _{4} | ||

c | _{5} | |

_{6} | ||

_{5} and _{6} |

The flowchart of the inverter open-circuit fault diagnosis is shown in Figure

The flowchart of inverter open-circuit fault diagnosis.

The simulation parameters of motor are given in Table

The inverter system parameters.

Description | Value |
---|---|

Frequency | 50 Hz |

DC side voltage _{dc} | 360V |

Stator resistance _{s} | 0.435 Ω |

Rotor resistance _{r} | 0.816 Ω |

Stator leakage inductance _{ls} | 4 mH |

Rotor leakage inductance _{rs} | 2 mH |

Mutual inductance _{m} | 69.31 mH |

Pole pair | 2 |

Moment of inertia | 0.089 kg·m^{2} |

The normal three-phase voltage of the actual system and the voltage extension observer.

The residuals between the actual voltage and the observed voltage.

From Figure

During the simulation, the driving signal of _{5} is removed at _{5}.

The three-phase voltage and voltage residual when the open-circuit fault occurs in _{5}. (a) The three-phase voltage when the open-circuit fault occurs in _{5}. (b) The voltage residual when the open-circuit fault occurs in _{5}.

From Figure

By looking up the voltage residual information table in Table _{5}. If _{th} is satisfied, the open-circuit fault occurs in _{5}. After 0.37 s, the system suddenly changes the load, and each phase amplitude of the voltage and voltage residual increase, but it can also detect that _{5} has an open-circuit fault. It shows that the method proposed in this paper has certain antinoise interference.

If the driving signals of _{5} and _{6} are removed at _{5} and _{6} are shown in Figure

The three-phase voltage and voltage residual when the open-circuit fault occurs in _{5} and _{6} at the same time. (a) The three-phase voltage when the open-circuit fault occurs in _{5} and _{6} at the same time. (b) The voltage residual when the open-circuit fault occurs in _{5} and _{6} at the same time.

The proposed fault diagnosis method is compared with other fault diagnosis methods; and the objector (for open-loop system, closed-loop system, or both), diagnosis time, robustness, cost, and fault type are the comparison index, and they are shown in Table

Comparison of the proposed fault diagnosis method and other fault methods.

Fault diagnosis method | Objector | Diagnosis time | Robustness | Cost | Fault type |
---|---|---|---|---|---|

The neural network method | Both | More than one cycle | Low | Low | Single |

The fuzzy logic method | Both | More than one cycle | Medium | High | Multiple |

Park’s vector approach | Open-loop | More than one cycle | Low | Low | Single |

Spectrum analysis method | Both | More than one cycle | Medium | High | Single |

The proposed method | Both | About 1/3 cycle | High | Low | Multiple |

In this paper, the mixed logic dynamic model of the inverter is established by the flow path of current when the inverter works normally and abnormally; and considering the dead time of the switching signal in the modeling process avoids the misdiagnosis of the fault. At the same time, a voltage expansion observer is designed to avoid the problem of increasing the fault rate by introducing other hardware circuits. The simulation results show that the method can be accurately located and has a short diagnosis time. In the future, it is possible to study the diagnostic method of the inverter of two IGBTs in different phases, where the open-circuit fault occurs at the same time, and add a certain fault-tolerant strategy to ensure that the inverter can work normally.

The inverter system parameters data used to support the findings of this study are included within the article.

The authors declare that there are no conflicts of interest regarding the submission of this manuscript, and the manuscript is approved by all the authors for publication.

This study was supported by the National Natural Science Foundation of China (nos. 61573282 and 61833013), the Key Research and Development Program (Key Projects) of Shaanxi Province (no. 2019KWZ-10), and the Key Research and Development Program (General Projects) of Shaanxi Province (no. 2020GY-194).