A multi-level converter submodule open circuit fault diagnosis and fault-tolerant operation strategy

Abstract

The present invention discloses an open-circuit fault diagnosis and fault-tolerant operation strategy for a multi-level converter submodule, wherein the open-circuit fault diagnosis strategy coordinates the diagnosed submodule with the redundant submodule, analyzes the output condition of the half-bridge energy storage submodule at the moment of an open-circuit fault, extracts the abnormal output voltage characteristics of the submodule in half a cycle, determines the fault location, and performs targeted fault-tolerant control. The open-circuit fault diagnosis and fault-tolerant operation strategy proposed by the present invention can diagnose the fault at the moment of an open-circuit fault in the energy storage submodule, and process it in the first place, which greatly improves the efficiency of fault diagnosis and the safety and reliability of the operation of the multi-level converter, and is simple and practical.

Description

Technical Field

[0001] The invention relates to an open circuit fault diagnosis and fault-tolerant operation strategy for a multi-level converter submodule, belonging to the technical field of power electronics application. Background Art

[0002] Considering the non-renewable nature of fossil energy, countries around the world are actively exploring renewable energy that can replace fossil energy to change their energy structure and achieve energy revolution. Among them, renewable energy represented by photovoltaic and wind power is becoming the object of vigorous exploration and development in countries around the world due to its advantages such as convenient access. In addition, compared with traditional fossil energy, photovoltaic and wind power not only have a continuous power generation capacity, but also do not pollute the environment.

[0003] Of course, the current renewable energy generation is not perfect. As photovoltaic power generation is affected by light intensity and temperature, and wind power generation is affected by wind force, these renewable energy generation are intermittent, random and unstable, which in turn affects the quality of electricity. Even direct use can cause damage to electrical equipment, resulting in a large number of abandoned solar and wind power. In terms of new energy vehicles, there are still problems such as inaccurate battery power estimation, which hinders the promotion of new energy vehicles to a certain extent, and also causes current new energy vehicle owners to have problems such as mileage anxiety.

[0004] Multilevel converters are widely used in photovoltaic, wind power and other renewable energy power generation systems because their output waveforms have the characteristics of high equivalent switching frequency, low harmonic content and simple and flexible control. To measure the performance and application value of a multilevel converter, it is necessary to compare the number of power switching devices, the voltage stress of the power switching devices, whether the control is simple and flexible, whether the fault diagnosis and fault-tolerant control are easy, and the quality of the output waveform under the same output level. Generally speaking, the fewer the number of power switching devices, the smaller the voltage stress of the power switching devices, the simpler and more flexible the control, the easier the fault diagnosis and fault-tolerant control, and the better the quality of the output waveform, the higher the performance and application value of this type of converter. Of course, in many cases, a converter cannot achieve all of the above advantages; therefore, we need to design a converter to solve as many problems as possible in the actual application scenarios of renewable energy power generation, so as to ensure that the system can achieve the index parameter operation and the lowest cost, so as to achieve the best use effect. By improving the topology of the multilevel converter, many problems of renewable energy power generation and new energy vehicles can be solved, but there are also potential problems of multilevel converters. For example, a series of issues such as open circuit and short circuit of power switches in multi-level converter topologies, short circuit faults on the DC side, and how to respond after a fault occurs to ensure that the system can operate stably and without interruption. Summary of the invention

[0005] In view of the existing knowledge and technology of multi-level converter fault diagnosis, a multi-level converter submodule open circuit fault diagnosis and fault-tolerant operation strategy is proposed. The fault diagnosis strategy can ensure that the multi-level converter containing a half-bridge energy storage submodule can operate normally when an open circuit fault occurs in the energy storage submodule. The purpose of the present invention can be achieved by the following technical solutions:

[0006] An open-circuit fault diagnosis and fault-tolerant operation strategy for a multi-level converter submodule, the multi-level converter comprising a left bridge arm, a right bridge arm, a filter inductor Lf, and a load Z; the left bridge arm and the right bridge arm are both formed by connecting N half-bridge energy storage submodules in series with a redundant submodule; the left bridge arm and the right bridge arm are connected on one side through the load Z and on the other side through the filter inductor Lf, thereby forming a single-phase multi-level converter; the half-bridge energy storage submodule is formed by two power switching devices S1 and S2 to form a half-bridge structure, the two ends of S1 and S2 being connected in series are connected to a lithium battery E, the two ends of S2 are used as output ends, and a filter capacitor C is provided at both ends of the lithium battery; the open-circuit fault diagnosis strategy utilizes the abnormal characteristics of the output voltage of the submodule in half a cycle during the occurrence of the open-circuit fault to determine the fault location and perform targeted fault-tolerant control.

[0007] The process of establishing the mathematical model is as follows:

[0008] 1) Establish a mathematical model of carrier phase shift modulation wave, which specifically includes:

[0009] Modulation wave mathematical model:

[0010]

[0011]

[0012]

[0013]

[0014] Where Cl,i(t) is the expression of the i-th carrier of the left bridge arm, and Cr,i(t) is the expression of the i-th carrier of the right bridge arm. and are the phase angles of the i-th carrier Cli of the left bridge arm and the i-th carrier Cri of the right bridge arm, respectively. The phase angle of the first point carrier Cl,1 is set to θc, ωc is the carrier angular frequency, where 1≤i≤N;

[0015] 2) Establish a symbolic function model:

[0016] D l,i (t) = sgn[C l,i (t)-M l (t)]

[0017] D r,i (t) = sgn[C r,i (t)-M r (t)]

[0018] M l (t) = Qcos(ωt-θ m )

[0019] M r (t) = -Qcos(ωt-θ m )

[0020] Wherein, Dl,i(t) is the sign function obtained by subtracting the i-th carrier of the left bridge arm from the corresponding modulation wave, Dr,i(t) is the sign function obtained by subtracting the i-th carrier of the right bridge arm from the corresponding modulation wave, Ml(t) is the dotted modulation signal of the left bridge arm, Mr(t) is the dotted modulation signal of the right bridge arm ω=2π / T, where T is the Fourier analysis period, ω is the angular frequency of the modulation signal, θm is the phase angle, and Q is the modulation ratio (Q≤1);

[0021] 3) The output voltage expression of the submodule under normal working condition is:

[0022]

[0023]

[0024] Wherein, Fl,i(t) is the SPWM output voltage waveform of the left bridge arm submodule SM1,i, and Fr,i(t) is the SPWM output voltage waveform of the right bridge arm submodule SMr,i.

[0025] 4) The open circuit failure of the submodule mainly occurs in the power device. The submodule topology is shown in the attached Figure 1 shown.

[0026] When the upper tube S1 is open, the expression of the submodule output voltage is as follows:

[0027]

[0028]

[0029] Where Vdiode is the conduction voltage drop of the anti-parallel diode of the switch tube.

[0030] When the lower tube S2 is open, the expression of the submodule output voltage is as follows:

[0031]

[0032]

[0033] Where E is the voltage of the battery in the submodule.

[0034] From the above analysis, it can be seen that when a switch tube open circuit fault occurs in a submodule, the output voltage of the submodule is not only related to the SPWM output, but also closely related to the direction of the load voltage, and the load voltage direction factor has a higher priority.

[0035] If the upper tube S1 is open, when the output voltage of the novel multi-level energy storage converter system is in the sinusoidal half-cycle interval where Uo(t)≤0, the output voltage of the submodule is -Vdiode. Although there are certain differences in the forward conduction voltage drops of the anti-parallel diodes of different switch tubes, the average output voltage of the half-cycle at this time must satisfy uK_mean≤0, which is significantly different from the actual value.

[0036] If the lower tube S2 is open, when the output voltage of the novel multi-level energy storage converter system is in the sinusoidal half-cycle interval of Uo(t)≥0, the output voltage of the submodule is E+Vdiode. At this time, the average output voltage of the half-cycle must satisfy uK_mean≥E.

[0037] When the submodule operates without fault, the average value of its output voltage must be between 0 and E.

[0038] The open circuit fault diagnosis strategy proposed by the present invention comprises the following steps:

[0039] 1) Measure the output voltage of each submodule and calculate the average output voltage uK_mean in each half power frequency cycle;

[0040] 2) Determine whether uK_mean satisfies the condition greater than 0 and less than E. If so, the submodule is not faulty. Otherwise, it is necessary to further determine the value range of uK_mean.

[0041] 3) If uK_mean is less than or equal to 0, the upper tube S1 of the submodule is open, otherwise the lower tube S2 is open.

[0042] The fault-tolerant design proposed in the present invention includes the following contents (corresponding to the case where the fault occurs in the right bridge arm):

[0043] 1) If it is detected that the upper tube S1 of the submodule is open, a driving signal with a duty cycle of 1 is given to the S2 switch tube of the faulty submodule, so that S2 is always in the on state; at the same time, the original driving signal of the faulty submodule is given to the redundant submodule SM1,R, that is, the redundant submodule is used to replace the faulty submodule.

[0044] 2) If it is detected that the lower tube S2 of the submodule is open, the S1 switch tube of the faulty submodule is kept in the on state, and the original driving signal of the faulty submodule is given to the redundant submodule SM1,R; at the same time, the S1 switch tube of the redundant submodule SMr,R of the right bridge arm is kept in the on state, and the S2 switch tube is kept in the off state, thereby offsetting the lithium battery voltage of the faulty submodule.

[0045] Beneficial effects of the present invention:

[0046] The present invention proposes an open circuit fault diagnosis and fault-tolerant operation strategy for a multi-level converter submodule. The open circuit fault diagnosis strategy utilizes the abnormal output voltage characteristics of the submodule in half a cycle during the occurrence of the open circuit fault to determine the fault location and perform targeted fault-tolerant control.

[0047] The open circuit fault diagnosis strategy proposed in the present invention can diagnose the fault at the moment when the open circuit fault occurs in the energy storage submodule and process it in the first time, which greatly improves the efficiency of fault diagnosis and the safety and reliability of the operation of the multi-level converter, and is simple and practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a flow chart of open circuit fault diagnosis and fault tolerance operation of the present invention and a circuit topology diagram of a multi-level converter to which it is applicable;

[0049] Figure 2 The waveform of the output voltage of the submodule in the normal state is from 0.96 to 1s, and the waveform of the output voltage of the submodule S1 open circuit is from 1s to 1.06s;

[0050] Figure 3 The waveform of the output voltage of the submodule in the normal state is from 0.96 to 1s, and the waveform of the output voltage of the submodule S2 in the open circuit is from 1s to 1.06s.

[0051] The definitions of the symbols in the figure are as follows:

[0052] 1.1 is the left bridge arm, 1.2 is the right bridge arm, 1.3 is the load, 1.4 is the filter inductor, 1.5 is the redundant submodule of the left bridge arm, 1.6 is the redundant submodule of the right bridge arm, 1.7 is the upper switch tube S1 of the half-bridge submodule, 1.8 is the upper switch tube S2 of the half-bridge submodule, 1.9 is the filter capacitor, and 1.10 is the energy storage lithium battery. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] like Figure 1 As shown, the multi-level converter described in the invention includes a left bridge arm, a right bridge arm, a filter inductor Lf, and a load Z; the left bridge arm and the right bridge arm are both formed by connecting N half-bridge energy storage submodules in series with a redundant submodule; the left bridge arm and the right bridge arm are connected on one side through the load Z, and on the other side through the filter inductor Lf, thereby forming a single-phase multi-level converter; the half-bridge energy storage submodule is composed of two power switching devices S1 and S2 to form a half-bridge structure, the two ends of S1 and S2 are connected in series to the lithium battery E, the two ends of S2 are used as output ends, and there is a filter capacitor C at both ends of the lithium battery; the open circuit fault diagnosis strategy uses the abnormal characteristics of the output voltage of the submodule in half a cycle during the occurrence of the open circuit fault to determine its fault location and perform targeted fault-tolerant control.

[0055] Follow these steps to troubleshoot:

[0056] 1) Measure the output voltage of each submodule and calculate the average output voltage uK_mean in each half power frequency cycle;

[0057] 2) Determine whether uK_mean satisfies the condition greater than 0 and less than E. If so, the submodule is not faulty. Otherwise, it is necessary to further determine the value range of uK_mean.

[0058] 3) If uK_mean is less than or equal to 0, the upper tube S1 of the submodule is open, otherwise the lower tube S2 is open.

[0059] The fault-tolerant design includes the following contents (corresponding to the case when the fault occurs in the right bridge arm):

[0060] 1) If it is detected that the upper tube S1 of the submodule is open, a driving signal with a duty cycle of 1 is given to the S2 switch tube of the faulty submodule, so that S2 is always in the on state; at the same time, the original driving signal of the faulty submodule is given to the redundant submodule SM1,R, that is, the redundant submodule is used to replace the faulty submodule.

[0061] 2) If it is detected that the lower tube S2 of the submodule is open, the S1 switch tube of the faulty submodule is kept in the on state, and the original driving signal of the faulty submodule is given to the redundant submodule SM1,R; at the same time, the S1 switch tube of the redundant submodule SMr,R of the right bridge arm is kept in the on state, and the S2 switch tube is kept in the off state, thereby offsetting the lithium battery voltage of the faulty submodule.

[0062] Example:

[0063] The system is simulated in MATLAB / Simulink. During the simulation, the number of sub-modules in each bridge arm is 4; the voltage of the energy storage lithium battery is 12V; the load resistance is 10.7Ω; the filter inductor is 5mH; the carrier frequency is set to 1kHz; and the modulation wave frequency is 50Hz.

[0064] like Figure 2 As shown, when an open circuit fault occurs in S1, the output waveform of the corresponding submodule will regularly show a half-cycle waveform with a constant value not greater than 0, and the remaining half-cycle waveform is normal, which is consistent with the fault diagnosis method described above.

[0065] like Figure 3 As shown, when an open circuit fault occurs in S2, the output waveform of the corresponding submodule will regularly show a half-cycle waveform with a value greater than the energy storage battery voltage, which is consistent with the fault diagnosis method described above.

[0066] The above method is only a more reasonable way to implement the invention. The protection scope of the present invention is not limited to the above implementation method. Any equivalent modifications or changes made by ordinary technicians in this field based on the content disclosed by the present invention should be included in the protection scope recorded in the claims. In the description of this specification, the description of reference terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0067] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. An open circuit fault diagnosis and fault-tolerant operation strategy for a multi-level converter submodule, characterized in that: The fault diagnosis and fault-tolerant operation strategy is to use the abnormal characteristics of the output voltage of the submodule in half a cycle during the open circuit fault to determine the fault location and perform targeted fault-tolerant control. The open circuit fault diagnosis strategy comprises the following steps: 1) Measure the output voltage of each submodule and calculate the average output voltage u in each half power frequency cycle K_mean ; 2) Judgment u K_mean Is it greater than 0 and less than E If the condition is met, the submodule is not faulty, otherwise further judgment is required. u K_mean The numerical range of 3) If u K_mean If it is less than or equal to 0, the upper tube S1 of the submodule is open, otherwise the lower tube S2 is open; The multi-level converter includes a left bridge arm, a right bridge arm, a filter inductor L f ,load Z The left bridge arm and the right bridge arm are both composed of N A half-bridge energy storage submodule is connected in series with a redundant submodule; the left bridge arm and the right bridge arm are connected on one side through a load Z and on the other side through a filter inductor. L f connected to form a single-phase multi-level converter; The half-bridge energy storage submodule consists of two power switching devices S 1 and S 2 constitutes a half-bridge structure, S 1 and S 2. Connect two ends of the series to lithium batteries E , S 2 Both ends are used as output terminals and have filter capacitors C And at both ends of the lithium battery; The fault-tolerant design of the left bridge arm fault submodule includes the following contents: 1) If the S1 on the submodule is detected to be open, a driving signal with a duty cycle of 1 is given to the S2 switch of the faulty submodule, so that S2 is always in the on state; at the same time, the original driving signal of the faulty submodule is given to the redundant submodule SM l,R , that is, the redundant submodule is used to replace the faulty submodule; 2) If the S2 of the submodule is detected to be open, the S1 switch of the faulty submodule is always turned on, and the original drive signal of the faulty submodule is given to the redundant submodule SM. l,R At the same time, the redundant submodule SM of the right bridge arm r,R The S1 switch tube is always in the on state, and the S2 switch tube is always in the off state, thereby offsetting the lithium battery voltage of the faulty submodule; When the fault occurs in the right bridge arm, it corresponds to the fault; The open circuit fault diagnosis and fault-tolerant operation strategy includes the following mathematical model: 1) Establish a mathematical model of carrier phase shift modulation wave, which specifically includes: Modulation wave mathematical model: In the formula, C l,i ( t ) is the left bridge arm i The expression of the carrier wave, C r,i ( t ) is the right bridge arm i The expression of the carrier wave, and The left bridge arm i Carrier C l,i and the right bridge arm i Carrier C r,i The phase angle of the first point carrier C l,1 The phase angle is set to θ c , ω c is the carrier angular frequency, where 1≤ i ≤ N ; 2) Establish a symbolic function model: In the formula, D l,i ( t ) is the left bridge arm i The symbol function obtained by subtracting the carrier wave from the corresponding modulated wave is D r,i ( t ) is the first i The sign function obtained by subtracting the carrier wave from the corresponding modulated wave is M l ( t ) is the dotted modulation signal of the left bridge arm, M r ( t ) is the dashed modulation signal of the right bridge arm ω =2π / T ,in, T is the Fourier analysis period, ω is the angular frequency of the modulating signal, θ m is the phase angle, Q is the modulation ratio, Q ≤1; 3) The output voltage expression of the submodule under normal working condition is: In the formula, F l,i (t) is the left bridge arm submodule SM l,i The SPWM output voltage waveform, F r,i (t) is the right bridge arm submodule SM r,i SPWM output voltage waveform; 4) The open circuit fault of the submodule mainly occurs in the power device. When the upper tube S1 is open, the expression of the submodule output voltage is as follows: In the formula, V diode is the conduction voltage drop of the anti-parallel diode of the switch tube. When the lower tube S2 is open, the expression of the submodule output voltage is as follows: In the formula, E is the voltage of the battery in the submodule.

2. The open circuit fault diagnosis and fault-tolerant operation strategy of a multi-level converter submodule according to claim 1, characterized in that: When a switch tube open circuit fault occurs in the submodule, the output voltage of the submodule is not only related to the SPWM output, but also closely related to the direction of the load voltage, and the load voltage direction factor has a higher priority.

3. The open circuit fault diagnosis and fault-tolerant operation strategy of a multi-level converter submodule according to claim 1, characterized in that: The upper tube S1 is open circuited, when the output voltage of the novel multi-level energy storage converter system is U o ( t )≤0 in the sinusoidal half cycle, the output voltage of the submodule is - V diode Although the forward voltage drop of the anti-parallel diodes of different switching tubes is different, the average output voltage of the half cycle must satisfy u K_mean ≤0, which is significantly different from the actual value; The lower tube S2 is open, when the output voltage of the new multi-level energy storage converter system is U o ( t )≥0 in the sinusoidal half cycle, the output voltage of the submodule is E+ V diode , at this time the average output voltage of the half cycle must satisfy u K_mean ≥ E； When the submodule operates without fault, its output voltage average value must be between 0 and E between.

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