Open-circuit fault diagnosis and fault-tolerant operation method for TAB converter

Abstract

The present invention provides a method for open-circuit fault diagnosis and fault-tolerant operation of a TAB converter, and relates to the technical field of fault diagnosis and fault-tolerant operation of power electronic converters. The method comprises: step S1: locating the open-circuit fault of the TAB converter; step S2: after the positioning is completed, by blocking the fault bridge arm drive signal and changing the phase shift angle range, the DC bias generated by the open-circuit fault is eliminated, the overcurrent problem is solved, and the power transmitted between the three ports is distributed to achieve fault-tolerant operation. The present invention can quickly and accurately locate the open-circuit fault of the switch device of the three-active bridge converter, eliminate the influence of the open-circuit fault, and reasonably distribute the power flow between the three ports to achieve open-circuit fault fault-tolerant operation.

Description

Technical Field

[0001] The invention relates to the technical field of fault diagnosis and fault tolerance of power electronic converters, and in particular to a method for open circuit fault diagnosis and fault tolerance operation of a TAB converter. Background Art

[0002] As the proportion of new energy and energy storage connected to the power system increases, the traditional AC power system faces huge challenges in terms of operational stability. Distributed DC systems can conveniently, flexibly and efficiently connect distributed power sources and DC loads, and have broad application prospects. Figure 1 In the power system structure shown in FIG. 1 including a distributed DC system, there are a large number of DC converters connecting the DC bus with various sources and loads.

[0003] The triple active bridge (TAB) converter is an isolated three-port DC converter with the advantages of high power density and bidirectional energy transfer. It is widely used in renewable energy power generation, uninterruptible power supplies, and multi-port access scenarios in electric vehicles.

[0004] Due to the characteristics of power electronic devices, switching elements become the most vulnerable components in the converter. According to statistics, about 46% of converter failures are caused by switching elements. It can be divided into short-circuit faults and open-circuit faults. Short-circuit faults will generate a large impact current. In order to avoid causing failures in other components, the fault must be quickly removed. In practical applications, short-circuit fault removal is often achieved through the protection function integrated inside the power switch tube. Open-circuit faults will cause the current inside the converter to produce a DC component and increase the current peak. Fault-tolerant strategies need to be adopted to eliminate the impact of the fault. Existing research on open-circuit fault detection and fault reconstruction methods is limited to two-port converters. The operation of the TAB converter involves three access ports. During fault reconstruction, it is necessary not only to ensure that the converter can achieve fault crossing, but also to ensure that when one of the ports fails, the impact on the power transmission process of the other two ports is minimized. Therefore, higher requirements are placed on the reliability operation of the TAB converter.

[0005] In the existing literature [1] Zhao Nan, Xie Wei, Zheng Zedong, Li Chi, Liu Jianwei, Huang Xudong. A dual active bridge converter and its open circuit fault redundant processing method [P]. Sichuan Province: CN112600437A, 2021-04-02. This document studies the open circuit fault tolerance strategy of the dual active bridge converter. When an open circuit fault occurs in the switch device of the secondary full bridge, all drive signals of the bridge arm where the faulty switch is located are blocked and the maximum duty cycle of the drive pulse is limited. When an open circuit fault occurs in the switch device of the primary full bridge, only the drive signal of the faulty switch device itself is blocked, and the current is limited by limiting the maximum duty cycle of the drive pulse. The solution described in this document cannot solve the problem of generating DC components when the primary full bridge has an open circuit fault, cannot ensure that the power of the normal port is consistent with that before the fault, and does not provide an accurate positioning solution for the open circuit fault.

[0006] Existing literature [2] Ma Tengfeng, Xie Yunxiang, Guan Yuanpeng, Hu Wang, Wang Xuemei. Switch open circuit fault analysis and fault-tolerant control strategy of isolated dual active bridge DC-DC converter considering parasitic parameters [J]. Electric Power Automation Equipment, 2021, 41(08): 149-155. This document proposes an open circuit fault fault-tolerant strategy for the switch tube of a dual active bridge DC-DC converter. By locking the faulty switch device to construct a symmetrical topology, the DC component generated during the open circuit fault is eliminated. This document does not study the fault-tolerant strategy when an open circuit fault occurs on the primary side.

[0007] No research on open-circuit fault diagnosis and fault-tolerant operation strategy of triple active bridge converters has been found in the existing literature. Summary of the invention

[0008] In view of the defects in the prior art, the present invention provides a TAB converter open circuit fault diagnosis and fault-tolerant operation method.

[0009] According to a TAB converter open circuit fault diagnosis and fault-tolerant operation method provided by the present invention, the scheme is as follows:

[0010] Step S1: locating the open circuit fault of the TAB converter;

[0011] Step S2: After the positioning is completed, the DC bias caused by the open circuit fault is eliminated by blocking the fault bridge arm drive signal and changing the phase shift angle range, solving the overcurrent problem and distributing the power transmitted between the three ports to achieve fault-tolerant operation.

[0012] Preferably, the step S1 comprises: analyzing the open circuit fault waveform of each switch tube of the TAB, and locating the TAB open circuit fault by using the midpoint voltage of each bridge arm;

[0013] In normal operation, when current flows through the upper bridge arm, the voltage value at the midpoint of the corresponding bridge arm is equal to the voltage on the DC side; when current flows through the lower bridge arm, the voltage value at the midpoint of the corresponding bridge arm is 0.

[0014] When an open circuit fault occurs, the midpoint voltage of the bridge arm will be added to a state equal to 0, which will cause the average midpoint voltage of the corresponding fault bridge arm to deviate from the normal value.

[0015] Preferably, the open circuit fault in the DC bias caused by the open circuit fault eliminated in step S2 includes: an open circuit fault on the DC bus side and an open circuit fault on the energy storage side;

[0016] When an open circuit fault occurs on the DC bus side or the energy storage side, the driving signals of the bridge arm where the faulty switch tube is located are all locked to form a symmetrical circuit, thereby eliminating the DC component;

[0017] Preferably, after an open-circuit fault occurs on the DC bus side and the energy storage side, during fault-tolerant operation, the maximum inductance current of each port is ensured to be no greater than the maximum inductance current during normal operation. When an open-circuit fault occurs on the DC bus side, the phase shift angle is changed to ensure that the DC bus absorbs power normally; when an open-circuit fault occurs on the energy storage side, the phase shift angle is changed to cut off the faulty energy storage side, and the remaining two ports transmit power normally.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. Accurately and quickly locate the open circuit fault of the switch device in the TAB converter by detecting the midpoint voltage of each bridge arm;

[0020] 2. By blocking the driving signal of the bridge arm where the faulty device is located, the fault-tolerant operation of the TAB converter switch device open circuit fault can be achieved;

[0021] 3. During fault-tolerant operation, the power among the three ports can be reasonably distributed after an open-circuit fault of the TAB converter by changing the phase shift angle range. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0023] Figure 1 The structure of the power system including the distributed DC system;

[0024] Figure 2 It is the topological structure diagram of TAB converter;

[0025] Figure 3 It is the equivalent circuit diagram of TAB converter (Y&Δ type);

[0026] Figure 4 This is the waveform diagram of TAB normal operation;

[0027] Figure 5 It is the current loop diagram of TAB under single phase shift control;

[0028] Figure 6 For S 21 Open circuit fault waveform;

[0029] Figure 7 For S 21 The state of the voltage change at the midpoint of the bridge arm during an open circuit fault;

[0030] Figure 8 For S 11 Open circuit fault operation waveform;

[0031] Fig. 9 For S 11 The state of the voltage change at the midpoint of the bridge arm during an open circuit fault;

[0032] Fig.10 This is the open circuit fault detection flow chart;

[0033] Fig.11 For S 21 Circuit topology diagram when open circuit fault is locked;

[0034] Fig.12 For S 21 Open circuit fault tolerance operation waveform;

[0035] Fig.13 For S 11 Open circuit fault tolerance operation waveform;

[0036] Fig.14 For S 21 , S 11 Open circuit fault detection simulation waveform;

[0037] Fig.15 For S 21 Open circuit fault tolerance operation simulation waveform;

[0038] Fig.16 For S 11 Open circuit fault tolerance operation simulation waveform;

[0039] Fig.17 The variation of three-port power when operating for open-circuit fault tolerance. DETAILED DESCRIPTION

[0040] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0041] The embodiment of the present invention provides a TAB converter open circuit fault diagnosis and fault tolerance operation method, referring to Figure 2 As shown, the method includes:

[0042] Step S1: locating the open circuit fault of the TAB converter.

[0043] In step S1: analyze the open circuit fault waveform of each switch tube of the TAB, and use the midpoint voltage of each bridge arm to locate the TAB open circuit fault; in normal operation, when current flows through the upper bridge arm, the midpoint voltage value of the corresponding bridge arm is equal to the DC side voltage; when current flows through the lower bridge arm, the corresponding midpoint voltage value is 0; when an open circuit fault occurs, the midpoint voltage of the bridge arm will add a state equal to 0, which will cause the average value of the midpoint voltage of the corresponding fault bridge arm to deviate from the normal value.

[0044] Step S2: After the positioning is completed, the DC bias caused by the open circuit fault is eliminated by blocking the fault bridge arm drive signal and changing the phase shift angle range, solving the overcurrent problem and distributing the power transmitted between the three ports to achieve fault-tolerant operation.

[0045] The open-circuit faults in the DC bias generated by the open-circuit faults eliminated in step S2 include: open-circuit faults on the DC bus side and open-circuit faults on the energy storage side; when an open-circuit fault occurs on the DC bus side, the bridge arm drive signals where the faulty switch tube is located are all locked to form a symmetrical circuit, thereby eliminating the DC component; when an open-circuit fault occurs on the energy storage side port, the DC component is also eliminated by locking the bridge arm drive signal where the faulty switch tube is located. On the basis of locking the faulty bridge arm drive signal, the phase shift angle range is changed to limit the fault current, and when the open-circuit fault occurs on the DC bus side, it is ensured that the DC bus side can absorb power normally, and when the open-circuit fault occurs on the energy storage side, the faulty energy storage is cut off, and the remaining two ports transmit power normally.

[0046] Next, the present invention will be described in more detail.

[0047] A TAB converter open circuit fault diagnosis and fault-tolerant operation method first realizes accurate and rapid positioning of the TAB converter open circuit fault. On this basis, the DC bias generated by the open circuit fault is eliminated by blocking the fault bridge arm drive signal and changing the phase shift angle range, solving the overcurrent problem and reasonably allocating the power transmitted between the three ports, thereby realizing fault-tolerant operation.

[0048] like Figure 2 Ports 1 and 3 of the TAB converter shown are connected to energy storage systems such as batteries and supercapacitors, and port 2 is connected to the DC bus side.

[0049] The basic working principle of TAB:

[0050] like Figure 2 The TAB shown in the figure is composed of three H bridges and a high frequency transformer. The three H bridges are H1, H2, H3, S 11 ~S14 is the switch tube of the primary side H1, S 21 ~S 24 is the switch tube of H2 on the secondary side, S 31 ~S 34 The switch tube of the tertiary side H3, D 11 ~D 14 , D 21 ~D 24 , D 31 ~D 34 They are the anti-parallel diodes corresponding to the switch tubes in H1, H2, and H3. The high-frequency transformer is a three-winding transformer, and the turn ratio of the three windings is N1:N2:N3. Each winding is connected to an H bridge, and the transformer enables the three H bridges to be electrically isolated and match the voltage ratio between the three. H1 , V′ H2 , V′ H3 Respectively represent the midpoint voltage difference of the three H-bridge arms, Figure 2 L1, L'2, L'3 are the sum of the leakage inductance and auxiliary inductance of the three windings of the transformer. L1, L'2, L'3 are used to realize energy transfer. L1 , i′ L2 , i′ L3 Represents the current of the three windings, Figure 2 The directions shown in are reference directions.

[0051] In the following analysis, f represents the switching frequency and T represents the switching period. TAB usually adopts single-phase shift control. Under single-phase shift control, S 11 With S 14 , S 12 With S 13 , S 21 With S 24 , S 22 With S 23 , S 31 With S 34 , S 32 With S 33 The driving signals of are kept consistent, and the duty cycle is 0.5. ij (i, j = 1, 2, 3, i ≠ j) is recorded as the phase shift angle between the three H bridges, d 12 +d 23 =d 13 . S 11 With S 21 The time difference between the driving signals is 0.5d 12 T, S 11 With S 31 The time difference of the driving signal is 0.5d 13 T, S 21 With S31 The time difference between the driving signals is 0.5d 23 T. By adjusting the phase shift angle between any two H bridges, the direction and magnitude of power flow can be controlled. For example, when d 12 When it is greater than 0, port 1 transmits power to port 2, and vice versa when it is less than 0. 23 When it is greater than 0, port 2 transmits power to port 3, and when it is less than 0, the opposite is true. According to the relative size of the phase shift angle, the working mode of the TAB converter can be divided into six types, as shown in the following formula (1). The actual power transmission direction in TAB needs to be comprehensively considered. 12 , d 13 , d 23 .

[0052]

[0053] TAB's operating status:

[0054] A: TAB normal working status:

[0055] When the TAB converter is operating normally, power can be transferred bidirectionally between each port. Here, taking mode 1 as an example, the inductor current of each port is analyzed in detail. Assuming that the switch tube and transformer are ideal components and ignoring the dead time, the midpoint voltage difference of the bridge arm of the three ports can be equivalent to three square wave voltages with a duty cycle of 0.5. Figure 3 The equivalent circuit of the TAB converter is shown in Figure 1. H2 、V H3 V′ H2 , V′ H3 L2 and L3 are the values ​​converted to the primary side, and L′2 and L′3 are the values ​​converted to the primary side. L1 is the primary inductor current, i L2 、i L3 The inductor current i′ on the secondary and tertiary sides are L2 , i′ L3 The value converted to the primary side. Figure 3 In (a), the value of V0 can be obtained by applying the KCL theorem:

[0056]

[0057] Where M is the defined equivalent inductance,

[0058]

[0059] Figure 3 The direction indicated by the arrow in (a) is the reference positive direction of the current. From the figure, we can see that the voltage and current expressions of inductors L1, L2, and L3 are as follows (4)(5):

[0060]

[0061]

[0062] During normal operation, the driving signal and key voltage and current waveforms are as follows: Figure 4 As shown, m ij (i=1~3, j=1~6) represents the rate of change of the inductor current at each port at the corresponding moment. The corresponding current loop during normal operation is as follows: Figure 5 As shown, according to the current path, a normal operation cycle can be divided into 12 states, corresponding to Figure 4 N a ~N l The dark part is the actual circuit of the current. L1 Take this as an example for specific calculation:

[0063]

[0064] The primary inductor current i in one cycle L1 (t) As shown in formula (7), V1, V2, and V3 are three square wave voltages V H1 、V H2 、V H3 The amplitude ( Figure 4 is the waveform under the condition of V1>V2>V3):

[0065]

[0066] From the symmetry of the inductor current, we know that the average inductor current is 0 in one cycle, so we have i L1 (t0) = -i L1 (t3),i L1 (t1)=-i L1 (t4),i L1 (t2) = -i L1 (t5), let t0 = 0, then t1 = d 12 / 2f, t2=d 13 / 2f, combined with the above formula, we can get:

[0067]

[0068] The same calculation method can be used to obtain the inductor current of the secondary winding and the tertiary winding at corresponding moments. The change rate of the inductor current of each port is as follows: Formula (9).

[0069]

[0070] Table 1 i L1 (t) Expression

[0071]

[0072] Table 2 i L2 (t) Expression

[0073]

[0074] Table 3 i L3 (t) Expression

[0075]

[0076] The expressions of the inductor current of each port are shown in Table 1, Table 2, and Table 3 above. Figure 3 (b) The Δ-type circuit shown in Figure 1 is used for power calculation. The reference directions of P1, P2, and P3 are shown in the figure. Referring to the power calculation formula of DAB, the transmission powers of the three ports of TAB are:

[0077]

[0078] To facilitate the analysis and comparison of power characteristics and current stress, it is assumed that the circuit operates under ideal conditions, L1=L2=L3=L, V1=V2=V3=V.

[0079] From formula (10), we can see that when d 12 =0.5,d 13 =0.5, the output power of port 1 is maximum, when d 12 =-0.5, d 13 =-0.5, the port 1 absorbs the maximum power; d 12 =-0.5, d 23 =0.5, the output power of port 2 reaches the maximum, d 12 =0.5,d 23 =-0.5, the power absorbed by port 2 is the maximum; d 13 =-0.5, d 23 =-0.5, the output power of port 3 is maximum, d 13 =0.5,d 23 =0.5, the power absorbed by port 3 is the maximum; the maximum power that each port can reach is as follows:

[0080]

[0081] According to Table 1, Table 2, and Table 3, the inductor currents at the three ports at each moment when the TAB converter works in mode 1 can be calculated. 12 =0.5,d 23 =0.5, the peak value of the inductor current at port one is the largest. Since the three ports are completely symmetrical and the phase shift angle range is also symmetrical, it can be seen that the maximum peak current of the inductor current at each port of the TAB converter is equal. The results are as follows:

[0082]

[0083] B: DC bus side open circuit fault:

[0084] This article assumes that the internal anti-parallel diode can still work normally when the switch tube has an open circuit fault, and does not consider the state where the anti-parallel diode cannot work normally.

[0085] The secondary winding S 21 Take open circuit fault as an example for analysis. Figure 6 YesS 21 The waveform of the drive signal and the inductor voltage and current after the circuit is opened. The left shadow part of the figure represents the transient process of the fault, and the right shadow part represents the state where the fault reaches a stable state. From the voltage waveform, it can be seen that the current change rate in each period is consistent with that in normal operation, but S 21 After the open circuit fault reaches steady state, i L2 (t4) = 0, it can be seen that the inductor current at port 2 generates a DC bias. 21 The process of open circuit fault is analyzed in detail as follows:

[0086] S 21 At the moment of open circuit fault, N a ~N g The status will not be affected, N g When the state ends, the secondary inductor current changes from positive to negative, and the current should flow through S 21 , due to S 21 An open circuit fault occurs. At this time, D 22 and S 24 Provides a current loop, secondary voltage V H2 becomes 0. From formula (4), we can see that the secondary side inductor voltage amplitude decreases and the direction is negative. Therefore, the secondary side inductor current conversion rate becomes smaller than that in normal operation. The circuit state at this time is recorded as The state lasts until time t4. There are four circuit states in the time period from t4 to t5. At time t4, the circuit enters N i state, and then the tertiary inductor current, the primary inductor current, and the secondary inductor current respectively enter the zero-crossing state. N k , During the time period from t5 to t6, since the secondary inductor current changes from positive to negative, the circuit is recorded as N l Because the inductor current has a DC bias, after several cycles, until the secondary side S 22 and S 23At the rising edge of the driving signal, the secondary current just drops to zero, indicating that the circuit has entered a fault steady state and D is no longer needed in the circuit. 22 Provides a freewheeling circuit. As shown in the shaded area on the right side of the figure, S 21 When the open circuit fault reaches steady state operation, the circuit operation sequence is: The above symbol E 21 The state with the subscript is S 21 A new state after an open circuit fault. 21 Current loop in which the bridge arm voltage changes during the transient process of an open circuit fault Figure 7 shown.

[0087] C: Open circuit fault on the energy storage side:

[0088] The primary winding S 11 Take open circuit as an example for analysis. Figure 8 YesS 11 The waveform of the driving signal and the inductor voltage and current after the circuit is opened. The left shadow part of the figure represents the transient process of the fault, and the right shadow part represents the state after the fault stabilizes. From the voltage waveform, it can be seen that the current change rate in each period after the fault reaches a steady state is consistent with that in normal operation, but S 11 After an open circuit fault, S 12 and S 13 When the driving signal rises, the primary inductor current is zero, which means that the inductor current generates a DC bias. 11 The process of open circuit fault is analyzed in detail as follows:

[0089] S 11 At the moment of open circuit fault, N a ~N c The status will not be affected, N c When the state ends, until time t3, the primary inductor current remains zero. The process in the time period from t1 to t3 is analyzed as follows: N c When the state ends, the primary inductor current should change from negative to positive, but due to S 11 An open circuit fault occurs, and only D 12 and S 14 Provided the forward current loop, assuming that the current flows through D 12 and S 14 , then the primary side V H1 becomes 0. From equation (4), we can see that the primary inductor voltage is less than zero, then the primary inductor current should decrease from positive to negative, so the current will not flow through D 12 and S 14 ; Assume that the current flows negatively through D 11 and D 14 , then the primary side V H1becomes V1. From equation (4), we can see that if the primary inductor voltage is greater than zero, the primary inductor current should increase from negative to positive, so the current will not flow through D 11 and D 14 , maintain at zero, during this period V H1 =Equal to the voltage on the primary winding of the transformer. The circuit is due to the primary inductor current dropping to zero, the secondary and tertiary inductor currents switching, S 31 With S 34 The change of driving signal enters the state During the time period from t3 to t4, it is recorded as and State, during the period from t4 to t5, the circuit is N k During the period from t5 to t6, the circuit state remains the same as normal. Due to the DC bias of the inductor current, after several cycles, until S 12 and S 13 At the rising edge of the driving signal, the primary current just rises to zero, indicating that the circuit has entered a fault steady state. As shown in the shaded area on the right side of the figure, the circuit operation sequence in the steady state is The above symbol E 11 The state with the subscript is S 11 A new state added when an open circuit fault occurs. 11 The current loop of the period corresponding to the change of bridge arm voltage during the transient process of open circuit fault is as follows: Fig. 9 shown.

[0090] TAB open circuit fault diagnosis and fault tolerance strategy:

[0091] After an open circuit fault occurs, in order to minimize the impact of the fault on the circuit, it is necessary to first accurately locate the open circuit fault location, and then reduce the impact of the fault through a fault-tolerant strategy. From the previous analysis, it can be seen that an open circuit fault of the switch tube in the TAB will cause the inductor current to produce a DC bias and increase the current. The DC bias of the current puts the transformer at risk of saturation, and the increase in current may cause an overcurrent risk of burning other devices. Therefore, after an open circuit fault occurs, it should be ensured that the fault current is not greater than the maximum inductor current of each port during normal operation, and the DC component of the current should be eliminated.

[0092] a. Open circuit fault diagnosis:

[0093] By analyzing the open-circuit fault waveforms of each TAB switch tube, it can be seen that when an open-circuit fault occurs, the corresponding bridge arm midpoint voltage difference and inductor current both have obvious changes. The bridge arm midpoint voltage difference and inductor current changes can be used to determine whether a fault has occurred. Since TAB has as many as 12 switch devices, S i1 and S i4 , S i2 and Si3 (i=1, 2, 3) When an open circuit fault occurs, the bridge arm midpoint voltage difference and the inductor current waveform are consistent, so it is impossible to distinguish the open circuit faults of these switch tubes. In order to solve this problem, a method for accurately locating TAB open circuit faults by using the midpoint voltage of each bridge arm is proposed, namely Figure 2 The V AG1 、V BG1 、V AG2 、V BG2 、V AG3 、V BG3 As can be seen from the figure, V AG1 、V BG1 、V AG2 、V BG2 、V AG3 、V BG3 The size is determined by the state of the upper and lower bridge arm switch devices. In normal operation, when the upper bridge arm flows through current, the corresponding bridge arm midpoint voltage value is equal to the DC side voltage, which are V1, V2, and V3 respectively. When the lower bridge arm flows through current, the corresponding midpoint voltage value is 0. The relationship between the bridge arm midpoint voltage and the corresponding square wave voltage can be known as:

[0094]

[0095] The TAB open circuit fault can be accurately located by using the average value of the bridge arm midpoint voltage within a cycle. From the above formula (13), it can be seen that during normal operation, the average value of the bridge arm midpoint voltage is as follows:

[0096]

[0097] By S 21 With S 11 New current loop state during open circuit fault transient ( Figure 7 , Fig. 9 ) It can be seen that when an open circuit fault occurs, the bridge arm midpoint voltage will add a state equal to 0, which will cause the average value of the corresponding fault bridge arm midpoint voltage to deviate from the normal value. For example, S 21 When an open circuit fault occurs, V CG2 The average value in one cycle is significantly reduced, while the midpoint voltage of other bridge arms is almost not affected. 22 When an open circuit fault occurs, V CG2 The average value in one cycle increases significantly, while the midpoint voltages of other bridge arms are almost unaffected. 24 When an open circuit fault occurs, the changes in the inductor voltage and inductor current are related to S 21 When an open circuit fault occurs, it remains the same, but V DG2 The average value in one cycle increases significantly, while V CG2 No significant changes, so S 21 With S24 Open circuit fault, S 23 Fault V DG2 The voltage of other midpoints is significantly reduced, and there is no obvious change in the voltage of the other midpoints. According to the same principle, the primary and tertiary sides can also use the corresponding bridge arm midpoint voltage to locate the position of the open circuit fault. The information of the bridge arm midpoint voltage when each switch tube is open is summarized in Table 4 below. Taking into account the influence of switching noise, electromagnetic interference, parasitic parameters and sensor measurement errors in actual power electronic systems, the voltage measurement value may also have a certain deviation when the TAB converter is operating normally. Therefore, the corresponding thresholds α, β, and γ are set to avoid misjudgment of faults. Based on this, the flow chart of open circuit fault detection and positioning can be obtained as follows: Fig.10 shown.

[0098] Table 4 Average bridge arm midpoint voltage when each switch device has an open circuit fault

[0099]

[0100]

[0101] b. DC bus side open circuit fault tolerance strategy:

[0102] From the previous analysis process, it can be seen that the fundamental reason for the generation of DC components is the asymmetry of the circuit after an open circuit fault. Therefore, when an open circuit fault occurs, the driving signals of the bridge arm where the faulty switch tube is located are all locked to form a symmetrical circuit, thereby eliminating the DC component. 21 Taking open circuit as an example, the driving signals of the faulty bridge arm are all locked. At this time, the circuit topology is as follows Fig.11 As shown. Port 2 is connected to the DC bus, then the fault-tolerant control target is that the energy storage system transfers energy to the DC bus. Therefore, the phase shift angle needs to be changed to d 12 ≥0,d 23 ≤0,d 13 ≥0, or d 12 ≥0,d 23 ≤0,d 13 ≤0. 12 ≥0,d 23 ≤0,d 13 Taking ≥0 range fault tolerance operation as an example, S 21 The current waveform when the open circuit fault is locked is as follows Fig.12 As shown, the shaded area on the left is S 21 The transient process of the open circuit fault has been described in detail in the previous article; the shaded area on the right is S 21In the stable state of open circuit fault tolerant operation, the phase shift angle has changed compared to the normal operation state. The stable state of fault tolerant operation can be divided into 12 states according to the converter current loop, but here we only need to analyze the power characteristics and current characteristics during fault tolerant operation. Therefore, the figure only classifies according to the midpoint voltage difference of the bridge arm, which can be divided into 8 operating states, as shown in the figure. As shown in the figure. The state corresponds to S 23 The driving signal is valid and the secondary inductor current is positive. At this time, the circuit is composed of S 23 and D 21 Provides a current loop, so V H2 becomes zero, The state corresponds to S 24 The driving signal is valid and the secondary inductor current is negative. At this time, the circuit is composed of S 24 and D 22 Provides a current loop, r ij represents the rate of change of the inductor current of the i-th port in each time period. The current value at each moment can be calculated by formula (4). Taking the secondary side inductor current as an example, the relationship between the secondary side inductor current is as follows:

[0103]

[0104] The inductor current of port 2 can be obtained from equation (15). The calculation results are shown in Appendix A. The expressions of the inductor current of each port are equations (A1), (A2), and (A3). Ideally, S 21 When the open circuit fault tolerance is running, the power expression of each port is (A4), and the inductor current expression of each port is (A5). According to (A5), the maximum values ​​of the inductor current of the three ports are as follows:

[0105]

[0106] In practical applications, the device model is generally selected based on the normal operating mode. Therefore, during fault-tolerant operation, the maximum inductor current of each port should be ensured not to be greater than the maximum inductor current during normal operation. Then:

[0107]

[0108] Under this fault-tolerant strategy, the phase shift angle range satisfies 0≤d 12 ≤0.5,d 23 ≤0,d 13 ≥0 or d 12 ≥0,d 23 ≤0,0≤d 13 ≤0.5. Calculation shows that they all satisfy the above formula (17). According to (A4), it can be concluded that the relationship between the power of each port and the phase shift angle satisfies formula (18). When d 12=0.5,d 23 = 0, port 1 reaches the maximum output power; when d 12 =0.5,d 23 =-0.5, port 2 reaches the maximum absorbed power; when d 12 =0.5,d 23 =-0.5, port 3 reaches the maximum output power, and the maximum transmission power expression of each port is as follows:

[0109]

[0110] According to calculation, S 21 The maximum inductor current of each port during open circuit fault tolerance operation is as follows:

[0111]

[0112] c. Open circuit fault tolerance strategy on the energy storage side:

[0113] When an open circuit fault occurs at the energy storage port, the DC component is eliminated by blocking the driving signal of the bridge arm where the faulty switch is located. The fault-tolerant control goal is to cut off the faulty energy storage side and allow power to be transmitted between the energy storage side and the DC bus side where no fault occurs. 11 Taking an open circuit fault as an example, in order to achieve the goal of fault-tolerant operation, the phase shift angle should be changed to 0≤d 12 ≤0.5, 0≤d 23 ≤0.5,d 13 ≥0 or 0≤d 12 ≤0.5, -0.5≤d 23 ≤0,d 13 ≥0 range, corresponding to the two states of the busbar transmitting power to the normal operation energy storage side and the normal operation energy storage side transmitting power to the busbar. 12 ≤0.5, 0≤d 23 ≤0.5,d 13 ≥0, for example, S 11 The waveform of the open circuit fault lockout fault tolerance operation is as follows Fig.13 The detailed process analysis is as follows:

[0114] S 11 When an open circuit fault occurs, the fault transient state is shown in the left shaded portion of the figure. This part of the process has been described in detail in the previous article and is omitted here. The fault bridge arm is blocked, and the circuit reaches a steady state after a period of time, as shown in the right shaded portion of the figure. 14 The rising edge of the driving signal is taken as the starting point of the steady state for analysis. According to the voltage difference of the bridge arm, it can be divided into eight operating states, which are respectively recorded as The corresponding port one inductor current loop is S 14 and D 12At t3, the current drops to zero and remains at S 13 The driving signal rises, during this period V H1 Equal to the transformer primary winding voltage, record this state as This state is analyzed as follows: At t3, the primary inductor current drops to zero. Assuming that the current continues to drop, the current should flow through D 11 and D 14 , V H1 is V1. According to formula (4), the current will rise, and then the current will return to zero. Therefore, the current actually remains zero during this period of time. The corresponding port one inductor current loop is S 13 and D 11 At t7, the current rises to zero and remains until S 14 The driving signal rises, during this period V H1 Equal to the transformer primary winding voltage, record this state as This state analysis process is Similar, no further details. 11 The expressions of the inductor currents of each port during the open circuit fault lockout fault tolerance operation are (A6), (A7), (A8) Ideally, S 11 The open circuit fault tolerant operating power expression is (A9) and the inductor current expression of each port is (A10).

[0115] Similarly, in the ideal case, S 11 Current stress and power characteristics during open circuit fault lockout operation. At this time, the maximum inductance currents of the three windings appear at t1, t1, and t2 respectively:

[0116]

[0117] According to calculations, the maximum fault current will not exceed the maximum current during normal operation. Combining formula (A9), the expression of the relationship between the power and phase shift angle of the three ports can be obtained. P1 is always equal to zero, that is, no power flows in port one. The expressions of P2 and P3 are as follows (21)(22). The power only flows between port two and port three. When d 12 =0,d 23 =0.5, the output power of port 2 reaches the maximum, and the absorption power of port 3 reaches the maximum:

[0118]

[0119] From the symmetry of the port, we can see that if the fault tolerance strategy adopted is 0≤d 12 ≤0.5, -0.5≤d 23 ≤0, then when d 13 =0,d23 =-0.5, the output power of port 3 is the maximum, and the absorption power of port 2 is the maximum:

[0120]

[0121] According to calculation, S 11 The maximum current of each port during open circuit fault tolerance operation is as follows:

[0122]

[0123] Example:

[0124] In order to verify the technical solution proposed in the present invention, a TAB converter simulation model is established based on the MATLAB-Simulink environment. The DC voltages of each TAB port are shown in Table 5.

[0125] Table 5 DC voltage of each port of TAB

[0126]

[0127] TAB parameter design:

[0128] 1. TAB inductor parameter design:

[0129] TAB auxiliary inductors L1, L2, and L3 need to meet the power transmission index. Here, the design is based on the maximum port transmission power of 100W. Ideally, from formula (11), it can be seen that the maximum power that TAB can transmit is:

[0130]

[0131]

[0132] Here, L1=L3=240μH, L2=160μH.

[0133] 2. TAB DC side capacitor design:

[0134] The main function of the DC side capacitor is to filter and reduce the impact of load disturbance on the voltage.

[0135]

[0136] In the formula, I o ——DC output current,

[0137] ΔU max ——The anti-interference index of the converter when the load is disturbed, generally 5% of the DC voltage.

[0138] Substitute into the calculation

[0139]

[0140] In the actual circuit, the DC output side also needs to provide an AC interface, and the capacitor filtering and voltage stabilization capability needs to be stronger, so C1=C2=C3=400μF is taken.

[0141] Simulation results:

[0142] In order to verify the effectiveness of the proposed open-circuit fault diagnosis and fault tolerance strategy for the three-active-bridge converter, the effectiveness of the open-circuit fault detection strategy is first verified. 21 and S 11 Take the example of open circuit fault diagnosis simulation, and set the open circuit fault to occur at 0.005s in the simulation.

[0143] like Fig.14 As shown, when S 21 or S 11 When an open circuit fault occurs, the inductor current generates a significant DC bias and the amplitude increases. The proposed open circuit fault diagnosis strategy can quickly locate the fault location. In the figure, Flag represents the fault flag, u AB ,u CD are the square wave voltages corresponding to the primary and secondary bridges, i L1 ,i L2 are the primary and secondary inductor currents respectively.

[0144] To verify the effectiveness of the fault-tolerant strategy, we set S 21 and S 11 An open circuit fault occurs, simulating an open circuit fault between the DC bus side and the energy storage side. 12 >0,d 23 >0,d 13 >0. S 21 The fault tolerance goal when an open circuit fault occurs is to make port 2 (DC bus side) absorb power and ports 1 and 3 output power. The result is as follows Fig.15 As shown. 11 When an open circuit fault occurs, the fault tolerance goal is to make port 1 (energy storage side) no longer participate in power transmission, and power is only transmitted between port 2 and port 3. Fig.16 As shown. Fig.15 , Fig.16 It can be seen that the proposed fault-tolerant strategy can quickly eliminate the DC bias. Fig.17 For S 21 and S 11 The power of the three ports in the open circuit fault tolerance operation is Figure 3 The power flow shown in (b) is the reference direction. 11 When the circuit is open, port 1 no longer transmits power, and power is only transmitted between ports 2 and 3. 21 When open circuit, ports 1 and 3 output power to port 2.

[0145] Appendix A

[0146] Secondary side S 21 The calculation results for open circuit fault tolerance operation are as follows:

[0147] From formula (15), S can be calculated 21 Open circuit fault tolerant operation current zero crossing time t2 and secondary side inductor current:

[0148]

[0149]

[0150]

[0151]

[0152]

[0153] S 21 The inductor current at each moment of the primary side during open circuit fault tolerance operation is as follows:

[0154]

[0155]

[0156]

[0157]

[0158] S 21 The inductor current at each moment of the tertiary side during open circuit fault tolerance operation is as follows:

[0159]

[0160]

[0161]

[0162]

[0163] Under ideal working conditions, the power of each port is as follows:

[0164]

[0165]

[0166]

[0167] Under ideal working conditions, the inductor current of each port is as follows:

[0168] Port 1:

[0169] Port 2:

[0170] Port three:

[0171] S 11 The calculation results for open circuit fault tolerance operation are as follows:

[0172] The current at each moment on the primary side is as follows:

[0173]

[0174] The current at each moment on the secondary side is as follows:

[0175]

[0176]

[0177]

[0178]

[0179] The current at each moment of the tertiary side is as follows:

[0180]

[0181]

[0182]

[0183]

[0184] Ideally, the power expression of each port is as follows:

[0185]

[0186] Ideally, the inductor current expression of each port is as follows:

[0187] Port 1:

[0188] Port 2:

[0189] Port three:

[0190] The embodiment of the present invention provides a TAB converter open circuit fault diagnosis and fault-tolerant operation method, which can quickly and accurately locate the open circuit fault of the three active bridge converter switch device; can realize the fault-tolerant operation of the open circuit fault of the three active bridge converter switch device; can realize the reasonable power distribution among the three ports after the TAB converter open circuit fault.

[0191] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A TAB converter open circuit fault diagnosis and fault-tolerant operation method, characterized in that: include: Step S1: locating the open circuit fault of the TAB converter; Step S2: After the positioning is completed, the DC bias generated by the open circuit fault is eliminated by blocking the fault bridge arm drive signal and changing the phase shift angle range, solving the overcurrent problem and distributing the power transmitted between the three ports to achieve fault-tolerant operation; The step S1 includes: analyzing the open circuit fault waveforms of each switch tube of the TAB, and locating the TAB open circuit fault by using the midpoint voltage of each bridge arm; In normal operation, when current flows through the upper bridge arm, the voltage value at the midpoint of the corresponding bridge arm is equal to the voltage on the DC side; when current flows through the lower bridge arm, the voltage value at the midpoint of the corresponding bridge arm is 0. When an open circuit fault occurs, the midpoint voltage of the bridge arm will be added to a state equal to 0, which will cause the average value of the midpoint voltage of the corresponding fault bridge arm to deviate from the normal value; the step S2 eliminates the DC bias caused by the open circuit fault, solves the overcurrent problem, and reasonably distributes the transmission power between the three ports, wherein the open circuit fault includes: an open circuit fault on the DC bus side and an open circuit fault on the energy storage side; When an open-circuit fault occurs on the DC bus side or the energy storage side, the driving signals of the bridge arm where the faulty switch tube is located are all locked to form a symmetrical circuit, thereby eliminating the DC component; after the open-circuit fault occurs on the DC bus side or the energy storage side, during fault-tolerant operation, the maximum inductance current of each port is ensured not to be greater than the maximum inductance current during normal operation, and when a fault occurs on the DC bus side, the DC bus is ensured to absorb power normally, and when a fault occurs on the energy storage side, the faulty energy storage is cut off, and power transmission is performed normally between the other two ports; Among them, the composition and working principle of TAB include: TAB is composed of three H bridges and a high frequency transformer. The three H bridges are H1, H2, H3, S 11 ~S 14 is the switch tube of the primary side H1, S 21 ~S 24 is the switch tube of H2 on the secondary side, S 31 ~S 34 The switch tube of the tertiary side H3, D 11 ~D 14 , D 21 ~D 24 , D 31 ~D 34 They are the anti-parallel diodes corresponding to the switch tubes in H1, H2 and H3 respectively; the high-frequency transformer is a three-winding transformer, and the turns ratio of the three windings is N1:N2:N3; each winding is connected to an H-bridge, and the transformer enables the three H-bridges to be electrically isolated and matches the voltage ratio between the three; TAB adopts single phase shift control. Under single phase shift control, S 11 With S 14 , S 12 With S 13 , S 21 With S 24 , S 22 With S 23 , S 31 With S 34 , S 32 With S 33 The driving signals of the two switches are kept consistent, and the duty cycle is 0.5; d ij It is recorded as the phase shift angle between the three H bridges, where i, j = 1, 2, 3, i ≠ j, d 12 +d 23 =d 13 ; S 11 With S 21 The time difference between the driving signals is 0.5d 12 T, S 11 With S 31 The time difference of driving signal is 0.5d 13 T, S 21 With S 31 The time difference between the driving signals is 0.5d 23 T, where T represents the switching period; TAB's open circuit fault diagnosis and fault tolerance strategies include: DC bus side open circuit fault tolerance strategy: When the DC bus side is open circuit, the fault tolerance control goal is to transfer energy from the energy storage system to the DC bus, and the phase shift angle needs to be changed to d 12 ≥0,d 23 ≤0,d 13 ≥0, or d 12 ≥0,d 23 ≤0,d 13 ≤0 range; Energy storage side open circuit fault tolerance strategy: The fault tolerance control goal is to cut off the faulty energy storage side, so that power can be transmitted between the energy storage side and the DC bus side where no fault occurs; change the phase shift angle to 0≤d 12 ≤0.5, 0≤d 23 ≤0.5,d 13 ≥0 or 0≤d 12 ≤0.5, -0.5≤d 23 ≤0,d 13 ≥0 range, corresponding to the two states of the busbar transmitting power to the normal operating energy storage side and the normal operating energy storage side transmitting power to the busbar.

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