APF Fault-Tolerant Operation Method Based on Residual Vector

Abstract

This invention discloses a fault-tolerant operation method for Active Power Filters (APFs) based on residual vectors, relating to harmonic mitigation and inverter control in power systems. The method includes: establishing a mathematical model of an active power filter (APF) with a T-type three-level topology; fault analysis based on fault characteristics using the DC-side capacitor voltage residual value; synthesizing a new virtual output vector from the residual voltage vector of the T-type three-level inverter to achieve fault-tolerant operation of the APF; and selecting different control strategies according to different fault types to improve harmonic compensation. This invention achieves improved harmonic compensation by selecting different control strategies based on different fault types. The control strategy eliminates the need to consider neutral point voltage balance, relying solely on hardware parameters. The virtual vector synthesized from the residual vector effectively participates in the inverter's vector output, thus reducing harmonics.

Description

Technical Field

[0001] The invention relates to the fields of harmonic control and inverter control in power systems, specifically to an APF fault-tolerant operation method based on residual vectors. Background Technology

[0002] Active power filters (APFs), as a new type of harmonic suppression device, have advantages such as a wide harmonic frequency compensation range, excellent tracking characteristics, good dynamic characteristics, and controllable compensation degree, making them a new generation of power quality conditioning devices. With the increase in nonlinear loads, a large number of harmonics are generated in the power grid. Due to their good harmonic compensation and stability, active power filters are widely used in the power grid. With in-depth research on inverters, three-level inverters have many advantages compared to two-level inverters. More and more active power filters are adopting three-level inverters.

[0003] Currently, there are two main methods for fault-tolerant operation control after inverter failure: software algorithm fault-tolerant control and hardware topology reconfiguration. Software algorithms alter the inverter's control strategy after a fault, using vector modulation to reconstruct or combine redundant and fault-free vectors, resulting in some waveform improvement. Hardware topology reconfiguration changes the inverter's topology using redundant components, enabling the inverter to output the voltage vector before the fault. It offers better harmonic compensation under fault-tolerant operation but increases costs.

[0004] After a power switching device fails, some of the output voltage vectors cannot be output normally. If the APF controller still uses the control strategy before the fault, its compensation effect will be greatly reduced. The power switching transistors may withstand greater reverse voltage and pass greater power, further damaging the APF system. Due to the importance of the power grid, the grid load changes constantly and has strict requirements on the waveform, which places even stricter demands on the operation and control of the APF. During operation, the APF must not only quickly and accurately locate the fault, but also ensure that the APF has a certain harmonic compensation effect after the fault, that is, a certain fault-tolerant operation capability. Summary of the Invention

[0005] To address the issue of reduced harmonic compensation effectiveness due to the inability to output the voltage vector corresponding to the faulty power transistor when a power device fails during active power filter (APF) operation, this invention proposes a fault-tolerant APF operation method based on residual vectors. Different control strategies are selected according to different fault types to improve harmonic compensation. First, based on fault characteristics, the fault and odd / even power devices are identified and located using the residual value of the DC-side capacitor voltage. Then, the phase power device and the upper / lower bridge arm power devices are located using the residual value of the inverter command voltage and output voltage, accurately pinpointing the location of the IGBT open-circuit fault. For different faults, in the case of a vertical power device fault, hardware reconfiguration is used to convert the T-type three-level inverter into a two-level inverter; in the case of a horizontal power device fault, only the normally output large vector and zero vector are used to achieve fault-tolerant operation of the APF.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A mathematical model of the active power filter (APF) for a T-type three-level topology is established. Based on fault characteristics, fault analysis is performed using the DC-side capacitor voltage residual value. This includes first determining the fault and locating odd and even-numbered power devices based on the fault characteristics and the DC-side capacitor voltage residual value, and then locating the phase power devices and upper and lower bridge arm power devices using the residual value of the inverter command voltage and output voltage to determine the fault location of the IGBT open circuit in the power device. A new virtual output vector is synthesized by the residual voltage vector of the T-type three-level inverter to enable fault-tolerant operation of the APF. Depending on the fault type, when a vertical power device fails, the inverter topology is reconfigured to convert the T-type three-level inverter into a two-level inverter; when a horizontal power device fails, the control strategy is directly switched.

[0008] Further, the specific steps of fault analysis:

[0009] 1) According to the formula for residual DC-side capacitor voltage Calculate the capacitor voltage residual ΔV of the inverter. dc In the formula, V dc1 V is the voltage across capacitor C1 on the DC side. dc2 This is the voltage across capacitor C2 on the DC side;

[0010] 2) According to the formula The value of λ is calculated to determine whether the inverter has malfunctioned; in the formula, λ is the criterion variable, λ=1 indicates that there is an open circuit fault in the power device, and λ=0 indicates that there is no fault; H λ This is the trigger threshold;

[0011] 3) Obtain the inverter control command signal output by the APF controller, and then according to the formula... Calculate the command voltage value that the inverter should output; where S a S b S c This indicates the switching state output by the controller in each cycle. , , This indicates the three-phase command voltage of the inverter;

[0012] 4) According to the formula Calculate the residual value ΔV between the command voltage and the actual output voltage. x In the formula, V ca V cb and V cc This refers to the actual three-phase output voltage of the inverter.

[0013] 5) ΔV x Substitute the value into the formula The criterion is used to determine the value of α; where α is the criterion variable, α=1 indicates a fault in an odd-power device, and α=-1 indicates a fault in an even-power device.

[0014] 6) ΔV x Substitute the value into the formula The criterion is used to obtain the value of β; where β is the criterion for judgment, and its value corresponds to the phase in which the faulty power device is located;

[0015] 7) ΔV x Substitute into the formula Criterion, calculate the value of γ; where γ is the criterion variable, γ=1 indicates upper arm failure, γ=-1 indicates lower arm failure, ΔV β This is the residual between the fault phase command voltage and the actual output voltage of the inverter;

[0016] 8) Based on the obtained α, β, and γ values, determine the faulty power device.

[0017] Furthermore, in the fault-tolerant operation of the APF, different output vector actions also require adjustment of the model prediction value function. The neutral point voltage balance is guaranteed by hardware parameters. In the fault-tolerant model predictive control, only the switch switching constraints and output vector difference issues need to be considered. Its fault-tolerant model predictive control value function is as follows:

[0018]

[0019] Where λ1 and λ3 are the weight coefficients of the cost function, S sw The number of switches to switch on / off states.

[0020] Furthermore, the fault-tolerant operation of the APF is subject to different fault-tolerant controls depending on the type of fault, which are divided into longitudinal power device fault control and transverse power device fault control.

[0021] Furthermore, the longitudinal power device fault control is as follows: when a longitudinal power device fails, the inverter topology is reconfigured to convert the T-type three-level inverter into a two-level inverter, and then the APF control strategy is changed from virtual vector-based model predictive control to residual vector-based fault-tolerant operation control strategy.

[0022] Furthermore, the fault control of the lateral power device is as follows: when the lateral power device fails, the topology of the T-type three-level inverter does not change, and it directly switches to a fault-tolerant control strategy.

[0023] This invention achieves the selection of different control strategies based on different fault types through the above-described technical solution, thereby improving the harmonic compensation effect. The control strategy eliminates the need to consider neutral point voltage balance, which can be guaranteed by hardware parameters. Furthermore, the virtual vector synthesized using residual vectors can effectively participate in the inverter's vector output, thus reducing harmonics. Attached Figure Description

[0024] Figure 1 This is a diagram of the APF structure of the T-type three-level topology involved in the present invention;

[0025] Figure 2 For the longitudinal direction S a1 Fault vector diagram;

[0026] Figure 3 This is a diagram of the T-type three-level topology reconstruction.

[0027] Figure 4 To reconstruct vector graphics;

[0028] Figure 5 For S a2 Fault vector diagram;

[0029] Figure 6 For S a2 Fault residual vector;

[0030] Figure 7 For fault-tolerant virtual vector synthesis;

[0031] Figure 8 For S a1 Simulation diagram of current under fault-tolerant operation;

[0032] Figure 9 For S a1 Simulation diagram of current under fault-tolerant operation;

[0033] Figure 10For S a1 Fault-tolerant vector diagram under fault conditions;

[0034] Figure 11 For S a1 Simulation diagram of current tracking under fault-tolerant operation;

[0035] Figure 12 For S a2 Simulation diagram of current under fault-tolerant operation;

[0036] Figure 13 For S a2 Simulation diagram of current under fault-tolerant operation;

[0037] Figure 14 For S a2 Fault-tolerant operation vector diagram;

[0038] Figure 15 This is a simulation diagram of current tracking under fault-tolerant operation. Detailed Implementation

[0039] The following description, in conjunction with the accompanying drawings, further illustrates specific embodiments of the present invention:

[0040] like Figure 1 The diagram shows the APF structure of the T-type three-level topology. A mathematical model of the active power filter (APF) of the T-type three-level topology is established. The T-type three-level inverter connects the DC side voltage midpoint through two reverse series power devices to achieve voltage balance at the midpoint. Compared with the NPC inverter, it reduces the number of clamping diodes by two, thus reducing the possibility of failure.

[0041] For ease of analysis, the DC-side capacitor voltage residual ΔV is defined. dc as follows:

[0042] (1)

[0043] In the formula, V dc1 V is the voltage across capacitor C1 on the DC side. dc2 This is the voltage across capacitor C2 on the DC side.

[0044] Because the controller employs an MPC control strategy, it selects the corresponding output vector based on the value function in each cycle, transforming the output vector into a switching state. This is based on the switching state S output by the controller in each cycle. a S b and S c The ideal output voltage of the inverter and the three-phase command voltage of the inverter can be calculated. , and As shown in the following formula:

[0045] (2)

[0046] Define the residual between the three-phase command voltage and the actual output voltage of a T-type inverter as:

[0047] (3)

[0048] In the formula, V ca V cb and V cc This represents the actual three-phase output voltage of the inverter.

[0049] when i ca When >0: If power device S a1 No fault, current flows from DC side midpoint O through S a1 The inverter outputs a positive potential when the power device S is connected to the load. a1 The fault occurs when current flows from the DC side midpoint O through S. a2 and D a3 When the inverter's A-phase output state changes from state 1 to state 0, the command voltage is greater than the actual output voltage, ΔV. a >0. The discharge capacitor changes from C1 to C2. Compared to the non-fault condition, the voltage across capacitor C1 increases while the voltage across capacitor C2 decreases. At this time, ΔV dc >0. Combining the above formula, the voltage residual is as follows:

[0050] (4)

[0051] when i ca When <0: Current flows from the load through D a1 The output is sent to DC side point P and is not affected by power device S. a1 The fault caused the inverter to output a high potential.

[0052] Based on the above analysis, the following table shows the A-phase S phase. a1 -S a4 The law of residual change under fault conditions.

[0053] Fault switch transistor Capacitor voltage residual Command voltage residual <![CDATA[S a1 ]]> <![CDATA[ΔV dc >0]]> <![CDATA[ΔV a >0]]> <![CDATA[S a2 ]]> <![CDATA[ΔV dc <0]]> <![CDATA[ΔV a >0]]> <![CDATA[S a3 ]]> <![CDATA[ΔV dc >0]]> <![CDATA[ΔV a <0]]> <![CDATA[S a4 ]]> <![CDATA[ΔV dc <0]]> <![CDATA[ΔV a <0]]>

[0054] Due to a series of factors such as switching trigger delay, power device on-state voltage drop, and dead time, even when the power devices are fault-free, a residual voltage ΔV will still exist on the DC side of the capacitor in a T-type three-level inverter. dc It will oscillate around 0. Because the disturbance is bidirectional, the data can be discretized and then summed, ΔV dc Transformed into the following formula:

[0055] (5)

[0056] In the formula, N is the number of sampling points of the controller in one cycle, and V dc2 (n) represents the voltage across capacitor C1 at the nth sampling point, V dc2 (n) represents the voltage across capacitor C2 at the nth sampling point.

[0057] In this way, we only need to give ΔV dc By setting a threshold, it is possible to determine whether a power device has malfunctioned.

[0058] (6)

[0059] In the formula, λ is the criterion variable, where λ=1 indicates the presence of an open-circuit fault in the power device, and λ=0 indicates the absence of a fault; H λ This is the trigger threshold.

[0060] In addition, based on the bus capacitor voltage variation pattern under fault conditions, the power devices can be further located:

[0061] (7)

[0062] In the formula, α is the criterion variable, and α=1 represents an odd-power device (an odd-power device is S). a1 and S a3 ) fault, α=-1 indicates even-numbered power devices (even-numbered power devices are S a2 and S a4 )Fault.

[0063] When a fault occurs in one phase of a T-type three-level inverter, that phase of the inverter cannot output the expected voltage. The voltage residual of that phase is greater than the voltage residual of the other two phases. Since the voltage residual caused by the positive and negative cycles of the command current will cancel each other out, it is discretized.

[0064] (8)

[0065] To avoid errors in judgment, the judgment is performed after a delay of half a power grid cycle following the fault signal λ being 1.

[0066] (9)

[0067] In the formula, β is the criterion for judgment, and its value corresponds to the phase where the faulty power device is located.

[0068] By determining the sign of the residual voltage of the faulty phase, the location of the fault can be further determined, thus identifying the bridge arm where the faulty device is located (the upper bridge arm device is S). a1 and S a2 The lower bridge arm device is S. a3 and S a4 ).

[0069] (10)

[0070] In the formula, γ is the criterion variable, γ=1 indicates an upper arm failure, γ=-1 indicates a lower arm failure, and ΔV β This is the residual between the fault phase command voltage and the actual output voltage of the inverter.

[0071] The fault location is determined based on the corresponding output values ​​of α, β, and γ when each power device has an open circuit fault. The power device open circuit fault diagnosis and location table is shown below.

[0072] Power device transistor λ α β γ <![CDATA[S a1 ]]> 1 1 1 1 <![CDATA[S a2 ]]> 1 -1 1 1 <![CDATA[S a3 ]]> 1 1 1 -1 <![CDATA[S a4 ]]> 1 -1 1 -1 <![CDATA[S b1 ]]> 1 1 2 1 <![CDATA[S b2 ]]> 1 -1 2 1 <![CDATA[S b3 ]]> 1 1 2 -1 <![CDATA[S b4 ]]> 1 -1 2 -1 <![CDATA[S c1 ]]> 1 1 3 1 <![CDATA[S c2 ]]> 1 -1 3 1 <![CDATA[S c3 ]]> 1 1 3 -1 <![CDATA[S c4 ]]> 1 -1 3 -1

[0073] As shown in the table, when a fault occurs, the faulty tube can be located using the above judgment criteria.

[0074] The following section analyzes the longitudinal and transverse IGBT fault outputs of the T-type inverter.

[0075] When the longitudinal device S a1 When an open circuit fault occurs, i ca When the value is greater than 0, the output state of phase A of the inverter changes from state 1 to state 0. Therefore, the corresponding output voltage vector will also be affected and cannot be output, which is called the fault vector. Among the affected vectors are 3 large vectors, 2 medium vectors, 3 small vectors, and 1 zero vector. The analysis will focus on phase A as an example. a1 Fault vector diagram as follows Figure 2 As shown, u1, u2, u3, u 11 ,u 12 ,u 14 ,u 16 ,u 24 ,u 27 This refers to the fault vector. Without intervention, the controller will continue to use the original vector, and when the fault vector is involved, it will be unable to output voltage correctly, resulting in poor compensation. Since fault-tolerant control operates based on faults, it needs to avoid fault vectors, which requires switching the APF to a fault-tolerant control program.

[0076] For a T-type three-level topology APF, fault tolerance can be achieved through software algorithms. Since the T-type inverter is a three-level topology, there are redundant vectors among the 27 output vectors. Although their switching functions differ, their output voltage vectors are the same. This can be addressed by reducing the modulation depth, using only some small vectors and zero vectors located within the output, but this leads to APF throttling operation, and the inverter's output vectors cannot meet harmonic compensation requirements. Increasing the inverter's DC-side voltage through algorithms not only requires higher-voltage DC-side capacitors but also places higher demands on power devices, increasing the cost of fault-tolerant operation.

[0077] To improve harmonic compensation after an APF failure, fault-tolerant operation can be achieved by modifying the hardware reconfiguration method. The T-type three-level topology reconfiguration diagram is shown below. Figure 3 As shown.

[0078] Three anti-parallel switches, T1, T2, and T3, are added to the existing T-type inverter APF. Under normal operating conditions, the horizontal power switch outputs a potential of 0. However, the output vector of the inverter can be altered by operating the added controllable switches. With T1 turned on and T2 and T3 turned off, the horizontal switch is directly connected to the high-potential side of capacitor C1, resulting in a 1-level output. Similarly, with T3 turned on and T1 and T2 turned off, the horizontal switch is directly connected to the low-potential side of capacitor C2, resulting in a -1-level output. This topology reconfiguration effectively transforms the T-type three-level structure into a two-level topology.

[0079] Because the T-type three-level APF is three-phase symmetrical, with phase A S a1 Analysis of the output vector of a T-type inverter in the event of an open-circuit fault. ca A fault vector only exists when the output voltage is >0, resulting in a voltage of 1. Therefore, only the vector change under this condition is analyzed. The inverter topology changes, and the originally defined voltage vectors for the switching states also change. For example, when the switching state is (0, -1, -1), it becomes (1, -1, -1) after reconfiguration, and all voltage vectors of phase A with an output voltage of 0 are converted to output voltages of 1. The fault-tolerant operation reconfiguration vector diagram of the APF is shown below. Figure 4 As shown, the quantity outside the box represents the original defined switch states, and the quantity inside the box represents the new output vector after topology reconstruction.

[0080] Similarly, taking phase A as an example, for the transverse device S... a2 The fault operation characteristics were analyzed. Similar to the lateral device S... a1 Operating characteristics, but their fault vectors are different. When the lateral arm S a2 A fault occurs and the current is outputting in the positive direction. At this time, the inverter output potential changes from 0 to -1. S a2 Fault vectors such as Figure 5 As shown, u4,u 10 ,u 13 ,u 15 ,u 18 ,u 20 ,u 22 ,u 23 ,u 26 This is the fault vector.

[0081] Among the affected vectors are 2 medium vectors, 6 small vectors, and 1 zero vector. a2 Fault Residual Vector Figure 6 As shown.

[0082] Unlike S a1 Fault, S a2 The fault vectors affected by the fault contain redundant vectors, but do not affect the large vectors. Therefore, fault-tolerant control can be achieved solely through software algorithm optimization, and the original control strategy can still achieve good harmonic compensation. Although the fault vector can be replaced by other output vectors with the same voltage, using only these remaining small and medium vectors will lead to excessive capacitor voltage residuals, disrupting the DC-side bus voltage balance, causing APF control system malfunctions, and even further damaging the inverter. Therefore, when the lateral power device S... a2 After a fault occurs, remove all medium vectors, small vectors, and fault zero vectors from the T-type three-level inverter.

[0083] Analysis of the power devices reveals that regardless of whether a fault occurs in a horizontal or vertical power device, after hardware reconfiguration or software algorithm adjustments, the resulting faults exhibit commonalities: the vectors they affect are identical. Furthermore, due to the simplified output vector, none of the three-phase bridge arms have a zero-potential output under fault-tolerant control. The DC-side neutral point no longer directly exchanges energy with the AC side. Therefore, the software control strategy does not need to consider neutral point voltage balance; it can be ensured solely through hardware parameters.

[0084] In the fault-tolerant control strategy, the residual action vector is directly used, which effectively transforms the T-type three-level inverter into a two-level inverter. For the APF (Automatic Power Filter), the reduction in the number of levels also means a reduction in the number of candidate output vectors in model predictive control, shortening the time for value optimization in each cycle of the model prediction value and significantly reducing the effectiveness of harmonic compensation. To compensate for the insufficient number of candidate output vectors, a model prediction strategy based on the residual action vector is proposed.

[0085] Under fault-tolerant control, the output vector can only be synthesized from the residual voltage vector. Compared with the synthesis of three-level virtual vectors, the synthesized virtual vector is less numerous. The synthesis method of virtual vector under fault tolerance is shown in the table below:

[0086] Composite vector Synthesis method <![CDATA[v1]]> <![CDATA[0.5u 13 +0.5u 15 ]]> <![CDATA[v2]]> <![CDATA[0.5u 15 +0.5u 17 ]]> <![CDATA[v3]]> <![CDATA[0.5u 17 +0.5u 19 ]]> <![CDATA[v4]]> <![CDATA[0.5u 19 +0.5u 21 ]]> <![CDATA[v5]]> <![CDATA[0.5u 21 +0.5u 23 ]]> <![CDATA[v6]]> <![CDATA[0.5u 23 +0.5u 13 ]]>

[0087] The virtual vector composite graph of the remaining vector is as follows Figure 7 As shown.

[0088] The switching fluctuations between the two selected output voltage vectors should be minimized to avoid an excessive number of switching changes. During synthesis, a period T is used. s The vector is synthesized by dividing the process into two parts, t1 and t2. Following the principle of minimizing changes to the switches, a suitable synthesis method is selected.

[0089] Similarly, using residual vectors to synthesize virtual vectors increases the candidate set of vectors, but also burdens the computational speed of the arithmetic unit. It also uses sector positioning proposed in Chapter 3, but the difference is that the fault-tolerant control program only locates the large sector where the reference output vector is located.

[0090] The range of candidate output vectors is narrowed down to the vector set within each sector. The vector set assigned to each sector is shown in the table below.

[0091] Small sector Assigned vector 1 <![CDATA[u 25 , in 26 , in 13 , in 15 , v1, v1´]]> 2 <![CDATA[u 25 , u 26 , u 15 , u 17 , v2,v2´]]> 3 <![CDATA[u 25 , u 26 , u 17 , u 19 , v3, v3´]]> 4 <![CDATA[u 25 , in 26 , in 19 , in 21 , v4, v4´]]> 5 <![CDATA[u 25 , in 26 , in 21 , in 23 , v5, v5´]]> 6 <![CDATA[u 25 , you 26 , you 23 , you 25 , v6, v6´]]>

[0092] Different output vector actions also require adjustments to the value function of the model prediction. Neutral point voltage balance is ensured by hardware parameters. In fault-tolerant model predictive control, only switching constraints and output vector differences need to be considered. The value function of its fault-tolerant model predictive control is shown below:

[0093]

[0094]

[0095] (11)

[0096] Where λ1 and λ3 are the weight coefficients of the cost function, S sw The number of switches to switch on / off states.

[0097] During normal operation of the APF, switch T2 is in the default on state, and the lateral power devices are directly connected to the midpoint of the inverter's DC-side capacitor through the on-state T2. Switches T1 and T3 are in the default off state. When there is no open-circuit fault in the power devices, the T-type inverter is in a three-level output state. Under normal conditions, the APF adopts a model predictive control strategy based on virtual vectors.

[0098] Once an open-circuit fault occurs in the T-type inverter, the core component of the APF (Automatic Power Filter), the fault is quickly diagnosed and its location is pinpointed. Different fault-tolerant controls are implemented depending on the specific fault. The following discussion addresses different fault scenarios in two categories:

[0099] (1) When the inverter malfunctions and the fault diagnosis system determines that the longitudinal power device transistor is faulty, the inverter topology reconfiguration is initiated. A trigger pulse is sent to the added switch transistor through a software algorithm to turn off switch transistor T2 to disconnect the direct connection between the AC side and the DC side neutral point. The fault of the longitudinal power device in the upper arm triggers switch transistor T1, and the fault of the longitudinal power device in the lower arm triggers switch transistor T3. Then the APF control strategy changes from model predictive control based on virtual vectors to fault-tolerant operation control strategy based on residual vectors.

[0100] (2) When the inverter malfunctions and the fault diagnosis system identifies a fault in the horizontal power device transistor, since switch T2 is in the default on state, switches T1 and T3 are in the default off state. No controller trigger signal or other operations are required. The T-type three-level inverter topology remains unchanged and directly switches to a fault-tolerant control strategy.

[0101] To verify the accuracy and practicality of the residual vector-based APF fault-tolerant operation method, a simulation model was built in MATLAB / Simulink. The simulation results of fault analysis of the A-phase power device are used as an example.

[0102] (1) Power device S a1 Simulation analysis under open circuit fault

[0103] Figure 8 S is shown a1 Simulation diagram of current under fault-tolerant operation, by Figure 9 (a) It can be seen that the APF has a good harmonic compensation effect when there is no fault. At 0.1s, the power device S a1 In the event of an open-circuit fault, without switching the fault-tolerant control strategy, the current compensation effect is poor, and the waveform exhibits significant distortion. Figure 9 (b) It can be seen that its waveform distortion rate reaches 6.20%, which exceeds the acceptable range, and fault-tolerant control must be used.

[0104] Figure 9 The image shows the power device transistor S. a1 Simulation diagram of current under fault-tolerant operation, such as Figure 9 As shown in (a), the APF is operating normally, and the power device transistor S occurs at 0.1. a1 Fault. After 0.023 seconds, based on the accurate location of the power device transistor by the fault detection system, the fault-tolerant control circuit sends a pulse at 0.123 seconds to control the turn-off and turn-on of the auxiliary switching transistor, switching to a fault-tolerant control strategy. For example... Figure 9 (b) and Figure 9 As shown in (c), after the fault is detected and converted to a fault-tolerant operation control program, the waveform becomes smoother, and the waveform distortion rate decreases significantly from 6.10% before the fault to 2.81%. Although the waveform quality is lower than before the fault, it is within the internationally specified standards. Since the fault is an open circuit fault in phase A, the waveform distortion rates of the remaining two phases are both lower than those of phase A. The waveform distortion rate of phase b is 2.38%, and the waveform distortion rate of phase c is 2.78%.

[0105] Fault tolerance vector effect diagram as follows Figure 10 As shown, vector 6 is a virtual vector, located in the power device transistor S. a1Before the fault is detected, the previous control strategy is still in use. When the output vector is composed of the output voltage of the faulty transistor, it will affect the compensation accuracy at that moment. Using the faulty vector to construct a virtual vector will further reduce the compensation effect. And in the power device transistor S... a1 Under fault-tolerant operation, the virtual vector synthesized using only the remaining vector can effectively participate in the inverter vector output, thereby reducing harmonics.

[0106] The magnitude of the current tracking error has a significant impact on the harmonic compensation effect of the APF. The current tracking effect under fault-tolerant operation control is verified. Figure 11 The image shows the power device transistor S. a1 Simulation diagram of current tracking under fault-tolerant operation, power device S a1 An open-circuit fault occurred at 0.1 seconds. After the fault occurred but before the fault-tolerant operation control program intervened, current tracking deviated, with the error reaching tens of amperes. After a delay, the fault-tolerant operation control program intervened, reducing the current tracking error and restoring the tracking performance to a level not significantly different from before the fault. This verifies the effectiveness of the fault-tolerant control program after a longitudinal IGBT fault.

[0107] (2) Power device S a2 Simulation analysis under open circuit fault

[0108] Figure 12 S is shown a2 Simulation diagram of current under fault-tolerant operation, by Figure 12 (a) It can be seen that at 0.1s, the transverse power device S a2 As discussed in previous sections, an open-circuit fault does not cause a large output vector fault in lateral power devices. Therefore, after the fault occurs, the waveform distortion rate does not increase significantly, from the original 2.24% to 2.95%. Although the harmonic distortion rate does not increase significantly, using the control strategy before the fault will cause the APF to operate under harsh conditions.

[0109] Power device transistor S a2 Fault-tolerant operating current simulation, such as Figure 13 As shown, after 0.021s, the position of the power device transistor is located at 0.121s. Without involving any changes in the hardware structure, it is directly converted to a fault-tolerant control strategy, and the current harmonic distortion rate decreases from 2.95% to 2.51%.

[0110] Figure 14 The image shows the power device transistor S. a2 Vector effect diagram under fault-tolerant operation. It can be seen that after 0.121s, after the fault-tolerant program starts, the virtual vector synthesized using the remaining vector can effectively participate in the inverter vector output and reduce harmonics.

[0111] Figure 15 The image shows the power device transistor S. a2 Simulation diagram of current tracking under fault-tolerant operation, power device S a2 An open-circuit fault occurred at 0.1s. No significant error was observed in the current readings after the fault occurred and under fault-tolerant control.

[0112] Regarding the APF fault-tolerant operation method based on residual vectors proposed in this specification, the following explanations are required to fully reflect the patent protection requirements:

[0113] 1. Although this invention proposes a fault-tolerant operation method for active power filter systems, the fault diagnosis method proposed in this invention is also applicable to other control systems (such as SVG systems, grid-connected inverter systems, etc.) that use T-type three-level inverters as the main topology.

[0114] 2. Although this invention addresses the control problem of active power filters employing fault-tolerant operation, the residual vector APF fault-tolerant operation method in this invention is also applicable to other control methods that use a T-type three-level inverter as the main topology.

Claims

1. A fault-tolerant operation method for APF based on residual vectors, characterized in that: Includes the following steps: A mathematical model of an active power filter (APF) with a T-type three-level topology is established. Based on the fault characteristics, fault analysis is performed using the DC-side capacitor voltage residual value. This includes first determining the fault and locating the odd and even number power devices based on the fault characteristics and the DC-side capacitor voltage residual value, and then locating the phase power devices and upper and lower bridge arm power devices using the residual value of the inverter command voltage and output voltage, thus determining the fault location of the IGBT open circuit in the power device. A new virtual output vector is synthesized from the residual voltage vector of the T-type three-level inverter to enable fault-tolerant operation of the APF; Depending on the fault type, when a vertical power device fails, the inverter topology is reconfigured to convert the T-type three-level inverter into a two-level inverter; when a horizontal power device fails, the control strategy is switched directly.

2. The APF fault-tolerant operation method based on residual vectors according to claim 1, characterized in that: Specific steps for fault analysis: 1) According to the formula for residual DC-side capacitor voltage Calculate the capacitor voltage residual ΔV of the inverter. dc In the formula, V dc1 V is the voltage across capacitor C1 on the DC side. dc2 This is the voltage across capacitor C2 on the DC side; 2) According to the formula The value of λ is calculated to determine whether the inverter has malfunctioned; in the formula, λ is the criterion variable, λ=1 indicates that there is an open circuit fault in the power device, and λ=0 indicates that there is no fault; H λ This is the trigger threshold; 3) Obtain the inverter control command signal output by the APF controller, and then according to the formula... Calculate the command voltage value that the inverter should output; where S a S b S c This indicates the switching state output by the controller in each cycle. , , This indicates the three-phase command voltage of the inverter; 4) According to the formula Calculate the residual value ΔV between the command voltage and the actual output voltage. x In the formula, V ca V cb and V cc This refers to the actual three-phase output voltage of the inverter. 5) ΔV x Substitute the value into the formula The criterion is used to determine the value of α; where α is the criterion variable, α=1 indicates a fault in an odd-power device, and α=-1 indicates a fault in an even-power device. 6) ΔV x Substitute the value into the formula The criterion is used to obtain the value of β; where β is the criterion for judgment, and its value corresponds to the phase in which the faulty power device is located; 7) ΔV x Substitute into the formula Criterion, calculate the value of γ; where γ is the criterion variable, γ=1 indicates upper arm failure, γ=-1 indicates lower arm failure, ΔV β This is the residual between the fault phase command voltage and the actual output voltage of the inverter; 8) Based on the obtained α, β, and γ values, determine the faulty power device.

3. The APF fault-tolerant operation method based on residual vectors according to claim 1, characterized in that: In the fault-tolerant operation of the APF, different output vector actions also require adjustments to the value function of the model prediction. The neutral point voltage balance is guaranteed by hardware parameters. In the fault-tolerant model predictive control, only the switching constraints and the output vector difference problem need to be considered. Its value function for fault-tolerant model predictive control is as follows: Where λ1 and λ3 are the weight coefficients of the cost function, S sw The number of switches to switch on / off states.

4. The APF fault-tolerant operation method based on residual vectors according to claim 1, characterized in that: The fault-tolerant operation of the APF is divided into longitudinal power device fault control and transverse power device fault control according to the fault type.

5. The APF fault-tolerant operation method based on residual vectors according to claim 4, characterized in that: The longitudinal power device fault control is as follows: when a longitudinal power device fails, the inverter topology is reconfigured to convert the T-type three-level inverter into a two-level inverter. Then, the APF control strategy is changed from virtual vector-based model predictive control to residual vector-based fault-tolerant operation control strategy.

6. The APF fault-tolerant operation method based on residual vectors according to claim 4, characterized in that: The fault control of the horizontal power device is as follows: when the horizontal power device fails, the topology of the T-type three-level inverter does not change, and it directly switches to a fault-tolerant control strategy.

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