A fault-tolerant control method for an active clamped three-level three-phase rectifier unit

Abstract

The present invention discloses a fault-tolerant control method for an active clamped three-level three-phase rectifier unit. The present invention gives full play to the converter topology and the hardware redundancy performance of the active clamped three-level three-phase rectifier unit itself without adding other hardware circuits. By analyzing the output states and redundant paths of single-tube faults and double-tube faults, faults are classified according to the performance of fault redundancy, and fault-tolerant control of single-tube and double-tube faults is achieved for fault-tolerant fault types, and is not limited by the modulation degree of the converter. The fault of the rectifier module is isolated by injecting reactive current, and the rectifier unit is restored to the operating level before the fault by reactive compensation, thereby realizing the stable operation of the three-level active neutral point clamped three-phase rectifier unit.

Description

Technical Field

[0001] The invention relates to the technical field of power supply, and in particular to a fault-tolerant control method for an active clamped three-level three-phase rectifier unit. Background Art

[0002] The diode neutral point clamped (NPC) three-level structure is often used in high-power applications due to its low cost, but the uneven loss causes uneven junction temperature distribution, thus limiting its capacity. The active clamped (ANPC) three-level topology structure that uses power devices instead of clamping diodes not only inherits the advantages of NPC, but also provides new degrees of freedom for the loss distribution of power devices. The three-level ANPC topology structure has been maturely applied in many fields such as wind power generation, solar power generation, variable frequency speed regulation of motors, and power quality management. However, the failure of power semiconductor devices is a key issue for the safe operation of PWM rectifiers. As the number of switching devices in the ANPC structure rectifier increases, the probability of failure also increases. After the failure, the system will experience problems such as overvoltage, overcurrent, and increased harmonics. It is necessary to study effective fault-tolerant methods. Fault-tolerant methods can be divided into hardware-based fault-tolerant methods and software-based fault-tolerant methods. Hardware fault-tolerant strategies have the advantages of covering many fault types, a wide fault-tolerant range, and no need to derating output. However, this also leads to increased complexity and cost of fault-tolerant circuits. Software-based fault-tolerant strategies do not increase additional design costs, but their fault-tolerant capabilities are limited. Therefore, the key to software fault-tolerance lies in using control to give full play to the existing redundant performance of the structure.

[0003] The document "Open-Circuit Fault Tolerant Control Strategy for Three-Level ANPC Inverters Based on Hybrid Carrier Modulation" proposes a fault-tolerant control method based on hybrid carrier modulation. When operating in the derating fault-tolerant mode, the modulation index is limited to 0.577. The document "Open-Circuit Fault Tolerant Control for Outer Switches of Three-Level Rectifiers in Wind Turbine Systems" proposes a fault-tolerant control method for the outer tube of the bridge arm of NPC-type three-level and T-type three-level rectifiers. The reference voltage is compensated within the phase difference range between the rectifier current and the equivalent modulation voltage so that the rectifier outputs zero level as much as possible, but this method is limited by the modulation index and power factor. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides an active clamped three-level three-phase rectifier unit fault-tolerant control method which solves the problem that the existing fault-tolerant method is limited by the modulation index, resulting in poor fault-tolerant capability.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] A fault-tolerant control method for an active clamped three-level three-phase rectifier unit is provided, which comprises the following steps:

[0007] S1. Obtaining the operating state change of a single three-level ANPC three-phase rectifier in an active clamped three-level three-phase rectifier unit under a single-tube fault; wherein the active clamped three-level three-phase rectifier unit is composed of two three-level ANPC three-phase rectifiers connected in parallel;

[0008] S2, obtaining the operating state change of a single three-level ANPC three-phase rectifier in an active clamped three-level three-phase rectifier unit under a double-tube fault;

[0009] S3. According to the operating state changes under the single-tube fault and the operating state changes under the double-tube fault, the faults of the active clamped three-level three-phase rectifier unit are classified according to the fault tolerance capability to obtain faults that can be fault-tolerant and faults that cannot be fault-tolerant;

[0010] S4. The method of injecting reactive current to eliminate the phase difference between the modulation voltage and the current is used to tolerate faults that can be tolerated, and reactive compensation is performed through the three-phase rectifier module to complete the fault-tolerant control of the active clamped three-level three-phase rectifier unit.

[0011] Furthermore, when the single-phase middle switch tube S of a single three-level ANPC three-phase rectifier x1 In case of a fault, the operating state changes from [P] to [O];

[0012] When the single-phase middle switch tube S of a single three-level ANPC three-phase rectifier x2 In case of a fault, the operating state changes from [P] to [OL], or from [OU] to [N];

[0013] When the single-phase middle switch tube S of a single three-level ANPC three-phase rectifier x3 In case of a fault, the operating state changes from [N] to [OU], or from [OL] to [P];

[0014] When the single-phase middle switch tube S of a single three-level ANPC three-phase rectifier x4 In case of a fault, the operating status changes from [N] to [O];

[0015] When the single-phase middle switch tube S of a single three-level ANPC three-phase rectifier x5 In case of failure, the operating status changes from [OU] to [P];

[0016] When the single-phase middle switch tube S of a single three-level ANPC three-phase rectifier x6 In case of a fault, the operating state changes from [OL] to [N];

[0017] The operating state [O] indicates that the output of the bridge arm including [OU] and [OL] is zero level; the operating state [P] indicates that the output is 0.5V dc ; Operation status [N] means output -0.5V dc ; V dc is the DC side voltage; [OU] is the switch tube S passing through the upper half bridge arm x2 And switch tube S x5 The output level is 0; [OL] is the switch tube S through the lower half bridge arm x3 And switch tube S x6 The output of the flow is 0 level; x=a, b, c, respectively representing the a phase, b phase and c phase of a single three-level ANPC three-phase rectifier.

[0018] Furthermore, for a double-tube fault in the same bridge arm:

[0019] If the switch tube S in a single three-level ANPC three-phase rectifier x1 And switch tube S x2 Fault and x <0, the operating state changes from [P] to [OL], or from [OU] to [N]; i x Represents the output current of phase x;

[0020] If the switch tube S in a single three-level ANPC three-phase rectifier x1 And switch tube S x2 Fault and x >0, does not affect the bridge arm output;

[0021] If the switch tube S in a single three-level ANPC three-phase rectifier x1 And switch tube S x3 Fault and x <0, the operating state changes from [P] to [O];

[0022] If the switch tube S in a single three-level ANPC three-phase rectifier x1 And switch tube S x3 Fault and x >0, the operating state changes from [N] to [OU], and the next operating state changes from [OL] to [P];

[0023] If the switch tube S in a single three-level ANPC three-phase rectifier x1 And switch tube S x6 Fault and x <0, the operating states [OU] and [P] cannot be switched within a unit switching cycle, and the bridge arm outputs are all 0 level; the operating states [OL] and [N] cannot be switched within a unit switching cycle, and the actual output of the bridge arm is -0.5V dc ;

[0024] If the switch tube S in a single three-level ANPC three-phase rectifier x2 And switch tube S x6 Fault and x <0, the operating state changes from [P] to [N], the next operating state changes from [OU] to [N], and the operating state [OL] changes to [N], and the bridge arm output voltage is always -0.5V dc ;

[0025] If the switch tube S in a single three-level ANPC three-phase rectifier x3 And switch tube S x4 Fault and x >0, the operating state changes from [N] to [OU], or from [OL] to [P];

[0026] If the switch tube S in a single three-level ANPC three-phase rectifier x3 And switch tube S x4 Fault and x <0, does not affect the normal output of the bridge arm;

[0027] If the switch tube S in a single three-level ANPC three-phase rectifier x3 And switch tube S x5 Fault and x >0, the operating state changes from [N] to [P], the next state changes from [OL] to [P], and the bridge arm output voltage is always 0.5V dc ;

[0028] If the switch tube S in a single three-level ANPC three-phase rectifier x4 And switch tube S x5 Fault and x >0, the operating state changes from [N] to [OL], or from [OU] to [P];

[0029] If the switch tube S in a single three-level ANPC three-phase rectifier x1 And switch tube S x4 Fault, it is equivalent to the switch tube S x1 In the negative half cycle, a single tube fails and the switch tube S x4 In the positive half cycle, a single tube fails, that is, when i x <0, the operating state [P] is converted to [O], i x >0, the operating state [N] is converted to [O];

[0030] If the switch tube S in a single three-level ANPC three-phase rectifier x1 And switch tube S x5 Fault, it is equivalent to the switch tube S x1In the negative half cycle, a single tube fails and the switch tube S x5 In the positive half cycle, a single tube fails, that is, when i x <0, the operating state [P] is converted to [O], i x When >0, the operating state [OU] is converted to [P];

[0031] If the switch tube S in a single three-level ANPC three-phase rectifier x2 And switch tube S x3 Fault, it is equivalent to the switch tube S x2 In the negative half cycle, a single tube fails and the switch tube S x3 In the positive half cycle, a single tube fails, that is, when i x <0, the operating state [P] is converted to [OL] or [OU] is converted to [N], i x >0, the operating state [N] is converted to [OU] or [OL] is converted to [P];

[0032] If the switch tube S in a single three-level ANPC three-phase rectifier x2 And switch tube S x4 Fault, it is equivalent to the switch tube S x2 In the negative half cycle, a single tube fails and the switch tube S x4 In the positive half cycle, a single tube fails, that is, when i x <0, the operating state [P] is converted to [OL] or [OU] is converted to [N], i x >0, the operating state [N] is converted to [O];

[0033] If the switch tube S in a single three-level ANPC three-phase rectifier x2 And switch tube S x5 Fault, it is equivalent to the switch tube S x2 In the negative half cycle, a single tube fails and the switch tube S x5 In the positive half cycle, a single tube fails, that is, when i x <0, the operating state [P] is converted to [OL] or [OU] is converted to [N], i x When >0, the operating state [OU] is converted to [P];

[0034] If the switch tube S in a single three-level ANPC three-phase rectifier x3 And switch tube S x6 Fault, it is equivalent to the switch tube S x3 In the positive half cycle, a single tube fails and the switch tube S x6 In the negative half cycle, a single tube fails, that is, when i x >0, the operating state [N] is converted to [OU] or [OL] is converted to [P], i x When <0, the operating state [OL] is converted to [N];

[0035] If the switch tube S in a single three-level ANPC three-phase rectifier x4 And switch tube S x6 Fault, it is equivalent to the switch tube S x4 In the positive half cycle, a single tube fails and the switch tube S x6 In the negative half cycle, a single tube fails, that is, when i x >0, the operating state [N] is converted to [O], i x When <0, the operating state [OL] is converted to [N];

[0036] If the switch tube S in a single three-level ANPC three-phase rectifier x5 And switch tube S x6 Fault, it is equivalent to the switch tube S x5 In the positive half cycle, a single tube fails and the switch tube S x6 In the negative half cycle, a single tube fails, that is, when i x >0, the operating state [OU] is converted to [P], i x When <0, the operating state [OL] is converted to [N];

[0037] For a double-tube fault located in different bridge arms:

[0038] The fundamental wave period is divided into six regions according to the direction of the three-phase current, which are recorded as R1, R2, R3, R4, R5, and R6 respectively; the non-same-phase double-tube open-circuit faults in the same working area are respectively a-phase and b-phase faults, a-phase and c-phase faults, and b-phase and c-phase faults;

[0039] In region R1, the double-tube fault includes switch tube S a3 And switch tube S b6 Fault, switch tube S a4 And switch tube S b6 Fault, switch tube S a5 And switch tube S b6 Fault, switch tube S a3 And switch tube S c5 Fault, switch tube S a4 And switch tube S c5 Fault, switch tube S a5 And switch tube S c5 Fault, switch tube S b6 And switch tube S c5 Fault;

[0040] In region R2, the double-tube fault includes switch tube S c1 And switch tube S a5 Fault, switch tube S c2 And switch tube S a5 Fault, switch tube Sc6 And switch tube S a5 Fault, switch tube S c1 And switch tube S b6 Fault, switch tube S c2 And switch tube S b6 Fault, switch tube S c6 And switch tube S b6 Fault, switch tube S a5 And switch tube S b6 Fault;

[0041] In region R3, the double-tube fault includes switch tube S b3 And switch tube S a5 Fault, switch tube S b4 And switch tube S a5 Fault, switch tube S b5 And switch tube S a5 Fault, switch tube S b3 And switch tube S c6 Fault, switch tube S b4 And switch tube S c6 Fault, switch tube S b5 And switch tube S c6 Fault, switch tube S a5 And switch tube S c6 Fault;

[0042] In region R4, the double-tube fault includes switch tube S a1 And switch tube S b5 Fault, switch tube S a2 And switch tube S b5 Fault, switch tube S a6 And switch tube S b5 Fault, switch tube S a1 And switch tube S c6 Fault, switch tube S a2 And switch tube S c6 Fault, switch tube S a6 And switch tube S c6 Fault, switch tube S b5 And switch tube S c6 Fault;

[0043] In region R5, the double-tube fault includes switch tube S c3 And switch tube S a6 Fault, switch tube S c4 And switch tube S a6 Fault, switch tube S c5 And switch tube S a6 Fault, switch tube S c3 And switch tube S b5 Fault, switch tube S c4And switch tube S b5 Fault, switch tube S c5 And switch tube S b5 Fault, switch tube S a6 And switch tube S b5 Fault;

[0044] In region R6, the double-tube fault includes switch tube S b1 And switch tube S a6 Fault, switch tube S b2 And switch tube S a6 Fault, switch tube S b3 And switch tube S a6 Fault, switch tube S b1 And switch tube S c5 Fault, switch tube S b2 And switch tube S c5 Fault, switch tube S b3 And switch tube S c5 Fault, switch tube S a6 And switch tube S c5 Fault;

[0045] In the faults in the above six areas, the operating state changes of the two bridge arms caused by the double-tube fault are the same as the operating state changes of the bridge arms under the corresponding single-tube fault.

[0046] Furthermore, the fault that only makes the operating state [P] or [N] abnormal is recorded as Type I fault; the fault that the operating state [O] has redundant output but the operating states [P] and [N] are out of control is recorded as Type II fault; the fault that only the zero-level output is affected and has a redundant path to output the O level normally is recorded as Type III fault; Type I fault, Type II fault and Type III fault are recorded as faults that can be fault-tolerant; other faults are recorded as faults that cannot be fault-tolerant.

[0047] Furthermore, for type III faults, fault tolerance is performed through redundant O-level paths; for type I and type II faults, reactive current is injected to make the phase difference between the equivalent modulation voltage and current of the three-level ANPC three-phase rectifier zero for fault tolerance control.

[0048] The beneficial effects of the present invention are as follows: the present invention gives full play to the hardware redundancy performance of the converter topology and the active clamping three-level three-phase rectifier unit itself without adding other hardware circuits. By analyzing the output state and redundant path of single-tube faults and double-tube faults, the faults are classified according to the performance of fault redundancy, and fault-tolerant control of single-tube and double-tube faults is achieved for fault-tolerant fault types, and is not limited by the modulation degree of the converter. The fault of the rectifier module is isolated by injecting reactive current, and the rectifier unit is restored to the operating level before the fault by reactive compensation, thereby realizing the stable operation of the three-level active neutral point clamping three-phase rectifier unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is a schematic diagram of the process of this method;

[0050] Figure 2 It is a three-level ANPC three-phase rectifier topology;

[0051] Figure 3(a) shows S a1 Changes in working status that occur under fault conditions;

[0052] Figure 3(b) shows S a2 Changes in working status that occur under fault conditions;

[0053] Figure 3(c) shows S a6 Changes in working status that occur under fault conditions;

[0054] Figure 3(d) shows S a3 Changes in working status that occur under fault conditions;

[0055] Figure 3(e) shows S a4 Changes in working status that occur under fault conditions;

[0056] Figure 3(f) shows S a5 Changes in working status that occur under fault conditions;

[0057] Figure 4 It is the transfer between the operating states of each single tube failure;

[0058] Figure 5(a) shows S a1 +S a2 Changes in operating conditions that occur under open circuit faults;

[0059] Figure 5(b) shows S a1 +S a3 Changes in operating conditions that occur under open circuit faults;

[0060] Figure 5(c) shows S a1 +S a6 Changes in operating conditions that occur under open circuit faults;

[0061] Figure 5(d) shows S a2 +S a6 Changes in operating conditions that occur under open circuit faults;

[0062] Figure 5(e) shows S a3 +S a4 Changes in operating conditions that occur under open circuit faults;

[0063] Figure 5(f) shows S a3 +S a5 Changes in operating conditions that occur under open circuit faults;

[0064] Figure 5(g) shows S a4 +S a5 Changes in operating conditions that occur under open circuit faults;

[0065] Figure 6 It is the working range of single-phase switch tube;

[0066] Figure 7 It is the working range of the three-phase switch tube;

[0067] Figure 8 shows S a2 , S a3 Redundant zero-level path fault tolerance for failures;

[0068] Fig. 9 It is the working range of the switch tube divided by time;

[0069] Figure 10(a) shows the vector relationship of the normal operation of the rectifier;

[0070] Figure 10(b) shows the vector relationship of the rectifier fault-tolerant operation;

[0071] Fig.11 This is the fault-tolerant control block diagram of the rectifier unit;

[0072] Fig.12 The three-phase current of the faulty rectifier module, the voltage of the A-phase bridge arm, the phase, and the fault-tolerant control signal waveform;

[0073] Figure 13(a) shows the FFT analysis of the current when the module is operating normally;

[0074] Figure 13(b) shows the module S a2 FFT analysis of fault current;

[0075] Figure 13(c) shows the module S a2 FFT analysis after failure but zero-level fault tolerance of bridge arm;

[0076] Figure 13(d) shows the module S a2 FFT analysis after failure and fault-tolerant control;

[0077] Fig.14 Active and reactive output waveforms of faulty and normal modules of the rectifier unit;

[0078] Fig.15 It is the active and reactive output waveform of the rectifier unit before and after fault tolerance;

[0079] Fig.16 FFT analysis of AC side current after fault-tolerant control of rectifier units;

[0080] Fig.17 It is a three-level ANPC three-phase rectifier unit topology. DETAILED DESCRIPTION

[0081] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0082] like Figure 1 and Fig.17 As shown, the active clamping three-level three-phase rectifier unit fault-tolerant control method comprises the following steps:

[0083] S1. Obtaining the operating state change of a single three-level ANPC three-phase rectifier in an active clamped three-level three-phase rectifier unit under a single-tube fault; wherein the active clamped three-level three-phase rectifier unit is composed of two three-level ANPC three-phase rectifiers connected in parallel;

[0084] S2, obtaining the operating state change of a single three-level ANPC three-phase rectifier in an active clamped three-level three-phase rectifier unit under a double-tube fault;

[0085] S3. According to the operating state changes under the single-tube fault and the operating state changes under the double-tube fault, the faults of the active clamped three-level three-phase rectifier unit are classified according to the fault tolerance capability to obtain faults that can be fault-tolerant and faults that cannot be fault-tolerant;

[0086] S4. The method of injecting reactive current to eliminate the phase difference between the modulation voltage and the current is used to tolerate faults that can be tolerated, and reactive compensation is performed through the three-phase rectifier module to complete the fault-tolerant control of the active clamped three-level three-phase rectifier unit.

[0087] The schematic diagram of the three-level ANPC three-phase rectifier is as follows: Figure 2 As shown, the AC power supply is connected to the filter inductor L of the rectifier, R is the equivalent resistance of the filter inductor, S x1 To S x6 (x=a, b, c) are the 6 switch tubes of each phase bridge arm, and C1 and C2 are the DC side capacitors.

[0088] Ideally, the capacitor voltages of C1 and C2 are both 0.5V. dc (V dc is the DC side voltage), then the three-level ANPC three-phase rectifier can output 0.5V in all three phases dc , 0, -0.5V dcThere are three levels, represented as [P], [O], and [N]. For the zero level, the structure has four redundant switching states. When each phase of the three-level ANPC three-phase rectifier outputs the [O] level, there are two current flow modes. One is through the S of the upper half bridge arm. x2 and S x5 The second one is through the S of the lower half bridge arm. x3 and S x6 Flow, corresponding to the [OL1] and [OL2] switch states. The valid switch states are shown in Table 1.

[0089] Table 1: ANPC effective switch status

[0090]

[0091] According to the current flow, [OU1] and [OU2] are both called [OU] state, [OL1] and [OL2] are both called [OL] state. The working modes and output voltages of each phase when they work normally under different current directions are shown in Table 2.

[0092] D xi (x=a,b,c;i=1,2,3,4,5,6) represents the switch tube S xi For an anti-parallel diode, the current flowing from the AC side to the DC side is defined as positive, and vice versa as negative.

[0093] Table 2: Operating modes of three-phase ANPC rectifier

[0094]

[0095] This embodiment only considers the influence of switch tube failure. In the working modes of Table 2, Mode I and Mode VIII do not have switch tube working, so they are not discussed. In addition, the open circuit failure of the switch tube mainly affects the corresponding current direction and the level of the system's expected output. That is, when i x <0, S of each bridge arm x1 , S x2 , S x6 Only when a fault occurs will the corresponding current path change, thereby changing the output state, while the other switch tubes are not affected; similarly, S x3 , S x4 , S x5 The fault only affects i x >0. Taking phase A as an example, the working state changes when a single switch tube fails as follows Figure 3(a) to Figure 3(f)As shown. In the circuit diagram on the left, the solid arrows indicate the current path during normal operation, and the dotted arrows indicate the current path after the corresponding switch tube fails. In the waveform diagram on the right, the upper part indicates the output state during normal operation, and the lower part indicates the output state during the corresponding failure. The dotted line indicates the output state before the failure, and the solid line indicates the output state after the failure. a1 When a fault occurs, it only affects the current path of mode V. At this time, S a2 , S a6 The current flows through D a5 —S a2 , S a6 —D a3 The two paths continue to flow, and the actual level of the bridge arm changes from [P] level to [O] level, as shown in Figure 3(a). a2 When a fault occurs, the current paths of mode V and mode VI are affected. If the fault occurs in mode V, the current flows through S a6 —D a3 The bridge arm level changes from [P] to [OL] if the current is in mode VI. a4 —D a3 The path continues to flow, and the level status changes from [OU] to [N]. a2 The impact and changes of the fault are shown in Figure 3(b). a6 When a fault occurs, the current path of mode VII is affected and the current now flows through D a3 , D a4 The bridge arm level changes from [OL] to [N] during the continuous flow, and its path and operating state change are shown in Figure 3(c). Based on the above analysis, it can be analyzed that S a3 , S a4 , S a5 When the fault occurs, x The influence of the working mode >0 is shown in Figure 3(d), (e), and (f), respectively.

[0096] The transition between the operating states of each single tube failure is as follows: Figure 4 As shown, F sax =1(x=1,2,3,4,5,6) means S ax When an open circuit fault occurs, [O] indicates that the output of the bridge arm including [OU] and [OL] is at zero level. sa1 =1 can be summarized as the transition from state [P] to state [O]; correspondingly, F sa4 =1 will force state [N] to move to state [O]; F sa2 =1 Force state [P] to state [OL], state [OU] to [N]; corresponding to F sa3 =1, then force state [N] to move to state [OU], state [OL] to move to state [P]; F sa5=1 Force state [OU] to transfer to state [P]; F sa6 =1 forces state [OL] to transition to state [N].

[0097] In this embodiment, the double-tube fault is classified according to whether the faulty switch tube is in the same bridge arm or in different bridge arms. Taking bridge arm A as an example, the double-tube fault in the same bridge arm is analyzed, which includes S a1 +S a2 Fault, S a1 +S a3 Fault, S a1 +S a4 Fault, S a1 +S a5 Fault, S a1 +S a6 Fault, S a2 +S a3 Fault, S a2 +S a4 Fault, S a2 +S a5 Fault, S a2 +S a6 Fault, S a3 +S a4 Fault, S a3 +S a5 Fault, S a3 +S a6 Fault, S a4 +S a5 Fault, S a4 +S a6 Fault, S a5 +S a6 Fault.

[0098] For S a1 +S a2 Fault, as shown in Figure 5(a), when i a <0, when the output state is originally [P], the current cannot flow from the upper half bridge arm, thus passing through S a6 , S a3 The anti-parallel diode continues to flow, and the level state becomes [OL]; for the output state originally [OU], this fault causes the current to flow through S a3 , S a4 The anti-parallel diode continues to flow, and the bridge arm level state changes to [N]. a >0, the current only needs to flow through S a1 , S a2 The failure of the anti-parallel diode will not cause the bridge arm output to deviate from the normal value. a1 +S a2 Open circuit fault and S a2 The impact of a single-tube open circuit failure is the same.

[0099] For S a1 +S a3 Fault, as shown in Figure 5(b), when i a <0, S a3 The fault does not affect the current flow path. a1 A single-tube failure is similar, causing the state [P] to change to [O]; when i a >0, S a1 The fault does not affect the current flow path, which is equivalent to S a3 A single-tube failure causes state [N] to change to [OU], and the next state [OL] to change to [P]. That is, the double-tube failure is equivalent to S a1 and S a3 Single tube failure occurs in the negative half cycle and the positive half cycle respectively. a1 +S a4 Fault, S a1 +S a5 Fault, S a2 +S a3 Fault, S a2 +S a4 Fault, S a2 +S a5 Fault, S a3 +S a6 Fault, S a4 +S a6 Fault, S a5 +S a6 All faults are equivalent to abnormal state transfer caused by the failure of two single tubes at different times.

[0100] For S a1 +S a6 Fault, as shown in Figure 5(c), when i a <0, the original [P] state current can only pass through S a2 , S a5 The anti-parallel diode continues to flow, and the [OU] and [P] states cannot be switched within a unit switching cycle, and the bridge arm outputs are all 0 level; while the original [OL] state current can only pass through S a3 , S a4 The anti-parallel diode continues to flow, and the [OL] and [N] states cannot be switched within a unit switching cycle, and the actual output of the bridge arm is -Udc / 2.

[0101] For S a2 +S a6 Fault, as shown in Figure 5(d), when i a <0, it is in the normal [P] state, and the current can only flow through S a3 , S a4The anti-parallel diode is used for freewheeling, the bridge arm level [P] changes to [N], and the next normal state [OU] current can only pass through S a3 , S a4 The anti-parallel diode is connected to the bridge arm for freewheeling, and the bridge arm level becomes [N]; at the same time, the current can only flow through S in the [OL] state. a3 , S a4 The anti-parallel diode is used for freewheeling, so under the double-tube fault, when the current is less than zero, the output voltage of the bridge arm is always -U dc / 2.

[0102] For S a3 +S a4 Fault, as shown in Figure 5(e), when i a >0, the original bridge arm is in normal output state [N]. Since the current cannot flow from the lower half bridge arm, the current can only flow through S a5 , S a6 The anti-parallel diode continues to flow, and the bridge arm state changes to [OU]; if the bridge arm originally outputs [OL], S a3 The open circuit allows current to flow only through S a1 , S a2 The anti-parallel diode continues current, and the output becomes [P]; and when i a <0, the current mainly flows through S a3 +S a4 The anti-parallel diode continues to flow, and its failure does not affect the normal output of the bridge arm, so S a3 +S a4 Fault and S a3 The impact of the failure is the same.

[0103] For S a3 +S a5 Fault, as shown in Figure 5(f), when i a >0, the normal bridge arm output is [N], but the current only flows through S a1 , S a2 The anti-parallel diode continues to flow, and the operating state [N] changes to [P], and the next state [OL] can only continue to flow in this way and change to [P]; Based on this analysis, the bridge arm has only one state [P] under this fault, that is, when the current is greater than zero, the output voltage of the bridge arm is always U dc / 2.

[0104] For S a4 +S a5 Fault, as shown in Figure 5(g), when i a >0, the normal output [N] state is due to the current can only pass through S a3 , S a6The anti-parallel diode is freewheeling, and the bridge arm can only output [OL], and the transition between [OL] and [N] cannot be realized; and for the original normal output [OU], the current can only flow through S a1 , S a2 The anti-parallel diode continues to flow, and the bridge arm state is always [P] within a unit switching cycle.

[0105] When the double-tube fault occurs in different bridge arms, first, analyze the working range of the switch tube, such as Figure 6 As shown, the switch tube S x3 , S x6 The switch tube S works most of the time in the positive and negative half cycles of the current. x1 , S x2 , S x3 and S x4 The length and position of the working interval are determined by the phase difference δ between the rectifier current I and the equivalent modulation voltage V. δ is composed of the phase difference θ between the AC voltage E and the rectifier equivalent modulation voltage V and the power factor angle Φ (the phase difference between the AC voltage E and the rectifier current I). When operating at a unit power factor, |δ|=θ, and the length of the working interval of the two clamping switches in the bridge arm is π-|δ|. On this basis, according to the direction of the three-phase current, the fundamental period is divided into six regions, denoted as R1, R2, R3, R4, R5, and R6 respectively. The working ranges of the 18 switch tubes of the ANPC three-level rectifier are divided as follows: Figure 7 As shown. Taking R1 as an example, when i a >0, in the normal state within the range of δ, the A bridge arm needs to be controlled to switch between zero level and negative level. At this time, S a3 , S a4 Provide a corresponding current flow path, and in the π-δ length range, the A phase equivalent modulation voltage begins to be greater than zero. Under normal conditions, the A phase bridge arm is controlled to switch between zero level and positive level. At this time, S a5 Provide a current flow path for the bridge arm output zero level; Phase B and Phase C only need S b6 , S c5 From the above analysis, in each working area, one phase needs two internal and external switch tubes other than the clamp switch tube to provide a current flow path for the normal output of the bridge arm, while the switch tubes of the other two phases correspond to S x5 or S x6 Work within this range.

[0106] In summary, the two-phase double-tube open circuit faults in each working area include 7 types, and there are 42 fault conditions in the 6 working areas, as shown in Table 3.

[0107] Table 3: Two-phase double-tube open circuit fault types in the same working area

[0108]

[0109]

[0110] According to the analysis of single-tube fault, the A bridge arm S a1 or S a4 When a fault occurs, the P or N level cannot be output, and an abnormal state transition of P→O or N→O occurs. Under this fault, the bridge arm has no other redundant path to output the P or N level normally, and the three-phase current is still distorted. a1 and S a4 Faults that only cause P or N to be abnormal are classified as Type I faults. a2 or S a3 When a fault occurs, the current corresponding to the [P], [OU] or [N], [OL] states has no flow path, but the ANPC O level has a redundant path, as shown in Figure 8. If the circuit needs to output the O level and detects S a2 Failure, then S a6 conduction, current can flow through S a6 —D a3 Path continuous flow, similarly, if the circuit needs to output O level and detects S a3 Fault, can control S a5 conduction, current can flow through D a2 —S a5 Therefore, this kind of fault in which the O level has redundancy and can be output normally but the P level and N level are out of control is classified as a type II fault, which also includes S a1 +S a2 Fault (S a4 +S a3 Failure), S a1 +S a6 Fault (S a4 +S a5 Fault). When the A bridge arm S a5 / S a6 Fault or S X5 +S Y6 (S X6 +S Y5 ) fault, only the zero-level output is affected, and there are redundant paths to output the zero level normally. This type of fault is classified as a Type III fault. a2 +S a6 Fault or S a3 +S a5 Fault, the P or N of the A bridge arm cannot be output normally, and under the same current direction, ANPC has no fault tolerance to output O level, and can only output N level or P level respectively. This kind of fault in which almost half of the cycle is affected and the current distortion is the most serious is classified as Type IV fault.

[0111] For type III faults, the above analysis shows that the fault can be fault-tolerant through a redundant O-level path. For type IV faults, it can only output N level or P level, and there is no redundant path to output O level, so it cannot be fault-tolerantly controlled.

[0112] For type I and type II faults, Figure 7 The working range of the single-phase switch tube represented by is divided into four time periods: T1, T2, T3 and T4. Fig. 9 As shown in Figure 10, combined with the above analysis, type I and type II faults only make the bridge arm P or N level unable to output normally in the T1 and T3 periods, resulting in current distortion. Therefore, the phase difference between the rectifier equivalent modulation voltage and current can be set to 0, thereby eliminating the T1 and T3 periods, isolating type I or type II faults, and restoring the rectifier current to normal. As shown in Figure 10(a) and Figure 10(b), the rectifier current is converted to I tor As shown in Figure 10(a), under unity power factor, vector E and vector I rec In phase, the angle between the inductor voltage vector and the current vector is φ, and the phase difference between the rectifier equivalent reference voltage vector and the current vector is δ. According to the cosine theorem, In the fault-tolerant mode, the relationship between the rectifier fault-tolerant current vector and other vectors is shown in Figure 10(b). At this time, vector I tor With vector V ref The d axis represents the active current. Due to the unity power factor, I q =0, then I rec =I d , so the injected reactive current I' q Satisfy |I' q |=|I d |tanδ. Where E is the AC power supply voltage vector, V ref is the rectifier reference voltage vector, I rec is the rectifier current vector, V L is the inductor voltage vector, L is the inductance, R is the equivalent resistance, I tor is the fault-tolerant current vector, I d is the d-axis component of the fault-tolerant current, I' q is the q-axis component of the fault-tolerant current.

[0113] Fault isolation is achieved by injecting reactive current, but the power factor of the rectifier is also reduced. For a rectifier unit consisting of two three-phase ANPC rectifier modules in parallel, the reactive power generated by the faulty module in fault-tolerant mode due to type I or type II faults can be compensated by the normal three-phase rectifier module, so that the subway three-phase rectifier system can still ensure the power quality of the three-phase grid side and operate at a unity power factor.

[0114] Fig.11 This is a control block diagram of reactive power compensation for a normal module when a three-phase rectifier unit has a module working in fault-tolerant mode. In the figure, the active current reference value of the faulty module is The DC side voltage v dc With a given voltage reference The difference is then adjusted by PI to obtain the injected reactive current given value. The reference value of the αβ axis is obtained through coordinate transformation, and then the model predictive control is used to achieve the effect of stabilizing the DC voltage and isolating the fault. At the same time, due to the need for fault tolerance to compensate for the reactive current of the faulty module, the reactive current of the faulty module is taken and reversely input into the reactive current given of the normal module to achieve the purpose of reactive compensation.

[0115] In one embodiment of the present invention, the A phase S a2 The specific implementation example of open circuit fault is analyzed for fault tolerance:

[0116] like Fig.12 As shown, S a2 The three-phase current simulation waveform of the rectifier module 1 under fault conditions is divided into four stages: normal operation, S a2 Fault, S a2 The bridge arm is fault-tolerant, which enables normal zero-level output and fault-tolerant control. Figure 13(a) to Figure 13(d) is the current harmonic distribution corresponding to each stage. During normal operation, the zero-crossing point of phase A current coincides with the zero-crossing point of AC power supply voltage. The current THD before the fault is 1.38%. After the fault, the harmonic content increases and the THD becomes 3.04%. After the redundant zero-level path fault tolerance of the A bridge arm, the bridge arm can output zero level, and the corresponding THD decreases. Subsequently, after the fault-tolerant control of injecting reactive current is adopted, the zero-crossing point of phase A current coincides with the zero-crossing point of phase A bridge arm voltage, that is, the modulation voltage is in phase with the rectified current, and the corresponding current harmonic content is reduced, and the THD is 1.11%. Fig.14 S a2 The fault module and normal module of the fault-tolerant control have active and reactive waveforms. After the fault-tolerant control algorithm is put into use, the fault module generates reactive power, while the normal module generates the opposite reactive power, so that the entire rectifier unit can still maintain high power factor operation (such as Fig.15 Its harmonic distribution is shown in Fig.16As shown, the current THD is 1.58% and the power quality is good.

Claims

1. A fault-tolerant control method for an active clamped three-level three-phase rectifier unit, characterized in that: The following steps are involved: S1. Obtaining the operating state change of a single three-level ANPC three-phase rectifier in an active clamped three-level three-phase rectifier unit under a single-tube fault; wherein the active clamped three-level three-phase rectifier unit is composed of two three-level ANPC three-phase rectifiers connected in parallel; S2, obtaining the operating state change of a single three-level ANPC three-phase rectifier in an active clamped three-level three-phase rectifier unit under a double-tube fault; S3. According to the operating state changes under the single-tube fault and the operating state changes under the double-tube fault, the faults of the active clamped three-level three-phase rectifier unit are classified according to the fault tolerance capability to obtain faults that can be fault-tolerant and faults that cannot be fault-tolerant; S4. Tolerance is performed on faults that can be fault-tolerant by eliminating the phase difference between the modulation voltage and the current through a redundant O-level path or by injecting reactive current, and reactive compensation is performed through a three-phase rectifier module to complete fault-tolerant control of an active clamped three-level three-phase rectifier unit; When the single-phase middle switch of a single three-level ANPC three-phase rectifier S x1 In case of a fault, the operating state changes from [P] to [O]; When the single-phase middle switch of a single three-level ANPC three-phase rectifier S x2 In case of a fault, the operating state changes from [P] to [OL], or from [OU] to [N]; When the single-phase middle switch of a single three-level ANPC three-phase rectifier S x3 In case of a fault, the operating state changes from [N] to [OU], or from [OL] to [P]; When the single-phase middle switch of a single three-level ANPC three-phase rectifier S x4 In case of a fault, the operating status changes from [N] to [O]; When the single-phase middle switch of a single three-level ANPC three-phase rectifier S x5 In case of failure, the operating status changes from [OU] to [P]; When the single-phase middle switch of a single three-level ANPC three-phase rectifier S x6 In case of a fault, the operating state changes from [OL] to [N]; The operating state [O] indicates that the output of the bridge arm including [OU] and [OL] is at zero level; the operating state [P] indicates that the output is 0.5 V dc ; Operation status [N] means output -0.5 V dc ; V dc is the DC side voltage; [OU] is the switch tube through the upper half bridge arm S x2 And switch tube S x5 The output is 0 level; [OL] is the switch tube through the lower half bridge arm S x3 And switch tube S x6 Flow output 0 level; x=a,b,c , respectively represent the single three-level ANPC three-phase rectifier a Mutually, b Harmony c Mutually; For a double-tube fault in the same bridge arm: If the switch tube in a single three-level ANPC three-phase rectifier S x1 And switch tube S x2 Fault and i x <0, the operating state changes from [P] to [OL], or from [OU] to [N]; i x express x Output current of the phase; If the switch tube in a single three-level ANPC three-phase rectifier S x1 And switch tube S x2 Fault and i x >0, does not affect the bridge arm output; If the switch tube in a single three-level ANPC three-phase rectifier S x1 And switch tube S x3 Fault and i x <0, the operating state changes from [P] to [O]; If the switch tube in a single three-level ANPC three-phase rectifier S x1 And switch tube S x3 Fault and i x >0, the operating state changes from [N] to [OU], and the next operating state changes from [OL] to [P]; If the switch tube in a single three-level ANPC three-phase rectifier S x1 And switch tube S x6 Fault and i x <0, the operating states [OU] and [P] cannot be switched within a unit switching cycle, and the bridge arm outputs are all 0 level; the operating states [OL] and [N] cannot be switched within a unit switching cycle, and the actual output of the bridge arm is -0.5 V dc ; If the switch tube in a single three-level ANPC three-phase rectifier S x2 And switch tube S x6 Fault and i x <0, the operating state changes from [P] to [N], the next operating state changes from [OU] to [N], and the operating state [OL] changes to [N], and the bridge arm output voltage is always -0.5 V dc ; If the switch tube in a single three-level ANPC three-phase rectifier S x3 And switch tube S x4 Fault and i x >0, the operating state changes from [N] to [OU], or from [OL] to [P]; If the switch tube in a single three-level ANPC three-phase rectifier S x3 And switch tube S x4 Fault and i x <0, does not affect the normal output of the bridge arm; If the switch tube in a single three-level ANPC three-phase rectifier S x3 And switch tube S x5 Fault and i x >0, the operating state changes from [N] to [P], the next state changes from [OL] to [P], and the bridge arm output voltage is always 0.5 V dc ; If the switch tube in a single three-level ANPC three-phase rectifier S x4 And switch tube S x5 Fault and i x >0, the operating state changes from [N] to [OL], or from [OU] to [P]; If the switch tube in a single three-level ANPC three-phase rectifier S x1 And switch tube S x4 Fault, it is equivalent to a switch tube S x1 In the negative half cycle, a single tube fails and the switch tube S x4 In the positive half cycle, a single tube fails. i x <0, the operating state [P] changes to [O], i x >0, the operating state [N] is converted to [O]; If the switch tube in a single three-level ANPC three-phase rectifier S x1 And switch tube S x5 Fault, it is equivalent to a switch tube S x1 In the negative half cycle, a single tube fails and the switch tube S x5 In the positive half cycle, a single tube fails. i x <0, the operating state [P] changes to [O], i x >0, the operating state [OU] is converted to [P]; If the switch tube in a single three-level ANPC three-phase rectifier S x2 And switch tube S x3 Fault, it is equivalent to a switch tube S x2 In the negative half cycle, a single tube fails and the switch tube S x3 In the positive half cycle, a single tube fails. i x <0, the operating status [P] is converted to [OL] or [OU] is converted to [N]. i x >0, the operating state [N] is converted to [OU] or [OL] is converted to [P]; If the switch tube in a single three-level ANPC three-phase rectifier S x2 And switch tube S x4 Fault, it is equivalent to a switch tube S x2 In the negative half cycle, a single tube fails and the switch tube S x4 In the positive half cycle, a single tube fails. i x <0, the operating status [P] is converted to [OL] or [OU] is converted to [N]. i x >0, the operating state [N] is converted to [O]; If the switch tube in a single three-level ANPC three-phase rectifier S x2 And switch tube S x5 Fault, it is equivalent to a switch tube S x2 In the negative half cycle, a single tube fails and the switch tube S x5 In the positive half cycle, a single tube fails. i x <0, the operating status [P] is converted to [OL] or [OU] is converted to [N]. i x >0, the operating state [OU] is converted to [P]; If the switch tube in a single three-level ANPC three-phase rectifier S x3 And switch tube S x6 Fault, it is equivalent to a switch tube S x3 In the positive half cycle, a single tube fails and the switch tube S x6 In the negative half cycle, a single tube fails, that is, when i x >0, the operating status [N] is converted to [OU] or [OL] is converted to [P], i x When <0, the operating state [OL] is converted to [N]; If the switch tube in a single three-level ANPC three-phase rectifier S x4 And switch tube S x6 Fault, it is equivalent to a switch tube S x4 In the positive half cycle, a single tube fails and the switch tube S x6 In the negative half cycle, a single tube fails, that is, when i x >0, the operating state [N] changes to [O], i x When <0, the operating state [OL] is converted to [N]; If the switch tube in a single three-level ANPC three-phase rectifier S x5 And switch tube S x6 Fault, it is equivalent to a switch tube S x5 In the positive half cycle, a single tube fails and the switch tube S x6 In the negative half cycle, a single tube fails, that is, when i x >0, the operating state [OU] is converted to [P], i x When <0, the operating state [OL] is converted to [N]; For a double-tube fault located in different bridge arms: According to the direction of the three-phase current, the fundamental wave period is divided into six areas, which are marked as R1, R2, R3, R4, R5 and R6 respectively; the non-same-phase double-tube open-circuit faults in the same working area are marked as a Harmony b Phase failure, a Harmony c Phase failure, and b Harmony c Phase failure; In region R1, the double-tube fault includes the switch tube S a3 And switch tube S b6 Fault, switch tube S a4 And switch tube S b6 Fault, switch tube S a5 And switch tube S b6 Fault, switch tube S a3 And switch tube S c5 Fault, switch tube S a4 And switch tube S c5 Fault, switch tube S a5 And switch tube S c5 Fault, switch tube S b6 And switch tube S c5 Fault; In region R2, the double-tube fault includes the switch tube S c1 And switch tube S a5 Fault, switch tube S c2 And switch tube S a5 Fault, switch tube S c6 And switch tube S a5 Fault, switch tube S c1 And switch tube S b6 Fault, switch tube S c2 And switch tube S b6 Fault, switch tube S c6 And switch tube S b6 Fault, switch tube S a5 And switch tube S b6 Fault; In region R3, the double-tube fault includes the switch tube S b3 And switch tube S a5 Fault, switch tube S b4 And switch tube S a5 Fault, switch tube S b5 And switch tube S a5 Fault, switch tube S b3 And switch tube S c6 Fault, switch tube S b4 And switch tube S c6 Fault, switch tube S b5 And switch tube S c6 Fault, switch tube S a5 And switch tube S c6 Fault; In region R4, the double-tube fault includes the switch tube S a1 And switch tube S b5 Fault, switch tube S a2 And switch tube S b5 Fault, switch tube S a6 And switch tube S b5 Fault, switch tube S a1 And switch tube S c6 Fault, switch tube S a2 And switch tube S c6 Fault, switch tube S a6 And switch tube S c6 Fault, switch tube S b5 And switch tube S c6 Fault; In region R5, the double-tube fault includes the switch tube S c3 And switch tube S a6 Fault, switch tube S c4 And switch tube S a6 Fault, switch tube S c5 And switch tube S a6 Fault, switch tube S c3 And switch tube S b5 Fault, switch tube S c4 And switch tube S b5 Fault, switch tube S c5 And switch tube S b5 Fault, switch tube S a6 And switch tube S b5 Fault; In region R6, the double-tube fault includes the switch tube S b1 And switch tube S a6 Fault, switch tube S b2 And switch tube S a6 Fault, switch tube S b3 And switch tube S a6 Fault, switch tube S b1 And switch tube S c5 Fault, switch tube S b2 And switch tube S c5 Fault, switch tube S b3 And switch tube S c5 Fault, switch tube S a6 And switch tube S c5 Fault; In the above six fault areas, the operation status changes of the two bridge arms caused by the double-tube fault are the same as the operation status changes of the bridge arms under the corresponding single-tube fault; A fault that only makes the operating state [P] or [N] abnormal is recorded as a Type I fault; a fault in which the operating state [O] has redundant output but the operating states [P] and [N] are out of control is recorded as a Type II fault; The fault in which only the zero-level output is affected and there is a redundant path to output the O level normally is recorded as a Type III fault; Type I faults, type II faults and type III faults are recorded as faults that can be fault-tolerant; Other faults are recorded as faults that cannot be fault-tolerant; For type III faults, fault tolerance is performed through redundant O-level paths; for type I and type II faults, reactive current is injected to make the phase difference between the equivalent modulation voltage and current of the three-level ANPC three-phase rectifier zero for fault tolerance control.

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