CN104852614B - A kind of three-phase bridge PWM rectifier switching tube open fault fault tolerant control method - Google Patents

Abstract

The invention discloses a three-phase bridge type PWM rectifier switch tube open-circuit fault fault-tolerant control method, which belongs to the field of three-phase AC-DC conversion. The invention aims to solve the problems of imperfect multi-pipe fault fault-tolerant control, high hardware cost and the like existing in the existing fault-tolerant control scheme. The method utilizes the feature that the local space voltage vector changes when any switch tube in the three-phase bridge PWM rectifier is open-circuit faulty, and by correcting the PWM switching mode, that is, reselecting the basic voltage vector and adjusting its action sequence and time, re- Synthesize to restore or approach the original rotating reference voltage vector, maintain the normal operation of the system, and realize fault-tolerant control operation. The method disclosed by the invention can realize effective fault-tolerant control operation for single and multiple switching tubes in a three-phase bridge PWM rectifier with simultaneous open-circuit faults, requires only software algorithms, is simple and easy to implement, and does not require additional hardware costs.

Description

A fault-tolerant control method for open-circuit faults of switching tubes of three-phase bridge PWM rectifiers

technical field

The invention discloses a switch tube open-circuit fault fault-tolerant control method for a three-phase bridge PWM rectifier, belonging to the field of three-phase AC-DC conversion.

Background technique

Compared with the traditional uncontrolled rectification or phase-controlled rectification scheme, the three-phase bridge PWM rectifier has the advantages of controllable DC voltage, unit power factor, small grid-side current harmonics, and bidirectional flow of energy. Power occasions have been widely used. In PWM rectifiers, faults occur frequently due to the limitations of power switching devices' withstand voltage, current and impact resistance, or improper control, which seriously affects the operational reliability of the system. The survey shows that about 38% of the power conversion system failures are caused by the failure of power switching devices, mainly including short-circuit faults and open-circuit faults. The former will cause great harm in an instant, and requires quick action with the help of hardware protection; the latter will not cause the system to shut down, but will cause grid-side current distortion, DC-side voltage pulsation, etc., and the converter will work in an abnormal state for a long time, which may cause secondary damage. Fault. Therefore, after fault isolation, appropriate topology reconfiguration and fault-tolerant control algorithms need to be implemented to ensure uninterrupted operation of the system and restore the performance before the fault as much as possible, that is, to achieve fault-tolerant operation of the system. Therefore, solving the fault-tolerant control problem of the rectifier has become the key to ensure the continuous and stable operation of the system.

In recent years, research on fault-tolerant control of power converters has focused on three-phase motor drives (three-phase bridge inverters), and a relatively complete theoretical system has been formed. The "bridge arm redundancy topology" can realize the isolation and switching of the faulty bridge arm by controlling the bidirectional thyristor connected between the faulty bridge arm and the redundant bridge arm. The topology reconstructed by this method is the same as the normal one, and the control strategy does not need to be adjusted, but the system cost is increased. In order to overcome this shortcoming, "Switch Redundant Topology" replaces redundant bridge arms with two capacitors connected in series, so that the topology after a fault becomes a three-phase four-switch structure. The shortcoming of this method is that the DC voltage utilization rate is reduced by half. The "three-phase four-arm fault-tolerant topology" controls the bidirectional thyristor connected between the midpoint of the AC side and the redundant bridge arm, so that the system works in the two-phase three-arm mode after a fault. The disadvantage is that the faulty phase loses power. "Two-phase four-switch topology" replaces the redundant bridge arm in the three-phase four-arm topology with two capacitors in series, and makes the system work in two ways after a fault by controlling the bidirectional thyristor connected between the midpoint of the AC side and the bridge arm of the capacitor. The disadvantage of the four-phase switching mode is that the DC voltage utilization rate is reduced by half, and the fault phase loses power. The above four methods all belong to the combination of hardware topology and software fault tolerance, which need to increase the cost of hardware. This type of method is also applicable to rectifiers, but due to the existence of freewheeling diodes in three-phase rectifiers, the phase current where the switch tube fails will not completely lose half of the cycle like the inverter, so a more economical software fault tolerance can be used type program control. Some schemes propose a fault-tolerant control method for a three-phase three-level rectifier. By modifying the switching mode, the reference voltage vector is corrected to realize the fault-tolerant operation of the rectifier without additional components. The above methods only consider the open-circuit fault mode of a single switch tube, and the fault-tolerant control is invalid when multiple tube faults occur. From the perspective of reliability, it is not comprehensive enough to study only single-tube faults, and it is necessary to study the fault-tolerant method under simultaneous open-circuit faults of multiple tubes.

To sum up, the fault-tolerant control methods proposed in the existing literature for the open-circuit faults of switching tubes of three-phase bridge PWM rectifiers still have many shortcomings in terms of realizing multi-tube open-circuit fault fault tolerance, no hardware cost, and simple implementation algorithms.

Contents of the invention

The technical problem to be solved by the present invention is to propose a fault-tolerant control method for open-circuit faults of switching tubes for three-phase bridge PWM rectifiers in view of the deficiencies of the above-mentioned background technology.

The present invention adopts following technical scheme for realizing above-mentioned purpose of the invention:

A three-phase bridge PWM rectifier switching tube open-circuit fault fault-tolerant control method based on the modified PWM switching mode includes the following steps:

Step 1, according to the information of the detected open circuit fault, determine the sector affected by the fault according to Table 1, where the gray area is the area where the vector change is only affected by the zero vector, and the semi-shaded area is the area affected by both the zero vector and a valid vector Area.

Step 2, collect the three-phase network side currents _ia , _ib , _ic , and determine the sector through coordinate transformation, and perform normal SVPWM operation.

Step 3, for the sector affected by the fault determined in step 1, use the only available correct voltage zero vector to replace the fault zero vector, and adjust the action sequence and time of the correct zero vector and the correct effective voltage vector to correct the PWM switch mode.

Step 4, drive the corresponding switch tube with the switch signal corresponding to the corrected space voltage vector.

Table 1 Affected sectors corresponding to any switch tube open circuit fault

The three-phase bridge type PWM rectifier switching tube open-circuit fault fault-tolerant control method according to claim 1, characterized in that, said step 3 specifically includes the following steps:

Step 3-1, according to Table 2, determine the change of fault zero vector and effective vector after the switch tube open circuit fault.

Table 2 Changes of basic voltage vector before and after any switch tube open circuit fault

Step 3-2, in the case of a single-tube fault, for the sector whose vector change is only affected by the zero vector, that is, the gray area in Table 1, the discontinuous PWM technology is used to remove the fault zero vector and replace it with an available zero vector Realize full compensation; for the sector affected by both the zero vector and one valid vector, that is, the half-shaded area in Table 1, replace the faulty zero vector with the available zero vector, and add half of the action time of the faulty valid vector to the useful The original reference vector is orthogonally mapped to the available effective vector by vector mapping method to realize partial compensation. The fault voltage vector is modified from (1) to (2):

Where: V _zero and They are the wrong zero vectors under normal conditions and open-circuit faults respectively, Vactive is the valid vectors that can be used after the faults, and V _n and V _n+1 are the valid vectors.

When n=7, replace with n=1; when n=-1, replace with n=5; when n=0, replace with n=6.

Step 3-3, for the area affected by multi-tube faults in the case of multi-tube (2 switching tubes) faults, if two switching tubes of the same bridge arm fail at the same time, the single-tube fault as in step 3-2 can be used Fault-tolerant control method; if two of the upper tubes or two of the lower tubes of the three bridge arms fail at the same time, use the partial compensation method as in step 3-2; if one of the three upper tubes and three lower tubes If one of them fails simultaneously, no compensation is required.

The present invention adopts the above-mentioned technical scheme, which can meet the requirement of fault-tolerant control operation under the condition that a single switch tube of a three-phase bridge PWM rectifier is open circuit, or multiple switch tubes are open circuit faults at the same time. The program is based on DSP programming, and the algorithm is simple and easy to implement without adding additional hardware costs. It can better improve the three-phase current balance under fault conditions, reduce the voltage ripple on the DC side, and improve system performance and reliability.

Description of drawings

Fig. 1 is a schematic diagram of the main circuit topology of the three-phase bridge PWM rectifier of the present invention;

Fig. 2 is a control block diagram of the three-phase bridge PWM rectifier and its fault tolerance control method according to the present invention

Fig. 3 is the three-phase current waveform under normal conditions of the three-phase bridge PWM rectifier of the present invention and the basic space voltage vector diagram in the αβ two-phase stationary coordinate system;

Fig. 4 is three-phase bridge type PWM rectifier S of the present invention S ₁ open-circuit fault before and after sector III and sector II voltage vector composite diagram;

Fig. 5 is three-phase bridge type PWM rectifier S ₁ and S ₃ of the present invention open-circuit fault front and back sector V voltage vector synthetic diagrams simultaneously;

Fig. 6 is three-phase bridge type PWM rectifier S ₁ open-circuit fault tolerance before and after the voltage vector synthetic diagram of the present invention;

Fig. 7 is a sector III switch mode diagram before and after the open-circuit fault tolerance of the three-phase bridge PWM rectifier S ₁ of the present invention;

Fig. 8 is a sector II switch mode diagram before and after the open-circuit fault tolerance of the three-phase bridge PWM rectifier S ₁ of the present invention;

FIG. 9 is a diagram of the current vector trajectory in the αβ coordinate system before and after the open-circuit fault tolerance of the three-phase bridge PWM rectifier S ₁ according to the present invention.

Explanation of symbols in the figure: S ₁ to S ₆ are the first to sixth switching tubes, D ₁ to D ₆ are the first to sixth freewheeling diodes, L is the three-phase filter inductor, C _f is the DC side filter capacitor, R _L is the DC load. i _d and _id ^* are active current setting and feedback, i _q and i _q ^* are reactive current setting and feedback, ed _and e _q are grid voltage d-axis and q-axis components.

Detailed ways

Below in conjunction with accompanying drawing, the technical scheme of invention is described in detail:

FIG. 1 is a schematic diagram of the main circuit topology of the three-phase bridge PWM rectifier according to the present invention. The first to sixth switch tubes S ₁ to S ₆ are three-phase bridge arm power tubes a, b, and c, D ₁ to D ₆ are the first to sixth freewheeling diodes, L is a three-phase filter inductor, and C _f is DC side filter capacitor, R _L is the DC load, e _a , e _b , e _c are the three-phase grid voltage, _ia , i _b , _ic are the three-phase grid side current, the reference direction is as shown in the figure, U _dc is the DC side Output voltage, O is the midpoint of the AC side, and N is the negative pole of the DC side.

Fig. 2 is a control block diagram of the three-phase bridge PWM rectifier system and its fault-tolerant control method according to the present invention. The based system includes a three-phase PWM rectifier topology unit connected between the power grid and the DC side load and a control unit connected with the rectifier topology unit. Wherein, the rectifier control unit includes a voltage loop for realizing DC side output voltage stabilization, a current loop for grid side current control, a SVPWM unit connected to the current loop, and a fault-tolerant control unit connected to the SVPWM unit. When there is fault information input, the output of the SVPWM unit passes through the fault-tolerant control unit, that is, after the PWM switching mode is corrected, it is input to the switching tube for driving the rectifier.

Fig. 3 is the three-phase current waveform and the basic space voltage vector diagram in the αβ two-phase static coordinate system of the three-phase bridge PWM rectifier under normal conditions. When the rectifier is working normally, assuming that the harmonics of the current waveform on the three-phase network side are very small, the current waveform is shown in Figure 3(a). Within a fundamental wave cycle, the current can be divided into 12 regions (Z ₁ in Figure 3(a) ~Z ₁₂ ). Assuming that the power factor is 1, the three-phase current is in the same phase as the three-phase grid voltage.

The basic space voltage vectors of the rectifier in the αβ two-phase stationary coordinate system are shown in Fig. 3(b), where V ₁ ~ V ₆ are the effective space voltage vectors, the amplitudes are all 2U _dc /3, and the mutual difference is 60°, V ₀ and _V7 are zero vectors.

Normally, the expression of the reference voltage vector is as follows:

In the formula: T _s is the switching period, T ₁ and T ₂ are the effective vector action time, T ₀ is the zero vector action time, n is the sector number where the space vector is located.

V ^* is the output voltage of the PI current regulator. Under normal circumstances, the direction of rotation is counterclockwise, and the track of its apex is a circle.

Fig. 4 is a composite diagram of sector III and sector II voltage vectors before and after the open-circuit fault of the three-phase bridge PWM rectifier _S1 of the present invention. Taking _S1 on the upper arm of the A-phase bridge arm as an example, analyze the SVPWM operation of the three-phase PWM rectifier after a single-tube open circuit fault. After the S ₁ open circuit fault, the rectifier A-phase current i _a negative half-cycle distortion is obvious, and there is current only in a specific area. When _ia < 0, the freewheeling diode D ₁ cannot be turned on, and S ₁ cannot be turned on due to an open circuit fault, so the zero vector V ₇ (111) will change into the effective vector V ₄ (011), and at the same time the effective Vector V ₂ (110) will become V ₃ (010), and effective vector V ₆ (101) will become V ₅ (001). The sectors where i _a <0 are part of sector III, sector IV, and sector II, sector V (ie, Z ₄ ˜Z ₉ in FIG. 3( a )). In sector III (Z ₅ , Z ₆ ), the voltage vector is normally synthesized by the active vectors V ₃ , V ₄ and the zero vectors V ₀ , V ₇ . However, the open-circuit fault of the switch tube S1 causes the zero vector V ₇ to change, and the fault voltage vector can be expressed as

The sector vector post-failure changes are only affected by the zero vector. Figure 4(a) shows the composite voltage vector diagram of sector III before and after the fault (the vector indicated by the dotted line is the voltage vector after the fault, the same below). The situation of Z ₄ in sector II is different from that of sector III. Normally, the voltage vector in this sector is composed of effective vectors V ₂ , V ₃ and zero vectors V ₀ , V ₇ . When S ₁ is open-circuit faulted, both the zero vector V ₇ and the effective vector V ₂ change, and the fault voltage vector can be expressed as

The change of the sector vector after failure is jointly affected by the zero vector and one valid vector. Figure 4(b) shows the synthetic diagram of the voltage vector of sector II before and after the fault, and the voltage vector is shifted from sector II to sector III.

Define F as the fault sequence number. For example, the error zero vector of S1 open circuit fault is V ₄ , so F of S ₁ is 4. The change of the basic voltage vector before and after considering the open circuit fault of any switch tube is shown in Table 1. Formulas (2) and (3) can be expressed as general formulas applicable to S ₁ ~ S ₆ :

Where: V _zero and They are the wrong zero vectors under normal conditions and open-circuit faults, V _active is the effective vectors that can be used after the fault, and V _n and V _n+1 are the effective vectors.

When n=7, replace with n=1; when n=-1, replace with n=5; when n=0, replace with n=6. If any switch tube of the three-phase PWM rectifier has an open-circuit fault, all expressions of the single-tube open-circuit fault voltage vector can be obtained according to formula (4) and Table 1.

Fig. 5 is a composite diagram of sector V voltage vectors before and after simultaneous open-circuit faults of the three-phase bridge PWM rectifiers S ₁ and S ₃ according to the present invention. There are three situations for the failure of two switch tubes: two switch tubes of the same bridge arm, such as S ₁ and S ₂ ; two of the upper tubes of three bridge arms or two of the lower tubes of three bridge arms, such as S ₁ and S 2 ₃ ; one of the three upper tubes and one of the three down tubes, such as S ₁ and S ₄ .

If S ₁ and S ₂ fail at the same time, since S ₁ and S ₂ are in the same bridge arm, the condition for the rectifier to be affected by the open circuit fault of S ₁ is _ia <0, and the condition for the rectifier to be affected by the open circuit fault of S ₂ is _ia >0 , so although the 12 regions Z ₁ ~ Z ₁₂ are all affected by the open-circuit fault of the switch tube, each zone is only affected by the fault of one switch tube. Therefore, this fault condition is similar to the single-pipe open-circuit fault condition.

If S ₁ and S ₃ fail at the same time, the condition that the rectifier is affected by the open circuit fault of S ₁ is _ia < 0, and the condition that the rectifier is affected by the open circuit fault of S ₃ is i _b < 0, so there are 10 areas in the 12 areas ( Z ₁ and Z ₄ ～ Z ₁₂ ) are affected by faults, and two areas (Z ₈ , Z ₉ ) are affected by two switching tube faults at the same time, including sectors IV and V. In these two areas, under normal conditions S ₁ , S ₃ and S ₆ participate in the work; when S ₁ and S ₃ fail, only the effective vector V ₅ (001) and the zero vector V ₀ (000) can participate in the synthesis The voltage vector, other effective vectors and zero vectors all become V ₅ , so the action time of V ₅ is α+β+γ, and the general formula of the fault vector is:

V _fault3 ＝(α+β+γ)V _active +γV _zero (5)

The remaining 8 regions (Z ₁ , Z ₄ ～Z ₇ , Z ₁₀ ～Z ₁₂ ) are only affected by single-tube faults, and the fault situation is still similar to that of single-tube open-circuit faults.

If S ₁ and S ₄ fail at the same time, the condition that the rectifier is affected by the open circuit fault of S ₁ is i _a <0, and the condition that the rectifier is affected by the open circuit fault of S4 is i _b >0, so there are 8 areas in the 12 areas (Z ₂ ～ Z ₉ ) are affected by faults, and four of them (Z ₄ ～ Z ₇ ) are affected by faults of two switching tubes at the same time. The two faulty tubes belong to the upper and lower tubes of different phase bridge arms respectively, so in these four areas, zero vectors V ₀ and V ₇ cannot be generated, which are respectively converted into other effective vectors, and the action time of these effective vectors is increased, and its The general formula of the fault vector is:

V _fault4 ＝(α+γ)V _n +(β+γ)V _n+1 (6)

Fig. 6 is a voltage vector composite diagram before and after open-circuit fault tolerance of the three-phase bridge PWM rectifier S ₁ according to the present invention. By adopting a discontinuous PWM (Discontinuous PWM, DPWM) technology, that is, using another available zero vector, the compensation for the wrong zero vector can be realized. For the case where the voltage vector is only affected by the fault zero vector, such as sector III and sector IV (Z ₅ ～ Z ₈ ) when S ₁ is faulty, the DPWM formula (2) is corrected as

Wherein the fault zero vector γV ₄ is removed and γV ₀ is increased for compensation. Figure 6(a) shows the composite voltage vector diagram of sector III before and after _S1 fault tolerance. The voltage vector after compensation It is consistent with the original reference vector V ^* , so by modifying the switching mode, the reference voltage vector can be completely restored, that is, normal control can be restored in these areas.

For the case where the voltage vector is jointly affected by a fault zero vector and a fault effective vector, such as the faulty sector II and part of sector V (Z ₄ , Z ₉ ) of S ₁ . Full vector compensation is not possible due to failures resulting in only one active vector V _active being available. However, the method of vector mapping can be used to realize partial compensation of the vector, and the compensated voltage vector will be as close as possible to the original reference vector. As shown in Figure 6(b) in sector II, V ₃ is the adjacent available effective vector, so the original reference vector is orthogonally mapped to V ₃ to obtain the compensated voltage vector And using DPWM technology, formula (3) is revised as

Among them, the fault zero vector γV ₄ is removed, γV ₀ is increased to realize compensation, and in order to get as close as possible to the original vector, αV ₃ /2 is also removed, and its action time is added to V ₀ . In this region, the system performance can be restored to the greatest extent by using the adjacent effective vectors to participate in the compensation.

Formulas (7) and (8) can be expressed as general formulas applicable to S ₁ to S ₆ :

That is, formula (4) can be revised as (9).

As analyzed before, the simultaneous open-circuit fault of multiple switching tubes can be considered as a combination of single-switching fault conditions. From the perspective of fault-tolerant control, a single-switch fault-tolerant control method can be used for areas that are only affected by single-switch faults; and a special fault-tolerant control method should be used for areas that are jointly affected by multiple switching tube faults, as discussed below:

If two switching tubes (such as S ₁ and S ₂ ) of the same bridge arm fail at the same time, each area in Z ₁ ~ Z ₁₂ is only affected by the fault of one switching tube, and a single-switch fault-tolerant control method can be adopted to realize Fault-tolerant operation purpose.

If two of the upper tubes or two of the lower tubes (such as S ₁ and S ₃ ) of the three bridge arms fail at the same time, Z ₈ and Z ₉ among Z ₁ to Z ₁₂ are simultaneously affected by the failure of the two switch tubes. At this time, the fault vector is synthesized by a remaining valid vector _V5 and zero vector _V0 . Since V ₅ is the nearest available vector, a partial compensation method can be used.

If one of the three upper transistors and one of the three lower transistors (such as S ₁ and S ₄ ) fails simultaneously, Z ₄ to Z ₇ among Z ₁ to Z ₁₂ are simultaneously affected by the failure of two switching transistors. There is no zero vector available at this time, so the distortion vector cannot be compensated.

Fig. 7 is a switch mode diagram of sector III before and after the open-circuit fault tolerance of the three-phase bridge PWM rectifier S ₁ according to the present invention. Fig. 7(a) is the switching mode in sector _III after the switch tube S ₁ has an open-circuit fault. The vector γV ₇ is removed, ie the S1 on-time is reduced by 2γ. Fig. 7(b) shows the switching mode in sector III after the switch tube S ₁ open-circuit fault fault-tolerant control measures are taken. In the figure, the reduced part compared with the fault case is marked by hatching, the fault zero vector γV ₄ is removed, and γV ₀ is increased to achieve compensation, that is, the conduction times of S ₃ and S ₅ are reduced by 2γ.

Fig. 8 is a switch mode diagram of sector II before and after the open-circuit fault tolerance of the three-phase bridge PWM rectifier S ₁ according to the present invention. Fig. 8(a) is the switching mode in sector _II after the switch tube S ₁ has an open circuit fault. The vector γV ₇ is removed; the fault vector αV ₃ is added, and the original effective vector αV ₂ is removed, that is, the conduction time of S ₁ is reduced by 2 (α+γ). Fig. 8(b) is the switching mode in sector II after the switch tube S ₁ open-circuit fault fault-tolerant control measures are taken. In the figure, the reduced part is marked by hatching compared with the fault case. The fault zero vector γV ₄ is removed, and γV ₀ is added to achieve compensation, and in order to get as close as possible to the original vector, αV ₃ /2 is also removed, and its action time is added to V ₀ , that is, the conduction time of S ₃ and S ₅ is reduced by α+2γ and 2γ respectively.

FIG. 9 is a diagram of the current vector trajectory in the αβ coordinate system before and after the open-circuit fault tolerance of the three-phase bridge PWM rectifier S ₁ according to the present invention. Figure 9(a) shows that under normal conditions, the current trajectory is a complete circle; Figure 9(b) shows that after the S ₁ open circuit fault, the left half of the current trajectory is seriously missing; Figure 9(c) shows that After implementing the PWM switching mode correction algorithm, the current trajectory is compensated to approximate a circle, but there is a gap in sector II because only partial compensation can be achieved in this region.

To sum up: the present invention adopts the above-mentioned technical scheme, and can realize the fault-tolerant control operation of a single switching tube open circuit or multiple switching tubes simultaneously open circuit faults for the three-phase bridge PWM rectifier. The program is based on DSP programming, and the algorithm is simple and easy to implement without adding additional hardware costs. It can better improve the three-phase current balance under fault conditions, reduce the voltage ripple on the DC side, and improve system performance and reliability.

Claims (2)

1. a kind of three-phase bridge PWM rectifier switching tube open fault fault tolerant control method, which is characterized in that this method is included such as Lower step：

Step 1, according to the information of the open fault detected, by the sector that table 1 determines to be influenced by failure, grey area is The region that vector variation is only influenced by zero vector, penumbra region are the area by zero vector and an effective vector joint effect Domain；

The corresponding impacted sector of 1 either switch tube open circuit failure of table

Step 2, three-phase current on line side i is gathered_a、i_b、i_c, determine sector through coordinate transform, carry out normal SVPWM operations；

Step 3, sector is influenced by failure on what is determined in the step 1, the wherein only available correct voltage zero vector of use, Instead of failure zero vector, and sequence of operation and the time of correct zero vector and correct effective voltage vector are adjusted, correct PWM switches Pattern；

Step 4, corresponding switching tube is driven with the corresponding switching signal of revised space voltage vector.

2. three-phase bridge PWM rectifier switching tube open fault fault tolerant control method according to claim 1, feature exist In the step 3 specifically comprises the following steps：

Step 3-1 determines the situation of change of failure zero vector and effective vector after switching tube open fault by table 2；

Basic voltage vectors situation of change before and after 2 either switch tube open circuit failure of table

Step 3-2, under single tube fault condition, for the region that vector variation is only influenced by zero vector, i.e. grey area in table 1 Domain using discontinuous PWM technologies, removes failure zero vector, is replaced realizing full remuneration with available zero vector；For by zero The region of the effective vector joint effect of vector sum one, i.e. penumbra region in table 1, failure null vector is replaced with available zero vector Amount, and the half of the action time of effective vector of failure is added on useful zero vector, i.e., the method mapped using vector, It on former reference vector orthogonal mapping to available effective vector, will realize that part compensates；False voltage vector is modified to by (1) (2)：

In formula：V_zeroWithRespectively under normal circumstances with zero vector wrong after open fault, V_activeFor that can make after failure Effective vector, V_nAnd V_n+1It is then effective vector；

As n=7, replaced with n=1；During n=-1, replaced with n=5；During n=0, replaced with n=6；

Step 3-3, for the region by multitube failure joint effect in multitube (2 switching tubes) fault condition, if same bridge arm Two switching tubes break down simultaneously, the single tube failure tolerant control method such as step 3-2 can be used；If three bridge arm upper tubes Two or two of down tube break down simultaneously, the method compensated using the part in such as step 3-2；If in three upper tubes One in one and three down tubes is broken down simultaneously, without compensating.