CN109067215B

CN109067215B - Switching frequency-based two-level PWM rectifier fault-tolerant control method

Info

Publication number: CN109067215B
Application number: CN201810928037.9A
Authority: CN
Inventors: 冯延晖; 秦伟; 黄凯; 邱颖宁
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2018-08-15
Filing date: 2018-08-15
Publication date: 2021-04-06
Anticipated expiration: 2038-08-15
Also published as: CN109067215A

Abstract

The invention discloses a switching frequency-based two-level PWM rectifier fault-tolerant control method, which comprises the steps of selecting a sector division mode to carry out sector division; determining the influence of a fault switch tube on each sector and the change of basic voltage vectors before and after a fault; determining the basic voltage vector of each sector and the acting time of the basic voltage vector before the fault; adjusting the action time of the basic voltage vector of the sector influenced by the fault switch tube; determining the conduction time of a three-phase switching tube; improving the frequency of the triangular carrier wave to ensure that the total distortion rate of the three-phase current meets the current input requirement of the system; and modulating the conduction time of the switching tube with a triangular carrier, determining the PWM pulse of the switching tube, determining the on-off of the switching tube, and finishing frequency fault-tolerant control. The invention can reduce the pulsation of the current track circle, increase the control precision of the controller and improve the fault-tolerant control effect of software when accurately compensating the sector influenced by the fault switching tube.

Description

Switching frequency-based two-level PWM rectifier fault-tolerant control method

Technical Field

The invention relates to a power conversion and control technology, in particular to a two-level PWM rectifier fault-tolerant control method based on switching frequency.

Background

With the development of power electronic technology, the three-phase two-level PWM rectifier has sinusoidal input current, bidirectional energy flow and adjustable direct-current voltage, and is widely applied to the fields of medium and high-power occasions such as offshore wind power generation, new energy electric vehicles and the like. In most cases, the rectifier needs to work continuously for a long time in a severe industrial environment, and the rectifier fails inevitably due to factors such as unreliability and improper control of the power switch tube. To avoid major accidents and to reduce down time, the system must be fault-tolerant controlled to restore as much performance as possible before the failure.

The existing three-phase two-level PWM rectifier fault-tolerant mode is divided into two categories of hardware fault-tolerant control and software fault-tolerant control, wherein the software fault-tolerant mode can carry out fault-tolerant processing on a fault by changing a system operation strategy and control parameters when a switching tube fails, the existing hardware layout of the system does not need to be changed, redundant parts do not need to be added, and the original system non-failure device is utilized to recover to the operation state before the fault to the maximum extent. Chinese patent 201510277790.2 proposes a fault-tolerant control method for a three-phase bridge PWM rectifier, which corrects a reference voltage vector by correcting a switching pattern, thereby realizing fault-tolerant operation of the rectifier. The method does not perform accurate compensation aiming at the influence of a fault switching tube on each sector, performs compensation on the sector without the fault of the switching tube, and belongs to overcompensation. The article "PWM rectifier fault-tolerant control system based on NCAV and circuit equivalent replacement" proposes a fault-tolerant control method of a PWM rectifier based on an equivalent circuit, which does not perform precise compensation for the influence of a faulty switching tube on each sector, and does not perform compensation in a sector where a plurality of fault vectors commonly influence, which belongs to under-compensation. A thesis 'rectifier fault-tolerant control method based on space vector control' provides a rectifier fault-tolerant control method based on space vector, a unified sector partition function is not established in the method, fault-tolerant control on faults of a plurality of bridge arm switch tubes cannot be achieved, although accurate compensation of a single switch tube can be achieved, negative effects of the fault switch tube on a system are not considered, and the effect of the fault-tolerant control is not optimal.

Disclosure of Invention

The invention aims to provide a switching frequency-based two-level PWM rectifier fault-tolerant control method, which can further reduce the negative influence caused by a faulty switching tube by improving the switching frequency on the basis that a fault-tolerant control system carries out accurate compensation on a sector influenced by the fault of the switching tube.

The technical solution for realizing the purpose of the invention is as follows: a fault-tolerant control method of a two-level PWM rectifier based on switching frequency comprises the following steps:

step 1, selecting a sector division mode to carry out sector division;

step 2, determining the influence of the fault switch tube on each sector and the change of basic voltage vectors before and after the fault according to the position of the fault switch tube;

step 3, determining the basic voltage vector of each sector and the acting time of the basic voltage vector before the fault;

step 4, adjusting the action time of the basic voltage vector of the sector influenced by the fault switching tube according to the sector influenced by the fault switching tube, the change of the fault basic voltage vector and the action time of the basic voltage vector before the fault;

step 5, determining the conduction time of the three-phase switch tube according to the action time of the basic voltage vector and the condition that the sector is influenced by the fault switch tube;

step 6, according to the switching frequency of the system in normal operation, improving the frequency of the triangular carrier wave to enable the total distortion rate of the three-phase current to meet the current input requirement of the system;

and 7, modulating the conduction time of the switching tube with a triangular carrier, determining the PWM pulse of the switching tube, determining the on-off state of the switching tube, and finishing frequency fault-tolerant control.

Compared with the prior art, the invention has the following remarkable advantages: 1) the invention can realize the improvement of the single-tube fault, double-tube fault and three-tube fault-tolerant control effects of the two-level PWM rectifier; 2) the invention considers the influence of a fault switch tube on a system, and comprises the problems of reduction of equivalent switch frequency in the compensation process, increase of circular pulsation of a current track after fault-tolerant control and the like; 3) the invention only needs to reconstruct the SVPWM algorithm in the main controller, and the algorithm is simple and easy to realize.

Drawings

FIG. 1 is a control block diagram of a three-phase two-level PWM rectifier system topology and a fault frequency fault-tolerant control method thereof.

FIG. 2 is a flow chart of the method for improving the fault-tolerant effect of the two-level PWM rectifier based on the switching frequency according to the present invention.

Fig. 3 is an eight-sector basic space voltage vector diagram in an alpha and beta two-phase stationary coordinate system under the fault-tolerant control condition of the three-phase two-level PWM rectifier of the present invention.

Fig. 4 is a twelve-sector basic space voltage vector diagram in an alpha and beta two-phase stationary coordinate system under the fault-tolerant control condition of the three-phase two-level PWM rectifier of the present invention.

Fig. 5 is a schematic view of the sector distribution of the Q1 tube fault of the three-phase two-level PWM rectifier of the present invention under the eight-sector division mode affected by the faulty switching tube.

Fig. 6 is a schematic diagram of the sector distribution of the two-transistor fault of the three-phase two-level PWM rectifiers Q1 and Q4 under the eight-sector division mode, which is affected by the fault switch.

Fig. 7 is a schematic diagram of the distribution of sectors affected by a faulty switching tube when a three-phase two-level PWM rectifier Q1 tube fault is in a twelve-sector division mode.

Fig. 8 is a schematic diagram of the sector distribution of the two-transistor fault of the three-phase two-level PWM rectifiers Q1 and Q4 under the twelve-sector division mode under the influence of the fault switch transistor.

Fig. 9 is a schematic diagram of the sector distribution of the two-transistor fault of the three-phase two-level PWM rectifiers Q1 and Q3 under the twelve-sector division mode under the influence of the fault switch transistor.

Fig. 10 is a schematic diagram of the sector distribution of the two-transistor fault of the three-phase two-level PWM rectifiers Q1 and Q6 under the twelve-sector division mode under the influence of the fault switch transistor.

Fig. 11 is a schematic view of the distribution of sectors affected by the faulty switching tube in the twelve-sector division mode of the three-phase two-level PWM rectifiers Q1, Q3 and Q5 according to the present invention.

Fig. 12 is a sector viii voltage vector composite diagram of the Q1 tube fault of the three-phase two-level PWM rectifier of the present invention in the twelve-sector division mode.

FIG. 13 is a normal sector single cycle PWM generation diagram for a three-phase two-level PWM rectifier Q1 according to the present invention.

Fig. 14 is a current vector locus diagram of an alpha and beta two-phase stationary coordinate system in two states of fault-tolerant control and frequency fault-tolerant control when a three-phase two-level PWM rectifier Q1 tube fault is in an eight-sector division mode.

Fig. 15 is a current vector locus diagram of an alpha and beta two-phase stationary coordinate system under two states of fault-tolerant control and frequency fault-tolerant control in an eight-sector division mode when a three-phase two-level PWM rectifier Q1 and a Q4 double-tube fault occurs.

Fig. 16 is a current vector locus diagram of an alpha and beta two-phase stationary coordinate system in two states of fault-tolerant control and frequency fault-tolerant control in a twelve-sector division mode when a two-transistor fault of the three-phase two-level PWM rectifiers Q1 and Q3 is detected.

Fig. 17 is a current vector locus diagram of an alpha and beta two-phase stationary coordinate system in two states of fault-tolerant control and frequency fault-tolerant control in a twelve-sector division mode for three-tube faults of three-phase two-level PWM rectifiers Q1, Q3 and Q5 of the invention.

Fig. 18 is a voltage waveform diagram of a direct current bus under four states of normal operation, fault-tolerant operation and frequency fault-tolerant control of a Q1 tube of the three-phase two-level PWM rectifier according to the present invention.

The reference numbers in the figures illustrate: 6 power switching tubes in Q1-Q6 three-phase two-level PWM rectifiers, 6 fly-wheel diodes in D1-D6 three-phase two-level PWM rectifiers, 6 thermal fuses in F1-F6 three-phase two-level PWM rectifiers, and L_a,L_b,L_cIs a rectifier three-phase filter inductor, U_a,U_b,U_cIs the three-phase power grid phase voltage. i.e. i_a,i_b,i_cThree-phase network side current phase, n is the natural neutral point of AC side, C is the voltage-stabilizing capacitor of DC side, U_dcThe output voltage is the DC side output voltage. Theta is the angle of the three-phase current, u_d,u_q,i_d,i_qIs a voltage current feedback value under a dq two-phase rotating coordinate system,

a given voltage and current value under a dq two-phase rotating coordinate system,

is a reference voltage component in an alpha and beta two-phase static coordinate system. t is t_fAt the time of Q1 failure, t_comTime of fault-tolerant control of Q1, t_com1The time of frequency fault tolerant control of Q1.

Detailed Description

The invention is further illustrated by the following examples in conjunction with the accompanying drawings.

FIG. 1 is a control block diagram of a three-phase two-level PWM rectifier system topology and its fault-tolerant control method. The whole system comprises a topology unit and a control unit. The topology unit comprises a three-phase power grid input, a three-phase PWM rectifier and a direct current side load. The control unit comprises a voltage ring for realizing direct current side output voltage stabilization, a current ring for network side current control, a fault diagnosis unit for realizing fault location and diagnosis of the switching tube, an SVPWM unit connected with the current ring and a reconstruction frequency fault-tolerant SVPWM unit after frequency fault-tolerant control. When the fault diagnosis algorithm diagnoses the position of the fault switch tube, the normal SVPWM unit outputs the reconstructed SVPWM output PWM pulse after switching to the frequency fault-tolerant control to drive the power switch tube to work, so as to realize the frequency fault-tolerant control.

For the topology of the three-phase two-level PWM rectifier system, the method for improving the fault-tolerant effect of the two-level PWM rectifier based on the switching frequency of the invention, as shown in fig. 2, includes the following steps:

step 1, selecting a sector division mode to carry out sector division, wherein the sector division mode comprises an eight sector division mode and a twelve sector division mode, and the specific process of the two sector division modes is as follows:

(1) if the eight-sector division method is adopted, a symbol function is defined:

wherein i ═ a, B, C, D, E, F;

as the faults of the three bridge arms of a, b and c correspond to different sector division coordinate systems, in order to accurately carry out fault-tolerant control on fault sectors, a function N of the three sector division coordinate systems is defined_a,N_b,N_c。

Let N_a＝H(A)+H(B)+4H(C)+3H(D)

Let N_b＝4G(B)+3G(C)+G(D)+H(E)

Let N_c＝3H(B)+H(C)+4H(D)+H(F)

Determination of the calculated value N from Table 1_a,N_b,N_cCorresponding relation with actual sector number

TABLE 1 calculation of value N_a,N_b,N_cCorresponding relation with sector

Sector numbering	Ⅰ	Ⅱ	Ⅲ	Ⅳ	Ⅴ	Ⅳ	Ⅶ	Ⅷ
									Calculating the value N _a	6	2	4	3	7	5	1	8
Calculating the value N _b	2	4	3	7	5	6	1	8
									Calculating the value N _c	4	3	7	5	6	2	1	8

According to reference voltage components in alpha and beta two-phase static coordinate systems

Determining a rotating reference vector V_ref ^*When rotating the reference vector V_ref ^*Rotating for one circle to obtain a calculated value N_aThe sequence of change of (A) is: 6 → 2 → 1 → 4 → 3 → 7 → 8; calculating the value N_bThe sequence of change of (2 → 1 → 4 → 3 → 7 → 8 → 5 → 6; calculating the value N_cThe sequence of change of (a) is 4 → 3 → 7 → 8 → 5 → 6 → 2 → 1;

selecting different sector division functions according to the positions of the fault switching tubes, and selecting the sector division function N when the a-phase bridge arm switching tube has a fault_aThrough N_aThe change sequence of the actual sector numbers is determined, that is, the eight-sector division is as shown in fig. 3 (a); when a b-phase bridge arm switching tube fault selects a sector division function N_bThrough N_bThe change sequence of the actual sector numbers is determined, that is, the eight-sector division is as shown in fig. 3 (b); when a c-phase bridge arm switching tube fault selects a sector division function N_cThrough N_cThe change sequence of the actual sector numbers is determined, that is, the eight sectors are divided as shown in fig. 3 (c);

(2) if a twelve-sector division method is adopted, a symbol function is defined:

wherein i is a, B, C, D, E, F.

Let N ═ sign (A) + sign (B) +2sign (C) +2sign (D) +4sign (E) +3sign (F)

Determining the corresponding relation between the calculated value N and the actual sector number through the table 2;

TABLE 2 calculated value N and sector corresponding relation

Calculating the value N	1	2	3	4	5	6	7	8	9	10	11	12
													Sector numbering	Ⅷ	Ⅱ	Ⅲ	Ⅶ	Ⅳ	Ⅸ	Ⅻ	Ⅰ	Ⅹ	Ⅵ	Ⅴ	Ⅺ

Determining a rotating reference vector V_ref ^*When rotating the reference vector V_ref ^*After one rotation, the change sequence of the calculated values N is as follows: 8 → 4 → 2 → 1 → 3 → 6 → 5 → 9 → 11 → 12 → 10 → 7 → 8, i.e. the order of change of the actual sector numbers, i.e. the division of the twelve sectors is shown in FIG. 4.

And 2, determining the influence of the fault switch tube on each sector and the change of the basic voltage vector before and after the fault according to the position of the fault switch tube.

Determining the influence of a fault switch tube on each sector, wherein the method for dividing the sector type comprises the following steps: if an eight-sector division mode is adopted, determining the sectors affected by the fault switching tube in the eight sectors, namely fault sectors, according to the tables 3-5; if a twelve-sector division mode is adopted, determining the sector influenced by the fault switch tube in the twelve sectors according to the table 6;

TABLE 3 affected sectors corresponding to eight-sector a-phase bridge arm switching tube fault

Table 4 affected sectors corresponding to eight-sector b-phase bridge arm switching tube fault

TABLE 5 affected sectors corresponding to eight-sector c-phase bridge arm switching tube faults

TABLE 6 affected sectors corresponding to twelve-sector single switch tube failure

In tables 3-6, the gray parts indicate that the sectors are affected by the faulty switching tube, i.e. faulty sectors, and the white parts indicate that the sectors are not affected by the faulty switching tube, i.e. normal sectors.

The method for determining the basic voltage vectors before and after the fault of the switching tube comprises the following steps: determining the change conditions of basic voltage vectors, namely a fault zero vector and an effective vector before and after the fault of the switching tube according to the table 7, and determining a fault voltage vector;

TABLE 7 Voltage vector variation before and after single switch tube failure

In table 7, the upper and lower switching states of the same bridge arm are set to be complementary, that is, the upper bridge arm of the same bridge arm is turned on, the lower bridge arm must be turned off, the state is recorded as 1, and similarly, the upper bridge arm of the same bridge arm is turned off, the lower bridge arm is turned on, the state is recorded as 0, and three bridge arms have 8 switching state combinations, where "000", "100", "110", "010", "011", "001", "101", "111" correspond to eight basic voltage vectors, and the eight basic voltage vectors include six effective vectors and two zero vectors, on the premise that the same bridge arm is complementary.

Step 3, determining the basic voltage vector of each sector and the acting time of the basic voltage vector before the fault, wherein the specific method comprises the following steps:

first, the intermediate variables are defined as:

in the formula (I), the compound is shown in the specification,

is a reference voltage component in an alpha and beta two-phase stationary coordinate system, U_dcFor the output voltage of the DC side, T_sIs a sampling period;

then, determining the action time T of the effective vector in the basic voltage vector of each sector₁And T₂；

If the voltage vector is eight sectors, determining the action time T of the effective vector in the basic voltage vector of each sector according to tables 8-10₁And T₂；

TABLE 8 a relationship between the action time of the sector and the basic voltage vector during the phase bridge arm failure

TABLE 9 b relationship between the action time of the sector and the basic voltage vector during the phase bridge arm failure

TABLE 10 c relationship between the action time of the sector and the basic voltage vector during the phase bridge arm failure

If the voltage vector is twelve sectors, determining the action time T of the effective vector in the basic voltage vector of each sector according to the table 11₁And T₂；

TABLE 11 sector vs. base Voltage vector action time relationship

Then, the effective vector is applied for a time T₁And T₂Calculating the action time T of the zero vector in the basic voltage vector₀＝T_s-T₁-T₂；

Finally, overmodulation judgment is carried out, namely whether the sum of two times is greater than a sampling period is judged after the action time of two non-zero basic voltage vectors is calculated, if the sum of the two times is greater than the sampling period, the output voltage is seriously distorted, the two times need to be redistributed, and the distribution principle is as follows:

the resultant reference voltage rotation vector V_ref ^*The proportionality coefficients are:

namely:

step 4, adjusting the action time of the basic voltage vector of the sector influenced by the fault switch tube according to the sector influenced by the fault switch tube, the change of the fault basic voltage vector and the action time of the basic voltage vector before the fault, wherein the specific method comprises the following steps:

(1) adopts an eight-sector division mode

For the sector only affected by the zero vector and without simultaneous fault of the zero vector, the normal zero vector is used to replace the fault zero vector, i.e. the action time of the normal zero vector is set as T₀Realizing the fault-tolerant control of the sector;

for the sector which is affected by a plurality of fault voltage vectors and has no simultaneous fault of zero vectors, the normal zero vector is used for replacing the fault zero vector to complete the compensation of the zero vector, the effective vector without fault is used, the effective vector action time is calculated based on the compensation principle to synthesize the reference voltage rotation vector V again_ref ^*Such as a mapping method, an equiaxed component method, an equimode method and the like, thereby realizing the fault-tolerant control of the sector;

(2) adopts a twelve-sector division mode

For the sector only affected by the zero vector and without simultaneous fault of the zero vector, the normal zero vector is used to replace the fault zero vector, i.e. the action time of the normal zero vector is set as T₀Implementing fault-tolerant control of the sector, T₀Acting time of zero vector before fault;

for the sector which is affected by a plurality of fault voltage vectors and has no simultaneous fault of zero vectors, the normal zero vector is used for replacing the fault zero vector, the effective vector without fault is used, and the compensation principle is based onCalculating effective vector acting time to synthesize reference voltage rotation vector V again_ref ^*Such as a mapping method, an equiaxed component method, an equimode method, etc., so as to realize the fault-tolerant control of the sector;

for the sector with simultaneous fault of zero vectors, because no normal zero vector exists in the sector, the output vector can not be adjusted, and the reference voltage rotates the vector V_ref ^*The output module value reaches the maximum, and the sector can not carry out fault-tolerant control;

for the sector which is affected by a plurality of fault vectors and has a fault at the same time, because the sector has no normal zero vector, the output vector can not be adjusted, and the reference voltage rotates the vector V_ref ^*The output modulus reaches the maximum, and the sector can not carry out fault-tolerant control.

Each compensation time determination method is described in detail below.

The mapping method is a method commonly used in the prior art, and is not described herein again.

The normal mode method is to make vector V before fault_ref ^*The compensation time of the effective vector is calculated in conformity with the modulo length of the effective vector. Namely, the normal zero vector is used to replace the fault zero vector to complete the compensation of the zero vector, and the effective vector without fault is used to rotate the reference voltage by a vector V_ref ^*Orthogonally mapped to the effective vector, rotating the vector V based on the reference voltage_ref ^*Calculating action time of normal effective vector by using equal modulus principle

Implementing fault tolerant control of the sector.

The equiaxed component method is the vector V to be before failure_ref ^*And projecting the effective vector on a beta axis, and calculating effective vector compensation time based on the same components. I.e. replacing the fault zero vector by a normal zero vector and rotating the reference voltage by a vector V_ref ^*Projected on a beta axis, calculating the compensation ratio of the normal effective voltage vector based on the principle of equal beta axis components, namely setting the action time T of the normal effective vector₁+T₂Implementing fault-tolerant control of the sector, T₁And T₂The action time of two effective vectors before the fault.

Step 5, determining the conduction time of the three-phase switch tube according to the action time of the basic voltage vector and the condition that the sector is influenced by the fault switch tube, and redefining the fault sector T_a,T_b,T_cTime variable, compensation of fault vector in each fault sector, i.e. replacement of fault vector based on specific equivalence principle by using effective vector, rotating reference voltage by vector V_ref ^*The method can be used for re-synthesizing or approximately recovering in a fault sector, and comprises the following specific steps:

(1) adopts an eight-sector division mode

Preferably, for a sector which is not affected by a fault vector, the conduction time of a three-phase switch tube is defined as:

in the formula, T_sFor a sampling period, T₁And T₂The action time of the effective vector;

for the sector which is only affected by the zero vector and has no simultaneous fault of the zero vector, the conduction time of the three-phase switch tube is changed only in the sector affected by the zero vector, and the T is redefined_a,T_b,T_c；

When the position of the fault switch tube is the upper bridge arm, redefining as:

when the position of the fault switch tube is the lower bridge arm, redefining as:

for the influence of effective vector andthe zero vector does not have a sector with simultaneous fault, only the conducting time of the three-phase switch tube needs to be changed in the sector influenced by the zero vector, and the T is redefined according to the action time calculated according to the compensation principle_a,T_b,T_cThe compensation principle is different from the definition formula.

The mapping method is a method commonly used in the prior art, and how to redefine T is not described herein again_a,T_b,T_c。

For the isocode method: when the position of the fault switch tube is the upper bridge arm, redefining as:

for the equiaxed component method: when the position of the fault switch tube is the upper bridge arm, redefining as:

then, determining the switching time of each sector according to tables 12-14;

TABLE 12 relationship between the conduction time of the three-phase switching tube and the sector in the case of eight-sector a-phase bridge arm failure

TABLE 13 relationship between the conduction time of the three-phase switching tube and the sector in case of eight-sector b-phase bridge arm failure

TABLE 14 relationship between the conduction time of the three-phase switching tube and the sector in case of eight-sector c-phase bridge arm failure

(2) Adopts a twelve-sector division mode

for receiving multiple fault voltagesThe sectors which are affected by the vectors together and have no simultaneous fault of the zero vectors only need to change the conduction time of the three-phase switch tube in the sector affected by the zero vector, and the action time calculated according to the compensation principle redefines T_a,T_b,T_cThe different definition formulas of the compensation principle are different, and the specific calculation formula is the same as that of the eight sectors.

Then, determining the switching time of each sector according to the table 15;

TABLE 15 on-off time distribution relationship of different sectors of twelve sectors

Sector numbering

Ⅰ

Ⅱ

Ⅲ

Ⅳ

Ⅴ

Ⅵ

Ⅶ

Ⅷ

Ⅸ

Ⅹ

Ⅺ

Ⅻ

Conduction time T of A-phase switch tube_a

T_a

T_b

T_c

T_b

T_a

T_b

T_c

T_b

T_a

Conduction time T of B-phase switch tube_b

T_b

T_a

T_b

T_c

T_b

T_a

T_b

T_c

Conduction time T of C-phase switch tube_c

T_c

T_b

T_a

T_b

T_c

T_b

T_a

T_b

And 6, according to the switching frequency of the system in normal operation, improving the frequency of the triangular carrier wave to enable the total distortion rate of the three-phase current to meet the current input requirement of the system. The frequency, the amplitude and the phase of the triangular carrier wave are set in the main controller, and the triangular carrier frequency is increased within an allowable range, namely the switching frequency of the power switching tube is increased.

And 7, modulating the conduction time of the switching tube with a triangular carrier, determining PWM (pulse-width modulation) pulse of the switching tube, determining the on-off state of the switching tube, and finishing frequency fault-tolerant control, wherein the specific method comprises the following steps of: the method comprises the steps of modulating a triangular carrier with the conduction time and the period of a switching tube as sampling periods, determining the action sequence of a vector based on a symmetry principle and a THD minimum principle by adopting a DPWM (digital pulse width modulation) technology, adding dead zone time into modulated pulses according to the on-off time of the power switching tube to obtain 6 paths of PWM (pulse-width modulation) pulses, acting the output 6 paths of PWM pulses on a power switching tube driving circuit, and driving the corresponding power switching tube to be turned on and off by the driving circuit to finish frequency fault-tolerant control.

The method for improving the carrier frequency can increase the equivalent switching frequency, reduce the current track circular pulsation after fault-tolerant control, improve the effects of single-tube fault, double-tube fault and three-tube fault-tolerant control of the two-level PWM rectifier and reduce the influence of a fault switching tube on a system. The scheme is simple and easy to realize through a reconstruction controller SVPWM algorithm, and extra hardware cost is not required to be increased.

To demonstrate the effectiveness of the method of the present invention, the following simulation experiment was performed.

Example 1

The present embodiment is described by using a single-tube fault Q1 of a three-phase two-level PWM rectifier in an eight-sectorization mode, when a short-circuit fault occurs in the Q1 tube, the Q1 tube is converted into an open-circuit fault by a thermal fuse, and when an open-circuit fault occurs in the Q1 tube, a frequency fault-tolerant control method is described by analyzing the state of the three-phase two-level PWM rectifier in an eight-sectorization mode under the Q1 switching tube fault according to table 16.

TABLE 16Q 1 eight-sector one-cycle State analysis of PWM rectifiers under switching tube failure

The schematic diagram of the distribution of the sectors affected by the faulty switching tube in the eight-sector division mode of the Q1 tube fault of the three-phase two-level PWM rectifier is shown in fig. 5, and under the Q1 tube fault, the normal ground reference voltage rotation vector is controlled for the sectors not affected by the faulty switching tube in the table 16, and the reference voltage V is modulated by the continuous pulse width through the seven-segment switching sequence_ref ^*And (4) synthesizing. For the sectors affected by the faulty switch tube in the table 16, software fault-tolerant control is performed by redefining the faulty sector T_a，T_b，T_cTime variable, compensation of fault vector in each fault sector, i.e. replacement of fault vector based on specific equivalence principle by using effective vector, rotating reference voltage by vector V_ref ^*It can be resynthesized or approximately recovered in the failed sector. The frequency, amplitude and phase of the triangular carrier wave are set in the main controller, the triangular carrier frequency is increased within an allowable range to minimize the output THD (total distortion rate of three-phase current) of the system, and the time variables T of all sectors are used_a，T_b，T_cAnd respectively modulating with the improved triangular carrier to obtain 6 paths of PWM pulse signals. 6 paths of pulse signals are input into a power switch tube driving circuit, so that frequency fault-tolerant control of single tube faults of a three-phase two-level PWM rectifier Q1 in an eight-sector division mode is achieved, and fig. 14 is a current vector locus diagram of an alpha and beta two-phase static coordinate system in two states of fault-tolerant control and frequency fault-tolerant control of the three-phase two-level PWM rectifier Q1 in the eight-sector division mode, so that the influence of a fault switch tube on a system can be further reduced after a fault-tolerant algorithm is implemented by adopting a frequency fault-tolerant control algorithm. When other single switching tubes are in fault, fault tolerance is carried out by adopting the frequency fault tolerance control method.

Example 2

The present embodiment is illustrated with a three-phase two-level PWM rectifier with multiple tube faults in an eight-sector division.

When two switching tubes in a three-phase two-level PWM rectifier fail simultaneously, as shown in fig. 1, the following four situations are divided:

a. the upper and lower switching tubes of the same bridge arm simultaneously break down;

b. two upper pipes of different bridge arms simultaneously break down;

c. two lower tubes of different bridge arms simultaneously break down;

d. one upper pipe and one lower pipe of different bridge arms are in failure.

Because the short-circuit fault can be converted into the open-circuit fault through the thermal fuse, the fault of the switching tube can be converted into the open-circuit fault through the turn-off controller after other fault diagnoses, and the open-circuit fault is explained here.

In case a, the case where the a-phase arm upper and lower switching tubes Q1 and Q4 fail at the same time will be described. Under the eight-sector division mode, the sectors affected by Q1 and Q4 switching tube faults are complementary through a graph shown in FIG. 6 and a graph shown in Table 1, the acting polarity range of the A-phase current is also complementary, the situation can be regarded as two single-tube faults to carry out fault-tolerant control, and when the Q1 has an open-circuit fault, the frequency fault-tolerant control method is explained through state analysis of a three-phase two-level PWM rectifier under an eight-sector division mode under the double-tube fault of Q1 and Q4 according to a graph shown in Table 17.

TABLE 17 eight-sector one-cycle state analysis of PWM rectifier under Q1, Q4 double-transistor fault

Fig. 6 shows a schematic diagram of sector distribution of a fault switching tube influence of a double-tube fault of the three-phase two-level PWM rectifiers Q1 and Q4 in an eight-sector division mode, wherein under the condition of a double-tube fault of Q1 and Q4, a normal ground reference voltage rotating vector is controlled for a sector which is not influenced by the fault switching tube in table 17, and continuous pulse width modulation is realized through a seven-segment switching sequence to reference voltage V_ref ^*And (4) synthesizing. For the sector affected by the fault switch tube in the table 17, the software fault-tolerant control is carried out, and the fault sector T is redefined_a，T_b，T_cTime variable, compensation of fault vector in each fault sector, i.e. replacement of fault vector based on specific equivalence principle by using effective vector, rotating reference voltage by vector V_ref ^*It can be resynthesized or approximately recovered in the failed sector. The frequency, amplitude and phase of the triangular carrier wave are set in the main controller, the triangular carrier frequency is increased within an allowable range to minimize the output THD (total distortion rate of three-phase current) of the system, and the time variables T of all sectors are used_a，T_b，T_cAnd respectively modulating with the improved triangular carrier to obtain 6 paths of PWM pulse signals. 6 paths of pulse signals are input into a power switch tube driving circuit, so that eight paths of pulse signals are realizedThe frequency fault-tolerant control of double-tube faults of the three-phase two-level PWM rectifiers Q1 and Q4 in a sector division mode is shown in a figure 15, which is a current vector locus diagram of an alpha and beta two-phase static coordinate system in two states of fault-tolerant control and frequency fault-tolerant control of double-tube faults of the three-phase two-level PWM rectifiers Q1 and Q4 in an eight-sector division mode, and the influence of a fault switching tube on a system can be further reduced after a fault-tolerant algorithm is implemented by adopting a frequency fault-tolerant control algorithm. When the upper and lower switching tubes of the bridge arm of the frequency fault-tolerant control method simultaneously break down, the frequency fault-tolerant control method is adopted for fault tolerance.

For the conditions b, c and d, because three different eight-sector division functions are adopted for the faults of the switching tubes of the bridge arms of the phase a, the phase b and the phase c, the faults all relate to fault-tolerant control of different bridge arms, and cannot be subjected to fault-tolerant control or frequency fault-tolerant control.

When three or more switching tubes simultaneously break down, the failures all relate to fault-tolerant control of different bridge arms due to three different eight-sector division functions adopted by the failures of the switching tubes of the a-phase bridge arm, the b-phase bridge arm and the c-phase bridge arm, and the failures cannot be controlled in a fault-tolerant manner or in a frequency fault-tolerant manner.

Example 3

In the embodiment, a single-tube fault Q1 of a three-phase two-level PWM rectifier in a twelve-sector division mode is used for explaining the frequency fault-tolerant control method, when a short-circuit fault occurs in a Q1 tube, the Q1 tube is converted into an open-circuit fault by a thermal fuse, and when an open-circuit fault occurs in a Q1 tube, the three-phase two-level PWM rectifier in a twelve-sector division mode under the Q1 switching tube fault is analyzed according to a table 18.

Twelve-sector single-cycle state analysis of PWM rectifier under fault of switching tube of Table 18Q 1

Fig. 7 shows a schematic diagram of the distribution of the sectors affected by the faulty switching tube in the twelve-sector division mode of the Q1 tube fault of the three-phase two-level PWM rectifier, and under the condition of the Q1 tube fault, for the fans not affected by the faulty switching tube in the table 18The region is controlled by the normal ground reference voltage rotation vector, and the continuous pulse width modulation is realized on the reference voltage V through a seven-segment switching sequence_ref ^*And (4) synthesizing. For the sector affected by the fault switch tube in the table 18, the software fault-tolerant control is carried out, and the fault sector T is redefined_a，T_b，T_cTime variable, compensation of fault vector in each fault sector, i.e. replacement of fault vector based on specific equivalence principle by using effective vector, rotating reference voltage by vector V_ref ^*It can be resynthesized or approximately recovered in the failed sector. The frequency, amplitude and phase of the triangular carrier wave are set in the main controller, the triangular carrier frequency is increased within an allowable range to minimize the output THD (total distortion rate of three-phase current) of the system, and the time variables T of all sectors are used_a，T_b，T_cAnd respectively modulating with the improved triangular carrier to obtain 6 paths of PWM pulse signals. The 6 paths of pulse signals are input into a power switch tube driving circuit, so that frequency fault-tolerant control of single tube faults of a three-phase two-level PWM rectifier Q1 in a twelve-sector division mode is achieved, and fault tolerance is achieved by the frequency fault-tolerant control method when other single switch tubes are in faults.

Example 4

The present embodiment is illustrated with a two-transistor fault with a three-phase two-level PWM rectifier in a twelve-sector division.

a. two upper pipes of different bridge arms simultaneously break down;

b. two lower tubes of different bridge arms simultaneously break down;

c. the upper and lower switching tubes of the same bridge arm simultaneously break down;

d. one upper pipe and one lower pipe of different bridge arms are in failure.

In case a, a case where the transistors Q1 and Q3 in the two arms of a phase and B phase fail at the same time will be described. Fig. 9 is a schematic diagram of the distribution of sectors affected by a faulty switching tube in a twelve-sector division mode of a double-tube fault of the three-phase two-level PWM rectifiers Q1 and Q3 according to the present invention, it can be known from fig. 9 that the sectors affected by the double-tube fault of Q1 and Q3 are partially overlapped, each sector is analyzed according to the sector, and a frequency fault-tolerant control method is explained by analyzing the state of the three-phase two-level PWM rectifier in the twelve-sector division mode of the double-tube fault of Q1 and Q3 according to table 19.

Twelve-sector one-cycle state analysis of PWM rectifier under double-transistor faults of Table 19Q 1 and Q3

Fig. 9 shows a schematic diagram of a distribution of sectors affected by a faulty switching tube in a twelve-sector division mode when a fault occurs in two transistors Q1 and Q3 of a three-phase two-level PWM rectifier, and under the condition of a fault in two transistors Q1 and Q3, a normal ground reference voltage rotation vector is controlled for a sector not affected by the faulty switching tube in the table 19, and continuous pulse width modulation is realized through a seven-segment switching sequence to reference voltage V_ref ^*And (4) synthesizing. For the sectors affected by the failed switch in the table 19, software fault-tolerant control is performed by redefining the failed sector T_a，T_b，T_cTime variable, compensation of fault vector in each fault sector, i.e. replacement of fault vector based on specific equivalence principle by using effective vector, rotating reference voltage by vector V_ref ^*It can be resynthesized or approximately recovered in the failed sector. The frequency, amplitude and phase of the triangular carrier wave are set in the main controller, the triangular carrier frequency is increased within an allowable range to minimize the output THD (total distortion rate of three-phase current) of the system, and the time variables T of all sectors are used_a，T_b，T_cAnd respectively modulating with the improved triangular carrier to obtain 6 paths of PWM pulse signals. Inputting 6 pulse signals toIn the power switch tube driving circuit, frequency fault-tolerant control of double-tube faults of a three-phase two-level PWM rectifier Q1 and a Q3 under a twelve-sector division mode is achieved, and fault tolerance is achieved by the frequency fault-tolerant control method when other single switch tubes are in fault. Fig. 16 is a current vector trajectory diagram of an α and β two-phase stationary coordinate system in two states of fault-tolerant control and frequency fault-tolerant control when a fault of a Q1 and a Q3 double-tube of the three-phase two-level PWM rectifier is in a twelve-sector division mode, and it can be seen that the influence of a fault switching tube on the system can be further reduced by using a frequency fault-tolerant control algorithm after the fault-tolerant algorithm is implemented. When two upper pipes of different bridge arms simultaneously fail, the frequency fault-tolerant control method is adopted for fault tolerance.

In case B, a description will be given of a case where the two arm lower tubes Q4 and Q6 of the a-phase and the B-phase fail at the same time. It can be known from table 4 that the sectors affected by the Q4 and Q6 switching tube faults are partially overlapped, each sector is analyzed according to the sector, and the frequency fault-tolerant control method is explained according to the state analysis of the three-phase two-level PWM rectifier in the twelve-sector division mode under the Q4 and Q6 double-tube faults in table 20.

TABLE 20 twelve-sector one-cycle state analysis of PWM rectifier under Q4, Q6 double-transistor fault

The sector influenced by the fault switch tube in the twelve-sector division mode of the double-tube fault of the three-phase two-level PWM rectifier Q4 and Q6 is shown in table 20, under the condition of the double-tube fault of Q4 and Q6, the normal ground reference voltage rotating vector is controlled for the sector which is not influenced by the fault switch tube in the table 20, and the reference voltage V is subjected to continuous pulse width modulation through a seven-segment switching sequence_ref ^*And (4) synthesizing. For the sectors affected by the failed switch in the table 20, software fault tolerance control is performed by redefiningDefective sector T_a，T_b，T_cTime variable, compensation of fault vector in each fault sector, i.e. replacement of fault vector based on specific equivalence principle by using effective vector, rotating reference voltage by vector V_ref ^*It can be resynthesized or approximately recovered in the failed sector. The frequency, amplitude and phase of the triangular carrier wave are set in the main controller, the triangular carrier frequency is increased within an allowable range to minimize the output THD (total distortion rate of three-phase current) of the system, and the time variables T of all sectors are used_a，T_b，T_cAnd respectively modulating with the improved triangular carrier to obtain 6 paths of PWM pulse signals. The method is characterized in that 6 paths of pulse signals are input into a power switch tube driving circuit, so that frequency fault-tolerant control of double-tube faults of a three-phase two-level PWM rectifier Q4 and a Q6 under a twelve-sector division mode is achieved, and when two lower tubes of different bridge arms simultaneously break down, the frequency fault-tolerant control method is adopted for fault tolerance.

In case c, the case where the a-phase arm upper and lower switching tubes Q1 and Q4 fail at the same time will be described. It can be known from fig. 8 and table 4 that the sectors affected by the Q1 and Q4 switching tube faults are complementary, and the acting polarity ranges of the a-phase current are also complementary, and this situation can be regarded as two single-tube faults to perform fault-tolerant control, and the frequency fault-tolerant control method is explained by analyzing the state of the three-phase two-level PWM rectifier in the twelve-sector division mode under the Q1 and Q4 double-tube faults according to table 21.

TABLE 21 twelve-sector single-cycle three-state sector comparison under Q4 and Q6 double-tube fault

FIG. 8 is a schematic diagram of the sector distribution of the fault of the two-transistor Q1 and Q4 of the three-phase two-level PWM rectifier under the twelve-sector division mode, and the two-transistor Q1 and Q4 are connected under the condition of the fault of the two-transistor Q8926 and Q4As can be seen from table 21 and fig. 8, all sectors fail. Under the condition of double-tube faults of Q1 and Q4, the sectors which are not affected by the faulty switch tube in the table 21 are controlled by the normal reference voltage rotating vector, and the continuous pulse width modulation is realized by the seven-segment switching sequence to the reference voltage V_ref ^*And (4) synthesizing. For the sector affected by the fault switch tube in the table 21, the software fault-tolerant control is carried out, and the fault sector T is redefined_a，T_b，T_cTime variable, compensation of fault vector in each fault sector, i.e. replacement of fault vector based on specific equivalence principle by using effective vector, rotating reference voltage by vector V_ref ^*It can be resynthesized or approximately recovered in the failed sector. The frequency, amplitude and phase of the triangular carrier wave are set in the main controller, the triangular carrier frequency is increased within an allowable range to minimize the output THD (total distortion rate of three-phase current) of the system, and the time variables T of all sectors are used_a，T_b，T_cAnd respectively modulating with the improved triangular carrier to obtain 6 paths of PWM pulse signals. The method is characterized in that 6 paths of pulse signals are input into a power switch tube driving circuit, so that frequency fault-tolerant control of double-tube faults of a three-phase two-level PWM rectifier Q1 and a Q4 under a twelve-sector division mode is achieved, and when upper and lower switch tubes of the same bridge arm simultaneously break down, the frequency fault-tolerant control method is adopted for fault tolerance.

In case d, a description will be given of a case where the a-phase upper arm switching tube Q1 and the B-phase lower arm switching tube Q6 both fail. It can be known from fig. 10 that the sectors affected by the Q1 and Q6 switching tube faults are partially overlapped, each sector is analyzed according to the sector, and the frequency fault-tolerant control method is explained by analyzing the state of the three-phase two-level PWM rectifier in a twelve-sector division mode under the Q1 and Q6 double-tube faults according to table 22.

Twelve-sector one-cycle state analysis of PWM rectifier under double-transistor faults of Table 22Q 1 and Q6

Fig. 10 shows a schematic diagram of the distribution of sectors affected by the faulty switching tube in the twelve-sector division mode when a fault occurs in the two Q1 and Q6 transistors of the three-phase two-level PWM rectifier, and under the condition of a fault in the two Q1 and Q6 transistors, the normal ground reference voltage rotation vector is controlled for the sectors not affected by the faulty switching tube in the table 22, and the reference voltage V is modulated by continuous pulse width modulation through a seven-segment switching sequence_ref ^*And (4) synthesizing. For the sectors affected by the faulty switch tube and having at least one undistorted zero vector in the table 22, software fault-tolerant control is performed by redefining the faulty sector T_a，T_b，T_cTime variable, compensation of fault vector in each fault sector, i.e. replacement of fault vector based on specific equivalence principle by using effective vector, rotating reference voltage by vector V_ref ^*It can be resynthesized or approximately recovered in the failed sector. For sectors (such as sector III, sector IV and the like) affected by two switching tube faults at the same time, zero vector V is simultaneously lacked₀、V₇The duty ratio cannot be adjusted, and the reference voltage rotation vector V cannot be recovered_ref ^*Fault-tolerant control cannot be performed in these sectors. The frequency, amplitude and phase of the triangular carrier wave are set in the main controller, the triangular carrier frequency is increased within an allowable range to minimize the output THD (total distortion rate of three-phase current) of the system, and the time variables T of all sectors are used_a，T_b，T_cAnd respectively modulating with the improved triangular carrier to obtain 6 paths of PWM pulse signals. The method comprises the steps of inputting 6 paths of pulse signals into a power switch tube driving circuit, thereby realizing frequency fault-tolerant control of double-tube faults of a three-phase two-level PWM rectifier Q1 and a Q6 in a twelve-sector division mode, and carrying out fault tolerance by adopting the frequency fault-tolerant control method when one upper tube and one lower tube of different bridge arms are in fault. Because fault-tolerant control cannot be carried out on part of sectors, the fault-tolerant control effect is poor under the condition, and the influence of frequency fault-tolerant control on a fault switch tubeThe sound is not significantly improved.

Example 5

The present embodiment is illustrated with a three-phase two-level PWM rectifier with three-transistor failure in a twelve-sector division.

When three switching tubes in a three-phase two-level PWM rectifier fail simultaneously, as shown in fig. 1, the following four situations are divided:

a. the upper tubes of the three bridge arms of the phase a, the phase b and the phase c simultaneously break down;

b. the lower tubes of the three bridge arms of the phase a, the phase b and the phase c simultaneously break down;

c. two upper tubes and one lower tube of different bridge arms have faults.

d. One upper pipe and two lower pipes of different bridge arms are in failure.

In case a, the case where the three bridge arms Q1, Q3, and Q5 of phase a, phase B, and phase C fail at the same time will be described. Fig. 11 is a schematic diagram of the distribution of sectors affected by the faulty switching tube in the twelve-sector division mode of the three-phase two-level PWM rectifiers Q1, Q3 and Q5 according to the present invention, it can be known from fig. 11 that the sectors affected by the Q1, Q3 and Q5 switching tube faults are partially overlapped, each sector is analyzed according to the sector, and the frequency fault-tolerant control method is explained by analyzing the state of the three-phase two-level PWM rectifier in the twelve-sector division mode of the Q1, Q3 and Q5 two-tube faults according to the table 23.

Twelve-sector single-cycle state analysis of PWM rectifier under three-tube faults of Table 23Q 1, Q3 and Q5

FIG. 11 is a schematic diagram showing the distribution of the sectors affected by the faulty switching tube in the twelve-sector division mode of the three-phase two-level PWM rectifiers Q1, Q3 and Q5 according to the present invention, wherein in the case of the three-tube fault of Q1, Q3 and Q5, it can be known from tables 23 and 11 that all the sectors are faulty, and the fault-tolerant control is performed on the sector affected by the faulty switching tube in table 23 by redefining the faulty sector T_a，T_b，T_cTime variable, compensation of fault vector in each fault sector, i.e. replacement of fault vector based on specific equivalence principle by using effective vector, rotating reference voltage by vector V_ref ^*It can be resynthesized or approximately recovered in the failed sector. The frequency, amplitude and phase of the triangular carrier wave are set in the main controller, the triangular carrier frequency is increased within an allowable range to minimize the output THD (total distortion rate of three-phase current) of the system, and the time variables T of all sectors are used_a，T_b，T_cAnd respectively modulating with the improved triangular carrier to obtain 6 paths of PWM pulse signals. 6 paths of pulse signals are input into a power switch tube driving circuit, so that frequency fault-tolerant control of three-phase two-level PWM rectifiers Q1, Q3 and Q5 under a twelve-sector division mode is achieved, and faults occurring on three bridge arms of an a phase, a b phase and a c phase simultaneously are fault-tolerant by adopting the frequency fault-tolerant method.

For the case b, the simultaneous failure of the lower tubes Q4, Q6 and Q2 of the three arms of the a-phase, the b-phase and the c-phase is used for explaining the case, the table 4 shows that the sectors affected by the simultaneous failure of the switching tubes of S4, S6 and S2 are partially overlapped, each sector is analyzed according to the sector, and the frequency fault-tolerant control method is explained according to the state analysis of the three-phase two-level PWM rectifier under the twelve-sector division mode under the failure of the three tubes Q4, Q6 and Q2 in the table 24.

TABLE 24 twelve-sector single-cycle three-state sector comparison under Q4, Q6 and Q2 three-tube fault

Under the condition of Q4, Q6 and Q2 three-tube faults, all the sectors are in fault as can be seen from the table 24, the sectors affected by the fault switching tube in the table 24 are subjected to software fault-tolerant control, and the fault sectors T are redefined_a，T_b，T_cTime variable, compensation of fault vector in each fault sector, i.e. replacement of fault vector based on specific equivalence principle by using effective vector, rotating reference voltage by vector V_ref ^*It can be resynthesized or approximately recovered in the failed sector. The frequency, amplitude and phase of the triangular carrier wave are set in the main controller, the triangular carrier frequency is increased within an allowable range to minimize the output THD (total distortion rate of three-phase current) of the system, and the time variables T of all sectors are used_a，T_b，T_cAnd respectively modulating with the improved triangular carrier to obtain 6 paths of PWM pulse signals. 6 paths of pulse signals are input into a power switch tube driving circuit, so that frequency fault-tolerant control of three-phase two-level PWM rectifiers Q4, Q6 and Q2 under a twelve-sector division mode is achieved, and faults occurring at the lower tubes of three bridge arms of a phase, a phase b and a phase c are fault-tolerant by the fault-tolerant method.

For the cases c and d, it can be known from table 4 that the sectors affected by the simultaneous failure of the three switching tubes are partially overlapped, and the overlapped part will result in two zero vectors V₀、V₇Meanwhile, the fault, the duty ratio cannot be adjusted, and the reference voltage rotating vector V cannot be recovered_ref ^*Fault-tolerant control cannot be performed in these sectors. For the frequency, amplitude and phase of the triangular carrier wave set in the main controller, the triangular carrier frequency is increased within the allowed range to minimize the system output THD (total distortion rate of three-phase current), and the time variable T of all sectors is used_a，T_b，T_cAnd respectively modulating with the improved triangular carrier to obtain 6 paths of PWM pulse signals. Inputting 6 paths of pulse signals into a power switch tube driving circuit to complete fault-tolerant frequency control, wherein two upper tubes and one lower tube of different bridge armsThe fault tolerance method is adopted for fault tolerance when a fault occurs simultaneously and one upper pipe and two lower pipes of different bridge arms simultaneously fail. Because fault-tolerant control cannot be carried out on part of sectors, the fault-tolerant control effect is poor under the condition, and the influence of frequency fault-tolerant control on a fault switch tube is not obviously improved.

Example 6

The present embodiment is illustrated with a four-tube fault or above for a three-phase two-level PWM rectifier in a twelve-sector division. When four or more switching tubes in the three-phase two-level PWM rectifier have faults at the same time, as shown in Table 4, the area of the sector overlapped by the fault switching tubes reaches more than half of the area of the total sector, and the zero vector V is adjusted₀、V₇And meanwhile, the fault sector can not carry out frequency fault-tolerant control, and the system is stopped to run and the switching tube is replaced.

Claims

1. The fault-tolerant control method of the two-level PWM rectifier based on the switching frequency is characterized by comprising the following steps of:

step 1, selecting a sector division mode to carry out sector division;

step 4, adjusting the action time of the basic voltage vector of the sector influenced by the fault switching tube according to the sector influenced by the fault switching tube, the change of the basic voltage vector before and after the fault and the action time of the basic voltage vector before the fault;

step 7, modulating the conduction time of the switching tube with a triangular carrier, determining PWM (pulse-width modulation) pulse of the switching tube, determining the on-off state of the switching tube, and finishing frequency fault-tolerant control;

the sector division mode of the step 1 comprises eight sectors and twelve sectors, and the specific process of the two sectors division is as follows:

(1) adopts an eight-sector division mode

Six variables are defined:

in the formula of U_α、U_βVoltage components under an alpha and beta two-phase static coordinate system;

defining a sign function:

wherein i ═ a, B, C, D, E, F;

as the faults of the three bridge arms of a, b and c correspond to different sector division coordinate systems, in order to accurately carry out fault-tolerant control on fault sectors, a function N of the three sector division coordinate systems is defined_a,N_b,N_c；

Let N_a＝H(A)+H(B)+4H(C)+3H(D)

Let N_b＝4G(B)+3G(C)+G(D)+H(E)

Let N_c＝3H(B)+H(C)+4H(D)+H(F)

TABLE 1 calculation of value N_a,N_b,N_cCorresponding relation with sector

Sector numbering Ⅰ II Ⅲ Ⅳ Ⅴ Ⅳ Ⅶ Ⅷ Calculating the value N_a 6 2 4 3 7 5 1 8 Calculating the value N_b 2 4 3 7 5 6 1 8 Calculating the value N_c 4 3 7 5 6 2 1 8

Determining a rotating reference vector V_ref ^*When rotating the reference vector V_ref ^*Rotating for one circle to obtain a calculated value N_aThe sequence of change of (A) is: 6 → 2 → 1 → 4 → 3 → 7 → 8 → 5; calculating the value N_bThe sequence of change of (2 → 1 → 4 → 3 → 7 → 8 → 5 → 6; calculating the value N_cThe sequence of change of (a) is 4 → 3 → 7 → 8 → 5 → 6 → 2 → 1;

selecting different sector division coordinate system functions according to the positions of the fault switching tubes, and when the fault of the a-phase bridge arm switching tube selects the sector division coordinate system function N_aThrough N_aDetermining the change sequence of the actual sector numbers according to the change sequence to obtain the division of eight sectors; when a b-phase bridge arm switching tube fault selection sector divides a coordinate system function N_bThrough N_bDetermining the change sequence of the actual sector numbers according to the change sequence to obtain the division of eight sectors; dividing coordinate system function N when fault selection sector of c-phase bridge arm switching tube_cThrough N_cDetermining the change sequence of the actual sector numbers according to the change sequence to obtain the division of eight sectors;

(2) adopts a twelve-sector division mode

Six variables are defined:

defining a sign function:

wherein i is A, B, C, D, E, F

Let N ═ sign (A) + sign (B) +2sign (C) +2sign (D) +4sign (E) +3sign (F)

TABLE 2 calculated value N and sector corresponding relation

Calculating the value N 1 2 3 4 5 6 7 8 9 10 11 12 Sector numbering Ⅷ II Ⅲ Ⅶ Ⅳ IX XII Ⅰ X Ⅵ Ⅴ Ⅺ

Determining a rotating reference vector V_ref ^*When rotating the reference vector V_ref ^*After one rotation, the change sequence of the calculated values N is as follows:

8 → 4 → 2 → 1 → 3 → 6 → 5 → 9 → 11 → 12 → 10 → 7 → 8, i.e. the order of change of the actual sector numbers, i.e. the division of the twelve sectors.

2. The switching frequency based two-level PWM rectifier fault-tolerant control method according to claim 1, characterized in that step 2 determines the influence of the faulty switching tube on each sector and the change of the basic voltage vector before and after the fault according to the position of the faulty switching tube: if an eight-sector division mode is adopted, determining the sectors affected by the fault switching tube in the eight sectors, namely fault sectors, according to the tables 3-5; if a twelve-sector division mode is adopted, determining the sector influenced by the fault switch tube in the twelve sectors according to the table 6;

3. The switching frequency-based two-level PWM rectifier fault-tolerant control method according to claim 1, characterized in that step 2 determines the change conditions of basic voltage vectors, namely a fault zero vector and an effective vector, before and after a switching tube fault according to a table 7, and determines a fault voltage vector;

TABLE 7 Voltage vector variation before and after single switch tube failure

4. The switching frequency based two-level PWM rectifier fault-tolerant control method according to claim 1, wherein the specific method for determining the action time of the basic voltage vector of each sector before the fault in the step 3 is as follows:

first, the intermediate variables are defined as:

in the formula (I), the compound is shown in the specification,

TABLE 11 sector vs. base Voltage vector action time relationship

in the formula, T₁'、T₂' action time, T, of redistributed valid vectors₀' is the action time of the reassigned zero vector.

5. The switching frequency based two-level PWM rectifier fault-tolerant control method according to claim 1, wherein the specific method for adjusting the action time of the basic voltage vector of the sector affected by the faulty switching tube in the step 4 is as follows:

(1) adopts an eight-sector division mode

For the sector only affected by the zero vector and without simultaneous fault of the zero vector, the normal zero vector is used to replace the fault zero vector, i.e. the action time of the normal zero vector is set as T₀Implementing the sectorFault-tolerant control;

for the sector which is affected by a plurality of fault voltage vectors and has no simultaneous fault of zero vectors, the normal zero vector is used for replacing the fault zero vector to complete the compensation of the zero vector, the effective vector without fault is used, the effective vector action time is calculated based on the compensation principle to synthesize the rotating reference vector V again_ref ^*Realizing the fault-tolerant control of the sector, wherein the compensation principle comprises a mapping method, an equiaxial component method and an equiaxial method;

(2) adopts a twelve-sector division mode

for the sectors which are affected by a plurality of fault voltage vectors and have no simultaneous fault on the zero vector, the normal zero vector is used for replacing the fault zero vector, the effective vector without the fault is used, the effective vector action time is calculated based on the compensation principle to synthesize the rotating reference vector V again_ref ^*Realizing the fault-tolerant control of the sector, wherein the compensation principle comprises a mapping method, an equiaxial component method and an equiaxial method;

for the sector with simultaneous fault of zero vectors, because no normal zero vector exists in the sector, the output vector can not be adjusted, and the reference vector V is rotated_ref ^*The output module value reaches the maximum, and the sector can not carry out fault-tolerant control;

for the sector which is affected by a plurality of fault vectors and has a fault at the same time, because the sector has no normal zero vector, the output vector can not be adjusted, and the reference vector V is rotated_ref ^*The output modulus reaches the maximum, and the sector can not carry out fault-tolerant control.

6. The switching frequency based two-level PWM rectifier fault-tolerant control method of claim 1, wherein the method for determining the conduction time of the switching tube of each sector in step 5 is as follows:

(1) adopts an eight-sector division mode

For the sector which is not affected by the fault vector, the conduction time of the three-phase switch tube is defined as follows:

for the sector affected by the effective vector and without simultaneous fault of the zero vector, the conducting time of the three-phase switch tube is changed only in the sector affected by the zero vector, and the action time calculated according to the compensation principle redefines T_a,T_b,T_cDifferent definition formulas of the compensation principle are different, and the compensation principle comprises the following steps: mapping, iso-modeling, equiaxed component methods;

for the isocode method:

then, determining the switching time of each sector according to tables 12-14;

(2) Adopts a twelve-sector division mode

for the sector which is affected by a plurality of fault voltage vectors and has no simultaneous fault of the zero vector, the conduction time of the three-phase switch tube is changed only in the sector affected by the zero vector, and the T is redefined according to the action time calculated by the compensation principle_a,T_b,T_cDifferent definition formulas of compensation principles are different, and a specific calculation formula is the same as that of the eight sectors;

then, determining the switching time of each sector according to the table 15;

Sector numbering Ⅰ II Ⅲ Ⅳ Ⅴ Ⅵ Ⅶ Ⅷ IX X Ⅺ XII a phase openingClosing pipe conduction time Ta T_a T_b T_c T_c T_b T_a T_a T_b T_c T_c T_b T_a Conduction time T of b-phase switch tube_b T_b T_a T_a T_b T_c T_c T_b T_a T_a T_b T_c T_c conduction time T of c-phase switch tube_c T_c T_c T_b T_a T_a T_b T_c T_c T_b T_a T_a T_b

。

7. The switching frequency-based two-level PWM rectifier fault-tolerant control method of claim 1, wherein in step 7, the conduction time of the switching tube is modulated with the triangular carrier wave adjusted in step 6, a DPWM technology is adopted, the action sequence of the vector is determined based on a symmetry principle and a THD minimum principle, the modulated pulse is added into dead time according to the conduction and disconnection time of the power switching tube to obtain 6 paths of PWM pulses, the output 6 paths of PWM pulses are acted on the power switching tube driving circuit, and the driving circuit drives the corresponding power switching tube to be turned on and off, so that the frequency fault-tolerant control is completed.