CN106208648A - A kind of STATCOM power model abnormality eliminating method - Google Patents

Abstract

The present invention relates to a kind of STATCOM power model abnormality eliminating method, detecting the state that each power model returns, if there being abnormality, then, disconnect the connection between STATCOM and bus, and control STATCOM ground connection, it is achieved STATCOM DC voltage discharges；Use conductor each abnormal power model to carry out short circuit to realize bypassing, and the correspondence position of each abnormal power model is set to controller；Judge whether STATCOM meets redundancy running condition, when meeting this redundancy running condition, readjust the corresponding relation between normal power module and control bit；Use Pressure and Control strategy to realize the asymmetric of STATCOM to restart.The method is applicable to the STATCOM of none-disk terminal mechanism, and by artificially bypassing abnormal module, and controller is readjusted the corresponding relation between normal module and control bit according to the artificial abnormal module position arranged and realized asymmetric restarting control.

Description

STATCOM power module exception handling method

Technical Field

The invention relates to an exception handling method for a STATCOM power module.

Background

A static synchronous compensator (STATCOM) is a dynamic compensation and treatment device for power quality problems based on a power electronic switching device, has the advantages of wider working range, larger capacity, faster response speed, good harmonic characteristics, small size and the like, and represents the development direction of dynamic compensation for the power quality problems as a fourth generation compensation device. At present, in order to be applied to high-voltage and large-capacity occasions, a power module is generally connected in series to form a chain structure so as to be suitable for the high-voltage and large-capacity occasions, wherein the power module can adopt an H-bridge structure, a three-level structure or a multi-level structure, and the higher the voltage level is, the more the number of the power modules which need to be connected in series per phase is, which undoubtedly increases the fault possibility of the equipment. Due to the adoption of the serial connection structure, when one or more power modules are abnormal in a certain phase, the whole device stops running, so that the reliability of the device is reduced.

In order to improve the reliability of the device, common power module exception solutions include: firstly, the power module is short-circuited by controlling the way that the switching tubes on the left and right bridge arms or the switching tubes under the left and right bridge arms in the power module are simultaneously switched on, thereby realizing the bypass of the module. The method can be realized only when the control circuit, the driving circuit and the corresponding power switch tube of the power module are normal, and the power switch tube is a vulnerable device, so the bypass mode can not completely solve the problem of abnormity of the power module. Secondly, a switching mechanism is adopted to realize the bypass of the whole power module by adopting a short circuit at a primary output port of the power module, and the switching mechanism usually adopts a contactor or a thyristor and other switching devices. But has the following disadvantages: 1) the reliability problem mainly depends on a control element in the power module to realize bypass, and bypass and redundant operation cannot be realized after a control circuit or a bypass mechanism in the power module is abnormal; 2) the redundancy operation cost is high, a bypass mechanism is required to be assembled on each power module in the bypass operation, and the cost and the complexity of equipment are increased due to the large number of chain-type STATCOM power modules; 3) the redundancy operation method is poor in applicability, capacity reduction operation and asymmetric phase voltage output are generally needed in operation after bypass, and symmetric line voltage output is achieved through neutral point drift, so that the processing method is limited in application range and only applicable to the chain-type STATCOM in a Y-type wiring mode.

Disclosure of Invention

The invention aims to provide an exception handling method for a STATCOM power module, which is used for solving the problem that the existing handling method is poor in reliability when the STATCOM power module is abnormal.

In order to achieve the above object, the present invention provides a STATCOM power module exception handling method, including the following steps:

(1) detecting the states returned by the power modules, if the states of the power modules are abnormal, disconnecting the STATCOM from the bus, controlling the STATCOM to be grounded, and realizing the discharge of the STATCOM direct-current voltage;

(2) the method comprises the following steps of carrying out short circuit on each abnormal power module by using a conductor to realize a bypass, and setting corresponding positions of each abnormal power module to a controller;

(3) judging whether the STATCOM meets a redundancy operation condition, readjusting the corresponding relation between the normal power module and the control bit when the redundancy operation condition is met, and transmitting the adjusted corresponding relation between the normal power module and the control bit to the controller;

(4) and the controller adopts a voltage-sharing control strategy to realize the asymmetric restarting of the STATCOM.

The means for readjusting the correspondence between the normal power module and the control bit in step (3) is as follows: for any phase, the normal power modules in the phase are reordered according to the sequence of all the power modules of the phase under the normal condition, and the sequence number corresponding to each normal power module is the control bit corresponding to the normal power module.

The means for realizing the asymmetric restarting of the STATCOM by adopting the voltage-sharing control strategy in the step (4) comprises the following steps:

1) readjusting and calculating the initial phase delay of the modulated triangular wave and the given value of the direct-current voltage of each normal power module of each phase according to the number of the bypass power modules and the number of the normal power modules of each phase;

2) distributing each adjusted parameter to each corresponding normal power module;

3) controlling the STATCOM to be switched on and started;

4) and obtaining pulse control signals of each corresponding normal module according to the adjusted parameters, and correspondingly controlling each normal power module according to the obtained pulse control signals to realize asymmetric restarting.

The redundant operating conditions are as follows: and for any phase, when the sum of the number of the abnormal power modules and the number of the power modules which are bypassed by the phase is less than or equal to the number of the standby power modules of the phase.

The calculation formula of the initial phase delay of the modulated triangular wave in the step 1) is as follows:

$\left\{\begin{array}{c}{\mathrm{\θ}}_{an}=(n-1)\×\frac{T_a}{2\×N_a}\\ {\mathrm{\θ}}_{bn}=(n-1)\×\frac{T_b}{2\×N_b}\\ {\mathrm{\θ}}_{cn}=(n-1)\×\frac{T_c}{2\×N_c}\end{array}\right.$

wherein the value of N starts from 1, and the end value of N is the number N of normal power modules of the corresponding phase_a、N_b、N_c；θ_anIs the adjustment value of the triangular wave initial phase delay of the phase-A nth normal power module_bnIs the adjustment value of the triangular wave initial phase delay of the nth normal power module of the B phase_cnIs the adjustment value of the triangular wave initial phase delay of the N-th normal power module of the C phase, N_aNumber of A-phase normal power modules, N_bNumber of B-phase normal power modules, N_cNumber of C-phase normal power modules, T_aPeriod of A-phase triangular carrier, T_bPeriod of B-phase triangular carrier, T_cThe period of the C-phase triangular carrier wave.

The calculation formula of the given value of the direct current voltage in the step 1) is as follows:

or

Wherein, U_{ref_a}Is an adjustment value of a given value of A-phase DC voltage, U_{ref_b}Is an adjustment value of a given value of B-phase DC voltage, U_{ref_c}Adjustment value for given value of C-phase DC voltage, N_aNumber of A-phase normal power modules, N_bNumber of B-phase normal power modules, N_cIs the number of C-phase normal power modules, N is the number of all power modules per phase, U_ref0When all power modules are normal, a given DC voltage is initially set, U_{sum_ref}For a given total dc voltage value.

In the step 1), the dc average voltage value of each phase is calculated, and the calculation formula is:

$\left\{\begin{array}{c}{U}_{avr\_a}=\underset{n=1}{\overset{Na}{\mathrm{\Σ}}}{U}_{dc\_an}/N_a\\ U_{avr\_b}=\underset{n=1}{\overset{Nb}{\mathrm{\Σ}}}{U}_{dc\_bn}/N_b\\ U_{avr\_c}=\underset{n=1}{\overset{Nc}{\mathrm{\Σ}}}{U}_{dc\_cn}/N_c\end{array}\right.$

wherein, U_{avr_a}For adjusted A-phase DC voltage average, U_{avr_b}For adjusted average value of B-phase DC voltage, U_{avr_c}For the regulated average value of the C-phase DC voltage, N_aNumber of A-phase normal power modules, N_bNumber of B-phase normal power modules, N_cNumber of C-phase normal power modules, U_{dc_an}Is the DC voltage value of the n-th normal power module of the A phase, U_{dc_an}Is the DC voltage value of the n-th normal power module of the B phase, U_{dc_an}The value of the direct current voltage of the nth normal power module of the C phase is obtained.

According to the abnormal processing method provided by the invention, the abnormal state of the abnormal module is eliminated through the artificial positioning bypass operation of the abnormal power module, the corresponding relation between the normal power module and the control bit is readjusted, and finally, the asymmetric restarting control is carried out, so that the maximum restarting of the STATCOM after the fault is realized, the problems of the reliability and the applicability of the existing STATCOM power module bypass mode and the abnormal processing method are solved, the reliability of the method is greatly improved, the application range is wide, the capacity operation is not required to be reduced, and the reactive power and harmonic compensation effect is good.

And the method is suitable for the STATCOM without a bypass mechanism, when an abnormal module exists, the abnormal module is manually bypassed, then the position of the bypass of the power unit is manually set in the controller, the controller readjusts the corresponding relation between the normal module and the control position according to the position, and finally the controller carries out asymmetric restarting control according to the newly identified corresponding relation. Therefore, the method can simply solve the problem of restarting the STATCOM power module without the bypass mechanism after abnormality, ensures that the STATCOM is subjected to emergency treatment before the manufacturer maintains the STATCOM, enables the STATCOM to continuously treat the power quality problem, and furthest plays the compensation role of the STATCOM.

Meanwhile, the exception handling method is suitable for positioning bypass of any power module realized by a bypass instruction and restarting control. In addition, the exception handling method is not only suitable for the chain type STATCOM of the Y-type wiring mode, but also suitable for the STATCOM of the delta-type wiring mode, and is wider in application range.

Drawings

FIG. 1 is a general flow diagram of a STATCOM power module exception handling method;

FIG. 2 is a detailed flow diagram of a STATCOM power module exception handling method;

FIG. 3 is a schematic diagram of a power module in normal operation;

FIG. 4 is a schematic diagram of the connection of the power module when bypassed;

FIG. 5 is a schematic diagram of a link formed by an abnormal power module and a normal power module;

FIG. 6-a is a schematic diagram of the correspondence between modules and control bits without abnormal power modules;

FIG. 6-b is a diagram illustrating the correspondence between modules and control bits when abnormal power modules are present;

FIG. 7 is a schematic view of a control parameter adjustment process;

in fig. 6-b, the black boxes represent abnormal power modules and no control bits are allocated, and the white boxes represent normal power modules and control bits are allocated.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

In this embodiment, the STATCOM takes a chain STATCOM which is more commonly used as an example. The STATCOM is provided with a main controller in a matching way, and the main controller is connected with the STATCOM and used for controlling the operation of the STATCOM, so that the asymmetrical restarting control method of the STATCOM power module can be arranged in the main controller and used as a control program of the controller to realize the control of the STATCOM. In addition, if the STATCOM does not have a matched main controller, but is controlled by a control system of the whole power system, the asymmetric restart control method is set in the control system as a software program to realize the control of the STATCOM.

As shown in fig. 1 and fig. 2, the exception handling method of the STATCOM power module includes the following steps:

step 1: the STATCOM main controller detects the state returned by the STATCOM three-phase power module in real time, when the abnormal state is detected, the abnormal power module or the fault power module exists in the power module in the STATCOM, and then the connection between the STATCOM and the bus is controlled manually, namely the connection between a primary loop of the STATCOM and the high-voltage primary bus is disconnected, so that the STATCOM is in a power-off shutdown state. In order to ensure the safety of the STATCOM after the shutdown, after the disconnection, the primary circuit of the STATCOM is grounded, and the completion of the discharge of the DC voltage of the STATCOM is waited, so that the safety is ensured. The STATCOM stops working, and a foundation is laid for subsequent exception handling.

Step 2: the abnormal power module is manually bypassed. As shown in fig. 3, the power module includes a core portion 1, and a primary loop input connection end 2 and an output connection end 3, where a connection end 4 is reserved at the input connection end 2 and a connection end 5 is reserved at the output connection end 3. When the power module is an abnormal power module, for example, a fault occurs, then, the conductor 6 which is in line with the device limit operation is adopted to short-circuit the connection end 4 and the connection end 5, as shown in fig. 4, generally, the short-circuit conductor 6 is a lead or a busbar.

After short circuit, a bypass state corresponding to a current corresponding position is set in a main controller of the chain type STATCOM, namely the position of each bypass power module in each phase is uploaded to the main controller. In this embodiment, for example, the upper computer may be used to set the bypass state of the corresponding position in a communication manner or input the switching value to the corresponding bypass position in a soft pressing plate manner to set the bypass state. In any way, the main controller is made to know the position of each abnormal power module, so that subsequent control is facilitated. Fig. 5 is a structural relationship diagram of the abnormal power module and the normal power module in the STATCOM.

And step 3: according to the steps, the number of the abnormal power modules in each phase of the current three phases can be obtained, and then whether the STATCOM meets the redundant operation condition or not is judged, namely whether the STATCOM can operate redundantly or not is judged.

In this embodiment, a specific redundant operation condition is given as follows: and for any phase, when the sum of the number of the abnormal power modules and the number of the power modules which are bypassed by the phase is less than or equal to the number of the standby power modules of the phase. If the STATCOM meets the redundant operating condition, bypass control can be performed.

For convenience of explanation, the redundant operating condition is described in detail using an inequality, which is as follows:

the main controller of the chain type STATCOM detects the states returned by all the modules in real time and acquires the number of the current three-phase abnormal modules: n is a radical of_ya、N_yb、N_ycThe number of all power modules in each phase is N, and the number of standby power modules in each phase is N_byNumber of three-phase bypassed blocks (number of blocks to be bypassed) N_pa、N_pb、N_paWhen the following relations are met, the three phases of the chain type STATCOM have redundant operation capacity, and the main controller sends a module positioning bypass instruction to the three-phase abnormal power module to obtain a bypass state; otherwise, the device does not have the redundant operation capability and cannot be restarted, and at the moment, the whole machine is disconnected with the bus by switching off the breaker.

$\left\{\begin{array}{c}{N}_{ya}+N_{pa}\≤N_{by}\\ N_{yb}+N_{pb}\≤N_{by}\\ N_{yc}+N_{pc}\≤N_{by}\end{array}\right.$

Wherein N is_yaIs the number of A-phase anomalous power modules; n is a radical of_ybIs B is differentThe number of constant power modules; n is a radical of_ycThe number of the C-phase abnormal power modules; n is a radical of_paThe number of bypassed power modules for phase a; n is a radical of_pbThe number of bypassed power modules for phase B; n is a radical of_pcThe number of bypassed power modules for phase C; n is a radical of_byThe number of standby power modules per phase.

And 4, step 4: and when the redundant operation condition is met, readjusting the corresponding relation between the normal power module and the control bit in each phase, and transmitting the adjusted corresponding relation to the main controller.

For any phase, assuming that the number of all power modules in the phase is N, then, in a normal state, that is, when there is no abnormal power module in the phase, the N power modules have an order, the serial number of each power module is the control bit of the corresponding power module, the control bit of module 1 is 1, the control bit of module 2 is 2, the control bit of module 3 is 3, … …, and the control bit of module N is N, as shown in fig. 6-a. When M abnormal power modules exist in the phase, N-M normal power modules are left in the phase after the M abnormal power modules are bypassed, the N-M normal power modules are reordered according to the sequence of all the power modules under the original abnormal condition, when the abnormal power modules are encountered, the abnormal power modules do not correspond to the control bit number any more, and the control bit number which is not distributed at the moment corresponds to the first normal module next to the control bit number until all the normal power modules are paired again. Therefore, the control bits in the N-M normal power modules are 1 to N-M. Taking M as an example, as shown in fig. 6-b, the module 3 and the module 7 are abnormal power modules, and in the original case, the control bits of the module 3 and the module 7 are the control bit 3 and the control bit 7, respectively, after bypassing the two power modules, the control bit of the module 1 is 1, the control bit of the module 2 is 2, the module 3 is in the bypass state, and the control bit is not allocated, so the module 4, which is the next normal module next to the module 3, is allocated as the control bit 3, the control bit of the module 5 is 4, the control bit of the module 6 is 5, and the module 7 is in the bypass state, and the control bit is not allocated, so the module 8, which is the next normal module next to the module 7, is allocated as the control bit 6, the control bit of the module 9 is 7, … …, and the control bit of the module N is N-2.

And 5: and the main controller realizes the asymmetric restarting of the STATCOM by adopting a voltage-sharing control strategy according to the corresponding relation between the adjusted normal power module and the control bit.

This embodiment gives a specific control procedure.

(1) And readjusting the initial phase delay and the direct-current voltage given value of the modulation triangular wave of the normal power module of each phase according to the number of the bypass power modules and the number of the normal power modules of each phase, and acquiring the initial phase delay of the triangular wave corresponding to each normal power module and the direct-current voltage given value of each power module. In addition, the average value of the direct current voltage of each phase after bypass can be obtained and can be used for closed-loop control. Fig. 7 shows a sequence of adjustment, but this is only one embodiment, and it should be noted that the initial phase delay of the triangular wave and the dc voltage set value of each power module are not in sequence.

The method comprises the following specific steps:

the method for adjusting the initial phase delay of the triangular wave in the phase-shift carrier modulation method comprises the following steps: the initial phase delay calculation formula of the triangular wave after the adjustment of the nth control bit of each phase is as follows, wherein the value of N starts from 1, and the ending value of each phase N is the number N of the normal power modules of the corresponding phase_a、N_b、N_c；

$\left\{\begin{array}{c}{\mathrm{\θ}}_{an}=(n-1)\×\frac{T_a}{2\×N_a}\\ {\mathrm{\θ}}_{bn}=(n-1)\×\frac{T_b}{2\×N_b}\\ {\mathrm{\θ}}_{cn}=(n-1)\×\frac{T_c}{2\×N_c}\end{array}\right.$

Wherein,

θ_anthe initial phase delay of the triangular wave after the nth control bit of the phase A is adjusted is unit second;

θ_bnthe initial phase delay of the triangular wave after the nth control bit of the phase B is adjusted is unit second;

θ_cnthe initial phase delay of the triangular wave after the adjustment of the nth control bit of the phase C is carried out, and the unit second is obtained;

N_a-number of phase a normal power modules;

N_b-number of B-phase normal power modules;

N_c-number of C-phase normal power modules;

T_athe phase-shift phase carrier modulation method A is used for triangular carrier period in unit of second;

T_bthe phase-shift phase carrier modulation method B is used for triangular carrier period in unit of second;

T_cthe C phase shift phase carrier modulation method is used for triangular carrier period and unit second.

The method for adjusting the given value of the direct-current voltage of each power module is as follows:

or

Wherein,

U_{ref_a}-new dc voltage setpoint of phase a in volts;

U_{ref_b}-new dc voltage setpoint of phase B in volts;

U_{ref_c}-new dc voltage setpoint of phase C in volts;

N_a-number of phase a normal power modules;

N_b-number of B-phase normal power modules;

N_c-number of C-phase normal power modules;

n-number of all power modules per phase;

U_ref0when all the power modules are normal, the given direct current voltage is initially set in unit volt;

U_{sum_ref}-a given total dc voltage value in volts.

When the direct current total pressure control and the voltage-sharing control are carried out, the main controller calculates the direct current voltage returned by the power module which is not bypassed according to the bypass state of the returned power module, obtains the direct current average voltage value of each phase, namely neglects the direct current voltage of the bypassed unit, and corresponds the direct current voltage of the power module to the Nth control position of the 1 st control position of each phase_a、N_b、N_cCalculating the average value of the module direct current voltage of the control bit by the following method;

$\left\{\begin{array}{c}{U}_{avr\_a}=\underset{n=1}{\overset{Na}{\mathrm{\Σ}}}{U}_{dc\_an}/N_a\\ U_{avr\_b}=\underset{n=1}{\overset{Nb}{\mathrm{\Σ}}}{U}_{dc\_bn}/N_b\\ U_{avr\_c}=\underset{n=1}{\overset{Nc}{\mathrm{\Σ}}}{U}_{dc\_cn}/N_c\end{array}\right.$

wherein,

U_{avr_a}-the mean value of the dc voltage after phase a adjustment, in volts;

U_{avr_b}-the mean value of the dc voltage adjusted in phase B, in volts;

U_{avr_c}-the mean value of the dc voltage after C phase adjustment, in volts;

N_a-number of phase a normal power modules;

N_b-number of B-phase normal power modules;

N_c-number of C-phase normal power modules;

U_{dc_an}the direct current voltage value of the power module corresponding to the nth control bit of the phase A is in unit of volt;

U_{dc_an}the direct current voltage value of the power module corresponding to the nth control bit of the phase B is unit volt;

U_{dc_an}the unit of the direct current voltage value of the power module corresponding to the nth control bit of the C phase is volt.

(2) The control parameters are adjusted to obtain the initial phase delay of the adjusted triangular wave, the direct current voltage set value of each power module and the direct current voltage average value of each phase, the adjustment values are used as compensation instructions of corresponding control bits of phase-shifting carrier modulation, direct current total pressure control and voltage-sharing control, and the compensation instructions are distributed to the corresponding normal power modules according to the control bit numbers corresponding to the normal power modules in a matching mode.

(3) And the main controller of the STATCOM ignores the abnormal state returned by the power module of the corresponding bypass according to the bypass state of the power module input from the outside, so as to shield the abnormal state, the abnormal state is considered to be eliminated, the STATCOM can be considered to be in a normal state, and the main controller controls the closing starting of the STATCOM.

(4) And readjusting the driving pulse signals corresponding to the normal power modules according to the obtained adjusted parameters, and then correspondingly controlling the normal power modules according to the obtained driving pulse signals to realize the asymmetric restarting of the chain type STATCOM.

Due to the number N of three-phase normal power modules_a、N_b、N_cThe triangular wave initial phase delay, the direct current voltage setting and the direct current average voltage of the three-phase normal power module can be obtained through the formulas at a certain moment when the conditions are equal or unequal. Wherein when N is_a、N_b、N_cWhen the three phases are not all equal, the three-phase triangular wave initial phase delay, the direct current voltage setting and the direct current average voltage are not equal, and at the moment, the chain type STATCOM is in an asymmetric restarting state; when Na, Nb and Nc are all equal, for a special example of the method, the initial phase delay of three-phase triangular waves and the given direct-current voltage are equal, and the chain type STATCOM is in a symmetrical restarting state. And for any power module bypass method of the chain-type STATCOM, as long as the bypass mode that the alignment bypass of the power module and the return of the bypass state to the main controller can be realized through the bypass instruction can be adopted, the exception handling method of the chain-type STATCOM power module provided by the invention can be adopted.

The positioning bypass and the asymmetric restarting are completed, when the state returned by the main controller detection module is not new abnormal, all the steps can be skipped in the subsequent operation process, and the adjusted parameters are directly utilized to carry out the asymmetric restarting control of the STATCOM by adopting the original voltage-sharing control method. And when the module returns a new abnormity, the abnormity processing method is carried out again for control.

Through the steps, the exception handling of the chain-type STATCOM power module can be realized, the chain-type STATCOM after the fault has the maximum restarting capability, and the problems of reliability and applicability existing in the existing exception handling method of the chain-type STATCOM power module are solved. The method is suitable for the STATCOM without a bypass mechanism, when an abnormal module exists, the abnormal module is manually bypassed, then the position of the power unit bypass is manually set in the controller, the controller readjusts the corresponding relation between the normal module and the control position according to the position, and finally the controller carries out asymmetric restarting control according to the newly identified corresponding relation. Therefore, the method can simply solve the problem of restarting the STATCOM power module without the bypass mechanism after abnormality, ensures that the STATCOM can continuously treat the power quality problem before the manufacturer maintains the STATCOM, and furthest plays the compensation role of the STATCOM.

The specific embodiments are given above, but the present invention is not limited to the described embodiments. The basic idea of the present invention lies in the above basic scheme, and is not limited to the calculation process of each parameter. Variations, modifications, substitutions and alterations may be made to the embodiments without departing from the principles and spirit of the invention, and still fall within the scope of the invention.

Claims (7)

1. A STATCOM power module exception handling method is characterized by comprising the following steps:

(1) detecting the states returned by the power modules, if the states of the power modules are abnormal, disconnecting the STATCOM from the bus, controlling the STATCOM to be grounded, and realizing the discharge of the STATCOM direct-current voltage;

(2) the method comprises the following steps of carrying out short circuit on each abnormal power module by using a conductor to realize a bypass, and setting corresponding positions of each abnormal power module to a controller;

(3) judging whether the STATCOM meets a redundancy operation condition, readjusting the corresponding relation between the normal power module and the control bit when the redundancy operation condition is met, and transmitting the adjusted corresponding relation between the normal power module and the control bit to the controller;

(4) and the controller adopts a voltage-sharing control strategy to realize the asymmetric restarting of the STATCOM.

2. A STATCOM power module exception handling method according to claim 1, wherein the means for readjusting the correspondence between the normal power module and the control bit in said step (3) is: for any phase, the normal power modules in the phase are reordered according to the sequence of all the power modules of the phase under the normal condition, and the sequence number corresponding to each normal power module is the control bit corresponding to the normal power module.

3. A STATCOM power module exception handling method according to claim 1, wherein the means for implementing asymmetric restart of a STATCOM using a voltage sharing control strategy in said step (4) comprises the steps of:

1) readjusting and calculating the initial phase delay of the modulated triangular wave and the given value of the direct-current voltage of each normal power module of each phase according to the number of the bypass power modules and the number of the normal power modules of each phase;

2) distributing each adjusted parameter to each corresponding normal power module;

3) controlling the STATCOM to be switched on and started;

4) and obtaining pulse control signals of each corresponding normal module according to the adjusted parameters, and correspondingly controlling each normal power module according to the obtained pulse control signals to realize asymmetric restarting.

4. A STATCOM power module exception handling method according to claim 1, wherein the redundant operating conditions are: and for any phase, when the sum of the number of the abnormal power modules and the number of the power modules which are bypassed by the phase is less than or equal to the number of the standby power modules of the phase.

5. A STATCOM power module exception handling method according to claim 3, wherein the calculation formula of the modulated triangular wave initial phase delay in step 1) is:

$\left\{\begin{array}{c}{\mathrm{\θ}}_{an}=(n-1)\×\frac{T_a}{2\×N_a}\\ {\mathrm{\θ}}_{bn}=(n-1)\×\frac{T_b}{2\×N_b}\\ {\mathrm{\θ}}_{cn}=(n-1)\×\frac{T_c}{2\×N_c}\end{array}\right.$

wherein the value of N starts from 1, and the end value of N is the number N of normal power modules of the corresponding phase_a、N_b、N_c；θ_anIs the adjustment value of the triangular wave initial phase delay of the phase-A nth normal power module_bnIs the adjustment value of the triangular wave initial phase delay of the nth normal power module of the B phase_cnIs the adjustment value of the triangular wave initial phase delay of the N-th normal power module of the C phase, N_aNumber of A-phase normal power modules, N_bNumber of B-phase normal power modules, N_cNumber of C-phase normal power modules, T_aPeriod of A-phase triangular carrier, T_bPeriod of B-phase triangular carrier, T_cThe period of the C-phase triangular carrier wave.

6. A STATCOM power module exception handling method according to claim 3, wherein the given value of dc voltage in step 1) is calculated by the formula:

or

Wherein, U_{ref_a}Is an adjustment value of a given value of A-phase DC voltage, U_{ref_b}Is an adjustment value of a given value of B-phase DC voltage, U_{ref_c}Adjustment value for given value of C-phase DC voltage, N_aNumber of A-phase normal power modules, N_bNumber of B-phase normal power modules, N_cIs the number of C-phase normal power modules, N is the number of all power modules per phase, U_ref0When all power modules are normal, a given DC voltage is initially set, U_{sum_ref}For a given total dc voltage value.

7. A STATCOM power module exception handling method according to claim 3, wherein in step 1), the average dc voltage value of each phase is further calculated, and the calculation formula is:

$\left\{\begin{array}{c}{U}_{avr\_a}=\underset{n=1}{\overset{Na}{\mathrm{\Σ}}}{U}_{dc\_an}/N_a\\ U_{avr\_b}=\underset{n=1}{\overset{Nb}{\mathrm{\Σ}}}{U}_{dc\_bn}/N_b\\ U_{avr\_c}=\underset{n=1}{\overset{Nc}{\mathrm{\Σ}}}{U}_{dc\_cn}/N_c\end{array}\right.$

wherein, U_{avr_a}For adjusted A-phase DC voltage average, U_{avr_b}For adjusted average value of B-phase DC voltage, U_{avr_c}For the regulated average value of the C-phase DC voltage, N_aNumber of A-phase normal power modules, N_bNumber of B-phase normal power modules, N_cNumber of C-phase normal power modules, U_{dc_an}Is the DC voltage value of the n-th normal power module of the A phase, U_{dc_an}Is the DC voltage value of the n-th normal power module of the B phase, U_{dc_an}The value of the direct current voltage of the nth normal power module of the C phase is obtained.