CN113972818B - Fault-tolerant operation method and device under fault of submodule of modularized multi-level converter - Google Patents
Fault-tolerant operation method and device under fault of submodule of modularized multi-level converter Download PDFInfo
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/32—Means for protecting converters other than automatic disconnection
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
Abstract
The invention discloses a fault-tolerant operation method and device under a fault of a submodule of a modularized multi-level converter, which are used for reducing a direct-current bus voltage reference value to a new steady-state value when the submodule is in fault, and ensuring the stable working state of each submodule while not obviously reducing the system performance. Meanwhile, the modulation ratio is considered, and the on-load voltage regulating transformer is adopted to regulate the voltage of the alternating current side so as to realize fault-tolerant operation.
Description
Technical Field
The invention relates to a fault-tolerant operation method and device under a fault of a submodule of a modularized multi-level converter, and belongs to the technical field of power electronics.
Background
In recent years, the rapid development of the high-voltage direct-current transmission technology reduces the transmission cost, improves the transmission efficiency, reduces the environmental pollution and brings remarkable social and economic benefits. Modular Multilevel Converters (MMCs) are widely used in the field of high voltage direct current transmission. The MMC adopts a submodule cascading mode, so that the manufacturing difficulty of the required IGBT is reduced, the switching loss is reduced, and the quality of the voltage waveform is improved. Therefore, the reliability of the submodule is an important index for measuring the performance of the MMC, and the reliable operation of the system under the fault condition of the submodule is very important.
Currently, redundant submodules are mainly adopted to realize fault-tolerant operation of a system, but the cost and the size of the MMC converter are increased due to the existence of the additional redundant submodules. And the bypass switch has loss, so that the system efficiency is reduced.
Disclosure of Invention
The invention aims to provide a fault-tolerant operation method and device for a modularized multi-level converter submodule under fault, which do not use redundant submodules, can not obviously reduce the performance of a system, and can solve the problems of submodule redundancy, large equipment size, high cost and the like.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the invention provides a fault-tolerant operation method under a fault of a submodule of a modularized multi-level converter, which comprises the following steps:
detecting the voltage of the submodules of the modularized multi-level converter in real time, and obtaining the fault quantity of each phase of submodule in the half bridge of the modularized multi-level converter;
according to the fault quantity of the submodule, the voltage reference value of the direct-current bus is adjusted as follows:
wherein V is DC Is the actual measurement value of the voltage of the direct current bus in normal operation,for the reference value of the direct current bus voltage during the fault period, N is the number of the sub-modules in the half bridge, F max The fault quantity of each phase sub-module in the half bridge is the maximum value;
and detecting the voltage change range of the direct current bus in real time, and if the voltage change range exceeds a preset threshold value, adjusting the voltage of the alternating current power grid according to the modulation ratio until the modulation ratio requirement is met.
Further, the method comprises the steps of,
if only one sub-module in the half bridge fails, the failure quantity F of each phase sub-module in the half bridge is obtained a ，F b ，F c Then in the a phase, b phase and c phase of the other half bridge respectivelyBypass F a ，F b ，F c The sub-modules work normally;
if the sub-modules in the upper bridge arm and the lower bridge arm have faults, the half bridge with the most faulty sub-modules is taken as the reference, and the fault quantity F of the sub-modules of each phase in the half bridge is obtained a ，F b ，F c The sub-modules are bypassed in the a phase, the b phase and the c phase of the other half bridge, so that the number of the sub-modules for normally working of the upper bridge arm and the lower bridge arm of the same phase is ensured to be the same.
Further, the preset threshold is ±10%.
Further, the adjusting the ac grid voltage according to the modulation ratio includes:
if the voltage drop of the direct current bus is more than 10% and the modulation ratio m is more than or equal to 1, the voltage of the alternating current power grid is reduced through an on-load voltage regulating transformer OLTC until the modulation ratio is controlled within the range of 0.7 < m < 1;
if the DC bus voltage rises by more than 10% and the modulation ratio m is less than or equal to 0.7, the AC network voltage is raised by the on-load regulating transformer OLTC until the modulation ratio is controlled within the range of 0.7 < m < 1.
Further, the modulation ratio is calculated as follows:
wherein m is modulation ratio, V DC Is the actual measurement value of the voltage of the direct current bus in normal operation, V jO V is jO Amplitude, v jO Is formed by peak value of + -V DC M-level ac voltage generated by the modular multilevel converter of/2.
Further, the on-load voltage regulating transformer OLTC is connected in series with an ac side of the MMC converter.
Further, the on-load tap position is adjusted in steps of 2.5% during the step down or step up of the ac grid voltage by the on-load tap changer OLTC.
The invention also provides a fault-tolerant operation device under the fault of the submodule of the modularized multi-level converter, which comprises:
the detection module is used for detecting the voltages of the submodules of the modularized multi-level converter in real time and obtaining the fault quantity of each phase of submodule in the half bridge of the modularized multi-level converter;
the adjusting module is used for adjusting the voltage reference value of the direct current bus according to the fault quantity of the submodules in the following mode:
wherein V is DC Is the actual measurement value of the voltage of the direct current bus in normal operation,for the reference value of the direct current bus voltage during the fault period, N is the number of the sub-modules in the half bridge, F max The fault quantity of each phase sub-module in the half bridge is the maximum value;
the method comprises the steps of,
and the correction module is used for detecting the voltage change range of the direct current bus in real time, and if the voltage change range exceeds a preset threshold value, the alternating current power grid voltage is adjusted according to the modulation ratio until the modulation ratio requirement is met.
Further, the correction module is specifically used for,
if the voltage drop of the direct current bus is more than 10% and the modulation ratio m is more than or equal to 1, the voltage of the alternating current power grid is reduced through an on-load voltage regulating transformer OLTC until the modulation ratio is controlled within the range of 0.7 < m < 1;
if the DC bus voltage rises by more than 10% and the modulation ratio m is less than or equal to 0.7, the AC network voltage is raised by the on-load regulating transformer OLTC until the modulation ratio is controlled within the range of 0.7 < m < 1.
The beneficial effects of the invention are as follows:
the invention provides a fault-tolerant operation method under the fault of a submodule of a modularized multi-level converter, which does not use a redundant submodule and does not obviously reduce the performance of a system. When the sub-module fails, the voltage reference value of the direct current bus is reduced to a new steady-state value, and the working state of each sub-module is ensured to be stable while the system performance is not obviously reduced.
Drawings
FIG. 1 is a topological structure diagram of a MMC-based bi-directional VSC-HVDC system;
FIG. 2 is a circuit configuration diagram of an MMC;
FIG. 3 is a schematic diagram of an MMC submodule circuit;
FIG. 4 is an equivalent circuit diagram of an MMC;
fig. 5 is a flow chart of a fault-tolerant operation method under the fault of a submodule of the modular multilevel converter provided by the invention;
fig. 6 is a simulation result in the embodiment of the present invention.
Detailed Description
The invention is further described below. The following examples are only for more clearly illustrating the technical aspects of the present invention, and are not intended to limit the scope of the present invention.
The invention provides a fault-tolerant operation method under a fault of a submodule of a modularized multi-level converter, which comprises the following steps:
firstly, establishing a mathematical model of a sub-module based on a topological structure of a bidirectional high-voltage direct-current transmission (VSC-HVDC) system of a modularized multi-level converter (MMC);
then, according to the topological structure of the bidirectional high-voltage direct-current transmission system based on the modularized multi-level converter (MMC) and the mathematical model of the submodule, a system fault-tolerant operation (FTO) algorithm based on controlling the direct-current side voltage is provided, and the direct-current side voltage (V DC ) Dropping to a new steady state value;
finally, comprehensively considering that the harmonic distortion rate of the MMC output alternating-current voltage is in a reasonable range, and the reduction range of the direct-current bus voltage is limited by the modulation ratio m, and adopting an on-load voltage regulating transformer OLTC to regulate the alternating-current power grid voltage to realize fault-tolerant operation.
Referring to fig. 1, a topology structure diagram of a high-voltage direct-current transmission system at two ends based on a Modular Multilevel Converter (MMC) is shown, wherein both ends of the converter are connected with an alternating-current power grid, and an MMC control structure is adopted. Taking the left structure as an example (the right structure is similar and therefore will not be described in detail): v sabc 、i sabc Is an alternating current network voltage,A current; the PLL is a phase locked loop; obtaining a d-axis component and a q-axis component through abc-dq coordinate transformation; v d 、i d 、The reference value is d-axis voltage, current component and current component; v q 、i q 、/>The reference values are q-axis voltage, current components and current components; v (V) DC Is a direct current voltage; />Is a direct current voltage reference value; p (P) 1 For active power of AC network, P 1 * Is an active power reference value; v is AC network voltage, V 1 * Is an ac voltage reference. The controller is of a double closed-loop control structure (PI control is adopted), the outer ring controller adopts direct-current voltage control or active power control, the output is a d-axis current reference value, and the active power is controlled; and controlling and outputting a q-axis current reference value by adopting alternating voltage to control reactive power. The inner loop control is controlled by feedforward decoupling (ω is grid angular frequency, L s For ac sensing inductance) outputs d, q-axis voltage value v sd 、v sq After dq-abc coordinate transformation, PWM modulation is adopted, and the working states of all sub-modules of the MMC are controlled through a sequencing algorithm.
The controller 1 area and the controller 2 area are similar, and when electric energy flows from the 1 area (2 area) to the 2 area (1 area), the controller 1 area (2 area) will perform V DC Control and ac bus voltage vcontrol, the controller 2 zone (controller 1 zone) will perform active power pcontrol and ac bus voltage vcontrol.
The MMC circuit structure is shown in fig. 2, the converter is provided with 6 bridge arms, and each bridge arm is formed by connecting a reactor and N sub-modules SM-1 and SM-2 … … SM-N in series. Wherein R is arm 、L arm The resistor and the inductor are bridge arm resistors and inductors; r is R s 、L s The resistor and the inductor are the alternating current side resistor and the inductor; v sj 、i sj Is AC side voltage and current; v jkn And C jkn Is the output voltage and capacitance of each sub-module, where subscript j e a, b, c represents the phase, k e U, L represents the upper leg (U) and lower leg (L) of each phase j, N = 1,2, …, N represents the sub-module number. Fig. 3 shows a topology of a specific sub-module, and T1 and T2 represent switches.
Considering the large capacity power transfer between zones 1 and 2, for ease of analysis, consider the case where power flows from the transmitting side (VSC 1) to the receiving side (VSC 2), where the VSC1 needs to control the dc side voltage V DC And an ac bus voltage v s1 VSC2 needs to control active power P 2 And an ac bus voltage v s2 。
Fig. 4 shows a circuit diagram of the equivalent of each phase of an MMC connected to an ac power supply. V (V) DC The voltage of the direct current bus is represented, the point O is a neutral point, i Uj And i Lj Representing the current flowing in the upper and lower legs of phase j, where j e a, b, c, i circ,j Represents the circulating current of phase j, v cjkn The capacitor voltage of the nth sub-module of the j-phase k bridge arm is represented by S jkn E0, 1 is the switch state of the nth sub-module of the j-phase k bridge arm in the system, and the voltages of the upper bridge arm and the lower bridge arm generated by the MMC in the j-phase are given by the following formula:
assuming that O is the midpoint of the dc bus, applying kirchhoff's voltage law to the upper and lower legs of the MMC yields:
the corresponding kirchhoff current law is used for 'j', and the following is obtained:
the circulating current in each loop is given by:
theoretically, the steady-state nominal voltage on each sub-module capacitance is equal to V Cjkn ＝V DC N. But in a practical system V CjUn A cross-current ripple will be generated based on this nominal voltage:
upper bridge arm (p) jU ) And lower arm (p) jL ) The instantaneous power expression of (2) is as follows:
v jO is formed by peak value of + -V DC M-level alternating voltage generated by MMC of/2. Consider v only jO And i sj Is obtained by the following fundamental component:
wherein m is the modulation ratio, ω is the AC grid angular frequency, θ is the phase angle, I m Is the peak value of the current. Substituting equation (9) and equation (5) into equation (8), the bridge arm power can be written as:
as seen from equations (10) and (11), since the DC power component is zero, i circ Should have a direct current component, i as can be seen from fig. 4 circ-DC ＝I DC /3，I DC Is the current of the direct current side of the converter. Other terms indicate that the bridge arm power has an oscillating power, including fundamental and second order frequency components. The fundamental frequency component corresponds to the ac grid line current. The second order harmonic component is caused by the oscillating power. The higher harmonic component can be found in the bridge arm power considering higher harmonics in the MMC output voltage and current, but with smaller amplitude compared to the fundamental and second harmonic components. Thus i circ,j With dc components, second and other higher order even harmonic componentsCan be written as:
the bridge arm current in equation (5) can be written as:
the ac component will cause voltage fluctuations in the capacitor voltage, which can be derived from the voltage-current relationship across the capacitor from substituting equations (13) and (14) into equation (7), equations (15) and (16):
wherein C is capacitor capacitance, V CjUn (0) And V CjLn (0) Is an initial value. In addition, device voltage drops can also lead to voltage ripple. i.e circ Control helps reduce second order ripple in the capacitor voltage but increases i sj And i circ The third harmonic and higher order harmonic components of (c) also increase.
Based on the above circuit structure, a Fault Tolerant Operation (FTO) algorithm for a system is proposed, wherein the system works with lower performance during fault, see fig. 5, specifically as follows:
firstly judging whether each phase submodule has fault, and supposing that F exists in upper bridge arms of a phase, b phase and c phase respectively a ，F b ，F c And the individual sub-modules fail. Then bypass F in lower bridge arms of a phase, b phase and c phase respectively a ，F b ，F c And normal operating sub-modules. Thus, the number of effective submodules in the a phase, b phase and c phase in the fault is N-F respectively a 、N-F b And N-F c 。
The voltage of the sub-module needs to be detected in real time during normal operation, when the voltage value of the failure sub-module is seriously deviated from the voltage of the normal sub-module, the failure of the sub-module is obtained, and the number of the sub-modules with failures of each phase can be counted by utilizing a program.
If the upper bridge arm and the lower bridge arm simultaneously fail, the bridge arm with more sub-modules fails is used as a reference, and the other bridge arm is bypassed, so that the number of the normal sub-modules of the upper bridge arm and the lower bridge arm is ensured to be the same, and the balance of the upper bridge arm and the lower bridge arm is ensured.
In general, F max Not exceeding 15% of the number N of sub-modules.
Let F max Is F a ，F b And F c Is the maximum value of (a). To maintain the voltage across the sub-module at a set levelWithin the counting value, the direct current bus reference voltage V during fault DCF The design is carried out according to the formula (17):
wherein V is DCF Is the reference value of the DC bus voltage during the fault. In this way, the nominal voltage of the submodule capacitor during a fault will be limited to that defined by V CjUn ＝V DC /(N-F max ) Within the design values given, the most sub-modules in the bridge arm fail at this time. And each phase operates by using symmetrical sub-modules in the upper bridge arm and the lower bridge arm, and the analysis in the normal operation is still effective under the fault-tolerant operation condition of the MMC. A 10% increase or decrease in dc bus voltage is acceptable, depending on the criteria for hvdc transmission.
On the other hand, in order to make the harmonic distortion rate of the MMC output AC voltage within a reasonable range, the reduction range of the DC bus voltage is limited by the modulation ratio m, where m is shown in formula (18) from formula (9), where V jO V is jO Amplitude, v jO Is formed by peak value of + -V DC The M-level alternating voltage generated by MMC of/2 is the measured value.
V DC Is the voltage of the direct current bus under normal operation.
Detecting the voltage of a direct current bus in real time, and when the voltage of the direct current bus is reduced by more than 10 percent and m is more than or equal to 1, reducing the voltage of an alternating current power grid by using an on-load voltage regulating transformer (OLTC) to control the modulation ratio to be within the range of 0.7 < m < 1 so as to realize fault-tolerant operation; when the direct-current voltage rises by more than 10% and m is less than or equal to 0.7, the modulation ratio is controlled within the range of 0.7 < m < 1 by using an on-load voltage regulating transformer OLTC to raise the voltage of the alternating-current power grid so as to realize fault-tolerant operation. As shown in fig. 1, the on-load voltage regulating transformer OLTC is connected in series to the ac side of the MMC converter.
During the step-up or step-down using the on-load tap-changing transformer OLTC, OLTC adjusts the tap position in steps of 2.5%.
The validity of the proposed control strategy is verified by simulation as follows.
The system simulation parameters are shown in table 1.
TABLE 1
The capacitance voltage across each sub-module was 1.6kV, so an Insulated Gate Bipolar Transistor (IGBT) device rated at 3.3kV was selected. The capacitance value is selected by limiting the ripple of the dc capacitance voltage of the submodule to within 10%. The generation of second harmonic resonance is avoided by selecting a suitable bridge arm inductance. A recent level modulation method (NLM) with an average switching frequency less than 250Hz is used. As shown in fig. 1, a phase locked loop is used to keep the converter synchronized with the ac grid. Dynamic response ratio V of converter current loop dc1 、P 2 、Q 1 And Q 2 The dynamic response is faster. Therefore, the control structure internally uses a current controller with higher bandwidth for external V dc1 And P 2 A controller with a smaller bandwidth is used. In the simulation, to simulate a fault, a bypass IGBT switch is connected to the output of the submodule. In normal operation, this switch is closed. By detecting v Cjkn Faults can be detected.
Considering the general case of a submodule failure in the controller VSC-1, in the controller VSC-1 there are two submodule failures in the a-phase upper leg (F a =2), there are 1 sub-module faults in the arm on phase b (F b =1), no submodule failure of leg on c-phase (F c =0). The dc voltage waveform is shown in fig. 6. In fig. 6, the HVDC system is operating normally. At t=0.6 s, a fault occurs. As shown in FIG. 6, V DC Reference value of (2)Reduced to (22/24) V DC ＝0.92V DC . As shown in FIG. 6, V DC The controller uses about 0.06s to correct the voltage to the new reference value of 0.92V DC . Although the three phases of the controller VSC-1 are running at different levels, v a1 、v b1 And v c1 Is unchanged. v a1 、 v b1 And v c1 The THD value of (c) was increased by only 0.1%. a phase capacitance voltage is from V DC N=1.667 kV down to 0.92V DC 0.92 n=1.667 kv, phase b capacitance voltage from V DC N=1.667 kV down to 0.92V DC 0.95n=1.6kv, phase c capacitance voltage from V DC N=1.667 kV down to 0.92V DC N=1.53 kV. In addition, V DC2 The variation of (2) has no effect on the output voltage and line current of the controller 2 region; the d-axis and q-axis components of the VSC-1 and VSC-2 currents are tracking reference values with zero steady state error.
Another embodiment of the present invention provides a fault tolerant operation apparatus under fault of a submodule of a modular multilevel converter, including:
the detection module is used for detecting the voltages of the submodules of the modularized multi-level converter in real time and obtaining the fault quantity of each phase of submodule in the half bridge of the modularized multi-level converter;
the adjusting module is used for adjusting the voltage reference value of the direct current bus according to the fault quantity of the submodules in the following mode:
wherein V is DC Is the actual measurement value of the voltage of the direct current bus in normal operation,for the reference value of the direct current bus voltage during the fault period, N is the number of the sub-modules in the half bridge, F max The fault quantity of each phase sub-module in the half bridge is the maximum value;
the method comprises the steps of,
and the correction module is used for detecting the voltage change range of the direct current bus in real time, and if the voltage change range exceeds a preset threshold value, the alternating current power grid voltage is adjusted according to the modulation ratio until the modulation ratio requirement is met.
In the embodiment of the invention, the correction module is specifically used for,
if the voltage drop of the direct current bus is more than 10% and the modulation ratio m is more than or equal to 1, the voltage of the alternating current power grid is reduced through an on-load voltage regulating transformer OLTC until the modulation ratio is controlled within the range of 0.7 < m < 1;
if the DC bus voltage rises by more than 10% and the modulation ratio m is less than or equal to 0.7, the AC network voltage is raised by the on-load regulating transformer OLTC until the modulation ratio is controlled within the range of 0.7 < m < 1.
It should be noted that the embodiment of the apparatus corresponds to the embodiment of the method, and the implementation manner of the embodiment of the method is applicable to the embodiment of the apparatus and can achieve the same or similar technical effects, so that the description thereof is omitted herein.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical aspects of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the above embodiments, it should be understood by those of ordinary skill in the art that: modifications and equivalents may be made to the specific embodiments of the invention without departing from the spirit and scope of the invention, which is intended to be covered by the claims.
Claims (6)
1. A fault tolerant method of operation in the event of a modular multilevel converter submodule failure, comprising:
detecting the voltage of the submodules of the modularized multi-level converter in real time, and obtaining the fault quantity of each phase of submodule in the half bridge of the modularized multi-level converter;
if only one sub-module in the half bridge fails, the failure quantity F of each phase sub-module in the half bridge is obtained a ，F b ，F c Then bypass F in the a phase, b phase and c phase of the other half bridge respectively a ，F b ，F c The sub-modules work normally;
if the sub-modules in the upper bridge arm and the lower bridge arm have faults, the half bridge with the most faulty sub-modules is taken as the reference, and the fault quantity F of the sub-modules of each phase in the half bridge is obtained a ，F b ，F c The sub-modules are bypassed in the a phase, the b phase and the c phase of the other half bridge, so that the number of the sub-modules for normally working of the upper bridge arm and the lower bridge arm of the same phase is ensured to be the same;
according to the fault quantity of the submodule, the voltage reference value of the direct-current bus is adjusted as follows:
wherein V is DC Is the actual measurement value of the voltage of the direct current bus in normal operation,for the reference value of the direct current bus voltage during the fault period, N is the number of the sub-modules in the half bridge, F max The fault quantity of each phase sub-module in the half bridge is the maximum value;
detecting the voltage change range of the direct current bus in real time, and if the voltage change range exceeds a preset threshold value, adjusting the voltage of the alternating current power grid according to the modulation ratio until the modulation ratio requirement is met;
the adjusting the ac grid voltage according to the modulation ratio includes:
if the voltage drop of the direct current bus is more than 10% and the modulation ratio m is more than or equal to 1, the voltage of the alternating current power grid is reduced through an on-load voltage regulating transformer OLTC until the modulation ratio is controlled within the range of 0.7 < m < 1;
if the DC bus voltage rises by more than 10% and the modulation ratio m is less than or equal to 0.7, the AC network voltage is raised by the on-load regulating transformer OLTC until the modulation ratio is controlled within the range of 0.7 < m < 1.
2. The fault tolerant method of operation under fault conditions of a modular multilevel converter submodule according to claim 1, wherein said preset threshold is ± 10%.
3. A method of fault tolerant operation in the event of a modular multilevel converter submodule failure according to claim 1, wherein the modulation ratio is calculated as follows:
wherein m is modulation ratio, V DC Is the actual measurement value of the voltage of the direct current bus in normal operation, V jO V is jO Amplitude, v jO Is formed by peak value of + -V DC M-level ac voltage generated by the modular multilevel converter of/2.
4. The fault tolerant method of operation under fault conditions of a modular multilevel converter submodule according to claim 1, wherein said on-load tap changing transformer OLTC is connected in series on an ac side of an MMC converter.
5. A fault tolerant method of operation in a modular multilevel converter submodule fault according to claim 1, characterized in that the tap position is adjusted in steps of 2.5% during lowering or raising the ac grid voltage by means of an on-load tap changer OLTC.
6. A fault tolerant operation device under fault of a modular multilevel converter submodule, characterized in that it is adapted to implement a fault tolerant operation method under fault of a modular multilevel converter submodule according to any one of claims 1 to 5, said device comprising:
the detection module is used for detecting the voltages of the submodules of the modularized multi-level converter in real time and obtaining the fault quantity of each phase of submodule in the half bridge of the modularized multi-level converter; if only one sub-module in the half bridge fails, the failure quantity F of each phase sub-module in the half bridge is obtained a ，F b ，F c Then bypass F in the a phase, b phase and c phase of the other half bridge respectively a ，F b ，F c The sub-modules work normally; if the sub-modules in the upper bridge arm and the lower bridge arm have faults, the half bridge with the most faulty sub-modules is taken as the reference, and the fault quantity F of the sub-modules of each phase in the half bridge is obtained a ，F b ，F c The sub-modules are bypassed in the a phase, the b phase and the c phase of the other half bridge, so that the number of the sub-modules for normally working of the upper bridge arm and the lower bridge arm of the same phase is ensured to be the same;
the adjusting module is used for adjusting the voltage reference value of the direct current bus according to the fault quantity of the submodules in the following mode:
wherein V is DC Is the actual measurement value of the voltage of the direct current bus in normal operation,for the reference value of the direct current bus voltage during the fault period, N is the number of the sub-modules in the half bridge, F max The fault quantity of each phase sub-module in the half bridge is the maximum value;
the method comprises the steps of,
the correction module is used for detecting the voltage change range of the direct current bus in real time, and if the voltage change range exceeds a preset threshold value, the alternating current power grid voltage is adjusted according to the modulation ratio until the modulation ratio requirement is met, and the specific adjustment mode is as follows:
if the voltage drop of the direct current bus is more than 10% and the modulation ratio m is more than or equal to 1, the voltage of the alternating current power grid is reduced through an on-load voltage regulating transformer OLTC until the modulation ratio is controlled within the range of 0.7 < m < 1;
if the DC bus voltage rises by more than 10% and the modulation ratio m is less than or equal to 0.7, the AC network voltage is raised by the on-load regulating transformer OLTC until the modulation ratio is controlled within the range of 0.7 < m < 1.
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| CN207588733U (en) * | 2017-03-15 | 2018-07-06 | 中电普瑞科技有限公司 | A kind of flexible mother controller and its control system |
| CN109905047A (en) * | 2019-03-15 | 2019-06-18 | 南京工程学院 | A kind of MMC-STATCOM self-adaptive redundant operation method |
| CN110323930A (en) * | 2019-08-07 | 2019-10-11 | 国网山西省电力公司电力科学研究院 | A kind of modular multilevel DC solid transformer and failure tolerant method |
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| CN207588733U (en) * | 2017-03-15 | 2018-07-06 | 中电普瑞科技有限公司 | A kind of flexible mother controller and its control system |
| CN109905047A (en) * | 2019-03-15 | 2019-06-18 | 南京工程学院 | A kind of MMC-STATCOM self-adaptive redundant operation method |
| CN110323930A (en) * | 2019-08-07 | 2019-10-11 | 国网山西省电力公司电力科学研究院 | A kind of modular multilevel DC solid transformer and failure tolerant method |
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