CN110707910B - Network-disconnection protection strategy of distributed control system of modular multilevel converter - Google Patents

Network-disconnection protection strategy of distributed control system of modular multilevel converter Download PDF

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CN110707910B
CN110707910B CN201910861554.3A CN201910861554A CN110707910B CN 110707910 B CN110707910 B CN 110707910B CN 201910861554 A CN201910861554 A CN 201910861554A CN 110707910 B CN110707910 B CN 110707910B
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杨顺风
陈海宇
王海宇
熊成林
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Southwest Jiaotong University
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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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Abstract

The invention discloses a network-breaking protection strategy for a distributed control system of a modular multilevel converter, eachThe sub-controller creates an array to store and refresh the target output current phase or the target output voltage phase sent by the main controller; when a network disconnection fault occurs, the sub-controller uses the stored phase signal as a fundamental frequency component in the modulation wave and continues to generate a modulation signal containing a direct current component and a fundamental frequency alternating current component; simultaneously, the modulation ratio of the capacitance voltage balance ring to the modulation signal after the network is disconnected is adoptedM break And adjusting to control the capacitor voltage of the network breaking submodule. The invention effectively reduces the influence of the network failure of the sub-controller on the whole modular multilevel converter; the whole system can keep stable in the process of network failure; the whole system has fault ride-through capability for short-time network failure, and can reasonably protect the system for long-time network failure.

Description

Network-disconnection protection strategy of distributed control system of modular multilevel converter
Technical Field
The invention relates to the technical field of power system control, in particular to a network disconnection protection strategy of a distributed control system of a modular multilevel converter.
Background
The Modular Multilevel Converter (MMC) is a novel power electronic topology which is suitable for high-voltage high-power occasions, in particular to the field of high-voltage direct current (HVDC).
However, due to the limitation of voltage withstanding of power electronic devices, when the modular multilevel converter is applied to the field of high-voltage direct-current transmission, a large number of sub-modules are often required. At this time, if a centralized control structure is adopted, that is, a central controller is adopted to control all the sub-modules, a large number of optical fibers are needed for the system, and the central controller needs to have extremely strong control capability. Therefore, the modular multilevel converter with a large number of sub-modules usually adopts a distributed control topology, the distributed control topology is composed of a main controller and sub-controllers corresponding to the sub-modules, the main controller is connected with the sub-controllers through a communication network, and the control of the system is dispersed between the main controller and the sub-controllers, so that the system does not need a large number of optical fibers and the calculation burden of the controllers is reasonably distributed.
When the modularized multi-level converter adopts a distributed control system, if the main controller is adopted to perform output current control, and the sub-controllers execute average capacitance voltage control, circulation control and capacitance voltage balance control, the main controller needs to send five control quantities, namely a target circulation value, an actual circulation value, a target capacitance voltage value, a target output voltage value and a target output current phase value, to the sub-controllers through a communication network, so as to complete all control loops of the modularized multi-level converter distributed control system.
When a certain sub-controller has a network disconnection fault, the sub-controller cannot receive the five control data, and can only obtain the capacitance voltage value of the sub-controller by sampling the capacitance voltage of the sub-module to be controlled. At this time, no matter whether the sub-controller continues to perform the original control procedure, it will generate a modulation signal lacking the fundamental frequency alternating current component and will eventually cause the flying rise of the capacitance voltage of the network breaking sub-module controlled correspondingly and the instability of the whole system.
At present, no results are published for the network breaking problem of the sub-controllers in the distributed control system of the modular multilevel converter, so that research on the problem is necessary.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a grid-breaking protection strategy for a distributed control system of a modular multilevel converter, which can effectively reduce the influence of a grid-breaking fault of a sub-controller on the whole modular multilevel converter, so that the whole system has fault ride-through capability for a short-time grid-breaking fault, and can protect the system for a long-time grid-breaking fault. The technical scheme is as follows:
a network-breaking protection strategy of a distributed control system of a modular multilevel converter is characterized in that each sub-controller creates a number of groups to store and refresh a target output current phase or a target output voltage phase sent by the main controller; when a network disconnection fault occurs, the sub-controller uses the stored phase signal as a fundamental frequency component in the modulation wave and continues to generate a modulation signal containing a direct current component and a fundamental frequency alternating current component; simultaneously adopts the capacitor voltage balance ring to breakModulation ratio M in post-network modulated signalsbreakAnd adjusting to control the capacitor voltage of the network breaking submodule.
Further, the specific protection process comprises the following steps:
step 1: when the sub-controller detects that the broadcast signal of the main control is not received in the corresponding time, the network failure fault is defaulted to occur, and the duration time of the network failure fault is timed;
step 2: if the sub-controller detects that the duration of the network failure is less than the latest protection time t set by the systemsetIf so, judging that the network failure is short-time network failure, and entering steps 3, 5, 6, 7 and 9;
if the sub-controller detects that the duration of the network breaking fault reaches the latest protection time t set by the systemsetIf so, judging that the network failure fault is a long-time network failure fault, and entering the steps 4, 5, 6, 7, 8 and 9;
and step 3: the sub-controller converts the sub-module capacitance voltage uc *The target value is set as a nominal value;
and 4, step 4: the sub-module capacitor voltage u is immediately transmitted by the sub-controllerc *The target value is set to 0V;
and 5: controlling the capacitor voltage of the broken network submodule through the submodule capacitor voltage balancing ring;
step 6: comparing the result of the sub-module capacitance voltage balance loop with an initial modulation ratio MinitAdding the amplitude M as a fundamental frequency component of the modulation signalbreak；
And 7: according to the formula
Figure BDA0002199932400000021
Generating a final modulation signal, generating a driving signal through modulation, and controlling the capacitor voltage of the network breaking submodule to reach a target value; wherein,
Figure BDA0002199932400000022
outputting a current phase signal for the stored target;
and 8: cutting off the broken net submodule out of the system;
and step 9: and finishing the network breaking protection.
Furthermore, if the master controller finds that the loss time of one sub-controller reaches the set time tsetAnd then, the main controller will default that the sub-module corresponding to the network breaking sub-controller is cut out of the system, and then the main controller will arrange another alternative sub-controller and the sub-module access system to complete the protection of the network breaking fault.
The invention has the beneficial effects that: the invention effectively reduces the influence of the network failure of the sub-controller on the whole modular multilevel converter; the whole system can keep stable in the process of network failure; the whole system has fault ride-through capability for short-time network failure, and can reasonably protect the system for long-time network failure.
Drawings
Fig. 1 is a control block diagram of a sub-controller network-breaking protection strategy.
Fig. 2 is a flow chart of system network failure protection.
Detailed Description
The invention is described in further detail below with reference to the figures and specific embodiments. The invention can make the sub-controller after the network is broken still generate the modulation signal containing the fundamental frequency alternating current component with the basically correct phase through the mode of storing the target output current phase sent by the main control; the capacitor voltage of the broken network submodule is effectively controlled through a capacitor voltage balancing ring; a complete network-breaking protection strategy is provided, and reasonable solutions are provided for long-time and short-time network-breaking faults respectively.
After the sub-controller is disconnected, the sub-controller cannot receive the control information of the main controller and can only detect the capacitance voltage of the sub-module to be controlled through the voltage sensor.
The network disconnection protection strategy proposed by the patent is as follows: normally, each sub-controller creates an array to store and refresh one of the five control quantities sent by the main controller, namely the target output current phase. When the network breaking fault occurs, the sub-controller uses the stored phase signal as the fundamental frequency component in the modulation wave to continue to produceA modulated signal is generated that includes a DC component and a fundamental AC component. Meanwhile, in order to stabilize the capacitance voltage of the network-breaking submodule, a capacitance voltage balancing ring is adopted to balance the modulation ratio M in the modulated signal after network breakingbreakAnd adjusting to control the capacitor voltage of the network breaking submodule. A specific control block diagram of the network disconnection protection strategy is shown in fig. 1.
In the drawings
Figure BDA0002199932400000031
Outputting the current phase signal for the stored target, MinitIs the modulation ratio u under the rated working condition of the systemc *For the net-breaking submodule capacitor voltage target value, uCkAnd the actual value of the capacitor voltage of the network breaking submodule is obtained. It can be seen that the capacitor voltage deviation value is fed back into the proportional (P) controller to change the magnitude of the stored target output current, i.e. MbreakAnd the control on the capacitor voltage of the network breaking submodule is further realized.
As shown in fig. 2, the protection process of the whole system after using the network-breaking protection policy is as follows: and when the sub-controller detects that the main control broadcast signal cannot be received at the corresponding time, the network disconnection fault is caused by default, the network disconnection protection strategy is started, and the duration time of the network disconnection fault is timed. When the duration of the network failure is shorter than the latest protection time t set by the systemsetUnder the condition that the sub-controller is used for protecting the sub-module target capacitor voltage u in the strategy of network disconnectionc *And the set value is set as a rated value, so that the stability of the capacitor voltage of the grid-breaking submodule is maintained, and the system continues to operate stably. When the sub-controller detects that the duration of the network failure reaches the set latest protection time tsetWhen the fault occurs, the fault is judged to be a long-time fault. The sub-controller immediately converts the sub-module target capacitance voltage uc *And setting the voltage to be 0V, controlling the voltage of the capacitor of the network breaking submodule to fall to 0, and then cutting the network breaking submodule out of the system. Meanwhile, if the master controller finds that the loss time of one sub-controller reaches the set time tsetThen, the main controller will default that the broken network sub-controller has cut off the corresponding sub-module out of the system, and then the main controller will arrange another replacementAnd the supplementary controller and the sub-module are connected into the system, so that the system finishes the protection of the network failure.
The specific protection process comprises the following steps:
step 1: when the sub-controller detects that the broadcast signal of the main control is not received in the corresponding time, the network failure fault is defaulted to occur, and the duration time of the network failure fault is timed;
step 2: if the sub-controller detects that the duration of the network failure is less than the latest protection time t set by the systemsetIf so, judging that the network failure is short-time network failure, and entering steps 3, 5, 6, 7 and 9;
if the sub-controller detects that the duration of the network breaking fault reaches the latest protection time t set by the systemsetIf so, judging that the network failure fault is a long-time network failure fault, and entering the steps 4, 5, 6, 7, 8 and 9;
and step 3: the sub-controller converts the sub-module capacitance voltage uc *The target value is set as a nominal value;
and 4, step 4: the sub-module capacitor voltage u is immediately transmitted by the sub-controllerc *The target value is set to 0V;
and 5: controlling the capacitor voltage of the broken network submodule through the submodule capacitor voltage balancing ring;
step 6: comparing the result of the sub-module capacitance voltage balance loop with an initial modulation ratio MinitAdding the amplitude M as a fundamental frequency component of the modulation signalbreak；
And 7: according to the formula
Figure BDA0002199932400000041
Generating a final modulation signal, generating a driving signal through modulation, and controlling the capacitor voltage of the network breaking submodule to reach a target value; wherein,
Figure BDA0002199932400000042
outputting a current phase signal for the stored target;
and 8: cutting off the broken net submodule out of the system;
and step 9: and finishing the network breaking protection.

Claims (2)

1. A network-breaking protection strategy of a distributed control system of a modular multilevel converter is characterized in that each sub-controller creates a number of groups to store and refresh a target output current phase or a target output voltage phase sent by a main controller;
when a network disconnection fault occurs, the sub-controller uses the stored phase signal as a fundamental frequency component in the modulation wave and continues to generate a modulation signal containing a direct current component and a fundamental frequency alternating current component; simultaneously, a modulation ratio M in the modulation signal after the network is disconnected is adjusted by adopting a capacitance voltage balance ringbreakAdjusting to control the capacitor voltage of the network breaking submodule; the specific protection process comprises the following steps:
step 1: when the sub-controller detects that the broadcast signal of the main control is not received in the corresponding time, the network failure fault is defaulted to occur, and the duration time of the network failure fault is timed;
step 2: if the sub-controller detects that the duration of the network failure is less than the latest protection time t set by the systemsetIf so, judging that the network failure is short-time network failure, and entering steps 3, 5, 6, 7 and 9;
if the sub-controller detects that the duration of the network breaking fault reaches the latest protection time t set by the systemsetIf so, judging that the network failure fault is a long-time network failure fault, and entering the steps 4, 5, 6, 7, 8 and 9;
and step 3: the sub-controller converts the sub-module capacitance voltage uc *The target value is set as a nominal value;
and 4, step 4: the sub-module capacitor voltage u is immediately transmitted by the sub-controllerc *The target value is set to 0V;
and 5: controlling the capacitor voltage of the broken network submodule through the submodule capacitor voltage balancing ring;
step 6: comparing the result of the sub-module capacitance voltage balance loop with an initial modulation ratio MinitAdding the amplitude M as a fundamental frequency component of the modulation signalbreak；
And 7: according to the formula
Figure FDA0002926340810000011
Generating a final modulation signal, generating a driving signal through modulation, and controlling the capacitor voltage of the network breaking submodule to reach a target value; wherein,
Figure FDA0002926340810000012
outputting a current phase signal for the stored target;
and 8: cutting off the broken net submodule out of the system;
and step 9: and finishing the network breaking protection.
2. The grid-breaking protection strategy of the distributed control system of the modular multilevel converter according to claim 1, wherein if the master controller finds that the loss-of-connection time of one of the subcontrollers reaches the set time tsetAnd then, the main controller will default that the sub-module corresponding to the network breaking sub-controller is cut out of the system, and then the main controller will arrange another alternative sub-controller and the sub-module access system to complete the protection of the network breaking fault.
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CN102195508A (en) * 2011-06-03 2011-09-21 中国科学院电工研究所 Modulation method of modular multilevel converter (MMC)
CN102957167A (en) * 2012-11-06 2013-03-06 郭高朋 Modularized multi-level converter-based wind power generation and grid connection system
CN103199729A (en) * 2013-04-10 2013-07-10 国家电网公司 Modularization multi-level converter submodule grouping stair wave modulation method
CN104538986A (en) * 2014-12-31 2015-04-22 阳光电源股份有限公司 Parallel inverter control method, host, slave machines and system
CN109119995A (en) * 2018-08-14 2019-01-01 中南大学 It is a kind of for cascading the hierarchical control method and system of STATCOM

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CN103248252B (en) * 2013-03-07 2015-02-11 中国矿业大学 Modulation strategy for modular multilevel transducer

Patent Citations (5)

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Publication number Priority date Publication date Assignee Title
CN102195508A (en) * 2011-06-03 2011-09-21 中国科学院电工研究所 Modulation method of modular multilevel converter (MMC)
CN102957167A (en) * 2012-11-06 2013-03-06 郭高朋 Modularized multi-level converter-based wind power generation and grid connection system
CN103199729A (en) * 2013-04-10 2013-07-10 国家电网公司 Modularization multi-level converter submodule grouping stair wave modulation method
CN104538986A (en) * 2014-12-31 2015-04-22 阳光电源股份有限公司 Parallel inverter control method, host, slave machines and system
CN109119995A (en) * 2018-08-14 2019-01-01 中南大学 It is a kind of for cascading the hierarchical control method and system of STATCOM

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