CN112152438A - Method and system for starting MMC (Modular multilevel converter) in hybrid direct-current transmission system - Google Patents
Method and system for starting MMC (Modular multilevel converter) in hybrid direct-current transmission system Download PDFInfo
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Abstract
The invention relates to a method and a system for starting an MMC in a hybrid direct-current power transmission system, which comprise the following steps: uncontrolled charging is carried out on the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a first preset voltage and a second preset voltage respectively; controllably charging the MMC until the capacitance voltage of a half-bridge submodule and the capacitance voltage of a full-bridge submodule in the MMC both reach the starting rated voltage of the MMC; according to the technical scheme provided by the invention, the MMC after uncontrolled charging is subjected to voltage-sharing control charging to realize that the capacitance voltages of the full-bridge submodule and the half-bridge submodule in the MMC tend to be consistent, and then full-bridge submodule half-bridge and integral alternate conduction charging are sequentially carried out on the MMC, so that the capacitance voltage of the MMC neutron module simultaneously reaches a rated value, and the fault rate of starting the MMC is reduced.
Description
Technical Field
The invention relates to the technical field of flexible direct current transmission, in particular to a method and a system for starting an MMC in a hybrid direct current transmission system.
Background
The modular multilevel converter high-voltage direct-current transmission (MMC-HVDC) has become a development trend in the field of the voltage source converter high-voltage direct-current transmission (VSC-HVDC) in the future due to unique technical advantages.
Most of Modular Multilevel Converters (MMCs) in the current engineering adopt a half-bridge sub-module structure, but the MMC based on the half-bridge sub-module cannot process a fault of a direct current overhead line through self action of the Converter, because even if an Insulated Gate Bipolar Transistor (IGBT) in the half-bridge sub-module topology structure is turned off, an alternating current system can still feed current to a fault point through a diode connected in inverse parallel with the IGBT, and the influence on the alternating current system is equivalent to a three-phase short circuit. Under the condition that the high-voltage large-capacity direct-current circuit breaker technology is not mature, the fault current of a direct-current line is cut off by depending on the locking of a converter and the simultaneous tripping of an alternating-current side circuit breaker, so that the restart recovery time of the whole system is long, usually in the order of seconds, and the transient stability of an alternating-current and direct-current power transmission system is not facilitated.
To half-bridge submodule piece MMC's not enough, the scholars have proposed the MMC based on full-bridge submodule piece that has direct current trouble clearance ability, high voltage direct current transmission system based on full-bridge submodule piece MMC can block rapidly or export the negative pressure and cut off direct current fault current after taking place the direct current circuit trouble, and need not jump the exchange side circuit breaker, the back system can resume the operation rapidly after the trouble is amputated, consequently full-bridge submodule piece MMC is applicable to more based on remote overhead line's mixed direct current transmission system. However, the number of power switches used in the full-bridge sub-module is 2 times that of the half-bridge sub-module, so that the cost and the loss are greatly increased.
For this reason, another scholars has proposed an MMC in which a half-bridge submodule and a full-bridge submodule are mixed, so that the MMC can reduce cost and loss during operation, and has a dc fault clearing capability.
However, due to the difference of the charging rates of the full-bridge submodule and the half-bridge submodule in the uncontrolled charging stage MMC, after uncontrolled charging is finished, the capacitor voltage of the full-bridge submodule is inconsistent with the capacitor voltage of the half-bridge submodule; at this time, the MMC is controllably charged, and the situation that the full-bridge sub-module capacitor reaches or even exceeds the rated voltage and the half-bridge sub-module capacitor does not reach the rated voltage may occur, so that the starting cannot be completed.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a starting method of an MMC in a hybrid direct-current power transmission system, the method carries out voltage-sharing control charging on the MMC after uncontrolled charging so as to realize that the capacitance voltages of a full-bridge submodule and a half-bridge submodule in the MMC tend to be consistent, and then carries out half-bridge and integral alternate conduction charging on the MMC in turn so as to ensure that the capacitance voltage of the sub-module of the MMC reaches a rated value simultaneously.
The purpose of the invention is realized by adopting the following technical scheme:
the invention provides a starting method of MMC in a hybrid direct-current power transmission system, wherein the hybrid direct-current power transmission system consists of an alternating-current system equivalent power supply, an alternating-current circuit breaker, a starting resistor and the MMC which are sequentially connected, wherein two ends of the starting resistor are connected with a starting resistor bypass switch in parallel, and the MMC consists of a half-bridge submodule and a full-bridge submodule, and the improvement is that the method comprises the following steps:
uncontrolled charging is carried out on the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a first preset voltage and a second preset voltage respectively;
controllably charging the MMC until the capacitance voltage of a half-bridge submodule and the capacitance voltage of a full-bridge submodule in the MMC both reach the starting rated voltage of the MMC;
the initial state of the alternating current circuit breaker is disconnected, the initial state of the starting resistor bypass switch is disconnected, the initial state of the half-bridge sub-module in the MMC is locked, and the initial state of the full-bridge sub-module in the MMC is locked.
Preferably, it is right MMC carries out uncontrolled charging, until in the MMC the capacitor voltage of half-bridge submodule piece and the capacitor voltage of full-bridge submodule piece to first preset voltage and second preset voltage respectively, include:
controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be open, the working state of the half-bridge sub-module in the MMC to be locked, and the working state of the full-bridge sub-module in the MMC to be locked;
and finishing the operation when the capacitor voltage of the half-bridge submodule in the MMC is charged to a first preset voltage and the capacitor voltage of the full-bridge submodule in the MMC is charged to a second preset voltage.
Preferably, the first preset voltage U is determined according to the following formulaF；
Determining the second predetermined voltage U according toH；
In the above formula, UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHThe number of half-bridge sub-modules in the MMC.
Preferably, it is right that MMC carries out controllable charging, and the capacitor voltage of half-bridge submodule piece and the capacitor voltage of full-bridge submodule piece all reach in the MMC starting rated voltage includes:
carrying out voltage-sharing control charging on the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a third preset voltage;
carrying out half-bridge transformation on the full-bridge submodule until power switch tubes T4 of the full-bridge submodule in the MMC are all conducted;
the MMC is subjected to integral alternate conduction charging until the capacitance voltage of a half-bridge submodule and the capacitance voltage of a full-bridge submodule in the MMC reach the starting rated voltage of the MMC;
and one end of a power switch tube T4 of the full-bridge submodule in the MMC is connected with the voltage cathode of the full-bridge submodule, and the other end of the power switch tube T4 is connected with the capacitor cathode in the full-bridge submodule.
Further, it is right MMC carries out voltage-sharing control and charges, and the capacitor voltage of half-bridge submodule piece and the capacitor voltage of full-bridge submodule piece all reach the third and predetermine voltage in up to MMC, include:
step 1: initializing the MMC to carry out voltage-sharing control charging at the time t being 0;
step 2: controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be open, and the working state of the half-bridge sub-module in the MMC to be locked;
and step 3: selecting N among all full-bridge submodules of the MMC1A full bridge submodule, and controls said N1Bypassing the full-bridge sub-modules, and locking the rest full-bridge sub-modules;
and 4, step 4: judging whether the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a third preset voltage or not, if so, ending the operation; otherwise, let t be t +1, and return to step 3.
Further, the step 3 comprises:
the number of bypassed full-bridge submodules N is determined as follows1：
In the formula of UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHThe number of half-bridge sub-modules in the MMC is shown; u is a third preset voltage;
arranging the full-bridge sub-modules in the MMC in descending order according to the capacitance voltage of the full-bridge sub-modules in the MMC, and selecting the front N in the sequence1A full bridge submodule.
Further, it is right that MMC carries out full-bridge submodule half-bridge ization, until full-bridge submodule's power switch pipe T4 all switches on in the MMC, include:
controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be closed, the working state of the half-bridge sub-module in the MMC to be locked, and the working state of the full-bridge sub-module in the MMC to be locked;
the operation is finished when the power switch tubes T4 of the full-bridge sub-module in the MMC are all conductive.
Further, it is right that MMC carries out whole rotation and switches on to charge, and the capacitor voltage of half-bridge submodule piece and the capacitor voltage of full-bridge submodule piece all reach in the MMC the start rated voltage of MMC includes:
and 4, step 4: initializing the MMC to carry out integral alternate conduction charging at the moment m being 0;
and 5: controlling the working state of the alternating current circuit breaker to be closed and the working state of the starting resistor bypass switch to be closed;
step 6: selecting N among all sub-modules of the MMC2A sub-module and controls the N2A sub-module bypass, and the other sub-modules are locked;
and 7: judging whether the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC both reach the starting rated voltage of the MMC, if so, ending the operation; otherwise, let m be m +1, and return to step 6.
Further, the step 6 comprises:
the number of bypassed submodules N is determined as follows2：
In the formula of UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHFor the number of half-bridge submodules, U, in MMCCThe starting rated voltage value of the modular multilevel converter is obtained;
according to the capacitance voltage of the MMC neutron modules, arranging the MMC neutron modules in a descending order, and selecting the front N in the sequence2A sub-module; wherein, MMC neutron module includes full-bridge submodule piece and half-bridge submodule piece among the MMC.
The invention provides a starting system of MMC in a mixed direct-current transmission system, the mixed direct-current transmission system consists of an alternating-current system equivalent power supply, an alternating-current breaker, a starting resistor and the MMC which are sequentially connected, starting resistor bypass switches are connected to two ends of the starting resistor in parallel, the MMC consists of a half-bridge submodule and a full-bridge submodule, and the improvement is that the system comprises:
the uncontrolled charging module is used for uncontrolled charging the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a first preset voltage and a second preset voltage respectively;
the controllable charging module is used for controllably charging the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach the starting rated voltage of the MMC;
the initial state of the alternating current circuit breaker is disconnected, the initial state of the starting resistor bypass switch is disconnected, the initial state of the half-bridge sub-module in the MMC is locked, and the initial state of the full-bridge sub-module in the MMC is locked.
Preferably, the uncontrolled charging module is configured to:
controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be open, the working state of the half-bridge sub-module in the MMC to be locked, and the working state of the full-bridge sub-module in the MMC to be locked;
and finishing the operation when the capacitor voltage of the half-bridge submodule in the MMC is charged to a first preset voltage and the capacitor voltage of the full-bridge submodule in the MMC is charged to a second preset voltage.
Preferably, the first preset voltage U is determined according to the following formulaF；
Determining the second predetermined voltage U according toH；
In the above formula, UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHThe number of half-bridge sub-modules in the MMC.
Preferably, the controllable charging module includes:
the voltage-sharing control charging unit is used for carrying out voltage-sharing control charging on the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a third preset voltage;
the full-bridge submodule half-bridge unit is used for performing full-bridge submodule half-bridge on the MMC until power switch tubes T4 of the full-bridge submodule in the MMC are all conducted;
the integral alternate conducting charging unit is used for carrying out integral alternate conducting charging on the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC both reach the starting rated voltage of the MMC;
and one end of a power switch tube T4 of the full-bridge submodule in the MMC is connected with the voltage cathode of the full-bridge submodule, and the other end of the power switch tube T4 is connected with the capacitor cathode in the full-bridge submodule.
Further, the voltage-sharing control charging unit is configured to:
step 1: initializing the MMC to carry out voltage-sharing control charging at the time t being 0;
step 2: controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be open, and the working state of the half-bridge sub-module in the MMC to be locked;
and step 3: selecting N among all full-bridge submodules of the MMC1A full bridge submodule, and controls said N1Bypassing the full-bridge sub-modules, and locking the rest full-bridge sub-modules;
and 4, step 4: judging whether the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a third preset voltage or not, if so, ending the operation; otherwise, let t be t +1, and return to step 3.
Further, the step 3 comprises:
the number of bypassed full-bridge submodules N is determined as follows1：
In the formula of UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHThe number of half-bridge sub-modules in the MMC is shown; u is a third preset voltage;
arranging the full-bridge sub-modules in the MMC in descending order according to the capacitance voltage of the full-bridge sub-modules in the MMC, and selecting the front N in the sequence1A full bridge submodule.
Further, the full-bridge submodule half-bridge unit is used for:
controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be closed, the working state of the half-bridge sub-module in the MMC to be locked, and the working state of the full-bridge sub-module in the MMC to be locked;
the operation is finished when the power switch tubes T4 of the full-bridge sub-module in the MMC are all conductive.
Further, the whole alternately conducting charging units are used for:
and 4, step 4: initializing the MMC to carry out integral alternate conduction charging at the moment m being 0;
and 5: controlling the working state of the alternating current circuit breaker to be closed and the working state of the starting resistor bypass switch to be closed;
step 6: selecting N among all sub-modules of the MMC2A sub-module and controls the N2A sub-module bypass, and the other sub-modules are locked;
and 7: judging whether the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC both reach the starting rated voltage of the MMC, if so, ending the operation; otherwise, let m be m +1, and return to step 6.
Further, the step 6 comprises:
the number of bypassed submodules N is determined as follows2：
In the formula of UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHFor the number of half-bridge submodules, U, in MMCCThe starting rated voltage value of the modular multilevel converter is obtained;
according to the capacitance voltage of the MMC neutron modules, arranging the MMC neutron modules in a descending order, and selecting the front N in the sequence2A sub-module; wherein, MMC neutron module includes full-bridge submodule piece and half-bridge submodule piece among the MMC.
Compared with the closest prior art, the invention has the following beneficial effects:
the technical scheme provided by the invention carries out uncontrolled charging on the MMC until the capacitance voltage of a half-bridge submodule and the capacitance voltage of a full-bridge submodule in the MMC reach a first preset voltage and a second preset voltage respectively; controllably charging the MMC until the capacitance voltage of a half-bridge submodule and the capacitance voltage of a full-bridge submodule in the MMC both reach the starting rated voltage of the MMC; increased a voltage-sharing control charging stage in controllable charging stage, come in proper order to realize full-bridge submodule piece and half-bridge submodule piece's electric capacity voltage among the MMC and tend to unanimously, then carry out full-bridge submodule piece half-bridge and whole rotation to MMC in proper order and switch on charging, make MMC neutron module electric capacity voltage reach the rated value simultaneously, reduced the fault rate that the MMC started.
Drawings
FIG. 1 is a flow chart of a method for starting an MMC in a hybrid DC power transmission system;
FIG. 2 is a diagram of a hybrid DC power transmission system network topology;
FIG. 3 is a diagram of a MMC network topology;
fig. 4 is a flow chart of a start-up system for an MMC in a hybrid dc power transmission system.
Detailed Description
The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a starting method of an MMC in a hybrid direct-current power transmission system, wherein the hybrid direct-current power transmission system consists of an alternating-current system equivalent power supply, an alternating-current circuit breaker, a starting resistor and the MMC which are sequentially connected, wherein two ends of the starting resistor are connected with a starting resistor bypass switch in parallel, the MMC consists of a half-bridge submodule and a full-bridge submodule, and as shown in figure 1, the method comprises the following steps:
step 101, uncontrollable charging is carried out on the MMC until the capacitor voltage of a half-bridge submodule and the capacitor voltage of a full-bridge submodule in the MMC reach a first preset voltage and a second preset voltage respectively;
in the preferred embodiment of the present invention, the number of half-bridge sub-modules and full-bridge sub-modules on each bridge arm of the MMC is the same.
102, controllably charging the MMC until the capacitance voltage of a half-bridge submodule and the capacitance voltage of a full-bridge submodule in the MMC reach the starting rated voltage of the MMC;
in the optimal embodiment of the invention, the starting is the basis of the normal operation of the flexible direct current transmission system, and the essence of the starting is that the active alternating current system carries out uncontrolled charging and controllable charging on the capacitance of the MMC sub-module through the starting resistor, so that the capacitance voltage of the sub-module finally reaches the rated value.
The initial state of the alternating current circuit breaker is disconnected, the initial state of the starting resistor bypass switch is disconnected, the initial state of the half-bridge sub-module in the MMC is locked, and the initial state of the full-bridge sub-module in the MMC is locked.
In the preferred embodiment of the present invention, the network topology of the hybrid dc power transmission system is shown in fig. 2, where U isSFor an equivalent power supply of an alternating current system, AC _ BRK is an alternating current circuit breaker, R is a starting resistor, R _ BRK is a starting resistor bypass switch, and UDCIs a direct current voltage;
as shown in fig. 3, the half-bridge sub-module in the MMC is composed of an IGBT power device T1, an IGBT power device T2 and a capacitor;
the full-bridge submodule in the MMC consists of an IGBT power device T1, an IGBT power device T2, an IGBT power device T3, an IGBT power device T4 and a capacitor; in the figure, point 1 is the voltage positive pole of the full-bridge submodule; point 2 is the voltage negative of the full bridge submodule.
One end of a power switch tube T1 of a full-bridge submodule in the MMC is connected with a voltage anode of the full-bridge submodule, and the other end of the power switch tube T1 is connected with a capacitor anode in the full-bridge submodule;
one end of a power switch tube T2 of the full-bridge submodule in the MMC is connected with the voltage cathode of the full-bridge submodule, and the other end of the power switch tube T2 is connected with the anode of a capacitor in the full-bridge submodule;
one end of a power switch tube T3 of the full-bridge submodule in the MMC is connected with the voltage anode of the full-bridge submodule, and the other end of the power switch tube T3 is connected with the capacitor cathode in the full-bridge submodule;
and one end of a power switch tube T4 of the full-bridge submodule in the MMC is connected with the voltage cathode of the full-bridge submodule, and the other end of the power switch tube T4 is connected with the capacitor cathode in the full-bridge submodule.
Specifically, the step 101 includes:
controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be open, the working state of the half-bridge sub-module in the MMC to be locked, and the working state of the full-bridge sub-module in the MMC to be locked;
and finishing the operation when the capacitor voltage of the half-bridge submodule in the MMC is charged to a first preset voltage and the capacitor voltage of the full-bridge submodule in the MMC is charged to a second preset voltage.
Specifically, the first preset voltage U is determined according to the following formulaF；
Determining the second predetermined voltage U according toH；
In the above formula, UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHThe number of half-bridge sub-modules in the MMC.
In the preferred embodiment of the present invention, as shown in fig. 3, for the half-bridge sub-module in the MMC, the charging can be performed only when the charging current direction is positive, and for the full-bridge sub-module in the MMC, the charging can be performed regardless of whether the charging current direction is positive or negative; therefore, after the MMC is charged uncontrollably, the capacitance voltage of the full-bridge submodule in the MMC is twice the capacitance voltage of the half-bridge submodule in the MMC, and the capacitance voltage of the full-bridge submodule in the MMC and the capacitance voltage of the half-bridge submodule in the MMCThe sum of the two is the peak value U of the equivalent power line voltage of the alternating current systemMNamely:
UF×2NF+UH×NH＝UM
UF＝2UH
obtaining by solution:
further, the step 102 includes:
step a, carrying out voltage-sharing control charging on the MMC until the capacitor voltage of a half-bridge submodule and the capacitor voltage of a full-bridge submodule in the MMC reach a third preset voltage;
b, half-bridging the full-bridge sub-module of the MMC until power switch tubes T4 of the full-bridge sub-module in the MMC are conducted;
c, performing integral alternate conduction charging on the MMC until the capacitance voltage of the half-bridge sub-module and the capacitance voltage of the full-bridge sub-module in the MMC both reach the starting rated voltage of the MMC;
and one end of a power switch tube T4 of the full-bridge submodule in the MMC is connected with the voltage cathode of the full-bridge submodule, and the other end of the power switch tube T4 is connected with the capacitor cathode in the full-bridge submodule.
Specifically, the step a includes:
step 1: initializing the MMC to carry out voltage-sharing control charging at the time t being 0;
step 2: controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be open, and the working state of the half-bridge sub-module in the MMC to be locked;
and step 3: selecting N among all full-bridge submodules of the MMC1A full bridge submodule, and controls said N1Full bridge submoduleA bypass, and locking the rest full-bridge sub-modules;
and 4, step 4: judging whether the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a third preset voltage or not, if so, ending the operation; otherwise, let t be t +1, and return to step 3.
Further, the step 3 comprises:
the number of bypassed full-bridge submodules N is determined as follows1：
In the formula of UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHThe number of half-bridge sub-modules in the MMC is shown; u is a third preset voltage;
in the preferred embodiment of the present invention, the full-bridge sub-module capacitor voltage in the MMC is equal to the full-bridge sub-module capacitor voltage in the MMC, and if the third preset voltage is U, U needs to satisfy:
UF＜U＜UC
in the above formula, UCThe starting rated voltage of the MMC.
Then there are:
U×2(NF-N1)+U×NH＝UM
obtaining by solution:
arranging the full-bridge sub-modules in the MMC in descending order according to the capacitance voltage of the full-bridge sub-modules in the MMC, and selecting the front N in the sequence1A full bridge submodule;
in the preferred embodiment of the present invention, if there are X bridge arms, then each bridge arm is selected
A full bridge sub-module bypass.
Specifically, the step b includes:
controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be closed, the working state of the half-bridge sub-module in the MMC to be locked, and the working state of the full-bridge sub-module in the MMC to be locked;
the operation is finished when the power switch tubes T4 of the full-bridge sub-module in the MMC are all conductive.
In the preferred embodiment of the present invention, after the half-bridge sub-module capacitor voltage in the MMC and the full-bridge sub-module capacitor voltage in the MMC reach U (third preset voltage) at the same time, firstly, N1 bypassed full-bridge sub-modules are switched to the locked state again, and then the power switch tube T4 of the full-bridge sub-module in the MMC is turned on (as shown in fig. 3, the power switch tube T4 of the full-bridge sub-module in the MMC is an IGBT power switch device having a lower corner in the full-bridge sub-module), at this time, the half-bridge sub-module in the MMC and the full-bridge sub-module in the MMC have the same characteristics, and at this time, half.
Specifically, the step c includes:
and 4, step 4: initializing the MMC to carry out integral alternate conduction charging at the moment m being 0;
and 5: controlling the working state of the alternating current circuit breaker to be closed and the working state of the starting resistor bypass switch to be closed;
step 6: selecting N among all sub-modules of the MMC2A sub-module and controls the N2A sub-module bypass, and the other sub-modules are locked;
and 7: judging whether the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC both reach the starting rated voltage of the MMC, if so, ending the operation; otherwise, let m be m +1, and return to step 6.
Further, the step 6 comprises:
the number of bypassed submodules N is determined as follows2：
In the formula of UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHFor the number of half-bridge submodules, U, in MMCCThe starting rated voltage value of the modular multilevel converter is obtained;
according to the capacitance voltage of the MMC neutron modules, arranging the MMC neutron modules in a descending order, and selecting the front N in the sequence2A sub-module; the MMC neutron module comprises a full-bridge submodule and a half-bridge submodule in the MMC;
in the preferred embodiment of the present invention, if there are X bridge arms, then each bridge arm is selected
The sub-module bypasses.
In the preferred embodiment of the present invention, the start-up control operation of the MMC in the hybrid dc power transmission system is shown in table one:
The invention provides a starting system of MMC in a mixed direct-current power transmission system, wherein the mixed direct-current power transmission system consists of an alternating-current system equivalent power supply, an alternating-current circuit breaker, a starting resistor and the MMC which are sequentially connected, wherein two ends of the starting resistor are connected with a starting resistor bypass switch in parallel, the MMC consists of a half-bridge submodule and a full-bridge submodule, and as shown in figure 4, the system comprises:
the uncontrolled charging module is used for uncontrolled charging the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a first preset voltage and a second preset voltage respectively;
the controllable charging module is used for controllably charging the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach the starting rated voltage of the MMC;
the initial state of the alternating current circuit breaker is disconnected, the initial state of the starting resistor bypass switch is disconnected, the initial state of the half-bridge sub-module in the MMC is locked, and the initial state of the full-bridge sub-module in the MMC is locked.
Specifically, the uncontrolled charging module is configured to:
controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be open, the working state of the half-bridge sub-module in the MMC to be locked, and the working state of the full-bridge sub-module in the MMC to be locked;
and finishing the operation when the capacitor voltage of the half-bridge submodule in the MMC is charged to a first preset voltage and the capacitor voltage of the full-bridge submodule in the MMC is charged to a second preset voltage.
Specifically, the first preset voltage U is determined according to the following formulaF；
Determining the second predetermined voltage U according toH；
In the above formula, UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHThe number of half-bridge sub-modules in the MMC.
Specifically, the controllable charging module includes:
the voltage-sharing control charging unit is used for carrying out voltage-sharing control charging on the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a third preset voltage;
the full-bridge submodule half-bridge unit is used for performing full-bridge submodule half-bridge on the MMC until power switch tubes T4 of the full-bridge submodule in the MMC are all conducted;
the integral alternate conducting charging unit is used for carrying out integral alternate conducting charging on the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC both reach the starting rated voltage of the MMC;
and one end of a power switch tube T4 of the full-bridge submodule in the MMC is connected with the voltage cathode of the full-bridge submodule, and the other end of the power switch tube T4 is connected with the capacitor cathode in the full-bridge submodule.
Specifically, the voltage-sharing control charging unit is configured to:
step 1: initializing the MMC to carry out voltage-sharing control charging at the time t being 0;
step 2: controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be open, and the working state of the half-bridge sub-module in the MMC to be locked;
and step 3: selecting N among all full-bridge submodules of the MMC1A full bridge submodule, and controls said N1Bypassing the full-bridge sub-modules, and locking the rest full-bridge sub-modules;
and 4, step 4: judging whether the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a third preset voltage or not, if so, ending the operation; otherwise, let t be t +1, and return to step 3.
Specifically, the step 3 includes:
the number of bypassed full-bridge submodules N is determined as follows1：
In the formula of UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHThe number of half-bridge sub-modules in the MMC is shown; u is a third preset voltage;
arranging the full-bridge sub-modules in the MMC in descending order according to the capacitance voltage of the full-bridge sub-modules in the MMC, and selecting the front N in the sequence1A full bridge submodule.
Specifically, the full-bridge submodule half-bridge unit is configured to:
controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be closed, the working state of the half-bridge sub-module in the MMC to be locked, and the working state of the full-bridge sub-module in the MMC to be locked;
and finishing the operation when the power switch tubes T of the full-bridge submodule in the MMC are all conducted.
Specifically, the whole alternately conducting charging units are used for:
and 4, step 4: initializing the MMC to carry out integral alternate conduction charging at the moment m being 0;
and 5: controlling the working state of the alternating current circuit breaker to be closed and the working state of the starting resistor bypass switch to be closed;
step 6: selecting N among all sub-modules of the MMC2A sub-module and controls the N2A sub-module bypass, and the other sub-modules are locked;
and 7: judging whether the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC both reach the starting rated voltage of the MMC, if so, ending the operation; otherwise, let m be m +1, and return to step 6.
Specifically, the step 6 includes:
the number of bypassed submodules N is determined as follows2：
In the formula of UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHFor the number of half-bridge submodules, U, in MMCCThe starting rated voltage value of the modular multilevel converter is obtained;
according to the capacitance voltage of the MMC neutron modules, arranging the MMC neutron modules in a descending order, and selecting the front N in the sequence2A sub-module; wherein, the MMC neutron module comprises a full-bridge submodule and a half-bridge submodule in the MMC。
As will be appreciated by one skilled in the art, 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 flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams 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 solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (18)
1. The utility model provides a start-up method of MMC among mixed direct current transmission system, mixed direct current transmission system comprises alternating current system equivalent power, alternating current circuit breaker, starting resistance and the MMC that connects gradually, the parallelly connected starting resistance bypass switch in starting resistance both ends, the MMC comprises half-bridge submodule piece and full-bridge submodule piece, its characterized in that, the method includes:
uncontrolled charging is carried out on the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a first preset voltage and a second preset voltage respectively;
controllably charging the MMC until the capacitance voltage of a half-bridge submodule and the capacitance voltage of a full-bridge submodule in the MMC both reach the starting rated voltage of the MMC;
the initial state of the alternating current circuit breaker is disconnected, the initial state of the starting resistor bypass switch is disconnected, the initial state of the half-bridge sub-module in the MMC is locked, and the initial state of the full-bridge sub-module in the MMC is locked.
2. The method of claim 1, wherein the uncontrollable charging of the MMC until the capacitive voltage of the half-bridge sub-module and the capacitive voltage of the full-bridge sub-module in the MMC reach a first preset voltage and a second preset voltage, respectively, comprises:
controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be open, the working state of the half-bridge sub-module in the MMC to be locked, and the working state of the full-bridge sub-module in the MMC to be locked;
and finishing the operation when the capacitor voltage of the half-bridge submodule in the MMC is charged to a first preset voltage and the capacitor voltage of the full-bridge submodule in the MMC is charged to a second preset voltage.
3. The method of claim 1, wherein the first predetermined voltage U is determined as followsF；
Determining the second predetermined voltage U according toH；
In the above formula, UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHThe number of half-bridge sub-modules in the MMC.
4. The method of claim 1, wherein controllably charging the MMC until both the capacitive voltage of the half-bridge sub-module and the capacitive voltage of the full-bridge sub-module in the MMC reach a start-up voltage rating of the MMC comprises:
carrying out voltage-sharing control charging on the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a third preset voltage;
carrying out half-bridge transformation on the full-bridge submodule until power switch tubes T4 of the full-bridge submodule in the MMC are all conducted;
the MMC is subjected to integral alternate conduction charging until the capacitance voltage of a half-bridge submodule and the capacitance voltage of a full-bridge submodule in the MMC reach the starting rated voltage of the MMC;
one end of a power switch tube T4 of the full-bridge submodule in the MMC is connected with the voltage negative electrode of the full-bridge submodule, and the other end of the power switch tube T4 is connected with the negative electrode of a capacitor in the full-bridge submodule.
5. The method of claim 4, wherein the step of voltage-sharing charging the MMC until the capacitor voltage of the half-bridge submodule and the capacitor voltage of the full-bridge submodule in the MMC reach a third preset voltage comprises:
step 1: initializing the MMC to carry out voltage-sharing control charging at the time t being 0;
step 2: controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be open, and the working state of the half-bridge sub-module in the MMC to be locked;
and step 3: selecting N among all full-bridge submodules of the MMC1A full bridge submodule, and controls said N1Bypassing the full-bridge sub-modules, and locking the rest full-bridge sub-modules;
and 4, step 4: judging whether the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a third preset voltage or not, if so, ending the operation; otherwise, let t be t +1, and return to step 3.
6. The method of claim 5, wherein step 3 comprises:
the number of bypassed full-bridge submodules N is determined as follows1：
In the formula of UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHThe number of half-bridge sub-modules in the MMC is shown; u is a third preset voltage;
arranging the full-bridge sub-modules in the MMC in descending order according to the capacitance voltage of the full-bridge sub-modules in the MMC, and selecting the front N in the sequence1A full bridge submodule.
7. The method of claim 4, wherein the half-bridging the full-bridge sub-module of the MMC until the power switch transistors T4 of the full-bridge sub-module in the MMC are all turned on comprises:
controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be closed, the working state of the half-bridge sub-module in the MMC to be locked, and the working state of the full-bridge sub-module in the MMC to be locked;
the operation is finished when the power switch tubes T4 of the full-bridge sub-module in the MMC are all conductive.
8. The method of claim 4, wherein the globally rotating conduction charging of the MMC until the capacitive voltage of the half-bridge sub-module and the capacitive voltage of the full-bridge sub-module in the MMC both reach a start-up voltage rating of the MMC, comprises:
and 4, step 4: initializing the MMC to carry out integral alternate conduction charging at the moment m being 0;
and 5: controlling the working state of the alternating current circuit breaker to be closed and the working state of the starting resistor bypass switch to be closed;
step 6: selecting N among all sub-modules of the MMC2A sub-module and controls the N2A sub-module bypass, and the other sub-modules are locked;
and 7: judging whether the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC both reach the starting rated voltage of the MMC, if so, ending the operation; otherwise, let m be m +1, and return to step 6.
9. The method of claim 8, wherein the step 6 comprises:
the number of bypassed submodules N is determined as follows2：
In the formula of UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHFor the number of half-bridge submodules, U, in MMCCThe starting rated voltage value of the modular multilevel converter is obtained;
according to the capacitance voltage of the MMC neutron modules, arranging the MMC neutron modules in a descending order, and selecting the front N in the sequence2A sub-module; wherein, MMC neutron module includes full-bridge submodule piece and half-bridge submodule piece among the MMC.
10. The utility model provides a start-up system of MMC among mixed direct current transmission system, mixed direct current transmission system comprises alternating current system equivalent power, alternating current circuit breaker, starting resistance and the MMC that connect gradually, the parallelly connected starting resistance bypass switch in starting resistance both ends, the MMC comprises half-bridge submodule piece and full-bridge submodule piece, its characterized in that, the system includes:
the uncontrolled charging module is used for uncontrolled charging the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a first preset voltage and a second preset voltage respectively;
the controllable charging module is used for controllably charging the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach the starting rated voltage of the MMC;
the initial state of the alternating current circuit breaker is disconnected, the initial state of the starting resistor bypass switch is disconnected, the initial state of the half-bridge sub-module in the MMC is locked, and the initial state of the full-bridge sub-module in the MMC is locked.
11. The system of claim 10, wherein the uncontrolled charging module is to:
controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be open, the working state of the half-bridge sub-module in the MMC to be locked, and the working state of the full-bridge sub-module in the MMC to be locked;
and finishing the operation when the capacitor voltage of the half-bridge submodule in the MMC is charged to a first preset voltage and the capacitor voltage of the full-bridge submodule in the MMC is charged to a second preset voltage.
12. The system of claim 11, wherein the first predetermined voltage U is determined as followsF；
Determining the second predetermined voltage U according toH；
In the above formula, UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHThe number of half-bridge sub-modules in the MMC.
13. The system of claim 10, wherein the controllable charging module comprises:
the voltage-sharing control charging unit is used for carrying out voltage-sharing control charging on the MMC until the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a third preset voltage;
carrying out half-bridge transformation on the full-bridge submodule until power switch tubes T4 of the full-bridge submodule in the MMC are all conducted;
the MMC is subjected to integral alternate conduction charging until the capacitance voltage of a half-bridge submodule and the capacitance voltage of a full-bridge submodule in the MMC reach the starting rated voltage of the MMC;
and one end of a power switch tube T4 of the full-bridge submodule in the MMC is connected with the voltage cathode of the full-bridge submodule, and the other end of the power switch tube T4 is connected with the capacitor cathode in the full-bridge submodule.
14. The system of claim 13, wherein the voltage sharing control charging unit is to:
step 1: initializing the MMC to carry out voltage-sharing control charging at the time t being 0;
step 2: controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be open, and the working state of the half-bridge sub-module in the MMC to be locked;
and step 3: selecting N among all full-bridge submodules of the MMC1A full bridge submodule, and controls said N1Bypassing the full-bridge sub-modules, and locking the rest full-bridge sub-modules;
and 4, step 4: judging whether the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC reach a third preset voltage or not, if so, ending the operation; otherwise, let t be t +1, and return to step 3.
15. The system of claim 14, wherein step 3 comprises:
the number of bypassed full-bridge submodules N is determined as follows1：
In the formula of UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHThe number of half-bridge sub-modules in the MMC is shown; u is a third preset voltage;
arranging the full-bridge sub-modules in the MMC in descending order according to the capacitance voltage of the full-bridge sub-modules in the MMC, and selecting the front N in the sequence1A full bridge submodule.
16. The system of claim 13, wherein the full-bridge sub-module half-bridges a unit to:
controlling the working state of the alternating current circuit breaker to be closed, the working state of the starting resistor bypass switch to be closed, the working state of the half-bridge sub-module in the MMC to be locked, and the working state of the full-bridge sub-module in the MMC to be locked;
the operation is finished when the power switch tubes T4 of the full-bridge sub-module in the MMC are all conductive.
17. The system of claim 13, wherein the integral alternately conducting charging units are configured to:
and 4, step 4: initializing the MMC to carry out integral alternate conduction charging at the moment m being 0;
and 5: controlling the working state of the alternating current circuit breaker to be closed and the working state of the starting resistor bypass switch to be closed;
step 6: selecting N among all sub-modules of the MMC2A sub-module and controls the N2A sub-module bypass, and the other sub-modules are locked;
and 7: judging whether the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in the MMC both reach the starting rated voltage of the MMC, if so, ending the operation; otherwise, let m be m +1, and return to step 6.
18. The system of claim 17, wherein the step 6 comprises:
the number of bypassed submodules N is determined as follows2：
In the formula of UMThe voltage peak value of an equivalent power line of the alternating current system; n is a radical ofFThe number of full-bridge sub-modules in the MMC is set; n is a radical ofHFor the number of half-bridge submodules, U, in MMCCThe starting rated voltage value of the modular multilevel converter is obtained;
according to the capacitance voltage of the MMC neutron modules, arranging the MMC neutron modules in a descending order, and selecting the front N in the sequence2A sub-module; wherein, the MMC neutron module comprises a full-bridge submodule and a full-bridge submodule in the MMCAnd half-bridge sub-modules.
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| CN201910563520.6A CN112152438A (en) | 2019-06-26 | 2019-06-26 | Method and system for starting MMC (Modular multilevel converter) in hybrid direct-current transmission system |
| PCT/CN2019/104256 WO2020258512A1 (en) | 2019-06-26 | 2019-09-03 | Method and system for starting mmc in hybrid direct current transmission system |
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| CN113595075A (en) * | 2021-08-04 | 2021-11-02 | 全球能源互联网研究院有限公司 | Starting method and device of low-frequency power transmission system |
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| CN105119508B (en) * | 2015-09-18 | 2017-09-22 | 山东建筑大学 | Full-bridge and the modularization multi-level converter and startup method of half-bridge submodule series-parallel connection |
| CN106787087A (en) * | 2017-01-09 | 2017-05-31 | 许继集团有限公司 | Hybrid MMC sequences pressure charging method, startup method and device |
| CN107681877B (en) * | 2017-10-12 | 2019-06-11 | 华中科技大学 | A kind of mixed type MMC starting method of the submodule containing full-bridge |
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