CN113178884B - Pre-charging method and system of hybrid direct current converter - Google Patents

Pre-charging method and system of hybrid direct current converter Download PDF

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CN113178884B
CN113178884B CN202110340879.4A CN202110340879A CN113178884B CN 113178884 B CN113178884 B CN 113178884B CN 202110340879 A CN202110340879 A CN 202110340879A CN 113178884 B CN113178884 B CN 113178884B
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voltage
module
sub
output unit
string
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CN113178884A (en
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时珊珊
蔡旭
魏新迟
方梓熙
方陈
杨建平
沈冰
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Shanghai Jiaotong University
State Grid Shanghai Electric Power Co Ltd
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Shanghai Jiaotong University
State Grid Shanghai Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/02—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries for charging batteries from ac mains by converters
    • H02J7/04—Regulation of charging current or voltage
    • H02J7/06—Regulation of charging current or voltage using discharge tubes or semiconductor devices
    • 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
    • H02M1/36—Means for starting or stopping converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2207/00—Indexing scheme relating to details of circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J2207/20—Charging or discharging characterised by the power electronics converter
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/28—The renewable source being wind energy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Power Engineering (AREA)
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Abstract

The invention provides a pre-charging method and a system of a hybrid direct current converter, which comprises the following steps: establishing a circulating current voltage for an alternating current output unit and a high-voltage sub-module string of the hybrid direct current converter; when the circulating current voltage and the capacitor voltage of the alternating current output unit and the high-voltage sub-module string are stable, circulating current control voltage is generated, and the sub-module capacitor voltage of the alternating current output unit and the high-voltage sub-module string is balanced; and when the sub-module capacitor voltage of the alternating current output unit and the sub-module capacitor voltage of the high-voltage sub-module string are balanced, generating direct current control voltage, and ending the pre-charging when the sub-module capacitor voltage of the alternating current output unit and the sub-module capacitor voltage of the high-voltage sub-module string continuously rises to rated voltage. The voltage-sharing method can slowly realize the voltage-sharing of the internal module of the auxiliary converter; after voltage sharing of the sub-modules in the auxiliary converter is completed, current on the direct current side can be controlled to charge in a near step, and finally all the sub-modules can reach rated values.

Description

Pre-charging method and system of hybrid direct current converter
Technical Field
The invention relates to wind power generation, flexible direct current transmission and power electronic technologies in the field of power systems, in particular to a pre-charging method and a pre-charging system for a hybrid offshore wind field direct current converter constructed by the same submodule.
Background
Modular Multilevel Converters (MMC) have the characteristics of high voltage level, high efficiency and small harmonic, and become the most competitive converter topology in high-voltage direct-current power transmission. However, the MMC is huge in size and weight, so that the construction cost is high when the converter station is constructed on the sea.
The hybrid direct current converter is formed by mixing a diode rectifier and a fully-controlled auxiliary converter, wherein the diode rectifier is used for transmitting active power of the wind power plant, the fully-controlled auxiliary converter is used for realizing black start of the wind power plant, compensating reactive power and harmonic power in a system in a steady state, and providing stable wind power plant grid voltage for phase-locked synchronization of the wind turbine generator. Compared with the traditional MMC scheme, the number of the submodules is greatly reduced, the construction cost is greatly reduced, the size and the weight are also obviously reduced, and the modular MMC is very suitable for offshore direct current transmission.
In the existing hybrid dc converter, the auxiliary converter is still a modular multilevel topology, and can be started only by precharging, but the technology for effectively precharging the auxiliary converter is lacking in the present field so as to meet the requirement of the offshore dc transmission.
Through search, the following results are found:
the invention discloses a mixed type marine wind field direct current converter with the application number of 201711288924.6, and provides a topological structure of the marine wind field direct current converter, compared with an MMC converter with a complete voltage grade, the structure can greatly reduce the number of submodules and IGBTs, reduce the system cost, and can actively establish wind field intranet voltage in the starting stage of a wind field, provide starting power of the wind field and realize black starting of the wind field. However, this structure has not been studied on how to perform the precharge and start-up when its auxiliary converter is constructed using the same seed module.
In summary, although the offshore wind farm dc converter has been researched and developed in a great deal in the art, a technology for precharging an auxiliary converter thereof is still lacking, so that the application of the offshore wind farm dc converter is limited.
At present, no explanation or report of the similar technology of the invention is found, and similar data at home and abroad are not collected.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a pre-charging method and a pre-charging system for a hybrid direct current converter under the same submodule construction condition.
According to an aspect of the present invention, there is provided a precharge method of a hybrid dc converter, including:
establishing a circulating current voltage for an alternating current output unit and a high-voltage sub-module string of the hybrid direct current converter;
when the capacitor voltage of the alternating current output unit and the high-voltage sub-module string is stable, generating a circulation control voltage, and balancing the sub-module capacitor voltage of the alternating current output unit and the high-voltage sub-module string;
and when the sub-module capacitor voltage of the alternating current output unit and the sub-module capacitor voltage of the high-voltage sub-module string are balanced, generating direct current control voltage, and ending the pre-charging when the sub-module capacitor voltage of the alternating current output unit and the sub-module capacitor voltage of the high-voltage sub-module string continuously rises to rated voltage.
Preferably, the ac output unit of the pair of hybrid dc converters and the high-voltage sub-module string establish a circulating current voltage, and the circulating current voltage includes:
the control signal of the alternating current output unit comprises: ac voltage component U 2 And a circulating current voltage u cir (ii) a The control signal of the high-voltage sub-module string comprises: DC voltage component U 1 Circulating current voltage u cir Circulating current control voltage delta u cir And a DC control voltage Deltau dc (ii) a The modulation voltage of the high-voltage submodule string and the alternating current output unit is as follows:
Figure GDA0003920039790000021
wherein m is u For the modulation voltage of the high-voltage sub-module string, m l Is the modulation voltage of the AC output unit;
DC voltage component U 1 Indicating the direct current carried by the auxiliary converter partVoltage component, DC voltage component U 1 Gradually changes from V in the process of continuously equalizing the voltage of the capacitor dc1 Change to V dc2 ：
Figure GDA0003920039790000022
Wherein, V dc1 End value of the DC voltage component, V, for the submodule string dc2 End value of the DC voltage component borne by the AC output unit, N 1 、N 2 The number of the modules of the high-voltage sub-module string and the number of the bridge arm modules of the alternating current output unit, U dc Is a DC bus voltage, U 2 Is U in size dc -U 1 (U dc Minus U 1 )；
And then establishing and obtaining the circulating current voltage of the alternating current output unit and the high-voltage sub-module string.
Preferably, the method of generating a circulating current control voltage includes:
subtracting the module capacitor average voltage of the high-voltage sub-module string from the module capacitor average voltage of the alternating current output unit, and generating a circulating current instruction amplitude value through a PI (proportional integral) controller;
multiplying the circulating current instruction amplitude by a standard sinusoidal signal to obtain a circulating current instruction;
and subtracting the actual circulating current from the circulating current instruction, and obtaining a circulating current control voltage through a proportional controller.
Preferably, the method for generating a dc control voltage includes:
subtracting the module capacitor average voltage of the high-voltage sub-module string from the module voltage instruction value of the high-voltage sub-module string, and obtaining a direct current instruction value through a PI (proportional integral) controller;
and subtracting the actual direct current value from the direct current instruction value, and obtaining direct current control voltage through a PI (proportional integral) controller.
Preferably, the method for judging the sub-module capacitor voltage balance between the alternating current output unit and the high-voltage sub-module string comprises the following steps:
Figure GDA0003920039790000031
wherein the content of the first and second substances,
Figure GDA0003920039790000032
is the module capacitor average voltage of the high voltage sub-module string,
Figure GDA0003920039790000033
is the average voltage of the module capacitor of the AC output unit, Δ u set Is a voltage error judgment value.
Preferably, the method for judging that the sub-module capacitor voltage of the alternating current output unit and the high-voltage sub-module string rises to the rated voltage comprises the following steps:
Figure GDA0003920039790000034
Figure GDA0003920039790000035
wherein the content of the first and second substances,
Figure GDA0003920039790000036
is the module capacitor average voltage of the high voltage sub-module string,
Figure GDA0003920039790000037
is the average voltage of the module capacitor of the AC output unit, u m1_ref Is a module voltage command value, u, of a high voltage sub-module string m2_ref Is a module voltage command value, deltau, of the AC output unit set Is a voltage error determination value.
According to another aspect of the present invention, there is provided a precharge system of a hybrid dc converter, including:
the circulation current control module generates circulation control voltage after the circulation voltage and the capacitance voltage of the alternating current output unit and the high-voltage sub-module string are stable, and balances the sub-module capacitance voltage of the alternating current output unit and the high-voltage sub-module string;
and the direct current control module generates direct current control voltage after the alternating current output unit and the sub-module capacitor voltage of the high-voltage sub-module string are balanced, so that the alternating current output unit and the sub-module capacitor voltage of the high-voltage sub-module string continuously rise to rated voltage, and the pre-charging is finished.
Preferably, the current circulating control module includes:
the circulating current instruction amplitude generation module subtracts the module capacitor average voltage of the high-voltage sub-module string from the module capacitor average voltage of the alternating current output unit and generates a circulating current instruction amplitude through the PI controller;
the circulating current instruction generating module is used for multiplying the circulating current instruction amplitude by a standard sinusoidal signal to obtain a circulating current instruction;
and the circulating current control voltage generation module subtracts the circulating current instruction from the actual circulating current and obtains a circulating current control voltage through the proportional controller.
Preferably, the dc current control module includes:
the direct current instruction generation module subtracts the module capacitor average voltage of the high-voltage sub-module string from the module voltage instruction value of the high-voltage sub-module string to obtain a direct current instruction value through a PI (proportional integral) controller;
and the direct current control voltage generation module subtracts the direct current instruction value from the actual direct current value and obtains direct current control voltage through the PI controller.
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following beneficial effects:
1. the invention provides a practical and effective pre-charging scheme suitable for the topology of an auxiliary current converter aiming at the auxiliary current converter in the hybrid direct current converter, and the scheme can balance the module capacitance voltage difference caused by the asymmetric topology of the auxiliary current converter, so that the whole current converter can be constructed by using the same seed module.
2. The pre-charging method and the pre-charging system for the hybrid direct current converter, provided by the invention, aim at the problem that when the same submodule is adopted for construction, the voltage difference of the submodules of the two parts is 3 times after the topology of the auxiliary converter is subjected to uncontrolled rectification charging, and can slowly realize the voltage sharing of the internal module of the auxiliary converter.
3. According to the pre-charging method and system for the hybrid direct current converter, provided by the invention, after voltage sharing of the sub-modules in the auxiliary converter is completed, the direct current side current can be controlled to be charged in one step, and finally all the sub-modules can reach the rated value.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
fig. 1 is a flowchart illustrating a precharge method of a hybrid dc converter according to an embodiment of the present invention;
fig. 2 is a topology of a hybrid dc converter according to a precharge method of the hybrid dc converter according to an embodiment of the present invention;
fig. 3 is an auxiliary converter topology according to a precharge method of a hybrid dc converter according to a preferred embodiment of the present invention;
fig. 4 is a control block diagram of a precharge method of a hybrid dc converter according to a preferred embodiment of the present invention;
fig. 5 is a flowchart of a precharge method of a hybrid dc converter according to a preferred embodiment of the present invention;
fig. 6 is a voltage waveform diagram of sub-module capacitors simulated by the pre-charging method of the hybrid dc converter according to a preferred embodiment of the present invention;
fig. 7 is a diagram illustrating a dc side current waveform simulated by a precharge method of a hybrid dc converter according to a preferred embodiment of the present invention;
fig. 8 is a schematic diagram illustrating components of a pre-charging system of a hybrid dc converter according to an embodiment of the present invention.
Detailed Description
The following examples illustrate the invention in detail: the embodiment is implemented on the premise of the technical scheme of the invention, and a detailed implementation mode and a specific operation process are given. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention.
Fig. 1 is a flowchart of a precharge method of a hybrid dc converter according to an embodiment of the present invention.
As shown in fig. 1, the precharge method of the hybrid dc converter provided in this embodiment may include the following steps:
s100, establishing a circulating current voltage for an alternating current output unit and a high-voltage sub-module string of the hybrid direct current converter;
s200, delaying a set time after establishing the circulating current voltage, generating a circulating current control voltage after stabilizing the capacitance voltages of the alternating current output unit and the high-voltage sub-module string, and balancing the sub-module capacitance voltages of the alternating current output unit and the high-voltage sub-module string; s100, when the circulating current voltage is built, the capacitor of the high-voltage sub-module is also charged, so that the voltage of the capacitor of the high-voltage sub-module changes. And after the circulating current voltage is stable, the capacitor voltage of the high-voltage sub-module is also stable.
And S300, after the sub-module capacitor voltages of the alternating current output unit and the high-voltage sub-module string are balanced, generating direct current control voltage, and finishing pre-charging when the sub-module capacitor voltages of the alternating current output unit and the high-voltage sub-module string continuously rise to rated voltage.
In S100 of this embodiment, as a preferred embodiment, establishing a circulating current voltage between the ac output unit and the high-voltage sub-module string of the hybrid dc-to-dc converter may include the following steps:
the control signal of the alternating current output unit comprises: ac voltage component U 2 And a circulating current voltage u cir (ii) a The control signals of the high-voltage submodule string comprise: DC voltage component U 1 Circulating current voltage u cir Circulating current control voltage delta u cir And a DC control voltageΔu dc (ii) a The modulation voltage of the high-voltage submodule string and the alternating current output unit is as follows:
Figure GDA0003920039790000051
wherein m is u For the modulation voltage of the high-voltage sub-module string, m l Is the modulation voltage of the AC output unit;
DC voltage component U 1 Representing a DC voltage component, U, borne by the auxiliary converter portion 1 Gradually changes from V in the process of continuously equalizing the voltage of the capacitor dc1 Change to V dc2 ：
Figure GDA0003920039790000061
Wherein, V dc1 End value of the DC voltage component, V, for the submodule string dc2 End value of the DC voltage component borne by the AC output unit, N 1 、N 2 The number of modules of the high-voltage sub-module string and the number of bridge arm modules of the alternating-current output unit are U dc Is a DC bus voltage, U 2 Is U in size dc -U 1 (U dc Minus U 1 )；
And then, the circulating current voltage of the alternating current output unit and the high-voltage sub-module string is established.
In S200 of this embodiment, as a preferred embodiment, the method for generating the circulating current control voltage may include the following steps:
s201, subtracting the module capacitor average voltage of the high-voltage sub-module string from the module capacitor average voltage of the alternating current output unit, and generating a circulating current instruction amplitude value through a PI (proportional integral) controller;
s202, multiplying the amplitude of the circulation current instruction by a standard sinusoidal signal to obtain a circulation current instruction;
and S203, subtracting the actual circulation from the circulation current command, and obtaining circulation control voltage through a proportional controller.
In S300 of this embodiment, as a preferred embodiment, the method for generating the dc control voltage may include the following steps:
s301, subtracting the module capacitor average voltage of the high-voltage sub-module string from the module voltage instruction value of the high-voltage sub-module string, and obtaining a direct current instruction value through a PI (proportional integral) controller;
and S302, subtracting the actual direct current value from the direct current instruction value, and obtaining direct current control voltage through the PI controller.
In S300 of this embodiment, as a preferred embodiment, the method for determining the sub-module capacitor voltage balance between the ac output unit and the high-voltage sub-module string may be:
Figure GDA0003920039790000062
wherein the content of the first and second substances,
Figure GDA0003920039790000063
is the module capacitor average voltage of the high voltage sub-module string,
Figure GDA0003920039790000064
is the average voltage of the module capacitor of the AC output unit, Δ u set An artificially set voltage error determination value can be adopted.
In S300 of this embodiment, as a preferred embodiment, the method for determining that the sub-module capacitor voltage of the ac output unit and the high-voltage sub-module string rises to the rated voltage may be:
Figure GDA0003920039790000065
Figure GDA0003920039790000066
wherein the content of the first and second substances,
Figure GDA0003920039790000071
is the module capacitor average voltage of the high voltage sub-module string,
Figure GDA0003920039790000072
is the average voltage of the module capacitor of the AC output unit, u m1_ref Is a module voltage command value, u, of a high voltage sub-module string m2_ref Is a module voltage command value, deltau, of the AC output unit set Is a voltage error determination value.
Fig. 2 is a flowchart of a precharge method of a hybrid dc converter according to a preferred embodiment of the present invention.
As shown in fig. 2, the precharge method of the hybrid dc-to-ac converter provided in this embodiment may include the following steps:
step 1, after an uncontrolled rectification stage is finished, firstly, controlling an alternating current output unit and a high-voltage submodule string to slowly establish a circulating current voltage to prepare for circulating current exchange power;
step 2, after the circulation voltage and the capacitor voltage are stable, putting a circulation current control module to generate circulation control voltage, and balancing the sub-module capacitor voltage of the two parts;
step 3, after the capacitor voltages of the sub-modules of the two parts are balanced, the sub-modules are put into a direct current control module to generate direct current control voltage, so that the capacitor voltages of the sub-modules of the two parts are continuously increased, and finally, the pre-charging is finished when the capacitor voltages of the sub-modules of the two parts reach rated values;
and 4, finishing the controllable rectification stage.
The precharge method provided by the preferred embodiment is described in further detail below with reference to the accompanying drawings.
The topology diagram of the offshore wind farm dc-out system based on the hybrid dc converter is shown in fig. 3, and is composed of a diode rectifier and an auxiliary converter, wherein the part containing sub-modules only has the auxiliary converter, so that the pre-charging of the hybrid dc converter is actually the pre-charging process of the auxiliary converter. The auxiliary converter topology is shown in fig. 4 and comprises three parts: a resonant branch 101, a high-voltage sub-module string 102 and an alternating current output unit 103. After a stable dc bus voltage is established in the onshore converter station, switch T4 in fig. 2 is closed to assist the converter to perform uncontrolled rectifying charging. In the process, the capacitance of the resonance branch circuit is charged to a rated value, the capacitance of the sub-module is partially charged, and the module capacitance voltage of the sub-module string is three times of the module capacitance voltage of the alternating current output unit.
The precharge control block diagram is shown in fig. 5. The control signal of the ac output unit 103 includes two parts: DC voltage component U 2 And a circulating current voltage u cir (ii) a The control signal for the high voltage sub-module string 102 includes four components: DC voltage component U 1 Circulating current voltage u cir Circulating current control voltage delta u cir And a DC control voltage Deltau dc . Modulation voltage m of high-voltage submodule string 102 and alternating current output unit 103 u And m l The calculation formula is as follows:
Figure GDA0003920039790000073
DC voltage component U 1 Representing a DC voltage component borne by the auxiliary converter part, the DC voltage component U 1 Gradually changes from V in the process of continuously equalizing the voltage of the capacitor dc1 Change to V dc2 The calculation formula is as follows:
Figure GDA0003920039790000081
wherein N is 1 、N 2 The number of the sub-module string modules and the number of the alternating current output unit bridge arm modules are U dc Is a DC bus voltage, U 2 Is U in size ddc -U 1 (U dc Minus U 1 )。
Circulating current control voltage delta u cir Generated by a circulating current control module, comprising:
module capacitor average voltage of high voltage sub-module string
Figure GDA0003920039790000082
Module for AC output unitAverage voltage of block capacitor
Figure GDA0003920039790000083
Subtracting, generating a circulating current instruction amplitude value through a PI controller, and multiplying the circulating current instruction amplitude value by a standard sine signal to obtain a circulating current instruction
Figure GDA0003920039790000084
And then is circulated with the actual circulation flow i cir Subtracting, and obtaining circulation control voltage delta u through a proportional controller cir . The purpose of this section is to exchange energy between the high voltage sub-module string and the ac output unit by generating a circulating current, so that the unbalanced voltages at the end of the uncontrolled rectifying phase are balanced.
DC control voltage Deltau u dc Generated by a dc current control module, comprising:
voltage instruction value u of module string of high-voltage sub-modules m1_ref Module capacitor average voltage of high-voltage sub-module string
Figure GDA0003920039790000085
Subtracting, and obtaining DC current instruction value via PI controller
Figure GDA0003920039790000086
The command value and the actual DC current i dc Subtracting, and obtaining DC control voltage delta u through PI controller dc . The purpose of this part is to control the absorption of energy from the dc bus so that the sub-modules can be boosted to the rated voltage.
The following is a simulation of the solution provided by the above embodiments of the present invention, and is described with reference to the accompanying drawings.
The high-transformation-ratio AC/DC converter topology is shown in FIG. 2, the voltage of a direct-current bus is 100kV, the inductance of a bridge arm is 10mH, the number of submodules of a series voltage divider is 42, the number of bridge arm modules of an alternating-current output port is 18, the capacitance of the submodules is 10mF, and the rated voltage is 2kV. The pre-charge resistance is 108 Ω; the resonant inductance is 1mH, and the resonant capacitance is 281.4uF.
And (3) constructing a corresponding simulation model in MATLAB/SIMULINK, wherein the simulation result is shown in fig. 6 and 7. 0-0.5S is an uncontrolled rectification stage S1, the module voltages of the two parts have a large difference, and the capacitor voltage of the high-voltage sub-module string module is three times that of the alternating current output unit module; then, a circulation voltage establishing stage S2 is carried out for 0.5-0.8S, and the sub-module capacitor voltage of the two parts is slowly increased at the moment; and 0.8-2S is a circulation power balance stage S3, and at the moment, a circulation current control module is put into the circulation power balance stage, so that the voltages of the sub-module capacitors are gradually equal. The amplitude of the circulating current is limited to 500A, the frequency of the circulating current is 300Hz, and the abscissa of the amplified waveform is 0.01s/div;2-2.8S is a direct current charging stage S4, at this time, the capacitor voltage of the sub-module string is charged to a rated value quickly, and the voltage of the capacitor of the alternating current output unit module rises as well because the circulation control module still plays a role in voltage equalization, and finally all the capacitor voltage reaches the rated value.
Another embodiment of the present invention provides a precharge system for a hybrid dc converter, as shown in fig. 8, the system may include: the device comprises a circulating current control module and a direct current control module;
wherein:
the circulating current control module generates circulating current control voltage after the circulating current voltage and the capacitor voltage of the alternating current output unit and the high-voltage sub-module string are stable, and balances the sub-module capacitor voltage of the alternating current output unit and the high-voltage sub-module string;
and the direct current control module generates direct current control voltage after the alternating current output unit and the sub-module capacitor voltage of the high-voltage sub-module string are balanced, so that the sub-module capacitor voltage of the alternating current output unit and the sub-module capacitor voltage of the high-voltage sub-module string are continuously increased to rated voltage, and the pre-charging is finished.
As a preferred embodiment, the circulating current control module includes:
the circulating current instruction amplitude generation module subtracts the module capacitor average voltage of the high-voltage sub-module string from the module capacitor average voltage of the alternating current output unit and generates a circulating current instruction amplitude through the PI controller;
the circulating current instruction generating module is used for multiplying the circulating current instruction amplitude by the standard sinusoidal signal to obtain a circulating current instruction;
and the circulating current control voltage generation module subtracts the circulating current instruction from the actual circulating current and obtains a circulating current control voltage through the proportional controller.
As a preferred embodiment, the dc current control module includes:
the direct current instruction generation module subtracts the module capacitor average voltage of the high-voltage sub-module string from the module voltage instruction value of the high-voltage sub-module string to obtain a direct current instruction value through a PI (proportional integral) controller;
and the direct current control voltage generation module subtracts the direct current instruction value from the actual direct current value and obtains direct current control voltage through the PI controller.
The precharging method and system for the hybrid direct-current converter provided by the embodiment of the invention provide a practical and effective precharging scheme suitable for the topology of the auxiliary converter aiming at the auxiliary converter in the hybrid direct-current converter, and the scheme can balance the voltage difference of the module capacitor caused by the asymmetric topology of the auxiliary converter, so that the whole converter can be constructed by using the same seed module; aiming at the problem that when the same sub-modules are adopted for construction, after the topology of the auxiliary converter is subjected to uncontrolled rectifying charging, the sub-modules of the two parts have 3 times of voltage difference, and voltage equalization of internal modules of the auxiliary converter can be slowly realized; after voltage sharing of the sub-modules in the auxiliary converter is completed, current on the direct current side can be controlled to charge in a near step, and finally all the sub-modules can reach rated values.
It should be noted that, the steps in the method provided by the present invention may be implemented by using corresponding modules, devices, units, and the like in the system, and those skilled in the art may implement the composition of the system by referring to the technical solution of the method, that is, the embodiment in the method may be understood as a preferred example for constructing the system, and will not be described herein again.
Those skilled in the art will appreciate that, in addition to implementing the system and its various devices provided by the present invention in purely computer readable program code means, the method steps can be fully programmed to implement the same functions by implementing the system and its various devices in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system and various devices thereof provided by the present invention can be regarded as a hardware component, and the devices included in the system and various devices thereof for realizing various functions can also be regarded as structures in the hardware component; means for performing the functions may also be regarded as structures within both software modules and hardware components for performing the methods.
The foregoing description has described specific embodiments of the present invention. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims (5)

1. A pre-charging method for a hybrid DC converter is characterized by comprising the following steps:
establishing a circulating current voltage for an alternating current output unit and a high-voltage sub-module string of the hybrid direct current converter;
when the capacitor voltages of the alternating current output unit and the high-voltage sub-module string are stable, a circulating current control voltage is generated, and the sub-module capacitor voltages of the alternating current output unit and the high-voltage sub-module string are balanced;
when the sub-module capacitor voltage of the alternating current output unit and the sub-module capacitor voltage of the high-voltage sub-module string are balanced, generating direct current control voltage, and ending pre-charging when the sub-module capacitor voltage of the alternating current output unit and the sub-module capacitor voltage of the high-voltage sub-module string continuously rises to rated voltage;
the method for establishing the circulating current voltage for the alternating current output unit and the high-voltage submodule string of the hybrid direct current converter comprises the following steps:
the control signal of the alternating current output unit comprises: ac voltage component U 2 And a circulating current voltage u cir (ii) a The control signal of the high-voltage submodule string comprises: DC voltage component U 1 Circulating current voltage u cir Circulating current control voltage delta u cir And a DC control voltage Deltau dc (ii) a The high-voltage submodule string and the AC transmissionThe modulation voltage of the output unit is:
Figure FDA0003920039780000011
wherein m is u For the modulation voltage of the high-voltage sub-module string, m l Is the modulation voltage of the AC output unit;
DC voltage component U 1 Representing a DC voltage component borne by the auxiliary converter part, the DC voltage component U 1 Is gradually changed from V in the process of continuously equalizing the capacitor voltage dc1 Change to V dc2 ：
Figure FDA0003920039780000012
Wherein, V dc1 End value of the DC voltage component, V, for the submodule string dc2 End value of the DC voltage component borne by the AC output unit, N 1 、N 2 The number of modules of the high-voltage sub-module string and the number of bridge arm modules of the alternating-current output unit are U dc Is a DC bus voltage, U 2 Is U in size dc Minus U 1 ；
Then establishing and obtaining the circulating current voltage of the alternating current output unit and the high-voltage sub-module string;
the method for generating the circulating current control voltage comprises the following steps:
subtracting the module capacitor average voltage of the high-voltage sub-module string from the module capacitor average voltage of the alternating current output unit, and generating a circulating current instruction amplitude value through a PI (proportional integral) controller;
multiplying the circulating current instruction amplitude by a standard sinusoidal signal to obtain a circulating current instruction;
subtracting the actual circulating current from the circulating current instruction, and obtaining a circulating current control voltage through a proportional controller;
the method for judging the sub-module capacitor voltage balance of the alternating current output unit and the high-voltage sub-module string comprises the following steps:
Figure FDA0003920039780000021
wherein, the first and the second end of the pipe are connected with each other,
Figure FDA0003920039780000022
is the module capacitor average voltage of the high voltage sub-module string,
Figure FDA0003920039780000023
is the average voltage of the module capacitor of the AC output unit, Δ u set Is a voltage error determination value.
2. The method for precharging the hybrid direct-current converter according to claim 1, wherein the method for generating the direct-current control voltage comprises:
subtracting the module capacitor average voltage of the high-voltage sub-module string from the module voltage instruction value of the high-voltage sub-module string, and obtaining a direct current instruction value through a PI (proportional integral) controller;
and subtracting the actual direct current value from the direct current instruction value, and obtaining direct current control voltage through a PI (proportional integral) controller.
3. The method for precharging the hybrid direct-current converter according to claim 1, wherein the method for judging the voltage rise of the sub-module capacitor of the alternating-current output unit and the high-voltage sub-module string to the rated voltage is as follows:
Figure FDA0003920039780000024
Figure FDA0003920039780000025
wherein the content of the first and second substances,
Figure FDA0003920039780000026
is the module capacitor average voltage of the high voltage sub-module string,
Figure FDA0003920039780000027
is the average voltage of the module capacitor of the AC output unit, u m1_ref Is a module voltage command value, u, of a high voltage sub-module string m2_ref Is a module voltage command value, deltau, of the AC output unit set Is a voltage error determination value.
4. A precharge system for a hybrid dc converter, comprising:
the circulation current control module generates circulation control voltage after the circulation voltage and the capacitance voltage of the alternating current output unit and the high-voltage sub-module string are stable, and balances the sub-module capacitance voltage of the alternating current output unit and the high-voltage sub-module string;
the direct current control module generates direct current control voltage after the alternating current output unit and the sub-module capacitor voltage of the high-voltage sub-module string are balanced, so that the sub-module capacitor voltage of the alternating current output unit and the sub-module capacitor voltage of the high-voltage sub-module string continuously rise to rated voltage, and the pre-charging is finished;
the circulation current control module still includes and establishes circulation voltage to mixing DC transverter's alternating current output unit and high-voltage submodule cluster, includes:
the control signal of the alternating current output unit comprises: ac voltage component U 2 And a circulating current voltage u cir (ii) a The control signal of the high-voltage sub-module string comprises: DC voltage component U 1 Circulating current voltage u cir Circulating current control voltage delta u cir And a DC control voltage Deltau dc (ii) a The modulation voltage of the high-voltage submodule string and the alternating current output unit is as follows:
Figure FDA0003920039780000031
wherein m is u Is the modulation voltage of the high voltage sub-module string,m l is the modulation voltage of the AC output unit;
DC voltage component U 1 Representing a DC voltage component borne by the auxiliary converter part, the DC voltage component U 1 Gradually changes from V in the process of continuously equalizing the voltage of the capacitor dc1 Change to V dc2 ：
Figure FDA0003920039780000032
Wherein, V dc1 End value of the DC voltage component, V, for the submodule string dc2 End value of the DC voltage component borne by the AC output unit, N 1 、N 2 The number of modules of the high-voltage sub-module string and the number of bridge arm modules of the alternating-current output unit are U dc Is a DC bus voltage, U 2 Is U in size dc Minus U 1 ；
Then establishing and obtaining the circulating current voltage of the alternating current output unit and the high-voltage sub-module string;
the circulation current control module includes:
the circulating current instruction amplitude generation module subtracts the module capacitor average voltage of the high-voltage sub-module string from the module capacitor average voltage of the alternating current output unit and generates a circulating current instruction amplitude through the PI controller;
the circulating current instruction generating module is used for multiplying the circulating current instruction amplitude by a standard sinusoidal signal to obtain a circulating current instruction;
the loop current control voltage generation module subtracts the actual loop current from the loop current instruction and obtains loop current control voltage through a proportional controller;
in the direct current control module, a method for judging the sub-module capacitor voltage balance of the alternating current output unit and the high-voltage sub-module string comprises the following steps:
Figure FDA0003920039780000033
wherein the content of the first and second substances,
Figure FDA0003920039780000034
is the module capacitor average voltage of the high voltage sub-module string,
Figure FDA0003920039780000035
is the average voltage of the module capacitor of the AC output unit, Δ u set Is a voltage error determination value.
5. The precharge system for a hybrid dc converter according to claim 4, wherein said dc control module comprises:
the direct current instruction generation module subtracts the module capacitor average voltage of the high-voltage sub-module string from the module voltage instruction value of the high-voltage sub-module string to obtain a direct current instruction value through a PI (proportional integral) controller;
and the direct current control voltage generation module subtracts the direct current instruction value from the actual direct current value and obtains direct current control voltage through the PI controller.
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