WO2022016510A1 - 一种电压不对称故障时的电流控制方法及系统 - Google Patents

一种电压不对称故障时的电流控制方法及系统 Download PDF

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Publication number
WO2022016510A1
WO2022016510A1 PCT/CN2020/104454 CN2020104454W WO2022016510A1 WO 2022016510 A1 WO2022016510 A1 WO 2022016510A1 CN 2020104454 W CN2020104454 W CN 2020104454W WO 2022016510 A1 WO2022016510 A1 WO 2022016510A1
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WIPO (PCT)
Prior art keywords
current
preset
converter
reactive current
voltage
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PCT/CN2020/104454
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English (en)
French (fr)
Inventor
邵章平
辛凯
郭海滨
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华为数字能源技术有限公司
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Application filed by 华为数字能源技术有限公司 filed Critical 华为数字能源技术有限公司
Priority to EP20945969.2A priority Critical patent/EP4156433A4/en
Priority to PCT/CN2020/104454 priority patent/WO2022016510A1/zh
Priority to CN202080005644.3A priority patent/CN114258620A/zh
Publication of WO2022016510A1 publication Critical patent/WO2022016510A1/zh
Priority to US18/151,987 priority patent/US20230178989A1/en

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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
    • H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
    • H02J3/0012—Contingency detection
    • 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
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B19/00—Programme-control systems
    • G05B19/02—Programme-control systems electric
    • G05B19/04—Programme control other than numerical control, i.e. in sequence controllers or logic controllers
    • G05B19/042—Programme control other than numerical control, i.e. in sequence controllers or logic controllers using digital processors
    • 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
    • H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
    • 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
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/20—Pc systems
    • G05B2219/26—Pc applications
    • G05B2219/2639—Energy management, use maximum of cheap power, keep peak load low

Definitions

  • the present application relates to the technical field of power electronics, and in particular, to a current control method and system in the event of a voltage asymmetry fault.
  • the grid voltage When a single-phase or two-phase fault occurs in the transmission line of the power grid, the grid voltage will appear asymmetrical faults, such as asymmetrical high-voltage faults or asymmetrical low-voltage faults.
  • the converter does not run off-grid, and injects positive-sequence reactive current and negative-sequence reactive current into the grid.
  • the negative sequence reactive current will cause the three-phase current of the converter to be unbalanced, which is easy to cause the problem of the overcurrent of the converter.
  • the converter is controlled to output three-phase current.
  • the converter is controlled to output three-phase current.
  • Adjust the injected positive-sequence reactive current and negative-sequence reactive current and use the adjusted positive-sequence reactive current and negative-sequence reactive current to control the converter to output three-phase current again, until all the output three-phase currents meet the requirements.
  • the present application provides a current control method and system in the event of a voltage asymmetry fault, which can meet the requirements of reactive current regulation time when a voltage asymmetry fault occurs.
  • the present application provides a current control method for a voltage asymmetry fault.
  • a first current limit value is obtained according to the positive sequence voltage after the fault and the positive sequence reactive current before the fault.
  • negative sequence voltage before the negative sequence voltage and the fault current to obtain a second value;
  • 2 to obtain a third current limit value I 3 and the fourth current I 4 I 1 according to a first current value and second current value I;
  • the I 3 and I 1 is proportional to the
  • the I 4 and I 2 is proportional to the; I 3 using the positive sequence clipping reactive current, negative sequence using the reactive current I 4 pairs Limit.
  • the method obtains the limit value of positive sequence reactive current and the limit value of negative sequence reactive current at one time, without repeated iterative calculation, and obtains positive sequence reactive current and negative sequence that meet the requirements in a short time. Reactive current, shorten the adjustment time of reactive current.
  • the three-phase voltage can be the three-phase line voltage, or the three-phase phase voltage. Voltage.
  • Whether the three-phase voltages are equal can be judged by the effective value of the three-phase voltages. Specifically, it can be determined whether the effective values of the three-phase phase voltages are the same, or whether the effective values of the three-phase line voltages are equal. Judging whether the minimum three-phase voltage is less than the low-voltage fault triggering threshold; or, judging whether the maximum three-phase voltage is greater than the high-voltage fault triggering threshold; if so, judging that a voltage asymmetry fault occurs.
  • the converter can be controlled according to the positive sequence reactive current command value after limiting and the negative sequence reactive current command value after limiting.
  • the reactive current command value and the negative sequence reactive current command value after the amplitude limit generate the driving pulse signal of the switch tube in the converter, so that the current of the converter will not appear overcurrent.
  • the present application also provides a method for limiting the positive sequence active current, that is, obtaining a fifth current limit value I 5 according to the I 3 and the I 4 , and using the I 5 to limit the positive sequence active current.
  • obtaining the I 3 according to the I 1 and the I 2 specifically includes: when the sum I 12 of the I 1 and the I 2 is less than or equal to a preset current, the I 3 is equal to the I 3 I 1 ; the preset current is the rated current of the converter or the maximum current of the converter; when the sum I 12 of the I 1 and the I 2 is greater than the preset current, according to the The ratio of I 1 to the I 12 and the preset current obtain the I 3 .
  • obtaining the I 4 according to the I 1 and the I 2 specifically includes: when the sum I 12 of the I 1 and the I 2 is less than or equal to a preset current, the I 4 is equal to the I 4 I 2 ; the preset current is the rated current of the converter or the maximum current of the converter; when the sum I 12 of the I 1 and the I 2 is greater than the preset current, according to the The ratio of I 2 to the I 12 and the preset current obtain the I 4 .
  • obtaining the fifth current limit value I 5 according to the I 3 and the I 4 specifically includes: obtaining the I 5 according to the I 3 , the I 4 and the preset current; the preset current is the rated current of the converter or the maximum current of the converter.
  • the I 3 is obtained according to the ratio of the I 1 to the I 12 and the preset current, specifically obtained by the following formula:
  • I LMT is the preset current.
  • the I 4 is obtained according to the ratio of the I 2 to the I 12 and the preset current, specifically obtained by the following formula:
  • I LMT is the preset current.
  • I LMT is the preset current
  • K 3 is the preset adjustment coefficient of the positive sequence active current, 0 ⁇ K 3 ⁇ 1.
  • I 1
  • I LMT is the preset current
  • U 01 is the positive sequence voltage before the fault
  • U N is the rated voltage of the converter
  • K 1 is the preset adjustment coefficient of the positive sequence reactive current
  • the preset current is the rated current of the converter or the maximum current of the converter.
  • I 1
  • I LMT is the preset current
  • U TR is the preset trigger threshold of the voltage asymmetry fault
  • U N is the rated voltage of the converter
  • K 1 is the preset adjustment coefficient of the positive sequence reactive current
  • the preset The current is the rated current of the converter or the maximum current of the converter.
  • the second current limit value I 2 is obtained according to the U 2 and the U 02 , specifically obtained by the following formula:
  • I 2
  • I LMT is the preset current
  • U N is the rated voltage of the converter
  • K 2 is the preset adjustment coefficient of the negative sequence reactive current
  • 0 ⁇ K 2 ⁇ 10 the preset current is the rated current or the maximum current of the converter.
  • I 3 using the positive sequence clipping reactive current I 4 using the negative sequence reactive current limiter; specifically:
  • I Q1 * is the positive sequence reactive current command value
  • I Q2 * is the negative sequence reactive current command value
  • I P1 * is the positive sequence active current command value.
  • the present application also provides a converter system, which can prevent overcurrent caused by the injected negative-sequence reactive current during a voltage asymmetry fault.
  • the method obtains the limit value of positive sequence reactive current and the limit value of negative sequence reactive current at one time, without repeated iterative calculation, and obtains positive sequence reactive current and negative sequence that meet the requirements in a short time. Reactive current, shorten the adjustment time of reactive current.
  • the system includes: a converter and a controller; the first side of the converter is used for connecting direct current, and the second side of the converter is used for connecting to a grid; the converter is used for converting direct current to alternating current The controller is used to obtain the positive sequence voltage U 1 after the fault and the negative sequence voltage U 1 after the fault when the voltage asymmetry fault occurs.
  • the three-phase voltage can be the three-phase line voltage, or the three-phase phase voltage. Voltage.
  • Whether the three-phase voltages are equal can be judged by the effective value of the three-phase voltages. Specifically, it can be determined whether the effective values of the three-phase phase voltages are the same, or whether the effective values of the three-phase line voltages are equal. Judging whether the minimum three-phase voltage is less than the low-voltage fault triggering threshold; or, judging whether the maximum three-phase voltage is greater than the high-voltage fault triggering threshold; if so, judging that a voltage asymmetry fault occurs.
  • the controller is further configured to obtain a fifth current limit value I 5 according to the I 3 and the I 4 , and use the I 5 to limit the positive sequence active current.
  • the controller is specifically configured to make the I 3 equal to the I 1 when the sum I 12 of the I 1 and the I 2 is less than or equal to a preset current; the preset current is variable The rated current of the current transformer or the maximum current of the current transformer; when the sum I 12 of the I 1 and the I 2 is greater than the preset current, according to the ratio of the I 1 to the I 12 and the sum The preset current obtains the I 3 .
  • the controller is specifically configured to, when the sum I 12 of the I 1 and the I 2 is less than or equal to a preset current, the I 4 is equal to the I 2 ;
  • the preset current is a variable current the rated current of the converter or the maximum current of the converter; when the sum of the I 1 and the I 2 and I 12 is greater than the preset current, according to the ratio of the I 2 to the I 12 and the sum of the The preset current obtains the I 4 .
  • the controller is specifically configured to obtain the I 5 according to the I 3 , the I 4 and a preset current; the preset current is the rated current of the converter or the Maximum current.
  • the controller is specifically configured to obtain the I 3 through the following formula:
  • I LMT is the preset current.
  • the controller is specifically configured to obtain the I 4 by the following formula:
  • I LMT is the preset current.
  • the controller is specifically configured to obtain the I 5 through the following formula:
  • I LMT is the preset current
  • K 3 is the preset adjustment coefficient of the positive sequence active current, 0 ⁇ K 3 ⁇ 1.
  • the controller is specifically configured to limit the positive-sequence reactive current and limit the negative-sequence reactive current in the following manner;
  • I Q1 * is the positive sequence reactive current command value
  • I Q2 * is the negative sequence reactive current command value
  • the controller is specifically configured to limit the positive sequence active current in the following manner;
  • I P1 * is the positive sequence active current command value.
  • the embodiments of the present application have the following advantages:
  • the first current limit is obtained according to the positive sequence voltage after the fault and the positive sequence reactive current before the fault
  • the second current limit is obtained according to the negative sequence voltage after the fault and the negative sequence voltage before the fault
  • the third current limit and the fourth current limit are obtained according to the first current limit and the second current limit; the limit value of the positive sequence reactive current is directly obtained based on the parameters obtained from the port of the converter, namely The third current limit, and the limit value of the negative sequence reactive current is directly obtained, that is, the fourth current limit.
  • the third current limit is used to limit the positive sequence reactive current
  • the fourth current limit is used to limit the negative sequence reactive current, so that the positive sequence is limited.
  • the reactive current does not exceed the third current limit
  • the negative-sequence reactive current does not exceed the fourth current limit, thereby preventing overcurrent caused by the negative-sequence reactive current injected during a voltage asymmetry fault.
  • the current control method can directly obtain the limit value of positive sequence reactive current and the limit value of negative sequence reactive current at one time, without repeated iterative calculation, and obtain the required positive sequence reactive current in a short time. Therefore, the adjustment time of the reactive current can be shortened.
  • the technical solution provided by this application can solve the negative sequence reactive current when the positive sequence reactive current and negative sequence reactive current that meet the requirements are injected into the power grid under the premise of meeting the time requirement in the event of a voltage asymmetry fault. The problem of overcurrent in the converter.
  • FIG. 1 is a schematic diagram of power transmission and transformation provided by an embodiment of the present application
  • FIG. 2 is a schematic diagram of an unbalanced current provided by an embodiment of the present application.
  • FIG. 3 is a flowchart of a current control method provided by an embodiment of the present application.
  • FIG. 4 is a flowchart for determining a voltage asymmetry fault provided by an embodiment of the present application
  • FIG. 6 is a flowchart of a method for obtaining I 4 provided by an embodiment of the present application.
  • FIG. 7B is an effect diagram of a reactive current adjustment provided by an embodiment of the present application.
  • FIG. 8 is a flowchart of another current control method provided by an embodiment of the present application.
  • FIG. 9 is a schematic diagram of a flow conversion system provided by an embodiment of the present application.
  • FIG. 1 this figure is a schematic diagram of power transmission and transformation provided by an embodiment of the present application.
  • the converter 103 can convert the direct current into alternating current and transmit it to the transformer 102, and the converter 103 can be an inverter.
  • the source of the DC power at the input end of the converter can be a DC power source, such as DC power provided by a photovoltaic power generation system.
  • the transformer 102 is used to transform the alternating current power transmitted by the converter 103 and then transmit it to the power grid 101 through a transmission line, where the power grid 101 is an alternating current power grid.
  • the converter 103 may also be a rectifier, that is, the alternating current from the power grid 101 transmitted by the transformer 102 is rectified into direct current. It is not limited in the embodiments of the present application.
  • the converter 103 can be a bidirectional converter, and can be used as a rectifier or an inverter in different scenarios.
  • the working environment is relatively harsh, and the actual scene is relatively complex, and the transmission line is prone to voltage asymmetry faults, such as single-phase faults or two-phase faults.
  • positive-sequence reactive current and negative-sequence reactive current can be injected into the power grid 101 .
  • the negative sequence reactive current is likely to cause the three-phase current of the converter 103 to be unbalanced.
  • the converter When there is an asymmetric fault in the grid voltage, in order to help the asymmetric recovery of the grid, the converter will inject positive-sequence reactive current and negative-sequence reactive current into the grid. However, the negative-sequence reactive current will cause the converter to The three-phase current is unbalanced, and the reasons for the current unbalance are introduced in conjunction with the accompanying drawings.
  • FIG. 2 is a schematic diagram of an unbalanced current provided by an embodiment of the present application.
  • the trajectories of the positive sequence current and the negative sequence current are both circular.
  • the dotted circle 1 is the trajectory of the negative sequence reactive current
  • the dotted circle 2 is the trajectory of the positive sequence reactive current
  • the solid ellipse 3 is the trajectory of the actual current.
  • the dotted circle 1 is a trajectory formed by clockwise rotation with the center O as the center and the negative sequence reactive current OA as the radius.
  • the dotted circle 2 is a trajectory formed by counterclockwise rotation with the center O as the center and the positive sequence reactive current OB as the radius.
  • the preset current is the rated current of the converter or the maximum current of the converter. When the sum of the positive sequence reactive current OA and the negative sequence reactive current OB exceeds the preset current, it means that overcurrent may occur.
  • the embodiment of the present application provides a current control method in the event of a voltage asymmetry fault.
  • this method directly obtains the limit value of the negative sequence reactive current and the limit value of the positive sequence reactive current through the parameters obtained at the port of the converter, and then uses the negative sequence reactive current limit value.
  • the limit value limits the negative sequence reactive current, and uses the limit value of the positive sequence reactive current to limit the positive sequence reactive current.
  • the method can directly obtain the limiting value of the positive-sequence reactive current and the limiting value of the negative-sequence reactive current at one time without repeated iterative calculation, so the adjustment time of the reactive current can be shortened.
  • FIG. 3 is a flowchart of a current control method provided by an embodiment of the present application.
  • Step 201 When a voltage asymmetry fault occurs, obtain the positive sequence voltage U 1 after the fault, the negative sequence voltage U 2 after the fault, the negative sequence voltage U 02 before the fault, and the positive sequence reactive current I Q0 before the fault.
  • the three-phase voltage can be the three-phase line voltage, or the three-phase phase voltage. Voltage.
  • FIG. 4 is a flowchart of determining a voltage asymmetry fault according to an embodiment of the present application.
  • the process includes:
  • Step 301 Determine the inequality of the three-phase voltages.
  • whether the three-phase voltages are equal can be judged by the effective value of the three-phase voltages.
  • Step 302 Determine whether the minimum three-phase voltage is less than the low-voltage fault triggering threshold; or, determine whether the three-phase maximum voltage is greater than the high-voltage fault triggering threshold.
  • the three-phase phase voltages are used in the subsequent process of judging the voltage asymmetry fault; if the three-phase line voltages are used to determine that the effective values of the three-phase voltages are not equal, Then, the three-phase line voltage is used in the subsequent process of judging the voltage asymmetry fault.
  • Step 303 If yes, determine that a voltage asymmetry fault occurs.
  • the embodiments of the present application do not limit the process of obtaining the post-fault positive sequence voltage U 1 , the post-fault negative sequence voltage U 2 , the pre-fault negative sequence voltage U 02 , and the pre-fault positive sequence reactive current I Q0 , for example: you can It can be obtained in real time; it can also be used to detect the three-phase voltage and three-phase current of the converter port in real time.
  • the positive sequence voltage U 1 after the fault and the negative sequence voltage U 2 after the fault are obtained.
  • the negative sequence voltage U 02 before the fault and the positive sequence reactive current I Q0 before the fault.
  • Step 202 Obtain a first current limit value I 1 according to I Q0 and U 1 , and obtain a second current limit value I 2 according to U 2 and U 02 .
  • the embodiments of the present application do not limit the specific implementation manner of obtaining the first current limit value I 1 , and those skilled in the art may select a method for obtaining the first current limit value I 1 according to actual needs.
  • I 1
  • K 1 is the preset adjustment coefficient of the positive-sequence reactive current; 0 ⁇ K 1 ⁇ 10; I LMT is the rated current of the converter or the maximum current of the converter.
  • the first current limit value I 1 is obtained according to I Q0 , U 1 , the preset current I LMT , the preset trigger threshold value U TR of the voltage asymmetry fault, and the rated voltage U N of the converter, and is specifically obtained by the following formula:
  • I 1
  • K 1 is the preset adjustment coefficient of positive-sequence reactive current; 0 ⁇ K 1 ⁇ 10.
  • U TR can be a low voltage fault trigger threshold or a high voltage fault trigger threshold;
  • I LMT is the rated current of the converter or the maximum current of the converter.
  • Example embodiments of the present application specific value U TR is not limited, for the low voltage and high voltage fault failure, different values U TR, a high voltage corresponding to the failure U TR is greater than the low voltage corresponding to the failure U TR.
  • the low voltage fault trigger threshold is 0.9
  • the high voltage fault trigger threshold is 1.1.
  • I 2
  • K 2 is the preset adjustment coefficient of negative sequence reactive current; 0 ⁇ K 2 ⁇ 10.
  • Step 203 I 1 and I 2 value to obtain a third current I 3, I 4 is obtained according to the fourth current value I 1 and I 2 according to.
  • I 3 is proportional to I 1
  • I 4 is proportional to I 2. Therefore, after obtaining I 1 and I 2 , I 3 and I 4 can be obtained according to I 1 and I 2 .
  • the technical solutions provided by the embodiments of the present application, in the process of obtaining I 3 and I 4 do not need to go through complex iterative operations, but directly obtain the limit value of the positive-sequence reactive current, that is, I 3 , and directly obtain the negative-sequence reactive current.
  • the limit value of the work current, that is, I 4 is, in the process of obtaining I 3 and I 4 .
  • I 3 and I 4 are not limited in the embodiments of the present application, and they may be obtained simultaneously or separately.
  • Step 401 Determine whether the sum I 12 of I 1 and I 2 is less than or equal to I LMT ; if so (ie, Y in the figure), go to step 402; if not (ie, N in the figure), go to step 403.
  • I 12 I 1 +I 2 .
  • I 1 and I 2 When the sum of I 1 and I 2 equal to I 12 of less than I when the LMT, show through U 1, U 2, U 02 I and Q0 obtained with I 2 I 1 I 12 and the sum does not exceed the LMT predetermined current I, therefore, I 1 can be directly used as I 3 , and I 3 is used to limit the positive-sequence reactive current, so that the sum of the positive-sequence reactive current and the negative-sequence reactive current does not exceed the preset current.
  • Step 403 When I 12 >I LMT , obtain I 3 according to the ratio of I 1 to I 12 and I LMT .
  • I LMT is the preset current. That is, according to the proportional relationship I 1 obtains I 3.
  • the solid-line ellipse 3 is the trajectory of the actual current, that is, the sum I 12 of I 1 and I 2 .
  • I 1 When the sum I 12 of I 1 and I 2 is greater than I LMT , after the positive sequence reactive current is limited by I 1, the sum of the positive sequence reactive current and the negative sequence reactive current will still exceed the preset current I LMT . Therefore, according to the ratio of I 1 to I 12 and I LMT, I 1 needs to be scaled down to obtain I 3 .
  • this figure is a flowchart of a method for obtaining I 4 provided by an embodiment of the present application.
  • the method includes:
  • Step 601 determining I and I 1 I 12 2 I is less than equal to the LMT; if (i.e., FIG Y), the step 602 is executed; if not (i.e., in FIG. N), the step 603 is executed.
  • I 12 I 1 +I 2 .
  • I 12 of I 1 and I 2 When the sum I 12 of I 1 and I 2 is less than or equal to I LMT , it means that neither I 1 nor I 2 obtained by U 1 , U 2 , U 02 and I Q0 exceeds the preset current I LMT , therefore, it can be directly I 2 is used as I 4 , and I 4 is used to limit the negative-sequence reactive current, so that the sum of the negative-sequence reactive current and the positive-sequence reactive current does not exceed the preset current.
  • Step 603 When I 12 >I LMT , obtain I 4 according to the ratio of I 2 to I 12 and I LMT .
  • I 1 and I 2 When I 1 and I 2 is greater than the sum of I 12 I LMT, show through U 1, U 2, U 02 I and Q0 I obtained after 1 and I 2, I 1 and I 2 and I 12 of the current exceeds a preset I LMT , therefore, it is necessary to reduce I 1 and I 2 in equal proportion according to the ratio of I 2 to I 12 and I LMT to obtain I 4 , and then use the adjusted I 4 to limit the negative sequence reactive current, Therefore, the sum of the negative sequence reactive current and the positive sequence reactive current does not exceed the preset current I LMT .
  • I LMT is the preset current. That is, according to the proportional relationship I 2 is obtained I 4.
  • I 4 is obtained with a principle of obtaining similar principles I 3, the specific principles, refer to step 403 in FIG. 2 and will not be repeated here.
  • I 3 and I 4 are directly obtained through U 1 , U 2 , U 02 and I Q0 , and then I 3 is used for positive sequence reactive power Limit the current so that the positive sequence reactive current does not exceed I 3 ; use I 4 to limit the negative sequence reactive current so that the negative sequence reactive current does not exceed I 4 . Therefore, the current control method provided by the embodiments of the present application can reduce the time required to obtain the required positive-sequence reactive current and negative-sequence reactive current.
  • Step 204 I 3 using positive sequence current limiter reactive, I negative sequence using four pairs of reactive current clipping.
  • I 3 to limit the positive-sequence reactive current can be limited to the command value of the positive-sequence reactive current, specifically
  • I Q1 * is the positive sequence reactive current command value
  • I Q2 * is the negative sequence reactive current command value
  • the converter can be controlled according to the positive sequence reactive current command value after the amplitude limit and the negative sequence reactive current command value after the amplitude limit. According to the positive sequence reactive current command value after amplitude limit and the negative sequence reactive current command value after amplitude limitation, the driving pulse signal of the switch tube in the converter is generated, so that the current of the converter will not be overcurrent. .
  • FIG. 7A is the prior art An effect diagram of a reactive current adjustment
  • FIG. 7B is an effect diagram of a reactive current adjustment provided by an embodiment of the present application.
  • the adjustment time for reactive current of the technical solution provided by the prior art exceeds 100 ms, while the adjustment time for reactive current of the solution provided by the embodiment of the present application in FIG. 7B is less than 30 ms. Obviously, 30ms shortens the adjustment time of reactive current compared with 100ms, thereby meeting the time requirement of the grid for reactive current adjustment.
  • the third current limit value is used to limit the positive sequence reactive current command value, and the positive sequence reactive current command value is limited by using the third current limit value.
  • the fourth current limit limits the negative-sequence reactive current command value, so that the positive-sequence reactive current does not exceed the third current limit, and the negative-sequence reactive current does not exceed the fourth current limit.
  • Negative sequence reactive current injected during symmetrical faults causes overcurrent.
  • the current control method can directly obtain the limit value of positive sequence reactive current and the limit value of negative sequence reactive current at one time, without repeated iterative calculation, and obtain the required positive sequence reactive current in a short time.
  • the technical solution provided by this application can solve the negative sequence reactive current when the positive sequence reactive current and negative sequence reactive current that meet the requirements are injected into the power grid under the premise of meeting the time requirement in the event of a voltage asymmetry fault.
  • the problem of overcurrent in the converter can solve the negative sequence reactive current when the positive sequence reactive current and negative sequence reactive current that meet the requirements are injected into the power grid under the premise of meeting the time requirement in the event of a voltage asymmetry fault.
  • the current control method provided in the second embodiment of the present application further limits the positive-sequence active current on the basis of limiting the positive-sequence reactive current and limiting the negative-sequence reactive current.
  • FIG. 8 is a flowchart of yet another current control method provided by an embodiment of the present application.
  • the steps 701 to 703 are similar to the steps 201 to 203 in the method embodiment 1, and are not repeated here.
  • step 701-step 703 the method further includes:
  • Step 704 Obtain the fifth current limit value I 5 according to I 3 and I 4 .
  • I LMT is the preset current
  • K 3 is the preset adjustment coefficient of the positive sequence active current, 0 ⁇ K 3 ⁇ 1.
  • I 5 can take the value of or K 3 ⁇ I LMT .
  • the process provides the I 5, without going through the iterative calculation, the I 3 and I 4 is obtained, according to I 3 and I 4 I 5 directly, thereby reducing Time to obtain the required positive sequence active current. Therefore, using the technical solution provided by the present application, the converter can limit the positive sequence active current, the positive sequence reactive current and the negative sequence reactive current in a relatively short period of time.
  • Step 705 I 3 using positive sequence current limiter reactive, I negative sequence using four pairs of reactive current clipping, using positive sequence active current I 5 pairs of clipping.
  • Using I 5 to limit the positive-sequence active current may be to limit the command value of the positive-sequence active current, specifically
  • I P1 * is the positive sequence active current command value.
  • the positive sequence active current command value After limiting the positive sequence active current command value, positive sequence reactive current command value and negative sequence reactive current command value, it can and the negative sequence reactive current command value after the limiter to control the converter. Specifically, it can be based on the positive sequence active current command value after the limiter, the positive sequence reactive current command value after the limiter and the limiter value of the reactive current.
  • the negative sequence reactive current command value generates the driving pulse signal of the switch tube in the converter, so that the current of the converter will not appear overcurrent.
  • the current control method provided by the embodiment of the present application can directly obtain the limit value of the positive sequence active current, the limit value of the positive sequence reactive current and the limit value of the negative sequence reactive current at one time, without repeated iterative calculation , the positive sequence active current, negative sequence reactive current and positive sequence reactive current that meet the requirements can be obtained, thereby reducing the time required to obtain the required positive sequence active current, negative sequence reactive current and positive sequence reactive current. Therefore, the converter can inject the required positive-sequence reactive current and negative-sequence reactive current into the power grid under the premise of meeting the time requirement, so as to solve the problem that the negative-sequence reactive current causes the converter to overcurrent.
  • FIG. 9 is a schematic diagram of a flow conversion system provided by an embodiment of the present application.
  • the converter system at least includes: converter 103 and controller 904 .
  • the converter system further includes a transformer 102 , which is described below by taking the example that the converter system includes the transformer 102 .
  • the first side of the converter 103 is used for connecting the direct current, and the second side of the converter 103 is used for connecting the first side of the transformer 102 .
  • the converter 103 can be a bidirectional converter, that is, it can convert direct current into alternating current and transmit it to the grid 101 , or rectify the alternating current transmitted by the grid 101 into direct current.
  • the second side of the transformer 102 is used to connect the grid 101 .
  • the transformer 102 can transform the alternating current transmitted by the converter 103 and then transmit it to the power grid 101 through a transmission line.
  • the system embodiment of the present application obtains the limit value of the positive sequence reactive current and the limit value of the negative sequence reactive current at one time through the controller 904 Amplitude, no need to go through repeated iterative calculations, so the adjustment time of the reactive current can be shortened. Then the controller 904 uses the amplitude limit value of the positive sequence reactive current to limit the positive sequence reactive current, and uses the amplitude limit value of the negative sequence reactive current to limit the negative sequence reactive current. Therefore, when the grid voltage has an asymmetric fault, it can not only meet the requirements of grid-connected standard reactive current regulation time, but also solve the problem of converter overcurrent.
  • the controller 904 is configured to obtain the positive sequence voltage U 1 after the fault, the negative sequence voltage U 2 after the fault, the negative sequence voltage U 02 before the fault, and the positive sequence voltage before the fault when a voltage asymmetry fault occurs.
  • reactive current I Q0, and U 1 I Q0 according to obtain a first current limit I 1, U 2 and U 02 according to obtain a second current limit I 2
  • I 3 is obtained according to the third current value I 1 and I 2
  • obtain the fourth current limit value I 4 according to I 1 and I 2 use I 3 to limit the positive sequence reactive current
  • the controller 904 can determine whether to transmit a voltage asymmetry fault by obtaining the three-phase voltage disconnected by the converter 103 .
  • For the specific determination process refer to Method Embodiment 1 and FIG. 4 , which will not be repeated here.
  • the first current limit value I 1 is obtained according to I Q0 and U 1
  • the second current limit value I 2 is obtained according to U 2 and U 02 .
  • the controller 904 can obtain I 1 in two different ways.
  • I 1
  • K 1 is the preset adjustment coefficient of the positive-sequence reactive current; 0 ⁇ K 1 ⁇ 10; I LMT is the rated current of the converter or the maximum current of the converter.
  • I 1
  • K 1 is the preset adjustment coefficient of positive-sequence reactive current; 0 ⁇ K 1 ⁇ 10.
  • U TR can be a low voltage fault trigger threshold or a high voltage fault trigger threshold;
  • I LMT is the rated current of the converter or the maximum current of the converter.
  • the controller 904 U 2 the predetermined current I LMT, the converter rated voltage U N U 02 and obtain a second current limit I 2, particularly obtained by the following equation:
  • I 2
  • K 2 is the preset adjustment coefficient of negative sequence reactive current; 0 ⁇ K 2 ⁇ 10.
  • the controller 904 can obtain I 3 and I 4 according to I 1 and I 2 .
  • the controller 904 directly obtains the limit value of the positive sequence reactive current, that is, I 3 , without going through complex iterative operations, and directly obtains the limit value of the negative sequence reactive current. , namely I 4 .
  • the power current is limited, so that the sum of the positive sequence reactive current and the negative sequence reactive current does not exceed the preset current; if not, it indicates the I 1 and I obtained through U 1 , U 2 , U 02 and I Q0 after 2, I 1 I 12 I and the LMT exceeds a preset current I, i.e., I 12> I LMT, therefore, the controller 904 and the like need to be scaled I 1, and then adjusted to give the reuse of I 2 3
  • the controller can adjust I 1 proportionally by the following formula:
  • I LMT is the preset current. That is, according to the proportional relationship I 1 obtains I 3.
  • the controller 904 uses I 3 to limit the positive-sequence reactive current, the sum of the positive-sequence reactive current and the negative-sequence reactive current does not exceed the preset current I LMT .
  • the sum of I 2 and I 12 exceeds the preset current I LMT , that is, I 12 >I LMT , therefore, it is necessary to reduce I 2 in equal proportion according to the ratio of I 2 to I 12 and I LMT to obtain I 4 , and then use the adjusted The obtained I 4 limits the negative-sequence reactive current,
  • controller I 2 may be adjusted proportionally by the following formula:
  • I LMT is the preset current. That is, according to the proportional relationship I 2 is obtained I 4.
  • the current control method can reduce the time required to obtain the required positive-sequence reactive current and negative-sequence reactive current.
  • the controller 904 can use I 3 to limit the positive sequence reactive current command value to achieve the purpose of limiting the positive sequence reactive current. Similarly, the controller 904 can also use I 4 to limit the negative sequence reactive current. The reactive current command value is limited.
  • controller 904 limits the positive-sequence reactive current command value through I 3 .
  • the controller 904 sets
  • controller 904 limits the negative sequence reactive current command value through I 4 .
  • the controller 904 sets
  • the converter can be controlled according to negative and then positive sequence reactive current command value limiter and the limiter sequence reactive current instruction value Specifically, the driving pulse signal of the switch tube in the converter can be generated according to the positive sequence reactive current command value after the amplitude limit and the negative sequence reactive current command value after the amplitude limit, so that the current of the converter does not appear overcurrent phenomenon.
  • the controller can use the third current limit value to limit the positive-sequence reactive current command value when generating the positive-sequence reactive current command value and the negative-sequence reactive current command value.
  • the negative-sequence reactive current command value is limited by the fourth current limit, so that the positive-sequence reactive current does not exceed the third current limit, and the negative-sequence reactive current does not exceed the fourth current limit, thereby preventing Negative sequence reactive current injected during voltage asymmetry fault causes overcurrent.
  • the controller of the converter system can directly obtain the limit value of the positive sequence reactive current and the limit value of the negative sequence reactive current at one time, without repeated iterative calculation, and obtain the required value in a short time.
  • Positive sequence reactive current and negative sequence reactive current so the regulation time of reactive current can be shortened.
  • the technical solutions provided by the embodiments of the present application can, under the premise of meeting the time requirement, inject positive-sequence reactive current and negative-sequence reactive current into the power grid in the event of a voltage asymmetry fault, so as to solve the problem of negative-sequence reactive current and negative-sequence reactive current.
  • the problem that the power current causes the converter to overcurrent.
  • the controller 904 further limits the positive-sequence active current on the basis of limiting the positive-sequence reactive current and limiting the negative-sequence reactive current.
  • the controller 904 may obtain the fifth current limit I 5 based on I 3 and I 4 .
  • the controller 904 also needs to limit the positive-sequence active current. Therefore, the sum of the positive-sequence active current, the positive-sequence reactive current and the negative-sequence reactive current satisfies the requirement of the preset current.
  • the formula for the controller 904 to obtain the fifth current limit value I 5 according to I 3 and I 4 is as follows:
  • I LMT is the preset current
  • K 3 is the preset adjustment coefficient of the positive sequence active current, 0 ⁇ K 3 ⁇ 1.
  • I 5 can take the value of or K 3 ⁇ I LMT .
  • the controller 904 does not need to go through repeated iterative calculations. After obtaining I 3 and I 4 , it can directly obtain I 5 according to I 3 and I 4 , thereby reducing the need for obtaining positive sequence active power that meets the requirements. current time. Therefore, the converter 103 can limit the positive-sequence active current, limit the positive-sequence reactive current, and limit the negative-sequence reactive current in a relatively short period of time.
  • the controller 904 uses I 5 to limit the positive-sequence active current, which may be to limit the command value of the positive-sequence active current, specifically
  • I P1 * is the positive sequence active current command value.
  • the controller limits the positive sequence active current command value, positive sequence reactive current command value and negative sequence reactive current command value, it can The current command value and the negative-sequence reactive current command value after the amplitude limit are used to control the converter. Specifically, the positive sequence active current command value after amplitude limitation, the positive sequence reactive current command value after amplitude limitation and the amplitude limitation can be used to control the converter. The negative-sequence reactive current command value is generated to generate the driving pulse signal of the switch tube in the converter, so that the current of the converter will not be over-current.
  • the controller can directly obtain the positive-sequence active current limit value, the positive-sequence reactive current limit value, and the negative-sequence reactive current limit value at one time, without repeating Iterative calculation can obtain positive-sequence active current, negative-sequence reactive current and positive-sequence reactive current that meet the requirements, thereby reducing the required amount of positive-sequence active current, negative-sequence reactive current and positive-sequence reactive current. time. Therefore, the converter can inject the required positive-sequence reactive current and negative-sequence reactive current into the power grid on the premise of meeting the time requirement, so as to solve the problem that the negative-sequence reactive current causes the converter to overcurrent.
  • At least one (item) refers to one or more, and "a plurality” refers to two or more.
  • “And/or” is used to describe the relationship between related objects, indicating that there can be three kinds of relationships, for example, “A and/or B” can mean: only A, only B, and both A and B exist , where A and B can be singular or plural.
  • the character “/” generally indicates that the related objects are an “or” relationship.
  • At least one item(s) below” or similar expressions thereof refer to any combination of these items, including any combination of single item(s) or plural items(s).
  • At least one (a) of a, b or c can mean: a, b, c, "a and b", “a and c", “b and c", or "a and b and c" ", where a, b, c can be single or multiple.

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Abstract

一种电压不对称故障时的电流控制方法及系统，当发生电压不对称故障时，根据故障后的正序电压和故障前的正序无功电流获得第一电流限值，根据故障后的负序电压和故障前的负序电压获得第二电流限值；根据第一电流限值和第二电流限值获得第三电流限值和第四电流限值；利用第三电流限值对正序无功电流限幅，利用第四电流限值对负序无功电流限幅，防止在电压不对称故障时注入的负序无功电流造成电流过流。该方法一次性地获得正序无功电流的限幅值和负序无功电流的限幅值，无需经过反复迭代计算，在较短的时间内获得符合要求的正序无功电流和负序无功电流，缩短无功电流的调节时间，解决负序无功电流使变流器过电流的问题。

Description

一种电压不对称故障时的电流控制方法及系统 技术领域
本申请涉及电力电子技术领域，尤其涉及一种电压不对称故障时的电流控制方法及系统。
背景技术
当电网的传输线发生单相或者两相故障时，电网电压会出现不对称故障，例如：不对称高压故障或不对称低压故障。为了降低不对称故障带来的影响，变流器不脱网运行，并向电网注入正序无功电流和负序无功电流。
然而，负序无功电流会造成变流器的三相电流不平衡，容易引起变流器过电流的问题。
为解决上述问题，根据给定的正序无功电流初始值和负序无功电流初始值，控制变流器输出三相电流，当检测到输出的三相电流有一相超过允许值后，则调整注入的正序无功电流和负序无功电流，利用调整后的正序无功电流和负序无功电流再次控制变流器输出三相电流，直至输出的三相电流全部符合要求。
上述解决方案，为了得到符合要求的三相电流，需要进行反复迭代，才能满足要求。获得无功电流所经过的时间较长，该较长的时间无法满足并网标准对无功电流调节时间的要求。
申请内容
本申请提供了一种电压不对称故障时的电流控制方法及系统，能够在发生电压不对称故障时，满足无功电流调节时间的要求。
本申请提供一种电压不对称故障时的电流控制方法，当发生电压不对称故障时，根据故障后的正序电压和故障前的正序无功电流获得第一电流限值，根据故障后的负序电压和故障前的负序电压获得第二电流限值；根据第一电流限值I 1和第二电流限值I 2获得第三电流限值I 3和第四电流限值I 4；所述I 3与所述I 1成正比，所述I 4与所述I 2成正比；利用所述I 3对正序无功电流进行限幅，利用所述I 4对负序无功电流进行限幅。防止在电压不对称故障时注入的负序无功电流造成电流过流。该方法一次性地获得正序无功电流的限幅值和负序无功电流的限幅值，无需经过反复迭代计算，在较短的时间内获得符合要求的正序无功电流和负序无功电流，缩短无功电流的调节时间。
本申请不限定判断电压不对称故障的具体方式，例如：可以通过变流器端口的三相电压来判断是否发生电压不对称故障，三相电压可以为三相线电压，也可以为三相相电压。
可以通过三相电压的有效值来判断三相电压是否相等。具体地，可以判断三相相电压的有效值是否相同，或者判断三相线电压的有效值是否相等。判断三相电压最小值是否小于低电压故障触发阈值；或，判断三相电压最大值是否大于高压故障触发阈值；如果是，则判断发生电压不对称故障。
例如，应用场景为三相电网，可以根据限幅后的正序无功电流指令值和限幅后的负序无功电流指令值对变流器进行控制，具体可以根据限幅后的正序无功电流指令值和限幅后 的负序无功电流指令值，生成变流器中开关管的驱动脉冲信号，进而使变流器的电流不会出现过流现象。
本申请还提供了对正序有功电流进行限幅的方法，即根据所述I 3和所述I 4获得第五电流限值I 5，利用所述I 5对正序有功电流进行限幅。
优选地，根据所述I 1和所述I 2获得所述I 3，具体包括：当所述I 1与所述I 2的和I 12小于等于预设电流时，所述I 3等于所述I 1；所述预设电流为变流器的额定电流或所述变流器的最大电流；当所述I 1与所述I 2的和I 12大于所述预设电流时，按照所述I 1与所述I 12的比例和所述预设电流获得所述I 3。
优选地，根据所述I 1和所述I 2获得所述I 4，具体包括：当所述I 1与所述I 2的和I 12小于等于预设电流时，所述I 4等于所述I 2；所述预设电流为变流器的额定电流或所述变流器的最大电流；当所述I 1与所述I 2的和I 12大于所述预设电流时，按照所述I 2与所述I 12的比例和所述预设电流获得所述I 4。
优选地，根据所述I 3和所述I 4获得第五电流限值I 5，具体包括：根据所述I 3、所述I 4和预设电流获得所述I 5；所述预设电流为变流器的额定电流或所述变流器的最大电流。
优选地，按照所述I 1与所述I 12的比例和所述预设电流获得所述I 3，具体通过以下公式获得：
Figure PCTCN2020104454-appb-000001
其中，I LMT为所述预设电流。
优选地，按照所述I 2与所述I 12的比例和所述预设电流获得所述I 4，具体通过以下公式获得：
Figure PCTCN2020104454-appb-000002
其中，I LMT为所述预设电流。
优选地，根据所述I 3、所述I 4和预设电流获得所述I 5，具体通过以下公式获得：
Figure PCTCN2020104454-appb-000003
其中，I LMT为所述预设电流；K 3为正序有功电流的预设调节系数，0<K 3≤1。
优选地，根据所述I Q0和所述U 1获得第一电流限值I 1，具体通过以下公式获得：
I 1＝|I Q0+K 1·I LMT·(U 01-U 1)/U N|
其中，I LMT为预设电流；U 01为故障前的正序电压；U N为变流器的额定电压；K 1为正序无功电流的预设调节系数；0<K 1≤10；所述预设电流为变流器的额定电流或所述变流器的最大电流。
优选地，根据所述I Q0和所述U 1获得第一电流限值I 1，具体通过以下公式获得：
I 1＝|I Q0+K 1·I LMT·(U TR-U 1)/U N|
其中，I LMT为预设电流；U TR为电压不对称故障的预设触发阈值；U N为变流器的额定电压；K 1为正序无功电流的预设调节系数；所述预设电流为变流器的额定电流或所述变流器的最大电流。
优选地，根据所述U 2和所述U 02获得第二电流限值I 2，具体通过以下公式获得：
I 2＝|K 2·I LMT·(U 02-U 2)/U N|
其中，I LMT为预设电流；U N为变流器的额定电压；K 2为负序无功电流的预设调节系数；0<K 2≤10；所述预设电流为变流器的额定电流或所述变流器的最大电流。
优选地，利用所述I 3对正序无功电流进行限幅、利用所述I 4对负序无功电流进行限幅；具体为：
|I Q1 *|≤I 3，|I Q2 *|≤I 4；
其中，I Q1 *为正序无功电流指令值；I Q2 *为负序无功电流指令值。
优选地，利用所述I 5对正序有功电流进行限幅；具体为：
|I P1 *|≤I 5；
其中，I P1 *为正序有功电流指令值。
本申请还提供一种变流系统，可以防止在电压不对称故障时注入的负序无功电流造成电流过流。该方法一次性地获得正序无功电流的限幅值和负序无功电流的限幅值，无需经过反复迭代计算，在较短的时间内获得符合要求的正序无功电流和负序无功电流，缩短无功电流的调节时间。系统包括：变流器和控制器；所述变流器第一侧用于连接直流电，所述变流器的第二侧用于连接电网；所述变流器，用于将直流电转换为交流电输送给所述电网，或，用于将所述电网传送的交流电整流为直流电；所述控制器，用于当发生电压不对称故障时，获得故障后的正序电压U 1、故障后的负序电压U 2、故障前的负序电压U 02和故障前的正序无功电流I Q0；根据所述I Q0和所述U 1获得第一电流限值I 1，根据所述U 2和所述U 02获得第二电流限值I 2；根据所述I 1和所述I 2获得第三电流限值I 3，根据所述I Q0和所述U 1获得第四电流限值I 4；利用所述I 3对正序无功电流进行限幅，利用所述I 4对负序无功电流进行限幅；其中，所述I 3与所述I 1成正比，所述I 4与所述I 2成正比。
本申请不限定判断电压不对称故障的具体方式，例如：可以通过变流器端口的三相电压来判断是否发生电压不对称故障，三相电压可以为三相线电压，也可以为三相相电压。
可以通过三相电压的有效值来判断三相电压是否相等。具体地，可以判断三相相电压的有效值是否相同，或者判断三相线电压的有效值是否相等。判断三相电压最小值是否小于低电压故障触发阈值；或，判断三相电压最大值是否大于高压故障触发阈值；如果是，则判断发生电压不对称故障。
优选地，所述控制器，还用于根据所述I 3和所述I 4获得第五电流限值I 5，利用所述I 5对正序有功电流进行限幅。
优选地，所述控制器，具体用于当所述I 1与所述I 2的和I 12小于等于预设电流时，使所述I 3等于所述I 1；所述预设电流为变流器的额定电流或所述变流器的最大电流；当所述I 1与所述I 2的和I 12大于所述预设电流时，按照所述I 1与所述I 12的比例和所述预设电流获得所述I 3。
优选地，所述控制器，具体用于当所述I 1与所述I 2的和I 12小于等于预设电流时，所述I 4等于所述I 2；所述预设电流为变流器的额定电流或所述变流器的最大电流；当所述I 1与所述I 2的和I 12大于所述预设电流时，按照所述I 2与所述I 12的比例和所述预设电流获得所述I 4。
优选地，所述控制器，具体用于根据所述I 3、所述I 4和预设电流获得所述I 5；所述预设电流为变流器的额定电流或所述变流器的最大电流。
优选地，所述控制器，具体用于通过以下公式获得所述I 3：，
Figure PCTCN2020104454-appb-000004
其中，I LMT为所述预设电流。
优选地，所述控制器，具体用于通过以下公式获得所述I 4：
Figure PCTCN2020104454-appb-000005
其中，I LMT为所述预设电流。
优选地，所述控制器，具体用于通过以下公式获得所述I 5：
Figure PCTCN2020104454-appb-000006
其中，I LMT为所述预设电流；K 3为正序有功电流的预设调节系数，0<K 3≤1。
优选地，所述控制器，具体用于通过以下方式对正序无功电流进行限幅，对负序无功电流进行限幅；
|I Q1 *|≤I 3，|I Q2 *|≤I 4；
其中，I Q1 *为正序无功电流指令值；I Q2 *为负序无功电流指令值。
优选地，所述控制器，具体用于通过以下方式对所述正序有功电流进行限幅；
|I P1 *|≤I 5；
其中，I P1 *为正序有功电流指令值。
从以上技术方案可以看出，本申请实施例具有以下优点：
当发生电压不对称故障时，根据故障后的正序电压和故障前的正序无功电流获得第一电流限值，根据故障后的负序电压和故障前的负序电压获得第二电流限值；根据第一电流限值和第二电流限值获得第三电流限值和第四电流限值；基于变流器的端口获取的参数来直接获得正序无功电流的限幅值，即第三电流限值，和直接获得负序无功电流的限幅值，即第四电流限值。获得第三电流限值和第四电流限值后，利用第三电流限值对正序无功电流进行限幅，利用第四电流限值对负序无功电流进行限幅，从而使正序无功电流不超过第三电流限值，负序无功电流不超过第四电流限值，从而防止在电压不对称故障时注入的负序无功电流造成电流过流。
该电流控制方法可以直接一次性地获得正序无功电流的限幅值和负序无功电流的限幅值，无需经过反复迭代的计算，在较短的时间内获得符合要求的正序无功电流和负序无功电流，因此可以缩短无功电流的调节时间。本申请提供的技术方案，在电压不对称故障时，可以在满足时间要求的前提下，将符合要求的正序无功电流和负序无功电流注入到电网中时，解决负序无功电流使变流器过电流的问题。
附图说明
图1为本申请实施例提供的输变电的示意图；
图2为本申请实施例提供的一种不平衡电流的示意图；
图3为本申请实施例提供的一种电流控制方法的流程图；
图4为本申请实施例提供的一种确定电压不对称故障的流程图；
图5为本申请实施例提供的一种获得I 3的方法流程图；
图6为本申请实施例提供的一种获得I 4的方法流程图；
图7A为现有技术的一种无功电流调节的效果图；
图7B为本申请实施例提供的一种无功电流调节的效果图；
图8为本申请实施例提供的又一种电流控制方法的流程图；
图9为本申请实施例提供的一种变流系统的示意图。
具体实施方式
为了使本领域技术人员更好地理解和实施本申请实施例提供的技术方案，下面结合附图对其应用场景进行详细的介绍。
参见图1，该图为本申请实施例提供的输变电的示意图。
其中，变流器103可以将直流电逆变为交流电传输给变压器102，变流器103可以为逆变器。变流器输入端的直流电的来源可以为直流电源，例如光伏发电系统提供的直流电。
变压器102用于对变流器103传输的交流电进行变压后通过传输线传输给电网101，此处电网101为交流电网。
另外，变流器103也可以为整流器，即将变压器102传输的从电网101过来的交流电整流为直流电。本申请实施例中均不限定。变流器103可以为双向变流器，在不同的场景可以作为整流器，也可以作为逆变器来使用。
由于实际工作过程中，工作环境比较恶劣，实际场景比较复杂，传输线容易发生电压不对称故障，例如单相故障或两相故障等。此时在保证变流器103不脱网的同时，可以向电网101注入正序无功电流和负序无功电流。但是负序无功电流容易引起变流器103的三相电流不平衡。
为了解决电流的过流问题，以及满足电网对于无功电流调节的时间要求，下面介绍本申请实施例提供的具体方法。
方法实施例一：
当电网电压出现不对称故障时，为了有助于电网的不对称恢复，变流器会向电网中注入正序无功电流和负序无功电流，然而负序无功电流会引起变流器的三相电流不平衡，下面结合附图介绍引起电流不平衡的原因。
参见图2，该图为本申请实施例提供的一种不平衡电流的示意图。
正序电流和负序电流的轨迹均为圆形。
其中，虚线圆1为负序无功电流的轨迹，虚线圆2为正序无功电流的轨迹，实线椭圆3为实际电流的轨迹。
虚线圆1是以圆心O为圆心，以负序无功电流OA为半径进行顺时针旋转形成的轨迹。
虚线圆2是以圆心O为圆心，以正序无功电流OB为半径进行逆时针旋转形成的轨迹。
预设电流为变流器的额定电流或变流器的最大电流，当正序无功电流OA和负序无功 电流OB之和超过该预设电流则说明可能出现过流。
由图可知，当负序无功电流OA和正序无功电流OB同向时，负序无功电流OA和正序无功电流OB的和将会超过预设电流，可能引发变流器过电流的问题。
为了满足无功电流调节时间的要求，又解决变流器过电流的问题，本申请实施例提供了一种电压不对称故障时的电流控制方法。当发生电压不对称故障时，该方法直接通过变流器的端口处获得的参数来获得负序无功电流的限幅值和正序无功电流的限幅值，再利用负序无功电流的限幅值对负序无功电流限幅，利用正序无功电流的限幅值对正序无功电流进行限幅。该方法可以直接一次性地获得正序无功电流的限幅值和负序无功电流的限幅值，无需经过反复迭代的计算，因此可以缩短无功电流的调节时间。在电网电压出现不对称故障时，既能满足并网标准无功电流调节时间的要求，又能解决变流器过电流的问题。
参见图3，该图为本申请实施例提供的一种电流控制方法的流程图。
本申请实施例提供的电流控制方法包括以下步骤：
步骤201：当发生电压不对称故障时，获得故障后的正序电压U 1、故障后的负序电压U 2、故障前的负序电压U 02和故障前的正序无功电流I Q0。
本申请不限定判断电压不对称故障的具体方式，例如：可以通过变流器端口的三相电压来判断是否发生电压不对称故障，三相电压可以为三相线电压，也可以为三相相电压。
参见图4，该图为本申请实施例提供的一种确定电压不对称故障的流程图。
该流程包括：
步骤301：确定三相电压的不相等。
例如可以通过三相电压的有效值来判断三相电压是否相等。
具体地，可以判断三相相电压的有效值是否相同，或者判断三相线电压的有效值是否相等。
步骤302：判断三相电压最小值是否小于低电压故障触发阈值；或，判断三相电压最大值是否大于高压故障触发阈值。
若利用三相相电压确定三相电压的有效值不相等，则在后续判断电压不对称故障的过程中均利用三相相电压；若利用三相线电压确定三相电压的有效值不相等，则在后续判断电压不对称故障的过程中均利用三相线电压。
下面以三相相电压为例，进行详细介绍。
若通过三相相电压确定三相电压的有效值不相等，则在判断三相电压最小值是否小于低电压故障触发阈值时，通过三相相电压最小值与低电压故障触发阈值进行比较；或，在判断三相电压最大值是否大于高压故障触发阈值时，通过三相相电压最大值与高电压故障触发阈值进行比较。同理，通过三相线电压来判断是否发生不对称故障与通过三相相电压来判断是否发生不对称故障的原理相同，仅是两者对应的故障触发阈值有所不同，在此不再赘述。
步骤303：若是，则确定发生电压不对称故障。
当三相电压最小值小于低电压故障触发阈值时；或，当三相电压最大值大于高压故障触发阈值时，则确定发生电压不对称故障。
确定发生电压不对称故障后，为了获得符合要求的负序无功电流和正序无功电流，需要通过故障后的正序电压U 1、故障后的负序电压U 2、故障前的负序电压U 02和故障前的正序无功电流I Q0来获得负序无功电流的限幅值和正序无功电流的限幅值，然后利用负序无功电流的限幅值对负序无功电流限幅，利用正序无功电流的限幅值对正序无功电流限幅，以使变流器利用限幅后的负序无功电流和限幅后的正序无功电流运行时，不会出现过电流问题。
本申请实施例不限定获得故障后的正序电压U 1、故障后的负序电压U 2、故障前的负序电压U 02和故障前的正序无功电流I Q0的过程，例如：可以为实时获得；也可以为实时检测变流器端口的三相电压和三相电流，在确定发生电压不对称故障时，再获取故障后的正序电压U 1、故障后的负序电压U 2、故障前的负序电压U 02和故障前的正序无功电流I Q0。
步骤202：根据I Q0和U 1获得第一电流限值I 1，根据U 2和U 02获得第二电流限值I 2。
为了满足不同标准的故障期间正序无功电流的要求，本申请实施例中提供两种获得第一电流限值I 1的实现方式。
本申请实施例不限定获得第一电流限值I 1的具体实现方式，本领域技术人员可以根据实际需要来选择第一电流限值I 1的获得方法。
第一种：
根据I Q0、U 1、预设电流I LMT、故障前的正序电压U 01和变流器的额定电压U N获得第一电流限值I 1，具体通过以下公式获得：
I 1＝|I Q0+K 1·I LMT·(U 01-U 1)/U N|
其中，I LMT和U N为变流器的参数，当变流器确定后，I LMT和U N均为已知量。K 1为正序无功电流的预设调节系数；0<K 1≤10；I LMT为变流器的额定电流或所述变流器的最大电流。
第二种：
根据I Q0、U 1、预设电流I LMT、电压不对称故障的预设触发阈值U TR和变流器的额定电压U N获得第一电流限值I 1，具体通过以下公式获得：
I 1＝|I Q0+K 1·I LMT·(U TR-U 1)/U N|
其中，K 1为正序无功电流的预设调节系数；0<K 1≤10。U TR可以为低电压故障触发阈值，也可以为高电压故障触发阈值；I LMT为变流器的额定电流或所述变流器的最大电流。
本申请实施例不限定U TR的具体取值，对于低电压故障和高电压故障，U TR的取值不同，高电压故障对应的U TR大于低电压故障对应的U TR。例如：低电压故障触发阈值为0.9，高电压故障触发阈值为1.1。
下面介绍第二电流限值I 2的获取方式。
根据U 2、预设电流I LMT、变流器的额定电压U N和U 02获得第二电流限值I 2，具体通过以下公式获得：
I 2＝|K 2·I LMT·(U 02-U 2)/U N|
其中，K 2为负序无功电流的预设调节系数；0<K 2≤10。
步骤203：根据I 1和I 2获得第三电流限值I 3，根据I 1和I 2获得第四电流限值I 4。
其中，I 3与I 1成正比，I 4与I 2成正比，因此，在获得I 1和I 2后，可以根据I 1和I 2获得 I 3和I 4。本申请实施例提供的技术方案，在获取I 3和I 4的过程中，无需经过复杂的迭代运算，而是直接获得正序无功电流的限幅值，即I 3，直接获得负序无功电流的限幅值，即I 4。
本申请实施例中不限定获得I 3和I 4的先后顺序，可以同时获得，也可以分别获得。
为了便于本领域技术人员理解，下面详细介绍具体获得I 3的过程，后续详细介绍获得I 4的过程。
参见图5，该图为本申请实施例提供的一种获得I 3的方法流程图。
本申请实施例提供的获取第三电流限值的方法包括以下步骤：
步骤401：判断I 1与I 2之和I 12是否小于等于I LMT；若是(即图中Y)，则执行步骤402；若否(即图中N)，则执行步骤403。
其中，I 12＝I 1+I 2。
步骤402：I 3等于I 1，即I 12≤I LMT时，I 3＝I 1。
当I 1与I 2之和I 12小于等于I LMT时，表明通过U 1、U 2、U 02和I Q0获得的I 1与I 2之和I 12未超过预设电流I LMT，因此，可以直接将I 1作为I 3，利用I 3对正序无功电流进行限幅，从而使正序无功电流与负序无功电流之和不超过预设电流。
步骤403：即I 12>I LMT时，根据I 1与I 12的比例和I LMT获得I 3。
当I 1与I 2的之和I 12大于I LMT时，表明通过U 1、U 2、U 02和I Q0获得的I 1和I 2后，I 1与I 2的和I 12超过预设电流I LMT，因此，需要对I 1进行等比例调整，然后再利用调整后得到的I 3对正序无功电流进行限幅，从而使正序无功电流与负序无功电流的之和不超过预设电流I LMT。
对I 1进行调整后得到I 3的具体过程如下：
Figure PCTCN2020104454-appb-000007
其中，I LMT为预设电流。即，根据I 1的等比例关系获得I 3。
结合图2，实线椭圆3为实际电流的轨迹，即I 1与I 2的和I 12。
当I 1与I 2之和I 12大于I LMT时，通过I 1对正序无功电流进行限幅后，正序无功电流和负序无功电流的和仍然会超过预设电流I LMT。因此，需要根据I 1与I 12的比例和I LMT对I 1进行等比例缩小得到I 3。
因此，利用I 3对正序无功电流进行限幅时，能够使正序无功电流与负序无功电流之和不超过预设电流I LMT。
下面介绍获得I 4的过程。
参见图6，该图为本申请实施例提供的一种获得I 4的方法流程图。
该方法包括：
步骤601：判断I 1与I 2的和I 12是否小于等于I LMT；若是(即图中Y)，则执行步骤602；若否(即图中N)，则执行步骤603。
其中，I 12＝I 1+I 2。
步骤602：I 4等于I 2，即I 12≤I LMT时，I 4＝I 2。
当I 1与I 2之和I 12小于等于I LMT时，表明通过U 1、U 2、U 02和I Q0获得的I 1和I 2均未超过预设电流I LMT，因此，可以直接将I 2作为I 4，利用I 4对负序无功电流进行限幅，从而使 负序无功电流与正序无功电流之和不超过预设电流。
步骤603：即I 12>I LMT时，根据I 2与I 12的比例和I LMT获得I 4。
当I 1与I 2之和I 12大于I LMT时，表明通过U 1、U 2、U 02和I Q0获得的I 1和I 2后，I 1与I 2之和I 12超过预设电流I LMT，因此，需要根据I 2与I 12的比例和I LMT对I 1与I 2进行等比例缩小得到I 4，然后再利用调整后得到的I 4对负序无功电流进行限幅，从而使负序无功电流与正序无功电流的之和不超过预设电流I LMT。
对I 2进行调整后得到I 4的公式如下：
Figure PCTCN2020104454-appb-000008
其中，I LMT为预设电流。即，根据I 2的等比例关系获得I 4。
获得I 4的原理与获得I 3的原理相类似，具体原理可以参见步骤403以及图2，此处不再赘述。
在以上获得I 3和I 4的过程中，无需经过反复迭代的计算，而是通过U 1、U 2、U 02和I Q0直接获得I 3和I 4，然后利用I 3对正序无功电流进行限幅，使正序无功电流不超过I 3；利用I 4对负序无功电流进行限幅，使负序无功电流不超过I 4。因此，本申请实施例提供的电流控制方法，可以降低获得符合要求的正序无功电流和负序无功电流所需要的时间。
步骤204：利用I 3对正序无功电流进行限幅，利用I 4对负序无功电流进行限幅。
利用I 3对正序无功电流进行限幅以及利用I 4对负序无功电流进行限幅，从而使正序无功电流与负序无功电流之和不超过预设电流I LMT。
利用I 3对正序无功电流进行限幅可以为对正序无功电流指令值进行限幅，具体为|I Q1 *|≤I 3；利用I 4对负序无功电流进行限幅可以为对负序无功电流指令值进行限幅，具体为|I Q2 *|≤I 4。
其中，I Q1 *为正序无功电流指令值；I Q2 *为负序无功电流指令值。
利用I 3对正序无功电流指令值进行限幅后，可以根据限幅后的正序无功电流指令值和限幅后的负序无功电流指令值对变流器进行控制，具体可以根据限幅后的正序无功电流指令值和限幅后的负序无功电流指令值，生成变流器中开关管的驱动脉冲信号，进而使变流器的电流不会出现过流现象。
为了本领域技术人员更好地理解本申请实施例提供的技术方案的技术效果，下面结合现有技术中的方案进行对比说明，分别参见图7A和图7B，其中，图7A为现有技术的一种无功电流调节的效果图；图7B为本申请实施例提供的一种无功电流调节的效果图。
从图7A可以看出，现有技术提供的技术方案对于无功电流的调节时间超过了100ms，而图7B本申请实施例提供的方案对于无功电流的调节时间小于30ms。显然，30ms比100ms缩短了无功电流的调节时间，从而满足电网对于无功电流调节的时间要求。
因此，本申请实施例提供的电流控制方法，在正序无功电流指令值和负序无功电流指令值生成时，利用第三电流限值对正序无功电流指令值进行限幅，利用第四电流限值对负序无功电流指令值进行限幅，从而使正序无功电流不超过第三电流限值，负序无功电流不超过第四电流限值，从而防止在电压不对称故障时注入的负序无功电流造成电流过流。该电流控制方法可以直接一次性地获得正序无功电流的限幅值和负序无功电流的限幅值，无 需经过反复迭代的计算，在较短的时间内获得符合要求的正序无功电流和负序无功电流，因此可以缩短无功电流的调节时间。本申请提供的技术方案，在电压不对称故障时，可以在满足时间要求的前提下，将符合要求的正序无功电流和负序无功电流注入到电网中时，解决负序无功电流使变流器过电流的问题。
方法实施例二：
本申请实施例二中提供的电流控制方法，在对正序无功电流进行限幅以及对负序无功电流进行限幅的基础上，进一步对正序有功电流进行限幅。
参见图8，该图为本申请实施例提供的又一种电流控制方法流程图。
其中，步骤701-步骤703与方法实施例一中步骤201-步骤203相类似，此处不再赘述。
在步骤701-步骤703的基础上，该方法还包括：
步骤704：根据I 3和I 4获得第五电流限值I 5。
当电网电压出现不对称故障时，为了保证安全性，还需要对正序有功电流进行限幅。
因此，在对无功电流进行限幅的同时，还需要对正序有功电流进行限幅。
根据I 3和I 4获得第五电流限值I 5的公式如下：
Figure PCTCN2020104454-appb-000009
其中，I LMT为预设电流；K 3为正序有功电流的预设调节系数，0<K 3≤1。
由上述公式可知，I 5的取值为
Figure PCTCN2020104454-appb-000010
和K 3·I LMT中的较大值。
当
Figure PCTCN2020104454-appb-000011
时，
Figure PCTCN2020104454-appb-000012
当
Figure PCTCN2020104454-appb-000013
时，I 5＝K 3·I LMT。
而当
Figure PCTCN2020104454-appb-000014
时，I 5可以取值为
Figure PCTCN2020104454-appb-000015
或K 3·I LMT。
本申请实施例提供的电流控制方法，在获取I 5的过程中，无需经过反复迭代的计算，在获得I 3和I 4后，即可根据I 3和I 4直接获得I 5，从而降低了获得符合要求的正序有功电流的时间。因此，采用本申请提供的技术方案，变流器能够在较短的时间内，对正序有功电流限幅、对正序无功电流限幅、对负序无功电流限幅。
步骤705：利用I 3对正序无功电流进行限幅，利用I 4对负序无功电流进行限幅，利用I 5对正序有功电流进行限幅。
利用I 3对正序无功电流进行限幅以及利用I 4对负序无功电流进行限幅的具体过程可以参见方法实施例一及步骤204，此处不在不再赘述。下面详细介绍利用I 5对正序有功电流进行限幅。
利用I 5对正序有功电流进行限幅可以为对正序有功电流指令值进行限幅，具体为|I P1 *|≤I 5。
其中，I P1 *为正序有功电流指令值。
对正序有功电流指令值、正序无功电流指令值和负序无功电流指令值限幅后，可以根据限幅后的正序有功电流指令值、限幅后的正序无功电流指令值和限幅后的负序无功电流指令值对变流器进行控制，具体可以根据限幅后的正序有功电流指令值、限幅后的正序无功电流指令值和限幅后的负序无功电流指令值，生成变流器中开关管的驱动脉冲信号，进 而使变流器的电流不会出现过流现象。
本申请实施例提供的电流控制方法可以直接一次性地获得正序有功电流的限幅值、正序无功电流的限幅值和负序无功电流的限幅值，无需经过反复迭代的计算，即可获得符合要求的正序有功电流、负序无功电流和正序无功电流，从而降低获得符合要求的正序有功电流、负序无功电流和正序无功电流所需要的时间。因此，变流器能够在满足时间要求的前提下，将符合要求的正序无功电流和负序无功电流注入到电网中，解决负序无功电流使变流器过电流的问题。
系统实施例一：
参见图9，该图为本申请实施例提供的一种变流系统的示意图。
该变流系统至少包括：变流器103和控制器904。
在某些实现方式中，变流系统进一步包括变压器102，下面以变流系统包括变压器102为例进行介绍。
变流器103第一侧用于连接直流电，变流器103的第二侧用于连接变压器102的第一侧。
变流器103可以为双向变流器，即可以将直流电转换为交流电输送给电网101，也可以将所述电网101传送的交流电整流为直流电。
变压器102的第二侧用于连接电网101。
变压器102可以将变流器103传输的交流电进行变压变换后通过传输线给电网101。
由于在实际工作过程中的场景比较复杂，传输线会发生电压不对称故障，例如单相故障或两相故障等。此时保证变流器103不脱网的同时，可以向电网101注入正序无功电流和负序无功电流。但是负序无功电流容易引起变流器103的三相电流不平衡。
为了解决电流的过流问题，以及满足电网对于无功电流调节的时间要求，本申请系统实施例通过控制器904一次性地获取正序无功电流的限幅值和负序无功电流的限幅值，无需经过反复迭代的计算，因此可以缩短无功电流的调节时间。然后控制器904利用正序无功电流的限幅值对正序无功电流进行限幅，利用负序无功电流的限幅值对负序无功电流进行限幅。因此，在电网电压出现不对称故障时，既能满足并网标准无功电流调节时间的要求，又能解决变流器过电流的问题。
具体地，控制器904，用于当发生电压不对称故障时，获得故障后的正序电压U 1、故障后的负序电压U 2、故障前的负序电压U 02和故障前的正序无功电流I Q0，根据I Q0和U 1获得第一电流限值I 1，根据U 2和U 02获得第二电流限值I 2，根据I 1和I 2获得第三电流限值I 3，根据I 1和I 2获得第四电流限值I 4，利用I 3对正序无功电流进行限幅，利用I 4对负序无功电流进行限幅。
控制器904可以通过获得变流器103断开的三相电压来判断是否发送电压不对称故障，具体判断过程参见方法实施例一及图4，此处不再赘述。
控制器904确定发生电压不对称故障后，根据I Q0和U 1获得第一电流限值I 1以及根据U 2和U 02获得第二电流限值I 2。
下面先介绍控制器904根据I Q0和U 1获得I 1后续介绍根据U 2和U 02获得I 2。
为了满足两种不同的限流标准，控制器904可以通过两种不同的方式获得I 1。
第一种：
控制器904根据I Q0、U 1、预设电流I LMT、故障前的正序电压U 01和变流器的额定电压U N获得第一电流限值I 1，具体通过以下公式获得：
I 1＝|I Q0+K 1·I LMT·(U 01-U 1)/U N|
其中，I LMT和U N为变流器的参数，当变流器确定后，I LMT和U N均为已知量。K 1为正序无功电流的预设调节系数；0<K 1≤10；I LMT为变流器的额定电流或所述变流器的最大电流。
第二种：
控制器904根据I Q0、U 1、预设电流I LMT、电压不对称故障的预设触发阈值U TR和变流器的额定电压U N获得第一电流限值I 1，具体通过以下公式获得：
I 1＝|I Q0+K 1·I LMT·(U TR-U 1)/U N|
其中，K 1为正序无功电流的预设调节系数；0<K 1≤10。U TR可以为低电压故障触发阈值，也可以为高电压故障触发阈值；I LMT为变流器的额定电流或所述变流器的最大电流。
下面介绍I 2的获取方式。
控制器904根据U 2、预设电流I LMT、变流器的额定电压U N和U 02获得第二电流限值I 2，具体通过以下公式获得：
I 2＝|K 2·I LMT·(U 02-U 2)/U N|
其中，K 2为负序无功电流的预设调节系数；0<K 2≤10。
由于I 3与I 1成正比，I 4与I 2成正比，因此，控制器904在获得I 1和I 2后，可以根据I 1和I 2获得I 3和I 4。控制器904在获取I 3和I 4的过程中，无需经过复杂的迭代运算，而是直接获得正序无功电流的限幅值，即I 3，直接获得负序无功电流的限幅值，即I 4。
控制器904根据I 1和I 2获得I 3的具体过程如下：
控制器904判断I 1与I 2的和I 12是否小于等于I LMT，即，I 12＝I 1+I 2；若是，则表明通过U 1、U 2、U 02和I Q0获得的I 1与I 2之和I 12未超过预设电流I LMT，因此，控制器904可以直接将I 1作为I 3，即I 12≤I LMT时，I 3＝I 1，利用I 3对正序无功电流进行限幅，从而使正序无功电流与负序无功电流之和不超过预设电流；若否，则表明通过U 1、U 2、U 02和I Q0获得的I 1和I 2后，I 1与I 2的和I 12超过预设电流I LMT，即I 12>I LMT，因此，控制器904需要对I 1进行等比例调整，然后再利用调整后得到的I 3对正序无功电流进行限幅，从而使正序无功电流与负序无功电流的之和不超过预设电流I LMT。
具体地，控制器可以通过如下公式对I 1进行等比例调整：
Figure PCTCN2020104454-appb-000016
其中，I LMT为预设电流。即，根据I 1的等比例关系获得I 3。
当I 1与I 2之和I 12大于I LMT时，通过I 1对正序无功电流进行限幅后，正序无功电流和负序无功电流的和仍然会超过预设电流I LMT。因此，需要根据I 1与I 12的比例和I LMT对I 1与I 2进行等比例缩小得到I 3，以使缩小后的得到的I 3与缩小后I 2之和I 12不超过预设电流I LMT。
因此，控制器904利用I 3对正序无功电流进行限幅时，能够使正序无功电流与负序无功电流之和不超过预设电流I LMT。
控制器904根据I 1和I 2获得I 4的具体过程如下：
控制器904判断I 1与I 2的和I 12是否小于等于I LMT，即，I 12＝I 1+I 2；若是，则表明通过U 1、U 2、U 02和I Q0获得的I 1和I 2均未超过预设电流I LMT，因此，可以直接将I 2作为I 4，即I 12≤I LMT时，I 4＝I 2，利用I 4对负序无功电流进行限幅，从而使负序无功电流与正序无功电流之和不超过预设电流；若否，则表明通过U 1、U 2、U 02和I Q0获得的I 1和I 2后，I 1与I 2之和I 12超过预设电流I LMT，即I 12>I LMT，因此，需要根据I 2与I 12的比例和I LMT对I 2进行等比例缩小得到I 4，然后再利用调整后得到的I 4对负序无功电流进行限幅，从而使负序无功电流与正序无功电流的之和不超过预设电流I LMT。
具体地，控制器可以通过如下公式对I 2进行等比例调整：
Figure PCTCN2020104454-appb-000017
其中，I LMT为预设电流。即，根据I 2的等比例关系获得I 4。
控制器904获得I 3和I 4的过程中，无需经过反复迭代的计算，而是通过U 1、U 2、U 02和I Q0直接获得I 3和I 4，然后利用I 3对正序无功电流进行限幅，使正序无功电流不超过I 3；利用I 4对负序无功电流进行限幅，使负序无功电流不超过I 4。因此，本申请实施例提供的电流控制方法，可以降低获得符合要求的正序无功电流和负序无功电流所需要的时间。
控制器904在获得I 3和I 4后，利用I 3对正序无功电流进行限幅以及利用I 4对负序无功电流进行限幅，从而使正序无功电流与负序无功电流之和不超过预设电流I LMT。
具体地，控制器904可以利用I 3对正序无功电流指令值进行限幅，以达到对正序无功电流进行限幅的目的，同理，控制器904也可以利用I 4对负序无功电流指令值进行限幅。
下面介绍控制器904通过I 3对正序无功电流指令值进行限幅。
控制器904设置|I Q1 *|≤I 3，其中，I Q1 *为正序无功电流指令值。
下面介绍控制器904通过I 4对负序无功电流指令值进行限幅。
控制器904设置|I Q2 *|≤I 4，其中，I Q2 *为负序无功电流指令值。
控制器904利用I 3对正序无功电流指令值进行限幅后，可以根据限幅后的正序无功电流指令值和限幅后的负序无功电流指令值对变流器进行控制，具体可以根据限幅后的正序无功电流指令值和限幅后的负序无功电流指令值，生成变流器中开关管的驱动脉冲信号，进而使变流器的电流不会出现过流现象。
因此，本申请实施例提供的变流系统，控制器可以在生成正序无功电流指令值和负序无功电流指令值时，利用第三电流限值对正序无功电流指令值进行限幅，利用第四电流限值对负序无功电流指令值进行限幅，从而使正序无功电流不超过第三电流限值，负序无功电流不超过第四电流限值，从而防止在电压不对称故障时注入的负序无功电流造成电流过流。该变流系统的控制器可以直接一次性地获得正序无功电流的限幅值和负序无功电流的限幅值，无需经过反复迭代的计算，在较短的时间内获得符合要求的正序无功电流和负序无功电流，因此可以缩短无功电流的调节时间。本申请实施例提供的技术方案，在电压不对称故障时，可以在满足时间要求的前提下，将符合要求的正序无功电流和负序无功电流注入到电网中时，解决负序无功电流使变流器过电流的问题。
系统实施例二：
结合图9，控制器904在正序无功电流进行限幅以及对负序无功电流进行限幅的基础上，进一步对正序有功电流进行限幅。
控制器904可以根据I 3和I 4获得第五电流限值I 5。
当电网电压出现不对称故障时，为了保证安全性，还需要对正序有功电流进行限幅。
因此，控制器904在对无功电流进行限幅的同时，还需要对正序有功电流进行限幅。从而正序有功电流、正序无功电流与负序无功电流之和满足预设电流的要求。
控制器904根据I 3和I 4获得第五电流限值I 5的公式如下：
Figure PCTCN2020104454-appb-000018
其中，I LMT为预设电流；K 3为正序有功电流的预设调节系数，0<K 3≤1。
由上述公式可知，I 5的取值为
Figure PCTCN2020104454-appb-000019
和K 3·I LMT中的较大值。
当
Figure PCTCN2020104454-appb-000020
时，
Figure PCTCN2020104454-appb-000021
当
Figure PCTCN2020104454-appb-000022
时，I 5＝K 3·I LMT。
而当
Figure PCTCN2020104454-appb-000023
时，I 5可以取值为
Figure PCTCN2020104454-appb-000024
或K 3·I LMT。
控制器904在获取I 5的过程中，无需经过反复迭代的计算，在获得I 3和I 4后，即可根据I 3和I 4直接获得I 5，从而降低了获得符合要求的正序有功电流的时间。因此，变流器103能够在较短的时间内，对正序有功电流限幅、对正序无功电流限幅、对负序无功电流限幅。
控制器904利用I 5对正序有功电流进行限幅可以为对正序有功电流指令值进行限幅，具体为|I P1 *|≤I 5。
其中，I P1 *为正序有功电流指令值。
控制器对正序有功电流指令值、正序无功电流指令值和负序无功电流指令值限幅后，可以根据限幅后的正序有功电流指令值、限幅后的正序无功电流指令值和限幅后的负序无功电流指令值对变流器进行控制，具体可以根据限幅后的正序有功电流指令值、限幅后的正序无功电流指令值和限幅后的负序无功电流指令值，生成变流器中开关管的驱动脉冲信号，进而使变流器的电流不会出现过流现象。
本申请实施例提供的变流系统，控制器可以直接一次性地获得正序有功电流的限幅值、正序无功电流的限幅值和负序无功电流的限幅值，无需经过反复迭代的计算，即可获得符合要求的正序有功电流、负序无功电流和正序无功电流，从而降低获得符合要求的正序有功电流、负序无功电流和正序无功电流所需要的时间。因此，变流器能够在满足时间要求的前提下，将符合要求的正序无功电流和负序无功电流注入到电网中，解决负序无功电流使变流器过电流的问题。
应当理解，在本申请中，“至少一个(项)”是指一个或者多个，“多个”是指两个或两个以上。“和/或”，用于描述关联对象的关联关系，表示可以存在三种关系，例如，“A和/或B”可以表示：只存在A，只存在B以及同时存在A和B三种情况，其中A，B可以是单数或者复数。字符“/”一般表示前后关联对象是一种“或”的关系。“以下至少一项(个)”或其类似表达，是指这些项中的任意组合，包括单项(个)或复数项(个)的任意组合。例如，a，b或c中的至少一项(个)，可以表示：a，b，c，“a和b”，“a和c”，“b和c”，或“a和 b和c”，其中a，b，c可以是单个，也可以是多个。
以上所述，以上实施例仅用以说明本申请的技术方案，而非对其限制；尽管参照前述实施例对本申请进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本申请各实施例技术方案的精神和范围。

Claims (23)

  1. 一种电压不对称故障时的电流控制方法，其特征在于，包括：
    当发生电压不对称故障时，获得故障后的正序电压U 1、故障后的负序电压U 2、故障前的负序电压U 02和故障前的正序无功电流I Q0；
    根据所述I Q0和所述U 1获得第一电流限值I 1，根据所述U 2和所述U 02获得第二电流限值I 2；
    根据所述I 1和所述I 2获得第三电流限值I 3，根据所述I 1和所述I 2获得第四电流限值I 4；所述I 3与所述I 1成正比，所述I 4与所述I 2成正比；
    利用所述I 3对正序无功电流进行限幅，利用所述I 4对负序无功电流进行限幅。
  2. 根据权利要求1所述的方法，其特征在于，根据所述I 3和所述I 4获得第五电流限值I 5，利用所述I 5对正序有功电流进行限幅。
  3. 根据权利要求1所述的方法，其特征在于，根据所述I 1和所述I 2获得所述I 3，具体包括：
    当所述I 1与所述I 2的和I 12小于等于预设电流时，所述I 3等于所述I 1；所述预设电流为变流器的额定电流或所述变流器的最大电流；
    当所述I 1与所述I 2的和I 12大于所述预设电流时，按照所述I 1与所述I 12的比例和所述预设电流获得所述I 3。
  4. 根据权利要求1所述的方法，其特征在于，根据所述I 1和所述I 2获得所述I 4，具体包括：
    当所述I 1与所述I 2的和I 12小于等于预设电流时，所述I 4等于所述I 2；所述预设电流为变流器的额定电流或所述变流器的最大电流；
    当所述I 1与所述I 2的和I 12大于所述预设电流时，按照所述I 2与所述I 12的比例和所述预设电流获得所述I 4。
  5. 根据权利要求2所述的方法，其特征在于，根据所述I 3和所述I 4获得第五电流限值I 5，具体包括：
    根据所述I 3、所述I 4和预设电流获得所述I 5；所述预设电流为变流器的额定电流或所述变流器的最大电流。
  6. 根据权利要求3所述的方法，其特征在于，按照所述I 1与所述I 12的比例和所述预设电流获得所述I 3，具体通过以下公式获得：
    Figure PCTCN2020104454-appb-100001
    其中，I LMT为所述预设电流。
  7. 根据权利要求4所述的方法，其特征在于，按照所述I 2与所述I 12的比例和所述预设电流获得所述I 4，具体通过以下公式获得：
    Figure PCTCN2020104454-appb-100002
    其中，I LMT为所述预设电流。
  8. 根据权利要求5所述的方法，其特征在于，根据所述I 3、所述I 4和预设电流获得所 述I 5，具体通过以下公式获得：
    Figure PCTCN2020104454-appb-100003
    其中，I LMT为所述预设电流；K 3为正序有功电流的预设调节系数，0<K 3≤1。
  9. 根据权利要求1-8任一项所述的方法，其特征在于，根据所述I Q0和所述U 1获得第一电流限值I 1，具体通过以下公式获得：
    I 1＝|I Q0+K 1·I LMT·(U 01-U 1)/U N|
    其中，I LMT为预设电流；U 01为故障前的正序电压；U N为变流器的额定电压；K 1为正序无功电流的预设调节系数；0<K 1≤10；所述预设电流为变流器的额定电流或所述变流器的最大电流。
  10. 根据权利要求1-8任一项所述的方法，其特征在于，根据所述I Q0和所述U 1获得第一电流限值I 1，具体通过以下公式获得：
    I 1＝|I Q0+K 1·I LMT·(U TR-U 1)/U N|
    其中，I LMT为预设电流；U TR为电压不对称故障的预设触发阈值；U N为变流器的额定电压；K 1为正序无功电流的预设调节系数；所述预设电流为变流器的额定电流或所述变流器的最大电流。
  11. 根据权利要求1-8任一项所述的方法，其特征在于，根据所述U 2和所述U 02获得第二电流限值I 2，具体通过以下公式获得：
    I 2＝|K 2·I LMT·(U 02-U 2)/U N|
    其中，I LMT为预设电流；U N为变流器的额定电压；K 2为负序无功电流的预设调节系数；0<K 2≤10；所述预设电流为变流器的额定电流或所述变流器的最大电流。
  12. 根据权利要求1-8任一项所述的方法，其特征在于，利用所述I 3对正序无功电流进行限幅、利用所述I 4对负序无功电流进行限幅；具体为：
    |I Q1 *|≤I 3，|I Q2 *|≤I 4；
    其中，I Q1 *为正序无功电流指令值；I Q2 *为负序无功电流指令值。
  13. 根据权利要求2、5或8所述的方法，其特征在于，利用所述I 5对正序有功电流进行限幅；具体为：
    |I P1 *|≤I 5；
    其中，I P1 *为正序有功电流指令值。
  14. 一种变流系统，其特征在于，包括：变流器和控制器；
    所述变流器第一侧用于连接直流电，所述变流器的第二侧用于连接电网；
    所述变流器，用于将直流电转换为交流电输送给所述电网，或，用于将所述电网传送的交流电整流为直流电；
    所述控制器，用于当发生电压不对称故障时，获得故障后的正序电压U 1、故障后的负序电压U 2、故障前的负序电压U 02和故障前的正序无功电流I Q0；根据所述I Q0和所述U 1获得第一电流限值I 1，根据所述U 2和所述U 02获得第二电流限值I 2；根据所述I 1和所述I 2获得第三电流限值I 3，根据所述I Q0和所述U 1获得第四电流限值I 4；利用所述I 3对正序无功电流进行限幅，利用所述I 4对负序无功电流进行限幅；
    其中，所述I 3与所述I 1成正比，所述I 4与所述I 2成正比。
  15. 根据权利要求14所述的系统，其特征在于，所述控制器，还用于根据所述I 3和所述I 4获得第五电流限值I 5，利用所述I 5对正序有功电流进行限幅。
  16. 根据权利要求14所述的系统，其特征在于，所述控制器，具体用于当所述I 1与所述I 2的和I 12小于等于预设电流时，使所述I 3等于所述I 1；所述预设电流为变流器的额定电流或所述变流器的最大电流；
    当所述I 1与所述I 2的和I 12大于所述预设电流时，按照所述I 1与所述I 12的比例和所述预设电流获得所述I 3。
  17. 根据权利要求14所述的系统，其特征在于，所述控制器，具体用于当所述I 1与所述I 2的和I 12小于等于预设电流时，所述I 4等于所述I 2；所述预设电流为变流器的额定电流或所述变流器的最大电流；
    当所述I 1与所述I 2的和I 12大于所述预设电流时，按照所述I 2与所述I 12的比例和所述预设电流获得所述I 4。
  18. 根据权利要求15所述的系统，其特征在于，所述控制器，具体用于根据所述I 3、所述I 4和预设电流获得所述I 5；所述预设电流为变流器的额定电流或所述变流器的最大电流。
  19. 根据权利要求16所述的系统，其特征在于，所述控制器，具体用于通过以下公式获得所述I 3：’
    Figure PCTCN2020104454-appb-100004
    其中，I LMT为所述预设电流。
  20. 根据权利要求17所述的系统，其特征在于，所述控制器，具体用于通过以下公式获得所述I 4：
    Figure PCTCN2020104454-appb-100005
    其中，I LMT为所述预设电流。
  21. 根据权利要求18所述的系统，其特征在于，所述控制器，具体用于通过以下公式获得所述I 5：
    Figure PCTCN2020104454-appb-100006
    其中，I LMT为所述预设电流；K 3为正序有功电流的预设调节系数，0<K 3≤1。
  22. 根据权利要求14-21任一项所述的系统，其特征在于，所述控制器，具体用于通过以下方式对正序无功电流进行限幅，对负序无功电流进行限幅；
    |I Q1 *|≤I 3，|I Q2 *|≤I 4；
    其中，I Q1 *为正序无功电流指令值；I Q2 *为负序无功电流指令值。
  23. 根据权利要求15、19或21所述的系统，其特征在于，所述控制器，具体用于通过以下方式对所述正序有功电流进行限幅；
    |I P1 *|≤I 5；
    其中，I P1 *为正序有功电流指令值。
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