CN113725854A - Seamless switching control method applied to flexible direct current comprehensive voltage regulating device - Google Patents

Seamless switching control method applied to flexible direct current comprehensive voltage regulating device Download PDF

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CN113725854A
CN113725854A CN202111022230.4A CN202111022230A CN113725854A CN 113725854 A CN113725854 A CN 113725854A CN 202111022230 A CN202111022230 A CN 202111022230A CN 113725854 A CN113725854 A CN 113725854A
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voltage
current
flexible direct
grid
direct current
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CN113725854B (en
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范建华
曹乾磊
李保安
宁振
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Qingdao Topscomm Communication 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
    • H02J3/001—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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • 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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
    • 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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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The invention discloses a seamless switching control method applied to a flexible direct current comprehensive voltage regulating device, which comprises the following steps: measuring the power grid voltage at the upstream of a grid-connected point of the flexible direct-current comprehensive voltage regulating device and the voltage of a filter capacitor of the three-level inverter in real time; measuring the current of a low-voltage user side and the filter inductance current of a three-level inverter in real time; calculating a hysteresis loop width value and upper and lower boundary values of the loop width according to the power grid voltage at the upstream of the device grid-connected point, the voltage of a filter capacitor of the three-level inverter and a preset switching period in the step 1; and carrying out seamless switching control on the device according to the reference voltage, the filter inductance current of the three-level inverter and the upper and lower boundary values of the width of the hysteresis loop. The invention can effectively improve the control stability problem of the current source mode and the voltage source mode of the low-voltage treatment device when the power grid fails without detecting the fault state of the power grid, realizes the uninterrupted power supply of the load, thereby realizing the seamless switching control of the grid-connected/off-grid mode of the device and having strong engineering practicability.

Description

Seamless switching control method applied to flexible direct current comprehensive voltage regulating device
Technical Field
The invention relates to the technical field of power electronic equipment control, in particular to a seamless switching control method applied to a flexible direct current comprehensive voltage regulating device.
Background
At present, the problem of low voltage is complained by more and more county power grid users, and the quality of life of residents is seriously influenced. The flexible direct-current comprehensive voltage regulating device based on the power electronic converter is favored by the national power grid and is used for solving the problem pain point of low voltage phenomenon caused by less distribution points of a transformer substation, overlong transmission line, too thin line and the like.
The low voltage device has two modes of operation: the device comprises a grid-connected mode and an off-grid mode, wherein the device in the grid-connected mode is a current source and sends compensation current to the grid; and the equipment in the off-grid mode is a voltage source and independently supplies power for a low-voltage load. When the power grid close to the compensation position of the device fails, the low-voltage treatment equipment in the original grid-connected operation mode is switched to an off-grid mode from a grid-connected operation mode; when the power grid recovers power supply, the equipment needs to be switched from voltage source control to current source control to continue grid-connected operation.
The hysteresis control is a nonlinear current tracking control technology, is commonly used in the field of power electronic converter control, has simple control method, high response speed and good stability, can realize the fast tracking control of current, and has better robustness.
At present, the control methods in two modes are more, such as droop control, grid-connected PQ control, virtual synchronous generator technology, off-grid VF (constant voltage constant frequency) control and the like, but the realization of seamless switching between the modes without shutdown is still a huge challenge. The control method needs to monitor the state of the power grid all the time, and if the state is determined to be a fault state, the reference current and the reference voltage are changed correspondingly, but it is difficult to ensure that the load power supply voltage and the load current are not distorted.
Disclosure of Invention
Aiming at the defects and shortcomings of the prior art, the invention provides a seamless switching control method applied to a flexible direct-current comprehensive voltage regulating device, which effectively solves the problem of control stability of a current source mode and a voltage source mode when a power grid fails in a low-voltage treatment device, and realizes uninterrupted power supply of a load, thereby realizing seamless switching control of a grid-connected/off-grid mode of the device.
The purpose of the invention can be realized by the following technical scheme:
a seamless switching control method applied to a flexible direct current comprehensive voltage regulating device is characterized in that the flexible direct current comprehensive voltage regulating device is installed in front of a low-voltage load user behind a long-distance power transmission line and comprises a three-level rectifier, a three-level inverter, a filter circuit and a direct current energy storage element; the three-level rectifier comprises an output side connected with the direct-current energy storage element and a rectifying side connected with the filter circuit; the rectifier direct-current energy storage element is connected with the inverter direct-current energy storage element through a direct-current power transmission line;
the method comprises the following steps:
step 1: measuring the power grid voltage at the upstream of a grid-connected point of the flexible direct-current comprehensive voltage regulating device and the filter capacitor voltage of the three-level inverter in real time;
step 2: measuring the current of a low-voltage user side and the filter inductance current of a three-level inverter in real time;
and step 3: calculating a hysteresis loop width value and upper and lower boundary values of the loop width according to the power grid voltage at the upstream of the device grid-connected point, the voltage of a filter capacitor of the three-level inverter and a preset switching period in the step 1;
and 4, step 4: and carrying out seamless switching control on the flexible direct current comprehensive voltage regulating device according to the reference voltage, the three-level inverter filter inductance current and the upper and lower boundary values of the hysteresis loop width.
Further, when a power grid region before the compensation position of the flexible direct-current comprehensive voltage regulating device fails, the power grid voltage at the upstream of the grid-connected point of the flexible direct-current comprehensive voltage regulating device is not affected.
Further, in the step 1, the power grid voltage at the upstream of the grid-connected point of the flexible direct-current comprehensive voltage regulating device is used as a hysteresis control reference voltage.
Further, the voltage of the filter capacitor of the three-level inverter in the step 1 participates in the calculation of the active damping control quantity, and the active damping adjustment coefficient is multiplied by the difference value between the voltage of the power grid at the upstream of the grid-connected point of the flexible direct-current comprehensive voltage regulating device and the voltage of the filter capacitor of the three-level inverter to obtain the active damping control quantity, wherein the difference is firstly made and then multiplied by the coefficient.
Further, the low-voltage user side current value obtained in the step 2 is used as a hysteresis control reference current value.
Furthermore, in the step 3, active damping control quantity participates in the calculation process of the upper and lower boundaries of the hysteresis loop width, the upper boundary value of the loop width is obtained by subtracting the active damping control quantity from the hysteresis loop control reference current value and then adding a half loop width value of the hysteresis loop, and the lower boundary value of the loop width is obtained by subtracting the active damping control quantity from the hysteresis loop control reference current value and then subtracting the half loop width value of the hysteresis loop.
Further, the specific rule for performing seamless switching control on the flexible direct current integrated pressure regulating device in the step 4 is as follows:
when the hysteresis loop control reference voltage is positive, if the filter inductance current of the three-level inverter is larger than the upper boundary of the hysteresis loop width, the inverter outputs a positive level to reduce the filter inductance current; if the filter inductance current is smaller than the lower boundary of the ring width, the inverter outputs zero level, so that the filter inductance current is increased.
When the hysteresis loop control reference voltage is negative, if the filter inductance current of the three-level inverter is greater than the upper boundary of the hysteresis loop width, the inverter outputs zero level to reduce the filter inductance current; if the filter inductance current is smaller than the lower boundary of the ring width, the inverter outputs a negative level, so that the filter inductance current is increased.
The invention has the beneficial technical effects that: the problem of control stability of a current source mode and a voltage source mode of the flexible direct-current comprehensive voltage regulating device when a power grid fails can be effectively solved without detecting the fault state of the power grid, uninterrupted power supply of a load is realized, seamless switching control of a grid-connected mode/off-grid mode of the device can be realized without a switching mode control method, and the flexible direct-current comprehensive voltage regulating device has strong engineering practicability.
Drawings
Fig. 1 is a schematic structural diagram and an electrical connection diagram of a flexible dc integrated voltage regulating device in an embodiment of the present invention.
Fig. 2 and 3 are basic schematic diagrams of hysteresis control in an embodiment of the present invention.
Fig. 4 is an overall flow diagram of the present invention.
Reference numerals: a is a power grid voltage sampling position at the upstream of a compensation position B of the flexible direct current comprehensive voltage regulating device, and S is a line switch; 1 is a transformer substation, 2 and 3 are line impedances, 4 and 5 are bypass loads, and 6 is a terminal low-voltage load; 7 is a three-current smoothing device, 71 and 72 are rectifier side filter inductors, 73 is a rectifier side filter capacitor, 74 is a rectifier side upper bus capacitor, and 75 is a rectifier side lower bus capacitor; 8 is a three-level inverter, 81 is an inverter side filter inductor, 82 is an inverter side filter capacitor, 84 is an inverter side upper bus capacitor, and 85 is an inverter side lower bus capacitor; t1, T2, T3 and T4 are IGBTs of the inverter.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
Examples are given.
As shown in fig. 4, a seamless switching control method applied to a flexible dc integrated voltage regulator includes the following steps:
step 1: as shown in figure 1, the network voltage U at the upstream A of the compensation position B of the flexible direct current comprehensive voltage regulating device is measured in real timeGridAAnd three-level inverter filter capacitor voltage UCap。
UGridAAs a reference voltage for hysteresis control, i.e. a desired value of the low-side load voltage, in order to keep the low-side load voltage always following UGridAWhen the grid-connected mode/off-grid mode is switched, the load voltage cannot be distorted;
according to UGridAAnd UCapCalculating active damping control quantity IDampThe calculation formula of (2) is as follows:
IDamp＝Kd*(UGridA-UCap)
in the above formula, KdThe active damping adjustment coefficient.
Step 2: real-time measurement of low-voltage user side current ILoadAnd three-level inverter filter inductor current Iinv。
ILoadReference current I as hysteresis controlrefI.e. iref＝iLoadThe purpose is for the inverter to supply all the current required by the load.
And step 3: according to UGridAAnd UCapAnd calculating a hysteresis loop width value H and upper and lower boundary values of the hysteresis loop width.
The calculation formula of the hysteresis loop width value is as follows:
when reference voltage UGridAIn order to be the right time,
Figure BDA0003241945460000031
when reference voltage UGridAWhen the voltage is negative,
Figure BDA0003241945460000032
wherein L is inductance of filter inductor on inverter side, and UdcPosFor bus voltage on the inverting side, UdcNegFor inverting the lower bus voltage, TPWMThe switching period of the inverter side IGBT is shown.
Upper boundary value of hysteresis loop widthrefHAnd a lower boundary value IrefLThe calculation formula of (2) is as follows:
IrefH＝Iref-IDamp+H/2
IrefL＝Iref-IDamp-H/2
refer to fig. 2 and 3.
Step (ii) of4: according to a reference voltage UgridA、IinvAnd carrying out seamless switching control on the flexible direct current comprehensive pressure regulating device according to the upper and lower boundary values of the width of the hysteresis loop.
When reference voltage UgridAIf the inverter filters the inductor current I, theinvGreater than upper boundary I of hysteresis loop widthrefHTurn on T1, T2, turn off T3, T4, and the inverter outputs a positive level Udc+To make the filter inductance current IinvDecrease; if the inverter filters the inductive current IinvLess than the lower boundary I of the ring widthrefLTurning on T3 and T2, turning off T1 and T4, and outputting zero level U by the inverterdc0To make the filter inductance current IinvAnd is increased.
When reference voltage UgridAWhen negative, if the inverter filters the inductive current IinvGreater than upper boundary I of hysteresis loop widthrefHTurning on T2 and T3, turning off T4 and T1, and outputting zero level U by the inverterdc0To make the filter inductance current IinvDecrease; if the inverter filters the inductive current IinvLess than the lower boundary I of the ring widthrefLTurning on T4, T3, turning off T2, T1, the inverter outputs a negative level Udc-To make the filter inductance current IinvAnd is increased.
The above-mentioned embodiments are illustrative of the specific embodiments of the present invention, and are not restrictive, and those skilled in the relevant art can make various changes and modifications to obtain corresponding equivalent technical solutions without departing from the spirit and scope of the present invention, so that all equivalent technical solutions should be included in the scope of the present invention.

Claims (7)

1. A seamless switching control method applied to a flexible direct current comprehensive voltage regulating device is characterized in that the flexible direct current comprehensive voltage regulating device is arranged in front of a low-voltage load user behind a long-distance power transmission line and comprises a three-level rectifier, a three-level inverter, a filter circuit and a direct current energy storage element; the three-level rectifier comprises an output side connected with the direct-current energy storage element and a rectifying side connected with the filter circuit; the rectifier direct-current energy storage element is connected with the inverter direct-current energy storage element through a direct-current power transmission line;
the method comprises the following steps:
step 1: measuring the power grid voltage at the upstream of a grid-connected point of the flexible direct-current comprehensive voltage regulating device and the voltage of a filter capacitor of the three-level inverter in real time;
step 2: measuring the current of a low-voltage user side and the filter inductance current of a three-level inverter in real time;
and step 3: calculating a hysteresis loop width value and upper and lower boundary values of the loop width according to the power grid voltage at the upstream of the device grid-connected point, the voltage of a filter capacitor of the three-level inverter and a preset switching period in the step 1;
and 4, step 4: and carrying out seamless switching control on the flexible direct current comprehensive voltage regulating device according to the reference voltage, the three-level inverter filter inductance current and the upper and lower boundary values of the hysteresis loop width.
2. The seamless switching control method applied to the flexible direct current integrated voltage regulation device according to claim 1, wherein in the step 1, when a power grid region before the compensation position of the flexible direct current integrated voltage regulation device fails, the power grid voltage at the upstream of the grid-connected point of the flexible direct current integrated voltage regulation device is not affected.
3. The seamless switching control method applied to the flexible direct current integrated voltage regulation device according to claim 1, wherein a grid voltage at an upstream of a grid-connected point of the flexible direct current integrated voltage regulation device in the step 1 is used as a hysteresis control reference voltage.
4. The seamless switching control method applied to the flexible direct current comprehensive voltage regulation device according to claim 1, wherein the voltage of the filter capacitor of the three-level inverter in the step 1 participates in the calculation of the active damping control quantity, and the active damping control quantity is obtained by multiplying an active damping regulation coefficient by a difference value between the voltage of a power grid at the upstream of a grid-connected point of the flexible direct current comprehensive voltage regulation device and the voltage of the filter capacitor of the three-level inverter, wherein the difference is taken first and then multiplied by the coefficient.
5. The seamless switching control method applied to the flexible direct current comprehensive voltage regulating device according to claim 4, wherein the low-voltage user side current value obtained in the step 2 is used as a hysteresis control reference current value.
6. The seamless switching control method applied to the flexible direct current comprehensive voltage regulating device according to claim 1, wherein active damping control quantity participates in the calculation process of the upper and lower boundaries of the hysteresis loop width in step 3, an upper boundary value of the hysteresis loop width is obtained by subtracting the active damping control quantity from a hysteresis loop control reference current value and then adding a half loop width value of the hysteresis loop, and a lower boundary value of the hysteresis loop width is obtained by subtracting the active damping control quantity from the hysteresis loop control reference current value and then subtracting the half loop width value of the hysteresis loop.
7. The seamless switching control method applied to the flexible direct current integrated voltage regulating device according to claim 1, wherein the specific rule for performing the seamless switching control of the flexible direct current integrated voltage regulating device in the step 4 is as follows:
when the hysteresis loop control reference voltage is positive, if the filter inductance current of the three-level inverter is larger than the upper boundary of the hysteresis loop width, the inverter outputs a positive level to reduce the filter inductance current; if the filter inductance current is smaller than the lower boundary of the ring width, the inverter outputs zero level, so that the filter inductance current is increased.
When the hysteresis loop control reference voltage is negative, if the filter inductance current of the three-level inverter is greater than the upper boundary of the hysteresis loop width, the inverter outputs zero level to reduce the filter inductance current; if the filter inductance current is smaller than the lower boundary of the ring width, the inverter outputs a negative level, so that the filter inductance current is increased.
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Cited By (1)

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