CN113725854B - 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 PDFInfo
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- CN113725854B CN113725854B CN202111022230.4A CN202111022230A CN113725854B CN 113725854 B CN113725854 B CN 113725854B CN 202111022230 A CN202111022230 A CN 202111022230A CN 113725854 B CN113725854 B CN 113725854B
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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
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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
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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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
- H02J3/38—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
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- 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)
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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 and the three-level inverter filter capacitor voltage at the upstream of the grid connection point of the flexible direct current comprehensive voltage regulating device in real time; measuring low-voltage user side current and three-level inverter filter inductance current in real time; calculating a hysteresis loop width value and loop width upper and lower boundary values according to the power grid voltage at the upstream of the grid connection point in the step 1, the filter capacitor voltage of the three-level inverter and a preset switching period; and performing seamless switching control on the device according to the reference voltage, the three-level inverter filter inductance current and the hysteresis loop width upper and lower boundary values. 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 power grid fault state, and realize uninterrupted power supply of the load, thereby realizing seamless switching control of the grid connection/grid disconnection mode of the device and having strong engineering practicability.
Description
Technical Field
The invention relates to the technical field of control of power electronic equipment, 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 life quality 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 of pain points of low voltage phenomenon caused by less distribution points, overlong transmission lines, too thin lines and the like of the transformer substation.
The low voltage device has two modes of operation: the method comprises a grid-connected mode and a grid-off mode, wherein equipment is a current source in the grid-connected mode, and compensation current is sent to an electric network; the device is a voltage source in off-grid mode and independently supplies power to the low-voltage load. When a power grid close to the compensation position of the device fails, the original low-voltage treatment equipment in grid-connected operation is switched from a grid-connected operation mode to an off-grid mode; when the power grid resumes the power supply, the equipment still needs to switch from voltage source control to current source control, continues the 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 the advantages of simple control method realization, high response speed and good stability, can realize rapid current tracking control, 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 realizing seamless switching between modes under the condition of no shutdown is still a great challenge. The control method needs to monitor the power grid state all the time, and if the power grid state is judged to be in a fault state, the reference current and the reference voltage are correspondingly changed, but the power supply voltage and the power supply current of the load are difficult to ensure not to generate distortion.
Disclosure of Invention
Aiming at the defects and drawbacks of the prior art, the invention provides a seamless switching control method applied to a flexible direct current comprehensive voltage regulating device, which effectively improves the control stability problem of a current source mode and a voltage source mode when a power grid of a low-voltage treatment device breaks down, and realizes uninterrupted power supply of a load, thereby realizing seamless switching control of a grid connection/grid disconnection mode of the device.
The aim of the invention can be achieved by the following technical scheme:
the seamless switching control method applied to the 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 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 inverter comprises an input side connected with the direct-current energy storage element and an inversion side connected with the filter circuit, and the three-level rectifier comprises an output side connected with the direct-current energy storage element and a rectification 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 and the three-level inverter filter capacitor voltage at the upstream of the grid connection point of the flexible direct current comprehensive voltage regulating device in real time;
step 2: measuring low-voltage user side current and three-level inverter filter inductance current in real time;
step 3: calculating a hysteresis loop width value and loop width upper and lower boundary values according to the power grid voltage at the upstream of the grid connection point in the step 1, the filter capacitor voltage of the three-level inverter and a preset switching period;
step 4: and performing 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 hysteresis loop width upper and lower boundary values.
Further, when a power grid area 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, the grid voltage at the upstream of the parallel point of the flexible direct current comprehensive voltage regulating device in the step 1 is used as a hysteresis control reference voltage.
Further, the three-level inverter filter capacitor voltage 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 between the grid voltage at the upstream of the parallel network of the flexible direct current comprehensive voltage regulating device and the three-level inverter filter capacitor voltage to obtain the active damping control quantity, namely 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.
Further, in the step 3, the active damping control amount is involved in the calculation process of the upper and lower boundaries of the hysteresis loop width, the hysteresis loop control reference current value is used for subtracting the active damping control amount and then adding one half of the hysteresis loop width value to obtain the upper boundary value of the loop width, and the hysteresis loop control reference current value is used for subtracting the active damping control amount and then subtracting one half of the hysteresis loop width value to obtain the lower boundary value of the loop width.
Further, the specific rule for performing the seamless switching control of the flexible direct current comprehensive voltage regulating device in the step 4 is as follows:
when the hysteresis control reference voltage is positive, if the three-level inverter filtering inductance current is greater than the hysteresis width upper boundary, the inverter outputs positive level, so that the filtering inductance current is reduced; if the filter inductor current is less than the lower boundary of the loop width, the inverter outputs zero level, so that the filter inductor current is increased.
When the hysteresis control reference voltage is negative, if the three-level inverter filtering inductance current is greater than the hysteresis width upper boundary, the inverter outputs zero level, so that the filtering inductance current is reduced; if the filter inductor current is less than the lower boundary of the loop width, the inverter outputs a negative level, so that the filter inductor current is increased.
The beneficial technical effects of the invention are as follows: the control stability problem of the current source mode and the voltage source mode of the flexible direct current comprehensive voltage regulating device when the power grid fails can be effectively improved without detecting the power grid failure state, uninterrupted power supply of a load is realized, seamless switching control of the grid connection/grid disconnection 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 voltage regulator in an embodiment of the present invention.
Fig. 2 and 3 are basic diagrams of hysteresis control in an embodiment of the present invention.
Fig. 4 is a general flow chart 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-electric current smoothing device, 71 and 72 are rectifying side filter inductors, 73 is rectifying side filter capacitors, 74 is rectifying side upper bus capacitors, and 75 is rectifying side lower bus capacitors; 8 is a three-level inverter, 81 is an inversion side filter inductor, 82 is an inversion side filter capacitor, 84 is an inversion side upper bus capacitor, and 85 is an inversion side lower bus capacitor; t1, T2, T3 and T4 are IGBTs of the inverter.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Examples
As shown in fig. 4, a seamless switching control method applied to a flexible direct current integrated voltage regulating device comprises the following steps:
step 1: as shown in fig. 1, the power grid voltage U at the upstream a of the compensation position B of the flexible dc voltage regulator is measured in real time GridA And three-level inverter filter capacitor voltage U Cap 。
U GridA As reference voltage for hysteresis control, i.e. the desired value of the load voltage on the low-voltage side, the purpose is to let the load voltage on the low-voltage side always follow U GridA When the grid-connected/off-grid mode is switched, the load voltage cannot be distorted;
according to U GridA And U Cap Calculating an active damping control quantity, wherein the active damping control quantity I Damp The calculation formula of (2) is as follows:
I Damp ＝K d *(U GridA -U Cap )
in the above, K d Is an active damping adjustment coefficient.
Step 2: measuring low-voltage user-side current I in real time Load And three-level inverter filter inductor current I inv 。
I Load Reference current I as hysteresis control ref I.e. i ref ＝i Load The objective is to have the inverter supply all the current required by the load.
Step 3: according to U GridA And U Cap And 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 the reference voltage U GridA In order to be positive in this respect,
when the reference voltage U GridA When the value of the voltage is negative, the voltage is higher,
wherein L is the inductance value of the inversion side filter inductance, U dcPos For the bus voltage on the inversion side, U dcNeg For inverting the lower bus voltage, T PWM Is the switching period of the inverter side IGBT.
Upper boundary value I of hysteresis loop width refH And lower boundary value I refL The calculation formula of (2) is as follows:
I refH ＝I ref -I Damp +H/2
I refL ＝I ref -I Damp -H/2
reference is made to fig. 2, 3.
Step 4: according to the reference voltage U gridA 、I inv And performing seamless switching control of the flexible direct current comprehensive voltage regulating device by using the upper and lower boundary values of the hysteresis ring width.
When the reference voltage U gridA If the inverter filters the inductor current I inv Greater than the upper boundary I of hysteresis loop width refH T1 and T2 are opened, T3 and T4 are closed, and the inverter outputs positive level U dc+ To make the filter inductance current I inv A reduction; if the inverter filters the inductor current I inv Less than the lower boundary I of the annular width refL T3 and T2 are opened, T1 and T4 are closed, and the inverter outputs zero level U dc0 To make the filter inductance current I inv Increasing.
When the reference voltage U gridA If the inverter filters the inductor current I when negative inv Greater than the upper boundary I of hysteresis loop width refH T2 and T3 are opened, T4 and T1 are closed, and the inverter outputs zero level U dc0 To make the filter inductance current I inv A reduction; if the inverter filters the inductor current I inv Less than the lower boundary I of the annular width refL T4 and T3 are opened, T2 and T1 are closed, and the inverter outputs a negative level U dc- To make the filter inductance current I inv Increasing.
The above embodiments are illustrative of the specific embodiments of the present invention, and not restrictive, and various changes and modifications may be made by those skilled in the relevant art without departing from the spirit and scope of the invention, so that all such equivalent embodiments are intended to be within the scope of the invention.
Claims (5)
1. The seamless switching control method applied to the 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 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 inverter comprises an input side connected with the direct-current energy storage element and an inversion side connected with the filter circuit, and the three-level rectifier comprises an output side connected with the direct-current energy storage element and a rectification 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 and the three-level inverter filter capacitor voltage at the upstream of the grid connection point of the flexible direct current comprehensive voltage regulating device in real time;
step 2: measuring low-voltage user side current and three-level inverter filter inductance current in real time;
step 3: according to the grid voltage U upstream of the grid connection point in the step 1 GridA Three-level inverter filter capacitor voltage U Cap Calculating a hysteresis loop width value H and upper and lower boundary values of loop width in a preset switching period;
when U is GridA The method is positive:
when U is GridA Negative:
wherein L is the inductance value of the inversion side filter inductance, U dcPos For the bus voltage on the inversion side, U dcNeg For inverting the lower bus voltage, T PWM The switching period of the inversion side IGBT;
the method comprises the steps of calculating the upper and lower boundaries of the hysteresis loop width, wherein active damping control quantity is involved in the calculation process of the upper and lower boundaries of the hysteresis loop width, subtracting the active damping control quantity from a hysteresis loop control reference current value, adding a half loop width value of the hysteresis loop to obtain an upper boundary value of the loop width, subtracting the active damping control quantity from the hysteresis loop control reference current value, and subtracting the half loop width value of the hysteresis loop to obtain a lower boundary value of the loop width;
step 4: seamless switching control of the flexible direct current comprehensive voltage regulating device is carried out according to the reference voltage, the three-level inverter filter inductance current and the hysteresis loop width upper and lower boundary values;
the specific rule for performing seamless switching control of the flexible direct current comprehensive voltage regulating device is as follows:
when the hysteresis control reference voltage is positive, if the three-level inverter filtering inductance current is greater than the hysteresis width upper boundary, the inverter outputs positive level, so that the filtering inductance current is reduced; if the filter inductance current is smaller than the lower boundary of the loop width, the inverter outputs zero level, so that the filter inductance current is increased;
when the hysteresis control reference voltage is negative, if the three-level inverter filtering inductance current is greater than the hysteresis width upper boundary, the inverter outputs zero level, so that the filtering inductance current is reduced; if the filter inductance current is smaller than the lower boundary of the loop width, the inverter outputs a negative level, so that the filter inductance current is increased.
2. The seamless switching control method applied to the flexible direct current integrated voltage regulating device according to claim 1, wherein in the step 1, when a power grid area before the compensation position of the flexible direct current integrated voltage regulating device fails, the power grid voltage upstream of the parallel network point of the flexible direct current integrated voltage regulating device is not affected.
3. The seamless switching control method applied to the flexible direct current integrated voltage regulating device according to claim 1, wherein the grid voltage upstream of the parallel point of the flexible direct current integrated voltage regulating 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 integrated voltage regulating device according to claim 1, wherein the three-level inverter filter capacitor voltage in the step 1 participates in calculation of an active damping control amount, and the active damping control amount is obtained by multiplying an active damping regulation coefficient by a difference between a grid voltage upstream of a parallel point of the flexible direct current integrated voltage regulating device and the three-level inverter filter capacitor voltage, which is noted as difference first and then multiplication coefficient.
5. The seamless switching control method applied to the flexible direct current integrated 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.
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| CN101515763A (en) * | 2009-03-27 | 2009-08-26 | 南京航空航天大学 | Series-parallel connection output tri-level half-bridge inverter and half period hysteresis control method thereof |
| CN105391328A (en) * | 2015-10-30 | 2016-03-09 | 上能电气股份有限公司 | Hysteresis loop control method for three-level inverter |
| WO2020117169A2 (en) * | 2018-12-03 | 2020-06-11 | Yildiz Teknik Universitesi | A dead-time control method for power electronics converters and a circuit for the application of this method |
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| CN101515763A (en) * | 2009-03-27 | 2009-08-26 | 南京航空航天大学 | Series-parallel connection output tri-level half-bridge inverter and half period hysteresis control method thereof |
| CN105391328A (en) * | 2015-10-30 | 2016-03-09 | 上能电气股份有限公司 | Hysteresis loop control method for three-level inverter |
| WO2020117169A2 (en) * | 2018-12-03 | 2020-06-11 | Yildiz Teknik Universitesi | A dead-time control method for power electronics converters and a circuit for the application of this method |
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