CN113991748A - Seamless switching control method for voltage source type inverter based on droop control - Google Patents
Seamless switching control method for voltage source type inverter based on droop control Download PDFInfo
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- CN113991748A CN113991748A CN202111207476.9A CN202111207476A CN113991748A CN 113991748 A CN113991748 A CN 113991748A CN 202111207476 A CN202111207476 A CN 202111207476A CN 113991748 A CN113991748 A CN 113991748A
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- 238000004088 simulation Methods 0.000 description 3
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- 230000000694 effects Effects 0.000 description 2
- 230000001052 transient effect Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
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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
- H02J3/40—Synchronising a generator for connection to a network or to another generator
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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
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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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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- 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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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- Engineering & Computer Science (AREA)
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Abstract
The invention relates to a voltage source type inverter control technology, and aims to provide a seamless switching control method of a voltage source type inverter based on droop control. The method comprises the following steps: acquiring and calculating the output voltage phase of the inverter and the bus voltage phase of the system by a phase-locked loop at two sides of a parallel switch of the voltage source type inverter, and subtracting the two phases to obtain a phase difference; adjusting the output phase of the inverter according to the phase difference to enable the phase difference value to be gradually close to 0 or 2 pi; and judging the lead and lag relationship of the phases between the inverter and the merging system, and triggering mode switching when the phase of the inverter leads the phase of the bus voltage and the phase difference between the two phases is less than a set threshold value. The invention considers the difference value of the output voltage phase of the inverter and the voltage phase of the alternating current bus at the moment of mode switching, and prevents the power back-flow phenomenon of the inverter. Different droop control equations are adopted before and after mode switching, power impact caused by mode switching is avoided, and mode switching is enabled to be in smooth transition.
Description
Technical Field
The invention relates to a seamless switching control method of a voltage source type inverter based on droop control, and belongs to the voltage source type inverter control technology in the micro-grid technology.
Background
In the process of widely applying renewable energy sources in a novel power system, a phenomenon that a current source control type inverter is off-grid on a large scale under adverse conditions such as system frequency fluctuation exists. The voltage source type inverter can provide voltage and frequency support for a power grid, and therefore the method becomes a method for reasonably utilizing new energy.
The operation of connecting a voltage source type inverter into an island microgrid system is called mode switching. The traditional voltage source type inverter based on droop control generally adopts a presynchronization control strategy with fixed step length, and the relation between the advance and the lag of a phase angle is not considered at the moment of mode switching, so that the backward flow of the output power of the inverter is easily caused; meanwhile, before and after mode switching, the change of power distribution is not considered, and the change of the output power of the inverter can trigger the parallel inverter system to generate a large frequency change rate, so that the stable operation of the system is adversely affected.
The invention aims to provide a seamless switching control method of a voltage source type inverter based on droop control, which considers the lead-lag of the output phase angle of the inverter and the change of the output power distribution at the moment of mode switching to realize the smooth transition of mode switching.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a voltage source type inverter seamless switching control method based on droop control, which is used for preventing the backward flow of power at the moment of parallel connection of inverters, inhibiting the frequency jump at the moment of switching a system and realizing the smooth transition of mode switching.
In order to solve the technical problem, the solution of the invention is as follows:
the seamless switching control method of the voltage source type inverter based on droop control comprises the following steps:
(1) the phase theta of the output voltage of the inverter is acquired and calculated by a phase-locked loop at two sides of a parallel switch of the voltage source type inverteriAnd a bus voltage phase θ incorporated in the systembusThe difference is made between the two to obtain a phase difference delta theta;
(2) adjusting the output phase of the inverter according to the phase difference delta theta to enable the phase difference delta theta to gradually approach 0 or 2 pi;
(3) determining the lead and lag relationship of the phase between the inverter and the integrated system when the inverter phase thetaiLeading bus voltage phase θbusAnd the phase difference Delta theta of the two is less than a set threshold value thetaminThen a mode switch is triggered.
As a preferable embodiment of the present invention, the method of calculating the phase difference Δ θ is represented by the following formula:
in the formula, delta theta is the angle difference between the output voltage phase of the inverter and the voltage angle of an alternating current bus; thetaiOutputting the phase for the inverter; thetabusIs the ac bus voltage phase.
As a preferred scheme of the invention, at the moment of connecting the inverters into the system in parallel, the control mode of the inverter droop equation is switched, and the droop coefficient is adjusted according to the power required to be distributed by the inverters;
the specific control equation of the inverter is shown as follows:
in the formula, ωThe actual output angular frequency of the inverter; omegarefOutputting an angular frequency reference value for the inverter; m is an active power droop control coefficient; p is the active power output by the inverter; n is the number of power supplies needing to be distributed; τ is the low pass filter time constant; s is a pull transform operator; t represents the current time; t is tpIs the mode switching time.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, the phase of the voltage of the inverter and the alternating current bus is acquired and calculated through the phase-locked loop, and the leading phase and the lagging phase are respectively processed to obtain the phase difference; and considering the difference value of the output voltage phase of the inverter and the voltage phase of the alternating-current bus at the moment of mode switching, and preventing the power back-flow phenomenon of the inverter from being generated.
2. The invention adopts different droop control equations before and after mode switching, avoids power impact caused by mode switching and enables mode switching to be in smooth transition.
Drawings
Fig. 1 is a flowchart of a seamless switching control method for a voltage source inverter based on droop control.
Fig. 2 is a diagram of an island microgrid switching simulation structure in PLECS software.
FIG. 3 is a graph comparing the control effect of the present invention and the control effect of the conventional handover.
Detailed Description
The technical scheme of the invention is explained in detail in the following with the accompanying drawings:
the invention has the innovation points that when the inverter is connected into the system in parallel, the phase of the output voltage of the inverter is controlled to be ahead of the potential of an alternating voltage bus, so that the inverter is prevented from being connected into the instantaneous power backflow; meanwhile, different droop control equations are adopted before and after mode switching, smooth transition of system power distribution is achieved, impact of frequency fluctuation in the system is restrained, and transient stability of the system is improved.
As shown in fig. 1, the specific implementation process of the present invention is as follows:
1. the phase theta of the output voltage of the inverter is acquired and calculated by a phase-locked loop at two sides of a parallel switch of the voltage source type inverteriAnd a bus voltage phase θ incorporated in the systembusThe difference is made between the two to obtain a phase difference delta theta;
2. adjusting the output phase of the inverter according to the phase difference delta theta to enable the phase difference delta theta to gradually approach 0 or 2 pi;
3. determining the lead and lag relationship of the phase between the inverter and the integrated system when the inverter phase thetaiLeading bus voltage phase θbusAnd the phase difference Delta theta of the two is less than a set threshold value thetaminThen a mode switch is triggered.
Otherwise, the output phase of the inverter is continuously adjusted.
The method for calculating the phase difference Δ θ is shown as follows:
in the formula, delta theta is the angle difference between the output voltage phase of the inverter and the voltage angle of an alternating current bus; thetaiOutputting the phase for the inverter; thetabusIs the ac bus voltage phase.
4. Switching the control mode of the droop equation of the inverter at the moment of connecting the inverter into the system in parallel, and adjusting the droop coefficient according to the power required to be distributed by the inverter; namely:
(1) before the inverters are connected into the system in parallel (t < t)p) The specific control equation of the inverter is shown as follows:
ω＝ωref-mp
(2) at the moment of connecting the inverters into the system in parallel (t is more than or equal to t)p) The specific control equation of the switching inverter is specifically shown as follows:
in the formula, omega is the actual output angular frequency of the inverter; omegarefOutputting an angular frequency reference value for the inverter; m is an active power droop control coefficient; p is active power output by the inverter(ii) a N is the number of power supplies needing to be distributed; τ is the low pass filter time constant; s is a pull transform operator; t represents the current time; t is tpIs the mode switching time.
And the power distribution among the parallel systems is in balanced transition by changing an output droop control equation of the inverter.
Specific application examples are as follows:
a simulation model of an inverter parallel connection island microgrid is built through PLECS software, and the structure of the simulation model is shown in figure 2. Firstly, a single inverter runs with load, the bus voltage of the island micro-grid is established, and then the other inverter is connected into a secondary island system. The frequency change in the islanded microgrid system in the process is shown in fig. 3.
The solid line in fig. 3 is the frequency change of the conventional mode switching control, and at 2.35s, the inverter is connected to the microgrid system, so that it can be seen that a frequency jump of 0.4Hz is caused to the system. The dotted line is the frequency change process of the improved seamless switching control technology, the inverter is connected into the microgrid system at 1.85s, and the frequency fluctuation is 0.12 Hz. Based on the switching mode, the system frequency is in smooth transition, and the transient stability of the parallel system can be enhanced.
In summary, the present invention adopts a seamless switching control method for a voltage source inverter based on droop control. The phase difference between the voltage phase output by the inverter and the voltage phase output by the alternating current bus is calculated through phase-locked loop acquisition. And when the phase difference is smaller than a set threshold and the phase of the inverter is ahead of the voltage phase of the bus, triggering mode switching control, and changing a droop control equation of the inverter at the moment of mode switching so as to adapt to power distribution of the inverter in a parallel system, inhibit oscillation and impact of frequency and realize smooth transition of grid-connected switching.
Claims (3)
1. A seamless switching control method of a voltage source type inverter based on droop control is characterized by comprising the following steps:
(1) the phase theta of the output voltage of the inverter is acquired and calculated by a phase-locked loop at two sides of a parallel switch of the voltage source type inverteriAnd a bus voltage phase incorporated into the systemθbusThe difference is made between the two to obtain a phase difference delta theta;
(2) adjusting the output phase of the inverter according to the phase difference delta theta to enable the phase difference delta theta to gradually approach 0 or 2 pi;
(3) determining the lead and lag relationship of the phase between the inverter and the integrated system when the inverter phase thetaiLeading bus voltage phase θbusAnd the phase difference Delta theta of the two is less than a set threshold value thetaminThen a mode switch is triggered.
2. The method of claim 1, wherein the phase difference Δ θ is calculated as follows:
in the formula, delta theta is the angle difference between the output voltage phase of the inverter and the voltage angle of an alternating current bus; thetaiOutputting the phase for the inverter; thetabusIs the ac bus voltage phase.
3. The method according to claim 1 or 2, characterized in that at the moment of connecting the inverters into the system in parallel, the control mode of the inverter droop equation is switched, and the droop coefficient is adjusted according to the power required to be distributed by the inverters;
the specific control equation of the inverter is shown as follows:
in the formula, omega is the actual output angular frequency of the inverter; omegarefOutputting an angular frequency reference value for the inverter; m is an active power droop control coefficient; p is the active power output by the inverter; n is the number of power supplies needing to be distributed; τ is the low pass filter time constant; s is a pull transform operator; t represents the current time; t is tpIs the mode switching time.
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Citations (5)
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|---|---|---|---|---|
| CN104485689A (en) * | 2014-12-12 | 2015-04-01 | 合肥工业大学 | Adaptive mode switching based droop control method |
| CN105790307A (en) * | 2016-04-21 | 2016-07-20 | 许继集团有限公司 | Inverter control method and system based on droop control |
| CN111628530A (en) * | 2019-11-28 | 2020-09-04 | 内蒙古电力(集团)有限责任公司内蒙古电力科学研究院分公司 | Pre-synchronization control method of emergency generator set based on droop control |
| CN112421658A (en) * | 2020-10-20 | 2021-02-26 | 内蒙古电力(集团)有限责任公司内蒙古电力科学研究院分公司 | Inertia link control method of energy storage inverter in emergency microgrid scene |
| CN112436545A (en) * | 2020-11-02 | 2021-03-02 | 华能通榆团结风力发电有限公司 | Control method for improving micro-grid operation stability under island/grid-connected dual mode |
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- 2021-10-16 CN CN202111207476.9A patent/CN113991748A/en active Pending
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104485689A (en) * | 2014-12-12 | 2015-04-01 | 合肥工业大学 | Adaptive mode switching based droop control method |
| CN105790307A (en) * | 2016-04-21 | 2016-07-20 | 许继集团有限公司 | Inverter control method and system based on droop control |
| CN111628530A (en) * | 2019-11-28 | 2020-09-04 | 内蒙古电力(集团)有限责任公司内蒙古电力科学研究院分公司 | Pre-synchronization control method of emergency generator set based on droop control |
| CN112421658A (en) * | 2020-10-20 | 2021-02-26 | 内蒙古电力(集团)有限责任公司内蒙古电力科学研究院分公司 | Inertia link control method of energy storage inverter in emergency microgrid scene |
| CN112436545A (en) * | 2020-11-02 | 2021-03-02 | 华能通榆团结风力发电有限公司 | Control method for improving micro-grid operation stability under island/grid-connected dual mode |
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| AMIRTHAGUNARAJ YOGARATHINAM等: "Stability-Constrained Adaptive Droop for Power Sharing in AC-MTDC Grids", 《IEEE TRANSACTIONS ON POWER SYSTEM》, vol. 34, no. 03, 31 May 2019 (2019-05-31), pages 1955 - 1965, XP011720105, DOI: 10.1109/TPWRS.2018.2890296 * |
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