CN116565827A - Injection frequency-based SOC (State of charge) balance control strategy of direct-current micro-grid energy storage system - Google Patents
Injection frequency-based SOC (State of charge) balance control strategy of direct-current micro-grid energy storage system Download PDFInfo
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- CN116565827A CN116565827A CN202310648551.8A CN202310648551A CN116565827A CN 116565827 A CN116565827 A CN 116565827A CN 202310648551 A CN202310648551 A CN 202310648551A CN 116565827 A CN116565827 A CN 116565827A
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- 238000004146 energy storage Methods 0.000 title claims abstract description 86
- 238000002347 injection Methods 0.000 title claims abstract description 25
- 239000007924 injection Substances 0.000 title claims abstract description 25
- 238000011217 control strategy Methods 0.000 title claims abstract description 9
- 238000005070 sampling Methods 0.000 claims description 6
- 230000001133 acceleration Effects 0.000 claims description 4
- 238000004364 calculation method Methods 0.000 claims description 3
- 230000001939 inductive effect Effects 0.000 claims description 3
- 238000000034 method Methods 0.000 claims description 3
- 238000010586 diagram Methods 0.000 description 10
- 238000007599 discharging Methods 0.000 description 5
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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
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/14—Balancing the load in a 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
- H02J1/00—Circuit arrangements for dc mains or dc distribution networks
- H02J1/10—Parallel operation of dc sources
Abstract
The invention discloses an injection frequency-based SOC balance control strategy for a direct-current micro-grid energy storage system, which mainly comprises a current sharing controller, an SOC equalizer and a voltage-current double closed-loop controller. In the current sharing controller, by injecting low-amplitude alternating current small signals into the energy storage unit and utilizing the characteristic that the frequency of the alternating current small signals is inversely proportional to the output current, the output current of the energy storage unit is accurately distributed in proportion to the capacity of the energy storage unit; the clipping link is utilized, so that the drop of the bus voltage can be effectively compensated, and the bus voltage is maintained near the rated value; in the SOC equalizer, each energy storage unit obtains the average value of the SOC of the energy storage system through a dynamic consistency algorithm, and current closed-loop control is designed according to the SOC information, so that the output current of each energy storage unit is dynamically changed along with the local SOC, and the SOC equalization is realized.
Description
Technical Field
The invention relates to the field of direct-current micro-grid energy storage systems, in particular to an SOC balance strategy of a direct-current micro-grid energy storage system based on injection frequency.
Background
Along with the increasing demand of the user side for direct current power, direct current micro-grids are receiving a great deal of attention at home and abroad. Due to the diversity and dispersion of distributed energy sources, an energy storage unit with a certain capacity is required to be equipped in a direct current micro-grid so as to consume the redundant energy of renewable energy sources or play a role in compensating when the renewable energy sources are insufficient in output. In order to improve the response speed and reliability of the energy storage system, a plurality of distributed energy storage units are required to form the energy storage system, wherein the capacities of the energy storage units may be different, so that part of the energy storage units are taken out of operation in advance due to over-charging and over-discharging, and the service life of the energy storage units and the stability of the direct current micro-grid are affected. Therefore, the output current needs to be regulated according to the capacity and the State-of-Charge (SOC) of the energy storage units, so that the output current of each energy storage unit is accurately distributed according to the capacity proportion and the SOC is balanced.
Disclosure of Invention
In order to achieve the above purpose, the technical scheme provided by the invention is as follows:
1) The multiple energy storage units pass through the corresponding converters and the line impedance R linek Parallel connected to the DC bus to supply the load R load Supplying power to the inductive current i at the starting point of each sampling period Lk Output current i ok Output voltage u ok State of charge SOC of energy storage unit k Sampling is carried out respectively;
2) In the current-sharing controller, the energy storage unit outputs current i ok Multiplying by a factor of 1/2 and dividing by its rated current I ratedk Multiplying the maximum deviation Deltaf of the injection frequency to obtain a virtual frequency Deltaf k Then rated frequency f * Subtracting the virtual frequency Deltaf k Obtaining the injection frequency f k Injection frequency f k The expression of (2) is:
3) Injection frequency f k The phase angle theta is obtained by an integrator with an integral coefficient of 2 pi k Taking sine function sin, multiplying amplitude A to construct energy storage unit to inject AC small signal u k Injecting a small alternating current signal u k The expression of (2) is:
u k ＝Asinθ k
4) Output current i of energy storage unit ok And output voltage u ok Fourier analysis FT is carried out to obtain fundamental wave current peak value I omk Phase angle theta of fundamental wave current iok Fundamental voltage peak value U omk Fundamental voltage phase angle theta uok Will fundamental voltage phase angle theta uok And fundamental current phase angle theta iok Subtracting, taking sine function sin, and multiplying with fundamental voltage peak value U omk Peak value of fundamental current I omk And a coefficient of 0.5 to obtain reactive power Q k Reactive power Q k Multiplying by reactive compensation coefficient d q Through a low-pass filter G lp (s) obtaining the voltage compensation quantity delta u through the amplitude limiting link k ；
5) In the SOC equalizer and the voltage-current double closed-loop controller, an alternating current small signal u is injected k And a voltage reference value U ref Adding and subtracting the output voltage u ok And a voltage compensation amount Deltau k Then pass through a voltage outer loop PI controller G V (s) obtaining a current inner loop reference current I ak Then the current inner loop is referenced with the current I ak And SOC balance current I bk Adding and subtracting the inductance current i Lk Then pass through a current inner loop PI controller G I (s) obtaining a driving voltage u sk Then comparing with the triangular carrier wave to obtain a modulation signal, wherein the SOC balances the current I bk The specific calculation process of (2) is as follows:
acquiring state of charge average value SOC of energy storage system by using dynamic consistency algorithm avg SOC of energy storage unit k Subtracting the state of charge average SOC of an energy storage system avg The result obtained is multiplied byObtaining an intermediate coefficient x, wherein ρ is an acceleration factor, ε is an accurate factor, taking an arcsin function arcsin from the intermediate coefficient x, and multiplying +.>Multiplying the absolute value of the reference current in the current loop by |I ak I, obtain SOC equilibrium current I bk SOC equalizes current I bk The expression of (2) is:
compared with the prior art, the principle and the advantages of the scheme are as follows:
the invention discloses an injection frequency-based SOC balance control strategy for a direct-current micro-grid energy storage system, which mainly comprises a current sharing controller, an SOC equalizer and a voltage-current double closed-loop controller. In the current sharing controller, by injecting low-amplitude alternating current small signals into the energy storage unit and utilizing the characteristic that the frequency of the alternating current small signals is inversely proportional to the output current, the output current of the energy storage unit is accurately distributed in proportion to the capacity of the energy storage unit; the clipping link is utilized, so that the drop of the bus voltage can be effectively compensated, and the bus voltage is maintained near the rated value; in the SOC equalizer, each energy storage unit obtains the average value of the SOC of the energy storage system through a dynamic consistency algorithm, and current closed-loop control is designed according to the SOC information, so that the output current of each energy storage unit is dynamically changed along with the local SOC, and the SOC equalization is realized.
Drawings
FIG. 1 is a main circuit diagram of an energy storage system according to an embodiment of the present invention;
fig. 2 is a control block diagram of a SOC balance control strategy of a dc micro-grid energy storage system based on injection frequency in an embodiment of the present invention;
FIG. 3 is a diagram showing an SOC waveform of the energy storage unit according to an embodiment of the present invention;
FIG. 4 is a graph showing a waveform of the output current of the DC side of the energy storage unit according to the embodiment of the present invention;
FIG. 5 is a graph showing a busbar voltage waveform of an energy storage system according to an embodiment of the present invention;
fig. 6 is a waveform diagram of injection frequency of each energy storage unit according to an embodiment of the present invention.
Detailed Description
The invention is further illustrated by the following examples:
FIG. 1 is a main circuit diagram of an energy storage system consisting of four energy storage units connected in parallel via DC-DC converters, a DESU k Is the kth energy storage unit, u ok Output voltage i for direct current side of kth energy storage unit ok For the direct current side output current of the kth energy storage unit, R linek For the line impedance corresponding to the kth energy storage unit, k=1, 2,3,4, the line impedance of the four energy storage units is 0.5Ω, 0.6Ω, 0.54Ω, 0.4Ω, R, respectively load Is the load resistance.
Fig. 2 is a control block diagram of a SOC balance control strategy for a dc micro-grid energy storage system based on injection frequency, comprising the steps of:
1) The multiple energy storage units pass through the corresponding converters and the line impedance R linek Parallel connected to the DC bus to supply the load R load Supplying power to the inductive current i at the starting point of each sampling period Lk Output current i ok Output voltage u ok State of charge SOC of energy storage unit k Sampling is carried out respectively;
2) In the current-sharing controller, the energy storage unit outputs current i ok Multiplying by a factor of 1/2 and dividing by its rated current I ratedk Multiplying the maximum deviation Deltaf of the injection frequency to obtain a virtual frequency Deltaf k Then rated frequency f * Subtracting the virtual frequency Deltaf k Obtaining the injection frequency f k Injection frequency f k The expression of (2) is:
3) Injection frequency f k The phase angle theta is obtained by an integrator with an integral coefficient of 2 pi k Taking sine function sin andmultiplying the amplitude A to construct an alternating current small signal u injected by the energy storage unit k Injecting a small alternating current signal u k The expression of (2) is:
u k ＝Asinθ k
4) Output current i of energy storage unit ok And output voltage u ok Fourier analysis FT is carried out to obtain fundamental wave current peak value I omk Phase angle theta of fundamental wave current iok Fundamental voltage peak value U omk Fundamental voltage phase angle theta uok Will fundamental voltage phase angle theta uok And fundamental current phase angle theta iok Subtracting, taking sine function sin, and multiplying with fundamental voltage peak value U omk Peak value of fundamental current I omk And a coefficient of 0.5 to obtain reactive power Q k Reactive power Q k Multiplying by reactive compensation coefficient d q Through a low-pass filter G lp (s) obtaining the voltage compensation quantity delta u through the amplitude limiting link k ；
5) In the SOC equalizer and the voltage-current double closed-loop controller, an alternating current small signal u is injected k And a voltage reference value U ref Adding and subtracting the output voltage u ok And a voltage compensation amount Deltau k Then pass through a voltage outer loop PI controller G V (s) obtaining a current inner loop reference current I ak Then the current inner loop is referenced with the current I ak And SOC balance current I bk Adding and subtracting the inductance current i Lk Then pass through a current inner loop PI controller G I (s) obtaining a driving voltage u sk Then comparing with the triangular carrier wave to obtain a modulation signal, wherein the SOC balances the current I bk The specific calculation process of (2) is as follows:
acquiring state of charge average value SOC of energy storage system by using dynamic consistency algorithm avg SOC of energy storage unit k Subtracting the state of charge average SOC of an energy storage system avg The result obtained is multiplied byObtaining an intermediate coefficient x, wherein ρ is an acceleration factor, ε is an accurate factor, taking an arcsin function arcsin from the intermediate coefficient x, and multiplying +.>Multiplying the absolute value of the reference current in the current loop by |I ak I, obtain SOC equilibrium current I bk SOC equalizes current I bk The expression of (2) is:
FIG. 3 is a waveform diagram of the SOC of the energy storage unit, the initial SOC of the energy storage system in the discharging mode 1 、SOC 2 、SOC 3 、SOC 4 90%, 85%, 83%, 87%, respectively, and when the SOC is higher than the average value, the SOC equalizes the current I bk > 0, let the output current i ok The discharging speed of the energy storage unit is increased, and the SOC of the energy storage unit with larger SOC is reduced more rapidly; when the SOC is lower than the average value, the SOC equalizes the current I bk <0, let the output current i ok The discharging speed of the energy storage unit is reduced, and the lower the SOC, the slower the SOC of the energy storage unit is reduced; eventually, SOC equalization is achieved at 2.4 seconds, after which the SOC rate of the energy storage unit drops the same.
Fig. 4 is a waveform diagram of the output current of the direct current side of the energy storage units, wherein the capacity ratio of the four energy storage units is 3:3:2:2, simultaneously, rated currents of four energy storage units are respectively set to be 12A, 8A and 8A, under a discharging mode, output currents of the energy storage units with large capacity are larger, output currents of the energy storage units with small capacity are smaller, and finally, the output currents of the four energy storage units reach balance in pairs in 2.4 seconds, the output currents of the four energy storage units are respectively 6A, 4A and 4A, and the output currents are 3 according to the capacity: 3:2:2 purpose of accurate distribution.
Fig. 5 is a waveform diagram of the bus voltage of the energy storage system, which may cause the bus voltage to fluctuate when the SOC is balanced, but the fluctuation is within the allowable range.
In the waveform diagram of the injection frequency of each energy storage unit in fig. 6, when the current of the energy storage unit is accurately distributed in proportion to the capacity of the energy storage unit, the injection frequency is balanced and is stabilized within the allowable frequency range.
The above embodiments are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, so variations in shape and principles of the present invention should be covered.
Claims (3)
1. The SOC balance control strategy of the direct-current micro-grid energy storage system based on the injection frequency is characterized by comprising the following steps of:
1) The multiple energy storage units pass through the corresponding converters and the line impedance R linek Parallel connected to the DC bus to supply the load R load Supplying power to the inductive current i at the starting point of each sampling period Lk Output current i ok Output voltage u ok State of charge SOC of energy storage unit k Sampling is carried out respectively;
2) In the current-sharing controller, the energy storage unit outputs current i ok Multiplying by a factor of 1/2 and dividing by its rated current I ratedk Multiplying the maximum deviation Deltaf of the injection frequency to obtain a virtual frequency Deltaf k Then rated frequency f * Subtracting the virtual frequency Deltaf k Obtaining the injection frequency f k Injection frequency f k The expression of (2) is:
3) Injection frequency f k The phase angle theta is obtained by an integrator with an integral coefficient of 2 pi k Taking sine function sin, multiplying amplitude A to construct energy storage unit to inject AC small signal u k Injecting a small alternating current signal u k The expression of (2) is:
u k ＝Asinθ k
4) Output current i of energy storage unit ok And output voltage u ok Fourier analysis FT is carried out to obtain fundamental wave current peak value I omk Phase angle theta of fundamental wave current iok Fundamental voltage peak value U omk Fundamental voltage phase angle theta uok Will fundamental voltage phase angle theta uok And the phase angle of the fundamental currentθ iok Subtracting, taking sine function sin, and multiplying with fundamental voltage peak value U omk Peak value of fundamental current I omk And a coefficient of 0.5 to obtain reactive power Q k Reactive power Q k Multiplying by reactive compensation coefficient d q Through a low-pass filter G lp (s) obtaining the voltage compensation quantity delta u through the amplitude limiting link k ；
5) In the SOC equalizer and the voltage-current double closed-loop controller, an alternating current small signal u is injected k And a voltage reference value U ref Adding and subtracting the output voltage u ok And a voltage compensation amount Deltau k Then pass through a voltage outer loop PI controller G V (s) obtaining a current inner loop reference current I ak Then the current inner loop is referenced with the current I ak And SOC balance current I bk Adding and subtracting the inductance current i Lk Then pass through a current inner loop PI controller G I (s) obtaining a driving voltage u sk Then comparing with the triangular carrier wave to obtain a modulation signal, wherein the SOC balances the current I bk The specific calculation process of (2) is as follows:
acquiring state of charge average value SOC of energy storage system by using dynamic consistency algorithm avg SOC of energy storage unit k Subtracting the state of charge average SOC of an energy storage system avg The result obtained is multiplied byObtaining an intermediate coefficient x, wherein ρ is an acceleration factor, ε is an accurate factor, taking an arcsin function arcsin from the intermediate coefficient x, and multiplying +.>Multiplying the absolute value of the reference current in the current loop by |I ak I, obtain SOC equilibrium current I bk SOC equalizes current I bk The expression of (2) is:
2. the injection frequency-based SOC balance control strategy of the dc micro-grid energy storage system of claim 1, wherein the range of the amplitude a in step 3) is 2-8.
3. The injection frequency-based SOC balance control strategy of the dc micro-grid energy storage system of claim 1, wherein the acceleration factor ρ in step 5) has a value range of 0.6< ρ <1.2, and the precision factor ε has a value range of 0.001< ε <0.01.
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| CN114977405A (en) * | 2022-06-02 | 2022-08-30 | 北京和瑞储能科技有限公司 | Charge state balance control method and system for series energy storage system |
| CN115882490A (en) * | 2022-12-27 | 2023-03-31 | 宁夏大学 | SOC-based storage battery improved droop control method and system |
| CN116031864A (en) * | 2023-02-20 | 2023-04-28 | 广东工业大学 | Energy storage system power distribution strategy based on improved SOC balance |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114977405A (en) * | 2022-06-02 | 2022-08-30 | 北京和瑞储能科技有限公司 | Charge state balance control method and system for series energy storage system |
| CN115882490A (en) * | 2022-12-27 | 2023-03-31 | 宁夏大学 | SOC-based storage battery improved droop control method and system |
| CN116031864A (en) * | 2023-02-20 | 2023-04-28 | 广东工业大学 | Energy storage system power distribution strategy based on improved SOC balance |
Non-Patent Citations (2)
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| MOHAMMAD JAFARI等: "Enhanced Frequency Droop Method for Decentralized Power Sharing Control in dc Microgrids", IEEE JOURNAL OF EMERGING AND SELECTED TOPICS IN POWER ELECTRONICS, vol. 9, no. 2, pages 1290 - 1301, XP011843828, DOI: 10.1109/JESTPE.2020.2969144 * |
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