CN114069774A - Photovoltaic energy storage system for tracking maximum power generated by photovoltaic cell and photovoltaic power generation system based on system - Google Patents
Photovoltaic energy storage system for tracking maximum power generated by photovoltaic cell and photovoltaic power generation system based on system Download PDFInfo
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- CN114069774A CN114069774A CN202111262146.XA CN202111262146A CN114069774A CN 114069774 A CN114069774 A CN 114069774A CN 202111262146 A CN202111262146 A CN 202111262146A CN 114069774 A CN114069774 A CN 114069774A
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/0013—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries acting upon several batteries simultaneously or sequentially
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/007—Regulation of charging or discharging current or voltage
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/007—Regulation of charging or discharging current or voltage
- H02J7/00712—Regulation of charging or discharging current or voltage the cycle being controlled or terminated in response to electric parameters
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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
- H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
- H02J7/35—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering with light sensitive cells
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
- H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
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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
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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Abstract
A photovoltaic energy storage system for tracking the maximum power generated by a photovoltaic cell and a photovoltaic power generation system based on the system relate to the control technology of the photovoltaic cell. The problem of exist among the photovoltaic power generation technology because the output characteristic of photovoltaic cell is influenced by external parameters such as the temperature of environment, illumination and lead to the generating capacity of photovoltaic cell unstable is solved. The photovoltaic energy storage system includes: the system comprises an energy storage battery pack consisting of N + X single batteries, a BEMS single controller and a BEMS module controller, wherein the BEMS single controller is used for connecting or cutting the corresponding single batteries into or out of a charging loop according to instructions of the BEMS module controller, and the BEMS module controller is used for controlling the overall charging control of the battery pack and also used for realizing photovoltaic maximum power tracking control. The photovoltaic power generation system is different from the prior art in that a DC/DC conversion module is omitted, and the photovoltaic energy storage system is adopted. The invention relates to a photovoltaic energy storage system and an improvement on the existing photovoltaic power generation system.
Description
Technical Field
The invention relates to a control technology of a photovoltaic cell.
Background
In the existing photovoltaic power generation technology field, since natural light is converted into electric energy, in practical application, the output characteristics of the photovoltaic cell are obviously affected by external parameters such as temperature and illumination of the environment, which leads to the power generation capability of the photovoltaic cell being in a passive state, namely: the output characteristics of the photovoltaic energy storage system change along with the change of the factors of the environment, so that the photovoltaic energy storage system in the photovoltaic power generation field is difficult to achieve the maximum energy storage effect on the premise of the change.
When a direct current access mode is adopted in an existing conventional photovoltaic energy storage system, besides that fluctuation of direct current voltage input by a pcs (power Conversion system) inverter in a certain range is allowed, the photovoltaic voltage is greatly fluctuated by light source change and has strong randomness, and when a battery pack is charged, the battery voltage can also change along with the change of capacity, so that a photovoltaic module and an existing battery pack are connected with an inversion direct current bus and cannot be directly connected, a DC/DC converter is required to be adopted for voltage matching, namely, the connection with the inversion direct current bus is realized through the DC/DC converter with a specific function, and a specific system connection block diagram is shown in fig. 1: the photovoltaic module needs to be connected with the battery module through a DC/DC converter and then connected with an alternating current power grid or a load through a DC/AC converter. For example, patent document CN 112994105 a published in 2021, 06/18 describes "a photovoltaic power generation system, a power control device, and an energy storage system" as such a configuration.
Aiming at the structure, according to the proportion and the system design of the photovoltaic module, the DC/DC can adopt boost, buck or bridge circuit design, and through intelligent control and PWM regulation, on one hand, the maximum input of the generating power of the photovoltaic module is realized, and on the other hand, the intelligent charging management or alternating current side power matching of the battery pack is realized. Due to the fluctuation and randomness of photovoltaic power generation power and the real-time control response characteristics of a DCDC conversion device, in order to guarantee the maximum power output of photovoltaic, the prior art is realized by a maximum power tracking algorithm, the algorithm must be selected among control response speed, control precision and calculation complexity to obtain the optimal control effect, and the algorithm is also a main research direction in the field, for example:
patent document CN 111208863 a published in 29/05/2020 describes "a method and an apparatus for fast tracking and controlling maximum power point of a photovoltaic cell", which realizes fast tracking of maximum power point of a photovoltaic cell by pulse sequence control, and solves the problem of large calculation amount in the prior art.
Patent document CN 112987839 a published in 2021, 06, 18 describes "a circuit and a method for tracking and controlling a maximum power point of a photovoltaic cell", which is based on a constant voltage method, and quickly tracks to a position near the maximum power point, and then accurately tracks the maximum power point according to a logical relationship between the output voltage and the output power of the photovoltaic cell, and is not affected by a hysteresis effect of a PI controller in the process of seeking the maximum power point, so that the tracking speed is faster and the tracking accuracy is higher.
Patent document CN 112732007 a published in 04/30/2021 describes "tracking control method and system for maximum power point of photovoltaic cell", which can greatly improve accuracy of tracking result compared with a method for tracking maximum power point by a fixed voltage method and a fixed current method, by acquiring current output current and current output voltage of photovoltaic cell, then using PSO algorithm to track maximum power point of photovoltaic cell on line in real time according to current output current and current output voltage of photovoltaic cell, and outputting global optimum voltage value.
In summary, in the field of photovoltaic power generation technology, in order to solve a series of problems caused by unstable power generation capability of a photovoltaic cell due to the influence of external parameters such as temperature and illumination of the environment on the output characteristic of the photovoltaic cell in the control technology of the photovoltaic cell, the main research direction in the prior art is to "guarantee maximum power output of photovoltaic", and based on the system architecture shown in fig. 1, the adopted technical means and research directions are concentrated on: a constant voltage method, a short circuit current proportionality coefficient method; or a disturbance voltage method and a conductance incremental method realized based on the sampling data; or artificial intelligence algorithms that have emerged in recent years, such as: fuzzy theory, a sliding mode algorithm and the like, and the final purpose is to realize real-time and accurate tracking of the maximum power point of the photovoltaic cell.
Disclosure of Invention
The invention solves the problem of unstable power generation capacity of a photovoltaic cell caused by the influence of external parameters such as temperature, illumination and the like of the environment on the output characteristic of the photovoltaic cell in the photovoltaic power generation technology, and provides a photovoltaic energy storage system for tracking the maximum power generation power of the photovoltaic cell and a photovoltaic power generation system based on the photovoltaic energy storage system.
The invention relates to a photovoltaic energy storage system for tracking the maximum power generated by a photovoltaic cell, which comprises: the system comprises an energy storage battery pack consisting of N + X single batteries, a BEMS single controller and a BEMS module controller, wherein the BEMS single controller is used for connecting or cutting the corresponding single batteries into or out of a charging loop according to instructions of the BEMS module controller, and the BEMS module controller is used for controlling the overall charging control of the battery pack and also used for realizing photovoltaic maximum power tracking control.
In the energy storage battery pack, N + X is the total number of the single batteries contained in the battery pack and is a fixed value, N is the number of the online single batteries and is a variable in the battery charging process, and X is the number of the offline single batteries in a standby state and changes along with the change of N.
Preferably, in the energy storage battery pack, the total output minimum voltage after the N single batteries are connected in series is ensured to be greater than the rated voltage of the corresponding photovoltaic electric component.
Further, the total output minimum voltage of the N single batteries which are connected in series is ensured to be more than 10% of the rated voltage of the corresponding photovoltaic electric component.
The BEMS module controller is internally embedded with a software module for realizing the control of charging of the whole battery pack and the tracking control of the maximum photovoltaic power, and the software module comprises:
the period control unit is used for controlling the maximum charging power tracking period in a timing mode;
a detection unit for detecting the charging current and the total voltage in the charging loop in real time;
the power calculation unit is used for obtaining the total charging power of the charging loop when each tracking period is finished;
when each tracking period is finished, adjusting an adjusting unit of the online batteries, wherein the adjusting unit is used for comparing the total charging power of the current tracking period with the total charging power of the previous tracking period, if the total charging power of the current tracking period is larger than the total charging power of the previous tracking period, the number N of the online single batteries is adjusted to be increased by 1, and otherwise, the number N of the online single batteries is adjusted to be decreased by 1;
at the end of each tracking cycle, a designated unit is sent for sending an instruction to the BEMS cell controller to increment the battery number N by 1 or decrement it by 1.
Further, the software module may further include:
the single voltage detection unit is used for detecting the terminal voltage of each single battery in the energy storage battery pack when each tracking period is finished;
when the number N of the on-line single batteries is adjusted to be increased by 1, an adding selection unit for adding the single batteries is selected, and the adding selection unit is used for selecting the single battery with the minimum single battery terminal voltage in the standby state to be connected in series into a charging loop in the next tracking period;
and when the number N of the online single batteries is reduced by 1, selecting a cutting selection unit for cutting the single batteries, wherein the cutting selection unit is used for selecting the single battery with the highest end voltage in the online batteries to be converted into a standby state in the next tracking period.
Further, the software module may further include:
the detection unit is used for detecting the terminal voltage, the monomer temperature and the online charging time of each monomer battery in the energy storage battery pack and calculating to obtain the charging index of each monomer battery in the standby state;
when the number N of the online single batteries is adjusted to be increased by 1, a charging selection unit for charging the single batteries is selected, and the unit is used for selecting the single battery with the minimum charging index of the single battery in a standby state to be connected in a charging loop in series in the next tracking period;
and when the number N of the online single batteries is reduced by 1, selecting a cutting selection unit for cutting the single batteries, wherein the cutting selection unit is used for selecting the single battery with the highest charging index in the online batteries to be converted into a standby state in the next tracking period.
Further, the software module may further include:
and when the number N of the online single batteries needs to be adjusted and 1 is added, outputting an overpressure judgment unit, wherein the overpressure judgment unit is used for further judging whether the total output voltage of all online single batteries in the adjusted energy storage battery pack is higher than the upper limit of the working voltage, and if so, not adjusting.
And when the number N of the online single batteries is required to be adjusted to be less than 1, outputting a pressing judgment unit, wherein the pressing judgment unit is used for further judging whether the output voltage of the adjusted battery pack is lower than the lower limit of the working voltage, and if so, not adjusting.
The invention also provides a photovoltaic cell power generation maximum power tracking method of the photovoltaic energy storage system, which is realized based on the following photovoltaic energy storage system, and the photovoltaic energy storage system comprises: the tracking method is a periodic tracking method, and specifically comprises the following steps:
detecting charging current and total voltage in a charging loop in real time;
when each tracking period is finished, obtaining the total charging power of the charging loop;
and when each tracking period is finished, comparing the total charging power of the current tracking period with the total charging power of the previous tracking period, if the total charging power of the current tracking period is larger than the total charging power of the previous tracking period, increasing the number N of the online single batteries by 1, and otherwise, decreasing the number N of the online single batteries by 1.
Further, the method may further include:
detecting the terminal voltage of each single battery in the energy storage battery pack when each tracking period is finished;
when the number N of the on-line single batteries is adjusted to be increased by 1, selecting the single battery with the minimum voltage of the single battery terminal in the standby state to be connected in series into a charging loop in the next tracking period;
and when the number N of the online single batteries is reduced by 1, selecting the single battery with the highest end voltage in the online batteries to be converted into a standby state in the next tracking period.
Further, the method may further include:
when each tracking period is finished, detecting the terminal voltage, the monomer temperature and the online charging time of each single battery in the energy storage battery pack, and calculating to obtain the charging index of each single battery in the standby state;
when the number N of the on-line single batteries is adjusted to be increased by 1, the single battery with the minimum charging index of the single battery in the standby state is selected to be connected in series into a charging loop in the next tracking period;
and when the number N of the online single batteries is reduced by 1, selecting the single battery with the highest charging index in the online batteries to be converted into a standby state in the next tracking period.
Further, the method may further include:
when the number N of the online single batteries needs to be adjusted and 1 is added, whether the total output voltage of all the online single batteries in the adjusted energy storage battery pack is higher than the upper limit of the working voltage or not is further judged, and if yes, no adjustment is made.
When the number N of the online single batteries needs to be adjusted to be reduced by 1, whether the output voltage of the adjusted battery pack is lower than the lower limit of the working voltage is further judged, and if yes, no adjustment is performed.
In the energy storage battery pack, N + X is the total number of the single batteries contained in the battery pack and is a fixed value, N is the number of the online single batteries and is a variable in the battery charging process, and X is the number of the offline single batteries in a standby state and changes along with the change of N.
Preferably, in the energy storage battery pack, the total output minimum voltage after the N single batteries are connected in series is ensured to be greater than the rated voltage of the corresponding photovoltaic electric component.
Further, the total output minimum voltage of the N single batteries which are connected in series is ensured to be more than 10% of the rated voltage of the corresponding photovoltaic electric component.
Based on the photovoltaic energy storage system, the invention also provides a photovoltaic power generation system which comprises a photovoltaic assembly, the photovoltaic energy storage system and the DC/AC converter, wherein the electric energy output end of the photovoltaic assembly is simultaneously connected with the power supply end of the photovoltaic energy storage system and the DC/AC converter direct current signal input end.
Furthermore, the photovoltaic power generation system can also comprise a plurality of photovoltaic modules and a plurality of photovoltaic energy storage systems, and each photovoltaic module is connected with one photovoltaic energy storage system in parallel.
The invention aims at the problem that the output characteristic of the photovoltaic cell is influenced by external parameters such as the temperature and the illumination of the environment to cause the unstable power generation capability of the photovoltaic cell in the photovoltaic power generation technology, does not follow the research direction of the prior art and researches how to realize the maximum power tracking based on the prior traditional photovoltaic energy storage system framework, but adopts a brand new idea to adjust the architecture of the photovoltaic energy storage system in principle, as shown in figure 2, the structure introduces a BEMS battery pack system and a battery pack control technology, is a new structural change to the existing photovoltaic energy storage system, and, based on such structural changes, the control method is also simplified a lot, and, the method has the following specific effects that the method meets the consistency requirement of the single battery for realizing energy storage on no performance, and the maintenance cost of the energy storage system is greatly reduced:
1. the invention adopts a reconfigurable controlled BEMS (Battery Energy Management System) Battery pack as an Energy storage element, omits a DC/DC converter which is necessary to be less in the existing photovoltaic Energy storage System, realizes the direct connection charging of the Energy storage element and a photovoltaic component, simultaneously exerts the advantage that the input direct current voltage of a PCS inverter allows the fluctuation within a certain range, realizes the simplification of the System constitution to the greatest extent and reduces the System cost.
2. In the photovoltaic power generation process, under the influence of sunlight intensity, angle, weather and the like, the power generation capacity of a photovoltaic assembly is always in fluctuation change, in order to ensure that the maximum power output of the photovoltaic assembly is always realized in the power generation process, a BEMS energy storage system needs to have the capacity of a maximum power tracking function, and the battery pack voltage is controllable and adjustable by dynamically adjusting the online battery number of a BEMS battery pack capable of being reconfigured and controlled in a charging and discharging mode, the invention selects the optimal online batteries and the number according to the fluctuation of the output power of the photovoltaic assembly in a trial and error mode to realize the maximum power tracking function, simultaneously, as the output of the photovoltaic assembly is always connected with the battery pack, the characteristic of zero-delay response of self-charging of the battery pack is exerted, the response requirement of the photovoltaic control is greatly reduced, and simultaneously the fluctuation of the photovoltaic power and the fluctuation of alternating current output are completely decoupled, the control of each unit in the optical storage system can be greatly simplified, so the method is completely different from the principle of the existing maximum power tracking technology.
3. Because most photovoltaic systems adopt a mode of connecting a plurality of photovoltaic components in series to provide high voltage required by the system, the light storage system is formed by adopting a mode shown in figure 3, and meanwhile, the flexible control patent technology of the reconstructed battery pack is utilized, namely grouping reverse synchronization trial and error is carried out in the series battery pack, the minimum total amplitude of voltage adjustment during trial and error is ensured, and finally, the method can ensure that each photovoltaic component realizes maximum power output and the minimum total output voltage fluctuation is ensured.
4. In the charging process, any single battery can be adjusted to be in an online or standby state, so that the consistency requirement on the single batteries in the battery pack is not required, the single batteries can be used in a mixed manner by various brands of batteries, and can also be used in a mixed manner by new and old batteries, the universality of the batteries is improved, and the service life of the old batteries is prolonged.
The photovoltaic energy storage system and the control method are suitable for the technical field of photovoltaic power generation.
Drawings
Fig. 1 is a block diagram of a conventional photovoltaic energy storage system.
Fig. 2 is a block diagram of a photovoltaic energy storage system according to the present invention.
Fig. 3 is a control principle diagram of the photovoltaic cell maximum power generation control according to the present invention.
Detailed description of the preferred embodiments
The photovoltaic energy storage system for tracking the maximum power generated by the photovoltaic cell in the first embodiment comprises: the photovoltaic power generation system comprises an energy storage battery pack consisting of N + X single batteries, a BEMS single controller and a BEMS module controller, wherein the BEMS single controller is used for controlling the charging of the single batteries, and the BEMS module controller is used for controlling the integral charging control of the battery pack and also used for realizing the tracking control of the maximum photovoltaic power.
The N + X single batteries in the battery pack are all provided with control switches, and any N single batteries can be connected in series.
In practical use, the energy storage battery pack according to the embodiment is connected in parallel with a photovoltaic module and used for storing electric energy generated by the photovoltaic module.
In the energy storage battery pack, the sum of N + X is the total number of single batteries contained in the battery pack and is a fixed value, N is the number of on-line single batteries and is a variable in the battery charging process, and X is the number of off-line single batteries in a standby state and changes along with the change of N.
BEMS single-body controller can realize connecting arbitrary N battery in the energy storage battery group in series.
In the configuration of the total number N + X of the series monomers of the battery pack, the minimum voltage of the online actual total output of the series monomers of the N + X batteries is ensured to be greater than the rated voltage of the photovoltaic battery pack.
Preferably, the actual output voltage of the N + X batteries after being connected in series is 10% higher than the rated voltage of the photovoltaic battery pack. For example, the following examples: the rated voltage of the photovoltaic battery pack is 100V, and the minimum online actual total output voltage of the N + X batteries which are connected in series is ensured to be more than 110V.
In this embodiment, there is no requirement for the consistency of the cells in the energy storage battery pack, that is: the energy storage battery pack can contain single batteries and new and old batteries of different models.
In the second embodiment, the photovoltaic energy storage system for tracking the maximum power generated by the photovoltaic cell according to the first embodiment is further defined, and in the second embodiment: a software module is embedded in the BEMS module controller and used for realizing the control of charging of the whole battery pack and the tracking control of the maximum power of photovoltaic, and the software module comprises:
the period control unit is used for controlling the maximum charging power tracking period in a timing mode;
a detection unit for detecting the charging current and the total voltage in the charging loop in real time;
the power calculation unit is used for obtaining the total charging power of the charging loop when each tracking period is finished;
when each tracking period is finished, adjusting an adjusting unit of the online single batteries, wherein the adjusting unit is used for comparing the total charging power of the current tracking period with the total charging power of the previous tracking period, if the total charging power of the current tracking period is larger than the total charging power of the previous tracking period, the number N of the online single batteries is adjusted to be increased by 1, and otherwise, the number N of the online single batteries is adjusted to be decreased by 1;
at the end of each tracking cycle, a designated unit is sent for sending an instruction to the BEMS cell controller to increment the battery number N by 1 or decrement it by 1.
The module controller can detect the charging current and voltage in the charging loop in real time in the charging process, and can calculate the charging power of the battery pack and the single battery thereof in the current state in real time by combining the voltage detection of the single battery of the unit controller, and determine the adjustment of the battery pack according to the change of the power. In practical application, the BEMS single-body controller randomly selects one single battery in a standby state to control the single battery to enter an online state according to a received instruction that the number N of the batteries is increased by 1, and the single batteries are connected in a charging loop in series; and when an instruction of subtracting 1 from the number of the batteries is received, cutting off any consistent single battery in the online state to enable the single battery to be in a standby state, and ensuring that the rest N-1 online single batteries are connected in the charging loop in series.
A software module is embedded in the BEMS module controller and used for controlling the number N of the online single batteries of the battery pack, so that the directional adjustment according to the photovoltaic output voltage is realized, and finally, the maximum value of the photovoltaic battery output power under the current illumination regulation is realized all the time.
The adjustment can realize the maximum power tracking of the photovoltaic power generation, and the tracking method is simple and easy to implement.
In the adjusting process, the tracking period can be set according to needs, and the shorter the period is, the more frequent the adjusting times are.
In the third embodiment, the photovoltaic energy storage system for tracking the maximum power generated by the photovoltaic cell according to the second embodiment is further defined, and in the third embodiment: the software module further comprises:
a single voltage detection unit for detecting the terminal voltage of each single battery in the energy storage battery pack when each tracking period is finished;
when the number N of the on-line single batteries is adjusted to be increased by 1, an adding selection unit for adding the single batteries is selected, and the adding selection unit is used for selecting the single battery with the minimum single battery terminal voltage in the standby state to be connected in series into a charging loop in the next tracking period;
when the number N of the online single batteries is reduced by 1, a cutting selection unit for cutting the single batteries is selected, and the unit is used for selecting the single battery with the highest end voltage in the online batteries to be converted into a standby state in the next tracking period
In the embodiment, a function of detecting the terminal voltage of a single battery is added to a software module, so that when the increase or decrease of the single battery is adjusted after each tracking period is finished, a certain single battery is appointed to be increased or decreased according to the terminal voltage of each battery, that is, the function of detecting the terminal voltage of the single battery is as follows: when the single batteries are required to be added, the battery with the lowest voltage in the standby state is selected to be added, so that each single battery in the energy storage battery pack can be fully charged as much as possible, and the energy storage efficiency of the whole energy storage battery pack is improved; when the single batteries need to be reduced, the selected voltage in the on-line single batteries is cut off, so that the overcharge phenomenon of certain single batteries is avoided.
The method is simple and easy to implement, and does not need a complex algorithm.
In practical application, the BEMS unit controller cuts off the designated unit battery from an online state or cuts the designated unit battery into a charging loop from a standby state according to a received instruction.
In the present embodiment, the photovoltaic energy storage system for tracking the maximum power generated by the photovoltaic cell according to the second embodiment is further defined, and in the present embodiment: the software module further comprises:
the detection unit is used for detecting the terminal voltage, the monomer temperature and the online charging time of each monomer battery in the energy storage battery pack and calculating to obtain the charging index of each monomer battery in the standby state;
when the number N of the online single batteries is adjusted to be increased by 1, a charging selection unit for charging the single batteries is selected, and the unit is used for selecting the single battery with the minimum charging index of the single battery in a standby state to be connected in a charging loop in series in the next tracking period;
and when the number N of the online single batteries is reduced by 1, selecting a cutting selection unit for cutting the single batteries, wherein the cutting selection unit is used for selecting the single battery with the highest charging index in the online batteries to be converted into a standby state in the next tracking period.
The online charging time refers to the accumulated charging time of the single battery, namely: the superposition of the online times in each previous tracking cycle.
In the third embodiment, the software module has similar functions to those added in the third embodiment, and all that is achieved is to selectively and appoint to add or remove a certain single battery after each tracking period is finished, but the principle is different. In the third embodiment, the selection is performed according to the voltage of the single battery, and in the third embodiment, the added or cut single battery is selected according to the charge index of the single battery.
In practical application, the BEMS unit controller cuts off the designated unit battery from an online state or cuts the designated unit battery into a charging loop from a standby state according to a received instruction.
The charging index of the single battery is obtained by calculating according to multiple parameters such as voltage, temperature, charging time, effective capacity of the battery and the like of the single battery and according to set weight coefficients, and battery indexes such as SOC, SOH and the like of the single battery can be used as selection indexes.
The adjustment method described in this embodiment is slightly more complex than the method described in the third embodiment, and requires more parameters to be detected, and an index for selecting a single battery needs to be calculated according to the detected parameters, but the actual calculation process is the existing method, and the calculation method is simple and easy to implement.
In an embodiment, the photovoltaic energy storage system for tracking maximum power generated by the photovoltaic cell according to any one of the second to fourth embodiments is further defined, and in the embodiment: the software module further comprises:
when the number N of the online single batteries needs to be adjusted and 1 is added, an overvoltage judging unit is output and used for further judging whether the total output voltage of all the online single batteries in the adjusted energy storage battery pack is higher than the upper limit of the working voltage or not, and if yes, no adjustment is performed.
And when the number N of the online single batteries is required to be adjusted to be less than 1, outputting a pressing judgment unit, wherein the pressing judgment unit is used for further judging whether the output voltage of the adjusted battery pack is lower than the lower limit of the working voltage, and if so, not adjusting.
The software module of the embodiment adds a function of judging the total voltage of all the on-line batteries of the energy storage battery pack during each adjustment and controls the function between the lower limit of the working voltage and the upper limit of the working voltage.
In practical application, when a photovoltaic power generation system using the photovoltaic energy storage system is in a state of no grid-connected equipment working, no other electric load or load shutdown, the method needs to be considered to adjust the number of the batteries on line within the allowable working voltage range of the energy storage battery pack, so that the maximum photovoltaic power generation power tracking within the maximum range is realized. The number of the online batteries is adjusted to be in an upper limit and a lower limit, and after the online batteries are adjusted to reach the upper limit and the lower limit, the online batteries are not subjected to overrun adjustment, so that the maximum power is tracked in a range, but the upper limit and the lower limit are set according to the types and the number of the batteries and the output of the photovoltaic battery assembly.
When other power generation equipment exists in a direct current bus in the photovoltaic power generation system using the photovoltaic energy storage system, the allowable fluctuation range of the working voltage of other equipment needs to be considered, and at the moment, the system can only meet the photovoltaic power generation maximum power tracking within a certain range. Therefore, the upper limit and the lower limit of the operating voltage need to be set according to the allowable fluctuation range of the operating voltage of other devices.
In either case, each tracking cycle in the control process takes into account whether the adjusted voltage is within the range, and if so, does not adjust.
Referring to fig. 2, a photovoltaic power generation system according to the present embodiment is described, which includes a photovoltaic module, a photovoltaic energy storage system, and a DC/AC converter, wherein an electrical energy output terminal of the photovoltaic module is connected to both a power supply terminal of the BEMS battery pack and a DC/AC converter DC signal input terminal.
The photovoltaic energy storage system described in this embodiment is implemented by using the photovoltaic energy storage system for tracking the maximum power generated by the photovoltaic cell described in any one of the first to fifth embodiments.
The difference between this embodiment and the existing similar photovoltaic energy storage system lies in: the photovoltaic energy storage system has the advantages that an indispensable DC/DC converter between the original photovoltaic assembly and the energy storage battery pack is omitted, the structure of the photovoltaic power generation system is simpler due to the adoption of the photovoltaic energy storage system, and the maximum power tracking method for photovoltaic power generation is simpler.
Referring to fig. 3, the structure of the photovoltaic power generation system according to the embodiment includes a plurality of photovoltaic modules, each photovoltaic module is connected in parallel with a BEMS battery pack as an energy storage element, the plurality of photovoltaic modules are connected in series to form a photovoltaic power generation structure, and each BEMS battery pack can realize maximum power generation power tracking and realize most effective energy storage for the photovoltaic module connected in parallel with the BEMS battery pack.
Description of beneficial effects;
1. the comparison test proves the beneficial effects of the photovoltaic energy storage system, in particular to a BEMS battery pack controlled by fixed N + X and a BEMS battery pack charging contrast experiment adopting maximum power tracking, which are disclosed by the invention:
two same photovoltaic power generation boards are selected, under the same experiment condition, the illumination intensity, the illumination angle and the cloudy state are respectively adjusted, the output voltage of the two boards is compared, and the output voltage stability of the scheme can be better.
By adopting the method of the invention, under the same photovoltaic module power generation condition, a conventional battery pack charging mode is adopted, so that serious use problems exist, and a BEMS battery control system is adopted, so that good battery use effect can be realized. The validation process for one experiment is set forth below:
because the voltage has certain variation range in the battery charging voltage process, the battery pack adopting the conventional BEMS technology realizes that the maximum power charging has certain actual photovoltaic condition in the charging process, in order to improve the photovoltaic charging effect, the battery pack system additionally provided with the control mode of the invention is adopted, under the specific illumination condition, the photovoltaic assembly is a mode of connecting two 275W monomers in series and two, the rated voltage is 72V, the same group of 24+8 BEMS battery packs consisting of 32 lithium iron phosphate battery monomers loaded with the BEMS system are adopted for photovoltaic charging control, and the data of the charging process is as follows:
batteries using conventional BEMS technology, namely: according to the BEMS battery pack control technology with fixed N + X, along with the gradual rise of the monomer voltage in the battery charging process, the battery pack voltage is increased from the lowest about 65V to the highest about 80V, and after the battery pack is charged for 1 minute under the fixed illumination condition, the battery pack enters a control steady state, data acquisition is started, and the data described in the table 1 are obtained: the following relationships between the photovoltaic power generation charging power, the total voltage of the battery pack and the number of online batteries are shown in table 1:
table 1:
in the fixed N + X mode, the output voltage of the battery pack is fixed at a certain charging state voltage, so it can be seen from the above data that the maximum charging power can reach about 300% difference under the worst illumination and online battery quantity matching condition, and in the voltage allowable range, the maximum power charging can be realized by automatically adjusting the online battery quantity in the N + X control, if the battery charging terminal stage needs to match 19 online batteries in the above tested illumination condition, and the initial charging stage of the battery deficiency needs 21 online batteries to realize the maximum power charging.
The change of the voltage of the battery pack in the charging process is always present, the maximum power charging can be realized when tracking control is adopted, and the battery use problems such as battery under-charging or over-charging or even explosion and the like of the battery pack can occur according to different control modes by the existing control mode when N + X control is fixed.
2. Application test: the photovoltaic energy storage system and the control technology thereof are trial-run in actual working conditions, and the trial-run result proves that the technology can solve the actual problems of the photovoltaic power generation base station and obtain unexpected technical effects, and the trial-run conditions are as follows:
the trial operation object is a photovoltaic base station in Kashi city, the base station is a typical photovoltaic base station, the basic working current is about 10A, the battery capacity is configured on site as a double-group 1000AH battery pack, because the charging management capability of the original charging device is limited, the batteries are seriously damaged, the phenomena of overcharge, burst and the like of a plurality of batteries occur, the growing range of the batteries during power supply is shortened, the maintenance cost of the batteries is extremely high, and even under the condition of enough illumination time in summer, the batteries can not guarantee the power supply requirement all day long.
According to the field situation, a part of old batteries with certain capacity are selected to be recombined, and the BEMS equipment is loaded to realize the mixed use of various batteries, so that the standby power capacity of the battery pack is realized. Aiming at the difference of various battery sources and the original use state, the N + X configuration mode is adopted for the battery combination, namely, each group of batteries adopts a 24+3 configuration mode, so that the performance of the battery pack is exerted to the maximum extent. After BEMS equipment is loaded, secondary utilization of a large number of retired batteries is achieved, on the premise that batteries and loads are reasonably configured, the existing batteries with the capacity meeting the use conditions are utilized, effective standby power duration is achieved, the whole winter from equipment installation to the next year is finished according to the on-site working condition monitored by remote monitoring software, except for the fact that power cannot be supplied for charging in continuous rainy days and haze days twice, continuous power supply of a base station is achieved in the rest of time, and the power supply requirements of users are met.
Claims (10)
1. A photovoltaic energy storage system for maximum power tracking of photovoltaic cell power generation, the system comprising: the system comprises an energy storage battery pack consisting of N + X single batteries, a BEMS single controller and a BEMS module controller, wherein the BEMS single controller is used for connecting or cutting the corresponding single batteries into or out of a charging loop according to instructions of the BEMS module controller, and the BEMS module controller is used for controlling the overall charging control of the battery pack and also used for realizing photovoltaic maximum power tracking control.
2. The photovoltaic energy storage system for tracking the maximum power generated by the photovoltaic cell as claimed in claim 1, wherein in the energy storage battery pack, N + X is the total number of the single cells contained in the battery pack and is a fixed value, N is the number of the on-line single cells and is a variable in the battery charging process, and X is the number of off-line single cells in a standby state and changes with the change of N.
3. The photovoltaic energy storage system for tracking the maximum power generated by the photovoltaic cells according to claim 1, wherein in the energy storage battery pack, the total output minimum voltage of the N cells after series connection is ensured to be greater than the rated voltage of the corresponding photovoltaic cell assembly.
4. The photovoltaic energy storage system for tracking the maximum power generated by the photovoltaic cells according to claim 3, wherein in the energy storage battery pack, the total output minimum voltage of the series connection of the N single cells is ensured to be more than 10% of the rated voltage of the corresponding photovoltaic electrical component.
5. The photovoltaic energy storage system for maximum power tracking of photovoltaic cell power generation according to claim 3, wherein a software module is embedded in the BEMS module controller for controlling the charging control of the whole battery pack and for realizing the photovoltaic maximum power tracking control, and the software module comprises:
the period control unit is used for controlling the maximum charging power tracking period in a timing mode;
a detection unit for detecting the charging current and the total voltage in the charging loop in real time;
the power calculation unit is used for obtaining the total charging power of the charging loop when each tracking period is finished;
when each tracking period is finished, adjusting an adjusting unit of the online single batteries, wherein the adjusting unit is used for comparing the total charging power of the current tracking period with the total charging power of the previous tracking period, if the total charging power of the current tracking period is larger than the total charging power of the previous tracking period, the number N of the online single batteries is adjusted to be increased by 1, and otherwise, the number N of the online single batteries is adjusted to be decreased by 1;
at the end of each tracking cycle, a designated unit is sent for sending an instruction to increment the number of batteries N by 1 or decrement by 1 to the BEMS cell controller.
6. The photovoltaic energy storage system for maximum power tracking of photovoltaic cell power generation according to claim 5, wherein said software module further comprises:
the single voltage detection unit is used for detecting the terminal voltage of each single battery in the energy storage battery pack when each tracking period is finished;
when the number N of the on-line single batteries is adjusted to be increased by 1, an adding selection unit for adding the single batteries is selected, and the adding selection unit is used for selecting the single battery with the minimum single battery terminal voltage in the standby state to be connected in a charging loop in series in the next tracking period;
and when the number N of the online single batteries is reduced by 1, selecting a cutting selection unit for cutting the single batteries, wherein the cutting selection unit is used for selecting the single battery with the highest end voltage in the online batteries to be converted into a standby state in the next tracking period.
7. The photovoltaic energy storage system for maximum power tracking of photovoltaic cell power generation according to claim 5, wherein said software module further comprises:
the detection unit is used for detecting the terminal voltage, the monomer temperature and the online charging time of each monomer battery in the energy storage battery pack and calculating to obtain the charging index of each monomer battery in the standby state;
when the number N of the online single batteries is adjusted to be increased by 1, an adding selection unit for adding the single batteries is selected, and the adding selection unit is used for selecting the single battery with the minimum charging index of the single battery in a standby state to be connected in a charging loop in series in the next tracking period;
and when the number N of the online single batteries is reduced by 1, selecting a cutting selection unit for cutting the single batteries, wherein the cutting selection unit is used for selecting the single battery with the highest charging index in the online batteries to be converted into a standby state in the next tracking period.
8. The photovoltaic energy storage system for maximum power tracking of photovoltaic cell power generation according to claim 5, wherein said software module further comprises:
and when the number N of the online single batteries is determined to be adjusted and added by 1, outputting an overpressure judgment unit, wherein the overpressure judgment unit is used for further judging whether the total output voltage of all online single batteries in the adjusted energy storage battery pack is higher than the upper limit of the working voltage, and if so, not adjusting.
And when the adjustment of the number N of the online single batteries is reduced by 1, outputting a pressing judgment unit, wherein the unit is used for further judging whether the output voltage of the adjusted battery pack is lower than the lower limit of the working voltage, and if so, not adjusting.
9. The photovoltaic power generation system is characterized by comprising a photovoltaic component, a photovoltaic energy storage system and a DC/AC converter, wherein the electric energy output end of the photovoltaic component is connected with the power supply end of the photovoltaic energy storage system and the direct current signal input end of the DC/AC converter at the same time.
10. The photovoltaic power generation system of claim 9, further comprising a plurality of photovoltaic modules and a plurality of photovoltaic energy storage systems, each photovoltaic module being connected in parallel with one of the photovoltaic energy storage systems.
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