CN113794218B - Electric vehicle retired battery secondary utilization system based on buck-boost circuit - Google Patents
Electric vehicle retired battery secondary utilization system based on buck-boost circuit Download PDFInfo
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- CN113794218B CN113794218B CN202111191485.3A CN202111191485A CN113794218B CN 113794218 B CN113794218 B CN 113794218B CN 202111191485 A CN202111191485 A CN 202111191485A CN 113794218 B CN113794218 B CN 113794218B
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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
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/54—Reclaiming serviceable parts of waste accumulators
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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
- H02J7/0047—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries with monitoring or indicating devices or circuits
- H02J7/0048—Detection of remaining charge capacity or state of charge [SOC]
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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
- H02J7/0068—Battery or charger load switching, e.g. concurrent charging and load supply
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
- H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
- H02M3/1582—Buck-boost converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
- H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
- H02M3/33584—Bidirectional converters
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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
- H02J2207/00—Indexing scheme relating to details of circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
- H02J2207/20—Charging or discharging characterised by the power electronics converter
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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
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/84—Recycling of batteries or fuel cells
Abstract
The invention discloses a secondary utilization system of retired batteries of an electric vehicle based on a buck-boost circuit, which relates to the technical field of batteries, wherein each retired battery in the system is connected to a public bus in parallel through a bidirectional isolation DC/DC converter and a buck-boost circuit in sequence, one end of an inverter is connected with the public bus, and the other end of the inverter is connected with an AC power grid; when the system is in a charging state or a discharging state, the control unit distributes system power and controls the work of each part of circuit based on battery information acquired from the BMS of each retired battery, the voltage, capacity, SOC value, insulation grade, residual life and other performances of the retired battery applied to the system can be different, meanwhile, the BMS of the retired battery can be utilized, the high-efficiency problem of energy conversion can be solved, the retired battery can be directly applied to the system to normally work without additional upgrading and improvement, the realization mode is simple, and the gradient reutilization of the retired battery is possible.
Description
Technical Field
The invention relates to the technical field of batteries, in particular to an electric vehicle retired battery secondary utilization system based on a step-up and step-down circuit.
Background
With the popularization of new energy vehicles, the number of the new energy vehicles is steadily and rapidly increased in China or even worldwide, but the problem is that the battery has service life, and when the battery capacity is reduced to below 80% of the nominal value with use, the battery needs to be retired. However, the retired battery has a large utilization space, just like the battery used on a toy car, and the remote controller can also be used for a long time, so that the retired battery needs to be further utilized.
However, the retired battery of the new energy electric vehicle does not have the same battery standard as the standard dry battery used in life, and the retired batteries of different vehicle types have larger differences in all aspects, including: (1) The voltage difference is large, the battery voltage range is wide, and even the voltage range difference between the same vehicle factory and different vehicle types is also large, for example, a class A00 vehicle has 144V voltage, and a bus has 600V or even 1000V voltage. (2) The battery capacity difference is large, the minimum capacity of the A00 class vehicle has twenty-several degrees of electricity, and the maximum bus battery capacity can be up to 200 degrees of electricity.
Because the difference of each aspect of different retired batteries is larger, the secondary utilization of the retired batteries is always an industrial difficulty, and if the existing energy storage architecture is directly applied to the retired batteries, the following various problems exist:
1. an existing common energy storage architecture is: according to the capacity requirement, firstly, the battery monomers (about 3.6V) are connected in parallel, and after the parallel capacity is reached, the parallel units are connected in series so as to achieve the required voltage. The energy storage battery is then a battery pack. In this architecture, the batteries are connected in series and parallel over a large area, so that the requirements for uniformity of the batteries are relatively high (voltage, capacity, shape, etc.), while as described above, uniformity of the actual retired batteries is low, so that this architecture is not suitable for retired batteries.
2. Another common energy storage architecture in existence is: one battery pack corresponds to one H-bridge power conversion unit, and each H-bridge power conversion unit can independently control whether a single battery pack is charged or discharged by adjusting the conduction polarity of an H-bridge, so that in-phase internal active equalization can be realized. In addition, the output power and the input power of the single battery pack can be adjusted through the duty ratio of the H-bridge power conversion unit. Therefore, this architecture is more suitable for the situations of different voltage ranges, different capacities, different battery pack performance, and even different battery pack types, that is, for the retired battery with lower performance consistency, but the following problems still exist in this architecture: (1) Most Battery Management Systems (BMSs) for retired batteries are used for managing and collecting direct voltage and direct current to perform fault and SOC monitoring, but the current of each unit in the above architecture is sinusoidal, which results in that the original BMS system needs to be upgraded or even replaced if the retired battery is applied to the above architecture, otherwise, the system is not supported for use, and the BMS system is integrated with the battery pack, so that the complexity and cost of recycling the battery pack are high. (2) In the above architecture, it is required that the insulation and voltage level of each battery pack reach the insulation and voltage level of the integrated power grid (because each battery pack may be at high voltage or low voltage). However, the insulation level of each retired battery is designed according to the voltage of the battery pack, so that in order to apply the retired battery to the system, secondary insulation needs to be added outside the retired battery, and additional operation is also needed. (3) Although the above-mentioned framework can achieve the in-phase internal active equalization, the equalization between different phases is difficult to achieve, which requires the battery pack capacity between the phases to be similar, and the above-mentioned framework can be applied after additional screening. Therefore, although the second architecture can make secondary use of the retired battery to a certain extent, there are additional requirements on other aspects of the retired battery, so that the retired battery needs to be screened and upgraded before the retired battery can be applied to the architecture.
Disclosure of Invention
The inventor provides an electric vehicle retired battery secondary utilization system based on a step-up and step-down circuit aiming at the problems and the technical requirements, and the technical scheme of the invention is as follows:
an electric vehicle retired battery secondary utilization system based on a step-up and step-down circuit, the system comprises: the system comprises a plurality of retired batteries, a bidirectional isolation DC/DC converter, a step-up and step-down circuit, a control unit, a public bus, an inverter and an alternating current power grid;
the battery terminal of each retired battery is connected with a corresponding step-up/step-down circuit through a corresponding bidirectional isolation DC/DC converter, each step-up/step-down circuit is connected to a public bus in parallel, one end of the inverter is connected with the public bus, and the other end of the inverter is connected with an alternating current power grid; the control unit is connected with the BMS, the inverter, the bidirectional isolation DC/DC converters and the buck-boost circuits of the retired batteries;
when the system is in a charging state or a discharging state, the control unit controls the electric energy transmission direction of the inverter according to the charging and discharging state, performs system power distribution based on battery information obtained from BMS of each retired battery, and controls the working states of each bidirectional isolation DC/DC converter and each buck-boost circuit according to a system power distribution result, wherein the system power distribution result indicates the actual charging and discharging power of each retired battery;
when the system is in a charging state, each retired battery is charged by the alternating current power grid, and when the system is in a discharging state, electric energy flows to the alternating current power grid from each retired battery.
The further technical scheme is that the battery information at least comprises rated power of the retired battery, and the system power distribution is performed based on the battery information obtained from the BMS of each retired battery, and the method comprises the following steps:
determining the actual charge and discharge power of each retired battery based on the sum of the charge and discharge power of the power grid and the rated power of all retired batteries;
the inverter is controlled to charge and discharge between the public bus and the alternating current power grid according to the electric energy transmission direction by using the power grid charging and discharging power, and the connected bidirectional isolation DC/DC converter and the voltage-increasing circuit are controlled according to the actual charging and discharging power of each retired battery so as to adjust the current and the voltage between the retired battery and the public bus, so that the retired battery is charged and discharged according to the actual charging and discharging power.
The further technical scheme is that the actual charge-discharge power of each retired battery is determined based on the sum of the charge-discharge power of a power grid and rated power of all retired batteries, and the method comprises the following steps:
taking the ratio of the sum of the charging and discharging power of the power grid and the rated power of all retired batteries as a power weight, wherein the power weight is smaller than 1;
and obtaining the actual charge and discharge power of the retired battery by the product of the rated power and the power weight of each retired battery.
The further technical scheme is that the battery information also comprises the SOC value of the retired battery, and the actual charge and discharge power of the retired battery is obtained by the product of the rated power and the power weight of each retired battery, comprising:
obtaining basic actual power of the retired battery by multiplying rated power and power weight of each retired battery;
determining the power offset of each retired battery according to the SOC value of each retired battery, and adding the corresponding power offset to correct the basic actual power of each retired battery to obtain the actual charge and discharge power of the retired battery;
when the system is in a charged state, the power offset of the retired battery with the SOC value within a first preset range of the average SOC value is 0, the power offset of the retired battery with the SOC value larger than the first preset range of the average SOC value is negative, the power offset of the retired battery with the SOC value smaller than the first preset range of the average SOC value is positive, and the sum of the power offsets of all the retired batteries is 0;
when the system is in a discharging state, the power offset of the retired battery with the SOC value within a second preset range of the average SOC value is 0, the power offset of the retired battery with the SOC value smaller than the second preset range of the average SOC value is negative, the power offset of the retired battery with the SOC value larger than the second preset range of the average SOC value is positive, and the sum of the power offsets of all the retired batteries is 0;
wherein the average SOC value is an average value of SOC values of all the retired batteries.
The battery information further comprises peak power of the retired battery, and the absolute value of the power offset of each retired battery is related to the peak power or the minimum effective power of the retired battery: when the power offset is negative, the absolute value of the power offset does not exceed the difference value between the basic actual power and the minimum effective power of the retired battery; when the power offset is positive, the absolute value of the power offset does not exceed the difference between the peak power of the retired battery and the base actual power.
When the system is in a charging state, the control unit adjusts the bidirectional isolation DC/DC converter and the buck-boost circuit connected with each retired battery, wherein the bidirectional isolation DC/DC converter comprises:
the control unit controls each step-up and step-down circuit to adjust bus voltage of the common bus to a target voltage value and provide the target voltage value for the bidirectional isolation DC/DC converter, and the target voltage value and the real-time voltage value of the retired battery accord with the transformation ratio of the bidirectional isolation DC/DC converter;
the control unit controls the current direction of each bidirectional isolation DC/DC converter to flow from the step-up/step-down circuit to the retired battery, and controls the current so that the product of the current and the real-time voltage value of the retired battery is equal to the actual charge/discharge power of the retired battery.
When the system is in a discharging state, the control unit adjusts the bidirectional isolation DC/DC converter and the buck-boost circuit connected with each retired battery, wherein the bidirectional isolation DC/DC converter comprises:
the control unit controls each buck-boost circuit to adjust the output voltage of the bidirectional isolation DC/DC converter to the bus voltage and provide the bus voltage for the public bus, and the output voltage of the bidirectional isolation DC/DC converter and the real-time voltage value of the retired battery accord with the transformation proportion of the bidirectional isolation DC/DC converter;
the control unit controls the current direction of each bidirectional isolation DC/DC converter to flow from the retired battery to the buck-boost circuit, and controls the current so that the product of the current and the real-time voltage value of the retired battery is equal to the actual charge-discharge power of the retired battery.
When the control unit detects that the retired battery fails or reaches a service life threshold value based on battery information in the process that the system is in a charging state or a discharging state, alarm information is sent to indicate that the retired battery is abnormal, and the abnormal retired battery is controlled to be disconnected with a public bus, and then power distribution of the system is carried out again.
The further technical scheme is that when the control unit detects that the voltage change rate of the retired battery reaches a preset rate threshold when the retired battery is charged and discharged, and/or detects that the ratio of the actual total capacity of the retired battery to the initial total capacity is lower than the ratio threshold, the retired battery is determined to reach a service life threshold, and the initial total capacity is the total capacity of the retired battery when the retired battery is accessed into the system for the first time.
According to the further technical scheme, the control unit controls the system to enter a charging state, a discharging state or an idle state according to the received control instruction, when the control unit receives the control instruction for indicating the control system to enter the idle state, the control unit controls the inverter to be disconnected with the alternating current power grid, controls all the bidirectional isolation DC/DC converters and all the buck-boost circuits to stop working, and sends a dormancy instruction to BMS of all the retired batteries, so that the system is in the idle state.
The beneficial technical effects of the invention are as follows:
the application discloses electric motor car retired battery reutilization system based on step-up and step-down circuit, this system combines together through hardware topology and software control, realized the electric energy reutilization to the retired battery of the great difference in performance, and the voltage of the retired battery of using in this system, capacity, the SOC value, insulating grade, surplus life-span etc. performance all can be different, can utilize the BMS of retired battery own and can solve the high-efficient problem of energy conversion simultaneously, need not to do extra upgrading and improvement just can directly use normal work in the system to the retired battery, the realization mode is simple, it is possible to let the echelon reutilization of the retired battery of new energy vehicle.
Drawings
Fig. 1 is a schematic diagram of a system topology of an electric vehicle retired battery secondary utilization system disclosed in the present application.
Fig. 2 is a schematic diagram of control logic of the electric vehicle retired battery secondary utilization system in a charged state.
Detailed Description
The following describes the embodiments of the present invention further with reference to the drawings.
The application discloses electric motor car retired battery reutilization system based on step-up and step-down circuit please refer to fig. 1, and this system includes a plurality of retired battery, two-way isolation DC/DC converter, step-down circuit (Buck-Boost), control unit, public bus, DC-to-ac converter and ac power grid.
The battery terminals of each retired battery are respectively connected with a corresponding step-up/step-down circuit through a corresponding bidirectional isolation DC/DC converter, the step-up/step-down circuits are respectively connected to a public bus in parallel, one end of the inverter is connected with the public bus, and the other end of the inverter is connected with an alternating current power grid. Specifically, the inverter is connected to an ac power grid through a grid-connected reactance. The control unit is connected with the BMS, the inverter, the bidirectional isolation DC/DC converters and the buck-boost circuits of the retired batteries.
The transformation ratio of the bidirectional isolation DC/DC converter is determined by the transformation ratio of the transformer inside the bidirectional isolation DC/DC converter, assuming that the transformation ratio of the transformer is 1: n, if the voltage across the bi-directional isolated DC/DC converter is not 1: n, the structural efficiency is very low (the worst case is half of the efficiency is not yet), and the voltage of the two ends of the bidirectional isolation DC/DC converter is bound in a moment-to-moment proportional relationship, namely the voltage proportional relationship of the two ends of the bidirectional isolation DC/DC converter is consistent with the transformation ratio relationship of the transformer, so that the efficiency of the system is always at the highest point (more than 95%). The voltage characteristic of the retired battery is that the higher the electric quantity is, the higher the voltage is, the lower the electric quantity is, and the lower the voltage is, so if one end of the bidirectional isolation DC/DC converter is connected with the retired battery, the voltage of the other end of the bidirectional isolation DC/DC converter changes along with the voltage change of the retired battery. However, the bus voltage of the common bus is required to be relatively stable, so that the other end of the bidirectional isolation DC/DC converter cannot be directly connected to the common bus, and therefore, a step-up and step-down circuit is connected between the bidirectional isolation DC/DC converter and the common bus, and the step-up and step-down circuit is not isolated, but can adjust the voltage of the bidirectional isolation DC/DC converter to be consistent with the bus voltage, so that the bidirectional isolation DC/DC converter can be directly connected. The transformation ratio of the bidirectional isolation DC/DC converters connected with different retired batteries can be the same or different.
When the system works, the control unit controls the system to enter a charging state, a discharging state or an idle state according to the received control instruction, and the control unit respectively introduces the following steps:
1. an idle state of the system.
When the control unit receives a control instruction for indicating the control system to enter an idle state, the control unit controls the inverter to be disconnected with the alternating current power grid, controls all the bidirectional isolation DC/DC converters and all the buck-boost circuits to stop working, and sends a dormancy instruction to the BMS of all the retired batteries, so that the whole system is in the idle state, and the energy consumption of the system in the idle state can be reduced to the minimum.
2. And in the charging state of the system, each retired battery is charged by the AC power grid, the system is in phase with the voltage sent by the AC power grid, and the current is opposite, so that the retired battery is charged. Please refer to the flowchart shown in fig. 2.
When the system is in a charging state, the control unit controls the electric energy transmission direction of the inverter according to the charging and discharging state, and specifically, the electric energy transmission direction of the inverter is controlled to be that an alternating current power grid flows to a public bus in the charging state. Meanwhile, the control unit performs system power distribution based on battery information acquired from the BMS of each retired battery, and controls the working states of each bidirectional isolation DC/DC converter and each buck-boost circuit according to a system power distribution result, wherein the system power distribution result indicates actual charge and discharge power of each retired battery. The specific system power allocation and control process is as follows:
1. the control unit determines the power grid charging and discharging power contained in the received control instruction for instructing the control system to enter the charging state, and the power grid charging and discharging power instructs the discharging power of the alternating current power grid in the charging state of the system.
2. And determining the actual charge and discharge power of each retired battery based on the sum of the charge and discharge power of the power grid and the rated power of all retired batteries. The rated power of each retired battery can be read from the BMS of the retired battery, i.e. contained in the battery information, and the actual charge-discharge power is determined by: taking the ratio of the sum of the charging and discharging power of the power grid and the rated power of all the retired batteries as a power weight, wherein the power weight is smaller than 1, and obtaining the actual charging and discharging power of the retired batteries by the product of the rated power of each retired battery and the power weight.
One way is to directly take the product of the rated power and the power weight of each retired battery as the actual charge and discharge power. For example, the charging and discharging power of the power grid is 50kw, the sum of the rated powers of all the retired batteries is 100kw, the calculated power weight is 1/2, at this time, 1/2 of the rated power of each retired battery can be used as the actual charging and discharging power of each retired battery, and if the rated power of the battery pack a is 10kw and the rated power of the battery pack B is 20kw, the actual charging and discharging power of the battery pack a is 5kw and the actual charging and discharging power of the battery pack B is 10kw can be determined.
The other way is that the basic actual power of the retired battery is obtained by the product of the rated power and the power weight of each retired battery, then the power offset of each retired battery is determined according to the SOC value of each retired battery, and the corresponding power offset is increased to correct on the basis of the basic actual power of each retired battery, so as to obtain the actual charge and discharge power of the retired battery.
When the system is in a charged state, the power offset of the retired battery with the SOC value within a first preset range of the average SOC value is 0, the power offset of the retired battery with the SOC value larger than the first preset range of the average SOC value is negative, the power offset of the retired battery with the SOC value smaller than the first preset range of the average SOC value is positive, and the sum of the power offsets of all the retired batteries is 0. The average SOC value is an average value of SOC values of all retired batteries, and the first predetermined range may be a custom range.
The absolute value of the power offset for each retired battery is related to the peak power or minimum available power for the retired battery: when the power offset is negative, the absolute value of the power offset does not exceed the difference value between the basic actual power and the minimum effective power of the retired battery; when the power offset is positive, the absolute value of the power offset does not exceed the difference between the peak power of the retired battery and the base actual power. The peak power of the retired battery may be read from the BMS, i.e., included in the battery information. The minimum available power is typically a custom small power value, such as 1kw. The method can ensure that the actual charge and discharge power obtained after correction by using the positive power offset does not exceed the peak power of the retired battery, and can also ensure that the actual charge and discharge power obtained after correction by using the negative power offset is not 0, i.e. no load can not occur, thereby avoiding the condition of low no-load efficiency.
For example, in the system, 15 retired batteries are total, wherein the SOC values of 13 retired batteries are all 30%, the SOC value of a battery pack A is 25%, the rated power is 10kw, the peak power is 13kw, and the SOC value of a battery pack B is 35%, the rated power is 20kw, and the peak power is 25kw. Assuming that the charging and discharging power of the power grid is 50kw and the sum of rated powers of all retired batteries is 100kw, the calculated power weight is 1/2, and then the basic actual power of the battery pack A is 1/2 of the rated power 10kw, namely 5kw, and the basic actual power of the battery pack AB is 1/2 of the rated power 20kw, namely 10kw.
At this time, it may be determined that the average SOC value is 30%, and assuming that the first predetermined range of the average SOC value is 28% to 32%, it may be determined that: the power offsets of 13 retired batteries with SOC values of 30% are all 0. The SOC value of the battery pack a is 25% smaller than the first predetermined range, so that the power offset of the battery pack a is positive and the absolute value does not exceed the difference between the peak power 13kw and the base actual power 5kw, that is, 8kw. The SOC value of the battery pack B is 35% greater than the first predetermined range, and therefore the power offset of the battery pack B is negative and the absolute value does not exceed the difference between its base actual power 10kw and the minimum effective power 1kw, that is, 9kw. Therefore, the power offset of the battery pack A is +8kw, and the power offset of the battery pack B is-8 kw, so that the actual charge and discharge power of the battery pack A obtained after correction is 13kw and the actual charge and discharge power of the battery pack B is 2kw.
It can be seen from the examples that after the second method corrects the power offset, the retired battery larger than the average SOC value can be charged with lower power, and the retired battery smaller than the average SOC value is charged with higher power, so that the SOC values of all the retired batteries are quickly closer to the average SOC value along with the charging process and tend to be consistent as soon as possible.
2. And controlling the inverter to charge and discharge between the public bus and the alternating current power grid by using the power grid charging and discharging power according to the power transmission direction. In this embodiment, the control unit controls the inverter to transfer electrical energy from the ac grid to the common bus according to the grid charging and discharging power determined in step 1, such as to transfer electrical energy from the ac grid to the common bus according to a power of 50 kw.
3. And controlling the connected bidirectional isolation DC/DC converter and the buck-boost circuit according to the actual charge and discharge power of each retired battery to regulate the current and voltage between the retired battery and the common bus, so that the retired battery is charged and discharged according to the actual charge and discharge power. The control unit adjusts the bidirectional isolation DC/DC converter and the buck-boost circuit connected with each retired battery, and the bidirectional isolation DC/DC converter comprises:
the control unit controls each step-up and step-down circuit to adjust bus voltage of the common bus to a target voltage value and provide the target voltage value for the bidirectional isolation DC/DC converter, and the target voltage value and the real-time voltage value of the retired battery accord with the transformation ratio of the bidirectional isolation DC/DC converter.
The control unit controls the current direction of each bidirectional isolation DC/DC converter to flow from the step-up/step-down circuit to the retired battery, and controls the current so that the product of the current and the real-time voltage value of the retired battery is equal to the actual charge/discharge power of the retired battery. The control process is dynamically carried out all the time, and as a whole, all the retired batteries are charged and have the same direction, so that the conditions of charging the existing retired batteries, discharging the existing retired batteries and forming circulation in the energy can not occur.
3. In a discharging state of the system, electric energy flows from each retired battery to the alternating current power grid, and the system discharges the alternating current power grid by having the same phase with the voltage and the same phase with the current emitted by the alternating current power grid. The discharge state of the system is similar to the process of the charge state described above, and thus the following process will not be developed in detail for the repetition.
When the system is in a discharging state, the control unit controls the electric energy transmission direction of the inverter according to the charging and discharging state, and specifically, the electric energy transmission direction of the inverter is controlled to be a public bus to flow to an alternating current power grid in the discharging state. Meanwhile, the control unit performs system power distribution based on battery information acquired from the BMS of each retired battery, and controls the working states of each bidirectional isolation DC/DC converter and each buck-boost circuit according to a system power distribution result, wherein the system power distribution result indicates actual charge and discharge power of each retired battery. The specific system power allocation and control process is as follows:
1. the control unit determines the power grid charging and discharging power contained in the received control instruction for indicating the control system to enter a discharging state, and the power grid charging and discharging power indicates the discharging power of the public bus to the alternating current power grid in the discharging state of the system.
2. And determining the actual charge and discharge power of each retired battery based on the sum of the charge and discharge power of the power grid and the rated power of all retired batteries. The rated power of each retired battery can be read from the BMS of the retired battery, i.e. contained in the battery information, and the actual charge-discharge power is determined by: taking the ratio of the sum of the charging and discharging power of the power grid and the rated power of all the retired batteries as a power weight, wherein the power weight is smaller than 1, and obtaining the actual charging and discharging power of the retired batteries by the product of the rated power of each retired battery and the power weight.
One way is to directly take the product of the rated power and the power weight of each retired battery as the actual charge and discharge power.
The other way is that the basic actual power of the retired battery is obtained by the product of the rated power and the power weight of each retired battery, then the power offset of each retired battery is determined according to the SOC value of each retired battery, and the corresponding power offset is increased to correct on the basis of the basic actual power of each retired battery, so as to obtain the actual charge and discharge power of the retired battery.
When the system is in a discharging state, the power offset of the retired battery with the SOC value within the second preset range of the average SOC value is 0, the power offset of the retired battery with the SOC value smaller than the second preset range of the average SOC value is negative, the power offset of the retired battery with the SOC value larger than the second preset range of the average SOC value is positive, and the sum of the power offsets of all the retired batteries is 0. The average SOC value is an average value of SOC values of all the retired batteries, and the second predetermined range may be a custom range.
The absolute value of the power offset for each retired battery is related to the peak power or minimum available power for the retired battery: when the power offset is negative, the absolute value of the power offset does not exceed the difference value between the basic actual power and the minimum effective power of the retired battery; when the power offset is positive, the absolute value of the power offset does not exceed the difference between the peak power of the retired battery and the base actual power. The peak power of the retired battery may be read from the BMS, i.e., included in the battery information. The minimum available power is typically a custom small power value, such as 1kw. The method can ensure that the actual charge and discharge power obtained after correction by using the positive power offset does not exceed the peak power of the retired battery, and can also ensure that the actual charge and discharge power obtained after correction by using the negative power offset is not 0, i.e. no load can not occur, thereby avoiding the condition of low no-load efficiency.
The specific method is similar to the charging state, and the second method is not separately illustrated, after the power offset is corrected, the retired battery larger than the average SOC value can be discharged with higher power, and the retired battery smaller than the average SOC value is discharged with lower power, so that the SOC values of all the retired batteries are quickly closed to the average SOC value along with the discharging process and tend to be consistent as soon as possible.
2. And controlling the inverter to charge and discharge between the public bus and the alternating current power grid by using the power grid charging and discharging power according to the power transmission direction. In this embodiment, the control unit controls the inverter to transfer electrical energy from the common bus to the ac grid according to the grid charging and discharging power determined in step 1, such as to transfer electrical energy from the common bus to the ac grid according to a power of 50 kw.
3. And controlling the connected bidirectional isolation DC/DC converter and the buck-boost circuit according to the actual charge and discharge power of each retired battery to regulate the current and voltage between the retired battery and the common bus, so that the retired battery is charged and discharged according to the actual charge and discharge power. The control unit adjusts the bidirectional isolation DC/DC converter and the buck-boost circuit connected with each retired battery, and the bidirectional isolation DC/DC converter comprises:
the control unit controls each buck-boost circuit to adjust the output voltage of the bidirectional isolation DC/DC converter to the bus voltage and provide the bus voltage for the public bus, and the output voltage of the bidirectional isolation DC/DC converter and the real-time voltage value of the retired battery accord with the transformation proportion of the bidirectional isolation DC/DC converter.
The control unit controls the current direction of each bidirectional isolation DC/DC converter to flow from the retired battery to the buck-boost circuit, and controls the current so that the product of the current and the real-time voltage value of the retired battery is equal to the actual charge-discharge power of the retired battery.
In addition, no matter when the system is in a charging state or in a discharging state, if the control unit detects that the retired battery fails or reaches a service life threshold value based on battery information in the charging state or discharging state process of the system, alarm information is sent to indicate that the retired battery is abnormal and wait for replacing the retired battery, and meanwhile, the control unit controls the abnormal retired battery to be disconnected with a public bus and then re-distributes system power. When the control unit detects that the voltage change rate of the retired battery reaches a preset rate threshold during charging and discharging, and/or detects that the ratio of the actual total capacity of the retired battery to the initial total capacity is lower than the ratio threshold, determining that the retired battery reaches a service life threshold, wherein the initial total capacity is the total capacity of the retired battery when the retired battery is accessed into the system for the first time.
Based on the system architecture and the operation process, the application has the following advantages for the application of the retired battery:
(1) The voltage output to the buck-boost circuit is in a fixed range no matter what the voltage value of the retired battery is, and the relationship between the voltage of the bidirectional isolation DC/DC converter and the bus voltage can be balanced due to the buck-boost circuit, so that the retired battery with different voltages can be connected to the common bus in parallel, and the retired battery with different voltages can be applied to the same system.
(2) The control unit controls different retired batteries to adopt different charging and discharging powers according to the battery information, so that the contradiction that different capacity battery packs co-operate in the same system is solved.
(3) The control unit can control the current direction, can accomplish initiative balanced, does not have the requirement to the SOC value of retired battery, as long as retired battery can also charge and discharge can, consequently make the battery package of different SOC states can be in same system operation, and along with charge and discharge's going on, the SOC value of retired battery can gradually draw close to the average, tend to unanimity moreover.
(4) Due to the fact that the bidirectional isolation DC/DC converter is arranged to carry out bidirectional energy transfer between the retired battery and the public bus, the retired battery can be isolated, insulation reinforcement is not needed for the original retired battery, and retired batteries with different insulation grades can operate in the same system.
(5) The hardware topology of the system enables the input and output current of the retired battery to be direct current all the time, so the BMS of the retired battery can be directly used without replacing and upgrading.
(6) The problem of high efficiency of energy conversion is solved because of the binding relation between the input and output voltage proportion and the transformer proportion of the bidirectional isolation DC/DC converter.
(7) The control unit monitors the state of the retired battery in the running process of the system, and when the battery is almost in service life or has faults and the state is abnormal, the retired battery with abnormal state is disconnected, so that the retired batteries with different service lives can reliably run in the system, and the system can not respond to the normal work of the system.
(8) Because no retired battery directly participates in phase output, the problem of phase-to-phase balance is not existed.
In a typical example, there are 15 retired batteries, and the information of these 15 retired batteries is as follows:
the system configuration is as follows:
the bus voltage is: 710V, for a 380Vac AC grid, the voltage margin is large enough to be on-grid by inverter modulation. During discharging, the inverter makes current and voltage flow to the alternating current power grid in the same phase through modulation. During charging, the inverter can control rectification, energy flows into the public bus from the alternating current power grid in a reverse direction through controlling voltage and current, and then the energy is transferred to the retired battery through the bidirectional isolation DC/DC converter and the Buck-Boost Buck-Boost circuit.
The total electric quantity of the system is 802 DEG electricity, and 80% of the back slope is needed to be utilized due to the gradient utilization of the battery, and the actual allowable capacity is 802 DEG electricity 80% >, 80% > = 513 DEG electricity because the gradient utilization of the battery is not full in one cycle and is not discharged, so that the efficiency is improved; can last to charge at 100kw for 5 hours; can last to discharge at 100kw for 5 hours after full charge; the 380Vac ac grid can be directly docked. From the above aspect, the highest duty ratio is not more than 18%, that is, even if the retired battery with the largest capacity fails or the service life is reached, the normal operation of the system is not affected in a short time, and the rest is enough to support.
What has been described above is only a preferred embodiment of the present application, and the present invention is not limited to the above examples. It is to be understood that other modifications and variations which may be directly derived or contemplated by those skilled in the art without departing from the spirit and concepts of the present invention are deemed to be included within the scope of the present invention.
Claims (7)
1. An electric vehicle retired battery secondary utilization system based on a buck-boost circuit, which is characterized by comprising: the system comprises a plurality of retired batteries, a bidirectional isolation DC/DC converter, a step-up and step-down circuit, a control unit, a public bus, an inverter and an alternating current power grid;
the battery terminal of each retired battery is connected with a corresponding step-up/step-down circuit through a corresponding bidirectional isolation DC/DC converter, each step-up/step-down circuit is connected to a public bus in parallel, one end of the inverter is connected with the public bus, and the other end of the inverter is connected with an alternating current power grid; the control unit is connected with the BMS of each retired battery, the inverter, each bidirectional isolation DC/DC converter and each buck-boost circuit;
when the system is in a charging state or a discharging state, the control unit controls the electric energy transmission direction of the inverter according to the charging and discharging state, performs system power distribution based on battery information obtained from BMS of each retired battery, and controls the working states of each bidirectional isolation DC/DC converter and each buck-boost circuit according to a system power distribution result, wherein the system power distribution result indicates the actual charging and discharging power of each retired battery;
when the system is in a charging state, each retired battery is charged by the alternating current power grid, and when the system is in a discharging state, electric energy flows to the alternating current power grid from each retired battery;
the battery information includes rated power of the retired battery and SOC value of the retired battery, and the system power allocation is performed based on battery information acquired from BMSs of the respective retired batteries, including:
taking the ratio of the sum of the charging and discharging power of a power grid and the rated power of all the retired batteries as a power weight, wherein the power weight is smaller than 1, obtaining the basic actual power of each retired battery by the product of the rated power of each retired battery and the power weight, determining the power offset of each retired battery according to the SOC value of each retired battery, and adding the corresponding power offset on the basis of the basic actual power of each retired battery for correction to obtain the actual charging and discharging power of each retired battery; when the system is in a charged state, the power offset of the retired battery with the SOC value within a first preset range of an average SOC value is 0, the power offset of the retired battery with the SOC value larger than the first preset range of the average SOC value is negative, the power offset of the retired battery with the SOC value smaller than the first preset range of the average SOC value is positive, and the sum of the power offsets of all the retired batteries is 0; when the system is in a discharging state, the power offset of the retired battery with the SOC value within a second preset range of the average SOC value is 0, the power offset of the retired battery with the SOC value smaller than the second preset range of the average SOC value is negative, the power offset of the retired battery with the SOC value larger than the second preset range of the average SOC value is positive, and the sum of the power offsets of all the retired batteries is 0; the average SOC value is the average value of the SOC values of all the retired batteries;
and controlling the inverter to charge and discharge between the public bus and an alternating current power grid according to the electric energy transmission direction and the power grid charge and discharge power, and controlling the connected bidirectional isolation DC/DC converter and the buck-boost circuit according to the actual charge and discharge power of each retired battery to regulate the current and voltage between the retired battery and the public bus, so that the retired battery charges and discharges according to the actual charge and discharge power.
2. The system of claim 1, wherein the battery information further comprises peak power of retired batteries, and wherein an absolute value of a power offset for each retired battery is related to the peak power or minimum available power of the retired battery: when the power offset is negative, the absolute value of the power offset does not exceed the difference value between the basic actual power of the retired battery and the minimum effective power; and when the power offset is positive, the absolute value of the power offset does not exceed the difference value between the peak power of the retired battery and the basic actual power.
3. The system of claim 1, wherein the control unit adjusts the bi-directional isolated DC/DC converter and buck-boost circuit to which each retired battery is connected when the system is in a charged state, comprising:
the control unit controls each step-up and step-down circuit to adjust bus voltage of the common bus to a target voltage value and provide the target voltage value for the bidirectional isolation DC/DC converter, and the target voltage value and the real-time voltage value of the retired battery accord with the transformation ratio of the bidirectional isolation DC/DC converter;
the control unit controls the current direction of each bidirectional isolation DC/DC converter to flow from the buck-boost circuit to the retired battery, and controls the current so that the product of the current and the real-time voltage value of the retired battery is equal to the actual charge-discharge power of the retired battery.
4. The system of claim 1, wherein the control unit adjusts the bi-directional isolated DC/DC converter and buck-boost circuit to which each retired battery is connected when the system is in a discharged state, comprising:
the control unit controls each buck-boost circuit to regulate the output voltage of the bidirectional isolation DC/DC converter to the bus voltage and provide the bus voltage for the public bus, and the real-time voltage value of the output voltage of the bidirectional isolation DC/DC converter and the real-time voltage value of the retired battery accord with the transformation ratio of the bidirectional isolation DC/DC converter;
the control unit controls the current direction of each bidirectional isolation DC/DC converter to flow from the retired battery to the buck-boost circuit, and controls the current so that the product of the current and the real-time voltage value of the retired battery is equal to the actual charge-discharge power of the retired battery.
5. The system of claim 1, wherein the system further comprises a controller configured to control the controller,
when the system is in a charging state or a discharging state, if the control unit detects that the retired battery fails or reaches a service life threshold value based on battery information, alarm information is sent to indicate that the retired battery is abnormal, and the abnormal retired battery is controlled to be disconnected with the public bus, and then system power distribution is carried out again.
6. The system of claim 5, wherein the system further comprises a controller configured to control the controller,
when the control unit detects that the voltage change rate of the retired battery reaches a preset rate threshold during charging and discharging, and/or detects that the ratio of the actual total capacity of the retired battery to the initial total capacity is lower than the ratio threshold, determining that the retired battery reaches a service life threshold, wherein the initial total capacity is the total capacity of the retired battery when the retired battery is accessed into the system for the first time.
7. The system of claim 1, wherein the system further comprises a controller configured to control the controller,
the control unit controls the system to enter a charging state, a discharging state or an idle state according to the received control instruction, and when the control unit receives the control instruction for instructing the system to enter the idle state, the control unit controls the inverter to be disconnected with the alternating current power grid, controls all the bidirectional isolation DC/DC converters and all the buck-boost circuits to stop working, and sends a dormancy instruction to BMS of all the retired batteries, so that the system is in the idle state.
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| CN117033953B (en) * | 2023-10-10 | 2023-12-29 | 深圳蓝锂科技有限公司 | Gradient utilization analysis method and device for achieving retired battery based on BMS |
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