CN113824143B - Electric vehicle retired battery secondary utilization system based on H bridge cascade connection - Google Patents

Electric vehicle retired battery secondary utilization system based on H bridge cascade connection Download PDF

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CN113824143B
CN113824143B CN202111191470.7A CN202111191470A CN113824143B CN 113824143 B CN113824143 B CN 113824143B CN 202111191470 A CN202111191470 A CN 202111191470A CN 113824143 B CN113824143 B CN 113824143B
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power
retired
battery
retired battery
batteries
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CN113824143A (en
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王勇
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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
    • 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
    • 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]
    • 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
    • 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
    • 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal 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
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal 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, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal 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, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal 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, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • H02M7/53875—Conversion of dc power input into ac power output without possibility of reversal 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, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output
    • 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
    • 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
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin
    • 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

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Charge And Discharge Circuits For Batteries Or The Like (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The application discloses an electric vehicle retired battery secondary utilization system based on H-bridge cascading, which relates to the technical field of batteries, wherein three bidirectional isolation DC/DC converters connected with each retired battery in the system are respectively connected into one phase line of an alternating current power grid through one H-bridge power converter, and all the H-bridge power converters are mutually cascaded; the control unit performs system power distribution based on battery information acquired from BMS of each retired battery and controls the work of each bidirectional isolation DC/DC converter and each H-bridge power converter, the voltage, capacity, SOC value, insulation level, 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 work normally without additional upgrading and improvement, and the gradient reutilization of the retired battery is possible.

Description

Electric vehicle retired battery secondary utilization system based on H bridge cascade connection
Technical Field
The application relates to the technical field of batteries, in particular to an electric vehicle retired battery secondary utilization system based on H-bridge cascading.
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
Aiming at the problems and the technical requirements, the inventor provides an electric vehicle retired battery secondary utilization system based on H-bridge cascading, and the technical scheme of the application is as follows:
an electric vehicle retired battery secondary utilization system based on H bridge cascade connection, the system comprises: the system comprises a plurality of retired batteries, a bidirectional isolation DC/DC converter, an H-bridge power converter, a control unit and an alternating current power grid;
each retired battery is respectively connected with three bidirectional isolation DC/DC converters, the three bidirectional isolation DC/DC converters connected with the same retired battery are respectively connected into one phase line of an alternating current power grid through one H-bridge power converter, and all the H-bridge power converters are mutually cascaded; the control unit is connected with the BMS of each retired battery, each bidirectional isolation DC/DC converter and each H-bridge power converter;
the control unit performs system power distribution based on battery information acquired from BMS of each retired battery, the system power distribution result indicates actual charging and discharging power of each retired battery, and the control unit controls duty ratios of each bidirectional isolation DC/DC converter and each H-bridge power converter according to the system power distribution result so that the retired battery charges and discharges according to the actual charging and discharging power and an alternating current power grid.
The further technical scheme is that the method for controlling three bidirectional isolation DC/DC converters and three H-bridge power converters connected with each retired battery according to the system power distribution result comprises the following steps:
the control unit controls the three bidirectional isolation DC/DC converters to respectively convert real-time voltage values of the retired battery into three paths of voltages with equal voltage values and mutually isolated voltages according to the transformation ratio, and the three paths of voltages are respectively provided for the three H-bridge power converters;
the control unit adjusts the duty ratios of the three H-bridge power converters, so that the phase of the equivalent voltage synthesized by the output voltages of the three H-bridge power converters is the same as the phase of the alternating current power grid, the amplitude of the equivalent voltage is lower than the voltage of the alternating current power grid, and current flows from the alternating current power grid to the retired battery and is charged according to the actual charge and discharge power of the retired battery;
the control unit adjusts the duty ratios of the three H-bridge power converters, so that the phase of the equivalent voltage synthesized by the output voltages of the three H-bridge power converters is the same as the phase of the alternating current power grid, and the amplitude of the equivalent voltage is higher than the voltage of the alternating current power grid, and current flows from the retired battery to the alternating current power grid, and the electric current is discharged according to the actual charge and discharge power of the 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:
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 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 battery information also comprises an 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;
and 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 on the basis of the basic actual power of each retired battery to obtain the actual charge and discharge power of the retired battery, wherein the power offset of each retired battery is positive or negative or 0.
For all retired batteries currently in a charging state, the power offset of the retired batteries with the SOC value within a first preset range of an average SOC value is 0, the power offset of the retired batteries with the SOC value larger than the first preset range of the average SOC value is negative, the power offset of the retired batteries 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 currently in the charging state is 0;
for all the retired batteries currently in a discharging state, the power offset of the retired batteries with the SOC values within a second preset range of the average SOC value is 0, the power offset of the retired batteries with the SOC values smaller than the second preset range of the average SOC value is negative, the power offset of the retired batteries with the SOC values 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 currently in the discharging state 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.
The further technical scheme is that the power offset of each retired battery is determined according to the SOC value of each retired battery, and the method comprises the following steps:
when the control unit receives a control instruction for indicating the system to enter a charging state, and when detecting that the maximum difference value of the SOC values of all the retired batteries reaches a first difference value threshold, controlling the retired battery with the lowest SOC value to charge according to peak power and controlling the retired battery with the highest SOC value to discharge, and determining power offset for all the rest retired batteries according to the SOC value;
when the control unit receives a control instruction for indicating the system to enter a discharging state, and when detecting that the maximum difference value of the SOC values of all the retired batteries reaches a second difference value threshold, the control unit controls the retired battery with the highest SOC value to discharge according to the peak power and controls the retired battery with the lowest SOC value to charge, and determines the power offset for all the rest retired batteries according to the SOC value.
When 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 a public bus, and then system power distribution is carried out again;
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.
The further technical scheme is that all H-bridge power converters are cascaded to form star connection or delta connection.
The beneficial technical effects of the application are as follows:
the application discloses an H-bridge cascade-based electric vehicle retired battery secondary utilization system, which combines hardware topology and software control to realize the electric energy secondary utilization of retired batteries with larger performance difference, and the retired batteries applied to the system can have different performances such as voltage, capacity, SOC value, insulation grade, residual service life and the like, meanwhile, the BMS of the retired batteries can be utilized, the high efficiency problem of energy conversion can be solved, the retired batteries 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 batteries of new energy vehicles becomes possible.
Drawings
Fig. 1 is a schematic diagram of a system topology of an electric vehicle retired battery secondary utilization system disclosed by the application.
Fig. 2 is a schematic diagram of control logic of the secondary battery utilization system of the electric vehicle in a charged state.
Detailed Description
The following describes the embodiments of the present application further with reference to the drawings.
The application discloses an electric vehicle retired battery secondary utilization system based on H bridge cascade connection, referring to fig. 1, the system comprises a plurality of retired batteries, a bidirectional isolation DC/DC converter, an H bridge power converter, a control unit and an alternating current power grid.
Each retired battery is respectively connected with three bidirectional isolation DC/DC converters, the three bidirectional isolation DC/DC converters connected with the same retired battery are respectively connected with one phase line of an alternating current power grid through one H-bridge power converter, and are actually connected with the alternating current power grid through grid-connected reactance and a grid-connected relay, and the grid-connected relay is not shown in fig. 1. All H-bridge power converters are cascaded with each other, and all H-bridge power converters are cascaded to form a star connection or a delta connection.
Because each retired battery exchanges energy with three phases at the same time, although each phase of current is alternating current, the three phases are overlapped together (the three-phase current relationship is ia+ib+ic=0), and the external input and output of the retired battery can be considered as direct current in practice, so that the original BMS system of the retired battery can be directly used. 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 application binds the voltage of the two ends of the bidirectional isolation DC/DC converter 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.
The cascade connection of the H-bridge power converter has the effect that the voltages output by all the modules are directly connected with an alternating current power grid in a serial connection mode, so that the voltages of all the modules can be different, and the problems that retired batteries with different voltages are operated in the same system are solved because the voltages of all the modules are in an additive relationship rather than being connected in parallel.
The control unit is connected to the BMS of each retired battery, each bi-directionally isolated DC/DC converter and each H-bridge power converter, and fig. 1 is only schematically illustrating the connection of the control unit to each retired battery for the sake of simplicity of connection. 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 grid-connected relay is controlled to be disconnected with the alternating current power grid, all the bidirectional isolation DC/DC converters and all the H-bridge power converters are controlled to stop working, and sleep instructions are sent to 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 the charging state of the system is that the alternating current power grid charges each retired battery. Please refer to the flowchart shown in fig. 2.
1. The control unit performs system power allocation based on battery information acquired from the BMS of each retired battery, and the system power allocation result indicates actual charge and discharge power of each retired battery, specifically:
(1) And 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. The power offset for each retired battery is either positive or negative or 0.
For all retired batteries currently in a charged state, the power offset of the retired batteries with the SOC values within a first preset range of the average SOC value is 0, the power offset of the retired batteries with the SOC values greater than the first preset range of the average SOC value is negative, the power offset of the retired batteries with the SOC values less than the first preset range of the average SOC value is positive, and the sum of the power offsets of all the retired batteries currently in the charged state 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.
In one embodiment, when the control unit receives a control command for instructing the system to enter a state of charge, the power offsets of all retired batteries are determined as described above. Or in another embodiment, when the control unit receives a control instruction for indicating the system to enter a charging state, and when detecting that the maximum difference value of the SOC values of all the retired batteries reaches a first difference value threshold, controlling the retired battery with the lowest SOC value to charge according to the peak power and controlling the retired battery with the highest SOC value to discharge, and determining the power offset for the rest of the retired batteries according to the SOC value and performing power offset adjustment according to the method. The method can discharge the retired battery with more electric quantity to the outside, and the retired battery with less electric quantity is charged rapidly according to peak power, so that the balance among the retired batteries can be achieved in a shorter time.
2. And the control unit controls the duty ratio of each bidirectional isolation DC/DC converter and each H-bridge power converter according to the system power distribution result, so that the retired battery charges and discharges according to the actual charge and discharge power and the alternating current power grid.
Specifically, the control unit controls the three bidirectional isolation DC/DC converters to respectively convert real-time voltage values of the retired battery into three voltages with equal voltage values and mutually isolated voltages according to the transformation ratio, and the voltages are respectively provided for the three H-bridge power converters. And then the control unit adjusts the duty ratios of the three H-bridge power converters, so that the phase of the equivalent voltage synthesized by the output voltages of the three H-bridge power converters is the same as the phase of the alternating current power grid and the amplitude is lower than the voltage of the alternating current power grid, and the current flows from the alternating current power grid to the retired battery and is charged according to the actual charge and discharge power of the retired battery.
3. In a discharging state of the system, electric energy flows from each retired battery to an 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.
The control unit performs system power allocation based on battery information acquired from the BMS of each retired battery, and the system power allocation result indicates actual charge and discharge power of each retired battery, and the determination method is similar to that in the charged state. The difference is that when determining the power offset of the retired battery, the power offset of the retired battery with the SOC value within the second predetermined range of the average SOC value is 0, the power offset of the retired battery with the SOC value smaller than the second predetermined range of the average SOC value is negative, the power offset of the retired battery with the SOC value greater than the second predetermined range of the average SOC value is positive, and the sum of the power offsets of all the retired batteries currently in the discharged state is 0.
Likewise, when the control unit receives a control instruction for instructing the system to enter a discharge state, the power offset may be determined for all of the retired batteries, or only for a portion of the retired batteries: when the maximum difference value of the SOC values of all the retired batteries reaches a second difference value threshold, discharging the retired battery with the highest SOC value according to the peak power, charging the retired battery with the lowest SOC value, and determining the power offset for the rest retired batteries according to the SOC values. The method can enable the retired battery with more electric quantity to discharge rapidly according to peak power, and the retired battery with less electric quantity to charge, so that the balance among the retired batteries can be achieved in a shorter time.
And the control unit controls the duty ratio of each bidirectional isolation DC/DC converter and each H-bridge power converter according to the system power distribution result, so that the retired battery charges and discharges according to the actual charge and discharge power and the alternating current power grid. Specific: the control unit controls the three bidirectional isolation DC/DC converters to respectively convert real-time voltage values of the retired battery into three paths of voltages with equal voltage values and mutually isolated voltages according to the transformation ratio, and the three paths of voltages are respectively provided for the three H-bridge power converters. The duty ratios of the three H-bridge power converters are adjusted, so that the phase of the equivalent voltage synthesized by the output voltages of the three H-bridge power converters is the same as the phase of the alternating current power grid, and the amplitude of the equivalent voltage is higher than the voltage of the alternating current power grid, and current flows from the retired battery to the alternating current power grid, and the electric current is discharged according to the actual charge and 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 retired batteries:
(1) The cascade connection of the H-bridge power converter has the effect that the voltages output by all the modules are directly connected with an alternating current power grid in a serial connection mode, so that the voltages of all the modules can be different, and the voltages are in an addition relationship rather than being connected in parallel, so that retired batteries 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 realize initiative equilibrium, does not have the requirement to the SOC value of retired battery, as long as retired battery can also charge and discharge, consequently make the battery package of different SOC states can be in same system operation. And when the electric quantity difference between the retired batteries is large, partial retired batteries are allowed to discharge and partial charge, so that the SOC values of all retired batteries gradually approach to the average value and tend to be consistent, and the SOC levels of battery packs in the same system are consistent in most of time.
(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) Because the retired battery corresponds to three phases simultaneously, and the sum of three-phase currents is 0, for the retired battery, the current input and output to the outside is always direct current, so the BMS of the retired battery can be directly used without replacing and upgrading the retired battery.
(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:
total voltage output capability of system (phase peak): 712V-998V, for a 380Vac ac grid, the voltage margin is large enough to be grid-connected by modulation of the H-bridge power converter. 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; there is no problem being able to sustain a power of 100kw for 5 hours. 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. The H bridge parameter is in the voltage range of 0-100V; a current range of 0-200A.
The above is only a preferred embodiment of the present application, and the present application 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 application are deemed to be included within the scope of the present application.

Claims (6)

1. An electric vehicle retired battery secondary utilization system based on H-bridge cascading, which is characterized by comprising: the system comprises a plurality of retired batteries, a bidirectional isolation DC/DC converter, an H-bridge power converter, a control unit and an alternating current power grid;
each retired battery is respectively connected with three bidirectional isolation DC/DC converters, the three bidirectional isolation DC/DC converters connected with the same retired battery are respectively connected into one phase line of an alternating current power grid through one H-bridge power converter, and all the H-bridge power converters are mutually cascaded; the control unit is connected with the BMS of each retired battery, each bidirectional isolation DC/DC converter and each H-bridge power converter;
the control unit performs system power distribution based on battery information acquired from BMS of each retired battery, the system power distribution result indicates actual charging and discharging power of each retired battery, and the control unit controls duty ratios of each bidirectional isolation DC/DC converter and each H-bridge power converter according to the system power distribution result so that the retired battery charges and discharges with the AC power grid according to the actual charging and discharging power;
the battery information at least comprises rated power of the retired battery and SOC value of the retired battery, and the system power distribution is performed based on the battery information obtained from BMS of each retired battery, and the system power distribution 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; obtaining basic actual power of each retired battery by multiplying the rated power of the retired battery by the power weight; determining power offset of each retired battery according to the SOC value of each retired battery, and adding corresponding power offset to correct the power offset on the basis of the basic actual power of each retired battery to obtain the actual charge and discharge power of the retired battery; for all retired batteries currently in a charged state, the power offset of the retired batteries with the SOC value within a first preset range of an average SOC value is 0, the power offset of the retired batteries with the SOC value larger than the first preset range of the average SOC value is negative, the power offset of the retired batteries 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 currently in the charged state is 0; for all retired batteries currently in a discharging state, the power offset of the retired batteries with the SOC value within a second preset range of an average SOC value is 0, the power offset of the retired batteries with the SOC value smaller than the second preset range of the average SOC value is negative, the power offset of the retired batteries 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 currently in the discharging state is 0; wherein the average SOC value is an average value of SOC values of all the retired batteries.
2. The system of claim 1, wherein the method of controlling the three bi-directional isolated DC/DC converters and the three H-bridge power converters to which each retired battery is connected based on system power allocation results comprises:
the control unit controls the three bidirectional isolation DC/DC converters to respectively convert real-time voltage values of the retired battery into three paths of voltages with equal voltage values and mutually isolated voltages according to a transformation ratio, and the three paths of voltages are respectively provided for the three H-bridge power converters;
the control unit adjusts the duty ratios of the three H-bridge power converters, so that the phase of the equivalent voltage synthesized by the output voltages of the three H-bridge power converters is the same as the phase of the alternating current power grid, the amplitude of the equivalent voltage is lower than the voltage of the alternating current power grid, and current flows from the alternating current power grid to the retired battery and is charged according to the actual charge and discharge power of the retired battery;
the control unit adjusts the duty ratios of the three H-bridge power converters, so that the phase of the equivalent voltage synthesized by the output voltages of the three H-bridge power converters is the same as the phase of the alternating current power grid, the amplitude of the equivalent voltage is higher than the voltage of the alternating current power grid, and current flows from the retired battery to the alternating current power grid and is discharged according to the actual charge and discharge power of the retired battery.
3. 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.
4. The system of claim 1, wherein the determining the power offset for each retired battery based on the SOC value for each retired battery comprises:
when the control unit receives a control instruction for indicating the system to enter a charging state, and when detecting that the maximum difference value of the SOC values of all the retired batteries reaches a first difference value threshold, controlling the retired battery with the lowest SOC value to charge according to peak power and controlling the retired battery with the highest SOC value to discharge, and determining power offset for the rest retired batteries according to the SOC values;
when the control unit receives a control instruction for indicating the system to enter a discharging state, and when detecting that the maximum difference value of the SOC values of all the retired batteries reaches a second difference value threshold, the control unit controls the retired battery with the highest SOC value to discharge according to the peak power and controls the retired battery with the lowest SOC value to charge, and determines the power offset for the rest retired batteries according to the SOC value.
5. The system of claim 1, wherein the system further comprises a controller configured to control the controller,
when 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 a public bus, and then system power distribution is carried out again;
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.
6. The system of claim 1, wherein all H-bridge power converters are cascaded to form a star connection or a delta connection.
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