CN105607003A - Energy storage unit capacity test method - Google Patents

Abstract

The invention discloses a method for testing the capacity of an energy storage unit. The method includes: preprocessing the battery strings in the energy storage unit, discharging the energy storage unit as a whole until the state of charge is 0; At the end of discharge, the charge cut-off voltage or discharge cut-off voltage of the battery string or single battery; when charging or discharging the energy storage unit, when one of the battery strings or battery cells reaches the set charge cut-off voltage or discharge cut-off voltage When charging or discharging, adjust the charging power or discharging power until a certain battery string or battery cell reaches the maximum or minimum value of the normal working range of the battery; during charging or discharging, record the voltage and current values of the energy storage unit, and calculate Obtain the test capacity value of the energy storage unit; calculate the difference between three adjacent test capacity values; if the difference is less than a set value, end the test and calculate the average value of the three test capacity values to obtain the capacity of the energy storage unit value.

Description

A method for testing the capacity of an energy storage unit

technical field

The invention relates to the field of electric power, in particular to a method for testing the capacity of an energy storage unit.

Background technique

In the energy storage system, among the performance parameters of the energy storage power station that many maintenance personnel pay attention to, the parameter that can most directly reflect the power generation performance of the energy storage system is the available capacity of the energy storage system. Whether the energy storage system has sufficient capacity is related to whether the energy storage system can complete various functions according to the initial design. The operator of the energy storage power station makes a decision on the operation mode according to the available capacity, and the capacity is the maintenance of the battery. An important basis to directly guide on-site maintenance work.

The capacity of the battery refers to the amount of electricity that can be obtained from the battery under certain discharge conditions. Lithium battery capacity is not a constant parameter, its change law is nonlinear, it will decay with the increase of the number of cycles, and is affected by multiple factors at the same time. The attenuation degree of the capacity of the energy storage system is not only related to the performance of the battery cell, but also related to the performance of the group. From the perspective of battery cells, the main factors are the charging and discharging voltage and current of lithium batteries, usage methods and environmental factors; from the perspective of grouped systems, the performance degradation rate is related to the grouping method, environment, and usage methods. On the other hand, the size of the capacity is related to the test method. For the same lithium battery cell or energy storage system, at the same time, the capacity test methods are different, and the capacity is also different.

At present, relatively complete capacity testing standards for lithium battery cells and lithium battery modules have been formed at home and abroad. For example, ISO12405:2012 "Test Specifications for Lithium-ion Power Battery Pack and Battery System for Electric Road Vehicles" and IEC62660-1 "Auxiliary Lithium-ion Batteries for Driving Electric Road Vehicles Part 1: Performance Test" passed by IEC in 2012 Wait, there are mainly QC\T743-2006 "Lithium-ion Batteries for Electric Vehicles", QB/T2502-2000 "General Specifications for Lithium-ion Batteries", national standards "Lithium-ion Power Battery Systems for Electric Vehicles" and so on. Standard capacity testing methods have been discussed in detail in [2].

For the standards of energy storage system capacity testing, there are currently two series of standards in China: one is the Q/GDW676-2011 "Energy Storage System Connected to Distribution Network" in the series standards of State Grid Enterprise Standard Energy Storage System Connected to Distribution Network The second is a series of industry standards for large-capacity energy storage power stations, which are still in the review stage. The provisions of these two standards for the capacity test method of the energy storage system are as follows: a) The energy storage system is discharged in one of the four modes of rated power, 1-rate current, rated power-constant voltage combination or 1-rate current-constant voltage combination, reaching Discharge termination condition, idle running to a stable state; b) The energy storage system is charged in one of the four modes of rated power, 1-rate current, rated power-constant voltage combination or 1-rate current-constant voltage combination, and the charging termination condition is reached. Run at idle to a steady state; c) Repeat test steps a and b in the same charge and discharge mode, and terminate the test when the difference in discharge capacity within 3 consecutive cycles is within 2%.

At present, the capacity test methods stipulated by domestic mainstream lithium battery energy storage manufacturers are also different. Table 1 lists the capacity test methods used by four energy storage manufacturers when performing energy storage system maintenance.

Table 1 Capacity test methods of some domestic lithium battery manufacturers

Since the scope of application of the standard includes various electrochemical, electromagnetic and other energy storage forms, considering the differences in system characteristics, the existing standard does not provide the cut-off conditions for capacity testing and the definite charging and discharging modes, so there is still a certain amount of time for engineering applications. limitations.

Contents of the invention

In order to overcome the limitations of the existing capacity testing methods in engineering applications, the present invention researches the testing standards of energy storage systems at home and abroad, investigates the capacity testing methods of domestic mainstream energy storage manufacturers, and combines the The capacity test conducted by the demonstration power station proposes a capacity test method suitable for various structural energy storage systems.

In order to achieve the above object, the present invention proposes a method for testing the capacity of an energy storage unit, the method comprising: step 1, performing pretreatment on the battery strings in the energy storage unit, and discharging the energy storage unit as a whole to The state of charge is 0; step 2, set the charge cut-off voltage or discharge cut-off voltage of the battery string or single battery at the end of charge or discharge; step 3, charge or discharge the energy storage unit, when When a battery string or battery cell reaches the charge cut-off voltage or discharge cut-off voltage set in step 2, adjust the charging power or discharge power until a certain battery string or battery cell reaches the maximum value of the normal working range of the battery. value or the minimum value; step 4, during the charging or discharging process in step 3, record the voltage value and current value of the energy storage unit, and calculate and obtain the test capacity value of the energy storage unit; step 5, repeat step 3 and step 4. Calculate and obtain multiple test capacity values of the energy storage unit; step 6, calculate the difference between the three test capacity values obtained by three consecutive executions in step 5; step 7, if the difference is less than one Set the value, end the test and calculate the average value of the three test capacity values to obtain the capacity value of the energy storage unit; if the difference is greater than a set value, return to step 5 and continue to obtain the capacity value of another energy storage unit , and calculate the difference between the three test capacity values obtained by three adjacent executions of the capacity value of the other energy storage unit through step 6.

The energy storage unit capacity test method of the present invention proposes a capacity test method suitable for large-capacity lithium battery energy storage systems through a large number of standard investigations and field tests. The condition is that any monomer reaches the cut-off voltage or any whole group voltage reaches the cut-off voltage, the selection of the cut-off voltage should be slightly lower than the battery management system (BMS, Battery Management System) protection voltage, and the capacity test of the present invention shortens the test duration, At the end of charge and discharge, the power is reduced by 20% of the rated power as the step size to obtain more data on the end of charge and discharge time. At the same time, several tests have been carried out on the tested energy storage unit, which is more conducive to data analysis and finding abnormalities in the later stage The performance of the energy storage system is significantly improved.

Description of drawings

The drawings described here are used to provide further understanding of the present invention, constitute a part of the application, and do not limit the present invention. In the attached picture:

FIG. 1 is a flowchart of a method for testing the capacity of an energy storage unit according to an embodiment of the present invention.

detailed description

The technical means adopted by the present invention to achieve the intended invention purpose are further described below in conjunction with the drawings and preferred embodiments of the present invention.

FIG. 1 is a flowchart of a method for testing the capacity of an energy storage unit according to an embodiment of the present invention. As shown in Figure 1, the method includes:

Step 1, pretreat the battery strings in the energy storage unit, and discharge the energy storage unit as a whole until the state of charge is 0;

Step 2, set the charge cut-off voltage or discharge cut-off voltage of the battery string or single battery at the end of charge or discharge;

Step 3: Charge or discharge the energy storage unit. When one of the battery strings or battery cells reaches the charge cut-off voltage or discharge cut-off voltage set in step 2, adjust the charging power or discharge power until a certain battery string The string or battery cell reaches the maximum or minimum value of the normal working range of the battery;

Step 4, during the charging or discharging process in step 3, record the voltage value and current value of the energy storage unit, and calculate and obtain the test capacity value of the energy storage unit;

Step 5, repeat step 3 and step 4 to calculate and obtain multiple test capacity values of the energy storage unit;

Step 6, calculating the difference between the three test capacity values obtained by three adjacent executions in step 5;

Step 7, if the difference is less than a set value, end the test and calculate the average value of the three test capacity values to obtain the capacity value of the energy storage unit;

If the difference is greater than a set value, return to step 5 to continue to obtain the capacity value of another energy storage unit, and calculate the difference between the three test capacity values obtained by performing three adjacent tests with the capacity value of another energy storage unit through step 6 difference.

In step 1, the specific steps of preprocessing are shown in Table 2 below:

Table 2 Capacity test preprocessing steps

In step 1, the purpose of the pretreatment is to adjust the battery strings with uneven states of charge to be basically consistent, and discharge the battery strings as a whole until the SOC is 0%. Prepare for capacity test. The pretreatment method is to repeat the steps listed in Table 2 twice.

In step 2, the end of charge is the period when the state of charge is greater than 90% during charging; the end of discharge is the period when the state of charge is less than 10% during discharge.

In step 4, the formula used to calculate and obtain the test capacity value of the energy storage unit is as follows:

${\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; test</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&Integral;</span>}_{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dt</span>}<span\; class="notranslate">\; ;</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Among them, E _Test energy storage unit capacity, Wh;

t ₀ is the charging or discharging start time, s;

t ₁ is the charging or discharging end time, s;

u(t) is the total voltage of the DC side during the capacity test of the energy storage battery, V;

i(t) is the total current of the DC side during the capacity test of the energy storage battery, A.

In order to explain the above energy storage unit capacity testing method more clearly, a specific example will be described below. improper qualification.

Combined with step 1, the energy storage unit is pretreated.

Combining step 2 and step 3, the present invention mainly makes improvements on the charging and discharging strategy and cut-off conditions in the design of the capacity test process.

Design improvements for cutoff conditions:

The design improvement of cut-off conditions can be used in large-capacity lithium battery energy storage systems. From the perspective of battery string control, the most important feature of this structure is that all battery strings on the DC side must be uniformly controlled. The two-stage converter is composed of AC-DC and DC-DC circuits. When multiple DC-DC currents are connected in parallel, the DC-side battery strings can be controlled separately. When a string reaches the cut-off condition, it can stop working. , other strings continue to charge and discharge until all strings reach the cut-off condition. Therefore, when the charging and discharging power is large and the consistency of the battery strings is very different, the battery strings of the energy storage unit of the two-stage converter will withdraw from operation one by one, and the current of the last exiting string will increase significantly, which means It is not good for guaranteeing battery life.

Therefore, in order to ensure battery safety to the greatest extent, the present invention unifies the cut-off conditions of various topological structures as under the entire large-capacity battery energy storage system (PCS, Power Conversion System), when any battery cell reaches the cut-off voltage or any group of battery strings reaches the cut-off voltage.

Generally, there are two ways to define the upper and lower voltage limits in energy storage systems. One is to give the working voltage range of a single battery from the perspective of normal battery operation. Generally, the lower voltage limit of domestic mainstream lithium battery manufacturers is about 2.5-2.8V, and the upper voltage limit It is about 3.6-3.8V; the second is the battery voltage over-limit alarm protection value of the battery management system. The setting of this value varies from manufacturer to manufacturer. Around V, due to the protection of the battery and the requirements of on-site production and operation, the cut-off condition is set to the normal working range of the battery, which should not be higher than the battery voltage over-limit alarm protection value.

Improvements in charging and discharging strategies:

In the relevant standards, the charging and discharging strategies for capacity testing are basically the same mode of charging and discharging. This paper found in many tests that for the energy storage system that has been in operation for a period of time, the consistency has deteriorated. (such as rated power) for charging and discharging, the cut-off condition will be reached soon at the end of charge and discharge (SOC (state of charge) is greater than 90% or less than 10%), and the monomer with abnormal performance at the end of charge and discharge will be more prominent. If the charging and discharging period is short and there is little data, it is not conducive to find abnormal monomers in the later data analysis.

Therefore, the present invention designs a charging and discharging strategy for performing power reduction operation at the end of charging and discharging. The less the charging and discharging current, the more conducive to fully charging or emptying the battery, and the longer the charging and discharging time. Therefore, considering various factors, it is designed to use 20% of the rated power as the step size, and to perform power reduction operation at the end of charging and discharging. Taking the wind-solar energy storage system as an example, a charging-discharging cycle can be controlled within 8 hours.

Taking an energy storage unit with a converter rated power of 250KW and a battery with a normal operating voltage range of 2.5-3.6V as an example, the charging and discharging process is shown in Table 3.

Table 3 Capacity test process

In Table 3, when the cut-off voltage reached gradually increases (charging) or decreases (discharging) during the charging and discharging process, the power parameter changes by 20% each time. Reach the normal working range of the battery, so reserve 10KW to continue charging and discharging, so as to fully charge or empty the battery.

Combining step 4, step 5, and step 6, do three cycle tests according to the steps in Table 3, and check the difference in discharge capacity three times.

Combined with step 7, if the difference is greater than 2% of a certain capacity value, then continue to step 5 and perform the fourth capacity test until the capacity difference is within 2%; if the three capacity differences are within 2%, end test.

Calculate the average value of these three capacity values to obtain the capacity value of the energy storage unit.

The capacity test method provided by this solution can be completed through external capacity test equipment, or can be calculated through the data recorded by the energy storage unit monitoring system. The two schemes realize the above charging and discharging process by regularly issuing commands to the energy storage converter (no need to make changes in software and hardware). If the converter has the function of editing programs in advance, it can also follow the above charging and discharging strategy Edit the program.

The energy storage unit capacity test method of the present invention proposes a capacity test method suitable for large-capacity lithium battery energy storage systems through a large number of standard investigations and field tests. The condition is that any monomer reaches the cut-off voltage or any whole group voltage reaches the cut-off voltage, the selection of the cut-off voltage should be slightly lower than the BMS protection voltage, and the capacity test of the present invention shortens the test time, and the final charging and discharging period is 20% of the rated voltage. The power is operated as a step-down power to obtain more data on the final charging and discharging time. At the same time, multiple tests have been carried out on the tested energy storage unit, which is more conducive to data analysis in the later stage to find abnormal monomers and energy storage systems. performance is significantly improved.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims (4)

1. an energy-storage units capacity test method, is characterized in that, described method comprises:

Step 1, carries out pretreatment to the battery pack string in described energy-storage units, and described energy-storage units entirety is discharged toState-of-charge is 0;

Step 2, is set in charging latter stage or electric discharge latter stage, the charge cutoff voltage of battery pack string or cell or putElectricity blanking voltage;

Step 3, carries out charge or discharge to described energy-storage units, when wherein a certain battery pack string or battery cell reachWhen the charge cutoff voltage that described step 2 is set or discharge cut-off voltage, adjust charge power or discharge power, untilA certain battery pack string or battery cell reach maximum or the minimum of a value of battery normal range of operation;

Step 4, in the charge or discharge process of step 3, records energy-storage units ground voltage value and current value, calculatesObtain the test capacity value of described energy-storage units;

Step 5, repeated execution of steps 3 and step 4, calculate the multiple test capacity values that obtain described energy-storage units;

Step 6, the adjacent difference of carrying out between three test capacity values that obtain for three times in calculation procedure 5;

Step 7, if described difference is less than a setting numerical value, finishes to test and calculate described three test capacity valuesMean value, obtains energy-storage units capability value;

If described difference is greater than a setting numerical value, return to step 5 and continue to obtain the capability value of another energy-storage units, andCalculate with the capability value of described another energy-storage units and carry out three test capacity values that obtain adjacent three times by step 6Between difference.

2. energy-storage units capacity test method according to claim 1, is characterized in that, in step 1,Battery pack string in described energy-storage units is carried out to pretreatment, and it is 0 that described energy-storage units entirety is discharged to state-of-chargeComprise:

Step 11, charges to described energy-storage units, and charge power is the specified of energy accumulation current converter in energy-storage unitsPower, reaches upper voltage limit and stops charging when a certain battery cell wherein reaches ceiling voltage or a certain group of string;

Step 12, leaves standstill described energy-storage units at least 30 minutes;

Step 13, discharges to described energy-storage units, and discharge power is the specified of energy accumulation current converter in energy-storage unitsPower, reaches lower voltage limit and stops electric discharge when a certain battery cell wherein reaches minimum voltage or a certain group of string;

Step 14, leaves standstill described energy-storage units at least 30 minutes, by consistent the state-of-charge adjustment of described battery pack string,And described energy-storage units entirety is discharged to state-of-charge is 0.

3. energy-storage units capacity test method according to claim 1, is characterized in that, in step 2,When described charging is charging latter stage, state-of-charge is greater than during 90%; Described electric discharge latter stage, state-of-charge was little during for electric dischargeDuring 10%.

4. energy-storage units capacity test method according to claim 3, is characterized in that, in step 4,The formula that calculates the test capacity value utilization that obtains described energy-storage units is as follows:

$E_{\mathrm{Test}}={\&Integral;}_{t_0}^{t_1}u\left(t\right)i\left(t\right)\mathrm{dt};---\left(1\right)$

Wherein, E_TestEnergy-storage units capacity, Wh;

t₀For charge or discharge zero hours, s;

t₁For charge or discharge finish times, s;

U (t) for energy-storage battery in the time carrying out volume test, DC side total voltage, V;

I (t) for energy-storage battery in the time carrying out volume test, DC side total current size, A.