1. Introduction to Lithium Ion Battery

1.1 State-Of-Charge (SOC)

Kahanan pangisian daya bisa ditetepake minangka kahanan energi listrik sing kasedhiya ing baterei, biasane dituduhake minangka persentase. Amarga energi listrik sing kasedhiya beda-beda gumantung karo fenomena saiki, suhu, lan penuaan, definisi status pangisian daya uga dipérang dadi rong jinis: Absolute State-Of-Charge (ASOC) lan Relative State-of-Charge (Relative State). -Of-Charge; ASOC) State-Of-Charge; RSOC). Biasane, kahanan relatif pangisian daya yaiku 0% -100%, dene baterei 100% nalika kebak lan 0% nalika kebak. Negara pangisian daya absolut minangka nilai referensi sing diwilang miturut nilai kapasitas tetep sing dirancang nalika baterei diprodhuksi. Status pangisian daya absolut saka baterei sing kebak anyar yaiku 100%; lan sanajan baterei sing wis tuwa wis kebak, ora bisa tekan 100% ing kahanan pangisi daya lan discharging sing beda.

Tokoh ing ngisor iki nuduhake hubungan antarane voltase lan kapasitas baterei ing tingkat discharge beda. Sing luwih dhuwur tingkat discharge, luwih murah kapasitas baterei. Nalika suhu kurang, kapasitas baterei uga bakal suda.

Tokoh 1.

Hubungan antarane voltase lan kapasitas ing tingkat discharge lan suhu sing beda

1.2 Max Charging Voltage

The maximum charging voltage is related to the chemical composition and characteristics of the battery. The charging voltage of lithium battery is usually 4.2V and 4.35V, and the voltage value will be different if the cathode and anode materials are different.

1.3 Diisi daya kanthi lengkap

Nalika prabédan antarane voltase baterei lan voltase pangisian daya paling kurang saka 100mV, lan daya saiki irungnya kanggo C/10, baterei bisa dianggep minangka kebak. Karakteristik baterei beda-beda, lan kondisi pangisian daya lengkap uga beda.

Tokoh ing ngisor iki nuduhake kurva karakteristik ngisi baterei lithium khas. Nalika voltase baterei padha karo voltase pangisi daya paling dhuwur lan arus pangisi daya mudhun menyang C/10, baterei dianggep wis kebak.

Gambar 2. Kurva karakteristik pengisian baterai Lithium

1.4 Tegangan Ngirit Mini

The minimum discharge voltage can be defined by the cut-off discharge voltage, which is usually the voltage when the state of charge is 0%. This voltage value is not a fixed value, but changes with load, temperature, aging degree, or other factors.

1.5 Kanthi Discharge

Nalika voltase baterei kurang saka utawa padha karo voltase discharge minimal, bisa kasebut discharge lengkap.

1.6 Tingkat pangisian daya lan debit (C-Rate)

The charge-discharge rate is an expression of the charge-discharge current relative to the battery capacity. For example, if 1C is used to discharge for one hour, ideally, the battery will be completely discharged. Different charge and discharge rates will result in different usable capacity. Generally, the greater the charge-discharge rate, the smaller the available capacity.

1.7 Siklus urip

Jumlah siklus yaiku jumlah kaping baterei wis ngalami pangisi daya lan discharging lengkap, sing bisa dikira saka kapasitas discharge nyata lan kapasitas desain. Nalika kapasitas discharge akumulasi padha karo kapasitas desain, jumlah siklus sapisan. Biasane sawise 500 siklus pangisian daya, kapasitas baterei sing wis kebak mudhun 10% ~ 20%.

Figure 3. The relationship between the number of cycles and battery capacity

1.8 Self-Discharge

Kabeh baterei mundhak nalika suhu mundhak. Self-discharge Sejatine ora cacat manufaktur, nanging karakteristik baterei dhewe. Nanging, penanganan sing ora bener ing proses manufaktur uga bisa nyebabake peningkatan self-discharge. Umumé, tingkat self-discharge tikel kaping pindho kanggo saben kenaikan suhu baterei 10°C. Discharge saben wulan baterei lithium-ion kira-kira 1 ~ 2%, nalika discharge saben wulan saka macem-macem baterei basis nikel yaiku 10-15%.

Figure 4. The performance of the self-discharge rate of lithium batteries at different temperatures

2. Pambuka kanggo Baterei Fuel Gauge

2.1 Introduction to Fuel Gauge Function

Battery management can be regarded as part of power management. In battery management, the fuel gauge is responsible for estimating battery capacity. Its basic function is to monitor the voltage, charge/discharge current and battery temperature, and estimate the battery state of charge (SOC) and the battery’s full charge capacity (FCC). There are two typical methods for estimating the state of charge of a battery: the open circuit voltage method (OCV) and the coulometric method. Another method is the dynamic voltage algorithm designed by RICHTEK.

2.2 Metode voltase sirkuit mbukak

The electricity meter using the open circuit voltage method is easier to implement, and it can be obtained by looking up the table corresponding to the state of charge of the open circuit voltage. The hypothetical condition of the open circuit voltage is the battery terminal voltage when the battery rests for about 30 minutes.

Ing macem-macem beban, suhu, lan tuwa baterei, kurva voltase baterei bakal beda. Mulane, voltmeter sirkuit mbukak tetep ora bisa makili kahanan pangisian daya; negara daya ora bisa kira-kira dening looking munggah meja piyambak. Ing tembung liyane, yen negara pangisian daya kira-kira mung dening looking munggah meja, kesalahan bakal gedhe banget.

The following figure shows that the same battery voltage is under charge and discharge, and the state of charge found by the open circuit voltage method is very different.

Figure 5. Tegangan baterei ing daya lan discharging

Tokoh ing ngisor iki nuduhake yen negara pangisian daya beda-beda banget ing macem-macem beban nalika discharge. Dadi, cara voltase sirkuit mbukak mung cocog kanggo sistem kanthi syarat sing kurang kanggo akurasi pangisian daya, kayata panggunaan baterei asam timbal utawa pasokan listrik sing ora bisa diganggu ing mobil.

Gambar 6. Tegangan baterei ing macem-macem beban nalika discharge

2.3 Metode pangukuran Coulomb

Prinsip operasi metode pangukuran coulomb yaiku nyambungake resistor deteksi ing jalur pangisi daya / pangisi daya baterei. ADC ngukur voltase ing resistor deteksi lan ngowahi dadi nilai saiki baterei sing diisi utawa dibuwang. Counter wektu nyata (RTC) nyedhiyakake integrasi nilai saiki karo wektu, supaya ngerti carane akeh coulomb mili liwat.

Gambar 7. Metode kerja dasar metode pengukuran Coulomb

Cara pangukuran Coulomb kanthi akurat bisa ngetung kahanan pangisian daya wektu nyata sajrone ngisi daya utawa mbuwang. Kanthi counter coulomb pangisian daya lan counter coulomb discharge, bisa ngetung kapasitas sing isih ana (RM) lan kapasitas pangisian daya lengkap (FCC). Ing wektu sing padha, kapasitas sing isih ana (RM) lan kapasitas pangisian daya lengkap (FCC) uga bisa digunakake kanggo ngetung status pangisian daya, yaiku (SOC = RM / FCC). Kajaba iku, uga bisa ngira-ngira wektu sing isih ana, kayata power exhaustion (TTE) lan full power (TTF).

Figure 8. Calculation formula of Coulomb measurement method

Ana rong faktor utama sing nyebabake penyimpangan akurasi metode pangukuran Coulomb. Kapisan yaiku akumulasi kesalahan offset ing pangukuran saiki lan pangukuran ADC. Sanajan kesalahan pangukuran kanthi teknologi saiki isih cilik, yen ora ana cara sing apik kanggo ngilangi, kesalahan kasebut bakal saya tambah kanthi wektu. Tokoh ing ngisor iki nuduhake yen ing aplikasi praktis, yen ora ana koreksi ing durasi wektu, kesalahan akumulasi ora ana watesan.

Gambar 9. Kesalahan kumulatif metode pangukuran Coulomb

In order to eliminate the accumulated error, there are three possible useable time points in normal battery operation: end of charge (EOC), end of discharge (EOD) and rest (Relax). When the charging end condition is reached, it means that the battery is fully charged and the state of charge (SOC) should be 100%. The discharge end condition means that the battery has been completely discharged and the state of charge (SOC) should be 0%; it can be an absolute voltage value or change with the load. When it reaches the resting state, the battery is neither charged nor discharged, and it remains in this state for a long time. If the user wants to use the rest state of the battery to correct the error of the coulomb measurement method, an open-circuit voltmeter must be used at this time. The figure below shows that the state of charge error can be corrected in the above state.

Gambar 10. Kondisi kanggo ngilangi kesalahan kumulatif metode pangukuran Coulomb

Faktor utama kaloro nyebabake penyimpangan akurasi metode pangukuran coulomb yaiku kesalahan kapasitas pangisian daya (FCC), yaiku prabédan antarane nilai kapasitas desain baterei lan kapasitas daya baterei sing bener. Kapasitas pangisian daya lengkap (FCC) bakal kena pengaruh suhu, tuwa, beban lan faktor liyane. Mulane, sinau maneh lan cara ganti rugi saka kapasitas daya lengkap penting banget kanggo metode pangukuran coulomb. Tokoh ing ngisor iki nuduhake kedadean tren negara kesalahan pangisian daya nalika kapasitas daya lengkap overestimated lan underestimated.

Figure 11. Tren kesalahan nalika kapasitas daya lengkap overestimated lan underestimated

2.4 Pengukur bahan bakar algoritma voltase dinamis

Pengukur bahan bakar algoritma voltase dinamis bisa ngetung kahanan pangisian daya baterei lithium mung adhedhasar voltase baterei. Cara iki kanggo ngira mundhak utawa nyuda kahanan pangisian daya adhedhasar bedane voltase baterei lan voltase sirkuit mbukak baterei. Informasi voltase dinamis bisa èfèktif simulasi prilaku baterei lithium kanggo nemtokake negara pangisian daya SOC (%), nanging cara iki ora bisa ngira-ngira kapasitas baterei (mAh).

Cara pitungan kasebut adhedhasar prabédan dinamis antarane voltase baterei lan voltase sirkuit mbukak, kanthi nggunakake algoritma iteratif kanggo ngetung saben mundhak utawa nyuda kahanan pangisian daya kanggo ngira-ngira kahanan pangisian daya. Dibandhingake karo solusi coulomb metering fuel gauge, voltase dinamis algoritma bahan bakar gauge ora bakal nglumpukake kasalahan liwat wektu lan saiki. Pengukur bahan bakar meter Coulomb biasane nyebabake estimasi sing ora akurat babagan kahanan pangisian daya amarga kesalahan sensing saiki lan baterei mandhiri. Sanajan kesalahan sensing saiki cilik banget, counter coulomb bakal terus nglumpukake kesalahan, lan kesalahan akumulasi mung bisa diilangi nalika kebak utawa kosong.

Algoritma voltase dinamis ngukur bahan bakar ngira kahanan pangisian daya baterei mung kanthi informasi voltase; amarga ora kira-kira dening informasi saiki baterei, ora nglumpukake kasalahan. Supaya kanggo nambah akurasi negara daya, algoritma voltase dinamis kudu nggunakake piranti nyata, lan nyetel paramèter saka algoritma optimized miturut kurva voltase baterei nyata nalika wis kebak lan kosong.

Gambar 12. Kinerja pengukur bahan bakar algoritma voltase dinamis lan optimasi gain

The following is the performance of the dynamic voltage algorithm under different discharge rate conditions. It can be seen from the figure that its state of charge has good accuracy. Regardless of the discharge conditions of C/2, C/4, C/7 and C/10, the overall state of charge error of this method is less than 3%.

Figure 13. Kinerja negara pangisian daya saka algoritma voltase dinamis ing kahanan tingkat discharge beda

Tokoh ing ngisor iki nuduhake kinerja negara pangisian daya nalika baterei short-daya lan short-discharged. Kesalahan pangisian daya isih cilik banget, lan kesalahan maksimal mung 3%.

Figure 14. Kinerja kahanan pangisian daya algoritma voltase dinamis nalika baterei wis kebak daya lan short-discharged

Dibandhingake karo kahanan ing Coulomb metering bahan bakar gauge biasane nimbulaké kahanan ora akurat saka pangisian daya amarga kesalahan sensing saiki lan baterei poto-discharge, algoritma voltase dinamis ora nglumpukake kasalahan liwat wektu lan saiki, kang kauntungan gedhe. Amarga ora ana informasi babagan muatan / discharge saiki, algoritma voltase dinamis nduweni akurasi jangka pendek sing kurang lan wektu nanggepi alon. Kajaba iku, ora bisa ngira kapasitas pangisian daya lengkap. Nanging, performs apik ing syarat-syarat akurasi long-term, amarga voltase baterei pungkasanipun bakal langsung nuduhake negara daya.