Why don’t the batteries of electric cars accurately show how much they have left?

So, back to the original question, why do electric vehicles (and lead batteries) seem inaccurate? This is because the power of electric vehicles (usually called SOC, or state of charge) is more difficult to measure than the power of mobile phones.

Er zijn verschillende redenen waarom elektrische auto’s moeilijker in te schatten zijn dan mobiele telefoons. Hier zijn enkele diepere punten:

Commonly used SOC estimation methods:

Let us start with one we know better: GPS. Now, mobile phone-based GPS positioning is accurate to the order of meters. As far as missiles are concerned, such positioning is not enough. Two things are missing: accuracy and real-time (ie, the number of seconds to successfully locate). So the missile has another compensation system: gyroscope.

Gyroscopen zijn een complete aanvulling op GPS-positionering via satelliet: ze zijn nauwkeurig (tenminste op de millimeterschaal) en realtime, maar het probleem is dat de fouten cumulatief zijn. Als u bijvoorbeeld een persoon blinddoekt en hem vraagt ​​in een rechte lijn te lopen, ziet u misschien geen tientallen meters, maar u kunt wel enkele kilometers lopen en 180 graden draaien.

Is er een manier om de informatie tussen GPS en gyroscoop samen te voegen om elkaar aan te vullen om de meest nauwkeurige positie te verkrijgen? Het antwoord is ja, Kalman-filtering is goed, dat is alles.

What does this have to do with the battery’s SOC estimation? There are two commonly used methods of measuring SOC:

The first method is the open circuit voltage method, which measures the state of the battery based on the open circuit voltage of the battery. This is easy to understand, but full high battery voltage, low battery power, power and voltage are corresponding. This method is similar to satellite GPS positioning, there is no cumulative error (because it is based on conditions), but the accuracy is low (due to various factors, the previous response has now been explained).

Het tweede type wordt ampère-uur-integrator genoemd, die de toestand van de batterij meet door de spanning (flow) van de batterij te integreren. Als u bijvoorbeeld een batterij van 100 kilowatt oplaadt en elke keer dat u de stroom meet en deze verhoogt tot 50 graden, is het resterende vermogen 50 graden. Deze methode kan worden vergeleken met zeer nauwkeurige gyroscopen (onmiddellijke meetnauwkeurigheid is minder dan 1%, 0.1% meetkosten zijn laag en gebruikelijk), maar de cumulatieve fout is groter. Bovendien, zelfs als de ampèremeter een godsmerk en volledig nauwkeurig is, zijn de integrale methode en de nullastspanningsmethode onafscheidelijk wanneer de ampèremeter wordt gebruikt. Waarom? Omdat de aard van de batterij zelf zal veranderen.

Academically, maybe some advanced car companies combine open circuit voltage and ampere-hour integration with Kalman filter algorithm to get the most accurate SOC estimation, but they often make mistakes because they don’t understand how to deepen the evolution of batteries. nature.

Electric vehicles developed by domestic automobile companies generally use the open circuit voltage method and the LAMV integration method: the following car leaves enough time (for example, the car is only turned on in the morning), and the open circuit voltage method is used to estimate the force start, SOC_start said. After the car is started, the battery status becomes chaotic, and the open circuit voltage method is no longer valid. Then, use the SOC_start-based amV integration method to estimate the current battery power.

An important factor that makes the SOC of electric vehicles difficult is the difficulty in modeling lithium battery packs. Or in other words, the research field that can make electric vehicle SOC estimation become more and more accurate. The nature of batteries and battery packs is the key direction. Improving instrument accuracy is not the current research direction that is accurate enough, and no matter how accurate it is, it is useless.