Why Is the Ac Injection Method More Suitable for Online Measurement of Battery Internal Resistance Than the DC Method?

There are two main methods for measuring the internal resistance of batteries: direct current discharge method and alternating current injection method (ACIR). The HZNZ-100 adopts the AC injection method, which is not a random choice, but the only practical technical route under the key requirement of "live online measurement".

The problem of direct current discharge method

The direct current method applies a brief high current discharge pulse to the battery, measures the voltage change before and after discharge, and calculates the internal resistance using Δ V/Δ I. This method measures the 'DC internal resistance', which can reflect the polarization characteristics of the battery.

The problem is that the DC method requires applying a large current (tens to hundreds of amperes) to the battery, which means that: firstly, the measurement will consume some of the battery's power, causing disturbance to the online operation of the DC system; Secondly, there are safety risks associated with high current operation near live battery packs; Thirdly, each measurement takes a long time, resulting in low efficiency when measuring a whole set of batteries.

The advantages of communication injection method

The AC injection method injects a small AC current signal of 1kHz into the battery (usually only in the range of a few milliamps to tens of milliamps), while collecting the response voltage signal. The internal resistance is calculated using Ohm's law V=I × Z.

The advantages are very obvious:

Safe and Non Destructive: The injected current is extremely small, which does not affect the battery's state of charge or the DC working voltage at both ends of the battery. It can be measured completely online, without power outage or disconnection of any connection. This is crucial for the DC system of the substation - during the measurement process, the DC system continues to supply power normally and the protective devices are not affected.

Fast speed: The AC injection method only takes 1-2 seconds to measure each battery cell. In HZNZ-100 automatic mode, changing the test clip takes 1-2 seconds to automatically complete the measurement. The internal resistance measurement of a group of 100 batteries can be completed in a few minutes, with extremely high efficiency.

Good repeatability: Standardized measurement conditions, consistent results of repeated measurements of the same battery, suitable for establishing long-term tracking databases.

Precautions

The voltage of the tested battery cannot be lower than 1.5V - when the voltage is too low, the internal chemical state of the battery is abnormal, the AC signal response is distorted, and the internal resistance measurement results have no reference value.