Testing of High Voltage Batteries
Testing of HV Batteries in the EV and HEV Range
The testing and verification of high-voltage batteries from the EV and HEV range is a typical application requiring modern testing systems. Whether it be performance, lifespan under defined loads or environmental conditions, the documentation of charging and discharging processes or resistance measurements: The systems used in this application not only need to deliver the usual standards of measurability, reliability and reproducibility, but they must also be cost-effective, safe, and flexible.
Avoidance of uncontrolled charging and discharging currents
One key feature for this application is the “currentless connection” of the battery, for example. This prevents the connected accumulator’s SOC (State Of Charge) from being changed. It is an important parameter for battery evaluation.
When a battery is connected to the DC controller, any uncontrolled charging or discharging currents from the battery must therefore be avoided. In the ERS series, the current battery voltage is measured via a sensing input at the consumer before the battery is connected. Based on this measurement, the internal control circuit (which is equipped with a decoupling capacitor) is regulated to the voltage potential of the battery connected as a consumer. Only then can the output voltage be connected via the DC output contactor at the power unit output.
Currentless connection of the battery is enabled by ensuring the same voltage potential on both sides of the contactor, protecting the battery from damage.
For the “battery test” application, the insulation monitoring function can be disconnected, guaranteeing the function of the battery’s own insulation monitoring.
Safety through voltage target values
For the safety of the connected batteries, the maximum charging voltage should never be exceeded during charging and the minimum discharging voltage should never be fallen short of during discharging. To safeguard these requirements, the internal control of the ERS power unit automatically switches to a voltage control type when the set and specified voltage target value is reached. The voltage set is kept constant and the current lowered accordingly, protecting the battery connected as the load.
To protect the connected battery, the set target values are constantly monitored for their permissibility by the control system within the device. If non-permissible target values are specified, these are ignored or lowered to the degree that no damage can be caused to the consumer. This means, for example, that the minimum target value for the voltage during the charging process must always be greater than or equal to the battery’s current voltage. If this range is not reached, the device emits a warning message to prohibit discharging of the connected battery.
It must be possible to set minimum or maximum target value changes for the use of battery qualification. To do this, the devices in the ERS series have corresponding target value ramps that can be set and changed.
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