Capacity Testing Principle with Battery Inverter Grid-Connected Technology

Background for Online Capacity Testing

With the intelligent development of power systems and the increasing number of substations, the maintenance workload of DC systems has become more demanding, and the need for intelligent monitoring and maintenance of batteries has become increasingly urgent. Battery inverter grid-connected technology, as one of the key technologies in the remote capacity testing design for operational power supplies, allows the discharge energy to be fed back into the grid without generating heat, thus avoiding the energy waste caused by traditional heating load discharges. This achieves a low-carbon, energy-saving, and environmentally friendly production process, which is of great significance to the strategy of sustainable development.

The commonly schemes for capacity testing of operational power supply batteries in engineering applications mainly include offline, online, and integrated modes. Among these, the online mode is widely promoted and applied due to its higher system safety, as the capacity testing process does not disconnect from the load, and its relatively low complexity for retrofitting.

Operating States of Capacity Testing System

The operating states are divided into standby floating charge, capacity discharge, and constant current charge. These states switch between each other during system operation, forming a complete operating cycle for capacity testing.

• Standby Floating Charge State
  In the floating charge state, the NC contactor CJ1/CJ2 is closed, and the charge and discharge switch K1/K2 opens. The battery is online, with the DC system supplying power to both the battery pack and the load. In the event of an unexpected power outage, the battery pack can directly supply power to the load, ensuring uninterrupted power supply.

• Capacity Discharge State
  During capacity discharge, the two battery strings alternate according to regulations. For example, while battery string 1 is discharging, battery group 2 remains in float charging. The NC contactor CJ1 opens, the charge and discharge switch K1 close, and the PCS module works. The module converts the DC power from the battery string into AC power and feeds it back into the grid, thus achieving online capacity testing. Upon completion of the discharge, the system automatically switches to constant current charging.

• Constant Current Charge State
  When the capacity testing is completed, the batteries stop discharging, and the PCS stops inverting. The NC contactor CJ1 and the charge and discharge switch K1 remain in the same state as during discharge. The PCS starts rectification charging, converting the AC power from the grid into DC power for pre-charging the battery. This then transitions into constant current equalization and trickle charging, ensuring smooth charging of the battery.

The above outlines the design and implementation of a capacity testing system based on battery inverter grid-connected technology. This method has been widely adopted by industry manufacturers. For example, DFUN has designed a remote online capacity testing solution, enabling centralized control of dispersed sites remotely, saving time, effort, and costs.

In addition to the capacity testing function, this remote online capacity testing solution also includes real-time battery monitoring and battery activation functions, truly achieving 24/7 real-time remote battery monitoring and maintenance.