34000A / 36000A Series Compact High Power DC Electronic Load Providing electric car charger and battery test solution

After several years of rapid developments and investments in new battery and electric traction technologies, the number and types of electric and hybrid vehicles is expanding rapidly.

Along with this growing field of vehicle types, infrastructure support of home chargers and rapid public electric chargers is growing fast as well.  

All electrified vehicles rely on rechargeable batteries for their electrical energy source. These batteries must be charged at regular interval using either alternating current or direct current charging technology. AC charging is convenient when drawing power from the utility grid. Prevailing industry charging standards use a variety for voltage and current ratings such as 120V / 12A, 120V / 16A; 220V / 12A, 220V / 16A, 220V / 80A and others depending on region. For fast public charging stations, three phase power is used to shorten charging times significantly. Often, on-board AC chargers are installed in the vehicle so they can be charged from any available AC outlet although charging times using on-board chargers can be quite long as they are often limited in voltage and current capability. However, ready access to standard grid power is an important convenience.For DC charging, standards are different by region as well. For Taiwan, Japan and the United State, 600V / 200A is typical. For Europe, 850V / 200A is commonly used while mainland China uses a 750V / 250A three phase DC charging standard. DC fast chargers are typically installed in public charging stations and can offer greatly reduced charging times due to their ability to deliver high voltage and high current at the same time for fast charging of DC batteries.

All 34000A and 36000A model DC loads can be equipped with an optional PLC interface for integration into charger and battery production line test systems. The PLC input accepts both digital I/O and analog 0-10V scaled analog signals to control operation of the DC load.  Contact Prodigit sales department for further details.

For higher levels of test integration, the Prodigit 9841 Battery Charge and Discharge integrated test system with associated test software offers both DC power and DC load capabilities for full charge/discharge testing, battery capacity (AH), power consumption and life cycle testing of automotive battery packs.

The 9841 battery charge and discharge test system can accommodate a full range of 

Prodigit electronic loads and has been adopted by the STC Bureau.

 Battery Charging Methods 

The most common batter charger mode for electric vehicle charging is to use constant current, constant voltage (CC-CV) mode. This means the battery is charged using a constant current level which allows quick charging of the battery while monitoring the battery voltages as it charges up. When the battery voltage reaches its peak voltage, the charger switches over to constant voltage mode preventing the battery voltage from reaching excessive levels.  This method is illustrated in Figure 1.

 Electric Vehicle Charging Station Test Method 

When charging electric vehicle batteries using an on-board vehicle charger or charging station, the battery represents a load to the charger. During the charging process, the battery voltage will increase slowly. To enhance the speed of the charger to detect the battery voltage, using an electronic load to simulate a battery and its impedance during charger design will enable better and faster test verification.

For battery simulation applications, the most commonly used Load operating mode is Constant Voltage (CV) which simulates the battery voltage or Constant Resistive mode which simulates the battery impedance.

In Constant Voltage (CV) mode load mode, the terminal voltage of the electronic load is held at the CV setting voltage value. By adjusting the CV setting value, battery states ranging from fully discharged state to fully charged state can be simulated easily.

In Constant Resistive (CR) mode, the terminal voltage of the electronic load is held at the multiple of the charge current and the CR setting value. By changing the CR setting value of the load, various impedance states of the battery can be simulated ranging from fully charged to fully discharged.

As mentioned, Constant Voltage (CV) mode can be used to simulate different state of charge (SoC) conditions of a battery pack during charge and discharge cycles. This include low battery voltage, increasing battery voltage during charging and high voltage state when fully charged. During each stage, the load monitors and displays important parameters such as voltage, power (Watt) and current. At the end of charge cycle, the load will transition to CC mode to CV mode which will be evident from the load display readouts as well. This approach is much more convenient than using actual batteries to test on-board chargers or charging station operation.

All 34000A/36000A Series electronic loads are equipped with built-in Over Power Limit (OPL) protection circuits to ensure safe operating when used in parallel mode. The purpose of the OPL feature is to limit the power to the load when the charger output power exceeds the maximum power rating of the load. In that case, the electronic load will automatically limit the input power at or near its maximum power specification and continue to operate at this power level.  The OPL function allows two or more electronic loads to be used in parallel for high power applications.

For example, a 20kW charger can be tested using a 25kW rated electronic load to apply over current, over power conditions to the charger under test. If a 20kW rated electronic load is used instead, no charger over power conditions could be tested.

In case only a 20kW electronic load is available, a 5 kW load model can be added at any time to be used in parallel with the original 20kW load in Constant Voltage (CV) or Constant Resistive (CR) mode of operation. His is illustrated in Figure 2.  This is due to the Prodigit load’s OPL function which allows CV or CR mode with parallel loads of unequal power ratings. This capability offers great flexibility in deploying multiple loads for a wide range of power requirements.

 Electric Vehicle Battery Test Methods 

Once an electric vehicle’s battery is fully charged, it can be driven till almost depleted for maximum driving range. In drive mode, the battery acts as a power source for the electric drive train. 

 1. CC+CV mode is aimed at battery discharge testing. 

In this mode, discharging of the battery starts in CC mode of operation by setting a current discharge level (CC Set point) and a discharge stop voltage level (CV Set point) which determines full state of charge for the battery under test. When the battery voltage drops to the CV set point level, the electronic load stops discharging so that the battery voltage is maintained at the CV set value. Operation in CC+CV mode is very straightforward as the load automatically switches from CC constant current mode discharge mode to CV constant voltage mode. This prevents the battery from being damaged due to excessive discharging. This mode of operation is illustrated in Figure 4.

Operation Procedure

•  Load input terminals are connected to the DUT 
•  Change to CC mode and setting CC current setting.
•  Press Limit key to setting the CV voltage and the display will show “Add.CV”.
•  Press START key to start up the CC+CV test, and press “STOP “key to stop CC+CV Test.

 2. CP + CV mode battery discharge test 

In CP + CV mode of operation, the electronic starts discharging the battery using a constant amount of power drain as determined by the CP set point. Once the battery voltage sags to the CV set point, the load transitions from CP mode to CV mode to maintain the discharged state battery voltage.

Operation Procedure

•  Load input terminals are connected to the DUT 

•  Change to CP mode and setting CP power setting.

 3. CC + UVP mode battery discharge test