Control Modes¶
The ARx Series MagnaLOAD DC electronic load automatically selects the appropriate regulation state depending on the selected control mode, programmed set-points and the voltage and current being driven by the connected DC source. The MagnaLOAD electronic load preferences regulation states depending on the selected Control Mode: Voltage Mode, Current Mode, Power Mode, or Resistance Mode.
Control Modes can be selected from the front panel menu system or by computer command. Changing the Control Mode while the DC input is enabled will cause the MagnaLOAD electronic load to stop processing power and enter Disabled status.
Voltage Mode¶
When Voltage Mode is selected, the MagnaLOAD electronic load will auto-crossover between voltage and power regulation, but will preference constant voltage regulation over all other states. In Voltage Mode, the MagnaLOAD electronic load will try to sink enough current to maintain the voltage set point in a constant voltage regulation state. The operating region for Voltage Mode is further described by Fig. 4.7. Programming a resistance set-point and current set-point is disabled in Voltage Mode as the two regulation states conflict with the voltage regulation state.
Trip-point settings for voltage and power can also be used to shutdown the MagnaLOAD electronic load when a programmed threshold is crossed.
Caution
Configuring the MagnaLOAD electronic load for Voltage Mode while the connected DC source is also trying to regulate voltage will produce regulation instabilities. Instead, an alternative control mode should be selected.
Simplified Voltage Mode Operation Diagram. Refer to Fig. 4.5 for operating profile constraints.
Current Mode¶
When Current Mode is selected, the MagnaLOAD electronic load will auto-crossover between current and power regulation, but will preference constant current regulation over all other states. In Current Mode, the MagnaLOAD electronic load will allow the input voltage fluctuate while trying to maintain the current set-point in a constant current regulation state. The operating region for Current Mode is further described by Fig. 4.8. Programming a resistance set-point and voltage set-point is disabled in Current Mode as the two regulation states conflict with the current regulation state.
Trip-point settings for current and power can also be used to shutdown the MagnaLOAD electronic load when a programmed threshold is crossed.
Caution
Configuring the MagnaLOAD electronic load for Current Mode while the connected DC source is also trying to regulate current will produce regulation instabilities. Instead, an alternative control mode should be selected.
Simplified Current Mode Operation Diagram. Refer to Fig. 4.5 for operating profile constraints.
Power Mode¶
When Power Mode is selected, the MagnaLOAD electronic load will auto-crossover between current and power regulation, but will preference constant power regulation over all other states. In Power Mode, the MagnaLOAD electronic load will allow the input voltage and current fluctuate while trying to maintain the power set-point in a constant power regulation state. The operating region for Power Mode is further described by Fig. 4.9. Programming a resistance set-point and voltage set-point is disabled in Current Mode as the two regulation states conflict with the current regulation state.
Trip-point settings for current and power can also be used to shutdown the MagnaLOAD electronic load when a programmed threshold is crossed.
Caution
Configuring the MagnaLOAD electronic load for Power Mode while the connected DC source is also trying to regulate power will produce regulation instabilities. Instead, an alternative control mode should be selected.
Simplified Power Mode Operation Diagram. Refer to Fig. 4.5 for operating profile constraints.
Resistance Mode¶
When Resistance Mode is selected, the MagnaLOAD electronic load will preference Constant Resistance (CR) regulation state over all other regulation states. The MagnaLOAD electronic load will operate in constant resistance regulation within the set-point boundaries indicated in grey in Fig. 4.10. If the connected DC source drives the DC bus to one of the bounding set-point limits, the MagnaLOAD electronic load will auto-crossover to the appropriate regulation state. To avoid auto-crossover, the bounding set-point limits should be set sufficiently high to increase the constant resistance operating range. Programming a current set-point and voltage set-point is disabled in Resistance Mode as the two regulation states conflict with the resistance regulation state. trip-point-settings for voltage, current, and power can also be used to shutdown the MagnaLOAD electronic load when a maximum desired limit is reached.
Simplified Resistance Mode Operation Diagram. Refer to Fig. 4.5 for operating profile constraints.
Shunt Regulator Mode¶
Shunt Regulator Mode is designed to regulate the DC bus voltage to ensure the voltage remains below a programmed limit. Shunt Regulator Mode can be used as a replacement for a braking resistor in a DC motor drive application, or as a protection device to prevent rising DC bus voltage from damaging other electronic devices.
When Shunt Regulator Mode is selected, the MagnaLOAD electronic load will only dissipate energy when the voltage passes a user-defined voltage threshold. The MagnaLOAD electronic load will remain idle at the DC bus voltage defined by the source until that DC bus voltage rises above a programmed voltage threshold. When DC bus voltage passes this voltage threshold, the MagnaLOAD electronic load will begin to process power, with the current rising rapidly to the current set point.
The voltage threshold is the programmed voltage set point plus 1% of the unit’s full scale voltage rating. For example, if an ARx6.75-1000-14 (6.75 kW, 0-1000 Vdc, 0-14 Adc) MagnaLOAD electronic load was programmed to 500 Vdc in Shunt Regulator Mode, the MagnaLOAD electronic load would begin dissipating energy at the voltage threshold: 500 Vdc + (1% of 1000 Vdc) = 510 Vdc. The MagnaLOAD electronic load would continue dissipating energy until the DC bus voltage drops below 500 Vdc.
When the product is dissipating energy in Shunt Regulator Mode, the current is regulated to the MagnaLOAD electronic load’s user-defined current set point.
Note
If the MagnaLOAD electronic load is not sized properly for the amount of current fed back onto the DC bus, the voltage on the DC bus may continue to rise beyond the MagnaLOAD electronic load’s voltage threshold.
Fig. 4.11 shows the voltage and current over time in Shunt Regulator Mode, as the DC bus voltage rises below the voltage threshold and the MagnaLOAD electronic load begins dissipating energy. trip-point-settings for voltage, current, and power can also be used to shutdown the MagnaLOAD electronic load when a maximum desired limit is reached.
Simplified Shunt Regulator Mode Operation Diagram. Refer to Fig. 4.5 for operating profile constraints.