What are the essential differences in the underlying logic of OCPP dynamic load balancing algorithm between 7KW single-phase and 11KW/22KW three-phase AC charging pile motherboards?

The OCPP dynamic load balancing of 7kW single-phase and 11kW/22kW three-phase piles has the same protocol framework, but three sets of underlying logic differences.

Power regulation granularity

• There is only one live wire for 7kW single-phase, and load balancing is a switch logic - either 7kW is fully open or 0kW is turned off. OCPP issues a charging plan that can only start and stop according to time slots or limit the overall current to 3.5kW.

• When the total demand exceeds the capacity, the gun will be turned off by polling or reduced by 50% alternately.

• 11kW/22kW three-phase independent control for each phase, continuously adjustable load balancing - three-phase year-on-year power reduction or single-phase independent regulation.

• OCPP can specify current limits for each phase, and the algorithm prioritizes meeting three-phase balanced loads before handling single-phase high current requirements to avoid overload tripping of a certain phase.

Phase sequence constraint

• 7kW single-phase without phase concept, only looking at the total power. Three phase must consider three-phase balance - if 8 out of 10 piles are connected to phase A, 1 to phase B, and 1 to phase C, phase A will experience instantaneous overload.

• The OCPP algorithm needs to incorporate a phase sequence allocation strategy: automatically allocate new piles to the phase with the lightest load, or force the three phases to be connected alternately. This requires the motherboard hardware to support phase sequence detection and single-phase independent relay control.

Depth of power grid interaction

• 7kW single-phase is a passive response - executed after receiving a power limit command from the cloud, without sensing the status of the power grid.

• The three-phase can be connected to the grid metering architecture (AMI), which reads the three-phase voltage, frequency, and power factor in real time. The OCPP algorithm adds active response: if the voltage of a certain phase drops below 210V, the power of that phase will be automatically reduced, and if the three-phase imbalance exceeds 15%, the load will be automatically redistributed.

• This requires the motherboard to integrate a power quality monitoring chip, which is usually not available for 7kW piles.

OCPP message difference

• Both use SmartChargeg.FHIR Profile, but the limit field of the 7kW pile only has a single current value, while the three-phase pile can be expanded into an array [limit_L1, limit_L2, limit_L3].

• When distributed in the cloud, the analysis of 7kW piles is simple, while three-phase piles need to verify phase sequence matching and balance constraints. Incorrect configuration may lead to single-phase overcurrent burning.

Algorithm complexity

• 7kW single-phase: greedy polling, first come, first served, over limit gun shutdown or 50% power reduction, with a code volume of approximately 500 lines.

• 11kW/22kW three-phase: Linear programming solution, with the objective function of maximizing three-phase balance and total charging capacity. Constraints include single-phase capacity, phase sequence allocation, and voltage drop threshold. The code size is about 3000 lines and requires floating-point operations or DSP coprocessors.

Conclusion:

7kW single-phase is switch type coarse adjustment, while three-phase is continuous fine adjustment+phase sequence constraint+grid coordination. Three phase piles require stronger computing power, more relay circuits, and more complex sampling, and cannot be upgraded by firmware flashing. The hardware architecture must be reserved.

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