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Charging Technology

What is phase balancing in OCPP Smart Charging?


Won Moon Joo and Dr. Jonas Schlund

March 10, 2022

AC chargers are commonly used to charge up electric vehicles, both at home and public locations. However, there isn’t just one type of power produced by an AC charger. You may have heard discussions going on about the benefits and drawbacks of 1-phase or 3-phase AC charger settings.

For example, this charger from EV Box (Elvi) offers speeds between 7.4 kW to 22 kW and selectable 1-phase or 3-phase.

EVBox Elvi via EVBox
Selectable 1-phase or 3-phase, 230–400V, 16 A and 32 A
(EVBox Elvi via EVBox)

If you take a closer look at the specifications, you may notice that there are several options for “Maximum output power.”

You are not simply limited to options for 1 or 3 phases, but also for the voltage (V) and current (A).

In this article, we will look into exactly what phases are and how they affect charging characteristics in home, public, and commercial settings.

What are ‘Phases’, and how do they affect charging speed?

In electricity, the phase refers to the current or voltage traveling along an existing wire, as well as a neutral cable. In other words, the phase refers to the distribution of load among the wires.

Unlike a direct current (DC) supply, an alternating current (AC) is constantly shifting between zero and peak values in a cyclical waveform shown below. 

single-phase graph

In a very simplified explanation, a 1-phase system uses two wires (one power wire and one neutral wire) to deliver current.

Meanwhile, a 3-phase system uses 3 wires (sometimes with an additional neutral wire).

A major advantage of a 3-phase system is that it can supply three times the amount of power, as well as deliver the power more consistently and with less material (fewer wires needed).

A 1-phase system will be subject to peaks and dips in voltage, but a 3-phase system will have the advantage of balancing the power with each phase signal 120 degrees apart.

Three phase system

For this reason, a 3 phase system will be able to accommodate more power and a faster-charging speed.

Phase Balancing with multiple chargers and vehicles

While the benefits of 3-phase systems are clear, it’s also important to note the balancing of the phases to provide a consistent flow of power from chargers to vehicles at one location.

Imagine a site with multiple level 2 chargers. 

All of these AC chargers use 3 phase charging to maximize the charging speed.

However, some electric vehicles are not compatible with 3 phases. This is because the charging speed of many vehicles is limited by their onboard hardware constraints and the vehicle can only charge with one phase. This means that when connecting a 1-phase vehicle to a 3-phase charger, the vehicle will only use single-phase charging.

Because a car battery needs DC power, and the grid supplies AC power, the onboard converter in the car is the limiting factor in the overall charging speed. Thus, the onboard converter is limiting its maximum charging speed, even if it is using a 3 phase charger (as it will only use one phase).

So, in our scenario, multiple vehicles may be charging on a single-phase only, when 3 phases are actually possible.

If too many EVs are charging on one out of three phases, there could easily be an imbalance and more power on one specific phase.

This is where optimization software can identify possible limitations and adjust the charging speed to avoid the overloading of phases.

For example:

Chargers 1, 4, 7 are  on L1, Chargers 2, 5, 8 are on L2, and Chargers 3, 6, 9 are on L3

If chargers 1, 2, 3, 4, 7 are active, it means that the power-on phase L1 might need to be reduced and the power on chargers 2 and 3 need to be increased to balance the three phases.

Unbalanced Phases graph

How to use OCPP for phase balancing

OCPP is a communication protocol that handles the communication between charging stations and the Charging Station Management System (CSMS).

OCPP is used to connect EV chargers and software backend systems using bilateral communication. The OCPP client (EV charger) and OCPP server exchange general information such as meter values (Wh, W, V, etc.) and start/stop charging events.

Through the OCPP protocol, the phase information can be sent on the meter values endpoint.

By knowing the phases of each charging session, power can be reduced or increased to help balance the load on each phase.

This can be done through OCPP’s smart charging functionality, which allows charging commands to be sent from the OCPP server to the EVSE.

By using this OCPP smart charging module, Ampcontrol is developing an algorithm that balances 3 phase systems.


Phase balancing is beneficial for EV charging, especially when it comes to charging up a fleet of vehicles. Balancing the power across three phases helps to deliver a consistent charging speed, which means that fleet managers can plan accurate charging schedules.

Smart charging software such as Ampcontrol can be used to take care of the OCPP protocol that makes phase balancing possible.

Read more about the grid, and how smart charging can help with grid volatility here.

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