Power Master for Phase Imbalance

How charging creates imbalance

Most AC charge points in residential and workplace settings are single phase. Each one loads exactly one phase of a three-phase supply, and which phase it loads was decided by whoever wired it.

• Points are distributed across phases at installation, often evenly and often not
• Usage is not distributed evenly regardless, because the cars that arrive do not consult the wiring diagram
• Six points spread two per phase can still put four vehicles on one phase on any given evening
• The building underneath is rarely balanced to begin with, so charging adds to an existing skew rather than to a clean baseline

So a design that is balanced on paper is unbalanced in operation, and the imbalance moves through the evening as vehicles arrive and leave.

How Power Master corrects it

Two mechanisms, and which one a site needs depends on whether the imbalance is something charging can allocate around or something built into the wiring.

1. 1

   Balancing by power

   The system monitors each phase continuously. Where one phase is carrying more than the others, it reduces the power offered on that phase and raises it on the lighter ones until the load evens out. The site keeps charging throughout; what changes is how the available current is distributed.

2. 2

   Switching the phase

   Where allocation is not enough, a charge point can be moved to a different phase using a phase switcher, so a point that was permanently loading the heaviest phase stops doing so.

The second is offered as a technology offering rather than as a catalogue product, because it is fitted to the site rather than bought off a shelf.

What imbalance actually costs

The first row is usually the one that gets attention, because it is the one that stops a site adding chargers it physically has the capacity for.

Measuring it properly

Imbalance cannot be inferred from a total. It has to be measured per phase, and the measurement has to be connected to knowledge of which charge point is on which phase.

• Per-phase current and voltage on the incoming supply, not an aggregate
• A phase map: which charge point is connected to which phase. This is frequently undocumented and has to be established at commissioning
• Neutral current, which is the direct expression of the imbalance
• Measurement over time, because a snapshot at midday says nothing about the evening

The phase map is the part that gets skipped and the part without which nothing else can be corrected. A controller that knows the site is unbalanced but not which chargers sit where can only reduce everything.

Correcting by allocation

The correction available to a charging system is allocation: deciding how much current each point may offer, with knowledge of which phase each one loads.

1. 1

   Allocate the next arrival to the least loaded phase

   Where several points are free, steering a new session to a point on the least loaded phase corrects imbalance before it forms. This costs nothing and requires only the phase map.

2. 2

   Rebalance during operation

   As the building's own load shifts through the evening, the phase that had headroom may not be the one that has it an hour later. Allocation has to move with it.

3. 3

   Limit per phase rather than per site

   The constraint is per phase, so the allocation has to be too. A total-based limit will trip the loaded phase while reporting headroom.

4. 4

   Use three-phase points where they exist

   A three-phase point draws evenly by construction and is the cleanest correction available. Where a vehicle only accepts single-phase, it does not help.

What allocation cannot correct

Worth being clear about, because the expectation this creates is otherwise unreasonable.

• Imbalance in the building's own load. Charging can avoid adding to it and cannot remove it
• A site where every charge point is on one phase, which is a wiring problem with a wiring solution
• Imbalance when every point is in use and every vehicle needs its full rate, at which point there is nothing left to allocate
• Voltage imbalance arriving from the network, which is the utility's

Where the imbalance is structural rather than operational, the honest answer is rewiring or a three-phase point, and we would say so rather than sell a controller that cannot fix it.

What commissioning has to establish

None of this works without knowing which charge point sits on which phase. That mapping is a commissioning input rather than something the system discovers, and it is the step most often skipped.

A controller that can see the site is unbalanced but does not know where each point sits can only reduce everything, which is not correction. It is just a smaller site.