25 Feb 2024

You down with OCPP?

Why is conformity with Open Charge Point Protocol (OCPP) charging profiles important?  The reason is hardware agnostic load balancing.
    
Some sites with charge points have a limited electricity supply, and load balancing can alleviate these problems by actively controlling the charging current for charge points on a site.
    
Let’s look at how load balancing works. Static load balancing means that each charge point is assigned a fixed maximum current. For a 48-amp installation, six charge points could be installed being 48/6 = 8 amps for each charge point. But what if only four cars are charging? It would make sense if the current could be changed according to the number of cars charging. Dynamic load balancing assigns each charge point a maximum current continuously based on how many cars are charging. If four cars were charging in the example before, each charge point would be assigned 12 amps, meaning a better charging experience for the end user. This allows for a greater number of charge points per site without reduced level of service during non-busy hours.

In practice
How is dynamic load balancing implemented in practice? Some manufacturers implement their own load balancing solution within the charge point software; i.e. using a web interface, app, etc.
    
Dynamic load balancing requires constant communication:

  •  What communication needs to happen when doing load balancing?
  •  User plugs car into charge point
  •  Charge points tells the system that a car has connected
  •  System recalculates the available current for the site
  •  System assigns new charging current to each charge point


The system also continuously recalculates the available current based on data from each charge point, with these available states:
1. Charging
2. Waiting to charge (Smart charging or delayed charging)
3. Finished charging
4. Not charging

Smart charging
However, not all manufacturers implement built-in load balancing using their own software.
    
This is where Monta’s software comes into play. So how does Monta do load balancing with just an internet connection to the charge points?
    
Monta connects to the charge point using OCPP 1.6J (Open Charge Point Protocol), the standard for communication between the charge point and the operator backend. The OCPP 1.6J standard includes so called feature profiles, where smart charging is one of these.
    
The smart charging profile allows the operator to change the maximum allowable charging current of the charge point by sending an OCPP SetChargingProfile. This is exactly the feature that can enable dynamic load balancing even across multiple brands. As aforesaid, there are many calculation steps that need to be processed before we are able to do this.
    
Monta has developed our own load balancing algorithm from the ground up. In order for this load balancing algorithm to work properly and safely, we need to test if the charge point brands have implemented the OCPP 1.6J ChargingProfile correctly. At our office in Copenhagen, Monta has a selection of 33 different models of charge points for testing purposes. These 33 charge points include the most used ones in our system. We set out to map whether every one of these models support the SetChargingProfile.

Test setup
The 33 charge points are located in Monta’s CPH office and are connected to Monta’s OCPP server environment. When sending SetChargingProfile, the charge point is allowing the EV to draw a certain amount of current, which is specified in this profile. This is communicated through the Type 2 interface using the Control Pilot (CP) pin.
    
When the cable is connected, Control Pilot pin is communicating a 1 KHz Pulse Width Modulated (PWM) signal from to charge point to the EV. The PWM is varying the length of the ON signal compared to OFF which can be measured in percentage, called the duty cycle.
    
The duty cycle directly conveys the amount of amps that is available for the EV. When the duty cycle is between 10% and 85%, the amount of amps allowed to be drawn is directly proportional to the duty cycle: Amps available = Duty Cycle 0.6A
    
In Monta’s lab, the electric vehicle is being simulated with a handheld EV simulator, where the Control Pilot signal is fed into an oscilloscope, a device measuring high frequency signals, allowing our engineers to instantaneously measure any changes in PWM signal set by the ChargingProfile.
    
Test setup for measuring changes in amp set by ChargingProfiles, with an oscilloscope and EV simulatorWe use this test setup to conduct test of ChargingProfiles on all 33 charge points in our office.
    
What do the test results mean? Supported means the charge point responds properly to an OCPP SetChargingProfile with parameter TxProfile. A proper response is measured, if the charge point adjusts the allowed charging current set by the SetChargingProfile within a reasonable amount of time. This includes going into SuspendedEVSE when SetChargingProfile is set to 0 A, and starting charging again when going from 0A to 6A-32A. 6A is the minimum charging current by the Type 2 standard. The charge point also needs to accept ClearChargingProfile which removes the previous charging profile, going back to the default current.
    
Partly Supported means that either SetChargingProfile or ClearChargingProfile is not functioning 100% properly. Not Supported means that both SetChargingProfile or ClearChargingProfile is not functioning.

Full flexibility
Why is load balancing with OCPP important? Can’t we just choose the manufacturers that do their own built-in load balancing? Firstly, OCPP is an open and free standard, which can be implemented by any charge point manufacturer anywhere at no additional cost. Secondly, since OCPP is standardised, if manufacturers conform to its specifications, they can be sure that dynamic load balancing will work perfectly on our platform. Remember that charge points with load balancing sell in greater volumes. Thirdly, manufacturers can save loads of engineering hours on developing a proprietary load balancing system because we have done all the hard work already.
    
Lastly, and most pertinently, site owners can switch to another charge point brand or even mix brands. Using OCPP Charging Profiles allows site owners to have full flexibility in their choice of charge points when upgrading existing sites, or planning new sites.
    
Monta has good communication with charge point manufacturers and will keep pushing for support of this feature. It’s a win-win for everyone.
    
At the time of writing, Monta integrates with 329 different charge point models.
    
Employees can save on large upfront costs and enjoy the benefits of switching to electric.