L7 Drive technology company based in Finland asked themselves a question:
What if there is another way to drive and control electric motors and battery electronics? What if the lithium battery pack doesn’t need to die because of single-cell failure?
L7 ELECTRIC DRIVE SYSTEM PROOF OF CONCEPT VIDEO
The electric kick-scooter in the video does not decrease the speed when the cell is removed from the lithium battery pack, nor does it stop. If this does not excite you just skip the whole article. This changes everything we know about modern brushless electric motor control and BMS!
L7 Drive has been designing and engineering leading-edge electric power-train technologies for markets around the world. They came up with this great idea to use one battery cell connected in parallel ( In usual systems today to increase the voltage the batteries are connected in series, in parallel for bigger capacity ) and to make a drive module with voltage converter that can increase and decrease the voltage of one single cell ( with many parallel connections ) ; and therefore decrees and increase the speed of an electric motor.
We do not have inside information, this is how we see L7 DRIVE technology working
Electric Motor speed constant is Kv. Depending on voltage level’s the RPM of motor increases or decreases.
In traditional BLDC drive systems, the full motor speed is achieved with pushing the max permissible current ( A ) into the motor at given system voltage. Voltage level remains the same with a small gap between the fully charged and drained battery.
If the Voltage of LI-ION battery is 60v and your motor Kv is 12 then the rotation speed ( rpm ) on motors shaft will be 60v x 12 = 720 Rpm. Full RPM speed is achieved by putting more amps into the system, not by changing the voltage level. For example, The 60v Li-ion battery works between 67.2V ( charging voltage ) and 46.4V ( Shutdown voltage ). When the bike is fully charged, the voltage level is 67.2 and this is when you feel the full beasty performance of your electric motorcycle. On 46.4V the bike’s battery is almost dead, bikes performance decreases and the bike stops.
L7 drive proof of concept DEMO electric motorcycle
Traditional BLDC DRIVE “constant voltage”, has the sweet spot where the motor is most efficient at 50 % of the power and 50 % of the speed. Be informed that different systems, different sweet-spots. Constant voltage gives you one sweet spot where the motor + traditional controller is most efficient. If the voltage controls the speed directly and changes with speed; the sweet spot is achieved most of the times ( because the system voltage is not constant ). We are not talking about that gap between the charged bike and fully drained battery.
L7 drive is about using one cell and increasing and decreasing the voltage with speed. Therefore we would have as many sweet-spots ( efficiency ) as the voltage range is. We are not sure what L7 is doing and how they are doing it, but we are pretty sure that is where the magic is made.
This is our opinion that as we stated above may be wrong. You can read the facts they used to describe their L7 BLDC motor Drive system yourself here:
The first one cell powertrain system in the world
Connect an electric motor to your battery with one single device from L7 Drive.
It is a new kind of electric powertrain with less electronic complexity and simple mechanical integration. Our device simultaneously manages the battery pack and controls the motor. It also offers multiple charging methods and optional connectivity with your smartphone. Different cloud based services are being developed and released in future. Assembly is clean and simple, one device is all you need. it means less parts to install and less chances of anything going wrong
Possibility of one weak cell stopping your journey is eliminated, because there are no series connections. The technology behind L7 Drive allows you to use parallel connected cells, or even just a single large capacity battery cell. Battery state of charge and lifetime calculations are greatly simplified, corresponding directly to increased reliability and cycle life.
TRADITIONAL WAY TO CONTROL EV ELECTRIC MOTORS
The modern but old way to control BLDC electric motors
Modern electric motor drives are very efficient. However, they are most efficient on full power, which is not used very often, especially in vehicles. Basically, the traditional way of constructing a battery powertrain requires us to raise the battery voltage, creating cell balance problems, and then needs the motor driver to lower the voltage in most driving situations. We thought this doesn’t make much sense.
L7 DRIVE WAY TO CONTROL EV ELECTRIC MOTORS
L7 Drive is a complete one device solution that turns the whole setup the other way around. We start with one large Li-ion battery cell, or a set of parallel-connected cells, which behave like one big cell. Our novel patented technology then raises the voltage to the motor, but only when needed, and only as much as needed. That way we can get the best efficiency on partial load, which is used most of the time.
Unbeatable Benefits
No need for BMS. One cell is always in balance with itself. Parallel connections balance the voltage automatically.
Full capacity is always usable. One weak cell will not stop the vehicle and a faulty cell will be isolated by a fuse.
Only one device is needed. L7 Drive takes care of the battery control, motor control and also controls the charging.
Voltage conversion works both ways, so L7 device can recuperate the motor braking energy back to the battery.
A simple AC-DC converter at voltage anywhere between the battery voltage and device’s maximum voltage can be used for charging.
L7 Drive unit can also charge the battery from unstable voltage sources, such as solar panels or a small wind generator. No separate inverter needed.
L7 Drive unit can produce the maximum power independent of the motor speed, so the launch power is always more than adequate.
L7 Drive technology is suitable for all Li-ion chemistries, so you can choose the chemistry and cell format according to your needs.
Scalability
L7 Drive technology is scalable from 250W to 15kW and upwards. Our first commercially available models are 250W unit for electric assisted bicycles and 2kW unit for electric scooters, e-rickshaws and other light electric vehicles. They can be used with any Li-ion battery type available today or in the future, with one big cell, or any parallel connected pack. A bigger unit becoming available late 2019 with 8kW power and integrated battery pack is designed for autorickshaws and other L5e or L7e class vehicles. L7 Drive technology is compatible with all available electric motor types. The first models will be made for BLDC.
Please discover more information with more clarity at L7 Drive website. The reason we wrote this with insufficient information to explain this system is that the worldwide magazines are missing on this revolutionary system that we think it’s going to change EV vehicles from the ground up since it is quite opposite to the way electric drive-train control is made today.
EvNerds
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