Intelligent, Not Just Smart
by Shivaram N V
Maximise power, efficiently -
Typically, efficiency and power of most devices (including biological) are negatively correlated. This means that you cannot achieve maximum efficiency at maximum power levels and conversely, maximum power levels at maximum efficiency. An easy way to maximise efficiency of the scooter is to operate at low or medium power levels. But where’s the fun in ‘medium’ power levels?
The approach we have taken for this is similar to how our ‘smartphones’ manage to achieve the same — the scooter transitions to RIDE mode at lower battery levels. The RIDE mode has been configured intricately for this exact purpose of maximising efficiency with minimum impact on power levels. In RIDE mode, the power levels are modulated in a manner that the ride continues to feel zippy, yet saves battery. Although similar to how our phones manage to achieve the same, keep in mind that the power demands of a scooter on city roads fluctuates significantly and these algorithms are designed accordingly. Added to this is the complexity of ensuring that these algorithms work smoothly to prevent sudden drop in power levels during a manoeuvre.
Maximise power, reliably -
Although reliability does not negatively correlate with either efficiency or power, it follows its own trajectory that is orthogonal to both power and efficiency. Limited lifespan of batteries and gradual decline in battery performance pose a serious challenge to providing maximum performance consistently, over the age of the scooter. This challenge is compounded by the fact that our battery consists of a whopping 3-digit number of individual Li-ion cells. While this makes the battery modular in design, it also adds to complications like differential heating, differential cooling, cell imbalance, etc. which in turn affect scooter performance. Let’s understand the basic mechanics behind the working of a battery to understand how we have gone about tackling this challenge.
Battery is a device that converts chemical energy of its components into electrical energy and powers the load it is connected to. And the battery will continue to provide electrical energy as long as it has the said chemicals in the required concentrations. Like any chemical reaction, the ones happening inside a battery are also accelerated by temperature. Higher the temperature, higher the rate of a chemical reaction and better the yield. But what is to be kept in mind is that higher temperatures also facilitate a lot of unwanted side reactions that “eat-up” into the concentrations of the chemicals. This means that the temperature of a battery must be maintained within a certain band to realise maximum performance, reliably.
Another parameter that greatly affects reliability of a battery is the voltage levels at which it is maintained and operated within. Battery voltage can be defined as the electric potential difference (electromotive force) between the positive and negative terminals of a battery. At lower voltages, it will deliver lower power. While higher voltages do mean that it can deliver higher power, it also means a higher probability of uncontrolled chemical reactions inside the battery. This means that the voltage of a battery must also be maintained within a certain band to realise maximum performance, reliably.
Whatever be the mode of the scooter, riding or charging, parked or vacation, we have algorithms actively running internally to ensure that both temperature and voltage are maintained at optimal levels. Some of these include
- Power modulation algorithms that ensure operation of battery and motor within specific voltage and temperature bands. These provide a gradual yet certain way of ensuring optimal voltage and temperature operating points in a manner that the rider can get used to the changing power levels.
- Charge optimisation algorithms to ensure that battery operates within the optimal voltage and temperature levels with minimum impact on charging time and efficiency.
Why not just protection mechanisms…
to maintain voltages and temperatures between the required limits? While having hard protection mechanisms would address this issue also, imagine how annoying having to stop the ride because of overheating of the system be? These algorithms ensure that power levels are tempered optimally so that temperatures and voltages stay within limits thereby preventing vehicle cut-off.
The Park Assist -
Every wonder why petrol two wheelers don’t have reverse functionality? The mechanism, mechanical or otherwise, for achieving rotation of the wheels in the other direction is bulky and expensive to implement this. Fortunately for us, our intelligent PMSM motor has an inbuilt mechanism of direction reversal with speed limitation functionality. But the park assist mode on our scooter presents a unique challenge — how to ensure minimum jerk to the rider while in reverse, yet ensure maximum torque required to climb out of a ditch in reverse? Food for thought.
Originally published at https://blog.atherenergy.com on June 28, 2019.
