Hello,
This is my first post in the FVEAA forums. I just joined after attending the March meeting. I have been on other EV boards and I'd like to post one of my ideas here for comment.
I started thinking about this when I realized how inexpensive 12VDC-120VAC inverters for the car have gotten these days. It all comes down to volume. How could that be used to reduce the price of EV components? They both use a lot of the same electronics.
The initial idea was to use a Master Controller that would have brains only, no power functions. The master would control multiple Slave Controllers with the power stages. Each battery would have its own slave and be the inexpensive, standard component. Each slave could act as both controller and charger. Since each slave would handle one battery it would work as a BMS system, all batteries given individual treatment. Batteries could be added or removed individually without impacting other batteries in the system as a whole.
A single transformer would transfer power from one part of the slave to another. All would be isolated electrically. I initially planed on a DC controller with the master giving each slave a voltage/current goal and the outputs would be added in parallel at the motor. I decided it would be inexpensive to add a 120VAC inverter stage in each slave so the system could have more uses. The master would synchronize the phase of each slave so the outputs could be combined. Well, if it would work for 60Hz single phase, why not change each slave to a universal controller output that can be DC, AC single phase or AC three phase? It could even do SepEx. 3-phase motors would run under 200Hz and the master would control it all.
I soon saw the biggest disadvantage of the system; going from 12V (or 6V) to a high-voltage motor had much more efficiency losses than starting with a higher voltage DC system. I still wanted to keep the modular aspect intact with the mass-produced slave controller. I decided that 4 batteries would be a good compromise. That would allow a golf cart, scooter or motorcycle to run with a single slave, but a car could use 3 or more to get the needed power and range. I still allow the 4 dc sections to operate isolated, but with the option of connecting the taps on the transformer so a string of 4 would cut switching losses by 75%. Each battery can be charged or drained individually one at a time as well so the BMS can keep the batteries equalized.
I realized that it would also be possible to replace on of the batteries with an ultracapacitor. This would help with more efficient regeneration and reduce the max currents on batteries when accelerating. Having one ultracap in each slave allows the maximum power of the combined slave units to be used at the same time.
While each slave would have autonomous control with microcontrollers the master controller would have most of the brains. Some type of off-the-shelf embedded system could be easily adapted to do the communication with the slaves and generated the master control signals for the inverters on each of the slaves. An off-the-shelf laptop would be connected for programming, data logging and advanced displays.
I designed the slaves to use a flyback converter, but I think now that it might be better to use a simple forward converter. The only issue with that is in series-hybrid mode where both the AC rectifier and DC storage sections need to transfer energy to the motor controller section at the same time. It could still work with multiple slaves, with one slave doing DC storage controller while another slave is doing AC rectifier controller. They would swap functions around to even out battery drain.
Here's a description of potential uses I wrote up once before:
Electric Vehicle Uses:
Motor Controller – AC or DC
Battery > Motor
Ultra Capacitor > Motor
Battery Charger (with BMS)
AC Input > Batteries
Regenerative Braking
Motor > Ultra Capacitor
Series Hybrid
Charger & Motor Controller
Regenerative Braking
Household Power Uses:
AC Line Conditioner
AC Input > AC Output
Inverter – Pure Sine Wave
Battery > AC Output
Uninterruptable Power Supply
Charger & Line Conditioner
Inverter when power drops
Solar/Wind Uses:
Reprogrammable
Microcontrollers will run everything
Most Inputs/Outputs can be adapted
Off Grid
Solar Panel > Batteries
Wind Generator à Batteries
Batteries > AC Output
On Grid
Inverter can match phase and feed back to grid
Distributed System
Central Master Controller will manage many slave controllers
Master will dictate voltage/current needs
Master will send timing info. All AC outputs in phase
Performance Data
Slaves will have many sensors to feed data to Master
Well, there is my crazy idea. What do you think? The electronic concepts may be tough to understand for some of you, but the general idea should be clear enough, I hope. My old Power Electronics professor gave it a quick once-over and didn’t see any major flaws. It wouldn’t be easy to build and may well be beyond what a do-it-yourselfer can whip up in the garage. I’ve worked at some electronics places that could do it, but it would require some money, time and expertise. What really makes the system appealing to me is the idea of using it for Solar and Wind storage as well. That would widen the market considerably and that would help bring down the price. I’m a firm believer in making the hardware as universal as possible and letting the software work out the details.
Thanks for reading about one of my wild fantasies. I’ve got more even crazier ones if anyone is a real glutton for punishment.
-- Paul Schlie
