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New EV Charger Design - Modular

43516 Views 68 Replies 14 Participants Last post by  PStechPaul
After delving deeply into the EMW 12 kW DIY charger, I think it would be best to make a new design. My concept is to make modules, each of which can be used on 120 or 240 VAC single or three phase, or up to 300 VDC. The modules would be 1.2 kVA for 120 VAC, and 2.4 kVA for 240 VAC or 300 VDC. They will be capable of being connected in parallel to obtain higher power. I think these modules could be built for a parts cost of less than $150 each. ;)

The IGBT I show here is an ultra-fast 35A 600V device that is designed for switching applications up to 100 kHz, so I think the inductor and capacitor size and cost may be greatly reduced. And this part is only about $1.50. :)

Here is a "first shot" at this design. It has been done using Mentor Graphics PADS 2004 and most of the parts are fully characterized with part numbers and approximate cost, as well as PCB decals so that a board can be made directly from the schematic. A BOM in Excel format can also be produced easily with a VBA script.

Here is a PDF which is a little easier to read:

And the BOM (preliminary) showing total parts cost less than $150:

This version is not PFC and non-isolated. It also has only a single pushbutton for start/stop, does not have a BMS connection, and has no display. But it has a serial port which can be connected to a Bluetooth module for viewing and logging data, and for commands. I am using only a 14 pin PIC16F1825 but it will probably need a 28 pin processor to provide the additional I/O needed. I have an Arduino UNO and I will try to add the connections to match its pinouts. I might also see if I can adapt the EMW control board with its display and function keys.

I am putting together an order to Mouser for some of the parts I will need for this design, and I am also going to get an AVR Dragon which is a $53 emulator/debugger/programmer which is really the very minimum needed for development of any serious design with the Atmel series microcontrollers. I plan to use this for analyzing the EMW charger (when I get a complete unit or the boards and parts needed), and hopefully be able to provide recommended modifications to the hardware and firmware to improve the reliability and performance. I think it may require a complete new set of boards, but many of the expensive components may be able to be re-used.
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...The use of coupled inductors (transformer) seems to be simple enough, if the simulation is to be believed. The low power non-isolated part might not be needed...
You are running a boost and a flyback converter off the same switch but the voltage feedback loop is only closed on the boost; the only reason this appears to work (in simulation) is because you have fixed the load resistance for each converter. In the real world, the voltage across the open-loop flyback converter will vary wildly with load (roughly speaking, it will act as a constant current source with current proportional to switch on time).

Now, a curious thing about the flyback converter is that it can automatically provide PFC when run in discontinuous mode (which is also when it is easiest to compensate for closed loop operation). Of course the bandwidth (transient response time) is terrible, but as long as you don't need to process much power or deal with widely varying loads it's a viable option.

Unfortunately, the discontinuous mode flyback subjects the switch and diode to high peak currents and voltages and so it is generally limited to an output power in offline universal input supplies (ie - 100-250VAC) to 100W or less. No way do you want to try to process 400W+ through a discontinuous mode flyback. Well, you can, but because the semiconductors and magnetics are poorly utilized in the flyback, the cost advantage of its apparently simplicity quickly erodes compared to the more conventional approach of a boost converter for PFC and a bridge converter for isolation/output regulation.
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