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Inexpensive ASIC DC Series controller, no uC, DSP or programming

18818 Views 127 Replies 11 Participants Last post by  Tony Bogs
Inexpensive DC Series and ACIM ASIC controllers, no uC, DSP or programming

Hi everyone. I have noticed a trend towards the use of DC series traction motors in DIY EV projects.

In this thread I am going to design an inexpensive, very basic, easy to build
but also efficient DC series motor controller with modern ASICs,
based on PWM control of the applied DC voltage and hysteretic control of the maximum motor current.

Why? I'm going to buy an EV for daily use, building one is mainly for the fun of it.
I don't have a lot of spare time or money to spend on it, so a DC traction conversion is the best option for the next couple of years.
A drivetrain based on a DC series motor is by far the easiest and least expensive way to get traction (high start-up torque) from a DC power source.
As demonstrated in a recent video of a €1000 build and in every ICE car with a DC series starter motor.

DC series motors have been used for propulsion for ages and back in the pre-IGBT era,
torque and speed of DC series motors were controlled by shifting a tap on a huge, high power series resistor bank.
Very inefficient of course, but that is the way it was done when I was EE student in my first year.
At the core, the driver of the vehicle is the most important part of the control mechanism,
being both the feedback path and the input. A very elegant control solution because of its simplicity.

In the design in this thread the resistor bank will be replaced with modern silicon in ASICs.
Yes, application specific integrated circuits, so there's no time consuming complexity from microntrollers,
digital signal processors, unnecessary and potentially unstable controllers (PID) in software and the biggest issue: bugs and programming errors.
The electronics only kick in automatically when the response of the driver is too slow for the protection of the power electronics and the motor: overcurrent protection.
That is what "very basic" means, but it takes very little effort to dress up the controller with whatever (automated) (protection) feature is wanted.
Examples: cruise control, monitoring (warning lights, gauges), reduction of the maximum motor current when there's not enough air flow across the cooler.

The schematic shows the heart of the controller: only three SOT-23 devices, the lvc4066 and the lvc14 can be replaced with a single lvc3157 SPDT device.
Current sensing for overcurrent protection is done with a low cost LEM sensor.
Hysteretic control is implemented with a low cost comparator (MCP6561) and a LTC6992 has a suitable frequency response for the conversion of the throttle input into a PWM signal for the power stage.

EDIT: The all hardware ACIM controller is introduced later on. Thanks again, Damien!





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Is this the final square wave to sine/ac circuit? Yeah, I think so, this looks really good.

If anyone thinks five (or are there six by now?) is a lot, take a look at the revision/patch list of a similar project in software.;)
Prototype diagrams after annotation and DRC.:)
Not that many parts, but still trying to get the number down.

And adding mods to make it really easy to hook it up to an Arduino (clone)
for setting the board up, monitoring, CAN bus ....
The digital pot to set the PWM frequency is a bit of fun of course while I'm wating for parts. This thread is about an all hardware controller.

But is possible to hook up an Arduino.

Major change:
The jumpers have been replaced with analog switches. In the end more versatile and less expensive.
Now the driver can select a slip setting from twelve options. Four in each mode of operation: high torque, eco (higher efficiency) and of course regen.
Again, I'm placing the driver at the controls.

There will be two throttles. One for driving and one for regen.

Parts selection. I've selected the MCP6242 (dual opamp) and the MAX9032/34 (dual/quad comparator).
Total less than €60 in parts on the PCB.

The ACIM board uses the same TACHO circuit as the DC series board.

Let's assume that the big Tesla S drivetrain will be used. Replacement of the DSP brain.
Current sensing filters: design is ready (updated version with a single switched cap device).
Overload/fault handling: ASICs have been selected.
Temperature sensors: straight forward multiplexer and a single protection ASIC.
Tacho: external pickup (for now) .
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This is nothing new, I've selected them some time ago: MCP25020/25050 for CANBUS system integration. No link, the Microchip website has issues right now.

With these the brain in the dash can control and monitor the ACIM drivetrain. Bringing it all back the future (or at least this millenium). :D

Darn, this almost makes me forget that this thread started as a DC series project.

Anyone know if advancement of the brush ring is a good idea to get more miles out of the brushes than say 2000?
Ah, no, sorry, now it's coming back to me. Forget I asked: I'm going to use it for a 15mph senior citizen project. 10 miles max per trip. :D
PLL: the VCO part of the 4046 and the digital pot circuits are no longer used. The LTC6990 is linear and it has the full range.
CAN MCP25020 diagram shows that the controller can be used without CAN: 9 pin parallel I/O connector.
PCB: The prototype circuit fits on a 3x3 inch board.
Still on breadboard. Scope screenshot showing the PLL based generation of sine and 3rd harmonic injected signals, input frequency step 300 to 400Hz.

BLUE: VCO input, step is close to the center of the track.
GREEN: square wave from the digital 120 degree phase shifter
RED: sine wave (LTC1069-1 elliptic filter)
YELLOW: sine with 3rd harmonic (LTC1065 Bessel filter)


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I've been kind of busy with 24/7 stuff, not at all EV related and much more important, so all of my projects are on halt.

But every now and then I have little bit of free time. Of course, I try to keep in touch with developments, visiting EV related sites

And I've spotted an interesting new chip from Toshiba for a project like this one: a fully hard wired, very simple to drive BLDC interface chip.
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