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

18817 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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i've used a similar circuit for current monitoring but added a low-value capacitor in parallel to R1.

This adds filtering against noise (PWM) and can be tuned to soften the hysteresis transistion (change slope and round over the edges).

i think you are using R2 and R3 to set the threshold voltage. If so then R3 should be tied directly to ground and the C3 cap should be on the node between R2 and R3.

One other consideration might be a light pull-up resistor to 5V on the output of the comparator.
What is the gate driver chip, can't read or find that part number?

i didn't understand all the diodes for the gate drive, plus the in-line zener, what was the point of all that?
In the third version of the schematic the voltage comparator reading the LEM current sensor has been changed to an LM2904 op amp, and it appears to be used as a non-inverting amplifier to provide the hysteresis.

i'm wondering about the function of the summing junction on the (-) input? Could the desired cutoff voltage from the current sensor just be set with a single voltage reference instead of summing 3 input voltages? Just curious about if you had a special reason that i'm overlooking or missed...

Also which LEM current sensor are you using?
i've been following with interest and noticed the HC4046 PLL chip with deja-vue.

Then it came to me--i had repaired an old HP LCR meter and that was the failed part. Fortunately i located the dip version in some old parts bins and was able to get it working again.

And there were two in the bin, so i've got a spare that i can use to breadboard up your clever circuit.
Tony--you are a top-class Electronics Wizard™, that's an impressive manipulation of the chips to bend to your will...


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